Saturday, December 29, 2007

Where Am I?

No, that wasn’t me whistling in to MRY in my Lear 25 for the golf tournament. (Hint: I don’t own a Lear.) But that could of been me shooting landings at the Camp Granite airfield out along Highway 62. Don’t bother looking for it on the Los Angeles sectional, by the way. Camp Granite was abandoned in 1944. Flying to places like that, you can’t look it up on a section and you don’t call the FSS for a weather briefing, you call the guy at the gas station at the junction, if the place is lucky enough to have such a thing, which most such places don’t. In fact, if you drew a circle fifty miles wide around Camp Granite, on any given day the odds are you’d be the only human in it. That’s the reality of the Great American Desert, which may help you to understand how someone like Steve Fossett could go missing and not be found.

California, my native state, is fairly large; lotsa people, too. But the people are clustered near work & water, which leaves the desert portions pretty empty. For example, Camp Granite is about five hundred miles from the Pebble Beach Golf & Country Club - - it isn’t even on the same sectional. In fact, you’d need more than forty dollars-worth of sectionals to cover the entire state of California (Los Angeles, San Francisco, Klamath Falls, Las Vegas and Phoenix). Even then, you wouldn’t have much luck finding Camp Granite... or any of the hundreds of abandoned airfields scattered across the western United States.

Forty bucks-worth of sectionals is kinda rich for my blood. Add to that the fact they don’t show abandoned airfields and you’ll get some idea why I use other kinds of charts, such as old road maps or the super-sectional from California’s own Division of Aeronautics, a state agency under CalTrans, our state department of transportation. The super-sectional costs about nine bucks and like road maps it isn’t supposed to be used for Air Navigation, with capital letters and all that. But when the air-nav charts don’t show the places you want to go, a good map - - even a 1955 Texaco road map - - and a healthy dose of common sense, will usually get you there.

As a point of interest, especially for the frugal airman, most states have some kind of aviation office; Department of Aeronautics, Aviation Bureau or what-have-you. And most of them offer some pretty good charts, usually copied from the FAA’s sectionals. Best of all, State charts are often free or, like California’s, cost less than the sectional(s) covering the same area.

A golf tournament isn’t someplace I’d pay to go and a Learjet can’t take me to the places I want to see. Most lightplanes will get me there, even a homebuilt puddle jumper that leaves my head sticking out in the breeze and requires an Armstrong starter to get the engine going. Once you arrive at the middle of Nowhere the Nazca-like lines that were visible from the air will vanish when viewed from the ground, the ghostly image of tent cities blown away on the desert wind. Indeed, if you lack the shaman’s gene there really isn’t much to see in the Great American Desert and the typical white man dismisses such places with a shrug; the WWII camps a page of history erased by the bureaucratic hand. But dry lakes were once inland seas and for those of us who can see the passage of time such places justify more than a casual visit.


31 Dec 2007 -- A sharp-eyed reader named Oliver (see the 'Comments') noticed I'd gotten my photos mixed-up, posting a pix of Camp Coxcomb (which is near Hwy 177) instead of Camp Granite. -- rsh

Thursday, December 20, 2007

The Scrimshaw Fleet

Fully rigged, glued to pallets of Sitka Spruce, protected by a coat of spar varnish applied with a Q-tip, the Scrimshaw Fleet sets sail for the Christmas Tree.

Protected by jelly jars, the tiny boats will be making whimsical voyages long after their builder has departed for Fiddler's Green.

-Dec 2007

Saturday, December 8, 2007

the Nina, the Pinta and the Rancho Bernardo

Scrimshaw II

"What are you making for the kids this year?" my wife asked about a week ago at breakfast.

Total blank. I was cracking walnuts to eat with chunks of Korean pears; I'd forgotten all about making gifts for the grandkids. "Little boats," I lied. "In fact, I'm working on them right now."

I continued to crack walnuts with the blade of my pocket-knife while I told her about Duke Haliburton and how he'd persuaded King Charles of Spain to out-source the transportation between Mexico and the Philippines, back around 1665. She gave me a suspicious look.

"Seriously. Duke Haliburton convinced crazy King Charles that out-sourcing would save him a buncha money. Then the Duke hired some Chinese guys to sail back & forth between Manila and Acapulco..."

"Chinese guys?" Her eyebrow arched up the way it does when she's on to me.

"Sure. It was a lot cheaper than building a galleon..."

"I suppose these chinese guys used a Chris-Craft."

"Don't be silly." I crunched my way through a couple of chunks of Korean pear. "Chinese guys sail junks."

"So... you're making the kids Chinese junks?"

"Right!" Whew, that was a close one.

"Three of them?"

"That's how many Duke Haliburton hired. Cost him twenty pieces of eight a month, each. For which he charged King Charles something like a million dollars."

That got a smile. "Things haven't changed much." Then she gave me that look: "I don't suppose you remember the names of those Chinese junks."

"Ah... the Nina, the Pinta and... uh... the Rancho Bernardo."

At which point she said something rude.


From that morning to this, I've added half an hour or so of Basic Boat Building to my breakfast schedule. As the little boats took shape my wife stopped making jokes about it.

Every kid knows walnut shells make perfect boats. In fairy tales. In real life they need some ballast, which I provided in the form of lead BB-shot, glued to the bilge before I started construction.

Small hull needs about eight BB's, bigger hulls can use up to twelve.

To make the decks I took a pair of scissors to some scraps of cardboard; the same stuff I've been using for gussets in my airplane rib experiments.

I made the sails out of a coffee filter, gluing on the battens. Straws from a whisk-broom provided the yards and booms; the battens are bristles from a defunct paint brush.

For masts I'd planned to use toothpicks but the only round ones we had were colored and the flat kind didn't look right, so I split some aircraft spruce with a razor-knife and turned the splinters into spars.

As you can see, the fleet isn't quite ready to get underway but they'll be sailing in formation under the tree by Christmas morning.


Every sailor does this sort of thing. The generic term for it is scrimshaw, which I wrote about last Christmas.

Junks are a bit easier to model than other types of sailing vessels because they don't have much in the way of standing rigging, although their running rigging is wacky enough to confound Confuscius. Oddly enough, the junk rig is superior in almost every way to the square-rig, something no Westerner will accept until they've actually used one.

-Bob Hoover

Wednesday, December 5, 2007

VW - Volkswagens and Sex

You like sex, right? (Come on, don't be shy. Just nod your
head if you don't wanna say it.) Okay!

So I guess that means you really enjoy changing those diapers,
right? Mixing up the formula? All those PTA meetings and
putting money aside for college... You're really hot for all
that stuff, right?

No??! Well... gee. I mean, that's the whole IDEA behind sex.

Ah! I see. You want the fun but not the responsibilities.
Ummm... okay. It's your life.

Unfortunately... (you knew that was coming, right? :-)

Unfortunately, old Volkswagens have a lot in common with sex.
The sexy part is roaring around, lotsa noise & chrome, a really
kewl ride ... or for geezers like me, driving off to the ends
of the earth, hitting rocks with hammers, catching fish, getting
chased by bears & stuff like that. It boils down to the same
thing: Having fun. Getting down & dirty. Like good sex.

But after you've had your fun you gotta face the
responsibilities -- the shitty diapers. That's the maintenance
and tune-ups and clutch-jobs and doing the brakes and all those
other unkewl things that YOU gotta do soz you can keep on
having fun.

The reason I'm writing this is because a lot of folks out there
are in it strictly for the Fun & Games. They want sex without
babies and a kewl ride without getting grease under their
fingernails. The problem is, it don't work that way. Not
unless you are stinking rich... in which case you wouldn't be
reading this anyway :-) Most folks aren't rich but neither
are they dirt poor. They let somebody else raise the baby...
and do the brake jobs. But of course that gets expensive as
so you gotta scrimp here & there. Never on the polish, of
course. Or that ohsewkewl bud vase. But you let a lot of
'unimportant' details slide, such as keeping your wheels
aligned or your shift linkage tight or whatever, firstly
because you yourself haven't any idea in the blue-eyed world
how to do such things.. and aren't about to learn since you're
only in it for the fun anyway, and secondly because you can't
afford to pay someone to do them because you've pissed away any
money you do happen to get on 'having fun'.

I hate to tell you this but you can't have it both ways. Oh,
you can. But not for long. All those 'unimportant' things
start to pile and, eventually, so do you. (Darwin was right
you know :-)

The point is, when it comes to Volkswagens you can't have your
fun without accepting the responsibility that goes with it.
Not if you want the fun to last. How long will it last?
Statistically, based on the transfer of VW titles (ie, ownership)
here in California, about thirty months. Two and a half
years. (*) That's when all those 'unimportant' things finally
catch up to you and you sell your bug or bus to the next kiddie
waiting in line because you have neither the bread nor the
brains to fix it.

Over and over and over again. That's the 'churn' that spells
survival for the VW-specific magazines and all those VW after-
market suppliers (who are becoming fewer each year, in case
you hadn't noticed).

Don't believe it? Check the archives of this Newsgroup.(**)
Where are the kiddies of yesteryear?

So what's the answer? It depends on the question :-)

Wanna earn up to $400,000 in 'hidden' income during your life?
Then keep your car forever. (ask Consumer's Union for the
article on this subject) That's right; just keep repairing it
instead of throwing it away every couple of years. Fuel, oil,
tires and maintenance accounts for only 7% of the cost of
owning a NEW car.(*) The rest gets pissed away renting the
money to pay for the thing, which isn't worth what it cost
to begin with, for the insurance and taxes and license and
all that other crap the System demands you must have.
Average cost? Almost a buck a mile for a full size sedan,
more for an SUV, less for a rice box. (Sound too high?
Check with the AAA. You're in for a surprise.)

Or you can buy an old bug or bus, fix it up and keep it that
way, you'll end up driving for about three cents a mile.
(It doesn't have to be a Volkswagen... the Forever Car
Philosophy applies to any repairable vehicle.)

Of course, that kinda thing means buying tools instead of
those kewl chrome rims, and manuals instead of that bitchin'
bud vase and planning slightly farther ahead than where to
go for lunch... and the record shows most kiddies
don't have the Right Stuff to do that. (Because it's not kewl,
of course :-)

Volkswagens and sex have a lot in common, when you think about it.
But so does divorce and Volkswagens. The sad part is that the
record shows most VW owners are only interested in a joy ride
instead of a stable, long-term relationship.

-Bob Hoover

* - The DMV data was for 1996. Vehicle cost data was 2000. This article first
appeared in 2002.
** - RAMVA

Wednesday, November 21, 2007

Cooking Airplane Ribs

Do any amount of travel, you gotta eat. Good trip, say up to Alaska or down through Central America, you’ll be gone thirty, forty days. That’s a lot of cooking. Even when you do your traveling by airplane, boon-docking old mining sites in the Mojave or whatever, you gotta eat, although going airborne, you generally do the cooking at home, rig it so’s you can eat it cold or just an aluminum-wrapped something you can lay on the coals of a fire.

If you write about your travels the facts of feeding yourself tend to creep into the typewriter so that pretty soon, thanks to blogs and Newsgroups and stuff like that, folks become aware of Bob’s Basic Biscuits, Beans a la Boom, Bajanese Salad and the other recipes - even cookies - that have made life away from home a bit more enjoyable and deserved mention because of it.

The point here is that most folks who drop by the shop are used to me putting down my tools to go check something in the oven, especially during the holidays when I shift into Pie-Making Mode. Which is what I was doing when The Visitor arrived, and why I carried the timer out to the shop as we went.

“Pies,” I said.

He nodded in understanding. “My wife said you had a good cookie recipe.”

We chatted about cooking while I replaced the stripped nut-plate on his spinner backing-plate, which was why he’d dropped by. While I worked he glanced around the shop but there wasn’t much to see. Major projects are on hold due to a lack of funds. To fill the time I’ve been doing some experiments with cardboard ribs and other such stuff. Actually, they’re not cardboard at all, they’re plain old-fashioned stick-ribs. But the gussets are made from heavy paper, like the stuff used to package a 12-pak of soda pop. Or the better stuff used to package a 12-pak of Colorado Kool-Aid. (This isn’t new, by the way. For the past several years I’ve posted occasional messages about alternative materials, including several recent articles posted to my blog.)

The ‘cardboard’ appellation came from a gentleman who took me to task for daring to even mention such a ‘stupid’ idea, unaware that paper or ‘fiber’ gussets had already been used by a pair of bicycle boys named Wright, a company called Aeronca, the late Paul MacCready and a few others dummies. Unfortunately, their work with paper gussets hasn’t made it onto the internet forcing all future dummies - like me - to conduct our own experiments. And to write about it so that when I fall screaming from the sky the NTSB can simply hit a button, peruse a few million words of gibberish and say: ‘Ah ha! When he made his casein glue he failed to properly neutralize the mixture!’ ( er... actually, the casein glue is another set of experiments. And if you read a bit farther down that page and you’ll see that my home-made casein glue worked jus’ fine, thanks... although I wouldn’t want to use it except in an emergency... such as living in a village in rural India... or being even poorer than I am.)

Among the many details no doubt included in the missing body of literature describing the use of fiber gussets is the fact they are hygroscopic, something I had to rediscover for myself. Unless treated, paper absorbs water. Since the ‘fibre’ I’m using is various grades of paper obtained by a series of dumpster dives, it too absorbs water. (My neighbors already have good reason to believe I’m crazier than a hoot owl in heat. When they found me fighting off the ‘possums to get at their garbage it produced only a few sighs of resignation and a request to put the lid back on when I was done.)

Since paper is hygroscopic that means some of my experiments have dealt with ways of waterproofing the stuff after the rib is assembled. So far, dilute varnish seems to be the best solution but the tricky bit was discovering I had to use at least two coats, the first being no more than 50% varnish. Of even more interest, at least to me, was determining the ideal moisture content for fiber gussets, and how to adjust it when the paper is too wet or too dry.

Which is why I shoved the repaired backing-plate into his hands and went scurrying into the house when the timer dinged. The pair of punkin’ pies were baking slowly to perfection on the top shelf but the cookie sheet of gussets cut from a Coors carton were done to a turn. The pies had to be baked; that’s what Thanksgiving is for, right? And it was just plain old fashioned common sense to slide a sheet of damp gussets in with them.

I come back out to the shop with the cookie sheet on high, put it gently on the bench and inspected the result. My nose told me the paper hadn’t been over-heated. By positioning the triangles of cardboard on the cookie sheet with their printed-side down I’ve found I can estimate their dryness by the amount of their curl. Ten minutes seemed to be just about perfect for that particular batch. And I may have said something to that effect as an aside, so the visitor wouldn’t feel slighted that I’d interrupted him by dashing off in mid-sentence. But when I turned his eyes were as wide as port-holes.

“Gussets,” I explained. He nodded then looked at his watch like he’d just discovered it lurking there on his wrist.

“For the ribs,” I waved toward the cardboard heat-box inside of which - and thus invisible to the normal eye - there was more than dozen ribs basking in seventy-degree warmth from a twenty-five watt light bulb.

“Right,” he says, edging toward the door. “Clare will probably want the recipe.” And with another mumble - glance at his watch he’s like, gone!

That’s when I figured out that he’s probably never read the posts about Chugger’s Rib and has no idea in the blue-eyed world that I’ve been searching for the Holy Grail. Or low-cost ways to build airplanes.

-21 Nov 2007


I'm afraid the gussets made from Coors 'Long-necker' packaging material haven't worked out. Turns out, the printed side of the package is coated with a plastic film that prevents the dilute varnish from soaking into the paper.

Although the gussets are more than adequate when it comes to their dry strength, if you can't prevent them from absorbing moisture you'd be better off to stick with plywood.

I will continue the experiments using the packaging material for 'Sprite,' of which I'm accumulated a good supply. Its thickness is only 0.017" (The Coors stuff was 0.030") which is right on the ragged edge for dry compressive strength and it takes only a tad of moisture (a foggy night will do it) to cause the gusset to fold up under a load. But when given two dilute coats of varnish the 'Sprite' gussets have survived my 'soak-test' -- leaving sample, varnished, gusseted T-joints in a pan of water over night.

So it goes.


Although a broken rib can be repaired, these things started out as scrap lumber. The last couple of nights have dipped into the low 40's, cold for southern California, and we heat with wood. The failed experiments were used as kindling but to their credit, some of them put up a hell of a fight on their way into the firebox :-)

-24 Nov 2007

Sunday, November 18, 2007

Year of the Blog

On 16 Nov 2006 I became a blogger by uploading ‘The World’s Ugliest Toolbox’ response to Google’s offer of free blogging space. Since then I’ve uploaded 264 others from a file of a thousand or so digitalized articles accumulated since about 1992. The material covers a broad range of interest and includes articles submitted for publication, successfully in a few cases but mostly rejected, especially so for the aviation-related material.

To provide this ‘free’ service Google attaches advertising to your material. When someone clicks on one of the ads, the advertiser pays Google, who shares a bit of the wealth with you. You are allowed to limit the number of ads and to block ads from companies you deem unsuitable. Of course, the more restrictions you impose on your site, the lower its potential income. And the thing has to generate SOME income or Google will simply kick you off.

Over the past year the blog has been visited 97,305 times. Those visitors clicked on 862 of the ads, for which Google paid me $292. That’s about 266 visitors a day and two clicks worth eighty cents, a tad shy of Minimum Wage even for a writer :-)

As soon as my blog appeared I got a few friendly jabs from fellow writers about getting rich through blogging. This message should lay their fears to rest :-) At the same time, a number of other folks asked if creating a blog was worth their time. I didn’t know. I said I would give it a year and tell them how things were going, which is what I’m doing here.

Over the course of the last year the blog has generated a fair number of comments, some of which I’ve posted. A lot of people have urged me to submit a particular article to various magazines, unaware that in most cases, I already have. If you want to see a particular type of article in your favorite magazine the person to talk to is the editor, not the writer.

Has the effort been worth-while? If you mean financially, no. But as a means of disseminating information, I think the blog has been a success.

-18 Nov 2007

Saturday, November 17, 2007

Chugger's Rib - IV

Does everyone understand that the strength in the joints of the sticks in a rib is due to the gussets and not the contact between the sticks? If not, you need to put on your thinking cap and do a few experiments until you understand how a load in the sticks behaves when it encounters a joint. You don't need to build a rib to teach yourself what is going on its joints. Use whatever is handiest -- match-sticks, toothpicks or whatever -- to make a basic T-joint and then break it. Make one without a gusset, then one with a gusset. Then try replacing the gusset with a thread or a piece of toothpick.

When you do this you will see that as you put a load onto the leg of the T, one side of the gusset will see that load in tension whilst the other side sees it as compression.

There's a bunch of common-sense assumptions here; that the load is imposed in-line with the axis of the rib and so forth... that I won't bother to go into; the key point I want to get across is that both tension and compression are present.

If you've made a sample joint using thread in place of a gusset, when you broke it you will have seen that while the thread does okay in tension it's worthless when it comes to compression, proving the old saw that you can't push a rope :-)

Cardboard doesn't do very well in compression either, and that's really what this posting is about. In fact, the only reason my cardboard-gusseted rib is able to bear its designed load has more to do with the number of bays in the truss and the spacing of those bays relative to the intended load, in that the load at any given joint is low enough so that it does not cause buckling on the side of the gusset subjected to compression.

This wasn't by accident. As mentioned in a previous post I've been messing with ribs for a couple of years now and you may have noticed that I've not bothered to post the results of my early experiments. Which were pretty awful :-) But even failure is data of a sort and I eventually came up with a rib that should do the job, even though the gussets are nothing but 'cardboard.'

Of course, a four-bay rib is heavier than a three-bay rib, but I assumed at the outset that using low-cost, commonly available materials would impose a weight penalty.

A second purpose of the experiments was to discover just how big that penalty would be, since another design-constraint was that the bird had to be able to fly -- safely -- behind a converted Volkswagen engine. And despite the hype from the hucksters, no matter what the VW's displacement might be, it's maximum sustainable output is only about forty horsepower, about the same as the Continental A40.

So what is that weight penalty? About four-tenths of an ounce per rib; about three-quarters of a pound for the whole wing.

Keep in mind, the normal or unaccelerated load on the wing is less than seven pounds per square foot or about 30 lbs per rib, and about a third of that will appear in the plywood D-cell that makes up the leading edge, leaving about 20 lbs to be dealt with by the remainder of the rib.


(Photos and drawings to follow)

Friday, November 16, 2007

VW -- More on Air Filters

(written in 2002)

I've just finished reading the thread on air filters. If you haven't read it, you probably should. Marvelous stuff. Laughed my ass off.

Yes, there is a standard for automotive air filters. SAE J726 (or maybe 826... there's more than one).

Read the specs? Okay, here's pop quiz: Other than the Beta test (ie, ratio of particles that make it through a filter as compared to the number of particles which go into a filter), have you ever wondered how they arrive at those "efficiency" figures? Come on, think about it. No filter is 100% perfect for all sizes of particulate contaminant. So what are they comparing things to? What is the nearest thing they have to a perfect air filter?

Would you believe it's a multi-stage kinetic type filter, usually having a water-bath catchment... covered by a thin film of silicon or mineral oil to reduce evaporation?

Although we're talking laboratories here, the principle is the same as the oil bath air cleaner on your veedub. Not small, though; you can walk inside some of them. And except for HVAC applications they're almost always used with pre- and post-filtering, including electrostatic precipitators. (Anyone who has ever worked at a chip plant knows about this stuff. Even old sailors, like me because the government has its own chip plant, inside the fence at Ft. Geo. Meade, home of the world's longest indoor shooting gallery... and one of the cleanest 'clean rooms' on the planet.)

But the subject of comparison also applies to the air filters for cars and the point a lot of folks missed is the fact treated paper filters (ie, a non-kinetic labyrinth-type filter) are compared to an oil bath filter (which typically scores about 99.9%).

And those marvelous K&N filters? Last time I checked, they're compared to paper filters. (Go on; lookit up; K&N has a web site and is justifiably proud of their product, which works at least as well as a paper filter, so long as it receives the proper periodic maintenance and liberal doses of K&N's magic elixir.)

All of which means that clunky, old fashioned oil bath air filter on your bug or bus is still a hands-down winner... for anyone who cares to do a bit of reading :-)

As for all that 'flow-rate' stuff... Anyone care to take a WAG at the flow-rate for your 1600cc engine, roaring along at 3500 rpm? No? Howzabout a 2550cc big-bore stroker turning five grand? (Hint: Be prepared to be underwhelmed.) But bigger is always better, right? So more flow has gotta be good, right? Horseshit. The fact a particular filter can flow more air doesn't mean your engine can use it. Those counter-top ‘comparison’ units are just a sales ploy; a kind of IQ test for the technologically naive.

Read the specs. Flow is relative to the pressure differential and restriction. The bottom line is that your oil bath air cleaner does just fine, folks. Always has and always will, so long as you give it the maintenance it requires. For stock engines an oil bath air cleaner has no problem providing more air than the engine can use. (If you think about it for a minute you'll understand why that has to be so.) In fact, the stock oil bath air cleaner works just fine for engines up to about 2200 cc so long as they don't spin over 5000 rpm, a fact you can work out for yourself with nothing more exotic than a #2 yeller pencil and basic arithmetic. Working it out will also give some idea how much you'll have to shorten the service interval when you use an air filter designed for a small engine on a big one. And the service interval of any air filter is a critical factor in determining its practicality.

Indeed, the service interval is one of those things the tea-cozy crowd doesn’t like to talk about. As with any labyrinth-type filter, their effectiveness is a function of surface area. Under harsh conditions, where you might need to service an oil-bath air cleaner as often as once a day, you may need to wash & re-oil a gauze & window-screen air filter every few minutes... which is why you don’t see such filters used for real-world applications.

Don't take my word for any of this. After all, nobody is right all of the time :-) Think for yourself. Go look it up. Work it out. It's your ride and it's entirely up to you what kind of filter you use. You're the Mechanic-in-Charge, not me.

In fact, lemme repeat that: You are the Mechanic-in-Charge. Making the right choices is up to you. All I've done here is express an opinion, albeit one based on experience. In effect, I've described a particular path. The decision to explore it -- or not -- is yours.

The only reason I've bothered to say anything at all is because automotive engineering is not subject to the democratic process. Having a big mouth doesn't automatically make you a good singer, nor a loud voice a good speaker (although it helps :-) The fact someone posts a thousand messages a month does not mean the messages contain anything worth reading. Apply that logic to the fact all your buds are using gauze & tea strainers for air cleaners and you'll see it only means its a popular idea, not necessarily a good one. The task of determining the merit of something is up to you. And I'm not just taking cars here. Every person is capable of error. That fact extends to every organization as well because organizations are nothing more than collections of people. And if you think an individual can screw up, our personal faults pale by comparison to the outright evil of which groups are capable. (And yes, you can look this up too if you wish. Although since 9-11 I've got a hunch most folks can figure it out for themselves.)

The wiser course, in my opinion, is to always think for yourself, even if doing so sets you apart from the majority. Because when push comes to shove, it's your life. And your ride. Not theirs.

-Bob Hoover

PS -- Oil bath air cleaners fell into disuse for passenger cars because of economic factors, environmental issues and the shear size of the damn things.

The size issue had to do with their height. To work properly an oil bath air filter must have a certain minimum height. If you had a 'tall' engine yet wanted a low hood line you had to move the oil bath air filter over to the side, as Volkswagen did with the Karmann-Ghia, Hudson with their dual-carbed 'Hornet' and others. But doing so increases the parts count and complexity of the system and such things carry an inherent increase in maintenance cost. Which leads to...

The key economic factor in the demise of oil bath air cleaners in cars had to do with the time needed to properly maintain them. I can't remember the Flat Rate Manual for servicing an oil bath air cleaner but it was on the order of 0.5 m/hr. No big deal when making 'good money' meant a dollar an hour. But nowadays spending half an hour to clean an air filter would be economic suicide for a dealer paying his line mechanics $37.50 an hour plus full medical, dental and so forth. (What's it take to change a treated paper air filter? Maybe a minute... if you've never done it before. Less, for an experienced mechanic :-)

The environmental issues with regard to oil bath air filters wasn't so much the oil you poured out of the thing. Hell, recyclers will pay you for the stuff. What really sets a tree-hugger's hair on fire is seeing that drum of sandy sludge -- the scrapings out of the bottom of the oil pan -- accumulate over in the corner of the lubrication bay. A high percentage of the particulate matter found in the air above most roadways is toxic. And you've just concentrated 55 gallons of the stuff (and usually hauled it off to the local dump). The solvent-filled parts washer you ran it through was another E-ticket ride for tree-huggers. Not only did it generate its own quotient of sludge, in normal use it pumped a few pounds of hydrocarbon aerosols into the air every day. By the time you've shifted to a water-based high pressure detergent washer, or added a vapor recovery system to your solvent tank and negotiated a HazMat contractor to collect & dispose of the sludge, servicing an oil bath air cleaner has become a very pricey proposition.

There's plenty of justification for doing away with oil bath air cleaners. But their ability to clean the air wasn't one of them. Indeed, such filters remain a standard method for many industrial applications, as a bit of research will show. - rsh

Thursday, November 15, 2007

VP -- Overheating

You'll find the original version of this thread on the Usenet Newsgroup devoted to air cooled Volkswagens. It began with a complaint of overheating by someone who done a lot of bolt-on modifications to their engine. They asked the Newsgroup if adding an after-market oil cooler would solve the problem. The general opinion was that it would not, since the engine had been heavily modified even through it still had the stock displacement, which is where we pick up the tale...

>Given that the items are external, I claim it as stock.


Dear D.....,

You've managed to miss the point.

Normally, only about 15% of the engine's waste heat will appear in the oil. If the engine is fitted with the dog-house type oil cooler and all other cooling system components are in place and functional, the oil cooling system provides about 120% of worse-case capacity.

The point you've missed is that elevated oil temperatures are a symptom rather than a problem. Normally, elevated oil temperature simply means the engine is being operated outside of its designed envelope -- the load is too heavy for the speed or the speed is too high for the ambient air temp, or both. And yes, on a hot day this can occur with just you on-board. The cure is to simply take your foot out. Alas, on a southern California freeway that can earn you a ticket for obstructing traffic, which is why a lot of VW bus owners have learned to fly by night :-)

The root problem is whatever is causing those elevated oil temperatures -- and that could be anything from low tire pressure to a loose nut on the steering wheel :-)

Ever had the measles? Your body temp can hit 105. Dunking you in ice water is a sure-fire treatment of the symptom -- it will bring your temperature down. Of course, the shock usually killed the patient :-)

Audit your cooling system. Every part is critical. Check to see that the deflector plate is installed on the underside of the heads. If running after-market dual-port tin the odds are the gull-wing deflector above the manifold hole is missing. Check your spark plug seals -- any loss of air pressure guarantees a loss of air flow.

Check your fan belt. And the diameter of your pulley. (Those wunnerful 'power pulleys' guarantee the engine will run hot.) Reach around behind the blower housing and feel every blade in the fan to insure you haven't picked up leaves or other debris.

Check your oil pressure. Elevated oil temp is one symptom of a worn-out oil pump.

Check your brakes, tire pressure and alignment. Low tires, draggy brakes and improper alignment all demand more work from the engine. The car may be doing 65 but the engine could be doing 90.

Ditto for the clutch & tranny. When was the last time you replaced your tranny lube? (Recommended interval is 2 yrs or 24,000 miles.)

What kind of shape is your engine in? Yeah, I know -- perfect :-) But a lot of 'perfect' engines show up here at the shop with complaints of over-heating. It's not uncommon to find excessive blow-by, indicating worn rings or valves. And excessive blow-by dumps a huge amount of excess heat into the oil. After-market carbs are one the main reasons for accelerated wear of pistons & valves, mostly because of their inadeqaute air cleaners. It only takes about a teaspoon of dust to trash an engine and anyone who has cleaned an oil-bath air filter knows the engine sucks in ten times that much between oil changes. The other failing of after-market carbs is running too rich a mixture, either because of inadequate manifold heating or running a mechanical advance distributor.


Conventional Wisdom as espoused by the magazines and after-market retailers say that if your oil is running hot you gotta spend some more money by adding one of their sooper-geewhiz oil coolers, with a fan yet, and mebbe one of those ohsokewl thermostatic valves that are guaranteed to leak. And lotsa hose. And fittings. And brackets. And other neat stuff.

Now the oil stays so cool it's kewl. Of course, the root problem -- whatever it is -- is still there, ticking like a time bomb. And when it goes off those wunnerful folks will have some more really kewl fixes you can buy. In fact, the experts have an answer for everything! The only question is, can you afford it?


Hot oil is a symptom. What you need to do is deal with the problem that produced that symptom. Adding an oil cooler is like trying to cure cancer with aspirin; the pain may go away but you're still gonna die.

-Bob Hoover

...then John writes:
>what I've found
>is that most air-cooled VW engines are filthy on their exterior.

(ie, as a major contributor to overheating)


Dear John (and the Group),

Good point.

A friend recently asked me to look at the air-cooled engine on a paving machine (!). I don't know anything about paving machines. Nor those nifty two-cylinder Honda engines. But he'd gone through two engines in two years and it was pretty obvious the Honda guy just wanted to keep selling him new engines at about two grand a pop.

The engine's fins were covered with fur.

Or what looked like fur. It was dust, glued to the aluminum fins with hydraulic fluid.

Actually, it didn't look all that bad... you could brush it off, which they did to the inlet grill every morning. But it would come right back because there was lots of oily vapor getting sucked in by the cooling fan and the machine spends it's life in a dusty environment.

It reminded me of a 40 horse with a leaky oil cooler -- the famous Volkswagen Toaster :-)

The really funny part was the reaction when I pointed out the layer of dust (which makes a dandy insulator). My friend doubted that such a thin layer of crud could be enough to over-heat the engine. But it was easy enough to rig a duct to insure it sucked in only outside air... and without the oily vapor, the aluminum fins stayed clean... and the thing didn't overheat. (Truth is, I think the thing originally came with such a duct... that someone had removed to make it easier to get at the hydrualics.)

Liv & lurn -)

-Bob Hoover

PS -- My personal favorite was the doctor's Porsche and the engine filled with leaves from a Chinese Elm that shaded his reserved parking space. Even when you showed him the cylinders packed solid with leaves he kept insisting they would blow right on through; that SOMEONE must of packed them in there on purpose. Makes you wonder about his diagnostic skills, eh? :-)

Then someone asked:

> What do >mean with the gullwing tins?


Look inside the stock DP cylinder-head tin-ware. There is a gull-wing shaped deflector that directs the blower's output toward the exhaust valves.

Making sure the deflector is a fairly tight fit against the fins immediately adjacent to the two upper-middle studs is a standard procedure when mantling a DP engine. Without a well fitted deflector the cut-out for the DP manifold end-castings is little more than a hole through which your cooling air can escape.

Your OP readings look okay. As a test, change to straight 30W and compare the results. No difference is good, anything else is a clue that needs to be checked out.

It would probably be a good idea to rig some instruments to check the stoichemistry of your mixture. Same for your ignition timing and compression ratio. The fact an engine runs does not mean it is running well.

There IS a reason for this sort of thing. Odds are, it will turn out to be something you've assumed to be okay... and therefore did not check.

-Bob Hoover

Then came several questions, the upshot of which made it pretty clear the person was expecting to find one single problem as the cause of their overheating


Your engine is a SYSTEM. All of its parts interact. Problems seldom have a specific single cause but are the accretion of numerous small problems, usually things deemed unimportant by the 'experts.'

The deflector plates on the underside of the heads serve to maintain adequate air pressure in the plenum space ABOVE the heads; the gull-wing deflectors direct the air to where it is needed most; the thermostatically controlled flaps are designed to align with the central fin on the cylinder head so that the densest slug of air from the blower is directed to the hottest parts of the heads... all 'unimportant' details. The failure of any one of them may go unnoticed until you get a really hot day, or climbing a grade with a heavy load. Then you will have more waste heat than the engine can managed.

You're looking for a smoking gun -- a single cause of all your problems. Odds are, you aren't going to find it. What you are finding are a host of small 'unimportant' problems, the combination of which have lead to an episode of overheating. Now the camel has his nose inside the tent because excessive heat carries a legacy of future problems; it's a genie that can't be stuffed back in its bottle.

Most people simply do not believe that such close attention to detail is necessary. Indeed, the archives of this Group contain dozens of messages from idiots saying exactly that when someone having more experience tries to explain why their failure to devote any attention to those 'unimportant' details is the reason thier ride is a piece of shit.

"All my buds say..."

"I've driven for ten years without..."

"Nobody does it that way!"


The good dope is in the manuals. The distillation of thousands of man-years of engineering excellence backed up by more than twenty million engine's-worth of experience. Build a few engines yourself and perhaps you can add to that sum-store of knowledge but most of what you read & hear about Volkswagens is from an idiot with one engine's-worth of experience expressing his expert opinion, or an after-market retailer preying upon your ignorance.

-Bob Hoover

Thursday, November 8, 2007

Chugger's Rib - III

A gentleman has taken me to task for daring to publish anything so stupid as an article about cardboard ribs. Unfortunately, he was unable to offer any cogent reason for my stupidity other than it simply wasn't done. So I will continue to seek answers for the stupid questions I ask myself, for while I've shared this information with you, it was never meant to be anything other than a private journey.

Stick-ribs are held together by gussets. Every joint usually gets two, one per side. The ribs on each end of the wing are often paneled with plywood -- a kind of over-all gusset -- to provide an anchor for the fabric. Those ribs will be discussed down below. But all of Chugger's other ribs are simply sticks & gussets.

Ideally, every gusset would be a different size and shape, reflecting the load at that particular joint. These are usually called polyform gussets and Fig 2 tells you why. But with twenty-eight ribs in the wing and up to forty gussets per rib (ie, twenty per side), if each is a different shape and size it imposes an enormous work-load on the homebuilder, not only in making more than a thousand gussets but in keeping them separate during construction, which for some builders can span several years. So instead of using unique, polyform gussets we come up with a universal gusset, meaning they are all of the same shape and size. Or nearly so :-)

The size of universal gussets is determined by the the joint which experiences the m
aximum load. For the rib shown, maximum strength is required on the joints adjacent to the front spar. But when we make all of the gussets that size they will be larger than needed for all of the other joints. And that means there will be some weight penalty. This penalty can be reduced by using gussets of different sizes but while the weight penalty falls as the number of sizes is increased, the more different sizes you have, the more it will cost to make your gussets, measured in both time and money.

Clearly, this is one of those cases where we need to compromise. Strength of course is never compromised so the remaining factors are weight, cost and time, with our choice of material lurking in the background. After a number of tests I settle on two sizes of gusset as a practical minimum, not counting the wedge-shaped gusset needed for the trailing edge.

Universal gussets may be square, rectangular, triangular or even segments of a circle.
but the choice of shape is usually based on your tools, time and materials, influenced by personal preference. And don't forget that the fuselage uses gussets too. In a popular design that used plywood ribs having lightening holes, the circular cut-outs were divided into halves and quarters and used as gussets on the fuselage.

As you can see from the drawing below I settled on a triangular shape, with the smallest size formed when needed by simply cutting one of the larger gussets in two.

Having amassed a carefully collected pile of packages that once held beer or soft drinks, I used a pair of 10" shears to lop them into pieces acceptable to a lever-type paper cutter. The paper cutter sheared the pieces int
o strips two inches wide and up to fourteen inches long. The strips were stacked two deep and chopped into enough two-inch squares to loosely fill a 2-lb coffee can. I've no idea how many there are but suspect I've more than enough for an airplane. Although I've not yet convinced myself that I want to build an airplane with 'cardboard' wings :-)

In either case, the ribs move through the jig in a stately procession completely aside from other activities and projects. The fourteen individual sticks used for the vertical and diagonal members have been cut in bundles to the required length but have not been given a detailed inspection until now. What I look for -- and discard -- is any stick having an irregular grain.

Fitting the sticks in the jig takes only a few minutes then comes mixing the glue (if required) and positioning the gussets, stapling them down by hand if I'm working after-hours and pneumatically when I'm not. All tolled, the process takes between twenty and thirty minutes and is done without interruption. Then the jig goes back on the rack and things are cleaned up & put away on a handy shelf.

A rib already glued & gusseted must have the staples removed, which takes about fifteen minutes. I've sharpened a scrap of steel for this chore, having found a pneumatically-driven staple embeds itself far deeper into a fiber gusset than a plywood gusset; deeply enough to render useless the staple-remover tools previously used.

When I have a spare moment the edges of gussets that extend beyond the upper camber of the rib are trimmed away using a razor if small or a flapper-disk in an angle-head grinder if large. No effort is made to fair the upper camber at this time; that task will be done using a belt sander, one rib at a time, just prior to assembly. Nor will any effort be made to block the ribs together on a set of false spars and sand them to perfectly-matching uniformity, since the resulting surface of the fabric-covered wing will be determined by the tape & fabric when the cover is stitched to the ribs.

Once a rib has been gusseted on one side, with the staples removed and gussets trimmed, it gets flipped over and sanded. This can take quite a while if using only sandpaper and a block of wood but takes only a couple of minutes with a powered block-sander. Since the wood is fairly soft the sandpaper is fairly fine. Particular attention is paid to the edges of the sticks, looking for any 'wild-grained' sticks missed in previous inspections.

I've used one such rib to experiment with attaching a plywood shear-web to the un-gusseted side. The wing requires at least one such rib per panel; two if the tip does not receive a bow. I used 1/8" luan for the ply and as you can guess, it came out heavy as hell. But hell for stout as well. The tricky bits are laying out the locations of the sticks so as to keep the staples aligned. But it also brought to light the 'handed-ness' of the rib in that you need both a left and a right, dictating the need for a second rib-jig of the opposite 'hand.' Fortunately, this is an easy matter to resolve since you already have assembled ribs to use as a pattern for the new jig. I will cover this in more detail in a future posting.

Once sanded the rib is ready to receive its second set of gussets. This is done with the rib flat on the bench and goes quite quickly. The rib is then put aside to cure.

I have been experimenting with ribs and gussets for a couple of years now. This has been a spare-time activity, recording what I've learned in a jumble of notes. Over that time our daughter has served a tour in Iraq, friends have passed away and a host of other things, problems as well as successes, have come and gone (including our recent brush fires.) The ribs were always there, used to fill spare time that developed when other projects became stalled for want of money, materials or a spare set of hands on the bucking bar.

I think the ribs will eventually find their way into a wing panel that will be covered with something inexpensive and then broken under bags of sand (always an interesting procedure). That should tell me if I've wasted my time with my 'cardboard' ribs :-)


Saturday, November 3, 2007

Keeping Up With The Past

After posting 'Chugger's Rib-II' several people suggested I try making the gussets out of drywall tape, having read of someone using that method. Someone else suggested I use regular fiberglas fabric.


Newsgroups: rec.aviation.homebuilt
From: Veeduber
Date: Sun, Oct 26 2003 1:51 pm
Subject: Drywall Gussets

It's all about strength to weight.

Feathers aren't very strong. But then, birds aren't very heavy.

Fabric is stronger than feathers, except for the quill. Even cotton fabric. Or resin-coated paper. And wood makes pretty good quill-stuff; so does grass. Bamboo is grass.

One of the tricky bits is carrying the load around a corner. Loads concentrate at corners. As they go around the corner the load often twists, converting simple bending moment calculations involving compression and tension into load-paths so complex we're forced to kneel at the alter of Delta Vee and work them out one prayer at a time.

Ultimately it comes down to the Fastener, the way we attach the vanes of the feather to the quill and the quill to the wing and the wing to the body of the bird.

Aluminum alloy scores high for practicality, being as strong as mild steel but only one-third the weight. To carry the load around the corner you simply bend the aluminum, trapping the load inside. To transfer the load you bend it again, poke a hole through it, plug the hole with an aluminum pin and hammer it tight, the number of pins determined by the load. (Hint: See ‘Riveting 101')

But wood scores highest for practicality because it is universally available and less expensive than metal or fiberglas or foam or castaway string bikinis. (ANYTHING can be made to fly.)

To turn a wooden corner we use gussets. And our fastener is usually glue.

All modern glues used in aircraft construction are stronger than the light, strong softwoods normally used for aircraft construction. Rather than telling us how many fasteners to use, with wood the load tells us how much surface area we must slather with glue. This is when we learn that a quarter-inch square is not a quarter of a square inch but only a sixteenth. With a butt joint only a sixteenth of an inch square even the strongest glue fails when the load tries to turn the corner. That's where the gusset comes in because a gusset allows us to multiply the area of the glue joint by a factor of at least 10. If the load is very large we add blocks at the corners, increasing the glue area still further and shortening the path the load must follow as it navigates the turn. The strongest corners are formed with glue blocks AND gussets, allowing us to multiply the gluing surface to WHATEVER is required to produce a safe joint. Of course, that makes them heavier. Such belt & suspenders methods are only used when know the extra weight is justified by the need for additional strength.


There is a natural order to the universe, such as the need to sow before you can reap, and in the universal constants of gravity, motion and so forth. Long before there were such things as Science or Engineering there were Natural Philosophers, fellows who studied the natural order of things and tried to understand them. That's not allowed today. Today, birds fly strictly in accordance with scientific principles and bumble-bees are forced to walk :-) But the natural order of things continues to exist. Just as there is a natural order to the planting of crops or the erection of a house, so too is there a natural order to building a airplanes.

Plywood is the most commonly used shear-web material found in wooden airplanes. It is also the most commonly used gusset material. In the natural order of building wooden airplanes, gussets are made from the residue of plywood left over from paneling operations, such as building the sides of the fuselage or making a built-up wing spar.

In the natural order of wooden aircraft construction you begin with a large plank of suitable wood and cut it to create your spar caps and longerons and stringers. In this way the largest and longest pieces are created first and the smallest pieces of wood, typically those used to make ribs, are made from the residue of the earlier cuttings.

In the natural order of wooden aircraft construction the fabrication of the ribs is not treated as a task in isolation. Fabrication of ribs is a minor event incidental to the construction of the airplane as a whole. During fabrication of the spars, tail feathers and fuselage, when you find yourself with a few spare minutes, you make a rib. Or add gussets to one already made. Or sand a rib. Or varnish it. No matter how many ribs are required, you will have finished them long before you are ready to assemble the wings and at the expenditure of no time at all since the effort has been distributed across all the other chores.

The small sticks used in the typical rib give it an airy, fragile appearance. In fact, when properly assembled, that fragile looking rib is overly strong by a factor of two or even three. Which is another way of saying an airy rib could be airier; that it is over-built and too heavy because of it. But so long as ribs must be assembled by humans with sausage-sized fingers we must accept quarter-inch sticks as the smallest practical size for ribs. In effect, we humans are the limiting factor when it comes to optimized ribs. This is a reflection of the Practical Factors versus those which are possible.

Frankly, the extra mass is no big deal. The typical light airplane has only two dozen ribs or so and the difference between optimal and practical is usually less than a pound even in an airframe that may gross out at half a ton or more.

The Practical Factors are why the gussets used on most airplane's ribs are overly thick and far heavier than needed. That's because gussets are free, the by-product of earlier steps in the construction.

If the builder has plenty of money they may opt for a sheet of ply specifically for their gussets but common sense usually prevails, especially after they run the numbers and see that they've just spent forty dollars to save three ounces. Twenty dollars a pound, we can live with. Two hundred dollars, we can't.


If you wish to save both weight and money on your gussets stop thinking of plywood and look elsewhere. Indeed, gussets and corner blocks represent a crude solution to the problem of carrying a load around a corner. The only reason we are still sawing out corner blocks and nailing down gussets is because that's how de Havilland did it in 1916.

Nowadays we have fiberglas. And staplers. And urethane glue.

Need a quick gusset? Saturate some fiberglas with glue and wrap it around the parts to be gussetted.

Messy, eh?

Try this: start with a pallet of some sort; cardboard or plywood. Lay a piece of plastic food wrap over the pallet and put your fiberglas on that. Now saturate it with glue and put the thing in place by handling the plastic wrap.

Not so messy, eh?

Urethane glue expands as it cures so it's customary to install a clamp or apply some weight to the sandwich until the glue has cured. In many cases you can leave the cardboard pallet in place and simply staple it down, driving the staples THROUGH the cardboard. Or put a weight on it. Or sandwich it between scraps of metal or ply and clamp it with clothes pins.

Fiberglas is too expensive! (I heard someone say.) They're probably thinking of fiberglas fabric, which is rather dear if ordered from an aircraft supplier. Local suppliers of fiberglas typically charge about half the amount asked by aircraft suppliers. (San Diego, CA.) Fiberglas tape is very handy for gussetting chores since the woven edge keeps it from unraveling. (But beware! Tapes are typically woven from six to eight ounce fabric; fine for gussets on a fuselage but much too heavy for those on a rib.)

If you want some lightweight fiberglas you can find it at any lumber yard. They call it Drywall Joint Tape. It comes in rolls, typically two inches wide by whatever length they happen to sell. Locally I can buy it in rolls as small as one hundred feet or as long as the market will bear. Professional drywall installers use rolls holding 500 feet and more. Cost is usually less than two cents per foot, dropping to about a penny per foot for the largest, commercial-grade rolls.

Most look at the eighth-inch mesh of drywall tape and turn up their nose. You can't make a cowling out of stuff like that nor cover the wings of a KR or Notsoeze. But it does a fine job at making gussets.

How? By folding it over or layering it until you have sufficient strands to give you the strength you need.

Glass fiber is stronger than steel. You can prove this for yourself by cutting a piece of drywall tape about a foot long then peeling off ONE STRAND of the stuff. Use a surgeon's knot to tie one end to a dowel or other bobbin of significant radius and the other end to the handle of a bucket. Then add weight to the bucket until the strand breaks. Now go weigh the bucket. Do that eight or ten times and average the result, you'll know how strong the stuff is. But doing it just ONCE should give you a good idea as to its usefulness.

How strong of a gusset do you need? (Be careful here; remember, your ribs were already twice as strong as needed.) You really don't need the strength of eighth-inch birch ply for a rib gusset. Nor even that of sixteenth inch in most cases. We only use those sizes because of the Practical Factors.

Making small ribs, such as for the Practice Wing? Then try two layers of drywall tape. As a matter of fact, before using this stuff you will have to learn how, and while you're doing so, go ahead and make up several different layers of fiberglas.

Remember that mention of the Natural Order of things? There is a natural rule for gusset strength too. Make a sample T-joint, allow it to cure, then break it. The sticks should ALWAYS break first. If your drywall gusset tore or came loose, try it again with an additional layer of fiberglas.

Why glue instead of resin? I think the proper question is, Why NOT glue instead of resin? We don't need the added strength of epoxy or vinylester resin; the weakest component in the structure is the WOOD and all modern glues are stronger than wood. Besides, the glue is right there, ready to go. In fact, urethane glue appears to be better for this type of thing than does resin because the glue expands as it cures. Once it has cured you trim away any excess and are left with cellular type of structure that is much lighter than a solid chunk of resin.

(If / When... Santa arrives with a digital camera, photos of this method will be posted in the Practice Wing file in the ‘files' archive of the Fly5kFiles mailing list over on Yahoo.)

- - - - - - - - - - - - - - -

Flying is all about strength to weight. Sez so, right there in all the books. But in modern-day America flying has become more about MONEY than anything else. Fiberglas gussets are universally available and inexpensive. They aren't in any of the books, of course. And never found at those wonderful seminars. Alas, the guys who are trying to keep grassroots aviation alive in America often can't afford either the books or the seminars. But they still fly, usually behind converted car engines and sometimes with a bit of drywalling on their ribs, not because of all the books or those expensive seminars but in spite of them.

-26 October 2003

Thursday, October 25, 2007

Chugger's Rib - II

For the last two months I've been making ribs.

The first one was made of Sitka spruce, aviation-grade plywood, T-88 epoxy and pneumatically-driven Arrow JT21 staples, which were then removed. When you include the cost of shipping the materials, each rib will cost between eight and twelve dollars.

For a load of 3.3g the central portion of the rib -- the part between the spars -- must be able to bear at least 88 pounds or 40 kilograms. The rib was tested in the manner described in... ( The rib was then laid aside and I began to experiment.

I made ribs out of different varieties of wood including redwood plaster lath and cedar fencing, as well as Western Hemlock and Douglas Fir. The wood was sawn to size with different types of saws -- table saw, band saw, sabre saw, jig saw and even a portable circular saw. The ribs were assembled in the jig previously mentioned (ie, Chugger's Rib) using gussets made of 1/8" doorskins (as described in... as well as aviation-grade plywood of 1/32" and 1/16" thickness. Some examples got the gussets applied to just one side of the rib, some to both. Then I tried gussets made of paper; some of which was thick, some was thin, some were done single-sided, some were both. I used Weldwood Plastic Resin and Gorilla Glue and Elmer's Ultimate Glue and some epoxy crap from the hardware store that came in tubes and T-88 and even Titebond III, although I didn't make a full rib for every combination of wood, sawyering, gusset-type, gusset-position and glue. I already knew how the glues performed with various woods but the ribs presented some new combinations, such as a cedar rib and mahogany gussets, or a Douglas Fir rib and paper gussets. Sometimes I'd use one glue for the central portion and a different glue for the trailing edge. All tolled, I made about two dozen ribs; almost enough for an airplane.

Then I broke them.

I didn't break them all at once, I broke them serially, usually after allowing them to cure for a week.

ALL of the ribs were strong enough to support the 88 lb load. My basic 'over load' was a 25 lb bag of lead bird-shot. For the first few ribs I loaded 2-pound pigs of melted wheel-weights onto the pallet until I got something to break -- often something on my test rig :-) It was all very precise and scientific and a total waste of time because the only factor of any value was where the failure would initiate rather than how much weight it took to break it. Since I could only discover the where by adding mass, if the rib passed the basic test I simply stepped on the pallet whilst supporting myself on the edge of the work bench, allowing my weight to come onto the pallet until failure occurred.

Except for the Sitka spruce used in my 'control' rib, all of the wood used in this experiment was scrap of one kind or another. The wood used in the rib shown in the illustrations is from a 6' piece of redwood plaster lath, picked up on a job site. Ripped on the band-saw, the 1-1/2" wide lath yielded four pieces of 1/4" square stock; twenty-four linear feet. Each each rib requires about 16' of 1/4" square stock.

The paper gussets were dug out of the garbage. In addition to the paper shown in the illustrations I used paper gasket material, a manila file folder and paper from a box of 'Wheaties.'

As a general rule, paper's strength is proportional to its thickness. However, the paper packaging for bottled beer appears to be stronger than that used for canned beer. I suspect the former is treated with a resin to improve its resistance to water.
Titebond III was used on the rib shown in the illustrations. All of the glues I tried performed equally well in that none of them failed at the glue-line. Urethane glues offered some advantage because of the fillet formed during their expansion. Gorilla Glue expands about twice as much as Elmer's Ultamate Glue and often caused a mess because of it. Titebond III proved to be the handiest as well as the least expensive.

Temperature was not a factor during the experiment, ranging from over eighty degrees to a low of about 65 (Fahrenheit scale). Relative humidity ranged between less than 10% to over 50%.

In some of the photos you can see a whitish dust. That is the residue of the brush fires we've had here in San Diego county. The stuff is so fine that it got into the shop & house. Vacuuming seems to be the only way to get rid of it and even then, it clogs the filter. Sweeping or brushing simply drives much of it back into the air.


Although 'fiber' gussets have been used in the past, I'm a bit wary about trusting my life to materials obtained by Dumpster diving. Low cost (ie, less than fifty cents per rib) and universal availability are the main advantages, followed by ease of fabrication (ie, gussets may be cut with scissors).

When using paper (ie, fiber) gussets you should apply a gusset to each side of the joint.

During testing the rib was not glued to the stubs used to emulate the spars. Failure of the rib usually occurred at the joint immediately adjacent to the spar, typically at about 4.3g (ie, ~115lb). When thicker gussets (ie, beer vs soda pop) were used at those joints allowed the rib withstood >5g. Once I've finished exploring the materials aspect I will glue a test-rib to the fixture to determine the rib's ultimate failure strength.

-25 October 2007

Note -- Why use different saws? Because a lot of you don't have a table saw.

The 12" band saw fitted with a 1/2" 8-tpi blade was the best alternative but was still pretty awful compared to a table saw. If all you have is a portable circular saw then make it into a table saw.

To use a saber saw or jig saw you have to start out with wood that is already 1/4" thick, such as plaster lath. This stuff is pretty shaggy -- they leave it rough to provide a good 'tooth' for the plaster or stucco. You'll need to clean it up with coarse sandpaper or a plane.

-rsh, 26 Oct


Brush Fires

We've had some. A lot of you asked how we were doing, others wanted to know why a California brush fire was such a big deal compared to their locally grown variety. I've posted a collective response on RAH and RAMVA.

Being a native Californian we're probably better prepared than most California families, although the main emphasis of our preparedness has been toward earthquakes. We keep the Important Stuff in one drawer of a filing cabinet and each of our vehicles carries a Bug-Out Kit that includes water, sturdy shoes, toilet paper and so on. I've also got a Medical Bag and that's what I want to talk about in this article.

Designed primarily for medical emergencies resulting from an earthquake, the medical bag focused on treatment of lacerations and fractures. But after breathing brush-fire smoke for the last week I've added a few items.

Saline nasal spray
Gauze face masks
Bronchial dilator

The saline nasal spray is commonly available. In a pinch you can make your own or even use plain distilled water. By preventing your nasal passages from drying out your body can filter out a lot of the crap suspended in the smoke before it gets to your lungs. And there is a lot of it -- your nose will run like a river of tar.

The face masks are more effective than a T-shirt or bandanna, although either will serve to keep out the particles of soot and charcoal. But only an industrial-grade mask can keep out the particles that clot your nose and end up in your lungs. And they don't make industrial-grade masks for children.

Smoke from a brush fire contains all manner of chemical contaminants, many of which trigger allergic reactions that can cause the air-ways in your lungs and bronchial tubes to swell. Bronchial dilators are medications that reverse the swelling. Albuterol is one such drug. It comes in an inhaler. You'll need a prescription for it, unless you buy it from an off-shore source.

An expectorant is anything that makes your lungs juicy and causes you to cough. (Breathe enough smoke, besides making you vomit, you'll be hacking up lungers that look like raisins.) For a first-aid kit the stuff you buy over the counter, such as Mucinex, should work well enough.

Oxygen is just that. The same thing you use in your plane. I've got an E-pax kit that includes a D-sized bottle of oxygen (about as big around as a thermos but two thermos-bottles in length), a regulator and two oxygen masks. Once you buy the bottle you can get it refilled at the airport ($) or at most welding supply houses. (Hint: Many welding supply companies are also the local source of USP-grade oxygen.)

If we don't learn from our experiences we're doomed to repeat them. This last week has been hell and the nearest fire was ten miles from the house. Even so, the smoke just about drove us out. Maybe this message will save a few of you from having to learn this lesson at first-hand.

-Bob Hoover

PS -- I'm depending on your common sense here. Read the labels. Learn to adjust the oxygen regulator.

Sunday, September 16, 2007

AV - Chugger's Tail

Back in May I mentioned I was using Pete Bower's Fly Baby as the basis for Chugger's tail. At that time (ie, 16 May 2007) I uploaded the drawings for the rudder and vertical stabilizer box-spars, which use 1/8" plywood shear-webs and 3/8" square cap-strips (as opposed to the 1/2" square cap-strips used in the original design). Chugger's tail is smaller in both height and span but I've tried to retain the elegant curves Pete used.

To ensure the four shear-webs would be identical, after rough-cutting them 1/8" door-skins I tacked them together on their center-lines and sanded them to final size as a single 1/2" thick slab. Since door-skins have an inner and outer face, when stacking them I made sure the rough-sawn blanks were oriented with the inner faces against each other.

The horizontal stabilizers use a built-up C-section for both their spars and diagonals whereas the elevators use box spars. As you can see in the drawings the diagonals are of a different size than the spars and are best handled as a matched pair. The six shear-webs for the spars are identical in taper but the elevator shear-webs are shorter. I treated these as matched sets of three, cutting the elevator shear-webs to length after sanding the stack to the proper taper.

Saturday, September 15, 2007

Design by Concensus

Back when the world was young and I still had hair the Navy hired a gaggle of eggheads to contribute to the design of what eventually became the Spruance-class of destroyers (i.e., DD-963 class). At that time I was the Leading Chief of the computer shop for Pac Fleet's cruiser-destroyer force. I was told to give the eggheads access to anything they wanted in the way of maintenance and repair data, which I did with a cheery aye-aye, sir.

Marvelous stuff, watching those eggheads at work, doing their computerized statistical analysis of equipment failures, tracking everything back to the manufacturer on one hand and the Navy schools on the other.

The product of their work was a list of recommended equipment to go into the new ships; only the best stuff as determined by its failure rate, required maintenance man-hours, mean time to repair and so forth.

Which was all bullshit, unfortunately.

At that time (early 1970's) ComCruDesPac had about 137 ships. The analysis covered such things as electric motors, pumps, air compressors, ammo hoists and so forth, the ancillary systems that are the glue of a modern-day warship. (The hull design and the turbine powerplants were determined by other groups.) The objective of the study was to determine the best of that equipment and on the surface, their methods of analysis appeared valid. But in providing them with data I noticed that while all destroyers had high-pressure air compressors (for example) some of them had never failed. (Not many... four, I think.) Same thing for the other components. All of the ships used a certain type of gear-head motors but a few ships had never reported any problems with them. Which brings up a point worthy of mention.

Even though built to the same plan, vessels within a given class are not identical. The ships are built at different yards and while their specs were identical their equipment came from a variety of manufacturers. In the case of electric motors for example, while most of the ships used motors from General Electric or Westinghouse a few of them had motors from manufacturers I'd never heard of. The key point here is that some ships had never reported any form of failure for certain pieces of equipment.

The bottom line is that the study failed to consider the possibility that some equipment had never failed. Their final report identified only equipment that had failed, giving high marks for designs and manufacturers that failed the least often.

Which completely ignored the Really Good Stuff.

- - - - - - - - - - - - - - - - - - - - - - - - - - - -

So what's all that got to do with airplanes? Quite a bit, when it comes to home-builts.

A fairly common thread on various aviation-related mailing lists and newsgroups is someone polling the subscribers in hopes of determining the ‘best' ...whatever. The best way to paint a spam can; the best brand of tire; the best vacuum pump and so on. Which gets down-right scary at times. (One such poll decided that the ‘best' aluminum was 6061 :-)

Polls and surveys, and the methods of statistical analysis that supports them, are valid tools. But only when your sample is an accurate reflection of the population being polled. Ask a room-full of pre-schoolers to define a balanced diet, don't be surprised if the answer is graham crackers and milk. In a similar vein, wood makes the best fuselage (according to builders of Pietenpol ‘Air Campers'), welding is easy (according to experienced weldors) and flying is inexpensive (according to people earning $100k p/a or more). In the case of the New Ship Design Study Group they failed to include the entire population of ancillary equipment, inadvertently limiting their investigation to equipment having a history of failure. (They were aware of the others but deemed them ‘statistically insignificant.’)


The Internet offers unprecedented access to information but does not provide any means of determining if that information is valid. Indeed, within the field of home-built aviation only a small percentage - - probably less than five percent - - of the available information is valid and even then, only in a particular case. The remainder is either skewed by commercial interest or is a reflection of ‘conventional wisdom,' wherein the poster is simply parroting something they have heard.

Common sense has become remarkably uncommon stuff in modern-day America. Given the risk inherent in rising above the ground on wings I believe the wiser course is to treat all information on the internet as invalid until you can test it yourself. Fortunately, with a technical subject such as aviation the required tests are fundamental and well defined. For the homebuilder, especially those lacking an engineering background, the tricky bit is devising methods of applying such tests to their particular situation.


PS - - So what happened with regard to selecting failure-prone equipment? I've no idea. By the time the first of the new class slid down the ways I'd been retired for a number of years. But it's interesting to note that several of the Spruance-class have been scraped after barely twenty years service. (Navy ships are designed for a minimum service life of thirty years.)

I identified the Really Good Stuff aboard our own ships and submitted a report on the matter, producing a minor controversy with regard to maintenance. Sailors know what I'm talking about and it really doesn't apply to anyone else.


(The above was originally posted to RAH in 2004. Recent posts to this blog [Chugger's Rib, 4 July 2007 and Chuggers Progress - III on 3 Sept 2007] have generated quite a bit of mail from folks who are upset by my failure to use Sitka Spruce, aviation-grade plywood and T-88 glue. The whole purpose of the Chugger files is to explore the use of less expensive materials that are commonly available. This isn't really a new idea. During World War II aviation was forced to use other woods, different glues and so on. History shows the planes (and gliders) flew just as well. Unfortunately, there isn't a lot of quantified data for those alternative materials. )

Monday, September 3, 2007

AV - Chugger's Rib

Labor Day, 2007.

Weather has been hot. A few miles north of us a mountain lion was seen drinking from a swimming pool and the coyotes are staying close to the few creeks that still have water. To hot to work in the shop, even with both fans going. Even the breezeway is pretty warm.

Too hot for welding and too sweaty for working on the fittings, I turned my attention to Chugger's wing. I have tentatively settled on the 4415 airfoil and needed some ribs for testing. I converted the 4415 coordinates into a rib drawing of the required chord, laid a few lines across it for alignment and printed it out. You'll find it in the Wing folder in the Chuggers Group, along with a pattern for the nose rib.

I didn't have a suitable piece of 3/4" plywood for the rib jig but did have some particle board that was wide enough. I don't like to use particle board for jigs because it's nothing more than thick paper and warps like a bitch but I glued a couple of stringers across the bottom and after the glue had cured, soaked it good with dilute varnish. That was a couple of days ago.

The several sheets that made up the pattern were trimmed along one edge using a straight-edge and razor. The jig board was given a coat of un-thinned varnish and each page of the pattern was painted with varnish on its back-side. The pages were then stuck to the varnished jig-board and aligned. Bubbles were chased to the edge of the sheet with my thumb and the whole thing was left to dry. But if you've never used this method, don't. It happens to be a quick & dirty method but varnish isn't a very good adhesive when applied to typing paper. It will hold the paper in position long enough to install the bits & pieces that will hold the rib's sticks in place. In doing so it will also fasten the pattern to the jig board. The whole thing will then get a coat of Deft Satin Finish Wax, which I understand is no longer available in the USA due to the tree-huggers. (The advantage of a wax finish is that nothing sticks to it.)

At this stage the thing looks like hell but it should work okay and only took a few minutes, if you don't count the clean-up :-)

I'm going to try using an Ison-type wing with wooden drag/anti-drag struts instead of wires or rods. The red hatch-mark is where the diagonal struts will pass through the rib. I'm also going to try building the ailerons in situ following the lead of Leonard Mulholland. I've not yet decided how to do the leading edge. I'd like to use 1/16" (1.5mm) birch ply but it is fairly expensive. Unfortunately the less expensive foam & fiberglas alternative, of which I've already built several samples, is about 3X heavier than the plywood.

I'm still tinkering with the leading edge but it looks as if I'm going to have to bite the bullet and run up to Corona (ie, Aircraft Spruce) for a couple of sheets of 1/16" ply.

After posting an article about building stick ribs in which I used 1/8" doorskin gussets attached with 1/4" aircraft nails and Weldwood 'Plastic Resin' glue I got several messages from people who found it impossible to use such small nails, having found they couldn't hold them with their fingers. The secret is to not hold them at all but to use the magnetic end of your tack hammer to pick them up and drive them into place. Unfortunately, that takes a bit of practice and since most of you are first-time builders I'll try using staples and/or pneumatically-driven 23 ga. wire brads.

The wing span will be a tad more than 28 feet, dictated by the available work-space (ie, about 15'). Chord is 56" so the wing's area will be approximately 125 square feet for a gross weight of 850 lbs, giving a 1-g loading of about 7 lbs per square foot. At 3.3-g that's about 22 lbs. With a rib spacing of 12" that's about 100 lbs per rib. Given the lift distribution of the NACA 4415 at its maximum angle of attack that means the portion of the rib between the spars will see about 80 lbs, the trailing edge will see almost no load at all and the remainder will be concentrated near the leading edge. One reason for cobbling-up a rib jig at this stage is that I want make and then break a few ribs to ensure they'll be strong enough.

According to the classic design formulas as published by Raoul J. Hoffmann (and others) in the 1930's, the aileron should be about 40% of the semi-span in length and 20% of the chord in width. As with the leading edge structure, this is another area I'm still tinkering with. If everything works out I'll post the required patterns in the Chuggers file archive.


PS -- Be sure to read Chugger's Progress - III posted on 4 July 2007. This post (ie, Chugger's Rib) produced a couple of comments that made it pretty clear their authors were not aware of what has gone before.