Saturday, June 9, 2007

AV - Tail Hook

I've called this a Tail Hook because I don't want people to use it for a glider hook, which is what it's usually called.

I made this one when I was drop-testing a landing gear. The maximum load was about 750 pounds and it handled that without any problems but it wasn't designed to tow a glider. Nor a banner. Or anything else.

But it does a nifty job of tying your tail down when you start the engine. Indeed, back when I was a kid a glider hook was often found on small planes that called for hand-starting.

The dimensions of the hook shown here were selected to match the tripod tower I used for my drop tests. But long as the function is not compromised you can make the thing out of just about any material, and of whatever size you need.

After cutting out the pieces I used a MIG welder to attach the side pieces to the mounting plate. With a bit of thought you can see how the side plates could be made from extruded aluminum angle and riveted to an aluminum mounting plate.

Similarly, the two pieces that make up the latching lever could also be fabricated from aluminum. But I think the hook should be made of steel. Not because of any strength issues but because you want the roller to bear against something harder than aluminum.

When installed, ensure the hook can flip all the way open. (See the photo.)


As mentioned in previous posts on this topic, socket-head pipe plugs are available as a bubble-pak'd item from after-market VW retailers. But as you can see in the photo the plugs are not anodized and do not include the 1/16-NPT size that is the best fit for the small oil galleries. (They give you 1/8-NPT's instead.)

However, this set of plugs may be the best option for lo-buck builders, who often substitute brass fittings for the full-flow oil filter connection and a brass 1/2-to-1/8 NPT bushing for installing the oil temperature sensor.



After posting 'Oil Plugs' on 1 June '07 several people wrote to tell me there were other types of control valve plugs available. Which I already knew... but the fact they thought I didn't means a lot of you might not be aware of what's out there, especially with regard to parts suitable for flying Volkswagens.

So let's take care of that.

Go over and click on the photo. (Don't mind the cat; he always does that.)

The left-most plug is the stock item. Next to it is a plug that has an M12 crankcase nut welded to it. Two of the flats are drilled for safety wire.

The two socket-head plugs in the middle of the picture are typical after-market parts. If you're careful and use the right set-up you can drill these for safety wire.

But the plugs I prefer to use are the hex-head type shown on the right-hand side of the picture. To drill them for safety wire I first open them up with a half-inch Slocum... what folks usta call a center-drill. (I think half-inch is about a #4.) Once you've opened them up axially you chuck them in a drill-vise and drill each of the six faces with a 1/16" drill bit spinning about 3000 rpm. I use a drop of hi-sulphur cutting oil. The drillings are then chamfered so as not to notch the safety wire.

Building just one engine means drilling only two plugs, which is a pain in the ass since it takes longer to do the set-up than to do the work. It becomes more efficient if you do about two dozen plugs at a time - - enough for twelve engines -- since that distributes the set-up across the whole batch. (Yeah, I know... but there it is.)


Mixed in with the friendly messages from people pointing out that other plugs are available was a couple that took me to task for even thinking about safety-wiring the plugs. As they pointed out, they had never had one come loose and that the odds of one doing so was probably ten-thousand to one.

Which is why we want to safety wire the things :-)

A lot of folks will miss that and beating them over the head with it is a waste of time, in my opinion. The truth is, there's a few threaded fasteners for which you can't provide safety wire or a Cotter key. But when you can you always do so even if the odds are 1:10000 because it shifts the odds even farther in your favor.