Tip: DIY Locking Tailwheel

[Toobuilder]

While fully functional, I've never been a fan of steerable tailwheels with the external chains, springs, etc. So in the spirit of "why not?", I decided to try a locking tailwheel for the Rocket. And of course, I didn't like what was commercially available, so I decided to whip up a prototype and see how it worked. Admittedly, the design goals, even if fully realized, are hardly a clear cut advantage over the Vans or similar designs. The design goals in no particular order are as follows:

Lighter (nailed it- this one is half the weight of the standard setup)
Less drag (probably - but doubtful I'm going to see a speed increase. I'm going to claim 50 knots until testing proves otherwise)
Less likely to snag on stuff (the wheel is smaller, but the whole assembly is shaped to slide over obstructions)
No load on the rudder (yep, no connection at all)

And the big one: satisfy my restless need to change a perfectly functional design for no apparent reason.

Anyway, the concept of operation revolves around a spring loaded pin that locks the kingpin within a few degrees of center. When locked, I have enough slop and flex in the stinger to perform shallow s turns on the runway, but I need to unlock for tighter stuff. I have made a few landings with the thing completely unlocked as well as locked. Neither are a problem in normal wind conditions. Now that it's installed "permanently", we'll see how it holds up in regular service.

I'll keep you posed as I get some hours on it.

[Tom Martin]

very cool Michael, any weight savings, that far back are important. Do you use a cable to unlock the pin?
Get flying, I want some flight reports!

[Toobuilder]

Thanks Tom. The locking pin is a 1/4 inch piece of hardened shafting that rides in the tube on top of the stinger socket. Also in that tube is a compression spring which provides the motivation for the pin to remain locked. Finally, and not very visible in the picture, is a cable guide that runs out of the tube, along the stinger, and up to one of the fuselage bulkheads. I was going to use a motorcycle throttle cable here, but I found a surplus push pull (heater, vent, etc) cable assembly laying around the shop. Since one end of this thing already has a nut for a bulkhead connection, it worked out well. I have a piece of music wire pulling the pin. This design differs from others I've seen in the respect that the actuating mechanism is completely enclosed - there's no wires to snag on brush, rocks, etc. Anyway, Fwd of the bulkhead connector, the music wire is crimped to 1/16 aircraft cable running through snap bushings all the way up to the fuselage bulkhead near my left knee. Currently, I just grab the cable and pull a little sideways to unlock the pin. Future plans include a dedicated lever mounted low on the throttle which will snap over center in the "unlocked" position. If This works out as planned, advancement of the throttle will automatically move the lever back to the locked position in case I forget.

Before anyone asks why I didn't do it like a T-6 or P-51 and have down elevator unlock the pin, I'll tell you that I did not want to find myself in a situation where I needed "down" elevator taxiing a Rocket. The tail is just too light and I don't want to get in the habit of casually moving off of full aft stick. I think that's a prop strike waiting to happen.

[pierre smith]

Michael, save some more weight by attaching the cable to your elevator pushrod, the way all Air Tractors are done.

With the elevators level, the stick is locked. With the stick all the way forward, it's unlocked and we steer with brakes and rudder taxiing, no cables at all.

Best,

Edit..didn't read your last paragraph regarding down elevators.

[F1Boss]

Originally Posted by pierre smith

Michael, save some more weight by attaching the cable to your elevator pushrod, the way all Air Tractors are done.

With the elevators level, the stick is locked. With the stick all the way forward, it's unlocked and we steer with brakes and rudder taxiing, no cables at all.

Best,

Edit..didn't read your last paragraph regarding down elevators.

Make it so the lock is engaged with the elevs full up, and dis-engages at the point the elevs are in trail. Seems like this would be owners- choice (the F1 has a heavier tail weight, so down elev is a smaller problem) as the owner could set it up either way (cable clamps to the elev push tube).

If the cable attached to the elev horn, the setup might be easier.

The Beech 18 uses a twist-lock cable to unlock a small pivot-mounted pc of 1/4" thick steel bar that lays in a slot to lock the wheel. As with your design, it allows some deflection so taxi is not such a problem. Operating this system is easy, and intuitive.

Great stuff, Mike!

Carry on!
Mark

[vfrazier]

Reducing weight is easy if you simply change to one of our lighter weight tires.
http://www.flyboyaccessories.com/category-s/23.htm

For your use, this one is probably optimal:
http://www.flyboyaccessories.com/4-i...ire-p/1003.htm

Clever design. There is always more than one way to skin a cat. I do have to ask, what's the weight of that long cable?

[Fhuber]

Michael, It looks like you have created a well thought out design to meet your needs. I continue to be amazed by all the great ideas folks on this site come up with to improve their aircraft. Nicely done!

Frank

[Toobuilder]

Originally Posted by vfrazier

Clever design. There is always more than one way to skin a cat. I do have to ask, what's the weight of that long cable?

It's 10 feet of 1/16th aircraft cable (no outer sheath) running through a few snap bushings.... It's only a few ounces.

The whole tailwheel assembly, cable, etc. weighs a little under 2.5 pounds on my digital fish scale. Contrast that with the vans assembly, chains, etc at a touch over 4.5 pounds

[vfrazier]

We have a smaller version of our Screaming Eagle tailwheel assembly that is intended for Sonex and other light taildraggers. It may be possible to put it on an RV or Rocket, but we haven't tested it on them. It weighs 33 ounces with the 4" tire.

http://www.flyboyaccessories.com/product-p/1130.htm

[jrs14855]

You can have the best of both worlds by using a single steering arm and disconnecting the steering arm for tight turns and moving the airplane around.
The release pin is set up on the steering arm, requires a retainer for the top.