Trophy Trainer - undercarraige location

[Ian Hewitt]

Hi Stunthangar,

Apologies for resurrecting a well worn thread..

I really like the look of the Trophy Trainer which I first encountered following the discussions on the Trifector thread. I have run off a copy of the plans that appeared there and have started cutting out a set of ribs - long hand.

I am a bit mystified about the details of the undercarraige location in the wings - specifically the location of the torsion bar blocks. I usually fly from a grass field near my home in Nottingham, England and it can be a little unforgiving sometimes. I am thinking that the blocks might need some ply re-inforcement to the leading edge of ribs in which they fit and maybe a ply spreader on the lower spar.

I would be grateful for any advice on this.

Best regards

Ian

[Tim Wescott]

Keep in mind that 1/8" music wire is pretty flexible.  If the landing gear is correctly designed and built, you'll have a spring in there that will absorb lots of shock.  With the forward sweep of that gear, you should be fine.  Don't glom on too much weight -- keep in mind that your block is up against the spar; just glue it there & you should be OK.  Do make a socket to receive the end of the wire.  The way that landing gear is arranged, as the wheel is pushed toward the wing the end of the wire plugged into the wing will want to turn toward the back of the airplane.

Here's a (unfortunately poor) picture of some landing gear that's lasted me well over 500 flights.  If you squint, you can see the socket in question -- it's a slot cut in 1/8" plywood, faced with 1/32" plywood and glued to the rib.  You'll see that it's no wider than the landing gear block.

The socket will serve as a doubler.  I'd use a modest doubler at the other end of the block, to spread the force to the wing.  You can probably just follow the plans and be OK.

As pictured, this is more stout than it needs to be.  If you ever find pictures of how Bob Hunt does this in his foam wings you'll see how much extra wood there is here.

[Ken Culbertson]

Let me build on Tim's response.    I come from the school that landing gear that is stronger than it needs to be to land and take off is just extra weight.  If you fly over grass it needs to be a bit stronger but not too much.  If you hit hard enough to damage the gear it is far better to have it break off clean than it is to take out half of the wing.  If glued to the spar and a couple of ribs it is plenty strong.  I use a longer block than most so that I can vary the stiffness of the gear by how long I make the center part.  It also makes it easy to make a second set for that huge prop someone talked you into trying and easy go back to the original when it doesn't help!  I also recess the block the thickness of the planking so that I can cover the opening with a bass plate held on by counter sunk brass screws instead of blind nuts then sand the whole thing flush.  No sense putting oddly shaped vortex generators on the bottom of the plane!  Consider putting an aluminum tube into balsa for the end blocks - lighter and be super careful to not put anything where the leadouts will be moving.  Nothing ruins your day faster than doing a bench check and hearing that rubbing sound then shining a flashlight down the leadout slot and seeing that lovely landing gear post in the way. 

Ken

[Ian Hewitt]

Many thanks for the responses - they are very helpful. The photograph is great Tim.

I can see how to move forward and what is involved.

Thanks again

Ian

[Brian Massey]

I've built 5 or 6 TTs over the years, going back to Tom's original that did not use landing gear blocks. I've almost always flown on grass, and have never had an issue. Glue the blocks well against the spar and ribs, and you should be good.

When trimmed out, they fly very well!!

Brian