jacobezzell

I'm thinking of kitbashing an LT-40 into a twin engine, and thought putting a twin stab tail on it like a B-25 would be cool, so I could have the rudders in the airstream of the engines. Anyone ever done this? Mainly I need help figuring out how to rig up the rudder servo(s). My last LT-40 was converted to a taildragger, if I could do that for this one too I'd like to... any way to run both rudders and a tailwheel off one servo?

This is what I'd want the tail to look like:

vmsguy

There's a B-25 build thread that I found really interesting. The author goes into picture detail of building twin tail, and controlling the rudders. See link below. When I read the thread, I thought his first idea of of controlling the rudders really intriging. But I think he put the center "arm" too far forward.

I did a couple drawings and attached them. The first one shows what the builder did. I think this shortened the range the rudders could travel. The blue lines are control linkages. By not being at 90 degree angle to the rudder arms, he couldn't get full travel on the control linkage before the rudder arm and the linkage became a straight line to the center control arm. As you can see in the second drawing, by moving the center control arm back as far as you can, you increase the amount of travel the control linkage has.

I know I'm not explaining it very well. Best thing is to try it. Hold a control arm in you finger and thumb, so it can pivot. Put a linkage on it. With the linkage running down your arm, you have a wide range of motion on that arm. But put the linkage away from your hand, you get less. Look at pictures below. #3, best amount of travel on control arm. #4, less travel. #5, almost no travel.

Hope this makes sense.


As for the LT-40's tail, it'll be interesting how you manage to get the line inside the tail. It's not very thick.

Oh, I saw another thread that was interesting. The builder was faced with your problem. He put a rudder-ette under the elevator. It really didn't do much. Except.. He ran the servo control to the rudder-ette. Then from it, a hard line out to each rudder. Kind-of interesting solution. Can't remember where I saw that thread though.

Here's the B-25 build thread:

http://www.rcuniverse.com/forum/m_48...tm.htm#4838368

jacobezzell

I think the rudderette idea is fantastic, I may end up doing it that way... especially because then I can mount the rudder servo in a dozen more ways than if I tried to slave both control surfaces off the servo directly. I could even run my tailwheel off the rudderette.... Genius! Thanks

Ed_Moorman

My Feedback: (1)

The Twin-Air 45 comes either as a single tail or a twin tail version. The twin tail conversion was talked out on RCU and done by Walt Kahres. They went through several different methods until they ended up with this one. After Walt flew his plane, the factory brought out a twin tail version using his method. I am attaching his photos from the Multi-Engine & Twin Forum.

I have seen this airplane fly several times and it has excellent rudder control and I know he didn't have digitals on rudder when I saw it.

jacobezzell

Wow, that is a super clean solution. Though, I'm suprised there isn't trouble with binding with that much twisting, do you know if you would have to use a better servo than a plain old Futaba 3004 Std BB servo (or equivalent?)

I can't tell, is that using steel cable inside the guide, or plastic rod inside, or something else?

w8ye

My Feedback: (16)

It looks like the yellow plastic type Nyrod to me. It has a plastic pushrod inside a plastic sleeve.

N1EDM

My Feedback: (2)

OK, I'm interested too. I might have another LT-40 in my future... this gave me an idea or two.

How about rudder sizes? Would one make each rudder, say, 75% the surface area of the stock rudder (to compensate for being out of the direct airstream)? What design factors should be considered? I would think that this is going to add a fair amount of tail weight, even with the lightening holes. Or am I wrong about that?

My reason for making this mod would be to use the LT-40 for a glider tug, so that the tow line would not hit the rudders...

I think I'm going to hate running across this thread... it'll be another project to play with

Bob

OzMo

My Feedback: (3)

be careful to secure the tubes well at each former. don't ask how i know. your rudder may need a stouter servo than an lt 40 do to the increased power and weight.