Bad Driver

Hi guys,

I am hoping an experienced designer/builder/flyer can give me some advice please?

I want to design & build a twin trainer model with a similar double fuselage layout to Twinmans 'Twin John' but due to transport & storage limitations it will need to have removable outer wing panels.

Initial approximate specs are 72" span with a centre section, inc. fuses, of 18" therefore each wing panel will be 27" long.

So my question is this... how much should an aluminium (7/8" or 1" diameter) wing joiner tube extend into the outer panels for good strength & security? Are there any rules of thumb, 30%, 50%?

I intend to fit the phenolics (tube outer, female pieces) between the spars and use shear-webs in the gaps above and below so the tubes are firmly coupled to the spars. I was thinking of running a single tube full length thru the centre section, having it protude the required amount into each panel.

I would appreciate any help, thanks.

(And apologies to Twinman for graffiting his image below)

Ed_Moorman

My Feedback: (1)

If your transportation can stand a longer wing, why not build a 1-piece wing and join the stabs in the center? I have a twin fuselage World Models Sky Raider Mach II done this way and it has worked well. It's about as simple as you can get for twin fuselages.

I clipped the stabs off so they butted up against each other, added hard tips and used landing gear clips and button head screws to secure them together for flying.

I built an extended center section which holds the receiver, battery and switch.

Each fuselage has its own servos. The throttles are on different channels and mixed.

I made a simple cradle to hold both fuselages at the correct distance for assembly.

If you want to do the plug in wings, contact Damon Young at [[email protected]]. He did a twin fuselage Sig Somethin' Extra with plug in wings. He can tell you how he did it.

jrf

My Feedback: (551)

Go in through the third rib bay. The outer rib should be plywood or at least doubled with plywood and you will need a tube stopper glued over the end of the female tube. It wouldn't hurt to use a plywood spar web between the fourth and fifth ribs. The root rib should be plywood as well. All of the stresses are concentrated on the root rib and the rib at the end of the tube.

Jim


Edited to correct rib call outs.

twinman

My Feedback: (2)

I am sooo honored. You will love this type of plane.
Ok, this and my twin fuse ugly stick did not use wing tubes..Lazy and in too much of a hurry.
The wing is one piece and in the Twin John case, useing dowels into the two fuses at the front of each wing and normal wing bolts at the back.
Unbolt the wing and lay a piece of plywood across the two fuse's in the area of the wing bolts and bolt it to the two fuse's to secure the double fuse assemblies. Viola..Done and it works.
My two cents.
Now this plane due to it's light size uses only one servo for the rudders and linkage across the two rudders, like the GP P-38. However, the main rudder, is controlled via Pull Pull system to reduce play in the linkage. One servo on the elevator, on one side.
Now, having said that. If you intend to really power up your project, use one servo for each rudder and two for the elevator. The old Wing Mfg used one elevator servo and many of them fluttered.
When I built the twin fuse ugly stick I used pull pull on the rudders and two servos.
The wider you build the engine spacing, the more aerobatic it will be and better knife edge, but slightly less stable on engine out. The Twin John uses two ST 45's and 12x4 props. It will easily take off and fly on one engine.
Good Luck,
Twinman

Bad Driver

Ed, Jim & George,

Many thanks for your replies!

Hopefully I have attached a 'sketch' of my initial design with most of the numbers on it - not too happy with the elevator aesthetics yet but I need to draw a full-scale side view to check the fin/rudder/hori.stab./elevator layout. I have gone for biggish rudders with lots of throw as suggested Mean't to be a sort of sports-fun-fly-trainer.

Lets see what happens.....

[Edit to attach larger image]

jrf

My Feedback: (551)

That design will work fine as is. I would personally double the size of the ailerons for more roll rate and lengthen the fuselage to 50" or more for better tracking. The tube extension into the outer panels looks perfect.

Jim

Bad Driver

Hi Jim,
Thanks for the vote of confidence in my design [sm=thumbup.gif] All based on Twinmans suggestions and using a neat little Excel spreadsheet (by Lee van Tassle) that I found somewhere. And not forgetting Profili for the airfoil.

Yup, I was wondering about making the root dimension of the ailerons 4", i.e they wil taper from 2"tip to 4"root, thus giving 50% more area, although I know it is less effective inboard of the wings. It'll look a little prettier too!

As for fus length I am limited by my small car, hence my original idea for the removable outer wing panels. Maybe if I fit the fus diagonally in the trunk (boot to us Limeys ) I might be able to gain a few more inches. I'll have to get the tape measure out.

BTW, I forgot to mention that the airfoil is a symmetrical NACA0016. The wing centre section passes through the centre of each fus and all will be glued up solid; the hori stab will have a carbonfibre tube spar to cope with any twisting forces. I'm hoping the smallish flap will help the elevator out once coupled together. Vertical fin & rudder will be about 95 square inches (~9.5% wing area) and the rudders themselves will be 50% of that.... not 3D size but should help with an engine-out scenario.

Once I get some money together I'll order up the balsa and start building

twinman

My Feedback: (2)

Hi Mr Driver,,,or Howdy from Texas
I actually was happy to see the center flap. I did that with my twin Ugly Stick and as you said, coupled it to the elevator, but I ALSO coupled the ailerons. Up elevator, down ailerons..and then flap. No, way to tip stall.
Eventually, couple the engines to the rudders for better knife edge and fantastic flat spins. To get out of the spin, reverse the rudder and so the engine thrust. Do not over do this mix, or the plane will flat spin too fast and the slower engine will starve for fuel..Been there, done that...GO to idle NOW neutralize the controls and let it fall out, if that happens.
My Twin John has a center to center space of 12 1/8" or 310mm. That just clears the 12 props.
Good Luck and keep us posted.
Twinman

Terror Dactyl

I have seen "The Flat Spin Form Hell" and it does take a while for the bird to fall out of it if the opposite side motor gone dead stick. I do remember at least once seing the nose get back up to flat as the ground caught the fall.

I will have to say it was hard to tell if the motor had died or not as we were not sure if we could hear any motor, due to the sound of knocking knees coming from the area of the field were the transmitter was.

I was given a chance to fly both and it is a joy to fly holes in the sky with either of them. Twinman is right in that you have to be carefull about the spin speed as you can actually spin them too fast (who would have thought).


I did actually watch Twinman take off the Twin John twice with only one engine running. It went through its paces a little sluggish but did fly very well, except when the spin direction had the motor go back to idle, but a slow and bad harrier is not a problem in this case.

Bad Driver

Hi George,
Can I take that as your seal of approval on my design? I promise I won't sue if it crashes, lol

But serously, are there any changes or other tips/advice you could offer?

The idea is for this to be an intro into flying warbird twins so I'm not too concerned with it's ability to flat spin, but some aerobatics would be cool.

Many thanks,
Steve

twinman

My Feedback: (2)

Hi to our British Cousin.
I am not worried about lawsuits. You guys have the English Rule and so a far legal system...boy am I going to hear on that one!
Your design will be a lot of fun. I have built two such planes and loved them.
Good Luck,
Twinman
PS If you want to bug, William Robinson...get a pointy nose somewhere. Tee Hee

William Robison

My Feedback: (3)

Bad Driver:

Attached is a picture of Twinman's "Gooseplane." You will note the straight taper of the nose. Yes, it's ugly but with the application of a suitable lubricant it is much more effective than a more attractive curved forward section of the fuselage.

Just be sure not to lean over when he's flying it.

Haw.

Bill.

Terror Dactyl

You forgot about the saying" where the sun dosent shine" or something like that I believe.

The Twin John will be a good exercise in building and get you used to seeing a different look in the air, BUT I guess that George forgot the disclaimer again.

When we have said that it will do almost everthing on one engine it is not a typical twin. It is like the Duelist I have. When I first got mine (used and only had to add a receiver) it had two very used K&B's on it and on the second flight one went deadstick but as there were other loud planes, in the air, I did not know it till I made a pass down the runway and that was after at least three turns and probably some stuff in the backside pass as well.

Most other birds will not be anywhere that nice. I guess what I am saying is unless you feel very "10' tall and bullet proof" make sure you use a gyro on the rudder or the remaining engine will carry the rest of the plane to the scene of the crash on an engine out condition.

twinman

My Feedback: (2)

William,
Your killing me.........but 9 points anyway.
Twinman
PS Now that design is NOT a trainer, but fun to fly.