Biplane Aileron Interconnection

[Steve Hargreaves - Moderator]

Anyone got any thoughts on how to interconect top & bottom ailerons on a biplane?

I have a Pitts Special with 4 ailerons (servos in bottom wing only) & the instructions show a control horn mounted towards the trailing edge of each aileron with a rod between to transmit the movement...this works except it introduces horrendous differential because the bottom (driven) control horn is moving through the arc of a circle hence the motion passed on is not linear. I have connected the link rod at the bottom hole of the control horn to try & minimise this effect & whilst it works I can't help feeling there must be a better way.

I had wondered about fitting a heli style ball-end to the very tip of each aileron & connecting those.....anyone got any better ideas???

[Mike Rolls]

Steve
If you use a link from the extreme TE of one aileron to the extreme TE of the other they will move the same amount - at least mine do. My method is to use a short piece of ply let into each aileron, projecting horizontally behind the TE, hole in each close to the TE. linked by a ros with a Z bend on one end, clevis on theother.
HTH
Mike

[Chris Dickens]

Steve
Your idea of ball link at the trailing edge will give you a just about perfect set up, fit them at the same point as the servo linkage, or middle of the length but make sure that you have adequate hard points to screw the balls to.
An even better solution would be two more servos in the top wing.
Chris

[Steve Hargreaves - Moderator]

Thanks Mike....that sounds a good plan.....I was thinking about letting a 2mm bolt into the aileron TE to take a ball joint but your idea sounds more secure!!!!

[Steve Hargreaves - Moderator]

Chris the extra two servos in the top wing would be a lot of hassle....the Pitts is only 42" span so it doen't really need them. I was thinking to carefully drill a 1.5mm hole into the TE & epoxy a 2mm bolt in there to about 25mm depth to take the ball.....think this will be strong enough? I'm really not sure how else to do it...letting some ply into the aileron might work but would be difficult to do neatly.......

[Myron Beaumont]

On the Flair puppeteer (funnily enough the final job for me to do ) there are small metal plates fixed 1/2 chord of the ailerons top and bottom ,opposite each other so the motion transmitted is linear (I hope if my knowledge of trig is correct ! )They are joined of course by the usual "bike spoke" with plastic clevises each end . Differential is increased by setting the drive control horn behind the centre line of the hinge as well as 70 degree offset (included angle ) on the servo driving plate between the two ball joints screwed into it . Can't see much difference with your Pitts except that my configuration runs off one central servo as you will have guessed.Grumpy Myron .

[Steve Hargreaves - Moderator]

Hi Myron......I'd be interested to see how it works out. You will have to connect a rod to these metal plates somehow & I would guess that means attaching something with holes in it above the surface of the aileron. This will raise your connection point away from the surface of the aileron thus excacerbating the non linear element of the motion.

As the metal plates are behind the pivot point they must by definition move in an arc around the pivot......an arc is not linear motion & I think you'll find that for 10mm up movement of the "driven" aileron you'll only get about 8mm of the "slave" aileron where as for down movement 10mm on the "driven" aileron will give you about 12mm of the "slave"....thats certainly what I'm finding anyway & it gets worse the greater the movement.

It seems to me that the only way around it is to connect at the trailing edge as you can get to the centre of the aileron "depth" (if you follow me) & reduce the differential effect since both trailing edges should move through the same arc being the same distance from the pivot point ie the hinge......

[Mike Rolls]

I've put a rough sketch of my method in the gallery (Mike Rolls)

Mike

[Mike Rolls]

In my sketch Ihave shown ailerons of equal chord - if they have different chords the 'horn'on the narrower will need extending if equal movement is desired.
Oh - and don't use clevises on both ends; vibration may cause the link rod to rotate within them.
Mike

[Bob Cotsford]

You could always have a ply, tufnol or aluminium rib in the aileron with a cut-out around it to allow a quicklink or ball-link to attach to the rib on it's centreline. That's the way it's done on a lot of full-size. On the Jungmeister the 'rib' also extends forward into the wing to allow a second link ahead of the aileron for a pull-pull drive.

[Myron Beaumont]

Mike
This is getting complicated but bear with me .with a fulcrum point Above each (or below) the ailerons. One compensates for the other (nearly)I appreciate what you're saying & have done a few drawings to see what is happening (back to the drawing board Eh)
Before I commit myself to finishing my Puppeteer,I'm satisfied that even a few degrees discrepancy won't affect it's flight .'cos lots have been built & flown .& so I'm told is a very gentle performer unlike a Pitts an aerobatic m/c .I think I'll stick to the plan & suck it & see .
Can't access your diagrams by the way -I'm not very good on this dirigible confuser .

[Myron Beaumont]

Steve
just realised I'm talking a load of C--p There is a small angular discrepancy between the upper & lower ailerons but Does it really matter ? I don't like to think that it's not Right but on the other hand "if it ain't broken don't fix it " someone once said
Get my drift ?

[Mike Rolls]

Myron
If you go to the gallery you shuold be able to access the gallery called (great originality) Mike Rolls.

On the geometry - the ailerons and the link effectively form a rhombus (if I have remembered my maths from nearly 60 years ago!) a quadrilateral in whihc both pairs of sides are parallel but the angles aren't right angles. The distance between the two ailerons on their hinge lines is fixed, so ar the aileron chords, the link is rigid, so when the driven ailerong moves the linked one has to move the same distance (unless you have excessive slop in the system.)

HTH
Mike

[Myron Beaumont]

Mike
Yep - found it (trapeziums or trapeziA) come to mind ! Must do a bit of thinking ,but as I said- If it's apparently worked on previous builds should I stretch my brain cell plus it's neuron anymore ? I'll answer that myself by saying that I want it as near perfect as possible
LITERALLY BACK TO THE DRAWING BOARD !
bY THE WAY -YOU MUST BE CLEVER TO WORK OUT HOW TO PUT A SKETCH ON THE SITE -i CAN'T EVEN SORT OUT CAPITAL LETTERS WITHOUT HER INDOORS !

[Mike Rolls]

Myron
Just checked - the figure I had in mine is a parallelogram (obvious, I suppose if I had thought of it). A rhombus is a parallelogram in whihc all 4 sides are of equal length (marvellous things, dictionaries).

On the adding pictures front -as one who needs both hands to find the on/off switch, it is quite simple. If you click on the gallery tab at teh top of the page it will take you through the process step by step. One thing it could tell you earlier than it dies is that the maximum file size is 250kb.
HTH
Mike

[Tom Sharp]

The top aileron is best set up with a differential so that there is very little down movement when compared with the bottom wing aileron's full down movement. This is due to the fact that the air passing though the upper and lower wings is pressurised and too much down movement on the top aileron will cause drag which can stall both upper and lower wings on the downgoing aileron side of a Pitts type model.

[Myron Beaumont]

Tom
Wow -Now I'm on a new learning curve !(this is my first bi-plane with ailerons-the last was a Veron kit 1/1/2 Strutter with none))
I find it very interesting- your comments etc. - just wondering how to proceed to do the job "proper".It's the last thing to decide what to alter/modify since I started about 150 hours ago.

Mike
What is 250 killer bites ?
when 'er indoors comes 'ome with another b--t kit I'll ask 'er !

[Mike Rolls]

Myron
The file size - if you look at the list of your picture files in Windows Explorer and hover the cursor over a file name it will show you, amongst other things, the size of the file.
HTH
Mike (HI can probably explain better!)

[Tom Sharp]

With the Puppeteer all four ailerons flap about so much that all aerodynamic theory goes out the window. But fly they do and well. I have even seen one flown without one aileron connecting rod connected to the bottom wing. And the pilot didn't even notice until it was pointed out to him after an uneventful flight.

[Myron Beaumont]

Thanks for comments each of you both !
Couldn't sleep pondering over the aileron question so I loosely assembled the ailerons on one side top & bottom (masking tape ).It was immediately obvious that with them hinged on the top surface together with the fact that my built -in metalplates 6mm above the lower aileron's top surface they move more or less the same amount over an arc of about 30 degrees i.e maybe 2mm difference at the most (measured withbleary eyes at 4.19 am. Maybe I'll now get some sleep now my brain has shut down at last.

[Steve Hargreaves - Moderator]

Blimey...you go to work for a day or two & the thread explodes!!!!

Tom...your theory sounds interesting if a little worrying...I was aiming for equal movement of all 4 ailerons but from what you say it sounds as though lots of differential is the way to go...I assume it also follows that as well as top aileron going more up than down bottom aileron should go more down than up as the upgoing side is in the "high pressure" area between the wings.....

Just having a play in the shed last night it seems to me that using ball joints will work well but might limit the movement as you can only get about 30 degrees on a ball joint before it fouls the screwhead or locknut.....my next plan is to use Mikes method of a ply horn let into the aileron but use the ball joinf fitted to side of the ply so the ball mounting screw is parallel to the hinge-line (is that clear??). This should mean almost unlimited movement......we'll see!! It also occurs to me that using this method you could incorporate some differential by assymetic ball spacing (oooo painful!!!) or angling the ply hoens slightly....

Incidentally Myron you'll probably find the Puppeteer will be ok as standard...my Pitts flies fine as it is but I do like responsive planes that move as soon as you touch the stick so I was looking to up the movement a bit & thats when I hit the snags!!!

[Tom Sharp]

Steve
The Pits wings are staggered, so the trailing edge of the bottom wing is away from the pressured area and should be set up as per normal.

[Evan Pimm 2]

And don't worry about `pressure' areas between biplane wings, there ain't any. There is no way any model airplane can go fast enough to change the pressure of the air enough to cause any aerodynamic changes that we would notice. Most biplanes will appreciate a bit of differential though, it helps with the adverse yaw, along with some aileron/rudder coupling.
Evan.

[the unmagnificent man]

Hi all, Steve, I used the screw and ball joint method in the top aileron and control horn attached to the bottom aileron. It works fine but I have to admit that due to the weather I havent actually flown it yet....Possibly tommorow....more soon. Good luck. Al

[Steve Hargreaves - Moderator]

Hi all....just an update....I modified the Pitts as per Mikes suggestions & let a 20mm tab of 1.5mm ply into the rear of each aileron & used a rod between...see pics

You can see where the old horn was but this works much better...no differential same movement top & bottom so all is good. Not flown yet but I'm sure it will be OK.

I was surprised how strong this method was...I cut a slot into the aileron using a dremel disc...slotted the ply in & ran cyano into the joint......doing a bit of testing with some scrap TE showed the TE would break before the ply & that was at quite considerable loading......

Just about to hit the submit button so I hope the picture upload works...here goes!!!