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excessive aileron play

Old 04-20-2010, 03:32 PM
  #1  
khelsea
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Default excessive aileron play

Does anyone see anything wrong with this setup? I have about 3/8 in play in the aileron that seems to be accenuated by the new MG gear servos I have. The linkage itself is tight but I'm thinking the combination of the layout and MGears is creating more play than I'd like. I have put those servos in another plane with HD Dubro hardware and it works good. Tnx, Lanny
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Old 04-20-2010, 04:11 PM
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TedMo
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Default RE: excessive aileron play

I have never seen a set-up like that and am not sure what you mean by play. To me play means movement allowed without movement of the control arms or horns.In respect to the servo movement. What I see here is improper location of the horns. The attachment of the control arm to the horn must be directly in line with the hinge pivot point. If not you will get more throw in one direction than in the other. Is that what you refer to as play?
Old 04-20-2010, 04:21 PM
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Default RE: excessive aileron play

Could the play come from the pockets where the hinges are inserted into?
Could the horn be bending when the pushrod is under tension?
Old 04-20-2010, 04:27 PM
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Jetdesign
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Default RE: excessive aileron play

Metal gear servos have gear 'lash' which is a small amount of play between the gear teeth. It prevents the rigid teeth from binding. Precision aerobatics pilots often choose plastic gears specifically to avoid the gear lash and have more precise control linkages.

I have had issues with the metal clevises you are using - often there is a small amount of 'play' in them as well. I use ball joints on both ends of the control rod.

I have never seen the setup you have either, but it looks to me like your hinge point has been shifted back by the type of hinges you are using, and thus I don't think your horns are improperly located.
Old 04-20-2010, 08:14 PM
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Gray Beard
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Default RE: excessive aileron play

I too have never seen a set up like that, like Ted mentioned, there is a problem with where you have the control horn and it looks like the control rod isn't the correct size?? Looks a bit on the short side?? The term play is sort of a mystery, play would be what we used to call slop, like when the holes in the horns start to wobble out a bit you get a little slop or play in the controls. Joe mentioned the metal gears lash, he is correct but it is very small, you would notice the slop in the over size holes in the horns more?? Slop, I like that term!!
Old 04-21-2010, 08:31 AM
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khelsea
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Default RE: excessive aileron play

Slop is a good word. Thanks for all the responses bbut let me expand. The linkage is somewhat scale supercub without the pullpull although if I knew this was going to happen I would have made it that way. Every joint in the system is tight, I even added a 440 nut to tighten up the clevis. I did have a ball joint there but went with the clevis because the servo arm was twisting. I can now hold the servo arm still and get no play at the aileron but when I let go the aileron will move the 3/8. The hinge design is of course friese style and has no play. so my only thought now is to move the attachment point on the servo arm closer to the servo and see if the play will diminish with more travel from the servo. Just one more thought could it be that being the pivot point on the arm on the aileron is behind the hinge line that it is cantilevering around it? I'm worried about flutter as this is a 1/4 scale clipped wing supercub with alittle more engine than it needs. Sorry for the long post. Lanny Khelsea
Old 04-21-2010, 09:10 AM
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Jetdesign
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Default RE: excessive aileron play

Do you get the 'slop' when the plane is powered up and the servos are working? If all the movement is coming from the servo arm, which is what it sounds like now, the problem is with the servo.

I can now hold the servo arm still and get no play at the aileron but when I let go the aileron will move the 3/8.
Moving the control arm in on the servo horn will help some.
Old 04-21-2010, 12:13 PM
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khelsea
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Default RE: excessive aileron play

Joe, The play is with the servo on or off. I did move the rod down as far as I could on the servo and now I'm down to 3/16 play, not as good as I would like but I'm going to fly it. Balancing the ailerons could help too so thats next. This slop is definetly being caused by the metal gear servos but I think if I'm this close and don't do any full throttle dives hopefully it will be OK. I'll report in the crash forum if it isn't. Thanks everyone for your help. Lanny Khelsea
Old 04-21-2010, 12:50 PM
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Jetdesign
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Default RE: excessive aileron play

What servos are you using? Sounds like that's where your problem lies if the slop is from the servo horn moving.

I just 'upgraded' to a fancy set of high speed, digital servos for my tail surface. Unfortunately they are also metal geared, and I am unhappy with the amount of 'slop' in the system. They are mini servos mounted right inside the stab, so my slop is probably less than yours.

For some servos you can get plastic replacement gears. I'm hoping Airtronics will come out with some for mine.

Good luck, I hope things work out well for you.
Old 04-21-2010, 02:21 PM
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Default RE: excessive aileron play

Hi!
You have mounted the control horn wrong on both flap and aileron!! It should not be mounted so far rearward on the flap/aileron.
It should be mounted so that the clevis hole is just over the hinge line when aileron sits in neutral position.

Second: You have no counter nut holding the metal clevis in place!!

Third: The servo horn on the aileron servo is mounted wrong!
The servo arm should be mounted so that there is a 90 degree angle between the arm and the aileron linkage when aileron sits in neutral position ...or if you want differential...More up then down...the servo arm mounted more forward so that there is less angle at neutral position.
Old 04-21-2010, 03:17 PM
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Gray Beard
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Default RE: excessive aileron play

Just to be sure I'm looking at the photo correctly {I'm a mite cockeyed} the outboard control is the aileron you are having a problem with?? Just double checking myself. If so then why not just move in the fiber control horn where it belongs and make up the correct length control rod? Joe, the brass geared servos are pretty good, the brass will wear over time but they are easy to replace, very solid control!! Other then the wear factor they should fill your need.
Old 04-21-2010, 05:03 PM
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gsoav8r
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Default RE: excessive aileron play

I have to throw in my 2 cents.
If Im looking at this right, and looking at the Robart hinge points? khelsea has installed and where the hinge pins are located, I think the control horn location is OK. The aileron and flap appears to Not be hinged at the trailing edge of the wing like we typically see on models.
My opinion is that if khelsea were to move the control horn forward he would realize aileron differential.
Cheers.
Old 04-21-2010, 05:06 PM
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Jetdesign
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Default RE: excessive aileron play


ORIGINAL: gsoav8r

I have to throw in my 2 cents.
If Im looking at this right, and looking at the Robart hinge points? khelsea has installed and where the hinge pins are located, I think the control horn location is OK. The aileron and flap appears to Not be hinged at the trailing edge of the wing like we typically see on models.
My opinion is that if khelsea were to move the control horn forward he would realize aileron differential.
Cheers.
I see what you do; looks to me like the control horns are lined up very close to the hinge/pivot point, maybe just the slightest bit aft which should be OK.
Old 04-21-2010, 05:22 PM
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JohnBuckner
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Default RE: excessive aileron play

Yes the surface in the foreground are flaps and the outboard is the aileron. both the surfaces (flap and aileron) are unusual because the both are slotted surfaces meaning the hingeline is recessed a considerable distance which causes the leading edge of the aileron to protrude above the wing when the rest of the surface is down below the wing and vice versa. This also opens a slot for air to flow through between the leading edge of the surface and the wing itself.

The idea is to improve roll response but this also has a tendency to minimise adverse yaw.

The control horn on the ailerron is corectly positioned considering where the hingeline actually is. The horn is slightly aft of the hingeline on the flaps however this is not important for flaps since both flaps are setup the same and since they both operate together in the same direction the is no deferential problems induced by the horns position.

As far as the slop is concerned 3/8 inch at the trailing edge when the servo is locked is to much, find the slop and fix it.

This is also a good reason to use plastic geared servos, I avoid the metal gear types.

John
Old 04-21-2010, 05:34 PM
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khelsea
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Default RE: excessive aileron play

Jaka, If you notice the ail horn is in line with the robarts and I have since put a stop nut to tighten the clevis. As of this morning the servo arms are moved forward to give it more up than down. Graybeard and Garcfield you hit it with moving the attachment point for the clevis closer to the pivot in the servo, it seemed to take up most of the slack. I hoped everyone noticed that these are pipercub friese style hinges and there is a slot that those arms go into, kind of hard to see in the pix but look at a real cubs linkage and you'll see it. The pix you see is of course the bottom of the wing and the aileron is closest to you. Again I'm down to 3/16 play and going to consider this good, if not you'll see me in the crash forum. Lanny Khelsea
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Old 04-21-2010, 05:42 PM
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Default RE: excessive aileron play

Could some of the play come from the bolt-hole in the pockets or slots where the hinges are inserted into?

Don't these pockets or slots limit the up movement of the aileron?
The clearance between the LE of the aileron and these pockets or slots seems to be too small as to allow proper up deflection.
Old 04-21-2010, 06:18 PM
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khelsea
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Default RE: excessive aileron play

John you're right on but the surface closest is the ail and furthest the flap. Heres a pix of the full size{akamaiimageforum}/thumbnails/44534/Jg13932.jpg Lanny Khelsea
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Old 04-21-2010, 10:53 PM
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Default RE: excessive aileron play


ORIGINAL: khelsea

John you're right on but the surface closest is the ail and furthest the flap.

In that case your aileron control horn is to far aft and will induce some differential.

All the long wing PA and J series Pipers have a full circuit cable aileron system with the cables runing through pulleys and back to the surface attaching to control horn top and bottom (Pull-Pull) as in your photo. Actually the old Aronca 7AC (which later morphed into the Citabria, Decathalon, Lancer) was closer to what we do on most of our models and that is a bell crank out in the wing that the the pull pull cables operated and a short pushrod to the the single horn.

This is the reason that a friend back in the sixties sought out a 7AC to use in his airshow act that featured loosing an aileron in flight and he was quite able to go about doing various rolls and sloppy flying. The Aroncas aileron system ment he could simply remove the short pushrod and replace the aileron hinge bolts with nails all attached to a single lanyard that run into the side window. At the appropriate point the lanyard was pulled and the aileron fell off and he continued on playing up on the sloppy flying. It was a pretty successful act untill he ran out of cheap ailerons or got tired of repairing them.

Sorry for running of at the mouth.

John
Old 04-22-2010, 09:51 AM
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Default RE: excessive aileron play

Hi!
Aaah ! Did not notice the off-set hinge line. Sorry!
Old 04-23-2010, 12:22 PM
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khelsea
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Default RE: excessive aileron play

Just in case anyone wants to know that is a Royal Supercub 1/4. I found the fuse, cowl, landing gear and a set of plans. Scratchbuilt the rest. Put in a wing tube, clipped the wings to 79, no dihedral, 50cc gasser, added flaps, rib stiching and solartex w/latex. Scale cub hinging and linkage. AUW 16 1/2. Maiden flight and hopefully more this Sunday. 89 days start to finish. First place in our local mall show. Thanks for everyone that contributed ideas, they were very helpfull. Lanny Khelsea

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