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orion

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You don't need the three fingers on the clevis fitting, just the outer two. The clevis fittings are standard AN hardware so if that's the way you want to go, pick what you need.

Personally, I'd probably tend to do two plates, seperated by a spacer, riveted together. The gap that would be created between the outer plates then can accept a rod-end bearing, which slides in between. This is substantially stronger and stiffer.

As far as the arm is concerned, you may want to increase the width toward the pivot. I prefer to use a bearing at the pivot so the area becomes wide enough to accept the bearing, plus sufficient edge distance to account for the structural requirement.
 

StRaNgEdAyS

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Hmmm this little piece of engineering is quite a challenge. :ermm: I'm quite enjoying this!
:D
Is this a little more like what you described?
The rod ends sits around a 5-13-5 bearing which fits between the plates.
I'm just working through all the possibilities here, and I'll use the one that best suits the purpose.
 

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orion

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Yes, that is a bit more like it. Remember though, the rod ends have spherical bearings and as such, the sandwiching plates will not sit on the rod end but will be offset as they will sit on the spherical bearing, which protrudes beyond the side envelope of the rod end body.

In order to maximize the stiffness of the installation, I would mount the bellcrank between two substantial plates, which would be ideally joined to a corner of a rib and a spar (front or rear). In this way the bellcrank is close to its mounting structure and thus is very rigid.

The pivot bearing of the bellcrank I had in mind is an actual ball bearing, not a tube as you have pictured.
 

StRaNgEdAyS

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Ahhh good stuff. I drew the rod ends with ball bearings, which is easy enough to alter. :whistle:
I see what you mean by the ball bearing pivot as opposed to the tube I drew. That was to facilitate mounting in the center of the rib, but I will re draw the bellcrank to mount in the corner of the rib/spar joint.
I'm searching about to try to find some good pictures of bellcranks in things like RV's, BD's, CH's and such to get a better idea of how they work.
 

StRaNgEdAyS

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I know most things aircraft are yet to come out of the stone (read imperial) age, but I just can't seem to bring myself to work in empirical measurements. :ermm:
Consequently I have spent a great deal of time searching for METRIC fittings. I finally found some :ban: from an Australian company (who else? :D) that import them from Germany.
I just thought I'd post their blurb to see if anyone has some comment.

Rod End and Spherical Bearings from Fluro-Gelenklager Gmbh

Product/Service Name
The Fluro production program consists of Rod End and Spherical Plain Bearings Series K and E to DIN 648. Stainless steel, maintenance-free and versions with lubrication fittings are available.
Fluro also offers a range of self-lubricating high performance Metric Rod End and Spherical Bearings designed for the race car and motorcycle industry.

Differentiating Features
The MS series of bearings have a tighter than normal fit and have proven themselves in European Formula 3 and Rally vehicles.

So what do you all think? :confused:
 

orion

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Much better.

The only other thing I might suggest is for you to work at the geometry so the whole thing did not take up so much room. Preferably do it in such a way that the two rod-end connections are in one plane. I know sometimes this is difficult to do but the easier you make the parts to make, the less hassle the building.

If this has to go into a confined area, such as one might expect at the rear spar, by the time you install the mounting structure (which usually has the mounting flanges pointing to the outside of the assembly, not the inside), you may be hard pressed to find enough space to put in the bolt that runs up the bearings or possibly may not have enough space left to put the nut between the mounting structure and the wing's skin.

Rigid, strong and small are genrally contradictions, but hey, that's the fun of airplane design.
 

StRaNgEdAyS

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If this has to go into a confined area, such as one might expect at the rear spar
Talk about a light coming on!
I've been drawing the assembly from behind the MAIN spar. Hence the rather challenging movement of the linkage pushrod that cuts an arc through the aileron connecting rod path.
 

Davefl42

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Now to throw a wrench in the works. Have you thought about control system stops? Some way to limit travel at the control surface. On the Piper and Cessna aircraft I work on they both have methods to control the total amount of travel at the control surface, and then a second stop to limit control system input at the yoke. There is a little more travel at the yoke than at the control surface and you get a springy feeling as the cables strech a little. By the way the drawings are excellent. I've been following this post and have learned a lot. Thanks everybody.
 

StRaNgEdAyS

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I have thought about control stops, and I haven't come up with anything better than running a pair of bolts between the plates to stop the bellcrank at the required angle. That ought to do the trick.:D
By the way the drawings are excellent.
Thanks! :D I have been getting a little better at this CAD thing...
 
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pylon500

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Ah Yes, it's ME :D
I've been playing with my plane moulds (and probably should be still!) and missed so much of this learning curve. :rolleyes:
I was a little amazed when you said you had never used differential ailerons on any of your models, :eek: but as you said, I've been watching the light go on with interest.
When reading the beginning of the post your problem seemed to be with concealing your aileron horns, to that end, you could have tried a 'skewed horn' system.
I haven't time to create in cad so I'll explain;
Imagine a 'T' shape, say three times higher than the width of it's top, the top width being the depth of your aileron spar, lay the 'T' on it's side (not flat on it's back) and attach it's top to the front of your aileron spar, you attach it via a hinge down the said top so that this 'T' can now swing inwards and outwards inside the wing in front of the aileron with a pushrod from the fuse to apply this movement.
OK, so your thinking 'Yeah, the arm swings, but nothing happens!' :confused:
Right!, now looking at the aileron and the 'T' from the front, rotate the top of the 'T' on the face of ther spar about 30º from the vertical and hold the aileron, when you move the push rod , the leg (or arm) of the 'T' will now have some vertical movement as well as inwards and outwards.
Now, if this arm was to run in a horizontal slot near it's tip to stop the vertical part of the movement, the aileron will move up and down! :ban:
This system is used in a few sailplanes, and a variation of this is used on the old Winjeel trainer, and another variation is used on the Cessna 400 and 500 (Citations) series aircraft.
In later posts you had got the drift of how to set up the differential system and was generating the cad drawings, I noticed that you depicted the aileron with some form of rod running along inside?
Is something actually there, or is this just a depiction of where the pivot axis of the aileron is? :confused:
Arthur.
 

orion

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The control system that Aurthur mentiones above is a really innovative configuration that came out for the RC airplane industry over fifteen years ago. I've looked at it several times however have not figured out how to make it so that you could manufacture it without any "slop". The geometry is such that it just naturally has a mechanical characteristic that it is very difficult to make without any built-in flexibility.

I have heard that it is incorporated into the airpalnes he mentions however I have not seen those to see how they overcame the potential for free relative movement.

Now, one last comment for "strangedays", you show your rod ends setup for something like a solid rod - you may want to switch that so that it works with tubular connecting rods instead of the solid ones. The solid one should be OK for a short connection such as the one from the bellcrank to the aileron however, the one running spanwise in the wing will probably need end up being a tube so that you can maximize the columanar stiffness in order to prevent buckling. Remember, even if you don't have a lot of compressive load on the system, under higher G maneuvering the loads are perpendicuar to the pushrod, which may be just enough to deflect the connecting member and make it act as a buckled column.
 

StRaNgEdAyS

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Yes you saw correctly, that is a rod running up the inside of the aileron.
It serves three purposes, it will locate the ailieron pivots inside spherical bearings at each end, it acts as the control force transmitter as the horn is attached to it and last but definately not least, it acts as the aileron spar.
I'm not 100% sure yet, but I may also need some central support/pivot point in the center of it as well.
 

StRaNgEdAyS

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I didn't see that one from you before I posted that last reply there Orion. The length of the pushrod from the bellcrank to the aileron horn is only 50.5mm (near as $#!^ to 2") long by 5mm dia but the linkage to bellcrank rod will be of a 10mm tubular section. I originally was going to step them down to 5mm threaded rod ends, but given your statement there, I'll investigate 10mm ones.

On the differential linkage on the RC models, upon reflection I probably DID use it, very little on the control horns, but as far as the bellcranks were concerned I used 90 degree transfers. (I really don't know why, but I really never thought about it much before)

edit: forgot to puit some stuff in there.
 
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Largeprime

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why not run the rod through the aleron straight through to the fusealage?

You can put the "joint" in the fuse and eliminate two 90 deg bends.
Joint has easy access.
The rod can become the piviot at each end of the aleron.

simpler, lighter, better access
so i must have missed something
 

StRaNgEdAyS

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That's a good idea, but for this to work it would have to run through a similar tube performing the same task for the flap, which has the control horn located on the end of its rod (they're actually tubes) inside the fuselage for this very reason. the controls for the elevators will be done in this manner also. BUT for the ailerons, (this is just my take on it) the biggest factor (as if the fitting the tube inside the flap tube isn't enough) against using this kind of linkage would be the twisting moment along its length (it IS over 2M (6 1/2") long) would be a significant flutter risk at high speed.
 
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