Aileron range/alignment

[billythefrog]

Hi everyone

I'm struggling with adjusting the range/travel of my aircraft's ailerons.

I was wondering if there was a standard process or procedure, perhaps used by pro aerospace engineers, to resolve these types of rigging issues.

Mechanically I think the control system (pushrods and bellcranks) in my aircraft is pretty standard:

The system comprises a central cable circuit attached to the yoke (with two turnbuckles in the circuit, port and stbd). From the rear of the cable circuit, pushrods laterally down each wing, each of which terminate at a bellcrank which converts the lateral pushrod movement into longitudinal movement of another pushrod (which connects to a horn on each aileron).

Adjustments-wise,

A turnbuckle on each side of the central (yoke) system cable circuit allows the cable to be tensioned and compensatory changes to the turnbuckles allow the 'zero' position to be altered (port or stbd).


The lateral (wing) pushrods are each adjustable by approximately 12mm (12 threads of a single M6 rose joint, at the wings/ bellcrank end of each pushrod).


The longitudinal pushrods from each wing's bellcrank to that wing's aileron are adjustable by approximately twice that much (a rose joint on each end of the pushrod).

I'm looking for any help or previous experience - at present my ailerons' range is 45% too much in the UP direction and 30% too much in the down direction and I've had to admit to myself that I simply don't understand how to fix this. I've been trying to boil this down to simple changes and their effects, but I've been unable to get anywhere near where I need to be.

Any help would be much appreciated.

Thanks

[Pilot DAR]

Before getting too far into this, is the airplane type certified? Does it have a maintenance manual with rigging instructions? If it is type certified, and does not have rigging instructions (rare, but possible - mine is such), the type certificate data sheet will tell you what the correct flight control deflections are to be. There are a number of safe/standard practices for adjusting turnbuckles (as well as special tools), and cable tension is important, once the rigging is correct.

If the airplane is non certified, the information you seek is a little less certain. Perhaps a type club for that airplane type...

In any case, the answer you seek here could only come with more information on what airplane you're discussing...

[sycamore]

It would help to know what your aircraft is,and if you have a manual for it,detailing `HOW`.
You should have or make small clamps to hold the ailerons level with the wing surface ,and a method of holding the stick absolutely central.The bellcranks should have rigging pins to hold them at datum.
Its then a matter of measuring all similar pushrods/turns ,equal both sides,and then adjusting the cables equally,but not tensioned fully..Then check ailerons for travel/equal,rinse,check adjust a/rqd.finally,ok tension cables,check,check..or,get a proper `gingerbeer to do it whilst you watch.....simples....
Whatever you do to one pushrod will require other(s) to be adjusted,and the `other side`....Keep note of each adjust ment,ie 1 turn IN/OUT...

[billythefrog]

Thanks both - it's a Tecnam P2002 Sierra, but not of the factory-manufactured/certified variety, so designated as a P2002-EA Sierra (Experimental). The certified (P2002-JF) and (UK LAA) homebuilt (P2002-EA) versions are structurally identical in this area.

The certified model has a Maintenance Manual which outlines of course the range values etc, as does the UK LAA TADS (type acceptance) document.

Neither of the above provide rigging instructions, the range/extension of the ailerons are far too great and I don't know how to fix that. Other builders don't seem to have had this problem. I'm a step away from thinking my kit - which was the first to be sold in the UK - has some incorrect part(s) supplied, or a manufacturing defect, but I want to try to cover all bases first before I go back to Tecnam in Italy. Tecnam UK has taken several forms since I first purchased the kit in 2005 :(

Correct assembly has been verified, I just can't seem to adjust the pushrods and turnbuckles to sort this out! Thanks again

[Pilot DAR]

As there is a certified version of the airplane, you can be pretty confident that the intended control deflection for your non certified one, will be very similar, or the same as the certified one. The maintenance manual for the certified one must give travel range and rigging instructions. That's your starting point.

In general, aileron travel will be limited to around 20 some degrees in the greater travel direction, and may be less to none in the opposite direction (Tiger Moth). A travel range exceeding 30 degrees would be aerodynamically very unusual. For reference, in Canada, flap extension angles on amateur built airplanes is not permitted to exceed 40 degrees. So if you're anywhere near that, you're way away from where you should be.

For sure, ask questions. too much aileron travel, and an aerodynamically stalled aileron will make for a very unpleasant to fly airplane!

[Jhieminga]

If the maintenance manual does not provide rigging instructions, you could contact Tecnam for clarification of the procedure as it is something they should be able to provide. Sycamore's description is a good starting point, but the factory should be able to supply more detailed instructions. Something else I was thinking of: do you have a maintenance organisation nearby, preferably one with experience of dealing with Tecnam types? A friendly chat with someone there might also be useful for you.

[scifi]

You say that the movement is a certain percentage too much. So you must have measured the degrees of actuation, and then done a calculation.
I would think the the push rods and bell cranks are just a way of getting the movement from the column to the ailerons. What you should be looking for is where are the column stops, and can they be adjusted. On most aircraft the neutral position results in about a 3 degree droop of both ailerons, which goes to zero when subjected to some airflow. The geometry of the bell cranks will give more upward movement than downward movement, to reduce any adverse yaw.

[Pilot DAR]

On most aircraft the neutral position results in about a 3 degree droop of both ailerons, which goes to zero when subjected to some airflow.

Gee, I hope not! That degree of freedom would be inviting flutter!

[DuncanDoenitz]

Billy,

I must confess that your post leaves me somewhat concerned. As a retired licensed engineer (mainly GA), my last employer was a Part-145 organisation responsible for maintenance on several examples of the 2002, although I was never personally very involved in its maintenance and can't speak from direct experience. Our Tecnams were not highly regarded by my colleagues, particularly in terms of build-quality (which should not affect your example), but I believe it is well designed to conventional airworthiness criteria. I am surprise by your absence of rigging data, either in the form of a maintenance manual or assembly process sheets. You have a kit, but no instructions? Some points to consider;

1. Almost no aeroplane has its flying control range-of-movement determined by how far you can move the stick. Each aileron should have "primary" stop, in the form of an adjustable-length bolt, normally acting on each aileron's input bellcrank, and limiting the movement of the aileron (whether it is attached to the rest of the control-system or not).

2. There should be a "secondary" stop adjacent to the control stick. The purpose of the secondary stop is, on a completely rigged system, to limit the amount of tension/compression that can be applied to the system when the ailerons are at full travel, to prevent overstressing the control system. When the stick is moved gently to the limits of travel (ie, when the primary-stops make contact) there should be a small gap at the secondary stops, which can be closed by further pressure on the stick.

3. The system must always be rigged initially with all its contituent parts in "neutral". There should be a means of securing the stick in neutral, perhaps a rigging pin or clamp. The ailerons should normally be placed in neutral by aligning with the T/E of the wing. This is important; the bellcranks should also be secured in neutral. It is not sufficient that the stick-and-aileron are neutral if the bellcranks are at weird angles, as this will give a non-linear nmovement of the aileron in response to movement of the stick.

4. With all the components in neutral, prepare the pushrods by screwing each rose bearing in equally. Install the pushrods by adjusting the rose bearings equally until the attachment bolts slide in freely. There should be a defined means of ensuring that the rose-bearings have sufficient threads engaged.

5. Install the cables and turnbuckles, tighten the turnbuckles to take up the slack whilst ensuring that the stick and bellcranks remain in neutral. Tighten the turnbuckles further (equally) to achieve the specified tension.

6. Remove all your rigging pins and clamps. Ensure that the controls move freely, in the appropriate direction, and to the correct range.

7. Absolutely vital;
a. make sure that you've removed all your tooling.
b. make sure that the controls move in the right direction.
c. make sure that all threads are sufficiently engaged.
d. make sure that all locking devices/safety-wire are installed and secure.
e. make sure that a competent person performs a duplicate inspection of b. to d.
f. check again that the controls movie in the right direction!

8. Although you've only asked about an aileron problem, everything applies to the other control systems as well.

[Pilot DAR]

e. make sure that a competent person performs a duplicate inspection of b. to d.

Yes, and for that person's sake, present them with the maintenance instructions for the airplane, so they can be confident that what they are agreeing is good, is actually what the maintenance manual says it should be! I've known the second set of eyes to not really know what they are looking at, and the first person really didn't either! And I have seen, and test flown, incorrectly rigged planes....

The one (a Cessna 206) had a very difficult to detect, but rather critical rigging error. I check it myself, and did not see it the first time either. When the mechanic told me he had corrected it, I insisted that he accompany me on the next test flight. He resisted, I insisted. It still wasn't right, once in the air, he then agreed with me! Eight hours later, it was correctly rigged, and flew properly!

[billythefrog]

Thanks all - I do have aileron deflection ranges specified for both the certified and homebuild versions, they're identical (+20 to -15) but with marginal differences in tolerance. No rigging instructions were supplied, so thank you all for the tips.

The problem I have is limiting travel - my range is too great and there are no travel stops in the (aileron control system) design - either primary (at the bellcrank in the wing) or secondary (at the yoke). At this point I may have to engineer this; what I'd really like is to understand why this would be necessary, i.e. root cause.

Echo Pilot DAR 's point about flap deflection - on this type, the UK (LAA) homebuilt specs have actually reduced flap deflection from 40 degrees (on the certified version) to 33 degrees (on the homebuilt) to prevent an observed unpleasant wing drop on stall at high AoAs.

[Fl1ingfrog]

the UK (LAA) homebuilt specs have actually reduced flap deflection from 40 degrees (on the certified version) to 33 degrees (on the homebuilt)​​​​​

I presume you are a member of the LAA. Have you discussed this with your local engineering inspector? From your comment above I'm presuming they will have considered this issue already or will do if you request their help.

[billythefrog]

I presume you are a member of the LAA. Have you discussed this with your local engineering inspector? From your comment above I'm presuming they will have considered this issue already or will do if you request their help.
Yes. Also the flap extension reduction is a Mandatory Permit Directive, with fairly clear instructions! Thanks

[wrench1]

The problem I have is limiting travel - my range is too great and there are no travel stops in the (aileron control system) design - either primary (at the bellcrank in the wing) or secondary (at the yoke). .
I find this the most interesting. While I can't speak for all aircraft, every one I've worked on had mechanical flight control stops. Is there not an OEM build book or drawings that you can reference? Without any stops how can the required deflection ranges +20 to -15 be maintained?

[billythefrog]

Yes, I have the Illustrated Parts Catalogue, the plans for the aircraft - there are no control stops in the aileron system so the only rational explanation is that aileron travel is down to the travel of the yoke / control stick. There are primary stops in the *elevator* (actually a stabilator) fitted at the factory, and given that the flap is electrically operated, there is a microswitch within the actuator / servo which is moved to limit the travel of the flap... but nothing on the aileron control system, or rudder control system!

[wrench1]

there are no control stops in the aileron system so the only rational explanation is that aileron travel is down to the travel of the yoke / control stick. m!
Well, that would be a first for me to see no stops anywhere to include on the yoke or control stick which some helicopters have. Perhaps a call to the OEM will clear this up as I see no way to limit your deflection requirements without stops nor do I see an OEM who fails to use them. But thats just me. Good luck.
​​​​​

[ericferret]

Yes, I have the Illustrated Parts Catalogue, the plans for the aircraft - there are no control stops in the aileron system so the only rational explanation is that aileron travel is down to the travel of the yoke / control stick. There are primary stops in the *elevator* (actually a stabilator) fitted at the factory, and given that the flap is electrically operated, there is a microswitch within the actuator / servo which is moved to limit the travel of the flap... but nothing on the aileron control system, or rudder control system!

I know nothing about this particularly aircraft or systems.
You seem to have a problem of excessive range. Adjusting rods wont fix that.
Is there somewhere where a radial motion is imparted into the system?
A little difficult to explain however.

Think of a bar that rotates about a fixed point at one end. If you attach an output at the opposite end for every degree of rotation it will impart a linear output.
If you move the output to a position halfway along the bar you will reduce the linear output for the same angular motion.
Thereby you have reduced the total range. Then the range can be "positioned" by a rod adjustment.

This type of adjustment is used on a number of helicopters for engine controls.

[billythefrog]

Billy,

I must confess that your post leaves me somewhat concerned. As a retired licensed engineer (mainly GA), my last employer was a Part-145 organisation responsible for maintenance on several examples of the 2002, although I was never personally very involved in its maintenance and can't speak from direct experience. Our Tecnams were not highly regarded by my colleagues, particularly in terms of build-quality (which should not affect your example), but I believe it is well designed to conventional airworthiness criteria. I am surprise by your absence of rigging data, either in the form of a maintenance manual or assembly process sheets. You have a kit, but no instructions? Some points to consider;

1. Almost no aeroplane has its flying control range-of-movement determined by how far you can move the stick. Each aileron should have "primary" stop, in the form of an adjustable-length bolt, normally acting on each aileron's input bellcrank, and limiting the movement of the aileron (whether it is attached to the rest of the control-system or not).

2. There should be a "secondary" stop adjacent to the control stick. The purpose of the secondary stop is, on a completely rigged system, to limit the amount of tension/compression that can be applied to the system when the ailerons are at full travel, to prevent overstressing the control system. When the stick is moved gently to the limits of travel (ie, when the primary-stops make contact) there should be a small gap at the secondary stops, which can be closed by further pressure on the stick.

3. The system must always be rigged initially with all its contituent parts in "neutral". There should be a means of securing the stick in neutral, perhaps a rigging pin or clamp. The ailerons should normally be placed in neutral by aligning with the T/E of the wing. This is important; the bellcranks should also be secured in neutral. It is not sufficient that the stick-and-aileron are neutral if the bellcranks are at weird angles, as this will give a non-linear nmovement of the aileron in response to movement of the stick.

4. With all the components in neutral, prepare the pushrods by screwing each rose bearing in equally. Install the pushrods by adjusting the rose bearings equally until the attachment bolts slide in freely. There should be a defined means of ensuring that the rose-bearings have sufficient threads engaged.

5. Install the cables and turnbuckles, tighten the turnbuckles to take up the slack whilst ensuring that the stick and bellcranks remain in neutral. Tighten the turnbuckles further (equally) to achieve the specified tension.

6. Remove all your rigging pins and clamps. Ensure that the controls move freely, in the appropriate direction, and to the correct range.

7. Absolutely vital;
a. make sure that you've removed all your tooling.
b. make sure that the controls move in the right direction.
c. make sure that all threads are sufficiently engaged.
d. make sure that all locking devices/safety-wire are installed and secure.
e. make sure that a competent person performs a duplicate inspection of b. to d.
f. check again that the controls movie in the right direction!

8. Although you've only asked about an aileron problem, everything applies to the other control systems as well.

Thanks Duncan. There are no stops in the design. I have the aileron and flap clamped both sides and the stick is clamped vertical with a sprit level (the a/c is also lat/long levelled). Agree with rigging a neutral setup but I'm not 100% what 'neutral' looks like at the bellcrank - I assume it would be the position where the wing pushrods (to the bellcrank from the yoke) exert the maximum movement of the bellcrank in both directions - in other words, the bellcrank arm is perpendicular to the wing pushrod where they connect at a rose joint? I need to call Tecnam again for advice but I can't say that their support has been exemplary

[ericferret]

Thanks Duncan. There are no stops in the design. I have the aileron and flap clamped both sides and the stick is clamped vertical with a sprit level (the a/c is also lat/long levelled). Agree with rigging a neutral setup but I'm not 100% what 'neutral' looks like at the bellcrank - I assume it would be the position where the wing pushrods (to the bellcrank from the yoke) exert the maximum movement of the bellcrank in both directions - in other words, the bellcrank arm is perpendicular to the wing pushrod where they connect at a rose joint? I need to call Tecnam again for advice but I can't say that their support has been exemplary

Further to my post above I have seen something similar when a control rod was attached in the wrong position on a bellcrank, misspositioning of a bellcrank might also give the same effect i.e too much angular movement.
Or rather too much output for the same angular rotation.

[billythefrog]

Thanks ericferret
Yes, I thought of that too but the construction matches that in the design (this has been checked by my LAA inspector)... And, besides, the wing pushrod wouldn't fit through the corresponding holes in the wing ribs if it were in the wrong place! :(

[Pilot DAR]

Billy, I know nothing of the type we've been discussing. But, in general

There are no stops in the design....... I need to call Tecnam again for advice but I can't say that their support has been exemplary

Is very worrisome to me! Every flight control stops at something, and the thought that your aircraft seems to not define that mechanically is a huge red flag for me! That says to me that something somewhere will either operate other than intended, or be damaged when the intended travel limit is exceeded. I've done a lot of test flying to assess control in modified certified airplanes. I've had a few scares with wrong flight control set ups - and they were defined! To be honest, for the information you have been able to provide thus far, I would decline to fly the airplane until these were not questions any more. I have found every now and then in aviation, something tells you to stop everything, and get more answers.

A newly modified airplane I first test flew this past spring, and test flew for 60 hours, had a few "not good enoughs". I tested for them, documented them, suggested changes, and suggested cautions for further flying to be done by a couple of other test pilots also flying the program. A week after briefing the next new test pilot, his check flight ended badly, there was a problem with control of an airplane system. They were too low to take the time needed to understand the problem, and mitigate it. They're okay, but a million dollar prototype is pretty badly damaged now. In hindsight, I might have popped up a redder red flag.....

A few responses in this thread read like red flags for your project to me, good on you for asking. Now you have to decide what to do going forward with a "not good enough" in your airplane...

[djpil]

Yes, I have the Illustrated Parts Catalogue, the plans for the aircraft - there are no control stops in the aileron system so the only rational explanation is that aileron travel is down to the travel of the yoke / control stick. ..I've been following this, looked at the IPC and Parts Catalog online and I see nothing as well, quite a surprise. Perhaps a telecon with Tecnam engineering?

[stevef]

Gee, I hope not! That degree of freedom would be inviting flutter!

The DC3/C47/Dakota ailerons are rigged to give 7/8" droop at control wheel neutral to offset the tendency for them to rise in flight. There are no physical bellcrank control limit stops. Very simply (!) put, the throws are adjusted by using the inner set of cable turnbuckles in the wings (tighten one, loosen the other). Then the cables between the inner and outer control rod bellcranks have to be adjusted. On top of this, the tensions must be within limits! You can end up chasing your tail sometimes as one adjustment can affect another. It's at least a day's work to correctly rig the system from scratch. :eek:
Small Cessna aileron rigging is kid's stuff in comparison.

[scifi]

Hi Stevef, thanks for your reassuring message re the Droops to be expected on most small aircraft. I was going to pen a rather long tome, along the lines that all engineering materials are not absolutely rigid. I am currently shifting several lengths of rail track, and can confirm that they bend by about a foot if lifted at just one end...!
The daily rig check for Gliders, involves someone holding the stick rigid, whilst a second person lifts and pushes each aileron up and down, usually about 2 inches for most glass or wood and canvas gliders. The walk-around check on GA aircraft also shows how much droop can be expected.

[Pilot DAR]

Hi Stevef, thanks for your reassuring message re the Droops to be expected on most small aircraft.

Though I have flown a DC-3T, I have not rigged one, so I defer to Stevef on the rigging, as perhaps he knows more than I'm If the DC-3 has freeplay in the the ailerons, it would be the only civil airplane I had ever encountered which such a characteristic. Droops in GA airplane flight controls is very uncommon. Certainly, freeplay in a flight control is an invitation to flutter (Jimmy Leeward's P-51 at Reno). When I have done dive testing in the GA airplanes I have flight tested, I have done very careful walk arounds checking for exactly that - nothing loose, no freeply. I declined to dive test a Piper Navajo, because there was 1/4" freeplay in the elevator trim tab - I insisted that it be corrected (the Cessna 310 allows 3/16", so we rigged to that freeply tolerance). While checking a Caravan, I found 3/8" freeply in the spoilers, but upon a review of Cessna data, that was just within limits - but there were limits!

If a Pilot finds any freeplay in a flight control or panel, it would be wise to have maintenance personnel confirm it's within limits before flying! My recollection of ailerons on a DC-3, is that the control wheel goes just about all the way around! When you've cranked in the normal amount of aileron, you're really only half way there!

[EXDAC]

Certainly, freeplay in a flight control is an invitation to flutter (Jimmy Leeward's P-51 at Reno). When I have done dive testing in the GA airplanes I have flight tested, I have done very careful walk arounds checking for exactly that - nothing loose, no freeply.

It's a long time since I was in flight test and it was avionics not aero. However, I recall that Douglas Long Beach did flutter testing with specially installed control links that had maximimum allowed in-service slop (free play). A flutter test with zero free play links would not be representative of conditions experienced during the life of the airframe.

[Pilot DAR]

A flutter test with zero free play links would not be representative of conditions experienced during the life of the airframe.

Definitely true! That's for flutter testing of the initial certification of the primary airplane [flight controls]. A certain maximum freeplay is required to be set up (if any is to be allowed in service), and the testing done with that. That is generally expressed for continuing airworthiness maintenance as an amount [in inches] which the trailing edge of a flight control may move freely. As I mentioned, an example of this was for the Cessna 310 elevator trim tab; 3/16" of an inch freeplay was allowed if I recall (it's been 15 years since I did that testing). When I dug into the Navajo limits, no freeplay limit was provided. My spidy senses told me that if I were to fly that plane through to 110% Vne, 1/4" of elevator trim tab travel would not be acceptable to me. This resulted in some stressful discussion with the airplane owner, with the maintenance shop in the middle. But, I asserted that the trim actuator was worn out. As Piper did not publish a limit, I applied the known Cessna limit, as the two were comparable airplanes of weight and speed. The Navajo trim actuator was disassembled, and indeed found to be well worn. An airworthy one was installed, the trim tab freeplay was negligible, and I flew the dive. I was testing wingtip survey booms, not the whole airplane.

A client took his 185 amphibian to a local airport on his way home from the weekend trip, and I was called to examine it. He reported that he had been in cruise flight (which as an amphib, is not rocket fast in a 185!), and it began to "shake like hell, and make a racket". He reported slowing it down, and eventually the shaking stopped, and he landed at the nearest airport with no delay (where we picked it up). It turned out that he had a broken elevator spar, and the outboard portion of the elevator (which appeared normal to look at) could be flexed an alarming amount - he'd had flutter. The balance weight was doing nothing to prevent flutter. The elevator was repaired, I reflew the plane, and he took it happily.

I agree that some freeplay may be acceptable in a GA airplane flight control (because the manufacturer's service manual says so), but I have yet to encounter a GA airplane where flight control freeplay or "drop" is a noticeable design feature. If there is no stated freeplay tolerance, it ends up being a pilot/local maintainer decision if the airplane is airworthy, that can be a tough one. Many maintenance manuals don't give some information a pilot or maintainer might want (Navajo!). Part 23 airplanes are required to be flutter free with the flight control system intact. I believe that part 25 airplanes must go further, and each control surface must be flutter free connected, or disconnected (can't use the flight control system to damp flutter). My certified airplane does not have any flight control counter balance weights, by design, so has a very slow Vne as a flutter margin.

[djpil]

Part 23 airplanes are required to be flutter free with the flight control system intact. ... My certified airplane does not have any flight control counter balance weights, by design, so has a very slow Vne as a flutter margin.FAR 23 introduced this requirement many years ago (somewhat changed since, especially for small simple airplanes): "after the failure, malfunction, or disconnection of any single element in the primary flight control system, any tab control system".

[stevef]

Though I have flown a DC-3T, I have not rigged one, so I defer to Stevef on the rigging, as perhaps he knows more than I'm If the DC-3 has freeplay in the the ailerons, it would be the only civil airplane I had ever encountered which such a characteristic. Droops in GA airplane flight controls is very uncommon. Certainly, freeplay in a flight control is an invitation to flutter (Jimmy Leeward's P-51 at Reno). When I have done dive testing in the GA airplanes I have flight tested, I have done very careful walk arounds checking for exactly that - nothing loose, no freeply. I declined to dive test a Piper Navajo, because there was 1/4" freeplay in the elevator trim tab - I insisted that it be corrected (the Cessna 310 allows 3/16", so we rigged to that freeply tolerance). While checking a Caravan, I found 3/8" freeply in the spoilers, but upon a review of Cessna data, that was just within limits - but there were limits!

If a Pilot finds any freeplay in a flight control or panel, it would be wise to have maintenance personnel confirm it's within limits before flying! My recollection of ailerons on a DC-3, is that the control wheel goes just about all the way around! When you've cranked in the normal amount of aileron, you're really only half way there!

PD - I may have explained the droop badly, the 7/8" below trailing edge 'neutral' is positively rigged (not floating) and the control wheel is central. The ailerons come up to 'true' (trailing edge) neutral in flight. As you know, the aileron profile has a distinct aerofoil camber.

[scifi]

The droop is caused by the weight of each aileron acting downwards when the aircraft is stationary. In flight the aileron is subjected to an upward force caused by the airflow. Let's say this aerodynamic force is about 40 pounds, for a typical Cessna 172. If on the ground two people both lift the ailerons with a force of 40 pounds each, then the half inch droop should go to zero, and the ailerons become in line with the trailing edge. A Cessna 172 is set up to have a certain amount of strain in each cable, which is measured by finding the deflection of the cable over a given length, when subjected to a known sideways load.

[Pilot DAR]

If on the ground two people both lift the ailerons with a force of 40 pounds each, then the half inch droop should go to zero, and the ailerons become in line with the trailing edge.

If two people each apply a lifting force of 40 pounds to the trailing edge of a 172's ailerons, something's probably going to be damaged (I've had to repair them for this). The "40 pounds" is the Cessna specified cable tension for the aileron control circuit. It's a closed cable circuit, so that cable tension can be measured anywhere the cable can be accessed easily. Excluding the control wheel chain part of the aileron control circuit, and the two aileron pushrods and their connections, there is no place where any freeplay could safely exist, the entire aileron control circuit is under 40 pounds tension.

For 172 aileron rigging, Cessna states: "Stop bushings should be centered in slots of aileron bellcranks in each wing when the control wheels are neutral, with correct tension on the aileron carry-thru cable. Pushrods are then adjusted to rig the ailerons neutral."

"Neutral" for Cessna ailerons is that the aileron trailing edges neatly meet the trailing edges of both the wing tips, and the outboard trailing edges of the flaps. Cessna does not describe any [permissible] "droop" in the aileron position. If it were to exist, it would be the result of horribly worn aileron pushrods/connections, or a broken pushrod connection in the aileron (which I had to repair on my Cessna). So if the 172 you're referring to has "droop" in the ailerons, which two people can easily reposition, it should be inspected for aileron control circuit damage.

This photo:


https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/800x600/ghq_aileron_gap_9eecba027568a68d1bbf6b070f9d6bb9475f7e86.jpg

Is the defect observed in the rigging of ailerons on a Cessna 185 amphibian I was called to review. (Essentially the same control system as a 172). All of the trailing edges med neatly except the gap shown. The airplane flew perfectly level. But, That gap is not permitted. As an aside, the 185 had had 182 wings installed, with a very, very vague reference to the swap in the technical records - but that mysterious wing swap was not a factor in the defective aileron gap - separate issue. To correct this defect, I required that both ailerons be rebuilt with the correct washout in them, and the wings be rerigged. After that, I test flew the plane, and got it so it flew very well, and the ailerons were correctly rigged. With that, and a number of other defects corrected (stall warning horn was operating very wrongly, landing gear warning system had errors, emergency landing gear operation was backward - yes... backward!), I approved the use of the 182 wings on the 185. Once this was all corrected (took 8 months in the shop, and 9 hours of my flight testing), the airplane was super!

For that airplane (as any), we assured correct aileron operation, no freeplay, correct neutral position, correct cable tension, and correct control wheel position. Understanding the operation and rigging of the control system is pretty important, and, as the pilot, being able to observe, and possibly question a defect is important.

[Silvaire1]

It is standard practice on many older types of aircraft to rig with aileron droop, particularly with cable operated control systems. For example, in older Piper manuals it is recommended to rig the ailerons approximately 1/4" to 3/8" of an inch lower than the wing at the trailing edge so that the air flow will lift them up to the neutral position. This is not the result of slack in the cables or free play anywhere in the system, and it is virtually unrelated to the weight of the ailerons. The cables stretch in flight due to aerodynamic lift regardless of being tensioned correctly, and the recommended practice makes them fair to the wing in flight. For a higher speed plane a stiffer control circuit might be necessary to prevent flutter but these are not high speed planes and the design and rigging recommendation works fine.

[billythefrog]

Firstly, thanks to all the people on this thread who have contributed to fixing my aileron range problem, and also the interesting background information on aileron rigging!

It turns out that, unbeknown to me, the aircraft design *does* have 'primary' aileron stops which were supposed to be fitted to the kit by the factory; I was not supplied with the parts (or instructions) to build them, anyway.
Longer story is I went to a local maintenance facility to look at a factory-built model, and there were the stops -- hidden discretely underneath an aileron hinge - they act on the 'leading edge' of the aileron when it is in its fully 'down' position.

When I receive the parts I've ordered, fixing the problem should be simple: Commensurate movement (more up than down) is fundamentally down to the geometry of the bellcranks :)

Thanks again all

[Pilot DAR]

Well done Billy?

Good on you for considering and asking the question in the first place, good instinct on that! And it's pleasing to see our community coming together with lots of great thoughts on the subject! Let us know how you make out when you get the stops installed! (and, check the rest of your kit for completeness!)

[Jan Olieslagers]

I need to call Tecnam again for advice but I can't say that their support has been exemplary In my limited experience, contacting Italian persons or companies is little effective unless done in Italian language. To make matters worse, writing usually works less well than calling - which makes you really need to speak Italian for effective communication, and quite specialised technical Italian, too, in this particular situation. Cannot you talk to their local distributor?