Aileron range/alignment
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Billy, I know nothing of the type we've been discussing. But, in general
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...
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
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...
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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. 
Small Cessna aileron rigging is kid's stuff in comparison.
Small Cessna aileron rigging is kid's stuff in comparison.
Got the Droops
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.
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.
Moderator
Hi Stevef, thanks for your reassuring message re the Droops to be expected on most small aircraft.
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!
Moderator
A flutter test with zero free play links would not be representative of conditions experienced during the life of the airframe.
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.
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!
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!
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.
Moderator
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.
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:
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.
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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.
Last edited by Silvaire1; 5th Dec 2023 at 04:10.
Thread Starter
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
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
Moderator
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!)
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!)
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I need to call Tecnam again for advice but I can't say that their support has been exemplary
