Static/mass balanced or not

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David36

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If some one can tell me details about aileron connection on this aircraft, I will post some photos:

photo1fc.jpg

photo3gw.jpg

photo2iop.jpg

Are these mass balance weights or do they have any effect on aileron balance? Basically, can you figure out visually if these ailerons are mass balanced or not? They are fabric covered.

Sorry for this stupid question, I don't have any knowledge on this aspect and I will like to know if these ailerons are balanced or not. I highlighted the linkage with blue circles.

Generally, is there a way to figure out if airplane surfaces are designed mass balanced or not, especially ailerons?

Thank you very much and Merry Christmas everyone!;)
 

Head in the clouds

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Hi David,

Merry Christmas to you too.

All the parts you have marked are the aileron control linkages, not the mass balances.

Occasionally, but not very often you might see mass balance weights on forward facing arms under the wing, so they might look a bit like what you have circled, but they would be at the centre of the aileron or out near the tip. That kind of balance weight is rare because it has to stick down into the airstream quite well below the wing so that it doesn't hit the wing when the aileron is deflected downwards. Sometimes there is a hole in the bottom surface of the wing to allow the weight to go up into the wing as the aileron goes down.

Nearly all ailerons are mass balanced if the aircraft flies faster than about 80mph, so the only exceptions would be some ultralights. The balancing is to prevent flutter which is an extremely destructive force, trail a piece of paper out of the car window to see an example of flutter. When an aileron flutters it acts as a servo tab to the whole wing, twisting it one way then the other very quickly, the wing can be destroyed in seconds.

Usually the aileron is shaped like a triangle in cross-section and the bottom front point of the triangle is ahead of the top front point. The hinges are placed at the top front point and that means that the bottom front is ahead of the hingeline so the weights are added at that bottom front corner, usually a strip of lead running spanwise and rivetted to the aileron.

Sometimes the aileron has a 'horn' at the wingtip, a section of the wingtip attached to the aileron and that provides a position forward of the hingeline to attach the weights.

Cheers,

Alan
 

Turd Ferguson

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Generally, is there a way to figure out if airplane surfaces are designed mass balanced or not, especially ailerons?
Just look for weights (usually lead) forward of the hinge line to balance (or partially balance) the weight of the control surface.

Cessna manages to hide the aileron balance weights inside the front edge, very inconspicuous. Most people don't know they are there.
 

cavelamb

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IIRC?

RV-6 ailerons have an iron pipe (with lead inside?) inside the leading edge of the aileron.
 

pwood66889

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Aileron mass balances were used on my ride when it came out. They were abandoned when they proved ineffective, and thought to catch on the grass.
As Turd Ferguson mentioned, the Cessas have a lead strip on the lower lip of the ailerons. Those puppies come loose! I used to check mine on every preflight.
Percy in SE Bama, USA
 

David36

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Thank you for your answers guys, I really appreciate, but still not clear to me.

So, visually you can't say if it's balanced or not because it doesn't have mass weights outside. I looked at hinge, but I can't see if it has leading edge weights and I can't disconnect the aileron from the airplane because it's not my airplane.

So, is there a way to figure out if are balanced by manipulating/moving surfaces outside or the controls in the cockpit or other way except removing the surface from the airplane? What I observed, unlike on other airplanes (e.g. Cessna 172), is that on this airplane the ailerons don't center/neutralise themself, that means if I deflect the stick to the left, it remains there when I let the stick go. Is that because of the light weight of the surface being fabric covered or it is related to the balance of the surface?
 

Dana

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Mass balancing doesn't tend to center the ailerons, because as one goes up, the other goes down. It won't tend to center any surfaces, though in the case of the elevator it might prevent it from dropping when the stick is free on the ground.

Many planes have differential ailerons, i.e. the aileron moves up more than it moves down; this is to reduce adverse yaw. Such a geometry may tend to make them self centering, but that has nothing to do with mass balancing.

-Dana

The sex was so good that even the neighbors had a cigarette.
 

Head in the clouds

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Thank you for your answers guys, I really appreciate, but still not clear to me.

So, visually you can't say if it's balanced or not because it doesn't have mass weights outside. I looked at hinge, but I can't see if it has leading edge weights and I can't disconnect the aileron from the airplane because it's not my airplane.

So, is there a way to figure out if are balanced by manipulating/moving surfaces outside or the controls in the cockpit or other way except removing the surface from the airplane? What I observed, unlike on other airplanes (e.g. Cessna 172), is that on this airplane the ailerons don't center/neutralise themself, that means if I deflect the stick to the left, it remains there when I let the stick go. Is that because of the light weight of the surface being fabric covered or it is related to the balance of the surface?
What's your reason for wanting to know this? It's not your plane so why aren't you asking the owner of it or its maintainer? You sound like a junior investigator... I've already answered all you've asked, forget the light weight, fabric etc, cable tension might be more what affects your thoughts. Open up and explain what you're after please...
 

David36

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Hi David,

Nearly all ailerons are mass balanced if the aircraft flies faster than about 80mph, so the only exceptions would be some ultralights. The balancing is to prevent flutter which is an extremely destructive force, trail a piece of paper out of the car window to see an example of flutter. When an aileron flutters it acts as a servo tab to the whole wing, twisting it one way then the other very quickly, the wing can be destroyed in seconds.
This the reason. We talked in another thread that many LSA are not mass-balanced and in a cable failure, disconnected surface, it might flutter even at low speeds. This makes me curious to know which are mass-balanced and which not.

The owner knows nothing about this subject and I can't contact the maintainer. And it was not necessary to know about this aircraft, I wanted to figure out also for other LSAs. I highlighted this aircraft because this one I use to fly, but it's not the only one.
 

wsimpso1

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Most ailerons are mass balanced with the mass spread along the the farthest forward region on the aileron as possible. On Cessna's, they can be seen with the aileron "up", on Mooney's they are on a horn at the outboard end, but usually they are not visible. Most types have a type forum or group. Good place to get all sorts of data. Disconnected cables are BAD. Better to prevent.

Billski
 

Turd Ferguson

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This the reason. We talked in another thread that many LSA are not mass-balanced and in a cable failure, disconnected surface, it might flutter even at low speeds. This makes me curious to know which are mass-balanced and which not.
In the event of a control disconnect, the control may flutter even if it's balanced due to the loss of rigidity. There were some cases where the 601XL's experienced flutter even though the control surfaces were balanced. This was because the system lacked adequate stiffness.

You should be able to find a CFI or mechanic who can answer your question or quite possibly the airplane handbook may tell you if the controls are balanced under systems description. However, I think you're worried about nothing.
 

David36

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There were some cases where the 601XL's experienced flutter even though the control surfaces were balanced.
They were not mass balanced before applying upgrades due to crashes. You mean they flutter even after they were upgraded and mass balanced?

This was because the system lacked adequate stiffness.
Well, you mean the airframe or the structure or the flight control system itself, exactly which part lacked adequate stiffness? The aileron surface?

quite possibly the airplane handbook may tell you if the controls are balanced under systems description.
From aircraft POH:

Aileron controls
They consist of two control sticks synchronized through a rod inside the stick
axle, a system of balance levers and control rods for conveying the motion from
sticks to the torque tube located inside the wing. The motion from torque tube to
aileron is conveyed by means of the lever attached to the tube and the outer rod that
actuates the aileron. Inside the wing, the torque tube is attached in two Teflon
bearings, similar to the control stick axle bearings in the cockpit.

The control sticks, control rods and torque tube are made of dural tube, while
the control stick axle is made of 4130 steel tube.
The control rods are of adjustable length, being fitted at the ends with eyebolts
and lock nuts for fastening them after adjustment.


I can't figure out if this balance levers are what I'm looking for, but I hope so.
 

Turd Ferguson

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From aircraft POH:

Aileron controls
They consist of two control sticks synchronized through a rod inside the stick
axle, a system of balance levers and control rods for conveying the motion from
sticks to the torque tube located inside the wing. The motion from torque tube to
aileron is conveyed by means of the lever attached to the tube and the outer rod that
actuates the aileron. Inside the wing, the torque tube is attached in two Teflon
bearings, similar to the control stick axle bearings in the cockpit.

The control sticks, control rods and torque tube are made of dural tube, while
the control stick axle is made of 4130 steel tube.
The control rods are of adjustable length, being fitted at the ends with eyebolts
and lock nuts for fastening them after adjustment.


I can't figure out if this balance levers are what I'm looking for, but I hope so.
Based on the description, it appears the aileron control system uses push/pull rods & torque tubes in lieu of cables, and that the system is "balanced" however, I think it's important to remember loss of continuity in the system means flutter protection may not work as advertised.

I think you are looking for some kind of affirmation that as long as controls are mass balanced, flutter is not possible, even in the event of a disconnect and that's simply not true.
 

BBerson

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Not all controls are 100% balanced. Could be less or none or 100%. Check service manual for this information.
 

David36

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Ok, it's possible I made some erroneous assumptions. I'll try to be more precise.

I see there are some emergency landings where pilots in standard certificated light airplanes lost one surface control (e.g. aileron(s) ) due to cable failure and they made a safe landing using the remaining controls. But usually, standard type certificated airplanes have mass balanced controls. Also, it seems that many, if not most LSA airplanes surfaces are not mass balanced, maybe because of low speed operation which makes flutter less of an issue at these speeds, but in a disconnected surface case things might change regarding flutter. So, I assumed that an unbalanced surface would be likely to flutter, that's why I asked about it.

If the plane relies on cable tension to prevent flutter, that cable seems like a trigger for a structural failure. Don't know, maybe this assumption is very wrong.

I figured out that manufacturers choose to static balance the surfaces due to flutter and it seems that this works even if they are freefloating, considering the successful outcome of some incidents. I understand that it does not guarantee virtually 100% flutter protection, but it seems it worked, if this was really what prevented them to flutter.

I don't know if other design aspect of the airplane prevented flutter or other aspects are in the ecuation, that's why I'm asking, I don't have any experience or knowledge, so please clarify this to me.

Well, basically, what prevents a surface to not flutter in a freefloating, disconnected scenario if not mass balanced surfaces? What design aspects are involved in this issue? How can you figure out if the plane is well-designed regarding this aspect, especially LSAs? We know ASTM standards are not very specific on flutter issues.

Thank you very much and I really appreciate your help!
 
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Dan Thomas

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Ok, it's possible I made some erroneous assumptions. I'll try to be more precise.

I see there are some emergency landings where pilots in standard certificated light airplanes lost one surface control (e.g. aileron(s) ) due to cable failure and they made a safe landing using the remaining controls. But usually, standard type certificated airplanes have mass balanced controls. Also, it seems that many, if not most LSA airplanes surfaces are not mass balanced, maybe because of low speed operation which makes flutter less of an issue at these speeds, but in a disconnected surface case things might change regarding flutter. So, I assumed that an unbalanced surface would be likely to flutter, that's why I asked about it.

If the plane relies on cable tension to prevent flutter, that cable seems like a trigger for a structural failure. Don't know, maybe this assumption is very wrong.

I figured out that manufacturers choose to static balance the surfaces due to flutter and it seems that this works even if they are freefloating considering the successful outcome of some incidents. I understand that it does not guarantee 100% flutter protection, but it seems it worked if this was what prevented them to flutter. I don't know if other design aspect of the airplane prevented flutter or other aspects are in the ecuation, that's why I'm asking, I don't have any experience or knowledge, so please clarify this to me.

Well, basically, what prevents a surface to not flutter in a freefloating, disconnected scenario if not mass balanced surfaces? What design aspects are involved in this issue? How can you figure out if the plane is well-designed regarding this aspect?
Not all production aircraft have mass-balanced controls. Airplanes like the American Champion series don't: the citabrias and Scouts and so on. Slower airplanes are less prone to control surface flutter. The old rule-of-thumb was 150 MPH Vne or below, but that's not a hard rule. A flexible surface, or flexible mounting points, or flexible wing or stabilizer can contribute considerably and some slowpoke ultralights have had flutter-induced crashes.

Failing control cables are extremely rare. Proper maintenance catches fraying or corroded cables, broken pulleys or brackets, loose bellcranks, slipping swages, and so on long before they become a problem. The rest of the airplane's structure is probably more at risk of failure than the control system is, simply because the airframe is usually more highly loaded and operating closer to its design limits than things like cables.

Dan
 

Dana

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Mass balancing doesn't prevent flutter per se; what it does is (since flutter is a resonance phenomenon) move the flutter point to a different airspeed, hopefully outside the aircraft's operating range. Even with no mass balance at all, it doesn't necessarily mean the surface will be prone to flutter, cables disconnected or not... as I said, it's a complex subject.

Whether or not an aircraft has undergone a full flutter analysis, ASTM or FAR 23 or whatever, the aircraft does need to be tested throughout the full flight envelope, with no evidence of flutter. Not with cables disconnected, no, but flight cable failure is an extremely rare occurrence in a well designed and well maintained aircraft.

-Dana

"If you want to build a ship, then don't drum up men to gather wood, give orders, and divide the work. Rather, teach them to yearn for the far and endless sea." - Antoine de Saint-Exupéry
 

David36

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Not all production aircraft have mass-balanced controls. Airplanes like the American Champion series don't: the citabrias and Scouts and so on.
In this case they might have the same potential problem. I figure out two possibilities: they were tested and there is no problem OR they don't meet the PART 23 FAR certification criteria, but I hope the first one is the answer.

I thought FAR 23 certified aircraft are designed (and maybe even tested) to be flutter free in disconnected surfaces scenarios since FAR 23 (unlike ASTM) requires that even for a disconnected trim tab, so I can't figure out that they are not flutter free in primary control surface disconnection:


"Freedom from flutter, control reversal and divergence up to VD/MD must be shown as follows:

(1) For aeroplanes that meet the criteria of sub-paragraphs (d) (1) to (d) (3) of this paragraph, after the
failure, malfunction, or disconnection of any single element in any tab control system."


The rest of the airplane's structure is probably more at risk of failure than the control system is, simply because the airframe is usually more highly loaded and operating closer to its design limits than things like cables.

Dan
I think, despite this, there are still more flight control failures than inflight breakups due to structural failure and I hope remain so.
 
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SVSUSteve

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I think, despite this, there are still more flight control failures than inflight breakup due to structural failure and I hope remain so.
See the quote on my signature line from someone much smarter than myself and think about the statement you just made. Without data, making such statements is questionable at best

I will point out that in the case of in-flight structural failure, it is not uncommon to find a wing or stabilizer still attached (dangling) by the control cables. That should tell you something about the tolerances of flight control connections and how hard they are to break. Almost all of the failures of them I have come across are caused by either shoddy maintenance (i.e., failure to completely reattach the connections), a lack of maintenance bordering on the boneheaded (leading to unrecognized/uncorrected corrosion or abrasion damage) or substitutions of non-aircraft grade parts in an effort to save money or time.
 

David36

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See the quote on my signature line from someone much smarter than myself and think about the statement you just made. Without data, making such statements is questionable at best
It was a mild phrase and I expressed so as not to interpret the purpose of our discussion is none other than a constructive one, but the statement is based on statistics. Just of curiosity, search and see how many incidents reports are on flight control failures and how many inflight breakups were due to structural failures. Both are very rare, but for the last you can actually count them on your fingers.

Almost all of the failures of them I have come across are caused by either shoddy maintenance (i.e., failure to completely reattach the connections), a lack of maintenance bordering on the boneheaded (leading to unrecognized/uncorrected corrosion or abrasion damage) or substitutions of non-aircraft grade parts in an effort to save money or time.
So, even because of that, it happens and considering the potential catastrophic consequences, I'm not so satisfied relying exclusively on cables not failing.

LATER EDIT:

Not all production aircraft have mass-balanced controls. Airplanes like the American Champion series don't: the citabrias and Scouts and so on.

Dan
View attachment 21603
Just found this Scout photo. Is that a mass balance on the aileron? Quite strange.
 
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