Static/mass balanced or not

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Detego

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... See someone much smarter than myself
... 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.


Interesting, was control surface flutter the cause of the "in-flight structural failure", before the Crash? Please
provide a reference or investigation report.








"She got her looks from her father. He's a plastic surgeon." - Groucho Marx
 

Turd Ferguson

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I think, despite this, there are still more flight control failures than inflight breakups due to structural failure and I hope remain so.
Just curious, what data did you use to obtain this conclusion? Does flight control failure includes things like flap failures? Cause those are a non-event where an elevator disconnect is likley to have serious consequences.

Of all the things I worry might happen in flight, control failure and inflight breakups don't rank very high. If they did, I probably wouldn't fly.
 

David36

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NTSB reports, FAA reports, Airworthiness Directives, articles and even personal experiences from old pilots. They covered primary flight controls, but there were also some flaps failures reports, but as you said, they are usually a non-event. BTW, are flaps prone to flutter?
 

SVSUSteve

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NTSB reports, FAA reports, Airworthiness Directives, articles and even personal experiences from old pilots. They covered primary flight controls, but there were also some flaps failures reports, but as you said, they are usually a non-event.
David, no offense but you come across as a bit paranoid.

BTW, are flaps prone to flutter?
Any structure is able to flutter if you expose it to the right condition. That said, I can't recall a single case of spontaneous flutter in a flap without someone massively violating the operating range of the aircraft (overspeeding in other words).
 
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BBerson

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The rudder cables of most light planes are just loosely connected. If you take your feet off the pedals in flight it is the same as no cable connection ( some have a small spring). Does this scare you?:devious:
 

SVSUSteve

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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.
I don't have to do a search because I am already quite familiar with the statistics since aviation safety research is what I do for a living.

So, even because of that, it happens and considering the potential catastrophic consequences, I'm not so satisfied relying exclusively on cables not failing.
You should not but you also have to balance bigger concerns against the odds of something terribly remote. It's akin to never leaving the house because of the fear of being struck and killed by lightning. The best approach beyond a conscientious design to avoid the remote consequences of a major cable failure is probably to equip your aircraft with a ballistic parachute. This honestly isn't something I would lose much sleep over.
 

David36

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That said, I can't recall a single case of spontaneous flutter in a flap without someone massively violating the operating range of the aircraft (overspeeding in other words).
So do I, but if he asked, I wondered about it.


The rudder cables of most light planes are just loosely connected. If you take your feet off the pedals in flight it is the same as no cable connection ( some have a small spring). Does this scare you?:devious:
I took your question more as a joke. :grin: Anyway, in that case, "If you take your feet off the pedals in flight it is the same as no cable connection", I figure out the cable doesn't play a big role on stiffness, so it's less of an issue, I do not see why should I worry about it.


I don't have to do a search because I am already quite familiar with the statistics since aviation safety research is what I do for a living.
So, how do you come on this:
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’m really interested.
 

Turd Ferguson

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BTW, are flaps prone to flutter?
That said, I can't recall a single case of spontaneous flutter in a flap without someone massively violating the operating range of the aircraft (overspeeding in other words).

A VK-30 fatal accident near Lapeer MI was due to the right flap fluttering and subsequent loss of control.
 

Turd Ferguson

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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.

I'm familiar with a number of AC 5xx and 6xx series breakup accidents and it's very unusual for a part to remain tethered to the structure by control cables after the main attachment of that part fails. Perhaps on an ultralight that is true.
 

Dana

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Talking about the VK-30, remember that you're talking about speeds far in excess of LSA speeds.

One thing to keep in mind is that it's not the static balancing that helps with flutter... it's the mass. You could add mass behind the hinge line and have the same effect, even though it wouldn't be "balanced". It may be that the built up surfaces of older designs were heavier than the aluminum sheet of newer planes, and so less prone to flutter.

Sharp trailing edges (like the upper and lower sheets of a sheet metal aileron) are more prone to flutter than a more blunt trailing edge (like a round tube of a fabric covered surface).

But as Steve has said, stop worrying about it. There are far more likely things to worry about.

-Dana

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Head in the clouds

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.....See the quote on my signature line from someone much smarter than myself .......
Quote?..... people-watching.gif Signature line?.... ;)

.....View attachment 21603
Just found this Scout photo. Is that a mass balance on the aileron? Quite strange.
Your link is broken but I'm quite familiar with the Skycraft Scout. Scouts never had ailerons they use wing-warping and those horns attached to the spar are the warping mechanism not mass balances.

BTW, are flaps prone to flutter?
My answer would have been that flaps cannot flutter because flutter is a function of the surface going one way and then the other passing the centreline and flaps have an up stop at the centreline. However I had forgotten that some flaps have a negative or reflexed position so I imagine that the VK-30 referred to must have reflexed flaps?

......One thing to keep in mind is that it's not the static balancing that helps with flutter... it's the mass. You could add mass behind the hinge line and have the same effect, even though it wouldn't be "balanced". It may be that the built up surfaces of older designs were heavier than the aluminum sheet of newer planes, and so less prone to flutter.
I'm not sure but I thought it was the other way around, that heavier control surfaces will flutter at lower speed and so the weight is added ahead of the hingeline to make the surface 'effectively lighter'. It looks like I may need to do some more reading...

Sharp trailing edges (like the upper and lower sheets of a sheet metal aileron) are more prone to flutter than a more blunt trailing edge (like a round tube of a fabric covered surface).
I didn't know that either and it's useful, thanks.
 

BBerson

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I always the thought controls should be light as possible to avoid flutter. That's why they covered the DC-3 ailerons in fabric, right?
So... Dana has confused us (or at least me)
 

Dana

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Think of any spring system, add mass and the resonant frequency goes down, which translates to lower speed for flutter. The key to eliminating flutter is to raise or lower the flutter speed to outside the aircraft's envelope (below stall or above Vne, though the flutter speed may itself determine Vne). But I could be wrong; as I said above it's not my area of expertise.

-Dana

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Dan Thomas

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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:



View attachment 21603
Just found this Scout photo. Is that a mass balance on the aileron? Quite strange.
No, that's not a mass balance. It can act somewhat as a mass balance, but it's an aileron spade, and its purpose is to reduce the stick forces when deflecting the ailerons. When the ailerons are neutral, that spade is edge-on to the relative wind and has no effect on the aileron. When the aileron is deflected up or down, the air strikes the top or bottom of the spade and helps to move the aileron against the airflow.

Those spades are optional. Most often found on airplanes used for aerobatics.

Go to this page:
American Champion Aircraft - Scout

...and scroll down to "Options." Under Accessories you'll see Aileron Spades.

Here's an article that explains them:

Aileron - Wikipedia, the free encyclopedia

Dan
 

autoreply

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I always the thought controls should be light as possible to avoid flutter. That's why they covered the DC-3 ailerons in fabric, right?
So... Dana has confused us (or at least me)
Well, two sides of the same coin.

Lighter means a higher flutter speed.

Where more mass helps is that it can bring the mode for 2 different vibrational modes farther apart. Think of wing bending/torsion (classical flutter) and a dolphining mode of the tail. Both individually would only flutter at very high speeds and be far outside your flight envelope. But if you're unlucky, both can reinforce each other at much lower frequencies and thus speeds. Driving one of those flutter modes down will remove that "combined" mode.

Flaps depend on their hard stops and the (lack of) play to avoid them fluttering. Introduce some wear and it gets mightily interesting real quick...
 

David36

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Your link is broken but I'm quite familiar with the Skycraft Scout. Scouts never had ailerons they use wing-warping and those horns attached to the spar are the warping mechanism not mass balances.
http://www.homebuiltairplanes.com/forums/attachment.php?attachmentid=21603

...but flight cable failure is an extremely rare occurrence in a well designed and well maintained aircraft.

-Dana
As I said, I just can't rely on this. I’m really not satisfied relying on cables since there are old pilots who had even more than one occurence regarding control cable malfunction over years.

There are far more likely things to worry about.

-Dana
For example? Like what? Please give some examples to figure out better what do you mean.
 
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Dan Thomas

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As I said, I just can't rely on this. I’m really not satisfied relying on cables since there are old pilots who had even more than one occurence regarding control cable malfunction over years.


QUOTE]

I started flying in 1973. I became a commercial pilot in '94, Instructor in '99, licensed mechanic in 2000. I know of ONE control cable failure, and that was a flap cable. A corroded flap cable. 3/32".

Primary control surfaces require 1/8" minimum, 7 x 19 galvanized cable. It has a breaking strength of 2000 pounds and a rated working load of 400 pounds. When fittings are attached, it is tested to 60 percent of breaking strength, 1200 pounds, for a minimum of three minutes, far beyond what it will experience in the airplane. 1200 pounds on the cable once installed would crush pulleys and buckle their brackets and and tear out control surface bellcranks and probably do extensive damage to the rest of the airframe structure.


Worrying about properly designed systems and their cables will lead to worrying about every other little thing in the airplane and you will never fly it. Build an airplane that has a good track record, follow the plans exactly, be a competent pilot, and you will be safe. Eliminating ALL risk means staying in bed.

Dan
 
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