Arrow PA-28 Experienced In-Flight Break-Up
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If Va is not related at all to the main spar structural limit, why does it vary with weight in the manner expected if it was?
I haven't been told this by an instructor; in fact I don't recall meeting an instructor who knew anything much "technical".
I haven't been told this by an instructor; in fact I don't recall meeting an instructor who knew anything much "technical".
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Great post SN3G, very well explained.
Having just stepped out of a PA28 having done some steep turns and stall practice, I can happily report that it didn't fail.
Maybe my steep turns are getting better because the seat of my pants returned a reading of 2G. After reading this thread future readings maybe invalidated by me
myself.
IO;
[Caveat - I'm a stude and you guys undoubtedly know more than me, I'm just suggesting a few ideas].
Could it be that for the majority of light aircraft surely Va is related to main spar strength in addition to other factors, if (as is detailed elsewhere) Va is usually determined by a single axis control input and it's usually the elevator.
I seem to remember reading that light aircraft were protected against spar failure because a rapid change in the lateral axis (i.e., elevator deflection) would cause the aircraft to stall before the loading on the wing became sufficient. However, having read SN3G's post and the AAIB report previously detailed in this thread, that looks like an exam question answer as opposed to the real world, where the forces on the aircraft (gusting wind, aileron changes).
However I think it's the AAIB report that points to a PA28 as having a spar that deforms at 5.7G - considerable.
Having just stepped out of a PA28 having done some steep turns and stall practice, I can happily report that it didn't fail.
Maybe my steep turns are getting better because the seat of my pants returned a reading of 2G. After reading this thread future readings maybe invalidated by me
myself.IO;
[Caveat - I'm a stude and you guys undoubtedly know more than me, I'm just suggesting a few ideas].
Could it be that for the majority of light aircraft surely Va is related to main spar strength in addition to other factors, if (as is detailed elsewhere) Va is usually determined by a single axis control input and it's usually the elevator.
I seem to remember reading that light aircraft were protected against spar failure because a rapid change in the lateral axis (i.e., elevator deflection) would cause the aircraft to stall before the loading on the wing became sufficient. However, having read SN3G's post and the AAIB report previously detailed in this thread, that looks like an exam question answer as opposed to the real world, where the forces on the aircraft (gusting wind, aileron changes).
However I think it's the AAIB report that points to a PA28 as having a spar that deforms at 5.7G - considerable.
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Message to my fans over here: sorry i couldn't answer earlier, i was logging solo hours in the air this week, some of you insisted that i got more of that, well i'm doing my best, i'm happy to know that you guys all had your mouth shut until you got over 1k hours logged.
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No sternone - just try to remember to think before blurting..
But if nothing else it started some interesting discussion.
Incidently the one inflight Mooney breakup (yes they do happen!!!) I found on the net, resulted (probably) from flutter.
But being unaware of the Bonanza's reputation is somewhat unforgiveable..
But if nothing else it started some interesting discussion.
Incidently the one inflight Mooney breakup (yes they do happen!!!) I found on the net, resulted (probably) from flutter.
But being unaware of the Bonanza's reputation is somewhat unforgiveable..
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Sterny baby
It's not how many hours you've got that counts, it's how you communicate your experience.
'No PA28s for me' probably isn't the best way of doing that.
This flutter thing is scaring the willies out of me but it seems to occur where there is some sort of related failure, e.g., the Whitman discussed below.
No chance of it just...happening... is there? I thought that modern aircraft had aerodynamic or mass balances to prevent it?
MM
It's not how many hours you've got that counts, it's how you communicate your experience.
'No PA28s for me' probably isn't the best way of doing that.
This flutter thing is scaring the willies out of me but it seems to occur where there is some sort of related failure, e.g., the Whitman discussed below.
No chance of it just...happening... is there? I thought that modern aircraft had aerodynamic or mass balances to prevent it?
MM
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In either case, this is a forum, so if you don't like me, i don't care, i don't have to live with you and you don't have to live with me. I learned so many things from PPRuNe it's amazing, and i like it. I'm only a click away from going away from your screen, how easy can that be ?
The one Mooney that broke up in flight was flying into a thunderstorm, the wing spar test they performed on the Mooney: the test rig broke before the wing spars did, they broke a static test fixture at 9,3G's while doing a destructive test on the J model.
Very intresting read about the flutter, be happy i say stupid things, we get these fine texts from it!!
The one Mooney that broke up in flight was flying into a thunderstorm, the wing spar test they performed on the Mooney: the test rig broke before the wing spars did, they broke a static test fixture at 9,3G's while doing a destructive test on the J model.
Very intresting read about the flutter, be happy i say stupid things, we get these fine texts from it!!
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Interesting reading as always SNS3Guppy, but what you are saying is that normal flight can cause an aircraft to fall apart around us.
Are you referring to the C130 that lost its wings unloading over a fire?
But, aren't those aircraft subjected to abnormal conditions and flying in extreme environments, hot, low level and abrupt maneuvring? I always thought it looked exceptionally dangerous...
Abrupt maneuvering is somewhat of a misnomer. In past times, however, aircraft over fires have experienced structural failures at speeds below turbulence penetration speeds (our drop speeds are considerably lower). The C-119, in particular, experienced a number of aileron and wing failures while maneuvering, even at low speeds, largely due to flitner tabs which allowed very light control forces and rapid pilot deflection of the controls. Abrupt movement suggests something different than a fast, but smooth application of the controls. The rate at which the airframe is loaded, as well as the amount and the way in which it is done, all combine to determine what's safe and what's not.
What we do, is make everything as normal as possible. An approach to a drop, be in the flats or on the mountainside, is flown like a traffic pattern with a downwind, base, and final, as stable as possible, configured similiarly to a landing (except for the landing gear, of course, and sometimes that gets used on a very steep drop). The point is, even in that type of flying, we strive very hard to keep airplanes way from the edges of the envelope, and to respect the airframe, and limitations.
This becomes extremely important when operating in severe or greater turbulence. Extreme care when operating the airplane and in maneuvering is very critial to one's own safety, and the longevity of the airframe.
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Oh yes Skyhawk-N, I made the schoolboy error of reading the whole thread and taking the quote by IO540 in context with the whole. I clearly forgot that there would be smart pedants reading waiting to seize on such a basic error.
You, on the other hand have managed to analyse IO540's post in splendid isolation and have skilfully proved him wrong as well as having a well justified pop at me.
Well done!
You, on the other hand have managed to analyse IO540's post in splendid isolation and have skilfully proved him wrong as well as having a well justified pop at me.
Well done!
Now getting back to your first post on this (what turned out to be) interesting thread.
All this wisdom from someone who went solo on 4th October 2007, and probably doesn't yet have a licence.
Last edited by SkyHawk-N; 15th Nov 2007 at 18:35.
Professional Student
My 2 cents; I once (unintentionally) dived a PA-28-160 to 2 knots past Vne. It was during IMC training, unusual attitude recovery. I was a little slow to recover during a diving UA (and I suppose so was the instructor!), and the ASI showed just past the redline.
A subsequent engineering inspection revealed no damage/stress/etc. We had plenty of height in hand, and recovered gently (it was a full power dive, but not at an overly steep dive attitude).
Undected faults aside (and also noting that I am not a qualifed airframe specialist/engineer/etc), I think had I, or the instructor, recovered with abrupt, substansial control inputs then there might have been damage to the aircraft or worse.
A subsequent engineering inspection revealed no damage/stress/etc. We had plenty of height in hand, and recovered gently (it was a full power dive, but not at an overly steep dive attitude).
Undected faults aside (and also noting that I am not a qualifed airframe specialist/engineer/etc), I think had I, or the instructor, recovered with abrupt, substansial control inputs then there might have been damage to the aircraft or worse.
Pompey till I die
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?!?!?
Why not cut sternone some slack? I may be wrong but english is his second language and as a result things may come out a bit wrong sometimes, this may be one of those cases. A friendly correction and steer would have been nice.
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Ok, I'm gonna stick my neck out again and prove I know nothing about this (after 15 years! 
).
I picked up my aircraft design textbook to try and understand where Va actually comes from. It says, "Maneuver speed, or pullup speed Vp, is the maximum speed at which the pilot can fully deflect the controls without damaging either the airframe or the controls themselves".
To me this suggests that at or below Va, movement of a control cannot generate the required aerodynamic load to cause a failure of any part of the airframe.
Further, Va is a speed picked as a design point and not actually defined from design parameters. It may be dictated by design requirements, or calculated through some empirical relationship.
Basically, the Va speed provides a point where the integrity of the airframe is checked. By analyzing the AoA or sideslip obtained by full movement of a control at Va, one can establish the airloads which the structure must meet. The text also implies that full movement of the ailerons at max load factor imposes instantaneous loads that frequently are critical to the wing structure. So pulling 3.8 gs and throwing the yoke could snap your wing, perhaps.
Sounds lika Va is a useful limit after all, but perhaps I'm not understanding what the book is saying.
).I picked up my aircraft design textbook to try and understand where Va actually comes from. It says, "Maneuver speed, or pullup speed Vp, is the maximum speed at which the pilot can fully deflect the controls without damaging either the airframe or the controls themselves".
To me this suggests that at or below Va, movement of a control cannot generate the required aerodynamic load to cause a failure of any part of the airframe.
Further, Va is a speed picked as a design point and not actually defined from design parameters. It may be dictated by design requirements, or calculated through some empirical relationship.
Basically, the Va speed provides a point where the integrity of the airframe is checked. By analyzing the AoA or sideslip obtained by full movement of a control at Va, one can establish the airloads which the structure must meet. The text also implies that full movement of the ailerons at max load factor imposes instantaneous loads that frequently are critical to the wing structure. So pulling 3.8 gs and throwing the yoke could snap your wing, perhaps.
Sounds lika Va is a useful limit after all, but perhaps I'm not understanding what the book is saying.
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Thanks! Then I'm not completely in the dark after all. I need to pick up a few POHs and see what they say, but I don't recall ever reading anything about single axis movement, but I understand the point and it makes perfect sense really. I don't remember enough from PPL ground school to recall whether Va was discussed in this manner...
I shall be more watchful of my students as of now.
I shall be more watchful of my students as of now.
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Quote: be happy i say stupid things, we get these fine texts from it!!
It'd be even better if you were to say smart things, we could then have fine texts with no nonsense in the middle of them.
Yes, I probably said a few silly things when I had less than 1k hours. In the 4k hours which have followed that (some in Mooneys), I've learned to be respectful of others, and simply try to behave well, as if I were I were in the same room with all of you...
Pilot DAR
It'd be even better if you were to say smart things, we could then have fine texts with no nonsense in the middle of them.
Yes, I probably said a few silly things when I had less than 1k hours. In the 4k hours which have followed that (some in Mooneys), I've learned to be respectful of others, and simply try to behave well, as if I were I were in the same room with all of you...
Pilot DAR
Moderator
Those wiser than I ware welcomed to comment, but my read of FAR Part 23.335 Design Airspeeds, (c) Design Maneuvering Speed Va, refers only to a formula relating to stall speed and the limit maneuvering load factor (G's). No other axis are mentioned.
It is therefore my understanding that Va is considered in isolation of the other two axis, and control inputs in those axis.
There is, therefore, no design assurance that a pilot will not damage the aircraft with full and abrupt use of ailerons or rudder during flight at speeds below Va.
That said, aside from perhaps aerobatic flying, how common is it to need to apply such control inputs in any axis anywhere near Va? In all my years of flying, I've only needed to hit a control stop twice, Once crosswind landing (okay I'll step into the fray: Ailerons in an Arrow), the other the elevator down stop, which I held for some time, to maintain control during a test flight of a horribly misrigged Cessna 206. Both of these events were very close to stall speed, thus breaking the airplane with control input was not a concern. Breaking it against the ground was though!
Pilot DAR
It is therefore my understanding that Va is considered in isolation of the other two axis, and control inputs in those axis.
There is, therefore, no design assurance that a pilot will not damage the aircraft with full and abrupt use of ailerons or rudder during flight at speeds below Va.
That said, aside from perhaps aerobatic flying, how common is it to need to apply such control inputs in any axis anywhere near Va? In all my years of flying, I've only needed to hit a control stop twice, Once crosswind landing (okay I'll step into the fray: Ailerons in an Arrow), the other the elevator down stop, which I held for some time, to maintain control during a test flight of a horribly misrigged Cessna 206. Both of these events were very close to stall speed, thus breaking the airplane with control input was not a concern. Breaking it against the ground was though!
Pilot DAR
Originally Posted by G-EMMA
Can I ask again if anyone has a link to the NTSB report that started this thread, I'm hopeless at searching the NTSB web site, I'm interested to know if the ailerons fell off because the outer wing sections failed or whether the ailerons came off first
Here it is:
http://www.ntsb.gov/ntsb/brief.asp?e...05X01726&key=1
It doesn't really say what happened first. It just said the ailerons were found detached. The UK accident report seemed to indicate that the aileron was seperated on G-BKCB because the wing failed between the two piano hinges. So, for a moment, the aileron was all that was holding the wingtip on.
I have followed the story, and the thread (minus the personal bashing), with some interest as I'm working on my instrument rating in an Arrow. She's an old girl, 1967 PA28R-180, with something like 4000 hours on it. I sure would like to know exactly what happened in both accidents, that I might learn from it.
Personally I have a lot of faith in the PA28 series aircraft. They have been around a long time. And I agree that any airplane, no matter how strong, can be broken if overstressed. Here's my favorite:
http://www.ntsb.gov/ntsb/brief2.asp?...97LA211&akey=1
There was a longer story about it in Soaring magazine, I should have kept it. This old timer flew into a towering cumulus cloud, became disoriented, and pulled a wing off a 1-26. Spun out of the bottom of the cloud. The pine trees stopped the rotation, then cushioned the fall. The glider ended up on its nose. His injury consisted of a cut shin stepping out of the cockpit. His wife took to calling him "Heaven's reject."
A couple years ago I met a structures guy from the company. We talked about that accident. The guy had to pull 9 g's to fail that wing. There's no way I could pull 9 g's in a 1-26 in any normal part of the flight envelope. He had to be going fast, as well as yanking the controls.
-- IFMU
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POH
In the POH of the C152 it says at flight load factor limits:
Flight load factors:
* Flaps Up: +4,4g, -1,76g
* Flaps Down: +3,5g
* The design load factors are 150% of the above, and in all cases, the structure meets or exceeds design loads.
I understand the above is on flight load limits, but can we assume that even passing Vne we still have some safety margin ?
Flight load factors:
* Flaps Up: +4,4g, -1,76g
* Flaps Down: +3,5g
* The design load factors are 150% of the above, and in all cases, the structure meets or exceeds design loads.
I understand the above is on flight load limits, but can we assume that even passing Vne we still have some safety margin ?
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Are those G limits instantaneous or sustained ? The POH probably won't say.
Could you comment G-EMMA in terms of testing? I'd imagine they'd put components into a test rig and subject them to testing until deformed, therefore it would be sustained.
I would imagine that in one or two of my more creative landings, I've subjected the airframe to a significant amount of G, though without an accelerometer even my finely tuned seat of pants wouldn't be able to say how much.
Also in turbulence or gusty conditions you can get bumped around significantly - again, without some sort of instrument I can only guess as to airframe stress.
I too fly old PA28s - about 1976 I think, with 1000s of hours on the airframe, probably mainly by low hours or ab initio PPLs, so they've probably been submitted to a bit of everything.
Could you comment G-EMMA in terms of testing? I'd imagine they'd put components into a test rig and subject them to testing until deformed, therefore it would be sustained.
I would imagine that in one or two of my more creative landings, I've subjected the airframe to a significant amount of G, though without an accelerometer even my finely tuned seat of pants wouldn't be able to say how much.
Also in turbulence or gusty conditions you can get bumped around significantly - again, without some sort of instrument I can only guess as to airframe stress.
I too fly old PA28s - about 1976 I think, with 1000s of hours on the airframe, probably mainly by low hours or ab initio PPLs, so they've probably been submitted to a bit of everything.