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Turbulence and feet per second

Old 26th Apr 2012, 11:14
  #21 (permalink)  
 
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Just an extra thought. If you do go too fast in turbulence, don't expect anything to "break". What will happen is reduced airframe life and possibly some very slight bent parts, by no means necessarily the wing itself.
You seriously test people?

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Old 26th Apr 2012, 15:01
  #22 (permalink)  
 
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Gotta agree with Uber on this one.

The difference between the limit (normal ~3.8) and the ultimate LF (+50%) might apply when the aircraft is new, but metal has memory and every time it gets flexed back and forth (ie by exceeding Va in bumpy stuff aka overstressing the airframe), it weakens just a bit further.

How long until the ultimate LF is equal to the limit LF? You can't tell and I ain't gonna try and find out!
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Old 26th Apr 2012, 16:49
  #23 (permalink)  
 
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From what I've been reading, in GA airplanes, Vno or the top of the green arc is a speed at which the aircraft is able to withstand up or downdrafts of up to 30 feet / second without over loading the plane
Most of the light aircraft we fly today were certified under the old CAR part 3 regs (pre '65). The certification criteria dictated that when operating in the green arc, the aircraft structure had to withstand an instantanious '50 per/sec vertical gust without bending anything. That's around 30 knots. I reckon if you happened hit a vertical gust of this magnitude whilst punching along at 160 kias in the 210, it'd certainly capture your attention quick smart. I've got absolutely no doubt one would be looking out the window at the wings rather suspiciously (mistakenly as it turns out).
When in the yellow arc by the way, the airframe has to be able to handle a '30 per/sec vertical gust, again without bending/breaking anything.

Another misconception that you quite often hear, is that it's OK to descend at cruise power in smooth air with the IAS in the yellow. Inncorrect.
The regs (CAR 3) state that the yellow arc is only for inadvertant excursions of airspeed . In other words, if you find yourself on the high side of Vno, get yourself and the aircraft back in the green arc on the ASI.

The C210 is deliberately limited by Cessna to avoid overstress in the un strutted wing/fuzelage attach area.
This has been the subject of debate for years but the end conclusion is that the way the wing attaches does warrant care in turbulent conditions.
The C210 was limited by Cessna (as was any other model manufactured by Cessna) to meet the requirements of CAR 3 under which the aircraft was certified. To say that it was hobbled by Cessna because the wing was strutless or because of the way that the wings attached to the fuselage is incorrect. The strutless wing easily met the requirements needed to gain certification under CAR 3.
The wing on the 210 when compared to say, an A36 or Saratoga/Lance, doesn't warrent any extra consideration other than the normal precautions that a pilot might take when operating in turbulent conditions.
The fact of the matter is, the spar carry through structure on the 210 is stronger the the strutted wing of the 206. So if you do happen the hit that 50' per/sec gust in your 210, relax.

As an aside, one of the strongest set of wings that Cessna ever put on aeroplane were strutless. These belonged to the 195 series. Because of a number of design considerations that were made at the prototype stage, the wing was overbuilt (not on purpose) i.e. it was heavier than it needed to be.
When Cessna tested the wings, they didn't break when they were supposed to. They went way, way past the point at which they were supposed to let go. So rest assured, when out driving in your 195, you'll break before the wings do!
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Old 28th Apr 2012, 12:34
  #24 (permalink)  
 
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das uber soldat, and makeithappencaptain,

That aeroplane did not crash because the pilot went ten or twenty knots too fast in turbulence. If you have read the report behind it, perhaps you might tell us what led to the crash. (Exceeded Va by 10 or 20kts in moderate turbulence on an otherwise fine day? Ha ha.)

There is a difference between going slightly too fast and going 50% too fast, or going into a mature thunderstorm. It's because I know that, that I spent years being allowed to test people. And seeing them, for example, do max rate turns above Va. Naughty naughty. But yet we didn't crash. No, of course I didn't condone it though.

If a pilot reading this forum goes away thinking that flying through moderate turbulence above Vb or Vra will break something, he will be surprised when he accidentally does it one day. Because there probably won't be anything to see to the casual eye - unless of course ten or a hundred other pilots have done so before him, or if he went up to Vne in moderate or severe turbulence! But it's still bad, because of fatigue and hidden parts that are damaged if only slightly. So even if there seems to be no damage, report it at least verbally to a friendly LAME who knows what look for.

Have you seen the slight wrinkling of an overstressed fuselage? It isn't obvious. Have you felt the excess play in a worn-out stabilator bearing? Again, not necessarily obvious.

That's the message I'm trying to say. Nothing to do with flight through thunderstorms.

Last edited by Oktas8; 28th Apr 2012 at 13:01.
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Old 28th Apr 2012, 13:22
  #25 (permalink)  
 
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Have you seen the slight wrinkling of an overstressed fuselage? It isn't obvious. Have you felt the excess play in a worn-out stabilator bearing? Again, not necessarily obvious.
All the more reason not to do it. How do you know previous pilots haven't gradually worn down that nice limit-ultimate margin? I'm not saying a 10 knot exceedance will bring you undone and I'm sure no-one will be "disappointed" the airframe didn't fail, but Va is set for a reason and to introduce a healthy fear/respect of exceeding this parameter is definitely not a bad thing imo.

I agree with using Va in lieu of Vb, as previously stated, the littlies don't have the same certification reqirememts.

My agreeing with Uber had nothing to do with the commander photo specifically, just not happy with the generalised understatement of what can happen. Worst case scenario, I know and no apologies for that, but it's the old/bold scenario that will keep you alive the longest. Remember the age of Australia's GA fleet.
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Old 29th Apr 2012, 04:02
  #26 (permalink)  
 
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If you are flying geophysical survey in a 210 then it alters the dynamics somewhat. Going high isnt an option, and if you slow down too much you can risk driving into the side of a hill.

Put your drink bottle on the seat next to you. If said drink bottle is regularly floating around the cabin, and you are also feeling those sickening big thumps every so often that are a bit painful, its time to go home....so go home!! The survey lines will still be there tomorrow to fly when hopefully it isnt so rough. Especially if it is my survey plane you are flying, they cost too much to fix!!!!

On another note, everybody worrying about the wings falling off may want to take a closer look at the tailplane of their 210. It will give up first you will find. My 210 has had its tail rebuilt 3 times now but the wing has only broken once.
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Old 29th Apr 2012, 06:55
  #27 (permalink)  
 
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Aileron 69,
I'm curious. When you say your C210 tail has broken 3 times was it the horizontal stabilizer to fuselage (forward attach fittings) that failed and if so after the first failure did you have the doubler mod fitted ?
Cheers RA
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Old 29th Apr 2012, 09:03
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The only catastrophic in-flight failure of a C210 that I can recall, occurred near Cloncurry back in the 70's. Wing failed at the flap/aileron junction, if I remember correctly.

Dr
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Old 29th Apr 2012, 11:40
  #29 (permalink)  
 
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C210 Cloncurry
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Old 29th Apr 2012, 21:19
  #30 (permalink)  
 
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There isn't enough information in the Accident Report to really determine what happened. However if the limited information available is accurate it appears this may have been a flutter event. I once heard an aircraft flutter and a sound a bit like a misfiring engine is a reasonable description. The witness statements that the aircraft had commenced a right turn do not fit the overloaded outboard section of wing failing in the downward mode scenario. If that scenario had occurred the right wing would be the broken one. Turning right would speed up the left wing and perhaps that was the straw that broke the camels back. C210's don't have a great flutter margin but it is of no concern providing it is flown inside the design envelope. There is an aileron beef up mod available. This was developed when people started playing with much more powerful engine installations such as turbines.
Cheers RA
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Old 29th Apr 2012, 22:09
  #31 (permalink)  
 
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The regs (CAR 3) state that the yellow arc is only for inadvertant excursions of airspeed
I don't see that in CAR 3. (I am aware of a reg which states that a pilot must do what the AFM states.)

How many G's can Light, Moderate, and Severe turbulence produce based upon their prescribed FPMs?
The standard equation for gust load factor:

with: a = (dCL/da) - lift curve slope - try 5 for a simple calculation
Ue = equivalent gust velocity (in ft/sec)
Ve = equivalent airspeed (in knots)
Kg = gust alleviation factor - try 0.85 for a simple calculation
W/S is wing loading in lb/sq ft
(I hope my memory has worked for the "try" numbers, I haven't had any coffee this morning yet)
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Old 30th Apr 2012, 03:00
  #32 (permalink)  
 
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Rutan:

Its broken in different places each time. The forward attach fittings have broken, so have the rear. We do now have the doubler mod fitted. It also needed the rear 2 or 3 (cant remember how many) bulkheads replaced as they cracked. Was a rather expensive process. I would say part of the cause of the bulkhead damage would be directly related to the stinger on the tail.

Cheers
Aileron
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Old 30th Apr 2012, 03:52
  #33 (permalink)  
 
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The Cloncurry Incident report states:


"A rapid application of a large amount of right wing down aileron control at speeds in the vicinity of the normal cruising speed could produce torsional loading in the left wing in excess of the design strength of the wing and result in
wing failure consistent with that which occurred in this accident."


So what do we consider to be a "safe" amount of control deflection at speeds above Manouvring Speed?
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Old 30th Apr 2012, 03:55
  #34 (permalink)  
 
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Thanks Capt! I wasn't aware that there were witnesses.

Bit of a mystery really.

Happened around the time I first started flying 210's - gave considerable food for thought.

Dr
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Old 30th Apr 2012, 18:48
  #35 (permalink)  
 
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Its broken in different places each time. The forward attach fittings have broken, so have the rear. We do now have the doubler mod fitted. It also needed the rear 2 or 3 (cant remember how many) bulkheads replaced as they cracked. Was a rather expensive process. I would say part of the cause of the bulkhead damage would be directly related to the stinger on the tail.
Wasn't there an SB that came out recently as a result of a stinger equipped a/c with this damage?
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Old 30th Apr 2012, 22:16
  #36 (permalink)  
 
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Sure was, it was the rear attach point on the Horizontal Stab breaking, and that caused the stab to move, jammed the elevator, and nearly brought the aircraft down. When other operators checked their aircraft about half found the rear attach points cracked and needing replacement.
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Old 1st May 2012, 00:26
  #37 (permalink)  
 
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Just had this arrive from Cessna today regarding Spar cap inspections.
This could ground a few aircraft.

https://support.cessna.com/custsupt/...df?as_id=37240
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Old 1st May 2012, 14:07
  #38 (permalink)  
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Thanks for that link 69.
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Old 2nd May 2012, 05:22
  #39 (permalink)  
 
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For most readers of this thread I'm probably teaching my grandmother how to suck eggs with this C210 pre flight check to determine if the horizontal stabilizer to fuselage attachments are ok.
Grip the outboard end of horizontal stabilizer and push it up and down a few inches (fairly slowly.don't use excessive force.)

You should hear an oil canning noise as the skin flexes. This noise is ok
If you hear a crunchy or grating noise DON'T FLY.

If this test only prevents 1 accident it was worth boring those who already include it in their pre flight checks.

To recognize the difference between an oil canning noise and the dreaded crunchy noise I
recommend the following procedure.

1) Empty one aluminum beer can

2) Lightly squeeze and release the can several times between thumb and forefinger. That noise is oil canning or in this case beer canning.

3)Now using a screwdriver or knife rip and tear a break approximately half way round the circumference of the can. Grasp each end of the can and slightly rotate the ends back and forth in opposite directions. That is the crunchy "DON"T FLY" noise.

When Mrs RA politely inquired why I had just drunk 8 VBs I just as politely informed her that the recommended procedure would have to stand up to peer group review and one couldn't be too careful. The mower shed isn't all that cold and uncomfortable.

I recommend the above procedure to anyone unsure of the noises they should be listening out for whilst performing the essential horizontal stabilizer pre flight check.
Cheers RA
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Old 2nd May 2012, 17:48
  #40 (permalink)  
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I'll try that horizontal stabilizer test tomorrow......a few inches though? Doesn't that seem like a bit much?
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