Simviation Forum - Overspeeding in Flight

Dec 24^th, 2004 at 4:50pm

Rocket_Bird Offline
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I was just wondering, a question to perhaps some real world pilots out there, particularly higherspeed aircraft types.... Do the planes every once in a while just jump past the overspeed marker on the airspeed indicator when encountering some heavier turbulence and wind? And if so, even so intermittently for a short corrected period of time, does that usually mean the aircraft would have to go straight to the shop?

In flight sim 2004, on real world weather anyways, often time, even when travelling 30-40 knots underneath the overspeed marker, the weather can suddenly push air aircraft by 50-60 knots in a heart beat even when it doesnt look that bad out. Is this unrealisticly modelled?

Cheers,
RB

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Reply #1 - Dec 24^th, 2004 at 5:08pm

beefhole Offline
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Airspeed indicator, not altimiter (you probably knew that) Grin

. My expertise stops there.

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Reply #2 - Dec 24^th, 2004 at 5:25pm

Rocket_Bird Offline
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woops, my bad

Cheers,
RB

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Reply #3 - Dec 26^th, 2004 at 10:21pm

jknight8907 Offline
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Not intentionally. Red line is known as Vne, Velocity Never Exceed. The reason you see this happening in FS is either because FS doesn't model smooth changes in wind direction (it is never as sharp and abrupt of a change as the sim shows), or you're flying too close to red line.

&&It is better to remain silent and be considered a fool, than to open your mouth and remove all doubt.&&&&There were once four people named Everybody, Somebody, Nobody and Anybody. Somebody had to do a job, but Nobody wanted to do it. Nobody could see that Anybody could do it, and Somebody got angry about that because it was Everybody's job. Nobody ended up doing it, and it so happened that Everybody blamed Somebody when Nobody did what Anybody could have done.

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Reply #4 - Dec 27^th, 2004 at 12:18am

TacitBlue Offline
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Im sure that the never excede is a little under-rated for safety reasons. for example, let say that exceding 150 Kts. will cause structural damage, so the Mfg. puts the Vne at 140. I could be wrong, but almost everything is under rated like that. i.e. pipes and valves.

A&P Mechanic, Rankin Aircraft 78Y

Aircraft are naturally beautiful because form follows function. -TB

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Reply #5 - Dec 27^th, 2004 at 10:10am

jknight8907 Offline
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Of course, but it's still a Never Exceed point, to avoid undue damage that would result if the plane was pushed right to the limit on every flight.

&&It is better to remain silent and be considered a fool, than to open your mouth and remove all doubt.&&&&There were once four people named Everybody, Somebody, Nobody and Anybody. Somebody had to do a job, but Nobody wanted to do it. Nobody could see that Anybody could do it, and Somebody got angry about that because it was Everybody's job. Nobody ended up doing it, and it so happened that Everybody blamed Somebody when Nobody did what Anybody could have done.

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Reply #6 - Dec 27^th, 2004 at 11:14am

Rocket_Bird Offline
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Ya, I found out in another forum that this was the case of poorly modeling, different weather in various regions in real weather is what they said. They also said the only way to solve this problem is to use programs like FSUIPC and Active sky, which are both expensive paywares...

I also notice something interesting last night though. It seems that whenever my airspeed indicator showed a sharp rise, my lift increases as well (my altitude goes up), and likewise whenever it shows a sharp drop, my lift also immediately drops. Now I was wondering if this can be related to a strong headwind or pressure zone when such things as abnormal airspeed rise occurs? As the pitot tube is pointed forward and is a measure of Indicated Air Speed, I was wondering if this could be the case? Could it just be the pitot system not measuring the correct airspeed because of this? I know an increase in lift also means increase in air on the airfoils. Just a thought...

Cheers,
RB

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Reply #7 - Dec 29^th, 2004 at 1:45am

OTTOL Offline
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Quote:

Of course, but it's still a Never Exceed point, to avoid undue damage that would result if the plane was pushed right to the limit on every flight.

Actually, the danger is not from catasrophic airframe failure but "mach tuck". Most subsonic wings have a critical mach number. Even though the airplane may be travelling below the speed of sound, air that is being accelerated over the top of the wing can exceed the speed of sound. Now, if you are in "coffin corner" and you experience a mach tuck......what will now happen when the aircraft is already past redline and now descending as result of the tuck?! As an example, Mmo on the Lear 25 is .83. I have flown with a Lear test pilot to .86 before we started to feel aileron buzz and wing buffet. This is approaching the point of what's known as limiting mach. Yes, there is most certainly a margin for error factored into the barbers pole.
Quote:

Do the planes every once in a while just jump past the overspeed marker on the airspeed indicator when encountering some heavier turbulence and wind?

One aspect of high altitude pilot training for a jet is planning for turbulence and the jump that does indeed occur with turbulence. This is modeled correctly. Usually though, it only amounts to about a .2-.3(10-20kias) mach variation. On my airplane Mmo is .82. In heavy turbulence, I'll pull it back to .76 or less. I used to fly air ambulance in a Lear 25 and we would exceed Mmo regularly on the descent during critical patient conditions. Even though pilots are trained to plan for this condition, not all turbulence can be forecast or foreseen. "Bumping the Barber's Pole" is a regular ocurrence. Quote:

And if so, even so intermittently for a short corrected period of time, does that usually mean the aircraft would have to go straight to the shop?

No, BUT.........modern jets that have ACARS can immediately notify the company if Mmo has been exceeded or for any number of other infractions. Big Brother is now a pilot as well?! 8)

.....so I loaded up the plane and moved to Middle-EEEE..........OIL..that is......

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