IAS, TAS & VNE
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IAS, TAS & VNE
Fellow pilot and I are discussing VNE.
One says that IAS at altitude is VNE, whereas the other says that TAS at altitude is VNE.
Eg. 9,500ft. IAS 100 knots; TAS is eg 115.
Aircraft VNE is 110.
Is the aircraft exceeding VNE?
Thanks.
One says that IAS at altitude is VNE, whereas the other says that TAS at altitude is VNE.
Eg. 9,500ft. IAS 100 knots; TAS is eg 115.
Aircraft VNE is 110.
Is the aircraft exceeding VNE?
Thanks.
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Interesting
Vne is a structural speed measured with IAS. That said, the Vne, commonly represented by the barbers pole actually varies with altitude so it cannot be said that the Vne is a fixed IAS.
Vne is a structural speed measured with IAS. That said, the Vne, commonly represented by the barbers pole actually varies with altitude so it cannot be said that the Vne is a fixed IAS.
Vne Vmo?
Barbers pole versus fixed red radial line.
The complexity behind a simple question.
Oh and there is this...http://www.pprune.org/forums/showthread.php?t=214121
Or this one...http://www.pprune.org/forums/showthread.php?t=226750
Barbers pole versus fixed red radial line.
The complexity behind a simple question.
Oh and there is this...http://www.pprune.org/forums/showthread.php?t=214121
Or this one...http://www.pprune.org/forums/showthread.php?t=226750
Last edited by Icarus2001; 5th Jul 2006 at 07:54.
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Vne is an KIAS limitation. As are most limitations - flaps, gear etc,.TAS is EAS corrected for atmospheric conditions & EAS is IAS corrected for position & compressibility errors.
Vne is a static value eg 350 KIAS. What the "barber pole" does is vary that IAS limitation to a Mach No. limitation for high altitude flight. eg Vne might be 350 KIAS until F270 then M.085.
Icarus2001 is correct.
Vne is a static value eg 350 KIAS. What the "barber pole" does is vary that IAS limitation to a Mach No. limitation for high altitude flight. eg Vne might be 350 KIAS until F270 then M.085.
Icarus2001 is correct.
With that provision for varying the red-line - constant CAS / IAS changing to constant M at altitude - there are some aeroplanes where that M is relatively low so its not compressibility effects. Flutter speed is a function of TAS so one way of maintaining the required margin is to use that M limitation - you'll find that its not much different from a constant TAS line - if you ever see an example of this.
Above would generally apply to aeroplanes with a VMO / MMO not VNE. I note that the initial question mentioned very low airspeeds so the above is probably totally irrelevant to that gentleman.
VNE needs to provide margin from static structural point of view, vibration & buffet plus flutter. EAS, TAS and M are the principal variables. Little, slow aeroplanes its a constant CAS or IAS. OOps, nearly forgot, if its fixed pitch prop there's margin from engine overspeed with throttle closed.
Above would generally apply to aeroplanes with a VMO / MMO not VNE. I note that the initial question mentioned very low airspeeds so the above is probably totally irrelevant to that gentleman.
VNE needs to provide margin from static structural point of view, vibration & buffet plus flutter. EAS, TAS and M are the principal variables. Little, slow aeroplanes its a constant CAS or IAS. OOps, nearly forgot, if its fixed pitch prop there's margin from engine overspeed with throttle closed.
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What was the question????
Gents and Gals,
I think the original post asked the question about wether an aircraft VNE was refferenced to the IAS or TAS.
He/she asked if his/her aircraft had a VNE of 110kts, and it was up at 9500 feet where on that day the TAS was 115kts, but due to the IAS being only 100kts at that height would it be exceeding its VNE?
Its a simple question with a simple answer...........but gee I love all the responses. Poor QNH is going to be one confused puppy!
Cheers J
I think the original post asked the question about wether an aircraft VNE was refferenced to the IAS or TAS.
He/she asked if his/her aircraft had a VNE of 110kts, and it was up at 9500 feet where on that day the TAS was 115kts, but due to the IAS being only 100kts at that height would it be exceeding its VNE?
Its a simple question with a simple answer...........but gee I love all the responses. Poor QNH is going to be one confused puppy!
Cheers J
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I agree with J430!
I hardly think that an aircraft with a VNE of 110kts is going to have a barbers pole or be referring to Mach numbers!!
The answer is no. Structural speed limits in a light aircraft are IAS. This is why I always climb as high as possible on a very turbulent day to keep the IAS below the turbulence penetration speed, whilst maintaining a reasonable TAS.
I hardly think that an aircraft with a VNE of 110kts is going to have a barbers pole or be referring to Mach numbers!!
The answer is no. Structural speed limits in a light aircraft are IAS. This is why I always climb as high as possible on a very turbulent day to keep the IAS below the turbulence penetration speed, whilst maintaining a reasonable TAS.
Last edited by M.25; 6th Jul 2006 at 01:44.
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Fellow pilot and I are discussing VNE.
One says that IAS at altitude is VNE, whereas the other says that TAS at altitude is VNE.
One says that IAS at altitude is VNE, whereas the other says that TAS at altitude is VNE.
Classic Dick has correctly stated the position regarding "barber poles"!
If this is not simple enough, get yourself a copy of Handling the Big Jets and read it on your days off.
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Amazing
I was wondering how long it would take to get a sensible answer before the thread was derailed.
It seems we have some stute contributors here for once.
Jack Red says it how it is I believe "Vne is a fixed KIAS value. It DOES NOT vary with altitude and is not subject to temperature and/or compressibility errors."
Funny how a simple innocent question here gets all sorts of BS some times. But its entertaining to follow.
Hope old mate QNH has his/her answer now. But it will be interesting to read all the other gravity defiant transportaion theorists comments.
Cheers J
It seems we have some stute contributors here for once.
Jack Red says it how it is I believe "Vne is a fixed KIAS value. It DOES NOT vary with altitude and is not subject to temperature and/or compressibility errors."
Funny how a simple innocent question here gets all sorts of BS some times. But its entertaining to follow.
Hope old mate QNH has his/her answer now. But it will be interesting to read all the other gravity defiant transportaion theorists comments.
Cheers J
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I would suggest speed limits are very closely related to TAS and G-limit loadings.
Think of it as like going over a speed hump in your car slowly or at a greater True Speed.
Incoming.....
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Think of it as like going over a speed hump in your car slowly or at a greater True Speed.
Incoming.....
BBBBBBBbbbbbbbbbzzzzzzzzzzbbbbbbbbbbbbzzzzzzzzzzzzzzzzzzzzz
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Vne is a static value eg 350 KIAS. What the "barber pole" does is vary that IAS limitation to a Mach No. limitation for high altitude flight. eg Vne might be 350 KIAS until F270 then M.085.
Maybe I have hit my head a few too many times but I am pretty sure limit G-loading comes into this and G-loading relates to movement in space, irrespective of how much air passes over the wings.
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I think there are two questions being answered here:
- how should Vne be interpreted by the pilot - IAS or TAS? (I think the answer will be in the POH)
and
- how is Vne calculated or defined by the aircraft manufacturer? (I think the answer is more complex than even the views expressed so far)
One is relevant to pilots, the other is relevant to aeronautical engineers. In some cases pilots and aeronautical engineers are the same thing.
A
- how should Vne be interpreted by the pilot - IAS or TAS? (I think the answer will be in the POH)
and
- how is Vne calculated or defined by the aircraft manufacturer? (I think the answer is more complex than even the views expressed so far)
One is relevant to pilots, the other is relevant to aeronautical engineers. In some cases pilots and aeronautical engineers are the same thing.
A
Perhaps someone can answer a relevant question for me.
When I fly my trendy little homebuilt at VNE which is 140 IAS at Sea Level, my ailerons become fairly stiff and they loosen up at lower speeds, say VMO which is 120 knots IAS.
When I fly at say 9,500ft at a 140 K TAS I get the exact same "stiffness;" it's like I'm flying at VNE at the lower level.
If I fly at 140 KIAS at 9,500ft it feels like the wings are gonna fall off and feels like I'm exceeding VNE significantly.
Any suggestions? Is this relevant to the discussion?
When I fly my trendy little homebuilt at VNE which is 140 IAS at Sea Level, my ailerons become fairly stiff and they loosen up at lower speeds, say VMO which is 120 knots IAS.
When I fly at say 9,500ft at a 140 K TAS I get the exact same "stiffness;" it's like I'm flying at VNE at the lower level.
If I fly at 140 KIAS at 9,500ft it feels like the wings are gonna fall off and feels like I'm exceeding VNE significantly.
Any suggestions? Is this relevant to the discussion?
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Originally Posted by Mr.Buzzy
Hmmmm so why does my twin otter manual show a difference of Vmo of 166kn at sea level to 112kn at 25000feet? Surely we dont risk breaking the sound barrier in a twotter?
Originally Posted by Andy_RR
- how is Vne calculated or defined by the aircraft manufacturer?
Maybe when testing the otter the IAS was not demonstrated any higher than 112kts at 25000ft - therefore they cannot publish an Vmo any higher than 112kts?
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Originally Posted by ace4bar's girlfriend
I'm sure 1013.2 asked the time - not how to build the watch
edited to add this link, which might be of interest: http://www.auf.asn.au/groundschool/flutter.html