Vne is true airspeed...
No the real Vne is in EAS, which is converted (via CAS) to IAS.
However, particularly in aeroplanes with a flutter issue (most high performance gliders) it can vary altitude, which in reality is an extra TAS limit being applied, built on flutter avoidance.
G
However, particularly in aeroplanes with a flutter issue (most high performance gliders) it can vary altitude, which in reality is an extra TAS limit being applied, built on flutter avoidance.
G
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So Vne is IAS, not TAS?
I reviewed about a dozen random Cessna and Piper type certificate data sheets across the history of their production. I found to my surprise, that the airspeeds on those sheets are listed in any of CAS, TIAS, or IAS. In some cases, it differs through vintage of the same aircraft.
As Peter correctly points out, putting a "placarded" limit in anything other than IAS, when the only information presented to the pilot is in IAS is silly. Having the pilot make the conversion from IAS to TAS or CAS, while hurtling toward earth at Vne, or balancing on the buffet of the stall seems silly. When I present limiting airspeeds for an aircraft in a placard or FMS, I present those speeds in IAS.
The older CAR 3 cerification basis introduces a rather confusing term for the marking of airspeed indicators: "True indicated airspeed", where the later FAR 23 does not use this term. FAR 23 does make a reference to providing the pilot with a means to determine Vne, if it varies with altitude.
So, after all that, I can imagine how an article might delve beyond simple IAS with reference to Vne, and how this could be confusing (I'm certainly more confused now, than I was before I tried to offer an answer to your question!). For your more basic flying practice, until you are trained otherwise, assume that the red line on the ASI (which is IAS, unless it moves) is Vne in IAS. (Two weeks ago I was test flying a Piper Cheyenne II, and it does have a moving red line on the ASI).
You will find many instances where details in aviation are self contradictory - just get used to it. To some degree, this is evidence of growth and learning in the industry, over it's entire history. Unlike cars, and other equipment with shorter lives (and less written), aircraft's service spans a comparibly long vintage. What was written at the time of entry into service about a very old aircraft, and is still valid for that aircraft in service today, would not be written the same way, or be valid for a newer aircraft.
But shouldn't that mean that a Vne+10% test should be done either at the service ceiling (using the ASI Vne+10%) or at a lower altitude, but then for a re-calculated TAS Vne, which is higher than the IAS Vne?
4400' doesn't seem like the service ceiling of the C172 at all...
(Am I making sense?)
4400' doesn't seem like the service ceiling of the C172 at all...
(Am I making sense?)
The dive in the 172 started a little closer than 4400 feet to the service ceiling. There is a little "give" in the application of the rules when testing. The 10% margin would cover this.
For the 172, things are not that critical. When mach speeds begin to become a factor, it all changes. I once had to do a dive to mach 0.57 (at a very high altitude), in a King Air B200. There was a lot more involved in the planning and conduct of that test.
Last edited by Pilot DAR; 6th Mar 2012 at 11:39.
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Thanks for clearing it up Genghis, of course, as usual, i forgot about EAS.
Nice summary Pilot DAR. Yes, sometimes things are not as clear as one thinks initially, i guess it is a good habit to keep an open mind and try to never stop learning about flying and probably the rest of it all as well.
Anyway, lately flew an aircraft where the VNE was not limited by any direct structual limit but rather by the maximum deploy speed of the parachute system. So called Ultra Lights over here (ULs can weigh up to 472kgs) have to have a parachute system for the whole aircraft and that quite often defines the VNE as structually much more is possible and indeed certified in other countries without that restriction.
Nice summary Pilot DAR. Yes, sometimes things are not as clear as one thinks initially, i guess it is a good habit to keep an open mind and try to never stop learning about flying and probably the rest of it all as well.
Anyway, lately flew an aircraft where the VNE was not limited by any direct structual limit but rather by the maximum deploy speed of the parachute system. So called Ultra Lights over here (ULs can weigh up to 472kgs) have to have a parachute system for the whole aircraft and that quite often defines the VNE as structually much more is possible and indeed certified in other countries without that restriction.
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The difference is that while most limits (Vs0, Va, Vm, ...) have a constant indicated value (and a variable true speed), Vne MAY be more constant as a true value but it actually is a bit more complicated.
