I don’t think anybody says flutter is the only factor.
It is also interesting that the Meridian has a Vmo of 188knots that is still below the Mirage Vne. The Meridian has however significant structural differences vs the Jetprop so is hard to directly compare eg a larger tail and a stronger main spar.
Above FL220 however you can’t exceed it in level flight at full power.
You still get ~ 260kt TAS out of it, at FL260, which is not bad at all, considering the fuel flow at that speed and the half-price fuel.
I don’t think anybody says flutter is the only factor.
I was addressing this where you did seem to sy that.
Is Vne really mostly a function of flutter for typical GA aircraft? What else could the major factor be? The wings are hardly going to get ripped off by the extra parasitic drag.
“mostly” is not same as “only”, Jason.
Cut me some slack – English is not my first language.
I thought we were having a discussion. I was just giving an example of where flutter is seemingly not at all an issue and other airframe strength issues dominate. Nothing to do with semantics.
Is Vne calculated and then demonstrated that the airplane does not fall apart at Vne + x% or is Vne determined during flight testing?
I believe it is calculated and then flight tested to a margin.
I don’t think they intentionally break the aircraft but it obviously needs testing to some margin over the redline speed.
And flutter is going to be a bigger problem higher up because a higher TAS can be achieved, for a given marking on the IAS-based airspeed indicator.
I have heard of methods used to trigger flutter (to see how much margin there really is) but I don’t know if they are ever used when testing a whole airframe.
Certainly some of these flight tests involve wearing a parachute. However getting out of say a PA46 in a hurry isn’t going to work, fairly obviously.
For spin tests they tend to have a little chute on the tail, to stop the spin.
That is what I was getting at, and that margin improves dramatically at lower levels
Yes, but… If you have got yourself close to Vne, you’ve been doing something unusual, and will that maneuver carry you beyond Vne, even though you try to recover? Thus, a margin. I do not establish faster Vne during testing, but I might establish a lower one if something shakes (then the new Vne will be 90% of the onset speed for that), or if I determine that the aircraft, if upset, would accelerate through Vne before a pilot could stop it. This is also a reason I cannot restrict Vne to be too low. There is an obvious margin required between normal flying, and upset recovery. When I spun the Caravan
I found that most recoveries were AT Vne, AND about 2.5G. There is very little margin left there. Were Vne to be restricted, you’d be pulling even more G to get out of the dive. All the elements must work together….
The other aspect could be required control force. During a high speed dive recovery, it can simply take too much pilot effort to recover the dive. I have had to trim out of a dive, because the control force was too great. One example was during spins in a Cessna 185 floatplane. The aircraft could fly faster within structural and flutter limits, but the pilot effort to recover a dive is too great, so Vne is reduced to prevent ever getting the plane there.
The other aspect could be required control force. During a high speed dive recovery, it can simply take too much pilot effort to recover the dive.
I remember that back in the 1980ies, a Dornier 228 (twin turboprop 19-seat commuter plane) was lost in an accident during the UK certification testing because of that. Both the British and German test pilots lost their lives because they were phyically not able to pull the aircraft out of the dive.
But there are many more reasons for Vne and each depends on different factors.
In my Grob 109B motorglider Vne is 130 kts (IAS) up to 6500 ft, 122 kts up to 10.000 ft, 116 kts up to 13.000 ft, 110 kts up to 16.500 ft, and 104 kts up to 20.000 ft.
These speeds all correspond to a true air speed of 146 kts, indicating that Vne is limited by flutter. This makes sense, since flutter margins are improved by making the structure stiffer, and that is difficult with the long and slender wings on gliders and motorgliders.
But in “graveyard spiral” accidents, what happens is that control is somehow lost (VFR pilot into IMC, for instance) and the airplane then enters a spiral dive. That is a high speed, high-G maneuvre, and in some cases the wings simply break off due to positive-G overloading. But in a significant portion of these accidents, the tailplane breaks off first. This is because the wings aerodynamic twisting moment is balanced by the downward lift of the tailplane, and as the (indicated) airspeed increases somewhat above Vne, the tail structure fails from static overload. With no tail to counteract the wing’s twisting moment, the airplane then pitches sharply down, immediately creating negative overload on the wings and causing them to break in the downward direction. To quote: “With any luck, the people on board are then knocked unconscious so they they do not have to attend the rest of the sequence.”
It seems that the above is easily recognized by accidents investigators becase they can tell from the wreckage that the wings have broken off in the downward direction from negative G.
When the above can happed to an airplane, it is obviously not Vne-limited by flutter, but by static aerodynamic forces and moments to the structure. And those are determined by indicated, not true airspeed.
