While VNE isnt determined by reference to a true airspeed in any production airplane, flutters onset is. That becomes our Vne limit.
Vne IS defined in terms of TAS (or combination of IAS and TAS) for a few certificated airplanes and many sailplanes to ensure that adequate flutter margins exist throughout the normal operating envelope.
Why didn’t Vans Aircraft mention that in their early kit builders instructions? I would think it’s because the limits they designed their kit components to are structural design limits, and are relative to Indicated Airspeed.
The designer sets Vne to insure that the airplane is safe to fly up to that speed for all engineering disciplines, i.e., loads, stress, stability & control, propulsion and flutter.
I believe that Van originally did not envision RVs flying to high altitudes. Van's considered them to be just all-around good sport planes and hence stated Vne in terms of IAS. Then Van's saw that pilot's were flying them to high altitudes, even into the lower Flight Levels, and realized that the existing Vne's may not be adequate to ensure proper flutter margins at altitude. So Van’s just took the existing Vne number and said it was no longer a constant IAS, but now a constant TAS number. Hence the the article
"Flying High and Fast" that discusses IAS vs TAS for Vne, along with Smokey’s sidebar article on his flutter incident with his stock RV-4 as he descended from 11,500’.
The flight limits (flutter) are determined by the manufacturer - you and me during Phase 1. Did I try to induce flutter during Phase 1 at Vne? NOPE. My builders manual recommended that I trust the engineering and flight testing done on my kit by Vans prior to kit production to ensure flutter margins and not to attempt that myself. I built my plane IAW designed plans and didn’t go there. Inducing flutter at or above Vne is likely a non-habit forming experience.
When it comes to items like Vne and some other design limits, I disagree. The RVs are kit-built airplanes designed by Van's Aircraft. A minuscule number of builders (maybe none) have the knowledge and/or capability to do comprehensive flutter analyses, conduct a ground vibration test, and conduct flight flutter tests on their completed airplanes to understand where the flutter boundaries are, and thus set Vne appropriately. Maybe some folks racing their RVs at Reno have done
some work along those lines, but only Van's has done the work and have the knowledge about their designs necessary to set Vne.
Also, when doing flight flutter testing, using stick raps and rudder kicks, one is NOT trying to induce flutter, but rather measure the amount of aeroelastic damping in the critical flutter modes at ever increasing speeds up to Vd. If that damping level goes below a certain point below Vd (usually g=0.03, where g is aeroelastic damping), then the test is terminated and everyone gets together and scratches their heads and looks for issues and fixes.
So much has been discussed about Vne relative to TAS that I’m pretty sure we all understand the distinction.
Unfortunately, I don’t believe that is the case. Many RV pilots and builders, even some on VAF, are unaware that Van’s has now redefined Vne for the earlier models in terms of TAS. As Scott M. points out though, more pilots/builders now know that is the case because of the discussions here and on other forums.
Our airplanes that are at least mildly aerobatic and are susceptible to Vne exceedance, so we need to be keenly aware of the possibilities whenever our nose is below the horizon in a maneuver, and we need to know that our throttle is a very important flight control in that situation.
Couldn't agree more. But in order to do that, RV pilots need to know what Vne is for their airplane and that number has to be supplied by Van's. Since Van's has now acknowledged that Vne should be in terms of TAS for the RVs (and it was many years ago that they did), they need to officially communicate that critical safety-of-flight information to builders and pilots of the older RV models via an SB or SL ASAP.