Fastest RV ever

[Chris Hill]

I think you got it bill...~245 ktas

[David Z]

So am I getting this right? Vans recommends, in the construction manual, Vne is 230mph indicated. Then he posts this http://www.vansaircraft.com/pdf/hp_limts.pdf implying it should be 230mph true.

Also, consider, in the article about HP Limits, there is a sub-section about a RV-4 breaking the true airspeed Vne and encountering flutter, but now Bill Wightman says his RV-4 did indicated Vne+10% at 12,000' and did not encounter flutter.

Is this differences in build quality? Eg. better balanced control surfaces.



On a side note, shouldn't the indicated numbers posted by Vans actually be read as calibrated numbers, since every installation will have different instrument errors?

[breister]

I actually called VANS once and they confirmed that they were sticking by TAS for VNE. I suspect that this is simply being prudently cautious. It typically isn't a problem for most models in straight and level cruise if you stick to the recommended engines, but there are always those seeking to mount a bigger / turboed engine.

As always, I recommend that people stick to the posted design limits and, if you just have to go faster, select an airframe designed for those speeds.

Now, here is an interesting thought: Since flutter is based only on control surfaces, what would happen if someone were to build a hybrid RV-X using tail and wings from "some other airplane?"

[David Paule]

Flutter depends on true airspeeds and is usually potentially more of a problem at higher altitudes, where there's less atmospheric dampening.

In FAR Part 23 (which a homebuilt doesn't need to follow) Vne is set at 90% of Vd, which is the certified max speed. So Bill's test of his RV-4 was rational.

[KRviator]

Originally Posted by breister

Now, here is an interesting thought: Since flutter is based only on control surfaces, what would happen if someone were to build a hybrid RV-X using tail and wings from "some other airplane?"

I think you'll find that aerodymanic flutter can occur to any part of the aeroplane, not just the control surfaces. To think it limits itself to just the movable surfaces is a dangerous train of thought.

That it usually occurs on this part of the airframe is simply because they are the most movable parts. Fly fast enough and you could well find your entire wing doing the higgidy-diggidy. For those who remember Ken Rand (of KR fame), he was doing a movie shoot with KR-1, fitted with a large dummy antenna to simulate a "drone". It got to a point that flutter set in, and he thought he'd shed a prop blade. He hit a tree on the approach and rolled the KR up into a ball. Survived though...

As usual, NASA has a beaut Youchoob video showing a spam-can undergoing flutter testing. Scary stuff.

[chinch]

Originally Posted by KRviator

As usual, NASA has a beaut Youchoob video showing a spam-can undergoing flutter testing. Scary stuff.

That's horrific!

[plehrke]

Originally Posted by Tom Martin

Chris
Yes there are RVs that have gone faster but you are treading on dangerous territory. No one really knows what one bump of turbulence would do do your aircraft at these speeds.

A turbulence bump or a small control stick input can excite the structure to flutter. Be carefull thinking that just beacause someone flew above a Van's listed Vne does not mean it is safe for all to fly at those speeds.

Originally Posted by Chris Hill

I dont know that Vans actually tests for VNE for the airframe since they have apparently not ripped the wings off in testing flutter. Must not have found that limit yet...

You can calculate flutter speed if you know the structual stiffness and all bending modes. Not an easy calculation and not very accurate. Not sure how Van's set Vne but do not believe he did a full flutter test. At the big companies they can only fly to a certain percentage of calculate flutter speed if no flutter test was done.

Originally Posted by KRviator

I think you'll find that aerodymanic flutter can occur to any part of the aeroplane, not just the control surfaces. To think it limits itself to just the movable surfaces is a dangerous train of thought.

That it usually occurs on this part of the airframe is simply because they are the most movable parts. Fly fast enough and you could well find your entire wing doing the higgidy-diggidy.

As usual, NASA has a beaut Youchoob video showing a spam-can undergoing flutter testing. Scary stuff.

Excellent video showing that the fixed structure can flutter just as easily and a movable control surface.

[Bill Wightman]

Guys - my previous post was absolutely NOT intended to say the RV4 is safe at speeds above the published VNE. Knowing what I know now, I would not repeat the test again. I basically tested my airplane to design dive speed, which is 10% above published VNE for certified aircraft. My rationale was to test my RV's flight envelope to the limits called out in FAR23.

I personally have found it hard to find good clarity on the VNE issue. I too called Vans and got a different answer than what was reported earlier in this thread. Depends on who you talk to, it seems to me. What we're dealing with now, in my view, is confusion stemming from having the published VNE as an indicated speed, while saying in their newsletter it should be TAS. Construction manuals sent out subsequent to the newsletter article did not contain corrections to put the two in agreement.

So, my *suggestion* is to search the forum and settle the matter for yourself. There's plenty of information: a wide range of opinion, thoughts on the "HP Limit" article, and enough technical input here on VAF to choke a horse.