Vne Testing

[David-aviator]

Take the airplane up to 8000' push the nose over and watch the ASI go up to the red line. VNE test done.

Wrong.

You just went through the red line at significantly more than VNE. Van has stated VNE is true airspeed, not indicated air speed. Quite a number of us did not know that until after the fact.

However you do it, be careful and know the criteria for this airplane. It is the first airplane I've flown that has such TAS limitations, not IAS.

dd

[Kevin Horton]

Originally Posted by Sig600

Anyone that tells me I HAVE to exceed a published limit (110% of Vne) can do it themselves. I'll likely never listen to anything they have to say on anything ever again either.

To Kevin's point, I'd rather stay within the safety margins all the time. 1500+ hours riding ejection seats, I've never once felt compelled to exceed the published limitations just because I had an "out."

BTW, If you think you can bail out after strucutral failure beyond Vne, you're shooting craps with your life.

No one told you that you HAD to exceed VNE. What you HAVE to do is defined by the regulations, not what some random person here suggests you do.

RVs are fairly low drag aircraft, with a relatively high thrust to weight ratio, and a VNE that is much lower than anything with an ejection seat. You'll find that you will be flying within 40 kt of VNE during a significant percentage of your flying time, which means that it doesn't take much of a piloting error or lapse of attention to unintentionally end up on wrong side of VNE.

[Chris Hill]

Vne... IAS vs TAS

Looking for some good reading or a good explaination on this. Thanks

[Danny7]

Chris this is probably the best thread, but a simple search of "vne tas ias" will bring up all the threads.

http://www.vansairforce.com/communit...ht=vne+ias+tas

[Ironflight]

And here is the heart of the matter - an article by Ken Krueger, Van's Chief Engineer:

http://www.vansaircraft.com/pdf/hp_limts.pdf

[Sig600]

Originally Posted by Kevin Horton

No one told you that you HAD to exceed VNE. What you HAVE to do is defined by the regulations, not what some random person here suggests you do.

RVs are fairly low drag aircraft, with a relatively high thrust to weight ratio, and a VNE that is much lower than anything with an ejection seat. You'll find that you will be flying within 40 kt of VNE during a significant percentage of your flying time, which means that it doesn't take much of a piloting error or lapse of attention to unintentionally end up on wrong side of VNE.

My point was that if you do find that failure point, the likelyhood of getting out, even with a chute in a "controlled" setting is 50/50 at best. A structural failure such as that RV-7A that lost it's rudder will impart G's and out of control flight in such a manner that the possibilities are infinate. At those airspeeds with even a modest amount of G, the ability to actually open the canopy and climb out may not be possible. Even at only 3 G's post failure, out of control, I would seriously question the ability of the average person to lift themselves out of the seat. I know I can leg press in excess of 600 pounds, but at 3 G's, there's no way I could physically lift myself out of the seat to egress.

You're right, these planes are slick and over powered. That means it requires a higher level of skill, attention and dicipline to operate inside the lines. Testing the boundaries to make up for inexcusable lapses in attention just doesn't add up to me.

[RV8R999]

Don't know about yours but my Op-Lims do not require Vne to be recorded to enter Phase-2.

"I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds Vso ______, Vx ______, and Vy ______,
and the weight ______ and CG location ______ at which they were obtained.?

Despite not being required it is my opinion everyone should test to at least VAN's Vne or your own personal limit (whichever is slower) and not beyond. Paint, how well you balanced your counterweights, friction in the system can change the margins from plane-to-plane.

If you do test to Vne, make yourself a IAS to CAS to TAS conversion chart accounting for DA and approach Vne (TAS) in very small increments, reseting all the variables each pass (alt, configuration, power settings, trim, etc.).

Do this test near the end of your test phase after you've gained some proficiency. I contacted and obtained a discrete squawk from ATC prior to this test and asked for some help with airspace deconfliction because this is a decidedly heads-down test sequence requiring 100% pilot-in-the-loop to hold the final Vne at whatever your converted IAS turns out to be. Oh..make sure your OAT is calibrated correctly so you actually know what your DA is first. I used two separate EFIS with two independent OAT probes to manually calculate the local IAS for Vne and compared to their displayed values of TAS through an intermediate range of IAS prior to conducting this test to ensure those calculations were in sync and OAT probe heating affects could be accounted for. The differences were due to Ps errors and accounted for in my chart which is what I flew by..not the EFIS display of TAS. It would be nice if the EFIS manufactures included a means to input the Ps corrections and display CAS but I digress...

BLUF: My -8 safely attained published Vne at both min and max GW at fwd and aft most CG (4 complete tests conducted).

good luck

[foka4]

I think the key issue in this discussion is whether an individual aircraft meets the performance capabilities specified by Vans. Though I respect the engineering of these aircraft as designed, I would never take my wife for a flight in my RV without KNOWING I had a margin of safety in MY aircraft for the flight envelope we operate in.

For many RVs, cruise flight at altitude is close enough to redline TAS that a redline test is practically a necessity to ensure safe operation. Better to learn a limitation alone than to take a passenger and not know your safety margin.

M

[Sig600]

Originally Posted by foka4

I think the key issue in this discussion is whether an individual aircraft meets the performance capabilities specified by Vans. Though I respect the engineering of these aircraft as designed, I would never take my wife for a flight in my RV without KNOWING I had a margin of safety in MY aircraft for the flight envelope we operate in.

For many RVs, cruise flight at altitude is close enough to redline TAS that a redline test is practically a necessity to ensure safe operation. Better to learn a limitation alone than to take a passenger and not know your safety margin.

M

Exactly my point. If you don't test it to failure (which you can only do once), how do you know what that margin of safety is?

[foka4]

The margin of safety I'm most interested in knowing is the margin between where I am operating and where I have tested. This has little to do with published numbers or failure points.

Experimental aircraft give us a lot of benefits, but also some obligations. In a sense, we are all test pilots. I think it's our obligation to test a certain flight envelope (with parachute in a safe piece of airspace), and the operate the aircraft in a smaller envelope thereafter.

We don't have to test to published VNE, but I think it's prudent to set your aircraft's redline several knots slower than the fastest you have test flown it.

M