[Andy Hill]

Sorry if it's been discussed elsewhere, but how fast has flutter testing been done to in an RV7?

There were some statements regarding this from Vans in the Canadian RV-7 accident report. You might also regard the accident as indicative of a (failed) flutter test (IIRC it was not confirmed as flutter).

 

[Kevin Horton]

Just found this thread. Sorry if it's been discussed elsewhere, but how fast has flutter testing been done to in an RV7? I'm looking into building an RV7 with supercharger. Want to know how much margin there is for VNE. I never knew that VNE was based on TAS and not indicated. Back in 1986 I flew RV4 number 57 to fly. I did 230 mph indicated at 9500-9000 feet. By my calculations I did about 235 knots TAS. I had the non-counter-weighted Rudder, and I slapped the stick and rudder really hard too.

No one outside Van?s knows how much flutter margin their engineering analysis suggests there is, or how fast they flew the RV-7A prototype during flutter testing, and I doubt they will release this information. There was an RV-7A accident in our area that was possibly due to flutter, in excess of VNE, but that is not conclusive.

Your RV-4 experience is not relevant to the RV-7, as the RV-7 has much more vertical stabilizer and rudder area. The increase area means the aerodynamic forces are much higher, and the increases mass means the inertial forces are higher. The increased span of the rudder and vertical stabilizer means the stiffness is different. All these are relevant to flutter, so the flutter speed for the RV-7 will be different from the flutter speed on the RV-4.

 

[Toobuilder]

...Your RV-4 experience is not relevant to the RV-7, as the RV-7 has much more vertical stabilizer and rudder area. The increase area means the aerodynamic forces are much higher, and the increases mass means the inertial forces are higher. The increased span of the rudder and vertical stabilizer means the stiffness is different. All these are relevant to flutter, so the flutter speed for the RV-7 will be different from the flutter speed on the RV-4.

And the biggie, the counterbalance on the -7.

However, even among like types, the total system frequency is likely different. Is one of the rudders 95% or 105% balanced? Are the hinges free from slop? Are the pilots feet on the rudder pedals or flat on the floor?

Lots and lots of variables.

 

[rvbuilder2002]

However, even among like types, the total system frequency is likely different. Is one of the rudders 95% or 105% balanced? Are the hinges free from slop? Are the pilots feet on the rudder pedals or flat on the floor?

Lots and lots of variables.

This statement is spot on.

RV's are not production line aircraft.
10 different examples built from the exact same kit could have 10 different levels of flutter margin when operating at VNE.
This alone is a good enough reason that a specific speed will never be published...

 

[Andy Hill]

No one outside Van?s knows how much flutter margin their engineering analysis suggests there is, or how fast they flew the RV-7A prototype during flutter testing, and I doubt they will release this information. There was an RV-7A accident in our area that was possibly due to flutter, in excess of VNE, but that is not conclusive.

In fact I reckon Vans did answer both questions as stated in the report:

The kit manufacturer had conducted flight testing of the RV-7A prototype. No indications of flutter were encountered at a speed of 217 knots. Additional theoretical flutter analysis was done where the flutter speed was calculated to be 300 knots for the baseline design

But as stated later, how much that can be translated to a specific homebuilt example is open to debate...

 

[kjlpdx]

interesting to learn about the high altitude limits. I was not aware of this until recently. I remember once, years ago, after flying over the summit of mt rainier deciding to see what the ceiling was for my -6a. at 18k' I was hanging just above stall [0-320 fp]. I shoved the stick forward to vne and headed home, amazed at the steep angle of descent. fat, dumb, and happy. won't pull that stunt again.

I share a regular-sized hangar with another -6a. my plane is on a small ramp so that the wings/wheelpants of the 2 planes interleave. I got tired of banging my head on the std pitot tube, so installed a leading edge tube that stuck about a foot forward. I also added a mechanical angle of attack vane to the tip. one day the vane jammed and the pitot tube started to flutter. wow, does THAT catch your attention real fast. the pitot was just a blur it was vibrating so fast. I slowed and it stopped. I have removed the vane and shortened the pitot tube to 6" and have had no problems.