What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Why is the VNE less on -6 versus -7 ??????????

rv969wf

Well Known Member
Can someone tell me why the RV-6 has a lower VNE than the -7??? I know the tail, wingspan, etc, etc. is different between the two, but why such a difference?

Another question: How are the Rockets, Dave Anders, Tracy Saylor, etc. and the really fast birds getting away with exceeding the VNE? :eek: Thicker skins on control surfaces??? Control surfaces balanced different??? Humm, just asking. :rolleyes:
 
Vne

Sorry, I don't have the answer but thought that this would be a good place to put in an inquiry. I'm getting ready to start making my POH for an RV-8 and a long time ago I found a document that showed all the speeds for all the different models. It included flap speeds, Vne, Vs ect. The only thing I can locate now is in on the Vans web site and it just shows some cruise speeds and various weights and power settings. Could someone hook me up. Thanks
 
rv969wf said:
Can someone tell me why the RV-6 has a lower VNE than the -7??? I know the tail, wingspan, etc, etc. is different between the two, but why such a difference?

Another question: How are the Rockets, Dave Anders, Tracy Saylor, etc. and the really fast birds getting away with exceeding the VNE? :eek: Thicker skins on control surfaces??? Control surfaces balanced different??? Humm, just asking. :rolleyes:

Don't know the answer to question #1.

#2, Some are beefed up but all have been tested to these speeds. I know of several who have gone close to 10% above the stated Vne without problems and designs are tested here and then have a lower limit set usually.

If you want to engage in this area of flight testing, be aware that sliders can't be opened in flight in 6s and 7s so parachute is only of use if the whole thing disintegrates!
:eek:

That part gave me the willies testing my 6A. I found out afterwards about the canopy thing and that Vne was TAS not IAS. So I was actually at about 193 knots TAS. A little knowledge is dangerous.

Wiser with age and more careful today.
 
The RV-7's rudder is counterbalanced. The original RV-6's is not. While I don't know for sure, my guess is that it has to do with the high speed flutter dynamics of the respective rudders. On the other hand, the early Harmon Rockets did not have counterbalanced rudders and are regularly flown faster than 250 MPH apparently without flutter problems. The faster airplanes fly, the less tolerent they are of anything that is not right. Small errors in building can get big in a hurry.
 
N788RV said:
Sorry, I don't have the answer but thought that this would be a good place to put in an inquiry. I'm getting ready to start making my POH for an RV-8 and a long time ago I found a document that showed all the speeds for all the different models. It included flap speeds, Vne, Vs ect. The only thing I can locate now is in on the Vans web site and it just shows some cruise speeds and various weights and power settings. Could someone hook me up. Thanks
I had a difficult time finding it, too. I think this is it, though: http://vansaircraft.com/pdf/speeds.pdf
 
N788RV said:
I'm getting ready to start making my POH for an RV-8 and a long time ago I found a document that showed all the speeds for all the different models. It included flap speeds, Vne, Vs ect. The only thing I can locate now is in on the Vans web site and it just shows some cruise speeds and various weights and power settings. Could someone hook me up. Thanks


You might start here.
 
I'm concerned about the VNE on my -6 !!!!!!

RV10Rob said:
I had a difficult time finding it, too. I think this is it, though: http://vansaircraft.com/pdf/speeds.pdf

Anyone know how VANs came up with the VNE numbers???? Did VANS take each plane to a set speed in small increments and feel a buzz or what??? Have any of these RV's been wind tunnel tested to see where the flutter is?

Reason I'm asking is because I've exceeded the VNE quite a few times in level flight and I'm very concerned.

I don't want to have someone writing a story about my -6 or myself in a million pieces on this forum. :eek:
 
Alan, you are correct to be worried, because our planes will flutter, the only question is at what speed. An excursion once or thrice to some speed exceeding redline does not mean it is safe; there are other variables. The only thing that can be said is that the odds go up of something bad happening as the speed goes up. I think it is true that VNE from a flutter point of view is perhaps the most difficult thing to establish in an aircraft design.

Nasa had a video of what I believe was some Piper or Beech design that they were exceeding redline on, and it was horrifying to see the slow motion video.

It is my understanding that there is usually no warning, just parts coming off.

Also, it is not just IAS that matters in this regard - TAS is a huge player as well. I believe Van had an article some years ago about why TAS is also important also. The gist is that the amount of time it takes for air to cross the elevator, for example, is important. Perhaps others will be able to point to the article.
 
Kitplanes had recently article where question was whether the Vne was with CAS or IAS. Needless to say but the flutter was also covered there. Good reading for a start. But generally better have Vne way bellow flutter because it's nasty. If you want to kill yourself, there are easier ways to do it. :eek:

I read March, April and May issues but can't remember in which one this article was.
 
rv6ejguy said:
That part gave me the willies testing my 6A. I found out afterwards about the canopy thing and that Vne was TAS not IAS. So I was actually at about 193 knots TAS. A little knowledge is dangerous.

Wiser with age and more careful today.

Same here, Ross. I took my -7A up to 220 indicated coming down from 8000' doing the VNE test. Thankfully, the airplane is slightly over built for sure. :)
 
Pirkka said:
Kitplanes had recently article where question was whether the Vne was with CAS or IAS. Needless to say but the flutter was also covered there. Good reading for a start. But generally better have Vne way bellow flutter because it's nasty. If you want to kill yourself, there are easier ways to do it. :eek:

I read March, April and May issues but can't remember in which one this article was.

The flight test program for a Cozy was quite concerned about elevator flutter so the recommended procedure was to test for it - 1 knot at a time - up to VNE. VNE in that airplane was IAS. Whether or not that was correct is unknown, but it is what was recommended. Perhaps the reason flutter is a TAS limitation in these airplanes is because that's how they were flight tested by the designer.

Military airplanes and commercial airliners use IAS for VNE, not TAS. There's no way a fighter pilot has time to figure TAS coming down in a dive trying to evade an enemy airplane.
 
David-aviator said:
Same here, Ross. I took my -7A up to 220 indicated coming down from 8000' doing the VNE test. Thankfully, the airplane is slightly over built for sure. :)

One of the great things about my EFIS is that it gives me a continuous display of TAS all the time. I probably look at that figure more than I do IAS, especially on descents from cruise. It is REALLY easy to exceed 200 knots True with these airplanes and the "standard" engines.

Flutter is just not well enough understood for me to go experimenting in that regime - anecdotal evidence unfortunately doesn't prove anything - it merely says that the dragon didn't wake up that particular time. Yes, there is margin to Van's number, but we simply don't know what it is. I don't panic if I see a little more than 200 (TAS), but I certainly try and reverse any accelerating trend immediately when I do.

If I wanted to see where the limit was, I'd want to do it with a parachute....and in somebody else's airplane!

Paul
 
Yes

Hi guys,
Years ago, an acquaintance named Nick Jones had his wing flutter and disintegrate while he was doing his F-1 test for an air race in Texas. His Cassutt had a slimmer and less torsionally rigid wooden wing and when the ailerons fluttered, at around 275-300 MPH, it instantly disintegrated and he managed to bail and tell about it.

My opinion is to ask Van but the early -6's didn't have a counterbalanced rudder and my later 6 does have one and also a taller tail (2001 model).

Rob Ray (Smokey) wrote the letter that was in the RVator after he had a bad experience in his -4.

I just got off the phone with Nick (an engineer) and he mentioned/elaborated on dynamic balance as well as static balance of the ailerons/elevators and rudder. One biggy; our 6's have thinner skins on the tail than the 7's which reduces torsional rigidity as well. This would be a concern regarding flutter issues. Dynamic balance is a calculation that gets lengthy but essentially comes down to the fact that it does not necessarily mean 100% static balance. When the F1 rocket guys cut the wings shorter, it stiffens them torsionally as well as reducing area. Thicker skins on the tails also increase resistance to flutter.

Bottom line as far as I'm concerned is that unless Van or another very qualified aero engineer says it's OK to exceed redline, I'm staying under it and remember it's TAS that determines redline, not IAS.

Regards,
 
David-aviator said:

Military airplanes and commercial airliners use IAS for VNE, not TAS. There's no way a fighter pilot has time to figure TAS coming down in a dive trying to evade an enemy airplane.

Good comments David. In terms of using IAS or TAS, I don't think that it is a matter of "choosing", so much as what actually determines the Vne. Sometimes, it is structural, sometimes, it's flutter, and sometimes could be something else. If it is structural, it is likely based on QBar, which is effectively IAS for the pilot. If it's flutter, it is more related to TAS, so that is the limit.

Bottom line - every design could be unique in what determines the final limits.
 
Ironflight said:
Good comments David. In terms of using IAS or TAS, I don't think that it is a matter of "choosing", so much as what actually determines the Vne. Sometimes, it is structural, sometimes, it's flutter, and sometimes could be something else. If it is structural, it is likely based on QBar, which is effectively IAS for the pilot. If it's flutter, it is more related to TAS, so that is the limit.

Bottom line - every design could be unique in what determines the final limits.

Exactly correct - structural limitations are based on Qbar (IAS) while flutter is entirely TAS - it's a function only of air velocity and not density or dynamic pressure. The difference between IAS and TAS becomes a nagging concern for us as we build these wonderful flyers with wall-to-wall engines and fly them in the teen's.
 
TAS vs IAS

I only have four hours on my new 6. My BMI G3 shows TAS and reads significantly lower than my IAS on my normal airspeed indicator. My IAS matches closely my flying buddies indications. Does this make sense?
 
JonJay said:
I only have four hours on my new 6. My BMI G3 shows TAS and reads significantly lower than my IAS on my normal airspeed indicator. My IAS matches closely my flying buddies indications. Does this make sense?

You're right to be skeptical Jon - TAS is almost always going to be higher than IAS, so my guess is that you have a calibration issue with something - which is certainly not surprising with only 4 hours on the airplane! I'd put that calibration task down a few rungs on the priority ladder behind basic envelope determination. ;)
 
pierre smith said:
Hi guys,
Years ago, an acquaintance named Nick Jones had his wing flutter and disintegrate while he was doing his F-1 test for an air race in Texas. His Cassutt had a slimmer and less torsionally rigid wooden wing and when the ailerons fluttered, at around 275-300 MPH, it instantly disintegrated and he managed to bail and tell about it......
I saw it happen once. Pieces were coming off faster than your brain could process he event. By the time it was evident what was happening, most of the empennage (rudder I believe was the source of the problem) and one wing had departed the plane. Ms. Ashley II, Reno, '99. http://www.taphilo.com/photo/reno1999.shtml
 
JonJay said:
I only have four hours on my new 6. My BMI G3 shows TAS and reads significantly lower than my IAS on my normal airspeed indicator. My IAS matches closely my flying buddies indications. Does this make sense?

I had to calibrate my BMA EFIS before it would show correct TAS. The procedure is in the install manual.

Kent
 
As one of the few who have survived wing flutter, I can assure you that it is quite exciting. Fortunately, I managed to get the speed down enough to stop the flutter. Ann and other witnesses on the ground said that the wingtip was a blur for several vertical feet. This was in a Moni Motorglider at 120 mph (maneuver entry speed), VNE on the Moni is 150 mph. The cause was determined to be a design flaw in that the aileron was 10' long with only a rib at each end. It had inadequate torsional rigidity. Flexing of the aileron induced the wing to flutter. Erv Culver did the analysis and recommended adding 3 more ribs and balancing the aileron to 25%. After rebuilding with all recommended mods, no more problems were encountered.
 
kentb said:
I had to calibrate my BMA EFIS before it would show correct TAS. The procedure is in the install manual.

Kent
Thanks. I am sure that is it. I have some sorting out to do with the BMA, EDM930, and SL30. Frankly, my analog guages work well and I have been more concerned with flying the airplane than cleaning this stuff up. I will be doing that once I follow Mel's advice and I am sure all of my issues are simple set up and calibrations. Right now, I have what I need to fly safely. Appreciate everyones help. This forum is great.
 
This is a good discussion. It is serious stuff. A friend of mine was test flying a Starduster for the builder and encountered aileron flutter at 160 MPH. The motion yanked the stick from his hand. He pulled the power and the plane stayed together. He was lucky to survive it.

A few issues back, there was a discussion of VNE in the RVATOR. I learned from it. Basically, IAS is a function of dynamic pressure. Flutter phenomenon is a function of velocity. The higher the altitude, the lower the IAS of VNE becomes. When Van assigns a value for VNE, that value covers only the realm the airplane is designed to fly in. Put in a turbocharger and take the airplane to 30,000', all bets are off.

I think, if we routinely fly beyond the limits the engineer has set for the airplane, we are in a place we shouldn't be. I know a guy who had his RV-4 to 260 MPH on several occasions. I wouldn't get in any airplane with him.
 
Last edited:
Low Pass said:
I saw it happen once. Pieces were coming off faster than your brain could process he event. By the time it was evident what was happening, most of the empennage (rudder I believe was the source of the problem) and one wing had departed the plane. Ms. Ashley II, Reno, '99. http://www.taphilo.com/photo/reno1999.shtml

I watched that one as well, from the box seats. Virtually instant confetti. Very sad day. There were several good camera's on the aircraft when it happened, I believe the concensus from the video was elevator flutter and lose a trim tab, then runaway flutter.
 
Last edited:
hngrflyr said:
I think, if we routinely fly beyond the limits the engineer has set for the airplane, we are in a place we shouldn't be. I know a guy who had his RV-4 to 260 MPH. I wouldn't get in any airplane with him.

Assuming a stock design as engineered, yes I would agree with you. Then there are folks like Bruce Bohannon and his RV-4 - not exactly stock, but safe, when safely flown - and most definitely overpowered and capable of MUCH more than designed for originally. Van is not the ONLY guy that knows how to design airplanes - just one of the most successful.

This is the proverbial "10% factor" - you must be at least 10% smarter than the device which you are attempting to operate.
 
Last edited:
kentb said:
I had to calibrate my BMA EFIS before it would show correct TAS. The procedure is in the install manual.

Kent
I could not find the calibration procedure in the install manual, but the TAS is indicated in knots, not mph. I feel kind of stupid as 155 or so knots matches up really close to my indicated airspeed of 178 mph.
The unit can be recalibrated in mph, but the ground speed indication can not, so no sense in changing it. So, problem solved, or, no problem to start with I guess. Thanks for the help.
 
Exceede VNE by 20% no problems no flutter . Solid as a rock ! Not sure why VNE so low.

It worked this time. Next time with slightly different conditions, a bit of turbulence, temp change ect.. we might be reading about your flight on the news.
As a addition to a ancient thread you can set VNE up as TAS in the Dynon and I am sure most other EFIS units.
 
Respect

"20% over Vne and rock solid"

Ah, what do those engineers know, anyway?

Respect the Vne, the life you save may be your own...
 
Military airplanes and commercial airliners use IAS for VNE, not TAS.

Commercial transport category airplanes have the airspeed limit set in IAS, but it's a moving target, not painted on the dial. There's two needles, one indicates the current airspeed. The other one looks like a "barber pole" and slowly decreases with altitude. My work plane (big twin turboprop) is 242kias from sea level to 14000', then slowly decreases to 207kias by 25,000ft. I am certain the engineers determined the limiting factors and set the airspeed limit safely and appropriately.

Once I finish my plane and get flying, I certantly won't be flying faster than the engineers intended.
 
Exceede VNE by 20% no problems no flutter . Solid as a rock ! Not sure why VNE so low.

What is the structural mode interaction (SMI) frequencies of your aircraft? What is the air load, buffet, control stick, gust/turbulence input, autopilot, input frequencies? If you do not know any of the above, I would not try it again.
 
Direct

I don’t want to be mean or say anything that will trigger you, however, I don’t want to read about you in a NTSB report either.

So, with that in mind, are you $&@& ??? ��

20% really? Do you have adsb?



Exceede VNE by 20% no problems no flutter . Solid as a rock ! Not sure why VNE so low.
 
Last edited:
As a addition to a ancient thread you can set VNE up as TAS in the Dynon and I am sure most other EFIS units.

I just did a search on the D-180 installation manual and I only found 1 instance talking about VNE but it doesn't show anything about it related to IAS or TAS. This old thread now has caught my attention, could you elaborate please?
 
In the SkyView models one can choose to set Vne in terms of IAS or TAS. If Vne is set to TAS, then the the Redline indication on the Speed Tape dynamically changes based on IAS, Altitude, and OAT.

Thanks, guess I'm out of luck for now. I'll just have to keep looking at the little TAS/DA display number.
 
Saw a few post on commercial and mil aircraft being IAS limited, IAS down low and becomes a mach limit at higher altitudes.
 
We all love to take our new Corvette, (Ford) Mustang, or Camaro out on a long stretch of highway to see what she'll do.

Airplanes are completely different. Treating them like they are just another new go-fast toy is the reason that the first few hours in a new plane are often the deadliest.

To all, you have got to understand what VNe is, AND what Va means. Here's an example of a flight envelope. Though this isn't an RV, your RV has something similar and going into the red areas is a good way to get seriously dead. F-104A flight envelope

Talking to no one in particular, but at the same time I'm talking to every one who flies, the FAA has given us a lot of rope with the experimental regs. Don't be one of the chumps that ends up hanging yourself with said rope.

As others have said, we don't want to read about you in the NTSB reports, we don't want to see your wife at the funeral, and we don't want to pay our insurance based on your foolishness.

Seeing a grieving wife at a funeral is too much to bear. Don't do that to her. Think!

Flame away. I've made my point.
 
I guess it's no longer included but Van's included a section on flutter testing in the build manual for my circa 1996 RV-6 kit. He was actually advocating that each builder perform that and other flight tests. As I recall, it read like it had been pulled from one of my aerodynamics text books. Not for the faint of heart and needs to be done carefully.
 
Vne

I am NOT advocating operation in excess of Vne. The reality is that of the airplanes being flown in Sport Class at Reno, many are being operated far above Vne. Some of the earlier racers like Dave Anders and Tracy Saylor did the same. The races frequently involve AT LEAST moderate turbulence.
The Wittman Tailwind first flew in 1953. In Dec 1953 it became the first EAB aircraft approved by the then CAA to carry a passenger(not for hire) The first five Tailwinds were required to be flight tested to at least 110% of Vne. One example inadvertently dove to near 300 m/h. Published Vne on the Tailwind is 185.
Question: If an EAB aircraft has not been tested at least one time to 110% of Vne, has that aircraft been properly tested??
 
....Question: If an EAB aircraft has not been tested at least one time to 110% of Vne, has that aircraft been properly tested??

I'd think that if the airplane was built in accordance to the plans, is an RV, and is loaded within the CG limits, that the speeds Van's has for Vne are a sufficient restriction. Testing should not go above that in any case. Van's did sufficient testing to qualify the plane to Vne (within its TAS limitations) and anything beyond that is perhaps on the verge of danger. You don't know.

Certified planes get tested to a speed (Vd on the V-n diagram) and then that speed is reduced 10% to establish the Vne. But that's only the flutter test airplane that goes to Vd. Every other airplane, even the flight test planes, only go to Vne, which is 10% lower.

Flutter is an instability issue. Without the right instrumentation,, there's no way to tell how close you are to fluttering.

Dave
 
Last edited:
I don't know if you've heard the old story of the guy who jumped off the empire state building. As he went by the 20th floor somebody heard him say "so far so good"
 
Vne

This report is worth a read for those that haven't seen it.
http://www.vansairforce.net/safety/G-GNDY.pdf

The Canadian report is a report on a 7 that came apart due to rudder flutter. So far no 6 has come apart from flutter that I know of but I think five 7's have and they all had the tall 9 rudder.

I looked at a 6 build manual and builder testing of flutter is not advised. It did say that the 6 was tested for flutter at 110% Vne
 
I own and fly a -6 with a -8 tail, so what is my Vne? :eek: ;)

On a serious note, here an excerpt of my builder's manual, SECT15R3.DOC 08/13/01, page 15-21 of the late series -6:

Flutter testing of factory prototypes has resulted in establishing a NEVER EXCEED SPEED (Vne) of 210 statute mph for the RV-4 and RV-6/6A, 230 statute mph for the RV-7/7A/8/8A and 190 statute mph for the RV-9A. This speed was determined through flutter testing at a speed of 20 mph above Vne. (FAA certification criteria require flutter testing up to Vne plus 10% or about 20 mph). The flutter testing performed consisted of exciting the controls by sharply slapping the control stick at various speed increaments up to this level. Under all conditions, the controls immediately returned to equilibrium with no indication of divergent oscillations indicative of flutter. This testing was performed on factory prototype aircraft, and the flutter free flight operation of subsequent amateur built RVs has substantiated published Vne.

The ?slap-the-stick? method of exciting the controls for flutter testing is potentially dangerous and requires a very skilled pilot trained to recognize the subtle control responses which indicate the onset of flutter. For this reason, it is suggested that amateur builders do not perform flutter testing of their RVs.
 
Given the number of RV-7s that have come apart in-flight, if I had an RV-7, it would have an RV-8 rudder on it.
Been thinking about this too since I'm preparing to fly my -7 with a -9 rudder. The -14 rudder structure is based on the -9 but appears to be stiffer.

(Warning - possible thread creep!)

In an airplane that isn't certified to FAR 23, margins past Vne belong to the Van's engineers and I don't blame them for not saying exactly how far past Vne they tested the large-tail 7 lest someone decide to go exploring. But it would be nice to have some confidence that there's test data to substantiate a reasonable margin past published Vne.

The EAA Flight Test Manual recommends setting Vne 10 percent below the manufacturer's number. Granted, the manual isn't specific to RVs and some other homebuilts may be not as well tested but in the absence of hard information on -7 flutter/loads margin I plan to restrict Vne on my airplane. Maybe not by 10 percent, but in the absence of some authoritative word from Van's, my Vne won't be 200 KTAS.

Dave
 
Last edited:
Back
Top