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

Vne Test Format

I'm not familiar with other threads on this subject, but no mention was made of the suggested flight profile while conducting flutter tests.

John Thorp (no stranger to flutter) recommended (of course) that you start slow,

As test speeds increase beyond the aircraft's straight and level speed a dive is employed to reach about 5 mph IAS above the "test" speed.

The technique is to enter a slight climb until the speed drops to the "test" speed, when the excitation pulse is initiated.

The aircraft has already flown at the next "test speed" and is slowing through the test speed, providing some limitation to the frequency the aircraft is exposed to.

One T-18 flutter test left the pilot with a disturbing sensation, until he realized the frequency back through the stick caused a blister to his hand.

The second point, this test protocol only tests one control surface at a time. A thorough test program would witness combined tests of two or three surfaces at a time (combination of simultaneous aileron-elevator pulsing for example)

Third point, in the above example, the undetectable flutter (until the blister) was at a higher speed, the pilot, feeling he was being careful, experienced another flutter event at about 180 MPH because of structural damage caused in the first incident.

Fourth point, reflected in the FARs is if you have a trim tab on a control surface, the Vne series should be repeated with the control arm (actuator) to the tab disconnected to determine if a broken connection will not contribute to flutter.

Be careful!
 
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There are continuing debates regarding IAS and TAS when determining Vne.
At ground level the two speeds are very close. As you climb indicated airspeed drops off. This was never really a factor with Cessna 172, for example, as they seldom went high. With the RV and Rocket type aircraft many of us regularly fly over 10,000 feet and there can be a huge difference between indicated and true airspeed. The actual number is somewhere between but as we can not easily determine what that real Vne number is, then take the safe route and use TAS. Most of the modern screens offer that on the EFFIS screen. If not it is easy to use one of the aviation apps and make yourself a little chart for the dash.
For example IAS for 5000, 10,000, and 15,000 feet vs. TAS at using standard lapse rate charts for temperature.
At the very least work it out for yourself and you can see the huge difference in IAS vs. TAS at higher altitudes.
Watch out during descents with power the TAS number will go increase at very quickly.
Use TAS, it may save your life.
 
Danger!

"...Fourth point, reflected in the FARs is if you have a trim tab on a control surface, the Vne series should be repeated with the control arm (actuator) to the tab disconnected to determine if a broken connection will not contribute to flutter..."

I would HIGHLY discourage this kind of test...from personal experience.

I had a C-421 that had a "failure" of the bolt connecting the right elevator trim tab to it's linkage. (The failure was due to negligence of the company that did the annul inspection.) The failure occurred at 16,000 feet climbing to a cruise altitude, at a speed SIGNIFICANTLY less than Vne.

When the bolt came out of the linkage, the right elevator began to flutter in a divergent mode, resulting in an airplane that was nearly uncontrollable. Luckily, the two elevator torque tubes are joined in the middle with bolts through a flange. These bolts sheared, separating the elevators. It also stopped the flutter.

This happened in the space of about 5 seconds.

The aircraft was flown to a successful landing with one elevator in control and the other in trail...lucky to say the least.

Flutter is nothing to mess around with, and it doesn't matter if you THINK you are the ace of the base...
 
Vne

The Canadian aircraft probably fluttered at 269 MPH. The recent poster claims 20% over VNE or 276 MPH.
G

The 6 above has the short tail. If you have a 6 or 7 with the tall tail, I would be very respectful of the stated Vne.
 
Trim Tab

Any one who intentionally attempts to fly with a trim tab disconnected is nuts. Twin Cessnas have history of trim tab issues. The Cessna 441 Conquest would up with a dual actuator on the elevator tab. This evolved from an inflight break up caused by the elevator trim tab problem.
Some of the model airplane inspired tabs and actuators found on EAB aircraft are scary just to look at.
I sincerely doubt that most pilots understand what a violent event flutter is and how little if any time there is to do anything about it.
Still total silence on the EAB airplanes that race at Reno way beyond Vne.
Glasair III Vne 335 statute, fastest Reno Glasair is doing well over 400 lap speeds.
 
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.

It's almost like that barber pole is converting IAS into TAS for your redline...
hmmmmm.

The only time Vne is not in TAS is when the engineers thought you couldn't get it fast enough and/or high enough for there to be an appreciable difference to matter. In some really old twin turbo props I flew, they just listed Vne limits in relation to Density altitude, but that was just a placarded conversion of an IAS to TAS. In other words Vne/Mmo is ALWAYS in TAS whether you know it or not because physics is a thing.
 
jrs14855 said: "Any one who intentionally attempts to fly with a trim tab disconnected is nuts."

Well . . . . From 23.629:

[snip]

(f) Freedom from flutter, control reversal, and divergence up to VD/MD must be shown as follows:
(1) For airplanes that meet the criteria of paragraphs (d)(1) through (d)(3) of this section, after the failure, malfunction, or disconnection of any single element in any tab control system.

and ...

John Thorp used this reference to dissuade builders from adding trim tabs to the ailerons.

FWIW
 
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regs

"... For airplanes that meet the criteria of paragraphs (d)(1) through (d)(3) of this section, after the failure, malfunction, or disconnection of any single element in any tab control system..."

Stupid is as stupid does...

Anyone who attempts this should say goodbye before they go...there may not be another chance.
 
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?.............

So in 13 years and 60+ replies with lots of hand-wringing and (good) advice, NO ONE has really answered the OP's question.

DC came close by posting Van's rationale of flutter testing and what I interpret from that is that Van's simply never bothered to retest the -4 and -6 to the higher speed they used for the later airframes.

Maybe that was a marketing decision to make the newer models more enticing. Or maybe they realized that the early kits had much more variability in build quality since all holes (except the spar) had to be builder-located and -drilled and so lots more opportunity for 'non-excellent' workmanship. Who knows.

.......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.
 
Any one who intentionally attempts to fly with a trim tab disconnected is nuts. Twin Cessnas have history of trim tab issues. The Cessna 441 Conquest would up with a dual actuator on the elevator tab. This evolved from an inflight break up caused by the elevator trim tab problem.
Some of the model airplane inspired tabs and actuators found on EAB aircraft are scary just to look at.
I sincerely doubt that most pilots understand what a violent event flutter is and how little if any time there is to do anything about it.
Still total silence on the EAB airplanes that race at Reno way beyond Vne.
Glasair III Vne 335 statute, fastest Reno Glasair is doing well over 400 lap speeds.

I'll provide some feedback from the air race arena. Nothing said here is intended to infer that Vne doesn't apply to a built-per-plans aircraft, or that exceeding Vne is OK, just because racers (at any venue) achieve the speeds they do. Our class has RVs and Rockets of many varieties racing. We've had Rockets over the stock 275mph Vne, and some RVs over the 210mph (4/6) or 230mph (7/8) stock Vne (and I'm using TAS, as directed by Vans...which more closely matches lap speeds). The Super Legacy and Super Glasair aircraft have already been mentioned in the quoted post.

As many know, many racers are modified. Thicker skins on portions, thicker stringers in some locations, modified bracing, improved trim tab systems, layup strengthening measures in the empennage of the fast glass planes. We operate in a highly scrutinized environment, with waivered airspace and strict SOPs and Rules of Competition. In Reno, we must certify that we have tested to 105% of our qualifying speed. We are scrutinized on modifications, and on the test program we apply to our aircraft after making them.

As speeds have increased, whether though drag reduction or HP increase (via engine increases or boost/nitrous additions), we've increased the scrutiny. We pay attention, and dig into the modifications and testing. We are not cavalier about the process...or the speeds.

We've also modified our operational procedures, especially during the downhill chute start, to keep our pilots and aircraft from delving into what might be considered clearly dangerous territory. For RVs in the Medallion heat, we come down the chute at 150 KIAS (that's about 190 MTAS, or 20-40 mph below stock RV Vne, depending on RV type), with a flat trajectory, and to a release point closer to the start pylon, to keep the speed in check. This provides a better margin, with less time for racers to be at full power while descending onto the course. In the end the pilot also has control over his or her speed with stick and throttle. Speeds for our other heats are selected with the same safety margin in mind. Rockets in the Bronze see about 170 KIAS in the chute prior to release.

Bottom line, in answer to the above question, is that the speeds in racing are not attempted without modification, testing, tech inspecting and review. If we have potentially unmodified aircraft pushing into high speed regimes with bolt-on HP mods, we scrutinize and counsel. Could a modified aircraft be considered to have a modified Vne? Probably a debate that could rage between manufacturer, builder, modifier, and pilots at large. The racing community has a long history of exploring the envelope...sometimes safely, with technological leaps sometimes being the result, and unfortunately sometimes not as safely. In a large air race meeting today, as a matter of fact, we discussed just this (modifications, testing, speed, and safety), and the emphasis is on safety. We owe it to the aviation event spectators to do the due diligence to ensure our racing is a safe as possible.

This post doesn't answer the OPs question either. One item I'll add, that may help there, is my story about being squeezed on a picnic bench during my first AirVenture Cup dinner, between Dave A and John H, probably the fastest RV drivers at the time, and still among them now. They trapped me there, and asked me "when are you putting a counterbalanced rudder on that plane". John had an -8, and Dave has a counterbalance rudder on his -4. They were being great mentors. Mine's a -6, built as a side-by-side Rocket (from the ground up, lots of mods) with a 540, and a Vne of 275mph. While most HR-IIs have a -4 tail, and a 275mph Vne, they talked to me about margin. I listened, and built and installed an -8 VS and rudder, with additional mods bounced off a (very) RV-knowledgable engineer. I still apply the Rocket Vne, but feel we added margin. This (the rudder counterbalance) may be one part of the answer to the OPs question, and would make sense (at least to me).

One last item I'll touch on is the disconnected trim tab test idea. FWIW, we had a Rocket flutter in the chute, when the trim tab attachment failed. A flaw in the trim tab control attachment that caused departure of the trim tab control horn...and the connected clevis...was discovered post-event. The event ended well, but did considerable damage to the elevator skins. Incorrect chute speed (too fast) resulting in a Vne exceedance (of about 10%) after race start was a factor as well. We don't know if the part failure or the flutter occurred first or simultaneously, but this may be an event to consider if one was considering testing with a disconnected tab. That seems more of a concept for the theorists to consider, than one for the test pilots to attempt (IMHO).

Last FWIW: one of my racing goals...to show mindset...is to do a level qual lap at my Vne. Another is to fly a Corsair on the course. One may be more achievable than the other! ;)

Cheers,
Bob
 
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Could be "shown" through any of analysis, test or demonstration, I'd hazard.

It was my understanding that various analysis approaches were "methods" which did only that, "approach" a solution to the issue

The point about "dissuade" was just that. John didn't design a trim tab in the aileron, he "adjusted" a flap. When builders countered his position with "(so and so) did it and has 850 hours on the aircraft"

John, a believer in free choice, would give one of his iconic "Cheshire Cat" grins and reply:

"Well, I guess his luck hasn't run out yet!"

YMMV (but the risk only increases!:D
 
Reno

Bob Mills-
Thank you for the very detailed and candid reply. I was in the pits at Reno shortly after the Rocket elevator event. I listened while the pilot explained to a small group what had happened. My recollection is that the airplane was hidden away somewhere, possibly at the request of FAA/NTSB.
That event reinforced my belief that adjustable trim tabs are treated very casually, especially on EAB but also on certificated airplanes.
I am familiar with some of the airframe racing mods on the Lancair Legacy's and with mods on one particular Glasair.
My concern with Reno is more than just Vne. The turbulence can sometimes be extreme. This is mitigated in recent years by running most of the F1 and Biplane races early in the day.
Many years ago a F1, a Miller pusher design, came apart during a F1 race. The airplane simply exploded. It was believed at the time that the airplane flew into a dust devil. That airplane was far stronger than most of the current Sport Class racers.
The recent Rocket tail failure puts this subject in and entirely different perspective.
 
Bob Mills-
Thank you for the very detailed and candid reply. I was in the pits at Reno shortly after the Rocket elevator event. I listened while the pilot explained to a small group what had happened. My recollection is that the airplane was hidden away somewhere, possibly at the request of FAA/NTSB.
That event reinforced my belief that adjustable trim tabs are treated very casually, especially on EAB but also on certificated airplanes.
I am familiar with some of the airframe racing mods on the Lancair Legacy's and with mods on one particular Glasair.
My concern with Reno is more than just Vne. The turbulence can sometimes be extreme. This is mitigated in recent years by running most of the F1 and Biplane races early in the day.
Many years ago a F1, a Miller pusher design, came apart during a F1 race. The airplane simply exploded. It was believed at the time that the airplane flew into a dust devil. That airplane was far stronger than most of the current Sport Class racers.
The recent Rocket tail failure puts this subject in and entirely different perspective.

Jim,

After that Reno Rocket incident, we moved the plane into my hangar, in coordination with the event organizer. The FAA and NTSB had full access to it, and did their investigation/inspection there. It was good to get it out of the eyes of the spectators, just from an event perspective. It was not long after the Galloping Ghost crash, and no one on the event side wanted to dredge up comparisons that could negatively impact public perception. Not meant to BS anyone, but the races were on fragile ground then in the public eye. We built and installed a new tail...with even more mods...over the next few months.

With respect to turbulence and Reno racing: If there was truly extreme, or even severe, turbulence on the course (that fit the official defs of those terms) , no one would be flying at that moment. Moderate yes, and there are dust devils as well. We call that out to each other if we see them. The F1s and Bipes fly early to avoid higher winds, primarily for takeoff and landing, but I'm sure bumps are a consideration too. I'm not familiar with the in-flight break-up of the formula you described, nor the aircraft itself, so I can't comment on its strength. However, Sport class aircraft are all 6g planes or more (such as RV's Rockets, Glasairs and Lancairs), so we are all well within our g margins. Its a common misconception that racing is done at high g. It's actually surprisingly much lower that you might think. As an example, one day at PRS, Peter Balmer and I took turns flying Mathias Haid's Thunder Mustang on the course. The 51 Aero telemetry data we use is extremely accurate, and for the hops, Peter and I flew almost identical lines...the biggest distance delta from any pylon between us was 30 feet (really amazingly close lines). Pete's max g was 1.7, and mine was 1.8, and that is flying the outer course in the 320 mph range. An RV or Rocket flying the Sport course would be in the same range (slower speed but slightly tighter course). On the Medallion course, the g is slightly higher (maybe up to 3), due to the tighter turns. Even in the L-39 on the outer course, in the mid-400's, I was pulling 3-4g's, unless I hit wake turbulence, where it'd spike to maybe 6 (I could always tell when I bumped 6, because the g-suit hose fitting would make a hissing noise...didn't wear a g-suit, the fitting's check valve would just crack open and make noise. The first time it happened was when I was testing a new set of wingtips to high g. During the 6 g test, it cracked open, and scared the bi-jeez outta me...since I was testing a structural mod. I laughed when I figured it out...then went back and got a new flight suit! ;)). But at current Sport speeds, even if you make a mistake on the course, and pull "hard" at a pylon, the g is not approaching our limits.

Bottom line is that an over-stress from encountering turbulence is not the biggest threat we face. Like I said earlier, if conditions are that bad due to wind, the landing performance issues would ground us first.

Finally, on the recent Rocket in-flight structural event...there are many things being looked at, and the fact it was during aerobatics puts it in a different regime from racing. We'll study and learn from this event, but early info indicates it's perhaps not Vne or turbulence related. No speculation here...looking for good, clear event parameters and the structural analysis.

Thread's like this are good to keep folks looking at operational and maintenance/mechanical factors (how we fly and maintain our incredible machines).

Cheers,
Bob
 
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It's almost like that barber pole is converting IAS into TAS for your redline...
hmmmmm.

The only time Vne is not in TAS is when the engineers thought you couldn't get it fast enough and/or high enough for there to be an appreciable difference to matter. In some really old twin turbo props I flew, they just listed Vne limits in relation to Density altitude, but that was just a placarded conversion of an IAS to TAS. In other words Vne/Mmo is ALWAYS in TAS whether you know it or not because physics is a thing.

It's scary the amount of pilots who still believe IAS/CAS is relevant to VNE at Altitude! Our Vans machines can quickly exceed VNE at high Alt even though the speedo shows well under VNE! So yes VNE is ALWAYS TAS! I used to drive LR35/6's years ago, it's pretty easy to get damned close to 'coffin corner' and exceed MMO easy all the while the speedo showing only around 230 kts!
 
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It's scary the amount of pilots who still believe IAS/CAS is relevant to VNE at Altitude! Our Vans machines can quickly exceed VNE at high Alt even though the speedo shows well under VNE! So yes VNE is ALWAYS TAS! I used to drive LR35/6's years ago, it's pretty easy to get damned close to 'coffin corner' and exceed MMO easy all the while the speedo showing only around 230 kts!
Love old threads coming alive but good topic.

True but in jets you have Vno/Mmo calculated and shown. In GA planes with steam gauges no so (until EFIS). Now we have TAS shown all the time. So no excuse.

However most low performance GA planes (fixed gear) are slow and hard to get them past Vne at least in level flight or normal descents from altitude. However not the case with the RV will get in trouble at high altitude and doing a high speed descent. There have been a few RV pilots live to tell about elevator flutter and suffer only wrinkled flight controls. So good point.

As far as RV-6 vs RV-7 those are tested values to that speed and the rudder originally on the RV-6 was not mas balanced. I know Van got a professional test pilot to fly the RV-7 envelope.
 
No, Vne does not always need to be stated in terms of TAS to ensure that the airplane has adequate flutter margins up to it's Absolute Ceiling.

It's the responsibility of the designer/manufacturer to set Vne to insure that the airplane will be flutter free and that proper margins of damping exist to Vne (with some margin) up to the Absolute Ceiling of the airplane. And that is whether Vne is stated as a constant IAS/CAS, constant TAS, or a combination of both (i.e., IAS/CAS up to a certain altitude, and then a constant TAS above that).

Just because a designer/manufacturer sets Vne as a constant IAS (or constant CAS) doesn't mean they have not taken flutter into account. It means that they just set Vne in terms of a constant IAS/CAS number that ensures that flutter will not occur within the operating envelope of the airplane.

But for Van's airplanes (excluding the RV-14s and RV-12s), Van's initially did not set Vne in terms of TAS, they set it in terms of IAS. Van's considered them to be just all-around good sport planes. 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 they just took the existing Vne number and said it was no longer a constant IAS, but now a constant TAS number. That was the conservative thing to do from a flutter perspective, and in doing so, they probably left a lot of flutter margin at the higher altitudes for many of the models.

However, with the exception of the RV14s and RV-12s, Van?s has been remiss in not publishing a Service Letter or Service Bulletin stating that important safety-of-flight information change in Vne for the other models. Many RV pilots and builders are unaware of this change (even those on the VAF forum).

In my RV-8, I do have Vne (230 MPH TAS) set to TAS in the SkyView Touch:



Many modern EFIS' for light GA airplanes allow Vne to be input in terms of IAS or TAS. What I'd like to see is a software update that allows Vne to be input in terms of IAS up to a certain altitude, and then TAS from there up. And for Van's to reassess Vne for the older models to recoup some of the lost downhill performance, say, between 10,000' and 23,000', and coming up with Vne as an IAS/CAS number up to a certain altitude, and then a constant TAS number above that (like what they did for the RV-12s).

It may not need to be stated in TAS because of reasons I already went over(dumbing it down), but physics dictates that it is in TAS. As in the airplane does not care what your ias is. Ever.
 
It may not need to be stated in TAS because of reasons I already went over(dumbing it down), but physics dictates that it is in TAS. As in the airplane does not care what your ias is. Ever.

No.

The Vne is what the manufacturer says it is and tests to. If the aircraft mfg. establishes the Vne as 200 KIAS and ensures that the aircraft has required structural and flutter margin at the service ceiling at that speed, then the Vne is in indicated airspeed for that aircraft as stated by the manufacturer.

If structural strength and not flutter margin is the limiting factor for establishing a particular aircraft's Vne, then the Vne would truly be based on indicated airspeed.

It all depends on the air frame and manufacturer.

Skylor
 
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There will always be debates, non believers and rocket scientists out there but a good article to read (if not already) is the one from the Vans website written by Ken Krueger on 'Flight high & fast':)
 
There will always be debates, non believers and rocket scientists out there but a good article to read (if not already) is the one from the Vans website written by Ken Krueger on 'Flight high & fast':)

Excellent article.
 
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