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RV-12 VNE

Hi Jon......

.......I don't believe it's Van determining that VNE is TAS. It applies to all airplanes. ....something most CFI's don't even know.

Regards,
 
So based on what is said above. That would mean that IAS of 150mph would be well over VNE at 5000 amsl. Is that correct?

Jim.
Melbourne Australia.
 
Little margin

Happy New Year!

That looks like just 22 knots difference between maximum cruise and Vne. Similar to several other craft. I guess it means those who are able to and choose to look for speed (fairings, pants, vp prop) will be eroding this margin.

Cheers...Keith
 
Not necessarily.....Jim..

So based on what is said above. That would mean that IAS of 150mph would be well over VNE at 5000 amsl. Is that correct?

Jim.
Melbourne Australia.

....It depends on the temperature. The higher the temp, the lower the IAS. Van himself wrote an article entitled "The gauge that lies" addressing the airspeed indicator. What you see is NOT what you have, in this case. At higher altitudes and/or temps, you'll indicate a lot less than what your TAS is. You need to calculate your TAS for these varying conditions.....the only way to know what will be indicated at VNE.

If you're showing 130MPH on a hot day at 5500' and 35 C, your TAS is close to 150 MPH, according to my E-6B....and within a few MPH of VNE. The air, in reality, is passing over the wings at 150 MPH or so.

Regards and Happy New year.
 
Happy New Year!

That looks like just 22 knots difference between maximum cruise and Vne. Similar to several other craft. I guess it means those who are able to and choose to look for speed (fairings, pants, vp prop) will be eroding this margin.

Cheers...Keith
Actually, it's NOT little difference when compared to the other RVs. How about the 180 hp RV-6 where 75% cruise is close to 200mph and VNE is 210?
 
A bit close for comfort

That leaves even less margin for error - especially on an aerobatic aircraft!
 
I am currently flying a Cessna 150 which has a VNE of 162 mph. That never concerned me much. However the maneuvering speed is 109 MPH. I think that is the more important number to pay attention to because above that speed abrupt control movement can damage the plane. Does anyone know the maneuvering speed of the RV-12?

Frank
 
Me Too

Frank, I also currently drive a buck 50. The reason we don't worry about Vne is that the only way we can hit it is in a full power dive with a tail wind. RVs typically cruise rather close to that speed and can, in fact, hit Vne in cruise at altitude, if one is not careful. They also typically cruise well above maneuvering speed and actually have to slow down to get to it.

In mine I have to lower the nose a little just to get to maneuvering speed.

To answer the question you actually asked, no, I don't know the maneuvering speed of the -12, but I do agree that this is a more important number to keep in mind at the lower end of the performance contuum.

Steve
 
.......I don't believe it's Van determining that VNE is TAS. It applies to all airplanes. ....something most CFI's don't even know.
Actually, for type-certificated aircraft, whether VNE is TAS or CAS is very clearly described in the FAA Type Certificate Data Sheet (TCDS), and it should also be clearly described in the POH or AFM. For example, for the Cessna 172, the TCDS lists the VNE as 160 mph CAS (later 172 variants have higher VNE). Cessna would have done the required analysis and testing to ensure that 160 mph CAS is safe at all expected altitudes and temperatures.

The confusion about VNE for RVs has arisen because Van just gave a speed without specifying whether it was CAS or TAS.
 
Pierre and Kevin:

Every airplane I've ever flown has VNE marked on the airspeed indicator (red line). The airspeed indicator shows us indicated airspeed. So, how is it possible that Vne would be defined relative to TAS?

I know some exceptional cases would be where we have an airplane with an air data computer, and Vne in many of those aircraft is a moving target. But, for light acft like ours, when would Vne EVER be defined as a TAS value???
 
But, for light acft like ours, when would Vne EVER be defined as a TAS value???

In situations where the kit airplane is often built with engines bigger than specified by the kit manufacturer.


In Kevin's example (C-172) the pilot has no way to choose the engine and propeller so the performance is relatively standardized/fixed (I know there are some STC's but the process of approving them makes them still fit in the same category). Cessna has proven that the performance capability's of a standard as delivered C-172 can not be flown in a condition that would allow the TAS to be outside of the safe range if CAS is used as the reference.

With an RV, if people put on bigger engines (or turbo's) that allow more power to a higher altitude where much higher TAS's are possible, using CAS as a reference would not be valid. If all builders would only use the recommended engine/prop combination's on any given RV model, then a CAS could be specified, but we all know that is not ever going to happen.
 
Rvbuilder: You could shut the engine off in the Skyhawk, point it straight down hill and exceed any published limit you like. Same could be said of our sport planes, so I don't see any relationship to installed HP and the ability to exceed design limits.

In terms of design limits, airframes are designed to withstand real physical airflow-induced loads. These loads build up on an airplane, in part, due to the dynamic pressure imparted by the airspeed of the airplane coupled with the properties of the air its flying in: namely the density of the air (disregarding mach effects).

Its dynamic pressure that matters. That's what deflects the airspeed needle (IAS reading) and what the airframe "feels" in flight. The airframe doesn't react to TAS in a real physical sense. 130 knots in your RV feels like 130 knots at sea level just as it does at 15000 feet even though the TAS's would be tremendously different. Its always a CAS (which is simply IAS corrected for instrument and installation error) or mach limit that comes into play in design terms.

As an example at high altitude, the B777 I fly has a Vne of about 340 knots INDICATED airspeed (dynamic pressure limit). At FL390 we usually see TAS values of over 450 knots, but the indicated speeds are around 260 or so. Not a problem, since we're well under the indicated speed for the airplane. Mach limit is what holds us back up high.

So, I still don't see how any pilot could obey the airframe limits if they're based on a parameter (TAS) that varies with speed, altitude, pressure, and temperature.
 
Found this on Vansaircraft:

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

It took going thought about 5 aerodynamics textbooks before finding one that actually specified True vs Calibrated/indicated. That book stated that Vne is specified in True. Which agrees with the above link.

The argument seems to center around the air molecules energy and flutter rather than dynamic pressure.

-Dave
 
Bill, you've answered your own question..

Rvbuilder: As an example at high altitude, the B777 I fly has a Vne of about 340 knots INDICATED airspeed (dynamic pressure limit). At FL390 we usually see TAS values of over 450 knots, but the indicated speeds are around 260 or so. Not a problem, since we're well under the indicated speed for the airplane. Mach limit is what holds us back up high...

If you're showing 260K with a VNE of 360 indicated, your TAS must be over 520 MPH, not near your real redline, which must be near Mach 1, no? Do you have a redline that moves South with increasing density altitude or a manual that shows decreasing redlines with altitude?

Thanks for chiming in,
 
Hi Pierre,

The numbers I posted earlier about the B777 are typical for econ cruise at altitude. At our cruise altitudes, everything we do is relative to mach number, not IAS or TAS. That's because we're operating well into the area where compressibility in the flow has huge effects on the aerodynamics on the wing.

At FL390 (from memory here) we see around 260 knots IAS at a mach of about .83 to .84. TAS will be in the vicinity of 460 knots, which is 530 mph (like you said). The redline on the airspeed tape at that point will be about mach .87, and we're running up there at mach .84, which is only about 6-7 knots under Vne at altitude. But the B777 is flying at a very efficient point right there, even though we're just a hare below redline.

Now to the point regarding your question:
If you're showing 260K with a VNE of 360 indicated, your TAS must be over 520 MPH, not near your real redline, which must be near Mach 1, no? Do you have a redline that moves South with increasing density altitude or a manual that shows decreasing redlines with altitude?
Redline is a moving target in these transport category jets that operate at high altitude and fairly fast speeds. We have a redline that respects either a dynamic pressure limit on the airframe, OR a mach limit, which ever is lower. It moves south as mach number becomes the limiting factor on our airspeed. With increasing altitude, the airspeed that will give us mach .87 (Vne) is less and less.

The "cross over" point where 340 indicated equals .87 mach is in the upper 20's if I remember right. So above the middle altitudes, the airspeed indicator's redline will move lower to reflect the mach limit rather than the IAS limit. (Its dynamically updated by the air data system) At high altitude, say around FL390, the Vne is still mach .87 but that equates to only around 270 knots indicated.

***********************​

Thanks to y'all who pointed out the Vans article on Vne. Now I see what they're talking about - they're concerned about FLUTTER. Considering that, I understand Ken Krueger's attention being turned to TAS. He's an accomplished engineer, and rightly points out the TAS concerns relative to flutter onset. Flutter is a dynamic phenomenon and physically is linked to the real flow speed around the aircraft - we call it TAS.

But this is a totally different animal than dynamic pressure limitiations. Flutter is something that Vans Aircraft Inc has as a concern about since they really don't know where these aircraft will flutter. And they will, if pressed hard enough.

Its not realistic for them to predict any kind of flutter onset speed since variations in build quality, control surface skin tension, trim tab slop, etc, would move that speed around in a big way.

BUT - Vne is defined in FAR23 as an indicated airspeed, like Ken points out in the article. They just don't want us Cowboys strapping on lots of HP and taking it up high where we could get into some super-high TAS territory, and then Ken and Van would be losing sleep at night.
 
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WOW! Thanks, Bill...a neat discussion...

....wherein we all learned something! Thanks for your insider information regarding ops in the flight levels and redline/mach concerns in the heavy airplanes you fly...we don't often get the chance to get this kind of information.

I guess the main issue that we all should take from this is to be careful. We've come a long way in experimental homebuilts, to where they routinely kick a$$ on the factory renditions but now we have another problem/concern...VNE and redlines because we're going so much faster than 20 years ago. I know first hand from a fella who fluttered his Cassutt, disintegrated the wings, bailed and lived to talk about it.

I've tested my RV to 230 MPH IAS and won't go there again but it's nice to know that I can go to redline, though I'd really rather avoid it.

A concern I have is with the Super -6's and Rockets. I don't know if anyone knows where their REAL redline is and sure hope that we don't find out the hard way.

Regards,
 
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Pierre - Your last comments about being careful were spot-on, IMHO.

I share your concern about the Super-6's and Rockets. Although they've been successful in their own ways, they're definitely eating into the flutter and structural margins that the rest of us live behind. I agree we really don't know how much "margin" there is in any of the RV's - Van himself probably could only hazard a guess.

As an engineer, I've never been able to crack the code on how/why Van chose the speed limitations he did for the RV-4 and 8. I think it was probably a mixture of past experience, engineering guesstimation, and a good dose of CYA. Flutter modes haven't been formally analyzed in any of the RV's to date as far as I know. So that explains their fear of us collectively pushing into those unknown areas while Vans Inc watches and waits for the worst.

Thanks for all the chat here its been fun and instructive!

Bill W
 
Flutter modes haven't been formally analyzed in any of the RV's to date as far as I know.

Bill W

Actually, both the RV-8, and RV-10 have both been through a GVT program. I believe the tests suggested that a safe margin exists between VNE and the expected onset of flutter. That's the the problem with a GVT, FEA, or any other type of analytical type test. The only way to know for sure if the test or analysis is correct, is to then go out and flight test to prove it. I don't think anyone has been willing to fly that test program.
 
Scott - great! I didn't know that. Who did the GVT, do you know?

Best thing we have going for us are the many thousands of hours flown in these birds and they've been mostly free of major defects. I've only read of one possible in flight flutter case - that was a sidebar in the Vans article you pointed out earlier.

Thx for your reply...

Bill
 
Back to the RV12 VNE below is the question and answer. There is an 's' infront of the mph. Does that mean anything?

Ken,
>
> Just a quick question. What is the VNE of the RV12? I cannot see it
> documented anywhere.
>
> Jim

Response
156 smph

Is it a typo or does the s have a meaning here?
 
Could the S stand for "statute"? I understand that would be a bit redundant since we're talking about miles per hour (not knots)....
 
A limiting safety factor:

The RV-12 is designed to Sport Pilot regulation, therefore restricted to a 10,000 feet altitude maximum.
The max altitude restriction on RV-12 would limit a wide TAS variance as compared to other RV's capable of (20,000) around twice the RV-12's limit.

Nick McCleskey
 
Rob is correct here. The altitude limitation is for the sport-pilot, not the aircraft. As is the daytime VFR limitation.
 
RV-12 maneuvering speed?

I know this question was posted earlier in this thread but remains unanswered... what is the RV-12 maneuvering speed?

Thanks in advance,

Stan
 
Picture of last day of flying last week, I quess she wanted to go home :)
Some RV-pilots asked me why I'm building such a slow RV model.
But the Final approach speed of my office is 190 smph on a windy day so that makes every RV model slow ;-) (but I'm still jealous when I see a very nice RV-8, maybe next plane to build).

Snel.jpg


BTW I don't know the RV-12 maneuvering speed.
 
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