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Vne

AeroDog

AeroDog

Well Known Member
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Today I sent an e-mail to Van's asking how Vne was established for the 12. Was it limited by flutter, or was it a result of structural considerations? I was told the information was proprietary. Why the secrecy? Anybody know the answer?

Jerre
 
My best guess is Vans has gone to a lot of trouble to get the plane listed as an E-LSA and lists the numbers to conform with the rules for LSA.
 
Geico266 said:
My best guess is Vans has gone to a lot of trouble to get the plane listed as an E-LSA and lists the numbers to conform with the rules for LSA.
Click to expand...

Admittedly I'm a newby at the LSA game, but as far as I can tell, Vne for powered light sport aircraft is not specified. Gliders, yes.

Jerre
 
I'd guess that they established the Vne to figure out what the aerodynamic loads would be, then tested it to verify that the plane was safe at that speed.

But that's only a guess.

Dave
 
Or...

They tested the wing to failure, divided the load by 1.5 (standard safety factor0 and compute Vne from that.

Wayne 120241/143WM
 
This still makes no sense at all to me. We are making an aircraft that "someone" knows how fast it can be safely flown, but it must be kept a secret from us? Absurd!
Now if they simply do not know or care, that is another matter entirely.
 
DonFromTX said:
This still makes no sense at all to me. We are making an aircraft that "someone" knows how fast it can be safely flown, but it must be kept a secret from us? Absurd!
Now if they simply do not know or care, that is another matter entirely.
Click to expand...

I suspect the decision to make this info "proprietary" has, at it's root, some concern about legal liability. No way to tell for sure, though.
 
This is just the latest example of how Vans is now being operated with both eyes on legal issues. It looks more and more that Vans is being run by lawyers not airplane people. FWIW just my opinion.
 
Well

If I were producing a kit that I knew was going to
1) have a regulation-set max low cruise speed
2) was going to be built mostly by 1st-time builders
3) be test-flown by relatively inexperienced test pilots (include ME in that category!)
4) be flown by a lot of low-time pilots

I'd calculate Vne as above and then set it substantially lower than that in the POH.

It takes a pretty good amount of forward push to get the bird up the the max speed in the test cards and I personally never PLAN to get it that fast again. Nice to know it holds togeter there, though.

Wayne 120241/143WM
 
Red line on D-180?

Is there a red line value programmed into the Van's settings of the D-180?

If so, that value would be Vne, wouldn't it?
 
DonFromTX said:
This still makes no sense at all to me. We are making an aircraft that "someone" knows how fast it can be safely flown, but it must be kept a secret from us? Absurd!
Now if they simply do not know or care, that is another matter entirely.
Click to expand...

Don, the speed at which it can be safely flown in calm conditions is Vne, and that number is no secret. You can also fly it faster, probably around 20%-25% until you have used up all the 50% `engineers design margin', and it should still hold together. No real secrets there either.

Beyond that, knowing whether the wings or tail come off first, and at what speed, is a bit academic but if anyone wants to find out I'd be very interested to know what happened. Van's have a reputation for being careful and conservative designers, and if that means their published Vne is slightly on the low side, that's OK by me. If I wanted a faster plane I wouldn't be building a 12 anyway.

I assume your last comment is tongue-in-check. Suggesting they don't know or care is obviously nonsense.
 
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It never ceases to amaze me how people always assume that speed limitations published by a kit manufacturer are always dumbed down (particularly RV's), and that surely it would be safe to exceed the published #'s.
Why is that?

If you want to be an armchair engineer, think about this...

People have raved about how great of an LSA airplane the RV-12 is, because on top of its great performance and fun handling, its low empty weight allows for a very generous useful load within the LSA gross weight limitation of 1320 lbs.

The only way this was accomplished, was by designing an airplane that was structurally sufficient for the design requirements specified in ASTM2245, but nothing more.

This was the design philosophy of the RV-12. It was conceived and designed to get every bit of performance and capability possible within the requirements of LSA. If you are expecting to build an RV-12 that goes beyond those performance limitations... then you are building the wrong airplane. If you just want to know more about how those limitations were derived... for you own peace of mind. You probably also are building the wrong airplane. The piece of mind should come by the fact that unlike all of the other RV models, the the RV-12 is actually a certificated airplane (as an S-LSA). This means that it has been extensively tested and shown to meet all of the requirements of numerous ASTM's that apply within the consensus standard for fixed wing LSA. All of these ASTM's are available for purchase by anyone that is interested in reviewing them.


Not an official company statement, but...
I think it would be assumed that anyone that complains about not being given more information beyond the published speed and G load limitations, and the fact that it is certified as a S-LSA, is just fishing for a chance to steal some of the margin from the design engineers (Read the side bar at the end of Vans related article HERE)
 
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rgmwa said:
....the speed at which it can be safely flown in calm conditions is Vne, and that number is no secret. You can also fly it faster, probably around 20%-25% until you have used up all the 50% `engineers design margin', and it should still hold together. No real secrets there either....
Click to expand...

Actually, that extra 50% only means that failure to support the load is pushed out that far. But permanent deformation damage is permitted in that range. So if you're using it up, you're already damaging the airplane, and you can expect permanent wrinkles and looser joints and so on, at a minimum.

Putting my professional aerospace structural analyst's hat on for just a moment, I've gotta say, "DON'T GO THERE!"

Dave
 
I would think the opposite. How will it look in court when someone goes past the secret VNE and breaks it up, and their only defense is that they could not allow the pilot to have that information for "legal reasons"? I don't pretend to be an attorney, and maybe that is why I cannot understand it.
mcencula said:
I suspect the decision to make this info "proprietary" has, at it's root, some concern about legal liability. No way to tell for sure, though.
Click to expand...
 
rgmwa said:
Don, the speed at which it can be safely flown in calm conditions is Vne, and that number is no secret. You can also fly it faster, probably around 20%-25% until you have used up all the 50% `engineers design margin', and it should still hold together. No real secrets there either.
Click to expand...
Be careful folks. The normal aviation 50% safety factor is on structural loads, not airspeed. The loads go up very quickly as the airspeed increases, so you would hit limit load at much, much less than 150% of VNE. And, from a flutter perspective, the margins are even less. I don't have a copy of the LSA requirements, but the older FAR 23 requirements on VNE only required that VNE be no faster than 90% of the speed at which flutter would occur. I.e, if you had a perfect airplane, you might get flutter at 111% of VNE. If you had some slack in the hinges, etc, flutter might occur at a slower speed than that.
 
I misread the start of this and then was screwed up all the way thru. I am sorry I did not read it well. Since I had never seen a VNE on the RV12, I thought that was the issue.
So just what IS this VNE, I have never seen it yet, maybe it is in stuff further down the kit?
 
David Paule said:
Actually, that extra 50% only means that failure to support the load is pushed out that far. But permanent deformation damage is permitted in that range. So if you're using it up, you're already damaging the airplane, and you can expect permanent wrinkles and looser joints and so on, at a minimum.

Putting my professional aerospace structural analyst's hat on for just a moment, I've gotta say, "DON'T GO THERE!"

Dave
Click to expand...

Agree totally (structural engineer's hat on). That margin over Vne does not belong to the pilot.
 
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Kevin Horton said:
Be careful folks. The normal aviation 50% safety factor is on structural loads, not airspeed. The loads go up very quickly as the airspeed increases, so you would hit limit load at much, much less than 150% of VNE. And, from a flutter perspective, the margins are even less. I don't have a copy of the LSA requirements, but the older FAR 23 requirements on VNE only required that VNE be no faster than 90% of the speed at which flutter would occur. I.e, if you had a perfect airplane, you might get flutter at 111% of VNE. If you had some slack in the hinges, etc, flutter might occur at a slower speed than that.
Click to expand...

You are right of course. My 20%-25% guess was based simply on wind pressure and speed. The actual design margin between Vne and airpeed at failure may well be less.
 
Retired from the nuclear power industry. Engineering margin BELONGS to the plant engineer and not the operator. To put it in terms of the RV-12, any engineering margin belong to the the Van's engineering team and NOT the owner/pilot. If the owner/pilot wishes to utilize this engineering margin, the owner/pllot MUST have a complete set of engineering calculations justifying why use of any part of the margin is acceptable. The numerical calculations would be way beyond the capability of most of us. Any guesses with regard to the structure or flutter potential is utter BS.

Sorry guys. Those that object MUST build another or fly another airplane!!

Just disturbs me a whole bunch when anyone suggests engineering margin is something that can be tampered with.
 
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And from a design engineer

Having heard from an aircraft stuctural engine, I'll simply say that I'm a (retired) professional design engineer (35 years at Wright-Patt) I totally agree and I do not plan on reaching Vne. And yes, I believe it's on the Dynon.

Wayne 120241/143WM
 
rgmwa said:
Agree totally (structural engineer's hat on). That margin over Vne does not belong to the pilot.
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Just for background -

In fact, it's not even a margin. It's really merely a recognition of the fact that most airplanes, and RVs are typical of the genre, are built of materials which fail at about 50% more load than at which they start taking a permanent set. So if your criterion is that it shouldn't take a permanent set at limit load (which is defined as the maximum applied operational load) then it will likely come apart at about 50% more load.

For Part 23 aircraft, the rules formalize this. It's necessary to do that because some modes of failure and some materials don't share that characteristic.

Dave
 
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MartySantic;5761Retired from the nuclear power industry. Engineering margin BELONGS to the plant engineer and not the operator. To put it in terms of the RV-12 said:
I'm not suggesting that the margins be tampered with. As a mechanical engineer (BS, MS, PhD) I'm simply curious about how they were established. I don't think my curiosity means I should build a different airplane.

Jerre
Click to expand...
 
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From the RV-12 POH

Vans provides Vne and other speeds (thie following is copied from the RV-12 POH which was referenced from a previous post).

How they determined these limits and what desogn feature imposed the various limits is, to my knowledge, not provided. It could be could be reasonably argued that knowledge of what design aspect defines the limit is not required for safe operation and could lead to unwarranted speculation of how much deference the end user gives to the published limit.

-Dave

Revision: 0 Date: 07/06/09

RV-12 3-3

AIRSPEED LIMITATIONS

AIRSPEED DESIGNATION CAS (kts)

Stall Flaps Down (@ gross weight 1320 lb) (VSO) 41
Stall (@ gross weight 1320 lb) (VS) 45
Flap Operating Range (VSO ? VFE) 41-82
Normal Operating Range (green arc) 45-108
Maneuvering (VA ? blue line) 90
Maximum Structural Cruise (VNO) 108
Caution Range (yellow arc) 108-136
Never Exceed (VNE ? red line) 136

Maximum Direct Crosswind Component 11kt
Maximum Wind Limitation 30kt

NOTE

CAS Calibrated airspeed is indicated airspeed (IAS) corrected for installation and instrument error.
IAS Indicated airspeed assumes zero instrument error only.
VNE Maximum safe airspeed, not to be exceeded at any time.
VNO Not to be exceeded except in smooth air only and then with caution.
VFE Not to be exceeded with flaps extended.
VA No full or abrupt control movements allowed above this airspeed.
 
Thanks

DaveLS said:
Vans provides Vne and other speeds (thie following is copied from the RV-12 POH which was referenced from a previous post).

How they determined these limits and what desogn feature imposed the various limits is, to my knowledge, not provided. It could be could be reasonably argued that knowledge of what design aspect defines the limit is not required for safe operation and could lead to unwarranted speculation of how much deference the end user gives to the published limit.

-Dave
Click to expand...

Thanks, Dave. I believe your last sentence nails it.

Sorry some of you think simple engineering curiosity should cause a thread to be characterized as "ridiculous."

Jerre
 
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