Vne

[iaw4]

 

I understand that I should never exceed Vne, and I do not ever want to even come close, but I am curious how conservative it is.  RV-7 Vans airplanes claim about 200 knots, perhaps also conservative.  what did the actual tests show about actual disintegration of the airframe?

 

[Warmi]

I think Vne limits are more related to potentially catastrophic flutter of controls rather than just pure airframe integrity. I am sure there’re is  some margin of error built in as it is always the case but I never saw any numbers ...

[Roger Lee]

Our Vne is set for chute operation. Our true Vne is higher, but why test fate. It can hurt.

[iaw4]

 

interesting.  the Vne's in the Vans were, I think, indeed for flutter.

one should never test fate!  but it is useful to know when the airplane will experience catastrophic failure.  for example, if I were to recover late from an inadvertent mistake, I then look at the instruments, and it tells me that the airplane is at Vne+5 knots, would I already be dead or do I still have a chance?  it's just information about extra safety margin (that no one should ever need).

 

[Ed Cesnalis]

3 hours ago, iaw4 said:

 

interesting.  the Vne's in the Vans were, I think, indeed for flutter.

one should never test fate!  but it is useful to know when the airplane will experience catastrophic failure.  for example, if I were to recover late from an inadvertent mistake, I then look at the instruments, and it tells me that the airplane is at Vne+5 knots, would I already be dead or do I still have a chance?  it's just information about extra safety margin (that no one should ever need).

 

Other than flutter, you want to look at your G-meter not your Air Speed Indicator.

[Tom Baker]

11 hours ago, iaw4 said:

 

interesting.  the Vne's in the Vans were, I think, indeed for flutter.

one should never test fate!  but it is useful to know when the airplane will experience catastrophic failure.  for example, if I were to recover late from an inadvertent mistake, I then look at the instruments, and it tells me that the airplane is at Vne+5 knots, would I already be dead or do I still have a chance?  it's just information about extra safety margin (that no one should ever need).

 

In my opinion with this airplane for you to make a mistake that would put you near VNE you were already likely doing something you shouldn't have been doing.

[iaw4]

3 minutes ago, Tom Baker said:

In my opinion with this airplane for you to make a mistake that would put you near VNE you were already likely doing something you shouldn't have been doing.

 

all agreed, but the same applies to spins.  one should never get into a spin.  this does not mean that one should not want to know what happens in a spin, and/or whether recovery would in theory still be possible.

 

[Warmi]

So looks like the manual specifies VNE of 163 CAS for a FD plane without a parachute in Australia and 159 with a chute - not sure why Australia gets to have slightly higher VNE even with the chute.. 

[Roger Lee]

Vne  used to be published to 166 and the factory was to 186, but chute opening needed to be lower. I have dove my CTSW up to 160 and was smooth as can be. 

This does not mean everyone should go test their plane for Vne. There is zero reason to do so. Each plane may be a tad different and some have even experienced shutter at much slower speeds.

[FlyingMonkey]

18 hours ago, iaw4 said:

 

interesting.  the Vne's in the Vans were, I think, indeed for flutter.

one should never test fate!  but it is useful to know when the airplane will experience catastrophic failure.  for example, if I were to recover late from an inadvertent mistake, I then look at the instruments, and it tells me that the airplane is at Vne+5 knots, would I already be dead or do I still have a chance?  it's just information about extra safety margin (that no one should ever need).

 

If you’re not dead then you still have a chance.  If you are screaming toward the Earth at 200kt, what does it matter to know the tail should not fail untill 220, or that it should have failed at 180?  If you are sill alive keep trying to recover the airplane.  If you are not alive, you can stop trying.

Vne is 145kts.  Don’t exceed it.

[FlyingMonkey]

7 hours ago, Tom Baker said:

In my opinion with this airplane for you to make a mistake that would put you near VNE you were already likely doing something you shouldn't have been doing.

True, but the airspeed builds fast with this slippery airframe.  I once went into a descending turn under power and hit 140kt very quickly.  Not a big deal, but it can happen.

[FlyingMonkey]

7 hours ago, iaw4 said:

 

all agreed, but the same applies to spins.  one should never get into a spin.  this does not mean that one should not want to know what happens in a spin, and/or whether recovery would in theory still be possible.

 

Speed is the same as a spin:  if you are still alive, keep attempting to recover.  What speed the tail will fall off will become apparent soon enough if your recovery fails.

[iaw4]

56 minutes ago, FlyingMonkey said:

Speed is the same as a spin:  if you are still alive, keep attempting to recover.  What speed the tail will fall off will become apparent soon enough if your recovery fails.

 

A coordinated flock of harpy eagles have escaped the local zoo for the sole purpose of attacking me.  they will fly into my engine and wind shield in a moment.  How far can I go trying to escape from them?  ;-).

[FlyingMonkey]

2 hours ago, iaw4 said:

 

A coordinated flock of harpy eagles have escaped the local zoo for the sole purpose of attacking me.  they will fly into my engine and wind shield in a moment.  How far can I go trying to escape from them?  ;-).

Unanswerable question.  The book says 145kt is the safe limit.  The limit at which actual failure occurs might be 150kt for my airplane, and 175kt for yours.  Or it could happen at 146kt.  It will be different for each individual airframe due to tiny variations in materials, or even how much the factory workers had to drink the nght before your airplane was built.

The only way to “know how far you can go” with your particular airplane is to fly it to structural failure.  I encourage you to to go out and find that answer and then report back to us.  

[FlyingMonkey]

31 minutes ago, Ed Cesnalis said:

I have been doing high speed returns to the field 3 times a week lately.  135kts  TAS seems to be my max descent speed. 

I'm usually above 13,000 and close to home so I lower the nose as much as I can to get 5,500, which is more than I can get level at that altitude and she just maintains 135 TAS  at that pitch trim all the way to my target altitude.

To test Vne I would need to overspeed my motor or stop it and dive steeply. 

I guess I could dive with a retarded throttle and see if that gets a higher speed.

That’s what I did, I went into the dive around 5200rpm and retarded it as I pitched down to keep the rpm under 5500.  I guarantee if you do that you’ll find a pitch attitude at which you will quickly exceed Vne, and it won’t be a very steep deck angle.

[Tom Baker]

3 hours ago, FlyingMonkey said:

True, but the airspeed builds fast with this slippery airframe.  I once went into a descending turn under power and hit 140kt very quickly.  Not a big deal, but it can happen.

Agreed that speed can build quickly. A descending turn with enough power for you to hit 140 very quickly is the kind of thing I was talking about. I have quite a few hours sitting in the right seat teaching people to do steep turns, and never had anyone get near that kind of speed.

[Mac Bowden]

For what it's worth and not for the record.

My aircraft, 2003 Ct2k, about 580 pounds empty weight,  long wingspan i.e. 30 feet,  no winglets,  NOT full span trim tab is placarded for 150 knots but have seen 160 knots in recovering from shallow dive.

Didn't notice any thing adverse but don't intend going there again. 

Mac

[iaw4]

 

thanks everybody.

it is interesting that there is no wind tunnel test for each airplane that waits until it flutters or falls apart in order to establish basic figures.  sort of like car  crash tests.  if done in a wind tunnel, even the dummy in it would not die, and the repairs would probably be modest if it is flutter that causes the failure.

 

[Warmi]

I guess because we are talking here about companies with a few dozen employees and rather small cash flow/budgets ....

[Tom Baker]

2 hours ago, iaw4 said:

 

thanks everybody.

it is interesting that there is no wind tunnel test for each airplane that waits until it flutters or falls apart in order to establish basic figures.  sort of like car  crash tests.  if done in a wind tunnel, even the dummy in it would not die, and the repairs would probably be modest if it is flutter that causes the failure.

 

The changes made to the CTLS over the CTSW were because of wind tunnel testing.

For flutter wind tunnel testing is not the best choice. Computer simulations and flight testing are better. The problem is that there are variables that can't be tested for, such as gust, shear, and control inputs. That is why they have a conservative number for VNE. However I would not recommend going past it because it is conservative.

[ct9000]

The VNE book speed is over 300 kilometres/hr about 162 Kt. but is limited by the parachute, and that varies by model of chute. Your a/c may be 145 or 162 or some other number. The flight manual says when in trouble to pull anyway even if above the labelled VNE. A Flight Design test pilot told me that he has tested VNE at over 330 kph. - about 175 Kt. many times, and they call that VD. ( not that social disease but V dive ) .  A big word of caution here, some CTSW had a flutter problem at much lower speed. I think that these were the ones with the full span trim tab. My SW would begin to flutter at about 142 Kt. and then there was an upgrade to the trim tab mountings to re-inforce the mounting of the hinges that solved the fault completely. Subsequently I upgraded the elevator to the shorter trim tab same as on the LS and never had any flutter issues again.    

[Doug G.]

I was taught during my last Flight Review to do an emergency desent by using a spiraling dive near vine. There were a couple of aviation deaths because of fires in flight last year in the general area. This was the method he had been taught flying for an airline to lose altitude as fast as possible while maintaining control.

[EFB]

My POH (section w.4.3) says emergency descents are best done using a slip “side slip with left wing forward / low, full right rudder, aileron left as needed to control flight path”.  That is not a typical method, as according to my instructor he had never seen that recommended before.  But we practiced it and it was pretty awesome.  I don’t remember exactly, but I think we got almost 2,000 ft/min descent rates while keeping the airspeed at approx. 95 knots.  

[EFB]

Section 3.4.3 not w.4.3.  Need more coffee...

[Roger Lee]

I've seen well past 2000 ft. loss at a straight dive at idle and 140 knots.