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Richard_Pottorff(at)msn.c
Guest

Posted: Sun Sep 23, 2007 5:02 am Post subject: More on VNE

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  At the risk of inciting a religious war, I found site backing up my  previous claim that VNE is dependent on TAS not IAS nor CAS:

  

 http://www.auf.asn.au/groundschool/flutter.html

  

  rule of thumb  #2. 



For most light aircraft it is reasonable that only one Vne is  specified in the Pilot's Operating Handbook or Flight Manual and that value may  have been calculated for a 'normal' cruising altitude, say 5000 feet, rather  than ISA mean sea level. 





If uncertain about a particular aircraft multiply the (density)  altitude, in 1000s of feet, by a factor of 1.5 to get the percentage DECREASE to  apply to the specified Vne for a corrected Vne appropriate to the altitude. For  example if altitude is 8000 feet and specified Vne is 100 knots then 8[000] ×  1.5 = 12%. Corrected Vne = 88% of 100 = 88 knots IAS/CAS. 



Table 1 is a  normal calculation of corrected Vne, you can see that the difference between the  140 knots specified and the corrected Vne is significant and that it appears  quite possible for turbocharged low drag aircraft to exceed corrected Vne in  level flight at higher altitudes. 



Vne as a maximum airspeed applies  only for smooth atmospheric conditions and for gentle control movements;  even vertical gusts associated with mild turbulence or control movements greater  than say 25% travel will lead to some nasty surprises, if operating close to but  below Vne. At such high speed the controls are very effective with a high  possibility for over-control applying extreme loads to the structures and some  aircraft control systems provide an inadequate feedback of the load being  exerted i.e. a high load can be applied with a relatively low stick force..  



Be aware: deliberately exceeding Vne is the realm of the test pilot –  who always wears a parachute!

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europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Sun Sep 23, 2007 9:32 am Post subject: Re: More on VNE

Wait a minute here.  The quoted cite sounds authoritative, but U.S. Regs for production aircraft state that Vne must be marked on the ASI.



If we got enough of a turbocharger to get to like FL450, we could indicate down near stall at max cruise velocity attainable, and contrary to what they say, our ailerons won't be very effective at all.  How can we possibly experience aileron flutter just above stall speed?



Fred F.

asarangan(at)YAHOO.COM
Guest

Posted: Sun Sep 23, 2007 11:15 am Post subject: More on VNE

Based on my reading, it is too simplistic to say that flutter depends

only on TAS. An exact model would have to include IAS and TAS, and not

necessarily in a linear fashion. In the example of flying at FL450, the

airplane is unlikely to encounter flutter with a dynamic pressure that

is near stall condition. However, it is true that the margin between

stall and flutter can significantly narrow at higher altitudes. I was

told that the U-2 only has a few knots margin between stall and flutter

at its highest operational altitude.





--- europa flugzeug fabrik <n3eu(at)oh.rr.com> wrote:



 	  Quote: 	
		   

 <n3eu(at)oh.rr.com>

 

 Wait a minute here.  The quoted cite sounds authoritative, but U.S.

 Regs for production aircraft state that Vne must be marked on the

 ASI.

 

 If we got enough of a turbocharger to get to like FL450, we could

 indicate down near stall at max cruise velocity attainable, and

 contrary to what they say, our ailerons won't be very effective at

 all.  How can we possibly experience aileron flutter just above stall

 speed?

 

 Fred F.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=135910#135910

mikenjulie.parkin(at)btin
Guest

Posted: Sun Sep 23, 2007 11:52 am Post subject: More on VNE

Here is another definition for the debate.

  

    VNE    The VNE , or the never exceed speed, of an aircraft is the V speed which    refers to the velocity that should never be exceeded due to risk of structural    failure, due to calculated factors such as wing or tail deformation or due to    aeroelastic 'flutter' (unstable airframe or control oscillation). VNE is    specified as a red line on many airspeed indicators. This speed is specific to    the aircraft model, and represents the edge of its performance envelope in    terms of speed. Well below the speed of sound, the VNE is read as Indicated    Air Speed (IAS), since the pitot indication is a direct measure of the dynamic    pressure for any given airspeed. At altitude, where TAS is higher than IAS,    aerodynamic damping is weaker than at lower levels (damping is proportional to    IAS) whereas inertia-induced disturbances are stronger (inertia grows with    acceleration, which is the time derivative of TAS). This condition, if    continued beyond tested limits, pre-disposes to unstable oscillations or    'flutter'. For instance, the TAS/IAS ratio at 40,000 ft on the ICAO ISA is    2:1, that is, TAS is approximately twice IAS.   

 Every aircraft I have ever flown stated the Vne as  indicated airspeed.  The Falcon 20 I'm away flying at the moment has its  Vne and Vno stated as an indicated airspeed.

 Just been to the bar to get a beer and a colleague of mine  answered the question - Vne is in indicated airspeed always.  How else  would the pilot know if he were exceeding it.  I have some respect for his  opinion as he recently retired from British Aerospace as a Senior Test Pilot, he  flew harriers and did much of the flight testing on the new Typhoon 2  fighter.

  

 I don't know why everyone is getting so hot under the  collar about the flight at Vne.  Ivan and Pete Clark did a lot of testing  of the europa.  I do it every year at permit renewal as required and it  really is a non event - I must confess however that I cannot see the point of  that particular part of the flight test schedule.

  

 Incidentally, at medium to light weights G-JULZ will  achieve Vne straight and level at 2000 feet (indicated airspeed)   914/Airmaster 'with the pedal to the metal'.  Andy Draper found the  ASI to reasonably accurate - I don't worry about it too much  anyway.

  

 I don't think we Rotax chaps need to worry too much  anyway.  It would be different if we all fitted Jabiru 6s - we could then  climb at some mind spinning rate towards the tropopause and cruise at a Mach No  - just to be cool.  Of course we would have to fit a larger fuel tank -  wouldn't we Bob?  One distinct advantage of the Jabiru is that at those  dizzy altitudes it can reach you will be able to keep the cabin warm -  apparently many of them overheat or have some type of cooling  issues.

  

 Oh! I have slipped the surly bonds of earth

And danced the skies on  laughter-silvered wings;

Sunward I've climbed, and joined the tumbling  mirth.................

  

 It makes me want to sign on again.

  

 Now don't get upset, just having a bit of a leg pull - you  are all getting far too serious.

  

 regards,

  

 Mike.

  

 "TAKE COVER!!!!..........INCOMING"

 



  

   [quote][b]

mikenjulie.parkin(at)btin
Guest

Posted: Sun Sep 23, 2007 11:57 am Post subject: More on VNE

Actually, I think that you were told wrong.



If you read Gary Powers' book the quote is "The U2 has only a few Knots 

between the stall and Critical Mach Number."  I didn' think that flutter was 

a big issue with irreversable power flying controls.



regards,



---

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Sun Sep 23, 2007 12:02 pm Post subject: Re: More on VNE

I used FL 450 only to exaggerate the raw effect of reduced aerodynamic pressure, and other things happen with really high performance aircraft way up there.  However, FAR Part 23 is clear that Vne is determined with reference to several things, all of which have to with pressure, IOW air density.  If there is a significant variance with Vne vs. altitude, then the ASI must have a way to so indicate.  No Part 23 airplane in the Europa's class has such an ASI, right?.  A simple red line (what don't move!) complies with the rules.



Fred F.

Mark Burton

Joined: 10 Jan 2006
Posts: 74

Posted: Sun Sep 23, 2007 12:29 pm Post subject: Re: More on VNE

Yes, but why not RAS or CAS given that IAS is not necessarily accurate due to position or instrument errors?



For example, I know that the ASI on my own aircraft progressively under-reads as speed is increased. However, if I change the static to use cockpit static, it then over-reads at low speed.



One of my customers who fitted a SmartASS talking ASI queried the fact that it was reporting quite different speeds to their mechanical ASI and, subsequently, discovered that their mechanical  ASI was actually untrustworthy and needed replacing. From memory, I think their ASI had been under-reading.



The point I am making is that the average ASI system (pitot, static, instrument, plumbing, position errors, etc.) is very unlikely to deliver an accurate IAS (within, say, +/- 1%).  This rather makes a mockery of the PFA's requirement to fly at VNE within one indicated speed unit. 



If you think about it, it's rather a chicken-and-egg situation because how can you check the accuracy of your ASI at VNE without flying at VNE (as indicated by the ASI!)?



Mark

ptag.dev(at)tiscali.co.uk
Guest

Posted: Sun Sep 23, 2007 12:45 pm Post subject: More on VNE

Mike …..all this mirth …must be a derivative of your temporary accommodation after the floods ?  

Just did the Vne test on G-PTAG you are right, quite a non-event . However have to do it again since the PFA need to know whether the Engine max. RPM is in danger with the CS prop on Manual, set fully course which I forgot to examine.  

   

Regards  

Bob H   

   

Ddo not archive…..  

     

Robt.C.Harrison  

  

   

-----Original Message-----

 From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Mike Parkin

 Sent: 23 September 2007 20:51

 To: europa-list(at)matronics.com

 Subject: Re: More on VNE  

     

Here is another definition for the debate.  

    

   

  

VNE   

The VNE , or the never exceed speed, of an aircraft is the V speed which refers to the velocity that should never be exceeded due to risk of structural failure, due to calculated factors such as wing or tail deformation or due to aeroelastic 'flutter' (unstable airframe or control oscillation). VNE is specified as a red line on many airspeed indicators. This speed is specific to the aircraft model, and represents the edge of its performance envelope in terms of speed. Well below the speed of sound, the VNE is read as Indicated Air Speed (IAS), since the pitot indication is a direct measure of the dynamic pressure for any given airspeed. At altitude, where TAS is higher than IAS, aerodynamic damping is weaker than at lower levels (damping is proportional to IAS) whereas inertia-induced disturbances are stronger (inertia grows with acceleration, which is the time derivative of TAS). This condition, if continued beyond tested limits, pre-disposes to unstable oscillations or 'flutter'. For instance, the TAS/IAS ratio at 40,000 ft on the ICAO ISA is 2:1, that is, TAS is approximately twice IAS.     

   

    

Every aircraft I have ever flown stated the Vne as indicated airspeed.  The Falcon 20 I'm away flying at the moment has its Vne and Vno stated as an indicated airspeed.  

    

Just been to the bar to get a beer and a colleague of mine answered the question - Vne is in indicated airspeed always.  How else would the pilot know if he were exceeding it.  I have some respect for his opinion as he recently retired from British Aerospace as a Senior Test Pilot, he flew harriers and did much of the flight testing on the new Typhoon 2 fighter.  

    

   

    

I don't know why everyone is getting so hot under the collar about the flight at Vne.  Ivan and Pete Clark did a lot of testing of the europa.  I do it every year at permit renewal as required and it really is a non event - I must confess however that I cannot see the point of that particular part of the flight test schedule.  

    

   

    

Incidentally, at medium to light weights G-JULZ will achieve Vne straight and level at 2000 feet (indicated airspeed)  914/Airmaster 'with the pedal to the metal'.  Andy Draper found the ASI to reasonably accurate - I don't worry about it too much anyway.  

    

   

    

I don't think we Rotax chaps need to worry too much anyway.  It would be different if we all fitted Jabiru 6s - we could then climb at some mind spinning rate towards the tropopause and cruise at a Mach No - just to be cool.  Of course we would have to fit a larger fuel tank - wouldn't we Bob?  One distinct advantage of the Jabiru is that at those dizzy altitudes it can reach you will be able to keep the cabin warm - apparently many of them overheat or have some type of cooling issues.  

    

   

    

Oh! I have slipped the surly bonds of earth

 And danced the skies on laughter-silvered wings;

 Sunward I've climbed, and joined the tumbling mirth.................  

    

   

    

It makes me want to sign on again.  

    

   

    

Now don't get upset, just having a bit of a leg pull - you are all getting far too serious.  

    

   

    

regards,  

    

   

    

Mike.  

    

   

    

"TAKE COVER!!!!..........INCOMING"  

    

   

    

   

  [quote]            - The Europa-List Email Forum -   --> http://www.matronics.com/Navigator?Europa-List              - NEW MATRONICS WEB FORUMS -   --> http://forums.matronics.com [b]

asarangan(at)YAHOO.COM
Guest

Posted: Sun Sep 23, 2007 3:21 pm Post subject: More on VNE

I read the Vne definition from wikipedia (which you posted) and your

observations that Vne is always given in IAS, and am having a difficult

time reconciling the two. If I am reading the wikipedia definition

correctly, it is saying that if the IAS is held constant (damping held

constant), as TAS increases with altitide, the inertia-induced

disturbances (derivative of TAS) will get stronger and predisposes the

airplane towards flutter.



I agree however that every airplane I have flown also had Vne given in

IAS. However, if you do a quick search on various discussion groups

(search for "Vne and flutter") the answer seems to be anything but

straight forward. Many sailplane pilots who fly up to 30-40k ft claim

Vne and stall can become the same. Others say no. The only thing that

most people seem to agree on is that Vne is difficult to pin down, and

it is neither IAS nor TAS.

--- Mike Parkin <mikenjulie.parkin(at)btinternet.com> wrote:



 	  Quote: 	
		   Here is another definition for the debate.

 

   VNE 

   The VNE , or the never exceed speed, of an aircraft is the V speed

 which refers to the velocity that should never be exceeded due to

 risk of structural failure, due to calculated factors such as wing or

 tail deformation or due to aeroelastic 'flutter' (unstable airframe

 or control oscillation). VNE is specified as a red line on many

 airspeed indicators. This speed is specific to the aircraft model,

 and represents the edge of its performance envelope in terms of

 speed. Well below the speed of sound, the VNE is read as Indicated

 Air Speed (IAS), since the pitot indication is a direct measure of

 the dynamic pressure for any given airspeed. At altitude, where TAS

 is higher than IAS, aerodynamic damping is weaker than at lower

 levels (damping is proportional to IAS) whereas inertia-induced

 disturbances are stronger (inertia grows with acceleration, which is

 the time derivative of TAS). This condition, if continued beyond

 tested limits, pre-disposes to unstable oscillations or 'flutter'.

 For instance, the TAS/IAS ratio at 40,000 ft on the ICAO ISA is 2:1,

 that is, TAS is approximately twice IAS. 

 

 Every aircraft I have ever flown stated the Vne as indicated

 airspeed.  The Falcon 20 I'm away flying at the moment has its Vne

 and Vno stated as an indicated airspeed.

 Just been to the bar to get a beer and a colleague of mine answered

 the question - Vne is in indicated airspeed always.  How else would

 the pilot know if he were exceeding it.  I have some respect for his

 opinion as he recently retired from British Aerospace as a Senior

 Test Pilot, he flew harriers and did much of the flight testing on

 the new Typhoon 2 fighter.

 

 I don't know why everyone is getting so hot under the collar about

 the flight at Vne.  Ivan and Pete Clark did a lot of testing of the

 europa.  I do it every year at permit renewal as required and it

 really is a non event - I must confess however that I cannot see the

 point of that particular part of the flight test schedule.

 

 Incidentally, at medium to light weights G-JULZ will achieve Vne

 straight and level at 2000 feet (indicated airspeed)  914/Airmaster

 'with the pedal to the metal'.  Andy Draper found the ASI to

 reasonably accurate - I don't worry about it too much anyway.

 

 I don't think we Rotax chaps need to worry too much anyway.  It would

 be different if we all fitted Jabiru 6s - we could then climb at some

 mind spinning rate towards the tropopause and cruise at a Mach No -

 just to be cool.  Of course we would have to fit a larger fuel tank -

 wouldn't we Bob?  One distinct advantage of the Jabiru is that at

 those dizzy altitudes it can reach you will be able to keep the cabin

 warm - apparently many of them overheat or have some type of cooling

 issues.

 

 Oh! I have slipped the surly bonds of earth

 And danced the skies on laughter-silvered wings;

 Sunward I've climbed, and joined the tumbling mirth.................

 

 It makes me want to sign on again.

 

 Now don't get upset, just having a bit of a leg pull - you are all

 getting far too serious.

 

 regards,

 

 Mike.

 

 "TAKE COVER!!!!..........INCOMING"

Gilles.Thesee(at)ac-greno
Guest

Posted: Sun Sep 23, 2007 5:12 pm Post subject: More on VNE

Andrew Sarangan a écrit :

 	  Quote: 	
		   

 I read the Vne definition from wikipedia (which you posted) and your

 observations that Vne is always given in IAS, and am having a difficult

 time reconciling the two. 


	


Andrew and all,



As you say things are not that straightforward.

Airplanes are designed for a specific Vd (Velocity dive) which is 

expected to be well below flutter velocity.

Test pilots must *demonstrate* Vdf where flutter is absent (Vdf < or = Vd).

After that, Vne is *calculated* to be Vne < or = 0.9 Vdf  < or = Vd. 

This takes into account any ASI inaccuracy with a reasonable safety margin.

Only test pilots are allowed to intentionnally exceed Vne up to Vd.



So provided the airplane is correctly rigged and control-balanced, there 

is no problem flying up to Vne in calm air.

Be aware though, that there is also a Vno and a Va (maneuvering speed) 

to comply with. At Va you are only allowed to actuate *one* control to 

full deflection at a time.



FWIW,

Best regards,

-- 

Gilles

http://contrails.free.fr

fklein(at)orcasonline.com
Guest

Posted: Sun Sep 23, 2007 7:51 pm Post subject: More on VNE

 	  Quote: 	
		   Airplanes are designed for a specific Vd (Velocity dive) which is 

 expected to be well below flutter velocity.


	


See an interesting flutter animation at: 

www.aircraftdesigns.com/flutter-analysis.html



do not archive

-- 

This message has been scanned for viruses and

dangerous content by MailScanner, and is

believed to be clean.

fklein(at)orcasonline.com
Guest

Posted: Sun Sep 23, 2007 8:08 pm Post subject: More on VNE

www.lancair.net/flutter.html  ...strictly for flutter gluttons...



do not archive

-- 

This message has been scanned for viruses and

dangerous content by MailScanner, and is

believed to be clean.

Richard_Pottorff(at)msn.c
Guest

Posted: Mon Sep 24, 2007 7:43 pm Post subject: More on VNE

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Here's a link to another VNE article. It also explains that just because  Vne is a red line on an ASI that it is not a constant speed, unvarying with  altitude. In fact, it decrease roughly 1.5% per 1000 feet of altitude.

  

 Stall speed changes with the airplane's load, and yet the stall speeds are  marked on the ASI.

  

  

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

  

By the way, Wikipedia doesn't vouch  for the information contained on its site, so its meaningless to me as far as  trying to prove assertions.



   [quote][b]

craigb(at)onthenet.com.au
Guest

Posted: Tue Sep 25, 2007 3:55 am Post subject: More on VNE

Thats why this part of the flight envelope is generally called coffin corner

cause you go any slower you stall, go any faster you break the plane, have

a look at the service envelope charts for a piper or cessna etc

you will see what i mean



--

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Tue Sep 25, 2007 4:37 am Post subject: Re: More on VNE

Why is any technical article found on the internet authoritative? Why wouldn't the FAA care enough to fix their Regs?  People die when airplanes break apart.



Fred F.

Fergus Kyle

Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada

Posted: Thu Sep 27, 2007 3:20 pm Post subject: More on Vne

Hi,

	The discussion on the topic has been interesting - I caught the

Australian article some time ago - and it brings up another facet.

	It is possible for an aircraft to climb to its Coffin Corner. I

know. I did. Coffin Corner is described as that density altitude at which

the Critical Mach No. and the stall come together as one. A knot faster and

the aircraft becomes uncontrollable, a knot slower and you stall.

	What do you do? Drop the flaps? - and they tear off? No they don't.

Open the Dive Brakes? - at altitude they are ineffective (In the Vampire,

doubling the drag with them took up to 5 minutes to slow effectively). Also

the engine runs at a minimum of 80%RPM just to stay lit at great height. The

real threat is that in entering Critical mach you lose control of the

machine. You won't regain mastery until the control surfaces achieve a

'grip', lower down in thicker air. During this interval, the heart hopes the

device stays together - and it usually does. 

	I understand the successor to the Vampire, the Venom, carried a much

more powerful engine (which allowed it to climb even higher). This permitted

a delayed Coffin Corner but made descent even more hazardous. I was told

those so trapped actually chose to spin down rather than to run out of

oxygen waiting to increase drag.

That led on occasion to loss of a wing when the spin extended suddenly

through the tropopause and into much thicker air. I don't remember flutter

ever being mentioned.

Cheers, ferg

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