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V Speeds

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kearney

Joined: 20 Sep 2008
Posts: 563

Posted: Mon Jul 27, 2015 8:05 pm Post subject: V Speeds

Hi



At KOSH I had a spirited discussion with a group of South Africans regarding flutter, IAS and TAS. The end result was a revisited Van's article on flutter that I had read many, many moons ago. (See http://vansaircraft.com/pdf/hp_limts.pdf)



I also reviewed the RV-10 v-speeds published by Vans in the flight  test doc after reading he flutter document. In particular I was surprised to note that the Vne published by Vans of 230 mph / 200 Kts was TAS and not IAS.  Many of the POH docs available on line quote a 200 KIAS value for Vne which, at higher altitudes, could lead to a reduced flutter safety margin. 



I am assuming that all the other V speeds should be KIAS and not KTAS not that there would be much of a difference except perhaps for the max maneuvering speed / max structural cruise speed.



Is this correct or am I missing something here?



Cheers



Les



Inquiring minds really need to know.

Mauledriver(at)nc.rr.com
Guest

Posted: Tue Jul 28, 2015 5:35 am Post subject: V Speeds

A quick response to test my own basic understanding - Vne is always 

expressed in TAS, Vstalls all in indicated.  I think the physics behind 

that  is what creates the 'coffin corner' at high altitudes.



Experts, please correct and explain.



On 7/28/2015 12:05 AM, kearney wrote:

 	  Quote: 	
		   



 Hi



 At KOSH I had a spirited discussion with a group of South Africans regarding flutter, IAS and TAS. The end result was a revisited Van's article on flutter that I had read many, many moons ago. (See http://vansaircraft.com/pdf/hp_limts.pdf)



 I also reviewed the RV-10 v-speeds published by Vans in the flight  test doc after reading he flutter document. In particular I was surprised to note that the Vne published by Vans of 230 mph / 200 Kts was TAS and not IAS.  Many of the POH docs available on line quote a 200 KIAS value for Vne which, at higher altitudes, could lead to a reduced flutter safety margin.



 I am assuming that all the other V speeds should be KIAS and not KTAS not that there would be much of a difference except perhaps for the max maneuvering speed / max structural cruise speed.



 Is this correct or am I missing something here?



 Cheers



 Les



 Inquiring minds really need to know.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=445292#445292





 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

flying-nut(at)cfl.rr.com
Guest

Posted: Tue Jul 28, 2015 6:03 am Post subject: V Speeds

I'm no expert, but my take is that TAS Vne will relate to a finite 

stress on the airframe, while the IAS stress will vary by temperature 

and altitude.  I think the Vne figure relates more to flutter and 

airframe design limits rather than the 'coffin corner'.  The 'coffin 

corner' is going to be that area where the stall speed at altitude 

becomes very close to the operating speed, and would be a function of 

the aircraft aerodynamics and available power.  I'm guessing that our 

normally aspirated aircraft would get into the 'coffin corner' near it's 

service ceiling ...... as excess lift and available power run out.

Linn

On 7/28/2015 9:32 AM, Bill Watson wrote:

 	  Quote: 	
		   



 A quick response to test my own basic understanding - Vne is always 

 expressed in TAS, Vstalls all in indicated.  I think the physics 

 behind that  is what creates the 'coffin corner' at high altitudes.



 Experts, please correct and explain.



 On 7/28/2015 12:05 AM, kearney wrote:

> 

>

> Hi

>

> At KOSH I had a spirited discussion with a group of South Africans 

> regarding flutter, IAS and TAS. The end result was a revisited Van's 

> article on flutter that I had read many, many moons ago. (See 

> http://vansaircraft.com/pdf/hp_limts.pdf)

>

> I also reviewed the RV-10 v-speeds published by Vans in the flight  

> test doc after reading he flutter document. In particular I was 

> surprised to note that the Vne published by Vans of 230 mph / 200 Kts 

> was TAS and not IAS.  Many of the POH docs available on line quote a 

> 200 KIAS value for Vne which, at higher altitudes, could lead to a 

> reduced flutter safety margin.

>

> I am assuming that all the other V speeds should be KIAS and not KTAS 

> not that there would be much of a difference except perhaps for the 

> max maneuvering speed / max structural cruise speed.

>

> Is this correct or am I missing something here?

>

> Cheers

>

> Les

>

> Inquiring minds really need to know.

>

>

> Read this topic online here:

>

> http://forums.matronics.com/viewtopic.php?p=445292#445292

>

>

> -----

> No virus found in this message.

> Checked by AVG - www.avg.com







 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

 07/28/15

Mauledriver(at)nc.rr.com
Guest

Posted: Tue Jul 28, 2015 7:52 am Post subject: V Speeds

Amateur analysis sans Web research continued:  The finite stress on the 

airframe thing I hadn't considered.  I was thinking about Vne relating 

to flutter and flutter being TAS (speed with with air molecules pass 

over surfaces) driven.



Then my recall of the 'coffin corner' issue be IAS stall speeds rising 

with altitude to meet the TAS Vne.  Go a bit slower and you fall out of 

the sky, go a little faster and control surfaces begin to depart.  

Doesn't apply to RV10 class stuff but rather high flying jets and 

stuff.  But now I'm having trouble making sense out that...



Bill "help!" Watson



On 7/28/2015 9:59 AM, Linn Walters wrote:

 	  Quote: 	
		   



 I'm no expert, but my take is that TAS Vne will relate to a finite 

 stress on the airframe, while the IAS stress will vary by temperature 

 and altitude.  I think the Vne figure relates more to flutter and 

 airframe design limits rather than the 'coffin corner'.  The 'coffin 

 corner' is going to be that area where the stall speed at altitude 

 becomes very close to the operating speed, and would be a function of 

 the aircraft aerodynamics and available power.  I'm guessing that our 

 normally aspirated aircraft would get into the 'coffin corner' near 

 it's service ceiling ...... as excess lift and available power run out.

 Linn

 On 7/28/2015 9:32 AM, Bill Watson wrote:

> 

>

> A quick response to test my own basic understanding - Vne is always 

> expressed in TAS, Vstalls all in indicated.  I think the physics 

> behind that  is what creates the 'coffin corner' at high altitudes.

>

> Experts, please correct and explain.

>

> On 7/28/2015 12:05 AM, kearney wrote:

>> 

>>

>> Hi

>>

>> At KOSH I had a spirited discussion with a group of South Africans 

>> regarding flutter, IAS and TAS. The end result was a revisited Van's 

>> article on flutter that I had read many, many moons ago. (See 

>> http://vansaircraft.com/pdf/hp_limts.pdf)

>>

>> I also reviewed the RV-10 v-speeds published by Vans in the flight  

>> test doc after reading he flutter document. In particular I was 

>> surprised to note that the Vne published by Vans of 230 mph / 200 

>> Kts was TAS and not IAS.  Many of the POH docs available on line 

>> quote a 200 KIAS value for Vne which, at higher altitudes, could 

>> lead to a reduced flutter safety margin.

>>

>> I am assuming that all the other V speeds should be KIAS and not 

>> KTAS not that there would be much of a difference except perhaps for 

>> the max maneuvering speed / max structural cruise speed.

>>

>> Is this correct or am I missing something here?

>>

>> Cheers

>>

>> Les

>>

>> Inquiring minds really need to know.

>>

>>

>>

>>

>> Read this topic online here:

>>

>> http://forums.matronics.com/viewtopic.php?p=445292#445292

>>

>>

>>

>>

>>

>>

>>

>>

>>

>>

>>

>>

>> -----

>> No virus found in this message.

>> Checked by AVG - www.avg.com

>>

>>

>

> -----

> No virus found in this message.

> Checked by AVG - www.avg.com

> 07/28/15







 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

 07/28/15

flyboy(at)gmail.com
Guest

Posted: Tue Jul 28, 2015 8:01 am Post subject: V Speeds

Close, but some corrections: For certified airplanes, Vne is an indicated airspeed limit.Â  In certified planes, you can safely dump the nose up to redline on the airspeed indicator and not worry about flutter.Â  The margins are such that your true airspeed at Vne (indicated) are within limits even at the service ceiling.



An RV-10 is not a certified plane, and Van's has kindly specified a Vne in true airspeed so that we know where the margins are, rather than limiting us to an indicated limit.

Now, "coffin's corner" is an entirely different situation.Â  You can not get anywhere near "coffin's corner" in an RV-10.Â  Coffins corner means that you're flying in a very narrow range between a stall and an overspeed.Â  At 21,000 ft, you're going to stall at somewhere around 60mph IAS.Â  Your maximum safe speed (230mph TAS) is at worst around 160mph on a very hot day.Â  That gives you a 100mph margin between a stall and an overspeed condition.Â  Not a corner at all--that's a lot of margin.Â  Coffin's corner only really applies to jets.Â  Most of the jets I've flown have somewhere around 10-20 knot spread between stall and overspeed at their service ceiling.

  [quote][b]

flying-nut(at)cfl.rr.com
Guest

Posted: Tue Jul 28, 2015 8:29 am Post subject: V Speeds

Awesome discussion!

High flying jets (read airliners ..... not the U2  ) have the power 

to go faster way up there, and their speeds (I think) are computed as % 

mach.  They also have a thing called 'mach buffet' ..... and knowledge 

of that is above my pay grade.  However, for this discussion of RV-10 

issues, you really have to work to get into the 'coffin corner' .... if 

you really can.



I think some web searches may shed some 'technical light' on the 

difference.  Stall speed being IAS is probably due to the fact that's 

what we see ..... and no conversion to TAS is necessary.  I think all 

the parameters that refer to flight in air would technically be more 

accurate but harder to display without some knob twisting.

Linn ...... final wheel pants and cowl work.  So much work with small gains.



On 7/28/2015 11:48 AM, Bill Watson wrote:

 	  Quote: 	
		   



 Amateur analysis sans Web research continued:  The finite stress on 

 the airframe thing I hadn't considered.  I was thinking about Vne 

 relating to flutter and flutter being TAS (speed with with air 

 molecules pass over surfaces) driven.



 Then my recall of the 'coffin corner' issue be IAS stall speeds rising 

 with altitude to meet the TAS Vne.  Go a bit slower and you fall out 

 of the sky, go a little faster and control surfaces begin to depart.  

 Doesn't apply to RV10 class stuff but rather high flying jets and 

 stuff.  But now I'm having trouble making sense out that...



 Bill "help!" Watson



 On 7/28/2015 9:59 AM, Linn Walters wrote:

> 

>

> I'm no expert, but my take is that TAS Vne will relate to a finite 

> stress on the airframe, while the IAS stress will vary by temperature 

> and altitude.  I think the Vne figure relates more to flutter and 

> airframe design limits rather than the 'coffin corner'.  The 'coffin 

> corner' is going to be that area where the stall speed at altitude 

> becomes very close to the operating speed, and would be a function of 

> the aircraft aerodynamics and available power.  I'm guessing that our 

> normally aspirated aircraft would get into the 'coffin corner' near 

> it's service ceiling ...... as excess lift and available power run out.

> Linn

> On 7/28/2015 9:32 AM, Bill Watson wrote:

>> 

>>

>> A quick response to test my own basic understanding - Vne is always 

>> expressed in TAS, Vstalls all in indicated.  I think the physics 

>> behind that  is what creates the 'coffin corner' at high altitudes.

>>

>> Experts, please correct and explain.

>>

>> On 7/28/2015 12:05 AM, kearney wrote:

>>> 

>>>

>>> Hi

>>>

>>> At KOSH I had a spirited discussion with a group of South Africans 

>>> regarding flutter, IAS and TAS. The end result was a revisited 

>>> Van's article on flutter that I had read many, many moons ago. (See 

>>> http://vansaircraft.com/pdf/hp_limts.pdf)

>>>

>>> I also reviewed the RV-10 v-speeds published by Vans in the flight  

>>> test doc after reading he flutter document. In particular I was 

>>> surprised to note that the Vne published by Vans of 230 mph / 200 

>>> Kts was TAS and not IAS.  Many of the POH docs available on line 

>>> quote a 200 KIAS value for Vne which, at higher altitudes, could 

>>> lead to a reduced flutter safety margin.

>>>

>>> I am assuming that all the other V speeds should be KIAS and not 

>>> KTAS not that there would be much of a difference except perhaps 

>>> for the max maneuvering speed / max structural cruise speed.

>>>

>>> Is this correct or am I missing something here?

>>>

>>> Cheers

>>>

>>> Les

>>>

>>> Inquiring minds really need to know.

>>>

>>>

>>>

>>>

>>> Read this topic online here:

>>>

>>> http://forums.matronics.com/viewtopic.php?p=445292#445292

>>>

>>>

>>>

>>>

>>>

>>>

>>>

>>>

>>>

>>>

>>>

>>>

>>> -----

>>> No virus found in this message.

>>> Checked by AVG - www.avg.com

>>>

>>>

>>

>>

>>

>>

>>

>>

>>

>> -----

>> No virus found in this message.

>> Checked by AVG - www.avg.com

>> 07/28/15

>>

>>

>

> -----

> No virus found in this message.

> Checked by AVG - www.avg.com

> 07/28/15







 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

 07/28/15

flyboy(at)gmail.com
Guest

Posted: Tue Jul 28, 2015 8:41 am Post subject: V Speeds

Here's what coffin's corner looks like on a PFD:Â http://www.pbase.com/flying_dutchman/image/124628692



It's a pretty routine scenario for airliners as we try to fly as high as we safely can to save on fuel.Â  Not a lot of margin, and it's not a good idea to hand-fly at those altitudes.Â  Or to fly too close to thunderstorms.

Not a problem in an RV-10 as you just can't get high enough.

On Tue, Jul 28, 2015 at 10:25 AM, Linn Walters <flying-nut(at)cfl.rr.com (flying-nut(at)cfl.rr.com)> wrote:

[quote]--> RV10-List message posted by: Linn Walters <flying-nut(at)cfl.rr.com (flying-nut(at)cfl.rr.com)>

 

 Awesome discussion!

 High flying jets (read airliners ..... not the U2  ) have the power to go faster way up there, and their speeds (I think) are computed as % mach.Â  They also have a thing called 'mach buffet' ..... and knowledge of that is above my pay grade.Â  However, for this discussion of RV-10 issues, you really have to work to get into the 'coffin corner' .... if you really can.

 

 I think some web searches may shed some 'technical light' on the difference.Â  Stall speed being IAS is probably due to the fact that's what we see ..... and no conversion to TAS is necessary.Â  I think all the parameters that refer to flight in air would technically be more accurate but harder to display without some knob twisting.

 Linn ...... final wheel pants and cowl work.Â  So much work with small gains.

 

 On 7/28/2015 11:48 AM, Bill Watson wrote:

  	  Quote: 	
		   --> RV10-List message posted by: Bill Watson <Mauledriver(at)nc.rr.com (Mauledriver(at)nc.rr.com)>

 

 Amateur analysis sans Web research continued:Â  The finite stress on the airframe thing I hadn't considered.Â  I was thinking about Vne relating to flutter and flutter being TAS (speed with with air molecules pass over surfaces) driven.

 

 Then my recall of the 'coffin corner' issue be IAS stall speeds rising with altitude to meet the TAS Vne.Â  Go a bit slower and you fall out of the sky, go a little faster and control surfaces begin to depart.Â  Doesn't apply to RV10 class stuff but rather high flying jets and stuff.Â  But now I'm having trouble making sense out that...

 

 Bill "help!" Watson

 

 On 7/28/2015 9:59 AM, Linn Walters wrote:

  	  Quote: 	
		   --> RV10-List message posted by: Linn Walters <flying-nut(at)cfl.rr.com (flying-nut(at)cfl.rr.com)>

 

 I'm no expert, but my take is that TAS Vne will relate to a finite stress on the airframe, while the IAS stress will vary by temperature and altitude.Â  I think the Vne figure relates more to flutter and airframe design limits rather than the 'coffin corner'.Â  The 'coffin corner' is going to be that area where the stall speed at altitude becomes very close to the operating speed, and would be a function of the aircraft aerodynamics and available power.Â  I'm guessing that our normally aspirated aircraft would get into the 'coffin corner' near it's service ceiling ...... as excess lift and available power run out.

 Linn

 

 

 On 7/28/2015 9:32 AM, Bill Watson wrote:

  	  Quote: 	
		   --> RV10-List message posted by: Bill Watson <Mauledriver(at)nc.rr.com (Mauledriver(at)nc.rr.com)>

 

 A quick response to test my own basic understanding - Vne is always expressed in TAS, Vstalls all in indicated.Â  I think the physics behind thatÂ  is what creates the 'coffin corner' at high altitudes.

 

 Experts, please correct and explain.

 

 On 7/28/2015 12:05 AM, kearney wrote:

  	  Quote: 	
		   --> RV10-List message posted by: "kearney" <kearney(at)shaw.ca (kearney(at)shaw.ca)>

 

 Hi

 

 At KOSH I had a spirited discussion with a group of South Africans regarding flutter, IAS and TAS. The end result was a revisited Van's article on flutter that I had read many, many moons ago. (See http://vansaircraft.com/pdf/hp_limts.pdf)

 

 I also reviewed the RV-10 v-speeds published by Vans in the flightÂ  test doc after reading he flutter document. In particular I was surprised to note that the Vne published by Vans of 230 mph / 200 Kts was TAS and not IAS.Â  Many of the POH docs available on line quote a 200 KIAS value for Vne which, at higher altitudes, could lead to a reduced flutter safety margin.

 

 I am assuming that all the other V speeds should be KIAS and not KTAS not that there would be much of a difference except perhaps for the max maneuvering speed / max structural cruise speed.

 

 Is this correct or am I missing something here?

 

 Cheers

 

 Les

 

 Inquiring minds really need to know.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=445292#445292

 

 

 

 

 

 

 

 

 

 

 

 

 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

 

 

 	
 

 

 

 

 

 

 

 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

 07/28/15

 

 

 	
 

 

 

 

 

 

 

 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

 07/28/15

 

 

 	
 

 

 

 

 

 

 

 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

 07/28/15

 

 

 	
 

 

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 [b]

jack(at)bedfordlandings.c
Guest

Posted: Tue Jul 28, 2015 9:57 am Post subject: V Speeds

Mach Buffet I know a little bit about.  It occurs when the airstream locally

exceeds the speed of sound, setting up small standing shock waves and flow

separation behind the shockwaves.



If a wing is flying at say .95 Mach, as the air flows over the curve of the

airfoil, it accelerates and may locally exceed Mach 1.0, , leading to

formation of a shock wave at that point.  Air behind the shock wave is

subsonic and is prone to separating from the wing, leading to a buffet of

the control surfaces much like the buffeting that occurs before a stall.



As the wing accelerates, the shock formation moves further aft on the wing,

until at supersonic speeds it is at the trailing edge.



Jack Phillips

Smith Mountain Lake, Virginia

Beginning (finally) to rivet some components of the fuselage kit

--

jesse(at)saintaviation.co
Guest

Posted: Tue Jul 28, 2015 4:22 pm Post subject: V Speeds

It's my understanding that Vne should be in Calibrated Airspeed, which is hard to come by and is somewhere between IAS and TAS, so to be conservative, Van's has used TAS as the Vne number. 

As was mentioned, certified airplanes probably have the safety margin and conversions between CAS and IAS to use IAS for Vne. 

The "coffin corner" issue probably couldn't be approached without a high power turbine. I doubt even a turbocharger could get it close unless maybe if it was a big turbo or set of turbos with inter coolers. 



Jesse SaintSaint Aviation, Inc. 

jesse(at)saintaviation.com (jesse(at)saintaviation.com)

C: 352-427-0285

F: 815-377-3694

Sent from my iPhone

On Jul 28, 2015, at 11:55 AM, Berck E. Nash <flyboy(at)gmail.com (flyboy(at)gmail.com)> wrote:

[quote]Close, but some corrections: For certified airplanes, Vne is an indicated airspeed limit.  In certified planes, you can safely dump the nose up to redline on the airspeed indicator and not worry about flutter.  The margins are such that your true airspeed at Vne (indicated) are within limits even at the service ceiling.



An RV-10 is not a certified plane, and Van's has kindly specified a Vne in true airspeed so that we know where the margins are, rather than limiting us to an indicated limit.

Now, "coffin's corner" is an entirely different situation.  You can not get anywhere near "coffin's corner" in an RV-10.  Coffins corner means that you're flying in a very narrow range between a stall and an overspeed.  At 21,000 ft, you're going to stall at somewhere around 60mph IAS.  Your maximum safe speed (230mph TAS) is at worst around 160mph on a very hot day.  That gives you a 100mph margin between a stall and an overspeed condition.  Not a corner at all--that's a lot of margin.  Coffin's corner only really applies to jets.  Most of the jets I've flown have somewhere around 10-20 knot spread between stall and overspeed at their service ceiling.

   	  Quote: 	
		  



D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

List"">http://www.matronics.com/Navigator?RV10-List

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//forums.matronics.com

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[b]

Bob Turner

Joined: 03 Jan 2009
Posts: 883
Location: Castro Valley, CA

Posted: Tue Jul 28, 2015 4:59 pm Post subject: Re: V Speeds

Calibrated airspeed is the same as indicated airspeed, if there are no instrument or pitot-static errors. 

Normally certified aircraft use CAS (or IAS) to specify Vne because this information is available to the pilot. Many airplanes do not display TAS. I can only imagine how few pilots would pull out an E6B as they nose over in a dive, to calculate TAS from CAS.

I am also disappointed that Vans has chosen a very unorthodox approach in specifying Vne in TAS, contrary to what most pilots were taught.

I would really like to know: is this number derived solely from ground vibration tests? Did Vans test-dive the aircraft, and if so to what speed, and what altitude?

_________________
Bob Turner
RV-10 QB

Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Tue Jul 28, 2015 8:32 pm Post subject: V Speeds

I think Vans stated Vne as a TAS because it is based on the design flutter speed, which IS a TAS, 200 kts or 230 mph for the -10. Flutter happens based on the speed of the molecules going past the control surface and what harmonics that induces in the control surface. Indicated is derived from the pressure the molecules exert on the pitot tube, and thinner air is more compressible so IAS goes down as altitude goes up.



As the manufacturer, you can either translate that TAS back to an indicated airspeed, plus a fudge factor to account for density altitude differences, or, if you have an EFIS, let it displace TAS as supplemental info and input your Vne as a TAS. I think I will still subtract 5 kts as a safety margin, in case the elevator or ailerons might flutter at lower speed with some bird droppings or frost or whatever.



On Tue, Jul 28, 2015 at 5:59 PM, Bob Turner <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)> wrote:

[quote]--> RV10-List message posted by: "Bob Turner" <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)>

 

 Calibrated airspeed is the same as indicated airspeed, if there are no instrument or pitot-static errors.

 Normally certified aircraft use CAS (or IAS) to specify Vne because this information is available to the pilot. Many airplanes do not display TAS. I can only imagine how few pilots would pull out an E6B as they nose over in a dive, to calculate TAS from CAS.

 I am also disappointed that Vans has chosen a very unorthodox approach in specifying Vne in TAS, contrary to what most pilots were taught.

 I would really like to know: is this number derived solely from ground vibration tests? Did Vans test-dive the aircraft, and if so to what speed, and what altitude?

 

 --------

 Bob Turner

 RV-10 QB

  

[b]

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
KCHD

Bob Turner

Joined: 03 Jan 2009
Posts: 883
Location: Castro Valley, CA

Posted: Tue Jul 28, 2015 10:00 pm Post subject: Re: V Speeds

[quote="Kelly McMullen"]I think Vans stated Vne as a TAS because it is based on the design flutter speed, which IS a TAS, 200 kts or 230 mph for the -10. Flutter happens based on the speed of the molecules going past the control surface and what harmonics that induces in the control surface. Indicated is derived from the pressure the molecules exert on the pitot tube, and thinner air is more compressible so IAS goes down as altitude goes up.



As the manufacturer, you can either translate that TAS back to an indicated airspeed, plus a fudge factor to account for density altitude differences, or, if you have an EFIS, let it displace TAS as supplemental info and input your Vne as a TAS. I think I will still subtract 5 kts as a safety margin, in case the elevator or ailerons might flutter at lower speed with some bird droppings or frost or whatever.



On Tue, Jul 28, 2015 at 5:59 PM, Bob Turner <bobturner> wrote:

 	  Quote: 	
		  --> RV10-List message posted by: "Bob Turner" <bobturner>

 

 Calibrated airspeed is the same as indicated airspeed, if there are no instrument or pitot-static errors.

 Normally certified aircraft use CAS (or IAS) to specify Vne because this information is available to the pilot. Many airplanes do not display TAS. I can only imagine how few pilots would pull out an E6B as they nose over in a dive, to calculate TAS from CAS.

 I am also disappointed that Vans has chosen a very unorthodox approach in specifying Vne in TAS, contrary to what most pilots were taught.

 I would really like to know: is this number derived solely from ground vibration tests? Did Vans test-dive the aircraft, and if so to what speed, and what altitude?

 

 --------

 Bob Turner

 RV-10 QB

  

[b] 	




If only the world was this simple. There are many different flutter modes possible. And they scale differently. For some the onset of flutter depends only on TAS. For others, the onset depends on the product of TAS and the square root of density - indicated airspeed. Still other modes have a density-airspeed scaling which is in between these two. And which mode is excited at any given time depends on the stiffness of the airframe part involved, etc. It really is as much art as science. But to say only TAS is important is an over simplification.

_________________
Bob Turner
RV-10 QB

amekler

Joined: 07 Oct 2010
Posts: 164

Posted: Wed Jul 29, 2015 1:39 am Post subject: V Speeds

Has anyone seen a TAS close to 200 kts at higher altitudes?

I typically fly at less than 10,000 feet and see TAS at 170 kts. A descent with power on could easily exceed 200 kts TAS.

Alan

 	  Quote: 	
		   On Jul 29, 2015, at 2:00 AM, Bob Turner <bobturner(at)alum.rpi.edu> wrote:

 [quote="Kelly McMullen"]I think Vans stated Vne as a TAS because it is based on the design flutter speed, which IS a TAS, 200 kts or 230 mph for the -10. Flutter happens based on the speed of the molecules going past the control surface and what harmonics that induces in the control surface. Indicated is derived from the pressure the molecules exert on the pitot tube, and thinner air is more compressible so IAS goes down as altitude goes up.

 As the manufacturer, you can either translate that TAS back to an indicated airspeed, plus a fudge factor to account for density altitude differences, or, if you have an EFIS, let it displace TAS as supplemental info and input your Vne as a TAS. I think I will still subtract 5 kts as a safety margin, in case the elevator or ailerons might flutter at lower speed with some bird droppings or frost or whatever.

 On Tue, Jul 28, 2015 at 5:59 PM, Bob Turner  wrote:

> 

> 

> Calibrated airspeed is the same as indicated airspeed, if there are no instrument or pitot-static errors.

> Normally certified aircraft use CAS (or IAS) to specify Vne because this information is available to the pilot. Many airplanes do not display TAS. I can only imagine how few pilots would pull out an E6B as they nose over in a dive, to calculate TAS from CAS.

> I am also disappointed that Vans has chosen a very unorthodox approach in specifying Vne in TAS, contrary to what most pilots were taught.

> I would really like to know: is this number derived solely from ground vibration tests? Did Vans test-dive the aircraft, and if so to what speed, and what altitude?

> 

> --------

> Bob Turner

> RV-10 QB

> 

> [b]

 If only the world was this simple. There are many different flutter modes possible. And they scale differently. For some the onset of flutter depends only on TAS. For others, the onset depends on the product of TAS and the square root of density - indicated airspeed. Still other modes have a density-airspeed scaling which is in between these two. And which mode is excited at any given time depends on the stiffness of the airframe part involved, etc. It really is as much art as science. But to say only TAS is important is an over simplification.

 --------

 Bob Turner

 RV-10 QB

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=445325#445325

Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Wed Jul 29, 2015 6:03 am Post subject: V Speeds

What is simple is that Vans has provided what they state was their design flutter speed, as a limitation that should not be exceeded.Â  Only if you want to play test pilot, with parachute, quick release door (oh wait, we already have that), recovery chute, etc and go do some dive testing................or if you are an aeronautical engineer and can get the same data that Vans used to re-evaluate their calculations, we have no way to further evaluate that number or to even decide how closely we should approach that number. We only know it is a published number, in TAS that Vans strongly recommends not exceeding.



I suppose another aeronautical engineer could design some new flight controls with a higher design value, publish some plans or sell completed control surfaces, but we don't have that situation today.



On Tue, Jul 28, 2015 at 11:00 PM, Bob Turner <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)> wrote:

[quote]--> RV10-List message posted by: "Bob Turner" <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)>

 

Â  

 If only the world was this simple. There are many different flutter modes possible. And they scale differently. For some the onset of flutter depends only on TAS. For others, the onset depends on the product of TAS and the square root of density - indicated airspeed. Still other modes have a density-airspeed scaling which is in between these two. And which mode is excited at any given time depends on the stiffness of the airframe part involved, etc. It really is as much art as science. But to say only TAS is important is an over simplification.

 

 --------

 Bob Turner

 RV-10 QB

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=445325#445325

 

 

Â  

 

 [b]

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
KCHD

kearney

Joined: 20 Sep 2008
Posts: 563

Posted: Wed Jul 29, 2015 7:03 am Post subject: Re: V Speeds

Hmmm



So my plan is to set my IAS limit to about 170 KIAS on the EFIS. At 10k this translates to about 201 KTAS give or take. Higher than that I'll keep on eye on the KTAS shown on the EFIS. Lower that that and it is a non-issue as I will normally be well below the limit.



I don't plan to tempt fate by messing with the flutter gods. They sound vengeful.



As a side note, and as I mentioned in my original post, there are a lots of docs quoting the RV10 Vne as 200 KIAS and not 200 KTAS. This is a big difference. I guess this only goes to show we had better be careful about what we take as gospel from the internet.



Cheers



Les

 	  Kelly McMullen wrote: 	
		  What is simple is that Vans has provided what they state was their design flutter speed, as a limitation that should not be exceeded.Â  Only if you want to play test pilot, with parachute, quick release door (oh wait, we already have that), recovery chute, etc and go do some dive testing................or if you are an aeronautical engineer and can get the same data that Vans used to re-evaluate their calculations, we have no way to further evaluate that number or to even decide how closely we should approach that number. We only know it is a published number, in TAS that Vans strongly recommends not exceeding.



I suppose another aeronautical engineer could design some new flight controls with a higher design value, publish some plans or sell completed control surfaces, but we don't have that situation today.



 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=445325#445325

 

 

Â  

 

 [b]

Rocketman1988

Joined: 21 Jun 2012
Posts: 63

Posted: Wed Jul 29, 2015 5:58 pm Post subject: Re: V Speeds

Y'all were talking about the coffin corner and thought you might like to have a visual. In this photo, the yellow bars on the speed tape represent Mach buffet above and stall below the indicated airspeed. We were not at our altitude ceiling, but as you climb, the two yellow bars get closer to the airspeed. At our ceiling, there is only a few knots above or below.  Also note the blue PLI (pitch limit indicator). It is only a few degrees above the current pitch in level flight. That PLI it where the stick shaker activates...

IMG_0168.JPG

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