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Vne and flutter (was engines)

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ron.mcgann(at)baesystems.
Guest

Posted: Wed Oct 18, 2006 4:07 pm Post subject: Vne and flutter (was engines)

Assumptions:

  

 Vne is  based on IAS, and for the -10 is 200kts (at) 5000'. 

 Vne is  adjusted by 1.5% for each 1000ft of alt.

 At  20000ft, Vne is therefore 15(000)*1.5% less than 200kts (ie 155kts  Indicated)

  

 Check  out the attached photo from a turbocharged -10 operating here in Oz.  Yes  that is 152 kts at 20120' (Note the TAS in the bottom left corner and yes, they  are knots!)

  

 If  published Vne is 200kts at sea level, Vne (at) 20000' is close to 140kts (70% of  200kts)

  If  published Vne is 200kts at 8000', Vne (at) 20000' is close to 164kts (82% of  200kts)

  



 Fast -  yes, but a bit too close to the edge for this little black duck!  I would  be interested if anyone knows what the designed Vne (and associated altitude)  actually is.

  

  

 FLY  SAFE

  

 Ron

 187  finishing.

  

 [quote]   --

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Dsyvert(at)AOL.COM
Guest

Posted: Wed Oct 18, 2006 5:50 pm Post subject: Vne and flutter (was engines)

Ron,

  

     I believe the following link will answer your  question.

  

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

  

 Dave Syvertson

  [quote][b]

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jesse(at)itecusa.org
Guest

Posted: Thu Oct 19, 2006 4:48 am Post subject: Vne and flutter (was engines)

I can’t find the fuel burn number on that screen.  Any help?  

     

Jesse Saint  

I-TEC, Inc.  

jesse(at)itecusa.org (jesse(at)itecusa.org)  

www.itecusa.org  

W: 352-465-4545  

C: 352-427-0285  

        

  

From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN, Ron

 Sent: Wednesday, October 18, 2006 8:07 PM

 To: rv10-list(at)matronics.com

 Subject: Vne and flutter (was engines)  

  

     

Assumptions:  

    

   

    

Vne is based on IAS, and for the -10 is 200kts (at) 5000'.   

    

Vne is adjusted by 1.5% for each 1000ft of alt.  

    

At 20000ft, Vne is therefore 15(000)*1.5% less than 200kts (ie 155kts Indicated)  

    

   

    

Check out the attached photo from a turbocharged -10 operating here in Oz.  Yes that is 152 kts at 20120' (Note the TAS in the bottom left corner and yes, they are knots!)  

    

   

    

If published Vne is 200kts at sea level, Vne (at) 20000' is close to 140kts (70% of 200kts)  

      

If published Vne is 200kts at 8000', Vne (at) 20000' is close to 164kts (82% of 200kts)  

    

   

  

    

Fast - yes, but a bit too close to the edge for this little black duck!  I would be interested if anyone knows what the designed Vne (and associated altitude) actually is.  

    

   

    

 Do not archive  

    

FLY SAFE  

    

   

    

Ron  

    

187 finishing.  

    

   

   	  Quote: 	
		      

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

 From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com]On Behalf Of James K Hovis

 Sent: Thursday, 19 October 2006 2:13 AM

 To: rv10-list(at)matronics.com

 Subject: Re: Re: engines  

    

Flutter and dynamic divergence are REAL issues every airframe designer (and for that matter, pilot) has to deal with especially so for higher-performance aircraft. There are two ways to set Vne in FAR Part 23. One, do ground vibration tests to find resonant frequencies (mainly shake the crap out of it and see if anything falls off) of the airframe, then go out and flight test to find its flutter point, then set the Vne at few per cent below this speed. The other is to use the canned Vne minimum speed formula based on wing loading. The canned formula is based on statistics from certified aircraft that if you set Vne at this speed or below, you won't encounter flutter. I suspect Van's took the conservative approach and set Vne based on the canned formula. Now as Van points out, weight affects flutter. Balance of control surfaces affect flutter (see Steve Whitman's crash several years ago), and horsepower available affects flutter. Most low-power spam-cans don't have the power to ever approach Vne except in steep dives, while adding power means the top speed capable (that point where the power available curve crosses the power required for level flight curve) creeps ever closer to the flutter point. Now, don't get me wrong, if someone want to drop in a 300hp engine into an RV, they are more than welcome to do it. However, they should get a professional test pilot to verify the Vne and flutter point for the configuration or get training on how to react when flutter happens (the time from flutter onset to complete divergence can be REAL small). Understanding the full ramifications of modifications to the original design and testing for it may save someone's life in the end.    

    

   

    

JKH 

 

    

    

   

  	
  

     

  

--

 10/17/2006

    

  

  

--

 10/19/2006

     [quote][b]

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bsponcil(at)belinblank.or
Guest

Posted: Thu Oct 19, 2006 6:09 am Post subject: Vne and flutter (was engines)

I was at the Cherokee Pilots Assoc fly-in a few  years back and talked to Karl Bergey, one of the lead engineers at Piper during  the late 60s early 70s.  Anyway, I asked why the Vne was different between  the Archer and Warrior because as far as I knew there wasn't any difference  between the airframes.  Expecting to hear "Well we beefed up this or that,  extended the HS by 1 inch, etc" I was surprised instead to hear that Vne was  calculated (at least at Piper) solely by the dive test during  certification.  Whatever the testpilot felt comfortable taking the plane up  to in the dive, subtract 20% and you had Vne.  The only  reason the Warrior and Archer have different Vne is because the  testpilot flying the Archer went faster in the dive.

  

 I wouldn't be surprised if this is how Vans  calculates theirs as well.

  

  

  

 -Brian

  

 #40497

 Iowa City, IA

  

 [quote]   [quote]     --

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glastar(at)gmx.net
Guest

Posted: Thu Oct 19, 2006 8:40 am Post subject: Vne and flutter (was engines)

Hello Brian,

 

 I don't think Van's does it this way, they most probably go along with FAR 23.1505 and calculate this speeds, similar to certified airplanes (at least how it is certified today). It's a function of several parameters so you get your flight envelope (see FAR 23.333) and have your limitations set FAR (23.335). Even kit planes are made today with some since background.

 

 br Werner

 

 Brian Douglas wrote: [quote]             

   I was at the Cherokee Pilots Assoc fly-in a few years back and talked to Karl Bergey, one of the lead engineers at Piper during the late 60s early 70s.  Anyway, I asked why the Vne was different between the Archer and Warrior because as far as I knew there wasn't any difference between the airframes.  Expecting to hear "Well we beefed up this or that, extended the HS by 1 inch, etc" I was surprised instead to hear that Vne was calculated (at least at Piper) solely by the dive test during certification.  Whatever the testpilot felt comfortable taking the plane up to in the dive, subtract 20% and you had Vne.  The only reason the Warrior and Archer have different Vne is because the testpilot flying the Archer went faster in the dive.

    

   I wouldn't be surprised if this is how Vans calculates theirs as well.

    

    

    

   -Brian

    

   #40497

   Iowa City, IA

    

   [quote]     [quote]       --

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LessDragProd(at)AOL.COM
Guest

Posted: Thu Oct 19, 2006 8:48 am Post subject: Vne and flutter (was engines)

For each RV-3, a flutter test to 10% above Vne was recommended by Van's  aircraft.  I read a little bit about this before my flight test.

  

 In an attempt to simplify from what I have read:

  

 The Vne is an airspeed based on analysis and design.

 This is an indicated airspeed (IAS), or Part 23 calls this an equivalent  airspeed (EAS).  The EAS being an IAS that uses a calibrated instrument  with a corrected pitot/static system.

  

 Flutter speed will vary from one aircraft to another of the same  design.  Although it is easy to identify when you've reached flutter speed,  because major components SUDDENLY separate from the rest of the aircraft.

 The flutter speed is a true airspeed (TAS).

 Flutter speed is a variable number, because the actual construction and  alignment of the aircraft WILL change this number.  Especially  sensitive are the hinged weight and balance of the flight controls.

  

 Given that Vne is less than the flutter speed at sea level;

 IF the IAS of Vne can be maintained with altitude, at some altitude Vne  WILL exceed the flutter speed.  (This is a bad thing.)

  

 Reading between the lines, here is what I am hearing Van's Aircraft  say:

  

 With the Lyc. 540 engine of 260 horsepower, in level flight the IAS will  not exceed the flutter speed of the aircraft.  (Most flight time will be  below 12,500'.  Very seldom will a flight occur near 18,000'.)

  

 With a turbo normalized Lyc. 540 engine (or an engine with more than 260  horsepower) in level flight at some higher altitude, the IAS could exceed  the flutter speed.  And will exceed the flutter speed, if the IAS is  allowed to increase at the start of a descent from a high enough cruise  altitude.

  

 (Flutter is a high frequency thing, which we humans don't feel very  well.  Major component separation is a low frequency occurrence, which we  would feel.    )

  

 Regards,

 Jim Ayers

 RV-3 sn 50

  

 In a message dated 10/19/2006 7:11:44 AM Pacific Daylight Time,  bsponcil(at)belinblank.org writes:

  	  Quote: 	
		     I was at the Cherokee Pilots Assoc fly-in a few    years back and talked to Karl Bergey, one of the lead engineers at Piper    during the late 60s early 70s.  Anyway, I asked why the Vne was different    between the Archer and Warrior because as far as I knew there wasn't any    difference between the airframes.  Expecting to hear "Well we beefed up    this or that, extended the HS by 1 inch, etc" I was surprised instead to hear    that Vne was calculated (at least at Piper) solely by the dive test during    certification.  Whatever the testpilot felt comfortable taking the plane    up to in the dive, subtract 20% and you had Vne.  The    only reason the Warrior and Archer have different Vne is because the    testpilot flying the Archer went faster in the dive.

    

   I wouldn't be surprised if this is how Vans    calculates theirs as well.

    

    

    

   -Brian

    

   #40497

   Iowa City,  IA

	


 

  

  [quote][b]

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ivowel(at)gmail.com
Guest

Posted: Fri Oct 20, 2006 5:39 am Post subject: Vne and flutter (was engines)

I am not an expert, but Vans seems to be very conservative when it comes

to such issues as specifications, Vne, etc.  It would not surprise me if

there is some wiggle room.  Alas, I would feel more comfortable with a

ballistic parachute if I were to try to exceed Vne on a semi-regular

basis.  An airplane, even an RV-10, is replaceable---you are not.



I have a 325hp engine of in my aircraft, which is really only the 260hp

engine fine-tuned a little bit better.  I have not flown the 260hp

engine, but from what I have observed in flight, the difference in

performance seems to be very small.  A turbo at high altitude, however,

might make a real difference.  of course, you then need oxygen, too.  It

becomes a much more complex (and potentially pilot-exhausting)

exercise.  with a parachute, this could be a nice thing to do, so.



PS: n325hp is still for sale, now at the reduced price of $209,000.



regards,



/iaw

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