REFLECTOR: HOW FAST? - Flutter

Thu Mar 22 11:58:50 CDT 2007

Tom,
   What you have been taught is correct.  However, what you said about "if there is less air....there is a less chance of detrimental effects" may not necessarily be true.  I am not an aeronautical engineer but here is what I believe to the basis of the IAS vs TAS agrument as it relates to flutter.
   If it's soley the speed of the air molecules passing over a control surface that induces flutter, then, TAS is how it should be measured and reported.  If the density of the air and the speed of air molecules passing over the control surface induces flutter, then, IAS should be how it measured and reported.
  Just my 2 cents (or less) worth...

Bruce

-------------- Original message -------------- 
From: "Tom Martino" <tmartino at troubleshooter.com> 

I have always understood it this way:

The thicker the air, the higher the indicated airspeed.  So, as you climb higher, your indicated speed decreases because of less air entering the pitot tube and ramming the diaphragm.  Is this correct?

Therefore, if there is less air … there is less chance of detrimental effects?  Therefore the airframe will tolerate higher True Airspeeds at higher altitudes?  So, in essence … indicated airspeeds can be used because it reads the actual effect of the air on the frame.

I am not sure this is correct but it what I have been taught over the years.

Tom
-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Scott Derrick
Sent: Thursday, March 22, 2007 8:39 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: HOW FAST? - Flutter

I read the article. like I said below , there's no real data in the article.  Just he said , she said stories.  No test data for proof, no references..

I've read a few nasa research articles that use TAS as a component for flutter limits, not the only component though. Its to bad but most of Nasa's work is in the high mach numbers or super sonic speeds. 

Here's a quote from Martin Hollmann from his analysis of a flutter problem he was investigating     .  A well known aerodynamic engineer. 

"I set up a very detailed flutter model. The model showed me that the Lancair 360 with the big tail had a critical flutter speed of 145 kts. at S.L. and 141 kts (194 kts TAS) at 20,000 feet. Fuselage twisting and bending were coupling as shown on the figures below."

No you'll notice that the Sea Level speed was 145 IAS, the 20,000 ft speed was 141 IAS(194 TAS).  Obvioulsy the IAS speed was lower at the higher altitudes but not by much.  The flutter speed in KTAS numbers would be 145 KTAS at sea level and 194 TAS at 20,000 ft.  So if using KTAS for this airplane you would have to increase your flutter speed as you climbed.  This is in total contradiction the article in Kitplanes.

Interesting another aerodynamicist did an analysis of the bit tail 360 and came up with a critical speed of 300 KTAS  

Scott

Ron Brown wrote: 
There's a great article in the April 2007 issue of Kitplanes (page 30) in which the author makes the case that it is indeed TAS that we should be worried about when considering flutter.

Ronnie
----- Original Message ----- 
From: Scott Derrick 
To: Velocity Aircraft Owners and Builders list 
Sent: Tuesday, March 20, 2007 10:28 AM
Subject: Re: REFLECTOR: HOW FAST?

It really depends on what the Vne is a limit for.  

If for structural load its IAS. 

If for flutter some of the equation should take into account TAS.  Though I've never seen any real scientific data to support how much should be attributed to TAS vs IAS for flutter. Just OWT's, historical references and he said, she said type of articles like at Vans web site.

Scott

Terry Miles wrote: 
Bob,
Just for the record, my understanding is that Vne is better thought of as a
true airspeed limitation.  When GA aircraft in general were no more than 180
hp engines, no effort was spent in calculating indicated versus true.  Now
with 300+ hp engines that can cruise at FL200+ this has to be taken into
account. 

If you wander over to the Van's Website there are a couple of articles there
about the topic in greater depth.
Terry

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of bulsr at bellsouth.net
Sent: Monday, March 19, 2007 11:36 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: HOW FAST?

How high were you and what was your indicated A/S? Scott S. I believe
expects to get near 300 TAS at altitude. The Vne of 200 being IAS.
Bob Buls
XLRG
Still building

From: "Tom Martino" <tmartino at troubleshooter.com>
Date: 2007/03/18 Sun PM 11:22:24 EST
To: "Velocity List" <reflector at tvbf.org>
Subject: REFLECTOR: HOW FAST?

OK, in speed tests this weekend, I was able to true out at 210 knots
pretty consistently.  I was at 23 inches and 2400 RPM.  I still had
throttle travel left.  Flight controls were solid and no sign of
flutter.  Should I push it even further?  At what point do I know I have
gone far enough?  

Tom Martino
173 Elite RG - 300 HP (IO-540)

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Subject: Re: REFLECTOR: HOW FAST? - Flutter
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