REFLECTOR: HOW FAST? - Flutter

Thu Mar 22 09:57:28 CDT 2007

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 <mailto:scott at tnstaafl.net>  
	To: Velocity Aircraft Owners and Builders list
<mailto:reflector at tvbf.org>  
	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>
<mailto:tmartino at troubleshooter.com> 
		Date: 2007/03/18 Sun PM 11:22:24 EST
		To: "Velocity List" <reflector at tvbf.org>
<mailto: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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