REFLECTOR: HOW FAST? - Flutter

Thu Mar 22 11:34:22 CDT 2007

yes, basically, as you climb- and maintain the same IAS as per the pressure
at the pitot, you will be progressively be traveling faster and faster since
it takes more speed to encounter the same molecules of air- you can continue
to climb and speed up until you run out of power/propeller efficiency which
proportionately drops at about the same rate.  You will also notice that the
speed of sound varies with altitude- this directly corresponds to the air
density through which it passes as well- I can not see how TAS has any
bearing on flutter speed except that it is tied somewhat to IAS. IAS is
basically a measurement of how much fluid (as a function of it's density) is
moving past the aircraft at any given moment- this is the same effect that
the flight surfaces experience- you would see a very high IAS of you were to
mount the pitot under a boat and move it through water at even a very low
TAS because of the density difference of water to air, and the aircraft
would flutter at the same IAS in water as it would in air, (modified for any
difference in viscosity.) 
  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Tom Martino
Sent: Thursday, March 22, 2007 9:57 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: HOW FAST? - Flutter

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  <mailto:reflector at tvbf.org> 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"  <mailto:tmartino at troubleshooter.com>
<tmartino at troubleshooter.com>
Date: 2007/03/18 Sun PM 11:22:24 EST
To: "Velocity List"  <mailto:reflector at tvbf.org> <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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