[NSRCA-discussion] Airplane angle of attack

Thu Oct 4 06:33:39 AKDT 2007

Do you gentlemen think an airplane presents better in the pattern with a
setup that looks:    a) on the step (tail slightly high) faster
appearance.

b) level  

c) tail slightly low, slower appearance.

If this is a dumb question I apologize in advance for my curiosity:-)

Thanks, Chris

________________________________

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of John
Ferrell
Sent: Thursday, October 04, 2007 8:35 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Airplane angle of attack

It is possible to ruin an otherwise good design with the geometry of the
thrustline/wing/stab placement as well as control surface geometry and
hinging. Top ranked pilots usually can make most anything look good
though.

It is not unusual for full scale airplanes to display the same airspeed
for two different angles of attack. The AOA that requires the least
power for a given airspeed is generally referred to as being "on the
step".  If a pattern airplane is configured in a manner that these two
operating points are close together the return to level flight presents
an increased workload.  I believe the current trend of high volume
fuselages makes it difficult to achieve an "on the step" condition.

Just my opinions of course...

John Ferrell    W8CCW
"Life is easier if you learn to plow 
       around the stumps"
http://DixieNC.US

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

	From: White, Chris <mailto:chris at ssd.fsi.com>  

	To: NSRCA Mailing List <mailto:nsrca-discussion at lists.nsrca.org>

	Sent: Wednesday, October 03, 2007 8:47 AM

	Subject: Re: [NSRCA-discussion] Airplane angle of attack

	Understanding that a lot of misinterpretation can happen in
reading or talking about things without actually being directed in
person on the subject article, I dismissed the following story. Now
after this post it has me curious again and I would be interested to
hear comments from people who may have been told the same.  

	The story comes as a result of a couple of local pilots who were
working on a well-known $2K arf from 2005-6 era that had no reference
lines on the fuse, nor measurements in the plans referring to Thrustline
or any clue as to where to start on fuselage angle to engine-wing-stab
setups.  Communication with the designer resulted in the customer being
told that it should be done by appearance.  (eg: the way you wish to see
your fuse angle in level flight cruise.)

	That seems very subject to interpretation and I would think if a
person were a few degrees off it would make a significant difference on
aerodynamic behavior during maneuvering. (mixing etc)

	There's probably a post on this somewhere, but Bob's comment led
me to think of that setup dilemma.   I've never seen or heard of an
airplane kit/arf without some reference to thrust line, until I heard my
local friends told me about this one.

	Is this scenario familiar to anyone out there? 

	(Gee, do I push send or not.......ok I'll send it.)

	Chris White

________________________________

	From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Bob
Richards
	Sent: Wednesday, October 03, 2007 7:13 AM
	To: NSRCA Mailing List
	Subject: Re: [NSRCA-discussion] Airplane angle of attack

	I never meant to draw any conclusion about the knife edge
performance of airliners or bombers in my original post. I was merely
stating that the reason we PATTERN FLIERS adjust the incidences of the
wing and stab (ON OUR PATTERN PLANES) has to do with aerobatic
performance. As far as I know, the reason the designers of airliners,
bombers, and most full-scale airplanes pick a incidence value has to do
mainly with efficiency in cruise.

	Bob R.

	rcmaster199 at aol.com wrote:

		I remember watching a clip of a full size multi engine
bomber type in test flight. The test pilot banked hard to knife edge
near the ground (maybe 500 ft) for some unknown reason and swiftly
proceeded to put it in. Don't remember the plane's or test pilot's
names. 

		Full scale fuselages are designed to minimize drag as
much as possible (for max range) so they tend to be pencil thin
comparatively speaking. Pencil thin fuses do not fly knife flight well
nor are they intended to do so. And the higher the weight the worse the
problem. At risk of being glib, that test pilot found the outside of the
envelope.

		MattK

		-----Original Message-----
		From: chris moon <cjm767driver at hotmail.com>
		To: nsrca-discussion at lists.nsrca.org
		Sent: Tue, Oct 2 4:28 PM
		Subject: Re: [NSRCA-discussion] Airplane angle of attack

		The optimum AOA on airliners is a function of wing
design. It's the 
		operator's job to try and stay near the optimum AOA for
maximum 
		efficiency. Lighter gross weights require either higher
altitudes or 
		lower true airspeed to be most efficient. Likewise,
heavier weights will 
		have you faster and or lower. I guess what I'm saying is
that the 
		optimum AOA is essentially dictated by wing design and
we juggle the 
		other variables in order operate the wing as efficiently
as possible. 

		I have rolled the 737, 757, 767 and A320 in the
simulator and they make 
		poor pattern planes. I'm sure there is a significant
downgrade for a 
		single roll that loses 5000+ feet of altitude. Don't
even ask about 
		knife edge performance. 

		Chris 

		Bob Richards wrote: 
		> That makes sense to me. The AOA depends on the load.
In an extreme 
		> case, very lightly loaded, I don't think you would
want to fly with 
		> the fuselage in a nose down attitude, that would
probably be 
		> inefficient. Better to have it slightly nose up in
cruise with a full 
		> load. JMHO. 
		> Of course, the reason WE would trim wing incidence
would have more to 
		> do with overall flight characteristics during
aerobatics, particularly 
		> with pitch coupling in knife edge flight. 
		> Bob R. 
		> 
		> 
		> */chris moon /* wrote: 
		> 
		> Tried to post this before but it did not go through. 
		> 
		> The optimum cruise angle of attack for jetliners is
somewhere between 
		> 2.5 and 5 degrees nose up. Usually closer to 2.5 or 3
degrees for an 
		> econ cruise. As fuel burns off and the gross weight
goes down, the 
		> airplane will need a lower angle of attack to maintain
flight which 
		> will take us away from our optimum angle (lower). So,
we will either 
		> climb to where the air is "thinner" and require a
higher aoa 
		> (angle of 
		> attack) to get us back to the 2.5 or 3 degrees or,
slow down and 
		> maintain the lower altitude thus requiring us to
increase the aoa 
		> back 
		> to optimum. The answer to your question is yes, a
jetliner flies at a 
		> nose high aoa in cruise. Lift from the fuselage would
probably be 
		> negligible other than "impact" lift - the force of the
relative wind 
		> against the raised fuselage bottom. 
		> 
		> Chris 
		> 
		> 
		>
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