[NSRCA-discussion] Airplane angle of attack
White, Chris
chris at ssd.fsi.com
Wed Oct 3 11:17:07 AKDT 2007
Hi George:-)
Thanks for that feedback, I appreciate it.... I thought it was a
strange statement for an ARF, but I do understand that when we draw an
airplane design we typically plan the thrust line based on the way we
want the airplane to present itself.
Good to hear from you George.
Take care....
Chris
Chris White
Sr. Aircraft Liaison Engineer
Data & Equipment Group
FlightSafety Simulation,
2700 N Hemlock Circle,
Broken Arrow, OK 74012
Phone 918/259-5526
Fax 918/259-4156
________________________________
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of george w.
kennie
Sent: Wednesday, October 03, 2007 12:55 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Airplane angle of attack
Hi Chris,
I heard the guy that said that, and at the time I thought he was a
little cucoo, but after thinking about it I decided that it could indeed
be possible. I think you have to realize that the attitude angle of the
fuse that would look good to your eye falls into a fairly narrow range
and therefore would probably produce a negligible deleterious effect to
the overall performance of the aircraft irrespective of where it was set
within those bounds. But then again there are probably good arguements
that would contest that.
G.
----- 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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>
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