[NSRCA-discussion] Airplane angle of attack
Ed White
edvwhite at sbcglobal.net
Wed Oct 3 16:44:22 AKDT 2007
I worked with a former B-52 pilot. He said the bank limit was around 60 degrees. Beyond that yaw-roll coupling overcomes what the spoilers can control. There is a famous video of this crash. If you look closely you can see the spoilers on the upper wing deflected full trying to bring it back, with no effect. He said what happens is that it rolls to 90 deg and drops the nose severely. Controls have little effect. It starts heading down and then the spoilers slowly become effective again and you can roll back to upright and recover. However, it takes every bit of 10,000 feet of altitude to recover to straight and level flight.
Most of us have seen the B-52 model that was build flown and crashed in the UK. If you watch the crash video, it looks like the same thing may have happened. Exceeded the bank limit and it rolled on its side and dropped the nose.
Ed
chris moon <cjm767driver at hotmail.com> wrote: .hmmessage P { margin:0px; padding:0px } body.hmmessage { FONT-SIZE: 10pt; FONT-FAMILY:Tahoma } Sorry Bob,
I knew you were referring to pattern planes and set ups. I was just
trying to be funny with the airliner knife edge comment.
The interesting thing about the B52 is that it has no ailerons and it
only uses spoilers for roll control. We can see the problem right away
if you put that plane in a high AOA banked turn then spoil the lift on
the opposite wing trying to get it to roll back to level. I believe
there is a bank limit on that plane beyond which you are not going to
get it back.
Chris
Bob Richards wrote:
> 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
> 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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