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Path: utzoo!linus!philabs!cmcl2!lanl!ths
From: ths@lanl.ARPA
Newsgroups: net.aviation
Subject: Re: re acrobatics (aerobatics?)
Message-ID: <28650@lanl.ARPA>
Date: Tue, 23-Jul-85 14:50:15 EDT
Article-I.D.: lanl.28650
Posted: Tue Jul 23 14:50:15 1985
Date-Received: Wed, 24-Jul-85 08:31:25 EDT
References: <385@tekred.UUCP>
Organization: Los Alamos National Laboratory
Lines: 53

> .......why
> did my flight instructor have me pull back on the stick to
> hold the nose up, in steep turns? I took these things on faith
> during training, but it would seem to me that whenever a turn
> of more than 45 degrees was initiated, one would use the elevators
> to turn, and feed in a little top rudder to hold the nose up.
> Does this work? Are there planes that don't fall off much in
> steep turns? Can you bank 90 degrees and make at least a partial
> turn? In the movies, (unless they tilt the camera) those hot
> fighters seem to fly forever on edge. Is that real? Thanks
> for the info. Norm
> 
> tektronix!tekred!normb

Although you could make a somewhat rational case for using "top rudder"
it would not be "aerodynamically" correct.  Recall from your basic ground
school days that when you bank an aeroplane you are tilting the "lift vector".
The lift vector will "loose" some portion of the vertical component.  Again
recall that there are two ways to produce lift - increase speed or increase
angle of attack.  Add power or back pressure accordingly.  Power will also
give added vertical component from its thrust if the nose has a positive
angle of attack (which it should if you are attempting to maintain level
flight.

The use of the controls remains the same regardless of the attitude of the
airplane. Elevator still controls pitch and rudder controls yaw.  Pitch is
what is going to increase angle of attack to give you lift from the wing.

As you pass thru 45 degrees of bank enroute to 90 degrees you could begin
to add "top rudder" to increase the "angle of the attack" on the side of
the aeroplane.  Because that is where you are going to get the "lift" to
"sustain" level flight when the wings reach 90 degrees of bank where the wings
are no longer supporting any of the weight of the plane.  It will all be on
the side of the fuselage.

You will note that during an air show these "knife edge" passes that are
made were begun at high rates of speed and in a descending pattern.
Exposing the side of the plane to the slip stream to produce lift is
also going to produce a tremendous amount of parasitic and induced drag.
Only planes with mucho power can sustain level flight.  The "ball" in the
inclinometer is going to be stuck hard in the corner of the tube.

To sum it up, never use "top" rudder in a steep turn, the plane will enter
"uncorordinated flight", you will create more drag, and your instructor
will never forgive you.  For all practical purposes, general aviation
aeroplanes cannot sustain level flight beyond a 70 degree bank, if for no
other reason that the G-forces (Gee, that's a good reason...crack!)

This discussion assumes that we are talking about general aviation airplanes.
F-16 pilots are excluded.

Ted Spitzmiller
(tried a "knife edge" in an Aerobat on a few occasions)