Re: T-tail

Date:         25 Sep 97 01:39:42 
From:         JLussier <jluss@ptialaska.net>
Organization: PTI Communications
References:   1 2
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JWizardC wrote:
> A note and a question:
>
> Note: (E-flat) - Most folkes don't take into account that the horizontal
> stabilizer also contributes lift to the aircraft. Granted, in most cases
> that lift is negligable, but it is there. It is my understanding that much
> of the problem with icing on modern T-tail turboprops is because of the
> increased dependance on the stab's contribution to total aircraft lift. T?
> F? I'm not real sure.
>
> Question: Is it not true that mounting the stabilizer and elevator on the
> top of the empannage gives one's design a **slight** increase on moment
> arm? I seem to recall a wee increase in leverage, therefore allowing the
> fuselage to be a wee bit shorter, and the stab a wee bit smaller, thus drag
> a wee bit smaller?

I beleive that most horizontal stabilizers actually contribute negative
lift, allowing the aircraft center of gravity to be stationed somewhere
forward of the wing center of lift.  This configuration provides for
dynamic pitch stability with pitch contolled by varying the negative
lift on the horizontal stabilator.  This configuartion leads to greater
pitch stability with an aft CG but greater effciency with a forward CG
(less negative lift required by horizontal stabilizer therefore less
lift required by wings).

There are some variants to this configuartion that I am not very
familiar with.  I beleive that some experimental aircraft use(d) forward
canards to control pitch, resulting an an inherently unstable but
manueverable configuartion that can (could) only be flown by wire.  This
is not to say that all canard aircraft are unstable.

I beleive the purpose of the T-tail is to ditance the horizontal
stabilizer from the turbulent flow off the wing.  This would provide for
a more consistent pitch response and control for various flap,slat, slot
configurations as well as providing undisturbed air at slower, critical
maneuvering airspeeds (approach and landing).

jrl
ATP