Blaine:
I can see this effect on a moderate sized glider where the plane has
inertia, however what happens when using a DLG?
I am trying to understand the observations we see when a light plane
is used. A DLG appears to be nearly at it's stall speed when
rudder deflection is added. Hence from a "Physical" view, my
plane appears to stall. I am using one of Watson's foam
tailgroups on my Photon I.
When a rudder stalls due to AoA deflection, what would a pilot
see? Is there less rudder response? If the plane is moving
significantly, I can see how all the Rudder yaw/roll is overcome by the
KE. When slow the mass of the wings etc appears to enter into the
observations.
Additionally, with the cruciform tailsgroups in DLG versus the
standard rudder/E config of say the Supra, I expect that the twist
induced by the tail of the Supra versus the twist balance of the
cruciform rudder there is more yaw induced in the DLG.
Am I looking at this incorrectly?
Thanks,
Chris Adams
-------- Original Message --------
Subject: [RCSE] re: Rudder Stalls and Turns
From: Blaine Beron-Rawdon <[EMAIL PROTECTED]>
Date: Wed, August 02, 2006 2:06 pm
To: Soaring <[email protected]>
Cc: Mark Drela <[EMAIL PROTECTED]>
Gents,
It is worth being wrong by two orders of magnitude when it draws Mark
Drela into the conversation!
I stand corrected. Thanks a lot, Mark.
Blaine Beron-Rawdon
Envision Design
San Pedro, CA
Date: Tue, 01 Aug 2006 17:56:05 -0400
From: Mark Drela <[EMAIL PROTECTED]>
To: [email protected]
Subject: [RCSE] re: Rudder Stalls and Turns
Message-ID: <[EMAIL PROTECTED]>
> There is a tendency for R/E models to pitch up when a turn is
> initiated due to gyroscopic precession.
>
Yes. But this precession effect is very very weak. In my simulation
of a BD being given a fast 30 degree rudder input, the nose pitches up
by only 0.03 degrees.
Nevertheless, in this ruddering maneuver of a r/e glider, there is
indeed a sudden large AoA increase of about 3 degrees (more than enough
to cause a "rudder stall"). But the cause is simply due to the linear
inertia of the glider, not to precession. Imagine this sequence
during a rudder turn, with the rotation angles exaggerated
to show the effect:
1) Glider is flying level in a straight line.
2) Glider yaws to the right 45 degrees (while still moving along the
straight line)
3) Glider rolls to the right 45 degrees along its now-yawed fuselage
axis (while still moving along the straight line)
You will see that the glider's belly now faces the oncoming wind
along the
original direction of motion, which constitutes an Angle of Attack
increase.
In reality, the glider's yaw, roll, and turn motions will all blend
together
with some lags between them, but the effect to cause the AoA increase
will still be there.
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