Throt/ Rud

[Keith Hoard]

I guess if you guys were REALLY serious about pattern models, you'd design
counter-rotating props for the engines. . .

 

 

 

Keith L. Hoard

Cordova, TN

khoard at midsouth.rr.com

 

 

 

  _____  

From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org] On
Behalf Of Rcmaster199 at aol.com
Sent: Thursday, January 27, 2005 12:17 PM
To: discussion at nsrca.org
Subject: Re: Throt/ Rud

 

Bob, this is exactly how I feel. Why not learn to use the sticks? 

 

On the money with P-Factor (not to be confused with K-factor) and GP also.
Slipstream is the key and it could be significantly straightened by doing
something similar to what Nat has done with the Xpress series of models.
Strakes surrounding  the CG help reduce the effects. This is a design
feature tha belongs on all pattern models. IMHO

 

MattK

 

 In a message dated 1/27/2005 8:18:27 AM Eastern Standard Time,
bob at toprudder.com writes:

Ed,

 

I am a very firm believer (no one will convince me otherwise) of exactly
what you describe. Slipstream effect is the whole reason we put right thrust
in our engines. It has NOTHING to do with torque, P-factor
<http://home.earthlink.net/~x-plane/FAQ-Theory-PFactor.html> , or gyroscopic
precession <http://www.cybercom.net/~copters/aero/gyro.html> .

 

The issue of transitioning from vertical to horizontal (either to inverted
or upright) is a gyroscopic precession issue. The best way to counter that
is to use lighter weight props turning at lower rpm -- less spinning mass
and less gyroscopic effect.

 

P-factor only exists at high angle of attacks, which does not happen in a
vertical climb. 

 

Torque tries to roll the plane, and some schools of thought are that, to
counter the torque-induced roll, the left wing has to lift more than the
right, causing more induced drag on the left. While this may be true for a
lot of planes while taking off, this does not apply to pattern planes in a
vertical climb since both wing panels would be fighting the torque equally.

 

Gyroscopic precession only occurs when the airplane is moving around its
pitch axis, as when pulling or pushing a corner. It is most noticeable when
the airplane is slow, since there is less aerodynamic stabilizing force
available from the rudder/fin.  IMHO, no throttle-rudder mix is going to
correct this. It might be possible to mix elevator to rudder, and
enable/disable the mix based on throttle position.

 

When I flew a Cap21 in pattern, I had to use left rudder when pulling an
inside corner at the top of square loops. I had to use a TON of right rudder
when pushing a corner, and this was with about 5 degrees of right thrust.

 

IMHO, learn to do it with your thumbs. Practice enough and it will become
automatic. Just my 2CW.

 

Bob R.



Edward Skorepa <edsko at xmission.com> wrote:

I'm confused too. I know, I know I shouldn't argue with someone like chip
but I believe the main reason we're putting right thrust is an asymmetric
vertical fin. On most conventional airplanes the area above thrust line is
much greater then area below. So, the spiraling slip stream  will hit the
top portion of the vertical fin from the left pushing tail to the right thus
right thrust. When inverted, the spiraling slip stream will hit vertical fin
from the right because fin is now on the opposite side and  pushes tail to
the left. To straighten the flight path, we need now the left thrust which
is already there. During inverted push ups, why do we need to use left
rudder? The spiraling slip stream misses completely vertical fin and the
right (left when inverted) thrust is causing airplane to yaw left. If you
have a big gasser, turn on smoke, do inverted push up and watch where the
smoke goes. However, Chip's approach of fixing the inverted push ups problem
is quite interesting and I'll try it on my new bird I'm working on right
now.

ed

 

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