The Murphy Builders Site

While researching the Rebel, I came across a relatively old review of a
Rebel equipped with a Rotax 912UL, in which the writer thought lateral
(roll) stability was not as good as it should be. The writer attributed
this to the design's small (1 deg.) dihedral, and also seems to
speculate it might have better roll stability with a heavier engine.

I'm wondering if Rebel owners/flyers on this list agree these criticisms
were and/or still are somewhat valid, and would appreciate comments on
Rebel handling stability, particularly with smaller engines. Thanks.

Ron

PS - There's a pretty cool online aerodynamics book, including Shockwave
animations demonstrating principles of flight, at
http://142.26.194.131/aerodynamics1/



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Ron,

We recently finished a Rebel (1650) w/0-320. The dihedral I set in the wings was only 0.1 deg. not the 1 deg. as set in the manual. Airplane flys great, lateral (roll)stability was not an issue.

This is how we set up our Rebel.

Jeff


----- Original Message -----
From: Ron Shannon <rshannon@cruzcom.com>
Date: Saturday, November 12, 2005 8:22 pm
Subject: Rebel lateral stability

While researching the Rebel, I came across a relatively old review
of a
Rebel equipped with a Rotax 912UL, in which the writer thought lateral
(roll) stability was not as good as it should be. The writer
attributedthis to the design's small (1 deg.) dihedral, and also
seems to
speculate it might have better roll stability with a heavier engine.

I'm wondering if Rebel owners/flyers on this list agree these
criticismswere and/or still are somewhat valid, and would
appreciate comments on
Rebel handling stability, particularly with smaller engines. Thanks.

Ron

PS - There's a pretty cool online aerodynamics book, including
Shockwaveanimations demonstrating principles of flight, at
http://142.26.194.131/aerodynamics1/



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Hi Ron !

I can't imagine what the reviewer was smoking !! I've flown
several Rebels with 912's, and ALL would fly hands-off all day long !
Cruising with negative flapperon increases the stability in
bumpy conditions, and is standard procedure. With engines over about
115 hp, you can use 2 notches of negative, for improved cruise.

Having flown several Rebels with O-235's, O-320's, Subarus,
etc, I would say that there's NO difference in lateral stability
with different engines - that just does not make sense ! My feeling
is that the original 1 degree of dihedral is just PERFECT -
-don't mess with it ! I've seen one Rebel where the dihedral was
increased to about 6 degrees - looked awful, flew worse (by accounts -
wouldn't even taxi that one ! ) and introduced all kinds of
problems to the control system (think - flexing aileron horns !!)

My next and final Rebel will have a 912-S ! The Rebel with the std.
912 is a delightful airplane to fly - roll rate was in the 2 seconds
range for 45-to-45 degree banks, climb was about 1,000 fpm solo,
stall was below 30 mph with flap, and cruise was 97 mph - all on
about 3 GPH of mogas !! :-) It is dynamically stable in all axes,
but very responsive. Being light (about 600-750 lb), it is easy to
push around on the ground single-handed, and would make an ideal
choice as an LSA - with the option of going to larger engines
at any time, if desired. The original Rebel flew well on Murphy
1500 straight floats - with 2 aboard, it outperformed an 85 hp
Aeronca Super Chief - so that is another option.

The only consideration in lateral forces is that you must be
VERY careful and accurate if building the stock factory wing tips.
It is very easy to be 1/4" out at the end of the wing - with the
underired roll input this adds ! Personally, I will use the
Fife Hoerner wing tips - they greatly improve performance, and
are beautifully made, so they just slip on, saving you about
60 hours of work ! Worth the extra money !

......bobp


-------------------------------orig.-------------------------
On Saturday 12 November 2005 11:22 pm, Ron Shannon wrote:

While researching the Rebel, I came across a relatively old review of a
Rebel equipped with a Rotax 912UL, in which the writer thought lateral
(roll) stability was not as good as it should be. The writer attributed
this to the design's small (1 deg.) dihedral, and also seems to
speculate it might have better roll stability with a heavier engine.

I'm wondering if Rebel owners/flyers on this list agree these criticisms
were and/or still are somewhat valid, and would appreciate comments on
Rebel handling stability, particularly with smaller engines. Thanks.

Ron

PS - There's a pretty cool online aerodynamics book, including Shockwave
animations demonstrating principles of flight, at
http://142.26.194.131/aerodynamics1/

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