right thrust only matters if the nose is up. Do a full power vertical climb
as close to vertical as you can and let go of the sticks and see which way
it yaws. If it goes right, it is too much. also check to see if it pitches
up or down when you do this. You may even need up or down thrust.
A plane designed for symmetrical flying should have
(i) No thrust offset of any sort
(ii) Thrust as near to CG and Cof drag as possible
(iii) No dihedral
(iv) Fully symmetrical wing section
(v) As much fin and rudder below teh cenbter line as above
(vi) plenty of fuselage side area for knife edge. and a fair bit in
front of the CG as well as aft.
(vii) Ailerons in the prop wash.
That way it will fly in almost any attitude.
Side thrust is normally used with dihedral to counteract torque rolling
via yaw. Its a bastrad way to do it. If teh ailerons are in teh wash,
just couple a tad of right stick to teh throttle. That should work even
Strange, I posted this message more than 11 hours ago and it has not
appeared yet. Here it is again below;
From: email@example.com (Wan)
Subject: Right thrust?
I'm in the process of repairing my electric 3D airplane. When I
checked the thrust line, it turned out to be about 3 degrees to the
right. I had thought that it should be 2 degrees.
My question; Is (Are) 3 degrees too much?
While we're at it, doesn't right thrust become left thrust when the
plane is inverted? Hmm....
firstname.lastname@example.org (Wan) wrote in message
Sorry for the double posts. Honest, when I checked, it was not here at
8 AM this morning.
I agree with the Natural Philosopher, however the plane's designer
calls for 1/8" of offset on the motor mount for right thrust. I had
built just about all my planes with zero, zero in the wing, tail
section and motor.
The plane is quite a zesty craft with verticals you'd not believe. I
just wanted to get it right again. So if I'm to follow your
commentary, I should shim the motor to align straight with the center
line of the fuse?
email@example.com (Wan) wrote in message
Right thrust does more than just compensate for nose-up flight. It
helps counter the left-turning tendency caused by the rotating
slipstream off the prop, most noticeable in the takeoff roll.
There are four forces that the prop imparts to the airplane,
besides the obvious thrust. The first is the rotating slipstream,
which, in an airplane that has a clockwise-turning prop (as seen from
the cockpit), strikes the fin on the left side and swings tail right,
nose left. The second is the higher angle of attack of the downgoing
blade, if the airplane is in slow flight or a climb, or in a
taildragger before the tail comes up on takeoff. This is on the right
side, and pulls the nose left. Third, The torque reaction puts more
weight on the left wheel on takeoff, creating a bit more friction and
pulling nose left, and in flight may cause a left-banking tendency.
Fourth, the gyroscopic precession of the prop will swing the nose of a
taildragger left as the tail comes up on takeoff.
Note that all reactions are to the left, and if the prop turns the
other way, they all pull the nose right.
Right thrust makes the airplane easier to fly. Down thrust makes
the airplane easier to fly. An experienced pilot doesn't need either
of them any more than an experienced cyclist needs training wheels.
They create some drag and hurt overall performance. Some full-scale
manufacturers use them, and others don't.
Dan_Thomas firstname.lastname@example.org (Dan Thomas) wrote in message
Thanks for the thorough explanation about right thrust, Dan. The four
points that you made have made the need for right thrust
understandable. So, if I'm a more experienced pilot, I would not need
A Mr. Winzer is succinct in his answer to my two questions in my
His post on 10-29-03;
answer to question #1--NO
answer to question #2--NO
His answer has me thinking, from the cockpit point of view, the prop
is still rotating clockwise so it doesn't change anything whether
right side up or upside down.
For now, I have no more questions.
I didn't, because frankly that statement makes no sense anyway.
IF you have dihedral, then anything that introduces a yaw, will end up
rolling the model.
Right thrust works to counteract power dependent rolloing moments via
dihedral. Right thrust works upise down - as does rudder, because when
upside dwon teh wings have ANHEDRAL if you like. To get an invrted
rudder only model to turn left, you do indeed use LEFT rudder, which
doesn't turn the plane INTO the desired bank, it turns it OUT, but the
(anhedral) rolls the plane in the OPPOSITE direction to the yaw, and if
you then take the rudder off, and apply some 'down' elevator, you can
turn your plane to the left...a most unnatural looking manouver to be
sure, but thtas how it works..
If you have no dihedral, then right thrust is going to simply make your
model yaw, and not actually turn it right.
IF you have sweepback, and no dihedral, then the effect is to always
roll in the direction of the yaw. So under these circumstances the right
thrust will roll the model to the right , right way up, and to the left,
when inverted. Its no surprise then that pattern models have no right
thrust and slightly sweptback wings, typically. This makes them behave
the same way either way up, and any propwash/torque effects are taken
care of by aileron trim, and, with teh ailerons inboard near the
propwash, the work under low airspeed conditions as well.
Sidethrust IMHO is an ugly way to get a scale model or trainer to track
straight when you haven't got a computer mixer. On a neutrally stable
aerobatoic model it shouldn't be necessary.
Now, there is an aerobatic low-wing homebuilt aircraft known
as the Jurca Scirocco that has NO dihedral. The designer felt that
dihedral was not always necessary for stability. This airplane will
roll in the proper direction when rudder is applied, even without
dihedral, partly because the fuselage blanks a bit of the inside wing
as a skid begins. Many high-wing airplanes have no dihedral either,
and behave perfectly normally, banking when yaw is introduced. The
Bede BD-4 is one. All of the Cessna high-wingers have only a degree or
so, and still bank with yaw.
There are other factors that will make a wingtip rise if the wing
is yawed a bit. I believe a minimizing of the tip vortex on the
leading tip has something to do with it.
Our first RC was a powered two-axis sailplane, with plenty of
dihedral. It banked normally using rudder whether right side up or
upside down, though it was difficult to keep it inverted.
In full-scale training, you will learn that the turn is
accomplished using bank angle, to change the lift vector from vertical
to toward the centre of the turn. The rudder is used ONLY to eliminate
the adverse yaw created in most airplanes as the downgoing aileron on
the outside wing creates more drag than the upgoing aileron and pulls
the nose a bit away from the desired turn direction. Rudder is a
coordinating device, not a turning device. Using rudder to turn
creates a skid, which at low speeds can result in an uncoordinated
stall and a spin.
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