Need another aero-d discussion...

[Ex-jazz]

I shoot:   Different distance between the wings' and rudder's aerodynamic centers? 
EDIT: (on the Z axis)

Cigar for the winner

[tf15pin]

My guess would be the size of the rudder (aerodynamic force that is exerted) and how far the force is exerted from whatever axis the aircraft is rotating about. Torque, moment, or couple (depending on if you are talking to a physicist or engineer) is basically the rotational equivalent to force and is defined as T = R X F (read: torque equals R Cross F) or the torque equals the vector cross product of the displacement vector and the force vector.


I guess in one sentence it would be that a larger or taller rudder  would cause the aircraft to roll more than a smaller or shorter rudder. Bigger meaning larger force, and taller meaning a larger displacement vector.

[Ex-jazz]

I know very little about coding, but mathematically couldn't/shouldn't it be treated as a symmetrical airfoil? IE. the fuselage and the vert stab.

I know, all I did was state obvious. Won't even try commenting on the coading part.

I'm currently using a symmetrical airfoil aoa data to generate the Z-axis torque, but it's oscillating pretty easily now.

[fbWldcat]

Cigar for the winner

Hopefully not a cigar from Zetanine's thread 

http://bbs.hitechcreations.com/smf/index.php/topic,291543.0.html

 

[Wmaker]

I'm currently using a symmetrical airfoil aoa data to generate the Z-axis torque, but it's oscillating pretty easily now.

Rgr, I might reply with a PM in a bit. Allthough I'm pretty sure you have everything in place that I'm thinking about and more.

[hitech]

I believe this is a very minor force and rolls right with left rudder if the rudder is above cg.

HiTech

[bozon]

Why some planes roll more then others when applying rudder?

I'll bite.
Another part of the effect is the length of the wings. When yawing one wing travels faster and the other slower than the center of the plane - the longer the wings, the larger is the airspeed difference and the more lift is gained/lost - the lift difference leads to a roll. This gives a pronounced roll when kicking the rudder and then a more mild sustained effect.

[RufusLeaking]

As the wing moves through the air it attracts a bunch of little critters in the air called Bernoullis (also known as "Lifties").  They run around on the top of the wing to hold it up.  When the Bernoullies get scared or upset because of things like having the wing tilt too much causing the air to get rough and tumble they jump off and the wing stalls.  If you get the airflow smooth again they'll come back and hold your wings up again.  Of course you can't see Bernoullis....they're invisible....obviously.

In Flight Screening, we were taught about "Lifties." 

You forgot the part about them stamping on the wings and tail prior to jumping off (wing buffet).

Mace obviously had military flight training.

[hitech]

Wow no one want's to discuss one of the word I can not spell? 

And no, that's not every word, just close.

HiTech

[dtango]

Haha, well I had thought about posting a nice nasty set of equations on roll & yaw/sideslip coupling to discuss your topic and elaborate a bit more on what bozon already mentioned but I'm having too much fun elsewhere!

[RTHolmes]

quick question - for a properly trimmed aircraft is the thrust line the same as the motion vector? ie. in level flight should the thrust line be parallel to the ground?

[bozon]

OK maybe some aero-engineer can enlighten me on how delta wing, elevator-less planes work. I mean planes like the Mirage or F-106.
Normally the torque to keep the wing in an angle against the airflow is provided by a separate elevator and a leverage due to the elevator being far aft of the main wings. In a delta the wing needs to both produce the lift and the counter torque to keep it in a constant angle of attack. How does that work?

[Charge]

Does the wing configuration really make a difference? If the control surface resides aft of CoL the angle change of the main foil will always be the same as the movement of the control surface i.e up - up. Then think of canard. It resides in front of CoL so it acts more like a flap or spoiler i.e. the angle change of the main foil is always the opposite to the control surface i.e. up - down. Even if that sounds logical one would think that employing a trailing edge flap would cause a significant nose down tendency and it must do so but it also needs a counter force from elevator surfaces or e.g. a steep landing angle where some part of the airframe acts as a lifting force as in Draken J35 which had a tail wheel to protect the exhaust nozzle on extreme angles. The counter force still needs to be more than the force of the flaps or the nose will come down. Thus it seems logical that nearly all modern deltas also have a canard to assist in vertical control.

http://www.vectorsite.net/avj35.html

This is also related to discussion we had years ago about the pitch tendency when deploying flaps in WW2 era planes. Some pitch down, as seems logical, but some are documented to pitch up? Is that actually more related to position and trim of the tail plane?

-C+

Ed. The Draken does not use flaps at all, AFAIK, but its large wing area to create lift or to slow down, thus the extreme angles and thus the tailwheel because the it uses high AoA to shorten take-off run..

[RufusLeaking]

Normally the torque to keep the wing in an angle against the airflow is provided by a separate elevator and a leverage due to the elevator being far aft of the main wings. In a delta the wing needs to both produce the lift and the counter torque to keep it in a constant angle of attack. How does that work?

What torque are you talking about?

Elevators are for controlling pitch.  If the engine thrust is in line with the center of gravity, there should be no adverse affect on pitch.   Jets are affected much less by engine torque than older prop planes.

In a conventional airplane, the center of gravity is forward of the center of lift.  The horizontal stabilizer, to which the elevators are attached, actually pull down. 

I am not sure about how a delta wing handles this.  On a delta wing plane, the trailing edge control surfaces act as both ailerons and elevators (elevons).

Thus it seems logical that nearly all modern deltas also have a canard to assist in vertical control.

Canards are forward of the center of gravity, so they pull up.  There is an efficiency in that the canard is helping to lift the weight as opposed to a conventional tail, which pulls down against the main wing.

[Ex-jazz]

What torque are you talking about?

Longitudinal stability net torque / moment, I assume.