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View Full Version : question about stalls?


edavis
11-19-2014, 10:44 AM
Why do we encourage the use of right rudder during the induction of stalls?


JamesNoBrakes
11-19-2014, 10:48 AM
Use rudder to keep the glare shield/dash from sliding left or right on the horizon. If it's not sliding, no rudder is necessary.

Yoda2
11-19-2014, 11:03 AM
Why do we encourage the use of right rudder during the induction of stalls?
Why do you ask this question? In what context? What ratings do you have, background?


Ewfflyer
11-19-2014, 11:08 AM
In the spirit of fun, try doing one with left rudder!

Simple answer, coordinated flight.

rwthompson67
11-19-2014, 11:43 AM
Why do we encourage the use of right rudder during the induction of stalls?

I assume you're talking about power on stalls? In this case, you will need quite a bit of right rudder leading up to the stall in order to maintain coordinated flight (centered ball).

For power off stalls, very little if any rudder input is required to keep it centered.

Hope that helps.

Cbusbased
11-19-2014, 03:40 PM
Torque and P-factor

JamesNoBrakes
11-19-2014, 04:44 PM
Torque and P-factor

Please explain why you need rudder to counter torque in the air :)

Yoda2
11-19-2014, 06:30 PM
JNB, Are you saying you only need to counter torque with aileron when airborne? It's OK, We'll wait :)

Cbusbased
11-19-2014, 07:12 PM
Torque is about the roll axis (roll) while P-factor is about the vertical axis (yaw). Thus, if you correct for the left-turning tendency (p factor) you must also correct with aileron correction in order to maintain coordinated flight.

JamesNoBrakes
11-19-2014, 09:22 PM
Torque is about the roll axis (roll) while P-factor is about the vertical axis (yaw). Thus, if you correct for the left-turning tendency (p factor) you must also correct with aileron correction in order to maintain coordinated flight.

Exactly, and of course on the ground the landing gear prevents the "roll", but more pressure is applied to the left gear due to the force still being there, "dragging" the airplane left.

I think this "force" is only an issue when accelerating the prop. At a steady state, the engine mounts and stabilizer surfaces are configured to eliminate any residual "torque" effect caused by friction/drag in the engine and moving parts, but you do get a little when you change power settings, "accelerating" or "decelerating" the prop. When you try to spin the prop faster, airplane wants to go opposite direction, but of course it's a LOT heavier than the prop, so the effect is still pretty minimal, not to mention there's probably some additional resistance caused by the static pressure around the aircraft.

Of course, this all gets confusing because the FAA calls P-factor, torque, slipstream and gyroscopic effects all "torque effects", which they are because they are all forces x distances for the most part, but the specific effect of "torque" when referring to the opposite effect of accelerating the propeller would of course be a roll about the longitudinal axis. "Torque effects" is kind of a poor name, but "left turning tendencies" isn't much better, as many of these forces are completely opposite of that in certain conditions.

Again, I can't say I've noticed when aileron is necessary in any flight not involving accelerating or decelerating the prop, and even then just a slight effect. It seems far more prevalent to find people offsetting P-factor with aileron, flying uncoordinated and keeping the airplane in enough right bank to offset the yaw to the left.

Thoughts anyone?

Cbusbased
11-20-2014, 05:39 AM
Ah, I'm picking up what you're laying down. The whole "...while on the ground" part went over my head. Haha

Hubble15
11-20-2014, 06:10 AM
JNB, you are in the ballpark generally, but mistaken that torque only affects roll during power changes. Torque effect is offset by rig ... for each power setting, there can be a corresponding "no roll" airspeed (tho sadly my plane rolls a bit to the right at nearly all normal speeds). If your airplane is rigged "right", then it will exhibit little to no roll at standard power/cruise speed pairings. The best way to see this is to accelerate near Vne and pull up to the vertical. Initially, very little aileron will be required to offset the rolling tendency. As the aircraft slows, progressively more right aileron (left with a russian motor) will be required. As the aircraft nears zero airspeed, the ailerons will not have sufficient effectiveness to prevent roll and, even with full right aileron, a left roll will commence. If the aircraft was otherwise balanced, it will torque roll to the left until it pivots in the tailslide. Flown the other way, airshow guys will begin rolling left in the vertical and the left rolls will continue in the tailslide.

Hubble15
11-20-2014, 06:12 AM
PS - only try the demo I described in an airplane certified for aerobatics

JamesNoBrakes
11-20-2014, 06:57 PM
JNB, you are in the ballpark generally, but mistaken that torque only affects roll during power changes. Torque effect is offset by rig ... for each power setting, there can be a corresponding "no roll" airspeed (tho sadly my plane rolls a bit to the right at nearly all normal speeds). If your airplane is rigged "right", then it will exhibit little to no roll at standard power/cruise speed pairings. The best way to see this is to accelerate near Vne and pull up to the vertical. Initially, very little aileron will be required to offset the rolling tendency. As the aircraft slows, progressively more right aileron (left with a russian motor) will be required. As the aircraft nears zero airspeed, the ailerons will not have sufficient effectiveness to prevent roll and, even with full right aileron, a left roll will commence. If the aircraft was otherwise balanced, it will torque roll to the left until it pivots in the tailslide. Flown the other way, airshow guys will begin rolling left in the vertical and the left rolls will continue in the tailslide.
Sounds reasonable, but I was thinking that accelerating a rotating mass vs just swinging it at a constant speed would take a lot more force, and consequently, cause a lot more opposite force.

But yes, I agree with most of this, it kind of blows a lot of "rote" learning that pilots are taught out of the water (generally because torque and gyroscopic effects are widely misunderstood), but it's completely sound. One has to be careful as well, as there can be other effects causing the aircraft to roll, like the vertical stab/rudder, which sits a distance from the longitudinal axis, so there'll always be a little "roll" (not even getting into an advancing wingtip) when using just the rudder, unless it's a submarine with the longitudinal axis bisecting the rudder.

As far as the "on the ground" part for Cbusbased, lets go back to torque and the "opposite" reaction. Propeller travels in a circle clockwise, so the opposite reaction will be for the airplane to try and move opposite of the prop, which would be counter clockwise. On the ground though, can the airplane "roll"? Not really, the wheels are supporting it, but what it can do is try to roll the airplane left (counter clockwise) and exert more pressure on the left main. Although friction is irrespective of pressure, tires are not rigid and in real conditions it usually causes more friction effectively and that increased friction on the left main gear tries to pull the aircraft left during the takeoff run.



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