splais

My Feedback: (25)

I have always wondered what the dynamics are the causes a plane, especially a taildragger warbird, to go left on takeoff [] if you don't control it with rudder. Someone out there must have a good basic explanation.

DavidAgar

My Feedback: (108)

Engine torque. If you move the throttle up a little at a time, you won't even notice it. It really appears if you go from idle to full power in a second, the torque will get you. Good Luck, Dave

ozzie454

When the tail is lower than the nose on any airplane it creates more effective pitch (and more thrust) on the decending right side blade until the propeller is square with the relative wind (the tail lifts).
Hope that helps

Roy

iflircaircraft

You will also see engine torque when you abort a landing and throttle up too quickly for a go round.

Tom

Dash7ATP

OK, Guys, Here's the skinny from an old Flight instructor.

First, it's not torque. Torque is a rolling force about the longitudinal axis. The force opposite that of turning the prop. It's effect would be to apply a heavier load on the left wheel, causing more drag on the left side. In flight, it's countered by aileron.

Second. Ozzie is correct about the pitch angle of the decending blade of the prop developing more thrust. That is called "P-Factor" and it is a Yaw or turning moment about the Vertical Axis. This is evident any time the plane is flying at ahigh angle of attact. Ahigh power slow airspeed climb is one instance, Thebeginning of the takeoff roll in a taildragger is another. It is countered by Right Rudder.

Third: Slipstream effect. The propellor blast from the propellor is actually rotating around the aircraft in a spiral motion, similar to the threads of a screw. This is easily seen on a real humid morning when you can see the condensation formed by the lower pressure of the prop tips. The faster the prop turns and the slower the plane is moving, the tighter these spirals are. This occurs at the beginning of the takeoff roll. The effect on the plane? A side force on the left side of the Vertical Stab, causing a left turning force, countered by - yep- right rudder., Actually, this effect is always there but to a lessor degree in cruise flight, as the spiral effectivelly becomes streatched out. Some aircraft counter this in cruise by off-setting the leading edge of thevertical staba degree or two to the left.

The forth effect, usually only noticed in tail draggers, is the gyroscopic effect of he spinning propellor. If you have ever held a spinning bycicle wheel by the axel and spun it you will have felt this action. If you are holding the wheel verticle and tried to turn to the left, The force acts on the wheel 90 degrees in the direction of rotation of the gyro. Since the prop is rotating clockwise as seen from the cockpit, if you lift the tail, (same as pushing forward on the top of the prop disc, It behaves as if you had pushed forward on the right side of the disc, causing a yaw to the left. Again , countered by right rudder. This effect was very bad in the WW I planes with the Rotary engines. The high spinning mass of the cylinders made the planes very difficult to manuver. The radial engine changed all of that.

Torque has become a catch -all phrase to explain the left turning tendency, but as you can see, it's actual effect on the ground is minimal compared to the others.

Dash

deatonbt

I know about inertia, acceleration, and horsepower from high school physics. I could not figure out how yaw was caused. I thought about slipstream hitting the rudder but didn't think that it had that much influence. I could feel superior in knowing that there is no such thing as centrifical <sp> <sp> force, but I would not admit out of shame that I really didn't understand why a plane a plane would yaw on take off. I now know that the guys at the field who explain it with such confidence really don't know either. Thank you for the explanation. The preceding comments are sincere.

- Brian
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Dash7ATP

Thanks for your comments, Brian, The slipstream effect is not pronounced.  The air doesn't flow around the aircraft as I may have implied, but there is a side force on the  left side of the Vertical Stab. As the speed picks up, it becomes less.  If the Vertical stab is offset ( usually in light planes with no rudder trim, like small Cessnas), it's designed to eliminate the need to hold rudder at cruise speed which is where you spend the most time. If you go into a divee and accellerate above cruise speed, the offset Vertical Stab may now induce a slight yaw to the right. At much higher speeds, the relative wind may actually become a negative angle of attact, and the "P-Factor" may cause a right yaw as well. 

Lots of little changes take place with airspeed changes and they all affect yaw, and pitch trim.

Joe

da Rock

MODEL AIRPLANES ARE DIFFERENT.

Why do model airplanes so often do what you describe?

The prop if "flying" and the model isn't when you firewall that throttle. The prop goes where it wants to before the wing, horizontal stabilizer, or vertical stabilizer can "stabilize" anything.

Model airplanes have engines far more powerful for their weight than full scale airpanes. There is way more power available and almost no weight to accelerate compared to full scale airplanes. We're basically talking about two different worlds here.

The prop has far more purchase on the air than the model does when the model is sitting still. Give that prop some throttle and it's already working at what it does. Nothing on the airplane will work that is responsible for steering the sucker except the tail wheel until that sucker has some airspeed. The rudder might be close, but nothing much else is anywhere as effective as your prop and your throttle. The stab might be close too, but unfortunately the elevator is almost always closer. Prop is flying, plane is just being pulled around.

It happens most often to taildraggers for two reasons. The plane sits there with the wing's AOA (angle of attack) already beyond stalled. The plane sits with the engine pointed at an angle that will pull the model directly into the air. Those two things are killers. But only if you push the throttle too fast.

Throttle up too fast and models follow the only thing that's "flying under control", the prop.

da Rock

Prop is flying before the model is.

splais

My Feedback: (25)

Great bunch of info guys, thanks.

Dash7ATP

Rock,
Your comments regarding the power to weight ratio certainly have a big effect on how the "model" behaves, but it still all boils down to the aerodynamic forces at work. You don't notice the hard yaw to the left with a high powered tricycle gear plane that is sitting level on the runway. There will probably be a small yaw, but that would be due to the added weight on the left wheel (due to torque)and the slipstream effect on the Vert. Stab. The biggest factor at work in a tail dragger in it's nose high attitude when you add power and begin to move forward is the "P-Factor". The downward moving blade is at a high angle of attact, and the upward moving blade is at a very low angle of attact. The result is a LOT more thrust from the right side of the prop disc.Itcan easily require full rudder for a few seconds to compensate for it.Inever got the chance to fly the P-51 or Corsair, but friends ofmine have. Iunderstand that standard procedure is full right rudder trim for takeoff. Once flying and the speed picks up, The right trim is reduced.

You may have noticed that once the taili is up and the plane is in a level attitude most of the left turning tendencies go away. With the prop shaft parallel to the actual direction of movement, the P-Factor no longer even exists.

Dash

da Rock

And the prop's aerodynamic forces are working while the model's aren't.

The prop pulls the wing forward in a stalled condition while the horizontal stab hasn't come "up on step" and the vertical stab isn't working well enough to control yaw. Whatever happens next happens as the models aerodynamic forces come on line. They don't usually come on line at 100%, nor do they all come on at the same time or rate.

You're absolutely correct about the aerodynamic forces, but their onset is controlled by the prop having almost complete control over the situation because it's forces are good to go.

splais was looking for a simple answer and it really is as simple as any aerodynamic one can be. None of our one liner, aerodynamic truisms ever is simple to explain, nor can almost any one liner be explained in less than a book's worth of words. But model crashes on take off almost always come down to a simple fact. If you firewall and pray, you might just as well pray for the model's dearly departed soul, cause the prop is going to drag that sucker to it's death.

Dash7ATP

For most of the grossly over powered models in the hands of unskilled pilots, you're probably correct. The power should never be just pushed to full power from a standing start. Is that how you do it? Give me a break. You just want to argue. I'm finished with this thread!

Dash

da Rock

Sorry you took offense. And I am surprised because my post basically explains who we're both saying the same thing. As I said, "You're absolutely correct...." then tried to explian about splais looking for simple etc

invertmast

My Feedback: (23)

The prop is "flying" before the wing is on a Full-scale, so the comment "MODEL AIRPLANES ARE DIFFERENT" is a mute point. ANY time the propeller is turning, it is essentially "flying"..

Go to any CERTIFIED FAA flight instructor and ask them why an airplane turns left on takeoff. I would be very surprised if ANY of them would say it is 100% the fault of torque 100% of the time. Like Dash7ATP said, it is a combination of multiple factors that cause it. It is never solely just ONE factor. (yes I am a currently an FAA Certified Flight Instructor!)

deatonbt

On a side but similar note, thirty years ago I had a Sig Kougar that would roll to the left when applying right rudder at full throttle. I figured that it was the large rudder mounted too far away from the longitudinal axis.

chistech

I think Dash thought you were insinuating that he must firewall the throttle and didn't understand "you" meant any pilot in general. I understood that you were basically agreeing with him just using different ways of explanation. That's the problems with emails and posts, words get misinterpreted. Oh Well!

Airplanes400

My Feedback: (349)

You're experiencing the left quardrant effect because you are on the west coast of the country. The further west you are, the greater the effect. Here on the east coast of the US, we still have the left quardrant effect, but it's not as severe as it is for you on the west coast. The people in Australia experience the opposite effect ... thier planes experience the right quardrant effect.

Somewhere in the middle of the Atlantic Ocean is the neutral zone where no left or right rudder is needed for takeoff. But that is useless to us since there is no land in the neutral zone. So, we all have to use rudder to offset the quadrant effect.

glazier808

My Feedback: (1)

+1

I like it!

Casey

Asanders

Brian, your Cougar sounds suspiciously like the F-100. My brother flew them in Vietnam. He said when you were going fast the ailerons were reversed. You had to use rudder or you would roll very quickly the other way.

acerc

All I can add at this point is, having a love for Corsairs call it what ya'll want but donut's are real easy. Simply line up on the runway come to a complete stop and floor it.To me it's pretty simple accelerate at an appropriate rate for the plan in question. Of course to answer the OP's original question, a good basic explenation-Too much throttle to soon. LOL

91zulu

My Feedback: (2)

I think that happens if there is a large gap between the control surface.

jester_s1

The explanations are solid for the effect. To minimize it, if you will find the throttle setting that lets you lift the tail by pushing forward with the elevator before rolling to full throttle for takeoff, you'll not have nearly as much yaw to contend with. The worst case scenario for P-factor is to get a taildragger rolling and just let the tail come up on its own from the airspeed. If you'll lift it yourself, you'll get a little yaw at the very beginning before the tail is up, and a little bit when you rotate for takeoff. Both will be predictable and easy to manage with right rudder.

mountainroad

My Feedback: (18)

"Somewhere in the middle of the Atlantic Ocean is the neutral zone where no left or right rudder is needed for takeoff. But that is useless to us since there is no land in the neutral zone. So, we all have to use rudder to offset the quadrant effect. "


I have been there, we took float planes. You just gave to be careful on approach because the Bermuda triangle is just off the end of the runway.