Trim!

[hitech]

Electric motor are not same torque curve as a gas motor, basicly an electric motor produces more torque when slower then set speed, It is the same as if you were running at full speed then started pushing the drill into somthing, the drill slows slightly,causing  less resistance in mag field, more current drawn, hence more torque.

Gas motors torque is releated to throttle input. But the engine torque is what is either accelerating the prop, or generating thrust. Not the other way around. Unlike a electric motor a gas motor will keep accelerating if not underload as long as you keep the throttle in it, and most probably explode.

Gas motors do not have a 100% flat torque curve, but they are relativly flat in the rpm ranges airplane motors use.


HiTech

[Straiga]

2. Slip stream, produces both roll force oposit torque and yaw force.

Slip stream is a left turning force. The prop slip stream hits the vertical stabilizer from the left and pushes the nose to the left. Not in the oposit from torque or yaw. Prop rotation clockwise the resultant torque is oposit (counterclockwise).

4 Turning Forces

Torque- on the ground relates to a left turning force.
Torque-in the air relates to a rolling motion.

P-factor-is only present in a nose up pitch attitude, that changes the angle of attack on the right side prop disk and relates in a yaw to the left in a clockwise rotating prop.

Prop Slipstream- is a left turning force.

Gyroscopic procession-is a left turning force in a tailwheeled airplane, in a tricycle gear airplane it is a right turning force.
This is because when you pitch the nose down the gyro effect is a resultant force which applied 90 degrees later in the prop rotation, relating to a left turning force. The nose gear airplane, when the nose pitches up the resultant force is applied also 90 degrees in the prop rotation which translates into a right turning force.

As for the drill if you pulled the trigger fast the drill will torque dramatically. If you pulled the trigger slowly you will feal little or no torque. So torque is not a constant. Same as in an airplane.

This tread was my attempt to point out that the AH planes show different trim settings in the cockpit from one another.
Also Auto-takeoff should reflect that some right rudder trim is needed, some up elevator trim is needed. Also in auto climb the elevator trim should not be in the full up position, but should reflect about 2 degrees up and have some remaining elevator trim left.

If I tookoff in an airplane and advanced power slowly and use rudder to maintain directional control and elevator this should be all the control input I would need except for crosswind takeoffs. If I abruptly applied power I would need full right rudder and brake, aileron probably full and still end up in a bad ground loop situation.

Straiga

[Cobra412]

I'll try and find this site I ran across when AH2 first came out in regards to how a Spitfire handles on take off and what is needed to ensure a safe take off.

IIRC it said that you needed to slowly walk the throttles up, input some right roll and input some right rudder.  The right roll was to help counter act the tendency of the left wing to dip due to torque from the motor.  The nose would have a tendency to want to come right then back to the left as the power was increased.  Obviously to counter this you'd use right rudder.  

All this was written by a pilot who owns and flies Spitfires.  I thought that the original ground modeling of the Spitfire was correct.  Sometime in the beta the ground handling was changed.  Reason I thought it was correct is I couldn't take off at all until I found the writeup from this pilot.  The second I used what he had said I was off the deck with no issues at all.  Then HTC changed something in the next beta that didn't require me to use this anymore.

[Straiga]

Cobra

I cant see using aileron upon the first power application in a Spit or ME-109. When the landing gear is close to the center of gravity there nothing to stop the roll effect, not even aileron because at zero airspeed there is no airflow across the ailerons to counter the roll. Rudder and elevator are the only effective control surfaces at this speed because they sit in the prop wash and having a constant airflow acrossed the control surfaces.
About 40- 50 is average speed for the airlerons to become effective. Some may be less some may be more depends on the mass of weight the ailerons have to move.
But I can see using ailerons on takeoff in a Spit or 109 after having effective ailerons to keep from dragging a wing tip, due to the narrow gear carriage.

When the landing gear are far apart like a P-47, P-51 the torque rolls the plane on to the left main landing gear, and compresses the oleo strut, this produces friction from the tire on the runway and pulls the airplane to the left (Yaw), just like a brake would work. At the time of lift off the torque is still present but not that pronounced, but is something that the rudder cant handle.

Remember after you takeoff when you use right aileron you get yaw to the left, so there for you will need more rudder to maintain a straight out climb. Then P-Factor comes in to play, this will also require more rudder.

Straiga

[Cobra412]

Jeff Ethell

Lining up for take-off is intimidating with that Rolls-Royce engine sticking way out in front. There is no sense in thinking too much about it. Throttle up slowly to prevent a lurch to the right (if in a Griffon Spit where the propeller turns the opposite direction from American aircraft)...left foot moves forward almost in concert with the left hand to keep the nose straight. Monster torque shoves the right wing down rapidly, very much like the P-40, until full left aileron and full (give or take a minuscule amount) left rudder is held. The Rolls is a wounded dragon bellowing horrendously.

[stantond]

Let me try that again...

I was talking about two different types of torque in my previous post.   The statement:

Originally posted by stantond:
So, like pulling g's in a drag racer or when turning an aircraft, dynamic torque is a transient effect. The torque seen and talked about related to horsepower is a transient effect when you are trying to stop or slow down an engines rotation by applying a load. That deceleration in rotation generates torque.

was confusing.  The acceleration due to turning an aircraft is caused by centripetal acceleration and is not transient. The torque generated when applying a load while the engine is at a constant rpm is due to the force created by adding more current for an electric motor or more fuel/air in a gas engine.  I agree with everything HiTech stated.

Basically (and I must use some math here) torque is the cross product of a force vector times a radial distance vector.

T= r x F

This torque can be static, for a static force F.  This torque can be constant, for a periodic, but not time varying force F.  This torque can be transient, or what I call a dynamic torque for a dynamic force F.

An example of a static force is from a torque wrench.  An example of a constant periodic force occurs in an electric motor, or gas engine at constant speed.  An example of a transient force occurs when changing the speed of an electric motor, such as during motor startup or when an engine changes rpm.  

I was trying to show, by using an electric hand drill, the dynamic torque effect.  This effect only occurs during a rapid speed change, such as starting an electric motor or rapidly revving an engine.  A rotational acceleration must occur for this dynamic torque to exist.  That is because the dynamic force F only occurs when a there is a rotational acceleration.  This purely rotational dynamic torque can be put in terms of inertia and rotational acceleration.  

It is this dynamic torque effect which causes a ground loop if the engine has enough inertia and is revved quickly.  This dynamic torque effect will also roll an aircraft at slow speeds when quickly changing rpm’s, provided the engine has enough inertial.  In both cases, the propeller speed is constant.

Hope this makes what I was talking about clearer.


Regards,

Malta

[hitech]

Stantond: One of us is still missing somthing.

The torque is beeing generated by the motor in either eletric or combustion motor. This torque is either acclerating the motor or used up by the prop to produce thrust. In either case for a given throttle setting the torque relative to the airframe  remains the same.

Im some how missing somthing if your saying the accleration is causing more torque than the motor can generate.


HiTech

[stantond]

QUOTE] Originally posted by HiTech
The torque is being generated by the motor in either electric or combustion motor. This torque is either accelerating the motor or used up by the prop to produce thrust. In either case for a given throttle setting the torque relative to the airframe remains the same.
[/QUOTE]


What I am saying is the torque relative to the airframe does *not* remain the same when accelerating the motor compared to the torque on the airframe when the prop produces thrust.  The dynamic torque due to inertial acceleration is directly transferred to the airframe when accelerating the motor.  There is a time needed after increasing the throttle for the motor to speed up.  That time is when dynamic torque occurs.

Dynamic torque comes from the overall torque budget which means torque to the propeller will be reduced until the motor stops accelerating.  When the motor reaches the intended speed, dynamic torque goes away, and all torque from the motor is provided to the propeller.  

The throttle has to be moved before dynamic torque will occur.  Changing the throttle has the effect of creating dynamic torque which is transferred directly to the airframe.  In differential terms, a gradual throttle (s) increase (small ds/dt) produces a small dynamic torque and an abrupt large throttle increase (large ds/dt) produces a maximum dynamic torque.




Regards,

Malta

[hitech]

Dynamic torque comes from the overall torque budget which means torque to the propeller will be reduced until the motor stops accelerating. When the motor reaches the intended speed, dynamic torque goes away, and all torque from the motor is provided to the propeller.

I 100% agree with this, but how is the total torque to the airframe changed when the total torque budget remains constant as you just stated? Because torque to the prop is taken by the airframe just as the dynamic torque is.


Also had another thought, are you basing this on knowledge of cars? If so the difference would be when at steady speed engine torque on a car is pitch, and torque is roll when engine is accelerating. Hence is different than an airplane where both are always roll.


Or am I missing somthing similar to a gear ratio change on the torque?




HiTech

[stantond]

HiTech,

This may take a while to accept but the propeller and rotating gears in the gearbox induce no torque on the airframe at constant speed.  Torque from the engine rotates the propeller, which as you know produces thrust.   As I understand, this thrust is asymmetrical and produces an external rotational force or 'torque' which is induced on the aircraft wings.   This 'torque' is due to airflow (I called it propwash) and not propeller rotation.

The torque from the engine to the propeller is not offset by a torque on the airframe through the engine.  Ideally, no torque would be transferred from the engine crankshaft,  propeller, or rotating gears through the engine block to the airframe.  Friction and engine vibration produce a small torque.

In an attempt to describe this for a constant speed engine.... the pistons move due to combustion forces which are converted to a rotational motion through a crankshaft.  The engine is designed to keep these forces on the crankshaft balanced.  The motion of these pistons and the rotation of a crankshaft place no torque on the airframe because of symmetry and the forces are balanced.  Bolting on a gearbox does not add some path for torque to get into the airframe.  Similary, putting a propeller on the gearbox offers no path either.  This same concept applies to propellers on a ship or submarine and big fan drives used in closed circuit wind tunnels.  


Regards,


Malta

[hitech]

Sorry stantond the prop drag must exatly = the torque produced by the engine or it would be accelerating.

Why do you think helicoptors have tail rotors.

Every action requires a = and oposit reaction.  

HiTech

[stantond]

Yes, my bad. Torque due to propeller drag was not considered, good point. All propeller drag torque will be transferred directly through the engine to the airframe.  I got hung up on inertial (dynamic) torque.

Helicopters need a tail rotor to balance out the rotor's airfoil drag torque.  Changing a helicopter rotor’s speed also causes torque.  However, the rotor airfoil drag causes all the torque at a constant rotor speed.

Newton’s laws certainly apply in both cases.

The torque output by an engine is equal to the amount of load, provided the load torque does not exceed the engine torque output limit.  In other words, an engine will only put out the amount of torque needed to balance the torque budget.  If there is insufficient engine torque to do that, I don't believe the engine will be able to speed up quickly so that dynamic torque can occur.  

My understanding of the constant speed variable prop pitch mechanism is that the angle of attack of the propeller, and its corresponding thrust and drag, change based on the available torque.  At takeoff, a maximum torque provides a coresponding maximum thrust, angle of attack, and prop drag.   The engine torque output is equal or greater than the torque required to rotate the prop at its constant speed.   A reduction in throttle position keeps the prop speed constant but reduces the angle of attack, thrust, and prop drag.  The more torque available,  the greater the angle of attack for more thrust.  

From what I have read, most, if not all WW2 fighters had more torque than required at takeoff.  This allowed rapid engine speed changes with resulting ground loops and torque induced rolls at low airspeeds.  I originally thought this was probably due to inertial dynamic torque.  But, a rapid propeller pitch change when the throttle is quickly moved at low airspeed might produce a more severe torque, due to a rapid change in propeller drag torque.  



Regards,

Malta

[hitech]

Constant speed props work conceptualy with torque, but acctualy just work off rpm, advance throttle  /more torque/ prop speeds up slightly , valve opens,pitch increases/ prop changes back to original rpm.


HiTech

[Toad]

Originally posted by Straiga

 I wish you guys could fly the real P-51D, I have, and my experiences flying it is what im telling you about.
 Straiga

I know some guys in the P-51 community. What's the tail number or nose art on your Dad's airplane?

I may have some pictures of it if he does airshows.

[Toad]

Punt for Straiga