Trim!

[TimRas]

Originally posted by hitech
Stantond: Torque is completely modeled and is not backwards on the f4.

HiTech

"At this slow speed, just a few knots above stalling, it took a lot of right rudder, even though in a left turn. And you didn't dare add power quickly since the powerful engine turning that large prop could make the aircraft roll uncontrollably to the left-the dreaded "torque roll." [ Fred Blechman on F4U-4]
http://home.att.net/~ww2aviation/Bentwings.html


"The aircraft stalls like a Piper Cub. Though a wing tends to drop, there isn't the slightest mean streak in it unless you cob the power, which produces a very violent torque roll" [ Jeff Ethell on Spitfire]
http://www.supermarine-spitfire.co.uk/flying.html

"I remember telling everyone I ever checked out in the Mustang to take it up high, lower the gear and flaps, then back it off to about 15 inches with the prop up to 3 grand... slow it down easy to about 130 mph... then SLAM in 61 inches fast. The resulting torque roll might have helped save a few lives on full power go-arounds" [Dudley Henriques on P-51]
http://www.warbirdalley.com/p51pr.htm


Can you really say torque in AH feels like in these quotes ?

[hitech]

The auto speed is set to Vy at sea level on all aircraft.

HiTech

[stantond]

I think I am confused.  Is there a setting for enabling torque that I do not have turned on?  

I can consistently take off in a F4U-1 using this step by step process with no rudder or aileron inputs:

1.  25-75% fuel, clean, engine at idle.
2.  elevator trim centered, rudder trim centered, aileron trim centered.
3.  2 notches flaps.
3.  hold stick back 1/2 way to engage tail wheel lock.
4.  100% throttle & wep as quick as controls will allow.
5.  Roll down runway (note that plane does veer slightly to left).
6.  Airborne as soon as 100 mph speed is attained while still on runway.

There just doesn't seem to be much torque I am seeing here (if torque is what I am seeing).  The P51 can be flow from takeoff using the exact same process but has slightly more of a veer to the left effect which has to be countered with a couple of right brake taps (but no rudder or aileron) to stay on the runway.  

Once airborne, the P51 tends to roll to the left.  The F4u seems neutral, sometimes wanting to roll left, sometimes right.  The F4U direction of roll to the right (that I though might be due to torque) was after setting trim to level flight then going to manual trim.

Am I alone on this?


Regards,

Malta

[muerto]

Am I alone on this?

That certainly is not my experience. Any aircraft I fly needs  constant rudder input to track during takeoff.  Some aircraft, a heavily loaded P-47 for instance, can be a real b***h to control during takeoff.

Do you have auto-takeoff switched on?

Is there still and easy flight mode in AH?

[brendo]

Wait one moment please

Before everyone continues to go around in circles again and again about trim, does no one realise:

The computer joystick in AH is not modeled the same as a real life aircraft stick. Therefore trim does not work the same as a real aircraft

What?

1. In Aces High, trim changes the center position of the stick

ie...... if I am fast at 320 MPH I set trim to level flight.....my stick is sitting in the neutral center position.
........ if I am flying 100 MPH slow, I put full up trim, I can now again fly level with the stick in the neutral center position.

2. In Real Life, my trim never changes my stick position. It only changes the Weight of the stick that my arms have to hold.

ie........ If I am fast, I set a small angle of attack, my arms hold that AOA for the speed. If I dial in some trip. IT DOES NOT CHANGE THE STICK POSITION. It just moves a tap on the elevator that takes the LOAD off my arms.
....... If I am real slow doing 70 MPH, I have a LOT of AOA, my stick is WAY back, nearly at max angle of attack (nealy stalled). If I give full up trim, my stick position STILL WILL NOT CHANGE. Only the effort needed to hold that Angle of Attack.


One more example to clarify.
Climbing in AH. Point nose up. Add up trim, until you return your stick to center. Let go of stick..... drink beer. Grab joystick again.

Climbing on real life. Point nose up. Stick comes back until you reach the right angle. Let go of stick....drink water.....plane nose drops... oops. Point nose up. Stick comes back until you reach right angle. Dial in up trim until no weight felt on stick. Let go of stick . Drink water. STICK STILL IS IN A UP ELEVATOR POSITION. Grab stick again.

- - - - - - - - - - - - - - - - - - - - - -
In summary:

- Aces high does not model control stick/trim inputs like real life.
- In real life, trim does not change your stick position. It changes the weight that you are holding for a given speed/AoA
- In Aces high, trim CHANGES your stick position to let you return your joystick to center.





- - - - - - -
P.S. I have fire-proof undies. Flame away.

[Cobra412]

Umm Brendo sorry to say but maybe the airframe you fly doesn't move the stick but that doesn't mean it doesn't on others.  The F-15s stick and rudders will move when trim is applied.  It's how the system is designed as to whether or not you will have corresponding movements when trimming.  Your little "reality check" isn't 100% correct.

[brendo]

Yeah I know that Cobra..... im talking 'old school' stuff here.

Do you remember the movie 'The final countdown' from the '80s?

[hitech]

brendo: In real aircraft that are normaly trimed , i.e. tab on control surface, changing trim position will always move the stick. Typicly you will percive this as just removing force, but think what would happen if you let go of that force with out triming, obviously the stick would move. Move the trim to remove the force, then let go, the stick dosn't move. Hence the trim has realy moved the stick center.

Your are correct AH dosn't move the stick center because it is just not posible with a spring return to center joy stick.


HiTech

[stantond]

Brendo,

I agree with your statements about trim.  My last post was about the effect of torque, not about trim.  Apparently, either no one reads my posts (which is probably true) or I cannot effectively communicate what I am trying to say.  I expect the latter may be true as well.

To rephrase my previous post, if the tail wheel is locked, torque effects (which I keep hearing from HiTech are modeled fully) do not show up.  A step by step process was written down in my previous post so anyone who wanted to repeat what I have noticed could.  The takeoff  process involves using manual trim with all the trim settings centered.  No rudder or aileron inputs are needed, which should be, to counter torque on takeoff.

Apparently, the torque effects only appear when in combat trim during takeoff.  Is that because the tail wheel is not locked?  That's what it looks like to me.  

I must confess, I am not certain what Stragia (who started this thread) was talking about.  I think he noticed differences between the trim settings in AH and a R/L P51.   I am not going to try and speak for him.

My confusion comes from not being able to see torque which is supposed to be modeled.  Do I not have the torque enabled setting toggled?  I did not know there was one, but if there is, how do you enable it?

Can someone explain why no torque appears when the trim is set so the tailwheel can be locked on takeoff?   Is this a bug?


Regards,

Malta

[straffo]

Stantond I don't think trim are neutral (at 0)  at take off.

I think they are setup for climb out.

HT will confirm or invalidate

[hitech]

stantond: The effects of locking a tail wheel change what you think would happen. Try this pop on runway, throttle low, pull stick back and release to make sure auto take off is off. Now advance throttle with no control input, what happens?


HiTech

[stantond]

HiTech,

Roger that, I already know what happens... the plane spins in what would be considered a ground loop.   My question is, why does that not happen with the tail wheel locked?  Is there not enough torque for a ground loop to occur with the tail wheel locked or is something else (like prop wash) causing the ground loop?  Locking the tail wheel removes all the ground loop effects regardless of power setting or change in rpm.  

That is where I got the notion that torque was not modeled in AH, while primarily flying the F4U.  After all, what pilot would try to taxi or take off in a plane without the tail wheel locked?  The F4U pilot’s manual tells you that! Once the tail wheel is locked, all ground loop effects are gone!

The torque effects I keep thinking about are due to a change in the engine speed, such as at take off or 'blipping' the throttle.  The ground loop effect happens with the engine at a constant speed, which is why I though it might be prop wash, or something else.   I believe you when you say torque is modeled.  I just don't quite see how it is modeled.

Not to prattle on aimlessly, but I am very impressed by the flight model.  Being able to use the F4U pilot’s manual to successfully take off and land the plane is very cool.  I have thoroughly enjoyed flying it!  Minor discrepancies such as torque and trim positions I have ignored.  Even as I write, I do not consider them significant details.  I do appreciate the interest you show in the flight models.



Regards,

Malta


Some history about how I got to this point:

Landing with combat trim on makes for quite an adventure with the F4U, usually ending with a busted plane.  Using manual elevator trim centered while landing allows locking the tail wheel on touchdown and a normal landing, just as described in the pilot’s manual.  Without the tail wheel locked, the F4U (in particular) is pretty much impossible to taxi with.  As an aside, I have never used auto take-off.

[hitech]

stantond: Start from the basics.
The 4 forces generated by the engine are.

1. Torque. a rolling force.
2. Slip stream, produces both roll force oposit torque  and yaw force.
3. P Factor produces both pitch and yaw forces.
4. Gyroscopic both pitch and yaw forces.

Torque by itself does not produce a yaw tendency, only a roll, as straiga describs it does produce a secondary yaw force do to increase load on 1 tire but this is very minor force.

The major force involved when starting a take off roll is only slip stream.

P factor and gyro, do not have any effect at the start of a take off roll.

Torque is computed simply

(Current HP) / RPM * 5252

Also torque is produce fairly linar to the throttle setting and is effected very little by the engine speeding up or slowing down.

HiTech

[TequilaChaser]

Originally posted by stantond

Landing with combat trim on makes for quite an adventure with the F4U, usually ending with a busted plane.  Using manual elevator trim centered while landing allows locking the tail wheel on touchdown and a normal landing, just as described in the pilot’s manual.  Without the tail wheel locked, the F4U (in particular) is pretty much impossible to taxi with.  As an aside, I have never used auto take-off.

Malta,
got a spare copy of that F4U manual :-)

for those that use Auto Take Off, as soon as you launch to the runway if you quickly move your stick you will knock off the auto take off feature before it retrims the plane for auto take off........

anyhow, taking off and landing without locking tail wheel is easy once you get the hang of it,  low throttle and rudder use ( rudder back and forth ) until speed picks up and raises tail of the deck, then u set to go, when landing do a flare landing at around 100 IAS/TAS and cut throttle to 0 at touch down, then alternate braking C & V keys

don't use CT as you said, and if you try to use the tail wheel lock in game and are to fast on landing you gonna bounce and break up the landing....

[stantond]

HiTech,

Indulge me for a moment.  I will be happy to discuss torque physics and math with you if you want, but a more experimental and everyday experience approach might be clearer.  If you have a power drill, such as one made by Black and Decker or Makita at home... or better yet an angle grinder, try this out.  

Hold the drill with your hand along the axis where the electric motor turns.  For a hand drill, that would be the axis where the chuck rotates.  An angle grinder's motor axis would be the cylinder you grip.

Turn them on and off quickly.  The effect is very brief because the transient is fast.  That rotational movement surge against your hand is dynamic torque.  An angle grinder usually has more dynamic torque than a hand drill and you normally have to hold it more firmly.  A dremel motor tool also shows dynamic torque.

Mathematically, dynamic torque is defined as:

T=I*a, where T is torque in ft-lb, I is rotational moment of inertia and a is the rotational acceleration.

Not surprisingly this equation has the same form as F=ma (force = mass * acceleration).

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.  The more torque an engine has the faster it can accelerate a rotational load, or convert that rotational torque to changing the rotating speed of a propeller on an aircraft.

My point being, there is a dynamic torque due to an acceleration of inertia just like there is a dynamic force due to acceleration of mass (or pulling g's).  That dynamic comes from changing the engine speed.  Without a change in engine speed, there is no dynamic torque.  That is the torque I am talking about.  That is also the torque describing the 'ensign eliminator' effect for the F4U.

Sorry that was not clear earlier.  Unfortunately, I do not have numbers for the rotational inertia of a R2800 P&W engine.  



Regards,


Malta


p.s. TC,  I will email you or contact you through the Damned email list.