P38 manual trim

[BnZs]

That's the nice thing about the Lightning, you don't need to mess with rudder or aileron trim at all, the only exceptions is if you have battle damage then trimming rudders or aileron might make it easier to home.


ack-ack

Yep. As a guy who hasn't invested in pedals yet, I've honestly wished at times you could turn CT off by axis, I'd just leave it on for rudder trim in single engine planes, it not being any big deal for elevator and aileron to be slightly out of perfect trim.

[nimble]

Did a few flights last night in the L, worked out very well. Very fun ride once you get used to the size. I was definately happy with the rudder control when nosing back over after a rope. Had an LA7 chasing me at about 8k co-e(or close enough) and was able to maintain that for half a sector or so by putting myself into a slight climb around 1.2k/min. It was the general fast plane/TnB setup to catch a con, in this case LA7 and spit16. Got enough distance to finish off the LA before the spit got back into icon range.

 The only real problems I am having so far is with my gunnery with the nose mounted guns and creating overshoots, the latter most likely because my main ride has been the p47. Didn't have too many problems with compression once I found the speed she starts locking up at, and the elevator remained functional even when the airframe started shaking(at least in a moderate equalize E with a con on 6 dive). Rolling scissors in it is definately much different than in the p47, but I can see myself getting very used to the rudder and extra vert. The high speed handling gave me little problems when I forgot I wasn't in a jug and tried to make a ki84 compress and move around to his 6 in a defensive spiral, recovered easily.

 Overall I definately like the ride a lot, just need to work on my gunnery with the nose mounted gun and remember it's a p-38 and not a jug. If anyone has tips on the gunnery aspect other than practice lemmee know! Thanks for all the input so far, appreciated as usual!

[Traveler]

As I read the many responses it became clear to me that many do not understand the purpose of trim in an aircraft.
In order to discuss Trim and it’s effects you need to review the forces acting on an aircraft.
The aircraft lift is the sum of the lift of all of the parts of the airplane and acts through the aircraft center of pressure. Each part of the aircraft has its own lift component and its own center of pressure. The major part of the lift comes from the wings, but the horizontal stabilizer and elevator also produce lift which can be varied to maneuver the aircraft.
The average location of the weight of the aircraft is the center of gravity (cg). Any force acting at some distance from the cg produces a torque about the cg. Torque is defined to be the product of the force times the distance. A torque is a "twisting force" that produces rotations of an object. In flight, during maneuvers, an airplane rotates about its cg. But when the aircraft is not maneuvering, we want the rotation about the cg to be zero. When there is no rotation about the cg the aircraft is said to be trimmed.
On most aircraft, the center of gravity of the airplane is located near the center of pressure of the wing. If the center of pressure of the wing is aft of the center of gravity, its lift produces a counter-clockwise rotation about the cg. The center of pressure for the elevator is aft of the center of gravity for all aircraft in AH.  A positive lift force from the tail produces a counter-clockwise rotation about the cg. To trim the aircraft it is necessary to balance the torques produced by the wing and the tail. But since both rotations are counter-clockwise, it would be impossible to balance the two rotations to produce no rotation. However, if the tail lift is negative it then produces a clockwise rotation about the cg which can balance the wing rotation.
Let us look carefully at the torques produced by the wing and the tail. The torque from the wing TW is equal to the lift of the wing W times the distance from the cg to the center of pressure of the wing dw.
TW = W * dw
The torque from the tail TT is equal to the lift of the tail T times the distance from the cg to the center of pressure of the tail dt. The lift of the wing and the lift of the tail are both forces and forces are vector quantities which have both a magnitude and a direction. We must include a minus sign on the lift of the tail because the direction of this force is negative.
TT = -T * dt
In trimmed flight, these two torques are equal:
TW = TT
W * dw = -T * dt
W * dw + T * dt = 0
The torque equation, as written here, is a vector equation. All of the quantities are vector quantities having a magnitude and a direction. If the distances are both positive (same side of the center of gravity), then the direction of the tail force must be different than the direction of the wing force to produce no net torque or rotation. However, if the distance to the tail were negative, then the lift of the of the tail could be positive and there would be no net torque. A negative distance to the tail would imply that the tail is on the front of the aircraft, ahead of the center of gravity. A tail at the front of the aircraft is called a canard and was the configuration first used by the Wright brothers.
The total lift of the aircraft is the vector sum of the wing lift and the tail lift. For the AH Fighter, the total lift is less than the wing lift; for the Wright brothers, the total lift is greater than the wing lift. The added lift was important for the Wright brothers because their aircraft had a very small engine and flew at low speeds (35mph). Since lift depends on the square of the velocity, it is hard to generate enough lift for flight at such low speeds.

In other words when an aircraft is out of trim.  It is not performing at it’s peak.  The pilot would be using energy to control forces acting on the aircraft to counter rotation.  Putting in control surface movements that would not be necessary if the aircraft was trimmed.  An aircraft that is out of trim is slower then a trimmed aircraft.  As fuel burns the CG is always changing requiring changes to trim.  People that are flying in AH with CT off are flying out of trim 99% of the time.

[CAP1]

As I read the many responses it became clear to me that many do not understand the purpose of trim in an aircraft.
In order to discuss Trim and it’s effects you need to review the forces acting on an aircraft.
The aircraft lift is the sum of the lift of all of the parts of the airplane and acts through the aircraft center of pressure. Each part of the aircraft has its own lift component and its own center of pressure. The major part of the lift comes from the wings, but the horizontal stabilizer and elevator also produce lift which can be varied to maneuver the aircraft.
The average location of the weight of the aircraft is the center of gravity (cg). Any force acting at some distance from the cg produces a torque about the cg. Torque is defined to be the product of the force times the distance. A torque is a "twisting force" that produces rotations of an object. In flight, during maneuvers, an airplane rotates about its cg. But when the aircraft is not maneuvering, we want the rotation about the cg to be zero. When there is no rotation about the cg the aircraft is said to be trimmed.
On most aircraft, the center of gravity of the airplane is located near the center of pressure of the wing. If the center of pressure of the wing is aft of the center of gravity, its lift produces a counter-clockwise rotation about the cg. The center of pressure for the elevator is aft of the center of gravity for all aircraft in AH.  A positive lift force from the tail produces a counter-clockwise rotation about the cg. To trim the aircraft it is necessary to balance the torques produced by the wing and the tail. But since both rotations are counter-clockwise, it would be impossible to balance the two rotations to produce no rotation. However, if the tail lift is negative it then produces a clockwise rotation about the cg which can balance the wing rotation.
Let us look carefully at the torques produced by the wing and the tail. The torque from the wing TW is equal to the lift of the wing W times the distance from the cg to the center of pressure of the wing dw.
TW = W * dw
The torque from the tail TT is equal to the lift of the tail T times the distance from the cg to the center of pressure of the tail dt. The lift of the wing and the lift of the tail are both forces and forces are vector quantities which have both a magnitude and a direction. We must include a minus sign on the lift of the tail because the direction of this force is negative.
TT = -T * dt
In trimmed flight, these two torques are equal:
TW = TT
W * dw = -T * dt
W * dw + T * dt = 0
The torque equation, as written here, is a vector equation. All of the quantities are vector quantities having a magnitude and a direction. If the distances are both positive (same side of the center of gravity), then the direction of the tail force must be different than the direction of the wing force to produce no net torque or rotation. However, if the distance to the tail were negative, then the lift of the of the tail could be positive and there would be no net torque. A negative distance to the tail would imply that the tail is on the front of the aircraft, ahead of the center of gravity. A tail at the front of the aircraft is called a canard and was the configuration first used by the Wright brothers.
The total lift of the aircraft is the vector sum of the wing lift and the tail lift. For the AH Fighter, the total lift is less than the wing lift; for the Wright brothers, the total lift is greater than the wing lift. The added lift was important for the Wright brothers because their aircraft had a very small engine and flew at low speeds (35mph). Since lift depends on the square of the velocity, it is hard to generate enough lift for flight at such low speeds.

In other words when an aircraft is out of trim.  It is not performing at it’s peak.  The pilot would be using energy to control forces acting on the aircraft to counter rotation.  Putting in control surface movements that would not be necessary if the aircraft was trimmed.  An aircraft that is out of trim is slower then a trimmed aircraft.  As fuel burns the CG is always changing requiring changes to trim.  People that are flying in AH with CT off are flying out of trim 99% of the time.

enroute to a fight, i'm usually on auto pile-it, or auto climb, so i think that's keeping me in trim.

when i'm near a fight, and on manual control, i'm trimmed for "hands off" which i think also has me in trim.

when i'm flying in rl, i'm trimmed for the speed i want to fly at, and that's pretty much the same thing i do in ah.  

BTW... it is friggin GREAT when you guys come in here and put up good answers like these sir!! i mean that seriously, not being sarcastic.

thanks!

EDIT:

you mentioned "center of pressure"

if i read correctly, in the other p38 thread, that is what the dive recovery flaps changed on the p38's, in order to pitch the nose up, correct?

[Ack-Ack]

The high speed handling gave me little problems when I forgot I wasn't in a jug and tried to make a ki84 compress and move around to his 6 in a defensive spiral, recovered easily.

You can safely dive at high speeds in the P-38 without really having to worry about entering into full compressability.  I can safely dive my P-38J at speeds in excess of 450mph IAS without the controls locking up due to compressability.  The key is throttle control and rudders.  Rudders you may ask?  Those rudders on the P-38 are big and you can use them in conjuction with the throttle to help keep the plane at the edge of compressability. 

Another tip when diving in the P-38 (especially if in the G or the J) is to try and keep high speed dives below 20,000ft where the air is thicker and you won't enter into full compressability.  Take care if you're above 20,000ft when doing dives or in a nose low turn fight, throttle control is the key above this altitude.  You can somewhat get away with it in the L above 20,000ft but you still have to be careful because you can lose position and advantage if you get too fast and need the dive flaps to recover.


ack-ack

[Ack-Ack]

People that are flying in AH with CT off are flying out of trim 99% of the time.

Those of us the fly with CT off due so because of the way CT works in game.  CT has a negative effect on flaps on planes such as the P-38 or other 'flap dependent' planes.  Also, unless one is grossly out of trim, using manual trim over CT will not cause one to lose a fight or have any perceived negative effect.

In the single engine fighters in this game, using manual trim over CT is basically personal preference but using manual trim over CT in the P-38 is recommended for the reasons already stated by me and others in this thread.

Thanks for your post though, it's really informative and helps explain the whole concept of trim for an aircraft. 


ack-ack

[nimble]

You can safely dive at high speeds in the P-38 without really having to worry about entering into full compressability.  I can safely dive my P-38J at speeds in excess of 450mph IAS without the controls locking up due to compressability.  The key is throttle control and rudders.  Rudders you may ask?  Those rudders on the P-38 are big and you can use them in conjuction with the throttle to help keep the plane at the edge of compressability.  

ack-ack

I think in the case of the spiral I may have confused compression with roll rate. The shaking nearing compression in the 38 looks a lot more severe than what I am used to. Anyhow, in a jug when I enter the spiral I can usually keep an eye on the con on my 6 and wait for his speed to start making his spiral wider than mine, do a quick roll, cut inside for a snapshot, and still be able to regain E if I miss while he is still recovering to get out of his dive and level. I'm going to give this particular move a few more tries in the 38 using a bit more rudder to help my roll, but it might just not be a good move to make in the P-38. Small sacrifice if that's the case, just need to get some more practice in It am sure!

[Traveler]

Those of us the fly with CT off due so because of the way CT works in game.  CT has a negative effect on flaps on planes such as the P-38 or other 'flap dependent' planes.  Also, unless one is grossly out of trim, using manual trim over CT will not cause one to lose a fight or have any perceived negative effect.

In the single engine fighters in this game, using manual trim over CT is basically personal preference but using manual trim over CT in the P-38 is recommended for the reasons already stated by me and others in this thread.

Thanks for your post though, it's really informative and helps explain the whole concept of trim for an aircraft. 


ack-ack

I’ve noticed in several posts where you state that CT has a negative effect on flaps.  I think that’s the way you put it.  You do understand that lowering or raising flaps has changes the center of lift of the airfoil, that is what causes the pitch change.  When in straight and level flight if you slow the aircraft and lower flaps, the nose will pitch up.  It does so in all aircraft.  Like wise if you  remove flaps the nose will pitch down.  That’s why in flight training we instructors spend so much time on approaches and balked landings.  The FAA mandates that the student correct for pitch change with elevator input, not trim.

If you change he shape of the airfoil and change the center of lift, you will have to change the amount of trim you are using to maintain a desired airspeed.

[Ack-Ack]

I’ve noticed in several posts where you state that CT has a negative effect on flaps.  I think that’s the way you put it.  You do understand that lowering or raising flaps has changes the center of lift of the airfoil, that is what causes the pitch change.  When in straight and level flight if you slow the aircraft and lower flaps, the nose will pitch up.  It does so in all aircraft.  Like wise if you  remove flaps the nose will pitch down.  That’s why in flight training we instructors spend so much time on approaches and balked landings.  The FAA mandates that the student correct for pitch change with elevator input, not trim.

If you change he shape of the airfoil and change the center of lift, you will have to change the amount of trim you are using to maintain a desired airspeed.

This is from an old thread from about 5 years ago from a discussion similiar to this.

Actually AKAK, yes and no.  CT does not take things like dive flaps, and flaps into account.  It does effectively counter dive flaps by trimming elevators down, but it does it in relation to speed not pitch.  IIRC elevator CT is basically a table of speed/trim angle.  So when manuevering flaps are deployed CT ends up giving you extra positive pitch, because it is working numbers from a clean configuration.

Waits to be told Im wrong, and corrected by HT

Problem with Combat Trim is that in some planes it can hinder performance and the envelope where CT is effective in a lot of cases is small.  It doesn't work very well at high or low speeds and with multi-engine planes.  Lephturn used to have a site that had an excellent write up on the various trim modes with the pros and cons of each, unfortunately it no longer seems to be up.

ack-ack

[Traveler]

This is from an old thread from about 5 years ago from a discussion similiar to this.

Problem with Combat Trim is that in some planes it can hinder performance and the envelope where CT is effective in a lot of cases is small.  It doesn't work very well at high or low speeds and with multi-engine planes.  Lephturn used to have a site that had an excellent write up on the various trim modes with the pros and cons of each, unfortunately it no longer seems to be up.

ack-ack

I have no idea if the aircraft models have changed over the years.  My hope is that they would continue to improve.  Is todays aircraft model as it was 5 years ago?  I don't know.  Is it based on a table look up of airspeeds or on a calculation?  I have no idea.   

I was just pointing out a truth from  applied aerodynamics that the pitch up motion from the use of flaps is the results of the shift of the center of pressure and is unreleated to the use of trim.

[Ack-Ack]

I have no idea if the aircraft models have changed over the years.  My hope is that they would continue to improve.  Is todays aircraft model as it was 5 years ago?  I don't know.  Is it based on a table look up of airspeeds or on a calculation?  I have no idea.   

The way CT works hasn't changed since it's been implemented.  I believe it's based on a speed table rather than calculations.  Too bad that Lephturn's site is no longer up, it really went into detail on how CT works and the magic behind it.

I was just pointing out a truth from  applied aerodynamics that the pitch up motion from the use of flaps is the results of the shift of the center of pressure and is unreleated to the use of trim.

That's why I liked your post about it, it went into nice detail that was easy to understand.  It also helps to quelch to the myth that using trim will make your plane turn tighter.  In fact, when I see one of those posts, I'm just going to link my reply to your post on the trim explanation.


ack-ack

[FLS]

As I read the many responses it became clear to me that many do not understand the purpose of trim in an aircraft...
...People that are flying in AH with CT off are flying out of trim 99% of the time.

That's BS. The OP might not understand trim but he asked a good question about trim in the P-38 and the answers were correct.  CT is not required to fly trimmed 99% of the time even if many people have no idea what that little ball is for. CT is a nice utility if you know when to turn it off.

I’ve noticed in several posts where you state that CT has a negative effect on flaps.  I think that’s the way you put it.  You do understand that lowering or raising flaps has changes the center of lift of the airfoil, that is what causes the pitch change.  When in straight and level flight if you slow the aircraft and lower flaps, the nose will pitch up.  It does so in all aircraft.  Like wise if you  remove flaps the nose will pitch down.  That’s why in flight training we instructors spend so much time on approaches and balked landings.  The FAA mandates that the student correct for pitch change with elevator input, not trim. 

The FAA does not concern itself with Combat Trim or stall fighting. As many responses mentioned, CT will screw you up if you're going very fast or very slow. In those cases having elevator trim centered is a better option.

I'm sure your trim explanation would be a welcome addition to the AH wiki.

[CAP1]

another thing that many might not realize.....in real life these aircraft had "tabs" to adjust the trim.

 in the game, the entire control surface moves to adjust the trim.

i think,.

[FLS]

Cap you could just as well say that in the game, trim moves the stick or rudder pedals to the desired control surface deflection then moves the trim tabs to balance the forces on the control surface so that you can fly hands off the stick. It may be coded simply as a control surface movement since the result is the same. The spring centered joystick most people use tends to confuse the trim issue. If you use a yoke without spring centering you wouldn't have to use pitch and roll trim since you could just leave the yoke in it's "trimmed" position.

[CAP1]

Cap you could just as well say that in the game, trim moves the stick or rudder pedals to the desired control surface deflection then moves the trim tabs to balance the forces on the control surface so that you can fly hands off the stick. It may be coded simply as a control surface movement since the result is the same. The spring centered joystick most people use tends to confuse the trim issue. If you use a yoke without spring centering you wouldn't have to use pitch and roll trim since you could just leave the yoke in it's "trimmed" position.

it does move the stick and pedals.....watch em as you adjust.

i think there was another thread......there are no trim tabs modeled in the game.