Question to Dudley Henriques RE: aileron use during takeoff

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Hobart Escin

Question to Dudley Henriques RE: aileron use during takeoff

Post by Hobart Escin »

Hi Dudley,

You detailed the following in your excellent takeoff guide posted here on the A2A forums:

"The kicker with aileron correction is that you need dynamic pressure on the ailerons to correct for the torque and if you reach a power setting that starts feeding in torque to your takeoff equation that your airspeed in the takeoff run (dynamic pressure AVAILABLE to the ailerons) isn't sufficient to handle, you won't have aileron available to help with the torque. It's notable that the amount of required right aileron for torque correction will vary somewhat in the A2A Mustangs as the inertia forces are changed a bit between the mil and civ versions. So don't just throw in a lot of right aileron. Let the airplane TELL YOU what it needs then give that to the airplane. This goes for BOTH aileron and rudder correction. The AIRPLANE will TELL YOU what it wants!!!!! Fly this way and you'll do just fine."

In the context of FSX and A2A's P-51 simulation, how does the desktop pilot get the proper 'feedback' from the virtual P-51 to sense how much aileron to use in the method you described? I can't quite fathom a way to effectively perceive the roll effect of torque on the ground during takeoff roll, and I end up trying to guess how much aileron to input as the sim aircraft unsticks and actually becomes airborne. I use rudder effectively to stay on centerline during takeoff, but I am at a complete loss as to how one can properly interpret what the A2A P-51 is needing aileron-wise to counteract torque on the ground. Perhaps the A2A Mustang is TELLING me what I need to do, but I'm not able to pick up on the right cues. :)

I read an article on R/W P-51 takeoff technique taught by the Stallion 51 school in Florida, and I seem to recall that the pilot author of that writeup mentioning that initially he was instructed to pull the stick back and fully to the right as power was applied, then gradually center the column as airspeed builds. This the technique I've adopted in the sim, and it works well enough in the context of FSX, but I really like your technique of reacting to the aircraft dynamically, instead of trying to anticipate control input ahead of time.

Thank you for whatever insight you can provide and also for your continued valuable input here at A2A.

EnDSchultz
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Re: Question to Dudley Henriques RE: aileron use during take

Post by EnDSchultz »

I know this was addressed to Dudley, but for my part, I just put in a few degrees of right aileron trim, somewhere between 3-5. That at least nulls out most of the roll tendency after liftoff that I'm not sure you can really feel for in the sim during the ground roll.

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DHenriques_
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Re: Question to Dudley Henriques RE: aileron use during take

Post by DHenriques_ »

Hobart Escin wrote:Hi Dudley,

You detailed the following in your excellent takeoff guide posted here on the A2A forums:

"The kicker with aileron correction is that you need dynamic pressure on the ailerons to correct for the torque and if you reach a power setting that starts feeding in torque to your takeoff equation that your airspeed in the takeoff run (dynamic pressure AVAILABLE to the ailerons) isn't sufficient to handle, you won't have aileron available to help with the torque. It's notable that the amount of required right aileron for torque correction will vary somewhat in the A2A Mustangs as the inertia forces are changed a bit between the mil and civ versions. So don't just throw in a lot of right aileron. Let the airplane TELL YOU what it needs then give that to the airplane. This goes for BOTH aileron and rudder correction. The AIRPLANE will TELL YOU what it wants!!!!! Fly this way and you'll do just fine."

In the context of FSX and A2A's P-51 simulation, how does the desktop pilot get the proper 'feedback' from the virtual P-51 to sense how much aileron to use in the method you described? I can't quite fathom a way to effectively perceive the roll effect of torque on the ground during takeoff roll, and I end up trying to guess how much aileron to input as the sim aircraft unsticks and actually becomes airborne. I use rudder effectively to stay on centerline during takeoff, but I am at a complete loss as to how one can properly interpret what the A2A P-51 is needing aileron-wise to counteract torque on the ground. Perhaps the A2A Mustang is TELLING me what I need to do, but I'm not able to pick up on the right cues. :)

I read an article on R/W P-51 takeoff technique taught by the Stallion 51 school in Florida, and I seem to recall that the pilot author of that writeup mentioning that initially he was instructed to pull the stick back and fully to the right as power was applied, then gradually center the column as airspeed builds. This the technique I've adopted in the sim, and it works well enough in the context of FSX, but I really like your technique of reacting to the aircraft dynamically, instead of trying to anticipate control input ahead of time.

Thank you for whatever insight you can provide and also for your continued valuable input here at A2A.
You have discovered one of the major differences between real flight and flight in the simulator.
First the problem; In BOTH cases involving aileron we have to correct for the EFFECT of torque with a correction in roll. In the real airplane we judge the amount of correction required during the run either by starting the run with the stick displaced into the anticipated direction then bleed it off during the run as the airplane "tells us" the amount of aileron we have in isn't needed and is excessive. In the real airplane we can do the reverse as well by starting the run with just a small amount of anticipated correction then adding it in as the airplane again "tells" us" we need more correction. In BOTH cases we are using dynamic pressure as the "tool" in getting the job done.
Now we enter the simulator; what's missing in the equation here is the dynamic pressure. It's present of course in the code but we can't feel it.
What we DO have working for us in the sim is eyesight which is an important cue for both the sim AND the real aircraft on the takeoff roll.
So what we have in the sim is a degraded cue system but a cue system nonetheless.
Using our eyesight in the sim, we will be more reactive as opposed to pro-active with the torque correction but it's more than doable . You can actually use the same technique as you would in the real plane but in the sim the corrective action will be more aggressive visually...more "sensitive".
The best technique for the sim has to be altered just a bit at the start of the run due to an FSX bug that's been in the program for eons. As you power up a tail wheel airplane in FSX you usually get a slight yaw to the RIGHT before you get the left yaw requiring right rudder to correct. What I usually do is relax the rudder when this happens rather than correct it and just hold it straight anticipating the left yaw THEN requiring the right rudder to correct that. Everything has to be done VERY smoothly. The slightest aggressive rudder will slew the airplane.
For the torque I simply have the stick slightly right and aft of neutral just enough to lock the tail wheel then playing the tail wheel off the ground as the power comes on up.
Torque if programmed correctly comes in play at around 75mph where the dynamic pressure WOULD be coming on line aerodynamically in the real plane. I simply watch the nose through the run keeping the wings level with whatever the airplane is telling me.
Bottom line is that the sim is more reactive than proactive but the visual cues are still in play and enough if you correct smoothly.
Dudley Henriques

Hobart Escin

Re: Question to Dudley Henriques RE: aileron use during take

Post by Hobart Escin »

Dudley,

Thank you for taking the time to respond. What you have explained makes perfect sense and I will practice honing my visual cues in the A2A sim to counteract the torque-induced rolling moment by using proper "reactive" aileron input as you described.

I have a follow up question in regard to the real P-51 (when you have time). What kind of force do you experience in the real Mustang that lets you interpret how effectively you are counteracting the torque roll moment on takeoff when moving the ailerons? In other words, does the stick force lessen or increase as you neutralize torque effect in the roll plane? As I try to visualize this in my head, it would seem that stick force would require increasing pressure (pilot reacting dynamically) as the effect of torque builds, but then taper off at the point where torque is neutralized enough to unload the left main gear, essentially balancing out the aircraft into a wings level state when unstick occurs. Again, I fully realize that this is not applicable to FSX for the reasons you mentioned; I just enjoy learning about the technique used in R/W P-51 flight.

Thanks again for all your help and knowledge.

Hobart Escin

Re: Question to Dudley Henriques RE: aileron use during take

Post by Hobart Escin »

EnDSchultz wrote:I know this was addressed to Dudley, but for my part, I just put in a few degrees of right aileron trim, somewhere between 3-5. That at least nulls out most of the roll tendency after liftoff that I'm not sure you can really feel for in the sim during the ground roll.
Crud, now you have me wondering why the P-51 POH (both sim and real-world) specifies zero degrees aileron trim for takeoff, but six degrees trim for right rudder. I understand that the rudder trim setting specification has more to do with being pre-trimmed for climbout rather than counteracting torque yaw on takeoff roll, but why not aileron trim too for unloading torque on takeoff like you mention? If it works in the sim it seems like it would work in the R/W. :?:

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DHenriques_
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Re: Question to Dudley Henriques RE: aileron use during take

Post by DHenriques_ »

Hobart Escin wrote:Dudley,

Thank you for taking the time to respond. What you have explained makes perfect sense and I will practice honing my visual cues in the A2A sim to counteract the torque-induced rolling moment by using proper "reactive" aileron input as you described.

I have a follow up question in regard to the real P-51 (when you have time). What kind of force do you experience in the real Mustang that lets you interpret how effectively you are counteracting the torque roll moment on takeoff when moving the ailerons? In other words, does the stick force lessen or increase as you neutralize torque effect in the roll plane? As I try to visualize this in my head, it would seem that stick force would require increasing pressure (pilot reacting dynamically) as the effect of torque builds, but then taper off at the point where torque is neutralized enough to unload the left main gear, essentially balancing out the aircraft into a wings level state when unstick occurs. Again, I fully realize that this is not applicable to FSX for the reasons you mentioned; I just enjoy learning about the technique used in R/W P-51 flight.

Thanks again for all your help and knowledge.
It lessens. As the dynamic pressure builds up relative to airspeed the stick forces become more effective using less force. Also the torque force lessens as you build up airspeed. It's most powerful at low speed high power. The correction is actually based on the visual cue basically. You can anticipate of course because you know where the correction will be targeted. It's a combination of anticipation and reaction to what the airplane is telling you.
The trick with this is not to get too bogged down in the physics where you can over work the problem.
When I'm discussing takeoffs in the Mustang with a new pilot flying one what I usually say is "just do what it takes to keep it straight and level during the run".
DH

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DHenriques_
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Re: Question to Dudley Henriques RE: aileron use during take

Post by DHenriques_ »

Hobart Escin wrote:
EnDSchultz wrote:I know this was addressed to Dudley, but for my part, I just put in a few degrees of right aileron trim, somewhere between 3-5. That at least nulls out most of the roll tendency after liftoff that I'm not sure you can really feel for in the sim during the ground roll.
Crud, now you have me wondering why the P-51 POH (both sim and real-world) specifies zero degrees aileron trim for takeoff, but six degrees trim for right rudder. I understand that the rudder trim setting specification has more to do with being pre-trimmed for climbout rather than counteracting torque yaw on takeoff roll, but why not aileron trim too for unloading torque on takeoff like you mention? If it works in the sim it seems like it would work in the R/W. :?:
The general setting most of us use in the civilian 51 community is 6-0-0. Leaving the aileron trim neutral allows you to "feel" the airplane from a neutral starting point. With trim in for roll, it's harder to judge how much correction is needed when coupled with the other "tools" you have in play correcting for torque. Personally I liked to keep the left main gear on the ground as long as I could as it helps a lot with torque correction. Lift that wheel too soon at slow airspeed and high power and it can cause a lot of problems in a hurry.
DH

Hobart Escin

Re: Question to Dudley Henriques RE: aileron use during take

Post by Hobart Escin »

Thanks for all of your insight Dudley; this really makes the A2A sim a lot more enjoyable through understanding the concepts and techniques you use on the real P-51. Regarding the A2A Mustang and the FSX initial pull to the right bug you mentioned, what I personally do is simply use just enough power to begin the takeoff roll at a fast taxi speed (about 1500 RPM) and wait for the buggy right yaw thing to work itself out (correcting all the while with modest left rudder to stay on centerline). Then, when I feel the right yaw kink fiddle out, I throttle up and correct with right rudder throughout the remainder of the takeoff.

What I like about this method is that by the time I reach 20 inches MP and above, I am on right rudder from then on and I can deal with the now correct left yaw tendency as would a real P-51 pilot. FSX seems to somehow factor in airspeed in regard to the buggy yaw behavior, and once you are about about 20 KIAS or so the erroneous right yaw tendency goes away.

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DHenriques_
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Re: Question to Dudley Henriques RE: aileron use during take

Post by DHenriques_ »

Hobart Escin wrote:Thanks for all of your insight Dudley; this really makes the A2A sim a lot more enjoyable through understanding the concepts and techniques you use on the real P-51. Regarding the A2A Mustang and the FSX initial pull to the right bug you mentioned, what I personally do is simply use just enough power to begin the takeoff roll at a fast taxi speed (about 1500 RPM) and wait for the buggy right yaw thing to work itself out (correcting all the while with modest left rudder to stay on centerline). Then, when I feel the right yaw kink fiddle out, I throttle up and correct with right rudder throughout the remainder of the takeoff.

What I like about this method is that by the time I reach 20 inches MP and above, I am on right rudder from then on and I can deal with the now correct left yaw tendency as would a real P-51 pilot. FSX seems to somehow factor in airspeed in regard to the buggy yaw behavior, and once you are about about 20 KIAS or so the erroneous right yaw tendency goes away.
:-) What you have just described is exactly the same way I handle FSX and takeoffs in the Mustang.
In real life you of course don't have this little right yaw bug. The technique there is almost the same however with the exception of the initial right correction of course.
The best technique for take off in any high powered fighter is modulated power application. You get it started slowly, let the airplane stabilize, feel positive pressures and feel for corrective action coming on line, then bring it on up slowly while correcting as necessary.
In the Bearcat where you don't lower the nose very much during the takeoff run due to the prop clearance, you can actually almost be airborne before you reach the recommended manifold pressure setting for takeoff.
Even in the Mustang, I've made takeoffs where for some reason or other I've allowed a rotation before reaching the full 55 inches available to me.
Dudley Henriques

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