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DCS P-51D Landing Physics and Ground Handling


midnabreu
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DCS Devs,

 

 

Thanks DCS DEVS for creating an amazing Mustang!!!

 

I would appreciate if you reconsidered augmenting the P-51D ground handling and landing characteristics.

Despite these constructive criticisms, thank you for the excellent and realistic flight model and combat environment.

 

- Burner

 

Potential Issues to look at...

 

  • Pronounced bounce on landing and take off (may be due to aft center-line tank causing extreme aft CG that the WWII Mustang was notorious for)
  • Overly sensitive unlocked tail wheel steering (suggested you lower sensitivity by 50-70%)
  • Overly sensitive brakes even with axis curve adjustments (suggested you lower sensitivity by 50-70%)

 

FLIGHT CHARACTERISTICS (Page 101)

As new equipment was added to the aircraft over the course of its development, in particular the radio equipment and the fuselage tank installed aft of the cockpit, the center of gravity (CG) has been moved back. This has resulted in decreased back pressure required to move the control stick. Instead of a force of 6 lbs. per G of acceleration, the required force in the P-51D is only 1 ½ lbs. Additionally, the stick forces begin to reverse as acceleration exceeds 4G. Great care must be taken not to black out or over-stress the airframe in sharp pulls and turns.

 

Special Flight Conditions (Page 107)

Full Fuselage Tank

Special care must be taken with the control stick when the fuselage tank contains more than 25 gallons of gas. In such cases, the flying characteristics of the aircraft change considerably – increasingly so as the amount of fuel in the tank is increased. When carrying more than 40 gallons of fuel in the fuselage tank, it’s necessary to avoid any high performance maneuvers. The fuel weight shifts the CG back, making the aircraft highly unstable during maneuvering.

 

 

kDtpvNe1XJc

 

 

 

Notice the very hard landing in real life and how the shock absorbers take the extreme hit. (The bounce was due to the mini grass ramp causing the aircraft to launch back in the air). This initial touchdown is made at 500-700fpm in my opinion and the absorbers do an excellent job.

 

Even with the forceful impact, the Mustang bounces about 2 feet in the air, thats it. The DCS Mustang bounces 10 feet on a 200 fpm decent.

 

 

 

EDIT: I went back and checked the original AAF MANUAL 51-127-5 and it does recommend FULL FLAPS on normal landings. Using full flaps fixes any of the adverse conditions mentioned in this critique. Thanks to all who are helping to resolve this and hopefully we can finally put this argument to rest. Also page 131 of the DCS manual does recommend full flaps for normal landings, so obviously I need to read the manual

 

Note: This test only applies to the TF-51 with a more forward CG than the regular P-51D.

The significant bounce is still apparent in the P-51D model.

 

***After some more testing of the TF-51/P-51D, I am almost certain this is a CG issue. The nose just wants to come up.

You have to shove the nose down past neutral to keep it on the ground. Also, during take off, the aircraft nose

wants to rise which it should want to fall initially.

 

 

 


Edited by midnabreu
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I must say, I find the DCS models have considerable breakaway power requirements, need more differential brake than I would have thought, are oddly tricky to turn accurately and do bounce a fair amount. There may be some kind of point here. But hey...cue the FSX bashing :)

 

I'm amazed at how much differential brakes the FW190 needs to taxi accurately around sharper corners, the 51 too. Try doing smooth accurate S turns down a taxiway, I can't really get it to feel like I would expect, and easily ends up in a jerky brake fest (in the beginning at least, now I can kind of 'work around' it). I have taxied a Supercub, Cub, and Harvard IRL, none of which needed even close to the amount of differential braking I need in the DCS models. There you only needed differential brakes if you were really doing very tight turns, ie with one wheel almost stationary. I must say the Harvard needed a HUGE effort on the pedals to get it to turn, but of course we don't get that in the sim...

 

Anyway, based on past performance, this'll be a huge thread that doesn't really go anywhere :D :D

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You're forgetting saitek rudder pedals that have a tendency to apply a wheel brake when they're in the mood just to make it more interesting taking off and landing (well mine do).

 

I'd sent them in. My Saitek pedals work absolutely fine.



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@ OP: Nothing wrong with the struts IMO. I had similar results when first attempting to land in DCS. Couldn't pull a two pointer for the love of it and it bounced all over the place. Then I read how one should land tail draggers.

 

With its CoG being behind the main wheels the plane will want to drop its tail upon landing. What other sims have taught us is to pull back on the stick when landing / flare. This is the opposite of what you should do once you feel the wheels touching the ground. Simply center the stick and all should be fine. Even if you do bounce it shouldn't be hard to recover if you know what to expect. The trick is "knowing" where the ground is. I usually center the stick half a second before anticipating the wheels will touch the ground. After you do it a couple of times you will find that you can really "drop" her on the ground and struts will absorb it. Makes up for landings on the unpaved and short runways.

 

Also worth mentioning is that the TF-51D is easier to land since it doesn't have a center fuel tank resulting in different CoG. At least from my experience (another squad mate shares this view).

 

 

... There you only needed differential brakes if you were really doing very tight turns, ie with one wheel almost stationary. I must say the Harvard needed a HUGE effort on the pedals to get it to turn, but of course we don't get that in the sim...

 

The only reason I use differential braking in P-51. Steerable tail wheel with its 6° of movement and a touch of brake in the direction where I am turning is almost always enough. Perhaps I am spoiled with my equipment. Those Crosswinds really do enable accurate control.


Edited by T}{OR

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WWII bomber formations | DCS P-51D: [TEST] TO distance / gross weight / temperature

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You're forgetting saitek rudder pedals that have a tendency to apply a wheel brake when they're in the mood just to make it more interesting taking off and landing (well mine do).

 

This works extremely well Altflieger. Check your brakes with Right CTRL ENTER

 

My Saitek Brake Axis Fix

DeadZone 0

Saturation X 80

Saturation Y 100

Curvature 0

Slider Checked!

Invert Checked!

 

 

 

 

 

EEkz, thanks for posting these video demonstrations. The point of my analysis is not to show that you can do a smooth landing,

but rather to demonstrate that the shock absorbers may be way over powered causing a unrealistic bounce.

 

In real life flying, the only time I've seen bounces are when you touch down too fast or too hard.

In the videos we touch down at 120 mph and 150 mph which is higher than the 90 mph -100 mph recommended speed. The overspeed should cause the bounce, not a 100-200 fpm decent. Its interesting in the TF-51 you touch down at 200 fpm and no bounce occurs.

 

 

 

I must say, I find the DCS models have considerable breakaway power requirements, need more differential brake than I would have thought, are oddly tricky to turn accurately and do bounce a fair amount. There may be some kind of point here. But hey...cue the FSX bashing :)

 

I have taxied a Supercub, Cub, and Harvard IRL, none of which needed even close to the amount of differential braking I need in the DCS models. There you only needed differential brakes if you were really doing very tight turns, ie with one wheel almost stationary. I must say the Harvard needed a HUGE effort on the pedals to get it to turn, but of course we don't get that in the sim...

 

Anyway, based on past performance, this'll be a huge thread that doesn't really go anywhere :D :D

 

Glad your bringing your real life experience with taildraggers. I can slam my real life Cessna 172 down at much harder descents shown with the DCS P-51 on short field approaches and not bounce as long as the speed is bleed off and throttle is cut. The airplane simply doesn't have any flying speed left. This is not how the DCS P-51 behaves at all.

 

My vision for this thread was to hopefully address this issue (and get the DCS DEVS attention) before the DCS WWII market takes off. Thanks again for the input.


Edited by midnabreu
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With its CoG being behind the main wheels the plane will want to drop its tail upon landing. What other sims have taught us is to pull back on the stick when landing / flare. This is the opposite of what you should do once you feel the wheels touching the ground. Simply center the stick and all should be fine.

 

Right, this is proper landing technique and I do mention that in the video. In these demos I do center the stick and it still produces a prominent bounce.

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I'm also somewhat curious about ground handling aspect of both simulations. I've never played FSX (my last experience with MS physics dates back to CFS2), so I cannot comment on this one. Have to admit, however, that DCS is the first sim I've "learned", which tries to simulate inherent directional instability of an aircraft with taildragger gear layout while taxying. That, coupled with noticeable differences in rudder authority depending on velocity of propstream, was quite a challenge for me when I was first trying to tame the Mustang in unlocked-tailwheel mode (still is to some extent, because I don't have proper rudder pedals).

 

I quite like it though - for me it's the first sim with warbirds, in which differential braking is not a gimmick but a necessity and where the term "groundloop" is a real danger rather than something I know only from the books and films. Is this effect a bit overdone in DCS? Or maybe it's not pronounced enough in FSX? Which one is closer to the truth I wonder. To answer it, we would have to find someone rich and stupid enough to do some ham-fisted ground handling tests on the real P-51 :D.

 

Having said that, I'm sure different aspects of physics modelling are going to be tuned many times during development of the remaining WWII plane modules, both before and after their release.

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

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This works extremely well Altflieger. Check your brakes with Right CTRL ENTER

 

My Saitek Brake Axis Fix

DeadZone 0

Saturation X 80

Saturation Y 100

Curvature 0

Slider Checked!

Invert Checked!

 

 

 

 

 

 

EEkz, thanks for posting these video demonstrations. The point of my analysis is not to show that you can do a smooth landing,

but rather to demonstrate that the shock absorbers may be way over powered causing a unrealistic bounce.

 

In real life flying, the only time I've seen bounces are when you touch down too fast or too hard.

In the videos we touch down at 120 mph and 150 mph which is higher than the 90 mph -100 mph recommended speed. The overspeed should cause the bounce, not a 100-200 fpm decent. Its interesting in the TF-51 you touch down at 200 fpm and no bounce occurs.

 

 

 

 

 

Glad your bringing your real life experience with taildraggers. I can slam my real life Cessna 172 down at much harder descents shown with the DCS P-51 on short field approaches and not bounce as long as the speed is bleed off and throttle is cut. The airplane simply doesn't have any flying speed left. This is not how the DCS P-51 behaves at all.

 

My vision for this thread was to hopefully address this issue (and get the DCS DEVS attention) before the DCS WWII market takes off. Thanks again for the input.

 

Sorry, is Cessna 172 a taildragger?

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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Included additional analysis video in first post. 20 degrees should be used for normal landings and full flaps for short field.

 

EDIT: I went back and checked the original AAF MANUAL 51-127-5 and it does recommend FULL FLAPS on normal landings. Using full flaps fixes any of the adverse conditions mentioned in this critique. Thanks to all who are helping to resolve this and hopefully we can finally put this argument to rest. Also page 131 of the DCS manual does recommend full flaps for normal landings, so obviously I need to read the manual


Edited by midnabreu
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Sorry, is Cessna 172 a taildragger?

 

Its not a question of it being a tail dragger. Its a matter of the shocks absorbing impact of which the P-51 has enormous shocks. If you have flown an aircraft in real life, you know that too much energy and an excessively hard landing are what produce a bounce.

 

The Mustang should NOT be bouncing on a gentle touchdown. Thats the point Yo-Yo.


Edited by midnabreu
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This issue may have to do with full flaps which should NOT be used on normal landings, just short field landings typically.

 

Nice flying. :thumbup:

 

That is another thing that I started doing when flying in DCS is lowering full flaps every time I land. Yeah, less than full flaps will make it a bit harder.

 

On this note I started looking at YT videos and P-51 landings. Almost all of them feature full flaps, be it a two or three point landing.


Edited by T}{OR
typo

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WWII bomber formations | DCS P-51D: [TEST] TO distance / gross weight / temperature

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On this note I started looking at YT videos and P-51 landings. Almost all of them of them feature full flaps, be it a two or three point landing.

 

Your absolutely right. I looked at the original Mustang Pilot Operating Handbook as well as a 1944 Pilot notes handbook....even the F-51D handbook recommends full flaps on normal landings. This technique seems to lower the noise and wings into the airflow and keep the Mustang down.

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Interesting. I started using full flaps since it helped me control the thing and after watching YT videos. Didn't know it was recommended.

 

Another thing, after watching A2A video they recommend 2° nose down trim for an empty center fuel tank. I found that even 1° is enough in DCS when taking off with no flaps. You can keep her on the runway as much as you want if you trim nose down.

 

Haven't tested it with TF-51D. That one should have CoG more forward due to not having the fuel tank behind a pilot and thus no trim is required from my experience / DCS tests.

P8Z68 | 2500k @ 4.5 | GTX 1080Ti | 2x8 GB @ 1600 | TM Hog (extended 7cm) & MFG Crosswind (S/N 007) | TIR v5

WWII bomber formations | DCS P-51D: [TEST] TO distance / gross weight / temperature

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The shock absorbers don't absorb energy, despite their name. If there's too much energy on touchdown, you're going to bounce. They bleed off some energy with movement but not a whole lot. It doesn't take much to bounce a plane in real life. Been there, done that. It's terrifying. If you're bouncing, you have too much energy. Airspeed, sink rate, combination of both, same thing, inertia....

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Its not a question of it being a tail dragger. Its a matter of the shocks absorbing impact of which the P-51 has enormous shocks.

 

So you don't understand why a tail dragger bounces when it is put down on the main wheels? You actually think it is the shock absorbers catapulting it back in the air?

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So you don't understand why a tail dragger bounces when it is put down on the main wheels? You actually think it is the shock absorbers catapulting it back in the air?

 

I do understand why a real life taildragger bounces, I think Ive explained this numerous times already. It has nothing to do with touching on the main wheels (regardless if its a 2 point or 3 point landing) or the airplane being a tail dragger. Like it has been stated previously, tricycle landing gear can bounce as well.

 

I was referring specifically to the DCS Mustang flight model being potentially catapulted by the coded shock absorbers (this was a theory). Real aircraft bounce due to airspeed and decent rate. You can even bounce on a crosswind with sideloading on the gear.


Edited by midnabreu
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Interesting. I started using full flaps since it helped me control the thing and after watching YT videos. Didn't know it was recommended.

 

Another thing, after watching A2A video they recommend 2° nose down trim for an empty center fuel tank. I found that even 1° is enough in DCS when taking off with no flaps. You can keep her on the runway as much as you want if you trim nose down.

 

Haven't tested it with TF-51D. That one should have CoG more forward due to not having the fuel tank behind a pilot and thus no trim is required from my experience / DCS tests.

 

***After some more testing of the P-51D, I am almost certain this is a CG issue. The nose just wants to come up. You have to shove the nose down past neutral to keep it on the ground. Also, during take off, the aircraft nose wants to rise which it should want to fall initially.

 

You have to go forward past neutral (which is where I think its behaves incorrectly) in the DCS Mustang to keep her on the ground.

Trimming down 1° absolutely helps in the DCS to keep the nose down.


Edited by midnabreu
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Do try it with TF-51D. Without center fuel tank its CoG lies move forward and it doesn't need any forward trim.

 

IIRC P-51D is some 600lb heavier than the TF-51D when both completely empty. With 68% fuel and 100% ammo (usual default loadout) - the difference is close to 1200lb.

 

 

Here is the A2A vid I was talking about:

 

From A2A, elevator trim required:

  • No fuselage tank: 0°
  • Empty fuelage tank: +2° (For DCS I wouldn't recommend more than 1°)
  • Full fuselage tank: +4°

 

If you want an interesting take off, load it up with fuel and external tanks. :)


Edited by T}{OR

P8Z68 | 2500k @ 4.5 | GTX 1080Ti | 2x8 GB @ 1600 | TM Hog (extended 7cm) & MFG Crosswind (S/N 007) | TIR v5

WWII bomber formations | DCS P-51D: [TEST] TO distance / gross weight / temperature

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I do understand why a real life taildragger bounces, I think Ive explained this numerous times already. It has nothing to do with touching on the main wheels (regardless if its a 2 point or 3 point landing) or the airplane being a tail dragger. Like it has been stated previously, tricycle landing gear can bounce as well.

 

I was referring specifically to the DCS Mustang flight model being potentially catapulted by the coded shock absorbers (this was a theory). Real aircraft bounce due to airspeed and decent rate. You can even bounce on a crosswind with sideloading on the gear.

 

Sorry, but you are deeply wrong... there is a great, profound difference between the tricycle gear plane and the tail dragger. The difference is in their CG position. As you can see, the taildragger has it aft the main wheels, tricycle - forward. (Why am I explaining it... there are a lot of sites where taildragger guru tell the same!).

 

So, the bouncing for these two types is very different too. For example, you have two identic planes but for our experiment having different undercarriage - tricycle and with the tailwheel (1 and 2 types, for convenience).

Let's consider that both planes have the same touchdown attitude - a little bit tail-heavy - to avoid nose wheel touching first for the type 1.

As you touch the ground having vertical speed, reaction forces that acts to the wheels will try to rotate airplanes around the CG that keeps moving down. But in different directions: type 1 to pitch-down reducing AoA and lift and pitch-up for type 2 INCREASING AoA and lift.

Just to clarify about CG keeping moving down - it's pure physics. Nobody can change velocity vector without applying a force during a certain time. That's why it's a true that shock absorbers do nothing during the first phase of struts compression in a touchdown. They only prolong the interaction reducing force acting to the airframe, but the whole impulse or momentum will be the same.

So, the main source of bouncing (I'd say - ballooning!) of the taildragger is not its undercarriage reaction but LIFT created with the excessive speed and increased AoA as a result of reaction forces.

TYpe 1 automatically reduces AoA allows to do nothing with the stick at touchdown. Type 2 requires stick forward light movement at touchdown to glue the plane to the ground. Some risky guys even use to brake wheels a little before touchdown

By the way, you noticed that DCS P-51 has differences at 2-point landing depending on its weight. If you try 7-8% that is typical for real life airshow landing you will see that it's way easier. If you try TF-51 that is lighter that P-51 because of removed armour, radio, guns, ammo boxes, etc., you will see that it's much easier.

 

Regarding the forgiving behavior of A2A... I can only suggest that they have the model CG closer to the main wheels than real plane has. DCS P-51 has it exactly where it must be regarding weigh and balance documents.

One could argue that moving CG forward will lead to earlier nose down rotating while applying power with main wheels braked. Yes, it is possible, but the trick is that it's very dependable on slipstream modelling... DCS simulation has it very detailed and true, for example.


Edited by Yo-Yo

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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I do understand why a real life taildragger bounces, I think Ive explained this numerous times already. It has nothing to do with touching on the main wheels (regardless if its a 2 point or 3 point landing) or the airplane being a tail dragger. Like it has been stated previously, tricycle landing gear can bounce as well.

 

I was referring specifically to the DCS Mustang flight model being potentially catapulted by the coded shock absorbers (this was a theory). Real aircraft bounce due to airspeed and decent rate. You can even bounce on a crosswind with sideloading on the gear.

 

If I may make a suggestion, please read "Stick and Rudder" by Wolfgang Langeweische. He explains very well on how to fly prop powered tail draggers and to debunk some of the myths as well as as pointing out and correcting common mistakes of flying.

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May I suggest something to those having problems with the bouncing. In a taildragger upon touchdown: CG goes down, AoA increases, lift increases, bump! So, try performing a stall landing. It will decrease airflow so much that even the inherent nose-up should not produce any significant bump.

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