DCS P-51D Landing Physics and Ground Handling

[midnabreu]

I understood the manual always recommending 3 point approach due to shorter landing on short improvised airstrips. There is no recommended landing speed approach for a two point landing. All mentioned landing recommendations are for 3 point attitude.

 

You absolutely right, there is no recommended 2 point approach speed. I guess we just did what WWII pilots did and test the aircraft in the field as the POH had basic limited information. Interesting, I found these historical Mustang pilot notes, http://www.avialogs.com/index.php/en/aircraft/usa/northamericanaviation/p-51mustang/nzap-2025h-pn-pilots-notes-for-mustang-p51d.html....

 

The documents on page 38 suggests that "the touchdown should be made as gently as possible, and the throttle closed only when the aircraft is on the ground." So you were right brother!

 

Also, historical video

states that if any bounce occurs, the pilot MUST go around, period.

[[DBS]TH0R]

Nice find! What is also interesting is that in both the historical Mustang pilot notes and the training video from ZenosWarbirds they recommend heavy nose up elevator trim for take off. This is in direct contrast to our findings in DCS and what is recommended in A2A's familiarization video.

 

Page 32 defines three different cases depending on the loadout - A, B and C.

 

I am away from my gaming rig until next week, but I am very interested in trying TO with these trim settings. The two possible reasons for using these settings, based on my current DCS P-51D experience, would be to attempt a three point take off (useful for muddy and short runways) or to help with holding the tail down for more directional control on TO.

 

I did try "Case A" TO once without holding the stick back and with A2A's recommended 6° nose down trim - the plane refused to taxi straight without tail wheel lock and stick fully back. :)

[chaos]

Enjoyed the discussion sofar. Pro's and cons to each side without either side resorting to yelling and name-calling. I've been wondering about the same issues for some time and I'd love to join the debate. I've flown the P-51 with keyboard/mouse and a CPU from way-back-when so it wouldn't be fair to make any comments . I always thought something was wonky about the FM in the low-speed regime though.

 

MFG pedals are waiting to be hooked up. Money for Rift CV1 set aside. Wishlist for new PC prepared. No matter what... i'll have a brand new PC by the end of January! :-)

Edited October 3, 2014 by chaos

[[DBS]TH0R]

You won't regret going with MFG-s. Milan has perfected the design over the year or so since they hit the market. Its not just the ergonomics and precision - CAM profile is what really makes them stand out.

 

Speaking of this discussion, I too have been enjoying it and as midnabreu calls it, his "journey". :)

 

I remember my first couple landings in DCS P-51D thinking "this can't be right..." - but after hours of practice and some reading how you should treat a tail dragger no other sim was the same for me since. After following what the manual recommends I wasn't able to land any other way but in 3 point attitude. DCS being what it is - I started watching YT P-51 landings and studded them before finding what works and what doesn't. It took some re-learning and letting go of the bad habits learned in IL21946.

 

A thing worth noticing, when I was teaching a squad mate of mine how to land a two pointer he failed on several first attempts. Also coming in too low and too slow. He then tried TF-51D and nailed it from first attempt. Took a bit longer to do it with P-51D.

[midnabreu]

It took some re-learning and letting go of the bad habits learned in IL21946.

 

Thats interesting Thor, I actually used the power until wheels touch technique in the IL2 1946 Mustang, and it gave me much greater control in a 2 point landing (which I always do for the most part). :smartass:

[[DBS]TH0R]

Thats interesting Thor, I actually used the power until wheels touch technique in the IL2 1946 Mustang, and it gave me much greater control in a 2 point landing (which I always do for the most part). :smartass:

Hehe, yeah I used to do it too occasionally only realizing is importance in DCS's P-51. But that is not what I am referring to. IL21946 doesn't have a CoG that shifts on account of ordinance dropped, fuel used and tank switching (all planes use one fuel tank). Tail wheel physics are basic, no proper differential breaking, and most importantly it has very basic torque modelling (simple pull to one side and that's it). No P-factor for tail daggers and no gyroscopic swing when the tail lifts up. Prop wash is another subject of discussion. The amount of power needed for taxiing alone (with full pitch) differs a lot...

 

On top of it all you can slam the throttle wide open on TO and land a two pointer no matter the approach. Ground feels like a cushion there. :)

Edited October 4, 2014 by T}{OR

[CorsairHundo]

Some good info in this thread. I was wondering why I've been bouncing like a bungy cord coming in at 120! I'll try the 150

[BitMaster]

They should model grass fields as it is far easier to taxi, take-off and land on grass than on any paved surface as those lack ony kind of side stability for he wheels as mentioned before.

 

I am not sure if the softer ground makes a big difference in dampening a monday-tueasday-wednesday landing ( each hop is a day, we say ), what really makes a difference is the 1-inch that your rubber goes into the grass and thus gets some kind of forward tracking as that is the way with the least resistance. It just tracks way better on grass.

 

Bit

[BitMaster]

Sometimes our R/C strip is used by RL aircraft, including US Army for MedEvac training,

 

Every time one of those HEAVY birds lands on our grass field, we have to redo the grass and soil because those heavy AC leave a deeeeeep track across our strip that would kill any R/C or UltraLight while taxiing.

 

Good thing is, at least for the Black Hawks and their MedEvac we get payed a compensation for redoing our strip, se we make money every time they ruin our strip :) A lil work but it pays

 

If a 2 inch deep track doesnt provide more straight tracking then I am completely nuts !

 

Only when the summer is LONG and the soil is baken you will only see a mere track pressed into the soil. As soon as it is moist they leave scarves.

[Anatoli-Kagari9]

Regarding the use of toe-brakes / differential brakes in either the p51d or the Fw190 in DCS, this is actually the sim I find modelling ground physics the best way among all flightsims I use.

 

I have no experience in such aircraft IRL, far from that, although I have had the chance to taxi a PA18 a few times IRL, and even fly it :), but observing movies of their RW counterparts taxiing, taking off and landing, or simply reading historical descriptions of how they handled, makes me belief this is by far the sim that comes closer to reality.

 

On aspect that DCS models, as far as I can glimpse, extremely well is the propwash on the tail surfaces efficiency. You do get realistic "come alive" response from your rudders and elevators with bursts of throttle, or simply while taxiing at the right power and speed settings.

[313_Nevo]

Imho P51 behaves quite well on the ground especially during the landing. Yesterday I bounced at touchdown but only once - I realized that my 3point attitude was not correct and made the small correction by pulling the stick and the second touchdown was just smooth :joystick:

 

What is my problem from time to time are the takeoffs :book:

[Anatoli-Kagari9]

Takeoffs can be tricky specially in the presence of a crosswind component.

 

If you know ( you should... ) from where the wind is blowing, and you have a x-wind component of more than 5 m/s ( ~10 knot ) be prepared to use the rudder and aileron to counter first the deflected propwash effects, and then, as they are softened out as the aircraft gains speed and propwash speed is reduced as well as aligned with the aircraft longitudinal axis, be prepared to counter any weathervanning tendencies...

 

During the initial takeoff run, due to the deflected propwash over the downwind wing, be prepared to use some rudder into the wind and aileron downwind.

 

Then, as the aircraft gains speed, the weathervanning effect will prevail, requiring the usual rudder downwind application.

 

If you are note heavy ( full tanks and & or amno ) it's best to takeoff without any flap deflection under x-wind situations. The use of flaps can magnify the deflected propwash effects.

 

DCS World may well be the first flight simulator simulating this peculiar, but apparently realistic effect. IRL, if you ask a taildragger pilot how she / he uses her / his controls during the takeoff run, specially in the presence of crosswinds, she / he will tell you - to keep the damn aircraft straight, just don't ask me how - couldn't care less about theory :) .... That's about how we're supposed to deal with it in DCS World too !

Edited December 1, 2014 by jcomm

[Zabuzard]

Thanks for this thread! I'm trying to land the Pony since some years and as I now landed with neutral trimming the touchdown was so easy. 3-point, 2-point, it got so easy after this tip.

And now it is clear to me why I had steering problems after touchdown. Every time it bounced slightly the aircraft steered hard to a side because of the tailwheel touching the ground for a short amount of time.

[Curly]

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.

 

I have a question about this statement. I get that linear momentum is conserved in a collision, but don’t the Oleo type shock absorbers, which the p-51 is fitted with, convert some of the kinetic energy into thermal energy during their compression? Thus dissipating some of the kinetic energy at impact.

 

shock absorbers do nothing during the first phase of struts compression in a touchdown.

I get that this would be true if the landing gear were simply springs, or dampened springs. But it seems that the landing struts have to absorb some of the energy of impact. Otherwise, carrier landings in a tricycle configurations, which you do not flair, would put tremendous strain on the nose gear as craft rotates nose down around the center of CG. It would also make

an even more dubious proposition. It makes sense that shocks are absorbing some of the kinetic energy of impact when you consider that the maximum rate of descent at touchdown for the F/A-18 is around 24 feet per second, and the travel of the landing gear is 25 inches. Or is there something I’m missing in regards to the equations of motion.?
Edited October 21, 2015 by Curly

[Tomsk]

So this was really fascinating for me, I learnt so much from this thread!! And I'll repeat the earlier comments about being really impressed with the tone that midnabreu has taken here, wish it was more common in internet forums!

 

So I had a go at learning wheel landings based on the information in this forum, here's my basic conclusions after many ... many ... practice wheel landings.

• As Thor says, it really helps to nail that speed when you wheels touch, if you're going too slow you'll have a hard time preventing the nose come up.
  
• Leave the power on, again otherwise you'll lose too much speed and up comes the nose which will mean a "bounce" (ballooning).
  
• When the wheels touch, come off the throttle fairly quickly, it helps keep the nose down.
  
• Neutral trim is a great tip, usually I like to trim for a speed on landing which for 150mph is (ish) 1 notch nose up, but neutral trim and holding the nose up with the stick actually works better here because it means when your wheels touch you can release back pressure and it gives a gentle holding the nose down force.
  
• DCS seems to be *very* sensitive to vertical speed on touchdown for wheel landings, even slightly too much and you will "bounce". It's sensitive enough for three pointers, but wheel landings you really have to get it right.
  
• If you bounce, full power and go around, I found it really hard to save them once they'd bounced.
  
• As always you have to watch the entire rollout like a hawk, but particularly I found when the tail came down it often destabilized the plane a little and extra care was needed. Eternal vigilance! I really can't imagine doing this without rudder pedals, but then I always hated twist grip rudder ...
  

 

All in all I found wheel landings quite a bit harder than 3 pointers, which I was fairly confident on. A three point landing also noticeably used up a lot less airfield, and were generally much more forgiving. If you bounce a little on a 3 pointer I found I could generally save it okay, I found it much harder on a wheel landing, and so overall I can see why the manual recommends three pointers where possible. That said I agree with an earlier comment, a well executed wheel landing is a thing of beauty. I've practiced enough that only about 1 wheel landing in 10 now results in a go around. When they go wrong the problem is always the same: not judging height above ground correctly and hitting it a little too hard and bouncing. I can nail the speeds, and glide paths just fine ... but judging the height I have left I find consistently tricky.

 

I have absolutely zero IRL flight experience and by no means an expert in flight sims, but from my uneducated opinion I find myself agreeing with midnabreu. Landings in the DCS P-51 seem a little unreasonably unforgiving of landing with too much vertical speed. The landing gear seem incredibly "springy". I found you really really have very little margin to work with here ... Maybe that's realistic but it's tough when you have no depth perception to gauge height above ground (can't wait for the Oculus Rift!).

 

Lastly, big thumbs up to Eagle Dynamics, love the way the P-51 handles in general. No idea if it's faithful to the real thing (I'll let others argue over that) but to me it has a really nice "feel" to it :-)

Edited October 22, 2015 by Tomsk

[BSS_Sniper]

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.

 

 

 

 

My group has been flying the P51 since it came out. Most of us are military and/or commercial pilots. Having said that, the only thing I can agree with you on is the bouncing on landing. The other stuff you mentioned I was concerned with too, at first. What I noticed is that, you probably too, I was taxing too fast, much faster than I would IRL. Slow your taxi down and try unlocking the tail wheel and then turning. What you will see is something that is realistic and controllable.

 

The one thing that we all agree on is that the plane bounces WAY too much and too high on landing. Like I mentioned before, most of us fly for a living so we are not coming in hot or too steep. We're landing at correct speeds and rate of decent. To bounce a plane the way we see it in game you would have to come crashing down hard. Planes just don't bounce like that. Once they are slow enough to land they stick to the ground because they should've lost enough lift to fly. So, I would hope that one issue could be fixed.

[Anatoli-Kagari9]

When ground physics are being considered, it's really apples from oranges comparing anything ( even the best add-ons like the whole A2A fleet represent ) with DCS.

 

You can smash your C182 or P51d Civil or whatever aircraft you choose in FSX / P3D at 1000fpm descent rate and you will stay in the rw, like never has happened wrong...

 

In DCS, just like IRL ( talking from my RW experience ) the secret is that of bleeding off the right amount of energy in the right time.

 

This being said, I confess I am yet to perform an acceptable wheels landing in any of the ww2 fighters in DCS, reason why I do it most time in FSX with my A2A's just to feel a bit better :-)

[[DBS]TH0R]

The one thing that we all agree on is that the plane bounces WAY too much and too high on landing. Like I mentioned before, most of us fly for a living so we are not coming in hot or too steep. We're landing at correct speeds and rate of decent. To bounce a plane the way we see it in game you would have to come crashing down hard. Planes just don't bounce like that. Once they are slow enough to land they stick to the ground because they should've lost enough lift to fly. So, I would hope that one issue could be fixed.

 

Please read the whole thread, in particular post #72:

 

http://forums.eagle.ru/showpost.php?p=2196786&postcount=72

 

The solution is to center the stick on touchdown for two point landing and she will hardly bounce at all. If you touch down at 130-140 IAS that is. The problem with this is knowing / feeling when your wheels will touch the ground. If you can't do it land on all three wheels at about 100 IAS.

 

The effect is known as "ballooning", not bouncing. In the tracks I provided here (probably won't work with current game version) I slammed her on the runway much harder than you would on a normal approach. The struts absorbed the impact and there was no ballooning. In short, do not keep pulling back on the stick like you would in other flight sims.

 

A video of me demonstrating the normal two wheel landing approach [8:30]:

 

[Anatoli-Kagari9]

Excellent wheel landing THOR.

 

And it's bouncing the correct term - ballooning is an aerodynamic effect caused by increased lift through deployment of lift augmentation surfaces ( like flaps ).

[[DBS]TH0R]

Thanks.

 

I was referring to the manual and Yo-Yo's posts #23 & #28.

[Yo-Yo]

Another round of the same discussion... but T)(OR gave the right answer. A little bit more wheelers of 2012, i think.

 

[Tomsk]

So I noticed in THOR's video that he's actually using even more nose down trim than neutral, so I tried that. It works well, you don't have to get the height quite so precisely right, when the wheels are about to touch let the nose go, power off, and the trim will hold it down. If you do it a little early it's a bit less pretty but it works okay, you can get away with a little bit late as well. As is so often the case in flying it seems that the key is choosing the right trim, I was finding wheel landings really hard with the wrong trim.

 

Overall I'm liking the wheel landings a lot now that I've got used to them, in many ways they are much nicer than a three pointer once you've got used to them. The difference is that at 150mph the P-51 feels like a plane, at 120mph it feels like a pregnant hippo. At 120mph the nose likes to swim around all over the place, at 150mph it is much nicer behaved. You can also see what you are doing much better at 150mph. It's also nice doing much of the roll out on two wheels where the plane feels nicer, and it's easier to see the horizon.

 

I've now watched lots of real life P-51 landings on youtube, and the vast majority are wheel landings. You can see why :-)

[Curly]

Ballooning is caused by a force acting on the aircraft. That force is created by and equal to the force of the gear colliding with the runway. According to Yo Yo, all the gear is doing is prolonging the collision. The landing gear causes the momentum changes over a greater time period so there is less force acting on the airframe at any give time frame. Though because momentum is conserved the total force acting on the airframe is the same. Which makes sense if you consider landing gear springs that store the kinetic energy of the impact and release them over time.

 

The momentum at landing with a positive sink rate causes the plane rotate about it’s CG. The reason why pushing the stick forward counters this ballooning behavior is that it creates a torque equal to but in the opposite direction of the hard landing torque.

So a Mustang weighing 5000kg impacting the runway at with a sink rate of1 meter per second. Impacts with a Force = M A

5000kg *1^2 = 5000 Newtons of force on landing.

 

So lets just assume that the moment arm from the elevator to the CG is the same distance as from the landing gear. When landing at 1ms, to counter the ballooning tendency of the aircraft the elevator has to generate 5000 Newtons of force.

 

If you get slow and cannot generate this force at the elevator than you will likely see the ballooning tendency as the noted in the video in post .

 

It’s not a CG or elevator effectiveness issue. What’s going is that the landing gear are acting as springs and simply displacing the force of the impact over a longer period of time. In realty the type of landing struts fitted to the P-51, oleo, reduces force at impact. During landing oil is forced through an orifice in the strut causing the temperature of the oil in the strut rise. Kinetic energy from the landing is transferred into thermal energy and dispersed thought the casing. Thereby dissipating part of the impact forces. Though they also function to prolong the collision and reduce forces on the aircraft ends up landing with a lower amount of Newtons of force.

See page 13-8 to 13-12 for a description of the oleo strut.

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch13.pdf

Edited October 23, 2015 by Curly

[Justin Case]

I find the Mustang quite pleasant to land using the three point method described in the manual, if your speed is low it won't bounce and the landing roll will be very short.

[Tomsk]

@Curly and Yo-Yo: Yes, big takeaway tail draggers do not behave on landing like a tricycle geared aircraft. I had previously said it seemed very "bouncy", and it is if you get it wrong, but it seems like that's just how tail draggers are.

 

@Justin Case: Yup it's definitely a bit easier for the beginner but I can definitely recommend learning two wheel landings also. As I understand it the real world tail draggers qualification (which is separate from a normal tricycle gear PPL) requires the pilot to be proficient with two wheel landings. This is neatly explained here:

 

http://www.bellanca-championclub.com/WheelLandings.html

Edited October 23, 2015 by Tomsk