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DCS P-51D Landing Physics and Ground Handling


midnabreu

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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 :-)

 

True, nose down trim helps. But once you get used to it you can land with no elevator trim at all. Definitely a recommendation to the guys having problems with two wheel landings.

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

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@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

 

What I'm asking is if the oleo strut and it's interaction are modeled. This would make two wheeled landings less bouncy. As the strut would absorb some the force of the impact. Thus lessening the monument / impulse which causes the pitch up encountered at touchdown.


Edited by Curly
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What I'm asking is if the oleo strut and it's interaction are modeled. This would make two wheeled landings less bouncy. As the strut would absorb some the force of the impact. Thus lessening the monument / impulse which causes the pitch up encountered at touchdown.

 

No strut can eliminate THE MOMENT. THe effect is not because of spring effect but because of AoA increasing. There is a good post above where all physics is explained.

If you place a cannon on a boat and fire, the overall speed the boat gets is INDEPENDANT on presence or absence oleo struts in the cannon installation. The only thing will differ - the FORCE acting to the boat frame.


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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So I'm guessing the effect of the shock absorbers is to distribute the effect of the force over a longer period of time? Same total change in momentum but smaller force over a longer time. That could make a huge difference ... if the upward momentum were spread out more that will lead to the force pushing the tail down to spread out more. That would give more time to catch it with the elevator or apply various other counter forces.

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So I'm guessing the effect of the shock absorbers is to distribute the effect of the force over a longer period of time? Same total change in momentum but smaller force over a longer time. That could make a huge difference ... if the upward momentum were spread out more that will lead to the force pushing the tail down to spread out more. That would give more time to catch it with the elevator or apply various other counter forces.

 

Can you correspond strut travel, the vertical speed you want it to absorb and the time you plan for your reaction?

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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Can you correspond strut travel, the vertical speed you want it to absorb and the time you plan for your reaction?

 

Not quite sure what you mean :-) But I can see that how the struts are modelled could have quite a big effect. It seems to me that the same moment spread over a longer time could be easier to deal with.

 

It could also be that having the force spread out could effect how the tail behaves. I'm sure the elevator surfaces would have a resistance to downwards movement. I could imagine that changes depending on whether that was a faster shorter impulse, or a longer slower impulse.

 

I'm not an expert on aircraft modelling (and Yo Yo definitely is so I defer to his judgement) but it does seem plausible to me that struts with shock absorbers would behave quite differently to entirely rigid landing gear, so you'd expect things to vary with how good the struts were at distributing the force over time ...

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Not quite sure what you mean :-) But I can see that how the struts are modelled could have quite a big effect. It seems to me that the same moment spread over a longer time could be easier to deal with.

 

It could also be that having the force spread out could effect how the tail behaves. I'm sure the elevator surfaces would have a resistance to downwards movement. I could imagine that changes depending on whether that was a faster shorter impulse, or a longer slower impulse.

 

I'm not an expert on aircraft modelling (and Yo Yo definitely is so I defer to his judgement) but it does seem plausible to me that struts with shock absorbers would behave quite differently to entirely rigid landing gear, so you'd expect things to vary with how good the struts were at distributing the force over time ...

 

I think that the best answer will give you an article of a RL taildragger expert where he explains how to avoid balooning performing a wheeler. :)

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 think that the best answer will give you an article of a RL taildragger expert where he explains how to avoid balooning performing a wheeler. :)

 

Ha :-) I've actually not got too bad at it now, nor quite as smooth as THOR but passable. My point was more that I could see Curly's question about how the struts were modeled could be relevant even though as you say the total change in momentum must be preserved :-)

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With a little more practice you will. The reason why I made that video in the first place was no wheel smoke on touchdown. :)

 

Like Yo-Yo says, the problem is change in AOA due to pulling back on the stick when or second before wheels touch the runway. With a proper technique you can drop her on the runway with descending speed up to 600ft/min IIRC and the struts will absorb the impact without even the slightest bounce or ballooning.

 

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

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The way I see it is it's actually easy to explain what is going on. Taildragger plane hits the ground on its wheels with a certain force, but because the struts are roughly perpendicular to the fuselage (along that nose-tail axis) and act as a giant "hinge", the tail will want to continue down on its momentum lifting the nose up in the process, increasing the AoA, and unless the pilot reacts correspondingly, cause a "ballooning" effect.

 

This is the only part Im kind of uncertain about, shock absorbing struts will give extra time for the pilot to react to the situation but will not really do much else. Is that right? Some people think that they will rebound with enough force to push the plane back into the air, or "bounce", but thats a misconception right?


Edited by OnlyforDCS

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You are correct about the "hinge" - while the weight of the plane tries to bring it down (let's ignore lift for a minute here), the reaction of the landing gear stops it, but as it is off the CoM, will create a moment that will tend to give the plane a nose up attitude. At that point, the increased AoA will be more likely to lift the plane back up in the air.

 

I'm not sure the damper gives you any appreciable amount of time to react: a somewhat hard landing on a tricycle plane can result in a bounce, which feels almost instantaneous. The plane, however, still settles down, because it's AoA is almost constant (it would even tend to decrease during the bounce).

Rather than giving you more time to react, the damper does just that: reduce the bouncing by preventing the spring from pushing you up too much.

 

A good way to make sure the plane can or cannot bounce purely from the high descent rate would be to literally drop it from a few feet with no horizontal speed, which is unfortunately impossible in DCS. You would still probably see the plane bounce from higher drops, until the gear can't withstand the reaction and breaks.

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Ha :-) I've actually not got too bad at it now, nor quite as smooth as THOR but passable. My point was more that I could see Curly's question about how the struts were modeled could be relevant even though as you say the total change in momentum must be preserved :-)

 

The sruts modelled as they should be modelled, nonlinear, if necessary, spring/gas force, asymmetric forward/reverse travel damping, sometimes, as for Mi-8, double-stage struts are used.


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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You are correct about the "hinge" - while the weight of the plane tries to bring it down (let's ignore lift for a minute here), the reaction of the landing gear stops it, but as it is off the CoM, will create a moment that will tend to give the plane a nose up attitude. At that point, the increased AoA will be more likely to lift the plane back up in the air.

 

I'm not sure the damper gives you any appreciable amount of time to react: a somewhat hard landing on a tricycle plane can result in a bounce, which feels almost instantaneous. The plane, however, still settles down, because it's AoA is almost constant (it would even tend to decrease during the bounce).

Rather than giving you more time to react, the damper does just that: reduce the bouncing by preventing the spring from pushing you up too much.

 

A good way to make sure the plane can or cannot bounce purely from the high descent rate would be to literally drop it from a few feet with no horizontal speed, which is unfortunately impossible in DCS. You would still probably see the plane bounce from higher drops, until the gear can't withstand the reaction and breaks.

 

The "Stress test" video I posted above shows how the struts work almost in the same conditions.

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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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]:

 

 

We know how to land and the way it balloons/bounces is wrong. We have tried two wheel landings at 120-130 and three wheel at 90-100 and it rarely lands like a real plane should. You don't have to take my word for it. I'm taking the word of one of our pilots that has over 18k real world flight hours and many thousands in a tail dragger. Its just not modeled right here and seems to be a problem in a lot of sims. Even with my low few thousand commercial hours I can tell it just isn't right. The fact of the matter is that you have to learn how to fly the sim and that in itself kind of sucks, but we have to do the same in the multi million dollar sims that we use for our yearly checks. It would just be nice if they could reduce the balloon effect.

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We know how to land and the way it balloons/bounces is wrong. We have tried two wheel landings at 120-130 and three wheel at 90-100 and it rarely lands like a real plane should. You don't have to take my word for it. I'm taking the word of one of our pilots that has over 18k real world flight hours and many thousands in a tail dragger. Its just not modeled right here and seems to be a problem in a lot of sims. Even with my low few thousand commercial hours I can tell it just isn't right. The fact of the matter is that you have to learn how to fly the sim and that in itself kind of sucks, but we have to do the same in the multi million dollar sims that we use for our yearly checks. It would just be nice if they could reduce the balloon effect.

 

I can not tell if the thing flies like the real bird, since I haven't flown one. There was however, a thread where the Horsemen fly the DCS P-51D. Since using real life procedures does the trick and slightly higher speed than what you find in the manual does too, I will take their word over your friend.

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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We know how to land and the way it balloons/bounces is wrong. We have tried two wheel landings at 120-130 and three wheel at 90-100 and it rarely lands like a real plane should. You don't have to take my word for it. I'm taking the word of one of our pilots that has over 18k real world flight hours and many thousands in a tail dragger. Its just not modeled right here and seems to be a problem in a lot of sims. Even with my low few thousand commercial hours I can tell it just isn't right. The fact of the matter is that you have to learn how to fly the sim and that in itself kind of sucks, but we have to do the same in the multi million dollar sims that we use for our yearly checks. It would just be nice if they could reduce the balloon effect.

 

BSS Im sure that Yo-yo will take into consideration any reasonable complaint by a real taildragger pilot. First of all try to figure out what exactly seems 'wrong' with the FM (is it the bounce? Is it the balloning effect? How is it wrong. etc.) and PM Yo-Yo with a post with as much detail describing the problem as possible. However let me warn you right away that 'feeling' is not going to cut it as an argument. Your objections need to be argued reasonably and objectively. Try to include a track or a video showing what is wrong and suggestions for improvements.


Edited by OnlyforDCS

Current specs: Windows 10 Home 64bit, i5-9600K @ 3.7 Ghz, 32GB DDR4 RAM, 1TB Samsung EVO 860 M.2 SSD, GAINWARD RTX2060 6GB, Oculus Rift S, MS FFB2 Sidewinder + Warthog Throttle Quadrant, Saitek Pro rudder pedals.

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I can not tell if the thing flies like the real bird, since I haven't flown one. There was however, a thread where the Horsemen fly the DCS P-51D. Since using real life procedures does the trick and slightly higher speed than what you find in the manual does too, I will take their word over your friend.

Just to clear that up, I was actually there and chatting to the horsemen while they were doing this. Although it was close there are marked differences they noted, especially to do with the controller accuracy and interfaces. in total we have had them fly dcs with us (The Virtual Horsemen) 3 or 4 times now.

 

But ground handling was one of the areas the real pilots struggled with.

 

The problem comes with translating real pilot feedback against statistical data.

 

Pman

 

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That is very interesting, thanks. Which part of the ground handling did they have problem with?

 

Out of curiosity, did they later on try the TF-51D? Unless I am mistaken, this one should more closely resemble what they are flying.

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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Just to clear that up, I was actually there and chatting to the horsemen while they were doing this. Although it was close there are marked differences they noted, especially to do with the controller accuracy and interfaces. in total we have had them fly dcs with us (The Virtual Horsemen) 3 or 4 times now.

 

But ground handling was one of the areas the real pilots struggled with.

 

The problem comes with translating real pilot feedback against statistical data.

 

Pman

 

Sent from my SM-G925F using Tapatalk

 

This is indeed very interesting and supportive of the indications that a lot of real world pilots have problems with landings in every sim, not just in DCS. I think a big part of this is the fact that in a sim environment we are missing the real world feedback we would be getting from our body and the forces acting on it in every given situation. I wonder though if this is the whole picture or if something in the FM is slightly off. For example I've wondered when the plane touches down in a two-point does the sim take into account the friction of the wheels in relation to the ground?

Current specs: Windows 10 Home 64bit, i5-9600K @ 3.7 Ghz, 32GB DDR4 RAM, 1TB Samsung EVO 860 M.2 SSD, GAINWARD RTX2060 6GB, Oculus Rift S, MS FFB2 Sidewinder + Warthog Throttle Quadrant, Saitek Pro rudder pedals.

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This is indeed very interesting and supportive of the indications that a lot of real world pilots have problems with landings in every sim, not just in DCS. I think a big part of this is the fact that in a sim environment we are missing the real world feedback we would be getting from our body and the forces acting on it in every given situation. I wonder though if this is the whole picture or if something in the FM is slightly off. For example I've wondered when the plane touches down in a two-point does the sim take into account the friction of the wheels in relation to the ground?

 

I don't know the specifics of what is or is not taken into account, Yo-Yo would need to answer that.

 

The Horsemen always comment that what we do in the sim is harder then what they do in real life, Which we take as a big compliment by the way!

 

But they do rely on senses of movement and feedback from their gut that bar a totally enclosed immersive environment on a D-platform you just can't get from a PC.

 

It wasn't the landing that was a problem for what it is worth, and having conducted thousands of landings in the P-51 it really is quite natural when you don't fight it, you should see some of the things we can get away with if we are careful! It was more the handling of the aircraft on the take off roll that really got their goats.

 

I'm really not here to comment on my own thoughts on the P-51 FM, more just a case of clarifying what the Horsemen experienced when I have been with them and DCS

 

Pman

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And another one just in case it wasn't a fluke (attached)....slightly off centre line....~110mph. No bounce. Better than the previous attempt. I should add that I had approx 50% fuel, std day, no wind, no turbulence.

 

EDIT: Previously I stated I only had 10% fuel. That was inaccurate. 50% is correct.

2pt_landing.trk


Edited by Deki
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