Ground Handling / Tail Wheel and Rudder

[Nobody96]

braking

 

is this correct NeilWillis?

 

-Mathias

[Captain Orso]

Nnnnnnyyyyyyeeeeeee-no. Normally it would. Probably. If nothing is braking either of the front wheels and the applied pull is perfectly straight. If not you will start to turn with a ever decreasing radius, simply because the tail gets thrown out of the turn the more the faster you turn.

 

If you are bored and not convinced: get into a hardwarestore. At least here in Germany most of them have shopping carts that have castoring wheels only on one end. Put the castoring in the back and give the whole thing a push and see how long it will go in a straight line. Or put yourself on a harvester, drive around a little and see how these things handle on a straight line.

 

-Mathias

 

Actually you would have to attach a bar about 25cm long to the actual shopping cart push-bar perpendicular to the it and pointing a bit above parallel to the ground, because the propeller, from which the accelerating force is originating, is also in front of the main wheels and exactly this should have a stabilizing affect on turns.

 

At any rate, what you are stating is confirming my observation completely. If the tail-dragger affect worked exactly as you describe, then with an unlocked tail wheel I could never taxi in a stable circle without using brakes, and this was my first bone of contention.

 

About the sideways-facing tail wheel on the stopped aircraft. When the engine is accelerated--discounting the torque of the engine/propeller motion--it pulls the aircraft along its facing vector. If the aircraft, instead of straightening the tail wheel, starts to turn, that means that the force needed to turn the tail wheel is greater than the force needed to turn the aircraft :doh:

[sobek]

If the aircraft, instead of straightening the tail wheel, starts to turn, that means that the force needed to turn the tail wheel is greater than the force needed to turn the aircraft :doh:

 

So? You do realize that the tail wheel has a lever of several meters on the whole plane, while the tendency of the tail wheel to straighten itself out is much smaller due to the small lever it has with regard to its pivot?

[Captain Orso]

Yes, I do.

 

Please think about what you are saying. The tail wheel is made specifically to swivel freely when unlocked.

 

To barrow Nobody96's analogy, you go shopping and take a shopping cart standing there with the front wheels turned sideways. You pull on the handle, but instead of the wheels straitening and the cart coming with you, the cart simply swings around in a circle. I bet you'd go look for another cart and not laugh at yourself for expecting it to do something else.

[sobek]

As opposed to you pulling a shopping cart, the prop doesn't impose stabilising sideway forces onto the plane...

 

If you push a cart with wheels sideways, it will go sideways for a little while until the wheels have straightened to a point where the friction forces reach an equlibrium.

Edited March 12, 2015 by sobek

[Art-J]

Wait, If I understand correctly, Capt argues just about apparent high force needed to straighten out the wheel in DCS taildraggers in low speed, tight turn conditions. To me, it doesn't seem to be excessive, given the fact that tail wheel pivot is very close to tyre's contact patch and friction of tyre being turned on the spot is always much higher than that of the tyre which is already rolling straight, so the effect seemed to be more or less expected/natural to me, at least when I'm starting to taxi.

 

Maybe it's a bit overdone at slightly higher speeds, however, I don't know. It's been almost a year since I tested this aspect for the last time (when first learning the WWII plane a'la DCS) so I don't feel confident enough to comment on it.

 

The question is not about directional instability of taildraggers (I believe nobody's arguing about that?), so let's avoid going off topic and concentrate on the matter above.

[Crumpp]

Wait, If I understand correctly, Capt argues just about apparent high force needed to straighten out the wheel in DCS taildraggers in low speed, tight turn conditions. To me, it doesn't seem to be excessive, given the fact that tail wheel pivot is very close to tyre's contact patch and friction of tyre being turned on the spot is always much higher than that of the tyre which is already rolling straight, so the effect seemed to be more or less expected/natural to me, at least when I'm starting to taxi.

 

Maybe it's a bit overdone at slightly higher speeds, however, I don't know. It's been almost a year since I tested this aspect for the last time (when first learning the WWII plane a'la DCS) so I don't feel confident enough to comment on it.

 

DCS's ground behavior is spot on IMHO. Based on my experience owning and flying taildraggers.

 

Each aircraft is a little different. The DCS P-51 and Dora both remind me of a heavier Pawnee. Very honest in their ground handling.

 

The worst taildraggers I have ever flown for ground handling are a Luscumbe 8E and an OV-1 Birddog. Both of those aircraft felt extremely unstable and have a reputation for loving to ground loop. You taxi them no faster than a walk.

[Captain Orso]

Everything I say here is met with skepticism, which is fine. But unless you've done it yourself, you are either relying on memory--everybody's memory if subject to being flawed--or somebody else's memory--same issue--and are speculating; albeit with a large amount of experience to fall back on.

 

I would ask you guys with hundreds of hours of experience to try this simple and quick experiment. This should take no more than a few minutes time to setup and run and an experience pilot should have no issue performing it:

 

- Park the P-51D on a tarmac with plenty of room to maneuver, with the trailing end of the tail wheel pointed at about 90° to the right, as if you had just come out of a sharp right turn.

- Press <Ctrl><F2> to get a free, outside view of the P-51D.

- Position your view to behind the P and as close to the ground as you can get, so that you have an unobstructed view of the tail wheel.

- Without changing your view, advance the throttle very slowly, until the P starts to move.

- Allow the P to taxi for about 60 seconds without changing the throttle or any controls.

- Observer what your experience is.

 

Do the same with the tail wheel turned 90° to the left and see if there's any difference.

 

I am looking forward to hearing about your experiences.

[HeadHunter52]

Humor....You always see "that guy" online racing around on the ground until the column of smoke appears to take his place.

 

:smartass:

 

Ain't that da troot

[Art-J]

I would ask you guys with hundreds of hours of experience to try this simple and quick experiment. This should take no more than a few minutes time to setup and run and an experience pilot should have no issue performing it:

 

- Park the P-51D on a tarmac with plenty of room to maneuver, with the trailing end of the tail wheel pointed at about 90° to the right, as if you had just come out of a sharp right turn.

- Press <Ctrl><F2> to get a free, outside view of the P-51D.

- Position your view to behind the P and as close to the ground as you can get, so that you have an unobstructed view of the tail wheel.

- Without changing your view, advance the throttle very slowly, until the P starts to move.

- Allow the P to taxi for about 60 seconds without changing the throttle or any controls.

- Observer what your experience is.

 

Do the same with the tail wheel turned 90° to the left and see if there's any difference.

 

I am looking forward to hearing about your experiences.

 

Did some test runs with elevator pushed forward all the time to keep the tailwheel unlocked. The wheel turned to the left straightened itself quite easily. The same wheel turned to the right had serious problems with doing so, screeching on the taxiway Tokyo drift style :D, meaning more throttle than before was required to keep the airplane moving. Then it straighten itself out eventually.

 

Given the fact that spiral slipstream and P-factor are pulling the plane to the left all the time and this is not symmetrical situation, some difference was expected, although not to such an extent I admit. It seems almost as if the wheel spindle was badly rusted and void of any grease ;).

 

Something doesn't seem to be quite right here, but it's not really noticeable in usual taxiing situations (with differential brakes and rudder), so I'm not that much bothered with it. I'd rather see ED guys improving engine management and damage modeling first :).

[Captain Orso]

Thanks for trying the test Art-J :thumbup:

 

I think this falls a lot under the same premise as something I read in these very forums about a Swedish (I think it was) trainer-jet. After being thoroughly tested by test pilots and trainers, it was put into service. Of the very first group to train with it, half of them fatally crashed it :cry:. Apparently, if you flew it optimally, it worked like charm. But if your flying skills were less then good, it would not forgive any mistakes and thus the crashes :doh:.

[Bluedog]

After being thoroughly tested by test pilots and trainers, it was put into service. Of the very first group to train with it, half of them fatally crashed it

Interesting but sounds a bit "anecdotal". Any firm details available?

 

My apologies for straying off the topic but statement like that is just aching to be challenged.

 

 

(Those only interested in P51 tail-wheels look away now)

 

With respect, I'm skeptical on several counts:

 

 

Firstly, (and from the description as Swedish and jet trainer, I'm assuming it's the Saab 105) the aircraft would have been designed/developed with fairly benign handling qualities in mind. It would have been rigorously tested by the company test pilots. Now, these self-same test pilots would have completed an experimental test pilot course; and one of the prime considerations drilled into these pilots would be to assess and test aircraft with the intended role in mind; and the lowest common denominator of aviator likely to fly the particular aircraft also in mind. In this case it would have been assessed as a training aircraft and the LCD would be a marginal pilot.

 

 

So, the test pilot, even though his flying skills might be above the average he would have "looked" at the aircraft from a flying instructor's and a student pilot's viewpoint. This doesn't mean it would be foolproof - something might slip through but anything nasty and out of the ordinary would most likely have been picked up.

 

 

Likewise, before introduction into service, I'd assume the aircraft would also have been assessed by similarly trained and similarly focused service test pilots before handing it over to the end user. The same rules would have applied. The training school instructors would also have gained considerable experience on the aircraft before putting it in the hands of student pilots. Of course the student pilots would have been under strict supervision by the instructors and worked through specific sequences; so presumably if there was a serious problem with the aircraft in student pilots' hands it would have most likely shown up when Cadet Prune mishandled the aircraft during dual training.

 

 

And think of what the particular airforce would have done if it lost several aircraft all at once and all flown by student pilots. So a course of 10 students loses 5 aircraft (and their lives) within in a few months. Maybe it was a course of 20, or 30; who knows. Think of the hue and cry. In any event the aircraft would have been grounded well before those several aircraft bit the dust.

 

 

Certainly the Swedish airforce would have done so; but perhaps it was the Elbonian airforce.

 

 

Or perhaps it was due to SkyDemons: see here:

 

 

Just to make sure, I did a Google search on the topic. Nothing found.

Edited March 23, 2015 by Bluedog
Additional text

[Ala13_ManOWar]

I'll make my try, back on first topic :).

 

... A free castoring wheel should straighten on the aircraft being put into motion and not affect the direction of travel of the aircraft. ...

The problem is IMHO you are starting from a mistaken statement. A free castoring wheel in an aircraft is under a lot of weight, so not completely "free", and usually wheel just keep the last direction it was put in. A stopped aircraft with a wheel not looking straight will start moving the direction the wheel is looking at for quite a while even you stepping opposite pedal (that's why you usually want to straighten the wheel before taxi, RL I mean). That happens even in tricycle gear aircraft like C152... so if you are flying a high powered and weighted tail wheel fighter I wouldn't expect anything less. The only way to operate is anticipate when you know how it works. RL C152 indeed isn't easy to taxi at first just because the castoring wheel, until you realize how much to anticipate, then it's a piece of cake. P-51 will be much harder being a tail wheel like every tail wheel.

 

I give you an example, you entered and line up runway, but unlocked wheel for the turn. Then you lock again (try to) pulling back your stick, but you stopped right ended the turn. When you apply throttle the first move forward of the aircraft will be always the last direction your wheel was left, and usually even the wheel is still unlocked. That's because 'free' doesn't means it's like a windmill, free means wheel will keep faced where it stopped and lasts a while to reach a certain position being 'free', sometimes quite a while.

 

so

 

But when I'm turning a curve in the parking area of some airfield and release the tail rudder to centerline, the aircraft does not stop turning along a curve. This makes no sense to me! Even when I push the tail rudder in the opposite direction, the aircraft continues to turn in the original direction of turn.

Yes, aircraft will straighten it's path... with time, even 'a lot of time' if you're looking it to be instantly, so you've to react sooner if you look for your straight line. What you're describing in the other hand are a direct controlled wheel, then of course you center pedals and get a straight line instantly but this isn't our case. Castoring wheels are a bit mad.

 

 

And a last thought, not related to castoring wheel but related to taxi. Another mistaken statement, you are thinking about a tail wheel running straight when you apply power... but that's not true, a tail wheel will always want to go any way but straight (because CG as mentioned sooner), that's why you need a lock, so why should it straighten its path so easily when you release pedal? You always will have to 'fight' a bit, or a lot, to get your straight line.

 

S!

[Captain Orso]

Interesting but sounds a bit "anecdotal". Any firm details available?

 

My apologies for straying off the topic but statement like that is just aching to be challenged.

 

 

(Those only interested in P51 tail-wheels look away now)

 

With respect, I'm skeptical on several counts:

 

 

Firstly, (and from the description as Swedish and jet trainer, I'm assuming it's the Saab 105) the aircraft would have been designed/developed with fairly benign handling qualities in mind. It would have been rigorously tested by the company test pilots. Now, these self-same test pilots would have completed an experimental test pilot course; and one of the prime considerations drilled into these pilots would be to assess and test aircraft with the intended role in mind; and the lowest common denominator of aviator likely to fly the particular aircraft also in mind. In this case it would have been assessed as a training aircraft and the LCD would be a marginal pilot.

 

 

So, the test pilot, even though his flying skills might be above the average he would have "looked" at the aircraft from a flying instructor's and a student pilot's viewpoint. This doesn't mean it would be foolproof - something might slip through but anything nasty and out of the ordinary would most likely have been picked up.

 

 

Likewise, before introduction into service, I'd assume the aircraft would also have been assessed by similarly trained and similarly focused service test pilots before handing it over to the end user. The same rules would have applied. The training school instructors would also have gained considerable experience on the aircraft before putting it in the hands of student pilots. Of course the student pilots would have been under strict supervision by the instructors and worked through specific sequences; so presumably if there was a serious problem with the aircraft in student pilots' hands it would have most likely shown up when Cadet Prune mishandled the aircraft during dual training.

 

 

And think of what the particular airforce would have done if it lost several aircraft all at once and all flown by student pilots. So a course of 10 students loses 5 aircraft (and their lives) within in a few months. Maybe it was a course of 20, or 30; who knows. Think of the hue and cry. In any event the aircraft would have been grounded well before those several aircraft bit the dust.

 

 

Certainly the Swedish airforce would have done so; but perhaps it was the Elbonian airforce.

 

 

Or perhaps it was due to SkyDemons: see here:

 

 

Just to make sure, I did a Google search on the topic. Nothing found.

 

Thanks for your reply Bluedog. Dang, but you must be upset at me for what I posted to feel you have to sick CHL after my ass :huh:. (I've been subbed to him for ages BTW ;)).

 

It was a bad idea that I posted that. It's not a fair argument, because I have no actual evidence that it actually happened--only something I remember reading in the forum a couple of weeks ago, which I cannot even quote or directly reference, and cannot be personally certain was actually factual--, and it leaves anybody who might feel aggrieved by the statement with nothing of substance to counter, with only smoke at which to strike.

 

My heartfelt apologies.

[Bluedog]

No problem Cap'n - all a bit of fun as far as I'm concerned. I doubt if anyone was aggrieved, except maybe the guys that believe in Skydemons.:smilewink:

[Captain Orso]

I'll make my try, back on first topic.

 

Many thanks for that Ala13, and for your answer in general.

 

The problem is IMHO you are starting from a mistaken statement. A free castoring wheel in an aircraft is under a lot of weight, so not completely "free", and usually wheel just keep the last direction it was put in.

 

Yes, sorry if I gave you the impression that I thought the unlocked tail wheel would rotate on its vertical axis freely without any resistance at all. As with every moveable object, it requires force to put it into motion. And as with every joint, the greater the pressure on that joint, the greater the resistance to activation.

 

A stopped aircraft with a wheel not looking straight will start moving the direction the wheel is looking at for quite a while..

 

What you are saying is that the force required to put the unlocked tail wheel into rotation around its vertiacal axis is greater that the force requred to put the entire rest of the 10,000 lb aircraft into rotation around the center point between the main wheels. That's the tail wagging the dog.

 

..even you stepping opposite pedal (that's why you usually want to straighten the wheel before taxi, RL I mean).

 

No, the premmise is that the aircraft is motionless at the beginning of the experiment. The only way--in the game--to straighten the tail wheel is by excerting acceleration on the aircraft in its facing direction. In-game this is causeing the aircraft to turn sharply allong the facing axis of the tail wheel. The 'unlocked' tail wheel is thus stearing the aircraft, instead of the aircraft stearing the 'unlocked' tail wheel. If the 'unlocked' wheel is stearing the aircraft, then it is not 'unlocked' but under the constraint of some resistance, which it must overcome inorder for the tail wheel to be straightened.

 

That happens even in tricycle gear aircraft like C152... so if you are flying a high powered and weighted tail wheel fighter I wouldn't expect anything less. The only way to operate is anticipate when you know how it works. RL C152 indeed isn't easy to taxi at first just because the castoring wheel, until you realize how much to anticipate, then it's a piece of cake. P-51 will be much harder being a tail wheel like every tail wheel.

 

I give you an example, you entered and line up runway, but unlocked wheel for the turn. Then you lock again (try to) pulling back your stick, but you stopped right ended the turn. When you apply throttle the first move forward of the aircraft will be always the last direction your wheel was left, and usually even the wheel is still unlocked. That's because 'free' doesn't means it's like a windmill, free means wheel will keep faced where it stopped and lasts a while to reach a certain position being 'free', sometimes quite a while.

 

so

 

 

Yes, aircraft will straighten it's path... with time, even 'a lot of time' if you're looking it to be instantly, so you've to react sooner if you look for your straight line. What you're describing in the other hand are a direct controlled wheel, then of course you center pedals and get a straight line instantly but this isn't our case. Castoring wheels are a bit mad.

 

 

And a last thought, not related to castoring wheel but related to taxi. Another mistaken statement, you are thinking about a tail wheel running straight when you apply power... but that's not true, a tail wheel will always want to go any way but straight (because CG as mentioned sooner), that's why you need a lock, so why should it straighten its path so easily when you release pedal? You always will have to 'fight' a bit, or a lot, to get your straight line.

 

S!

 

I asked at the very beginning of this thread to please not post 'this is how you're supposted to to it' advice. I have read numerouts thread about 'how you are supposed to do it'.

 

This thread askes the question, 'does the program represent physical reality?' or do I misunderstand the way the tail wheel functions, and if so, what do I misunderstand.

 

The summery of arguments I've read are saying that it requires and enourmous force to straighten the 'unlocked' tail wheel and claim this is supported by physics. This is not the case, not in the least. Stearing the aircraft with the tail wheel works on the principal of 'wheel and axel' the aircraft being the wheel and the center-point of the main-wheels the axis around which it turns.

THOUGHT EXPERIMENT: The aircraft is being put into a rotation around the centerpoint of its main-wheels by the tail wheel.

 

Think this through, imagine you are standing at the tailsection of the aircraft just to the outside of the left elivator. How hard do you have to push on the elivator toward the tail rudder to put the aircraft into rotation?

 

This is the force the game is demonstraighting being necessary to straighten the tail wheel.

[Ala13_ManOWar]

Yourself have the answer mate :).

 

I asked at the very beginning of this thread to please not post 'this is how you're supposted to to it' advice. I have read numerouts thread about 'how you are supposed to do it'.

Didn't mean that mate, I just tried to show some examples you probably experienced.

 

 

This thread askes the question, 'does the program represent physical reality?' or do I misunderstand the way the tail wheel functions, and if so, what do I misunderstand.

I'm have nothing to do with ED staff, but I clearly see P-51 model representing quite well what I can know myself. So I would say yes it is modelled, and the best model out there I know in a simulator, really close to the real thing.

 

 

 

The summery of arguments I've read are saying that it requires and enourmous force to straighten the 'unlocked' tail wheel and claim this is supported by physics. This is not the case, not in the least. Stearing the aircraft with the tail wheel works on the principal of 'wheel and axel' the aircraft being the wheel and the center-point of the main-wheels the axis around which it turns.

THOUGHT EXPERIMENT: The aircraft is being put into a rotation around the centerpoint of its main-wheels by the tail wheel.

 

Think this through, imagine you are standing at the tailsection of the aircraft just to the outside of the left elivator. How hard do you have to push on the elivator toward the tail rudder to put the aircraft into rotation?

 

This is the force the game is demonstraighting being necessary to straighten the tail wheel.

That's it, even being a castoring wheel you need more force to straighten that you seems to think. In your experiment, well I have not taxi by hand a real P-51 but I have done many times other aircraft, and a rotated wheel standing on ground is very difficult, almost impossible, to straighten by your hand. That's why you see those long tow bars used to steer and taxi aircraft on ground, tricycle or tail wheels. With a tow bar you can move the wheel just fine because the "lever" effect. As said, unlocked doesn't means you can move it like a feather. And a tail dragger, even more one like P-51 with its weight standing over the tail wheel, I can guess (and of course it's a guess) it's even harder to move than usual GA I can know.

 

S!

Edited March 23, 2015 by Ala13_ManOWar

[Yo-Yo]

+1 Just try to steer your car with stopped engine as hydro or electro booster is off... :)