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Ground Handling / Tail Wheel and Rudder


Captain Orso

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I'm sorry if these questions are really dumb or redundant, but what I've read in the forum is often so ambiguous or ignore answering the question more-or-less saying, you don't have to know, just do what I tell you.

 

The tail wheel has absolutely no steering mechanism, nothing which might cause the wheel to rotate around it's mounting axis--seen from above, turning clock-wise or counter-clock-wise--other than the motion of the aircraft, correct?

 

The tail wheel can be locked. When locked it still has a freedom of motion of 6°.

 

Is this 3° to the left of center and 3° to the right of center for a total of 6° of turning freedom, or 6° both left and right for a total of actually 12° turning freedom?

 

The manual says to push the stick forward to unlock the tail wheel. How far forward do you have to push the stick to unlock the tail wheel?

 

The manual also says to pull the stick backward to lock the tail wheel. How far do you have to pull the stick back to lock the tail wheel?

 

Once I've pushed the stick forward enough to unlock it, will it remain unlocked if I release the stick into neutral position?

 

Once I have pulled the stick back far enough to locked the tail wheel, will it remain locked if I release the stick into neutral position?

 

Can the tail wheel be locked in a position other than centered?

 

I know that there is a force caused by accelerating the engine speed and a smaller force simply by the engine crank shaft and propeller turning while the rest of the engine and aircraft remain stable along the axis of the crankshaft and propeller, but I'm not concerned about that here unless it is relevant to ground handling.

 

With the tail wheel unlocked I apply power to the engine. The aircraft starts rolling forward straight ahead. I apply right tail rudder and the aircraft starts turning to the right, caused by the prop-wash hitting the tail rudder which pushes the tail to the left.

 

The force causing the aircraft to taxi along a curve is the prop-wash being deflected by the tail rudder. With no prop-wash deflected by the tail rudder the aircraft should immediately return to a straight forward motion.

 

Why should it do this? Because an object moving along a straight line is motionless relative to the direction of motion. To cause the object to move away from its direction of motion requires a force. Moving along a curve is a constant deviation from the direction of motion. This requires a constant force to cause the deviation from the direction of motion. Remove the force causing the deviation from the direction of motion and the deviation will stop; in other words, the aircraft stop moving along a curve and resumes moving straight ahead.

 

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.

 

The only thing I can think of which might be causing this would be that I am locking the tail wheel in this turning position and the tail wheel is causing the aircraft to turn.

 

So why will the aircraft not return to a straight motion?

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The tail wheel has absolutely no steering mechanism, nothing which might cause the wheel to rotate around it's mounting axis--seen from above, turning clock-wise or counter-clock-wise--other than the motion of the aircraft, correct?

 

Incorrect!

 

When your stick is neutral or pulled back, the tail wheel is "locked"...in a loose sense. It's actually tied into the foot pedals and you can steer the aircraft with it with ease.

6 degrees left or right.

 

If you push the stick forward you unlock it and put it in free-castoring mode, where the only way to control the aircraft is via the toe brakes.

 

For reference:

 

DCS P51D manual, page 27 :)

Located at:

...\Eagle Dynamics\DCS World\Mods\aircraft\P-51D\Doc

Now, the Fw190, Me109, Mig15 and Mig21 on the other hand are only steerable via the brakes and all have free castoring wheels.

 

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.
Of course it's going to continue on in the curve when your tailwheel is unlocked, once you've started turning the tailwheel will rotate as far it in can go in one direction. Nothing short of using the opposite toe brake will allow you to correct it.

 

If you'd done loops with the tail wheel "locked" (stick pulled back), when you return the foot pedals to the middle it'll straighten up providing you're still moving.


Edited by Buzzles
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I find the ground handling for both the FW-190 and P-51 to be spot on. They both taxi very easily if one uses standard taildragger techniques.

 

You do not need a lot of power to taxi.

 

Unless you want to make a sharp turn, keep the stick back at all times. When you use differential braking do not forget to tap the brake on the opposite side of the turn to stop the turn.

 

It cannot be said enough in a taildragger....keep the stick back at all times.

 

If there is wind, do not forget to add wind corrections. The basic rule is hold the stick, put your thumb up and point it downwind. Do that until the aircraft wants to taxi straight instead of being blown off course. Taildraggers are flown from the tie downs to the tie downs.

 

Keep your speeds slow and controllable.

 

With a little practice, you will be racing all around the airfield in no time.

 

:thumbup:

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1. No, I do not have a pen. 2. Indicating 250

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I use differential brakes. It is very hard when i use forward stick technique. If i use usually i can't control it properly

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12 degrees R/L stick to gut and rudder control, free castoring stick to full forward and brakes to control.

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Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.

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An inadvertent contradiction in terms, perhaps?

 

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

 

:smartass:

Answers to most important questions ATC can ask that every pilot should memorize:

 

1. No, I do not have a pen. 2. Indicating 250

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its nice how in the golden era cartoons used to deliver information. now all you have are facts and numbers, no humor.

AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS

 

Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.

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So many things to say and so little time :(

 

Many thanks to all the answers, but the main question was never answered. "So why will the aircraft not return to a straight motion?".

 

Incorrect!

 

When your stick is neutral or pulled back, the tail wheel is "locked"...in a loose sense. It's actually tied into the foot pedals and you can steer the aircraft with it with ease.

6 degrees left or right.

 

If you push the stick forward you unlock it and put it in free-castoring mode, where the only way to control the aircraft is via the toe brakes.

 

For reference:

 

DCS P51D manual, page 27

Located at:

...\Eagle Dynamics\DCS     World\Mods\aircraft\P-51D\Doc

Now, the Fw190, Me109, Mig15 and Mig21 on the other hand are only steerable via the brakes and all have free castoring wheels.

 

*sigh* I read the manual previously. When you reference that page I read the Surface Control Lock section about 6 times, trying to figure out what you were culling from that section that I couldn't, before I realized that you were referring to the Landing Gear section :doh:

 

There it says: "When the control stick is in the neutral position of pulled back, the tail wheel is locked". Hmmmmm "the neutral position of pulled back" ..... "position of pulled". When I read this the first time I wondered about the wording, but assumed it meant that the stick is pulled back with no lateral movement, in other words, no aileron change. What it's supposed to say "the neutral position or pulled back"; OR!! GAAH.gif

 

Of course it's going to continue on in the curve when your tailwheel is unlocked,

 

No, the unlocked tail wheel is a free castoring wheel, which means it swings freely. Between the force of the aircraft and the drag of the wheel the wheel loses and orients itself to the motion of the aircraft and therefore has practically no influence on the motion of the aircraft itself, other than allowing the tail section move in which ever direction the sum-total of all forces are moving it.

 

Using Google I found this thread, which says a lot on the subject: Swirling tailwheel. The most important post I find is Swirling tailwheel Post #66.

 

I believe you pulled that illustration from the same thread too ESA_maligno :thumbup:, which says a lot, but not everything.

 

once you've started turning the tailwheel will rotate as far it in can go in one direction.

 

The unlocked tail wheel rotates around it's vertical axis freely and does not influence the direction of motion of the aircraft.

 

Nothing short of using the opposite toe brake will allow you to correct it.

 

No, that is not physics. It works the other way around. To cause the aircraft to move along a curved line you must apply force in the direction of the curve. No force, no curve. With the tail wheel moving freely, the rudder centered and the engine pulling only straight ahead, that is the direction the aircraft should be moving, even if it is in the middle of a turn.

 

The exception to this is if the center of gravity gets pushed outside the track (the wheel base width). Think of an isosceles triangle with the odd angle at the tail wheel and the two equal angels at the wing wheels. The CG is somewhat

 

If you'd done loops with the tail wheel "locked" (stick pulled back), when you return the foot pedals to the middle it'll straighten up providing you're still moving.

 

That's not the situation. The one I described in my first post is with the tail wheel unlocked. Were the tail wheel locked the aircraft would have turned in the direction of my pushing the rudder, not because of the rudder being turned, but because the rudder and tail wheel are locked together through cables when the wheel is 'locked'. But I could turn the rudder in the opposite direction for as long as I wanted without any affect. This I subsequently discovered to be explained in the thread linked above.

 

BTW the engine was turning about 1200 RPM. What I learned from the above linked thread is that at the RPM's the engine turn at taxiing speed, does not produce enough prop-wash to actually steer the aircraft on the ground. So counter-steering without revving up the RPM's (bad for the engine on the ground) to cause enough prop-wash will do little to nothing for maneuverability on the ground.

 

From my understanding, there are two ways to initiate a turn smaller than the 6° left and right from centerline of the locked tail wheel:

- Revving the engine enough to cause enough prop-wash for the rudder to be able to turn the aircraft. (bad for the engine)

- Having and maintaining enough taxi-speed to use the breaks to turn the aircraft, without causing the aircraft to lose all of its forward motion. Tricky to learn.

 

So differential breaking is the preferred method IRL as it is in the forums, but my main question was still never answered, why if there is no other force causing the aircraft to taxi in a circle, does it not proceed in a straight line?

When you hit the wrong button on take-off

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Capt, I don't quite understand Your point either :D (although not being native English speaker, maybe I've lost something between the lines of Your post). Are You complaining about or praising the ground handling behaviour of DCS Pony? Are You asking why all taildragger airplanes are inherently directionally unstable on the ground?

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I guess if nothing else my plight is amusing :wassat:

 

I'm not sure I understand your question but...

So we know the CG is behind the main gear, and the steering wheel is behind etc.

 

When you unlock the wheel, the plane will keep moving in circle because it is, in fact, NOT locked.

When the wheel is locked, the wheel follows your rudder movement and is kept straight.

 

Now, maybe you're referring to the fact the wheel has to be central to be locked ?

 

Although it has not been stated anywhere I have been assuming that the tail wheel will not lock unless it is on centerline and that with the stick in a neutral or pulled back position, when the tail wheel comes into centerline it will lock.

 

When the tail wheel is unlocked it appears to posses an inordinate amount of resistance actually swiveling freely. I was playing around with it just now. With the tail wheel unlocked I put the aircraft into a tight left turn and stopped leaving the tail wheel turned about 90° to the left. I then released the stick to the neutral position. I assume that the tail wheel is still 'not locked' because it has not reached centerline.

 

I now apply throttle until the aircraft starts to move, which is by starting to turn to the left, the direction the tail wheel is point the tail. I applied some taps to the right landing gear break to get the aircraft to straighten out, which it then did and the tail wheel started to follow and straighten out too.

 

So the tail wheel was not yet locked, or else it would not allow itself to be forced back onto centerline, unless I broke it, through the stress, but that didn't seem to be the case. Once it was on center line it appeared to now be locked and was steerable.

 

Capt, I don't quite understand Your point either :D (although not being native English speaker, maybe I've lost something between the lines of Your post). Are You complaining about or praising the ground handling behaviour of DCS Pony? Are You asking why all taildragger airplanes are inherently directionally unstable on the ground?

 

I'm complaining about the unlocked tail wheel acting like it needs a large amount of force to straighten out, before which it causes the aircraft to turn in circles as if the tail wheel were locked in a turning position.

When you hit the wrong button on take-off

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Experience.

When you hit the wrong button on take-off

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@Captain Orso: Just to be sure. You don't expect the tailwheel to straiten itself out, do you? It wouldn't, because physiks. Every driving thing that has its steering in the back will not straiten itself out. Harvesters, pushed trailers, the lot. In fact they will try to get into a turn. The reason for that is pretty simple when you think about it:

 

During a turn, because of inertia, the plane wants to keep its original direction. With a free swiveling tailwheel, the tail is actually allowed to do so, the front is not though. This results in a turn that normally tightens itself. Its like swinging a stone on a string, where the stone is the tail of the airplane.

 

The force you need to straighten out the plane again is the force you need to overcome the inertia of the planes tail.

 

-Mathias

My System: Intel Core i7-4770K, Asus ROG Strix RX480 O8G, 24GB Ram

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The factor you overlooked is the position of the centre of gravity in relation to the main undercarriage wheels. This in effect amplifies any imbalance, and will cause any turn to increase dramatically rather than the aircraft returning to equilibrium and the turn decreasing.

 

Also, you found the spelling error in the first reference frustrating. Why not take the care therefore to spell "brake" and "break" correctly - a brake stops, and a break is something you take with light refreshments, or something that cleaves an item into two or more parts. I do of course fully understand that English isn't your first language, but it does make a huge difference were someone to wish to read these articles later by doing a search. Please don't, therefore, take this as a dig at you personally.

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Personally I avoid unlocking the tail wheel.

 

Instead I leave the stick centered and use rudder / tail steering to it's maximum advantage with the assitance of differential braking. She soon swings where I want her pointing with some light taps on the left / right brake. It has been good enough in most situations I've encountered up to now.

 

Once I get that tail wheel unlocked, I find it's a PITA to get it back center and lock it again. I just end up going round and round even if I try to cancel it out with opposite braking. I guess like everything else, it's an artform that just takes some practice.

 

Obviously it can be done else WWII pilots would have spent more time spinning around on the tarmac trying to control the plane than in the air lol.

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@Captain Orso: Just to be sure. You don't expect the tailwheel to straiten itself out, do you?

 

clap.gif YES! Yes, that is what I am expecting. Finally somebody understood what I mean smiley-whew.gif

 

It wouldn't, because physiks. Every driving thing that has its steering in the back will not straiten itself out. Harvesters, pushed trailers, the lot. In fact they will try to get into a turn. The reason for that is pretty simple when you think about it:

 

During a turn, because of inertia, the plane wants to keep its original direction. With a free swiveling tailwheel, the tail is actually allowed to do so, the front is not though. This results in a turn that normally tightens itself. Its like swinging a stone on a string, where the stone is the tail of the airplane.

 

The force you need to straighten out the plane again is the force you need to overcome the inertia of the planes tail.

 

-Mathias

 

Nnnnnnyyyyyyeeeeeee-no. *sigh* This explains nothing about a sideways oriented tail wheel on a stopped aircraft--which means no lateral inertia vector--not straightening out when the aircraft is put into motion, nor an aircraft with an unlocked tail wheel doing a stable unchanging turn whos radius is inside that of a the turn the same aircraft can do with a locked tail wheel.

 

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

When you hit the wrong button on take-off

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clap.gif YES! Yes, that is what I am expecting. Finally somebody understood what I mean smiley-whew.gif

 

 

 

Nnnnnnyyyyyyeeeeeee-no. *sigh* This explains nothing about a sideways oriented tail wheel on a stopped aircraft--which means no lateral inertia vector--not straightening out when the aircraft is put into motion, nor an aircraft with an unlocked tail wheel doing a stable unchanging turn whos radius is inside that of a the turn the same aircraft can do with a locked tail wheel.

 

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

 

I'm no mathematician but the way I see it is on a P-51 from stationary with an unlocked tail wheel, the moment you apply power it will try to pull left because of the torque of the prop. The free caster movement allows this to happen way more than a locked tail wheel would.

 

This is also why you have to dial in rudder trim on take off to counteract the prop reaction which is trying to pull the aircraft to the left even with a locked tail wheel.

 

Unless I'm missing the point?

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The factor you overlooked is the position of the centre of gravity in relation to the main undercarriage wheels. This in effect amplifies any imbalance, and will cause any turn to increase dramatically rather than the aircraft returning to equilibrium and the turn decreasing.

 

So what you are saying is that any variation from absolute straight motion, if not immediately corrected will inevitably lead to a turn of ever decreasing radius until a ground-loop is achieved. Do I understand that correctly?

 

Also, you found the spelling error in the first reference frustrating.

 

Yes, it was not readily recognizable as a spelling error and changed the meaning of the statement to the point of it being incorrect.

 

Why not take the care therefore to spell "brake" and "break" correctly - a brake stops, and a break is something you take with light refreshments, or something that cleaves an item into two or more parts.

 

Neil, please don't get your panties all in a bunch. Yes, I misspelled 'brake' about a thousand times. Thank you for pointing that out. shame.gif

 

From the context I don't think anybody could have thought I didn't meant 'brake' when I wrote 'break'.

 

I do of course fully understand that English isn't your first language,

 

I'm not sure if your trying to be condescending or just naturally achieving it. *psst* Niel - I'm not German. I'm a --how did one colleague put it, oh yeah--a "focken Yank". He was Scottish BTW :beer:

 

but it does make a huge difference were someone to wish to read these articles later by doing a search.

 

Yes, that is true. That might happen.

 

Please don't, therefore, take this as a dig at you personally.

 

To quote James the butler: Well, I'll do my very best! wink2.gif

When you hit the wrong button on take-off

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I'm no mathematician but the way I see it is on a P-51 from stationary with an unlocked tail wheel, the moment you apply power it will try to pull left because of the torque of the prop. The free caster movement allows this to happen way more than a locked tail wheel would.

 

This is also why you have to dial in rudder trim on take off to counteract the prop reaction which is trying to pull the aircraft to the left even with a locked tail wheel.

 

Unless I'm missing the point?

 

That is a good point. I'll have to try the start with the tail wheel turned the the right to see what happens. Thanks :thumbup:

When you hit the wrong button on take-off

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Personally I avoid unlocking the tail wheel.

 

Instead I leave the stick centered and use rudder / tail steering to it's maximum advantage with the assitance of differential braking. She soon swings where I want her pointing with some light taps on the left / right brake. It has been good enough in most situations I've encountered up to now.

 

Once I get that tail wheel unlocked, I find it's a PITA to get it back center and lock it again. I just end up going round and round even if I try to cancel it out with opposite braking. I guess like everything else, it's an artform that just takes some practice.

 

Obviously it can be done else WWII pilots would have spent more time spinning around on the tarmac trying to control the plane than in the air lol.

 

There are just some situations where the most rational solution is to do a very tight turn on the tarmac.

 

It certainly doesn't help that I'm still waiting on a good set of rudder pedals and using stick swivel to control the rudder yuck.gif

When you hit the wrong button on take-off

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The final sentence was there to point out that I wasn't trying to be condescending, though i apologise for the presumption that you may have been a native German.

 

I guess I just come across the wrong way.

 

I agree, your meaning wasn't unclear, but as I said, try doing a search, and you'll miss easily 50% of all postings on brakes, some of which, like this thread, are very relevant.

 

I just saw the irony of the example.

 

As for the castor effect when a stationary aircraft with an unlocked tail wheel starts to move, you are entirely correct. It should straighten the tail wheel, and apart from torque induced forces, the aircraft should move in a straight line, and not start to turn under the influence of the tail wheel, which would always be designed with a castor angle to encourage it to straighten anyway.

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The final sentence was there to point out that I wasn't trying to be condescending, though i apologise for the presumption that you may have been a native German.

 

I guess I just come across the wrong way.

 

I agree, your meaning wasn't unclear, but as I said, try doing a search, and you'll miss easily 50% of all postings on brakes, some of which, like this thread, are very relevant.

 

I just saw the irony of the example.

 

Yea, don't worry about it. I'll get over it :smilewink:

 

As for the castor effect when a stationary aircraft with an unlocked tail wheel starts to move, you are entirely correct. It should straighten the tail wheel, and apart from torque induced forces, the aircraft should move in a straight line, and not start to turn under the influence of the tail wheel, which would always be designed with a castor angle to encourage it to straighten anyway.

 

Wow, I may have finally gotten one right. :huh:

 

Thanks Neil! thumbsup.gif

 

Hurray me! :cheer3nc:


Edited by Captain Orso

When you hit the wrong button on take-off

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

 

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

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