Wheel alignment for warbirds  
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Wheel alignment for warbirds - 6/6/2008 1:30:17 PM   
The Raven



Posts: 594
Joined: 1/6/2005
From: Melbourne, AUSTRALIA
Status: offline 		Hi guys,

I have a Sportsman Aviation P-40 with standard mechanical retracts etc. After spending much time learning to master (or is that luck out on) landings I'm still having a fair share of nose overs. I realise not all of this is due to me but a number of factors such as runway condition etc.

As I have to look over my retracts again, can anyone suggest any common alignment techniques that will help reduce nose overs. For example, toe-in will tend to generate nose overs BUT will toe-out do the opposite?

Any suggestions would be much appreciated. My cowl is starting to accumulate too many epoxy repairs.....
       Post #: 1

RE: Wheel alignment for warbirds - 6/6/2008 1:54:37 PM   
carlbecker



Posts: 1636
Joined: 7/29/2002
From: Fairfax, VA, USA
Status: offline 		USUALLY a LITTLE (one degree or less) toe-in helps tracking. USUALLY ANY toe-out will make straight tracking more difficult. Shimming the struts forward would be the first thing I would try.

(in reply to The Raven)
       Post #: 2

RE: Wheel alignment for warbirds - 6/6/2008 3:01:56 PM   
BobH


 

Posts: 4378
Joined: 4/1/2003
From: Springfield, VA,
Status: offline 		Carl I agree about the toe in but the FW 190 has toe out.. I can't imagine why but thats what recommended for the model too.

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RE: Wheel alignment for warbirds - 6/6/2008 3:24:24 PM   
Tommy_Gun



Posts: 716
Joined: 4/7/2004
From: Ione, CA, USA
Status: offline 		Toe -In is the wrong way to go.

I used to do this to all my planes until just recently when a friend explained to me how I should try a little toe out instead.

If you look at the dynamics, toe -in will make the plane more unstable.

If the plane swerves to the LEFT on the runway, the weight is transferred to the RIGHT main.
If the right main has toe in, this makes the swerve to the left more pronounced.

Instead add just a small amount of toe out to each main wheel.
Now the weight transfer from a swerve will act to pull the plane back into a straight line.

I didn't believe it at first either when I was first told about this.

I have since tried it on all my .60 sized WW2 fighters IT WORKS!

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RE: Wheel alignment for warbirds - 6/6/2008 6:43:34 PM   
Nickrc3



Posts: 402
Joined: 1/12/2002
From: Miami, FL, USA
Status: offline 		Good tip...
Thanks Tommy Gun.

(in reply to Tommy_Gun)
       Post #: 5

RE: Wheel alignment for warbirds - 6/6/2008 8:17:35 PM   
carlbecker



Posts: 1636
Joined: 7/29/2002
From: Fairfax, VA, USA
Status: offline 		I am not sure on swerves and how much that loads up the outside wheel. Most cars use toe-in and it keeps the car staight down the highway. I have used toe-in on some airplanes and had success. I am easy on the throttle and rudder so that there are not great changes in direction. I try to fly in a scale manner with long take off runs. I recommend you test different setups and use what works for you and your plane.

(in reply to Nickrc3)
       Post #: 6

RE: Wheel alignment for warbirds - 6/6/2008 9:29:50 PM   
kahloq



Posts: 1797
Joined: 1/1/2006
From: Fort Collins, CO, USA
Status: offline
quote:

ORIGINAL: Tommy_Gun

Toe -In is the wrong way to go.

I used to do this to all my planes until just recently when a friend explained to me how I should try a little toe out instead.

If you look at the dynamics, toe -in will make the plane more unstable.

If the plane swerves to the LEFT on the runway, the weight is transferred to the RIGHT main.
If the right main has toe in, this makes the swerve to the left more pronounced.

Instead add just a small amount of toe out to each main wheel.
Now the weight transfer from a swerve will act to pull the plane back into a straight line.

I didn't believe it at first either when I was first told about this.

I have since tried it on all my .60 sized WW2 fighters IT WORKS!


Im sorry, but thats backwards. Toe-IN creates a more stable taxi and rollout...toe-out is what puts the pressure on the wheels making it more difficult to keep straight. However, it does work on some planes, but on most wardbirds, you do not want toe-out.

As far as nosing over, if its not too nose heavy for CG, then the position of the gear extended relative to the wing is partially what is causing this. I concur with others that shimming the back retract rail a little to help get the strut further forward will help. I've done thios on my KMP Me-109 and H9 1.50 P-51.

Another common issue is pilots trying to slow the plane down after touchdown too quick. Sometimes it does require letting it settle on the mains and letting it bleed off speed, then allow it to drop the tail. Once the tail is down, you may need to hold a lot of elevator in to keep it from nosing over once the plane has slowed down enough that it wont jump back into the air. I've done it too and either caused it to baloon back up in the air eneded up nosing over duie to not enouhg elevator input. If your good enough to do this and not land too hard, you can try 3 pointing the landing. Not too scale, but can work

(in reply to Tommy_Gun)
       Post #: 7

RE: Wheel alignment for warbirds - 6/6/2008 10:14:38 PM   
vertical grimmace


 

Posts: 1145
Joined: 3/13/2004
From: ft collins , CO, USA
Status: offline 		My WW1 birds like Toe -in. Sometimes I lose some of it and I get ground loop problems. These types of aircraft must have the gear set up accurately all of the time. This toe out comment may be a little Trolly! be careful with that advice and try it on something you do not care about first.

I think the main issue with the post is nosing over though. I think you should make sure the CG is correct and if that is OK then move the wheels forward.

(in reply to kahloq)
       Post #: 8

RE: Wheel alignment for warbirds - 6/7/2008 8:36:54 AM   
Tommy_Gun



Posts: 716
Joined: 4/7/2004
From: Ione, CA, USA
Status: offline 		Sorry to disagree kahlog, but I stated it just as I meant it.

I said nothing backwards.

If you read my post you will see that I too used to use toe in as a rule.

Now instead I use just a small amount of toe out and it has made a notable difference in the ground handling of my warbirds.

Instead of just discounting a different idea as wrong or backwards, why not give it a try?

And no vertical grimmace there is no "troll" in this suggestion.

Go take a corner in your car and tell me which way your body weight is moved when you turn left or when you turn right.

Now think it through. If the weight transfers to the wheel on the outside of the turn and that wheel has toe in, it will make the vehicle swerve harder INTO the direction of the existing turn. This is not a desirable result.

I'm not going to get into a pissin contest here. All I can tell you is that in 33 years of RC modeling, I never learned anything by just stating that something or someone was wrong without a little testing first.





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RE: Wheel alignment for warbirds - 6/7/2008 2:48:22 PM   
paladin


 

Posts: 1610
Joined: 2/13/2002
From: Vestal, NY, USA
Status: offline 		Toe-in is not about ground loads. On takeoff as the plane goes hurling down the runway the wing starts to load up with the aircraft wt.. if you were able to put a scale under the wheels just before takeoff it should read almost zero. It is also impossible to get both wheels off the ground at the same time which leaves one wheel still in contact with the ground only for a millisecond. Toe out turns into the dead wing, toe in turns into the flying wing. At this point in the flight we have established that the strut loading is near zero so any side load will clearly overtake the ground force. Toe out will pull the plane into the dead wing slowing it down and speeding the flying wing up, a situation that is self perpetuation. Toe in however turns the plane into the flying wing slowing it and increasing the speed of the dead wing allowing for a equalization and controlled liftoff.

Should you have OLEO’s you will notice that they have a lot of play in the toe plane. When setting the toe you want the worst case after taking up all the play to be zero to toe in. on my Zeroli corsair that meant that with play my toe-in was 0 to 8 degrees toe-in. rotating retracts are the worse offenders for play.

Joe


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RE: Wheel alignment for warbirds - 6/7/2008 4:19:02 PM   
Tommy_Gun



Posts: 716
Joined: 4/7/2004
From: Ione, CA, USA
Status: offline 		Most of the ground handling problems I have seen have NOT happened at flying speed.

They are typically at a speed where the wing is not yet supporting the weight of the aircraft during the takeoff roll or on the landing roll out.

And on a side note, the runway I fly from on a weekly basis is 22 feet wide. This may not seem out of the ordinary to some of you, but quite a few folks that fly with us as visitors comment on how narrow the runway is compared to what they are used to.

I only mention this as it would seem pertinent to the discussion in that I have no trouble with any of my warbirds in ground handling from the above mentioned runway.

OK as an attempt at honesty, my Skyshark 109 has given me one or two thrills when the set screw on the wheel strut was not quite tight enough. But it does have a scale strut angle on it.




< Message edited by Tommy_Gun -- 6/7/2008 4:28:08 PM >

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RE: Wheel alignment for warbirds - 6/7/2008 7:10:54 PM   
kahloq



Posts: 1797
Joined: 1/1/2006
From: Fort Collins, CO, USA
Status: offline
quote:

ORIGINAL: Tommy_Gun

Sorry to disagree kahlog, but I stated it just as I meant it.

I said nothing backwards.

If you read my post you will see that I too used to use toe in as a rule.

Now instead I use just a small amount of toe out and it has made a notable difference in the ground handling of my warbirds.

Instead of just discounting a different idea as wrong or backwards, why not give it a try?

And no vertical grimmace there is no "troll" in this suggestion.

Go take a corner in your car and tell me which way your body weight is moved when you turn left or when you turn right.

Now think it through. If the weight transfers to the wheel on the outside of the turn and that wheel has toe in, it will make the vehicle swerve harder INTO the direction of the existing turn. This is not a desirable result.

I'm not going to get into a pissin contest here. All I can tell you is that in 33 years of RC modeling, I never learned anything by just stating that something or someone was wrong without a little testing first.



First...where do you get that I discounted a different idea?
2nd...Paladin is absolutely correct. I'm simply telling you that your understanding of whats going on is not quite right. I did tell you though, that your description of what is happening is backwards. And yes....that is correct. Your example: turn the wheel of your car left, which way does YOUR body lean....obviously to the right. But, since you have muscles to counter that, you can keep from going full over. And, which way does the muscles in your body push during this....to the left!!!!! A car is setup with toe-in on the steer tires so when the weight transfers to the right due to centrifugal force, the right wheel toe-in forces an opposite reaction(to some degree). Why do you think the steering wheel tries to center itself(if the car is aligned properly) when you let go of the steering wheel? This is why, the opposite tire is pushing back at the direction of the turn.
Same with a plane. When a plane starts to veer left, the load on the left tire with toe-in will try to counter that and due to the toe-in direction, the left wheel will push right helping to keep the plane form overreacting to the left veer situation. Weight is not transfered to the right wheel on a left veer, instead, the right wheel actually gets "lighter" aggravating the left veer if toe-out is in place.
With toe-out, the left tire will contrinue to pull the plane left forcing an increasingly worse leftward veer until the plane gorundloops if not corrected by the pilot. This is also why planes with toe-out are generally more uncontrollable at less then flying speed on the gorund. Once the tail lifts, toe-out is no longer acting as forcefully.

Also, where do you get off assuming i've never tried various setups? A little presumptious there.
Anyhow...I dont really care whether you agree or not with what I and also Paladin have stated. We are trying to help you understand the mechanics of the situation. You are free to have your opinion, whether it based in fact or not.

(in reply to Tommy_Gun)
       Post #: 12

RE: Wheel alignment for warbirds - 6/7/2008 8:05:55 PM   
Flyfast1


 

Posts: 382
Joined: 9/25/2005
From: Livermore, CA, USA
Status: offline
quote:

ORIGINAL: Tommy_Gun

Most of the ground handling problems I have seen have NOT happened at flying speed.

They are typically at a speed where the wing is not yet supporting the weight of the aircraft during the takeoff roll or on the landing roll out.

And on a side note, the runway I fly from on a weekly basis is 22 feet wide. This may not seem out of the ordinary to some of you, but quite a few folks that fly with us as visitors comment on how narrow the runway is compared to what they are used to.

I only mention this as it would seem pertinent to the discussion in that I have no trouble with any of my warbirds in ground handling from the above mentioned runway.

OK as an attempt at honesty, my Skyshark 109 has given me one or two thrills when the set screw on the wheel strut was not quite tight enough. But it does have a scale strut angle on it.






Tommy, just wanted to say that's a nice hangar of planes! The ME109G is a beaut!

Raven, regarding the nose over issue, I would say start with no toe-in (or toe out) and see if the elevator can be used on rollout to keep the plane from nosing over. Toe in may cause the plane to slow down faster which may make the nose over worse. With my warbirds I add some up elevator at the end of my rollout to keep the tail on the groundjust be careful not to do this too soon, or the plane may want to start flying again. As others have suggested, after verifying the cg, then shim or angle the gear forward to address the nose over problem.

Let us know how it works out for you!

-Ed B.

< Message edited by Flyfast1 -- 6/7/2008 8:06:25 PM >

(in reply to Tommy_Gun)
       Post #: 13