jaka

Hi!
Does anyone know if any full scale WW11 fighter used toe-in or toe-out on there landing gear wheels?

Walt Thyng

My Feedback: (9)

Probably neither, but on a model toe in of 1-3 degrees really improves handling.
Walt

TFF

Most real planes use toe in. The idea is if you put one wheel down it steers to the center while you put the other down, toe out will slam the opposite side down without pilot control, and then it acts as a dampener as it is slightly scrubbing off speed and both wheels are pointed to the center. But as with anything you can always find an exception.

BobH

My Feedback: (2)

The FW190 used toe OUT. Not much but some. I suspect lots used toe out as well.

bogbeagle

Aerodynamicists reckon that toe-out is the better solution .... so I hear.

MajorTomski

Well my learned aero profs at Parks College always taught TOE IN.

When a conventional gear plane is up on the mains and rolling, if the plane yaws SLIGHTLY, say to the left, then the left wheel now rolling parallel to the line of motion and has a lower rolling resistance. The right wheel is now scrubbing, creating a higher rolling resistance, creating a force that pushes aft on the right wheel, thus stopping the unwanted left yaw an re ballancing the drag between the two wheels.

Toe out does just the opposite. It makes the initial yaw worse.

CanDo

I suspect the alignment has to do with the design of the gear and which way it moves or bends due to the loads and rolling friction. If the axles are supported from the inside (towards the fuselage, like a car), you tend to need a little toe-in to keep the tires pointing straight ahead under load. If the gear is strong enough, you may not need to compensate at all.

bogbeagle

Page 377 of Stinton's "Design of the Aeroplane" states that toe-out (a degree or two) will slightly improve the handling of a conventional undercarriage.



I did have a very full explanation of the theory, but I can't lay my hands on it, just now. Suffice it to say that, when I read this explanation, it blew apart my pre-conception that toe-in was desirable.

Bax

My Feedback: (11)

Likely, CanDo's answer is the correct one. It all depends upon the geometry of the gear and the placement of the gear on the aircraft. Basically, you design to theory, try it out, and then fix it to make it work the way you want it to work. That's why airplanes get flight-tested (and cars and trucks get test-driven, etc.).

pattnut

Set up your wheels on your MODEL airplane with some toe IN as well as some positve camber, for all the reasons that the front (steering) wheels of autos are done that way.

Old Dawg

Tmoth4

My Feedback: (1)

Toe-OUT can help when the plane has already started to ground-loop. In other situations: normal taxiing, takeoff, landing, and crosswinds toe-IN helps keep it going straight.

Toe-IN has always helped ground-handling on my models. Some were virtually impossible to control without it.

Jim

Wayne22

My Feedback: (2)

...yeah, what he said...

Wayne22

My Feedback: (2)

I posed this question to a friend who used to restore warbirds...here is his answer.....

Chris Nicastro

My Feedback: (3)

From my experience and observations toe out on RC planes is better than toe in. Reason is toe in on a poor landing will promote the plane to trip over its wheel and help it to begin a cart wheel. With toe out if you place one wheel on the ground while in a yaw the wheel is pointing outward when it touches down. As another member mentioned it can cause the other gear to slap down but the toe out geometry will not induce a cartwheel or wing tip scrape as easily.
Anyway Ive been doing this for years, suggested to everyone in the club that has issues like this, and I have great landings. The planes track down the runway at full speed just fine as well.
I dont suggest this for tricycle gear only for conventional planes and especially for planes like Spitfires, Bf 109, AT-6 and any narrow track warbirds. I do this for all of them regardless though.

Also make sure your axle is in front of your wing leading edge or as far forward as your model will allow. This coupled with toe out really inproves ground handling and prevents nose overs.

JeffH

My Feedback: (43)

The article I read said that with toe-in, when the plane yaws left, it loads the right tire more. Agreed. Since we are turning left, the rim is trying to push through the outside of the tire, to the right. This causes the tire to tuck under the rim which will cause it to hook left even harder. With toe-in, the tire is already trying to turn, left for the right tire and right for the left tire, and therefore any extra turn load(yaw) will cause the tire to tuck under worse thereby making the yaw harder to compensate for. With toe-out, when the plane yas left, loading the right tire, it tries to pull to the right correcting for the yaw.
That article explained much better than I, but it makes sense to me. I set mine up straight or a touch of toe out. I fly mainly on grass and with our small wheels, even giant scale, I am not convinced either makes a huge difference. On a hard surface, it is a different story.

There are many other things to consider, tire composition, hardness(air pressure or foam vs. rubber), weight of the plane, stickiness of the surface, rudder/nosewheel throw, etc. When I flew UAVs, we had an inflatable nosewheel. When inflated to X PSI, the plane was a bear. It would turn and hook and was difficult to recover to a straight takeoff run. In effect the the nosewheel had too much grip. Going back to my drag racing days(less PSI = more traction), I suggested that we increase the PSI to lessen the contact patch. It worked like a charm. The nosewheeal would now slip just a bit and we had much straighter take off runs. ANother UAV that I flew had a very hard, solid nosewheel. It wouldnt turn for crap after a certain speed. You could see the nosewheel skidding along the runway and the plane would take forever to respond to a yaw correction on the ground.

spinnetti

Good explanation.... I'm a race car guy, and toe-in is more stable.. I know on the FW-190, they have toe adjustment right on the strut, and they'd get a wheel aligment like you'd do on your car in "modern times". In general, zero toe or a touch of toe-in will make things more stable. Toe out generally will make it turn easier, but also less stable. In a plane with small tail volume and without individual wheel brakes, a bit of toe out would be helpful to turn, but can't imagine wanting toe out otherwise

spinnetti

dupe

Chris Nicastro

My Feedback: (3)

Were talking two degrees maybe three its not a huge amount. Its just enough to keep things tame in certain conditions. i bet if I didnt tell you my plane had any toe adjustment nobody would notice but everyone notices how well it behaves and asks or wonders why.

Give it a try its not going to do any harm.

Axle location relative to the CG is another important point. If the axle is too close to the CG the plane will nose over easily. Keep the axle out as far forward as possible with some toe out and the plane will be very stable.

Take a close look at the Me. Bf 109. It not only has a narrow track the axles have toe out and the axle center is forward of the LE.

Red B.

The Supermarine Spitfire is a good example of a WWII fighter aircraft that had toe-in.

Here is an interesting read:

[link=http://spitfiresite.com/2010/04/spitfire-mk-ix-xi-and-xvi-variants-much-varied.html/3]The Spitfire site[/link]

"According to Rolf Meum, who has accumulated 100+ hours of Spitfire flying with the Old Flying Machine Company, Duxford, the teardrop-shaped blisters above the wheel wells correlate to a modified wheel axle geometry adapted to tarmac/concrete runway operation. The original “grassfield” undercarriage had a substantial toe-in. As tarmac, concrete and PSP runways became usual during the course of the war, the toe-in resulted in severe wear on the port main wheel due to the engine torque during take-off. With the modification, the toe-in was decreased, but the wheels could no longer lie flat in the wheel wells and therefore needed more space to fit."

spinnetti

Makes perfect sense.. the slip angles on grass are much higher.. on pavement its hard on the tires. The 109 and 190 are great opposite examples of landing gear design and alignment (109 bad, 190 good)....

kahloq

There's no way in hell I'd put toe-out on a me-109, especially on pavement. That a recipe for disaster..

ARUP

None... use all flight controls until stopped especially the rudder. What works for one situation doesn't for another. With 'zero' set the airplane track is constant and unchanging. The only variable is pilot input. With toe-in or toe-out caster changes variably depending on how high the tail is. With 'zero' set in track, caster is constant and unchanging. The only reason autos have toe-in is to take up the multiple linkage slack that occurs. It's just a wee bit but helps with tire wear. I have a hot rod VW (an oxymoron, I know!). The dumb ***** previous owner lowered the front end, only. The toe-in was the same but the caster was now off and awful handling was the result of the 'cool stance'! It was a scarey 'bump steering' S.O.B. until I added caster shims to the bottom of the beam to put the caster at the stock design setting. Now it is a sweet heart, again. Be sure your wheels fit the axles. I bush all hubs on my wheels so there isn't but ~0.01" play. Some have less because I use 'nested' brass tubes... one size on the axle and the next size up in the hub. Overkill? Maybe. Works for me.

Ed

Toe-In ? Utter Bunkum !


Sep 2006 - The great toe in/toe out debate

Written by PDR September 24, 2006, 10:52:00 AM 1156 Views Rating: (17 Rates) You have rated this file. Print


Which way should your wheels point? Ever wondered?

We’ve all heard this one from time to time – should my model have toe-in, toe-out or neither in its wheels. Lots of people have said lots of things on probably every model aircraft forum created since Pontius was a pilot. There has even been an oft-quoted chapter of a book by a “retired Boeing engineer” which was so at variance with the basic laws of physics that I have to assume the author was having a bad hair day. I’m rather hoping that the following explanation will put this one to bed by explaining WHY toeing the wheels does things. But I’m not going to hold my breath...


Firstly I should come clean about the title. I put the word “debate” in there to be kind. There is no “great debate” – it’s a matter of basic, fundamental physics and no debate is needed.


Before we start we need to understand is how wheels work. You might think this is obvious – the wheel (of whatever colour) is the single simplest machine man has ever invented, I hear you say (wrongly). But it’s surprising how many people don’t really understand them. When a wheel is rolling along the ground it has a low rolling resistance and very few other forces acting on it. But this is only true PROVIDED the axis of the wheel is at right angles to the direction it’s rolling in. If you point the wheel in a different direction its rolling resistance increases slightly, but it also develops a “side” or “turning” force. This is what actually makes your car start turning when you steer, which is just as well or our roundabouts would be clogged cars that failed to make the corner. This applies to all wheels; aeroplane wheels are no different to those of cars, buses or bicycles in this respect. Actually it doesn’t apply to roulette wheels or the wheel of fortune, so I’d better change that to “it applies to most wheels”. But I digress.


So how much force do the wheels develop? Well this is quite a complex question, but for our purposes we can simplify it by saying that the grip of any two wheels will be identical provided they are carrying the same weight. If they are carrying different weights then the forces they develop will differ in proportion to the difference in the weights they carry. I’m sure that if I really tried I could think up a more long-winded way of saying that, but in the mean time that will have to do.



So what happens when an aircraft starts rolling along, and why do some track dead straight whilst others behave like they have an attack of St Vitus Dance? As a general rule the wheels on an aeroplane are mounted at ground level because experience has shown this can dramatically improve the ground handling. But most of the REST of the aircraft’s mass is mounted at the top of the undercarriage to get better propeller ground clearance and improve the airborne handling. So when the aircraft turns on the ground the tyre grip acts at one end of a long lever (the undercarriage leg) against the aircraft’s inertia at the other end, and this is the nub of the problem.


Let’s start by considering a tail-dragger. It starts of down the runway straight and true, but then a bump, gust or rudder input pushes it one way and it starts turning. At this point the wheels will be pushing it one way, reacting against the inertia of the aircraft which wants to push it another. As we said earlier, the two forces act at opposite ends of a lever, so they generate what we generally call a “torque couple” because we like to have complicated terms to stop people realising how easy engineering is and nicking our jobs. This force couple makes the aeroplane lean harder on the wheel that’s on the outside of the turn, and takes weight off the wheel that’s on the inside.



Now all of this is pretty academic, because the two wheels are pointing in the same direction so it really doesn’t matter HOW they share the workload. But what if they AREN’T pointing in the same direction? What if they are toed-inwards? What do we MEAN by toe-in? The diagram should make it clear so that we don’t talk cross-purposes. If the wheels are toed, then they must each be generating a sideways turning force but in opposite directions, and as the wheels are normally carrying the same weight these forces cancel out.

But with our turning tail-dragger, (with the wheels toed-in) what happens? Well we said earlier that the turning or side force is proportional to the weight on the wheel, and that when turning the outboard wheel has more weight on it. So it should be obvious that the outboard wheel now develops a side-force that is bigger than the one developed by the inboard wheel, so it wins. And as the wheels are toed inwards it can be seen that this force will tend to make the turn tighter, which will increase the weight on the wheel, which will make it tighter still and so on until we have the classical ground-loop or just a model that simply won’t hold a straight line on the ground – it is an unstable situation.

On the other hand, if the model has toe-OUT then the increased turning force tends to REDUCE the turn, which reduces the weight shift and all is normal again – a STABLE situation.


So the next time someone tells you that a tail dragger needs toe-in either ignore him or put salt in his coffee, because he’s not helping you! Now there is a long-standing myth, perpetuated in the American book I mentioned earlier, that toe-in increases stability because the outboard wheel (being presented at an angle to the direction of travel) somehow develops “road drag”, pulling the model straight again. Well as we can see from the above, firstly this isn’t true, and secondly even if it was it would be completely obliterated by the side-force generated by the tyres, and thirdly it isn’t true. So it’s what we engineers technically refer to as “utter bunkum”.


The one remaining aspect to cover is the trike undercarriage layout. Now this behaves in an almost identical way, but now the wheels (being at the back rather than the front) push in the opposite direction. So with a little thought it should be obvious that if the wheels are at the back you need toe-in for stability, whereas if they are at the front you need toe-out for stability.

bogbeagle

Thanks, ED.

You posted the engineer's explanation that I was searching for.

Won't make any difference, though.

JL1

My Feedback: (93)

That must be why my 1/4 Camel was almost unmanageable on take off and landing until I realized it had toe out and calmed right down when I set it up with 1/8th toe in.