Why are the nosewheels on the Constellation canted in a few degrees? Is it to ensure both tyres have ground contact during tight ground turns?

I've observed that on the A320 during tight turns that one wheel comes completely off the ground. The A320 nose leg also sits at an angle; would it benefit (if needed) from angled nosewheels?

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    $\begingroup$ Are you asking about the cant of the wheels themselves (I would call it out, not in, though—the tops are further apart), or of the strut? $\endgroup$ – Jan Hudec Jun 10 '19 at 13:48
  • $\begingroup$ Ahhh now I get it. $\endgroup$ – John K Jun 10 '19 at 20:16

@JohnK gives an excellent explanation for castor - the horizontal offset between the steering axis and the tire contact point.

But maybe the question is about camber. That is the angle between the vertical axis of the tire and the vertical direction relative to the ground. The camber angle on the Connie's nose wheels is called positive camber, and an extreme case can be found on the tractors of that time. Curiously, it is a distinct characteristic only of US tractors like the John Deere (left) and Farmall (right) tractors below (picture source).

Vintage tractors

The reason is easier steering in rough terrain. As a tractor discussion board explains:

I have read that positive camber is intended to align the kingpin axis with the center of the tire contact patch. Supposedly this reduces the force required to steer the axle. If that theory is true, then changing the height of the tires would change the intersection point of the camber angle and the kingpin angle; it's improbable that swapping between, say, the correct R4 tires and the correct R1 tires for your tractor would make significant differences.

However, I am not convinced by the theory that the positive camber is there for steering ease. Here is why: I think it would be easier to roll a tire around in a circle than it would be to simply twist it, especially if one considers the tire will be pushing dirt out of the way as it twists.

I think the reason for the positive camber is to attenuate the camber thrust that can occur when the tires encounter uneven terrain. This would tend to help the tractor track straighter, and require less steering input to maintain a straight course. That characteristic, along with the caster geometry, should make the tractor track straight naturally, rather than tending to turn more when either a steering input is made or some uneven terrain is encountered.

The author of this post has his own theory; however, the point made in his first sentence actually has merit: Since steering in automobiles and European tractors is made easier when the steering axis runs through the contact point of the tire with the ground, positive camber is an attempt to reduce the steering roll radius of the twin tires which indeed should make steering easier.

steering axis inclination

Steering axis inclination reduces the roll radius in cars (picture source); since the sideways axis inclination could not be used in nose gears or tractors, both resorted to tire camber.

  • $\begingroup$ Yep I was convinced he was talking about the angle of the main strut. My bad. Thanks Peter. $\endgroup$ – John K Jun 10 '19 at 20:17
  • $\begingroup$ @JohnK: Me too, at first. Only Jan's comment made me read the question again. $\endgroup$ – Peter Kämpf Jun 10 '19 at 20:44
  • $\begingroup$ The angle of the main strut remains important to the design, as the wheel must roll slightly in the turn. "Castoring" seems to be actually be an unstable condition, there for a castoring wheel should "trail". However, in the rake, the roll factor keeps it from turning when gyroscopic forces are present, but it "castors" unstably at low speeds, making turning easier. This is why John's initial work was appreciated. The cant probably made the farmers wheel shake a lot less as uneven terrain was crossed. Plus the inward leaning angle definitely schmooshed the soft ground aside. $\endgroup$ – Robert DiGiovanni Jun 10 '19 at 21:08
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    $\begingroup$ One problem that strikes me right away with the Connie's cambered wheels is during a high speed directional input the roll-under load on the "up-turn" tire must be massive. $\endgroup$ – John K Jun 10 '19 at 21:35
  • $\begingroup$ @JohnK Camber is an important tool in tuning a race car to go around corners. While an F1 car is considerably lighter than the Connie, cornering at 150MPH pulling 5G puts a fair bit of stress through the system. Tires don't roll off their beads. $\endgroup$ – FreeMan Nov 24 '20 at 19:21

It's basically for the same reason motorcycle forks are canted or raked.

For a nose gear, you have two options to give the wheel assembly a natural self-aligning, or castering, tendency.

You can make it work like a shopping cart caster like the sketch on the right, with a vertical strut and the wheel on an offset dogleg fork so that the wheel contact point B is aft of the steering or pivoting axis point A. A lot of airliners do it this way and it has the advantage of a flat contact pattern all the way around, as well as the ability to caster 360 degrees when the scissors is disconnected. But it's heavier.

If you want to make the strut straight without the dogleg, which is a bit lighter, you make it like the sketch on the left, and angle the pivot axis of the strut so the pivot axis intersects the ground forward of the wheel's axis (called the caster or rake angle - the distance between A and B is called "trail"). Like a motorcycle fork, or a car's front suspension. This gives a natural castering tendency, which is why you can take your hands off the handlebars on a motorcycle and it doesn't veer off.

Raking the strut is almost the universal configuration on single tire nosewheel light planes, but doesn't work that well for turning with double tire wheels because one lifts off the ground when it turns, putting a lot of stress on the axle and wearing the tires unevenly, but this is significant only when making fairly sharp turns so you can get away with it because things are moving slowly. On the other hand, double tires also enhance the rolling stability because both tires want to stay planted by gravity and the only way is when straight - easy to imagine if you mentally increase the rake to 90 degrees - so you need less steering rake than you might otherwise need with a single tire.

enter image description here

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    $\begingroup$ I don't see how this answers the question. Motorcycle has only one front wheel that is not canted. However, Constellation has two wheels on the nose gear, and they don't have common, level, axle, but are tilted outward. $\endgroup$ – Jan Hudec Jun 10 '19 at 5:55
  • $\begingroup$ Motorcycle forks have an angle to allow the rider to control the leaning of the bike by altering the aligning of the axis of the two gyroscopes (aka wheels). It has nothing to do with self aligning or shopping carts wheels. And the reason a motorbike stays up is because of the gyroscopic inertia of the wheels. $\endgroup$ – Diego Sánchez Jun 10 '19 at 10:16
  • $\begingroup$ @Jan Hudec The canting helps LOW SPEED steering. Think of the 2 wheels as right and left halves of one wheel. But once the "wheel" spins up, gyroscopic physics takes over. $\endgroup$ – Robert DiGiovanni Jun 10 '19 at 11:03
  • $\begingroup$ en.wikipedia.org/wiki/Caster_angle $\endgroup$ – John K Jun 10 '19 at 12:52
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    $\begingroup$ @JohnK, please, read the question again, and look up a picture of a constellation. The point is that the wheels themselves are canted, not the strut/fork/rake. $\endgroup$ – Jan Hudec Jun 10 '19 at 13:22

Have to give MikeY, Quiet Flyer, and John K credit for helping me get this one, along with some reading on chopper (motorcycle) rake design.

When a forward rake is "turned", it rolls and yaws, resulting in the tire being slightly on its side while it is turning. This is why the Constellation tires are canted a few degrees. The outside tire can lift completely off the ground as it rolls upwards when the wheel assembly is turned.

Why a raked fork? We know a spinning disk has stability and will resist being turned out of its plane of rotation. Since a raked fork rolls the wheel to its side, the assembly can only be turned with effort against the spinning wheel. This stability would be very important to a long nose strut such as the one found on the Constellation. Any wobbling would be disasterous.

Whether the A320 would benefit from angled wheels, if the rake or length of the strut is not as great as the Constellation, probably not as much. But with the Constellation, it is expected that the inside tire will bear the turn.

  • $\begingroup$ You might be on the right track, but I don't really see the argument. The outer wheel lifts because the strut is canted, but I don't see how canting the wheels themselves (outward) changes it (and I do believe it has something to do with the stability—I just don't see what from your argument). $\endgroup$ – Jan Hudec Jun 10 '19 at 5:59
  • $\begingroup$ Some more reading revealed it makes farm tractors steer easier. The rake is what gives the wheel assembly stability. $\endgroup$ – Robert DiGiovanni Jun 10 '19 at 9:36
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    $\begingroup$ Raking the steering axis so it intersects the ground forward of the wheel axis makes the wheel want to trail. The dimension of the two intersect points on the ground is called "trail" for that reason. The rake angle itself is actually destabilizing statically, making the wheel want to flop over. When rolling, the wheel overcomes this and want to trail, like a caster, and gyro forces provide additional stability. $\endgroup$ – John K Jun 10 '19 at 13:35
  • $\begingroup$ And the pitch to the ground of the wheel is called "camber", oh my goodness! But this is actually a very ingenious way to deal with the long strut of the Constellation, it does not want to turn at high speeds (just after touch down) but can be turned at low speeds. The cant of the wheels helps by narrowing the ground contact, reducing "handle bar" torque (manual steering tractors love this), and the "flop" is the tire rolling on it side as well as yawing. $\endgroup$ – Robert DiGiovanni Jun 10 '19 at 15:24

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