Wing wheel from Craggy Aero

On Friday, May 1, 2020 at 8:47:48 PM UTC-7, 2G wrote:
On Friday, May 1, 2020 at 10:36:38 AM UTC-7, wrote:
Not exactly true. Tom inquired about a wing wheel, wing cuffs and a tow bar. I explained that tow bars were out of stock and wing wheels and wing cuffs are custom fabricated. Because of my involvement in another project, I informed him that delivery times were questionable, if at all possible. I don't recall receiving a check at all.

As far as "scrubbing" being "inevitable," also not true. Over 300 of my wing wheels are out there, and if properly positioned and aligned with the direction of travel, they track well.

But you can't convince Tom, since he is always right.

Come on, Mark. I sent you the check - I've got a copy of it - along with a purchase order, which I also have a copy of. You said you could make more money on another project. I said, "Ok, then shred the check and forget it, no hard feelings."

Scrubbing is what happens when you turn a tire on a radius. I have seen it happen with my Cobra wing wheel. If the wing is long enough and the turning radius tight enough, you get to the limit where the wing wheel is at the exact center of the turn and is being turned around a point. This scrubbing pushes the wing wheel sideways and is very obvious with the Cobra wing wheel. It's not me that's right, it's physics that's right.

Tom

If the wing wheel is biased forward, so that it is inline with the main gear axle, there will be no scrubbing as the geometry is correct for any radius turn. The further behind the main gear the wing wheel is, the larger the problem. My complaint on the Cobra was the wheel was too small for rough ground, so I fitted a much larger one. It seems like the Craggy wheel is much smaller still. Probably works well on pavement.

Scrubbing is what happens when you turn a tire on a radius.

If the wing wheel is biased forward, so that it is inline with the main gear axle, there will be no scrubbing as the geometry is correct for any radius turn.

Ignoring who said and did what, I just learned a useful geometry lesson.

Assuming 'scrubbing' is when the rubber on a tire rubs instead of rolls over the pavement.

Another symptom is 'hopping' where the wheel tracks wrong and rolls out of position flexing the mount. Eventually, there is enough force from the flex to make the wheel hop back into position. Definitely some 'scrubbing' involved as well. Definitely a worrying situation because the flex is putting weird loads on the flying parts.

If the wing wheel is vertical and in line with the line of travel, why would there be scrubbing when you are going straight?

If in addition, the axle of the wing wheel points to a line directly above the main wheel, why would there be scrubbing when the glider makes a turn?

Maybe in the limit, neither one of these can be aligned perfectly, but if you put the wing wheel in the right place it ought to work pretty good.

That explains why my old wing wheel still hopped on curves even after I adjusted it so it points straight ahead. Also why the new MM one doesn't.

Guess a swivel might be another out of the hole, but not the only way.

On Sunday, May 3, 2020 at 6:17:40 AM UTC-7, wrote:

Scrubbing is what happens when you turn a tire on a radius.

If the wing wheel is biased forward, so that it is inline with the main gear axle, there will be no scrubbing as the geometry is correct for any radius turn.

Ignoring who said and did what, I just learned a useful geometry lesson.

Assuming 'scrubbing' is when the rubber on a tire rubs instead of rolls over the pavement.

Another symptom is 'hopping' where the wheel tracks wrong and rolls out of position flexing the mount. Eventually, there is enough force from the flex to make the wheel hop back into position. Definitely some 'scrubbing' involved as well. Definitely a worrying situation because the flex is putting weird loads on the flying parts.

If the wing wheel is vertical and in line with the line of travel, why would there be scrubbing when you are going straight?

If in addition, the axle of the wing wheel points to a line directly above the main wheel, why would there be scrubbing when the glider makes a turn?

Maybe in the limit, neither one of these can be aligned perfectly, but if you put the wing wheel in the right place it ought to work pretty good.

That explains why my old wing wheel still hopped on curves even after I adjusted it so it points straight ahead. Also why the new MM one doesn't.

Guess a swivel might be another out of the hole, but not the only way.

To be correct geometry for a specific radius turn, the wing axle must point towards center of the turn radius. The axle lines of the main and wing wheel intersect at this center. If the main wheel is the center, then the wing axle must point towards it. A swiveling wheel will align itself to this geometry. For a non swiveling wheel to be correct geometry for *any* radius, the axles have to be in line (more specifically their projection to the ground plane has to be on a line), guaranteeing that both axle lines intersect at the circle center regardless of radius. The wing wheel will then not scrub, even if it is the center of the turn. It will turn about its vertical axis, just as the main gear (or indeed the swiveling wheel) must, in other circumstances. That is not "scrubbing" as the term is usually applied.

And now, back to the popcorn....

On Sunday, May 3, 2020 at 4:48:52 PM UTC+1, jfitch wrote:
On Sunday, May 3, 2020 at 6:17:40 AM UTC-7, wrote:

Scrubbing is what happens when you turn a tire on a radius.

If the wing wheel is biased forward, so that it is inline with the main gear axle, there will be no scrubbing as the geometry is correct for any radius turn.

Ignoring who said and did what, I just learned a useful geometry lesson..

Assuming 'scrubbing' is when the rubber on a tire rubs instead of rolls over the pavement.

Another symptom is 'hopping' where the wheel tracks wrong and rolls out of position flexing the mount. Eventually, there is enough force from the flex to make the wheel hop back into position. Definitely some 'scrubbing' involved as well. Definitely a worrying situation because the flex is putting weird loads on the flying parts.

If the wing wheel is vertical and in line with the line of travel, why would there be scrubbing when you are going straight?

If in addition, the axle of the wing wheel points to a line directly above the main wheel, why would there be scrubbing when the glider makes a turn?

Maybe in the limit, neither one of these can be aligned perfectly, but if you put the wing wheel in the right place it ought to work pretty good.

That explains why my old wing wheel still hopped on curves even after I adjusted it so it points straight ahead. Also why the new MM one doesn't.

Guess a swivel might be another out of the hole, but not the only way.

To be correct geometry for a specific radius turn, the wing axle must point towards center of the turn radius. The axle lines of the main and wing wheel intersect at this center. If the main wheel is the center, then the wing axle must point towards it. A swiveling wheel will align itself to this geometry. For a non swiveling wheel to be correct geometry for *any* radius, the axles have to be in line (more specifically their projection to the ground plane has to be on a line), guaranteeing that both axle lines intersect at the circle center regardless of radius. The wing wheel will then not scrub, even if it is the center of the turn. It will turn about its vertical axis, just as the main gear (or indeed the swiveling wheel) must, in other circumstances. That is not "scrubbing" as the term is usually applied.

And now, back to the popcorn....

That is true assuming that the leg of the dolly is vertical and a non-vertical leg would make a negligible difference on a single tight turn. However with a noticeably non-vertical leg and a fixed wheel (e.g. and in my case, on the dihedraled outer part of a D2C or V3 wing) then on a straight tow, no matter how accurately the cuff is alinged, the wheel will tend to turn itself (like how you lean to turn a bike). It will then either relieve itself by bouncing, or by skidding back to position, or it will twist the dolly until you stop and go and sort it - depending on the surface and the weight on the dolly from ballast.

On Sunday, May 3, 2020 at 9:54:13 AM UTC-7, wrote:
On Sunday, May 3, 2020 at 4:48:52 PM UTC+1, jfitch wrote:
On Sunday, May 3, 2020 at 6:17:40 AM UTC-7, wrote:

Scrubbing is what happens when you turn a tire on a radius.

If the wing wheel is biased forward, so that it is inline with the main gear axle, there will be no scrubbing as the geometry is correct for any radius turn.

Ignoring who said and did what, I just learned a useful geometry lesson.

Assuming 'scrubbing' is when the rubber on a tire rubs instead of rolls over the pavement.

Another symptom is 'hopping' where the wheel tracks wrong and rolls out of position flexing the mount. Eventually, there is enough force from the flex to make the wheel hop back into position. Definitely some 'scrubbing' involved as well. Definitely a worrying situation because the flex is putting weird loads on the flying parts.

If the wing wheel is vertical and in line with the line of travel, why would there be scrubbing when you are going straight?

If in addition, the axle of the wing wheel points to a line directly above the main wheel, why would there be scrubbing when the glider makes a turn?

Maybe in the limit, neither one of these can be aligned perfectly, but if you put the wing wheel in the right place it ought to work pretty good..

That explains why my old wing wheel still hopped on curves even after I adjusted it so it points straight ahead. Also why the new MM one doesn't.

Slightly related, bicycle and motorcycle dynamics (or any two wheeled vehicle) are quite a complex subject and only recently fully described mathematically (in the last ten years or so). The solutions are too complex to solve so numeric methods are used.

Not only complex but very few people who ride bikes or motorcycles even know how they initiate a turn. Most assume that if you want to turn left, you pull back on the left handlebar, but in fact to turn left (while moving at a reasonable speed) you push on the left handlebar. The dynamics cause the bike to lean left, and the geometry causes the wheel to turn left to compensate. It is one of the reasons it is hard to learn how to ride a bike, the handling changes with speed.

Try it, push lightly with your fingertips, the handlebar will push back after the turn is initiated. Hang glider turning dynamics are related.

Rick

On Sunday, May 3, 2020 at 3:05:50 PM UTC-7, RR wrote:
Slightly related, bicycle and motorcycle dynamics (or any two wheeled vehicle) are quite a complex subject and only recently fully described mathematically (in the last ten years or so). The solutions are too complex to solve so numeric methods are used.

Not only complex but very few people who ride bikes or motorcycles even know how they initiate a turn. Most assume that if you want to turn left, you pull back on the left handlebar, but in fact to turn left (while moving at a reasonable speed) you push on the left handlebar. The dynamics cause the bike to lean left, and the geometry causes the wheel to turn left to compensate. It is one of the reasons it is hard to learn how to ride a bike, the handling changes with speed.

Try it, push lightly with your fingertips, the handlebar will push back after the turn is initiated. Hang glider turning dynamics are related.

Rick

All turns, whether on the ground or in the air, have one immutable thing in common: there must be a lateral force to cause an object with momentum in a straight line trajectory to change that trajectory. A wheel can have its axle turned and the tire generates this force by friction with the ground, as occurs while executing a turn in a car. If some other force is applied to the car to turn it, such as a wind gust, the tire will resist this turning force until the applied force exceeds the grip of the tire. The car will then skid. The same thing is going on with a glider's wing wheel as it is being forced to turn around a curve by the towing vehicle. This lateral force will be the same regardless of the design of the wing wheel, it will just be less apparent with some than with others. This force MUST be transmitted to the wing - there is no other place for it to go.

Tom