This is asked with some regularity on this forum.

Simple answer: If it saved money, it would be done. Currently, the cost motor solution seems to be more than the cost of extra tyre wear.

You'd also introduce additional threats to the operation. What if the mains on one side spin up and the other ones don't? Would this introduce a lot of yaw? Would there have to be a quick disconnect? All solvable, of course, but solving such problems costs money.

This doesn't mean it won't ever be done. The cost equation is not static over time. Electric motors are becoming ever smaller, lighter, and more powerful.

What about landing on a conveyor belt?

Rather than electrically powered motors, perhaps small vanes on the wheel hubs could use the slipstream to spin the wheels up?

IIRC there is a patent to add little scoops on the tires to spin them up from the airflow.
The issue is you would also spin them when you take-off, too.

You'd therefore have to brake them more on retraction and I guess brake wear is more costly than tire wear.

You'd also be adding weight to the gears with motors etc.

ReverseFlow wrote:

IIRC there is a patent to add little scoops on the tires to spin them up from the airflow.
The issue is you would also spin them when you take-off, too.

You'd therefore have to brake them more on retraction and I guess brake wear is more costly than tire wear.

You'd also be adding weight to the gears with motors etc.

Brakes are applied prior to retraction anyway so it would not change wear at all. Carbon brakes wear per application, not depending on application force.

Avatar2go wrote:

Starlionblue wrote:

This is asked with some regularity on this forum.

Simple answer: If it saved money, it would be done. Currently, the cost motor solution seems to be more than the cost of extra tyre wear.

You'd also introduce additional threats to the operation. What if the mains on one side spin up and the other ones don't? Would this introduce a lot of yaw? Would there have to be a quick disconnect? All solvable, of course, but solving such problems costs money.

This doesn't mean it won't ever be done. The cost equation is not static over time. Electric motors are becoming ever smaller, lighter, and more powerful.

Ok, thanks for the information. I thought someone here might know the answer. I hadn't thought about the asymmetric spin possibility, seems like that would be a significant concern.

I'm really not sure about the asymmetric yaw. We can land with a locked brake and I guess even large wheels aren't much compared to the weight of the airliner itself. Still, it is a failure mode that must be considered.

Starlionblue wrote:

ReverseFlow wrote:

IIRC there is a patent to add little scoops on the tires to spin them up from the airflow.
The issue is you would also spin them when you take-off, too.

You'd therefore have to brake them more on retraction and I guess brake wear is more costly than tire wear.

You'd also be adding weight to the gears with motors etc.

Brakes are applied prior to retraction anyway so it would not change wear at all. Carbon brakes wear per application, not depending on application force.

Regarding the brake wear, even steel brakes wouldn't have that much incremental wear from the marginal effort of slowing down the rotation.

There are a couple other questions that come to mind with the weathervane tires:
1. I think some types allow a certain number of inop brakes depending on the runway lengths, etc. After takeoff, they wait a few minutes to spin down, and then retract. Weathervanes would take that option away because the wheels would keep spinning. Is that an acceptable penalty?
2. How much of a drag penalty do you pay for the weathervanes? If F=ma, m=~150 kg per wheel (guess), and you need to spin up 10 wheels to 130 kts, how much energy do you need to take from the plane in the form of drag to achieve that? How much of a penalty do you pay on takeoff with OEI?
3. What's the cost of molding those weathervanes into the tires vs retreading?
4. What happens if I get a birdstrike on the tire that knocks half of the weathervanes off?

Starlionblue wrote:

ReverseFlow wrote:

IIRC there is a patent to add little scoops on the tires to spin them up from the airflow.
The issue is you would also spin them when you take-off, too.

You'd therefore have to brake them more on retraction and I guess brake wear is more costly than tire wear.

You'd also be adding weight to the gears with motors etc.

Brakes are applied prior to retraction anyway so it would not change wear at all. Carbon brakes wear per application, not depending on application force.

Avatar2go wrote:

Starlionblue wrote:

This is asked with some regularity on this forum.

Simple answer: If it saved money, it would be done. Currently, the cost motor solution seems to be more than the cost of extra tyre wear.

You'd also introduce additional threats to the operation. What if the mains on one side spin up and the other ones don't? Would this introduce a lot of yaw? Would there have to be a quick disconnect? All solvable, of course, but solving such problems costs money.

This doesn't mean it won't ever be done. The cost equation is not static over time. Electric motors are becoming ever smaller, lighter, and more powerful.

Ok, thanks for the information. I thought someone here might know the answer. I hadn't thought about the asymmetric spin possibility, seems like that would be a significant concern.

I'm really not sure about the asymmetric yaw. We can land with a locked brake and I guess even large wheels aren't much compared to the weight of the airliner itself. Still, it is a failure mode that must be considered.

Good point.

https://www.boeing.com/commercial/aerom ... _05_1.html

However for brake to vacate it is said that it saves brake wear.

https://www.flightglobal.com/easa-clear ... 32.article

Another thought - scoops would also be extra drag at times you don't want it

Edit: Here's thd patent (German)

https://www.freepatentsonline.com/DE202009001104U1.html

I personally haven’t changed many tires for flat spotting in my careeer- If any. I don’t think landings impact tire wear that much. You generally get your money’s worth out of the tire. Makes me think any kind of wheel spin up device is largely irrelevant.

Thrusty69 wrote:

I personally haven’t changed many tires for flat spotting in my careeer- If any. I don’t think landings impact tire wear that much. You generally get your money’s worth out of the tire. Makes me think any kind of wheel spin up device is largely irrelevant.

Black rubber marks at touchdown beg to differ.
A good number for discussion would be the cost of tyres in operations. How many cycles do tyres last, and what is the cost per tyre (including labor costs for service)?
If I remember correctly, 1 lb of weight costs something like $0.25 in fuel per cycle on medium haul. Weight of spinup device would be a few lb, and that would add up.

From a few calculations like that I did over time, my main impression is that airborne weight is expensive. If you can cut down on weight, it often makes sense to do so, even if that costs in a long run. Only essential thing should be up there.

kalvado wrote:

Thrusty69 wrote:

I personally haven’t changed many tires for flat spotting in my careeer- If any. I don’t think landings impact tire wear that much. You generally get your money’s worth out of the tire. Makes me think any kind of wheel spin up device is largely irrelevant.

Black rubber marks at touchdown beg to differ.
A good number for discussion would be the cost of tyres in operations. How many cycles do tyres last, and what is the cost per tyre (including labor costs for service)?
If I remember correctly, 1 lb of weight costs something like $0.25 in fuel per cycle on medium haul. Weight of spinup device would be a few lb, and that would add up.

From a few calculations like that I did over time, my main impression is that airborne weight is expensive. If you can cut down on weight, it often makes sense to do so, even if that costs in a long run. Only essential thing should be up there.

Speaking of weight you don't need.
Someone once joked to me that the 3 things airlines don't like are:
- Landing gears
- Windows
- Pilots

There are concepts around where the aircraft sits on a 'chariot' on ground and then somehow lands on one at its destination negating the need for landing gears.
Obviously many issues with that.
The U2 has got its wing wheels that fall off on take-off or the Me 163 Komet during WW2 which had a dolly that it took off from. But doing something like this on an airliner would be another scale!

Bad Idea for Stopping Distance - One big safety point everyone is missing, is that the drag from the touchdown helps to shorten the stopping distance. Therefore the expensive motor / scoop "solution" to the cost of tire wear will all be made up for when even one hull is lost to overruns not to mention less utility from aircraft that can no longer use shorter runways at high gross weights. Then in the "scoops" case there's less braking effectiveness in the RTO (Rejected Takeoff) case, thereby further reducing the weight carrying capacity of any aircraft with such a system installed. Why would anybody spend money on such a risk-prone "solution" to a problem that doesn't really exist? Tires will wear out from heat and exposure to extreme temperature and pressure variations of the flight cycle anyway. The additional wear and tear from skidding touchdowns is negligible in the grander scheme of things.

aeropix wrote:

Bad Idea for Stopping Distance - One big safety point everyone is missing, is that the drag from the touchdown helps to shorten the stopping distance. Therefore the expensive motor / scoop "solution" to the cost of tire wear will all be made up for when even one hull is lost to overruns not to mention less utility from aircraft that can no longer use shorter runways at high gross weights. Then in the "scoops" case there's less braking effectiveness in the RTO (Rejected Takeoff) case, thereby further reducing the weight carrying capacity of any aircraft with such a system installed. Why would anybody spend money on such a risk-prone "solution" to a problem that doesn't really exist? Tires will wear out from heat and exposure to extreme temperature and pressure variations of the flight cycle anyway. The additional wear and tear from skidding touchdowns is negligible in the grander scheme of things.

I heavily doubt that touchdown tire wear and spinup would be a big contribution towards braking. There is a reason ABS was developed to allow braking without tire slipping - first introduced on airliners, as far as I remember. Tires spinup would also be a relatively small contribution, probably a fraction of a knot, if not a fraction of 0.1 knot.