Wheel Spin-Up, pre-landing..?
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Wheel Spin-Up, pre-landing..?
With all the damage done to Tyres, Runway Numbers and Piano Keys, I wonder why the MLG wheels are not spun-up prior to Landing.
Maybe adding an electric motor would be a bit difficult, but some form of wind-driven arrangement might be possible. The change in angular momentum of a heavy wheel, going from 0 to 120 knots in less than one second is quite considerable, I will leave the mathematics to those with a slide-rule to calculate.
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Maybe adding an electric motor would be a bit difficult, but some form of wind-driven arrangement might be possible. The change in angular momentum of a heavy wheel, going from 0 to 120 knots in less than one second is quite considerable, I will leave the mathematics to those with a slide-rule to calculate.
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With all the damage done to Tyres, Runway Numbers and Piano Keys, I wonder why the MLG wheels are not spun-up prior to Landing.
Maybe adding an electric motor would be a bit difficult, but some form of wind-driven arrangement might be possible. The change in angular momentum of a heavy wheel, going from 0 to 120 knots in less than one second is quite considerable, I will leave the mathematics to those with a slide-rule to calculate.
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Maybe adding an electric motor would be a bit difficult, but some form of wind-driven arrangement might be possible. The change in angular momentum of a heavy wheel, going from 0 to 120 knots in less than one second is quite considerable, I will leave the mathematics to those with a slide-rule to calculate.
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I doubt the shock load on the gear or airframe is particularly significant.
It's true that the runway puts a rearward force on the tire that has to be countered by the axle and the gear. But the force can't be all that great. First, there's only sliding friction between the tire and runway before it's run up, which means that the force imparted to the gear should be significantly less than braking to the point just before the wheels lock. Second, and even more significant, only a fraction of the aircraft weight is on the tires at spin up. This further (and I think extensively further) limits the friction force and the load on the gear.
The wear on the tire is obvious, of course. But it may be cheaper to replace the tires more often than to pay for and haul around a pre-spin mechanism.
It's true that the runway puts a rearward force on the tire that has to be countered by the axle and the gear. But the force can't be all that great. First, there's only sliding friction between the tire and runway before it's run up, which means that the force imparted to the gear should be significantly less than braking to the point just before the wheels lock. Second, and even more significant, only a fraction of the aircraft weight is on the tires at spin up. This further (and I think extensively further) limits the friction force and the load on the gear.
The wear on the tire is obvious, of course. But it may be cheaper to replace the tires more often than to pay for and haul around a pre-spin mechanism.
1. Putting a spinup device on the aircraft landing gear will cost the operator money, which is OK, but why should an operator spend money to protect the "numbers and piano keys" - whose cost is the responsiblity of the airport authority? Maybe - if the airports give landing fee rebates to aircraft that use the device. (In our deams... 
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2. Therefore the costs of adding such a device (certification per aircraft type, required inspections and maintenance (down time plus labor), weight penalty on payload (cash income, fuel expense) have to be less than simply replacing the tires as needed, to actually produce a benefit.
3. Possibly addressable - but spinning tires/wheels produce gyroscopic forces. May produce control surprises on short final with yaw or roll. Ever heard that "RUm-M-m-M-mblebleble" as the gear retracts on some planes, vibrating while changing plane of rotation, before the autobrakes stop them for stowing? Lot of gyro precession going on there.
Depends on how late and how fast the spinup can take place. 50 foot callout? 200 foot? Required complete as part of "landing configuration/stable" (500-1000 feet)? At "gear-down?"
)2. Therefore the costs of adding such a device (certification per aircraft type, required inspections and maintenance (down time plus labor), weight penalty on payload (cash income, fuel expense) have to be less than simply replacing the tires as needed, to actually produce a benefit.
3. Possibly addressable - but spinning tires/wheels produce gyroscopic forces. May produce control surprises on short final with yaw or roll. Ever heard that "RUm-M-m-M-mblebleble" as the gear retracts on some planes, vibrating while changing plane of rotation, before the autobrakes stop them for stowing? Lot of gyro precession going on there.
Depends on how late and how fast the spinup can take place. 50 foot callout? 200 foot? Required complete as part of "landing configuration/stable" (500-1000 feet)? At "gear-down?"
Years ago, you could get a 'gravel kit' for some Lears and Citations.
It would spin up the nose wheel so it wouldn't spray gravel (you hoped!) down the throat
of the engines on touchdown.
It would spin up the nose wheel so it wouldn't spray gravel (you hoped!) down the throat
of the engines on touchdown.
I don't know how the cost / benefits equation would work out here but I understand that usi get electric motors for taxi is also seriously considered. Maybe it could be envisioned in that context?
More tyre wear occurs on takeoff than landing, when the aircraft is heavier.
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Is that your opinion, or do you have a source for that information? No offense meant, but it sounds unlikely to me - where does the tyre wear come from on a wheel that is neither driving or braking the vehicle. Presumably a small amount from the flexing of the tyre, but surely not as much as under braking?
Primarily tyre scrubbing at high weights and adhesion on the runway due to tyre temps raising on the takeoff roll. remember, when the aircraft starts its takeoff run, the tyres hold all of the aircraft weight.
At touchdown, the wings even with spoiler deployment are holding 40%+ of the aircraft weight still so far less friction caused scrubbing. plus fuel fractions mean the aircraft will be around 30% lighter at touchdown.
I believe the citation has something similar for gravel landings.
Thread Starter
Quote.... Depends on how late and how fast the spinup can take place. 50 foot callout? 200 foot? Required complete as part of "landing configuration/stable" (500-1000 feet)? At "gear-down?"
If it was a windmill type of device fitted to each wheel, then the spin-up would commence as soon as the MLG was deployed, giving the wheels lots of time to reach speed.
The only downside of this might be that you would lose the jolt on landing, which could account for one or two knots of taxi speed. Also that jolt is a good indication to the pilot that the plane is actually on the ground..
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If it was a windmill type of device fitted to each wheel, then the spin-up would commence as soon as the MLG was deployed, giving the wheels lots of time to reach speed.
The only downside of this might be that you would lose the jolt on landing, which could account for one or two knots of taxi speed. Also that jolt is a good indication to the pilot that the plane is actually on the ground..
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Think about having that much mass spun up and hanging below the airframe. Now, think about gyroscopic forces that would occur when you are trying to correct the flight path. Think about playing with those little gyro's in physics class and imagine that on a much grander scale.
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Have you ever noticed the second landing after a bounce is a lot smoother. It's that jolt we feel as a bump that does it. The second touch is with the wheels spun up.... Easiest way is with moulded rubber "wings" to let airflow spin the tyres up, but the tyre company would have to agree to that.
Can't ever see that happen, like turkey's voting for Christmas.
Can't ever see that happen, like turkey's voting for Christmas.
Think about having that much mass spun up and hanging below the airframe. Now, think about gyroscopic forces that would occur when you are trying to correct the flight path. Think about playing with those little gyro's in physics class and imagine that on a much grander scale.
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https://pdfs.semanticscholar.org/69b...86bc6daff5.pdf
What is interesting, is that most wheel spinning patents use compressed air, not electric motors...
I see much more value in the nose gear drive for taxi that spinning up the landing gear to save tires.
What is interesting, is that most wheel spinning patents use compressed air, not electric motors...
I see much more value in the nose gear drive for taxi that spinning up the landing gear to save tires.
@Dave Reid and Scifi - you guys will have to get together and get your stories straight. Wheels are spinning after takeoff for, what, 10-15 seconds? "Positive rate!" - "GEAR UP!" And often immediately braked while still retracting. Decelerating.
Scifi expects them to spin up on gear deployment, 90 seconds (on average) before touchdown. And during the phase of flight where one is trying to nail a target 3 feet wide (the centerline). And where braking defeats the whole idea - they are accelerating to match landing speed.
Scifi expects them to spin up on gear deployment, 90 seconds (on average) before touchdown. And during the phase of flight where one is trying to nail a target 3 feet wide (the centerline). And where braking defeats the whole idea - they are accelerating to match landing speed.
