Wheel Spin-Up, pre-landing..?

[scifi]

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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[Matt48]

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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Yes, the rubber burnt and the shock load on the gear and airframe must be considerable, but I have a theory that the Dunlops and Goodyears of the world keep buying up patents.

[Chu Chu]

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.

[stilton]

This again ?!

[pattern_is_full]

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... ;) )

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?"

[Capt Fathom]

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.

[Pugilistic Animus]

Too heavy and cumbersome sounding. And the motor would be quite large and require tons of electricity

[washoutt]

In the late 1940's, they did tests with a Constellation with pre-spin. The tests were abanoned, with no follow up. I don't why, any historians in the house?

[atakacs]

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?

[VinRouge]

More tyre wear occurs on takeoff than landing, when the aircraft is heavier.

[farsouth]

More tyre wear occurs on takeoff than landing, when the aircraft is heavier.

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?

[VinRouge]

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?

https://www.prnewswire.com/news-releases/goodyear-recommends-aviators-know-aircraft-tire-wear-limits-111465249.html

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.

[farsouth]

Thanks very much, interesting and informative!

[scifi]

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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[Willit Run]

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.

[Derfred]

Also that jolt is a good indication to the pilot that the plane is actually on the ground..

What jolt? ;)

[RVF750]

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.

[DaveReidUK]

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.

You mean like the gyroscopic forces that occur immediately after take-off when the wheels are still spinning ? Really ?

[underfire]

https://pdfs.semanticscholar.org/69b9/0838fa710379b556c79685590e86bc6daff5.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.

[pattern_is_full]

@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.

[A Squared]

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.

Not significant. Just as an example, the props on the plane I fly are much heavier than the wheel assembly, much larger in diameter, and rotate faster. All of that equates to higher procession. Granted, the props will precess in pitch and yaw, while the wheels would precess in roll and yaw. But if you are rolling on final at a rate faster than you pitch on takeoff rotation, you're doing it wrong.

[Pugilistic Animus]

Let's face the facts here, Yes, such a device will never occur...this device is at a level of muppettry just a little above circular runway.

[A Squared]

Let's face the facts here, Yes, such a device will never occur...this device is at a level of muppettry just a little above circular runway.

For the Record, I wasn't arguing that it was a good idea, just that gyroscopic precession wasn't one of the real reasons it wasn't a good idea.

[tonytales]

Way back when before most of you were born they put molded rubber cups on the side of the giant main wheels of the Douglas XB-19 experimental bomber. The huge (for the day) aircraft had a single main wheel on each gear that was about seven feet in diameter. I know, because I stood inside one of the tires as a kid at a museum in New York. The cups would catch the air like a pinwheel and spin the tires up - no motors, no air jets. Never saw the results of the experiment but I suspect huge spinning main wheels in flight caused a deal of vibration and rumble.

[megan]

Reading the literature it seems that tyre wear is predominately caused by factors other than those imposed at touchdown eg scrubbing during turns, braking. Pre spin does seem to greatly reduce the wear imposed by touchdown, but the wear caused by touchdown in any event is negligible when compared to the other causes. Many patents have been filed for pre spin systems but the fact that none have been taken up, other than for gravel ops, would suggest an economic case can't be made.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092250.pdfFrom the results of the many tests which were made in the basic study of wheel spin-up drag loads, certain inferences may be drawn regarding the probable effects of prerotation on tire wear. It would seem that prerotation should greatly decrease tire wear. On the other hand, no appreciable amount of tire wear was evident in the impact-basin tests, even though the program involved some 450 simulated landings without prerotation, covering a range of vertical velocities up to 9.6 feet per second and initial skidding velocities up to 273 feet per second. The tires on an airplane having the same type of landing gear were worn out, however, in a substantially smaller number of landings under much less severe impact conditions. Since the only source of tire wear in the impact-basin tests is the wheel spin-up process, the much larger rate of wear in the flight landings appears to be due to sources other than wheel spin-up, perhaps braking and turning conditions. From these considerations it would appear that prerotation should have little effect on tire life.If you wish to spring the dollars an SAE report here,

https://www.sae.org/standards/content/air5800/

[Chris Martyr]

This again ?!

Indeed stilton . This is actually quite a well-worn subject .

The majority of tyre wear occurs once the MLG is in firm contact with the ground and the anti-skid system is kicking in , especially in varying conditions . Spinning up the wheels is of very little consequence . Otherwise , I'm sure that better men than us would have designed it in about 60 years ago ............[or more]

[Pilot DAR]

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.

This.

A ten or so HP motor per wheel, heavy, expensive, difficult to maintain, operates in a horrible environment for longevity, really difficult to operationally check pre flight, and consumes lots of power, when electrical power is least in excess. Such a system would require maintenance dependent sprag clutch to disengage the motor, should it seize ('cause you don't want to land with a locked mainwheel - that puts even more rubber on the runway!).

[Jetjock330]

There was Lear Jet 25 from Pretoria in 1989-90's belonging to Gert De Klerk, which had the pre spin nose wheel. The nose wheel impeller type vains on one side and a bleed line from windshield anti ice blowing, when needed over the impellers, to pre-spin the nose wheel. They tried to reduce the pick up of stones in order to land on dirt strips, possibly in Angola! and elsewhere. I have no idea where the Lear is today or how well it worked, but it did exist! I have seen it.

[Tailspin Turtle]

The Vought F7U-3 Cutlass had a bleed-air line running down the nose landing gear strut that spun two paddle wheels. one on each nose gear wheel, to reduce kickback loads on the nose-landing-gear strut-mounting structure at touchdown. See https://tailspintopics.********.com/2015/08/its-not-that-easy-to-get-it-right.html and scroll down.

The problem with the link is that the asterisks are automatically substituted for a word that Prune apparently considers verboten. If you want to see the post, google tailspintopics and search for F7U-3...

Thanks to Doug for the pilot note.

[DaveReidUK]

The Vought F7U-3 Cutlass had a bleed-air line running down the nose landing gear strut that spun two paddle wheels. one on each nose gear wheel, to reduce kickback loads on the nose-landing-gear strut-mounting structure at touchdown. See https://tailspintopics.********.com/2015/08/its-not-that-easy-to-get-it-right.html and scroll down.

From the F7U-3 Pilot's Notes:

https://cimg6.ibsrv.net/gimg/www.gmforum.com-vbulletin/375x410/f7u_3_pilot_s_notes_01afb013fbf06f7a22564196bce2400c85b513eb .jpg

[pilotmike]

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..
.
Indeed. As I'm so often told, that's the only way anyone realises I have actually landed!;)
Gets coat etc.

[scifi]

I did the opposite once... Touched down with a good thump, four seconds later applied the brakes, and one second after landed again, all wheels locked...

Good to see that they had thought of this even in 1955. However tyre pressures were 25psi then, and now its 225psi. with heavier wheels.
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[rickseeman]

The think some early Canadair 600's have that

[planett]

I've flown 3 types of 500 series Citations with the nose wheel spin up kit, most recently the C560 V. It uses the bleed air from the windshield heat to spin the wheel with vanes. The valve is adjustable from the cockpit to keep the speed between green and red light limits. The fairing also uses ram air to spin the wheel, so it actually rotates without bleed air. I'm told it was developed for a Lear. It weighs 10lbs when installed. Remarkably few stone chips in the leading edge, bottom wing skin, and virtually no fan damage in decades of use on gravel. The nose wheel casters so it touches down straight and kicks up fewer rocks.

The kit imposes a 200 knot gear speed limit and is removed in winter so it doesn't get packed with snow. The gravel is usually firm and not loose then. Nothing helps you when the gravel is soft in the spring and runway condition reports are 2 days old!

[Bagheera S]

Pre spinning wheels is regularly suggested but has never been taken up to any significant degree ( I never knew about the Cutlass NLG.... many thanks for the info). The aircraft landing systems industry wide standards committee, the SAE A5 has seen pre spinning suggested so many times they’ve produced a standard response which from memory is AS5400;- This is factually based, professionally referenced and details the rationale for not doing it. In summary, most of the tyre wear comes from braking + turning at MTOW, a spin up motor torque/power requirements are surprisingly high (it includes a few sums), cups/vanes will never match the landing speed/take way too long and if such a system really was used to lower touch down loads, what does the pilot do on the day the system doesn’t work ....or it jams ?

From memory there’s a reference to a trial conducted by RAE on Tornado where a chap wrote to his MP demanding that this obvious cost saving be investigated. The MP asked questions to the Defence Ministry so the RAE were duly tasked to give it a go. Hence they modified a couple of tyres with rubber cups to provide an urge to spin up. When the trials aircraft took off the pilot braked the wheels to a stop in flight, released the brakes and watched to his horror one wheel spin up in the correct direction and the other spin up in the wrong direction! He made several attempts to see if he could get both spinning in the same direction but failed, so did a very slow descent rate landing with an initial skip to get all the wheels spinning correctly. Upon investigation it was discovered a local turbulent airflow between the fuselage and wheel would cause at least one to spin in the wrong direction. Unsurprisingly the idea was quickly abandoned..........the devils always in the detail.

Wheel pre-spinning is the most patented inventions related to aircraft landing systems over the last 40+years with literally hundreds of fillings, but still we see no practical applications....that alone really tells you all you need to know.

[D120A]

Spinning wheels before landing adds to the energy of the aircraft at the threshold, energy that has to be disposed of via the brakes before you come to a stop. Tyres are cheaper than brake packs, so pre-spinning is 'out' - QED.

I recall a similar conversation with a car fleet engineer who hated to see vehicles being braked by engaging a lower gear, putting reverse strain on his beloved gearboxes. "Brake pads are cheaper than gearboxes" he said.

[Derfred]

Ahh but could this engineer quantify what additional wear engine braking would have on his gearbox? Or was he just making **** up?

[DaveReidUK]

Spinning wheels before landing adds to the energy of the aircraft at the threshold, energy that has to be disposed of via the brakes before you come to a stop. Tyres are cheaper than brake packs, so pre-spinning is 'out' - QED.

I recall a similar conversation with a car fleet engineer who hated to see vehicles being braked by engaging a lower gear, putting reverse strain on his beloved gearboxes. "Brake pads are cheaper than gearboxes" he said.

It doesn't do the clutch a lot of good either, and brake pads are cheaper (and easier to change) than clutches.

[underfire]

Imagine the hp or air pressure required to get a landing set up to 140kts...cost/ benefit analysis. a 4 pack, 6 pack?

brake pads are cheaper than cycling the engine rev thrust. Compare an overhaul vs brake pads/tires.

brakes and tires are sacrificial

[A Squared]

It doesn't do the clutch a lot of good either, and brake pads are cheaper (and easier to change) than clutches.

I suppose that true if you don't know how to downshift. It's quite possible to downshift and engage the clutch with virtually zero relative rotation.

[A Squared]

Ahh but could this engineer quantify what additional wear engine braking would have on his gearbox? Or was he just making **** up?

I'm inclined toward the latter. I've never heard of compression braking harmful to a transmission. Certainly, it is completely normal for trucks, and in fact trucks are frequently equipped with devices which increase the effectiveness of compression braking. I'm not seeing a reason why compression braking would be any more harmful to a gear train than accelerating.

[TBM-Legend]

My father worked on a project at 3AD RAAF Amberley in WW2 on a project to spin the mains on B-24 Liberators to save tyre wear. Ultimately the project faded away and the war ended.

[Mk 1]

I suppose that true if you don't know how to downshift. It's quite possible to downshift and engage the clutch with virtually zero relative rotation.

Heel and toe technique - initially developed to ensure that when the rear tyres were lightly loaded braking down to a corner that the sudden imposition of further braking forces when you lift off the clutch in a lower gear didn't give you compression lockup.

A very usefull technique as it makes driving smoother and at the cost of a tiny fraction of fuel reduces wear on your clutch and engine mounts.

[scifi]

One useful bit of information regarding gears is that if the efficiency is less than 50% then they are not reversible. i.e the output will never drive the input. This is most often seen with high ratio worm gears, such as used in car jacks... when you stop turning, the weight of the car does not spin the handle in the reverse direction...
Gears- Gear Efficiency (http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html)
For normal car gearboxes, the efficiencies are over 95% so can be turned both by the engine and by the wheels.
.
Now where were we.?... Ooh yes pre-spun aircraft wheels....