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Wheel Spin-Up, pre-landing..?

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Wheel Spin-Up, pre-landing..?

Old 14th Jul 2018, 19:03
  #21 (permalink)  
 
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Originally Posted by Willit Run View Post
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.
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Old 14th Jul 2018, 20:10
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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.
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Old 14th Jul 2018, 20:13
  #23 (permalink)  
 
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Originally Posted by Pugilistic Animus View Post
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.
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Old 15th Jul 2018, 19:03
  #24 (permalink)  
 
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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.
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Old 16th Jul 2018, 05:41
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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/c...9930092250.pdf
From 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/
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Old 17th Jul 2018, 19:44
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Originally Posted by stilton View Post
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]
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Old 17th Jul 2018, 19:54
  #27 (permalink)  
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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.
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!).
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Old 17th Jul 2018, 20:37
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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.
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Old 18th Jul 2018, 00:03
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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/...-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.

Last edited by Tailspin Turtle; 18th Jul 2018 at 17:03. Reason: Explain link failure
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Old 18th Jul 2018, 06:45
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Originally Posted by Tailspin Turtle View Post
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/...-it-right.html and scroll down.
From the F7U-3 Pilot's Notes:

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Old 18th Jul 2018, 12:05
  #31 (permalink)  
 
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Originally Posted by scifi View Post
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.
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Old 18th Jul 2018, 13:46
  #32 (permalink)  
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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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Old 18th Jul 2018, 17:41
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The think some early Canadair 600's have that
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Old 20th Jul 2018, 03:51
  #34 (permalink)  
 
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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!
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Old 22nd Jul 2018, 14:46
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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.
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Old 23rd Jul 2018, 13:31
  #36 (permalink)  
 
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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.
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Old 23rd Jul 2018, 15:19
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Ahh but could this engineer quantify what additional wear engine braking would have on his gearbox? Or was he just making shit up?
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Old 23rd Jul 2018, 18:34
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Originally Posted by D120A View Post
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.
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Old 23rd Jul 2018, 23:06
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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

Last edited by underfire; 23rd Jul 2018 at 23:19.
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Old 24th Jul 2018, 03:32
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Originally Posted by DaveReidUK View Post
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.
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