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Normally when an aircraft is descending with its wheels down, they do not rotate until they SCREECH up to speed (0-200+kph in 1 second) upon impact with the ground. There's quite a bit of smoke and burned rubber involved in that.
I've read about how some aircraft might be equipped with electric motors
to pre-spin the wheels, so that they don't screech, and thus the tires don't get so much wear and tear. But motors are weighty, so most planes don't have this feature.
However, there is an alternative. Let's start with a gadget known as a "Pelton Wheel" (see link). Let's imagine cutting it in half so we have two disks instead of one. Now let's make it out of rubber, and attach the halves to the side-walls of an aircraft tire (actually the tires should be constructed this way). The part of the wheel that contacts the ground is not changed in any way. Only a small amount of weight is added!
It's important to mount the tire so that at the ground, the concavities of the rubber cups are facing forward, and the convexities of the cups are facing rearward. Now consider a decending plane that is lowering its wheels: It is moving through the air at 200+kph, and those cups on the sidewalls are going to catch some of the air passing by. The wheel will therefore start to spin.
Some experimentation may be needed to figure out big the rubber cups really need to be, so that the wheel spins up to just the right speed as the plane lands on the ground.
Pelton Wheel
http://en.wikipedia.org/wiki/Pelton_wheel
As mentioned in the main text [Vernon, Sep 12 2008]
June 16 2008 tire blow out
http://abcnews.go.c...ireStory?id=5180508
Airliner's Tires Blow out Upon Landing in Phoenix [piwoslaw, Sep 12 2008]
Preserving Aircraft Tires
http://mb-soft.com/public/planetir.html
Numbers... [piwoslaw, Sep 12 2008]
Patent already filed
http://www.med.miam...dspace/UM06-23.html
The only difference I see is rubber "impellers" vs. rubber "cups". [scad mientist, Sep 12 2008]
Literature on the subject
http://yarchive.net...tire_prespin.html#2
Published landing gear design book addresses this and says that research shows this is not cost effective. [scad mientist, Sep 12 2008]
"WheelTug" for aircraft
http://www.electron...14729284371103747#!
Electric wheel taxis aircraft to runway without using jet fuel [benbradley, Apr 05 2014]
Almost 35 years ago I experimented with a similar effect on motorcycle wheels in flight...
http://wildguzzi.co...x.php?topic=68761.0
[normzone, Apr 08 2014]
Pilot's reasons why this is not done
https://www.youtube...watch?v=AJRf1jDiaXw
Why not make plane-tires spin,before landing?! [benbradley, Sep 15 2020]
[link]
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I think this will not only save the ground crew some work and the airline some money, but will increase the safety of landings. Tire blow-outs are a nuicence at least, and a real safety hazard sometimes. For example on June 18 2008 a Southwest Airlines jet's tires caught fire [see link] (this was from an overheated brake, but the forces acting on a tire at landing can also cause high temperatures). Even if a tire blows and noone gets hurt, then the runway is closed for some time, causing delays... |
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[Vernon] You're not the only one who good got this good idea. See link for some calculations. |
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Tires are designed to take those loads. |
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If you are going to add material to the wheel, you might as well put it in the treads, where it is most needed. |
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I just started wondering: What does the airflow look like under a landing airplane? Might there be some turbulence etc. that would somehow interact with the wheels, messing up the direction and/or speed of their spin? This is probably a dumb question. Sorry. |
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// put it in the treads, where it is most needed. // |
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Well, why not indeed? Make the tread thicker, and appropriately cup shaped. |
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There's actually an advantage to the sudden drag induced when the tyres contact the runway. |
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In the final stage of landing, called the flare, the aircraft is in the ground-effect region and actually experiencing increasing lift as it descends, even though it is shedding forward momentum. As the tyres contact, the plane brakes, the airspeed drops, and the lift is reduced, thus reducing the chances of rebounding into the air ...... |
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There's no way induced drag from LG tyres does anything to a 747. |
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A Savonius turbine, as you seem to be describing, will never reach wind speed, as it relies on drag i.e. turning slower than the wind to operate. So delete the last paragraph in the idea body and I'll be happy. |
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//I've read about how some aircraft might be equipped with electric motors to pre-spin the wheels, ... ...But motors are weighty, so most planes don't have this feature.//
Well, just consider hydraulic motors instead. I believe they are just a fraction of the weight of your proposed "pelton-wheel" tire construction. |
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a small gas turbine to spin up the wheels using pneumatics would be sooo simple, small compact light, soo easy, how can you resist it? The simplicity, the robustness the flaky crust. Edit the idea, you know you want to, it'll be so great! Please? Everyone is doing it! |
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There's something to be said for coming up with an idea for something that is not a problem. This one, in particular, is idiotic. |
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And I'm sure the purveyors of aircraft tyres agree with you. |
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So the plan is, basically, to cover the tires with rubber spoons. |
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If said spoons were half the distance from the rim to the hub, and they worked well enough to have their effective air speed 75% (quite possible) of the ground speed. Then the rim of the tire would be zipping around at 150% of ground speed. |
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Not much use for landings, but for take off - the faster the plane goes, the more the wheels are spun, thus dragging the plane forward - catapulting it off the end of the runway. [+] for perpetual motion machine! |
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What [Maxwell Buchana] said three years ago. Tyres may be
designed to take this abuse, but only for so long before they
are replaced, costively. And even then there are blowouts,
as pointed out. Even if vanes on the wheels or tyres only
matched the landing speed very approximately, it would
reduce the scrubbing. |
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As for slowing the plane after touchdown: cars brake more
effectively when they're not skidding, and I presume the
same is true for aircraft. |
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I'd do it by taking some bleed air off the engine compressors, running it through an intercooler, ducting it down to the wheels, and using that compressed air to spin up the wheels through turbine blades built into the brake discs, then keeping the air going to cool the brakes. All technology is already on the plane, and you get cooled brakes. |
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However, as [8th of 7] says, as presently done, the energy needed to spin up the wheels comes from the forward momentum of the airplane. The jolt you feel when the wheels hit is partly the loss of forward momentum, and you going forward into your seatbelt. |
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If you pre-spin the wheels (which takes a lot of energy) you are going to have to take that energy back out of the plane to get it to stop, whether through brakes or thrust reversers. |
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Adding more tread weight to the wheels increases the braking effect of spinning them up on landing. Think of wheels as giant rubber brake pads, and you won't be far wrong. |
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Halfbakerywise, you could brake a plane by having a hold-full of wheels that drop down, touch the ground in a cloud of smoke, then get discarded or hoisted back up once they are spinning. (If they keep spinning on the ground, they are driving the plane forward, which is where wheel weight is bad (but as [8th of 7] says, you get the braking effect when transferring from air to ground, when you really need it, and can deal with flywheel effects later once you've slowed a bit). |
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Overall, I'd favor pre-spinning, but it isn't all bad to not have it. Tire blowouts are avoidable with proper tires and maintenance (although when they do happen, it is at the worst time (however, if you pre-spin the wheels, you are still going to be dropping an airplane on to them, and will still get the blowouts that do happen as you land, which will still be bad, and the airplane will be travelling a bit faster than with un-spun wheels....)). |
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So why not just rubberise the belly of the plane, and land it in a big belly flop? |
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//pre-spin the wheels (which takes a lot of energy) you are
going to have to take that energy back out of the plane to
get it to stop// |
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A couple of quick calculations suggest that each wheel has
about half a megajoule of energy when its spinning at
landing speed (about 120mph). I guess there are ten or
twelve wheels, so spinning them up to speed will require
(or absorb) maybe 5MJ of energy. |
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The kinetic energy of a 747 at 120mph is about 500MJ, so
tyre-scrubbing can only absorb about 1% of the kinetic
energy - the other 99% must be absorbed by the brakes
(and by reverse thrust or whatever). |
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So, it just seems wrong to use tyre-scrubbing as a
means of braking. |
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//So why not just rubberise the belly of the plane, and
land it in a big belly flop?// |
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Or....OR!.... OK, how about this. The plane has to fly quite
accurately into a large rubber wall with a hole in it. The
hole is slightly smaller than the fuselage of the plane (this
is important). At the
same time, the nose of the plane opens, and latches are
releases so that the entire floor of the plane slides out (at
120mph) like a giant baking tray, complete with seated
passengers. The floor (plus passengers) is then
decelerated slowly. |
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Meanwhile, a replacement floor (pre-loaded with seated
passengers) is accelerated up to 120mph in the opposite
direction. It shoots out of the hole in the rubber wall,
straight into the now-empty plane. |
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Meanwhile, the shell of the plane is brought to a halt, and
then rebounds, so that it recovers its kinetic energy and is
travelling (now in the opposite direction) at close to
120mph. Because of this (and some good timing), the new
floor (plus seated passengers) actually comes to rest in the
aircraft much like the mini driving into the coach in the
[original version of] The Italian Job. |
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Gadulka! Passengers offloaded, new passengers onloaded,
and none of the aircraft's kinetic energy is wasted! |
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The plane will need to be modified so that it can fly
backwards as well as forwards, and there are a few other
details to resolve. |
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[Max], I really like that idea. It's better than mine, which is simply to take a note from the Flintstones, and use clutched chain-driven linkages from pedals in front of each passenger. |
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Their collective energy could spin the wheels up, and it would give them a way to feel like they're contributing something during the landing, instead of just helplessly sitting there. |
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And welcome to the Halfbakery, [Wayne Scotting]. |
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You are a gentleman, [Normzone]. |
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And indeed, welcome [Wayne]. Any relation to our
Norwegion
friend, [Skir Tingbörd]? |
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Couldn't they just glide over the runway for a bit and
touch the tires down a few times to spin them up a
little bit at a time? |
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Or even better, put a windmill at the top of the
plane with a direct link to spin the tires. This would
also help slow the plane down during landing. Maybe
the windmills could be incorporated into the flaps,
which would look cool. |
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[nomocrow], this Idea is about mounting the equivalent of windmills right on the wheels. |
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[MaxwellBuchanan], thanks for the math. I knew the energy of rotation of the wheels wasn't much of a percentage, but I couldn't figure it. |
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However much it is, the landing spinning up the wheels slows the plane. Some. |
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Let me clarify a bit on what I said earlier. |
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Dropping the plane in on the tires is more of a stress than is the second or so of skid. Pre-spun or not, you still have the tires taking a hell of a jolt. It's way worse than driving off a curb. |
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Yes, it is shocking to see the tires skid and smoke as 160-mile-an-hour rubber meets tarmac. But a few seconds later, the brake pads do much the same thing, with asbestos pads hitting rapidly rotating steel. And nobody complains about that. Brake pads are designed for braking--tires are designed for landing. |
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Pre-spun tires would be nice, but aren't really needed. They are also fairly obvious, and sticking a wind-spinner on them is also obvious. |
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Um, if this windspinner works like a champ, won't it make it harder to get the wheels to stop spinning when taking off and raising the landing gear? I know on some planes the pilot needs to hit the brakes so the tires don't centrifuge out too big for the wheel wells. (That may be trivial, but it's going to add wear-and-tear to the brake pads (and runway over-runs are almost as bad as blown tires)). |
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Another option is to evacuate the wheel wells and use maglev bearings, so the wheels are still spinning (from takeoff) when it's time to land. A shame about any stowaways in there, but you can't win 'em all. |
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Digikey on Twitter tweeted a link to this article on "WheelTug" (see link) last December 7 (2013) - it made me think of this very thing (speeding up tires for landing, both with electric motors and with the Pelton Wheel type thing), so I came here to add an idea exactly like this one. I'm only five years late on this one, I'm getting better... |
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Don't feel too bad about it. One of my early posts turned
out to be Widely Known To Exist for something like twenty
years. |
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I wonder if it'd be worth it to have electric motors on the wheels. Useful, for this sort of thing, perhaps taxiing as well. |
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Am I going to be the first one to point out that any
type of air-catching device on the landing gear is
going to add tons of drag, which is something you
usually want to minimize when you're flying a plane?
This would be like having the speedbrakes deployed
anytime the landing gear were down - including
takeoff and go arounds. |
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Erm, you are talking about yourself...and taking the 'n' which is better than taking the 'p'. |
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Surely the obvious way is for all the passengers to get bicycle pedals, and those could be connected by chains, then geared up, so giving them some exercise and spinning up the wheels..... |
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Obviously business class get gold-plated pedals and a steward/ess to do the pedaling for them. |
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[lurch] you can't get energy for free, it has to come
from somewhere. To accelerate the wheels up to
speed would take lots of force on the spinning
mechanism, which adds up to more force on the
aircraft as a whole. |
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lurch, this is completely non-intuitive to anyone outside the aerodynamics discipline, but a system like this to drive the wheels will add more drag than the gear themselves; extracting work from the airflow causes drag. The same is true of propellers; a windmilling propeller has more drag than a stopped propeller, assuming fixed pitch. (a feathered propeller has less drag than a non-feathered propeller when stopped) |
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This whole thing is one of those "why hasn't someone thought of this before?" ideas, with the answer being "They have thought of it. It's not worth it." The reason is twofold: One, there's the added weight. The cost to carry around the extra weight is more than the savings in tires. Two: most of the wear on the tires comes not from that initial spin-up on contact, but rather from braking and scrubbing in turns. It's been estimated that the touchdown scrub accounts for about 2% of the tire wear for large aircraft. |
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//On a turbofan I don't know how the reversing is achieved because
I've never worked on them. // |
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Diverters that hinge in to the low pressure side and turn the flow
forwards. |
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// Regardless, that is how the plane is slowed // |
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On puddle-jumpers, the prop is fixed pitch, so you just have to wait. |
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// and the LG brakes aren't (or rather, shouldn't be) applied at all until
the aircraft has slowed to taxi speed. // |
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The big civil jobs tend to use a mix of reverse thrust and braking,
depending on runway condition, prevailing met, all-up weight, and
available stopping distance. But they have elaborate anti-lock
systems to reduce skidding and tyre wear. |
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Light aircraft have toe brakes for differential braking to augment the
nosewheel steering. Skidding is avoided by making the brakes fairly
pathetic, with no power assist, so it isn't actually possible to lock the
wheels. |
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//On puddle-jumpers, the prop is fixed pitch, so you
just have to wait.// |
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The props on anything bigger than a Cessna 172 are
variable. Most puddle jumpers can use "beta range"
(reverse thrust) to slow down with their props. Some
of them barely have wheel brakes at all. |
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//Light aircraft have toe brakes for differential
braking to augment the nosewheel steering. Skidding
is avoided by making the brakes fairly pathetic, with
no power assist, so it isn't actually possible to lock
the wheels.// |
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Pathetic indeed, but you can lock up the brakes
pretty
easily if you aren't careful. It's like driving a 1960s
muscle car on a wet road. |
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Runways typically have angle of approach visual aids, which puts the aircraft down at the far end of the runway. Thusly, the smaller the aircraft the lesser the need for brakes. |
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//puts the aircraft down at the far end of the runway // |
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Our understanding is that "the far end of the runway" is a
Bad Place to land, as after crossing a taxiway or two and the peri track
there are usually some lights on poles, then a fence, possibly a public
road, and then it's into someone's front garden, the whole process
being
really rather loud and expensive. |
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Landing at the near end of the runway seems to be the preference of
experienced pilots, i.e. those that are still alive. |
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Catherine wheels? Would look pretty at night. |
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I added a video of a pilot discussing adding motors to do
this. He gives several reasons why it's not done, but his last
one applies here. Planes sometimes land at an angle to the
runway due to a crosswind. He says if the wheels were
already spinning in such a landing, the running wheels would
push the plane off the runway. I'm not totally convinced. |
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We are. Weathercocking during a crosswind landing is a bitch ... actually worse with a tricycle type than a taildragger. Touch down with only one side of the maingear and it's oh-so-easy to drop a wing and then it's an Expensive Noise and back to "Chapter One: Buying an Aeroplane". |
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As we noted 12 years ago, the main point of a landing is to stop flying as soon as possible, but in a controlled way. Anything that might impair deceleration, or directional control (and remember, as your airspeed drops you progressively lose rudder authority and thus steering until the nosewheel's in contact) is a Bad Thing. |
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If you're lucky enough to have more than one engine, then differential throttling is an option, or you can pull one of the props into Beta ... otherwise you concentrate on getting down to taxi speed ASAP. |
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Simply line each runway with a pair of steel rails, say
1435mm apart, and swap airplane tires for appropriate steel
wheels. Land on the rails. If the wheels skid a bit it's really
okay. Run the rails the length of the runway and have them
curve over to the ramp and boarding gate. Problem solved. |
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Yes, that worked perfectly for the Fi 103 - on takeoff, at least. |
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But somehow they never mastered landing the things... |
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Here's an idea: spin the wheels opposite the
direction of travel, for faster deceleration. |
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Good idea. You first ... we'll just sit here with the crash crew, and work the video cameras. |
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Do you mind leaving your wallet, and house and car keys in the crew room ? It will save having to break in. |
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The Reichenberg was indeed intended to be dropped from a parent aircraft (as with the Ohka) but there were a very few tests of the ramp-launch; the acceleration is severe, but manageable. |
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It's not a true "catapult"; it's a free-piston system, using steam from oxidising HTP with a Calcium Permanganate catalyst, similar to the initial Walter engine designs for the Me163. There's a sacrificial rubber tube in the centre of the launch ramp that the follower piston runs through. |
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