Caterpillar track as landing gear

[ARS]

So... I'm seeing this kind of landing gear...

And I'm confused about precisely what's the advantage of using caterpillar track as landing gear since usually that thing is associated and seen on tanks, tractors and bulldozers, and those usually moves slowly (most of the time), and aircraft landing and takeoff is usually performed in high speed

So can anyone explain to me what's the advantage and disadvantage of this kind of landing gear? What's the practical reason of using it?

[kerbiloid]

They want to land/takeoff on/from a soft, muddy ground.
Trucks have greater area, they make lesser pressure.

Trucks are not slow, just slow vehicles use trucks.

Spoiler

 

 

[Green Baron]

Remains the disadvantage: weight and complexity.

Edited September 10, 2017 by Green Baron

[kerbiloid]

They tried to use at once Airplane Plus, Kerbal Foundries and BDArmory

Spoiler

 

[YNM]

2 hours ago, Green Baron said:

Remains the disadvantage: weight and complexity.

Compared to dozens of landing gear ?

[DerekL1963]

17 minutes ago, YNM said:

Compared to dozens of landing gear ?

Large numbers of simple things are not as complex as inherently complex things.

[Green Baron]

They build rather gears with a row of low pressure balloon tyres today, like in many transport aircraft. If one tyre pops there are 7 left. If one track rips then they'll have to walk ...

Edited September 10, 2017 by Green Baron

[GDJ]

4 hours ago, ARS said:

So... I'm seeing this kind of landing gear...

And I'm confused about precisely what's the advantage of using caterpillar track as landing gear since usually that thing is associated and seen on tanks, tractors and bulldozers, and those usually moves slowly (most of the time), and aircraft landing and takeoff is usually performed in high speed

So can anyone explain to me what's the advantage and disadvantage of this kind of landing gear? What's the practical reason of using it?

Well, as others have stated it has a huge advantage over tires due to surface area over softer soil/landing surfaces. Also since the tracks aren't pneumatic in nature, blowouts are eliminated (which is a good thing!).

Disadvantages would be greater friction drag for takeoffs and tracks aren't inherently self centering, which means the mechanisms to keep the tracks on the rollers are going to be complex. Another problem is the smaller rollers have to turn at a ungodly high RPM during takeoff and landing, so that means more labour to make sure everything is dynamically balanced to a very high precision, and maintenance is going to be higher. Because of the increased amount of parts in each truck, weight will be an issue as well.

So they do have a place in transporting goods to more remote areas that might not have the best surfaces for landing aircraft, but generally trucks aren't really needed in most aircraft today. In the early days of aviation, they would be a godsend especially with the lack of paved landing surfaces, but not now. Also tire technology has, for the most part, eclipsed the need for this kind of landing technology.

Edited September 10, 2017 by GDJ

[Bornholio]

This is why

XB-36 specifically, they ended up using a multi-truck wheeled gear design as the additional rough field operation was deemed unneeded. 

It is also quite a bit lower ground pressure than large multiwheeled designs and for the same landing gear volume able to support much more weight.  It is somewhat heavier and much more expensive. At the time the single wheel for it was heavier and crushed concrete and asphalt tarmacs very rapidly.

http://www.dtic.mil/dtic/tr/fulltext/u2/a279100.pdf Aircraft Tire/Pavement Pressure Distribution research from late 80's

Most other uses are focused on the ground pressure.  a quick estimate of ground pressure is the inflation pressure of the tire (25-45 for autos) and (150-400 psi for aircraft), an M1 Abrams at 70tons is only 15psi.  Peak pressures are usually about double this for a round tire across the contact surface.  Tracks are closer to 1.6x average for peak contact surface.  This all adds up to dramatic surface pressure reductions. Similar results come from ski's and they of course are much lighter and simpler.  X-15 used rear skis instead of wheels for that reason.  Additionally dead load on a given concrete pad is the limit but this in only the case in the largest aircraft.

Landing on dry lake bed the ground pressure for the gear mus be low. Commonly aircraft that emergency land on dirt need gear repair. The X-15 wanted to land on dry lake beds as an alternate, Rogers and Delmar dry lakes specifically.

 

Edited September 18, 2017 by Bornholio
b-36 comparison

[kerbiloid]

1 hour ago, Bornholio said:

XB-36 specifically, they ended up using a multi-truck wheeled gear design

That plane with 6 propellers facing back and 4 additional turbojets?
Why I am not surprised with trucks?..

[mikegarrison]

B-36 tried the track. They also tried one ginormous tire per main gear. It was simply a heavier plane than anybody had dealt with before, and they didn't know how to distribute the weight on the ground. Eventually they went to a multi-wheel truck for each gear, which was new (or at least extremely uncommon) at the time.

These days that's what everybody does. 2, 4, or 6 wheels per truck, and if that's not enough when spread out over two main gear they just add more main gear. 747 has 4 wheels * 4 main gear posts. 777 decided to go with 6 wheels * 2 main gear posts (This was the first 6-wheel truck, I think). A380 has 4 wheels * 2 posts plus 6 wheels * 2 posts. A340 had 4 wheels * 2 posts plus 2 wheels * 1 center post. Etc.

[magnemoe]

3 hours ago, YNM said:

Compared to dozens of landing gear ?

Yes, if you have 12 lading wheels you can loose some, you don't want an track break in 250 km/h and the track ending up in the wing.
Standard for military transports who can land on dirt runways is to use lots of wheels. 

Yes you could wrap an track around the wheels it would reduce the ground pressure to less the half but with increased risk. 

[mikegarrison]

3 minutes ago, magnemoe said:

Yes, if you have 12 lading wheels you can loose some, you don't want an track break in 250 km/h and the track ending up in the wing.
Standard for military transports who can land on dirt runways is to use lots of wheels. 

Yes you could wrap an track around the wheels it would reduce the ground pressure to less the half but with increased risk. 

That particular arrangement is also used because besides distributing the weight, it keeps the posts short. Works with roll on / roll off cargo loading. Doesn't work for a low-wing config, though.

[magnemoe]

Just now, mikegarrison said:

That particular arrangement is also used because besides distributing the weight, it keeps the posts short. Works with roll on / roll off cargo loading. Doesn't work for a low-wing config, though.

True, its an military design, military want cargo planes who can land on dirt runways, because of this you want high wings, you also want roll on roll off. 
Civilian cargo planes tend to be based on passenger planes however I think 747 was first designed as an cargo plane. 
Military cargo planes also have rear hatch for air drop and faster loading. 
You can buy an civilian C-130 if you want
 

[Vanamonde]

A number of posts have been removed from this thread because people were about to come to blows over the original intention of the 747 design, which has nothing to do with caterpillar landing gear, which is what this thread is about. 

[magnemoe]

13 minutes ago, Vanamonde said:

A number of posts have been removed from this thread because people were about to come to blows over the original intention of the 747 design, which has nothing to do with caterpillar landing gear, which is what this thread is about. 

Feeling very guilty 

[mikegarrison]

8 hours ago, Vanamonde said:

people were about to come to blows

More than a little overstated, but I agree it was all off-topic.

[NSEP]

My geuss is rough terrain. Tanks and Buldozers have tracks for rough terrain, soooo.

I sort of see a point in it for (far-future) spacecraft. There are no landing gears on an unexplored distant plant, so an SSTO kind of thing could use this, if someone in the future comes up with a track that can withstand the landing speed of a spaceplane.

[wumpus]

On 9/10/2017 at 11:50 AM, DerekL1963 said:

Large numbers of simple things are not as complex as inherently complex things.

I suspect the difference between the two is not the complexity (we've seen enough wheels on a plane that you could probably "simply" put a tread around them) but the failure modes.  Lose a tire/wheel and you barely notice it (well, not the Concorde, but I'm sure they put that many wheels on sturdier aircraft).  Lose a tread and the plane crashes.

It certainly would be more complex to have a tread.  But I'd be a lot more concerned with the difference in failure modes.  I'd expect that doubling the number of wheels would spread said complexity around the aircraft in terms of increased mass (I'd expect the bracing needed to support the extra mass is "complexity" as well as the more powerful engines), but that is worth it to trust your landing gear.

[magnemoe]

2 hours ago, wumpus said:

I suspect the difference between the two is not the complexity (we've seen enough wheels on a plane that you could probably "simply" put a tread around them) but the failure modes.  Lose a tire/wheel and you barely notice it (well, not the Concorde, but I'm sure they put that many wheels on sturdier aircraft).  Lose a tread and the plane crashes.

It certainly would be more complex to have a tread.  But I'd be a lot more concerned with the difference in failure modes.  I'd expect that doubling the number of wheels would spread said complexity around the aircraft in terms of increased mass (I'd expect the bracing needed to support the extra mass is "complexity" as well as the more powerful engines), but that is worth it to trust your landing gear.

This, it the tread break during landing or takeoff you have an serious problem, for one the belt itself will move fast and is pretty heavy and can easy damage the plane. 
Then you don't have the tread anymore.
One benefit it had is that you need ABS brakes with lots of axles, the B-29 has two wheels but they have one axle so both will lock at once.
If one axle locks you will not notice and this can easy blow the tires on the axle. 
They had mecanical ABS brakes back then but they was new technology and probably had issues too. 

[kerbiloid]

In KSP with KerbalFoundries it is possible to make even a plane with screw conveyor chassis. At least an amphibia.
https://www.google.ru/search?q=шнекоход&newwindow=1&dcr=0&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjMw_j4qaXWAhUFG5oKHVgcAucQ_AUICygC&biw=1920&bih=977

Shocked that nobody tried this irl.
(Or we don't know about such hero).

Edited September 14, 2017 by kerbiloid

[DDE]

@kerbiloid, these things are REALLY heavy.

[mikegarrison]

25 minutes ago, DDE said:

@kerbiloid, these things are REALLY heavy.

To be fair, all landing gear for large planes are really heavy.

[magnemoe]

1 hour ago, mikegarrison said:

To be fair, all landing gear for large planes are really heavy.

Think main issue is that they would have to be powered to roll. lots of friction,  they would also have to roll very fast to get takeoff and landing speeds. 
Yes its the perfect design for swamps 
However no planes has powered wheels that I know about, has been some interest because taxing with jet engines is very inefficient. but it would increase weight and complexity 

[mikegarrison]

4 hours ago, magnemoe said:

Think main issue is that they would have to be powered to roll. lots of friction,  they would also have to roll very fast to get takeoff and landing speeds. 
Yes its the perfect design for swamps 
However no planes has powered wheels that I know about, has been some interest because taxing with jet engines is very inefficient. but it would increase weight and complexity 

Electric taxi has been discussed a lot, but it has issues.

There is no general rule for ground idle. It's set high enough to keep the fire going in the engine, but that can be different for different engines. Some airplanes will start rolling with the engines on ground idle unless the brakes are applied. Others need the throttle to be pushed up in order to start rolling. And taxiways are not all level.

Also, engines need to come up to operating temperature before they get shoved up to full power. So part of what is happening during taxi is that the engines are warming up. It's possible that they would have to be running anyway even if you did have electric taxi.