1
$\begingroup$

The first thing that one notices after seeing an aircraft, is that it's quite a heavy flying machine. And so, one would expect monumental tires on these vehicles, yet they don't exist.

How is it that such small tires cannot only carry the weight of planes like 747s and A380s, but also prevent getting too damaged during touchdown?

Is there a certain mechanic that prevents the collapse of landing gear and bursting of the tires?

Improve this question
$\endgroup$
1

4 Answers 4

Reset to default
3
$\begingroup$

I think your question is based on a perception that isn't shared by all.

Yes, airplanes can be very large, and numerically quite heavy when loaded at max gross, but appearances can be deceiving and they are actually fairly light for their size. They are mostly hollow, and designed to be as light as possible... because they need to fly after all! Consider that they are made of thin (compared to overall size) aluminum, and that much of the overall size you perceive is in the volume of the fuselage, which contains a lot of air.

Realize too that the visual appearance of size doesn't always match well with actual density or mass. Mentally scaling up other more familiar wheeled vehicles or die cast airplane models may create a subconscious illusion that airplanes are much more massive than they actually are.

I don't have the engineering chops to math it out for you, (if you are looking for strength calculations) I can only say that my perception has never been that the tires are too small.

Is there a certain mechanic that prevents the collapse of landing gear and bursting of the tires?

Yes, a team of design engineers will spend years making sure the gear is strong enough.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Despite the fact that LCCs pack as many people as possible into the cabin, even a full passenger aircraft is probably more air than "stuff" at take-off. $\endgroup$
    – FreeMan
    Commented Jun 21 at 11:37
3
$\begingroup$

In addition to the number of tires and strength of the landing gear, an important factor is pressure. Typical car tire pressure is on the order of 35 PSI. Typical large airplane tire pressure is on the order of 200 PSI!

While I don't know all the engineering behind it, my understanding is that higher pressure = support more weight. Consider that a small "donut spare" will be inflated to 60 PSI rather than the 35 PSI of a typical car tire, because that allows the smaller spare tire to, within certain constraints, handle as much load as a regular tire.

Improve this answer
$\endgroup$
4
  • 1
    $\begingroup$ Yeah: it is the pressure of the gases which support the aircraft, so you need enough pressure to support the weight. OTOH with too much pressure we have something like solid tires which do not damp irregularities of runways/taxiways (and landing). $\endgroup$
    – Giacomo Catenazzi
    Commented Jun 7 at 7:18
  • 1
    $\begingroup$ "my understanding is that higher pressure = support more weight." Indeed, pressure opposes weight. Weight is distributed on a small contact area with ground, pressure (in Pa, 1 psi = 6894 Pa) times this area (in m²) must be equal to weight (in kg) acting on the wheel. Thus 10 psi can counter about 6 tons on an area of 30x30cm. $\endgroup$
    – mins
    Commented Jun 8 at 16:19
  • 1
    $\begingroup$ Most civil airways require a pressure below 120psi otherwise the tarmac might get damaged. 200psi is more common for an aircraft carrier. "While I don't know all the engineering behind it" that's very easy: force is pressure times contact surface; contact surface is mainly dependent on the physical dimensions of the tire $\Rightarrow$ higher pressure, smaller tire. $\endgroup$
    – sophit
    Commented Jun 10 at 3:55
  • 1
    $\begingroup$ Consider also, that heavy road-going truck tires (semi tractor-trailers, dump trucks, etc.) have tire pressures in the 100-120 PSI range to support weights upwards of 80,000 lbs. $\endgroup$
    – FreeMan
    Commented Jun 21 at 11:35
2
$\begingroup$

That's quite easy: you split the weight among several wheels (22 for an A380 for example) and design the landing gear strong enough (their weight can be as high as 8% of the empty weight, corresponding to around 20t for an A380).

This nice presentation (pdf) gives an overview of the landing gear development for the A380.

Improve this answer
$\endgroup$
0
$\begingroup$

While it seems nearly impossible for the landing gears to be able to handle the aircraft load, there is a lot more that stays hidden. 3 of them are:

  • Hydraulics that dampen a lot of load (dynamic mostly for the Max Landing Weight), and,
  • The kinematics, that distribute the load across multiple linkages
  • The last one hiding in plain sight is the number of wheels x number of landing gears. While a small/medium sized aircraft may have 2 wheel long landing gears, a Boeing 777 could have an additional wheel or a larger aircraft like the A380 could have multiple of them (even on the wings!!)

Always remember manufacturers need to comply to stringent standards like AC23.1309 and at times also develop the products based on recommended practices like ARP4754 to ensure the design is absolutely safe (almost) with a very high factor of safety (we are talking about a number greater than 1.2)

Improve this answer
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .