Tyres/brake temperature simulation

[Britjet]

I don't know the figures you mention but I think a tire pressure warning would be expected long before 9.
Randomness would be a good idea as well, I think.

I will get some tire pressure messages tonight and report back the BTMS..

Peter

[Hardy Heinlin]

... I think a tire pressure warning would be expected long before 9.

You mean the tire should deflate long before the temperature goes to 9?

When you're in the sim, can you also check if the tire pressure rises with the tire temperature? And do you hear any explosive noise in the cockpit when the tire deflates?


Cheers,

|-|ardy

[Will]

I'm a fan of randomness; it make the world live and breathe. I'll defer to the experts on what parameters should be though.

[Hardy Heinlin]

7 is displayed when the temp is between 672° and 766°.

I suggest the random trigger for the fuse plug should be enabled when above 720°.

Probability of a trigger:

20% at 7
80% at 8
100% at 9
... approximately.

[emerydc8]

Hi Hardy,

I calculated the heavyweight landing I did at 75 million foot-pounds. As Peter mentioned above -- it doesn't get any worse than that. I would expect all the fuse plugs to melt. A previous carrier I worked for rejected a takeoff out of Narita because they switched runways on them at the last minute and they were in a hurry to beat the curfew. In their rush to get to the other end, they didn't notice that the V-speeds had dropped out until they were well into the takeoff. They rejected at 190 knots. All the plugs blew and they put 16 on the rims. The captain was fired not for the incident itself but for lying that they were only doing 160 when they aborted.

My comment about the classic was that it would take much less to thermal the tires. Even a normal max landing weight landing will sometimes get you into the red. In this picture https://drive.google.com/file/d/0B-WRh0Hf7VdZbnZEY2xPVFRKVXM/view?usp=sharing  we landed at max landing weight at a certain military base in Afghanistan that is run by the British. Adding 10 knots for the windshear and the long taxi to the ramp got us up to a 9 (900 F on the classic) on at least one tire. The good news is that we were fast enough with a case of bottled water and were able to pour it on the rim (not directly on the brake) of the hottest tire. This kept it from thermaling out. 

I have never heard of a thermal plug not melting before the tire explodes, but maybe others have.

[Hardy Heinlin]

Hi Jon,

in beta 6 or 7 I get the temps easily to the 9 when rejecting at 190 kt.

Note that an RTO at, say, 150 kt is not the same as a landing at 150 kt. When rejecting, it takes some seconds until the engines have spooled down from take-off power to idle; during this phase there is still forward thrust while braking and the deceleration starts more slowly; the aircraft remains at high speed for a bit longer. Whereas when landing at the same speed, the engines are already at idle.

In beta 7, the fuse plugs may melt at 7 already.


Cheers,

|-|ardy

[emerydc8]

Plus the fact that you can physically outbrake max autobrakes, but you cannot outbrake RTO.

[Britjet]

In a not very scientific (!) session I did 2 RTOs at EGLL in the "big" sim.
The RTO was made at 396 Tonnes at ISA +15 with no reverse, no wind, and RTO autobrake.

The first RTO followed a couple of landings with what I would describe as moderate manual braking from 130kts at 250 tonnes. (this took the brakes to 2)
The second RTO was with cool brakes.
First RTO - within 5 minutes, all brakes at 7 or above - some at 9 - with most tyres deflated and a wheel well fire.
Second RTO - within 5 minutes all brakes maxed at 6 or 7 with one or two tyres deflated.

HTH


Peter

[Hardy Heinlin]

Thanks, Peter!

Pilots & engineers:
Would it be realistic to increase the tire pressure by 10 psi with every indicated 100°-increase of the brake temperature?


Cheers,

|-|ardy

[torrence]

My Physics 101 is a little rusty.  But I think that if the tire volume is constant (i.e. it cant swell up significantly before bursting) and you know or calculate the tire temp (approx also the gas temp) the gas law for pressure is just that P1/P2 = T1/T2, with Ti in deg K (0C=273K).  You'd have to check if your suggested delta P per delta T approximates this in the relevant T,P range for the tires.

Cheers,
Torrence

[Hardy Heinlin]

Yes, at least it shows the P/T ratio is linear. The problem is, I don't know the ratio of tire temperature to brake temperature.

However ...

Assuming the fuse plug is supposed to melt at 800°, and assuming this corresponds to a pressure of 20% below max tire pressure.

Assuming the max pressure at which the tire actually explodes by design is 360 psi.

Then we can conclude:

360 psi - 20% = 300 psi

800° corresponds to 300 psi

Normal pressure at 0° is ca. 200 psi

delta P = 100 psi
delta T = 800°

Add 0.125 psi for every 1° above 0°

One could derive the tire temp from that. But that's not required anymore, actually ... :-)


Cheers,

|-|ardy

[Britjet]

I will do an RTO or two this weekend in the sim and make a note of any tire pressure changes.
Peter

[Will]

Hardy, now you've opened a can of worms. :-)

If tire pressure is dependent on temperature, then we would expect to see a gradual decrease in pressure as the gear equilibrates to the chilly wheel well at altitude, followed by a return to normal pressure as the aircraft comes in for landing, right?

[Phil Bunch]

What about tire brand effects and recap (rebuilt) tires vs new tires?

Are they all the same or are there substantial/significant variations with respect to ease of ignition or heat transfer rate parameters?

Do all 747-400s have similar brakes and brake pads, or does this matter with respect to wheel well fires and temperatures?

[Hardy Heinlin]

Will, OK, I'll add TAT as well :-) I can do that in 5 seconds. The effect will be very small though.

Phil, you mean remolded tires? Are they allowed in aviation?


|-|ardy

[Will]

Hardy, just for completeness' sake, I think it would be TAT while the gear is extended, and then ambient when the gear is tucked inside the wheel well, since the skin of the plane would draw off any component of TAT caused by compression or kinetic heating. (Wait, forget that; I'm sure the difference between TAT and ambient temperature wouldn't result in much of a change in tire pressure.)

[Hardy Heinlin]

Yes, but on the other hand, the closed wheel well too may be warmer than the OAT, due to the static warmth near the cabin, and due to the friction at the fuselage skin, and due to the brake heat itself. The temp difference is unknown. But warmer than OAT, I guess. So that part will be a simplification :-)

[Blake H]

Great Work. Thanks for the mod.

On the malfunction page is it possible to have an individual selection of tyres to blow. This would be more realistic.

Additionally, yesterday I was scrapping the bird on the landing gear strut with the current tyre blow malfunction. I noticed there was no wheel well fire. Would this be true after a landing or RTO. With half of the mains out and the nose wheel steering tyres deflated.

Many thanks,

Blake Hauswirth

[Hardy Heinlin]

On the malfunction page is it possible to have an individual selection of tyres to blow. This would be more realistic.

It's random controlled. Why would it be more realistic if you selected the tires yourself?

The wheel well fire occurs sooner or later when the brake temp is above 7.

Wheel well fire can also be activated on the Fire page.


Regards,

|-|ardy

[John H Watson]

The factors which affect temperature seem to be endless 

It's also known that the tyres get very hot simply by taxying long distances at high weights due to the flexing of the tyre (I don't know how much this affects the tyre pressures, though).

Next we have to programme no wheel well fire indications on really windy days... The flames are blown away from the fuselage and not up into the wheel wells where the overheat detectors are.... assuming there are flames...

https://www.youtube.com/watch?v=qc_v6tXsv6g

Phil, you mean remolded tires? Are they allowed in aviation?

Retreaded tyres are the norm.  In theory, this can be done up to 10 times.