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Brake fire... should I file insurance?

rv8ch said:
DanH ran some numbers a while back as well, and the takeaway for me was that you get one full speed full braking stop. After that stop, you better have lunch and let the brakes cool cuz if you try it again, you're in dangerous territory.
Click to expand...

yep, these are delta temperatures and are added to the current rotor temperature. if I want to catch my aircraft on fire all I need to do is a couple quick consecutive high speed taxi tests with hard braking. if my rotors are worn it's even easier.
 
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rv8ch said:
DanH ran some numbers a while back as well, and the takeaway for me was that you get one full speed full braking stop. After that stop, you better have lunch and let the brakes cool cuz if you try it again, you're in dangerous territory.
Click to expand...

I found that I could do a max performance stop, taxi back, take off, once around the pattern and repeat continuously. By the time I made it back down the discs had cooled to ambient. The in-flight airflow cools things very quickly.
 
Steve Melton said:
I ran some numbers for the kinetic energy of an aircraft transferred to heat at the rotor web. this does not account for pad heating or any other heating, nor for cooling of the rotor for braking elapsed time. it is simply the total aircraft energy turned into heating the rotor web. what was interesting is the effect rotor web thickness has on the temperature.

hypothetical numbers:
brake outer rotor dia = 6 inches
brake inner rotor dia = 3 inches
steel specific heat (constant) = .125 BTU/lb-F
aircraft landing speed = 60 kts
aircraft weight = 1700 lbs


rotor web thickness:
.275 inch, total delta theoretical max temperature = 1580 F
.225 inch, total delta theoretical max temperature = 1935 F

the theoretical delta temperature for these two thicknesses = 355 F

or another way, every .001 inch rotor thickness reduction = +7 degrees in max delta rotor temperature

conclusion: the thinner the web the higher the rotor temperature, duh

hey, take it easy on the brakes!
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Steve,
FWIW.
I did and energy balance a few years back and it turned out only about half the kinetic energy went into the brakes. Aero drag takes up a big chunk.

Energy-Dissipation.JPG

('Distance' is total landing distance from threshold, so includes flare etc.)

Matco uses about 500 deg F temp rise as their limit and they too assume all energy goes into the disc.
 
N91CZ said:
Steve,
FWIW.
I did and energy balance a few years back and it turned out only about half the kinetic energy went into the brakes. Aero drag takes up a big chunk.

Energy-Dissipation.JPG

('Distance' is total landing distance from threshold, so includes flare etc.)

Matco uses about 500 deg F temp rise as their limit and they too assume all energy goes into the disc.
Click to expand...

yep, I should have also stated I didn't account for any other friction or wheel inertia draws. however, your aero friction draw seems high since I can easily roll 3000 ft with no brakes or only several hundred feet with brakes. my numbers are simply the full aircraft kinetic energy put into the rotor steel web and the resulting delta temperature. are the standard RV brakes undersized, maybe, but I like the total performance and light weight concept. be careful with them.
 
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Steve Melton said:
however, the your aero friction draw seems high since I can easily roll 3000 ft with no brakes or only several hundred feet with brakes.
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Steve,
The majority of the aero drag component occurs while still flying - between the round out and touching down at something near stall. Once rolling aero drag drops way off. And of course you can swap energy between the rolling resistance and braking columns as well.
 
in my opinion, the greatest risk of a fire from a well built standard RV doesn't come from the engine compartment, it is the wheel brakes.
 
Steve Melton said:
however, your aero friction draw seems high since I can easily roll 3000 ft with no brakes or only several hundred feet with brakes.
Click to expand...
Of course, the options there aren't either-or. You can roll 3000' with no brakes (ie. Aero drag only) or you can roll several hundred feet with brakes and also with Aero drag. Unless you've found a way to remove the aero drag when you apply the brakes... :)
 
this is a simple analysis for all the kinetic energy put into "one" rotor. it does not account for aero drag or wheel inertia or any other friction. in the real world you have two rotors but sometimes you use one more than the other such as in a high crosswind. it is an upper boundary calculation. in other words, one of my rotors can never be greater than ~1500F unless it's on fire. :)

and also, if one of my brakes fail there is a high probably of injury and/or damage to the aircraft. check them often.
 
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