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  #31  
Old 12-30-2019, 01:24 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by snopercod View Post
....So when I tell you that peak brake disc temperatures are over 700F on landing and 400F on rollout, I have data to back that up.
I believe you John. I'm sure no one disputes that the disc gets quite hot.

The proven way to reduce maximum disc temperature for any given braking situation is to increase disc mass...see the previous kinetic energy examples.

At odds here is the rate of heat dissipation, not maximum temperature.
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  #32  
Old 12-30-2019, 02:32 PM
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I'm going to contact Ferrari and tell them they're doing it wrong:

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  #33  
Old 12-30-2019, 02:47 PM
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Originally Posted by snopercod View Post
I'm going to contact Ferrari and tell them they're doing it wrong:

Apples to oranges....vastly different operating environment (and brakes!).

If somebody wants to add draggy ducts to their RV wheel pants that is fine with me. I won't be putting any on my 20 year-old RV-6, however.
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  #34  
Old 12-30-2019, 03:02 PM
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Originally Posted by snopercod View Post
Any you have the engineering data to back up that assertion?

A member the Lancair community (aerospace engineer) has actually instrumented his brakes and recorded the hard data on brake temperatures during taxi, landing, and rollout. I have his graphs here on my computer. So when I tell you that peak brake disc temperatures are over 700F on landing and 400F on rollout, I have data to back that up. Someone in your community should instrument his brakes and you could go from there.
Please, proceed to proceed. You have an opportunity to educate us all.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #35  
Old 12-30-2019, 05:26 PM
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Originally Posted by airguy View Post
You have an opportunity to educate us all.
You want me to educate you on how forced air cools off hot metal?
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  #36  
Old 12-30-2019, 06:26 PM
cajunwings cajunwings is offline
 
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Default Fire.

Flow thru ventilation would be fine if there was airflow on the ground, but there isn?t much available for brake cooling. Probably not needed if flight. Louvers on top of the pants might do some good to vent off heat on the ground.


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  #37  
Old 12-31-2019, 06:36 AM
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Originally Posted by cajunwings View Post
Louvers on top of the pants might do some good to vent off heat on the ground.
That (or a few holes) sound like a good idea to me. You would get some natural convection even it the plane were standing still. I got out my Heat Transfer book from engineering school and tried to calculate how much air flow one would need to keep the brakes cool. Reynolds Number, Nusselt Number??? Sorry, that stuff is just beyond me in my old age. (It was probably beyond me in my youth, too ) Anyway, I'm tired of discussing this; I think I'll move on...
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  #38  
Old 12-31-2019, 07:42 AM
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Quote:
Originally Posted by snopercod View Post
You want me to educate you on how forced air cools off hot metal?
When there's no airflow to force it, sure, I need some education on how that's going to be accomplished.
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  #39  
Old 12-31-2019, 08:15 AM
rocketman1988 rocketman1988 is offline
 
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Default Umm...

You may want to look up Convective Cooling to get some idea of how heat transfer occurs without forced air...it appears, from your post, that you are not familiar with it...
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  #40  
Old 12-31-2019, 09:52 AM
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Your brakes will heat up during your landing roll to their maximum temp, so you're probably only concerned about the last half of that roll where the highest temps will be. That's when you're moving from about 40mph down to about 10mph. At those speeds, you won't be getting enough air through any ducts that would put out a fire... You'll get enough air to stoke one though, just like blowing on the embers of a campfire.

As for cooling, i'd expect the effect to be minimal. The temperature is maximizing as your ability to blow air into the space is diminishing rapidly (as you slow down). You'll be hottest just before you stop, and will have almost no airflow.

Keep in mind your wheel rotating creates airflow up into the rear of your wheelpant, that will swirl around and exit elsewhere. That alone would create more airflow than a dedicated duct. In fact, a duct may reduce the cooling provided now, by changing the pressure distribution in the wheelpant and reducing the effectivity of the air drawn in at the rear of the wheel.

Clearly, instrumented testing is needed.
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