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Use Venturi effect for cooling air?

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SR 7106/08/2020 08:38:24
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463 forum posts
140 photos

Its all very technical, why dont you just make an airflow through it, try it, if it dont get hot you have cracked it, vent it through the cockpit so you dont have to cut holes in the fuselage, simple

Ron Gray06/08/2020 08:44:04
2320 forum posts
1000 photos

Personally I wouldn’t worry about cooling for the battery, it shouldn’t get that hot, if it does then something is wrong with the leccy setup. I would look to see if the esc could fit inside the cowl, if it can then as long as you have an exit for the air then there will be sufficient cooling for it. If it has to go as you’ve shown in your illustration then can you cut an air exit hole just in front of b/b? I do like to keep things simple and not over think them.

Robin Colbourne06/08/2020 11:54:03
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640 forum posts
17 photos

This is more or less what aircraft engines do; they don't just sit in a big empty space under the cowling. If you look at a Lycoming or Continental, the air is forced past the cooling fins by ducting and shrouds, then exits into a low pressure area to encourage the flow. Ideally the exiting air should be warm, which shows it is taking the heat with it.

Richard Clark 206/08/2020 12:43:07
426 forum posts
Posted by Nigel R on 06/08/2020 08:17:51:

 

hi richard

1) hasn't answered the temperature related efficiency question

I mean, I'll state my POV; heat relates to power relates to I2R(approximately, because reactance etc), so at any given sensibly sized ESC the current will not affect junction temperature within ESC until a point on that curve where the power dissipation begins to rise rapidly due to nature of second order curve. Maybe you have a more sophisticated understanding, hardware isn't my speciality.

2) hasn't answered why you say it 'disguises' the inefficiency

Again, my POV, you just need to cool the device a certain amount. If you need X amount of cooling - in our case facilitated by airflow - to maintain a low enough junction temp that your ESC operates "efficiently" then, well, er, so what? Airflow isn't disguising anything; it is just a means of achieving an end. Again, maybe you can help me understand what I'm missing here, but this is the basic process the hardware guys at my work operate with.

3) ok - but that means that the ESC isn't sized correctly for the current

4) ok - but again means that the ESC isn't sized correctly for the current

Your example in the second post appears to concur with my reply to 3 & 4 above, as things relate to the ESC, ignoring the motor aspect of your setup.

Edited By Nigel R on 06/08/2020 08:19:41

1) Maybe because a superbeing in the sky in which some believe likes it that way

AFAIK that's the only 'deeper' answer that exists at present. I would add that there does not HAVE to be a 'reason' for things. Some things do have a reason but it's not essential. Believing a reason is essential is merely an artefact of human linear thinking. (EG: Having got ourselves stuck with the 'big bang' hypothesis we are now saddled with looking for a probably non-existent cause of it. We just can't help it.)

2)  I will try  again to   the best of my (limited) ability. The  cause of the heat is 1  above. It's inherent in the process and it occurs in the motor coils, which are internal. That heat conducts and radiates to the surface of  the motor It doesn't stop the process, which is constant and at a given current  and load stays unchanged whatever you do. That you pass the  conducted/radiated heat  to the air by fitting  a heatsink and letting air flow though it doesn't slow  the process as it can only deal with  what is the   effect of the process, not the process itself. It may stop the motor  from melting  but that's all,  it doesn't change point 1.

The 'proper' way to do this stuff is to not get into the  areas of operation  where  these unwanted  effects become significant, which is where I started. Cut your hole and be  happy

PS: I usea discarded inrunner EDF motor in my 65 inch Aeronca Sedan. They work fine on big props instead of  small fans  with the lower current  caused by the much smaller number of cells and  work in their  maximum  efficiency area so don't get hot.  The only way the air gets out on   mine is the little   slit where the 'real'  exhausts poke out.

Edited By Richard Clark 2 on 06/08/2020 13:26:42

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