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-   -   1/24 C-130 power (http://www.Wattflyer.com/forums/showthread.php?t=73206)

schafe 02-17-2014 10:13 PM

1/24 C-130 power
 
I want to make sure I have things correct on this. I am working on a 1/24 scale C-130. I have already purchased the motors that fit into the nacelles. I want to use 3 cell lipos for flight. I have 45 amp ESCs. The prop that gets me closest to 45 amps results in about 40 amps and 420 watts which I measured with my watt meter.

Now I take 420 watts times 4 for the total motors to equal 1680 total watts. I am planning on 100 watts per pound hoping for a plane that will fly ok on 50-75% throttle and maybe carry a jeep or something for fun. Now divide 1680 by 100 to equal 16.8 pounds.

Am I correct that the plane cannot exceed 16.8 pounds?

Thanks for the advice.

Wildflyer 02-17-2014 10:27 PM

I am wondering the same thing, as I have 4 - 450+ watt motors, that I may build a B-17 with.

In my nitro days if you put 2 .30 engines on a twin, it would act and preform like it had a .90 motor on it.

People explained it by relating it to the swept area of the propellers. They said the area of props on the 2 - .30 engines, was more equal to the area of a single prop on a .90 (roughly)

I know a couple of twins I built back then, startled the heck out of my when they took off.

I don't as yet know of a calculator for multis.

fhhuber 02-17-2014 10:42 PM

Flight is possible at below 30 watts per pound. 100 watts per pound is considered appx thrust = weight.

What weight range is appropriate for the model has more to do with the size of the aircraft (wing area) than the power you are sticking on it. Aircraft performance will depend on wing loading more than how much power is available.

schafe 02-18-2014 12:11 AM

That is another question I had - how does wing area come into the picture. I calculate that the area of the wing is about 400 sq in. I'm assuming that it is the area of just the bottom not the entire area of the wing including the top, leading edges, etc.

fhhuber 02-18-2014 01:33 AM

Wing area is based on the overhead view "plan form" of the wing. If you cover that with 1 inch square graph paper and count up the squares covered (adding partials by % covered) you get the wing area for a monoplane. (biplanes/triplanes you have to do each wing separately and add them)
You'll get the same number by breaking it up into rectangles and triangles, using basic geometry and adding.

Weight/area = wing loading.

http://www.radiocontrolinfo.com/RCca...Calculator.php
Pick the chord entered to get the actual wing area at the actual span.

400 sq in wing at "just" 5 lbs will have a HIGH stall speed... 16 lbs is way out.

You may be trying to put too much power in too small of an aircraft and making a very large prop driven car. It looks to me like you need 1/4 of the power you are sticking in the airplane.


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