The same old power to weight question
02-17-2014, 10:00 AM
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The same old power to weight question
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 amp 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?
How does wing area come into this?
Thanks for the advice.
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?
How does wing area come into this?
Thanks for the advice.
02-20-2014, 07:06 AM
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Scale models have relatively small wing area compared with non-scale RC planes, so your wing loading will be fairly high... that means your C-130 will have to fly fairly fast to stay aloft.
As a guide, for model rc airplanes, if the wing loading is under 10 ounces per square foot, they will be suitable for the slow flying, gentle handling that you need in arf electric rc airplanes used as basic trainers. From 10 to 20 ounces per square foot will include intermediate trainers, flying a little faster, having more power and being a little more demanding in terms of needing a bit more speed for landing and taking off. Above 25 ounces/sq. foot you begin to find the warbirds, military scale-type models, many of which fly wonderfully, but at the same time are not forgiving of letting the speed get too low while close to the ground. You need to be carefull "lest the ground rise up and smite thee"!
As a guide, for model rc airplanes, if the wing loading is under 10 ounces per square foot, they will be suitable for the slow flying, gentle handling that you need in arf electric rc airplanes used as basic trainers. From 10 to 20 ounces per square foot will include intermediate trainers, flying a little faster, having more power and being a little more demanding in terms of needing a bit more speed for landing and taking off. Above 25 ounces/sq. foot you begin to find the warbirds, military scale-type models, many of which fly wonderfully, but at the same time are not forgiving of letting the speed get too low while close to the ground. You need to be carefull "lest the ground rise up and smite thee"!
Last edited by Dr Kiwi; 02-20-2014 at 07:08 AM.
02-25-2014, 09:36 AM
#3
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 amp 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?
How does wing area come into this?
Thanks for the advice.
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?
How does wing area come into this?
Thanks for the advice.
As stated by Dr. Kiwi, the wing area does not come into play when looking at power to weight ratio. It comes into play with wing loading. Wing loading will impact the flight speed and low speed handling. Kiwi did a pretty good job of laying it out.
If you want to read up on motors and power to weight ratios you can look here:
EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.rcuniverse.com/forum/m_7100376/tm.htm
