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Weight, Wing Loading, Max Thrust, etc...???

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Weight, Wing Loading, Max Thrust, etc...???


Old 11-18-2004, 10:32 AM
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Default Weight, Wing Loading, Max Thrust, etc...???

Can anyone give me some info (or point me to a web site) on the relationships between the total weight of a plane, wing loading, and max thrust? I'm going to build an electric plane (an E-SPAD, actually) and I want to be able to figure out if I have enough wing area and not too much weight for a given amout of thrust.

I'm assuming that max thrust needs to be greater (maybe much greater) than the weight to be able to get good vertical performance, and that the higher the wing loading is, the faster you'll have to fly to keep it in the air. Are there good "rules of thumb" for the relationships between these parameters? For example, looking at a Great Planes electric power system, they claim it produces 17 - 18 oz of thrust, and is recommended for planes up to 56oz in weight and with up to 20oz/ft^2 of wing loading...

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Old 11-18-2004, 05:56 PM
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Default RE: Weight, Wing Loading, Max Thrust, etc...???

The first step in designing a plane is deciding what performance you want.

Since you talk about verticals, I assume you want strong acrobatic or even 3D performance.

You're on the right track, thrust would have to be higher than weight by a good amount to hover. However, most sport/pattery style acrobatics can be performed with much less thrust.

Wing loading doesn't matter if you are hovering, but obviously matters the rest of the time. As you noted, a higher wingloading does require you to fly faster to generate enough lift to stay in the air, but there is more to it than that. Lower wingloading will generally improve acrobatics as well.

The reason you see a power system that produces less than 20oz of thrust advertised for a 50+ oz plane is that they are expecting slow/parkflyer type performance, a slow "floater", not an acrobatic plane. So you'd want to get the weight way down for that power system to get acrobatic performance out of it.

My designing has been glow-powered so far, and mostly combat planes, so I don't have more specific help for you in your exact case.

There is a program called something like "motocalc", and a few websites that have calculation programs to predict performance of various motor/battery/gearbox/prop combinations for electrics. You'll want to get familair with using one of those, and it's limitations, there are a lot more variables in electric power systems than in glow.
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