[NSRCA-discussion] What Weight Airplane?

[Ron Van Putte]

John - You are going to get as many different answers as there are  
responses.  The best answer is, "It depends."

It depends on how you want to fly.   For doing just takeoffs, some  
gentle maneuvering, with very little vertical, and landing, you can  
use 50-100 watts per pound of total airplane weight.  For more  
aggressive maneuvering, you'll need 100-150 watts per pound.  For  
extreme 3D flying. you'll need 150-225 watts per pound.  None of  
these numbers answer your question.

Average watts equals average source volts times average current.  The  
average current divided into the pack's mah rating will tell you  
about how long you can expect to fly.  The answer still isn't here.

Let's try an example.  Suppose you assume the airplane will weigh two  
pounds.  Flying the way I think you want to fly, your airplane should  
use about 250 watts (2 pounds times 125 watts per pound).  With a 3S  
pack, your average voltage will be just under 12 volts.  Since power  
is amperes times volts, your motor will consume about 20 amperes.   
With a 2100 mah pack (2.1 ampere-hour) consuming an average of 20  
amperes. you flight time would be about 6 minutes (2.100 ampere-hour  
divided by 20 amperes then times 60 minutes per hour).  Is that long  
enough?  If not, the airplane weight is too large for that pack for  
fairly aggressive maneuvering.  If you settle for less aggressive  
maneuvering, the flight time will increase for that weight.

Now, you can start out assuming that you want to fly for a certain  
number of minutes and work the equations in reverse to determine the  
required weight of the airplane for your kind of flying, but, as I  
used to say to my students, this is left as an exercise.

Ron Van Putte




On Sep 26, 2007, at 8:27 AM, John Ferrell wrote:

> I recently bought a heli with 2100-3s packs and I have been slowly  
> working my way towards an airplane that uses these packs.
>
> What airplanes-size-weight are you using with these packs?
>
> The Vanquish and Brio 10 need more than that..
> John Ferrell    W8CCW
> "Life is easier if you learn to plow
>        around the stumps"
> http://DixieNC.US
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