|Re: OT - model airplanes|
Message #15 Posted by Stefan Vorkoetter on 31 Jan 2008, 3:20 p.m.,
in response to message #14 by Randy
Electric models vary in size from little 50W models (generally around 16oz or so and 2sq.ft of wing), to well over 1000W (size and weight varies, depending on what the goal is). We tend to use 14 or 16ga wire in the small models, and 12 or 10ga wire in the larger ones. And we usually keep the wire lengths to inches, not feet.
Yes, there are resistive losses throughout the system, but we try to keep them to a minimum.
A typical F5B class aircraft from a few years ago used 27 1200mAh Sub-Sub-C cells, and pulled around 80A. With the voltage depression that comes at those currents, that's about 2kW. Full throttle run time would be under a minute, but such planes were typically only climbed at full throttle (vertically, to speck height in seconds), and then flew a race course in a high speed glide. Repeat until time is up. The person who flew the most laps wins.
(If one used cells with tabs in this application, either the tabs or the spot welds would melt in seconds.)
A more average sport aircraft like I fly now has the following specs:
Weight: About 45 oz or 1.4 kg
Wing Span: 48" or 1.2m
Wing Area: 3 sq.ft or 28 sq.dm
Battery: 8.4V (7 cells, 4000 mAh Sub-C NiMH)
That's only about 250W (1/4kW) for 8 minutes at full throttle, much longer at cruise throttle.
It's a whole different world from collecting calculators.
You can learn more at http://www.stefanv.com/rcstuff
Edited: 31 Jan 2008, 3:21 p.m.