Keith Shaw’s Radical RC 1905 Wright Flyer Part 5

Pilot Front Detail

Pilot Front Detail

At the field. Note the “cross-country fuel tanks”. Each tank contains two A123 cells inline, housing made of 1/64 ply and card stock. The 4 cells and holders weigh about the same as a 4 amp-hr 3s LiPo pack, but produce a little higher voltage. I pull 32 amp at full throttle, but the two flights so have been a half throttle. 6-7 minutes consumes about 1 amp-hr out of the 2.2 amp-hr available.

Detail Rear View

Detail Rear View

Cross Country Tank Detail

Keith, an astounding amount of detail. I love the fantasy tanks. You mention flying it. I’m going through the emails one at a time as I’m posting them in the schedule.

I have noticed that although this model should be very energy hungry, when cruising around at slow speeds, it seems almost magical how little energy is used. Think about all that weight, you have to be around 60 ounces, all those struts, two props, two motors and two no-load currents (something worth a whole blog post to explore), both those wings and your only using about 150mah a minute.

I’ve never seen a mah per minute chart based on weight or style or anything else for that mater. However it seems if there were such a guideline out there, something is wrong. This model in my mind should not fly as long as it does on so little energy and so little battery mass relative to machine weight.

A little quick math shows cruise current should be about 9 amps (150ma per minute x 60 minutes). However, when you deduct the no load current (not sure what it is for those motors) we’re talking maybe only 7 amps at cruise for the pair of motors. Figuring a at load depressed voltage of 3.3v x 7 amps _ only 23.1 watts. Further, it would imply that two 14 watt brushed IPS gearbox’s would be able to keep this machine aloft and still have an excess 4.9 watts for climb. It seems impossible, yet, I know it is true.

Dave

Share
This entry was posted in Blog Entries, Building and tagged , , , , , , , . Bookmark the permalink.