Thanks for the responses, here is an update:
I ran the numbers in eCalc (access from Castle Creations website). With the Maxford drive kit (16 x 8 prop) and including my battery leads extension it predicts 866 W and warns:
- "The Pitch Speed should be at least twice as large as the estimated Stall Speed. Increase your propeller pitch."
.... but as mentioned before, I only get 580W in static test.
Recalculating for a 16 x 10 prop eCalc says 1025W with no warnings, and at 17 x 10 it says 1225W again with no warnings. This is more like it and closer to 100W/lb.
I installed a Zinger 17 x 10 wood prop and got 1060W peak in static test. So power draw is still a bit lower than estimated. but a lot closer with the 17x10 prop than with the 16x8.
To allow loading the batteries from the front with the leads pointing aft, so the connections can be made through the gunner hatch, I made a series battery connector, a shunt (for our local field rules), and a battery lead extension. This creates a lot of extra connectors, wire, and solder joints directly in the power circuit, which is immediately suspect. Everything is EC5 connectors and 10 ga. good quality wire and I added a capacitor pack just going into the ESC. I went through and checked for any unusual resistances in the circuit, and found nothing over 0.1 ohms. In static test at full load I found no unusual heat building up in any of the leads or connections. So, all the excess connection grodge does not seem to be the problem but, if doing it over, I would get the ESC up forward as far as possible (we have a bit of nose weight anyway), connect the batteries at the front, and put the shunt up front through the bottom of the cowl to minimize all the lead lengths.
We also went over the airframe and found all the control 'horn' rod fittings had completely loosened off in the very short running and flight time on the aircraft so far (control horns are a threaded rod with a cup washer and nut on either side). So watch out for this, we will set them all back up again and use red loctite or a dab of epoxy on the threads. If I were to do it over again I would chuck out all the Maxford hardware and find better stuff.
Also one more HS-55 aileron servo is gone already, so that is 3/4 failed before we are really in the air. So again, I would advise against buying the Maxford supplied servo kit and finding some better servos on your own instead.
Cheers, will report again on our next attempt to fly