I am trying to use the eCalc web site and have a question about what it all means. In particular, there are two current/power indications, one in the row labeled "Motor" (which is what is plotted by the points on the graph), and one just below it in the row called "Optimal Efficiency". For my particular power system, it seems like the second one is matching more closely to what I am reading on my power meter at full throttle (static).

Here's my example. A Hacker A40-10L-14P (500 rpm/V), 5S and 12x8. I measure about 800W in the real thing, and the Motor and Optimal efficiency numbers in ecalc read 460 and 800. What do the two different numbers mean?

I am trying to use the eCalc web site and have a question about what it all means. In particular, there are two current/power indications, one in the row labeled "Motor" (which is what is plotted by the points on the graph), and one just below it in the row called "Optimal Efficiency". For my particular power system, it seems like the second one is matching more closely to what I am reading on my power meter at full throttle (static).

Here's my example. A Hacker A40-10L-14P (500 rpm/V), 5S and 12x8. I measure about 800W in the real thing, and the Motor and Optimal efficiency numbers in ecalc read 460 and 800. What do the two different numbers mean?

Check out www.motocalc.com, free for 30 days, then $39. IMHO, it's a little easier to use. But as indicated, just my opinion.

There are several different Hacker motors, in this size. One is the Hacker A40-10L, the other is the Hacker A40-10L V2. They have different KV ratings. The A40-10L V2 (500KV) will pull about 600 watts on your 12X8 prop and 5S LiPo. The original Hacker A40-10L (600KV), the other will pull about 850 watts on the same prop/battery system. These figures are from the motocalc.com program.

Motocalc predicts the motor efficiency will be in the 88% level, a very good value. I've got the A40-10L motor, and a club member has the A40-10L V2 motor. They will use different props on the same battery pack. They are real power houses for their size.

DennyV
Retired and the days are just too short, busier than ever!

What would the best motor calculation be for a twin plane or do you just divide the weight by two? Im building a Cessna 421 twin,71 inch wing span,763 sq/in wing area,11 to 12 lbs.

What would the best motor calculation be for a twin plane or do you just divide the weight by two? Im building a Cessna 421 twin,71 inch wing span,763 sq/in wing area,11 to 12 lbs.

I'd go for www.motocalc.com, free for 30 days, then $39. This program covers multi electric power systems.

At perhaps 130 watts per pound, that would be 1500 watts for both, or 750 watts on each motor. There are a lot of motors that would do the job. As for me, something on the order of a Hacker A40 series, like an $$$$ A40-10L.

DennyV
Retired and the days are just too short, busier than ever!

Thanks,I will be using Hacker.I am thinking of going with A40-14S V2.It is a bit lighter.Thanks for your help.

Hi
This Cessna is a rather heavily loaded model with a wing loading of about 37 ounces per square foot, assuming a 12 pound model. You don't want to under power it.

The Hacker A40-10L will turn an 11-6 prop at about 11,000 RPM using a 6S 4000 Mah LiPo battery. That will be pulling about 40 Amps, or 80 Amps for the pair of them. This comes out to about 1600 watts for both motors, giving you about 130 watts per pound of airplane. One thing to watch for on a twin is prop clearance to the fuse, and prop clearance to the ground. I've got a Hacker A40-10L motor in my collection of Hackers.

And, if you need more power, you can go to an 11/7 or a 12/6 prop, and still be within the motors ratings. IMHO, the extra four ounces of motor weight won't be noticeable.

(I've got an 82 inch wingspan giant scale Cessna 172 with a Hacker A60-5S motor. Prop is a 19X12. And the prop didn't clear the ground, so both the landing gear and the nose gear had to be extended. That is a 16 pound model, with the motor running about 2400 watts. It flies very well. The flaps are very effective, and are used during takeoff and landings. The take off roll is a very un-scale like 25 or 30 feet.)

DennyV
Retired and the days are just too short, busier than ever!