Monday, May 16, 2016

HobbyKing Aether 3.7 Review Part 5

Power System

Power system information in the manual is very lean.

The expectation is that the modeler will pick the power drive of choice. Considering that plane is being marketed as an entry level ALES plane it would have been beneficial if they would have specified the power drive fully. (motor+esc+prop+battery).
I decided to use HobbyKing's motor recommendation: 

This is a relatively inexpensive "outrunner in a can" glider motor. It retails for about  $36.00.

My initial calculations on eCalc called for a 14x9 prop. However this proved to be problematic

Warning: eCalc does not explicitly tell how what size folding propeller "yoke" is using in its calculations. This lead me to believe I could use a 14x9 prop safely. This proved to be wrong. the 55mm turbo-spinner combination proved to be too much for my battery in real life.

After talking with the eCalc folks it was pointed out that they used 42mm for their calculations. I am using a 55mm turbo-spinner-yoke combination. Therefore I recomputed by power requirements by adding 13mm to prop size. 

This is the second set of calculations in eCalc using a 14x8 propeller and a 55mm folding prop yoke:

Follow this link for the actual eCalc worksheet .

Warning: This prop-motor combination will damage you battery if it cannot handle 40-50C continous discharge. 

Warning: This glider does not cool the motor properly for continuous operation beyond 30 secs at full throttle level.

On the maiden flight the motor at full throttle ripped the plane of my hands. Climbing to altitude per ALES rules should not be a problem.

This are the initial power components. The battery with the white tape was replaced because it could not handle the current load.

The ESC is rated to 70 Amps.

The small battery is my receiver and servo battery.

This battery has no problem handling the 50 Amp load that the prop and motor demand.

It is necessary to enlarge the center hole so that the motor fits correctly.

There are 8 pre-drilled holes on the fiberglass firewall. 4 are used to mount the motor. I enlarged the other 4 so that the motor would have some "air-intakes for ventilation"

After installing the motor. We can see that there is some space for air to squeeze into the motor. The built-in fan and the motion air coming through the "turbo spinner" should provide enough cooling for the 30-sec motor run.

There is plenty of space in the Aether to mount the motor.
The rear shows the Glider Drive built-in fan.
 I used a 55mm turbo spinner. This spinner allows air to penetrate the motor for cooling.

I tested the whole affair on the ground using an inline power meter. this allowed me to double check eCalc.

Go to Part 6
Back to Part 4
Back to Part 3
Back to Part 2
Back to Part 1


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  4. First, thank you for your great writeup. I'm a bit confused when you say "will damage you battery if it cannot handle 40-50C continous discharge.".
    50C of what battery capacity? If I have a 5Ah battery, 50C is 250A :) Did you mean 50A which could be 10C on a 5Ah battery or 20C on a 2.5Ah battery?

    1. The initial battery was rated at 25C the power calculator indicated the power drive was going to need a 50C battery. It was a mistake to put a 25C battery for test. I could have damaged the battery. Thankfully it just gave the 25C and , of course , the RPMs were way below what it needed to be.
      For example, a 2200 mAh lipo pack with a 30C rating is supposed to be able to support 2200mAh (or 2.2Ah) X 30 load which is 66 amps.