# Optimal current draw on 10-15kg airplane

Hi!
I’m looking for info about how much normally typical 10-15kg airplane draws current? at 28m/s
As much I found in the logs, it’s around 50A (cruise)
Maybe somebody with experience can confirm that

Thanks!

what voltage, current only says nothing.

oh sorry, 30V, 8s battery

There is no hard and fast rule for weight=power for aircraft.
Each aircraft design has different characteristics.
Trimming an aircraft in flight can have major effects on power consumption.

As an example, we set up a fixed high wing 2m trainer weighing in at 9kg, that required about 50A for cruise.
This was unacceptable, and by changing the prop/motor combination, and correctly trimming the aircraft for the most efficient cruise, we were able to get the current down to 12-15A.
It still took 50A for takeoff, but that gave a good strong climb out.

You would need to provide a lot more details about the aircraft and what you are trying to achieve.

1 Like

Aircraft cover a wide spectrum, but for a 5kg airplane cruising at 18m/s, our power draw is roughly 130 watts. At 8s, that is roughly 4A. Your aircraft at 10kg, if it is efficiently set up, should be roughly double that in cruise (at the same speed). If you’re trying to fly at 28m/s, that is normally quite fast and would draw a lot more power.

Did you try eCalc? https://www.ecalc.ch/

Yeah the ecalc has been my friend, just there is so much options and this topic helps me a bit with my choice.
How much does the servos for flight surfaces use battery? Is that number so little that there is almost no point to think about it?

We found you can go from 12A to 35A just by changing the flight trim of the aircraft.

Yes, almost neglectable.

by flight trim you mean? Trims of the flight surfaces?

I am not sure if you have resolved your issue. However, here is how I suggest you to calculate what current draw to expect for a reasonable plane configuration.

Reasonable is defined by the glide ratio or Lift/Drag = L/D ~ 10. Of course there are designs that can triple this value, while others that may slightly undershoot.

At 10kg mass, your lift is roughly 10 x gravity ~100N. So your Drag will be 100/ (L/D) = 10 N. Propulsive Power = Drag x Speed = 10 x 28 = 280W
Accounting for 65% efficiency (propulsive & mechanical, electrical losses). Your electrical energy input would be 280/.65= 430W.

Power = Voltage x Current
or
Current = Power / Voltage

@3S. Current = 430 / 11.1 = 39 Amperes,
@4S Current = 430 / 14.8 = 29 Amperes

etc.

So your 50A (if at cruise) seems high, but I think the culprit is the velocity of 28m/s. It is just too high for this size aircraft. Either you like speed or your aircraft is configured so badly that the wing can generate the needed lift at only such high velocity. Or you are way past the acceptable wing loading / mass for the wing area. Look into the recommended ranges and the answer should just pop out.

Regards

Cem