Electric: power+rpms=flight time (How long can I fly?)

[Jack155Q4]

Hi all,

My first post here. Very glad to be a member, it is very informative. I am a member on RCHeliaddicts.co.uk and was recommenend this site by a member who I bought my Twister 3D Storm from.

I thought you may be interested in the Li-Po Flight Time calculator I made last week.
Hope it is of some use:

Li-Po Flight Time Calculator

Thanks,
Jack

[Bullitt5094]

Is there any empirical data to back-up any of these theories? Seems like there are some folks running around with expensive data loggers that could run a few tests. I'm feeling the forumla in the first post using a cubed factor is a little much. It seems like the squared factor is closer to what I've experienced as I've raised the head speed on my stuff.

[jhauto]

I have to take some time to validate it,but really thanks for your sharing.

[brtmac]

The power required to move an object through a fluid (air is considered a fluid) increases as the cube of the velocity ( http://en.wikipedia.org/wiki/Drag_(physics) ).

The blades have drag, even when not providing lift (parasitic drag). This drag increases as the cube of the speed of the blade. So, as you increase rotor speed you cube your power consumption, even while sitting on the ground generating no lift.

Increased rotor speed gives increased ability to generate lift because you get more lift with the same pitch. And, you can only go so low on rotor speed because at some point the pitch necessary to hover will be too close to the stall pitch of the blade and you won't be able to generate enough lift to do anything useful.

So, it's all give and take. High head speeds for crazy power, but low run times. Low headspeeds for long runtimes, but less insane power. The best thing to do is find the lowest speed that gives you the power you want. This is where the overall weight of the heli comes in. The lower the weight, the less power you need to do what you want. The less power you need, the lower the headspeed you can run. The lower the headspeed, the less parasitic power drain you have (power needed to just spin the rotor, not generate lift) and the longer runtime you get.

Another way to think about is that a given motor/esc/battery setup has a maximum useful power output. The more of that you use to shove the blades through the air, the less you have available for actually generating lift. What does happen is that when you increase pitch to generate lift, and you hit the peak output of your motor/esc/battery combo, you have to start barrowing from the headspeed bank and you bog. It's quite likely that for a lot of the headspeed crazy setups out there you'd actually have *more* real power to generate lift by lowering the headspeed.

[foolforspeed]

Originally Posted by gwright

S. (the one that will fly old/smooth style 3D for 9+ minutes but not the radical stuff you guys do these days). . Flight times go down relative to current, so going from 2000 to 2100 takes me down from 9.5 to 8.2 minutes.

I'm absolutely impressed that you can get that kind of flight time even just hovering. The best I've ever got out of an electric heli was 6 minutes and that was in the good ole newby days.

[Gregor99]

Originally Posted by foolforspeed

I'm absolutely impressed that you can get that kind of flight time even just hovering. The best I've ever got out of an electric heli was 6 minutes and that was in the good ole newby days.

It can be done with low to moderate headspeeds, small to moderate sized motor, a light model and smooth collective management.

[Slyster]

Old thread! But yesterday I flew my Goblin 500 (first flight!) at lowish headspeed with a 6s5000 and the smaller choice of Quantum motor.. and after 5 full minutes of sport flying I had around 60% left in the lipo.

[Gregor99]

My Compass Knight 600 on 8s with 5000mah pack and 1800 HS, 9 minutes of sport flying. Synergy E7 with 5300 packs at 1900, 8 minutes of sport flying/smooth 3d.

In the end, I found that I prefer a shorter flight times with lighter packs. With a good field charging setup, there's always a fresh pack waiting. At the end of the day, I've flown as much as I want to.

[desertstalker]

Originally Posted by foolforspeed

I'm absolutely impressed that you can get that kind of flight time even just hovering. The best I've ever got out of an electric heli was 6 minutes and that was in the good ole newby days.

Nice thread necro, last post before yours was 2009...

On topic: I can get 9+ mins easily from most helis, just dont run the stupid HS that everyone seems to "need" these days. I get 9:30 on my G500 at 2150 RPM (520mm mains) and 9mins on my P500 at 2100RPM (470mm) both on typical packs for the class (4400 and 3000 respectively).