Flying low T/W copters

When it comes to the control of vehicles with low T/W the problem of control is much more difficult and saturating the motor commands happen very often which can lead to an unstable platform.

Wondering if anyone has flown which some success low T/W’s (not helicopter) and what they have changed tune-wise to keep platform in the air. I have only done some sim’s of this so far and results don’t look great. Have even considered other controllers from academia that appear to handle this problem better.


Why would you seek to fly underpowered aircraft in the first place ? For any professional application, I just find that surprising.

I’d rather aim for good power reserves, for redundancy, and ability to handle strong wind or weather phenomena like microbursts.

It is not desirable to fly low T/W for fixed-pitch controls but trade-offs sometimes have to be made for a given design/payload.

I don’t think any other controller will do miracles, but the easiest way you can squeeze out a bit more is to disable YAW_HEADROOM

When you mention low T/W ratio, what kind of a ratio do you have in mind?

I’m not sure I have specific T/W just pushing a simulated vehicle down with more payload trying to understand what current limitations are. I’ve gone down to 1.4-1.5. For most flyers I assume T/W are much much higher but trying to carry a bit of a extra payload for short duration of a flight is sometimes desired. Just wanted to see if many people push their systems and if they do what they change tune wise.

Yaw headroom is something I’ve looked into - in sim it seems to make some positive impact

I think you’re barking up a very dangerous tree.

Once you start encroaching into the STABILITY THROTTLE head room above ~60% throttle, all bets are pretty much off.

First off, the last 5% of the throttle range above 50% (95% to 100%) has no impact on thrust, so now we are down to having 35% of the entire throttle range to use.
Second, if you have voltage scaling enabled, ArduCopter will raise throttle to compensate for voltage sag. This is fine with a properly loaded aircraft, but once you go over weight your hover current goes up, and the rate of voltage sag goes right along with it… At some point ArduCopter will start chasing the voltage sag, but it will never catch up, and we all know that dead batteries will carry the aircraft all the way to the scene of the crash…

Totally understand what your saying - the sim vehicle I’m flying has a large battery so the SAG isn’t an issue. The issue as you pointed out is there isn’t much throttle range to use for attitude adjustment. This is more of a study than anything and am just trying to see if it can be done for short flights. I basically want to fly at good T/W - load vehicle with payload - fly - land take it off - and be done with it. Flight would be short but if I’m gonna crash every time I load whole vehicle needs to be changed drastically. I know with limited bandwidth it won’t be a sporty aircraft - I just want it to stay in air and be semi-controllable.

You can’t take any shortcuts. Build the aircraft to hover at 50% throttle at your full expected TOW and be done with it.