I’m getting quite inconsistent efficiency measurements in cruise flight and am assuming it may be dead prop alignment position but I’m not convinced that this is the cause of 35% Wh/km spread.
Current/volt measurements?
I have 2 sensors onboard, one native on the Matek H743 wing and an additional I2c sensor. Both agree quite well and they have been tested against 2 other power meters.
Airspeed measurement?
When the upwind/ downwind legs are compared with GPS groundspeed I think the airspeed is accurate.
Some tests were done with straight out and back legs and some were done in a large circle. I did a few flights at 18m/s where I started the lift props to randomise the stop positions and there was indeed a spread of measurements.
I have almost finished the Kite2 which will have a prop alignment system so that will be interesting to compare.
If anyone enjoys a puzzle, please check the logs to see if I have missed something.
Thank you for conducting such impressively precise test flights and for sharing the log files.
My experience of comparative efficiency measurements — which unfortunately is anecdotal rather than statistical — has shown that thermal conditions during flights have also a significant impact.(Motorised pilots often overlook the effect that even weak thermals can have on efficiency measurements.)
I noticed a possible thermal-related effect during your circuit flights:
At the same airspeed and altitude, the pitch fluctuates between about +5° and -2°. I can’t prove it, but this could also be due to different thermal zones. The required power fluctuates significantly as a result. The fluctuation seems too irregular to me to be a phygoid oscillation. In any case, I would take the pitch record into account in your analysis.
As I mentioned, I’ve observed this through anecdotal experience, with widely varying results depending on weather conditions. Here’s an extreme example: While flying through a thermal bubble, the 2-motor (XUAV-Clouds) required no power maintainig altitude.
Hi Rolf. Thanks for taking a look at it and sorry for slow response.
I have just got my VTOL prop alignment system working and immediately got 26% lower power draw than the average of many other flights. I think the random positioning of the props is likely the cause of variable results.
If the measurement variability turns out to be significantly lower than 26% in future test flights, you’re right. Of course, I hope you’re right, but I’m curious to see.
Looks like you were right about the effects of rough conditions. A few days ago I did my first flight with the prop alignment system and got a remarkable 1.9Wh/Km at 18ms. Today I tried a speed ramp up test and got very disappointing results. It was very gusty. I think I need to calm down the throttle as it was all over the place. I’m a little concerned that on days like today a relaxed throttle may lead to a stall. Motor power is the orange trace.
I’m probably stating the obvious, but shouldn’t we specify fuel consumption per unit of time (at a given speed), similar to how it’s done for airplanes?
I think the challenge in accurately determining the advantage of the aligned propellers is the difficulty of repeating flights under nearly identical weather conditions.
In any case, the silhouette looks much better from below. Congratulations on your mechanics working so well.
You’re absolutely right, fuel/battery capacity consumption determines time in the air rather than distance covered at a specific cruise airspeed. Flight performance is always directly affected and changes according to the atmospheric condition at the location and altitude of the aircraft. The basis of the flight planning is on the average weather condition, i.e. temperature, dew point, atmospheric pressure, velocity and direction of the wind aloft of the flight path.
I think I’m doing both measurements. Watts is showing the power needed to loiter at various speeds and Wh/Km is more useful if you need to get somewhere.
Full disclosure… I’m not an engineer and what I present here should be taken as pure conjecture and based on personal experience in flying full scale and R/C VTOLs.
IMHO Watts is good to determine if your aerodynamic design changes are improving the efficiency, based on each flight then maybe taking the average across the number of flights. In FW mode, you need to be using either minimum or normal cruise airspeed only regardless of weather condition. Power consumption could vary wildly say between flying in winter vs. summer. High temperature and humidity and altitude could cause loss of propeller efficiency of up to 20% then add the loss of lift efficiency from your wings will cause your motor to consume more amps/fuel to maintain the cruise speed necessary for the flight maneuver or condition.
Wh/Km is only useful for “good to know” as a datapoint for the give flight/mission. Distance travelled will decrease with a headwind and increase with a tailwind. In a flight/mission flown between two waypoints, assuming wind direction and velocity stays constant, if the first leg encounters a headwind, the Wh/Km will be lower than the return leg but taking the average of the entire flight is your datapoint.
But what if the return leg takes place the next day and wind is opposite the day previous, then Wh/Km will be severely lower. If you planned the mission based on Wh/Km and didn’t plan to recharge/refuel for the return leg, your aircraft will not make it back home. We haven’t included the MC mode consumption for takeoff and landing unless you have a separate battery for your quad motors.
