After several years of limited progress, a friend of mine and I are pushing forward on my long endurance UAV project.
VTOL booms have been added and engine testing is ongoing.
I previously converted a Radian Pro to VTOL and was very happy with Pixhawk 2.1/Ardupilot so I am going down the same path with the ‘big bird’.
How do you plan on getting 2 days of flight time? Are you going to be restarting the engine here and there so you can climb, then soar with the gas engine off?
A climb/glide flight profile isn’t a bad idea, but it would be impractical for us.
Propeller efficiency would be less-than-ideal because of the induced losses (from high disc loading during climb), but engine BSFC would likely more than offset that … at least assuming a fixed pitch propeller.
That said, we won’t do it because:
- We won’t have engine restart capability
- With the model aircraft altitude limit of 400’ AGL we would be restarting the engine every 3 minutes or so
- We don’t have fuel injection (all it takes is 1 start failure to be forced into an abrupt deadstick situation … possibly at night)
The original plan was to make a variable pitch propeller to get the best propeller efficiency AND get very high BSFC out of the engine. I have experience designing and building propellers at my day job. However, this is a personal project … and I don’t have the time (and would rather not spend the money) to make a custom hub. A custom VPP shouldn’t be necessary to break the VTOL endurance record which currently stands at 32 hours. Also, the control logic necessary to support VPP operation would have to be created.
We will be going conventional at first. The engine will swing a fixed-pitch propeller sized for minimum acceptable climb rate such that propeller efficiency and engine BSFC numbers should be sufficient to exceed 32 hours. In this condition, I doubt we will be able to comfortably operate at the maximum allowed weight of 55 pounds, but we should be able to carry enough fuel to set a record. After that … time permitting … options include:
- high compression engine mods – such as re-machining the wristpin bore in the piston.
- installing different engine (as long as we can still get low power efficiency)
- installing a larger alternator and using it to boost climb rate when fully loaded (parallel hybrid)
One of those options should let the aircraft comfortably operate with a full load of fuel and maximum possible endurance.
The biggest obstacle is time.
My job sometimes gets very busy and my wife and I have our first baby due in 2 days!
variable pitch is possible, with lua scripting and airspeed and motor current and RPM sensing, you could optimise the pitch to RPM to airspeed and current draw