Hi Chris,
if i have ROTOR RUN UP TIME = 7 s , then CRITICAL ROTOR SPEED must be 40% ?
In ArduPilot the rotor runup time will determine the critical speed. Setting it to 40% will make the critical speed 40% of 7 seconds. I would recommend setting the critical to more like 90% and set the runup time to match the actual amount of time it takes to get the rotor to full speed.
This setup is better?:
ROTOR RUN UP TIME = 8s
CRITICAL ROTOR SPEED = 65%
Well, it’s probably better than what you had. With 8 sec and 65% as it is running up the code will assume the helicopter is able to fly with whatever rotor speed is reached at 5.2 seconds from throttle hold “off”.
Is that really the case? Don’t use random numbers and hope it works. If it takes 8 seconds to get the rotor to full speed, say that’s 1000 rpm, assume a linear rotor acceleration and 90% would be approximately 900 rpm.
It normally takes at least 5 seconds to get stuff turning during clutch slip with a piston. And then normally, even in warm weather at least a 30 second ground run at flight idle before a cold engine reaches adequate temperature to accept throttle without stalling or balking.
Use the real world numbers. Otherwise if you try an auto takeoff with it you may be in for unpleasant surprise when it loads up and loses power or flames out on takeoff. Do not use push-button electric settings for a piston engine. I am never in a big hurry to get a piston helicopter off the ground until I am sure it is properly warmed up and ready to accept load. Doing otherwise will result in a scored cylinder, stuck rings or stuck valves eventually in flight. And then you got a real autorotation power-out emergency on your hands because you abused the engine. Helicopters go to maximum engine load when you lift up into hover. So set this accordingly.
@Loren_DS when I fly my piston helicopters in moderately warm weather, around 75-80F ambient, I adjust the mixture so they run about 165F in cruise flight. When we bring them in after a flight and it goes into hover, in the minute or two it takes to maneuver the helicopter to the landing area it’s not usual to see the engine temp climb from 165 to 185F. 200F is overheat and in hot weather it will hit overheat within a couple minutes of hover time. And this is with a centrifugal fan-cooled engine.
This is because the engine works harder in hover than it does in cruise flight.
If you use the Auto Land feature with piston helicopters, it’s not “if” it’s “when” you will have an engine failure due to shutdown with high core heat in the engine.
All the same applies in reverse on takeoff starting up a cold engine.
So use a little common sense and your experience flying the helicopter without an autopilot in it to make these settings to prevent problems with your engine. Especially the F-50/F-100 engines are infamous for sticking valves and/or experience a seized engine in flight due to overheat. Take care of it and don’t push its temperature limits on either takeoff or landing and you will get better results than what most people get with those engines. They run them too lean and they run REALLY hot, but because of the valves they have the same problem in reverse during warmup. Keep that in mind.
thanks for your advice Chris.
@Loren_DS here is a typical runup. If you watch the seconds, from where the rotor first starts turning to the clutch fully engaged is 14-15 seconds. You can push it slightly harder than that but it torques the helicopter on the ground pretty bad if you do.
And then, of course, I increase to flight idle watching the engine temp rise before going to governor. Overall, in my experience a really fast runup for a piston is 30 seconds. More like a minute, on average. If it is really cold weather it will ground run for 2 minutes or more at flight idle before going to governor-on. They don’t warm up very good at low idle, and in fact, running the mixture at full rich at low idle will load the engine up cause it to lose power when throttle is applied. It takes some moderate load on the engine to get a decent temp rise and keep it cleaned out so it will run.
Thanks , I’ll keep it in mind.