Does anyone have experience with performing long distance fixed wing emergency landings with APM on board? Any problems with failsafe/RTH kicking in?
I fly medium/long range (~10km)/ low altitude (<1% of distance) in flat rural areas and I've always figured that if battery would run out I'd simply point the plane at a suitable field, stick the plane in FBW and cut throttle and glide it down. If i were to loose video 10m-20m AGL it'd be OK as FBW would glide it by itself the last few meters.
The other day i realized the obvious: when altitude gets low enough that my 5.8Ghz video goes, my 2.4GHz FRSky may well failsafe too - resulting in the landing being aborted, APM gain some altitude, and likely crash at a less favorable location. Worse yet, i may not even know where it went down unless it ascends enough for video to be re-established.
Is this something that has happened to people? Is there anything that could be done about it? Ideally it'd be nice to have a special "emergency landing flavor" of FBW flying mode that the pilot could enter just prior to executing the final descent; behaving like regular FBW except APM not allowing direct transition from this mode to RTL - but maybe the use case is too narrow to warrant such a feature?
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Could you use a CH 7 or CH8 option to turn failsafe on or off? If you recognize this kind of situation, you could flip failsafe off and it will therefore not try to RTL.
my frsky rx has no provisions for in-flight change of failsafe behavior. one can either set it up to emit preconfigured values on all channels, or to not emit any ppm at all.
you're not saying that APM has provisions for turning failsafe of by means of a priori signaling on a spare channel? if that was the case i could set up frsky to not emit ppm and then use that a spare channel to indicate whether i wanted lack of ppm to result in CIRCL/RTL or something else, but that seems a bit too good to be true :(
@Jonas,
I think Pedals2Paddles is just fantasizing about what could be coded.
As far as your FrSky Rx failsafe, I was just throwing out the idea of using "preconfigured values on all channels" rather than the APM's failsafe function. One of those values would be to select your mode channel to the FBW value, the Throttle channel to low, and all other channels to neutral. If the FrSky looses signal with this set up, it will switch to (or stay in) FBW, cut the throttle, and glide to a landing straight ahead. No Circling and no RTL.
Since Pedals2Paddles idea hasn't been implemented yet, you would have to use telemetry to toggle on/off THR_FAILSAFE depending on whether you want to have RTL activated upon signal loss
Maybe not directly related but ArduPlane has the concept of "Rally Points" which can be set-up ahead of the flight and when it does an RTL it will go to the nearest rally point instead of home. I think it affects all situations where RTL is invoked though including pilot invoked so if you really wanted your plane to come home you'd have to fly it home until home was the closer than any rally point.
i have to admit i wasnt aware of "rally points". this would be quite useful if i used apm "as it was intended to" :), i.e. with a laptop and an xbee link, but being that im "only" using it as a osd/rth on steroids, i almost never hook it up to mission planner and, in fact, have to disassemble part of my rig in order to do so - not really feasible in he field.
Perhaps mountainous terrain where a direct line home is not possible?
What happens to the plane once it reaches it's rally point? I presume it loiters until the battery is depleted and crashes within the WP radius.
Maybe the Pixhawk will allow an autoland plan for each Rally in the future.
Has anyone tested the new option 2 "GLIDE" for FS_LONG_ACTN and FS_SHORT_ACTN?
I know the text says:
"A short failsafe event in stabilization modes will always cause an immediate change to CIRCLE mode"
However maybe GLIDE does work when in FBW. That would make sense, why should it be an option for Auto modes only?
You could just turn off the throttle failsafe and use your receiver's failsafe function to select FBW switch position. That's pretty scary to not have RTL at all.
i quickly looked at the docs. as you say it doesnt seem like it is possible to configure short failsafe behavior for stabilized modes, but may still be worth having a look at.
We had a midair collision recently with two APM equipped planes, flying in Auto and while they weren't that far away at around 600m, my plane with FPV equipment on board lost it's prop. The other plane was thrown off course but returned to the mission and flew happily on with minor damage to a wing.
I noticed the loss of altitude and with the FPV looked for a place to land, at that moment the plane hit a waypoint and turned, I took over without disengaging Auto and managed to land in Auto without damage although I think if I had left it alone it would've probably landed fine unless an obstacle or rock was in the way. The glide slope in Auto was very gentle.
Personally I think the use would be limited and would add to an already overcrowded APM code.
congratulations on the successful emergency landing! :) your case seems somewhat different though as you 1) were close in enough that you maintained control until touchdown 2) didnt have a prop anymore so no possibility to ascend.
us who use APM exclusively as a backup for conventional FPV flying commonly have APM set up to switch to RTH when receiver goes into failsafe. this is great for most cases, however it would be really bad during a long range emergency landing as outlined above.
i suppose one could work around this by sticking the plane into loiter mode over the desired ditching spot and then just wait... watching it depleating the last few percents of battery and then slowly descent as the motor is unable to maintain altitude. if rth kicks in during the last few seconds there wont be juice enough to ascend or travel any serious distance. not ideal though.
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