emergency landing

[mazi14]

I am using iNav with several differen fixed wings for years, but I experienced "emergency landing" for the first time recently. Based on telemetry log from radio it looks like GPS was working fine at that time, so I wonder what else could trigger "emergency landing". Yes, I flew on the edge of radio control and "fail safe" was triggered first. The plane went to RTH then. When radio signal recovered, I took over the control again. This is common and did not surprised me. But FC decided for "emergency landing" then and I was not able to abort it. The plane landed (crashed) several km away. Affected plane is Nano Talon EVO with SpeedyBee F401 wing mini FC. iNav version is 7.1.2, transmitter FrSky Q7 with ELRS external module (modified R9), receiver BetaFPV nano. Is possible that "emergency landing" could be triggered by radio receiver? When I fly on the edge of radio range, the OSD shows quite often strange characters, different "fly modes" or even iNav start up screen with its logo. Friend of mine told me that this can happen because of some interference (power wires close to FC). Have you experienced this as well?

[sensei-hacker]

Emergency landing can occur when the GPS or other essential navigation sensors cut out during RTH.
It can also occur when the winds aloft are carrying the aircraft away from home during RTH. Note the wind at 200 feet altitude is generally significantly stronger than at the surface, below the tree line.

Flying near radar installations or powerful transmitters of any kind can cause very significant interference that can even reboot the flight controller. Flying near RF transmitters such as for TV can of course also interfere with your RF control. So if your control signal got significantly worse pretty quickly, that could be RD interference.

When flying past line of sight, you can look at a sectional chart to see where the radio towers are, paying particular attention to the navigation aids marked on the chart. Those navigation aids are transmitters that can interfere - but they also mark the airways where manned aircraft will be flying! The sectional will also show you all of the little airfields you probably wouldn't know about if you don't look at a chart. (There's one about every 10 miles in the US).

Power wires near signal wires can absolutely cause harmful interference as well. The inductive interference is proportional to the current in the wire (so the main battery wires and motor wires are the biggest issue). Multiplied by the size of the loop formed by positive and negative leads, so keep those wires short and keep the negative and positive together with same tape or wrap. But it's inversely proportional to the distance CUBED. So putting your signal wires or sensors a little further away from the power wires makes a big difference!

A good way to wire is to try to have the power wires in front and on the left, signal wires and sensors in the rear and on the right. (Or vice versa, but typically you want the battery up front).

Ps - if you're thinking "I thought it was distance squared", that's for the radiative field, the energy radiated out that keeps traveling further and further away. The inductive near field "clings" to the source, so it drops with d² X d = d³.

[wdunn001]

you may not of realized you were close to a transmitter or even someone could of pointed a yagi at you. many reason something like this could occur. rf lost is absolutely a reason. were you able to collect black box data? might lead to some insights.

[mazi14]

The problem is not loss of RF signal, I experience it quite often (every flight). RTH is triggered in this case and everything is fine. Problem is loss of GPS data (signal ?) at the same time. So far nobody has mentioned other thing that could trigger "emergency landing". There is no loss of GPS coordinates visible in the transmitter telemetry log. Unfortunately, I do not log FC data to black box :-(

After "emergency landing" of the plane far away I went to a potential place of landing and I was able to restore RF connection. I got current GPS coordinates of the plane and searched for it there, but I was not succesfull (there are trees and tall bushes.). I had a partial lucky, because next day I had a call from a lady that found the plane by accident. Unfortunately the plane is broken and not complete. Spare parts are not available any more :-(

[breadoven]

It is also possible to manually trigger an emergency landing either by rapidly toggling Poshold mode 5 times or using the Multifunction function. I guess an erratic RF signal could inadvertently activate these functions by chance but it seems unlikely. Seems more likely that something went wrong with Failsafe aborting out of RTH which can revert to an emergency landing if something unexpected happens. There is the possibility of a timing issue with the triggering/cancelling of RTH during Failsafe that could cause the unexpected to occur especially if the RF signal is erratic, but having looked at it before it not obvious how this could happen.

Did the plane appear to be flying back home in RTH ? (related to RTH sanity triggering an emergency landing).

It should also always be possible to escape emergency landing by switching out of all Nav modes, so Acro or Manual mode, so long as there's no Failsafe active.

Shame about the log, would have made it much easier to work out what went wrong.

[mazi14]

I really appreciate your input! What does it mean "Multifunction" function? I would bet that "emergency landing" was triggered by receiver and it was not GPS issue. This plane was my the first attempt with ELRS receiver. All my other planes with iNav use original FrSky R9 receivers. I tried (of course) to abort somehow "emergency landing", but I am not sure, which FM I swapped. Whole "emergency landing" lasted 18 secons only untill I lost video. Plane was diving too much fast.

I can remember that I saw "loitering" FM in OSD briefly right before "emergency landing", which was not definitelly switched on by me.

Yes, when fail safe first time has triggered RTH, plane turned toward home. I tried to restore my desired direction then (like I always do). There was second fail safe then. A little bit fight between me and FC.

I usually perform whole flight in manual mode and when RTH is triggered I try to get back to manual asap.

I have not felt need for black box logging untill now.