7HV mid air stall- well possibly.

[atomiccomp]

Today I had my 7HV fail to pull out of a 25mph dive. As it descended I suddenly became aware that it wasn't pulling out and it went through to trees and landed in soft mud, Damage is minimal
being a servo gear set, 1 mainblade, feathering shaft and the links from the head to swash.

I have checked the logs and as expected (I hit throttle hold and the motor cut as expected) the issue seems mechanical. The vortex log shows nothing but 'nothing to report' and I use a taranis with plays Voyager red alert loudly if the radio link or main power goes off and I also have a scorpion BUG. On recovering the model it was still responding to stick movements and the vortex appeared to be working fine.

The only issue I am wondering about is is it possible it somehow stalled in mid-air as it was windy and I was running a fairly low head speed (1750-1800 rpm)? I had spent the flight doing a mix of slow 3D and fast banking turns ect. Until that point the model was flying fine.

I plan to bin or sell the model as spares or repairs as I don't trust it now.

[Peteski]

I've never had a heli stall on me yet and it seems unlikely in a dive with reasonable forward speed, but be interesting to hear what more experienced flyers say. Maybe your elevator servo simply failed? I presume you tried to pitch it up and add some collective and there was no response?

[Granpappy]

Sorry to hear this. Descending in your own downwash can make you lose lift and cyclic control. Best way out of it is drop the collective and put in forward elevator to get out of the situation. Then pull a shed load of collective to recover. Pretty rare in an RC Heli though.

[trillian]

I think the only way it would be caused by a weather situation would be some kind of freakish down-draft which I think is unlikely. 1750-1800 isn't really very low.

So were you applying full positive collective and nothing was happening? If it wasn't a radio / electrical thing then the only kind of mechanical issue I have seen that might cause something like that is where the grip bearings lock up temporarily, I had that happen on a heli once and it was quite scary.

[milly0812]

We all get failures once in a while, find the problem fix it and get on with it. Saying you don't trust it now is a bit silly it could be a number of things eg esc cut and went to soft start, motor bullet solder, one way bearing to name a few. The 7hv is a tank as it's just proved lol

[Grumpy]

'Stall' as such is something that's pretty unlikely in a heli unless you were flying VERY low headspeed or pulling very high 'g'.. neither of which appear to be the case. Vortex ring state (what Granpappy was referring to) can only happen at high rates of descent with very low forward speed, so doesnt seem to be the case.

As per previous post, if it's all working ok i'd just give it a good check over and keep flying it.

[atomiccomp]

During the descent neither pitch or cyclic fore and aft worked, it behaved like it had locked out although it hadn't as the TH worked. It all happened very quickly and I wasn't able to test anything else before it went in.

All the servos are working fine except one now has a notchy spot when moved by hand. which I think has happened in the crash, however I will never know for sure.

Either way it's very baffling.

Thanks for your input guys and girls. I realize fixing it is the way to go and understand the 7HV has a bit of a following however I'm quite happy to bin the it. I wasn't terribly impressed with how it flew, it always felt over weight and was a whopping 5.4 KG's ready to fly. I have a 6HV (original) which is everything the 7HV should have been but wasn't, light, fast and nimble.

[Granpappy]

Vortex ring state (what Granpappy was referring to) can only happen at high rates of descent with very low forward speed, so doesnt seem to be the case.

25 mph vertical descent rate is not that slow, and with a tail wind, who knows.

Did you notice whether the rotor speed decayed? That would point to a OWB slipping. I think an esc reset would show on the log.

[atomiccomp]

25 mph vertical descent rate is not that slow, and with a tail wind, who knows.

Did you notice whether the rotor speed decayed? That would point to a OWB slipping. I think an esc reset would show on the log.

it was diving into wind and all sounded normal. I've checked the OWB and its fine to be honest I'm certain that if the esc had shut down I could have easily autoed it. I've autoed out of worse! it just didn't respond to cyclic commands. The problem with these
crashes is they happen so fast you miss trying different things for example I didn't try to roll it or try negative pitch or maybe I did but don't remember! I tried to pull out and when it didn't I hit TH and just watched it go in. The whole event took about 2-3 seconds.

[Grumpy]

25 mph vertical descent rate is not that slow, and with a tail wind, who knows.

I'm assuming that 25mph was the estimated forward speed, and with a headwind as clarified in the last post it just doesnt seem to gel with vortex ring.. The only times i've experienced it is in fast descent while having very little or no forward speed, and even then at 1700-1800RPM a 7HV (unlike full size helis) has more than enough 'oomph' to punch out of vortex ring by sheer brute force.

[Peteski]

25 mph vertical descent rate is not that slow, and with a tail wind, who knows.

I presumed the 25 mph was his forward speed diving nose down into the wind. In which case a stall would be extremely unlikely. I've only ever lost lift in my own downwash when coming down vertically with zero forward speed, which is not a dive. It sounds more like he lost cyclic control of pitch for whatever reason.

[atomiccomp]

Sorry guys, I meant a vertical dive into a 25 mph wind. I've no idea how fast it was going whilst it was diving. the dive started at about 150 ft from a stall turn and as I started to level off it simply refused to pull out and crashed.

[jasoncook]

Hi, sounds like it locked out the log would show it going into hold as that is what it would be set too if it lost signal, if the blades were still turning even at a reduced RPM you would have some cyclic control maybe not enough to punch out but it would just feel wooly until they nearly stopped.

[hedge]

Nothing in the logs, full failsafe set up, gotta be a failed servo - elevator? I've over heated my fair share of tail servos and before they fail they get awful sloppy and unresponsive - then lock out.

[tomatwalden]

Today I had my 7HV fail to pull out of a 25mph dive. As it descended I suddenly became aware that it wasn't pulling out and it went through to trees and landed in soft mud, Damage is minimal

When you say it refused to pull out - Did you however manage to get the heli horizontal again? ie. did the elevator work but the heli went in flat, or did the nose refuse to pitch up from the dive?