Polish HEMS EC135 almost losing it on landing
 

Great pilot job with recovery...but what is wrong with Holly fenestron and Airbus H135?

Nothing wrong with the helicopter
looks like a downwind approach and turning into wind in the high hover.
Fenestron dont like wind from some angles - lots of pedal movement necessary to do it smoothly.
would better have flown a turn with speed, still, he got away with it and has a story to tell and others can learn

If that was yesterday or today and the windspeeds in Poland were anywere near what we had in Germany, no wonder he nearly lost it. That fenestron and fin offers a huge surface for crosswinds. If he was even downwind in these winds, he's lucky he didn't crash it.

In the beginning somebody taught me to approach into the wind. I suppose that even holds true if the wind is very strong?

Approach was with 250-260 heading wind from 230 at 15 kt ... The video is from mirror so to make it real You should see it also in mirror...

I would consider this straight into the wind. So what is wrong with the anti torque device (did somebody ask this question already?)

Not sure which way the wind was blowing, but it sure looks like a classic case of http://www.faa.gov/documentLibrary/m...ar/ac90-95.pdf, albeit with things spinning in the EU direction instead of the US direction.

Great recovery.

The 135 rotates in the conventional way as does the 145 i.e. anti-clockwise, NOT the same as other Airbus Helicopter product. I have had to reverse it down taxiways or completely sideways in strong winds.

Someone with a video camera on every flight
 

Interesting footage and no assumptions made here as I have no idea of the circumstances. An ops director once told me "Assume that the authorities, Chief Pilot, Director of Ops and Safety Director are watching every take off and every landing". With social media it is so very true. Every 'boring' or 'routine' flight, is a good flight.

Well that's damn interesting. How do we account for the left yaw, then?

Mirror image inverts apparent direction of yaw.

so approach into wind, passing the vehicles, then turning downwind for the landing?
with 15 knots of wind?
Manageable - but you have to anticipate that wind from about 30-45 degree out of centerline, regardless if it is from the front or back, might give some wobble due to disturbed airflow around the fenestron.
No way to hurry through an outside landing-
Proper assessment of the landing site, how to approach and how to depart later shouldn’t be rushed. As you can see here, instead of landing and helping time will be wasted for paperwork (luckily only)

I'm such a dolt! Of course, thank you! :}

Big DC windbreak
 

That mahoosive distribution centre opposite would I suspect create some interesting dynamics and that coupled with little bit of fenestron stall - looks like it induced a little sphincter twitch..... still good recovery and fly away to calm the nerves.... remember this happening in a gazelle in Germany many moons ago - never seen an airtrooper run so fast 🤣🤣

Fenestron stall doesn't exist.

Glad that you seem to have better knowledge than the AAIB - they seem to think it existed and so did we 89-95 - BAOR / NI / Op Granby

https://assets.publishing.service.go...TURP_01-92.pdf

very old report and still, there is no fenestron stall
just inappropriate Pedal movement
with Fenestron you have - non linear - longer travel

I've had a couple of vinos, probably missed something, but where are people getting wind speed and direction from that video?

Yes the same information was widespread in the UK Mil and I was flying the Gazelle at Shawbury during that period but was never convinced about the theory.

The whole construct of Fenestron Stall was demolished when Aerospatiale demonstrated recovery from in excess of 120 deg/sec left yaw with full right pedal and it stopped perfectly (albeit with the little red Tq light flashing).

It was later understood that Fenestrons have different handling characteristics to conventional TRs and need prompt and sometimes large pedal movements to control undemanded yaw where the pilot has got behind the curve regarding actual pedal position compared with required pedal position,

just from our Polish meteo website and pilot report about that flight :)

Fenestron technology has changed vastly since the design of the Gazelle. Modern fenestrons are linear in there power delivery and feel no different to a conventional tail rotor.

Airbus recently published two Information Notices about unanticipated yaw. One for the French product range and one for the German. It dispels a lot of commonly held misunderstandings of loss of yaw control and recovery.

FNW.

That's certainly not true in the two fenestron equipped helicopters I've flown: the EC130 and the Cabri G2. Are those modern enough?

There's a lot more money in the 135 & 145 markets. Maybe that is where design improvements have got most attention...

I've flown 120,130 and 135 fenestron. The 135 is hugely different in it's handling and feel to the other two, a lot of this is probably due to the 135 being built around an autopilot. The 135 is wiggle the toes as compared to muscle up that leg with the 130 and less so 120. The 135 I have also found to be linear whereas the other two very non linear in the thrust available. All of them use a lot of torque though, especially near the limits.

Agreed - the 365N3 has an extra overtorque limit specifically for yaw applications

I used to instruct on the Gazelle, in the mid 1980s. No-one had ever heard of "Fenestron Stall" despite the aircraft having been in service for quite some years.

I went away on a different job for a year and then went back to refresh on it, at the same base, with CFS and an instructor I knew of old. No-one told me that "Fenestron Stall" had by then then been invented/discovered and handling restrictions imposed. on the first flight I tried to do what I thought was a normal pre-takeoff lookout turn (must have done thousands before in exactly the same conditions) and was immediately told off because I'd dared to put the wind on the "wrong" side.

Unanticipated yaw
 

The EC130 fenestron is derived from the EC135 one by symmetry. Aerodynamically it should behave similarly...

If you are interested in the unanticipated yaw topic and if you have time to spend the attached paper was presented last year in Warsaw and might explain the Polish event.

That may be so but they 'feel' very different, the fact that the main rotor spins in opposite directions notwithstanding. The 135 has autopilot intervention in the tail and you are often working the pedals to get the semas into range, the 130 doesn't have any intervention at all and feels in my opinion very dead. I found that you could fly the 130 with just one foot if you wanted as you merely need to modulate the amount of power pedal in use, much like a 500. In terms of the 130 gimme a conventional tail rotor squirrel (preferably a B3, the Swiss army knife of helicopters) any day, much more precise, intuitive and predictable. I just found the 130 an answer to a question that nobody asked.

I spent all of last week in a B2 and flew our 135 today, I'd walk past the 135 to get in the B2.

Thread drift.
I was on the Gazelle IFTU at Middle Wallop and as far as I know nobody had any flying problems with the fenestron despite performing prolonged max speed spot turns in either direction. I also don't recall any SAS on the IFTU aircraft. If that was the case then why and when was SAS fitted, and could that have caused any of the subsequent problems? I thought the Gazelle was a joy to fly but after flying/instructing on Hillers and Whirlwind 7's (where controlling RRPM with the collective twistgrip required constant attention) I felt that the ease of flying the Gazelle could introduce accidents caused by overconfidence rather than mechanical problems as had been experienced in the previous generation of helicopters.

76Fan - the AH1 Gazelle for AAC use didn't have SAS fitted although the ones for 3BAS (as was) did. The RAF and RN ones HT2/3 did have SAS fitted.

Many of us believe the SAS in the yaw channel was one of the problems as the series actuator could move the pitch of the blades without corresponding pedal movement until it ran out of authority. When that happened, the actual pedal position was often not where it needed to be and as the yaw started, the first application of pedal seemed to have little effect - this was why pilots thought they had a yaw control problem when in fact they just didn't have enough right pedal in.

AMDEC - its a very good paper but omits the effect or loss of effect of the vertical fin/vertical stabilisers as they gain or lose airspeed and reach critical AoA.

Thanks for that Crab, however one of the IFTU Gazelles in 1973 was an HT2 for the RN, and I delivered and did the conversion of some of the 705 Sqdn instructors onto the Gazelle in 1974. None, either AAC or the RN had SAS fitted at that time, but I never flew the Gazelle again after September '74.

Ah OK, I didn't fly the Gazelle until 83 so it must have been an add-on sometime between 74 and early 80s.

The 135 has a few little "quirks" but all completely understandable if you stand back and take a look at what is going on behind you.

Relative airflow from the forward quarters either left or right will induce some yaw instability from the wake of the horizontal endplates. Nothing too obtrusive but may screw up your camera shot. You can fly around it if you appreciate
what is happening but nothing to get too concerned about. They removed them on the "3" and increased the height of the fin tip cap.

Another factor is the "A of A" of the fin. It can upset you a little more than a conventional aircraft but again not much to be too concerned about. Just be aware that as per the RFM a "run on" is NOT recommended with loss of TR drive.
Reason being you will feel fat dumb and happy until the fin stalls and loses effect which you probably won't recover from. Hence the recommendation to perform a full-on autorotation.

Authority - no issue - the thing will reach 65 knots or more sideways at the stops.

Power - yes it can use more in the hover. And conversely less in the cruise.

Like a lot of these things too much BS gets read into it. Your the "pilot in command" - just fly the thing - don't ever become a passenger!!

As alluded to in the report - "Light helicopters with low experience pilots are the preferred victims."

I would say it is included, even if not explicitely. The pedal curve gives the amount of pedal that is necessary to zero the yawing moment. The fin contribution is therefore included and may lead to an accident on the pedal curve, for example when the fin stalls.

That was sort of my point - the differing conditions of crosswind as IAS is reduced towards the hover, combined with any ingestion of the MR vortex by the TR can cause the vertical stabilisers to lose lift earlier than in a pure headwind and cause unexpected yaw variations.

Tailfin, fenerstron and SAS all had a hand in Fenestron Stall in a Gazelle in which I was a passenger. We departed Shawbury in a 20kt wind and promptly had a generator failure, we therefore returned to the landing point and having lost the generator, we had also lost SAS/Heading Hold. This made the pedal inputs much more responsive in the hover. As we carried out a lookout turn left prior to taxiing back, we passed through the downwind and the wind caught the tail fin. The rate of yaw increase caught the pilot out and he went to full right pedal. We then continued to spin several times and thought we had a tail rotor failure.I could see his right pedal was fully forward and totally ineffective.His immediate reaction was to gain a few feet clear of the ground but as he applied collective we started to pitch nose up and he over-corrected with nose down, by this stage we had probably gone through 6 revolutions, he couldn't bring himself to release the right pedal and unstall the fenestron (partly because we had never heard of fenestron stall, let alone discussed a solution). He then put down the collective and accepted the ensuing hard landing. He did keep us as level as possible and the aircraft was a Cat3. The fenestron was fine. I am certain Fenestron Stall exists, even though the Aerospatiale test pilots were not able to re-create that situation. In any case, they would have been briefed and ready to respond....not quite the same in my opinion.

There were at least two occasions of "fenestron stall" at MW. One was a solo student rapidly pirouetting out of dispersal before recovering control.

The other was me. Mutual tac sortie on the APC. Hover taxying across a field up on the ink pen ridge, flying from the lefthand seat. Saw what I thought was a line of beaters(pheasant shoot) ahead, so stuck in a boot full of left pedal to turn away. The aircraft spun rapidly to the left. Tulles power to get away from the ground which, of course didn't help. Thought I put in full right pedal, but maybe I didn't. My stick buddy was an experienced crewman, saw that I wasn't coping, took over and got things under control.

After we recovered our composure, we made our way home deciding not to tell anyone.

Oh, and I can't remember what they were, but they weren't beaters.

I've said it before here, "Fenestron Stall" is simply French for mishandling. There is another translation from ancient Greek which means "failure to anticipate". The aircraft spinning is very real, the Fenestron Stalling, not so much...