Primarily for general aviation discussion, but other aviation topics are also welcome.
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By CloudHound
#1654651
OK, so it's up to me to be the one to mention quartering tailwinds affecting the fenestron in the hover and taxi phase,

Said it. Carry on.
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By Rob L
#1654655
CloudHound wrote:OK, so it's up to me to be the one to mention quartering tailwinds affecting the fenestron in the hover and taxi phase,

Said it. Carry on.


It's like tailwheel aircraft: "quartering tailwinds affecting the tail in the landings and taxi phase"

Much the same it appears :wink:
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By carlmeek
#1654666
Sorry for my absence from the thread, busy day!!

In answer to running cost and fuel burn, it’s somwhere in the 160 litres per hour region. I’m yet to get a price on delivered jet a-1 so can’t give a proper running cost but I’m hoping it to be quite a lot less than retail of around a pound.

The Fenestron issue is one that has a lot of fokelaw and rumour around it. Someone invented the myth of “Fenestron stall” and then disproved it.... but there have been some incidents. My instructor, examiner and a very experienced pilot have passed on some good tips for avoiding it which can probably be best summed up by “don’t show off”. There certainly have been incidents of pilots coming in very hot, pulling lots of power and running out of anti-torque pedal. Wise advice that I shall keep close.

When I first jumped in a gazelle I was really freaking out about how sensitive the hydraulically assisted controls were. Total opposite to my enstrom. After a few short hours I now love it, and if I ever want to do some muscle building I can just switch the hydraulics off! Landings with it off require almost all my strength.

Now I need to do lots of flying and build some experience of the type. I love the fact this machine is 2 years older than me, has 10,500 hours, and is still going strong. The guys at Falcon maintain it to the highest standard I’ve ever seen. If my enstrom was the helicopter version of a battered Cessna 152, the gazelle is the helicopter version of a brand new cirrus. It’s literally immaculate and you would eat your dinner off the top of the fuselage under the gearbox and engine covers.

Nice weather next week please and I can bring it home!
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By carlmeek
#1654670
That sounds fun, haven’t been in a magazine since my RV-10 build :)
By Cessna57
#1654673
Did it fly into DX about a week ago?
I went “ooh, that’s unusual” as I watched one land whilst untying our PA28. (and I still have the pictures!)

If you come in again, (If indeed it was you?) I’ve heard they like a little ballast when flying, AND I could point out the fabulous local landmarks to you, just let me know when you’re arriving and I’ll be there. :wink:
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By RichardDavies
#1654675
Very very nice, I look forward to snapping a few pictures if you ever decide to visit Lee on Solent airfield with this beautiful Gazelle.

Still yet to see your RV-10 even though I know you have visited.
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By Dave W
#1654681
carlmeek wrote:Someone invented the myth of “Fenestron stall” and then disproved it.... but there have been some incidents.

I know (well, knew - what follows is memory, and likely in error in detail) a bit about this, as many years ago I was involved in a technical analysis and review of the issue.

There was a slew (close to double figures, I think) of accidents in the UK (and maybe elsewhere: Aerospatiale were cagey about that) late 80s/early 90s where the aircraft were hovering in light winds when, it was thought by the crews reporting what had happened, that the fenestron had suffered an aerodynamic stall. A very rapid rotation occurred, and the handling pilot reaction in many of the accidents had been to dump the collective - leading to contact with the ground whilst still yawing, which typically resulted in a rollover. Fortunately there were (I believe) no serious injuries.

UK MOD, thinking it was actually an aerodynamic stall, then published a Warning in the Aircrew Manual (ACM) to the effect that if you did experience the apparently uncommanded rapid yaw, don't quickly apply anti-yaw pedal because (it was felt) this would drive the fenestron aerofoil further into stall.

The accidents typically occurred in low wind conditions; there was an associated (UK MOD) theory that the main rotor downwash/tip vortices were entrained into the fenestron duct, and it was that which initiated the uncommanded yaw, since - so the theory went - the anti-torque thrust was lost due to the aerodynamic interaction.

Despite ACM advice to avoid certain wind conditions, thought conducive to initiating the "stall", and the Warning mentioned above, the accidents unfortunately kept occurring.

So MOD eventually contracted Aerospatiale to provide advice, and in due course funded a trial with an RN Gazelle, instrumented by them including flow tufts on the fenestron fin and rear fuselage and a camera on a horizontal stab endplate looking at the fenestron. The trials were flown by an Aerospatiale test crew and an A&AEE Boscombe Down 'D' Squadron test pilot (Fleet Air Air Arm, IIRC) went down to Marignane to observe the trials and fly in the aircraft.

The trials were conclusive, in that there was no aerodynamic stall of the fenestron. The trial condition replicated the majority of the UK accidents in that a spot turn to the left was initiated and the resulting yaw left to accelerate - which with a large initiating pedal input it rapidly could, especially with some relative wind strengths and directions (low-ish speed from the rear quarter, IIRC). The yaw became highly disorientating and it was evident that pilots could believe that control had been lost.

The trial showed that the yaw acceleration, and eventually the yaw itself, would be controlled by application of full right pedal deflection; although a significant and sustained over-torque typically resulted. Stopping the yaw took some time; it could rotate greater than 360 degrees following application of recovery pedal IIRC. The videos were very impressive and I think were released to the operational and training Gazelle units on VHS casettes. The edited versions showed the external video of the tufted fenestron with an inserted simultaneous view of the torquemeter. Obviously, there was also a supporting technical report (and A&AEE commentary), and before long the advice in the ACM was amended to reflect what was actually happening, and to provide handling advice and (I think) an amended low speed flight envelope to avoid getting into the problematic situation in the first place. The ACM deleted all reference to "fenestron stall"; I think the term "yaw divergence" was used instead, possibly later still changed to "undemanded yaw".

The above preceded later common UK use of the term "Loss of Tail Rotor Effectiveness" (LTE).

I think there was a little later a similar civil Gazelle accident in the UK. The resulting AAIB report referenced the A&AEE and Aerospatiale reports on the Marignane trials, and described the UK MOD history a little; this I suppose would have been around the early/mid 90s.

Following this change in ACM content and in operator training, the accident rate from this cause decreased (almost?) to zero.


Final anecdote: I remember the first meeting at Aerospatiale Marignane to discuss the issue. There was a large conference room with an enormous oval table. At the side of the conference room there was a long glass windowed enclosure in which the simultaneous technical translators sat, and we all wore translation headphones working via IR transmitters in the roof above the table centre.

The meeting was long and complex, going into some detail about the hazards that (at that stage) the UK felt could exist in the Gazelle design, with around 30-40 people in the room. It was conducted in French and English, and as it came to an end everyone was inevitably tired but still focussed on the serious subject.

The French chairman drew the meeting to a close and said, in French, something like: "Thank you to our English friends for making the trip over to La France; I wish you all a safe flight home."

The French could not understand why all the English speakers in the room suddenly fell about in hysterical laughter.

That was because the female translator had rendered the sentence as: "Thank you to our English friends for making the trip over to La France; I wish you all a safe flight home. But not in a Gazelle helicopter, huh?" :lol: :lol: :lol:

It's a fabulous type, and what a view. I flew quite a bit on trials after the events above, and loved every minute of it - but especially the ones where I managed to get a bit of stick time and ad hoc instruction. I particularly remember one trip with an AAC tp over Salisbury Plain, at high speed following the contours at below tank turret height. Just magic. :D

(Apologies for hijacking your thread, @carlmeek - it's just that it sent me down an enjoyable part of Memory Lane!)
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By carlmeek
#1654741
That’s very interesting Dave!

Before I did my type rating, I had read similar and had a preconceived concern. My instructor essentially debunked it, but was very keen on always spot turning slowly (but not crazy slow!) to ensure a runaway to the left didn’t occur. I believe incidents are likely heavy booted pilots getting too much yaw on.

In further talks with a 1000 hour gazelle pilot, he recommended turning to the right when in marginal very windy tailwind conditions. You can never run into trouble initiating a turn to the right, as if you do it just stops turning right, as right pedal increases thrust. Left pedal reduces thrust so then needs to be “caught” if you end up rotating too quickly.

I shall add Lee and Staverton onto my list of places to visit in the near future! One of my first missions will be flying the London Heli lanes and crossing Heathrow.

Weather is bloody miserable down here, not much chance of flying at the moment.
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By carlmeek
#1655420
Yes and Yes! Obviously back in 1977 they hadn't invented stealth....

Today visited Goodwood and Shoreham.

Mine's bigger than yours!!
Image

Image

Video of approach and landing into Goodwood 32. A bit long and boring...
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