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Guimbal Cabri G2

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Guimbal Cabri G2

Old 29th Jul 2015, 13:45
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Fenestron

Matthew,

the pilot has a temporary lapse forgetting that it has a fenestron, not a tail rotor
How would you say differs a fenestron from a conventional tail rotor in terms of handling?
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Old 29th Jul 2015, 19:29
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Hot and Hi,

See http://www.airbushelicopters.com/web...73-67-04en.pdf (section 3)

There's also a similar service letter from Guimbal on the topic "12-001 Yaw control in approach" but I can't find an online copy.

Matthew
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Old 30th Jul 2015, 05:55
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Thank you Matthew, very clear. Sounds manageable. No two helicopter types have the same TR response anyway (e.g., transition from EH28 to RH22 or RH44).

A good exercise to program the "TR pedal travel vs effectiveness curve" for a given a/c type into your muscle memory is to circle around a centre point, with the nose pointing to that centre point at all times. Start CCW direction (in case of CCW spinning MR), then increase speed, then with stronger wind. Then the same the other way round, which obviously requires even more, and quicker pedal movements.

One of the problem with PPL training is IMHO that people are not brought into challenging situations and they therefore do not know how their helicopter behaves at the limits.
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Old 30th Jul 2015, 07:36
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There are 2 things that may catch-out pilots on first moving to Fenestron tails. Nothing to be frightened of, just understand the physics of the machine you are flying and act appropriately.


One is that the thrust increase / peddle position is not linier, as shown in the Eurocopter service letter (link above), and the amount of pedal input needed is therefore much more than the un-initiated might expect.


The second is that the Fenestron tail is aerodynamically shaped - it is a wing - which provide anti-torque in forward flight. The total anti-torque provided to the pilot is therefore the sum of the tail and the fan. On approach, as speed bleeds, the thrust provided by the tail will reduce and without action by the pilot to replace this with additional fan input the heli will begin to crab through inadequate anti-torque (to the left for EC120, G2). If you let this start then peddle input to correct the crab occurs as speed continues to bleed on approach, further reducing the effect of the tail, and it is easy for the novice Fenestron driver to underestimate the amount of peddle needed to deal with BOTH of these events. As a result the crab worsens despite (inadequate) peddle input. Then something horrible and very sudden can happen: because the Fenestron is a "wing", the crab is changing the angle of attack. When this reaches 20 degrees the "wing" stalls and in an instant the driver loses all of the anti-torque provided by the wing, being left only with the effect from the fan. The machine was crabbing anyway (insufficient peddle input) and suddenly it will snap into a (fairly violent) torque spin.


Torque-spin like this can be controlled - bury your power foot (right for EC120, G2) to the peddle stop and keep it there. It will likely take a couple of revolutions to control the spin; but it will IF YOU KEEP YOUR FOOT TO THE STOP.


All helicopters have operating parameters, so fly within them. Do not let Fenestron machines yaw to torque as you bleed speed on approach, use the appropriate amount of power peddle early.


In several years operating EC120s I have not ever had a machine snap into torque spin on approach, though I did abandon 1 approach in my early days on type because in the particular conditions I was not quick enough to control the yaw on approach; rather than take a chance by continuing with a boot-full of right foot I simply added speed and went around. Not my finest moment - and didn't make that mistake on the subsequent approach.


Take a G2 flight with an instructor and he can demonstrate all this to you.
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Old 3rd Aug 2015, 23:07
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G2: child's play

Christchurch teen proves he can pilot French helicopter by flying to school | Stuff.co.nz
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Old 17th Aug 2015, 01:35
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edit:
apparently one doesn't need an STC when Lycoming themselves give a go:
"With the Lycoming engine model approvals, the EASA SIB immediately allows ASTM D 7547
Grade UL 91 use on European Union based aircraft such as the
Cessna 152....Diamond DA40 and DA42-L360; Helicoptères Guimbal’s Cabri G2;..."
EASA approves 31 more Lycoming engines for UL91 fuel | Helihub - the Helicopter Industry Data Source
I know it is a bit late but I hate leaving this uncommented: we should always have in mind that even if the engine is approved for Mogas-use, it does not mean that the airframe is. Fuel lines, tanks, liners and so on might not be approved and deteriorate significantly faster or even dissolute parts which might end up spoiling the fuel. In the best of the cases you might notice higher engine wear. In the worst case you might get an in-flight engine failure.

More about it here: https://www.diamondaviators.net/foru...180-t3481.html
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Old 17th Aug 2015, 14:00
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rokami,

There are two different issues in your post;

Firstly UL91 is not Mogas and is approved without any additional procedures or restrictions as an alternative fuel to 100LL in the Cabri G2 . This is confirmed in Guimbal Service Letter SL 13-001 A, see quote below.
- Unleaded AVGAS UL91, designed to replace AVGAS 100 LL in Europe, can
be used with complete interchangeability.


The same service letter also approves the use of Mogas in the Cabri subject to certain conditions, see extract below

- Unleaded automotive gasoline is approved as an alternate fuel, under
conditions of supply that are commented hereafter, and by respecting additional limitations that have low impact on practical use


I regularly use UL91 in my Cabri.
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Old 18th Aug 2015, 22:36
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rokami,

There are two different issues in your post;

Firstly UL91 is not Mogas and is approved without any additional procedures or restrictions as an alternative fuel to 100LL in the Cabri G2 . This is confirmed in Guimbal Service Letter SL 13-001 A, see quote below.
- Unleaded AVGAS UL91, designed to replace AVGAS 100 LL in Europe, can
be used with complete interchangeability.

The same service letter also approves the use of Mogas in the Cabri subject to certain conditions, see extract below

- Unleaded automotive gasoline is approved as an alternate fuel, under
conditions of supply that are commented hereafter, and by respecting additional limitations that have low impact on practical use

I regularly use UL91 in my Cabri.
I did not say UL91 was Mogas. I was simply referring to the post I quoted.

I just wanted to call attention to the common misunderstanding that the engine-STC would allow the use of alternate fuels also on the airframes. I know that Guimbal has taken care of that and I have not put that in doubt at any time. Every aircraft manufacturer, and especially Guimbal, has to be applauded for taking the step to certify their airframe for cheaper fuels.
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Old 14th Sep 2015, 20:08
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As nothing was posted so far... G2 down in Poland a week ago during a training flight, from low altitude. Most important, no casualties (instructor + pilot on board).
Nothing official published so far regarding the casue.
Helicopter from the Academic Centre for Aviation Training/Polish Air Force Academy.
Low quality pictures (article only in Polish)
Pod Sochaczewem rozbi? si? ?mig?owiec. Nikt nie ucierpia? - Rmf24.pl

Arrakis
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Old 14th Sep 2015, 21:31
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Plus one in Christchurch New Zealand.



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Old 14th Sep 2015, 22:21
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"The pilot was checked by ambulance staff but walked away without injuries."

https://www.tvnz.co.nz/one-news/new-...ch-q10366.html
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Old 15th Sep 2015, 06:51
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Is it my imagination or are there rather a large amount of accidents for the number produced, I was told 4 weeks ago that 11 out of about 100 had gone down, with these 2 that would make an attrition rate of 13% I know that it is a small sample but.
Comments please and I am not bashing the machine just curious
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Old 15th Sep 2015, 07:59
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.

Hello H500,

Your figures are nearly correct, They are now more than 110 G2 builded.

When you say "an attrition rate of 13%", you mean than 13% of the G2 are not flying anymore ?

If I'm not wrong, all the G2 builded are still flying.

About the reasons of the accidents, I can't answer because I don't know the circonstances exept for the one in France (July 2013), the pilot (and owner) and a friend are flying and :
"In cruise flight, they heard some noise that they found was caused by the baggage door, left open, flapping in the airstream. The pilot decided to land immediately in a field in front of him. In short finals with no anticipation, he was disoriented by the bright sunlight and an obstacle, and made a very hard landing with no yawing motion and moderate forward speed.The helicopter bounced significantly and hit the ground again on the left side. "

The helicopter sustained significant damage. After been repaired, it's still flying in 2015.

.

Last edited by HeliHenri; 15th Sep 2015 at 08:18.
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Old 15th Sep 2015, 08:06
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The NZ crash sounds like either TR failure or a lack of experience with fan TR's.
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Old 15th Sep 2015, 09:54
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HH
I meant that 13 % of those made have had serious accidents ! That would appear to be a high attrition rate, most seem to have been fenestron issues which having been a 341 pilot is a lack of training ! Mind you I don't know what the fenestron is like on a Cabri, I know in a 341 it gets interesting but doable to do spot turns in a 30 kt wind. Anyone like to comment who have flown both types ?
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Old 15th Sep 2015, 12:10
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I currently fly the R22 but I've been considering getting a G2 rating for a while now. We all know the drawbacks of the R22 so I won't list them off all over again, but it does appear that the G2 has more than its fair share of accidents - fortunately no fatalities thus far... To my inexperienced eye, each of these accidents 'seem' to be associated with mishandling of the tail whilst close to landing, with subsequent loss of control due to further mishandling of the situation.

It is easy to just say the R22 is under engineered, but I'd argue that the majority of its accidents have been a result of pilot handling errors (it's just that it is far less forgiving than most other helicopters). My question is, how easy is it to control the tail of a G2? Are these handling errors occurring because it is trickier than other helicopters and so inexperienced pilots are failing to keep up with it?

Without this tail issue, I'd switch to the G2 almost in a heart-beat. But the frequency of these accidents (whilst non-fatal), does give me reservations.
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Old 15th Sep 2015, 12:17
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The tail is very easy to control.


Lead with your foot, keep the yaw from developing and the tail is easily controllable. Let the yaw get out of hand, and then with 20 degree angle of attack on the tail you will be "surprised" by the snap into torque spin. See my post #826 above if you want more detail.
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Old 15th Sep 2015, 12:30
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Not sure I would be put of from doing a TR on the G2, percentage wise the R22 has probably had its fair share of 'accidents'...

I was asked recently if I wanted to do a TR on a G2, struggling to see the point really, I could just TR on something larger and more usable
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Old 15th Sep 2015, 12:57
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@GS-Alpha

There is no "tail issue" on a Cabri G2. The aircraft has an Fenestron, that is the difference!

Also - in all the reported accidents there has NOT been a fatality so far! And I know of only two incidents where a technical issue MIGHT have been the problem. It seems in all other cases the problem was between the headset.

Fly save
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Old 15th Sep 2015, 14:00
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Yes from what I can see, most if not all of these accidents have been a result of pilot handling errors. I do not dispute that. I am trying to ascertain the general opinion as to why these handling errors are occurring. It seems to be consistently the same thing, so you would have thought the problem would be targeted during training, and people would be particularly well practiced and wary of the characteristics of the fennestron tail as a result. Yet the accidents still seem to be occurring. I am pretty inexperienced on rotary wing, having pretty much exclusively flown the R22. I suspect this is the case with each of the pilots in question. Does that therefore leave me susceptible to such an accident? This I suppose, is my real question. When working hard, people often revert to their initial or more familiar type...
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