Guimbal Cabri down at Kemble

[gellis]

Reports of a small chopper on its side at Kemble this morning?

[Thomas coupling]

Probably napping. catching some Zzzzz's before the day starts:O

[HeliCraig]

Although no details on it, HeliHub is reporting that a Guimbal Cabri was involved in something at Kemble yesterday.

26-Oct-11 G-UIMB Guimbal Cabri G2 Kemble, UK | Helihub - the Helicopter Industry Data Source (http://www.helihub.com/2011/10/26/26-oct-11-g-uimb-guimbal-cabri-g2-kemble-uk/)

[helihub]

thanks HeliCraig. I will add more details when available. I understand Bruno Guimbal will be on site today

[gellis]

I understand that it is not on its side but rather looks like a problem with a skid - it is reported as covered so not easy to see what the problem is

[FLY 7]

I hope it's nothing serious.

I'd like to see the Cabri doing well and developing bigger variants.

[Thomas coupling]

Puncture.....?

[ShyTorque]

Very tricky to deal with, those skid punctures. :D

[bvgs]

I believe there is an STC for run flat skids:O

[206 jock]

Piccy and a bit more detail here (http://www.wiltsglosstandard.co.uk/news/cotswolds/9330517.Investigation_after_helicopter_crashes_at_Cotswold_A irport/?ref=rss&ref=erec)

Eye witness report alleges that at around 30', it 'started to spin, the engine quit, and it dropped in' (not my words).

With the recent Dutch accident, there must be a little concern at the Cabri factory.

[jonwilson]

Never buy the A model of any helicopter I was told many years ago. I believe in it.
Hopefully nothing wrong with the Cabri but with the recent 66 accidents there could be some sense in this.

[Helinut]

Unless you like taking risks buy version 2.1 - same as software :ok:

The only manufacturers who manage to do their own development testing make road vehicles.

[MartinCh]

30' and 'spinning'? That suggests low airspeed. Max perf take off?

Whatever happened to design or engine, looks pretty crashworthy, as per the original reports on G2 thread. I hope all the bugs get ironed out and Cabri does well.

[Puma51]

With the few helicopters out in the field and the many accidents the G2 already seems to get a bad reputation. Overconfidence into the new design advertised to be so much better than the Robinsons? 5000ft hover at ISA? Increase power available please!

[ChippyChop]

Crikey I'm not surprised that poor little thing fell over with that 747 bearing down on it

[helihub]

Let's put the speculation aside once and for all. Helicopteres Guimbal has issued the statement below. Their openness and clarity on the incident is evident and many have congratulated Bruno for his enlightened approach, suggesting other manufacturers may like to follow his example.

Here goes.....

We at Helicopteres Guimbal are saddened to announce that two days after receiving its Certificate of Airworthiness from the CAA, the first Cabri in the UK had an incident that will delay its presentation in the country by a few weeks.

Cotswold Helicopter Centre are the exclusive Guimbal distributor in the UK and their first machine – appropriately registered G-UIMB – was delivered a month ago during Helitech, where it attracted a great deal of positive interest.

The helicopter was flying a demo flight with the recently-qualified instructor, when it made a hard landing.Both pilot and passenger suffered no injury.

The damage to the helicopter is limited to the tail and landing gear structure. The rotor blades and the transmission suffered no damage from the hard landing at a high rate of yaw. This is a tribute to the very high control power offered by the high-inertia, semi-articulated rotor, and to the strong structure. The incident is attributed to the pilot having limited experience of Fenestron tail rotor dynamics and European rotation helicopters resulting in loss of control in yaw whilst hovering.

The incident is worth some analysis to make sure that it will not happen again.

In the early nineties, Eurocopter and the British Royal Navy conducted a thorough flight test campaign on a British Gazelle to address a row of similar incidents or accidents involving yaw control. The Fenestron concept was under scrutiny.

These tests eventually proved that the Fenestron was totally free of so-called LTE (loss of tail rotor efficiency), and had always a very high manoeuvrability.

They also proved that the specific characteristics of all shrouded tail rotors require higher pedal inputs in the hover than conventional tail rotors, though its controllability is about 50 % higher.
Eurocopter released several Service Letters, the last dated 2005, to address this matter. The Fenestron is now a reference worldwide in terms of controllability and safety, reducing the accident rate dramatically compared to other concepts.

In the same manner, Helicopteres Guimbal will release a Service Letter to help new Cabri pilots, and particularly those with only counter-clockwise rotating rotors experience, get the best of the machine. We are also modifying our flight training programme in conjunction with Cotswold Helicopter Centre.

The Cabri has been tested to yaw rates in excess of 180°/sec and winds in excess of 50 kts in every direction with great success.

With more than 5000 flight hours in training in the recent years, the Cabri has been proven to provide increased safety, due to its high inertia rotors, innovative seats and fuel system crashworthiness.

The first British Cabri will soon be flying again and we trust Cotswold Helicopter Centre and its instructors to bring it a bright future in the UK.

[9Aplus]

:* Lot of small crash-y incidents - and surprise, pilots are walking away...
No fire, no serious injuries, only damage of airframes....

For me that is more than good reputation, after some obvious mishandling :cool:

My vote goes for Bruno and his positive attitude of resolving / improving of
training and handling procedures. Sure will be space for minor technical
updates, but so far I am more than ready to put my a** in that cage :ok:

[FLY 7]

Interesting explanation. Would that also explain some of the EC120 incidents?

[John R81]

I think what catches people out is related to the sail area of the tail and not the power of the fan v a conventional blade design. Get the wind on the wrong side of the tail and you have an additional turning force significantly greater than would be experienced in a conventional tail design. The onset of rotation is rapid / instant, and the rate of yaw high. It is very easy to freeze or become disorientated and react incorrectly. However, get your right foot in - all the way - and keep the ship level and you will recover. Freeze and you are going to star in a train wreck.

Keep thinking of the wind and it won't happen

Note - my experience is 120

[birrddog]

John, would that be from a gust or when turning tail into wind, or both?

If it was a sail would the aircraft not weather cock into wind? Or the pilot reacting with delayed control inputs keeps the rotation going?

[Matari]

I appreciate Guimbal's explanation, but once you get beyond the sales pitch, he said in so many words "pilot error." We've seen the same from other light, two-seat helicopter manufacturers.

I would like to have seen him add more details of the event: Wind was at "X" knots from "Y" radial, pilot was transitioning / taxying / pedal turning in hover, etc.

He says the pilot lost yaw control while hovering, then had a hard landing. Did the pilot dump collective when things went pear shaped? More details might have helped new pilots better understand the ship's flight characteristics.

I wonder if the authorities have come to the same conclusion as the manufacturer?

But good on him for recognizing some deficiencies in the training program and implementing changes. Seems a sturdy little ship, good to see competition in the marketplace.

[John R81]

Birddog

I am not a CPL and compared to many guys here my hours are low. Here is my view, but I welcome any more experienced PPrune member to correct / improve.

The rapid accellaration of yaw effect can be generated in gusty conditions or it can simply be a result of turning through the wind thoughtlessly. It actually happens to some degree on every turn to the left, even in mild wind, but mild wind = smaller additional torque force hence small accelaration. Control is simple, though the distance that you need to move your right foot can catch out somone unused to the machine. Practicing left turns in (first) little wind and (then) slightly increased winds (and stopping before the wind strength means that you do something daft) will show you the effect, and how the yaw rate effect increases with increasing windspeed.

Turning left through a high wind brings significant additional torque load onto the tail due to the sail area. Accelaration in yaw can be high; literally "stunningly so" for some people in some conditions. If your mind is not ahead of the aircraft (if it was, why were you turning left through the wind in an EC120 / Gazell / Guimbal / etc?) it may startle you and your reaction may be slow; perhaps some people even freeze. The accellaration in yaw is rapid. It can reach a sufficient rate of yaw (before your control inputs begin to have any effect) to buld the momentum to take the machine through a full rotation - weather-cocking and your right boot will bring it to a halt but it may not be until the 2nd or 3rd full rotation if your reaction to the initial yaw is not quick enough. During that time your job is to keep it level and away form the ground / other expensive objects. Not as easy as it sounds with a rotation rate that might have reached 30+ RPM.

Training mantra "To the right, avoids a fright" is best followed. Don't use a left turn unless you have considered the wind direction and strength, remaining power available, and when to begin the anticipatory right boot movement (it is best to be increasing the right boot before you put the tail through the wind).

The aircraft is perfectly manageable; it just requires that you understand its characterisics and limitations and fly accordingly. Personally, you may never get me out of this model; except into a Guimbal once I cannot afford the EC120.

[victor papa]

John R81, brilliant post! In short dont critisise what you dont yet understand. Understand the fenestron and she is your best friend no matter the type-fly it like a tail rotor good luck!

[Puma51]

Hi helihub and John,

I tried, let the G2 turn non power pedal 270 deg letting go of the pedal then put in full opposite pedal. The turn stopped, but only after a scary 120 deg! The fenestron did not stall, which is very good, but it took far too long to stop the turn. Imagine the same situation at 5000ft... Right, Bruno says a lot, but certainly not all.

[s1lverback]

Echo...Good Post John..when I turn left in the 120 it is more ease of pressure on right pedal rather than any positive input on left pedal...and slow :}

If she goes around, stay level and get away from the ground :ok:

[jonwilson]

'Training mantra "To the right, avoids a fright" is best followed.'

This depends on whether the blades turn clockwise or anti clockwise doesn't it?

Left pedal turns in a anti clockwise rotating helicopter require more power than right turns but in an aircraft with blades turning the other way the opposite is true is it not?

Do they turn clockwise or anti clockwise in the Cabri?

[Shawn Coyle]

Does this machine have a governor?

[griffothefog]

JW,

Its French... What do you think this thread has been about exactly.:{

[Frog Fan]

It does have a governor, and a very complete basic equipment list:

BASIC EQUIPMENT
Electronic CDI ignition
Smart engine governor
Two-axis electric trim with pilot & copilot control
High-energy crash-certificated stroking seats
Disc rotor brake
Four-points harnesses with inertia reel
Cabin heater
Keyless entry and starting lock
Fast – removal copilot controls
Handling wheels
Removable customized cabin flight bag
Multi-function vehicle & engine display :

Smart power indicator
High precision capacitive fuel gage
Fuel flow with displays :

- Flight time remaining
- Instant fuel flow
- Average fuel flow



Self-closing electrical magnetic

plugs – MGB & TGB


Automatic carburetor heater
Carbon monoxide detector
Flight time counter
Flight log
Stopwatch
Complete engine monitor


A very interesting aircraft, I can't wait to try one myself :ok:

[s1lverback]

Hi JW, Cabri & EC120 main rotors turn clockwise so right torque pedal..

You are right re: anti-clockwise, though on types I have flown (H500, CBi300, E480), I have not experienced such a pronounced effect on right turns in wind. Positive left pedal action in the 120 (even in light wind) can catch you out.

From the EC & Helicoptersafety websites:
Clockwise: http://www.eurocopter.com/site/docs_wsw/RUB_36/1673-67-04en.pdf
Anti-clockwise: http://www.helicoptersafety.org/pdfs/1692-67-04en.pdf

[John R81]

JW - my apologies. On EC120, Gazelle, etc. Clockwise blade, as you say.

[Shawn Coyle]

Unless the governor incorporates a yaw rate sensor, anytime you have a rapid yaw rate, you'll have an effect on rotor RPM that will not be what you'd expect. In fact, it will be the opposite of what would happen without a governor.
In the Cabri, if you're yawing with the direction of rotation of the main rotor, you'll climb (if you don't touch the collective). If you're yawing counter to the direction of rotation, you'll descend, and it may be difficult to stop the descent.
Think about the governor as counting rotor blades passing over the tail boom. It wants to keep that constant, and so if you're yawing with the rotor, the governor will think the rotor has slowed down. It adds fuel to get the rotor back to the 'correct' rate of rotation, but this is actually faster with respect to the earth than it appears from within the frame of reference of the helicopter. Hence the climb.
Opposite if you're yawing counter to the direction of rotation.
Could be part of the explanation for the incident.

[lotusexige]

Shawn, does the governor actually measure rpm relative to the fuselage or does it work on absolute rpm?

You don't by any chance ahve any relations/ancestors from Donegal in Ireland? Coyle is a pretty common name there.