Gazelle: Flying, operating, buying
Senis Semper Fidelis
Join Date: Feb 2001
Location: Lancashire U K
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Loose nut,. .. .I am green and rigid with envy, what a superb piece of kit you will be flying, so light and responsive , but as others are trying to tell you, be very careful , a very good friend of mine who has one of these beasts , has a copilot who very nearly went to Valhala a few weeks ago with the left spot turn,(about 12knts from right rear) I think only the person beyond the clouds saved the situation, so when you lift and are free of all ties to mother earth follow procedures, the Gazelles deserves its name, forget the MG THIS IS "The GAZELLE" in every way!. .Have fun and fly safe, . .. .My Regards
Join Date: Apr 1999
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Crab - sorry ..... I didn't appreciate that such pedal applications would cause overtorques in all helicopters! I really only thought the Gazelle could overtorque! . .. .Sarcasm over .... I agree the SAS issue and it probably (aint saying as a definite) played a significant role in the spin factor. I used to fly SAS out for this reason in displays, especially when doing 90 deg nose up pedal turns to the LEFT, Or when carrying out fully inverted spot turns to the left at the top of a loop. . .. .I agree the SASless machines gave the pilot a greater appreciation of YAW control and a such will probably have resulted in fewer prangs in the Army beast. However, I know the RAF had a few of these go off up at Shawbury or in that neck of the woods. This YAW problem is a general Gazelle issue and one I hope I never have to experience in real anger. . .. .eden - at peace with my pedal
Join Date: Nov 1999
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The civil crashes would need looking at again as certainly in one of them the pilot involved took off with the Hydraulics off!!!! and ran out of idea's at the same time as running out of puff with the tail rotor control. The aircraft being at a low AUM and 8 degrees of pitch being close to being light on the skids(Gaz drivers will understand.). .. .You also might find that the incidents that involved the service aircraft could well be down to that fact that Army aircraft tend to operate at higher AUM so they require a greater input of pedal to counter the Tq required to get airbourne.ie, the pitch angle is greater and the airflow also greater through the hole in the back? just a thought!
There have been a few curious Gazelle accidents over the years. One of the first was an Army Gazelle that crashed killing three at Wallop in the early seventies. The pilot who survived said the cyclic froze and he was unable to recover from a manoevre. I believe it was put down to jack stall and later on the Army installed a hydraulic accumulator to help counteract the problem.. .. .About 1977 while a Gaz was under maintenance we discovered that a mis-manufacture of the discs at the base of the cyclic allowed the stick to jam solid and no amount of force would allow aft stick movement. A problem similar to that in the crash. The aircraft serial number was XW851 which was within 2 of the lost aircraft. Sadly the accident aircraft had long gone to the tip and it was not possible to say that this was the cause of the original accident. . .. .As no AD was ever issued it is possible that some of the very early civil Gaz's still have this as a dormant problem. About 5 years ago I wrote this up for the CAA, the silence is deafening!!!!!!!
Crab: I think you'll find the opposite is true. Those gazelles without SAS suffer this phenomenon more so:. .. .AAIB 2002/1 the gazelle crash report states:. .. ."EUROCOPTER remind you that in some configurations (hover flight, flight at low speed in light wind etc), starting a turn to the left can induce a high-rate turn if the pilot does not apply quickly the suitable position to the yaw pedal. If the pilot attempts to counter this high-rate turn by applying the amount of right yaw pedal that corresponds only to hover flight control, this is not sufficient to start actual deceleration, thus allowing the pilot to regain his bearings. . .. .In this situation, right yaw pedal, and if necessary, full right yaw pedal, must be applied quickly, and held, to stop the turn to the left. Any delay in complying with this procedure will increase the time necessary to slow the helicopter. This effect is NORMAL and must not give rise to doubts as to the performance of the tail rotor. In all cases, the helicopter will stop turning. . .. .A reminder is also given that all turns to the left, in hover flight conditions or at slow speed, must be made applying moderate left rudder.' . .. .Additionally, the Ministry of Defence Gazelle (All Marks) Aircrew Manual, Advance Information Leaflet 1/93, contained the following information relating to loss of yaw control in the hover:. .. .'In light wind conditions, an extremely rapid build up of yaw rate can follow a relatively small left pedal application during low speed flight or in the hover, particularly with the ASE disengaged. In this event, immediate and positive application of right pedal, up to the maximum, should be applied and maintained to arrest the rate of yaw. Recovery action may be ineffective if the pedals are returned only to the hover position, and the yaw rate may initially continue to increase before deceleration and an eventual steady hover is established. Furthermore, if the pedals are not returned as far as the original hover position, a steady hover will never be achieved and the aircraft will stabilise at a particular rate of yaw which may be very high. Pilots may misinterpret this as a loss of yaw control. Be warned that any delay in applying corrective action will require progressively larger right pedal inputs to achieve a steady state hover and may lead the pilot to believe that he has lost control. Yaw rates of up to 165° per second to the left can rapidly be arrested by applying full right pedal without any discernable loss of fenestron performance. In the hover and at low forward speeds, ensure that pedal turns to the left are always made slowly and smoothly.' ". .. .Personally I put it down to the Army's size 15 boot <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" /> <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" /> <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />
Join Date: May 2001
Location: Escrick York england
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just a point about limitations on permit to fly 341 . .if you cant fly over built up areas how can you fly in southern england or come to think of it land at a airport .what is the caa defination of built up areas ?
Join Date: Jan 2002
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MD 600 driver,. .. . When I was training in R22's I was taught to always fly around a built up area so that landing clear would be possible, which I believe is safe flying and if it means flying longer that suits me, I believe my interpretation of this part of the permit should allow me to stay legal. I am very low time still so am I being over cautious and missing the piont of flying heli's ?? (advice needed & much appreciated).
Join Date: Mar 2000
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It depends upon the words of the restrictions in the Permit.. .. .There were lots of rumours going round not so long ago about daft restrictions which the CAA were intending to place on ex-mil Gazelles.. .No flying over built up areas. .No passengers except essential groundcrew. .Maximum of 4 pob. .etc. .Could you post the actual restrictions which the CAA put on the Permit to Fly?. . . . <small>[ 06 March 2002, 14:18: Message edited by: Heliport ]</small>
Join Date: Nov 2000
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Loose Nut,. .. .Congrats! Anyone who has the $$$ to own their own has me crying <img border="0" title="" alt="[Frown]" src="frown.gif" /> . .. .You enjoy yourself, and stay safe. Being cautious never hurt anyone. <img border="0" title="" alt="[Smile]" src="smile.gif" />
TC, the warning about yaw rates with SAS off only highlights what I am saying - RAF and Navy Gazelles were flown for 90% of the time with SAS in so the pilots generally lacked the sensitivity to yaw control that non SAS pilots developed. Most NAvy and RAF Gaz drivers were ex Sea King or Wessex - the Sea King pilots were awful to convert to Gazelle on the QHI course as they tried to lead with pedal all the time and overcontrolled on the very light pedals (neck brace advisable).. .Eden - who cleared the Navy Gazelles for pedal turns to the left, loops and inverted pedal turns? it certainly wasn't the manufacturer or Westlands and it definitely wasn't Boscombe Down. Did someone in the FAA have massive balls and sign a Service Deviation or were people making it up as they went along? The Sharks always did a good display but I dont remember seeing any of the manoeuvres you describe.
Join Date: Dec 2001
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One of the things missing from the discussion on the loss of fenestron effectiveness / yaw divergence / whatever, is the effect that high yaw rates have on the governor, which in turn will affect the lift on the main rotor.. .When yawing to the left in the Gazelle, the governor will sense this as a higher-than-normal N2 speed, and will attempt to reduce fuel flow to get the N2 speed back to normal. At high rates of yaw, this will significantly affect the main rotor speed, (i.e. reducing it). . .If you don't believe this, try a pedal turn to the left in the hover without touching the collective- you will descend - best to try this starting with the wind on the left hand side so you end up into wind.. .Turning to the right in the hover, and you will climb. Works in every helicopter I've ever flown that has a governor - the only difference is due to the direction of rotation of the main rotor.. .So, in a high yaw rate to the left, not only will you be disorientated by the rate of turn, but you will proabably be descending without knowing it as well.... .Best regards to all, and the Gazelle is one of my favorite (or is it favourite) machines. Wish I had one...
Shawn,. .. .Whilst I hear what you're saying, I have believed that the effects that you relate are caused by the unloading/loading of torque requirements to the tail rotor, not the Nr variation. ISTM that if you turning in the direction of the main rotor, less torque is required at the (anti torque) tail rotor, therefore with a fixed collective setting, more power transfers to the Main Rotor, thus more lift. And vice versa for turning against the main rotor.. .. .I would expect any variation in power demands due to Nr fluctuation to be quite minor in comparison.
Shaun, one of the oddities of the Gazelle is that it has a reset governor and does not experience static droop as a result of applying power. The Nr is tightly controlled at 380 +/- 2 so any descent or climb is due to variations in Tq not NR.
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Loose nut, nice thread -- dont listen to all the hoo ha about fen stall ( it just dont exist) I have been flying the A/C for a number of years and if you want someone who can read a map and is happy in either seat I AM YOUR MAN - you lucky lucky lucky Bstard. <img border="0" title="" alt="[Cool]" src="cool.gif" />. . . . <small>[ 07 March 2002, 20:09: Message edited by: I.P Stop ]</small>
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For those who don't believe the governor has an effect on height control in the hover- just try even slow to moderate rate turns in both directions without touching the collective. Turning in the opposite direction of rotation of the main rotor will cause the following to happen: The rotor RPM will initially increase as the pedal is applied (it needs a bit of a push on the pedal to get this effect- don't be too abrupt, but don't be too gentle either). The tail rotor is initially being unloaded, and this will cause the rotor RPM to rise. The governor will attempt to get the rotor RPM back to normal and the 'tighter' the governor, the more pronounced the effect - the Gazelle has a pretty tight governor. For free turbine helos, you'll see the N1 and TOT decrease, for the Gazelle, you'll see the TOT go down slightly. Once the rate of turn is developed, the helo will start to descend. Opposite will happen if you turn in the same direction of rotation as the main rotor. Never seen it not work.. .Tried it in a Bell 407 with the governor in manual mode (fixed fuel flow), and there was no height change. With the governor in automatic mode, there was a pronounced change in engine and height.. .Buy me a beer if it works...
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Loose Nut
As a PPL, I'm slightly hesitant about offering any advice in the company of contributors who are obviously genuine experts on the Gazelle - I came to the Gazelle along a similar route to you (via R22 and B206).
My advice, for what it's worth, is to get your basic conversion finished, and then arrange a few hours more advanced instruction with an ex-mil instructor who still instructs on the Gazelle.
I don't know if Eden or Crab are still instructors or where they are based but, in the South East, I can strongly recommend Al Gwilt who's an ex AAC instructor/display pilot and still instructs on the Gazelle. I found it an enormous help.
Al Gwilt can be contacted through the MW Helicopters @ Stapleford or direct at [email protected].
Wishing you lots of enjoyment flying your Gazelle is almost superfluous - you can't not enjoy flying a Gazelle!
[ 08 March 2002, 01:07: Message edited by: Flying Lawyer ]
As a PPL, I'm slightly hesitant about offering any advice in the company of contributors who are obviously genuine experts on the Gazelle - I came to the Gazelle along a similar route to you (via R22 and B206).
My advice, for what it's worth, is to get your basic conversion finished, and then arrange a few hours more advanced instruction with an ex-mil instructor who still instructs on the Gazelle.
I don't know if Eden or Crab are still instructors or where they are based but, in the South East, I can strongly recommend Al Gwilt who's an ex AAC instructor/display pilot and still instructs on the Gazelle. I found it an enormous help.
Al Gwilt can be contacted through the MW Helicopters @ Stapleford or direct at [email protected].
Wishing you lots of enjoyment flying your Gazelle is almost superfluous - you can't not enjoy flying a Gazelle!
[ 08 March 2002, 01:07: Message edited by: Flying Lawyer ]
Crab, I was certainly in a non SAS a/c when I spun on my pilot's course. As was the basic stude who pirouetted out of dispersal at MW back in the early 90s. . .. .I thought perhaps you'd been posted as you've been quiet for a while. Mind you, once you crabs get your feet under the table at MW, it takes a very sharp pointy stick to winkle you out. I gather that Dave Griffiths is back.. . <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />
Mighty Gem, I'm not saying you can't embarrass yourself in a non SAS Gazelle, Loss of Tail Rotor Effectiveness or Yaw divergence is a very real problem in many helicopters. The term Fenestron Stall was supposed to cater for the case where in crosswinds from the right of more than 10 Kts, the laminar flow around the duct of the Fenestron (which allegedly produced a large percentage of the anti-torque thrust)broke down and caused the initial left yaw which started the whole pirouette thing. Many of us were never convinced by this but it was the official RAF and Navy view at the time and at Shawbury we spent a couple of years taxying sideways (crabs after all) into and out of dispersal at 10' which was far more dangerous than the percieved risk of Fenestron Stall.. .Shawn - you are correct of course that the climb descent will happen in any helo, I was only taking issue with your original post stating that it was due to Nr variations. PS thought your book was very good - got any free copies for an old QHI?