Gazelle down at Rand

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skytrooper
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Re: Gazelle down at Rand

Unread post by skytrooper » Mon Feb 04, 2019 3:53 pm

It would be nice if the pilot could post here to give some insight.
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Re: Gazelle down at Rand

Unread post by Alouette » Mon Feb 04, 2019 4:44 pm

The gazelle HT Mk 2 was the standard for the British Royal Naval and in term of its airframe and engine didn't differ from the other military gazelles. There are about 13 different models, not that CAA would be aware of that. The cross wind specifics are very clear, namely, up to 30 kts at SL, decreasing by 5 kts per 3000ft, but not less than 18 kts. Service ceiling 20,000 ft, not that one would push the crosswind at any high height. It is worthwhile for any gazelle pilot to read Eurocopter service letter no 1673-67-04 on fenestron performance. If that aircraft was a G model then you can expect performance problems because they are not suited to high and high. They don't have the upgraded fenestron and are limited to 1800 kg.
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Re: Gazelle down at Rand

Unread post by cage » Mon Feb 04, 2019 4:57 pm

Great insight Alo, ta
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Re: Gazelle down at Rand

Unread post by Jason » Mon Feb 04, 2019 5:10 pm

rather interesting read, i might be drifting off topic so mods feel free to remove but as was mentioned some Gazelle (not sure if all) are not that suited for Hot and High conditions, i always thought (i have no experience on any of them) that the Gazelle was more powerful or better suited for highveld than Allo II and III - is this a Fenstron limitation or just engine power?
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Re: Gazelle down at Rand

Unread post by jimdavis » Mon Feb 04, 2019 5:36 pm

Alouette wrote:
Mon Feb 04, 2019 4:44 pm
The gazelle HT Mk 2 was the standard for the British Royal Naval and in term of its airframe and engine didn't differ from the other military gazelles. There are about 13 different models, not that CAA would be aware of that. The cross wind specifics are very clear, namely, up to 30 kts at SL, decreasing by 5 kts per 3000ft, but not less than 18 kts. Service ceiling 20,000 ft, not that one would push the crosswind at any high height. It is worthwhile for any gazelle pilot to read Eurocopter service letter no 1673-67-04 on fenestron performance. If that aircraft was a G model then you can expect performance problems because they are not suited to high and high. They don't have the upgraded fenestron and are limited to 1800 kg.
Thanks so much Alouette. Very informative.

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Re: Gazelle down at Rand

Unread post by Peregrine » Mon Feb 04, 2019 6:24 pm

Informative indeed, thanks Alouette. So at 6000ft the limit is 20 kts, comfortably above the prevailing value on the day of the accident as kindly posted by Cage.

In your experience Alouette, does the Gazelle have a critical wind azimuth in the hover? What if the accident Gazelle was hovering with the wind in this critical azimuth while waiting to cross the active runway, and then the pilot started a transition towards the pad when cleared - is it likely that directional control could have been lost? Considering that the helicopter rolled to the right, could it be that it yawed to the right with maximum right pedal applied, and the pilot put it down with a sideways speed component, causing a roll-over?
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Re: Gazelle down at Rand

Unread post by Euro Flyer » Mon Feb 04, 2019 7:12 pm

cage wrote:
Sun Feb 03, 2019 5:48 pm
Peregrine wrote:
Sun Feb 03, 2019 5:41 pm
Yes, that’s more like your normal astute and helpful input thanks Cage.

So the worst wind in the late morning was likely to have been fairly steady NNW at up to about 12 mph. Probably not a prime suspect?
If I was going to take a stab in the dark, I would suggest there is a possibility that being a new import there's a chance the PIC may have been a bit green on type. Could be completely wrong.
The runway is right near the pads, don't see why a lot of "manoeuvring" would be needed, you'd mostly just wait on the pad.
Besides, if after all these years tanglefoot hasn't snagged a skid around there, then it can't be that much of a risk ;)
With the above in mind, wonder which machine(s) the pilot flew more regularly and trained on prior to the Gazelle.

Could it be the Gazelle was his/her first foray on to a type with a rotor system which rotates the other way?

There is a school of through which says when under pressure (for whatever reason), an individual typically reverts to “type” … in other words trained on and flew (for arguments sake) the Robinson family of machines and had become well versed with the type(s)/procedures etc. Converts to the Gazelle, still building experience, gets caught by a gust (for example) and instinctively reverts to “type” to correct which wouldn’t necessarily be as required.

I think that makes sense.

I guess it could also be that the pilot did all his training on the Gazelle in which case reverting to “type” wouldn’t apply.

EF
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Re: Gazelle down at Rand

Unread post by Bearcat » Mon Feb 04, 2019 7:15 pm

Alouette wrote:
Mon Feb 04, 2019 4:44 pm
The gazelle HT Mk 2 was the standard for the British Royal Naval and in term of its airframe and engine didn't differ from the other military gazelles. There are about 13 different models, not that CAA would be aware of that. The cross wind specifics are very clear, namely, up to 30 kts at SL, decreasing by 5 kts per 3000ft, but not less than 18 kts. Service ceiling 20,000 ft, not that one would push the crosswind at any high height. It is worthwhile for any gazelle pilot to read Eurocopter service letter no 1673-67-04 on fenestron performance. If that aircraft was a G model then you can expect performance problems because they are not suited to high and high. They don't have the upgraded fenestron and are limited to 1800 kg.
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Re: Gazelle down at Rand

Unread post by cage » Mon Feb 04, 2019 7:29 pm

P, aren't ducted fans meant to be "immune" to critical azimuth regions or is this another fenestron myth?
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Re: Gazelle down at Rand

Unread post by cage » Mon Feb 04, 2019 7:46 pm

Not sure how relevant the following military test doc is as it covers the 342 which has a larger fan.
Has some performance information that may shed some additional light.
https://apps.dtic.mil/dtic/tr/fulltext/u2/a016921.pdf
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Re: Gazelle down at Rand

Unread post by jimdavis » Mon Feb 04, 2019 8:43 pm

Euro Flyer wrote:
Mon Feb 04, 2019 7:12 pm

There is a school of through which says when under pressure (for whatever reason), an individual typically reverts to “type” … in other words trained on and flew (for arguments sake) the Robinson family of machines and had become well versed with the type(s)/procedures etc. Converts to the Gazelle, still building experience, gets caught by a gust (for example) and instinctively reverts to “type” to correct which wouldn’t necessarily be as required.
Absolutely right EF. The effect of 'primacy' in flying training is critically important. In this context it is the natural tendency for pupils to revert to what was first learned.

I know it is slightly off topic, but it is crucial in our current state of transition from steam to electronic cockpits. I think this is the basic cause of the checkpit cockups that keep showing up in fly-by-wire transitions.

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Re: Gazelle down at Rand

Unread post by vildwillie » Mon Feb 04, 2019 10:27 pm

Euro Flyer wrote:
Mon Feb 04, 2019 7:12 pm
cage wrote:
Sun Feb 03, 2019 5:48 pm
Peregrine wrote:
Sun Feb 03, 2019 5:41 pm
Yes, that’s more like your normal astute and helpful input thanks Cage.

So the worst wind in the late morning was likely to have been fairly steady NNW at up to about 12 mph. Probably not a prime suspect?
If I was going to take a stab in the dark, I would suggest there is a possibility that being a new import there's a chance the PIC may have been a bit green on type. Could be completely wrong.
The runway is right near the pads, don't see why a lot of "manoeuvring" would be needed, you'd mostly just wait on the pad.
Besides, if after all these years tanglefoot hasn't snagged a skid around there, then it can't be that much of a risk ;)
With the above in mind, wonder which machine(s) the pilot flew more regularly and trained on prior to the Gazelle.

Could it be the Gazelle was his/her first foray on to a type with a rotor system which rotates the other way?

There is a school of through which says when under pressure (for whatever reason), an individual typically reverts to “type” … in other words trained on and flew (for arguments sake) the Robinson family of machines and had become well versed with the type(s)/procedures etc. Converts to the Gazelle, still building experience, gets caught by a gust (for example) and instinctively reverts to “type” to correct which wouldn’t necessarily be as required.

I think that makes sense.

I guess it could also be that the pilot did all his training on the Gazelle in which case reverting to “type” wouldn’t apply.

EF
As a helicopter pilot I fly helicopters with counter clockwise rotating as well as clock wise rotating blades, I could not tell you about muscle memory as you refer to, I just know what pedal to apply to stop the yaw I feel in my ass or see over the nose it's instant instinct, and I doubt seasoned helicopter pilots think about it. In all helicopters left pedal is left and right is right, just like American cars the clutch is still on the left as in our cars. Now the indicators in some cars do catch me out when switching :oops:

The memory effects you refer to I could understand or appreciate if we are moving from Aeroplane to helicopter and so on as the two types are very diferent.

Cage ....?
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Re: Gazelle down at Rand

Unread post by Peregrine » Tue Feb 05, 2019 6:32 am

cage wrote:
Mon Feb 04, 2019 7:29 pm
P, aren't ducted fans meant to be "immune" to critical azimuth regions or is this another fenestron myth?
Apart from the fenestron, there is a possibility of directional instability caused by main rotor vortices / downwash over the tail surfaces (vertical as well as horizontal), as well as unsteady flow breakaway over these surfaces during higher out-of-wind speeds. Downwash over the tail boom may also have undesirable effects.
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Re: Gazelle down at Rand

Unread post by PJL » Tue Feb 05, 2019 7:24 am

Alouette wrote:
Mon Feb 04, 2019 4:44 pm
The gazelle HT Mk 2 was the standard for the British Royal Naval and in term of its airframe and engine didn't differ from the other military gazelles. There are about 13 different models, not that CAA would be aware of that. The cross wind specifics are very clear, namely, up to 30 kts at SL, decreasing by 5 kts per 3000ft, but not less than 18 kts. Service ceiling 20,000 ft, not that one would push the crosswind at any high height. It is worthwhile for any gazelle pilot to read Eurocopter service letter no 1673-67-04 on fenestron performance. If that aircraft was a G model then you can expect performance problems because they are not suited to high and high. They don't have the upgraded fenestron and are limited to 1800 kg.
What a great post Alouette, I am a fixed wing pilot but have always been facinated with chopers!!

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Re: Gazelle down at Rand

Unread post by cage » Tue Feb 05, 2019 7:27 am

Peregrine wrote:
Tue Feb 05, 2019 6:32 am
cage wrote:
Mon Feb 04, 2019 7:29 pm
P, aren't ducted fans meant to be "immune" to critical azimuth regions or is this another fenestron myth?
Apart from the fenestron, there is a possibility of directional instability caused by main rotor vortices / downwash over the tail surfaces (vertical as well as horizontal), as well as unsteady flow breakaway over these surfaces during higher out-of-wind speeds. Downwash over the tail boom may also have undesirable effects.
Indeed, the 342 test doc I shared notes that the fan requires more power IGE than OGE, presumably due to dirty air in a hover.
Last edited by cage on Tue Feb 05, 2019 7:36 am, edited 1 time in total.

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