Shrieking Gazelles

[xbdt]

XB: Are you 100% sure?

I thought that 'some' Gaz's had the roof panels in metal and just the final quarter 'skylight' in plexi. Yes, I know that some of the plexi 'skylights' are 2/3 painted also.

Yes 100% sure. All plexi there. It is one clear panel, but painted according to the interior finish.

[Savoia]

Very well.

I had been led to believe that some models were covered in metal and sound proofing installed in that section of the roof but .. this must obviously have been one of those 'Gazelle myths' one hears from time-to-time!

[Zishelix]

First hand information, much appreciated!

So, she wasn't with Great Lakes Helicopters, Buffalo Airways, Northland Helicopters and Rotor Breeze?

My #1042 file obviously needs correcting.

I have lots of pictures from when he bought it from Ed in Alberta.

Any chance you could share some of those pics with us?

[Savoia]

Gazelle Roofs!

I was informed years ago that some Gazelles used in a VIP/private role had metal roofs installed and sound-proofing added in an attempt to reduce cabin noise levels.


SA341 F-ZWRH

The photo above is, I believe, an example (albeit an early example) but .. rumour has it that later Gazelles also had metal roofs!

Obviously installing sound-proofing beneath perspex would not be as effective as with using metal (one assumes).

[Zishelix]

This is one of the early Gazelles with the metal roof

[Savoia]

And this also is another metal roof example:

[xbdt]

Regarding metal roofs:

• Post #186 is not a metal roof. Center part is aluminium. Left and right part is plexi where the rear 2/3 of the panel are painted white in this case.
• Post #185 is, as I mentioned, a prototype and not the production aircraft.
• Post #184 is the same as for post #186.

[Zishelix]

Wow! Looks like the Santa visited your back yard that day Thanks for share.

Btw, so it was only Mr. Tercier and the owner before you in her log book?

[xbdt]

It is not my backyard, but the one from Ed Tercier.

I saw Great Lakes Helicopters in the books, but not (yet) the others.

[Savoia]

Great stuff!

Zishelix is doubtless very happy to see those photos - as indeed we all are!

Thanks too for the clarification on the roofs. As they say on 'Mythbusters' .. "Myth Busted!".

Ground Resonance

Following on from the ground resonance discussed on the previous page .. something I posted a couple of years back on 'another' forum:

Not all types of helicopters are susceptible to ground resonance. Two-bladed helicopters are exempt because their “teetering” rotors are a single rigid structure, like a see-saw. The only rotors that can produce ground resonance are those with three or more blades. Multi-bladed rotors have lead-lag hinges, which allow blades to speed up and slow down at different points as they circle the mast while the helicopter is moving forward. The hinges keep the fluctuating lift and drag forces on each blade from inflicting excessive stresses on the rotor hub. Snubbers and dampers limit the motions of the blades.

Because it is massive and spinning at a high speed, the rotor of a helicopter must be properly balanced. If the lead-lag hinges allow the blades to depart from perfect symmetry, the rotor’s center of gravity shifts slightly to one side of the mast, throwing the system out of balance.

Anything that’s springy has a favorite frequency of vibration (its natural frequency) which is determined in part by its size and mass. That’s why tuning forks always produce a certain tone, and why boats of different sizes rock at different rates. When two things with the same or similar natural frequencies are in contact, or sometimes even merely close to each another, and one of them begins to vibrate, it may “excite” the other to vibrate as well. The ability of one vibrating object to create this sympathetic vibration in another is what enables the rotor blades to gain control of the entire helicopter.

The helicopter’s airframe has its own natural frequency, which can be excited by an out-of-balance rotor. Usually there is a triggering event: a bump or a landing or takeoff on sloping ground or with a little sideways or forward motion. A jolt moves the mast while the blades, because of the freedom of motion allowed by their hinges, lag a little behind. The rotor, now slightly out of balance, begins to wobble like a slowing top. If the characteristic vibration frequency of the airframe is close enough to the rate of rotation of the rotor, it joins the dance, amplifying the rotor wobble.

The destruction is wrought by the considerable energy stored in the rotor blades. The shaking rapidly grows in violence, exceeding the strength of the mast, transmission mounts, and landing gear. The cyclic control in the cockpit flails about so violently that the pilot cannot hold it, the rotor blades strike the tail boom or the cockpit, parts begin falling off, and moments later the helicopter may be a heap of scrap.

If ground resonance begins, the pilot’s best option is to get the helicopter into the air. Once the tires or skids are no longer touching the ground, the vibration fades. If the rotors do not have sufficient speed for flight the next best remedy is to eliminate lift by reducing blade pitch; shut down the engine; and hope for the best while waiting for the rotor to slow.

The wait-and-hope approach is only sometimes successful, so a better solution to ground resonance is to prevent it. Helicopters with multiple-blade rotors have shock-absorbing landing gear with powerful dampers that allow it to soak up the energy that would otherwise set the helicopter shaking. When ground resonance occurs in these craft, it is usually because tires or shock absorbers have been improperly serviced.

In December 2005 this Alouette III landed at Escalante National Monument in Utah when, upon landing, it suffered ground resonance .. apparently shaking itself to pieces in just four seconds!

[Zishelix]

Ah yes, you said it was "a truck with the container" infront of your house... my fault.

So probably it was leased to the Great Lakes Helicopters.

I wonder if Mr. Tercier has any photos of his Gazelle from when he bought it from the Vought.

[xbdt]

I just checked the whole registration history, but no signs of Buffalo Airways, Northland Helicopters Alberta or Rotor Breeze Aviation Ltd.

Tercier Motors is/was the company of Ed Tercier. I called Tercier motors last year and I was able to get him on the phone and have a chat with him :-) I think he was about 84 years old and he told me he sold the Gazelle with pain in his heart.

Besides this, I think that the Gazelle is less prone for ground resonance than an Alouette II or III as the Gazelle has no lead-lag hinges. This is what the french called the NAT rotor head (Non Articulée en Trainée).

Of course, there is lead-lag, but the movement is 'bending' the composite main rotor blades. This movement is then damped with the elastomeric dampers.

[Zishelix]

Then probably my info about reg CF-BBN is also incorrect. Oh well, this happens when relying on public sources.

Thanks once again for your help!

[Savoia]

We saw F-GEHA on the previous page .. so this seems like a good opportunity to share another angle:


SA341G F-GEHA c/n 1064 (This is a Vera Lynn Photograph)

I think if you are going to fit high skids on the Gaz .. that it is worth investing in some fairings to cover the cross-tubes because the craft tends to look a little 'gangly' otherwise!


Moroccan Air Force SA342L CN-AID fitted with high skids .. and skid fairings!

[xbdt]

High skids looks nice, certainly with fairings, but they are not so common. They tend to vibrate in flight. I'm looking for rigid gear type fairings but they are hard to find...

[Savoia]

I'm looking for rigid gear type fairings ..

It would be a nice touch to your craft!

If no one has any to spare, you might ask Hélidax if they have some.

[Zishelix]

Excuse my curiosity xbdt, are you in contact with Eurocopter's (now Airbus Helicopters) Former Range Helicopters Unit?
I mean, what kind of customer support AH provide for Gazelle owners?

[xbdt]

I do have an account and price list from Airbus Helicopters. All parts for the Gazelle are available from them, but the prices are very very very high. Therefore I have to seek the net, ask my contacts in UK and France to get new parts or parts with good remaining times. It is still possible to find all parts at 1/10th of AH price.

[Zishelix]

Is there a reason for AH to keep so high prices on Gazelle spare parts?

[Savoia]

Is there a reason for AH to keep so high prices on Gazelle spare parts?

So you eventually give-up the Gaz and buy a new EC120 or AS350B3.

And if you don't .. the high prices are the penalty!

[Zishelix]

I have the same assumption Ah, the producer's philosophy...

[Savoia]

What would be interesting to know is if one day Sud Aviation .. Aérospatiale .. Eurocopter .. Airbus .. (or whatever they will call themselves next) one day sell the Gaz type certificate .. whether you could re-engine the beast (with a more economical engine .. in terms of operating and maintenance costs) and re-produce the aircraft for the private market.

I don't think there would be much demand but there may be 'some' demand!

Btw, Airbus did in fact update the Gaz Type Certificate earlier this year!

[xbdt]

They raise the price about 9 to 10% each year. This is of course to promote their 120-130-135-350 series. Also all french ex-military Gazelles are sold by the government and exported out of Europe. AH they do not want to see it flying in Europe as they prefer to sell new aircraft.

The Gazelle is one of the best aircraft available today and they know it. It has been engineered 40 years ago, without computers! Imagine these engineers today... :-)

Today the engineers are not inventing anything anymore compared to 40-50 years ago. Now they outsource everything.

[Zishelix]

Newer Isn't Always Better! In this case for sure... but my judgement is too subjective, of course.

[xbdt]

Zishelix, do you have some other pictures of the early C-GDUG? I saw on another forum that Scullcap had some, but I cannot see these. You may still have these, Thanks,

[Zishelix]

You mean this one Skullcap posted on VF?



And there is also this one from 1978:


(Photo Mick Bajcar)

Btw, any chance you contact Mr. Tercier for some photo of his Gazelle when he bought it from Vought... and/or about those other C-GDUG's operators/aircraft history?

[xbdt]

I just sent him an email; we'll see if he answers...

[Zishelix]

Much appreciated!

[xbdt]

I do have some other pictures from before re-doing the interior. It looked like a coffin inside, really awful! Not sure if everybody wants to see this

[Savoia]

Knowing Zis .. if it involves a Gazelle .. he will be keen to see it!