Loop and roll with a helo

[mora]

Check this video!

http://hagar.up.ac.za/christo/Bell407Loop.wmv

This happened in South Africa. The stunts were unauthorized and the pilot got his licence revoked. The chopper is grounded and possibly scrapped as the manufacturer requires replacement of the whole powertrain etc. before allowing it to fly again.

Source

[Raubvogel]

That guy watched too much Airwolf when he was a kid.

[Furball]

ever seen a westland lynx do aerobatics? its amazing - i think westland designed a rotor system that not only made it the fastest helicopter in the world but fully aerobatic too.

[Staga]

IIRC Westland Lynx was first helo capable to do aerobatics... already 15-20y ago.

Edit: Make it 30y.

[Mini D]

Those moves looked well practiced.

[Mini D]

Mora, do you fly helos?  I read through the whole thread and am somewhat confused at Bell's condemning of the helo that did this.

Both of those maneuvers had centrifical force as the main component.  This force would have been minimal at the top of the loop.  Basically, there wasn't anything in the maneuvers that would have induced excessive stress.  The main risk of both of them would be insufficient forward momentum with catastrophic results.  But, if enough forward momentum was present to complete the meneuvers, the resulting stresses would have actually been the least at the top of the move.

I understand the need to get the point across that loops are way too dangerous to be arbitrarily doing, but it seems that there is a direct conflict of interest when having the manufacturer do this as opposed to the civil authority.  The move could have been considered feloneous endangerment, but it really didn't put excessive stress on the helo.

[mora]

No, I don't fly them. It probably didn't stress it significantly. Like you said it seems that Bell just wants to send a strong message.

[Roscoroo]

Originally posted by Staga
IIRC Westland Lynx was first helo capable to do aerobatics... already 15-20y ago.

Edit: Make it 30y.

You shure ??? In the Air force they used to show a film of a HH-53 doing a loop and barrel roll . that was back from the 60's

[Raubvogel]

Originally posted by Mini D
Mora, do you fly helos?  I read through the whole thread and am somewhat confused at Bell's condemning of the helo that did this.

It has to do with the rigidity and type of rotor system. Lynx has a semi-rigid main rotor that allows it to do **** like that without worrying about it.

[Mini D]

To an extent raub.  I still don't see excesive force being the key here.  The main issues are going to be forward velocity and forward "thrust" to weight ratios.  Flexing the rotors due to inverted (-) Gs could be catastrophic, though I don't think that actually occured with that maneuver.  Lingering an instant too long inverted definately would.  This isn't a case of flying inverted, it's a case of floating through the inverted portion of flight with enough velocity.  It's not as if the rotors are actually generating an force to keep it inverted.

PS... by "rigid", I assume you mean the rotors don't flex nearly as much as a result of the lift being generated.  Or does this imply that there is a full tilt functionality of the whole rotor assembly on some helos?

[CavPuke]

There are 3 basic types of main rotor systems,  Fully articulated (common in rotor systems with more than 3 blades), semi - rigid (teetering type), and rigid rotor system.  Bell also uses a system of mating 2 semi-rigid rotors to a common mast, the Bell 412 is the best example that comes to mind.  The BO105 which has a fully rigid rotor system is a snap to do rolls loops etc in.  The UH-1 series of aircraft (including the AH-1) uses a semi-rigid system.  As long as you keep the rotor system loaded with at least 1g you can roll the aircraft.  If you unload the rotor system while inverted you will encounter "Mast Bumping".  This will result in the rotor system, and more than likely the transmission , departing from the airframe.  It's highly unlikely than you can loop a semi rigid system because of the bleed off in airspeed at the top of the loop resulting in negative g loading of the main rotor.  Not saying that it hasn't been done or impossible, but I wouldn't give it a whirl (pardon the pun).  All of my time has been in semi rigid and fully articulated helo's,  at no time did I ever think about exceeding the design limitations of the aircraft.  BTW you can encounter mast bumping in straight and level flight due to turbulence.  Hope this helps.

[Mini D]

That's pretty much along the lines of what I was thinking.  The centrifical force being maintained is the key for most of these moves.  Speed and forward thrust being the absolute necessities.  The biggest problem is that someone would try something like this with a helo that cannot get to the speed and maintain it long enough through the loop to allow for > 0 g's (or whatever the magic number between 0 and 1 is).

[rpm]

I used to live across the street from Bell in Hurst, Texas. It was'nt that long ago you would see Cobras doing full loops all day long over the landfill.

I guess this is a little like the disclaimer you see in fine print during car commercials. "Professional stunt driver on a closed course. DON'T TRY THIS AT HOME!" After looking at Bell's website, maybe the pilot read the sales material a little too long.

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