Good Vibes: A flight into NVH

I was absolutely delighted when I found it was a JetRanger. When my dad invited me as his +1 on a pleasure flight he received as a birthday present, I was fearful that it would be a Robinson R44 – the aviation equivalent of a Toyota Camry. A JetRanger, though, and a 1986 example at that – we’re talking late Toyota Cressida territory here. Much more my cup of tea.

But how, I asked myself, might I scrape a car-focussed Redusernab article out of a brief helicopter trip? Well, having linked burgers and steering feel, I figured it must be possible, and when that single Allison turboshaft whistled into life, I suddenly knew my angle. To properly get your head around Noise, Vibration and Harshness, you’ve gotta hitch a ride in a heli.

Bell JetRanger III

This is Epping Forest. Quiet, peaceful, serene. That is until Bell JetRanger III wakes up. There are far noisier helicopters, of course, but any helicopter makes a right old racket when awoken. The actual noise level depends on a number of things; not least the type of engine in use, and the size, shape and angle of rotor blade attack. When running at idle, all systems engaged in the pre-flight pursuit of correct operating temperature and hydraulic pressures, All you should hear is engine, transmission and the ‘whip, whip, whip’ sound as each blade slices through the air.

At that point, though, all the blade is doing is slicing. Not yet has it begun to claw at the air. Until the pilot grabs a bunch of collective and alters the angle of attack of each blade away from the horizontal, the rotor isn’t generating enough lift (or, effectively, thrust) to overcome the heli’s weight. And it’s not until that happens that the full noise will tear at your eardrums.

That’s how life is for onlookers, anyway. That moment when the blades swivel is marked by an abrupt change in spectator behaviour. Where they had been gawping in fascination and capturing the moment with smartphone or video camera, all of a sudden they’re leaping aside for cover, shielding expensive equipment and grimacing while anything not tied down is thrown into their collective face. And that’s what we’ll call it. “Collective face” is the expression you make while watching a helicopter pounce into the sky from a dry, dusty field.

Bell JetRanger III up, up, away!

Thing is, though; for those inside the helicopter, the noise, wrath and fury is nothing like as devastating. That’s mainly because you’ll have donned a seriously effective set of noise-cancelling headphones plumbed into an intercom system that links pilot and passengers. It can’t cut all the noise out – the ever-present, whiffling “phwephwephwephweph” (correct spelling) sound of the rotors and whistle of the turbine are just outside the scope of noise-cancelling kit – but that which remains forms a pleasant, topical reminder of your chosen form of transport. Take your headphones off, though, and face a cacophony more violent than Metallica could manage if rolled down a mountainside in a metal dustbin.

Really, though, that noise, which can only be described as harsh – the H of the NVH holy trinity – represents the only real flavour of harshness the JetRanger experience provides. We’ve covered Noise, now only vibration remains, and there’s a lot of it, but none of that encountered in my brief flight was what you’d call harsh.

Tuning into the vibrations of the JetRanger is like deconstructing an orchestra; there are so many frequencies vying for your attention. There’s one, though, which is better described as a pulsation than a vibration, that dominates proceedings. It’s a relatively low-frequency throb, which I’m guessing is caused by a slight imbalance of the rotor assembly because it seems to match the rate at which the latter rotates. 

Bell JetRanger III turboshaft

This throb has a knock-on effect, in as much as that the sturdy aluminium skeleton of the helicopter might be unfazed by it, but the featherweight exterior panels and myriad plastic trims that line the cabin are rather more prone to shimmy. As a result of the constant throb, everything on board will eventually resonate at whatever frequency triggers it off – its harmonic, in other words. You can feel it through the seat of your pants, with a noticeable buzz through the frame of your chair. You can see it, too, in the blurred edges of reflections on glossy surfaces. Some of these vibrations are so gentle you can barely feel them at all, but you know they’re there. 

No doubt, were it not for the tumult of the gas turbine and gearbox, you’d be able to hear them, too,    but the sound of the orchestra is loud enough to drown out the chatter of the crowd, with those noise-cancelling headphones serving to further stop up your ears. 

Thing is, though; while car manufacturers (and presumably helicopter makers) seek to keep on top of NVH, eliminating it altogether isn’t necessarily the right thing to do. The NVH formula could, in essence, be rewritten as N+V=H, and exactly how much H is too much is entirely subjective. What might be regarded as way too H in a Rolls Royce would seem appallingly sterile and soulless in a Ferrari. 

Bell JetRanger III flight

To possibly a greater extent than performance, ride, handling or design, the components of NVH are responsible for giving a vehicle its character. While a complete absence of any N, V or H might equate to technical perfection, total competence and efficiency is rarely a driving force in romance. 

The eager way the JetRanger pounced off the ground when forward cyclic and full collective were applied helped to make it feel sprightly and perky, but the way it throbbed and shimmied made it feel alive. It’s entirely probable that more delicately balanced examples of the breed exist, but would they be as enjoyable to travel in? The answer to that is “probably”.

I wasn’t in the chopper for more than ten minutes. Take-off, a fling around the countryside, and then landing. For a flight of that duration, all is experience and excitement. We didn’t even touch on endurance. That latter term might begin to apply if the end of our journey wasn’t in sight. Once you go beyond savouring the moment and stray into merely tolerating it, it can be painful if your transport has too much character. Sometimes you just want things to shut up and leave you alone.

I’ve yet to test either, but I’ll wager Ferrari uses different NVH formulas for the sprinty 488 and the leggy GTC, which are cars with very different mission parameters. Noise, Vibration and Harshness aren’t necessarily forces to eliminate, but forces to hone. Too little of each can be as undesirable as too much, and here we’re wading waist-deep into subjective territory.

With today’s mainstream cars so closely matched, a reviewer will undoubtedly condemn car any that exhibits more noticeable noise or vibration than its rivals – although the quality of actual exhaust note, it should be pointed out, is regarded separately to the overall noise level when travelling. This is a double-edged sword, though. NVH being a key ingredient of what we dub ‘refinement’, is a huge factor in determining how ‘good’ a car is – but not so much in influencing how much we’ll love it.

Those whose most memorable experiences were characterised by silence and isolation from sensation are surely outnumbered by those who cherish moments of vibrance, excitement and stimulation. The cars we remember most fondly tend to be those coloured by flaws. A helicopter with no noise, vibration or harshness would feel like a hot air balloon – which I have just added to my “must experience” list as I type.

Perhaps ironically. though, the moment that the JetRanger threw grit in my face is the memory that registers most vividly.

(All images copyright Gianni Hirsch / Hooniverse 2019)

By |2019-07-12T08:10:30+00:00July 12th, 2019|All Things Hoon|6 Comments

We the Author:

RoadworkUK is the online persona of Gianni Hirsch, a tall, awkward gentleman with a home office full of gently decomposing paper and a garage full of worthless scrap metal. He lives in the village of Moistly, which is a safe distance from London and is surrounded by enough water and scenery to be interesting. In another life, he has designed, sold, worked on and written about cars in exchange for small quantities of money.