Question to experienced dual rated helicopter/fixed-wing pilots

[outofwhack]

Imagine flying A to B in a Cessna 172 encountering very strong thermal activity requiring frequent full scale deflection of ailerons just to keep the wings level.

Is it more safe or less safe to be in a semi-rigid teetering head helicopter in those conditions? (assume identical weight)


I've wanted to know the answer to this for a long time. I'm sure the helicopter has added gyroscopic stability which helps keeps the disk level but surely the consequences of an upset are much more dire.

Right now I'd take the Cessna every time.

OOW

[jayteeto]

I am double licenced. Easy question to answer, I would rather be in the bar :ok:

[paco]

I'd take the helicopter. It can ride that sort of stuff a lot easier. But then again, the bar is even better :)

phil

[Sir Niall Dementia]

I swing both ways (as they say in my office!)

The helicopter every time over the 172, however if the 172 is going stop to stop then I'd rather be in the boss's jet, that wouldn't even notice it.

Recently flew a helicopter IMC in a beam wind of 60kt, gusting 80 down the Pennines and it was a lot better than being in a 172!

However I really wanted to be in the bar then:\

SND

[chopjock]

Consider a plank and a helicopter parked up on the apron, side by side in a gale.
Which one would be bouncing around the most while you are watching them from the bar?

[hihover]

I'd prefer to to be with JT2 in the bar.

Any flight which requires full scale travel of any flight control needs to be reconsidered, however, I think I know what you mean. There is some flexibility in the rotor system which will absorb some of the feedback forces before a corrective input is required, there is no such flexibility in a light aeroplane.

I've never really thought about it this way but my gut feeling tells me I'd rather be in a helicopter.

"Semi-rigid teetering head"....Which helicopter are you thinking of?

Tam

[Phoinix]

Good point chopjock :)

[outofwhack]

I'm thinking Bell47 or any type that could suffer a mast bump.

In Oz, flying a sailplane, I once encountered a thermal so strong it tipped my glider damn near vertically 90degrees nose down. Not sure if it was a massive up gust under the tail or a similarly massive down gust as I left the thermal but it pitched the glider dramatically.

I might not be around if I'd gone through that air in a helicopter - good reason to stay relatively low level agl where thermals haven't had time to gather much upward velocity. I was probably 4000 - 6000 feet agl on a very strong thermic day in north-west NSW.

The reason I brought up the original question is because my fixed-wing hours far exceed my rotary hours. I am confident in judging what conditions would be uncomfortable in a fixed-wing but I still use a much larger safety margin in rotary.

Interesting comment that a high speed fixed-wing aircraft like an exec jet [higher wing loading] suffers less from turbulence. If that is true - could the small surface area of a helicopter blade equate to high wing loading and thus less response to [slow] gusts?

oow

[HeliHenri]

So the great lesson of these answers is that if you want to own a bar near an airfield, choose a windy area ! :}
.

[hihover]

Helicopters fly through thermals all the time, what we don't tend to do in a helicopter is ride the thermal then try to get out of it.

My advice - meet us in the bar. Sailplanes look particularly scary to me.

Tam

[Sir Niall Dementia]

OOW;

I'm pretty sure the B47/B206 have wind speed and gust limits, but they are pretty high, just to protect from mast bumping. I've no technical knowledge of the Robinson series (only spent 22 mins in one in 25 years/10 000 hours rotary) but I seem to remember that Robbos also have wind speed/gust limits, in fact it may even have been the cause of a fatal in the last couple of years. Certainly a pitch down of nearly 90 degrees would probably cause mast bumping with all the possible outcomes that implies.

A rigid head like the EC135 would be fairly bumpy but if flown in VS mode rather than Alt Hold would be fine, something like an A109 or S76 would definately handle a lot worse than a 172 ever could in far greater comfort.

From gliding days I remember flying in conditions like you mention and once cracked the canopy of a Pirat with my head:{

SND

[outofwhack]

SND,

Gotta strap in better!

I flew through some rotor flying wave in NZ and had a camera on my lap fly up and smash to smithereens on a Ventus canopy - thank god it was just my cheap camera and not the canopy.

OOW

[Sir Niall Dementia]

OOW;

You weren't flying in the Helm were you? I went there on a gliding holiday and the turbulence on the edge of the wave there was the worst I have ever experienced: anywhere.

SND

[SASless]

I prefer stirred to shaken.....especially in the Bar.

[outofwhack]

I havent flown at Helm. Had quite a few hours flying sailplanes out of Omarama in the south island, frequent wave but I'd say its more interesting flying on 'low days' without easy wave conditions and then the mountains seem much bigger as they loom above you. Some of the valleys down there are un-landable to fixed-wings and you need to know around which turn there is a landable spot if things aren't going good. Its great doing a lead and follow exercise with a local pilot. Sure adds pucker factor and keeps you constantly visualising how the mountains channel the prevailing wind and its vital to avoid the down going or turbulent air.

Back to the subject... the cpl syllabus doesn't talk much about BIG upsets - so here's my next question....

So, if a teetering-head helicopter experienced such massive turbulence [that we know exists] and it was literally tossed upside down isn't the only solution:

1. Initially keep the stick centred, disk level to the fuze [thinking time]

2. Raise the collective if power and revs allow to load up the disk as much as poss.

3. If achieve a feeling of positive g [pressure on butt] gently fly it out to straight and level [half loop?][as an rc modeller i used to loop a teetering helicopter (bell+hiller system) even from level flight +ve g the whole way around - but models likely have superior power to weigh, greater cyclic control and strength whereas I suspect most full-size helicopters would run out of steam just past vertical - aren't Chuck's 'loops' in the MBB105 really just a tumble at the top as he runs out of speed].

4. If you are still hanging in your straps [no pressure on butt] you better do something sooner than later or you are going to drill a shallow hole in the ground. What now? Keep waiting for +ve g? Pitch back and pray? Roll?

I am left wondering whether at stage 4 the collective should be pulled in large fashion in an attempt to load up so you have a chance of avoiding mast bump as you manoeuvre and [assuming you still have forward speed] wouldn't the best way out be to fly the bottom half of a barrel roll [back stick with roll input] Wouldn't a pure back cyclic be more likely to send you past Vne.

oow
p.s. kinda looking forward to flying non-teetering rotors - they seem much less to worry about but then helicopter pilots are rarely 'happy go lucky' sorts ;)

[Sir Niall Dementia]

OOW;

If your helicopter ends up as you describe then you definately should not have left the bar!

With a teetering head, lower trousers and force cyclic as far up your a**e as possible. It won't help, but will give the accident investigators/coroners court something to talk about and ensure you a place in aviation legend!

SND

[outofwhack]

Yep I'm in full agreement with that - the possibility of dying with a smile on your face!

[cockney steve]

Shirly! that's ergonomically impossible!

Now, a Rectal Collective may be a different proposition!

Punch-line of hoary old joke:-
Small urchin...."Rectum, Vicar ? I should say so!-blew them to smithereens."

[paco]

About 30 years ago Ken Kendall (who I believe used to fly for Gleneagles, or it might have been Wasp) was flying his 206 in the Highlands when he got caught between two crosswinds and was flipped over. He went with it rather than tried to fight it and lived to tell the tale. He said afterwards he was glad he had the presence of mind to do that. I think I would probably try lateral loading of the disk because there is not so much fuselage to move as there would be if you try fore and aft.

Phil