Can helis fly in tunnels?

[Vortex what...ouch!]

After several beers the other day we were discussing mission impossible, you know the first film. Anyway the bit with the helicopter in the tunnel. After much discussion we decided it would probably not be able to fly because of all the re-circulation of air caused by the tunnels walls which would screw everything up. No discernible technical reasons for this conclusion just beer and waffle. Oh yeah and if it had to lift off in the tunnel we think with the downwash going up the wall and back into the rotors it would probably not have the force to lift off (vortex ring?).

So what do you very clever people think could a helicopter fly in a tunnel?

[CRAN]

I agree with your reasoning for the lift-off and hover. NO WAY, the recirculation would be so severe as to produce an inflow into the top of the rotor that removed virtually all of the incidence of the blade sections. If you were to continue adding collective pitch eventually you would have the lift force for the aerofoil section pointing backwards (i.e. DRAG, resisting rotoation) and just consuming torque and power without producing any lift in the vertical direction.

Furthermore, the whole process would be horribley unsteady, and their would be lots of uncommanded pitching and rolling that at the high power settling we are discussing are likely to rollover the aircraft. However, the comment about ring vortex is not accurate. Ring vortex is when the vortex structures in the wake build up under the disc and in the plane of the disc due to a high Rate of descent. In the tunnel case the same vortex structures would be recirculated by the tunnel wall and injested from the top of the disc. Much of the unpleasantness would result in the same manner, i.e. high loads, high vibration, uncommanded pitching and rolling but it wouldn't be Ring Vortex it would be Blade Vortex Interaction due to Recirculation.

The interesting one is high speed foward flight. Fundementally as long as the tunnel was big enough, then I see no reason why a helicopter could not be flown into it at speed, through it and out the other end. As we know in high speed flight the wake is skewed almost horizontally behind the helicopter, and the streamtube in which the wake can be considered to exist in the regime is much flatter and diagonally orientated. So the flow into and out of the rotor would be affected only subtley in high speed flight. I guess with a lightly loaded rotor and the helicopter flying at say 5ft, you would need about 1.5 rotor diamaters of head room in a semi-circular tunnel. (The number is a finger in the air guess I haven't done the sums!)

However, I think that the wake of the helicopter would be very severe, again due to recirculation and so a second helicopter would not be able to follow......which brings me onto the final point. Even if you could fly a helicopter in a tunnel, you couldn't chase a train - the wake from the train would flip you over!

Hope this helps

Open the flood gates!

CRAN (..........not Cron, or Crum......C R A N!)
:D

[Remmington]

It can be done - I was "flown" in a 206 through some caves in South Africa by an un-named nutter, the same who also sat burning & turning while a motor cycle jumped over the central rotor.....

[Old Man Rotor]

Many many years ago there was a 206 not far from my house slinging something down the inside of a Power Station Cooling Tower...........I suspect the ground cushion would have been a bit of a doozey...however I think the top opening is about 40 metres across so there was a bit of room [but narrowing half way down]....but still a life experience!!!

[Lord Mount]

Try this:

http://www.youtube.com/watch?v=5-A8eiIzqlU&NR


LM

[i4iq]

"Can helis fly in tunnels?"

I guess thats a yes then... although why not take the trouble to film it from outside as well?

[Cyclic Hotline]

Are you nuts?

Do you know how dangerous it would be to get out of a running helicopter on a public road?

You could easily get run over!:eek: :\

[Devin]

I know of a helicopter being hovered in a hanger and out the door. It isn't a tunnel but definatly a lot of recieculation. Lack of ground handling wheels was said to be the reason.:bored:

[HOGE]

Flying a Hughes 500 out of the hangar was seen in the film "Deadly Encounter". I suspect the real danger in doing something like that is from all the crap in the average hangar that would be blown everywhere.

[Vertical T/O]

Don't know if anyone has seen 'The Italian Job'. The chase scene where the helicopter flew in under the road (near enough to a tunnel) was actully flown. Mad Pilot but good flying.

[bayou06]

While I don't quite agree that the severity of the turbulence and unstable hovering flight would be tremendously severe (I believe the size and shape of the tunnel would be a significant factor), just much higher power required to hover. Additionally, I believe the other factors would play a role in the forward flight portion. In the MI5 senerio, the aircraft was chasing a speeding train at say, 50-70 mph. What do you think the wake turbulence coming off the train effect would be on the aircraft? In the confined space of that tunnel, the margin for error for managing precision forward flight would be slim. Most likely, most pilots would only manage a few hundred yards before a blade stike or some other type of contact with the interior of the tunnel. Just my .02 worth.

[rotorrookie]

Thank God for Hollywood! always gives us something to talk about:}

[chornedsnorkack]

While I don't quite agree that the severity of the turbulence and unstable hovering flight would be tremendously severe (I believe the size and shape of the tunnel would be a significant factor), just much higher power required to hover.

Why exactly?

Imagine a helicopter hovering in a well just slightly wider than the rotor... no recirculation, because the only way for the air to get back out of the well is up through the disc.

Does it take less or more power than hovering in ground effect? In free air?

What happens if the rotor disc is near a ceiling?

What happens in vicinity of walls? Probably a question of stability...

[FredFri]

Try this:

http://www.youtube.com/watch?v=5-A8eiIzqlU&NR

LM

Looks like (some) brazilian pilots are just gone crazy:ooh:!
(refering to the "accident in the waiting..." thread)

More about it here on FlightGlobal (http://www.flightglobal.com/Articles/2006/11/10/Navigation/197/210497/Video+Brazilian+helicopter+pilot+completes+Mission+Impossibl e-style+tunnel+interior.html)

[Chickenhawk1]

...the remake of the Italian Job a couple of years ago had a black MD500, I think it was, in that 'room'. I don't know where the disc got the air from but he was in the hover too. There was really no room for any errors there...

[Graviman]

Imagine a helicopter hovering in a well just slightly wider than the rotor... no recirculation, because the only way for the air to get back out of the well is up through the disc.

Countary to expectation this: The downwash flowing over the wall has a boundary layer, where the air is stagnant. This region causes the downwash to be pulled outwards, as a local rotation is set up (coanda effect - yup same as wing). This means that the conditions are right for the downwash to be returned, by squeezing past the blade end gap. Heli ends up as if in a weak vortex ring state. Net result is collective goes up so you need more power.

What happens if the rotor disc is near a ceiling?

The restriction to inflow means that to maintain the same disk pressure (which is what keeps the heli airborn), the velocity through the rotor is reduced. Net result is collective goes down, like ground effect, so you need less power.

Quite sad that i studied this stuff really... :\

Mart

[lartsa]

there is some interesting info on the pilot that flew in the itallian job at
http://www.imdb.com/name/nm0701042/

[Chairmanofthebored]

i reckon i would make it all the way down a tunnel and out the other side without collecting anything on the way through. why do you guys say **** like

I don't know where the disc got the air from but he was in the hover too. There was really no room for any errors there...

In the confined space of that tunnel, the margin for error for managing precision forward flight would be slim. Most likely, most pilots would only manage a few hundred yards before a blade stike or some other type of contact with the interior of the tunnel. Just my .02 worth.

all the people i work with hover in confined areas with limited room and all of them i would rate to fly down a simple tunnel and out the other side. it can't be hard the issue is the mindset to do it in the first place. you all need to get out more and get some exposure to commercial operations.

[McHover]

Chickenhawk,


Alan Purwin at Helinet in Van Nuys CA is the pilot responsible for the remarkable stunts in the Italian Job. He's an extremely skilled professional who's a pleasure to work with.

There's a bunch of these guys working in Hollywood who appear to have the best jobs in the world. It would make a good thread to hear about their exploits...

Long may the real stunts continue. Don't CGI us out of existence.


Mc Hover

[Gomer Pylot]

If you want to work with no margin for error, hover alongside a live powerline with breathing, self-loading freight in a basket out the side or on your nose, and hold the ship absolutely steady while he works on the wires. Flying through a tunnel is a piece of cake in comparison. That's a job I don't want, and won't have.