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Can you start a heli's blades mid-air?

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Old 09-07-2005, 10:46 PM
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Default Can you start a heli's blades mid-air?

I was watching the most recent bond movie. I just caught the end and am not sure which one it is...it's the one with Halle Berry. Anyway, in their big escape scene, they ride a heli as it slides out of a cargo plane, start the engine and rotor as they fall. Of course, they get it flying just before impact and fly away safely. I was just wondering if this is possible. I'm not worried about how long it takes to start the turbine in the heli, I'm just wondering if it is possible to spin the rotors up to speed while the heli is falling at terminal velocity. I'm thinking that it is not, but I want to hear some expert opinions.
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Old 09-08-2005, 07:59 AM
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Default RE: Can you start a heli's blades mid-air?

Picture rotor blades bent straight up.
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Old 09-08-2005, 09:57 AM
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Default RE: Can you start a heli's blades mid-air?

I see your point. I've seen that most full scale heli's rotor blades droop a little when it is sitting. So, without the centrifugal forces holding the blades out, they would fail under the weight of the heli. Thanks.



-edit for spelling
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Old 09-08-2005, 10:10 AM
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Default RE: Can you start a heli's blades mid-air?

It's the same priciple as a long thin sailplane wing, as long as it is flying through the air its fine. Force it straight down at terminal velocity and SNAP
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Old 09-08-2005, 10:24 AM
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Default RE: Can you start a heli's blades mid-air?

OK, so the situation shown the movie couldn't have happened. But, what if the heli was dropped with full negative collective. Could the rotors spin up in aoutrotation before they snapped? It's kind of a pointless question - I'm just wondering if it's possible.
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Old 09-08-2005, 01:29 PM
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Default RE: Can you start a heli's blades mid-air?

I doubt it, I don't think it would ever obtain a stable fall but I do know one thing for sure.


I wouldn't want to be the one to try it.
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Old 09-08-2005, 02:05 PM
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Default RE: Can you start a heli's blades mid-air?

RC helis have done full blade stop autos. The trick is to get them spinning again before the heli starts tumbling out of control. Not something that I'm going to try with anything I own unless people start paying for my helis.
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Old 09-08-2005, 03:04 PM
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Default RE: Can you start a heli's blades mid-air?

RC Heli blades are a lot shorter and stiffer than real heli blades.

I agree, no blade stop autos for me (on purpose anyway)
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Old 09-08-2005, 05:55 PM
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Default RE: Can you start a heli's blades mid-air?

I've done full blade stop autos on an RC heli ..........on my G2 But since my success rate is only about 10%, Im not gonna try it with my heli.
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Old 09-08-2005, 11:00 PM
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Default RE: Can you start a heli's blades mid-air?

Somewhere I saw where they used rockets on the ends of the rotors to spin helicopter blades to speed quickly, can't remember if it was a movie or documentary, was a few years ago.

Pat
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Old 09-22-2005, 09:18 PM
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Default RE: Can you start a heli's blades mid-air?

[b]Pat:

You might be thinking about the Hiller "Hornet." It had a ram jet engine at each rotor tip, and a hand crank in the cockpit for the initial spin of the rotor - necessary to get the air flow for the RJ engines to start.

Unsuccessful for several reasons. Not the least was the noise, also sealing problems feeding the fuel through the rotor hub, Tou also needed Uncle Sam paying your fuel bill, ram jets are anything but economical.

But an air start? Doubt it.

A couple interesting pages on the H-23 Hornet:

http://www.fantasyofflight.com/aircraftpages/hornet.htm
http://kapowiezone.blogspot.com/2004...net-coupe.html

Bill.
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Old 10-18-2005, 03:52 AM
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Default RE: Can you start a heli's blades mid-air?

The reason this wouldn't work is well known to full scale pilots. Full scale helicopters have a very limited range of collective pitch travel compared to RC models. There are definite high and low RPM limits for the rotor system, with the low end being the greatest concern. Lower rotor RPM causes the aircraft to descend due to loss of lift. Adding collective pitch to compensate causes an increase in drag at the blade, further decreasing RPM. Once reaching a certain point, the blade stalls and drag exceeds the power available from the engine, with RPM decreasing even further. There is insufficient negative collective pitch to allow a recovery of RPM and the rotor speed continues to decay until the aircraft augers in. Since helicopters are usually flown fairly low, most crash before RPM reduces to the point of blade structural failure.
In a helicopter with a low inertia rotor system, such as the Robinson R22, there are flight conditions in which full down collective pitch is required within 2 seconds of an engine failure to prevent reaching an unrecoverable low rotor RPM. No surprise that maintaining rotor RPM is the most important lesson learned in flight training!

DT56

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Old 11-08-2005, 12:11 AM
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Default RE: Can you start a heli's blades mid-air?

You've got to be real quick to enter an auto in the R22 if you want to live to talk about it. Frank Robinson says you've got about 1.1 seconds to react before low rotor rpm kills you. The R44 is an entirely different beast. Autos are a non-event for all practical purposes.. When I got my checkout in the Raven II, I had to do a full down auto, pick up and do a 180 pedal turn and set it down again. PLENTY of inertia to do so..

As for starting blades in midair? No way. They'd tulip up on you in a heartbeat. No centrifugal force to keep 'em from doing so.. Now if they made real helo blades as stiff as our models.. Possible.
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Old 12-15-2005, 01:30 AM
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Default RE: Can you start a heli's blades mid-air?

Nice thread here. I am a real life helicopter mech. No that cant happen what they did in that movie. In a real heli centrifigal force is what keeps the blades from snapping. I have seen seven broken blades from real life helicopters that were broken from nothing more than high winds on the ground. If the blades flex with enough pressure they will snap and peel apart. Blades have a main spar with honeycomb filler and skin over the top. Bell helicopter manual will give limits on some of their helicopter blades. Take the 206B for instance. The maint manual says any more than 100 pounds of force in any direction up or down on a stationary blade may cause failure. Helicopters are scientific marvels and maintenance nightmares. I like'em anyway I don't fly r/c helis. I wish I could at least try one some time but I don't have the money for them. Just remember there is a lot of stuff on tv that is nothing but crap. If you don't believe that you may wanna watch an old episode of star trek LOL

Wes
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Old 12-11-2006, 09:02 PM
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Default RE: Can you start a heli's blades mid-air?

As far as re-starting inflight, it can be done. As stated above, rotor RPM is the single most crucial instrument to watch when doing autos. If rotor RPM goes too high, you overspeed and if it goes down, it underspeeds. In an emergency, you are more concerned with underspeeding as a stationary rotor renders your helicopter useless and you just fall out of the sky. Rotor overspeed...keep it below limits as it will easily overspeed, but is easier to correct with a little collective application, whereas underspeed, you drop the collective smoothly, maintain aircraft trim, maintain rotor rpm and monitor airspeed.

I have logged over 100 full autorotations in a 206 and it glides so beautifully. As far as restarts, I have done that, also.....but in a really nice sim. With the 206, you can only attempt re-start when below 12000 ft PA because you may hot start the engine. It took us about 3,000 ft after the engine was re-started, but it did it. I don't know if I would try that real-world because so much can go wrong!

Hope all that answers your questions.

-Steve
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Old 12-11-2006, 09:45 PM
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Default RE: Can you start a heli's blades mid-air?

I work on Ensrom 280's and get to fly them when I have time. They have a clutch on the drive so the blades dont stop or get dragged down. My owner/CFI/friend with 10,000 in helis( more in planes all civilian time) does 1/2 his approaches as autos. Effortless for him. i on the other hand am still working on that last transition to level abve the ground. The aircraft is easy to auto though, full down collective, glide in, aft cyclic to slow to about 10-15 kts, fwd cyc to level, up collective. Now if I can do it without getting out of shape! Much better A/C for training than an R22.

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Old 12-11-2006, 09:52 PM
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Default RE: Can you start a heli's blades mid-air?

The heli would tumble when it left the plane. There would be nothing to control it, even IF you could get the blades up to speed.

Rod
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Old 12-11-2006, 09:53 PM
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Default RE: Can you start a heli's blades mid-air?

I've never flown piston heli's, but I have heard it's no fun compared to turbine. I guess I'm spoiled that way. I have heard horror stories about the TH-55's and manually using the throttle to maintain RPM. People failed out of flight school because of that commonly from what I hear. Now, I fly a heli with 2 turbines and 2 rotor heads, no autos though....safer that way.

Autos were difficult for me to get, and I'm not 100% on them, hence the reason I did over 100 in primary. Everything else is fine. For me, entry was easy, glide and airspeed was easy, decel was easy, but cushion just before tochdown......ever heard of spike knock in the 206? I've heard it a few times!!
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Old 12-11-2006, 10:00 PM
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Default RE: Can you start a heli's blades mid-air?

Oh yeah, I haven't seen the movie you're referencing, so I don't really know what happened. I was talking about the re-start as if you had a flame out or something like that in flight.....in most instances, safest alternative is just to autorotate.

-Steve
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Old 12-11-2006, 10:23 PM
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Default RE: Can you start a heli's blades mid-air?

I prefer controling the engine seperatly. We have an early F28A '71 and a new 2004 F280FX. The FX has a corralator so it acts similar to a tubine and most people prefer it but I like being able to do minor adjustments. my friend always laughs at me because I like the old one better. He does too but the new one is so pretty.
Two rotors, That is a whole nother ball game. I guess you are not doing hammer head turns with that one. I'm glad I dont have to work on it! My son's great grandfather's last tour in the Navy had him flying big helos off Ships(his first was being launched off back of battleships in Kingfishers durring WW2). When retiring he was getting civilian checkrides and the FAA guy wanted him to do a full auto. Being a 20,000+lb ship he told the man no, cant because of regs. FAA said he had to. He said ok and dropped the collective all the way. The drop had the FAA screaming and crying momma! He was so distracted he did not notice the power come on to cushin the drop. After they land the FAA guy ran away!

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Old 12-12-2006, 08:37 AM
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Default RE: Can you start a heli's blades mid-air?

What was he flying that was 20,ooo+ lbs? I have noticed that the heavier the aircraft, the faster you have to drop the collective because the force of gravity will bleed off rotor RPM oh so fast! We actually go into a sort of negative collective, but never in real life. I have heard that they used to do full autos, but stopped because it was just a maintenance nightmare.

I'll never forget the first simulated engine failure I had in a 206...it scared the crap out of me. I really thought I was going to die, and then my instructor jsut sat next to me telling me what to do, ever so calmly. It was amazing because I reacted slowly trying to not over correct, but all worked out and we recovered about 100 AGL. After that, they were a little more difficult because he wasn't telling me what to do, only pointing out things I should be paying attention to, such as rotor rpm and airspeed.

It's great fun flying helichoppers. Don't know what a hammer head turn is, but you'd be surprised how maneuverable a tandem rotor system is.

-Steve
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Old 12-12-2006, 08:50 PM
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Default RE: Can you start a heli's blades mid-air?

The perfect hammer head would have you pull up to vertical and when the airspeed drops to 0 you do a 180 pedal turn andgo down vertical. Now cant do one like that but we can pitch up about 60 degrees and do one.

I dont remember what type of helo he was flying;I was always more intrested in the planes he flew he ran a repair depot before the helos and he got to fly it if it was on the field. He has over 35 diffrent Navy planes in his log book. Also after WWII he flew as the emergncy system in the early drones. He had to disable the system by pulling a giant cannon plug i f something went wrong because you could not out muscle the actuators. He had to do it once. and almost could not get it apart.

Tom
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Old 12-30-2006, 12:32 AM
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Default RE: Can you start a heli's blades mid-air?

to the best of my knowledge once the blades stop spinning the heli falls from the sky not to say it is impossible but highly unlikley. Dont think i will be trying to find out with my heli.
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Old 03-14-2007, 06:30 PM
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Default RE: Can you start a heli's blades mid-air?

I think I'll throw my two cents in.

Theoretically it would be possible provided a few things happened before hand. Realistically though, it would be doubtful due to the reasons listed above. Theory was, a long time ago, that man couldn’t fly. Now we have the ability to exceed mach 2, live in space, land on the moon and hover OGE with a 9 ton external load. Given a few more years in development, and I’m sure that this could (though not sure how many people would want to try it) become reality.
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Old 03-14-2007, 06:52 PM
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Default RE: Can you start a heli's blades mid-air?

Just for grins, check out this website. [link=http://www.griffin-helicopters.co.uk]griffin-helicopters[/link] You'll find some crazy real life helicopter videos. Have you ever seen a BO-105 do an inverted piroquet? There is also a video of a British MKII Chinook being put through its paces. Hope you all enjoy.
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