Maximum speed of a helicopter.

"Keep in mind that the maximum speed a rotor helicopter can reach, in theory, before spinning out of control is just over 250 miles per hour..."

listverse.com...

The use of the term "rotor helicopter" makes me wonder whether whoever wrote this doesn't know the difference between their head and their aXX. (Is there another type of helicopter?)

Anywhoo, I know there's a few people here that know their stuff when it comes to aircraft and am wondering if any have heard anything like this.

Is there any reason to believe a helicopter would "Spin out of control" after reaching a certain speed?

reply to post by Americantrucker

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I am a private pilot, but not a rotorcraft pilot, but I don't think there is anything in physics that limit the speed of a rotorcraft! The author is probably thinking about the "Doppler Effect" where the forward moving blade is traveling faster than the rearward moving blade, and when they approach the speed of sound then it has a lot of dynamic effects that would affect the flight. Each helicopter's design takes this into account when choosing the number of blades, the pitch, the length, the thickness, etc.

However, I did find this:


wiki.answers.com...

Upon more looking, I couldn't find any helicopter that went faster than 249 mph!

The fictional "Airwolf" from the TV show was reported to do 350 in the TV series, but it was based off the Bell 222 which only does 149 in reality!

Maybe there is something to this!

reply to post by Americantrucker

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Retreating blade stall limits forward speed as you described. For rotor helicopters.



That's why we make you fixed-wing types get a rotorcraft add-on rating.



[edit on 25-9-2009 by Chakotay]

reply to post by Chakotay

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LOL! All due respect! I'll stick to fixed wing, I prefer "gliding" to "auto-rotation!" I like all my teeth and bones where they are!

I am slightly curious about flying one, and I have friends that love it, but they look pretty difficult to me.

reply to post by getreadyalready

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You are flying a machine that wants to fly. We are not. I believe that makes you a very wise pilot, and me a wiseguy.

Americantrucker, its because the speed of the retreating blade is subtracted from airspeed, and the apeed of advancing blade is added to airspeed. For lift to be equal accross the rotor disk, the rertreating blade has to operate at a higher angle of attack. When angle of attack increases beyond a critical limit, the retrating blade stalls and lift is reduced. Due to 90 degree control lag, this pitches up the rotor and decelerates the helicopter. Because of high forces involved, not reccomended.

[edit on 25-9-2009 by Chakotay]

Yes, the forward travelling blades must remain sub sonic, and the reverse travelling blades create less lift, as forward speed increases.

For continuous horizontal flight there is definitely a limiting speed for a pure rotary wing helicopter.

While helicopters can now perform some pretty impressive aerobatics, none has ever broken the sound barrier, and never will.

FIRST RESPONSE mentioned Airwolf. Ah, that crazy Stringfellow Hawk. Grew up watching it.

I would assume that a helicopter, dropped from high orbit in a vacuum would attain a speed greater than 249mph. A craft with a single rotor propelling it would reach a speed limit.
I have found a helpful article on the subject.


But, on a technicality, turbofan engines could be considered a rotor. While the operating principal is not the same, similar physics definitions could be applied.

reply to post by Silver Shadow

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Blade tips go supersonic on rapid descents, making the 'WAP-WAP'. But fuselage is speed-limited by RBS. And more so at altitude.

Arrowmancer, that re-entry mode was actually a project: Roton.

[edit on 25-9-2009 by Chakotay]

Yes, but rotor tip speeds, are not the same as sustained forward speed
.
You don't need rotor lift to drop out of the sky like a stone.

We are talking about maximum possible sustained forward speed in level flight of the whole helicopter..


[edit on 25/9/2009 by Silver Shadow]

Blackhawk around 184 MPh
Chinook About 184 MPh
Huey Cobra 195 MPh
Apache 227 Mph




Now THAT is pretty damn close to 250...

thelongestlistofthelongeststuffatthelongestdomainnameatlonglast.com...

Never heard of that myself, but you're not the only one saying it...might be like the sound barrier was...pretty scared of it, till you break it...

In a conventional helicopter it is not possible, however, with unconventional designs similar to this...

en.wikipedia.org...

www.cartercopters.com...

Just an idea. Have a two bladed rotor that turns into a Oblique Wing at high speeds. Propel it with jets...

[edit on 25/9/2009 by C0bzz]

There is something that limits the forward speed of a helicopter, it is called retreating blade stall and it has to do with the different speeds between the blade that is going forward in a forward flight (the advancing blade) and the one that is going backward or the retreating blade. This difference in speed produces dyssymetry of lift where the advancing blade produces more lift than the retreating blade. The dissymetry of lift is compensated by blade flapping. The advancing blade flaps up, thus reducing the angle of attack which reduces lift and the retreating blade flaps down, increasing the angle of attack and increasing lift, therefore correcting for the inherent dissymmetry of lift. You can only go forward so fast before the retreating blade reaches the critical angle of attack and begins to stall, and if the condition is allowed to develop, the helicopter starts to roll on its side.

Coaxial rotor systems like the Russian Ka-50 or the Sikorsky X2, alleviate this problem somewhat because the rotors turn in opposite direction and cancel each other's dissymmetry of lift but, although they can go faster, they still have never exceed speed because the rotor tip blades reach supersonic speeds and lift is lost. This is the reason why helicopters are slower than airplanes.

The sikorsky X2 has a rumoured speed of 287mph

Sikorsky X2

The Sikorsky S 69 has a rumoured speed of 322 mph

Sikorsky S-69

Another limitation is the rotor having to provide a horizontal and vertical component for flight. The rotor disc actually behaves similarly to a solid disc or wing once you pass through a phase called ETL or effective translational lift. Basically, you need less power to maintain flight after a certain airspeed is exceeded.

The nice thing about a helicopter is that if you have an engine failure you can land just about anywhere. Helicopters can enter an auto forwards or backwards if you are in a hover. The downside is that the margin of error during an auto-rotation is quite narrow, especially in low inertia rotor systems like the R-22. You have about a second and a half to recognize the engine failure and get the collective down. If you don't, you will not be able to recover RPM and the rotor folds up like a clam. If you do get the collective down in time, but don't catch the rpm climb, an overspeed can kill you as well - you just have little bit more time to think about what your knees are going to taste like when you hit the ground.

Disclaimer: I'm a theist but not of the Abrahamic faiths. I have minor biblical scholar and scriptural skills. Also I am not a scientific/legal or medical expert in any field. Beware of my Contagious Memes! & watch out that you don't get cut on my Occams razor.All of this is my personal conjecture and should not be considered the absolute or most definitive state of things as they really are. Use this information at your own risk! I accept no liability if your ideology comes crashing down around you with accompanying consequences.

Explanation: 1stly regardless of any other contributing factors, the highest speed attainable by a helicopter coupled to the higgs field would be the Speed of Light.

2ndly the main contributing factors to maximum speed are...

Speed of Sound.

Cavetation.

Principles of Helicopter Aerodynamics.

Wave Drag.

Wiki Helicopters [see imitations under safety heading]

Personal Disclosure: Very interesting thread..S&F!

This is a great thread.

As I was reading through it about the single rotor problems associated with stall and asymmetric lift that would in fact cause the helicopter to spin out of control above a certain speed, I was wondering if a 2 rotor helicopter would overcome this limitation, and then I ran across the post saying the Sikorsky X2 COULD travel faster then 250 mph (rumor). The 2 rotor design would seem to at least address the issue of it spinning out of control due to asymmetric lift.

And "Is there another type of helicopter?"
The Sikorsky X2 is called a co-axial helicopter in the Wiki article en.wikipedia.org...

So yes that other type of helicopter, the coaxial type like the X-2 SHOULD be capable of going faster than the single rotor design, whether the rumor of its top speed is correct or not.

[edit on 28-9-2009 by Arbitrageur]

Hey there everyone, would you count the V-22 Osprey as a helicopter? It definitely is not a fixed wing aircraft.

en.wikipedia.org...

Here is a cool video:

YouTube Link

Thats the wiki for it, you can find a little better site at:
www.bellhelicopter.textron.com...

Anyway, the top speed right now is 250 knots = 287.5mph. They are working on an upgrade to 270 knots = 310.5. The reports are that it will be able to fly faster than any turboprop airplane out there.

It is fast as a helicopter, however the turboprop powered Tu-95 Bear flies at over Mach 0.8, which is dramatically faster than the V-22.

I would call it a twin rotor helicopter that morphs into a fixed wing aircraft with very big propellers!

Fastest helo that I know of is the Chinook. Top speed of the Chinook is supposedly classified but you can find different variant of speeds online. Might be outdated info but that's the last thing I got from talking to the Chiefs and other people around base, this info is about a year old. No one really had a definite answer.

[edit on 29-9-2009 by johnwayne]