Can you fly with one blade missing?

[manfromuncle]

Sounds daft, but bear with me..

I remember reading a story once, possibly from the Korean war, where a heli was shot down and the pilots removed the damaged blade and managed to get it airborne again (albeit with some serious shaking!) to avoid capture by the enemy.

Anyone heard of this story? Do you think it's possible?

I might have read it in this:

http://www.amazon.co.uk/Tales-Helico.../dp/1560989521

But I don't have the book here so I can't check.

[HillerBee]

Impossible. The imbalance would roll the helicopter over in seconds. Blades on a Hiller or Bell47 in those days weighed around 85 pounds. An imbalance on a Hiller of a .1 ounce make them already shake like .....

[Flying Bull]

Don't think so.
You might have a chance if you have 4 blades and remove 2 - but thats only a guess.
Going through all the accidents, where a helicopter touched someting with the blade - and knowing how tiny the bolts on the main gear box are - and having had vibrations, only to a lost sctoth tape - one blade off would rip out the gear box in moments.
Greetings Flying Bull

[kiilik]

Hey. I have heard the same story, that a copter crew was shot down in vietnam. They flew with "Killer egg" four bladed, similar to 500. So they removed damage blade and the oposite blade and took off before captured.

Dont know is it true

Regards Kiilik

[ericferret]

I believe that a Bell 205/212 lost a blade in the Philipines, aircraft flying in formation reported that the aircraft had "blown up".


A number of years ago a Hughes 500 was involved in a mid air with a Bell 47(Bristows)
in Kent.

The 47 blade got a bit mangled but the aircraft landed safely.

The 500 lost 9 inches off one blade tip including all the weights and went on to land with no casualties.

The damage to the 500 was substantial due to the vibration.

The instrument console sheared off at the base, and there was little structure left retaining the tailboom. It was possible to move the boom end up and down about 18 inches.
Tough aircraft!!!!!!!!!!!

[Rotating Star]

A rotor sytem with an odd number of blades and missing one of its blades would shake itself to bits well before flight rpm.
With an even number of blades (eg 4), if you remove 2 opposing blades you would need twice the angle of attack on the remaining blades to produce the same amount of lift. Assuming you could raise the lever high enough would the resulting pitch angle cause the blades to stall?
Any deciples of Prowty out there care to enlighten us?

[donut king]

Someone should try it!!!!

[ericferret]

http://www.flying-circus.org/roll%20...on%20unit.html

Someone did
One Tom Wiktorek to be exact.

[NutLoose]

Yes it can be done........................ and THE PROOF to show it, see

http://www.popasmoke.com/visions/image.php?source=4225

[docstone]

I recall a video of a US Super Stallion loosing as blade whilst mid-air refuelling - all seems well until the helo appears to catch up with the refueler and as he tries to compensate the refueling line disconnects and flies upwards taking out at least one blade.

The helicopter certainly doesn't fall out of the air or appear to tear itself apart - quite what happened next isn't covered on the video, hope all walked away (probably with a few hefty dry cleaning bills).

[NLJ]

Ouch!

docstone,

the video I think you are referring to can be seen here:
http://www.youtube.com/watch?v=iyAMC7miuy4
The blades remain intact, but the refuelling probe gets trimmed!

[mechchick]

I would not like to do the vibe run....and I think the 2 pers (well now theres a quandary there wouldnt be any 2 pers with 1 blade missing lol) would just about kill the drivers kidneys!!

Given that the blades cone when under load and the loading is spread across the disc (in a perfect world) I can see that you would lose altitude very quickly (no autos on one blade - you are the deadmans curve then!!)
and it would probably be safe to make the assumption of the flight ending in a large smoking hole...

Dunno I will ask our test pilot what he reckons - I bet I know what his reaction will be F off!!!

[nodrama]

Both a British Army Lynx and a Gazelle, and a Bristow 76 have lost a MR blade in flight in previous years. No survivors. I think to get a helicopter back on the ground and walk away would depend greatly on what stage of flight it happened and on a great amount of luck.

[skadi]

As far as I remember my BO105 groundcourse several years ago, the centrifugal force on one blade at 100% NR is about 10 metric tons!!!
So loosing one complete blade would result in an massive imbalance and total destruction of the dynamic system in a very,very short time .

skadi

[Graviman]

Originally Posted by Rotating Star

Any deciples of Prowty out there care to enlighten us?

Any out of balance would seriously affect fatigue life, and it would not be long before the rotor parts failed. Any unusual vibration is bad - get the machine down.

In theory removing half the blades, if system is still in balance, doubles the blade pitch. This means machine limits are halfed, so any manouvre will stall the blades with a good chance of overtorque on the transmission. Not generally a good idea.

[212man]

Bristow 76

and

in a mid air with a Bell 47(Bristows)

Sadly, one and the same pilot. One of life's true gentlemen

[NickLappos]

The problem with the loss of a large piece of rotating mass is not the loss of lift (most rotors have enough collective pitch to give the remaining blades the angle necessary to make up the lost lift.)

The vast problem is the whirling imbalance, which is usually several times the mass of the helicopter. For a 10,000 lb helo, the blade might have 30,000 lbs of centrifugal force (physics jocks please forgive me) so that the loss of a blade can give you as much as 3 g's of lateral imbalance.

This is not just a pilot shaking problem, it is also a primary structural nightmare. The fuselage usually has a lateral natural frequency of about 3 to 5 Hz. To see this vibration on your helo during your next walk-around, try to shake your helo by grabbing the tail and giving it some tugs laterally. Find the natural frequency by shaking it where it "likes" the frequency and shakes a bit more, like "pumping" a swing to make it get higher. For many helos, this natural fequency is lower than 1 per revolution, so it can be excited by the big imbalance due to the loss of the blade. For larger transports, this frequency is the torsional-lateral tuning of the vertical tail and the tailcone.

If a blade is lost, the shaking can literally tear the aircraft apart, typically by collapsing the tail cone where it attaches to the fuselage. Look at this terrible video carefully, and note how each airframe failed in the same way, at the same place, long before the ground was struck:

http://www.thatvideosite.com/video/868

[Mark Nine]

During my 'Battle Damage Repair' course in the Army, we were told it was possible to saw up to 1 metre off the end of all 4 Lynx main rotor blades if they were damaged.
Knowing what I do about M/R track and balancing, you would have to be spot-on with the measuring of the saw line to prevent a massive unbalance.
Centrifugal pull of one Lynx M/R blade = 55 tons!!!!

[Flying Bull]

Hi Mark Nine,
The Lynx can take it (partly).
There where two near similar incidents, one with two german Navy Lynx and relative short later with two british Lynx, they just didn't belive and had to try themselves ;-)
While doing formation flying - they flew just a little bit to close and touched rotorblades....
On both occasions all helicopters managed to land - the germans on their frigates, the british did it over land - so no deck landing required.
From the german side:
One helicoter lost parts on all four main rotor blades....
the other one had bend edges.
The one with the bend edges had the worst vibrations.
Couple of years later one Lynx lost a part out of one blade - about an meter or so from the point where the folding gear is normally attached.
They decided to ditch and were rescued later.
But prolonged flight isn't recommended ;-)

Greeting Flying Bull

[skadi]

Flying Bull wrote:
The one with the bend edges had the worst vibrations.

I suggest, that in this case the vibrations came from the disturbed aerodynamis ( out of track etc. ) rather than from mechanical imbalance due to different masses. Same reason as for the partly loss of scotch tape .

skadi