Extra blade
Joined: Nov 2003
Posts: 185
Likes: 0
Ricky,
That's a very good question.
You are right to think that the 'lift' would increase with an extra blade...it makes sense doesn't it? Extra airfoil, extra lift....
....but lift is different to 'performance', so it is not as simple as that.
Adding an extra blade means that there is also added weight and drag.
That needs a bigger engine to turn the blades and provide the power to create enough lift to pick up the extra weight.
Also, the 2-bladed (tetering head) is a special design which is quite light weight. Once you go to three or more blades the rotor hub (head) gets more complicated, also adding weight.
I suppose for a small helicopter such as the R22, the 'performance' economics do not warrent the extra blade.
You can see helicopters with more blades, but they generally have bigger engines, and really need the extra lift.
I hope this is the sort of answer you were looking for!
(I tried to be gentle!)
cl12pv2s
That's a very good question.
You are right to think that the 'lift' would increase with an extra blade...it makes sense doesn't it? Extra airfoil, extra lift....
....but lift is different to 'performance', so it is not as simple as that.
Adding an extra blade means that there is also added weight and drag.
That needs a bigger engine to turn the blades and provide the power to create enough lift to pick up the extra weight.
Also, the 2-bladed (tetering head) is a special design which is quite light weight. Once you go to three or more blades the rotor hub (head) gets more complicated, also adding weight.
I suppose for a small helicopter such as the R22, the 'performance' economics do not warrent the extra blade.
You can see helicopters with more blades, but they generally have bigger engines, and really need the extra lift.
I hope this is the sort of answer you were looking for!
(I tried to be gentle!)
cl12pv2s
Joined: Mar 2003
Posts: 813
Likes: 2
From: the hills of halton
I remember seeing a trade off study many years ago on benefits of going from 4 to 5 blades , as I recall it was marginal benefit . Now here's a question is there a benefit in having odd number of main blades and even number of tail blades or vice versa ?
Joined: Oct 2002
Posts: 1,796
Likes: 1
From: 1 Dunghill Mansions, Putney
A couple of years ago, Rinke was offering its JAG 233 with 3, 4, 5, 6, 7 or 8 blades (see here). Don't know whether the concept was ever proven, but it raised a few eyebrows.
Then there was Sikorsky's 'fly-it-home' 3-blade configuration for the CH-53, test-flown in '72: see 3-blade Sea Stallion.
I/C
Then there was Sikorsky's 'fly-it-home' 3-blade configuration for the CH-53, test-flown in '72: see 3-blade Sea Stallion.
I/C
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
Actually, the lift would reduce, and the power needed would rise noticibly if you added an extra blade onto most helicopters. The total thrust (lift) that could be produced would be theoretically greater, if you pulled the helo into a stall condition, but in normal hover and forward flight, the extra blade would actually cost you performance Why?
1) The blade would give you too much area, so that the net angle of attack would drop, and the blades would operate below best efficiency
2) The extra blade and its attachment hardware, and the extra meat on the swashplate all weigh more, so that it robs payload.
3) The extra blade has its own parasite drag, so it eats engine power just to spin it around, while not producing any more lift (except near stall, a long way away from normal flight).
That doesn't mean that 3 blades is worse than 2 blades, it means that when a helo is designed for 2 blades adding an extra blade is worse than leaving things alone. In fact, if you removed a blade from most helicopters, the hover performance would go up (the lift per horsepower would increase). But because you had less blade area, you would encounter stall earlier, at lower speed and lower altitude, so that speed and range would suffer.
1) The blade would give you too much area, so that the net angle of attack would drop, and the blades would operate below best efficiency
2) The extra blade and its attachment hardware, and the extra meat on the swashplate all weigh more, so that it robs payload.
3) The extra blade has its own parasite drag, so it eats engine power just to spin it around, while not producing any more lift (except near stall, a long way away from normal flight).
That doesn't mean that 3 blades is worse than 2 blades, it means that when a helo is designed for 2 blades adding an extra blade is worse than leaving things alone. In fact, if you removed a blade from most helicopters, the hover performance would go up (the lift per horsepower would increase). But because you had less blade area, you would encounter stall earlier, at lower speed and lower altitude, so that speed and range would suffer.
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
No SASless, they switched from 2 fat blades to 4 skinny blades, so the change was quite OK, especially when the four skinny ones had good airfoils, unlike the ancient airfoils on the 212. The Question asked here was about adding an extra blade, not swapping all the blades for a whole new set.
Joined: Feb 2002
Posts: 364
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From: Just over there....no there.
Don't laugh too hard, the Russians built a one bladed helicopter that actually flew! Looked a bit like a Mil 10 and had a counter-weight in place of the other blade. The blades chord was huge 
Rick
Rick
Combine Operations
Joined: May 2005
Posts: 687
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From: U.K.
Yes, I've seen a small number of experimental helicopters with one main blade and one tail rotor blade. I understand they all flew reasonably successfully. I suspect with a pretty vicious 1:1, though.
Joined: Mar 2003
Posts: 813
Likes: 2
From: the hills of halton
