3-bladed R44 or R66
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Joined: Dec 2003
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From: Melbourne, Australia
3-bladed R44 or R66
After homoculus' comment in the other thread, I was wondering what people would say about a 3-bladed R44 or R66?
Purely from theory, in terms of design, cost, performance/handling, maintenance, safety and effect on engine/transmission? Would it improve them or have a negative impact (apart from cost) on the machines?
Just curious.
Purely from theory, in terms of design, cost, performance/handling, maintenance, safety and effect on engine/transmission? Would it improve them or have a negative impact (apart from cost) on the machines?
Just curious.
Joined: Oct 2004
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From: HLS map - http://goo.gl/maps/3ymt
After homoculus' comment in the other thread, I was wondering what people would say about a 3-bladed R44 or R66?
Purely from theory, in terms of design, cost, performance/handling, maintenance, safety and effect on engine/transmission? Would it improve them or have a negative impact (apart from cost) on the machines?
Just curious.
Purely from theory, in terms of design, cost, performance/handling, maintenance, safety and effect on engine/transmission? Would it improve them or have a negative impact (apart from cost) on the machines?
Just curious.
Joined: Jul 2014
Posts: 446
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From: South East Asia
2 bladed machines have a vibration mode that is mostly vertical (because blade pass the front and back location in tandem at the same time, front and back being where most the lift is generated)
3 blade machines have some lateral vibration moment for that same reason (blade do not pass the high lift azimut in tandem) Therefore 3 blade machine like the astar (AS350) have a mass spring system in the rotor head hub to cancel out that sideways vibration moment
the R44 long rotor mast might be ill equipped to receive
1/ lateral vibration moment
2/ torsional moment of a rigid rotor head
remember an articulated rotor head wants to pull the fuselage in a new direction thus changing the attitude
a rigid rotor head wants to apply moment on the rotor shaft to force the fuselage into a new attitude
Then if you I think about the Enstrom long mast and 3 bladed head, it seems to be technically viable.
3 blade machines have some lateral vibration moment for that same reason (blade do not pass the high lift azimut in tandem) Therefore 3 blade machine like the astar (AS350) have a mass spring system in the rotor head hub to cancel out that sideways vibration moment
the R44 long rotor mast might be ill equipped to receive
1/ lateral vibration moment
2/ torsional moment of a rigid rotor head
remember an articulated rotor head wants to pull the fuselage in a new direction thus changing the attitude
a rigid rotor head wants to apply moment on the rotor shaft to force the fuselage into a new attitude
Then if you I think about the Enstrom long mast and 3 bladed head, it seems to be technically viable.
Joined: Jul 2014
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From: South East Asia
What I was trying to say is that it would not be as easy as putting an additional blade as they did on the H145 going for 4 to 5 blade. and instantly claim another 150Kg of payload.
purely a 3 blade rotor would also be less aerodynamically efficient (more friction drag as well as well as induced drag for the same trust)
It would probably require a brand new design from head to toes, Something we have all hoped the cabri G4 would become, affordable, safe, modern...
purely a 3 blade rotor would also be less aerodynamically efficient (more friction drag as well as well as induced drag for the same trust)
It would probably require a brand new design from head to toes, Something we have all hoped the cabri G4 would become, affordable, safe, modern...
Joined: Sep 2018
Aviation Qualifications: CPL
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From: California
Oh you wanted "informative and interesting"? Well, as much as I love flying the 22, I have to admit that Robbies are simply the answer to the question, what if you took a homebuilt and made it certified?
As such the Robinson philosophy has always been light weight = more affordable. Add another blade = more weight = more expensive. Not to mention Frank's original vision of people using his design to commute to work,...and you can't park your chopper in between two cars (like the picture they show at the Safety Course) if you have more than two blades.
Besides, they're not going to redesigned the entire helicopter to handle one more blade just for those out there who aren't "comfy" flying with just two blades!
,...just like the rest of the industry isn't going to stop making or using singles just to satisfy the, "never fly anything but a twin" crowd!
As such the Robinson philosophy has always been light weight = more affordable. Add another blade = more weight = more expensive. Not to mention Frank's original vision of people using his design to commute to work,...and you can't park your chopper in between two cars (like the picture they show at the Safety Course) if you have more than two blades.
Besides, they're not going to redesigned the entire helicopter to handle one more blade just for those out there who aren't "comfy" flying with just two blades!
,...just like the rest of the industry isn't going to stop making or using singles just to satisfy the, "never fly anything but a twin" crowd!
Joined: Apr 2010
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From: USA
The other issue is that the Cabri requires 20 or so additional continuous horsepower from the engine compared to the R22 Beta II to obtain the performance that it does. So the derating cannot be as conservative in the G2.
Thus in a putative 3-bladed R44 one might expect to seen HIGE, and possible HOGE, performance fall off, and engine derating changed to a less conservative value.
Of course the real issue is cost, which will rise by a factor of 1.5 for both capital and operating, but you didn't want to discuss that
Joined: Oct 2024
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From: Roanoke Virginia
What I was trying to say is that it would not be as easy as putting an additional blade as they did on the H145 going for 4 to 5 blade. and instantly claim another 150Kg of payload.
purely a 3 blade rotor would also be less aerodynamically efficient (more friction drag as well as well as induced drag for the same trust)
It would probably require a brand new design from head to toes, Something we have all hoped the cabri G4 would become, affordable, safe, modern...
purely a 3 blade rotor would also be less aerodynamically efficient (more friction drag as well as well as induced drag for the same trust)
It would probably require a brand new design from head to toes, Something we have all hoped the cabri G4 would become, affordable, safe, modern...
Joined: Sep 2002
Aviation Qualifications: CPL
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From: Great South East, tired and retired
front and back being where most the lift is generated
The retreating blade tries its hardest to create enough lift, battling the wind from behind.. The advancing blade has to throw away all that beautiful lift it gets from moving into the extra airflow. The only place where the fight is equal is fore/aft.
Joined: Oct 2024
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From: Roanoke Virginia
You might find that the lift is constant all the way around. If you suddenly got more lift when the blades are fore/aft, the vertical vibration would be awful.
The retreating blade tries its hardest to create enough lift, battling the wind from behind.. The advancing blade has to throw away all that beautiful lift it gets from moving into the extra airflow. The only place where the fight is equal is fore/aft.
The retreating blade tries its hardest to create enough lift, battling the wind from behind.. The advancing blade has to throw away all that beautiful lift it gets from moving into the extra airflow. The only place where the fight is equal is fore/aft.
The only downside to having more blades is cost.
More blades means you can make the blades with reduced chord and shorter and at reduced RPM.
Noise is generally lower with more blades.
The Osprey for example really could use more blades as increasing the blade chord would make the already bad vibration worse! Engineers have compensated by increasing the tip speed.. on the Osprey it's 559 mph!
In forward flight every time the blade passes in front of the wing the whole aircraft jumps!
Joined: Jul 2014
Posts: 446
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From: South East Asia
You might find that the lift is constant all the way around. If you suddenly got more lift when the blades are fore/aft, the vertical vibration would be awful.
The retreating blade tries its hardest to create enough lift, battling the wind from behind.. The advancing blade has to throw away all that beautiful lift it gets from moving into the extra airflow. The only place where the fight is equal is fore/aft.
The retreating blade tries its hardest to create enough lift, battling the wind from behind.. The advancing blade has to throw away all that beautiful lift it gets from moving into the extra airflow. The only place where the fight is equal is fore/aft.
Joined: Jul 2014
Posts: 446
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From: South East Asia
Robinson is now working on a multi-blade model
The only downside to having more blades is cost.
More blades means you can make the blades with reduced chord and shorter and at reduced RPM.
Noise is generally lower with more blades.
The Osprey for example really could use more blades as increasing the blade chord would make the already bad vibration worse! Engineers have compensated by increasing the tip speed.. on the Osprey it's 559 mph!
In forward flight every time the blade passes in front of the wing the whole aircraft jumps!
The only downside to having more blades is cost.
More blades means you can make the blades with reduced chord and shorter and at reduced RPM.
Noise is generally lower with more blades.
The Osprey for example really could use more blades as increasing the blade chord would make the already bad vibration worse! Engineers have compensated by increasing the tip speed.. on the Osprey it's 559 mph!
In forward flight every time the blade passes in front of the wing the whole aircraft jumps!
R44 1089Kg 225hp 4.8Kg/hp
EC120 1715Kg 504hp 3.4Kg/hp
H500 1610Kg 425hp 3.8kg/hp
So even with the benefit of the lightweight turbine engine and a heavier airframe nobody come close to the weight carrying capability of the R44 per hp.
You bring a good subject, the drivers have changed, look at Archer aviation and Joby, their creative design make you think about blades differently, aiming for different drivers (noise)
Joined: Nov 2007
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From: Munich, Germany
If I'm not mistaken, with a three-bladed rotor you can get ground resonance, which is not an issue in an R22/R44. So in addition to a completely new rotor head, the Robinson would also need appropriate dampening means, e.g. in the landing gear. All of which would lead to a rather more complex aircraft.
Joined: Nov 2000
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From: White Waltham, Prestwick & Calgary
You don't automatically get GR with more rotor blades, it's whether they have drag dampers or not. Actually, the teetering head is the most susceptible to ground resonance as a design.
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From: Poplar Grove, IL, USA