3-bladed R44 or R66

[Tickle]

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.

[Aucky]

Originally Posted by Tickle

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.

An Enstrom?

[Agile]

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.

[md 600 driver]

Surely. The first thing that Robinson has to do is learn to make a blade that lasts before starting to make a heli with 3 on it

[Agile]

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...

[Robbiee]

Totally unnecessary, and a complete waste of time and money!

[Bell_ringer]

3 blades? Why? Do Robbie owners want a 50% greater chance of chopping off the tail?

[Tickle]

Thanks, Agile, for the informative and interesting explanation.

[Robbiee]

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!

[aa777888]

Originally Posted by Tickle

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?

Comparing the R22 Beta II and the Cabri G2 is a very reasonable example of what might happen. They both use essentially the same engine. First we need to compare performance at an equivalent weight. The limiting factor here is the R22, which at full fuel (168 lbs) can hold 300lbs of people, so say 468lbs total. This would put the Cabri at approx. 1400 lbs equivalent (it can hold a lot more fuel). Looking at the POH for both machines, many of the performance parameters seem nearly equivalent, e.g. cruise speed, etc. However HIGE really falls off in the G2. HIGE is 9500ft in the R22 vs. 7000 in the G2 (standard day).

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

[500e]

Surely a percentage of that Hp is to compensate foe the Fenestron deficiency

[Bell_ringer]

If my maths adds up, the G2 is also 100lbs heavier overall.