Rpm speeds of H-13 and 206

[Dale1937]

Many years ago I used to work on H-13 and H-34s. I know there are other names for them now but that was then.

I can not remember what the acutual rpm of the rotor is at the head as well as the tip of the blades on both the H-13 and the much newer Bell206.

I know many of you folks will have the answer and I might only retain the information for awhile before I forget so I can have the answer in print from you.

Thanks
Dale

[Arm out the window]

I should know the numbers for the 206 - only a year or so since I flew one, but the memory must be going! I think it's about 380.

205 is burnt into my brain - 324 rotor rpm at 6600 N2, about 5 blade revs per second - amazing to think of that weighty gear spinning so fast.

[Um... lifting...]

394 for the B206 variant I once flew.

[Ancient Rotorhead]

Bell206B - 394rrpm.
Bell47 G3B-1 -333 to 370rrpm which is read at 3000 to 3200 erpm

Quoted from the FLIGHT MANUAL

AR

[Agaricus bisporus]

I can not remember what the acutual rpm of the rotor is at the head as well as the tip of the blades on both the H-13 and the much newer Bell206.


Hmm. Not too sure what to make of that question?

[Um... lifting...]

Tip speed on a 206:

Given:

Rotor Diameter: 33'4" = 33.33'
RRPM at 100%: Nr = 394
Useful Constant: pi = 3.14159
Nautical Mile: NM = 6076.12'
Vne for B206: Vne = 122 knots
Mach 1 at Sea Level = 661.5 knots

Rotor circumference = pi * Rotor Diameter ~ 104.7'
(or, as I used to tell my students... 3 * 33 1/3 + a little... call it 105')
Tip speed in hover or on ground = Rotor circumference * Nr ~ 41,255'/min
(or, as I used to tell my students... 105 * a little less than 400... call it 41K'/min)
41,255'/min = 2,475,325'/hr = 407.385 knots
(or, as I used to tell my students... * 60 minutes, divided by 6000'... or divided by 100... call it 410 knots... 400 to make the math easy)

Tip speed in flight = 407.385 +/- Vne
285KTAS < Tip speed in flight < 530KTAS
0.43 Mach < Tip speed in flight < 0.80 Mach
(or, as I used to tell my students... +/- 120 knots... call it 280 to 520... call Mach 1 about 650... it's about M0.4-M0.8)

You should be able to work all those for any helicopter you wish on your own now.
Increases in RRPM, Rotor Diameter, and TAS broaden that tip speed range, which leads to many potential aerodynamic issues, which is why Nr decreases with Rotor Diameter and is partly why blade count tends to increase with Rotor Diameter.

[Dale1937]

Thank you UM Lifting

Very good answer.

Dale

[Dale1937]

Sorry forgot to reply to your statement about the 206 age. You have to remember I was working on helicopters when we still used rubber bands to crank up the rotor. That was over 50 years ago.

At present I have a pretty good set up for helicopter flight sims. 55"tv in combination with 3 montiors plus all controls.
I am a very happy old man.

Thanks again for the reply

Dale