phil wrote:
Would seamless pipe (4130) be a proper "tube type" material to use
for a shaft turning max 2000 RPM @ 200hp, 300 hp max? The ends need to
be splined to slip onto a gear.
If seemless pipe won't work, what might do the trick? It must be
hollow because I need to run a tube through it.
Dimensions are everything. Do you have a sketch?
What RPM is the engine generating 300 HP? Also what type of engine?
Four cylinder piston engines at 200 HP have much worse torque
pulses than 2 rotors or a six cylinder piston engine.
What is on the end of the shaft?
Paul Lamar
Since no one answered, I'll give my two cents:
1. I would suggest to use seamless mechanical tubing of near
90,000 - 110,000 psi tensile or higher, such as 1340, 3140, 4140, 4340, etc.
Even 1050 or 1060 might do. The higher steels are better against corrosion.
Do not use "pipe" per ASTM specs.
2. A quick calculation at 8000 psi stress and 300 hp shows that
you need about 19,400 mm3 polar section modulus Zp.
Suitable tubing is 2.5 in OD with 1/4 in wall (29,600 mm3),
or 3 in OD with 3/16 in wall (35,800 mm3)
Using a spline at the ends makes the 1/4 wall better suited.
A 3" OD Tube with 1/4" wall has 44,900 mm3 which might be overkill.
This is of course a rough calc for a reasonably short shaft, without
any consideration for vibrations and assuming a fairly even torque.
Instead of steel you may want to use seamless Alu-tubing that is lighter.
I am not sure what stress is used for Aluminium. Perhaps 4000 psi for 6061 T6
or of the 7 series Al. With Al the polar moment should be near 40,000 mm3.
A 4" tube with 1/4 wall has ~85,000 mm3. Quite safe.
A 4" tube with 3/16" wall is ~67,000 mm3.
No responsibility, of course, just a suggestion of the approximate size
required.
Rolf Pfeiffer
I can see I'm way over my head here. :) But it's a learning experiance
at the least.
I'll assume aluminum would be an easier material to learn with. Within
the next 6 months, I want to buy a lathe and small mill. I've seen a 3
in 1 mill in kitplanes that is CNC ready but the lathe is a bit short
for long term goals. I've been looking at a few Grizzly models that
won't bust the bank also(G3617 horizontal/vertical mill for $3000.00 and
the G4016 lathe for $2700.00).
My little "Evans Handbook" has charts up to 3" inch tubing, with a wall
thickness no greater than .250". I'm guessing I'll need something closer
to .500" at the least.
Can I turn pipe down so I have a shoulder for a bearing to come up
against to transfer the load? I have a very rough drawing I'll send. I
have no ideal on where to place the bearing properly, so I just guessed.
I'm open for any suggestions. :)
Max weight of aircraft would be about 2000 lb. I'm doing some rough
rounding, 500lb. passengers & "extras", 500lb of engines (two 13b's,
most likely turbocharged) 500 lbs of fuel and 500 misc for frame etc.
Very rough but at 2000 I'd still have only 10 lb per HP on one engine
(assuming 200 hp per engine).
Anyhow, attached is a sketch of the mast.
You are way over my head too. You need help from an experienced
helicopter design engineer. These things are not trivial.
Paul Lamar
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