Author Topic: Another turn on a proper prop  (Read 460 times)

Offline Doug Mace

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Another turn on a proper prop
« on: July 13, 2018, 11:17:31 AM »
(Pun intended)....I'd like to stir a pot inre SE5 props ( if it hasn't been stirred before) in the choice of 2 or 4 blades. I saw a very interesting thread provoking a series of well informed posts some while back over at the good ol' Aerodrome on the matter but haven't bothered trying to find it since so thought I'd toss it out here to our learned, gracious society (if it hasn't been tossed out before)....pretty much all I recall taking away from said Aerodrome post is that a slight majority of SE fliers preferred a two blade screw because four blades created a bit too much torque for an SE, what with it's smaller wing span etc and therefore making it that much more arduous to fly. And of course, being as how I've seen millions of photos of SE's in millions of books,  it's maybe....maybe?.....clear that 2 bladed machines maybe outnumbered 4 blades....maybe? So was it a personal choice by pilots? A squadron choice? A Wing choice? Or were personally requested props ordered from the factory? Unlikely, that, but it seems as though someone was making such a decision on some level. Or was it catch as catch can....they flew what they sent them via Candas? I only ask because it's time I built my WNW SE and need a nudge one way or the other. Ooh,ooh, and then there's Biff props and...oh, never mind.       -M
" 'One man's owl is another man's nightingale!' says the Rittmeister ".  - Lt Karl Bodenschatz, March 21, 1918

Offline Black Max 72

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Re: Another turn on a proper prop
« Reply #1 on: July 13, 2018, 12:13:28 PM »
I too would be interested, not just for the SE5, but in general what were the pros/cons of 2 blade vs 4 blade. Would they have required much more work to produce than a 2 blade (I'm thinking in terms of accuracy and balance) Just from looking at pictures it appear that a 4 blade prop is the same diameter as a 2 blade, would that then work out to be twice the weight? They would be damn heavy given the woods they were made out of! What effect would that then have on engine revs available? I would imagine that at twice the weight it would have to have had some effect on engine power, if so what benefit would be gained (in a power/thrust/weight sense) from a slower turning 4 blade prop? And then as you put in Doug, a 4 blade would have to produce more torque. Also did it have any negligible effect on the rate of fire from a synchronised machine gun, slower, faster? hmm
A very thought provoking thread indeed.

Dave Rickard
Rockhampton QLD

Offline Dave in Dubai

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Re: Another turn on a proper prop
« Reply #2 on: July 14, 2018, 06:19:44 PM »
An interesting discussion and a couple of thoughts pros v cons.....

If you add another two blades then you now have four blades or two more lift forces to the overall thrust vector which is providing the axial force to move the aircraft. The blades are essentially the medium by which chemical energy ( the fuel) is in turn converted into mechanical energy and thence thrust via the engine and propeller combination.

 With the four bladed propeller being a large spinning mass, generating thrust, then the gyrocopic effects were certainly greater than a two blader, controllability effects would certainly be more challenging on an aircraft with a small polar mass moment of inertia such as an SE-5/a. This may have been a desirable trait though as it would be a more manouvreable aircraft in the right hands.

For sure a four bladed propeller is a more difficult  proposition than a two bladed prop, nevertheless propeller production was a large scale enterprise and was highly refined and advanced given the materials and manufacturing capabilities of the day.

Bob Gardner has written a series of very well written ,illustrated and researched volumes on British and German WW1 propeller design and manufacture for anyone who is interested to read more? His books are the definitive work on the subject.

Manufacturing a wooden 4 blader in 1/32 could be a challenge.

Offline macsporran

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Re: Another turn on a proper prop
« Reply #3 on: July 14, 2018, 07:07:32 PM »
Albatros Publications do a volume entitled WWI British Propellers which I admit to not having bought. Perhaps this might shed the light you seek?
Ray might let you know if it deals with the physics etc, rather than purely manufacture. It's a fairly modest cost anyway.

Offline gbrivio

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Re: Another turn on a proper prop
« Reply #4 on: July 14, 2018, 10:58:04 PM »
I don't know the actual reasons of choice, but a four bladed propeller has lower vibrations and it's easyer to balance (despite having twice the blades). Furthermore each of the blades receive half the power of the two bladed. Less vibrations means longer engine life, less power per blade means longer propeller life. Higher torque was probably not a concern in the rotary engines era...
Just my point of wiew.