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[tonyH]

Current project calls for a 1/35 version of a single prop following the, if possible, Admiralty original spec which was 9ft 6inch diameter, 11ft 1.5 inch pitch and 35.25 sq ft. surface area.
This was a 1910 ish vessel with a single engine running at 500 revs aprox max. 


I've assumed 4blades and the pitch works out at about 1:1.2 but what is the area? It isn't the area of the circle described so is it the total surface area of the 4 blades or something else?


Off the shelf props tend to be either (a) 1:1 ratio for the standard props or (b) 1:1.5 for steam so does anyone know of a 80mm prop with a 1:1.2 ratio?
If not, and I have to follow the bespoke route, what does the 35.25 sq ft relate to because it will have a major bearing on the design?


Cheers
Tony

[Colin Bishop]

Apart from the appearance of the prop I'm not sure why you think the design is so critical on a scale model as the amount of thrust can easily be varied by the battery voltage, motor speed and, if necessary, gearing.
You don't say how big the model is but a prop of that sort of diameter would probably need gearing if fitted to an electrically driven model - or are you building a steam powered one?
Colin

[tonyH]

Nothing critical about it but I was trying to see if the surface area, if it related to the cumulative area of the blades, would correspond with the a,b,c,d e etc types on offer from Protean or Raboesch. Since the a,b,c,d etc. types tend to have either a 1:1 ratio as near as dammit, or 1:1.5 for steam, the 1:1.2 ratio of the original, combined with the surface area, must have had a reason for existence.
The model is 45" long with a 25lb displacement and I'm planning on using an old 850 7-pole which has a rev rating of 5000rpm at 12volts and ample torque, only some of which will be required.


Tony

[Netleyned]

A different answer if the Hull is a 45in Warship or 45in Tug. The spec for the 1/1 version sailed in the same scale water as the model.
Would not have thought blade area and pitch
Could be scaled exactly.
Ned

[tonyH]

Tug type displacement hull but what I thought from the original spec was that, judging from the figures, it was that the blades were rather large for the relatively low pitch angle and the revs of the engine.