Not arguing that, just noting the effect. Fatter blades actually were generally better until you hit critical Mach, which you do early with fat blades. This test aircraft comfortably outperformed DH-equiped Spitfires, up to a certain height. What do you reckon these were – 9% Clark-Y?

By the way, Ralph, did you notice this line in the Martlesham trials of a Spit with the thick wooden Rotols?:

“The results show that the maximum level speed is reached with the airscrew controlling at 2800 engine r.p.m. On increasing the r.p.m. to 3000 the speed was reduced, on the average by 4 m.p.h”. Similar effect to the Manchester..

Ok, so I am now confident that all de Havilland bracket-type, 5,000 series are of the basic shape equivalent to the Hamilton Standard 6105. This is contrary to an earlier post by me, for which apologies. I could show my workings but it would be tedious..

What threw me was the differing profile of the Spitfire’s blades, appearing to belong to a different sub-series from the longer blade variants of the 5,000 series. This was because they were telescoped, not just truncated – as was the practice when shortening blades beyond 6 inches. De Havilland gave them a different ‘full pattern’ length, upsetting the numbering sequence and confusing everybody for 80 years. What they had done was extrapolate backwards to create a virtual pattern blade which is what the telescoped blade would look like if the Spitfire blade was indeed a truncated version of a design and measured back from there! If you have just followed that the first time then you deserve a Nobel prize. My head hurts.

The clue was here.. from NACA report 3G26, 1943. Note the 6353 as per Lancaster blade, for which we have a table, has the same profile (profile is indicated by Activity Factor, a mathematical descriptor of geometry – if it varies in the same way with length, it’s the same profile)

[ATTACH=CONFIG]256211[/ATTACH]

So there we have it – an American pattern blade for very many types of British aircraft carrying de Havilland blades. Of course, P&P has the inner half of a Battle blade, that’s good to go. The outer part.. well, at the moment there are some thick-line-drawn graphs in an RAE R&M of the Spitfire blade which one can mathematically de-telescope to 13′ diameter from 10’9″ (cropped from 11’6″). I’ve done that, it seems to fit.

And then there is the ‘Lancaster’ blade table, which matches the extrapolated 5,000 series despite being Hydromatic EXCEPT for a peculiar and very large ‘bump’ in the thickness to chord curve, which I am trying to understand.

P&P – Had a nice pinot noir last night – In a funny way it helps with this insane pastime.

Seriously, it would be nice to set up a simple blade blank production and a programmable CNC , to produce blades to order both for authenticity and optimisation of performance. The two might even be the same thing, it seems folk knew (or at least cared) more then than they do now.

For example, there is a Spitfire I currently flying with a cut down Battle prop. Half-right, they were from the same blank (more on this later) – but the twist is far from optimal. My guess is it accelerates well, but struggles to meet the speeds ‘in the book’.

I will come up with my thoughts on production, and what shared common origins and what was a fresh design, in a bit. It seems it’s a lot simpler than it first appears.

HS blade numbers – they do seem to be sequential, not relating to anything about form. Still, one can work out the sequence of adaptions of basic designs from the numbers – so for example a 6105 is a cut-down 6103 (these are immediately consecutive, odd number meant right hand).

There is one match – the ‘H’ in DH6353A stands for ‘Hamilton’ – and it’s also the DP455800 blade, as per Lancaster. This is a basic blade shape for the 55,000 series, a major clue! I think I have found the US equivalent for the basic shape for the 5,000 bracket series as well.. working on it.

Regarding the numbers – thanks for those! Just what’s needed.

DP4551172TA and CP4551778TA both fit in as a continuations of the table, which is satisfying! The ‘T’ would stand for ‘telescoped’ – ie. blade shape changed to accommodate severe truncation.

456xxx is a whole new range to me, at 16ft. What was that for? Something 4-bladed, 6-spline, E-shank?? (oddly the 3-blade 6-spline E-shanks were numbered ‘455’ like the 5-spline ones, relying on the difference in lengths to distinguish them).

It’s all done with blade design curves, TT. You just need to know the variation of five things along the blade axis – chord, thickness/chord, angle, face alignment and edge alignment. You also need to know the aerofoil type used and the shank type.

As a starter for 10, here’s a Lancaster ‘needle’ blade, expressed as a table in its US equivalent, and minus the last 6 inches! You can safely assume this has a Clark-Y section.

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I am working on the others, but as this is where real value kicks in I might just hang fire on publishing any new tables (this one already existed) just yet!!

As promised, here’s part two, Hydromatics. Clocks, what do you have on the wooden props?

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This note totally overlooks the different propellers:

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