Rotol propeller for Spitfire 1

Yes, I’ve plotted up all the available data into a variety charts to highlight the differences. That leads to a whole lot of questions, especially when you look at that in the light of what was reported as ‘best’. These reports should be objective and unbiased, but……

I would be interested in what you can come up with there.

Ralph, did you notice the variation not just of speed with props in the Spit trials, but also in actual altitude of max speed with t/c, with the same engine and thus same full throttle height? Quite a big thing totally overlooked by the history of such things which only ever looks at engines and supercharging.

Some very odd interpretations came out of the Spitfire II trials. It is frequently said that Rotol were told by the Ministry to concentrate on making wooden blades as a result, no idea where in the performance data that seemed to be the way forward? Especially when it was a metal – bladed Rotol that did the best, even better than the dh in terms of absolute speed. I wonder whether in fact they were told to concentrate on making wooden blades thinner.

It’s a bit tricky but there is logic in it. The system appears to have changed in time, which complicates things. The other complication is that when a blade was serviced, the dimensions of the blade may have had to be changed and so the part number had to change as a result.
I am still looking into it, I think I have enough information now to figure it out.

Thanks

Yes, I did have sight of it about four years ago, at the FAST library. Regarding metal blades, there are some curves that show the effect of reducing tip length on t/c at 0.75r, and from that it is possible to extrapolate a little of the t/c curve for a few production blades. I only took copies of one, the Whirlwind’s 54409.

Did you reach any conclusions about blade drawing number allocation?

Beermat
Have you had access to a report from De Havilland Airscrews

Report R83
AIRSCREW PERFORMANCE CALCULATIONS by K. B. GILLMORE A. V. CLEAVER J. MULLIN, 1941

It references an earlier report, R15, on the subject.

In the history of the report section it advises that Mr F.M. Thomas presented a lecture to the Royal Aeronautical Society on the subject (“Practical Airscrew Performance Calculations”) in October, 1937), there maybe something of interest in that lecture for you. This report supersedes the method as presented in the earlier lecture.

United Aircraft Corporation presented a report of their investigations to industry in 1934, of which there were 20 copies.

While this may not cover Rotol products, there are tables giving details of propellers not put into production, giving details like profile, dimensions and who made the blades. Also giving reference to the aircraft for which they were considered for.

I have only a couple pages from the report as I was looking into how DH designated their propeller part numbers. The details of the blades did not photograph very well as they were printed on glossy photo paper.

I did not realise that for wooden blades, DH went out to various suppliers to have them made. Names like Horden Richmond, Jablo and Airscrew Co. come up.

Do you have better access than me to the National Archives? I’m in North Yorkshire. There are some interesting documents in this list: http://www.enginehistory.org/References/UKNA/Prop-AVIA.shtml

Yes I have that one and data from other R&Ms too but somehow those early metal Rotols are proving very ellusive. I really need that in order to see how much they differ from the DH of the same period. I sense, as you do, that the DH were somewhat different, they most certainly are visually, but without proof its just conjecture. We’ll get there, someone is sitting on the information I’m sure.

Oh, and there’s this – RM 2357

Spitfire I blade is t/c curve III, and there’s a later metal Rotol in there too – Curve IV

[ATTACH=CONFIG]256017[/ATTACH]

..but still no 1938-1940 metal Rotol. The field, as they say, is yours…

Ha – I didn’t mean to suggest that this was the font of all blade data. That came out wrong.

I have spent a several years now trying very many sources for UK blade data. There are copious US sources for the period that include blade design curves showing chord, t/c and twist, but when it comes to metal blades in the UK pre-1940 there’s an extraordinary ‘hole’ in the information.

The best route for me has been the measuring of relic blades – the guys at ARC dx were very helpful there – but only at certain points that enabled me to back up a couple of contentions, including de Havilland copying well documented US designs in some cases. I have nothing on metal Rotols pre 1940, but I am sure they are out there to measure, if only archaeological examples?

The US data, from NACA reports maiinly, does give a good general picture. It seems the Hamilton 6101 is as average a 1939-era blade as it gets.

If you do find anything I would be the keenest volunteer to receive any information – it has been a focus for a long time. I may not have pursued the Rotol avenues as much as DH, so I am sure it’s possible.

Here are some US values – check the h/b curves

[ATTACH=CONFIG]256016[/ATTACH]

Yes I have read your article, M&S and other easily accessible sources, but it is the full spread of t/c across the blade that I am seeking, not just the 0.7 values. Am I working on these lines too? Yes, I kind of got sucked into it.

Have you had a chance to read my TAH article? There’s a lot of t/c-related stuff in there from that period – also there’s some t/c and max speed data in M&S that looks very interesting plotted on a height graph. Are you working on these lines too?

Spitfire DH DP55409B blade, 1940, t/c 7.6% @ 0.7r

Final questions, for Rotol experts
Can anyone provide t/c versus radius data, not just at 0.7 radius, for any of these early forged alloy Rotol props.
RA611
RA621
RA630
RA640
or failing that any representative alloy blade from 1938-1940
Thanks

Hi Ralph! I don’t really do Rotol. Anne might be better.. or Dairwin (spelling)? But if it’s a de Havilland spinny thing question, bring it on!

Hi Matt, I thought you would be along soon 🙂
Yes the 3001700, 3001800 and 3001900 do all appear to be Vickers-Supermarine designs, and it is entirely plausible that Jablo could have made them.
Thanks for pointing out that additional datao on the DH, I’d missed that. The error gets repeated in various sources, unfortunately.
No doubt more questions will come soon.

Ah yes: http://www.woodenpropeller.com/Britishprops.htm

It’s confused by the fact that the same prop assembly might be called Jablo, Rotol Jablo, Supermarine Jablo, or Vickers Jablo. Jablo made the blades, possibly to a Vickers drawing. Of course Rotol only really describes the hub in these cases.

Where it does say Rotol it’s fair to assume it’s not fixed pitch

9.1 is almost certainly a typo that has crept in somewhere. If you look at the figures in the table immediately underneath, it says 0.7 radius on the blade is at 45.22″. This equates to a full radius of 64.6″, and a full diameter of 129.2″ – more or less the standard DH Spitfire I 10′ 9″

Are you sure the 3001700 wasn’t the wooden fixed-pitch prop? M&S call it that, and there’s no indication it was Rotol manufacture – more weight behind the idea that this was just a Vickers designation and no indication of prop characteristics, or even manufacturer.

Cheers,

Matt

For now I will have to assume that the diameter of 10’ 8” given in Morgan & Shacklady is correct, although they do not state whether it refers to 3001700 or 3001800. Also have to assume that 3001700 was used for the performance trials with K9787 but 3001800 was the production standard propeller (thicker t/c and coarser pitch?). 3001900 may have been a compromise between the other two?
Next issue. The transcription of the performance trials of K9783 with a DH 2-pitch, 3-blade, propeller, on http://www.spitfireperformance.com/k9793.html give a diameter of 9.1’. Other tests of MkI and II aircraft with DH propellers do not quote a diameter. 9.1’ seems very low given that the CS conversions appear to be 10’ 9”, as do the Rotol CS 3-blade propellers. Any comments?

Thanks for the Bump Tony.

Having moved on a bit with my search I think, but would be glad for confirmation, that this could be a Vickers-Supermarine drawing number and hence tells us nothing about the prop. characteristics. I suggest this as a related prop. reference says Vickers 3001700

Bump