BeermatI don’t understand how ‘RP’ is ‘speaking properly’. It is an accent, and a lot of the mangled vowels you hear in pre-war broadcasting are a legacy of an attempt to ape the curious speech patterns of the English upper aristocracy among the aspirant middle classes. The accent thus ‘received’ by generations of public school kids (I don’t think it still is taught)? is in fact heavily German-influenced, overlaid on Norman French, if you care to go back far enough. But then so many of our regional accents are, as John pointed out with the example of Geordie.
I think the BBC edict, both on accents and the airing of alternative political viewpoints, was an attempt to do the ‘All in it together’ ‘call me Dave’ thing, to head off rumblings of being led into total war by our upper classes – which were gathering momentum. I am sure there were elements who feared some kind of uprising. Now, wasn’t this the department George Orwell was working in at the time? Interesting stuff.
Edit – no, I checked – Orwell joined the Eastern Service, but with a similar remit in that the aim was to prevent the colonies taking the opportunity to rise against Empire.
He was also writing “The Lion and the Unicorn: Socialism and the English Genius” at the time – I haven’t read it, but I suspect you’d love it, JG.
BeermatAlthough I believe Petter had already decided on DH, with specific reference to CS as opposed to 2-position VP there is a document dated June 5th 1939 from the AM DTD, ‘Specification of Specific Requirements to Accompany the Contract Agreement’, which on Page 3 states ‘Airscrews – De Havilland Hamilton Standard Constant Speed Airscrews will be fitted’. It doesn’t call this an ‘Alteration’
Certainly there was no 2-pitch controller on production aircraft.
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BeermatHere’s the closest image of the Rotol blades I can find.
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BeermatTo be fair, the second prototype L6845 with the Rotols didn’t fly until late 1939. I’d need to check this, but I seem to recall propeller delivery was one of the delaying factors. As far as I know the Rotols were always CS, and it was L6844’s DH’s that were initially 2 position VP but very quickly given CSU’s.
The info about the Rotol blades being mag alloy is interesting.. I had made a wrong assumption based on vague knowledge of later Rotol blades.
BeermatI will find out. In the meantime, it might be worth noting the minimum fine pitch of the DH blades was 28 degrees (might be a factor in modelling the blades response to compressibility drag). Also note the (asymmetric) ram air effect on intake pressures – if you are looking at a complete model?
We have a lot of design data, (in the form of CAD) if you need it – it sounds like you are doing something quite sophisticated, if blade construction is a variable? Would carb and radiator intake design be useful, bearing in mind intake volumes (and thus boost) may have varied with blade efficiency, due to their positioning?
BeermatBlimey! Umm… the DH’s were standard forged aluminium alloy, machined from standard blanks to a profile. Same manufacturing process for Spit and WW (by the way, have you seen my DH bracket prop blade number decoding chart)? Not hollow as such, but with a tapered cavity at the root end to accommodate the spider leg. Trimmed 4.5″ per blade at tip from the ‘pattern length’.. stop me if you know this stuff?
Don’t know about the Rotols. Maybe Dural, but probably laminated compressed/processed wood. There are people on here who could tell you – it hasn’t really come up for me before.
BeermatFunnily enough the first prototype had handed De-H’s, and the second, the one that went for testing at Martlesham, had similarly-rotating (non handed) Rotols. A decision had been made by then that non-handed props would be the production standard, and this was why this aircraft was chosen as the official test example, even though it had different blades to those chosen for production.
Agreed about the computer modelling.. a challenge, though.
BeermatOh yes, I’d forgotten 378, and I hadn’t noticed that statement about thickness in the conclusion before.
Of course, this doesn’t touch on the effect of compressible flow – but then it was 1930! I think it took a new type of tunnel, the one detailed in 463, before such high-speed effects could be measured.
By the way, thanks for taking this on – it’s the kind of feedback/review I need.
BeermatNo, the significance is in the altitudes as much as the speeds. Picture the curves. The engine was the same, that’s the point of that bit. It was an attempt to measure propeller efficiencies, all else being equal (beyond unavoidable temps and moisture)
BeermatYes, gearing remained the same, and the recommended +9 was always used in the examples I have (though +12 was possible with 100 octane)
I got tip speeds @ 220mph TAS in the climb of 537mph, or Mach 0.78. At 0.7 radius, where t/c is 9.6%, this drops to 405 mph, Mach .59
Crucially, at 0.9 radius, where t/c is still 8.5%, I get 489 mph, or Mach 0.7. The curves in NACA TR 463 show that this is where the significant drag rises start, at 8% t/c.
..and that’s at minimum drag, not accounting for any angle of attack outside of that.
In level flight, 350 mph, I got tip speeds of Mach 0.88 at 17,000ft
Unfortunately I have nothing for the Rotol – though I guess it could be calculated for a hypothetical 9% Clark Y profile using known Rotol curves. That same TR shows this might start encountering drag rise significantly later, around Mach 0.775, at wherever 8% t/c lies.
All good fun.
BeermatSo according to the various files we have from the National Archive, Prototype L6845, with the Rotols, was climbed by Martlesham at both 2,850 and 2,840 RPM. I can’t find it climbing at 3,000 RPM, but this was the max level flight setting used for speed trials.
During cooling trials production WW P6997 with DH blades was also climbed at 2,850, and this agrees with the Pilot’s Notes, as does 3,000 RPM for all out max.
The Peregrine was geared at 0.477:1, so 2,850 engine RPM equates to 1,340 prop RPM. I have been down this route, and worked out tip speed rotationally and then combined it with forward speed using trig. Then I plotted speed relative to critical Mach along the blade for various altitudes and forward speeds taken from the climbing trials. You’ll need these.
The only problem we have is we only have proper data from Rotol equipped climbing trials, where the aircraft was probably going faster than it might have with DH blades. The DH data was from bomb-carrying trials, so we loose the ‘like with like’ element.
Of course, whatever the source the results will only ever show the blade coming up to a marginal state, as once a point on the drag curve was reached the aircraft wouldn’t then go any faster!
You’ll also need an estimate of the blade’s angle of attack (and be aware that it is different on up-going and down-going blades, as is absolute velocity) Please then consider how compressibility might affect the behaviour of a constant speed unit, when extra drag is poured on, and thus the angle of attack of the blade might change. Not to mention the effect of ‘Mach tuck’ on the blade. Angle of attack affects the drag of a blade in the compressibility zone in a complicated feedback mechanism… It suddenly gets complicated! Good luck. My brain almost melted getting to this point.
Hopefully what comes out the other end will show the problems kicking in at the heights in question – it did with me.
BeermatSounds like you’re doing some maths there!
The props were of course geared. Give me a mo, and I’ll come up with the figures.
BeermatHi Tony
Have a word with our Matt Painter, and/or Gunnar O.. Do you want me to PM Matt’s email?
Cheers,
Matt
BeermatOne NACA exploration of RAF and Clark sections at high speeds is here – http://naca.central.cranfield.ac.uk/reports/1934/naca-report-463.pdf
Blade curves for ‘our’ 54409, and some thickness curves for other contemporary blades, from ARC R&M 2357 “24-ft. Tunnel Tests on a Rotol Wooden Spitfire Propeller” – A.B. Haines 1942
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The Rotol prop under test in the latter was described as Clark Y along most of its length.
BeermatSo was the RAF6 used on the DH blades. This was the problem.
I read in a NACA test report paper from 1936 that the Clark Y (sorry about the misspelling) did prove superior to the RAF6 at critical speeds, and the author of the report said it was probably due to the effective camber difference due to the relative leading edge positions. But I agree, neither were designed with such things in mind. The trouble was, both were widely used in propeller design right up until the 1940’s when critical Mach was being frequently exceeded.
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