BeermatDouglas Adams would have loved this.
The answer is…. 42
Will explain shortly.
BeermatMight there possibly be a bit of confusion creeping in from the fact that many aircraft went ‘on charge’ with 43 Group after salvage and before being S.O.C. or otherwise disposed of? Perhaps this happened to this aircraft, and it was on the movement card as sometimes happened? It does appear, from another site, to have been held for a time after diving into the ground for ‘stores and scrappage’ – which was most unusual.
BeermatJust to say, though, that I have the 55100 sub-series at 0.7 radius angled for flat distribution at 25 degrees and with efficiency optimised for 170 mph with a Wright Cyclone on 16/11 ratio (the cruise of the DC-1 for which it was designed). It also worked for a Pegasus-engined Empire ‘boat at 150 mph.
By extrapolation it looks like 60 mph increments, such that a 55200 sub-series blade would be ‘flat’ at 31 degrees at 0.7, optimum efficiency meant for 230 mph, intended max speed of a Roc. 55300 is an unknown, but probably 38 degrees intended for a 290 mph optimum (with a Merlin on standard reduction, for example).
All of this is wrong in that this happened without understanding the ’15 degrees-off’ rule from 1938.
Do that, and a Lancaster – say optimised for 230 mph cruise – would be a 200. Old system would put it at 31 degrees. New system would have it at 31-15= 16 degrees, at 0.7r. HS130B table has the 6353 as.. 16.8 degrees at 0.7r.
Not bad. Not bad at all.
BeermatSo, Goshawk = evaporatively-cooled Kestrel, Peregrine = downdraft – oops, downdraught Kestrel?
I’ll do some diagrams at some point – I want to check the maths first – or even better get Trak-tor to do it!
BeermatPropeller theory yes – https://babel.hathitrust.org/cgi/pt?id=uc1.$b80327 is one of them, also try Aircraft Propeller Design (New York and London: McGraw-Hill Book Co. 1930), by Fred E. Weick, which is also available online. They both get into pretty heavy maths, but are useful to check a lot of the web-based info against.
What blades DH and Hamilton actually made and why – no. Not yet, anyway 🙂
BeermatBack on topic (ish).. I have had a bit of a lightbulb moment which I should have had a week ago. The Hamilton Standard tables that I have talk of a reference station – normally at 42″. The angle at this station is the angle at which the pitch change with distance is constant along the blade – ie. a flat distribution. This is the angle at 42″ which would enable butter-cutting (but as above isn’t the best angle for air-cutting, as it turns out).
So, the 6353 seems to have a ‘reference angle’ of 19.9 degrees.
I couldn’t work out why HS didn’t just use the UK method of putting a zero at 0.7 radius, and working back from there. I realise now that this doesn’t tell you enough about the geometry of the blade without complex maths, while the US version puts it on a plate.
Doing the complex maths (actually not, cheating by drawing it on a piece of paper) shows the Spit blade has a reference angle at 0.7 radius (about 48 inches) of 25 degrees inboard and 15 degrees outboard – it has two foci. This is because DH twisted it when they telescoped it. The average is around 20 degrees – which works out more or less the same as the later Lancaster blade, but done less elegantly by simply twisting half the blade twice as much.
All that remains for me is to untwist the Spitfire blade to get an original 5,000 series twist – and then work out where it fits on the ‘hundred’ sub-series. Are we having fun yet?
BeermatI’ll keep digging. Maybe an appeal in a different thread on here might yield something? There are a few Miles Masters with remains still visible on our hillsides, not to mention a few Fury-types. Maybe someone has a relic from when it wasn’t seen as such a bad thing to take them, which they might wish to put to good use?
Edit – the key large scale change between Kestrel XXX and the Peregrine was the down-draft carb. Was the Goshawk up-draft?
BeermatBritain is a low wage economy with endemic poverty caused by millions stuck in jobs for which the weekly wage is less than benefits because of zero hours, bogus self employment and compulsory unpaid periods. That is normal – while the talk is on preventing modern slavery, Aldi, for example, expect staff to work 30 minutes around each shift completely unpaid. At Poundland, this unpaid period for minimum wage staff is ‘at the manager’s discresion’ (sic). Probably not legal, but while it helps headlines lauded by those really not keeping up (John) that make it look, to them, like things are great, it will continue as we gently slide away from the developed world towards a broken third world economy.
And yes, it might press the ‘bile release’ button in your head but avoiding this disgusting and internationally embarrrasing situation – working people needing food banks – was precisely what unions were for.
Trumpeting ’employment’ figures only really works on those thinking like it’s the 1970’s and with no clue what’s really going on.
Look, I am not saying that tories are evil, or that this mess was somehow the plan. Thirty-eight years of one ‘ism’ with no real counter will screw up any nation. The disaster would be if we forgot that that there was an alternative, that a check and a balance isn’t the ludicrous idea of an old dreamer, which is pretty much the anti-Corbyn message, but a necessary movement away from an increasingly damaging political monoculture.
BeermatThat made even less sense than usual. Care to elaborate on that?
Or are we back to your socialist/liberal confusion again?
BeermatSod it, I’ll do it for you:
socialism
ˈsəʊʃəlɪz(ə)m
noun
a political and economic theory of social organization which advocates that the means of production, distribution, and exchange should be owned or regulated by the populace as a whole.
…absolutely no mention of international security arrangements, teaching methods, long hair, the judiciary, or anything else you have lately called ‘socialist’.
BeermatNo. It is possible to understand the value of an institution without being in love with it. I am a member of the R.A.C. and English Heritage, and am not ‘desperately in love’ with either. In fact, I am probably still a member of the Dennis the Menace Fan Club – but it is you who has the childish love of cartoonish extremes.
It is an agreement between governments, all of whom own those tools of war. Think about it.
And please, please, please look up socialism. You are making an idiot of yourself by continually misusing the word when you mean something else.
BeermatBy what means? By understanding the Maastricht Treaty.
This describes under Article J.1 the objectives of:
– Safeguarding the common values, fundamental interests, independence and integrity of the Union in conformity with the principles of the United Nations Charter
– Preserving peace and strengthening international security, in accordance with the principles of the United Nations Charter, as well as the principles of the Helsinki Final Act and the objectives of the Paris Charter
– Promoting international co-operation
– Developing and consolidating democracy and the rule of law, and respect for human rights and fundamental freedoms.
..and some other stuff in a similar vein.
So you see, that is why I claim it was intended, among other things, to avoid the disaster of another war sparked within Europe.
Your post about the Eurozone has limited relevance, in that the UK is not in it.
BeermatJohn, I could hear the stirring music rising in the background.. but your polemic only works if a) one equates a benign and sometimes inefficient bureaucracy with murderous fascism and b) one forgets that a founding principle of the union was to avoid us ever having to make that sacrifice over European rivalries or rogueries again.
It is not stupid to understand that interdependence has worked well for us, and we are no more ‘independent’ without the compromise it sometimes needed to get along. And for it to function there needs to be a common basis to the relevant legislation on which international trade and finance operates. This is not the same as some ‘foreign based’ oppressor denying you your freedom. Do you see jackbooted EU troops coming to kick down your door?
So please, don’t insult the memory of those who suffered true oppression (your despised Europeans, for example), or who took up arms against it. It is verging on poor taste.
BeermatThanks!
Yes, that ‘expansion’ problem (and how it got worse the ‘better’ the aerodynamic form of the fuselage taken in isolation) is the basis of my next TAH brain-dump / article.
Only thing is, the Hurricane could, I believe, have done with a bigger (or at least better-shaped) fillet. The full size 24-ft tunnel tests identified a thickened boundary layer over the root which got worse with the propeller on (higher free steam V). The wing’s high camber thick wing up against the slightly longitudinally convex ‘wall’ of the fuselage was enough to cause significant separation even at the very low speeds of the test. 9 lbs extra drag down to root interference at zero degrees AoA – the Whirlwind, with less upper surface curvature and a properly flat slab side, produced 1.8 lbs under the same conditions (a gentle breeze) and at plus 2 degrees.
I would be very interested indeed in the 1935 document. I have the work of Ower, but that was earlier, and all of the 1930’s American work (Klein et. al.) plus some Canadian (another Klein) and German (Muttray) material, but nothing British from 1935 apart from the known Supermarine stuff.
BeermatOK, so far I have managed to glean, largely from that NACA doc, that a ‘constant’ or ‘flat’ pitch set considerably less than the ‘on paper’ optimum is actually more efficient in real life, for reasons which are unexplained. In other words, design your twist to ‘cut the butter’ at 200 mph with 1,500 prop RPM if you want it to be efficient at 350 mph. Then you have the compromise between take off and max speed efficiency, described in ‘Airscrews – Part One’ (Malloy, 1938), which might make you want to introduce even more twist.
This was discovered in the late 1930’s, without doubt after the 6105 was designed. The apparently under-twisted 5,000 series blades are the theoretical ‘state of the art’ up until NACA 658 in 1938, with a twist designed (under an understandable misapprehension) to match airspeeds of 200-300mph. It was only understood later that you want ‘flat pitch distribution’ at 15 degrees to get max efficiency at 30 degrees. The 6127, the basis for the 4,000 series, already had this.
Shortly afterwards, DH ‘twisted down’ the 6105 to make the Spitfire’s 55400 basic blade, maximising its efficiency but in an unexpected direction. Then, at their own pace, DH undertook the redesign of the twist of it’s other, regular 5,000 series basic blades – thus taking the sub-series beyond the 100-400 range into the realms of the Lancaster’s 800 etc.
As a vast number of blades had been manufactured and were flying on thousands of well-known British aircraft while under the earlier and a it turned out surprisingly wrong school of thought, it is no mystery that this wasn’t well documented.
Efficiency curve for the 5868-9 / 6127-9 / 54409, from NACA 642, also 1938.
V/nD of 2.0 = 350 mph for the Whirlwind at 3,000rpm.
45 degrees at 0.75r = 47 degrees at 0.7r – the coarse pitch stop for the WW was at 48 degrees.
V/nD of 1.2 is 210 mph, climbing speed of the WW and near max efficiency for the blade at a 30 degree blade angle.
Minimum pitch stop of the WW was 28 degrees.
[ATTACH=CONFIG]256419[/ATTACH]
Note that this blade had a ‘flat’ or constant pitch distribution at 15 degrees – nowhere near the operating angle of peak efficiency.
From this it’s clear that the propeller was the right choice for the Whirlwind’s envelope (ignoring compressibility!) – but with very little margin given by the 20 degree range of the prop.
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