BeermatSo no aerodynamic improvements between 1929 S-6 and 1931 S-6B? Or was the reduced drag often referred to – as here – http://www.baesystems.com/en//en/heritage/supermarine-s6 – due to the float redesign?
BeermatGreat stuff – especially the construction pictures – and the further reference to interesting wind tunnel stuff that Mitchell nor the authors could divulge only makes me even more curious. But sadly not what I am really after – namely Aeronautical Research Council Memoranda Nos. 1281, 1296, 1297, 1298, 1299 and 1311 (also published as an ARC Monograph, No. 1300, ‘Collected reports on British high speed aircraft for the Schneider Trophy Contest of 1927’) and Monograph 1575 ‘Collected reports on British high speed aircraft for the 1931 Schneider Trophy Contest. With an introduction by H. M. Garner’. All mysteriously and annoying missing from the usual AERADE /ARC and NACA online sources for these reports. Unless anyone can find them??
BeermatJohn, you are not followimg the first rule – ‘know your enemy’. The EU is a bureaucracy. It doesn’t have an ideology beyond self-preservation. So it isn’t left wing ideology versus hard-headesness, there is no way, whichever way any argument within the EU goes, that the UK will emerge better off from any of this. It is so straightforward, it cannot be spun, and there are no angles to work or divisions to take advantage of. We have done a dumb thing and the best we can do is a political Dunkirk. Save what we can.
BeermatYes, I have seen that too – trying to dig it out of my copies. I also recall it saying that they would be a very useful handful of aircraft, or something of that ilk, as the only type capable of taking on armour.
BeermatNo worries, me posting that letter was really about the ‘minor defects’ that point to my theory – it just happened to have the bits about keeping the WW out of the fight in it.
Westland were very slow indeed – certainly the Ministry and the RAF were frustrated. In November 1940, Petter wrote a memo to Sholto Douglas stating “The Whirlwind is probably the most radically new aeroplane which has ever gone into service… New ideas I am afraid, even with the greatest care, always mean a certain amount of teething trouble… I really do not think these troubles have been any worse than they were on, say, the Spitfire… ”
In reply Sholto Douglas wrote, “… it seems to me that your firm is concentrating on producing large numbers of Lysanders, which nobody wants… instead of concentrating on producing Whirlwinds which are wanted badly.” Later, Petter was to blame Eric Mensforth for the delays. (Yes, that was pasted from Wiki for convinience, but I have photos of the originals in front of me).
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From Dowding. Airscrew revolutions and boost. Prototype ceiling with Rotols 31,000ft.
BeermatTaking the calculations and turning them around, something pretty alarming emerges.. CSU controlled blades encountering enough wave drag through compressibility will, if they don’t hit the stops first, pass through a drag minimum angle and go negative incidence, and stay there, at minimum pitch regardless.
The revs are now dropping as even minimum drag was too much to keep the revs at 2,850, never mind negative AoA. Whatever the AoA the drag on the blades is too high. Being stuck in negative incidence is an equivalent position to the blades being held too coarse in that you get under-speed, and there’s nothing the CSU can do about it. This is, I think, where our Whirlwind ends up in any climb – regardless of minimum pitch angles.
This would look and feel like an engine problem.
..especially when the prop starts windmilling and the boost pressure drops!
BeermatBob, here’s the part of the Wind Tunnel test that doesn’t appear via Aerade: https://1drv.ms/f/s!Av778LfDRcoyhS88vyTspS5kWg_K
Note the conclusion on page 6 about actual airscrew propulsive efficiency being reduced by 4% at observed top speed. Though they do factor in compressibility it is interesting that they have the airscrew in their calculations as 9% t/c (the figure for the American 5868) and not 9.6% (correct for the dH DP55409)
John – tell Farnborough, not me.
BeermatThanks John. Erudite as ever.
BeermatYes, it was just a single flight that was available, and the suggestion was to try it in the South. Dowding said no.
I hoped I had demonstrated that the Whirlwind was not a lame duck simply ‘because of the engine’. Indeed, where altitude was not a requirement the Whirlwind was not a lame duck at all. Just ask anyone who flew it in combat – there are still some around, and I have. None of them mention the engines as anything other than perfectly OK. The Exactor controls were dodgy, and lack of cross-feed and feathering were a worry, but as John McCLure DFC (Whirlwinds October 1941 to October 1943) said ‘as long as the props were turning I was happy, and they always did’.
The performance curves without the crippling fat dH propeller are normal, with a decay in boost pressure and therefore horsepower directly proportional to air pressure as one would expect of normal supercharging. The Whirlwind and the Peregrine were intended to operate at the altitude expected for interceptions in 1936, and they did. Performance dropped off above that optimum design altitude, as with all aircraft. No one called that basic fact of aircraft design a ‘failure’. It was the unexpected issues reported on top of this that spoiled the picture – and I believe the causes are those I have found.
I have not even mentioned the RAE’s wind-tunnel tests on a full-size aircraft that identified a mysterious difference between calculated and actual high-speed performance that they could only put down to a drop in propeller efficiency.
I don’t want the argument played out again either – next someone is going to say the ‘M’ word – and I don’t want to make any enemies of respected and knowledgeable commentators on here. But it does seem the zombie myth cannot be killed!
Dropping the Peregrine was a rational decision. Dropping the programme probably was too – there were certainly some straightforward resource issues about producing a twin to do a job handled adequately by singles at the time. But the aircraft held its own and did all that was in fact asked of it.
Props could have been changed regardless of anything else. There was a perfectly good Rotol design flown on the prototype, giving the Whirlwind precisely the altitude performance expected of an aircraft with an FTH of 15,800ft. Whatever the reason they were not used, it was not a ‘development’ decision.
No-one was interested in nursing Petter’s ego. The decision to allow Westland to break even on the Whirlwind was more to do with the John Brown Group who owned Westland Aircraft and who were in bed with the Government as a primary shipping and arms contractor.
BeermatOh, not at all, I am aware of the amount of work that went into the theory. I was really talking about the attention that is paid in hindsight by those that seek to analyse, discuss and understand aircraft performance and the factors that affect it. Not at the ‘high end’, of course (such as yourself).
Having said that, compressibility should not have been a nasty surprise in 1940. It was right there in 1932 – as in the excerpt I posted. It is hard to avoid the conclusion that hanging a propeller on an aircraft in 1939 that had an aerofoil doing the alarming thing visible from available test reports from 1932 within the ‘flight envelope’ does seem a little careless.
The problem isn’t one of propeller design, it might be more one of propeller selection, done without reference to compressibility.
This is a big grey area for me. I do know that the ‘dH’ blades on the prototype were in fact imported Hamiltons – you can see the logo in some pictures. The only US equivalent to the blade profile is the Bu. Aer design ‘5868-9’, but this is 9% t/c and not 9.6%. So how the 9.6 de Havilland 54409 blade came into being, whether it was off the shelf or tailored, British or American, is a mystery to me. If anyone can help it would be great.
BeermatWith the Whirlwind it looks like the prototype with Rotol props was thoroughly tested (the one with dH props seemingly wasn’t) – and then dH props were ordered for production on the basis of these tests because they were of the same diameter and the aircraft took off OK with both!
To be fair it may even have performed better in the take-off range with the dH props.
BeermatQuite right, of course. It is about very local acceleration over the aerofoil up to the speed of sound.
That noise is all energy wasted by the prop. It is a curious thing that all of an engine’s power that is translated into forward motion is via the propeller, but while people will argue forever about the finer points of fuel injectors, exhausts and intakes the big spinny thing doing all the work on the front tends to get ignored, despite having the single largest effect on the efficiency or otherwise of propulsion. Not overlooked by designers of course.
BeermatThe thing is it’s not a theory that should need proving as such – work was done on actual blades in test rigs , and the figures are there in black and white, including those for the RAF blade at 8% and 10% (ours was 9.6%)
http://naca.central.cranfield.ac.uk/reports/1938/naca-report-639.pdf from 1938 details work on actual spinning propellers in wind tunnels, but if one just looks at aerofoil testing without spinning them on propellers the effects were known from 1931/32. There was British work done, but the only publicly available work is that of NACA. This is our blade foil, from NACA report 463, by John Stack, in 1932 (V/Vc means Mach). The middle graph is drag at different angles of attack and Mach:
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Compressibility effects happened, and the drag was thoroughly recorded at ranges of Mach and incidence, including those encountered by a Whirlwind in the climb also according to test reports.
Our blade would follow the 4 degree line up to Mach 0.5, around 15,000ft and 165 mph TAS. A CD of around 0.033. By 30,000 and 139mph TAS our blade would be close to the 6 degree line and Mach 0.525 – CD around 0.048. In other words 45% more braking effect on RPM. This is only at 0.7 radius where most of the work is done – the tips are somewhere around Mach 0.79 and probably growling like a T6.
It may take virtual blades on a simulated Whirlwind to demonstrate it to a 2017 audience I guess. I understand that would need an effort because it is hard to get most software to accurately replicate compressibility effects.
BeermatNot supersonic – with thick aerofoils of the ‘wrong’ profile at any significant angle of attack you hit compressibility problems at as low as Mach 0.5!
The problem with lower prop rpm is lower thrust. The WW prop was designed to give maximum thrust at 2850 rpm x 0.477 reduction and about 4 degrees AoA (28 degrees pitch) in ‘climbing condition’ at 0.7 radius. This it did fine – it just got rapidly much draggier above Mach 0.55 at 0.7 radius (Mach 0.79 at tip) doing this.
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