More proof that it wasn't the Whirlwind's engines, and a question.

Beermat #31 wrote

“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.”

I have had in the past access to the Log Book of Flight Sergeant Frank Waldron of 137 Squadron who flew Whirlwinds from January 1942 to October that year before he was shot down. In all he flew 30 different Whirlwinds in 174 flights. I can hardly recall a time that he was forced to abandon a flight, once I think.

This is a wonderful thread and I delight in every addition to it.

Yes, 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.

Hi
There is/was another letter in the PRO/NA stating whirlwinds were not to be used in the BoB because of the 20mm cannon they were the only aircraft capable of attacking armoured vehicles in the event of invasion
I think in the Orb ? it mentions the Sqn low flying exercises
cheers
jerry

No 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).

My original point was just that it was a shame (for its reputation, if nothing more) that it was too late, not to allocate reasons. But if we can stray from the theme, then why so few? How did this compare, from first flight to first squadron (say 12 aircraft, or whatever number for which there is information) with its contemporaries? The Spitfire had its own problems getting into production. Were Westlands significantly slow, or just within some normal variation? But there will always be special cases: the Hurricane was built with standardised practice by personnel experienced with the tools: the Beaufighter utilised much of the Beaufort build-up. Perhaps the Defiant comes the closest?

If we shouldn’t stray too far from the thread, drop it for some other time.

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From Dowding. Airscrew revolutions and boost. Prototype ceiling with Rotols 31,000ft.

Taking 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!

Thanks for that! I didn’t immediately know what “Aerade” meant, but it didn’t take long to figure out, so now I’m off looking at things…

bob

Bob, 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.

Thanks John. Erudite as ever.

Beermat,

You can’t polish a turd.

Shouldn’t shun the ‘M’ word Bob, it is hallowed !

I hoped I had demonstrated that the Whirlwind was not a lame duck simply ‘because of the engine’…
Dropping the Peregrine was a rational decision. Dropping the programme probably was too…

Quite so, and I made a mistake myself- it is perhaps even more true that the Peregrine was a lame duck [Hmm, I’m getting my birds mixed up!] because of the Whirlwind (programme). But I was not intending to imply that either engine or airplane was a poor one. I also agree that the production order was for the benefit of the company, rather than for the individual, though it was one of those half-way measures that really didn’t answer either the argument “for” or “against”. (The argument that the Beaufighter was an adequate substitute for the Whirlwind is a questionable one, whatever the Beau’s merits.)

I wondered about the wind-tunnel testing, but don’t have any details. I speculate (and that’s all that it is) that little further effort was invested in the Whirlwind (such as producing alternate props to improve altitude performance) simply because it was seen as a dead-end and so wasn’t felt worth the distraction. I don’t know why DH was selected over Rotol for production, and I wonder if it might be another case of “Rotol’s got more important things to worry about right now.”

bob

p.s. The M word has already been mentioned, but I’m trying to shun it!

Yes, 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.

Interesting information.

The Whirlwind was a lame duck because of the engine, only because (as Graham said above) something had to give at Rolls Royce, and dropping the Peregrine was a perfectly rational decision. Had the decision instead been made that this engine and aircraft were required, I’m sure the engine could have been improved (as Rolls Royce suggested), props could have been changed, and so on. The only reason the small number of Whirlwinds was built (and thus Peregrines for them) was to satisfy Westland’s- or Petter’s- bruised ego. But I really don’t want to send this the way of every thread that arises concerning the Whirlwind!

As to why the Whirlwind wasn’t used during the Battle of Britain, here are the acceptances from production:
(zero until)
June: 2
July: 3
August: 1
Sept: 3
Oct: 1
A total of 10 production aircraft.

bob

Oh, 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.

I think you are underestimating all the engineering effort that had previously gone into understanding propeller design. Most of the wide-ranging experimenting you describe had been done before the end of the First World War, and absorbed into practice, mathematics, and data sheets. By the late 1930s a good understanding of just what would be required was available before design began. There are examples of trials with different makes of propeller, and of course continuous fine-tuning of blade design during the life of an aircraft, but generally the key parameters of the propeller design had been settled long before the first prototype flew. This need not mean that it was always available for that flight, or indeed early production examples. I doubt that the aircraft designers ever gave up expecting more… but compressibility was a nasty surprise.

With 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.

A while ago I was heavily into RC model aircraft where it was an easy thing to experiment with props of different makes, diameters and pitches as well as with two, three and four blades, all driven by the same engine. The variation on resulting performance was astonishing.
Obviously such trials are somewhat more difficult on full size aircraft and I bet in many cases, with the pressure of getting it into production, they gave up when something near expectations was achieved.

Richard

Quite 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.