Lancaster has Corsair blades?

What a brilliant pub! Great idea with the Cambridge aerodynamicists pulling beers. I can see an awkward silence where we work ourselves into a dumb corner and a deadpan bartender resolves with a comment out of the side of the mouth while pulling beer. In terms of subject matter, everything flows from a simple story or need. ‘Why the Whirlwind got its wings clipped’ which goes into the detail of the definition of an IC power plant : engine AND blades. This goes into breaking speed records then a jaunt across country in identical Cessnas with different blade setups. Second to the new pub in Scotland pays for the beer. You are ultimately appealing to the GA aircraft owner to explain 18% reduction in fuel expenses and 32% reduction in engine wear, as well as a few Texans trying to push Sea Furies past the sound barrier. Another episode is ‘Finding blades for a Napier Sabre’ which goes into manufacturing and national history, turning a RH tractor blade into a LH tractor, forging, a visit to a pub in the Czech Republic next to Avia, a visit to a pub next to a Jablo manufacturer in Germany etc. In truth just these two questions have enough meat in them for 5 x 30min episodes each, where the real challenge is post production editing of 150 hours of raw footage into 3 hours of final film. The whole lot can be filmed in two weeks, it will take 12 months to resolve a ‘guide script’ and 6 months of post production. Easy! The interactive bit is where it gets spark, inviting participation in evolving the guide script, and bringing interactions in during filming using actors to represent forum members asking questions, generally looking like scruffy out of work actors happy to be paid in beer! I really want to bring dead people in : a hyperactive Curtiss dissing Hamilton Standard, an intimidating Roy Fedden demanding Rotol, an angry Ratier chain smoking and carrying on about patent infringement, a totally intransigent Air Ministry official for numerous stage entries, various pilots in burnt flying suits talking about overspeeding an engine, failures in Fokker interrupter gear…there’s another topic : ‘I want to shoot through my propeller’ There’s a lot of fun to be had with that one!

I think this thing is like a milkshake of historical context, eg getting DC2s higher and leaner, as much as ‘how does it work’ as much as ‘how can we get it to work in 2021?’ We introduce the hard stuff like lift and drag in between a bite of fairy floss like dH being wooed by Ratier and HS and why RR and Bristol went Rotol, using German technology. I don’t have a lot of knowledge of Curtiss Electric, and there is Fairey Reed too. A lot is explained by ‘difficult’ personalities – Fairey, Curtiss… they remain ‘known’ in history as ‘tough guys to deal with’ while the smooth, effective, high EQ HS key driver does not. I am sure this person was compensated by having a very, very large yacht. HS went global while the others did not. I understand Japanese props were HS licence, I am sure the Russians copied them too.

Following is some guff on magnesium blades – I think uniquely British, even the Germans with their Teutonic love affair with magnesium didn’t seem to go there. Again it is context of history, 1940, Britain all alone, with dH having a licence for HS products, while the US government could not be seen to be actively assisting His Majesty’s Government. So dH says ‘we have magnesium, so don’t have a lot of aluminium, can you please help us redesign magnesium blades, intrinsically 30% lighter, capable of narrower shanks due to lower centrifugal forces’. No doubt HS would say, ‘sorry, too busy, but you go for it, happy for you to design new blades that fit into our hubs’. So Brits start thinking about new blade shapes, then this leads on to optimising existing aluminium blades while they are at it. All this is surmise, it is ‘fiction that fits the facts’. However, two bloke sitting on a bar stool can get away with a conversation, and the skeletal remains of a dH blade designer can wander in to correct the record, which would be entertaining.

We shouldn’t write the script. We should just post stuff in the rainbow from hard facts to the ridiculous, and the interactive forum can drive the outlines of the script. A loose comment here or there can be a little glint that we can follow into a rich vein. After all of this, and reading lots of yellowing books, old controversies in Flight letter to the Editor and using modern forensic engineering, we can just end up in a pub yarning away, with actors doing guest appearances representing Fairey, Reed, dH, Halford, Fedden, Curtiss etc. It’s just banter with dead people. The pub ought to have some history, something with WW2 grafitti on the roof.

There will be many moments when the conversation will come to an irrecoverable end. For this we need a barmaid that knows more than us, that can steer things back on track. Because its all such a patriarchal history we can just take this deft intervention on board with a grunt and a fresh pint and move on. So Anneroac, up for barmaid? It’s kind of Arthur Daley, Del Boy and Rumpole talking about props, I can run with the fairy floss, you can try and haul it back to Reality and when we both hit a dead end the barmaid will fix it, just like women built the whole Air Force in WW2.

It’s a good idea – I would be tempted to extend it to other dark arts like drag (I mean the aerodynamic force, not dressing like a sheila), stress and flutter. But definitely start with props. 10 episodes is pushing it, I’ll start writing a synopsis and see what we get. What I need help with – some analogy, easily found in a pub, that starts the conversation off. Not Ice cream, but something of that ilk. We need the visuals as part of the conversation – the more practical the illustration on camera the better.

Mate, I am up for something. I don’t think Millenials, who will really need the info, will know what a book is. For a technical topic, don’t underestimate the value of entertainment- Pilot Officer Prune led the way. My pitch to you is a series of YouTube’s linked to a website with reference and detail material. For the YouTube we sit in a good UK pub and just yarn away. We can script this stuff on this forum then sit down for two weeks in 2021 and film 10 episodes. The beauty of the forum is it’s interactivity which takes you down many pathways and can shape the ultimate episodes. This is not a money maker, but the pints should be tax deductible and we’ll get a laxative manufacturer to sponsor the filming to cover costs. How bout it? Some things that have come out from the interactivity of this topic on various posts are : (1) The folks who find this subject self evident are dead or on the ground trying to focus trying to find their teeth, therefore the information that they learned by osmosis in a career from 1920 to 1980 needs to be presented again, if historics are to be kept flying. (2) Folks are after the ‘look’ of blades for authenticity, without understanding function and there is a modern flight environment for display aircraft which may require a different function(3) a historic IC power plant is a combination of engine and prop, as the Whirlwind demonstrated. In this day of jet engines, this is not self evident. (4) Historic Prop design reflects national priorities – in 1935 in the US, sending DC2s from NY to LA for minimum fuel burn, in the UK rising up to a Zeppelin as fast as possible, never mind the fuel. The historic environment explains engineering choices as much as physics.(5) In 2020, we sit on the threshold of someone forging either new Rotol hubs to fit Jablo blades, or new HS blades to fit old HS hubs. Now is new 3D printing of titanium, pressure condensed hubs and components a pathway to short runs of historic components? (6) there is a tiny commercial market for optimised blades for the racing of historics, maintaining existing historics in the air in the face of diminishing supply of NOS blades and hubs or the return to flight of rare historics, eg those using British LH tractor blades. This market need technical support to navigate to an outcome. There is a role for a technical consultant, which is you Beermat ! But first let’s have a bit of fun developing a script for two weeks in a pub in summer 2021. For me, it’s the joy of learning. Should we start a new topic that lets folk ask questions about props on this forum to develop and guide a script? ‘Propeller Head’. Out of all the rants a motley crew can emerge that can guest on episodes, including dead people like the Wright Bros talking about their paddle blades, a crazed Frenchman called Ratier complaining about patent infringement, Constantinescu describing his first experiments with firing through blades etc. 2021 is enough time to book a ticket to a UK pub.

It’s a bit of a black art, understanding props. You either get it or you don’t – and there are plenty who don’t, or can’t.

The most often asked question when it come to props is “how does a constant speed propeller work?” As with most of this stuff it is quite straightforward really. The problem is trying to impart that to the non-technical person in a way they can understand.

Best of luck with that, Beermat.

Anon.

Icebergs and Ice cream.. the world of propellers is a weird and wonderful place.So here’s the thing – the reason it all seems so mysterious and full of witchery and riddles is because there has never been a ‘Big Book of Propellers’

With Ed’s gift for imagery and my nerdism I think we could put together something to fill the gap. You can get mathematical treatises and manufacturing company histories, but nothing to put things into focus for normal humans. Anyone know any publishers? Actually being serious here. Ed, you up for it?

I suspect it was the company PR that said it was unsinkable – no real expert ever said anything without qualifying it. Which may not have mentioned icebergs…

Not at all, Ed. It was the experts who said it was unsinkable – or were they the idiots?

Ahh, that’s Beermat with the good quote! I think in any difficult topic you need an Idiot and an Expert on the panel. Beermat is the expert. In the face of the wall of competence from the expert, most folks are cowed into silence. So the role of the Idiot is to get the Expert to roll their eyeballs and explain things s l o w l y using ice cream as an example…it’s amazing the illumination that can come out of basic principles. The Idiot, too idiotic to be cowed by the expert can also say dumb things like ‘ is that an iceberg ahead?’ which once every 28 times saves the ship, the other 27 times being saved by the Expert. Really what we are getting here on the fascinating topic of props is a barstool conversation, and I’m learning a lot and lovin it. Now does travelling through rain increase or decrease the speed of an aircraft, or does increased reaction of blades against raindrops balance increased resistance of fuselage to raindrops?

Yes, I was going to say that Rotol had made some mag-alloy blades – but they were fitted to the Whitley. The Rotol hubs were designed such that various materials could be used for the blades with a suitable adaptor.

One thing that seems to have emerged from our conversations, above, is that Mossie blades were from a shorter blank which, in itself, would lead to a thinner blade section. Think of it this way; as a tapered form which, the closer you cut it down to its base, the thicker it becomes i.e., more dumpy. The H-S method of starting with a longer blank would result in this happening, though it has to be said that, although the resulting section would be thicker, it probably didn’t make much difference to the efficiency of the prop. At least not enough to justify another method, and much easier under the pressures of war time production.

I was not aware that H-S or de-H had made production blades from different materials, though I can see that it would have been very easy to do so given the simple and universal way they were retained in the hub/barrel. Aluminium and copper were relatively plentiful in the US during WW2 so there would be no real need to investigate other materials, perhaps only to prove the case that they could be utilised.

Just to round off, I enjoy the colourful descriptions of P&P’s text and enjoyed this one: “creating a pressure differential through the relative speeds of ice cream over the surfaces of your spoon“. That’s a cracker!

Are you a teacher, by any chance?

Finally, thanks to Beermat for his facts and figures. They certainly helped to broaden the discussion.

Anon.

EDIT: I’ve quoted from Beermat’s post but P&P is the instigator of the interesting and hilarious but practical ice cream scoop analogy.

Rotol initially made magnesium blades, and one squadron of Spitfires was equipped with these in Spring 1940 – there’s a photo of one down in the sands of Dunkirk. However they were abandoned – I hadn’t realised that DH made some later in the war.

Of course you can learn a little bit from reading and then you can learn a lot from making a mistake, which is a tough but good school.

It’s much better to learn from the mistakes of others, cheaper too & sometimes rather entertaining. 😉

When I destroyed the industrial fan, I went into the library to hide, to eventually find an engineers handbook from 1890, which dealt with HP restrictions on steam engines, caused by cast iron flywheels shattering from centrifugal forces rather than the intrinsic capacities of steam engines. It was only after better metallurgy created stronger flywheels, able to resist centrifugal shattering, that more powerful steam engines could be developed. I think a 50 year old blade designer in 1941 would have learnt his craft on marine engines and marine propellers, so a lot of the basic stuff is there 130 years ago. Of course you can learn a little bit from reading and then you can learn a lot from making a mistake, which is a tough but good school.

dH also made blades out of magnesium, so the lighter blade might be that. Now I am not sure that Uncle Sam HS made magnesium blades, and generally if an aluminium formula worked and you had Alcoa, why change? Britishers finally made local magnesium from seawater and dolomite in 1939 and aluminium cost shipping and lives to U boats, and aluminium was needed for Spitfires, so magnesium blades were very attractive in 1941. Of course the big design issue is centrifugal force, as I learnt when over speeding an industrial fan, destroying it, so lower mass magnesium, for the same mechanical strength, could allow you to design a different shape, certainly less meat in the shank, a double benefit. I think fat shanks are about material strength and managing centrifugal and torque reactions. We don’t know about magnesium blades because it was probably just a British thing, it wasn’t needed after the war and whatever remained fizzed into powder.

Oh this is getting controversial! Now you’re saying the Trump Mosquito paddle blade has eaten more hamburgers than the British Mosquito paddle blade ! I need definite proof before I hand good beer money over on this. As a separate issue, my understanding of paddle blades relates to my experiences with ice cream tubs. So the fatter scoop digs out more ice cream than the thinner scoop. Now change ice cream for air and the fatter blade is chippy-chopping more air than the thinner blade, at same RPM. I would want to do this if the air is thinner, way up. So I associate paddle blades with the race to go to 40,000 feet, stay above the flak and lessen the chance of interception. Then I have to rise in England and land in Russia, so I lean out my engine, balance power and RPM to ice cream scoop as much thin, icy fraulein deutcher air as possible for the minimum fuel spend. So that’s why I have paddle blades. After the war I want to send my DC4 as far as possible for minimum fuel spend so I stick with the paddle blade formula. Toothpicks fade from memory. Toothpicks were really about getting Spitfires and Hurricanes up as fast as possible in 1940, which is all Britain cared about then. Then I’m told I’m joining 618 Sq to Highball Japanese cruisers at sea level, where I want to transmit as much power as possible into thick air, so I change my Mosquito setup from three paddles to four toothpicks, back to trying to push as much air past me as possible. Now my big ice cream scoop, so good for pulling big scoops of watery ice cream might not be that good for pulling big scoops of chunky, solid ice cream. I might find weird torque affects when I push the throttle to the gate, chasing the devilish Luftwaffe. I really need a chopstick and to put the tub up to my mouth and flick little bits of delightful dairy goodness, or thick air, into my gob as fast as possible. In fact four chopsticks, Bruce Lee style, would be better than one. I am sort of exploring Force = Mass x Acceleratation, where air density influences Mass, RPM deals with Accelaration, where I am stuck with an engine, or Force, in both cases of 1,000 HP. Really I am trying to keep my RPM in a fixed range, so the Conrad’s don’t pop out, so I invent a constant speed airscrew which makes a blade fatter or thinner within limits. So flip-flopping between scoop and chopstick. Now later in the piece I am using 130 octane and getting 2,000 HP, so I am finding that I can actually push more mass, so I can use my big ice cream scoop paddle blade on a ground attack aircraft, where fuel burn is a non issue, because I am landing at an airfield only 10 miles behind the front. I hope this has lifted the scientific tenor of discussion and I apologise to any vegans for not using vegetable based analogies. I guess blade design comes from marine work and if you look at devilish torpedo blade setups and understand that speed through fluid with a short, brutal ‘fuel’ burn was the aim you start to see ice cream moving, or at least I do. Really the whole theory is there in the varying blade configuration in a jet engine, which was originally designed by Frank Whittle to make butter.

There aren’t many places where I find people who know their stuff talk at length about propeller blades. Please go on, Mike!

Just to add that the broader ‘paddle’ was initially an American solution not just for power absorbtion (most of the power was transmitted around the 0.7r station, which was always kept broad, not the tip) but as a way of delaying the onset of Mach drag.

This kicks in according to thickness-to-chord ratio, not just thickness. Hamilton Standard, as noted, were incapable of making blades any thinner, so instead they made them broader to decrease thickness-to-chord around the tips and make them more efficient at high Mach.

This is why they proved better at high altitude on the Mosquito – the speed of sound gets lower the higher you go, and relative Machs are of course higher for any given rpm/forward speed.

De Havilland made their blades thinner – starting with their deliberate thinning of the HS 6339 from 9% to 7.6% t/c at 0.7r for the Spitfire’s 55409 (they didn’t do the same with the Whirlwind 54409 blade, with disastrous results).

I have heard it from several sources that the thinner DH versions of blades were preferred by pilots.

The broader DH Mosquito blades were from smaller blanks. They were 4551212, cut down 6 inches per blade from 13ft, while the US blades were complete paddles, cut down from 15ft, and fat. I don’t know about DH-made complete paddles, did you get a drawing number for the Mossie blade you had? Maybe it was an ‘Aussie Mossie’ blade?

I was specifically talking about “paddle” blades, not the pethora of “needle” (both those terms were coined by the prop manufacturers) blades which were in use either/and early on and on smaller aircraft types due to lower power absorbtion requirement.

Paddles became better all round, especially for radials where the inner sections of the blades pushed a bit more air through the motor before the speed increased as it got airborne. I really don’t think paddles could be easily, or successfully, reprofiled to needles for the Hurricane mentioned. The “meat” of the blade was not in the optimal place so I’m not surprised it looked a little wierd.

One might assume, with the Lancaster, that the engine’s power must have increased to require the switch from the “needle” to the “paddle” blades, the latter, at least theoretically, requiring or absorbing more power to match. Certainly not – the lanc stayed with the Merlin XX/20-series throughout. What happened was they realised the performance was better at height with the larger blade area, as well as a couple of other factors, so all it needed was some resetting of the blade angles to allow it to operate properly and not, as might be the case, to absorb too much power to the point that the engine would not achieve the requisite RPM at the correct throttle setting. In short; the paddle blade was more efficient and the altitude performance and slower speed cooling of the Lanc improved thereafter.

Of course, as is typical with this propeller lark, there comes along the exception(s) that defy the rule(s) so, what happened to the Lincoln? – they put a four-blade unit on with needle blades, so contradicting the theory that they were less efficient than the paddle. They did indeed put nice big paddle blades on the prototype Lincoln but, presumably, the needles worked better. Without research, perhaps the Lincoln was not meant to be a high-level bomber after all? All this lovely theory and testing stuff is now lost to the mists of time, apart from the odd snippet gleaned from some expert or other being quoted in an old publication.

Note also that Mosquito went from needle to paddle blade with the same engine. Same as the Lanc, they adjusted stuff and it worked better. Paddles became standard on Mossie as due to later major power increases they had to increase blade area as they couldn’t increase the diameter (the blade tips were only 3ins from the fuselage). However, it didn’t stop T.III trainers with Merlin 21/22 switching to paddle blades as well.

As an Aside; I owned a Mossie paddle blade prop some years ago and I was struck by the thinness and quality of the blades compared (roughly) to the US equivalent size used on C-47/B-24/B-17 etc. Of course the US H-S blades would have been cropped to suit their application, but they were much thicker and heavier. The Mossie (de-H) blade was very much thinner and lighter so I would certainly believe that they were made to that diameter, not cropped from a larger blank. It was certainly a very nicely made blade to which, in my eyes, the US-made blades did not compare favourably at all.

I could go on all night but I’d better not.

Anon.

I recall a deal where someone at Dx (Ray or Mark H maybe?) flew something with the prop from something else & didn’t like it one bit. Possibly a Buchon prop on a Spit or P51? It was one of those “right, we won’t do that again” moments.

P&P, dH Australia – they keep coming up as the link between British dH and the Americans, and I didn’t realise they made paddles as well. I’m sure you’re right about the Corsair and Mosquito, and of course that design is up there on the list of new forgings that will become useful in the future. Add to that the 6503 (everything from Battle to Lancaster and a fair few US designs too), 6339 (Spitfire), 6127/6128 right- and left-handers for British and US 800-1000hp radials and some LH Hercules blades (5511xx and/or5517xx) and that’s the ‘product set’ right there.

The ‘as long as it flies’ argument is all very well, but efficiency isn’t just about performance, it’s about fuel economy as well.

Beermat, dH Australia made paddle blades for Mosquito and many US types. The Corsair and Mosquito blade probably came from the same forging blank. DH Australia also made Fairey Reed metal props and later Hartzell blades until the 60’s. For anybody looking for Fairey Reed drawings for late 30’s Ansons, Gladiators, drawings exist at HARS Archives in NSW. Fairey Reed props are a limited pathway for low to high power fixed pitch LH tractor British radials to stay in the air, but these can, of course, used fixed pitch timber props. The real challenge are the constant speed setups of the 40’s.