2x Spitfire Vc trop propellor identification help needed

[elger]

Could use some help with this.

I'm doing research on 2 Spitfire Vc trops: BP955 (Dennis Barnham's Malta Vc) and RAAF 79 squadron's A58-137 (ex EE835). My question is very simple: what propellors were fitted to each of these aircraft? DeHavilland, Rotol, or a combination of both?

(though this might not be BP955, but it is Barnham in the cockpit and you can see the back of the propeller)

help would be appreciated!

[Giorgio N]

DH for both

[gingerbob]

Yep.

[elger]

thanks, both!

[tonyot]

I agree, DH for both but many of the RAAF Spits appear to have broader blades than the regular DH blades, especially the earlier deliveries.

Cheers

Tony O

[John Aero]

It's the width of blade that makes me think they're early Rotol and that middle spinner is quite chunky.

John

[Test Graham]

The early RAAF Spitfires were certainly DH, for they were the cause of many failures and losses during the fighting over Darwin. The two photos are both of later deliveries - the white tail points at operating in New Guinea (79 Sq?). Given the failure of the DH prop in high altitude combat (recognised in PR units in the UK earlier) it would seem logical the Rotol props would have been sent to Australia, but I wonder whether the slightly longer spinners may be evidence of the Hydromatic DH as opposed to the earlier ones? Rather than just looking at the width, the beefy shoulders at the roots are however typical of Rotol, and these can be seen on other RAAF Spitfires - not always later ones, either.

Re Barnham: I think it's BP955, though I don't think it can be proven (from what I've seen) and it has a DH prop.

[elger]

so it all is slightly more complicated than it seems at first glance. thanks, everyone!

[John Aero]

Just to put the prop construction into perspective, The DH props were forged metal alloy and so could have a slimmer hub fixture root profile. The Rotol blades used a compressed laminated wooden blade of the Jablo type and as such required a greater cross sectional area at the hub. The mechanism of the Rotol also required a longer taper of the spinner than the DH ones to accomodate the greater dia of the pitch change unit.

John

[gingerbob]

My understanding was that metal bladed props were favored for "other theatres", and specified for all Spit Vs for Australia. I had hoped that the answer might have been within "Darwin Spitfires", but Graham didn't mention it and I don't have the book yet. I'd rather not go off on a distraction just now, but perhaps later I'll root around and see what evidence I can come up with.

Remember that, unless I've missed something (entirely possible!), the type of Rotol on Spits by the time the Vc was in production was the later style that did not "round off" as it reached the spinner- that type was on some early Vs, but is more typically associated with the Mk.II.

bob

[Test Graham]

There's a lot in Darwin Spitfires about the shortcomings of the DH prop, but (from memory) no mention at all of Rotol.

Re Tropical use, it might be worth a glance into Spitfires over Imphal to see which prop was used. I don't recall SEAC Mk.V photos in any other source.

[Edgar]

I'm not sure what relevance (if any) this might have, but, on 31-7-42, a nameless Squadron Leader aka "O.7" reported, to M.A.P. A.P.1.C, that, over the following two months. production of Hydromatic propellors would be insufficient to meet the needs of Vb & Vc "as a considerable number of these propellors has to be sent overseas as spares."

He then states that an extra-large quantity (100 p.m.) of DH/5/39 propellors will become available (some from repair) for fitting to production aircraft, but, since DH/5/39 were not to be installed on aircraft held for Fighter Command Squadrons, he asked that they should be fitted only on tropicalised aircraft, and that "temperate aircraft receive the priority of available hydromatic propellors."

Edgar

[gingerbob]

Gee, Edgar, you might be on to something! I remember that note, but the timing is just right for shipping Vcs to Oz. I wonder if that might explain the prop CSU failures they experienced, similar to those experienced on the first Vs in the UK, two years earlier, with DH (bracket type, as opposed to Hydromatic) props! I confess I hadn't heard about the Australian prop problems until relatively recently, and it puzzled me why they'd have had such problems, when I thought the issue had been addressed long before, not to mention the new style of (DH) prop!

bob

[Test Graham]

I think we need an understanding of why DH/5/39 wasn't suitable for Fighter Command. In Australia they were carrying out intercepts at just below 30000ft, which is rather higher than FC usage. They had been given instructions to avoid problems by gentle handling (excuse me for not looking up the wording at the moment) which would be appropriate for PR work but not formation flyng at such altitudes nor combat. Whether the specific failure would have been avoided by the use of Hydromatic props I know not, but presumably Rotol ones would have done the job. If it does turn out that props known to be deficient were being sent out to Australia, then I think some fairly strong words would be appropriate.

The main benefit of the Hydromatic, as I understand it, was in increase in the pitch angles available, giving shorter take-offs. This was particularly relevant to their appearance on the deliveries to Malta, the relevant one being Operation Bellows in early August (the actual ferry was 11th August). Trials on Furious had led to the decision that the Hydromatic propeller was needed, so all 40 aircraft had them fitted. An interesting date in the light of Edgar's find.

[elger]

Here are 2 more shots of 79 Squadron aircraft from the Australian War Memorial, maybe they help with the identification?

Edited April 14, 2013 by elger

[Edgar]

Supermarine's R.T.O., in 1941, had asked for permission to introduce a modification into production, which consisted of a bleed, which they'd found had cured the problem of the prop "sticking" due to cold. One item I've seen mentioned, is that some considered that Merlins shouldn't be operated above about 3,100rpm, due the oil bubbling, at height, caused by aeration.

Edgar

[Work In Progress]

Interesting, that, Edgar, as it suggests that people were in the habit of ignoring the published rev limits with a fair degree of impunity, and at that stage in the war one can perhaps see why.

The "normal" red line for a Merlin was always listed at 3,000 rpm in the pilot's notes for all types fitted with constant-speed props, which makes sense as that's the RPM which coincide with the top of the power curve and there is no inherent advantage in running at higher RPM, providing the prop fitted is within the governing range at all speeds and heights being encountered in the flight envelope.

However, 3,000 RPM was not a 'hard' rev limit for the basic Merlin engine. While higher revs would undoubtedly increase wear, and take you beyond the power peak, they would not result in instant failure (for example, from valve float leading to valve/piston contact). it is known that Merlin engines were capable of hanging together at significantly higher revs. The Speed Spitfire engine was cammed and supercharged for peak power at 3200 RPM, and in the fixed-pitch Spitfires I have seen accounts of up to 3,600 RPM being used in high speed descents from high altitude. Can't find where at the moment but I know I've read it in the last three months somewhere.

However, the fact that you've seen people talking about the lack of wisdom of people running the engine over 3,100 - already 100 rpm over the red line - for a specific known reason, in the constant-speed prop era, strongly suggests that the 3,000 RPM pilot's notes limit was being regarded more as a 'guideline' than a limit. The most likely reason I can think of for this is once again the dive case from serious height. Given that the Spitfire was capable of far higher speeds than its 1941 contemporaries before it ran into compressibility issues, I speculate that people may have been fairly widely diving the aircraft beyond the self-governing range of the CS prop, i.e. the prop hitting the coarse pitch stops and the pilot continuing to dive at full throttle. In 1941, with the competition for the Spitfire II and VB hotting up, this might have been a useful escape tactic perhaps. Those pilots who had experience from the fixed-pitch prop days would have felt fairly comfortable ignoring the 3,000 RPM limit.

[Test Graham]

In the actions over Darwin, failure of the CSU in the dive would cause the engine to rapidly increase to 4,000 or even 4,200 rpm, the resulting failures being those of the oil seals through overheating and pressure rather than valve/piston contact. This caused oil to spray back over the canopy and glycol to escape into the engine with the result that white smoke poured from the exhausts, and the oil pressure dropped dramatically. Pilots who managed to "catch" the engine before reaching these speeds did manage to recover and even re-engage.

[Work In Progress]

Yes: however, in my post above I was actually digressing from the Darwin problems, rather than talking about accidental over-revving due to failure of the CSU. To me the reports related by Edgar imply that pilots may habitually have been using more than the published maximum on purpose, otherwise there would surely have been no discussion of the wisdom of using more than 3100 rpm given that the book already says 3000 rpm is all you are allowed.

It's merely a speculation but I couldn't think of any other reason why such a discussion would be taking place.

However, the reports you refer to above do provide further evidence of the Merlin's short-term mechanical tolerance of RPM well outside the normal permitted range.

Edited April 14, 2013 by Work In Progress

[Test Graham]

I agree: my posting was just to show the failure mode when over-revving not to present any kind of counter-argument to yours.

[gingerbob]

One other point, and I apologize for not doing my homework, but I've got lots of other calls on my time just now-

Graham, you referred to the more limited pitch range of the early DH prop vis a vis takeoff, but in the beginning of the Spit V the problem was over-revving in the dive. I seem to remember the range being adjusted, so if they gave to the high-speed aspect they'd have taken away from the low-speed one. Again, not disagreeing with what you said, but adding a different element.

bob

[Test Graham]

I have seen (but don't remember where, probably buried somewhere in STH) the values for the change in range, but it was definitely an increase in the difference between max. coarse and max. fine, not a case of robbing Peter to pay Paul. The result was certainly to benefit the take-off, but I don't know what if any difference there would have been in the dive. I think the other limit was unchanged, but I'm far from sure about that.

I've not seen any suggestion that the Hydromatic prop would actually have cured the problem, or indeed any mention of the Hydromatic in this context. Presumably it did. Even just a little more knowledge of the difference between the two could help. Ahh, Google....

http://files.asme.org/asmeorg/Communities/History/Landmarks/5572.pdf

This does suggests that the amount of redesign was pretty significant.

[John Aero]

Are there any pictures of the Hydromatic in situ without the spinner. From the Joe Smith tables they would seem to be little used on Spitfires.

John

[Test Graham]

If you mean "in situ" on Spitfires, I don't know of any photos offhand. have you something in particular in mind? As for their use on Spitfires, later versions than the Mk.V went over to Rotol anyway. As a working assumption, CB Mk.Vs will have had Rotols and Supermarine's the DH, so only late Mk.Vs would have been possible contenders. Post August 1942, perhaps all of which would have been Mk.Vc?

I feel there are a number of comments above that are possibly open to dissent from the better informed, but if they bring forth helpful comments I'm happy with that.

[gingerbob]

I have seen (but don't remember where, probably buried somewhere in STH) the values for the change in range, but it was definitely an increase in the difference between max. coarse and max. fine, not a case of robbing Peter to pay Paul. The result was certainly to benefit the take-off, but I don't know what if any difference there would have been in the dive. I think the other limit was unchanged, but I'm far from sure about that.

Sorry, we were talking at cross-purposes again. I was referring to an early fix for Spit V dive overspeeds being adjusting the range upward (in degrees), rather than changing to a different prop with a greater pitch-range. However, the other immediate solution (perhaps to both problems) was to use the Mk.II style Rotol as much as possible.

From the Joe Smith tables they would seem to be little used on Spitfires.

The what, John? I don't know any specifics about the later DH, now that I think about it- I just remember comments that it was coming (in late '41, perhaps?) It is possible that I took various comments and thoughts and convinced myself that I knew more than I actually did.

bob