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Spitfire Propeller Question


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#1 Spitfire addict

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Posted 27 October 2012 - 12:59 AM

Hello again,
I have been a bit prolific with the posts lately I know, but now that it is finally cooling down enough to work in the garage I can model again, so thusly the questions. Anyway, I do have a question I have been meaning to ask for quite some time. It seems that the props on the Spit Mk I thru V have a variety of propellers of varying types that were used (I've seen a few different props on the later model Merlin powered Spits), anywhere from the Rotol versions to the DeHavilland, along with different spinners of course. I understand the evolution somewhat but why were so many types used? Was there a method to the madness or was it more arbitrary? Did it have to do with who supplied the props to Castle Bromwich, Woolston, Itchen etc? If indeed all those facilities were installing the props. I imagine Edgar or Graham would know about this topic, but all are welcome to chime in.
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#2 gingerbob

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Posted 27 October 2012 - 01:31 AM

In the beginning was the fixed-pitch two-blade prop. British production of more sophisticated props was not yet established.

De Havilland got the license to produce Hamilton Standard variable-pitch props, and this became the standard on the Spit Mk.I, as a two-position prop (fine or coarse).

Meanwhile Rolls Royce and Bristol, the two dominant engine manufacturers, teamed up and created Rotol (get it?) to manufacture constant-speed props using a different pitch control mechanism, and different patents. They designed a prop that was intended to be suitable for both the Spitfire and the Hurricane, and this was tested on some Spit Is, and became the standard on the Mk.II and on the Hurri Mk.I (possibly with different diameters). There was not enough production initially to fit to everything. This prop used a blunt spinner, roughly hemispherical.

Fortunately it was quite an easy matter to convert the DH two-position prop to instead be constant-speed- basically the addition of a prop governor and control. DH did this as an emergency programme just in time for the Battle of Britain. In early '41 there was a shortage of Rotols (partly because of a higher rate of blade wastage than anticipated), so some late Mk.IIs used DH props.

The prototype Spit Mk.III first flew with a standard DH prop (in March '40) but was soon fitted with the Rotol designed for it- this became a standard on the Mk.V from late summer or autumn '41, and is the type with long, pointed spinner (though some Mk.Vs can be found using it with the Spit Mk.II style blunt spinner) and blades that are roughly triangular- an airfoil shape right to the spinner.

At about the same time, or a bit later perhaps, DH introduced a "Hydromatic" prop that worked differently. In the early days Rotols used a magnesium blade, but soon they used primarily a wood-composite blade. DHs were, I believe, solid aluminum blades. Spit Vs used all of the 3-blade props mentioned!

The Mk.VI (Spit) introduced a 4-blade Rotol, which was also used on early production Mk.IXs. That should take you far enough to answer the immediate question.

bob

Edited by gingerbob, 28 October 2012 - 09:36 AM.


#3 Spitfire addict

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Posted 27 October 2012 - 02:55 AM

Thanks mate, that gave me a good background on the prop situation. Luckily I have just about all the options with the DH and Rotol props in the Hasegawa Mk V. I am looking to make an early Mk V out of my Tamiya kit using the Hasegawa DH prop. There is a beautiful example of an early Mk V that is flying in Poland which is on YouTube, painted in the green and brown DFS. Anyway, I assume the types of props used were a product of time and supply.
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#4 gingerbob

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Posted 27 October 2012 - 08:35 AM

Yes, time and supply- as a general rule, Supermarine-built used DH (all Va, and early Vb) and early Castle Brom Mk.Vbs used Rotol. Also, the PRU Spits were early recipients of Rotols. You can find photos of one squadron's Mk.Vs with at least three different prop/spinner combinations!

Incidentally, backing up a bit, the Merlin III differed from the Merlin II partly by having a prop shaft that could take either DH or Rotol props. Which begs the obvious question: what was the Merlin II's shaft designed to fit?

bob

#5 Andrew Jones

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Posted 27 October 2012 - 11:13 AM

Yes, time and supply- as a general rule, Supermarine-built used DH (all Va, and early Vb) and early Castle Brom Mk.Vbs used Rotol. Also, the PRU Spits were early recipients of Rotols. You can find photos of one squadron's Mk.Vs with at least three different prop/spinner combinations!

Incidentally, backing up a bit, the Merlin III differed from the Merlin II partly by having a prop shaft that could take either DH or Rotol props. Which begs the obvious question: what was the Merlin II's shaft designed to fit?

bob


Always thought that was a bit odd, would seem logical to make the prop to fit the engine, rather than the other way round.

Andrew

#6 JMChladek

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Posted 27 October 2012 - 11:39 AM

Considering when the Merlin II engines came out in production (1937-38), only the fixed pitch two blade props were around, its possible the Air Ministry and Rolls hadn't thought far enough ahead to consider putting the universal shaft on it yet as the primary goal was to get the Merlin into standardized production first. The planes were needed for squadron level testing and familiarization, so might as well go with what you have rather than waiting a little longer for something better.

It doesn't seem like many Spitfires got the Merlin IIs though, just the earliest production batch. Merlin IIIs on the otherhand came out a little later and by that point, DH was doing their three bladed prop work. So I would say there was probably a version of the DH two speed prop fitted to the Merlin II equipped aircraft only, unless a decision was made to pull those engines out and replace them with Merlin IIIs when the props were converted. I am just guessing at that though as I don't know what procurement was like at the time. I have read though that there was a tiny handful of 2 bladed Watts prop equipped Spits around as late as May-June 1940. So I have to wonder if they were perhaps the very last Merlin II equipped Spits in the fleet and the shaft design precluded them from getting converted to DH props with the Merlin III powered aircraft. Since a fixed prop has no internal workings to worry about, it could be tooled up easily enough to work with one shaft or the other.

#7 gingerbob

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Posted 27 October 2012 - 11:57 AM

I believe, though, that the Fairey Battle (as an example) was using a DH from the outset, and went from Merlin I to II to III. It shouldn't be too hard to find an answer, but I'm not sure I'm going to be able to go looking right now. Bombers had priority over fighters for the VP props, but the Air Min knew they would be wanted on the fighters as soon as supply allowed.

I agree it seems odd to say "Err, Rolls Royce, terribly sorry old chap, but you're going to have to re-design your drive shaft to accommodate our new prop." Ah [he thinks], but since Rotol was half RR, perhaps it was a case of "This design is superior, so we'll make the shaft to take it."

bob

#8 Spitfire addict

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Posted 27 October 2012 - 01:02 PM

It would also seem to make sense that as the power plants increased in horse power other props were used that were perhaps more efficient? If you look at the Dehavilland prop blades, in comparison to the Rotol the chord was much smaller. With the greater horse power of the later Merlins the wider chord props could be utilized making the aircraft faster. Just a thought. Also, I just that about the Jablo props, who manufactured those?
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#9 Seawinder

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Posted 27 October 2012 - 03:21 PM

It would also seem to make sense that as the power plants increased in horse power other props were used that were perhaps more efficient? If you look at the Dehavilland prop blades, in comparison to the Rotol the chord was much smaller. With the greater horse power of the later Merlins the wider chord props could be utilized making the aircraft faster. Just a thought. Also, I just that about the Jablo props, who manufactured those?
Cheers


Jablo prop blade blocks were manufactured by Jablo, then milled, machined and sheathed by Rotol. Here are a couple of useful threads on the subject:

http://www.britmodel...fire +propeller
http://www.britmodel...er#entry1030399

Also this one, which involves the metal blades found on early Mk. IXs:
http://www.britmodel...er +yellow +tip

#10 Jennings Heilig

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Posted 27 October 2012 - 03:43 PM

I seem to have found a photo of a Mk.Vb with the bulbous spinner and the later Mk.V style Jablo prop, usually seen with the longer, more pointed spinner. Was that possible???

Edited by Jennings Heilig, 27 October 2012 - 03:44 PM.


#11 gingerbob

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Posted 27 October 2012 - 06:28 PM

Yes, I mentioned that in post 2 but may not have put it very clearly.

bob

Edited by gingerbob, 28 October 2012 - 09:36 AM.


#12 gingerbob

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Posted 28 October 2012 - 11:59 AM

From Flight 3 Nov '38:

The Merlin III, now being introduced into the R.A.F. in succession to the Merlins I and II, is actually the same
engine as the Merlin II, but embodies a standardised airscrew shaft to take either the De Havilland or Rotol
variable-pitch airscrews. Another modification is the provision of a dual drive for accessories at the front end.

But we knew that already!
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#13 Jennings Heilig

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Posted 28 October 2012 - 05:25 PM

Yes, I mentioned that in post 2 but may not have put it very clearly.


Cool, thanks! That answers a nagging question...

#14 Jennings Heilig

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Posted 28 October 2012 - 05:28 PM

One more question:

Wooden Rotol prop?? Jablo prop???

How does "Jablo" fit into the equation in Post #2??

#15 Seawinder

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Posted 28 October 2012 - 07:34 PM

One more question:

Wooden Rotol prop?? Jablo prop???

How does "Jablo" fit into the equation in Post #2??


I can't tell you which were used on which specific variants, but there were at least three different brands of wooden blades used by Rotol in their propellers: Jablo (Jablo Ltd. of London, Hydulignum (Hordern-Richmond Ltd.; like Jablo, non-impregnated, densified wood laminates), and Airscrew/Weybridge (laminated spruce and/or fir).

Edited by pnmoss, 28 October 2012 - 07:34 PM.


#16 John Aero

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Posted 28 October 2012 - 08:46 PM

The Merlin III first introduced a necked down propeller shaft with a smaller securing nut which was designed to protect the threads when fitting/changing propellers This was subsequently adopted for all later Merlins and was also adopted as the universal shaft for accepting Rotol and DH propellers. It would seem that around this time Bristol engines (the other half of Rotol) also adopted this universal shaft. It might be that the original difference was the number of splines used when DH's took on manufacture of an American design (Ham Std). The three manufacturers of "improved wood" propeller blades all employed very different blade construction. DH blades were of forged duralumin.

John

Edited by John Aero, 28 October 2012 - 10:58 PM.


#17 Jennings Heilig

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Posted 28 October 2012 - 09:22 PM

Ah so, so Jablo was just one manufacturer of the same type of compressed wooden blade. Gotcha. So a Rotol prop (assembly) could have blades made by any of those three manufacturers...

Muchos groceries amigo!

#18 Seawinder

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Posted 29 October 2012 - 02:27 AM

Ah so, so Jablo was just one manufacturer of the same type of compressed wooden blade. Gotcha. So a Rotol prop (assembly) could have blades made by any of those three manufacturers...

Muchos groceries amigo!


Yes. Hence the usefulness of the colored disks, which showed the material used in the blades and (sometimes) the sheathing. Here are two excerpts from the Rotol manual. The first shows the original colour denotations, the second the revised denotations starting sometime in 1944. After the revision, white disks denoted metal blades. I can't document it, but I believe Rotol used light blue disks for metal blades before the revision.

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#19 sloegin57

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Posted 29 October 2012 - 02:59 AM

If you go to the Flight Archive and to "Flight" for November 26 1942 (1942 - 2476.pdf), there is a very interesting article on how hydulignum prop blades were made (Hordern-Richmond Aircraft Company).

DR

#20 Spitfire addict

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Posted 29 October 2012 - 02:03 PM

I am still wondering why so many types of blades? The Air Ministry for the most part seemed to be quite particular about many things involving aircraft, and I haven't seen such a selection of props on other aircraft. The sleeves wouldn't explain the different shapes of propellers used. It would be interesting to find out which prop was the most effective of the different models used. From all the pictures I have seen of the later model Mk V Spits the Jablo/Rotol wide bladed props were the most used even with the universal shaft. Perhaps this was the most efficient prop for the powerplant and airframe in comparison to the DH or Hamilton Standard which seems to follow HS design standards (the same outline is seen on the Corsair, and I also wonder if a wider chord blade would have been more efficient.) I was just thinking that they could have standardized the props with allowance for the early and later universal shafts. It would also be interesting to see what the performance difference, if any, of the Spitfires that used either of the two types common on the Mk V.
Cheers