P-47 Prop question

Discussion in 'Aviation' started by Airframes, Feb 24, 2014.

  1. Airframes

    Airframes Benevolens Magister

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    Maybe this should be posted in the 'Technical' section, but I thought I might get a better response here.

    During the course of research for future projects, I've repeatedly come across anomalies regarding the type of prop fitted to various models of the P-47D.
    For example, in all descriptions of the type, the P-47D-22RE ('razorback) is shown as being fitted with the Hamilton Standard prop, whilst it's equivalent from the Evansville factory, the P-47D-23RA is described as being fitted with the Curtiss Electric 'paddle blade' prop.
    However, a number of photos, correctly captioned as, for example, P-47D-22RE, and supported by the serial number of the aircraft depicted, clearly show the Curtiss prop. This is also the case with the early 'bubbletop' P-47D-25 series.
    Perhaps, in these instances, a replacement Curtiss prop has been fitted, but as this anomaly crops up frequently, it is slightly puzzling.

    Does anyone have any thoughts or, better still, solid information on this subject?
     
  2. T Bolt

    T Bolt Well-Known Member

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    I know we had this discussion at one time Terry. I thought it was in my Razorback thread but I couldn't find it there. I have some info at home and will look tonight, but one thing you should know is that along with the Hamilton Standard prop, there were 3 different Curtiss Electric props used. The original non paddle blade prop used on the early models and 2 paddle blade props, one with symmetrical blades and one with asymmetrical blades.
     
  3. Airframes

    Airframes Benevolens Magister

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    Thanks Glenn, I thought you might have some info. I'm aware of the Curtis props, but it's that Hamilton prop which is bugging me. The shorter, 'blunt' boss on the Hamilton is very noticeable and, even in photos where the prop blades are spinning, or at an angle where the blades can't be seen properly, if the prop boss is visible, and it's 'blunt', then it's the Hamilton prop.
    So far, it appears that only the D- 22RE, which should have the Hamilton prop, is 'affected' - those D- 23RA photos and profiles show the correct Curtis prop. Same with the D- 25RE - seen with Hamilton and Curtis props!
    At first, I thought it was maybe just errors in the captions, in more than one book, but having checked the serial numbers, those shown as, for example, D-22RE, but with the Curtis prop, are indeed the correct model number.
    Even kit manufacturers have provided the Curtis prop, in kits where the Hamilton prop should be fitted. Hasegawa, for example, include one prop hub, one prop boss (Curtiss) and two types of prop blade - both Curtis !!
     
  4. T Bolt

    T Bolt Well-Known Member

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    I wrote this summery of info found in Burt Kinsy’s P-47 in Detail and Scale earlier this morning but it wasn’t there tonight when I checked so I guess I didn’t properly click the “Post” button, so here it is anyway

    There were 4 different props used on the P-47 throughout its production, three different Curtiss electric props and one Hamilton standard. All three Curtis props have a longer, pointed propeller boss while the Hamilton prop has a shorter rounded propeller boss.

    12’-2” Curtiss Electric thin blade, cuffed prop
    Installed on all models through the P-47D-21RA (Evansville plant)

    13’-1 7/8” Hamilton Standard paddelblade prop
    First installed on P-47D-22-RA (Farmingdale plant) and installed on some later production blocks at the Farmingdale plant although it does not state how late this prop was used there.

    13’-1” Curtiss Electric symmetrical, cuffed, padelblade prop and 13’-1” Curtiss Electric symmetrical, cuffed, padelblade prop
    These 2 props were used interchangeably on models from the P-47D-23-RE forward.

    Mr. Kinzy also stated that there was a lot of switching of props in the field so it does not necessary follow than a given aircraft of a certain production block will have the prop type as stated above…..
    So still nothing is certain unless you have a photo of the aircraft from which you can identify the prop type.

    Terry, in your email you mentioned a P-47D-22-RA. The info above stated that the HS prop started with The D-22-RA and the larger Curtiss props started with the D-23-RE. This seems to mean that this aircraft had the thin blade Curtiss prop installed at the factory, but from what I read about the 56th FG’s love for the paddelblade props as soon as they saw them, I think that a -22RA would be a very good candidate for a prop change by them.
    Now to the question of which paddelblade? This is purely conjecture on my part but I think a change to one of the Curtiss paddelblade props might be easier as it would already have the electric prop controls in the cockpit. I don’t know what kind of controls the Hamilton hydraulic prop would have, but I have one of these Curtiss prop switches and it is a very complicated three way toggle switch. I just can’t see it controlling a hydraulic device so I think the controls in the cockpit would also have to be changed. So It could be the HS prop, but I would go with either one of the Curtiss paddelblades, which one is up to you.
     
  5. Airframes

    Airframes Benevolens Magister

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    Thanks again for all your help Glenn (and I've also replied to your e-mail).
    Just one thing though - the Hamilton Standard prop was fitted to the P-47D-22RE, with the equivalent from Evansville being the -23RA, with a Curtiss prop.
    The photo I sent you of the 56 FG aircraft (shown below) is a -22RE, but with a Curtiss prop, and, as you noted, the Group preferred the 'paddle blade' type prop, and also had aircraft fitted with the HS prop at the same time.
    In the case of the 56th FG, it may just be that some testing of props versus performance was being undertaken, as we know they worked closely with Republic in the development of the P-47, or it may be just a case of changing props, although with different prop controls, that probably wasn't as easy as it sounds.
    But it's still puzzling that other examples crop up, in other Groups.
     

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  6. vikingBerserker

    vikingBerserker Well-Known Member

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    Great info Glenn, very interesting!
     
  7. T Bolt

    T Bolt Well-Known Member

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    That makes sense Terry, With Republic reps on site I can see a lot of experimenting going on and I'm sure those guys wouldn't let a little thing like the cockpit controls keep them from changing the props.
     
  8. Aaron Brooks Wolters

    Aaron Brooks Wolters Well-Known Member

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    #8 Aaron Brooks Wolters, Feb 27, 2014
    Last edited: Feb 27, 2014
    The book I have, states, and I don't know how accurate it is, but it says that the Curtiss Electric Paddle blade with a diameter of 13 feet, was first installed on the D-22. The Hamilton Standard was installed on the D-25 which was the first of the Bubble tops. Like I said, I don't know how accurate this is. The book is P-47 Thunderbolt In Action No. 208 by Larry Davis. And as far as miss matching props it may have had to do with were the aircraft was built, but I'm not sure. I'm not trying to step on any toes here in any shape, form or fashion, just tossing out what I have as far as info.
     
  9. nuuumannn

    nuuumannn Well-Known Member

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    Hi guys, I don't know whether this will be of any help to you, but I have had practical experience with the Ham Std Hydromatic props in the past - having worked on them. I have none with the Curtiss prop, but I have a basic idea of how it works. Both use different mechanisms in their hubs to achieve the same end.

    The Hydromatic prop relies on differential oil pressure acting on a piston located in the dome out front, hence why its so big, to change the blade angle. This works by the supply of oil from the governor, which 'senses' changes in engine rpm and consequently allows oil to flow through the prop shaft to a distributor valve in the hub. It doesn't require any further controls in the cockpit, apart from the condition lever (propeller pitch), which is a "master' control for determining which blade angle range to use at which engine power setting, which is controlled by the power lever, depending whether the aeroplane is on the ground or taking off or cruising, or what have you.

    The Curtiss prop, the action is all electric. The smaller hub has a speed reducer forward of the blades and an electric motor ahead of that fitted with a speed brake. The governor does the same job as it does on any aeroplane, but it sends electrical signals via a relay to the prop, which is fitted with slip rings on its shaft. these generate power via brushes which drives the motor, which in turn via the speed reducer, a mechanical device, converts the speed of the rotation of the prop to alter the blade angle. The switches in the cockpit also connect to the prop via the relay box. Their function is to configure the prop as either fully variable pitch using the condition lever and governor set up as installed in any VP equipped aeroplane or to set the prop at a fixed angle by shutting off the electrical signals to the governor. In effect this produces a fixed pitch condition, which can be over-ridden, but would be used during cruise or lengthy climbs and to feather the prop if necessary. On Ham Std props, feathering is also done electrically. Nominally however, with Curtiss props, the use of the condition lever was the same as any other aircraft.

    As for interchangeability - and I'm only guessing, the wiring would have been installed at the factory and instead of removing it to fit a Ham Std prop, it is most likely that it was terminated and left in situ and the cockpit switch panel was removed and the space blanked over. Glenn, if you look on the back of your switch panel, you'll see that the wires connect directly to the switches; removing these would be no problem at all; its something we do at work all the time, although these days, switch panels are connected to the aircraft wiring by cannon plugs, which make life easier, - it means you don't have to reconnect wires every time you change a box.

    Alternatively, the wiring could have been removed, which was quite possible in the field and it wouldn't have been a big task, although it might have been a bit awkward given space limitations. Just removal of the wiring itself, the relay, the switch panel and the prop. The governor wiring would stay in place if the aircraft has a feathering prop, although not all single-seaters had these - blade angle range determines that - but it wouldn't be too much effort in the field.

    Like I said, these scenarios are guesses, but are most likely. I've heard of Ham Std props substituting Curtiss Electric ones on other types during the war; the early British Liberators, specifically the Lib Mk.II was built with the Curtiss prop, but those ones diverted to the USAAC were retrofitted with the Ham Std props. A number of P-40 owners today have fitted the Ham Std prop to their aircraft rather than the original Curtiss prop - simplicity, I guess. Parts might be another reason to do it these days.
     
  10. Airframes

    Airframes Benevolens Magister

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    Thanks Grant. I had a (very) basic knowledge of how the two systems worked and, now that you've explained the set up, it probably wasn't such a big job to change the type of prop and connect the relevant cockpit controls.
    Aaron, thanks for the input, although the information in that particular book sounds a little inaccurate.
    In all the descriptions and technical specs I've seen, in fourteen different books, the -D22RE (razorback) is shown as the first to have the Hamilton Standard prop, with the -D25RE being the first of the bubbletops to have this prop fitted, both of these aircraft being produced at the Farmingdale factory.
    The equivalent to the Farmingdale -D22 razorback from the Evansville factory, was the -D23RA, and this is shown as the first to have the Curtiss, 13 ft paddle-blade prop, with the bubbletop from that factory being the -D26A, also with the Curtiss prop.
    I'm guessing then, that the photo evidence showing types apparently with the 'wrong' prop is simply a case of either 'available replacement', preferred replacement perhaps due to servicing requirements or, in the case of the 56th FG, perhaps some form of trials.
    Many thanks for the responses chaps.
     
  11. T Bolt

    T Bolt Well-Known Member

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    Some real good info there Grant, it explains a lot. So it may have been a simple operation to go from a Curtiss to a Hamilton and just leave the Curtiss controls there but disconnected, but going from a Hamilton to a Curtiss would have been a little more difficult because the cockpit controls would have to been installed.

    I posted these pics just to show what the Curtiss switch looks like. The first one shows the installation in the later "D" models on the left side of the control panel, but it was the same switch in the earlier models, only it was located in the main switch panel on the left cockpit wall at the floor.
     

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  12. Airframes

    Airframes Benevolens Magister

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    Good stuff Glenn. So it really was a simple electric switch selection - one for fixed pitch, and one for automatic constant speed.
    Must have been easy, rather than using a lever. Got me wondering now if the mechanical/hydraulic Hamilton system was preferred due to positive operation, if there's been experience of the switch system failing. I seem to remember reading incidents of electric pitch change units not working properly, with the prop stuck in the last selected position, or worse, between pitch settings, although I don't remember if this was on the P-47 or another aircraft type.
    See, modelling is educational!
     
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