Merlin 500-XX propeller governor

[Startiger]

I teach in a school for aviation technicians and we have a spare RR Merlin 500-XX propeller governor; I'd like to dismantle this unit to show my students "the real thing" not just a cutaway diagram.
Does any one have a cutaway or, even better, a manual of this item? We have some RR Merlin overhaul manuals but not for this particular version.
I'd like to avoid any damage/injury with the main spring and if guessing the right way to approach the piece could be very useful.
This engine was used with a FIAT G-59, most likely a -4B version (two place, training version); the propeller, as far as I know, was a FIAT-Hamilton Type 5010.
Thanks a lot for any help!

 

[dairwin]

Hi,

Your 500-XX for a Fiat. That will be the 500-20 model engine.

You mention 'propeller governor'. I assume you are referring to the Constant Speed Unit (CSU)?

I have a Merlin 500/29 which is equipped with a deHavilland CSU. However, the different types are quite similar, although I am not familiar with any Fiat specific CSU. (I suspect it is modelled on a deHavilland hydromatic type). There is at least one -20 manual I have which you can also acquire from the following website:

Rolls Royce Packard FIAT Motori Aviazione Merlin 500-20 Aircraft Engine Instruction Manual

Propeller type 5010 here:
FIAT 5010 Aircraft Propeller Maintenance Manual - Elica - Montaggio

DAI

 

[Startiger]

Thanks a lot dairwin! You are right 500-20 is the correct model and not 500-XX as I stated.
I'll look for these manuals. At present I can only look at "Motori di aviazione" (Aircraft engines), an old textbook (1965) for ITAF engine repairmen, very useful to understand the basic but not specific enough.
Sincerely I don't know if is a FIAT specific CSU; I'm writing from home and I have no chance to cross-check any plate on the item - I'll check tomorrow morning.

 

[Startiger]

The label riveted on the item reads:
Hydraulic Governor made by Mash-Kelvinator Corporation
Under license from Woodward Governor Co and Hamilton Standard propellers"
serial K17884E-W535 AC25051

 

[dairwin]

So it is a Hamilton Standard propeller governor, which is the same as mine (in effect). Nash-Kelvinator made the paddle blades on late-WW2 Ham Stan and DeHav propellers.

Today I happened to visit the Science Museum in London to take some photos of the Merlin MkIII there. Whilst there, I remembered your interest in the CSU and took the following photos of a sectioned CSU on a two-stage Merlin.

Not the same, but similar to the Ham Stan CSU. There is a spring inside, near the top, but nothing I believe that would be amiss for careful dismantling.

DAI

 

[Startiger]

I'll take a couple of snapshots of "my" governor in a short time... in the meanwhile many thanks for your pictures!

 

[vintage aero engines]

the xx is roman for 20

 

[dairwin]

the xx is roman for 20

Yes, however these late Merlins use standard numbering (Roman was used from MkI to XX only).

The 500 series engines are post WW2 Merlin numbers for either foreign military or civilian operators. The -20 specifically was used on a Fiat G59 aeroplane.