Hamilton Standard Hydromatic propeller - Australia

98octane · Jun 19, 2021

Thanks MiTasol. The welch plug in my prop was 6mm and in the centre of the screw thread, as you suggested. I decided to carefully drill it out, which worked perfectly. No damage. I'm cleaning it up anyway, so any debris will be removed.

Michael Hope · Jun 20, 2021

98octane said:
Hi everyone, I did buy the de Havilland prop and am finally getting around to cleaning it up.

I can't work out how to take the dome retaining nut off the dome (brass ring in the attached photos). I've unscrewed every screw I can find, but it still doesn't slide off even with force.

From old drawings of similar Hamilton Standard dome assemblies, it appears there may be ball bearings holding the dome retaining nut to the dome. Is this right?

I found this website useful, but doesn't answer my specific problem! de Havilland Propellers

Does anyone know how I can remove it?

Thanks in advance.

On the Hamilton Standard Propellers which have a welsh plug to seal the a row of loose ball bearings that have to be removed to remove the nut. It appears there is a welsh plug on two of your images. You can either drill it out by using a small diameter drill and then use a punch in the hole to work the welsh plug loose. Do not drill it the size of plug, the drill must be much smaller than the plug size.

Here is the text from H/S manual 140D in how to remove the nut:

The smaller steel dome shell for the 22D30 propeller is retained by wires and has no ball bearings to hold the nut to the dome shell.

98octane · Jun 20, 2021

Michael Hope said:
On the Hamilton Standard Propellers which have a welsh plug to seal the a row of loose ball bearings that have to be removed to remove the nut. It appears there is a welsh plug on two of your images. You can either drill it out by using a small diameter drill and then use a punch in the hole to work the welsh plug loose. Do not drill it the size of plug, the drill must be much smaller than the plug size.

Here is the text from H/S manual 140D in how to remove the nut:
View attachment 629204

The smaller steel dome shell for the 22D30 propeller is retained by wires and has no ball bearings to hold the nut to the dome shell.

Thanks Michael. I drilled it out using a smaller diameter drill bit and this worked perfectly. Took a while to get all the ball bearings out, though. Decades old grease in there!

Nevw · Oct 23, 2025

Michael Hope said:
By looking at the direction of rotation, it is not from a Beech 18 or Cessna Bobcat with the original powerplants from North America.

In my opinion, with over 40 years of propeller service work and licenced to recertify, the corrosion on the blades would not be able to be removed and still be within airworthy limits.

It is very easy to determine if the prop is for a British or American engine, Usually British engines rot a clockwise from when viewed from the front.
American engines rotate anticlockwise when viewed from the front by establishing the direction of rotation you can find out very easily what engine is called

MiTasol · Oct 23, 2025

That is correct for probably 90+% of engines but both countries produced engines with opposite rotations for specific purposes.

For that size prop though I doubt there was an opposite rotation engine so I would be thinking something like the Agricola ag aircraft or some of the later Percival designs - all British, as you suggest.

Hamilton Standard Hydromatic propeller - Australia

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