Rotol and D.H. Constant Speed Prop Operation

XBe02Drvr · Nov 4, 2020

nuuumannn said:
Same on the other P&WC turbines, the PW100 series for example, all free turbine engines.

Look at any turboprop parked on the ramp. If the props are feathered, you're looking at free turbine engines. I'm prejudiced, but I think they're the better way to go. My ladyfriend disagrees. She flew Dornier 228s, ATR72s, and SAAB 340s before she went on to jets, and she likes direct coupled turboprops. Now that she's retired, she hasn't touched an airplane since.

nuuumannn · Nov 4, 2020

Yup, I never worked on them, but our airline had Metros and Saab 340s before the Dashes and ATRs and a few of our guys have worked on Jetstreams with the Garret. I don't know if they have preferences, although most enjoyed working on the Saab compared to the Dash, but the Dash compared to the ATR. That one I can relate to. My previous turboprop experience was on C-130s and P-3s, so a little different, but I didn't do much engine work on those.

gecko · Nov 4, 2020

I fly a C208 with a PT-6A, and it does not feather automatically on shutdown. You still have to select it.

Thanks guys for posting the Rotol manual and the D.H. diagrams, they helped answer my remaining questions. The Rotol manual specifically talks about the positive coarse pitch condition - the same term used to describe the D.H. setting in the Spitfire notes, and it simply means the blades are held at the coarse stop when an R.P.M. is selected low enough that the blades hit the their coarse limit - so nothing new there. It is strange that the pilot's notes go out of their way to point this out for the D.H. only, when the Rotol operates the same way in that respect..

MiTasol - that handle wouldn't be Tok Pisin would it?

XBe02Drvr · Nov 5, 2020

gecko said:
I fly a C208 with a PT-6A, and it does not feather automatically on shutdown. You still have to select it.

I've never flown a PT6 powered single, just twins. Very interesting. The ones I flew, Be99, Be1900, C425, and DHC6, would go into a feather-like condition when the condition levers went to IDLE CUTOFF. They had a big spring in the dome that, when oil pressure bled down, would drive the blades toward feather. When autofeather was armed for takeoff an uncommanded large loss of torque in an engine would immediately dump oil pressure going to the prop and disarm the other engine's autofeather. Function checked before every takeoff.

Michael Hope · Nov 5, 2020

gecko said:
I fly a C208 with a PT-6A, and it does not feather automatically on shutdown. You still have to select it.

Thanks guys for posting the Rotol manual and the D.H. diagrams, they helped answer my remaining questions. The Rotol manual specifically talks about the positive coarse pitch condition - the same term used to describe the D.H. setting in the Spitfire notes, and it simply means the blades are held at the coarse stop when an R.P.M. is selected low enough that the blades hit the their coarse limit - so nothing new there. It is strange that the pilot's notes go out of their way to point this out for the D.H. only, when the Rotol operates the same way in that respect..

MiTasol - that handle wouldn't be Tok Pisin would it?

The C208 with the PT-6A series, can have an optional zero pitch lock installed to keep the blades at a neutral pitch, i.e. no forward or reverse thrust, when operating on floats so that when starting you do not have forward thrust that takes you where you do not want to go while the engine spools up. There are other aircraft on floats that have this feature, like the DCH-6 Twin Otter.

gecko · Nov 5, 2020

XBe02Drvr said:
I've never flown a PT6 powered single, just twins. Very interesting. The ones I flew, Be99, Be1900, C425, and DHC6, would go into a feather-like condition when the condition levers went to IDLE CUTOFF. They had a big spring in the dome that, when oil pressure bled down, would drive the blades toward feather. When autofeather was armed for takeoff an uncommanded large loss of torque in an engine would immediately dump oil pressure going to the prop and disarm the other engine's autofeather. Function checked before every takeoff.

Most (modern) single engine props will default to fine pitch via spring to enable the easiest possible restart if the engine quits, with twins on the other hand you want it feathered ASAP. I think that's the main reason for the difference. I've not seen a prop on an SE piston that feathered at all. On the caravan, the feather position on the prop lever overrides the governor via mechanical linkage when selected.

BarnOwlLover · Jun 28, 2023

Since the DH props were essentially similar to Hamilton props of the period, would the Rotol props be similar to the Aeroprop propellers? The XP-51G started out with a 5 bladed Rotol prop but it got replaced with a 4 bladed Aeroprop propeller (similar to the later P-51H).

Michael Hope · Jun 28, 2023

BarnOwlLover said:
Since the DH props were essentially similar to Hamilton props of the period, would the Rotol props be similar to the Aeroprop propellers? The XP-51G started out with a 5 bladed Rotol prop but it got replaced with a 4 bladed Aeroprop propeller (similar to the later P-51H).

The DeHavilland Propeller was originally a licensed built Hamilton Standard propeller, which DeHavilland then made their own modifications to. The Rotol propeller is nothing like a an Aeroprop propeller id design. The Rotol propeller has an external pitch change piston.
Here is an image of a four bladed Rotol as used on a MK VII. VII and IX Spitfire.

BarnOwlLover · Jun 28, 2023

Makes me wonder what the difference was between an Aeroprop and a Hamilton propeller, since both were used on Mustangs. Of note was that Hawker Typhoons and Tempests did use DH and Rotol props interchangeably it seems (same as P-51Ks with Aeroprops and later being refitted with Hamilton props, essentially converting them to P-51Ds).

MiTasol · Jun 29, 2023

On the Aeroprop the pitch change mechanism is inside the blades and there is no dome

On the Ham Std Hydromatics used on most post 1940 aircraft the pitch change mechanism is in the dome. Many earlier designs, and low horsepower designs, used HS props with external counterweights

image from manual in my collection

image from net

Rotol and D.H. Constant Speed Prop Operation

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XBe02Drvr

2nd Lieutenant

nuuumannn

Major

gecko

Airman

XBe02Drvr

2nd Lieutenant

Michael Hope

Airman 1st Class

gecko

Airman

BarnOwlLover

Staff Sergeant

Michael Hope

Airman 1st Class

BarnOwlLover

Staff Sergeant

MiTasol

1st Lieutenant

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