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understand that the D.H. used counterweights and oil pressure, but did the oil pressure work to increase, or decrease pitch? And the same for the counterweights - which direction did they act on the blades?
No, not the 23EX - I'm looking for those fitted to single-engine fighters. I believe the early D.H. ones were Type P.3-5-5-7 two-position props which got converted in the field to constant-speed operation, or the D.H. 5-20.
The Rotol I believe would be the RX2 or RX5.
Thanks, that is great info. Yeah, I'm pretty sure I've seen pictures of the external cylinder for the Rotol. If that is the case would that mean it definitely is dual acting, or is that still in question? Would the governor boosted oil pressure cause pitch to increase faster than it decreases? Does it move to fine pitch with a loss of oil pressure due to the twisting moment?The DE Haviland propeller was similar to Hamilton Standard 3D40 type. It used counterweights to increase pitch and oil pressure to decrease pitch. If you lost oil pressure the propeller would go to full coarse pitch.
The Rotol RX5 I believe to be an external cylinder propeller like the one below. If it is a dual acting propeller it uses high pressure governor oil to increase pitch and then engine oil pressure with centrifugal twisting moment on the blades to decrease pitch. The type of blade, i.e. wooden or metal makes no difference to the operation, just differences in the operating pressures required to change the pitch.
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I have touched and worked on these type of propellers but did not get involved with the pitch change oil supply What I read this morning, I believe they are to be the dual acting type, i.e. dual oil source, one the boosted oil pressure from the governor to low pitch, the engine oil pressure on the smaller diameter piston, the one with the rod in the cylinder. If all engine oil is lost, then engine would stop very shortly after, so the pitch would not really mater as it is now a very day for pilot.Thanks, that is great info. Yeah, I'm pretty sure I've seen pictures of the external cylinder for the Rotol. If that is the case would that mean it definitely is dual acting, or is that still in question? Would the governor boosted oil pressure cause pitch to increase faster than it decreases? Does it move to fine pitch with a loss of oil pressure due to the twisting moment?
Propeller theory for pitch change:I'm a bit confused now. In your first post, you say that boosted oil pressures increases pitch (toward coarse) and engine oil pressure and twisting moment decrease pitch. In your second post you say that boosted oil pressure and twisting moment decrease pitch. The first post makes more sense to me, but there's a lot I don't know.
One other question - the D.H. prop is mentioned in the Pilots Notes for the Spitfire and Hurricane to have a Positive Coarse Pitch setting (airscrew control fully back) where the blades are held in coarse pitch. The same paragraph mentions the Rotol prop, but it apparently does not have this setting. This has always confused me since I thought that having the control all the way back on either prop would effectively command 0 rpm thus ensuring the blades were held in the coarse setting. So how is this special setting on the D.H. different from what the Rotol does? Does the Rotol have a minimum governing rpm where the aft position governs the prop at some higher rpm rather than simply dumping pressure from the fine pitch side of the system?
A Hamilton Standard/De Havilland Counterweight type propeller will blow the cylinder cap if you put 300 PSI oil pressure into it, and the leather seals on the piston will probably leak also. Your statement only works for NON Counterweight blades in single acting propellers. In counterweight blades loose of oil pressure is always to coarse pitch.Thanks. Yes, the governor has its own pump which boosts engine oil (50-70 psi) to approx. 300 psi and ports it to the prop dome/cylinder to move and hold the blades in a selected course pitch. Runaway props are indeed most often governor failures, often a broken drive, in which case the system no longer provides the proper control or high pressure oil to the dome and the blades, counter weighted or not, decay to flat pitch by centrifugal force.
I stand corrected. Thanks.
The Hartzell as well as most other manufacturers, single acting type, with counterweights uses oil pressure to low/fine pitch, regardless of engine type, example is any aircraft with a P&WC PT-6A series engine when the propeller is stopped it is in a feathered position in most casesHi Tom, maybe you have been caught by working on the Hartzel counterweight props on some turbine engines. The mantra on them is oil IN TO drive the blade to COARSE. It is easy to forget that the HS props are the opposite because they are pretty thin on the ground these days.
This is generally the case with a "free turbine" engine where the power turbine turns independently of the gas generator spool. The starter has an easy job if it only has to spin the gas generator shaft. Direct coupled engines like Garrett TPE731s or the big Allisons can't hope to swing a feathered prop on the starter, so have to shut down and start up in a low pitch setting.with a P&WC PT-6A series engine when the propeller is stopped it is in a feathered position in most cases
example is any aircraft with a P&WC PT-6A series engine when the propeller is stopped it is in a feathered position in most cases