Correct prop feathering?

I think we’re trying to say the same thing Hamtech! Indeed any single-shaft turbine or piston is started in fine pitch as the drag from a feathered prop would mean too much resistance for the engine to overcome. In a turbine this would show up as excissively high TIT readings (or EGT). A piston engine would need a lot of fuel and a large starter to get it cranking enough to start. First off that means an extremely large starter (weight penalty) and a lot of electrical power to get it moving. The large amount of fuel will mean high cylinder temps, also bad on a cold engine.

Still you want to design your prop system in such a way that in case of failure the prop moves to the feathered position without any additional needed machinery or power. In small pistons this is usually done through a spring in the prop hub with oil pressure driving the prop to fine pitch during normal flight. A low pitch lock which engages below a certain RPM ensures that the blades don’t move to feather when shutting down. The system probably is pretty similar on most turboprops.

…The reason behind this is that ideally you want the prop to move to a feathered state on its own once you remove hydraulics/pneumatics/electrics or whatever drives the prop…Starting with a prop in its feathered state can only be done on a free-turbine engine though as on a direct drive turboprop or a piston engine the drag of the prop in that state is too much to get the engine started!

Almost there,”free turbine” turboprops can be started feathered as the design will not push the start temperatures up. Sometimes the only reason they are shut down and started feathered is to configure the aircraft correctly (example – fill a feathering oil reservoir).

A single shaft turboprop need to be started in fine to keep the start temperatures down.

– Hamtech.

… as I mentioned in my post above :rolleyes:

The techical term you are grasping for Mike, is Free turbine.

Rgds Cking

Thanks Mike,
I claim no expertese on turboprops. Nasty bast@ard things. Pure jet or big bangin’ pistons for me.

BTW, where was your answer to the original question? :rolleyes:

An impossibly feathered prop maybe? Nice model all the same 😀

Its all that ‘Mustang Fan’ blokes fault!

Actually, I was mostly bluffing… 😉

Too true you were matey. Turboprops don’t naturally rest in a feathered condition. Certainly some of them (PT-6 for example. i.e. the ones with a seperate turbine for the prop drive (Can’t remember the technical term)) Are stopped with the prop feathered so that they offer some resistance to prop rotation until the engine is definitely running. On others the prop blades remain at whatever pitch setting they were at when the engine was shut down.

Actually, I was mostly bluffing… 😉

Very interesting discussion, many thanks to all concerned for the education!

Starfire,

Make it look like these Canadian Seafire XVs and you will not go far wrong. 🙂

Mark

As mentioned before: a Spitfire cannot feather its propeller as it doesn’t have a feathering pump. The reason for feathering a prop is improved performance when flying a multi-engined aircraft with one engine out. Especially when this happens right after takeoff, you will then want the best climb rate you can get and getting rid of a windmilling prop is very important!

On a single engined aircraft a feathering option is never incorporated as once the engine fails you will be going down anyway, feathering will only add the option of putting the aircraft in a field that’s 5 miles away, instead of putting it in a field which is 3 miles away. Not much gain for carrying the extra weight around all the time! The odd one out as James mentioned is the Seafire which was recently restored. With six blades windmilling that aircraft will quickly try to imitate a brick once it gets quiet up front, and since the ex-Shack engine already had the mechanics fitted they decided to incorporate the function. Wise decision probably but I’m hoping the pilot doesn’t need to use it!

As James also pointed out many turboprops are started with the blades feathered. The reason behind this is that ideally you want the prop to move to a feathered state on its own once you remove hydraulics/pneumatics/electrics or whatever drives the prop. This is the safest system as feathering pumps, which are only used when badly needed, can also fail! The crash of the Dutch Dakota in 1996(?) was an example of this. Starting with a prop in its feathered state can only be done on a free-turbine engine though as on a direct drive turboprop or a piston engine the drag of the prop in that state is too much to get the engine started!

Thanks @ all. I will change that. (Glad I never glued the propeller blades to the spinner … or the spinner to the fuselage.)

On Seafire XV’s the prop does not feather in the conventionl sense.

On the ground the prop would look more appropriate in fine pitch, that is with greatest surface area within range to the direction of flight.

Mark

You NEVER see a ‘feathered’ prop on a Spitfire or Seafire. In theory, the prop blades can be turned that far, but it wasn’t achievable (I believe) while everything was connected up. Seen them in a ‘feather’ position when lying on the workbench, or on the RAF Display Flight static ‘assemble by numbers’ Spitfire XVIs.

Feathering was a device to reduce wind resistance and (IIRC) normally occours on multi-engined a/c from the late 30s onwards. Single engined, even with 5 blade props didn’t usually have a feather function, though on contraprops and the Sea Fury, that would be useful! You may note the comment about the feather button on the newly restored Seafire 47 contraprop- which is fitted thanks (I understand) to be possible due to being an ex- Shackleton engine.

Turboprops naturally ‘rest’ in a feathered position. Pistons (generally) don’t.

So, never feathered!

Cheers

It is not really the done thing on a single engined aircraft unless the gliding capabilities are very good. But in my day on Shackletons and other types is that you moved the pitch of the propeller from fine (ie Flat against the airstream) through to coarse pitch (ie that part of the blade showing the least wind resistance)