Lancaster - engine out?

[Hooli]

Forgive me if I'm wrong but at coarse pitch the prop would normally take a bigger chunk of air & theoretically move further forward for each turn? so wouldn't that make it spin faster?

[magpie215]

Just found out the ninth red swallowed a bird hence why only 8 displayed...apparently it is going to be reduced to spares.

[MOTORVATOR]

Hooli said:

Forgive me if I'm wrong but at coarse pitch the prop would normally take a bigger chunk of air & theoretically move further forward for each turn? so wouldn't that make it spin faster?

Nearly there. Bigger pitch takes a bigger chunk of air per revolution > same amount of air therefore will turn a finer pitch faster as it uses less per revolution.

[Eric Mc]

magpie215 said:

Just found out the ninth red swallowed a bird hence why only 8 displayed...apparently it is going to be reduced to spares.

The bird?

[Simpo Two]

dr_gn said:

Simpo Two said:

Eric Mc said:

If the prop cannot be fethered and it starts to windmill in the airflow, you can end up with a runaway prop and the whole propellor assembly or even the engine itself can be ripped off the wing.

How can a (passive) prop rotate faster than the air that's driving it round? If that happened wouldn't the airflow slow it back down?

Variable pitch propellers remember - its analagous to going from fifth to first in your car...

I had forgotten about the engine on the back. But unless the prop is accidentally put into fine pitch (first gear to use your analogy) which might break the engine by over-revving, I still don't see how it can spin faster than its design limits.

[Hooli]

MOTORVATOR said:

Hooli said:

Forgive me if I'm wrong but at coarse pitch the prop would normally take a bigger chunk of air & theoretically move further forward for each turn? so wouldn't that make it spin faster?

Nearly there. Bigger pitch takes a bigger chunk of air per revolution > same amount of air therefore will turn a finer pitch faster as it uses less per revolution.

Learn something everyday, I just assumed the airflow would be enough to wind it up in 'top gear'.

[MOTORVATOR]

Simpo Two said:

dr_gn said:

Simpo Two said:

Eric Mc said:

If the prop cannot be fethered and it starts to windmill in the airflow, you can end up with a runaway prop and the whole propellor assembly or even the engine itself can be ripped off the wing.

How can a (passive) prop rotate faster than the air that's driving it round? If that happened wouldn't the airflow slow it back down?

Variable pitch propellers remember - its analagous to going from fifth to first in your car...

I had forgotten about the engine on the back. But unless the prop is accidentally put into fine pitch (first gear to use your analogy) which might break the engine by over-revving, I still don't see how it can spin faster than its design limits.

Don't variable pitch props generally stay in fine pitch until a load is applied i.e. they stay fine until the revs are high enough for the hydraulics to power the blades into a coarser pitch?

So fine pitch is default I think.

[eharding]

MOTORVATOR said:

Simpo Two said:

dr_gn said:

Simpo Two said:

Eric Mc said:

If the prop cannot be fethered and it starts to windmill in the airflow, you can end up with a runaway prop and the whole propellor assembly or even the engine itself can be ripped off the wing.

How can a (passive) prop rotate faster than the air that's driving it round? If that happened wouldn't the airflow slow it back down?

Variable pitch propellers remember - its analagous to going from fifth to first in your car...

I had forgotten about the engine on the back. But unless the prop is accidentally put into fine pitch (first gear to use your analogy) which might break the engine by over-revving, I still don't see how it can spin faster than its design limits.

Don't variable pitch props generally stay in fine pitch until a load is applied i.e. they stay fine until the revs are high enough for the hydraulics to power the blades into a coarser pitch?

So fine pitch is default I think.

Depends on the application. General-purpose props tend to fail to the fine setting, so you can still get full power through the prop (although if you've lost oil pressure in the hub then the chances are the engine won't be lasting for long anyway). Aerobatic props tend to fail coarse, because all that larking about will naturally result in fluctuations in oil pressure to the hub, and you want to avoid the potential for overspeeding the engine.

[richw_82]

I'm assuming the Lancaster is similar to the Shackleton in that it has a reserve in the oil tank for feathering purposes. I don't have access to a scanner at work so I can't copy bits of the DH propeller manual I have.

This link explains the processes well regarding pitch change, feathering, and how it all works..

http://napoleon130.tripod.com/id697.html