Napier engines

[PMN1]

The Rapier and Dagger were air cooled but Napier moved to liquid cooled for the Sabre, what was the reasoning for this?

Would the Rapier and Dagger have been better engines if liquid cooled?

 

[OliverSedlacek]

The trade off in aero engines between air and water cooling depends on a lot of factors including intended installation and supercharging strategy. With 1940s technology then a 2000 BHP engine for a fighter will prioritise frontal area, which swings the decision in favour of water/glycol cooling. The Mustang and the Mosquito show how to do a 'no compromise' radiator installation so you don't then throw away your advantage through excess radiator drag.

 

[HoHun]

Hi,

The Rapier and Dagger were air cooled but Napier moved to liquid cooled for the Sabre, what was the reasoning for this?

I would speculate that the higher power of the Sabre in relation to the surface available for heat transfer made liquid cooling the better option. As it seems the two older air-cooled engines were in fact having some difficulties with cooling, maybe these difficulties could in fact have been avoided with liquid cooling, I guess. However, it's not necessarily easy to get liquid cooling to work well, and it does make for a more complex engine installation overall.

I suspect the reason Rapier and Dagger didn't do better is that a 24-cylinder engine that delivers the same power you can have from a contemporary 12-cylinder engine probably is going to be more expensive than the engine with the lower parts count. I have no idea of actual historical prices, though.

Regards,

Henning (HoHun)

 

[OliverSedlacek]

Cost isn't a big factor in a fighter engine if it buys you (reliable) power. In comparison to the contemporary V12s (Merlin, Griffon, DB601/5, DB603, Jumo 213) the smaller cylinder displacement of the Sabre meant it ran higher RPM with a consequent power increase.

 

[HoHun]

Hi Oliver,

Cost isn't a big factor in a fighter engine if it buys you (reliable) power.

If the government can procure a V12 of comparable power and reliability as an H24 at a lower price, fighters will be powered by V12's. Not that the Rapier or Dagger were know for great reliability (nor were they procured as fighter engines).

In comparison to the contemporary V12s (Merlin, Griffon, DB601/5, DB603, Jumo 213) the smaller cylinder displacement of the Sabre meant it ran higher RPM with a consequent power increase.

I suspect the reason Rapier and Dagger didn't do better is that a 24-cylinder engine that delivers the same power you can have from a contemporary 12-cylinder engine probably is going to be more expensive than the engine with the lower parts count. I have no idea of actual historical prices, though.

Regards,

Henning (HoHun)