4 bladed props

[richardc7]

Many WW2 birds were sporting 4 bladed props at the end of the war. Anyone know why?

[FLYBOYJ]

Originally Posted by richardc7

Many WW2 birds were sporting 4 bladed props at the end of the war. Anyone know why?

Based on higher HP engines, engineers determined that on some aircraft hey were able to get the maximum thrust efficency from a 4 blade propeller.

[SoD Stitch]

The late Marks of Spitfire (those with the larger Griffon engines, in particular) even had five-bladers by the end of the War.

[ccheese]

I've got a pic of a bf-109 [actually a HA-1009] with a RR Merlin in it
sporting a four bladed prop !!

Charles

[krieghund]

a three blade prop has a higher efficency but the diameter of the prop to accept the greater HP would exceed the length of the landing gear so the only way around was to add more prop blades. However, there are some sources that claim that a four blade is more efficent at high altitude.

Hope that helped

[Burmese Bandit]

Tip speed plus landing gear length is the short answer. If an engine has a high output you need either more prop area or a higher prop rpm to use that power efficiently. Higher prop rpms will make the prop tips exceed the speed of sound, causing tip vortex problems. Longer props with more area are more efficient, and they solve the problem of lower rpms, but you need a longer landing gear to get ground clearance for the props (hence the highly problematic and expensive telescopic landing gear of the P-47). Another solution is to add more blades to the props. This solves the problem, with the exception of propeller torque - but that could be solved with contrarotating props on the same axis, which is dicussed in another thread on this forum.

[Airframes]

Charles mentioned a 'Buchon' with a four-bladed prop, which was not uncommon after the BoB movie. I've got some pics (slides, unfortunately) of one of the BBMF's Hurricanes, in the early '80's, with a four-bladed prop. Didn't look at all right, but apparently, according to the BBMF pilots at the time, it made a heck of a difference to overall performance. BTW, this difference is allowing for the fact that the Merlin fitted, I think a 66, but not sure, was a later model with more output than the engines originally fitted to the various Marks of Hurricane.

[109ROAMING]

Me too Terry I've seen both the Hurricane and Buchon with 4 bladed props

my opinion -They look absolutely horible

maybe just because I'm not use to it but they do look hedius