Propeller cuffs

I have seen these on the propellers of radial-engined airplanes and read that they were used to force more cooling air over the cylinders. I have noticed them on P-51 B, C, D and H Mustangs, but I have not come across any explanation of their purpose. It seems to me that on a P-51, they would have little impact on engine cooling. I have also noticed that the Allison-powered P-51s and the P-51Ks didn't have them.
Does anyone have any information on the purpose of these propeller cuffs?
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Mike wrote:

they were used to force more cooling air over the cylinders. I have noticed them on P-51 B, C, D and H Mustangs, but I have not come across any explanation of their purpose. It seems to me that on a P-51, they would have little impact on engine cooling. I have also noticed that the Allison-powered P-51s and the P-51Ks didn't have them.

Google *is* evil...no matter what they claim...
Here's an NACA report, this one on the test of several differing prop/spinner/cuff combinations -
http://digital.library.unt.edu/ark:/67531/metadc65074/m1/1 /
Note that this series of tests were performed in 1940.
Here's an NACA report on the effects of propeller cuffs on cowled radial engines -
http://digital.library.unt.edu/ark:/67531/metadc61982/m1/1 /
Note that the date of this report is 29 March, 1944...and that this test is more specific in nature.
Reading though both reports there are essentially two reasons fo using cuffs or spinners beyond the baseline aerodynamics of the airplane - 1) to enhance the efficiency of the propeller - for a P-51 this would be a matter of the prop/spinner geometry; and/or 2) to enhance engine cooling flow in front of a radial engine. Enhancing the propeller efficiency would be the overriding reason for using a cuff, though. this holds true for any propeller - radial engine driven or not; as the actual power transmitted for flight is a function of the prop efficiency X the engine HP actually produced.
It would appear from the later 1944 test that the idea of enhancing cooling flow by altering the shape of the base of the blade wasn't actually working (well) in practice. One might also think that something like crews removing cuffs in the field to lighten the aircraft and gain a combat advantage may have also led to the later 1944 test in the first place; just speculating.
I also found this thread on the subject -
http://www.mustangsmustangs.us/thehangar/index.php?topic 8.0
"Others were remove due to breakage or damage of the cuffs for various reasons such as improper slinging while removing the propeller, hitting them with a hammer while using the dome wrench, rough handling, or even the dreaded bent blade which requires cuff removal for straightening, etc. The cuffs are fairly dense rubber like material and are somewhat brittle."
Note the poster's credentials -
http://pwp.att.net/p/s/community.dll?ep &groupid'7698&ck If cuffs were being removed in the field and no impact to engine maintenance was being noted, the field practice could have spread rapidly even though manufacturers would have continued to deliver props with cuffs as specified for procurement. It would have taken some time to revise the delivery spec, if ever.
--
- Rufus



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