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Constant Speed Props & Propeller twist.

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davidjoyce(at)doctors.org
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Posted: Sat Mar 21, 2009 2:50 am Post subject: Constant Speed Props & Propeller twist.

Fred, The twist of a blade along its length is fairly critical to engine 

cooling. Changing from a Woodcomp SR2000 with 12 degree twist to an SR3000W 

with about 26 degrees of twist has transformed my 914 cooling , totally 

eliminating the overheating on delayed take off or prolonged climbs. It has 

also added 4 kts to top speed and improved fuel consumption.

        As you can see from the attached mathematical analysis a 12 degree 

twist is optimised for air flow through  the prop of about 40 kts, which is 

what you get sitting on the ground  at about 1/2 throttle, before take off. 

At 100kts + you have negative AoAs in the central portion of the propeller, 

which doesn't help anything. It's no coincidence that all really fast planes 

(Spitfires, Red Bull racing planes, turboprops, etc) have props with twist 

more than 20 degrees. Regards, David Joyce, G-XSDJ

---

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