pushing rakish propeller

rosbullterier · Post by **rosbullterier** » Sun May 04, 2008 10:30 pm

Have become the proud owner of a raked two blade propeller . . . gasp . . .

Now it has a 10" diameter, a steepish rake and a fair amount of pitch (how do you calculate that?)

Maybe I am over estimating its performance. However before trying it there would seem a great deal of blade to push - how would a 102 from the mid 40's manage with just a 1: 2.5 reduction?

Rogermac · Post by **Rogermac** » Mon May 05, 2008 9:05 am

If you google propeller+pitch+measurement and propeller+pitch+calculation there's a stack of stuff on the principles of this.

timberman2004 · Post by **timberman2004** » Mon May 05, 2008 10:13 pm

yeah me too ....

( but for only 16 quid )

(( sorry couldn't help that one ))

so c'mon Andy and get the homework done ....downdraughts ?? Turbo ?? or just hook in the nitro ??

a twin blade GOT to be an easier push than a 4 blade clover leaf ???

god... these silly old engines are just a bit addictive

rosbullterier · Post by **rosbullterier** » Tue May 06, 2008 12:07 am

Thank you Roger. As soon as the motor is finished; I have a tachometer, just need a small GPS - I shall determine the prop effectiveness.

One article advises how through an equation by the diameter coupled with the blade depth side to side variation, the pitch can be found.
Another article states 'Deduction of the pitch of a propeller by measurement of its blade shape is a complex task beyond the skill of most boaters'. Ah well . . .

I'm still intrigued by how an early 102 turns a 10" prop with considerable pitch (albeit 2 blade) with the 2.5:1 reduction box!