C-85 Don's stroker mod. Need advice on prop

[Guest]

Re: C-85 Don's stroker mod. Need advice on prop

I've completed flight testing of my C-85-8 similar to the Don's Dream Machine mods (C-90/0-200 crank, rods & pistons). The installation & flight tests in our BC12D Taylorcraft went well, and I would welcome some advice on the pitch & diameter for our propeller.

For the flight tests, I've borrowed a MacCauley Klip-Tip 1B90 7143 (actually 70" dia). It comes from a standard C-85-8 equipped Taylorcraft, and works just fine on that aeroplane, in that it would just red line in Straight & Level cruise, but only just. This prop was cut down from a 7443 long ago.

With this same prop fitted to my modified engine, however, the static rpm is right at the upper limit of the static rpm permissable for the normal C85 (2350 rpm), and in S&L cruise it wants to leap through red line at full throttle. so it's over-revving. I think I need a coarser prop, but how much coarser should it be? 1" or 2" or more? And is the diameter right?



For info, my engine dyno'd at 93 hp at 2475 (100 rpm below the 2575 max). We might be getting close to 100 hp at the full 2575 rpm.

Any & all feedback / suggestions / experiences welcomed. Any Cub drivers with similar engine configuration care to comment?


I have a fresh Mac 7443 (from our old A-65) ready to be clipped & repitched. Then I can give the test flight prop back to its original owner.

Rob

Rob,

I use an 1b90-CM7049 on an a65. Climbs about 2000-2100 rpm at 60 mph as I recall.

Max rpm at level is 2300-2400 but it does not leap thru it, has to build up to it.

Dave

[Jim Herpst]

Re: C-85 Don's stroker mod. Need advice on prop

Doc,

Thanks. For my light weight modified clark y equiped Baby Ace I am not worried about climb or the like. I AM looking for the best overall prop for this plane. It was orginall equiped with a 72/48 which I checked the builders numbers for his prop in the logs....on and it was a Vagabond.

My 71/ 49 is close to perfect. I believe a 72/46 0r 72/45 WOULD be perfect

Thanks again for the offer/ reminder I do know I need more pitch than a 38

Jim

[Doc]

Re: C-85 Don's stroker mod. Need advice on prop

Anytime..... We have a good relationship with Jordan Propeller in San Antonio...very helpful with info, etc. I have had three props repitched by them with great results. These discussions are quite good. Doc