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Prop change for 108-1 with 150 Franklin?

6 Posts
4 Users
Posts: 18
Eminent Member
Topic starter

I have a 108-1 with the 150 engine and stock Sensenich prop (76JR53). I fly off a grass strip at 3600ft. Cruise flight is great, but takeoff climb is lacking. I don't want to go with a lower pitch prop and sacrifice cruise for climb. Would a composite wood prop of the same diameter and pitch be more efficient and provide an improvement in performance? (newer more efficient technology) Engine runs great, it's being all it can be without mods. I've heard that the resonant frequencies of the metal props contribute to the engine cracks more than the wood props. I'm reluctant to go with a metal prop.

Posted : 27/06/2018 5:36 pm
James Kepford
Posts: 55
Trusted Member

Hello Scott; I have checked the Type certificate data sheet for the Stinson, you are up against few hurdles hurdles, the 150 hp Franklin crankshaft
has a 8 bolt crankshaft, that limits you to a wood prop a MacCauley metal prop or a Sensenich metal prop, those are the only props in production
that is legal for your plane. Regarding a non certified prop I can't find a company building a prop using the 8 bolt design.

I fly from 2500 feet my climb with a cruise metal prop was dismal, I had it repitched to climb prop and am very satisified, it is a MacCauley
which you don't want to use.

I would suggest you contact Sensenich they are very knowledgeable, maybe build a prop to fill your needs, that is legal to install on your plane.

I hope this info helps.


Posted : 29/06/2018 1:32 am
Dennis Crenshaw
Posts: 300
Reputable Member

Jim, I too have a McCauley Met-L prop, klip-tip 76/54. Goes like gangbusters in cruise but is anemic on climb out especially in the summer. I typically fly myself or one other and half fuel to keep it light. Tomorrow ~96deg in central VA. Those kind of days I fly either early mornings or early evenings to avoid the worst heat. Luckily I fly off a 5300' paved county airport. I do on occasion go into some shorter grass strips; and I really have to watch my load. What pitch did you go to with your McCauley? I was thinking a 52 in. pitch might be a good happy medium.

Dennis Crenshaw. N6102M.

Posted : 29/06/2018 9:55 pm
Posts: 18
Eminent Member
Topic starter

Thank you for the input. I'm going to Air Venture & will look up the prop people. Maybe my concerns on the metal prop are unfounded. You know how a little knowledge can be dangerous.

Posted : 30/06/2018 6:58 pm
James Kepford
Posts: 55
Trusted Member

Hello; We repitched our McCauley 1A170/DM to a 76 49 from a 54. Before the change we were climbing in the yellow arc now we climb
at 2500 rpm at 2500 ft field altitude. We live in a valley at 2500 ft and are surrounded by mountains with a 14000 ft volcano 50 miles South,
we normally climb to 7500 ft when leaving the valley.

The yellow arc is not much of a problem, I usually cruise at 2400 or 2500 RPM which is out of the arc, it is OK to pass through the arc but
don't operate in the arc constantly. The metal prop is not a problem if not operated for long periods in the Yellow arc.

Talk to a prop shop they should have good suggestions on a specific angle to repitch your prop that will give better climb. We went with
the lowest pitch allowed because we land on unimproved strips and need the shortest take off run possible.

When I recover from the shock of our recent top overhaul, I used Southern Aero in Thomasville NC great people to work with, I am considering
installing vortex generators for better short field performance, I may have to buy a new living room carpet to offset the cylinder repair
before spending more money on the Stinson.

Have a good time at Oshkosh, if you come across good prop info let us know.


Posted : 01/07/2018 7:18 pm
Posts: 9
Active Member