Reduction effects on Torque

[Cajun_Ag]

As I understand it, you can get the torque increase from a reduction by simply multiplying the torque by the reduction ratio is that correct?
My engine produces 98hp @ 6750rpm, but maximum torque 231ft/lbs @ 6000rpm. My reduction I've designed is 2.85 which will spin the prop at 2368 & 2105rpm respectively @ 658ft/lbs. A little slow at these rpm, but I designed the unit off a max rpm of 7000 or 2456@prop. I hope to be able to find a wider blade so the overall set-up is quieter. When I go to a prop do I quote them the 658ft/lbs and 2105rpm?

[Duane Scarborough]

Cajun_Ag,

I think that you've got it right.

However, most prop builders will ask for more info than just torque and RPM. They'll want to know the whole story. Engine, engine RPM, HP, bolt pattern, reduction, rotation, pusher/tractor, etc., etc., etc.

Speaking of bolt patterns, what bolt pattern are you planning to use? With that much HP, you're at the high end of the range for the Rotax bolt pattern props, and getting well into the range for SAE-1 bolt pattern props.

There's always something....

I highly recommend that you start with an adjustable pitch prop. They're more expensive than wooden stick props, but you'll be able to fine tune the pitch without spending more money every time you want to experiment.

Duane

[Cajun_Ag]

Right now I have it designed as the Rotax bolt pattern mainly because that's what I know. I have the aluminum blank on it's way and will have it machined in the next few weeks so it's not too late to change the bolt pattern. I have a PM to Chuck right now on this same issue. Is there a bolt pattern that will give me greater flexibility with props. What do you think about your GSC? I like the quietness of the wood with the pitch adjustability of the hub.

[Duane Scarborough]

Cajun_Ag,

I like the GSC. It is EXTREMELY quiet. And so is the PowerFin. Of course, I guess they've gotta' be quiet hanging on the wall in the shop.

Of the 2 props, the GSC is the better looking prop. Wood just seems to look better to me.

Seriously, I have not ran the engine with a prop on it yet. I bought both the GSC, and the PowerFin at very good prices. Both of them seem to be good candidates for my engine / reduction combination. I'm hoping that I'll really like at least one of them.

Hopefully Spring will be here before long, so I can find out.

Here's an idea for you to consider, since you've not had the prop hub machined yet. Why not have it machined for BOTH the Rotax pattern and the SAE-1 pattern? Shouldn't cost much more, and would give you options.

Just a thought.

My reduction is machined for an Arrow Prop pattern, and I have 2 Rotax adapters. One for the AN-4 bolts (which my GSC prop needs), and one for 8 mm bolts (which my PowerFin needs). I just wanted to point out that there are at least 2 popular Rotax patterns.

Duane