I ran across this site yesterday for a company (Lonestar Hovercraft) selling PSRUs for airboat use here in the US. They have a kit ready to mount on the HF Predator 670cc (22 HP) engine. Cog belt or V-belt versions, 1.66 ratio (other ratios available). They've been running them on airboats for awhile, I don't have an independent source of info on reliability. Apologies if this is old news.
The price is $799-$924, which is quite an add-on for a $729 engine. Still, it does get the prop loads off the crankshaft, it does get the prop higher up (handy), and it does allow use of a larger,more efficient propeller. (And, it adds more things to go wrong.)
7 minute video on the V-belt product here, emphasis is installation.
Here's a video on the cog-belt version.
In the comments section: Total weight for engine+PSRU+ propeller is 121 lbs. They are turning 3-blade props of 52" to 59".
FWIW, a comment at the above video wrote:
This company also makes similar PSRUs for industrial engines made by Kohler, Honda, and B&S. They claim the larger PSRUs weigh about 15 lbs.
Design: The tension is adjustable, but none of their drives have the "live" idler as seen on the (no longer available) Valley Engineering unit.
Anyway, this might be a source in addition to Ace--a little closer to home.
Jan Carlsson's prop program says a 55" Dia 3-blade prop driven at 2182 RPM (3600 RPM engine speed) and designed for 85 MPH will have an efficiency of 80% at that airspeed, which gives an expected thrust of 78 lbs at that airspeed.
For comparison, a direct-drive 42" 2 bladed prop at 3600 RPM and optimized for 85 MPH would be expected to have an efficiency of 73.8% and an expected thrust of 72 lbs at that airspeed.
Same setups optimized for 50 MPH:
55" 3-blade with PSRU: 65.3% efficiency, 108 lbs of thrust
42" 2-blade, 3600 RPM direct drive: 54.3% efficiency, 90 lbs of thrust
The price is $799-$924, which is quite an add-on for a $729 engine. Still, it does get the prop loads off the crankshaft, it does get the prop higher up (handy), and it does allow use of a larger,more efficient propeller. (And, it adds more things to go wrong.)
7 minute video on the V-belt product here, emphasis is installation.
Here's a video on the cog-belt version.
In the comments section: Total weight for engine+PSRU+ propeller is 121 lbs. They are turning 3-blade props of 52" to 59".
FWIW, a comment at the above video wrote:
I have nothing much to add, except to say that the 1" shaft, with the keyway cutout, with the "lumpy" torque pulses of any V-twin might be something to watch in a direct-drive application.
This company also makes similar PSRUs for industrial engines made by Kohler, Honda, and B&S. They claim the larger PSRUs weigh about 15 lbs.
Design: The tension is adjustable, but none of their drives have the "live" idler as seen on the (no longer available) Valley Engineering unit.
Anyway, this might be a source in addition to Ace--a little closer to home.
Jan Carlsson's prop program says a 55" Dia 3-blade prop driven at 2182 RPM (3600 RPM engine speed) and designed for 85 MPH will have an efficiency of 80% at that airspeed, which gives an expected thrust of 78 lbs at that airspeed.
For comparison, a direct-drive 42" 2 bladed prop at 3600 RPM and optimized for 85 MPH would be expected to have an efficiency of 73.8% and an expected thrust of 72 lbs at that airspeed.
Same setups optimized for 50 MPH:
55" 3-blade with PSRU: 65.3% efficiency, 108 lbs of thrust
42" 2-blade, 3600 RPM direct drive: 54.3% efficiency, 90 lbs of thrust
