<https://southernairboat.com/community/threads/free-horsepower-why-isnt-somebody-doing-this.700/>
<http://schema.org/articleBody>
"Why not tap into the thrust generated by the prop to make some free boost?\n\nAccording to a thrust comparison test in US Airboat magazine a 4 blade Powershift Maximus makes 1100 lbs. of thrust @ 2000 rpm, prop length was not given.\n\nAssuming an 82\" prop that would be 5281 square inches of area generating 1100 lbs of pressure, or about .2 lbs of thrust per sq. in. \n\nIf the thrust was proportional from the center of the hub to the blade tip that wouldn't be enough to make much difference... But it is not, most of the thrust is generated somewhere towards the tip of the props, with little or none at the center. Guessing that 75% of the thrust is generated in the half of the prop nearest the tip I calculated an average of 1.5 psi generated in that half,  I would also guess somewhere along that half significantly higher pressures would be found.\n\nGiven a manometer you should be able to measure static pressure in different locations behind the prop to find the optimum spot to generate some free boost. \n\nAssuming an engine with a compression ratio of around 9:1, horsepower will essentially double at 14.7 lbs of boost. Or, 6.8% hp for every pound of boost. A 500 hp engine would gain 34 hp if you could achieve 1 psi of boost.\n\nIt seems to me it would be simple to run a duct from the air intake to a location behind the prop to take advantage of it."
<https://southernairboat.com/community/threads/free-horsepower-why-isnt-somebody-doing-this.700/>