Original Posted By: Michael Perez
I've done a lot of research about using auto engines to reproduce the older,slow turning, high-capacity WWI aero engines. Here are some things toconsider when thinking about using the Jeep or any other motor in a Piet.Firstly, you need to know the weight. Keeping it around or lighter than theweight of a Ford is probably wise. Heavier engines have been used, but itbecomes a cycle of diminishing returns.Don't get too caught up in HP. Torque is what spins a prop, HP keeps a carrolling down the highway. You want an engine that develops it's torque at alower rpm, the same speeds the prop needs to spin. If you have an enginedeveloping peak torque at 4,000, what will it develop at 2,000?. You can'tspin most props at 4,000.Using the formula to find torque of HP time 5252 divided by rpm, I'destimate that a very strong Ford (or Chris's Mitsubishi), turning at 2,200is developing about 170 ft lbs of torque to spin it's prop. This wouldprobably be a good starting point when choosing a motor.The faster the engine needs to turn up to develop it's power, the smallerthe prop becomes (corvair, 0200, etc) Two different breeds of cat; slowturning, torquey tractor type motors turning very large diameter propsverses higher revving engines turning smaller props much faster.One could always put a reduction drive to slow down the prop. This addscomplication, weight, length and another failure area, but there are somegood ones out there now. I really like the planetary one made by TracyCrook.FYI, the Ford is about 200 cubic inches in capacity. More than most peoplethink. It spins a 76X42 or 44 prop and a strong one can come close to 2,000static. This all needs to be coupled with a light airframe and it'll perform nicely.My guess, if Oscar's research on the Jeep motor is correct is that it wouldbe a bit weak, unless you were able to turn it up faster using a smallerprop. Like everyone says, build one up and see what it'll spin!Good luck!Douwe________________________________________________________________________________Date: Wed, 23 Oct 2013 03:37:11 -0700 (PDT)
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