Hmmm….thammer wrote:That motor sounds pretty good. What's the range on one of those?cessna170bdriver wrote:I know just enough about rocket science to be truly dangerous. (Ya wanna motor that develops as much thrust as a 170, but only weighs a pound or two? We got 'em.)
Miles
Assuming a 170 takes about 75% of 145hp to go 120mph (176 ft/sec), and has about 80% propeller efficiency, about 270 lb of thrust is required for cruise.
A pretty good liquid rocket has a specific impulse (thrust divided by propellant mass flow rate) of about 400. If my arithmetic is correct, that rocket would require 270/400=0.68 pounds mass of fuel per second to generate equivalent thrust of a 170 in cruise. Assuming the fuel used weighs around 8lb/gallon, that’s a about 0.085 of a gallon per second, or about 305 gallons/hour. Ignoring the fact that you can’t shove that flow rate through a 170s (3/8†??) fuel lines, the 38 gallons usable fuel would last less than 7.5 minutes, or less than 15 miles!!
Any of you who really are rocket scientists feel free to check the assumptions and math. This wouldn't be the first time I've screwed up a calculation like that.
Miles