barit1
4.5 lbf/hp seems pretty high to me, but I am open to seeing hard numbers.
Ryan FR-1 Fireball
Weights
OEW: 7,690 lbs
TOW: 11,651 lbs
Engines:
1 x R-1820-72W or R-1820-74W = 1,350 to 1,500 hp (respectively
1 x J31 = 1,600 to 2,000 lbf
BTW, the J31 jet engine (aka GE I-16) was 1600 lbf static thrust, not 2000 lbf.
If I recall correctly the early variants of the J31 produced 1,600 with later models producing around 2,000. Could be wrong though.
This might make the 4.5:1 prop thrust value on the conservative side.
Does the fact that the FR-1 was only able of doing around 275 mph on piston propulsion alone have anything to do with such a high prop-thrust?
Brian Abraham
The conversion from Thrust to Horsepower, and visa versa, is not a straight conversion of units, such as Kilometres per Hour to Miles per Hour, it depends upon the Thrust and the speed of the aircraft, as derived from the basic relationship where -
Power = Force X Velocity.
Understood
As a straight conversion to eliminate the constants of the various units used, the following formula applies -
Pa = Ta V / 325, where -
Pa = Propulsive Power available in Horse Power, Ta = Thrust available in Pounds, and V = Velocity in Knots (if working in MPH use 375 as the constant rather than 325).
Okay so
1.) Pa = Ta V / 325
2.) (1,350) = (x)(132)/325
3.) 1,350 = 132x/325
4.) (325)(1,350) = 132x
5.) 438,750 = 132x
6.) 438,750/132 = x
7.) 3,323.864 = 325?
Taking the RR Merlin engine as an example, at a given horsepower setting the thrust produced produced would be vastly different between a Spitfire fighter and a Lancaster bomber.
Different speeds, different propeller used?