The thrust evolution of the FU-24
The energy level of the basic FU-24 airframe has been transformed with respect to its overall performance, as compared to the early 225 and 240 bhp models which we flew during 1955 to mid-1960s. The static thrust produced by the 240 bhp Continental O-470 with its two-blade Hartzell propellor was about 950 pounds at sea-level.
When that feeble engine was replaced by the Continental IO-520 with 300 bhp, the static thrust increased to around 1,200 pounds. This increased the maximum level airspeed by only three or four knots. But, what the 300 bhp did do was improve the rate-of-climb to a safer figure as the empty weight did not increase very much.
A big change was made when the Lycoming IO-720 with 400 bph was fitted. This 8-cylinder engine with its three-blade propellor is much heavier and needed stronger engine mounts other changes. From memory, I think the 300 bhp model FU-24’s empty weight rose from about 2,250 pounds to perhaps 2,700 pounds with the IO-720 installed. Fuel consumption increased by 25%, along with the amount of fuel also increased. So, while the bhp increased by 25%, much of that benefit was lost. Also, the “400” takes a lot more distance to stop on level and wet airstrips; particularly when landing with a tailwind. The static thrust of the 400 bhp model is pretty close to 1,600 pounds.
The FU-24 converted to a 550 shp Walter or similar powered PT-6 has a very efficient propellor and its static thrust is up to about 2,200 pounds. That is a huge amount more than the thrust we first had available with the meek 225 bhp version.
In the early years, we flew the FU-24-240 at about 4,000 pounds. Then, with the FU-24-300 that weight was increased to around 4,400 pounds. With the FU-24-400, we could carry about 5,400 pounds. Goodness only knows what payloads are being carried in the 550 shp models…
Mike Feeney of Hamilton, New Zealand is a retired professional pilot and a long-time aviation journalist, technical and air safety writer. firstname.lastname@example.org