Originally Posted by
Chris Nicastro
In RC the engines dont put out the kind of power to make use of a scale diameter prop. In order to use a 4 blade at about 3200rpm like full scale Mustangs do you would have to use gear reduction, or change to electric power and use a larger than necessary brushless out runner motor. You need more torque not RPM. Even the Merlin engine has a gear reduction drive on the front of the engine to take 6000rpm and turn it into torque at half the RPM.
Actually, that reference to the Merlin is not true. The Merlin was never designed to run at that kind of RPM levels. In fact, to use them in the Unlimited class of hydroplanes, the oil passages were actually enlarged to handle a greater oil flow to handle the up to 4000RPM used to push the boats. Also, in aircraft use, the gearbox stepped down the RPM to keep the prop tips from going supersonic. Once the blades reached supersonic velocity, they became ineffective. This was a serious problem at higher altitudes where the speed of sound is less than at sea level. Please note the RPM and power listed under performance as well as the REDUCTION GEAR RATIO shown below for a model 61 Merlin:
General characteristics
- Type: 12-cylinder, supercharged, liquid-cooled, 60° "Vee", piston aircraft engine.
- Bore: 5.4 in (137 mm)
- Stroke: 6.0 in (152 mm)
- Displacement: 1,647 cu in (27 L)
- Length: 88.7 in (225 cm)
- Width: 30.8 in (78 cm)
- Height: 40 in (102 cm)
- Dry weight: 1,640 lb (744 kg)[SUP][nb 15][/SUP]
Components
- Power output: * 1,290 hp (962 kW) at 3,000 rpm at take-off.
- 1,565 hp (1,167 kW) at 3,000 rpm at 12,250 ft (3,740 m, MS gear)[SUP][nb 16][/SUP]
- 1,580 hp (1,178 kW) at 3,000 rpm at 23,500 ft (7,200 m, FS gear)
Since they didn't exceed 3,000, it can be assumed that the engines weren't going to be run faster than that under either normal or combat conditions