By Chris Hinds
Choose The Right Propeller For Your Engine
While all engines produce power the Propeller is essential to transmit this power. A more efficient propeller will transmit more power to the air. In the UK the most commonly available propellers for I/C engines are:
- Master Airscrew
- Precedent (Smart & Airflow)
- Menz 'S' and 'Ultra'
Of these propellers Menz 'S' and Precedent's 'Smart' range are suitable for large engines, these are wooden propellers so tend to break more easily than composite propellers. Mjenlik propellers are also suited to large models and are Carbon Fibre propellers. APC propellers are composite propellers and are excellent for most uses, they are not robust enough for beginners however. Graupner and Kyosho propellers are also composite propellers and are well suited to beginners, as a matter of preference I prefer a Graupner propeller. Kyosho props are a mildly quieter design than Graupner however. Master Airscrew props are noisy, inefficient propellers and their only redeeming feature is their strength against ground impacts - only buy if there is nothing else.
A table of my suggested propeller sizes follows. It would be fair to say that my recommended props are often much larger than those typically used in the USA but this helps significantly with noise reduction and therefore I will go with a larger prop. The engines will not bog down with these props, they just won't quite develop all the power they could. Though to be fair we do overpower anyway. Prop sizes are only slightly above US recommendations. If you field is noise sensitive (as many are) then head for one of the large sizes.
Engine Size Ideal Prop Size Propeller Size Range Engine Type Ideal RPM Range 0.10 7x4 7x4~6, 8x4 2-Stroke Glow 14000~16000rpm 0.15 8x4 7x5~6, 8x4~6 2-Stroke Glow 14000~16000rpm 0.25 9x5 9x4~6, 10x4~5 2-Stroke Glow 12000~15000rpm 0.32-0.36 10x5 9x6~8, 10x5~6, 11x4~5 2-Stroke Glow 12000~15000rpm 0.40 11x5 10x6~8, 11x5~7, 12x5~6 2-Stroke Glow 11000~12000rpm 0.46 11x6 10x7~9, 11x6~8, 12x5~7 2-Stroke Glow 10000~12000rpm 0.53 11x7 10x8~10, 11x7~9, 12x6~8 2-Stroke Glow 10000~11000rpm 0.61 13x6 12x8~10, 13x6~7, 14x5~6 2-Stroke Glow 9500~11000rpm 0.75 13x7 12x9~11, 13x7~8, 14x6~7 2-Stroke Glow 9500~10500rpm 0.91-1.08 14x6 13x10~11, 14x6~8, 15x6~8 2-Stroke Glow 9000~10000rpm 1.20-1.35 16x8 15x8~10, 16x8~10, 17x8 2-Stroke Glow 8500~9500rpm 1.40-1.80 18x8 17x8~10, 18x8~10, 20x6~8 2-Stroke Glow 8000~9000rpm 2.10 20x10 20x10, 22x8 2-Stroke Glow 8000~8500rpm Engine Size Ideal Prop Size Propeller Size Range Engine Type Ideal RPM Range 0.26-0.30 10x6 10x5~7, 11x4~5 4-Stroke Glow 10000~11000rpm 0.40-0.45 11x6 11x6~7, 12x5~6 4-Stroke Glow 10000~11000rpm 0.48-0.56 11x7 11x7~8, 12x6~7, 13x5~6 4-Stroke Glow 10000~11000rpm 0.63-0.72 12x7 12x7~9, 13x6~7 4-Stroke Glow 10000~11000rpm 0.80-0.91 14x7 13x8~11, 14x7~9, 15x5~7 4-Stroke Glow 10000~11000rpm 1.00-1.20* 14x8 14x7~8, 15x6~10, 16x6~8 4-Stroke Glow 9000~10000rpm 1.40-1.50** 16x8 16x8~12, 17x8~10, 18x6 4-Stroke Glow 8500~9500rpm 1.80-2.00 17x8 16x10~12, 17x8~10, 18x8 4-Stroke Glow 8000~9500rpm 2.40 20x8 18x10~12, 20x6~8 4-Stroke Glow 7500~8500rpm 2.70 20x10 20x8~12, 21x8~10 4-Stroke Glow 7500~8500rpm 3.00-3.20 21x10 20x10~12, 21x8~10, 22x8 4-Stroke Glow 7500~8500rpm Engine Size Ideal Prop Size Propeller Size Range Engine Type Ideal RPM Range 1.40-1.80 16x8 16x8~10, 17x8~10, 18x8 Gas 8500~9500rpm 40cc 20x8 18x10~12, 19x10, 20x8~10 Gas 6500~7800rpm 45cc 20x10 20x10~12, 21x8~10, 22x8 Gas 6000~7500rpm 50cc 21x10 20x12, 21x10~12, 22x8~10 Gas 6000~7200rpm 60cc 22x10 22x10~12, 24x8~10, 26x8 Gas 6000~7200rpm 75cc 24x10 24x12, 26x10~12 Gas 6000~6800rpm 100cc 26x10 26x10~12, 28x10 Gas 6000~6500rpm 150cc 32x12 30x10~12, 32x10~12 Gas 5500~6000rpm 200cc 34x11 32x12~14, 34x10~12, 36x10 Gas 5000~6000rpm
*The Yamada FZ120 is very powerful so a 16x8 is advised as a minimum, 15x10 being an alternative.
**The Yamada FZ140 Limited is more powerful than a Saito 180 so use the 1.80-2.00 prop sizes as a guide.
The figures are merely estimates - do not take them as gospel they are merely a rough guide. As aside notes:
The 3W and Desert Aircraft petrol engines are very powerful for their size and larger props should be used such as a 28x10 on a 100cc Twin from these manufacturers.
I generally like to prop the engine in the RPM ranges above, to develop power without excessive noise levels. In order to meet the UK limits a sensible mounting system (I like the Dubro Mounts) and an APC or similar propeller should be used, provided the manufacturer's silencer is adequate. Of the engines I have come across, O.S., Irvine and MDS Silencers are adequate without extra silencing fitted. The O.S. silencers are the best of the standard silencers though.