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Motor thrust

Old 11-17-2002, 03:28 AM
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rahtware
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Default Motor thrust

Does anyone know where I can find information on how much thrust different glow motors produce?
Old 11-17-2002, 07:53 AM
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KrisG
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Default Motor thrust

There are no fixed rules on this, as far as I know :

Downthrust depends upon position of engine/wing/stab in regards to each other ( e.g. high-wing aircraft need more downthrust than low wingers because the drag is mainly above the thrust line, which makes the plane pitch up with power applied).

Side thrust greatly depends upon the prop you put : if you work on lower rpm ( more up on the torque curve), you will need more side thrust. Also : the propwind does not go straight back, but is also rotating. I have read that the "corkscrew flow" over the fuselage influences this, so the shape of the fuselage is important.

In short : cut and try?
Old 11-17-2002, 10:45 AM
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Ollie
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Default Motor thrust

It is the prop-engine combination that produces the thrust. The size of the prop has to be matched to the RPM of the engine at a particular airspeed to produce maximum thrust. Every engines power output peaks at a particular RPM. The size of the prop has to allow the engine to reach that RPM. The thrust of the prop peaks when the airspeed is near the pitch-RPM speed.

The trick is to know how much RPM the engine will pick up between being adjusted on the ground and its RPM in the sky. Then pick a prop that gives the correct lower RPM on the ground so that the engine will reach maximum power in the sky and will also have the correct pitch speed.

Of course, many other factors are involved. Atmospheric pressure, temperature and humidity affect the engine's power producing ability. As little as one click of the needle valve can mean the difference between reaching peak power and not. Fuel formulation is a big determining factor as is carburator adjustment. The break in history of the engine also affects power. A properly broken in engine will produce more power than the same engine which is not properly broken in.

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