Hi all,

Im a university student in the UK, im doing a project on MAVs.

The design is a flying wing that will use ducted fans, my problem is i don't know how much thrust is required?
I heard that you need 1/3 of the aircrafts weight in thrust, is this true?

Any help would be much appreciated,


Ian.

1/3rd the weight would be a minimum value.
Long takeoffs, low climb rate.

Hi,
Static thrust gives you an idea about the plane's climb rate, it's ability to accelerate after an aborted landing, whether it's able to rise of the ground and whether it's able to hover.
But static thrust alone is not enough to predict whether the plane will fly, another important factor is the prop pitch speed, which should be above the stall speed.

Lets say you have a plane with known weight , lift and drag coefficients vs angle of attack. It rolls down a long glass runway on frictionless wheels. The slightest thrust will cause it to accelerate and continue to accelerate until the drag of the plane equals the engine thrust. If there is enough thrust for the plane to reach the speed at which the lift equals weight before drag equals thrust, it can just leave the ground. Any additional thrust can be used to allow the plane to gain altitude. Climb rate times weight is power - it takes horsepower to climb and enough thrust to offset drag as it climbs. So you need more than the minimum thrust to provide for a useful climb rate and take care of the less-than-perfect runway and wheels.

Very brave. Put a turbine in it and forget your problems.

Alternatively, get a download of FMS, or any other good model airplane simulator with a half decent physics engine in it. Create a model with the same geometry as the one you are planning and model the power plant until it has the performance that you require.

If you are modelling ducted fans, ensure that you make the model realistic. They are truly horrible and have no redeeming features apart from not having an exposed propellor, a feature that only a scale modeller could love.