Do propellers at different angles work the same? And do intersecting flows of air work the same?

Question

1. Say a propeller pushing thrust downwards generates 70 lbs of force. If you tilted the angle of the system to 45 degrees would it generate the same thrust?
2. If you had each rotor angled inwards of a system like this, assuming that the system is on the ground, would the airflow be the same or cancel each other out a bit? (the arrows is airflow direction)

Thanks

Answer 1

The motors would still generate the same amount of thrust, however it would be aimed in a different direction.

Think of the thrust as horizontal and vertical vectors. You can work out the ratio of these vectors using trigonometry to work out how much of that thrust is going to be effective in the downwards direction and how much will be horizontal.

Answer 2

The amount of force generated remains the same, however it is applied in a different direction; you therefore get an effective reduction in force for a given axis. To use the two extremes:

• If the airflow is straight down, all of the force is used for lift
• If the airflow is completely horizontal, none of the force is used for lift

Aligning the motor at angles between these splits the force between horizontal and vertical. The 'best' angle for your design of course depends on the type of aircraft; for a rotary wing aircraft you need to generate a lot of lift from the rotors but for a fixed wing you want thrust, while the aerofoils create the lift.

In your image, the airflow would remain the same but the two motors would be pulling against each other - this decreases efficiency, however the advantage can be improved manoeuvrability in flight as rather than just relying on gravity to roll and pitch the aircraft you can use the angled thrust to 'push' the aircraft around.