Intake Momentum Drag Yaw
# Intake Momentum Drag Yaw

Intake Momentum Drag is an aerodynamic phenomenon which effects turbo prop and jet-powered aircraft.

## Causes

Intake Momentum Drag is caused by the consequence of the speed of the air entering the engine increasing, but where the exit speed of the air from the engine remians constant. The outcome therefore is that the amount by which the engine increases air velocity is reduced. A reprecussion of this causes a slight reduction in the thrust of a jet engine.

### Intake Momentum Drag Yaw

Intake Momentum Drag Yaw is a further consequence of Intake Momentum Drag which effects V/STOL (vertical and/or short take-off and landing) aircraft such as the Hawker Siddeley Harrier.

This was an aspect in which the mass of air ingested by the intake of the engine during a crosswind could lead to a state of uncontrolled roll.

The phenomenon was identified during the test flying programme for the Harrier and which required precise investigation. This resulted in Test Pilot John Farley deliberately flying right into the edge of this condition repeatedly, so that a system to counter it could be developed.

