Originally Posted by
Andy_RR
WRT the Harrier, I was wondering if the jet plume induced any airflow over the wing to speak of that could generate a noticeable lift component (or more likely a noticeable horizontal thrust component that needed compensating for)
The harrier's nozzles would always have a net forward angle at the hover (still air) to offset the intake momentum. Essentially the engine sucks in a large massflow of air, so it effectively "sucks itself forwards". When high enough to be out of the jet-sheet the wing and fuselage play very little (if any) part in hover lift. But closer to the ground the let efflux hits the ground and spreads sideways into a jet-sheet. the jet sheet heading outboard is lost, but the inboard-heading part collides with the inboard-heading jet-sheet from the other side, deflecting the flow upwards. There is still quite a lot of energy in this flow, and where it hits the airframe it generates additional hover lift. Right from the get-go the Hawker chappies at Kingston recognised the potential benefits, so they designed features into the fuselage to trap this deflected jet-sheet. These are mainly comprised of the two strakes or cannon pods (Harriers are always fitted with strakes or pods - they never fly with neither) and the main-leg door which (with the gear down) closes off the gap between the pods/strakes at the back to trap air. Then at the front there is a small air dam called a "LID" (Lift Improvement Device) which extends when the wheels go down - the LID blocks the gap between the pods/strakes at the front so that the Pod/strake-LID-Mainleg-door combination forms an enclosed box to trap the deflected jet sheet. I no longer have the data to hand, but if I remember correctly the LIDs on the Harrier II provide something like 2,000lbs of extra hover lift.
There is something very strange going on in that video - I'm struggling to see what force the forward rake of the thrust vector is opposing. I'd need to look at it in a lot of detail to understand what's going on.
PDR