Has usong engine exhaust blown onto an airfoil ever been tried to make a vertical takeoff and landing aircraft?
Not possible engine blow to the air foil will make VTOL (vertical Take Off Landing). It will just make STOL (Short Take Off Landing), there is Antonon An-74, and Boeing YC-14. 1. Antonov An-74:2. Boeing YC-14:
These two airplanes are utilizing Bernouli's principle to create very fast wind blow (velocity 1, v1) above the wing, compare to the wind velocity below the wing (v2). Due to the different airspeed, than the airplane take off shorter than common airplane. From P1+0.5rhov1^2+rhogh=P2+0.5rhov2^2+rhogh, the rho is the air density (in kg/m cubic). The rhogh will cancel one each other as they has the same air and the altitude consider the same. Hence you then can calculate the v1 and v2, and then the take off distance.
VTOL is a lifting/flying process without any horizontal moving. See here some of VTOL and STOL.. So, by forcing the low pressure above the airfoil, it will just create almost VTOL. But almost VTOL is still STOL. Here is how VTOL is explained detailly. But not as you think.
Near as I know every attempt to do so has never worked out. It’s a very enticing design on paper but has always been a disappointment in real life. One of the best examples was from the 1970s. Designed as a supersonic replacements for the AV-8A Harrier, the Rockwell XFV-12A attempted to use this scheme for a vertical lift system. Unfortunately it never met the design metrics, and the program was ultimately canceled.
There are a few drones that use a non-rotating Coanda surface (blown by a ducted fan or centrifugal fan) for lift, with moving flaps for two-axis control (throttle is used to control altitude). This one is called Aesir, and there are a number of amateur-built copies, but I'm sure I've seen others with a different overall shape.
The advantage of this over a single-fan thrust-hover is simplified controls, no torque counteraction required, and considerably reduced power requirements. The disadantage is the relative fragility of the large, hollow Coanda lifting surface.