Dornier Do 29

remember, we have the Harrier and the Osprey.

The problem with VTOL and STOL is something called ground effect. When a aircraft is low to the ground, the air that the engines push to lift the craft bounces off the ground and hits back against the aircraft, usually in unpredictable ways. This can cause extra lift, but it can vary a lot. The way air behaves can change based on the type and shape of the ground it is flying over.

With Helicopters, ground effect is not as much of a problem, because the area of the copter is smaller compared to the size of the rotor. However, it is something pilots have to be careful with. Typical helicopters will start a flight by trying to up first thing to get out of the ground effect zone. Managing how the air bounces back to the airplane isn't something that was really mastered until the 80's. Even then, the Harrier is know as one of the hardest airplanes to fly.

It is fairly easy to build a STOL aircraft. It is a different story entirely to make it a safe, reliable aircraft. My guess is that was the problem with the Donier DO-29. Just because it is able to fly in a controlled test does not mean it is a safe and reliable aircraft, especially for combat conditions.

Keep in mind that both the Harrier and the Osprey have very checkered safety histories.

There are a bunch of prototypes out there using simular setups. Multiple "small" electric motors driving props where the full or partial wing will rotate for STOL/VTOL capability.

However, they are all just that, prototypes in various stages of development. So far nothing is anywhere near ready for production.

Due to the difficulty in flying STOL/VTOL aircraft, I do wonder how much demand there will be in the civilian market. They are expensive, hard to fly, accident prone, and don't really seam to offer much improvements over existing options for airplanes or helicopters. They tend to make more sense in military setting where they are willing to accept more risk, cost, and can better train pilots for the difficulties of such aircraft.