Thinking about lift by propeller airstream

[modelbuilder]

Hi everybody,

I stumbled upon the question how much lift a wing can create just by the airstream of the engines propeller. If you put enough propellers to the front of the wing (just like NASA´s LEAPTech does), can the airstream create lift although the airplane doesn´t move at all? In my first opinion there should be no difference - apart form the vortexes - if the airspeed is applied by propellers or by movement through the air. But on second thought the idea of an airplane taking off almost vertical just by its own propeller airstream seems odd..
Can somebody help here? :thumbsup:

[Todd copeland]

Moot point in my view. In order for the props to create that lift they are providing thrust in order to generate that lift and therefore the plane will be moving forward. Would you want another set of props in the opposite direction to counter it? Interesting thoughts though.

[rwanttaja]

Hi everybody,

I stumbled upon the question how much lift a wing can create just by the airstream of the engines propeller. If you put enough propellers to the front of the wing (just like NASA´s LEAPTech does), can the airstream create lift although the airplane doesn´t move at all? In my first opinion there should be no difference - apart form the vortexes - if the airspeed is applied by propellers or by movement through the air. But on second thought the idea of an airplane taking off almost vertical just by its own propeller airstream seems odd..
Can somebody help here? :thumbsup:
That was the idea behind the Custer Channel Wing (http://en.wikipedia.org/wiki/Custer_Channel_Wing), except it was a pusher that sucked air over a half-shroud.

4704

Ron Wanttaja

[Bill Berson]

I watched an experimental channel wing land. The pilot had difficulty getting down with powered lift. In order to land short he had to cut the power... But that cut the lift, so he pulsed the throttle....not very effective.
He abandoned the channel wing and went back to Cub type bush planes.

[dougbush]

To take off almost vertically, all those propellers would have to create as much relative wind as a conventional aircraft of that weight and wing area experiences on takeoff.

[FlyingRon]

Saw the Channel Wing at Garver years ago. I don't recall seeing it at Hazy yet, I'll have to ping Margy over the schedule. According to the hanging plan I have (which admittedly is very old), it was slated to go at the extreme northeast end of the aviation hangar on the level of the mezzanine.

[Jim Hann]

That was the idea behind the Custer Channel Wing (http://en.wikipedia.org/wiki/Custer_Channel_Wing), except it was a pusher that sucked air over a half-shroud.

http://eaaforums.org/attachment.php?attachmentid=4704&stc=1

Ron Wanttaja
That had one of these at MAAM at KRDG years ago. Anybody know if they still have it. Last time I was there it was outside looking pretty weatherbeaten and tired.

Jim

[Ron Blum]

Just remember too that if you are requiring the propeller stream for lift, what will happen when the engine quits? There have been a lot of experiments with boundary layer suction and blown surfaces in the past, but none have made it, probably due to failure modes that don't end well. With that said (and being positive), electric motors have a lot more reliability :o)

[crusty old aviator]

The slipstream coming off the props does not flow straight aft, therefore, the airflow would tend to wander left and right on it's way aft. The flow from one prop would also interfere with the flow from the adjacent props, therefore creating a lot of turbulence with higher pressure over the upper surface than needed for efficient lift. I get what your implying, but with every additional prop you place ahead of the leading edge, the airflow over the upper and lower surfaces becomes almost exponentially more complex. Like everything with aircraft, it's never easy and rarely simple.