induced airflow

[buttman]

I have never quite understood indiced airflow. Suppose there is an
multi-engine airplane with wing mounted engines. I've been taught that
while the engine is running, there is a greater amount of airflow over
the wing behind the prop. The prop is throwing air back over the wing
which is creating more lift over that portion. If the engine were to
quit, that increased airflow ceases, and the wing is creating less
life, even thought the aircraft as a whole may not have lost any
airspeed.

Now imagine that same airplane had 50 engines on each side, totaling
100 engines total. Also imagine that the airfcraft is very very very
light, say 100 lbs gross takeoff. If that plane was doing a run-up with
all of it's 100 engines running full throttle (imagine this plane has
super neodymium coated brakes), the enduced airflow over the wings
would surely be enough to lift the plane right up, would it not?

Acording to the induced airflow principle, upward force is being
created by the airflow, is it not? Since very little force is needed to
lift this plane off the ground, it should take off. But common sense
tells us that it won't. Newton's first law says that for every action
there is a opposite and equal reaction. As the induced airflow pushes
up on the wing, it also pushes down on the engine, creating no net gain
in lift. Is my line of thinking correct here?

[Jose]

> As the induced airflow pushes
> up on the wing, it also pushes down on the engine, creating no net gain
> in lift. Is my line of thinking correct here?

No.

Consider an engine on each side, pointing upwards. Run the engine, and
the plane lifts off like a helicopter.

Now imagine the engines pointing forward, but with a big flap behind the
engines to deflect the air downwards. (for simplicity's sake, no wing
to speak of) The same thing happens, except that there is also some
forward thrust (tether the plane for demo purposes). Retract the flap
and you'll have no lift, but more forward thrust.

The wing acts like the flap. It turns thurst into lift.

Jose
--
Money: what you need when you run out of brains.
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[Kyle Boatright]

"buttman" > wrote in message
oups.com...
>I have never quite understood indiced airflow. Suppose there is an
> multi-engine airplane with wing mounted engines. I've been taught that
> while the engine is running, there is a greater amount of airflow over
> the wing behind the prop. The prop is throwing air back over the wing
> which is creating more lift over that portion. If the engine were to
> quit, that increased airflow ceases, and the wing is creating less
> life, even thought the aircraft as a whole may not have lost any
> airspeed.
>
> Now imagine that same airplane had 50 engines on each side, totaling
> 100 engines total. Also imagine that the airfcraft is very very very
> light, say 100 lbs gross takeoff. If that plane was doing a run-up with
> all of it's 100 engines running full throttle (imagine this plane has
> super neodymium coated brakes), the enduced airflow over the wings
> would surely be enough to lift the plane right up, would it not?
>
> Acording to the induced airflow principle, upward force is being
> created by the airflow, is it not? Since very little force is needed to
> lift this plane off the ground, it should take off. But common sense
> tells us that it won't. Newton's first law says that for every action
> there is a opposite and equal reaction. As the induced airflow pushes
> up on the wing, it also pushes down on the engine, creating no net gain
> in lift. Is my line of thinking correct here?
>

The opposite reaction is the downwash of air from the wing. So, with a
light enough airplane and enough engines to move enough air over the wing,
an airplane such as you describe could lift off without a takeoff roll...

A number of aircraft have been flown over the years with "blown" surfaces,
where air is siphoned off of a jet engine and piped out to the wings where
it is directed over the wing, or more commonly, the flaps. The additional
airflow creates more lift than would be generated by the aircraft's movement
through the air.

KB

[Casey Wilson]

"buttman" > wrote in message
oups.com...
>I have never quite understood indiced airflow. Suppose there is an

<<<SNIP!>>>

As the induced airflow pushes
> up on the wing, it also pushes down on the engine, creating no net gain
> in lift. Is my line of thinking correct here?
>

No.

The number of fallacies in your hypotheses is overwhelming. Just one, for
example the opposite reaction at the engine is the forward thrust versus
your super brakes. Another...., the lift on the wings is counteracted by
weight(gravity). Forget the engines altogether, tether your enormously (sic)
light ship and rent a wind machine from Hollyweird. The ship will lift off
the ground, not push the wind machine over.