Hi Gianna,

If we estimate that the average vertical component of the downwash of a Cessna 172 traveling at 110 knots to be about 9 knots, then to generate the needed 2,300 lbs of lift the wing pumps a whopping 2.5 ton/sec of air!

Please explain from where the energy to pump 2.5 ton/sec is coming from. Some technical specs can be found here: http://en.wikipedia.org/wiki/Cessna_172 .

In your reply, I would recommend avoiding statements such as "I have faith that wings can do the magic". Please concentrate the reply in terms of energy. It is known fact 210hp can't lift 2,300 libs.

  Have fun 

It is known fact 210hp can't lift 2,300 libs.

  Have fun 

LOL
you are very funy
 
in french
des objets plus lourd que l'air ne peuvent pas voler

i get about 50 horsepower to keep the plane up.
the question is how much energy does it take to accelerate 2.5 tons of air to produce 2300 pounds of lift.
do the math.

Only OU if you keep walking/running

http://www.youtube.com/watch?v=Xxu3hYFGT2c

in flight the force to produce lift is part of the drag. by your numbers we have lots of power for lift.
who said anything about vertical flight,the climb rating on a cesna is 1000 feet per min.
from wiki Cruise speed: 122 kn (140 mph; 226 km/h)
or 62 m/s
 you have 14 hp for lift 14*75=1050 kg/m
(1050kg/ms)/62ms=72kg rounded off of thrust to keep it in the air.
all thats required for the plane to fly is for the forward speed to be converted to a much slower
downward speed with much larger mass.could that be your 2.5 tons?
looks like a form of leaverage.
 if you want details on this you should be in a forum for fluid dynamics.
fritznien

  Dear Gianna ,

Thank you for spending time thinking, writing calculations and putting effort to explain your point of view. I could not expect more. This is much appreciated. Now, I see how interesting is your proposal by bringing gliding to the topic. It makes easier to think with gliding because we can get rid of the power/thrust topic and concentrate on force/energy.

Your example is very useful. Assuming you are gliding at constant speed and direction, the resulting force is ZERO (drag compensates thrust and lift compensates weight). In this case, the thrust comes from the potential energy being converted into kinetic energy. The drag opposes inertia but the loss of altitude compensates the drag. I'm assuming there is nothing new here as you are a pilot. I'm writing this paragraph to help my own thinking.

Assuming that the gliding is gravity powered (instead of engine powered), I'll calculate the energy lost as a variation of the gravitational potential energy (dEnergy = m · g · dh). Where dEnergy means energy variation and dh means height variation. Therefore, the variation of potential energy per second is 1000kg * 9.8 * 3.3 = 32340J/s or 32340W.

1HP = 745W. So, we have 43HP.

Amazing: we are both getting the same result.

At this moment, we both agree that, in your example, the gliding is spending 43HP from the gravitational potential energy.

To be continued...

  Thank you for providing fun.

Hi l4zep,
I'm not sure if I understand you nor I'm sure about the need for the diagram.

I have a perception that the debate doesn't involve fluid dynamics yet as the amount of air pumped down from wings (creating lift) can be calculated using Newton physics.

  Please elaborate.