NASA says lift from air shoved down - can we trust NASA? - Page 11 - RC Groups
Nov 22, 2011, 02:03 PM
Ascended Master
Quote:
 Originally Posted by Taurus Flyer Of course you make pictures of that while the chopper is separate placed on floor, on his own legs and the plate on the scale! So you only measure the force as result of the dynamic pressure on that plate! Fix that chopper on the floor so it cannot fly away!! Cees
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What the hell does that prove?
Nov 22, 2011, 02:08 PM
Ascended Master
Quote:
 Originally Posted by Sparky Paul . ... Lemme put the thing on a scale and see what happens...
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Dun!
On the scale, taped to the flat plate, the thing weighs 1.65 oz.
Turn the motor on to maximum power, the weight on the scale drops to 1.25 oz.
It can't take off.
Remove the plate, the weight drops to zero as the heli takes off..
Going through .9 oz on the way to zero...

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Nov 22, 2011, 02:17 PM
Launch the drones ...
Quote:
 Originally Posted by slipstick Nope you're still confusing cause and effect. They generally demonstrate that when there is lift happening there is also some downward air flow happening. No causality proved or even indicated. Steve
If this air wasn't lifting the chopper, redirecting the air wouldn't redirect the choppers lift vector.
Nov 22, 2011, 02:28 PM
Launch the drones ...
Quote:
 Originally Posted by Sparky Paul . Dun! On the scale, taped to the flat plate, the thing weighs 1.65 oz. Turn the motor on to maximum power, the weight on the scale drops to 1.25 oz. It can't take off. Remove the plate, the weight drops to zero as the heli takes off.. Going through .9 oz on the way to zero...
Neat!

A larger plate will reduce the weight drop more, as some air will get by the current plate.

Also, though difficult to do, moving the plate closer to the rotors will also be effective in reducing the weight drop.

IOW, there's some air still being used in lift - it's not all being redirected sideways by the plate - we could see that in the way the chopper bounced along the ground with the plate attached - obviously, it was lighter with the rotors on.

This would be more accurate using a ducted fan in a tube, as no air would escape. I'd take the tube, and redirect the air sideways, and make those same measurements you made today.
 Nov 22, 2011, 02:28 PM Registered User ... Last edited by Steve Anderson; Sep 30, 2014 at 07:15 PM.
Nov 22, 2011, 02:33 PM
Ascended Master
Quote:
 Originally Posted by Steve Anderson Scale needs to be on grams for Bernoulli lift. Duh!
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We fought that war to among things not use Frog yards!
Nov 22, 2011, 02:34 PM
Ascended Master
Quote:
 Originally Posted by Tim Green Neat! A larger plate will reduce the weight drop more, as some air will get by the current plate. Also, though difficult to do, moving the plate closer to the rotors will also be effective in reducing the weight drop. IOW, there's some air still being used in lift - it's not all being redirected sideways by the plate - we could see that in the way the chopper bounced along the ground with the plate attached - obviously, it was lighter with the rotors on. This would be more accurate using a ducted fan in a tube, as no air would escape. I'd take the tube, and redirect the air sideways, and make those same measurements you made today.
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With the round rotor diameter plates, the helis don't hop at all!
The rectangular plates let some of the air get underneath the plate.
 Nov 22, 2011, 02:55 PM Registered User ... Last edited by Steve Anderson; Sep 30, 2014 at 07:15 PM.
Nov 22, 2011, 02:59 PM
I bail out, anywhere, anytime
Quote:
 Originally Posted by Sparky Paul . What the hell does that prove?
?

Sparky, don't you understand?

I did explane in that earlier post I am only interested in the dynamic pressure of the airflow.

By measuring the force on the scale and knowing the surface dimensions we can calculate the pressure. And that is the same as the pressure that is shown with a pitot tube. Only the pitot tube does need a few square mm's and you a whole plate.

That's why I use a pitot tube on my plane an not a l.p.

Cees
 Nov 22, 2011, 03:53 PM Ascended Master All I'm doing is answering the question can a heli with a large plate attached to the skids lift off. It can't. Why, is the downwash from the rotor impacts the plate. That's all. How much? In this case, there's a 1.2 oz shortfall in lift. No lift, no fly. Any one pitot-static and total pressure sensors I worked with in L-1011 Flight Test weigh more than all my helis combined. And I'm hardly going to overkill this trying to get some very low "dynamic pressure" readings from those things. The helis can't take off with the plate.
Nov 22, 2011, 03:56 PM
I bail out, anywhere, anytime
Quote:
 Originally Posted by Steve Anderson A little research and you can learn a lot. Wikipedia says Daniel had a fear of plates. So, Newton=lift=Berneulli until you tape the plate on and it scares away Bernoulli.
Steve,

When you mount that plate under a rocket it will not lift off either.

Cees
Nov 22, 2011, 04:07 PM
Sink stinks
Quote:
 Originally Posted by kcaldwel Actually, the pressure behind a building in a wind, or moving car or van, is not at a low pressure. Kevin
These objects experience completely separated flows in the wake, which certainly does result in a low pressure. That's where the increase in drag comes from.
Nov 22, 2011, 04:55 PM
greg
Quote:
 Originally Posted by kcaldwel Yes, there is down wash behind a wing.
from post #132 with the video of the tuft behind the trailing edge

isn't this agreeing that the video demonstrates air is forced downward when lift is generated?

of course the angle is small. if the air moves downward in the vicinity of the airplane at only 0.5 fps and the plane is traveling at 10 fps, the angle is only 3 deg.

greg
 Nov 22, 2011, 05:24 PM Suspended Account The plate on the skids experiment is very interesting. if I was asked what would happen before I ever witnessed it I would say that it would not lift off. It would be my instinct. The force of the down thrust is simply pushing the heli back down, cancelling the thrust. VP (Like blowing your own sail!)
Nov 22, 2011, 05:26 PM
I bail out, anywhere, anytime
Quote:
 Originally Posted by Victory Pete The plate on the skids experiment is very interesting. if I was asked what would happen before I ever witnessed it I would say that it would not lift off. It would be my instinct. The force of the down thrust is simply pushing the heli back down, cancelling the thrust. VP (Like blowing your own sail!)
VP

When you mount that plate under a rocket it will not lift off either.

Cees