MadSci Network: Physics

Re: How does a loop paper airplane gain lift?

Date: Fri Oct 20 09:39:52 2000
Posted By: Kenneth Chivers, Grad student, B.S. Aerospace Engineering, In school for MBA:Management of Information Systems, NAWCAD, Lakehurst, NJ
Area of science: Physics
ID: 968174426.Ph

In the "wingless wonder" example, the top part of the loop, where the 
straw was afixed is too disrupted to provide decent lift, however without 
the straw body any standard flight path, except straight down, would be 
impossible.  There are 2 components here.  First, is distributed weight, 
which affects stability.  Second, is distributed lift, the "wing" or as 
generalized, the lifting body/surface.

In your loop, as well as in the teacher's loop, the loop could easily 
break down into four simple sections-right, left, top and bottom-acting as 
four lifting surfaces.  The air flow is faster down the center of the 
loop, due to bernoulli's therom and the laws of conservation.  The volume 
flow rate ((m^3)/sec) must therefore be the same on the inside and outside 
of the loop.  Due to the resultant three-dimensional effect of the "loop" 
design, the air flowing into the loop is actually streamlined or tunneled 
in, while the air outside the loop is relatively unaffected and slower.  
The result is a lower pressure and faster moving air flow over the inner 
surface of the bottom half of the loop vs. the underside/outside portion.  
This results in lift, the upward difference in pressure between the two 

On the upper half of the loop, you have a more readily understood air 
flow, more like a traditional wing.  This upper half is the second 
contibuting lift surface.

It is the interplay between the lifting forces and gravity which lend 
to "flight."  Focusing on straight-forward flight, you'll need the center 
of lift either at or in-front of the center of gravity.  Only 
experimentation can find the best location for such a design.  

In your design you'd have to think a lot about this interplay, as 
your center of lift will tend to be behind your center of gravity and 
significantly impair flight.  You would also need a fairly rigid and 
extremely light material, and you'd have to think really hard about where 
you put the wheels.  In the end you'd be building a miniature, but very 
complex, ultra-light air craft.  It could be done, but you'd be looking at 
an expensive life-long hobby :)

Good luck!


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