A Critical Analysis of NASA's Incorrect Lift Theories in Aerodynamics

This essay critically examines three incorrect lift theories proposed by NASA: the "Longer Path" or "Equal Transits" theory, the "Skipping Stone" theory, and the "Venturi" theory. The author identifies flaws in each theory, such as the overemphasis on distance in the "Longer Path" theory, the disregard for the upper part of the airfoil in the "Skipping Stone" theory, and the misapplication of the Venturi effect in the "Venturi" theory. The analysis compares these incorrect theories with the principles outlined in the Guide to Aerodynamics, highlighting the discrepancies and providing a clear understanding of the correct aerodynamic concepts. The paper emphasizes the importance of accurate information in understanding lift and the behavior of airfoils, ultimately aiming to clarify misconceptions surrounding these fundamental concepts.

NASA Incorrect lift theories
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NASA Incorrect lift theories
NASA incorrect Theories
Abstract
Different authors have different explanations of the lift theory. The different theories
developed are therefore able to confuse learners on which they have to believe and use while
explaining the lifts. It is important therefore to identify the areas where the different theories
are able to represent false information (Bloor, 2011). This paper will identify the NASA
incorrect lift theories and highlight the false information in the specific theories. The
identification of the false information will be compared with what is explained in the guide to
Aerodynamics.
The first incorrect theory is known as the “Longer Path” or “Equal Transits” Theory.
It related to the Bernoulli’s effect. The theory explains that the top of airfoil is made longer
than the bottom part (Nicolosi et al., 2017). This helps the air molecules in the upper part to
move faster in order to meet the air molecules at the bottom part at the tail distance. This
creates lower pressure at the top and therefore enhancing the lifting of the airfoil.
According to Bernoulli’s equation;

NASA Incorrect lift theories
At V t = Ab V b
Increasing the distance in the upper area increases the area and therefore the air
molecules need to move at higher speed for the equation to balance. One of the incorrect
parts about this theory is the effect of the distance to affect the lifting of the airfoil (McLean,
2013). Taking for instance a paper airfoil of equal distance on top and bottom, the paper
airplane will fly fine. This explains that the distance is not the main cause of the lifting force
but the flow turning. Another incorrect part is that the upper air molecules move faster than
the bottom ones. Conducting an experiment on flow shows that the flow on lower part moves
faster than on top. In addition, it is clear that the air molecules at the beginning will not be
arranged the same at the tail. The Guide to Aerodynamics agreed on the Bernoulli’s effect on
airfoil but does not hold on the highlighted incorrect information.
The second incorrect theory is known as “Skipping Stone” Theory. The theory holds
that the lift is created by reaction force of air molecules striking the bottom part of airfoil.
One of the incorrect information about this theory is that the upper part of foil is not
considered anywhere yet is has air molecules striking (McLean, 2013). It can therefore be
assumed that airfoils with equal bottom area but different top area will have the same lifting
force which is not true. The theory does not explain the effect of air molecule interaction with
the upper part. This is because the top position is not a vacuum and has air molecules striking
as well. In addition, the theory does not address the effects of physical properties of the fluid
which affect the lift force. The Guide to Aerodynamics holds that this theory is only true
under high speed and attitude.

NASA Incorrect lift theories
The third NASA incorrect lift theory is the “Venturi ”Theory. It holds that the upper
surface of airfoil acts like a nozzle on which air accelerates. Using the conservation of mass,
the mass flow at any point will be a constant.
mass flow rate=m ˙¿ density x velocity x area=constant
Therefore the reduction of the area leads to an increase of velocity on top. This leads
to reduction of pressure at top and leading to lifting of the airfoil. One of the incorrect parts
of this theory is that it assumes the lift is caused by the upper part only (Drela, 2014). This
means that regardless of the shape of the lower part, the lift will be the same which is not
true. The foil is not a nozzle since it lacks one part to complete it to be a nozzle and therefore
comparing with nozzle is incorrect. Additionally, the velocity of air is higher at the centerline

NASA Incorrect lift theories
than the wall sections. The Guide in Aerodynamics does largely agree on the Bernoulli’s
effect to produce lift. Nevertheless, it does not agree with the point of comparing the airfoil
with nozzle and other incorrect information highlighted.

NASA Incorrect lift theories
References
Bloor, D. (2011). The Enigma of the Aerofoil: Rival Theories in Aerodynamics, 1909-1930.
Chicago: University of Chicago Press.
Drela, M. (2014). Flight vehicle aerodynamics. Cambridge, Massachusetts : MIT Press.
McLean, D. (2013). Understanding aerodynamics: Arguing from the real physics. Chichester,
West Sussex, U.K: Wiley.
Nicolosi, F., Ciliberti, D., Della, V. P., Corcione, S., & Cusati, V. (July 03, 2017). A
comprehensive review of vertical tail design. Aircraft Engineering and Aerospace
Technology, 89, 4, 547-557.