Theory of Stability of Laminar Flow 471 
ove 
_ Op Vitax 
—o— DRAG HP ae 
D' = DRAG AREA FROM 
FAIRED CURVE OF 
EXPERIMENTAL DATA 
5-29 
~l9-5 95-20 
15-9 
SCINSUFFICIENT DATA 
0 02 0.4 06 08 1.0 
RING THICKNESS (INCHES) 
DRAG HORSEPOWER 
Fig. D7. Maximum drag horsepower versus ring thickness 
RUN 15 -2/ 
(FINS AND Je W. DRAE-RiNE NWOT SHOWN ) 
(NOT EQUAL INTERVALS ) 
Fig. D8. Porpoise movements during 
acceleration, nose sections aligned 
to show body and tail movement. The fins have been removed from the sketches to improve 
clarity. 
In conclusion, it can be stated that no unusual physical or hydrodynamic phenomena 
were apparent in this porpoise study. These tests, however, have not proved that unusual 
characteristics do not exist. It is possible that: (a) turbulence in the tank water or the 
added chemicals affected the ability of the porpoise to control its boundary layer, (b) the 
porpoise did not exert maximum effort, or (c) that unknown factors affected the results due 
to the unnatural environment. A report is in process which contains more detailed informa- 
tion on the study. 
M. Landahl (Massachusetts Institute of Technology) 
I want to comment on an error in the boundary condition, but first I want to point out 
that the present author here is not the only one who happened to fall in that trap because it 
is very easy to do it. The reason for it is as follows: When you have a wall; of course, you 
know that the steady boundary layer is such that whatever waves you may have superimposed 
on top of this layer, all components of velocity must vanish at the wall. But when you have 
a flexible wall you have to consider that you must satisfy the boundary condition on the wall 
itself and not on the mean position and this gives an extra term due to the finer slope of the 
profile which accounts for this extra term. This problem is really quite intriguing in a way; 
when you straighten things like this out it turns out that this problem mathematically is very 
