A question if allowed. What are the aerodynamic drag penalties or
advantages in
this contrast.
Low wing monoplane on twin floats vs low wing monoplane on single
main float
with small wign tip stabilizers (IE Grumman duck).
In the former example the main float attachment scheme may be
central pylon(s),
peripheral struts, and/or a fuselage width faired in structure.
My thought exercise is prompted by the fact that, it would be easier
to
implement amphibious tricycle gear on single float, and single float
would be
able to handle higher sea conditions.
C. Smith



D. F. Hoerner, in his book "Fluid Dynamic Drag" [possibly
chapter 8] shows data for drag between two identical struts
when flown at varying distances apart.  When the two struts were
about 4 of their own diameters apart, total drag for the two
was about the same as it would be for a single such strut
multiplied by two.  When the struts were moved closer together,
however, total drag increased over 'single strut times two.'
This is called interference drag, and exists between any two
aerodynamic bodies relatively close together.  I would guess
from this, that if your single main float had a substantial
cross-sectional area, that it would have to be farther from
your fuselage than would smaller dual floats, in order to
minimize this kind of interference drag with the fuselage.
Gene Kahn


Good job Gene

Paul Lamar

Thanks for the reference. I think I've heard of this phenomena
before. It's the
reason for the dimples in the fuselages of execu-jets by the engine
pods. Any
other good title suggestions on the topic? Hoerners book runs around
$150 and
up. Maybe I should build some models and little tunnel, see for my
self. 8-D
C. Smith


Sorry, I don't have any other references on this topic.  Even though
Hoerner was written in
the early 60s, it is still respected and used.  When you get your
book, I was referring to page 8-3.
There is much in the Hoerner book that we can use to extrapolate/
estimate drag coefficients from the
data given in all sorts of diverse design examples.  So I recommend
looking that book over carefully
before you do anything else!

[Actually, I am at the same point you are.  There is an  "MIT degreed
aeronautical engineer [who] will
help you solve your problem. Structures, aerodynamics and powerplants.
Reasonable fee.  New
number 877-952-9290." advertised in the "services" section on page 133
of the March 2011 issue of
Sport Aviation.  I was also considering contacting the author of the
article, "Lightning Fast" on page 80
of the April 2011 Sport Aviation magazine.  He used "in-house
computational aerodynamic codes..."
to help shape his record-breaking CEA-308 airlplane.    I was even
thinking of using a water tunnel
to test my design.  Reynolds number must be  calculated from water
temp, density, model velocity
and model length, which I did.  It is easy to get the Reynolds  number
in a water tunnel to match
typical Reynolds numbers found in light single engine  aircraft [2.5
million to 9 million] per Darrol
Stinton's "The Design of the Airplane" 2nd Ed page 93 fig 3.4.  I used
water temp of 20C, density
of 1 gm/cc, [giving dynamic viscosity of 1.002 cP, and kinematic
viscosity of 1.004 cSt], characteristic
length of 2 meters, and model velocity of 2 m/s.  That gave me a
Reynolds number of 2 million.
You can use dye to visualize the water flow around the model.]

Gene Kahn