“Airplane Setup Methodologies”
Dave Scott made a serious
mistake in his “Airplane Setup
Methodologies” article [in the]
August 2013 issue. Dave Scott
wrote, “A neutral CG location at the
wing’s thickest point provides the best
overall handling without restricting
This is dangerous He should
have said a CG at 1/4 chord point.
The aerodynamic center of most
airfoil sections is at 25% to 26%.
[On] the old non laminar sections,
four digit and five digit NACA
[National Advisory Committee for
Aeronautics] sections, the thickest
point is at 25% to 27% chord, but
the newer NACA laminar sections
go back to 45%!
Dave is partly right. My Aerostar
(last built by Piper) uses a laminar 64
series with the thick point at 37%, the
Piper Cherokee uses a laminar section
series 65 with the thick point at 40%,
and the P- 51 uses a 66 series with the
thick point at 45%! If you put the CG
at the thick point of a laminar section,
bring a box to gather the pieces! Use
25% chord, period!
He also said, “A nose-heavy airplane
tends to be less stable and less
maneuverable, and … it will be less
maneuverable, but more stable.” Aft of
25% is less stable, and forward of 25% is
When the article was rewritten for
the magazine, the wording somehow
got jumbled. I double-checked the
article that I submitted to Model
Aviation and my original did state that
a nose-heavy airplane tends to be more
stable, etc. I originally wrote: “A nose-heavy airplane tends to be very stable,
less maneuverable, and will behave
differently depending on the speed. All
things considered, a neutral CG location
at the wing’s thickest point provides the
best overall handling without restricting
So, good catch!
The reason why I’m able to achieve
flight characteristics representative of
neither nose heavy nor tail heavy on
99.9% of the countless models I’ve set
up for our students adhering to the
wings thickest point rule-of-thumb
is because nearly all models use very
similar “cookie cutter” airfoils with the
center pressure points 25-30% of the
cord (indeed, I’ve yet to see a laminar
airfoil on a commercially built model).
Of course, you know that the FAA
requires most certified airplanes to
ensure the CG is ahead of the center
of pressure, e.g., to ensure the nose-lowering tendency during stall. Or as I
often put it, if one is going to err, nose
heavy is definitely better than tail heavy.
Thanks for your input, Stan!
1st US RC Flight School
Dave is indeed correct that the
wording was jumbled during editing.
MA regrets the error.
9 Model Aviation OC TOBER 2013 www.ModelAviation.com
If you have a letter to the editor, please submit it to MA Editor-in-Chief Jay Smith at
5161 E. Memorial Dr., Muncie IN 47302, or email to email@example.com.