A FolloW-up on Dihedral: The column
I wrote about dihedral in the September
issue generated a bunch of E-mail. This
month I will follow up on that topic; I’ll
clarify some things and re-emphasize
others. I will also discuss using a gyro to
augment spiral stability and give a source
for wing rods with larger bend angles.
I need to clarify “equivalent dihedral
angle” (EDA). The EDA of a flat-wing
glider is the angle between one side of the
wing and the horizon. I was inconsistent in
describing dihedral in the September
column. The conclusions of that column are
valid, but the numbers in the examples
change a bit. If I would have kept my
angles consistent, it would have made my
point more dramatically.
To reiterate, most current-generation
Thermal Duration aileron gliders use wing
rods with 5° bends in them. This means
they have an EDA of 2.5°. The models I
have been building use a 12-16° total bend,
or an EDA of 6-8°. My airplanes use 2.5-3
times as much dihedral as the typical stock
kit.
Repeating my conclusions, the dihedral does not reduce the
roll rate. The dihedral does not harm the straight-line performance
a perceptible amount. The dihedral does have a beneficial effect
on handling.
According to a few of the E-mails I received, people tried the
large dihedral angles with ailerons. All of the people who tried it
wrote that they liked it. John Erickson wrote:
“I fly all types of thermal duration but my favorite is hand
launch. I’ve had a couple of 9th place finishes at the IHLGF
[International Hand Launch Glider Festival] and this year I got
Mike Garton, 2733 NE 95th Ave., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
These models were used to test the effect of large dihedral on an aileron glider.
Author’s has 8° of dihedral per side; Frank Baldwin’s has normal 2.5° per side.
Instructions for Pole Cat Aeroplane Works XP-3 recommend 5.5-7.0 inches under one wing (5.30-6.75° dihedral per side).
6th. I’ve done very well on the Southern California circuit flying
my Photon, a built up polyhedral model. I attribute a lot of my
success this year to the Photon, mainly because it has made me a
better thermal pilot. It is easier to fly than my flat wing Raptor. I
give up some launch height, but I more than make up for it with
the outstanding handling and thermaling of the Photon.
“After reading your article and suspecting what you so clearly
put into words, I cut into my Raptor. I increased the angle from 9°
up to 12° (EDA is now 6). The effects were immediate. The
airplane is so much more stable and easier to thermal.”
Jerry Krainock stopped selling the Photon July 31 of this year.
86 M ODEL AVIATION
Reader Jim Halbert rapidly built some wings with different
dihedral angles and conducted his own comparative experiment.
“I made up several wings to test the SA7035-SA7038 with and
without 16 degrees (EDA = 8) dihedral. Very interesting. Your V16
works very well. I could see no difference in glide time over a poly
wing and landing with the V sure was a lot easier.”
I want to re-emphasize that large dihedral angles do not make it
more difficult to land. Available roll rate is the key to reacting to
gusts. I have flown four different designs with 12-16° total bend (6-
8° EDA). They are no more difficult to land in windy conditions
than any other aileron airplanes; I actually found them easier to land
in the wind than flat-wing models. Keep an open mind and try it.
I am not a beginning pilot looking for a crutch to avoid learning
something difficult. Many experienced pilots argue that they use top
rudder (also called cross-controlling) to coordinate thermal turns. I
can do that too. Yes, it works—when I can see the airplane well.
I also find that the pilot who does not have to worry about crosscontrolling
has more brainpower left to concentrate on centering the
circles in the core of the thermal. Imagine only having to move your
transmitter sticks once every two circles instead of two to three
times per circle.
My 38-ounce Two Meter has thermaled up through most of the
molded three-meter airplanes that it has encountered in the same
thermal. When the thermal is far away, it is like taking candy from a
baby.
Many pilots learn to fly with a polyhedral glider. Later they
usually try a flat-winged aileron glider. Without exception they find
that the flat-wing glider is more difficult to thermal and requires
more concentration to fly. I propose that pilots try adding ailerons
with the polyhedral (or large dihedral). They could consider it an
aileron trainer.
I would bet my computer radio that most pilots who try high
dihedral with ailerons will stop building low-dihedral aileron
A dual-output gyro can be used to electronically provide spiral
stability to low-dihedral aileron gliders. Text has details.
