D.H. 88 Comet.
All
spars
arran
-
gements
are
designed
as
„comb
boxes“.
That
is,
like
a
comb,
the
casing
elements
are
inserted
into
the
wing
along
the
spars
from
above
or
below.
This
leads
to
a
signifi
-
cant reduction in construction time.
A
frame
for
four
servos
is
provided
in
the
fuselage.
There
is
enough
mounting
s
p
a
c
e
for
two
elevator-,
a
rudder
and
a
tail
wheel
servo
in
stan
-
dard size.
Rudder,
elevator
and
ailerons
move
in
fillets.
The
axles
consist
of
core
and
0.8
mm
spring
steel
of
standard
Bowden
cables,
which
are
normally
used
for
controlling
rudders
of
all
types.
They
are
pulled
out
of
the
tubules
at
the
side
or
top,
so
that
the
rud
-
der
blades
can
be
easily
removed
at
any
time.
All
rudder
horns
are
included
in
the
kit
as
milled
fiber
glass
parts.
They
are
bonded
in
the
front
balsa
ele
-
ments
of
the
rudders.
This
results
in
reliable
and
practical controls.
The
vertical
and
horizontal
tail
fins
are
built
without
the
help
of
spe
-
cial
jigs.
I
n
s
t
e
a
d
locating
elements
in
the
regarding
fuselage´s
area
guarantee
right-angle
and
rail-guided
bonding.
Rud
-
der
and
elevators
are
placed
on
jigs
and
still
covered
there
with
balsa
on
the
upper
side.
As
already
mentioned
above,
all
jigs
can
be
(quickly)
removed
from
the
a
s
s
e
m
b
l
y
table
at
any
build
stage
and
b
e
located elsewhere without risking warpage!
Further
back
in
the
battery
duct,
the
battery
carrier
abutment
can
be
seen.
A
removable
aluminium
pin
in
the
middle
allows
the
abutment
to
be
relocated.
The
5.5mm
„gold
contacts“
glued
into
it
automati
-
cally
provide
the
electrical
connection
when
pushing
the
carrier
backwards.
They
also
contribute
to
secure
keep
the
battery
in
position.
In
addition
it
is
secured from the front.
An
unintentional
twisting
of
the
abutment
is
con
-
structively
prevented
by
means
of
a
pine
rod
direc
-
ting
backwards.
It
can
be
reached
through
the
canopy opening.
T
h
e
f
u
s
e
l
a
g
e
nose
is
remova
-
ble.
It
is
secured
by
four
strong,
guided
pin
magnets,
which
adhere
to
four
flat
magnets
on
the
fuse
side.
These
will
be
glued
to
the
back
of
the
four
balsa
blocks
visible
in
the
picture
above.
The
linear
guide,
combined
with
the
rare
earth
magnets,
reliably
ensure that the nose cannot bid goodbye in flight.
The
battery
pack
fixed
on
a
fiber
glass
carrier
is
inserted
from
the
front
into
the
appropriate
duct.
The
series
of
pictures
on
the
right
shows,
from
top
to
bottom,
how
to
take
the
battery
pack out.
The
battery
duct
is
fili
-
gree
and
robust
at
the
same
time.
It
allows
the
fiber
glass
battery
carrier
to
be
l
o
c
k
e
d
in
various
defined
positions.
Small,
milled,
circular
holes
in
the
duct´s
two
protruding
tongues serve this purpose.
This
concept
o
f
f
e
r
s
the
advantage
to
precisely
adjust
the
center
of
gravity
at
any
time
and
without
any
structural
change.
In
the
front
area,
under
the
duct,
a
receiver
bat
-
tery
and
a
battery
to
power
the
retractable
landing gear can be stowed away.
F
o
r
-
mers,
wings-
and
empennage
ribs
are
equipped
with
small
„legs“.
They
are
put
into
the
corresponding
slot
of
the
poplar
plywood
„jig“.
A
warpage
in
assembly
is
practically
impossible,
provided
that
a
straight
con
-
struction table is used as a base.
A
high-quality
STRONGAL®
f
u
s
e
l
a
g
e
-
s
u
r
f
a
c
e
c
o
n
n
e
c
t
i
o
n
f
r
o
m
Petrausch
Modellbau
with
16mm
pipe
thickness
ensures
safety.
Due
to
the
jig
system
explained
above,
an
absolu
-
tely
parallel
duct
of
the
two
tubes
in
the
fuselage
central
piece
and
outer
wings
is
guaran
-
teed.
Seven
screws
k
e
e
p
the
main
landing
gear
a
s
s
e
m
b
l
y
in
place.
It
can
be
mounted/dismounted
as
a
single
assembly
group
in
minutes.
The
brushless
outrunner
and
the
electronic
speed
controller
(ESC)
are
quite
easily
accessible
through
the
landing
gear
opening either.
By
doing
without
a
removable
fiber
glass
cowling,
weight
could
be
saved.
The
wheels
have
a
diameter
of
125
mm.
The
wheel
pant
slides
a
bit
into
the
inte
-
rior of the nacelle with the gear being extended.
High-power LEDs (e.g. Seoul Emitter, 3.5 W) can be
installed as position lighting in the wings and at the
rear. Due to the high core temperature, they must
be applied to heat sinks using thermal adhesive.
These are usually rodlike, made of aluminum and
have a diameter of 8 mm.
The
appro
-
priate
mount
p
o
s
i
t
i
o
n
s
have
already
been
structurally
prepared.
Control
via
constant
current
sources
can
be
done
by
the
gear
-
CONTROL.846
.
Technical Data
Scale:
20% (1:5)
Wingspan:
268 cm
Length:
177 cm
Take-off Weight:
7 .. 11 kg
Build Manual
D.H. 88 Comet
A Comet as an RC model?
Sometimes
the
Comet
is
said
to
be
„difficult
to
fly“,
because
of
her
incomparably
elegant
wing
outline.
It
is
said
that
she
tends
to
sudden
stalls
and
is
not
easy
to
pilot
basically.
Some
constructive
weaknes
-
ses
are
inevitably
„imported“
from
the
original
aircraft.
The
strikingly
tapered
wing
tips
of
the
origi
-
nal
aerodynamically
may
not
be
an
issue
for
the
full-scale
Comet
.
In
a
quarter
scale
model,
however,
the
running
length
of
the
air
flow
in
the
area
of
the
outer
wings
is
worryingly
short.
Moreover
the
flight
speed
is
correspon
-
dingly
lower.
In
the
tip
area
of
the
wing,
where
small
and
lar
-
ger
flow
detachments
actually
have
to
be
parried
with
the
aile
-
rons,
these
are
no
longer
fully
effective
as
a
result
of
the
physically
unavoida
-
ble
Reynolds
effect
-
also
known
as
the
„scale effect“.
The
flight
characteri
-
stics
of
a
model
air
-
craft
depends
on
the
design
of
its
wings
to
a
large
extent.
The
„scale
effect“
would
best
be
faced
by
defusing
the
taper
(apart
from
increa
-
sing
the
flight
speed),
because
this
would
increase
the
running
length
of
the
airflow.
However,
this
is
for
-
bidden
if
you
do
not
want
to
change
the
outline
(top
view)
of
the
model.
It
is
better
to
smartly
select
the
wing
airfoils
and
their
distribution
over
the
span.
Naturally,
Mr.
Reynolds
does
not
strike
so
hard,
when
the
angle
of
attack
of
a
cambered
airfoil
will
be
reduced
to
the
outside.
This
measure
is
acceptable
in
terms
of
keeping
to
the
out
-
lines
of
the
original
aircraft,
because
it
is
practically invisible.
The
RC
model´s
static
and
dynamic
intrinsic
stability
via
its
three
axes
must
be
„preset“
constructively.
In
this
regard,
too,
interventions
in
the
outline
of
the
model
are
largely
forbidden.
Again
other
variables
depend
on
the
stability,
for
example
the
landing
speed,
which
is
partly
determi
-
ned by the effectiveness of the flaps.
Flight Properties.
For
the
development
of
the
glattCAD
D.H
88
Comet
,
a
number
of
important
parameters
were
analyzed
and
determined
by
software.
They
were
incorpora
-
ted
in
the
construction.
The
Reynolds
effect
was
counteracted
with
the
implementation
of
a
mode
-
rate
twist
from
the
root
ribs
towards
the
tips
at
the
expense
of
aerobatic
capability.
Fow
slow
loops,
this
causes
the
glattCAD
Comet
to
fall
out
of
the
figure
at
the
apex.
This
can
also
happen
during
inverted
flight.
That
these
maneu
-
vers
do
not
really
want
to
succeed
is
the
price
paid
for
more
aileron
effectiveness and safety.
You
can
live
with
that,
because
the
original
Comet
was
not
intended
for
such
maneuvers
either.
In
order
to
improve
the
dynamic
stability
around
the
z-
axis,
the
tail
surfaces
have
been
slightly
enlarged
to
improve
the
chance
to
react
on
an
engine
failure
(combustion
engine).
The
theory´s
correctness
has
been confirmed in practice with excellent results!
However
certain
peculiarities
shall
also
not
be
con
-
cealed
which
could
only
be
countered
by
design
features to a limited extent.
It
takes
a
bit
getting
used
to
the
Comet´s
take-off
behaviour,
since
it
shows
the
ususal
breakout
att
-
empts
typical
of
a
twin-engined
plane.
But
experi
-
ence
proved
that
this
bad
habit
can
be
eliminated
with
the
installation
of
a
modern
electronic
gyros
-
cope.
Counter-rotating
propellers
are
also
recom
-
mended.
When
landing,
the
gyro
has
another
useful
task:
As
a
model
with
a
conventional
(taildragger)
undercar
-
riage,
the
glattCAD
Comet
also
tends
to
jump
if
the
landing is not optimal.
As
soon
as
the
tailplane
bobs
downwards
at
touch-down,
the
large
underside
area
of
the
fuselage
together
with
the
wings´typical,
rearward-
pulled
trailing
edges
at
the
root
ribs
support
the
ten
-
dency
to
bounce.
A
gyro
per
-
fectly
eliminates
this
rotation
about lateral axis.
The
glattCAD
Comet
is
desi
-
gned
to
be
driven
by
two
brushless
outrunners,
but
she
can
also
be
equipped
with
combustion
engines.
On
request,
suitable
fire
-
walls
for
the
rear
wall
mounting
are
supplied
for
the
chosen combustion motors.
Accessories Recommenda-
tion.
•
2 brushless outrunners
e. g.: 400 .. 450 gr, Ø 50 mm, length 60..65 mm,
KV = 250 .. 300 U/min/V
•
2 HV electronic speed controllers 50 .. 80 A
•
Lipo 8s, 5000 .. 5800 mAh
•
2 two-blade propellers ca. 15" x 12", best: left-
and right-turning
•
2 spinners Ø 76 mm
•
LED-lighting (according to your own idea;
see also manual for gearCONTROL.846)
•
Wheels Ø 125 mm, width 45 mm
It
is
sufficient
to
secure
the
jig
with
a
few
weights
or
needles
on
the
construction
table
against
slipping.
As
soon
as
a
few
more
components
have
been
installed,
a
fuselage
or
a
wing
half
can
be
easily
transported
to
another
work
station
together
with
the
jig.
Any
table
or
a
door
from
the
hardware
store
with
the
dimensions
165
cm
x
78
cm
is
perfect
as
a
building board for the assembly.
With
the
full-length
double
spar
pairs
made
of
pine
wood
and
the
balsa
on
the
front
and
back,
the
two
main
frame
boxes
are
very
sturdy
while
being
light
-
weight.
The
central
piece
of
the
Comet
includes
the
two
engine
nacelles
with
the
undercarriages
mounted
in
them.
The
width
is
78.5
cm
and
can
be
easily
put
in
a car with folded rear seats for transport.
An
electrical
connector
system
is
required
to
control
the
servo
and
the
LED
position
light
installed
in
the
outer
wing.
The
corresponding
slots
for
instal
-
ling
“multiplex”
connectors
are
already
milled
into
the root ribs.
The
undercarriage
kit
is
available
in
the
shop,
except
the
wheels.
It
includes
a
grinding
aid
of
milled
MDF
for
preparing
the
steel
tubes.
The
grinding
aid
has
some
grooves
and
holes,
so
that
the
tubes
can
be
prepared
for
hard-soldering.
Similarly,
a
jig
made
of
milled
vermiculite
helps
to
align
the
prepared
tubes
perfectly
to
each
other
for
the
welding
process
and
to fix them on the fireproof material.
The
landing
gear
is
retracted
and
extended
by
a
small
geared
12V
DC
motor
that
drives
a
spindle
on
which
the
drive
nut
slides.
Waterproof
micro
swit
-
ches
can
be
used
to
detect
the
end
position
and
switch
off
the
geared
motor.
The
switching
states
can
be
read
and
processed
by
the
glattCAD
gear
-
CONTROL.846
.
In
addition,
this
small
controller
can
also
switch
the
landing
headlight,
and
the
rear
and
wing position lightings.
Build Manual
D.H. 88 Comet
Unlike
the
original
Comet
,
which
has
a
tail
skid,
the
glattCAD
model
has
been
given
a
relatively
simple
tail
wheel
for
better
practicality.
Its
redesign
should
therefore
be
reserved
for
the
(scale)
modeller,
if
desired.
The
steering
is
carried
out
via
two
steel
braids.
Fiber
glass
rudder
horn,
spring
steel,
wheel,
adjusting
rings
and
steel
braid
are
included
in
the
kit.
Build Manual
D.H. 88 Comet
Build Manual
D.H. 88 Comet
Each
core
or
cable
that
is
to
be
run
over
a
longer
distance
in
the
model
lies
in
a
thin-walled
tube.
Long
party
straws
are
used
for
this
purpose.
The
corresponding
circular
holes
were
specially
desi
-
gned
in
the
related
components.
The
wire
ducts
(orange)
of
the
central
electrical
connection
bet
-
ween the fuselage and the wing is shown.
The
glare
shield,
an
area
for
the
instruments
panel
and
a
cockpit
tub
are
prepared
for
further
design
on
one´s own. Balsa of medium hardness is used here.
The
cockpit
unit
can
be
moved
out
in
one
piece.
To
lock,
pins
reach
into
the
fuselage
out
of
the
backside
of
the
unit.
The
unit
is
secured
by
a
Bowden
from
the open nose.
In
order
to
model
the
cockpit
canopy´s
typical
lat
-
tice
frame,
milled
fiber
glass
components
are
bonded
to
each
other.
This
results
in
a
stable
frame
-
work to be glued into the clear acrylic canopy.
The
flaps
servos
can
either
be
inserted
and
screwed
from
below
through
the
flap
openings
or
from
above
through
the
canopy
opening
into
two
vertical
servo
frames.
The
servo
arms
are
then
screwed
through the flap opening onto the servo drive.
The flaps are two-piece, as with the great original
Comet.
The aileron servos sit in prepared frames that can
be taken out of the wing at any time, e.g. to replace
a defective servo drive.
The
places
where
the
linkage
cables
are
glued
to
the
fuselage frames are already specified by design.
The
Bowden
tubes
thus
follow
a
perfect
curve
bet
-
ween
the
servo
and
the
rudder
horn,
which
has
the
largest
possible
radii.
This
minimizes
the
friction
of
the cores and the rudder lash.
The
wire
pairs
can
be
stored
cleanly
in
plastic
tubes
through the wing ribs, respectively fuselage formers.
Builder: Ludwig Retzbach
Builder: Ludwig Retzbach
© 2020-06 glattCAD Flugmodelle Info@glattCAD.de
Christoph Glatt Bauernstr. 77 86462 Langweid am Lech
Technical Details.
6.
„Comb Boxes“
5.
Tail Wheel
9.
Cockpit Unit
10.
Rudder
12.
Servo Frames
7.
Battery Pack
8.
Wire Ducts
1.
Jigs
2.
Main Frames
3.
Wing Connectors
4.
Main Landing Gear
11.
Flaps
13.
Position Lights
Technical Data.
Scale:
20% (1/5)
Wingspan:
268 cm (105.5“)
Length:
177 cm (69.7“)
Take-off Weight:
7 .. 11 kg
Technical Data
Scale:
20% (1:5)
Wingspan:
268 cm
Length:
177 cm
Take-off Weight:
7 .. 11 kg
Technical Data
Scale:
20% (1:5)
Wingspan:
268 cm
Length:
177 cm
Take-off Weight:
7 .. 11 kg
Technical Data
Scale:
20% (1:5)
Wingspan:
268 cm
Length:
177 cm
Take-off Weight:
7 .. 11 kg