Recently I became
interested in helicopters, and in typical fashion, I no sooner mastered
the basics of flying one than I started looking for a military scale
subject. Having read an article on control systems for
tandem-rotor helicopters, I set out to design a CH-47 Chinook (nothing
like jumping in the deep end of the pool). The design was
featured in the Winter 2008 issue of Air Age's RC Helicopter
Magazine. The vacuum-formed parts are available in a "parts pack"
for
$65 including shipping within
the continental U.S.
You can order by mail or
click the PayPal logo for
fast,
convenient on-line ordering.
Click here
for
assembly notes for the heli mechanics.
Click here for
assembly notes for the body shells.
Click
here for tips on assembling the
engine pods.
Scale: 1/24
Rotor Span: 25.4"
Body Length: 25.6"
Weight RTF: 40 OZ
Here's
the Chinook ready for another sortie. The 'Hook is a modest-sized
and affordable project, but it's a little more challenging to fly than
most conventional tailrotor helicopters. The complex drive train
is also targeted toward more experienced builders.
Here's
the CH-47 on an early test flight. Note the characteristic
nose-high attitude in hover. The Chinook was designed this way so
that it would assume a level attitude in cruising flight, making for a
more comfortable ride for the crew and passengers.
Here's
another shot of the Chinook hovering on an early test flight.
Note that the rotors are synchronized to be 90 degrees out of
phase. The Chinook requires gyro damping on both yaw and pitch,
and four custom mixers control lateral cyclic and DCP (differential
collective pitch) on the front and aft rotors.
Here's the Chinook climbing
out. The tandem rotor system is very efficient, and the CH-47
hovers on just 10 amps of current.
This
photo shows the Chinook with one body shell removed. As you
can see, the hardware installation is pretty snug. The aluminum
truss is the main structural member, providing a frame for the
helicopter mechanics and the drive shaft that connects the two rotor
systems together. The truss is tilted 6.5 degrees relative to the
Chinook's body to give the two rotors their proper orientation (this
accounts for the 'Hook's characteristic nose-high attitude in a
hover). Power is provided by a HET-RC EDF-4W motor, a Castle
Creations Phoenix 35 controller and a ThunderPower TP-2100-3S lithium
polymer battery.
This
photo shows the CH-47's mechanics. I used crown and bevel gears
from the popular Corona 120 helicopter to fabricate the drive shaft
assembly. You can see that the pitch servo pushrod has been
screwed to a rigid post to disable pitch input. Just two servos
(roll and collective) control each rotorhead. The fiberglass side
frames of the Revo-CP helis I used to build the prototype made mounting
them to the aluminum truss relatively easy.
