American Aircraft Modeler
if your path to flying an R/C helicopter involved first designing,
then building, and then troubleshooting the contraption. That was
the burden of pioneers. We have people like S.S.P. Helicopter designer
Gene Rock to thank for being able to enjoy the state-of-the-art
models that are available today. This article from the August 1972
edition of American Aircraft Modeler describes the process of machining
all the metal parts for an Enya .45-powered craft. Mr. Rock even
designed a very successful mechanical gyro for keeping the tail
under control. If you have ever tried flying an R/C heli without
any type of gyro (I have, on a DuBro Tristar), you will fully appreciate
what a pleasure it is to not have to manually counter torque changes
(throttle) with tail rotor stick input from the transmitter. I recently
bought a Blade MCX2 coaxial rotor helicopter for flying inside,
and the gyro is so good on that thing that you can put it in a full
speed pirouette in either direct, release the rudder stick, and
the model instantly stops spinning and holds its new heading - amazing.
OK, time to go blow the dust off your model lathe and buy some
metal stock. Let's see if you're up to it.
Learning to Fly the S.S.P.
by Gene Rock
I made my first helicopter, inspired by Glen Lee, back in 1962.
The model was free flight and it didn't fly simply because I didn't
know how to adjust tip weights. In 1963, Ken Norris' helicopter
spurred me on and the model failed - simply because I couldn't keep
the motors running. In 1967, John Burkam's model in the Challenge
of RC Scale took shape in my shop but still couldn't get off the
ground. This time the problem was mainly due to poor machining practices.
In 1969, I met John Burkam and started building rubber-powered models
like "Perini" published in 1969 in American Modeler. Rubber-powered
models offered a fast way to study helicopter stability. I learned
twice as much in the following year as I did in the previous seven.
Many evenings were spent observing John's "Super Susie" in flight.
Again I tried and failed but finally this past summer the "S5.P."
emerged. Being so fed up with failures, the tethering was skipped.
A few short bursts of the engine was enough to trim out the model.
Feeling brave, I gunned the engine and the model leaped into the
air and was ten feet off the ground before the engine was throttled
back - it has been flying ever since.
Gene Rock flies his S.S.P. Helicopter
Throttle linkage is spring-loaded to eliminate any slop. Precise
control is essential since no collective pitch control is used.
Throttle does it.
Two stage belt reduction to rotor shaft permits locating centrifugal
clutch on midshaft and the drive to the tail rotor via another
This is a Hiller rotor system except there is no flapping feedback.
Control is through application of cyclic inputs to the small
Complete head assembly is free to tilt in any axis. The body
or chassis tends to just hang under the rotor. The gyros keep
it stable at all times.
Unique among model helicopters is the gyro on the tail rotor.
This automatically cancels torque variations and wind gust inputs
allowing the pilot to concentrate on other flying duties.
Servo input to the tail rotor is via springs which precess the
tail gyro. Belt drive here is simple and positive. Note rugged
Radio installation worked out to balance the model just in front
of the main rotor shaft. Many Missing Links and Kwik Links are
Spindly landing gear system really helps when learning to fly
a chopper. It can be taxied on the gear, too. Note visible and
large fuel supply-an absolute must. Dead stick landings are
Scene at Dahlgren, Virginia for DCRC Record Trials where Gene
flew the "chopper" to a 650-ft. altitude record and attempted
a challenge of the duration record.
The "S.S.P." is similar
to Dieter Schluter's helicopter in every aspect except for size
and body. The rotor system is Hiller except that there is no feedback
from flapping. Rotor control is achieved by applying cyclic pitch
to the small paddles. This forces the gyro that the paddles are
attached to, to precess 90° later in the direction of the force.
When the plane of the gyro is changed with respect to the main rotor,
cyclic pitch is applied to the main rotor. Like the gyro, the main
rotor takes 900 to precess. Now the rotor plane is changed, changing
the thrust vector. Assume that we want the model to fly forward:
The swash plate is tilted so that it is high in back. This tilt
gives the paddies the most pitch on the left side. This in turn
precesses the gyro and makes it high in back of the model. With
the gyro high in back, the rotor blades have the most pitch on the
left side. This precesses the rotor and makes it high in back. The
model then flies forward.
The gyro performs many functions.
When a gust hits the model, the gyro is slow to respond, thus not
following the model but staying in its former plane. The gyro always
makes the rotor follow until the rotor describes the same plane
as the gyro. This resistance to changes applies the proper cyclic
to correct the model.
Throttle is used instead of
collective pitch to vary the thrust. This arrangement simplifies
the control system greatly and performs just as well as collective
pitch. The only disadvantage is that collective pitch cannot be
dropped for autorotation. A reliable engine is a must.
the model is achieved by changing the collective pitch of the tail
rotor. The collective setting of the tail rotor is constant over
the rpm range of the main rotor. When the engine rpm is changed,
there exists a torque fluctuation while the rotor is accelerating
or decelerating. During this brief interval the model will yaw.
The "S.S.P." incorporates a tail rotor gyro to automatically adjust
the tail rotor collective during this interval. With a tail rotor
gyro, the pilot has one less function to worry about and the amount
of time it takes to learn to fly is cut in half. A much simpler
tail rotor is shown without the gyro. The "S.S.P." is the only model
helicopter with a tail rotor gyro - the choice is yours.
One of the biggest factors in designing a helicopter is that
the exhaust fumes are constantly circulated through the rotor when
hovering near the ground. The model very quickly becomes completely
covered with castor oil. Balsa wood and the like cannot stand up
to this. The only wood used is in the rotor blades and is sealed
as well as possible. The rest of the model is metal. The radio compartment
is enclosed unlike most RC helicopters.
The "S.S.P." was
designed strictly as a trainer. The large landing gear allows many
pilot errors. The belt drive system does not require complicated
tools to set up. The engine has twice as much power as is needed
to hover which comes in handy when heading for an obstacle. This
allows you to gain altitude fast enough to keep the model out of
danger. Belts also allow a better weight distribution.
basic tools required for this project are: a lathe such as the
Unimat; a drill press (unless the Unimat is used); a complete set
of numbered drills from 1-60 and fractional sizes 1/16 - 1/2 by
1/32ths; bastard files; a hacksaw, but a bandsaw is preferred; micrometer;
taps 2-56, 4-40, 6-32 and 8-32; pop rivet gun; metal brake such
as that from Lafayette Radio. The average modeler does not have
all these tools, but maybe your neighbor does. Some of the machined
parts can be farmed out but this is expensive.
to tackle such a project is not an easy one. It requires about four
months work at 20 hours a week. The cost of the project is about
$120 without engine and radio.
The parts that are most important
have been dimensioned. The only dimensions that are critical are
the ones for mounting bearings or for press fits. The majority of
parts can be hand fitted. The mistake on one part can be compensated
for on its mating part. When drilling holes, align the parts that
have holes in common and drill or use one as a jig for the other.
When drilling to match, always use the tap drill first unless a
tapped hole is not required. When drilling a close hole such as
for a press fit, select a drill at least two sizes smaller and use
plenty of lubricating fluid. Drill again with one size smaller drill
and then the final hole very slowly and well lubricated with the
required drill. If reamers are available, use them instead. Since
1/16 music wire is slightly larger than .0625, a 1/16 drilled hole
makes a nice press for the 1/16 music wire. Always drill about 1-2
thousandths smaller for press fit. A part always looks nice and
is easier on the fingers if the sharp edges are broken.
The material 2024-6061 and 7075 is aluminum. The best material,
strength-wise, is 7075-T6; the next is 2024-T3 or T4; the least,
strength-wise, is 6061-T6. 6061-T6 is usually called for on the
drawing because of its availability. 2024-T3 or T-4 or 7075-T6
can be substituted for 6061-T6 unless the part is to be bent. If
7075-T6 is called for in a part, try to find it but the others can
be used. This aluminum along with the drill rod (steel) and 4340
steel can be obtained at large steel or aluminum outlets, such as
All machine screws and nuts should be epoxied on
final assembly, or use self-locking nuts. The only exceptions are
those that will be used frequently.
Before starting, study
the plans carefully and understand fully all mechanisms. Next,
make up a material list of all raw material needed and order it.
Order Part No. HK 102 from Stock Drive Products and ask for their
catalog. The total cost of these parts is $59.95. The kit HK 102
contains the 44 parts needed for the main and tail rotor transmissions.
The bearing for the swashplate and gyro-stabilized tail rotor can
be ordered from a local bearing outlet. The fiberglass arrow shafts
were purchased at an archery store. Set screws and machine screws
are available at an industrial hardware store. Sometimes machine
screws can be purchased at an electronic supply store.
Radio Box: Practice bending
on scrap material to find the difference between the final bends
and the original distance that you layed out. Use this difference
in laying out your flat pattern so that you will have the external
dimensions desired. Be very careful in making up the end plates-make
sure they match or shim. Drill all rivet holes but only install
those rivets that do not hold any additional part. Next, install
all landing gear structure.
Engine Mount: Make all of mount
from 3/16 aluminum. Holes to lighten this mount may exist if desired.
Make sure that the two surfaces on which the engine is mounted are
parallel to one another and perpendicular to the top of the radio
Cooling Fan and Engine Pulley: The cooling fan is bent
into shape with a ball peen hammer and then filed to the final shape.
The fan must be keyed to the prop shaft of the engine. The Enya
A5 has its prop drive washer keyed to the shaft and this makes an
ideal part to key the cooling fan to. Make sure that the engine
used has .8 horsepower at 13,000 rpm without muffler. The transmission
would have to be changed if the engine did not meet these requirements.
Tail Rotor Boom: Machine -22 and use to align the four No.
4-40 tapped holes in the back end plate. Next rivet -22 to the 3/4"
00 aluminum tubing. Cut the tubing slightly longer than shown and
crimp the aft end over 1/2" thick block. Then drill through with
1/2" drill at 45° angle for 1/2" aluminum tubing. Remove top and
bottom material from end to 1/2" dia. hole. Wrap around 1/2" tubing
and butt in back. Cut 1/2" OD tubing 1/2" longer than required and
install with eight rivets. Remove tail boom from radio box.
Intermediate Shaft: Machine the clutch shoes as one piece, preferably
while bolted to the pulley. Mark some identification so that when
cut apart they can be installed on the pulley in the same relationship
that they were machined. Part marking is a good practice to insure
proper final assembly. Cut apart and machine to final shape. When
gluing the cork to the bell housing abraid the housing first. Machine
-45 pulley and assemble intermediate shaft. File flats on the 3/16
mw for the set screws. Spin the assembly to 1000 rpm and check clutch
engagement. Adjust spring clips until 1000 rpm or greater clutch
engagement is achieved.
Swashplate: Machine all parts
as shown. -11 is a press fit over B-541 bearing. If hole is turned
larger than shown, epoxy -11 to bearing. The pins should be left
slightly long and ground on final assembly. Make sure the gimbal
does not bind with ±150 tilt. Remove any interference. The 9/32
brass tubing is to lock inner pins when swashplate is removed from
Machine all remaining parts for the hub,
gyro and rotor controls. Next, install -18 on rotor shaft.
Transmission: Install transmission structure to radio box and tap
the top 1/16 thick angles No. 4-40 for -3, do not install -8 or
-8A. Now align -8 and -8A using the long belt from the engine to
the intermediate shaft. Make sure the intermediate shaft and rotor
shaft are perpendicular to and in the center of the radio box. Put
about six lb. tension on the belt and fasten -8 and -8A. Align large
pulley on rotor shaft and file flat for cap head screw. Then heat
treat rotor shaft.
and Rotor Controls: Install the swash plate, -12, -12A, -13, -13A,
-14, -14A for rotor controls, the hub and gyro. Do not forget to
file flats for set screws on 1/8 mw for gyro, and use brass tubing
for spacing the swashplate on the rotor shaft (same as spacing for
Tail Rotor: Install tail rotor transmission
by using three to four lb. tension on belts. Machine and assemble
desired tail rotor and install. Finish bracing tail boom and add
tail skid and tail guard.
Landing Gear: Make up landing
gear and set aside. Remove rotor shaft by removing -3.
Blades: Rotor blades should be the easiest part. The finish on my
main rotor blade is a 5 thousandths layer of fiberglass which just
about makes the blades indestructible. The tail rotor blades are
given a coat of Pettit Hobpypoxy and then doped. Make two extra
sets. Quick blades can be had by using MonoKote. The main rotor
and tail rotor blades are held in place by a friction clamp. This
allows the blades to fold when striking an object. Static balance
your blades by adding small lengths of mw or the equivalent. Drill
into the light blade tip hardwood leading edge and epoxy in required
weight. The dynamic balance is taken care of by the hardwood leading
Radio Installation: My radio is installed on a 1/8
aluminum plate. The installation is optional. The right stick
on my transmitter controls cyclic; up is forward, down is aft,
right is right cyclic, etc. The left stick is yaw and engine control,
up is advance throttle, right stick is yaw to the right which means
the tail goes to the left. Lowering tail rotor collective makes
tile model yaw to the right, etc. Remember when hooking up the swashplate
that the rotor tilts in the same direction as the swashplate. Installing
a spring at the end of the tail rotor cable to keep the cable in
tension is desirable and is a must if the simplified tail rotor
is used. The engine throttle should also be spring loaded. Completely
Next Month-How to fly an RC chopper.
S.S.P. Helicopter Plans Sheet
S.S.P. Helicopter Machined Parts Sheet
The AMA Plans Service offers a full-size
version of many of the plans show here at a very reasonable cost. They will scale the plans any size for you. It is always
best to buy printed plans because my scanner versions often have distortions that can cause parts to fit poorly. Purchasing
plans also help to support the operation of the Academy of Model
Aeronautics - the #1 advocate for model aviation throughout the world. If the AMA no longer has this plan on file, I
will be glad to send you my higher resolution version.
Try my Scale Calculator for Model Airplane Plans.
Even during the busiest times of my life I have endeavored to maintain
some form of model building activity. This site has been created to help me chronicle my journey
through a lifelong involvement in model aviation, which
all began in Mayo, MD. There
is a lot of good information and there are lot
of pictures throughout the website that you will probably find useful, and might
even bring back some old memories from your own days of yore. The website began life around
1996 as an EarthLink screen name of ModelAirplanes, and quickly grew to where more server
Copyright 1996 - 2022
BSEE - KB3UON
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