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All shook up
The key to a smooth-operating helicopter is balancing the rotating
parts such as the cooling fan, clutch bell, main gear and the rotor
blades and using a dial indicator to check the runout (out-oftrue
condition) of the cooling fan, clutch and start shaft. Balancing
rotating parts is a complicated process and would take many pages
to explain; instead, we'll look only at how to use a dial indicator;
keep in mind that this is the method I use to check and adjust runout,
but it's by no means the only way to do things.
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Here are the basic tools needed to check the runout: a
heavy, stable metal plate, a dial indicator and a mount to
securely hold the engine.
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The cooling fan is checked first; it's only finger tight
on the engine, so adjustments can easily be made. The runout
should be less than 0.002 inch.
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Why use a dial indicator? Isn't just securely fastening the parts
to the engine good enough, especially if the fan uses a tapered
collet? Not really; you must remember that the fan and clutch assembly
are fastened directly to the engine's crankshaft and therefore are
turning at the same rpm. This can be anywhere from 10,000 to 14,000rpm,
or even greater. If the runout of these assemblies is greater than
0.002 inch, the bearings and the radio equipment will very quickly
fail due to excessive high-frequency vibrations.
Today, most helicopters use a brass tapered collet to center the
fan on the engine, however, the Venture 50 doesn't, so the need
to check the runout can't be overlooked. Checking runout isn't very
difficult, and you need only a few tools. Obviously you need a dial
indicator that reads in the thousandths, and you need a way to secure
the engine. I use a heavy, solid-steel plate that's 9x9 and 3/8-inch
thick so it doesn't move around. I then vertically mount a composite
engine mount (to which the engine is bolted) to the plate. This
simple and versatile method has served me well.
First, remove the glow plug (you want the engine to turn over easily),
and then install the fan loosely (finger tight) on the engine using
the prop nut. Secure the engine to the mount so it doesn't move;
it can be horizontal or vertical-whichever is more convenient. Position
the dial indicator's pointer on the lip of the fan hub. Rotate the
fan to find the high spot, and mark it with a felt-tip pen. Now,
rotate the fan while watching the dial; if the runout is 0.002 inch
or less, you can move on to the clutch. If it isn't, loosen the
fan and rotate it 180 degrees; repeat the process and check the
runout again. If the runout is less-great! If it isn't, return the
fan to its original position and rotate it again, but only 90 degrees
this time, and recheck the runout. Repeat this process until the
runout comes in.
Once the runout is 0.002 inch or less, tighten the prop nut a little
at a time, and check the runout after each tightening. If you apply
too much torque, the fan could move. To make sure that the prop
nut is fully tightened, remove the engine's backplate and use a
wooden dowel or toothbrush handle placed between the housing and
crankshaft to prevent the crank from rotating as you tighten the
nut. Don't use a piston-locking tool to jam the crankshaft. These
tools work by screwing into the glowplug hole, and as you tighten
the prop nut, the piston will be pushed against the end of the tool.
I have seen people punch a hole in the top of the piston using this
tool. Using a wooden dowel or toothbrush handle to jam the crankshaft
is much safer.
To give you an idea of how easy it is to do all of this, my Venture
took approximately 30 minutes to adjust the runout. After I balanced
the fan (about 13 minutes), it took me about 17 minutes to check
and adjust its runout. At first, the fan had a 0.005- inch runout.
After I had moved things around a few times, the runout was 0.001
inch. The clutch runout was 0.004 inch; after I rotated it 180 degrees,
it, too, was at 0.001 inch, and the start shaft was almost perfect.
Not too bad for a few minutes of effort! Now if the heli has a high
frequency vibration, you'll know it isn't the fault of the engine
assembly.
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As mentioned, there isn't much to do when assembling the Venture 50 3D;
the instructions cover the assembly process quite nicely. So instead of
going through it step by step, I'll cover the areas that aren't so obvious.
Because I knew that assembly would proceed rapidly, I first rounded up
the components so they would be readily available. The tail boom requires
only that it be plugged into the chassis and secured; the tail rotor assembly,
drive belt, horizontal stab mount and boom supports are factory installed.
Even the nuts and bolts that clamp the chassis around the tail boom have
been installed.
Before installation, be sure to twist the drive belt 90 degrees clockwise
(when looking at it from the front) before you slip it over the drive
pulley. The boom supports are attached to the chassis, and the boom is
pulled back to tighten the drive belt. The tail fins are attached to their
mounts, and I applied the decals to them before installing them. I installed
the tail-rotor pushrod next, and I sanded it so that it would slide more
easily in the boom-mounted pushrod guides.
Before you snap the ball link on the tail rotor bellcrank, take a few
minutes and adjust the pushrod so that it will move with the least amount
of resistance. That completes the mechanical assembly of the heli except
for the installation of the engine and servos. I told you there wasn't
much to do!
Engine and fuel system. To power the Venture, I used an O.S. 50SX-H
ringed engine. The engine is screwed to a castaluminum mount that is then
secured across the chassis with the engine head toward the rear; this
provides easy access to the glow plug. Before installing the engine in
the chassis, I dial indicated the cooling fan and clutch assembly (see
"All shook up" for details on this important step). After the
engine/cooling-, fan/clutch-assembly is dialed in, the engine and the
engine mount slides into the chassis after the carburetor is removed.
JR must have changed the mount after the instructions were written. The
pictures show 3x30mm bolts and locknuts being used to secure the engine
to the mount, when in fact, 3x12mm bolts are used; the engine mount has
been threaded for the shorter bolts. Before the fuel tank (which has already
been installed) and the engine can be plumbed, the 2-ounce header tank
needs to be installed; it's simply bolted to the left side of the chassis.
Adding the header tank to the fuel system is easy; the feed line from
the tank goes to the upper nipple on the header tank, and the feed line
from the header tank goes to the carburetor. Muffler pressure pushes fuel
from the main tank to the header tank. Besides increasing the fuel quantity
on board, the header tank improves engine performance and consistency
and provides an easy way to see how much fuel is left.
Radio installation. The swashplate requires 3 servos to drive it,
and these all must be the same. I used JR DS8231 digitals because of their
precise control and excellent power. The servos are mounted within the
chassis; I routed their leads inside the chassis as well. After the servos
have been installed, the manual becomes your best friend; it provides
detailed instructions on how to set up the CCPM system. If you're using
a JR radio, choose the pages that apply to your radio and follow the instructions
to the letter; you can't go wrong. The chassis has a molded-in battery
compartment under the front of the receiver-mounting tray. I wrapped my
receiver battery in foam rubber and placed it in the compartment. I also
wrapped the receiver in foam rubber and placed it on the mounting tray.
The tray has a bunch of molded-in lugs so that you can wrap rubber bands
around them to hold the radio equipment in place-a very smart setup. For
those who haven't dealt with a CCPM setup before, here are some pointers
to get you started:
• All CCPM servos must be the same make and model.
• Initially, the travel adjust values (ATV) for the CCPM servos
must be the same. If not, unwanted pitching and rolling of the swashplate
will be created during collective pitch inputs.
• The throttle/collective stick and swashplate needs to be in
the center of its travel during initial setup.
• The servo arms must be exactly horizontal. Minor adjustments
can be made using subtrim to center the arms.
• All pick-up points on the servo arms must be the same distance
from the center of the arm.
• The swashplate must be level fore/aft and left/right when
the servo arms are centered. Adjust the swashplate pushrods to level the
swashplate. Do not use subtrim; subtrim; this will upset servo-arm centering.
Then follow the instructions for your particular radio to set up the pitch
and throttle curves.
• Final details. All that is left is to trim the windshield,
attach it to the canopy and apply the remaining decals. The cut lines
on the windshield match the canopy very well, and four small screws secure
the windshield. The canopy has molded in recesses where the muffler resides,
so I decided to cut them out to provide cooling air for the muffler. I
really like that the muffler is enclosed; it reduces the risk of burning
yourself by touching it.
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| Four guides support the tail-rotor pushrod.
They wrap around the boom, and a single screw. |
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For a smooth-running heli, all rotating
parts should be balanced. Here, the cooling fan is being checked out
on a Robart High Point balancer. |
IN CLOSING
The JR Venture 50 3D ARF is one impressive helicopter. Its aerobatic prowess
is unmatched by any heli in the .50-size class, and it's a logical step
up from a .30-size heli. What little assembly there is goes quickly and
easily thanks to the simple mechanical layout and tiny parts count. The
icing on the cake, though, is the outstanding instruction manual; it goes
far beyond most other heli manuals and isn't overly technical. Whether
you're a novice, intermediate, or expert heli pilot, the Venture 50 3D
gives you a lot of bang for your buck!
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