Great Planes GPMR2400 User Manual

Undoubtedly, you have an airplane on which you are anxious to test
your C.G.Machine, so let’s get started!
TOOLS AND SUPPLIES REQUIRED FOR ASSEMBLY:
Thick or medium CA
Hobby knife
Phillips screwdriver
Small metal file
Thread locking compound
Small 90° triangle
Tissue or paper towel
Rubbing alcohol or glass cleaner
C.G. MACHINE PARTS
1. Examine all molded plastic par ts, and trim off any mold flashing
with a sharp hobby knife. Examine the ends of the metal rods for
burrs, and carefully remove them with a metal file or emery cloth.
ASSEMBLY SEQUENCE
2. Inser t the two 3/16" x 12" steel base joiner rods into the holes
in one of the molded plastic bases. Both of the bases are the same
so there is not a
right
or a
left
. The joiner rods should fit snug, but if
they are too tight, lightly lubricate them with bar soap. If the rods are
still too tight, carefully enlarge the holes in the base with a 3/16" drill
bit or a round file.
3. Join the other base to the joiner rods the same way.
4. Thread the two 2-56 threaded steel pivot balls into the ends of
the 1/4" steel upright rods with a drop of thread locking compound.
Carefully remove any burrs on the pivot balls with a small file. Clean
the pivot balls with a tissue.
5. Push the 1/4" steel upright rods all the way into the bases. If
there is much resistance, carefully enlarge the holes with a 1/4" drill
bit or a round file.
6. The plastic ruler set consists of two rulers, connected
by three
tabs. Use a hobby knife to cut part-way through each tab on both
sides of the rulers, then carefully flex and snap the rulers apart.Trim
the remaining tabs flush with the edge of the rulers,
then finish with a
flat sanding block and 220-grit or finer sandpaper.
7. Insert the .074" x 2-1/2" wire pointers into the plastic ruler end
caps.This should be a secure friction fit.
8. Slide the ruler end caps onto the rulers.When the ruler end caps
are fully seated, the pointers should be perpendicular to the ruler – you
can use a small 90° triangle to check. If it is necessar y to adjust the
fit, sand the end of the ruler slightly or trim the slot in the ruler end cap.
9. Apply a drop of thick or medium CA to both sides of the ruler at
the “zero” end, insert the ruler fully into the slot in the end cap, then
immediately confirm that the pointer wire is vertical. Attach a ruler end
cap to each of the rulers.
10. Check the fit of the rulers in the molded plastic ruler holders.
The rulers should slide freely in the ruler holders. If they do not,
carefully sand the edges of the rulers with a sanding block and fine
sandpaper until the rulers slide freely.
11. Loosely attach the ruler holder to the molded plastic socket cap
with a #4 x 3/8" screw.
12. Inser t the ruler through the r uler holder, then tighten the screw
only enough to provide friction. Do not overtighten the screw, as this
may deform the plastic.
13. Clean the top of the socket caps with a tissue or paper towel
dampened with rubbing alcohol or glass cleaner.Peel off the backing
from the foam rubber pads, then apply the pads to the tops of the
socket caps.
14. Snap the socket caps onto the steel balls on the upright rods.
There is not a front or a rear to the C.G.Machine so at this time it does
not matter onto which upright rod you install the socket caps.
15. Pivot the socket caps throughout their range of motion to check
for free movement.If there is a significant amount of fr iction between
the cap and the ball, remove the cap and snap it on again, moving
and spinning it around.If there is still too much friction, polish the steel
ball with 600-grit sandpaper and coat it with a thin film of bar soap.
16. Apply the peel-and-stick decal to the top edge of one of
the bases.
C.G. MACHINE
ASSEMBLY INSTRUCTIONS
Thank you for purchasing the Great Planes
®
C.G. Machine. We are
glad you realize the importance of properly balancing your model
and the effects the C.G. location has on the way it flies. Although
checking the C.G.is often one of those last minute “oh, I’d better do
that before I get to the flying field” procedures, the C.G.location can
have a profound effect on the way all models handle and respond to
control inputs.Therefore, determining and shifting your model’s C.G.
is an operation that you should perform with care and accuracy.
That’s where the Great Planes C.G.Machine comes into play.With
the Great Planes C.G. Machine, you can accurately and easily
balance your model according to the manufacturer’s recommendations,
and then make incremental changes to the C.G.location to alter your
model’s flight characteristics according to your flight skills
and preferences.
Great Planes Model Manufacturing
P.O.Box 788
Urbana, Illinois 61801
(217) 398-8970
Entire Contents © Copyright 2004 BALP01 v1.1
Not designed for
use with planes
under 2 lbs
flying weight.
Your C.G. Machine is now ready to use.
BALANCE Y OUR MODEL
To balance your airplane at a predetermined location:
1. Adjust the width of the bases so the upright rods clear the sides of
the fuselage and landing gear.
2. Determine the distance from the leading edge of the wing to the
balance point, from your airplane’s plans or instructions.
3. Slide the rulers to the distance determined in the previous step.
View the measurement in the center of the ruler holder windows.
Note: For maximum stability, balance high-wing airplanes right side
up and low-wing airplanes upside down.
4. Place your air plane in an approximately level attitude on the foam
rubber pads. Pivot the rulers until they are horizontal. Hold your
airplane as you move it forward until the leading edge of the wing
contacts the pointers.This is the position at which your model should
be balanced.
Note: In some cases, especially with high-wing tail draggers, the
landing gear may interfere with the upright rods. If that is the case,
turn the C.G. Machine 180° and switch the socket cap and ruler
assemblies.If this does not work, raise the front or back of the bases
to change the angle of the upright rods in relation to your airplane, but
not enough to make the bases unstable.
Note: If, for some reason, you need to spread the bases more than
12" apart, you may do so by substituting longer 3/16" base joiner rods.
5.Gently release the airplane...If the tail drops, the model is
tail heavy
and you must either add weight to the nose or move internal
components (battery, servos, etc.) forward. If the nose drops, the
model is
nose heavy
and you must either add weight to the tail or
move internal components aft.
See General Balancing Tips.
To measure where your airplane currently balances:
1. Slide the rulers out near the 7-inch line.
2. Position your airplane on the foam pads so it rests level.
3. Pivot the rulers so they are horizontal, then adjust the rulers until
the pointers touch the leading edge of the wing.
4. Read the distance in both ruler holder windows. Note: If the two
distances differ slightly, it is sufficiently accurate to use the
average
of
the two values.
HOW T O USE THE LEVEL
To assist you in accurately balancing your airplanes, we have included
a small, lightweight level vial.You can use this in various ways to help
determine when your airplane is truly level, rather than relying on
estimation.Although the level vial may be used alone , y ou may attach
it to the 1/2" x 3" plastic strip, with a small piece of double-sided tape
(cut from the included 1" square), carefully aligning the vial with one
edge of the strip.Attaching the vial to the plastic strip will allow it to be
taped to the side of the fuselage along a reference line. You can also
place the assembled level on the stabilizer.
GENERAL BALANCING TIPS
A. Always balance your airplane in a ready-to-fly condition with an
empty fuel tank (unless the fuel tank is
behind
the C.G.). Check your
airplane’s instruction manual for specific balancing instructions.
B. On models where the leading edge of the wing sweeps rearward,
the distance between the leading edge and the C.G.decreases along
the span. In other words, the leading edge of the wing gets closer to
the C.G.toward the wing tip.The C.G. shown on most plans is where
the wing meets the fuselage. This means the distance between the
leading edge of the wing and the C.G. is valid only next to the
fuselage; so, for tapered wings, you should position the upright rods
and the foam pads as close to the fuselage as possible.
C.Before you add weight to balance your model, if possible, rearrange
the internal components. Add weight only if you must.
D. If you must add nose weight, start with a Great Planes 1 oz. or
2 oz. spinner weight (a weight that fits inside your spinner, and takes
the place of the prop washer), as this places the weight far forward
where it has the most effect. If your plane does not have a spinner,
then use a Great Planes heavy brass prop nut.If this does not provide
enough weight to balance, add Great Planes stick-on lead weight to
the front of the model on the front or back of the firewall or another
location that will not interfere with other systems. Never mount
weights to the cowl of your model because it is not meant to support
additional weight.
E. Stick-on lead weight works well for tail weight too.You can stick the
weights directly to the covering, or cut an access hatch in the fuselage
and install the weights inside, then reinstall the hatch. Before you cut
the model open to install weights inside, you should first confirm the
amount of tail weight you require by test flying your model with the
weight stuck to the outside. Before you permanently stick weights to
the covering, remove all residual exhaust or other oil. Poke a few
pinholes through the covering in the area where you will place the
weight and apply a drop of thin CA to each pinhole to make sure the
covering is securely bonded to the structure (and the weight securely
bonded to the model).Attach the stick-on lead weight to the bottom of
the stab or fuse.
F. For the first flights it is common to balance the airplane at or
slightly
forward of the center of the recommended balance range.
For first flights it is desirable to have a model that is stable.
G.In addition to checking the C.G., you should also balance
your model
laterally
(from side to side). Lift your model several times by the
propeller and the vertical fin. This may require a helper if you have a
large model.Add weight to the wing tip opposite the heavy side of the
model until it balances.
TROUBLESHOOTING C.G. PROBLEMS
Your model may be nose heavy if:
You cannot lift the nose on final approach and it seems to overshoot
landings, or landing speeds are too high, or the model requires lots of
forward stick (down elevator) to hold it level while inverted, or your
aerobatic model will not snap roll or generally seems to be too stable.
Your model may be tail heavy if:
It seems unstable or overreacts to control inputs, or the tail drops
while in a high banked turn, or no forward stick (down elevator) is
required to maintain level flight while the model is inverted
(although
neutrally stable models such as contemporary pattern planes require
virtually no down elevator to maintain inverted flight),
or if upon
landing approach your model flares without adding any up elev ator, or
upon landing down elevator is required to prevent a stall.
ACCESSORIES
Here are some order numbers for Great Planes Accessories:
Great Planes Stick-on Lead Weight (GPMQ4485)
Great Planes 1/4-28 Brass Spinner Nut 2.5 oz. (GPMQ4640)
Great Planes 1 oz. Spinner Weight (GPMQ4645)
Great Planes 2 oz. Spinner Weight (GPMQ4646)
We hope you enjoy your Great Planes C.G. Machine and have an
easier time of balancing your next model and can improve the flight
characteristics of your current models.
PARTS LIST
Part#.......................Qty...........................................Description
NYLON141................2........................................................Base
NYLON138................2 .............................................Socket Cap
NYLON139................2.............................................Rule Holder
NYLON140................2 .........................................Rule End Cap
LEVEL01 ...................1.................................................Level Vial
LEVEL02 ...................1 ..............................1/2" x 3" Plastic Strip
WBNT262 ..................2 .............................Leading Edge Pointer
SCRW072..................2..........................2-56 Threaded Ball Link
FTAP001....................1......................1" x 1" Double-Sided Tape
FOAM002..................2 ..................Self-Stick Foam Rubber Pad
SCRW043..................2 ..................#4 x 3/8" Sheet Metal Screw
NYLON142................1 ........................................Rule Set (L&R)
ROD003.....................2............................1/4" x 16" Upright Rod
WIRES07...................2 .............................3/16" x 12" Base Rod
STKER46 ..................1 ..............................C.G.Machine Sticker
Printed In USA 3059256
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