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(New Millennium Sleek-Streek... pg. 3)
Warps
All models have warps; it is impossible to use natural fibers
that are subject to expansion and contraction due to humidity
and not have some inherent warping in your resulting structure.
Use warps to your advantage, and understand what are good warps
and what are bad.
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your wings. Are they twisted in the spanwise direction?
If they twist in a symmetrical fashion, this may not be
a bad thing (i.e., both wings twist such that the trailing
edges are up at the tips relative to the root of the wing).
This will result in washout (or washin if the trailing
edge at the tip is lower). |
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| If the
wings warp in opposition, this is essentially what the Wright
Brothers used to control roll on their airplanes, and your model
will indeed tend to roll when you fly it. You need to warp your
wing until each side has warps that are in symmetry. It is best
to achieve a washout in the wings as opposed to washin to start.
You may need to adjust the amount of washin in the wing to correct
a roll or excessive bank angle in the power climb phase, or
to tame a bad spiral in the glide phase. |
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| When
you wind the motor on your model, a stick fuselage such
as this will tend to bow and twist. The Sleek Streek has
a keel that tends to resist bowing in the vertical plane,
which provides consistent pitch trim during the power
climb phase. |
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Twist
is still evident when the motor is wound, and you will observe
that the tail goes from being square to the rest of the airplane
to one that has the right stabilizer tip significantly higher
than the left, as viewed from the aft end looking forward. When
launched, this twist will tend to force the model into a right
hand turn. Depending on the thrust angle of the propellor, the
model will turn in this direction under power, or torque will
pull it straight ahead, or to the left.
Warps can be remedied and influenced by using a tea kettle to
apply steam to the area of interest and twisting in the opposite
direction. Remove from the steam and hold until the material
cools off and begins to take the set you have made. This may
take repeated applications until you achieve desired results.
Generally, the stabilizer and fin can be twisted gently without
steam and corrected for warp, or add warp (tab) for pitch and
yaw adjustments.
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Flying
Make up a motor from one loop of 1/8 Tan Super Sport
rubber. This motor will be 1.3-1.5 times the length of the distance
from the rear hook to the prop shaft loop, when folded in half
to create a four strand motor. Use an O-ring purchased from
the hardware store at the fold, or a Crocket hook or other means
to wind the motor and disengage easily. Motors work best when
braided, but not mandatory. Install the motor onto the prop
shaft (O-ring end), and to the tail hook. For winding, you will
be removing the motor from the prop shaft. Lubricate the motor
before installing with Son-of a-Gun or rubber
lube sold by Sig, FAI Model Supply,
etc. If you have none of this, use some dishwashing soap to
lightly coat the rubber and extend it’s service life during
your flying session.
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| Adjust
the wing position to approximately that shown on the drawing
and check the center of gravity. Position the model on
your fingertips at approximately 60% aft from the leading
edge, near the fuselage and observe which way the model
tilts. |
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Good idea to put your contact info on the model! |
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If it
tilts forward and down, the model is noseheavy. If the nose
rises and the tail tilts down, the model is tail heavy. If the
model does not tilt at all, you are very close to the proper
CG for the prop and motor combination. If the model was noseheavy,
slide the wing forward until it balances slightly noseheavy
to level. If the model was tailheavy, slide the wing back until
you achieve the balance noted. A plastic propellor will likely
need the wing moved forward from where the drawing shows the
wing, as this was measured from a model with a balsa prop for
the design layout. Try to obtain a slightly noseheavy condition
to start.
Now you are ready for some initial test glides. Do not attempt
to power the model until you test glide, as a proper glide is
the foundation to obtaining good trim settings. From shoulder
height, push the model gently forward into whatever wind may
be present. It’s best to test outdoors in the early morning
or in the evening when the winds are not blowing, as this will
make it very hard to observe what is model trim and what is
just an upset due to the wind gusting, etc. Initially your model
should glide straight ahead and land about twenty feet or so
away. If it has an obvious nose down glidepath (shallow dive),
try moving the wing forward, as the model may still be noseheavy.
If the model pitches up and then falls, it’s likely tailheavy,
so move the wing aft before you try again. Continue to test
glide in this manner until you have the wing adjusted for a
smooth forward glide. It’s possible to fine tune for a
very flat floating glide, but save this until you get things
trimmed under power.
Observe the model for turning characteristics during the test
glides. Once you have a decent glide path established, which
way is it turning, if at all? Adjust the TE (trailing edge)
of the fin by warping to the right to initiate a shallow right
hand turn in the test glide. You can also influence this by
adding more washout in the right wing panel (twist TE up), or
adding washin on the left wing panel (twist TE down). Don’t
overdo the adjustments for tight turning characteristics, as
all your settings will be magnified when the model is under
power, and this may cause a steep turning pattern that results
in a spiral to the ground under power.
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Now begin test flights by winding your motor to about 400 turns
to start. Again facing into any wind, release the model in a
wing and fuselage level position from shoulder height, and observe
the flight characteristics that manifest. If you are on track
for good trim, the model should begin to fly in a shallow right
hand orbit, climbing very slightly, or just maintaining level
flight, followed by a shallow glide after the power drops off,
still continuing in a right hand turn. If your model starts
to pitch up into a climb and then falls in a stall, you will
need to add downthrust to the prop hanger. If the model begins
a flight to the left, this can be alright as long as the model
does not tighten up into a spiral that results in a crash. Generally,
it is desirable to turn to the right, as torque can be difficult
to deal with under high power. Typically the power turn is most
influenced by the thrust line settings, so adjust your prop
hanger by twisting the yoke such that the right propellor blade
is further aft than the left blade, when viewed from above the
model. Do not make extreme changes in thrust angles-a degree
or two at most will usually do the job. Add more thrust adjustment
until the model behaves the way you want it to (the essence
of FF modeling!). Usually a combination of down and side thrust
is required to keep a model from power stalling, and turning
away from torque. After your basic adjustments are made for
low power, begin adding more turns to the rubber-800, then 1000
turns. You will still need to fine tune as the power comes up,
and the whole exercise is to find the optimum climb and turn
under power, followed by a lingering glide after the motor has
expired and the prop goes into freewheel mode. Optimum climb
is the maximum climb possible without stalling, and turning
during climb helps achieve this. Even a slight stalling tendency
will degrade flight time, and for rubber power FF competition,
optimum climb is what all modelers are trying to achieve. A
Sleek-Streek will allow you to explore these
issues at low expense for material and time, so enjoy the experience!
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Resources:
Local hobby shop
for balsa, music wire, brass tubing, prop, rubber, rubber lube
(if you are lucky).
FAI Model Supply
for all sorts of rubber power modeling accesories, particularly
Super Sport motor rubber. PO Box 366, Sayre,
PA 18840-0366 USA, 1-570-882-9873 or ww.faimodelsupply.com
www.smallflyingarts.com For the best resources
in the world to learn about flying FF models!
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