Stevens Aero Model Build It! RingRat 250 User manual

RingRat 250
Wing Span: 26.5 inches | Wing Area: 250 square inches | Average Flying Weight: 12.5 ounces
Build Instructions - Version 1.24 (revised 01.07.2015)
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 1 of 29

Product Support
WARRANTY
Stevens AeroModel guarantees this kit to be free from defects in both material and workmanship at the
date of purchase. This warranty does not cover any component parts damaged by use or modification.
In no case shall Stevens AeroModel’s liability exceed the original cost of the purchased kit. Further,
Stevens AeroModel reserves the right to change or modify this warranty without notice.
LIABILITY RELEASE
In that Stevens AeroModel has no control over the final assembly or material used for final assembly,
no liability shall be assumed nor accepted for any damage resulting from use by the user. By the act of
using the user-assembled product, the user accepts all resulting liability.
If the buyer is not prepared to accept the liability associated with the use of this product, the buyer is
advised to return this kit immediately in new and unused condition to the place of purchase.
THIS PRODUCT IS NOT INTENDED FOR CHILDREN 12 YEARS OF AGE OR YOUNGER.
WARNING: This product may contain chemicals known to the state of California to cause cancer
and/or birth defects or other reproductive harm.
PRODUCT SUPPORT
This product has been engineered to function properly and perform as advertised, with the suggested
power system and supporting electronics as outlined within this product manual. Product support
cannot be provided, nor can Stevens AeroModel assist in determining the suitability or use of
electronics, hardware, or power systems not explicitly recommended by Stevens AeroModel.
For product assembly support, replacement parts, hardware, and electronics to complete this model,
please contact Stevens AeroModel at www.stevensaero.com.
Stevens AeroModel
26405 Judge Orr Rd., Colorado Springs, CO 80808 USA
719-387-4187 www.stevensaero.com
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 2 of 29

Project Checklist
Kit Contents
☐Laser cut wood (12 Sheets - See inventory on following pages)
☐Illustrated instruction manual
☐1 - Vinyl Windscreen Decal
☐1 - Pre-bent Landing Gear (0.093 in. dia.)
☐1 - .047 in. dia. x 24 in. music wire (taped to back of wood brick)
☐1 - 1/4 in. square x 24 in. length hardwood stock (Fuselage Stiffener)
☐1 - 3/8 in. square x 26 in. length balsa stock (Leading Edge)
☐Large Hardware Bag (4 x 6 in.)
1 - 1/2 in. x 12 in. strip 2-sided velcro (Battery Safety Straps)
1 - 2 in. length 3/32 in. OD Aluminum Tubing (Stock for Lead-out Crimps)
1 - Delrin Bellcrank
1 - 3 in. x 1/8 in. O.D. Nylon Tube (Lead-out Wire Guides)
1 - 3/16 in. x 2 in. Dowel (Gear Lug)
1 - 3/16 in. Square Basswood Stick (Part W8)
☐Small Hardware Bag (2 x 3 in.)
1 - 4-40 Blind Nut
1 - 4-40 x 3/8 in. Pan Head Machine Screw
2 - Du-Bro RC #4 Flat Washers [DUB323]
1 - Du-Bro RC 4-40 Hex Nut [DUB561]
1 - Du-Bro RC Micro Razor Control Horn [DUB936]
1 - Du-Bro RC Micro 2 EZ-Link [DUB920]
1 - Du-Bro RC Mini E/Z Connector [DUB845]
1 - Du-Bro RC Steel Landing Gear Strap [DUB158]
1 - .024 in. x 4 ft. Stainless Steel Lead-out Wire
2 - Rubber Wheel Retainers
8 - #2 1/4 in. Screws (Motor & Landing Gear Mounts)
6 - Mini Rubber Bands (Landing Gear Retention)
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 3 of 29
Required Building Supplies and Tools
☐2 in. Dia. Wheels [DUB200SL]
☐1/2 oz. Medium CA Glue
☐1/2 oz. Thick CA Glue
☐1/2 oz. Thin CA Glue
☐CA glue accelerator (kicker)
☐Balsa filler
☐Hobby Knife with ample supply of #11 blades
☐Small Phillips Screwdriver
☐Small Hammer
☐Sanding block with 400 and 600 grit paper
☐Heat Gun and Covering Iron
☐Small Needle Nose Pliers
☐Small Round Nose Jewelers Pliers
☐Small Flat File.
☐X-ACTO Pin Vise & Drill Set [XAC7155]
☐ZONA 4 in 1 Saw Set [ZON35251]
☐Scissors
☐Wire Cutters
☐Z-71 Thread Locker [PAAPT71]
☐3/4 in. x 4 in. length sticky back velcro
☐3/4 in. wide clear tape
☐1 Roll AeroLITE
☐2 - Shiny, New, Quarters (U.S. 25 Cent Coins)
Suggested Building Supplies
☐CA glue de-bonder
☐Long sanding bar
☐Razor Plane
☐Low Tack Painters Masking Tape
☐Design Master Aerosol Lacquer Paint
☐Deft Clear Spray Lacquer

Project Checklist Continued
Suitable Electronics & Equipment (Available at StevensAero.com)
SA-Sport Power System:
This power system is available from Stevens AeroModel (www.stevensaero.com) and combines
performance and affordability.
☐1 - SA Sport Park 400 Brushless Outrunner Motor [SUPA2212-6]
☐1 - SA Sport 30A Brushless ESC [SUP30AESC]
☐1 - Control Line Motor Timer
☐1 - Hyperion CX G3 1100 mAh 7.4V LiPo Power Pack [HP-LG325-1100-2S]
☐1 - Pair Deans Battery Connectors [WSD1300]
☐1 - GWS 7x3.5*3 E 3-Blade Propellor [GW/EP7035*3] or GWS 8x4 HD 2-Blade Propeller
☐1 - SIG 1/2A Control Handle with Dacron line and connectors [SIGSH544]
☐1 - SIG 0.012 Braided Stainless Steel Lines 52’ Pair [SIGSH454]
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 4 of 29

Laser Cut Parts Inventory
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 5 of 29

Laser Cut Parts Inventory
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 6 of 29

General Assembly Instructions
Thank you, for purchasing this Stevens AeroModel RingRat™250. A design inspired by the joy of flying.
This model has been developed and manufactured using state of the art CAD/CAM systems and features
a unique interlocking construction process that, when compared to traditional methods found in other
model aircraft kits, save countless hours of measuring, cutting, sanding, and fitting. We are certain that
you’ll find our kit to offer a truly exceptional build experience. As this kit is recommended for the novice
model builder and “pilot”; we invite absolute beginners to correspond with us, or to seek the help of
another seasoned builder. At any time should one run across a term or technique that is foreign please
don’t hesitate to contact our staff with your questions.
READ THIS
Please READ and RE-READ these instructions along with any other included documentation prior to
starting your build and or contacting our staff for builder support.
Pre-sanding
Do not skip this step. Prior to removing any parts from the laser cut sheet wood use a sanding block
loaded with 250-400 grit paper and lightly sand the back side of each sheet of wood. This step removes
any residue produced as a result of the laser cutting process and, as we have found that most stock wood
sizes run several thousandths of an inch over sized, slightly reduces the thickness of each sheet.
Leave your pre-sanded parts in the sheet until required in the assembly process.
Protecting your worktable
Use the poly tube that this kit was shipped in as a non-stick barrier between your worktable and the
product assembly. Promptly clean up any epoxy spills with rubbing alcohol and a disposable towel.
Bonding the assembly
As this product tabs, notches, and otherwise interlocks like a 3D puzzle we suggest that when fitting parts
you dry fit (use no glue) the parts together first. It’s advised to work 1-2 steps ahead in the instructions
using this dry-fit technique which allows ample opportunity to inspect the fit and location of assembled
components and realizes a benefit as each successive part contributes to pulling the entire assembly
square. Once you arrive at the end of a major assembly step(s) square your work on top of a flat building
table and revisit the dry fit joints with glue. Using the dry-fit process you’ll be able to recover from a minor
build mistake and will ultimately end up with a more square and true assembly.
Unless otherwise noted in the instructions, always use medium CA glue for bonding parts.
Never force the fit!
Remember this is a precision cut kit. Our machines cut to within 1 thousandth of an inch in accuracy,
Yet the wood stock supplied by the mill may vary in thickness by up to 20 thousandths. This variance in
the wood stock can cause some tabs/notches to fit very tight. Hey, dad always said it was easier to take
away material than add it back. With this in mind, should you find a joint or two to fit rather snug consider
lightly sanding a tight fitting tab rather than crushing and forcing your parts together. You’ll break fewer
parts in assembly and will end up with a more square and true assembly.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 7 of 29

Wing Construction
☐Locate the 4/40 blind nut within the hole in
W6L. Ensure that etching on W6 faces up.
☐With a hammer, seat blind nut firmly in W6.
Secure with medium CA at edge of nut flange.
☐Fit and bond trailing edge parts W3a and
W3b.
☐Dry fit R1 to trailing edge. DO NOT BOND
AT THIS TIME.
☐Fit gussets W4 to trailing edge and R1. Align
and bond.
☐With etching facing up, slide W6 through slot
in R1. Ensure that the end marked “LEFT”
extends through to the left side of R1.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 8 of 29

Wing Construction Cont.
☐Note that there is a relief in the top of the slot
to allow the head of the blind nut to pass
through the rib.
☐Fit one rib R2 to trailing edge and left side of
W6. Do not bond.
☐Fit the other rib R2 in the same manner.
Square structure on a flat surface and bond
all joints with medium CA, building up a fillet
along all joints between ribs and W6.
☐Fit and tack glue remaining ribs R3 and R4.
☐Fit upper front spar part W1a to notches in
ribs R1-R4. Do not bond.
☐In the same manner, fit lower front spar part
W1a to notches in ribs R1-R4.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 9 of 29

Wing Construction Cont.
☐Fit W1b 1/32 in. ply spar doubler to underside
of wing assembly within notches spanning
ribs R1 - R2 Left/Right and immediately
behind W1a forward spar (Illustration show
wing assembly inverted). Note: When
properly installed within pre-cut notches W1b
will extend 1/16 in. proud of W1a spar as
illustrated.
☐Insert rear spars W5 through all ribs as shown
in photo below. Center W5 to wing assembly
then tack glue W5 to retain parts within wing
only where W5 passes through R1.
☐Mark center of 3/8 in. square balsa leading
edge stock. Align mark with center of wing at
R1, then bond leading edge stock within
notch at leading edge of all ribs.
☐Build left wing tip. Fit and bond TL1a and
TL1b to form TL1 base of left tip.
Align and bond TL2a, TL2b, and TL2c atop
TL1 with thick CA as illustrated. Note: Use
alignment etch marks and inside edge of TL1
to assist in positioning TL2a/b/c parts.
Fit and bond TL3a and TL3b together to
create TL3. Using thick CA glue, align and
bond TL3 on top of TL1/ TL2 assembly
matching outside edges of parts and
enclosing slots for the line lead-out tubes.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 10 of 29

Wing Construction Cont.
☐☐ Dry fit left wing tip assembly to left side of
wing at trailing edge.
☐☐ Carefully nest leading edge stock within
slot at front of wing tip.
☐☐ With wing tip fit flush to rib R4, leading
edge, and trailing edge, bond with
medium CA.
☐Build right wing tip. Assemble and bond parts
TR1a and TR1b to form TR1. Repeat
process to create TR2 from TR2a/b and TR3
from TR3a/b.
Align and bond TR2 atop TR1 and TR3 atop
TR2 using thick CA.
Now, glue two (2) quarters in slot in right wing
tip for tip weight (about 11.5g of weight).
☐Repeat prior ☐☐steps to bond right wing tip
to right side of wing assembly.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 11 of 29

Wing Construction Cont.
☐Trim off excess leading edge stock with a
razor saw.
☐Fit and bond W9a and W9b to form W9 cross
grain rib doubler.
☐Bond, with thick CA, rib doubler W9 to
outside of right and left ribs R2, adjacent to
battery tray.
☐Install spar webs SW1 to back side of W5
rear spars aligning top edge of web with edge
of spars and sides of web between ribs R1
and R2. Orient grain as shown by arrows on
photo. Tack glue to hold web in position.
☐Align remaining webs SW2 and SW3, to top
edge of W5 rear spar and in between
remaining ribs. Again, orient parts with grain
as shown by arrows on photo. Tack glue to
retain parts within wing assembly.
☐Hold wing assembly flat against work surface
and thoroughly bond all joints where webs
meet ribs and W5 rear spars. Bond all dry fit
parts installed to this point.
☐☐ Fit and bond parts W2a and W2b
together to form W2 leading edge
sheeting. Starting with top of wing, align
arrow in center of sheet with center rib
R1, pointing towards leading edge stock.
Bond sheet to leading edge stock only.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 12 of 29

Wing Construction Cont.
☐☐ Starting in the center of the wing,
carefully bend down the sheeting and
bond to upper spar W1. Work from the
center out, one rib bay at a time.
☐☐ Bend end of W2 down to sit flush with
wing tip and bond. Note: W2 should stop
short of wing tip profile as illustrated.
☐Repeat steps marked with “ ☐☐” applying
instruction to complete bottom sheeting.
☐Center W11 over rib R1 and bond to front
spar only.
☐Press W11 flat against trailing edge and bond
with CA, then bond W11 to R1.
☐Carefully sand W11 to a smooth taper into the
trailing edge. Tip: apply making tape to areas
you wish to protect from the sanding process.
☐Invert wing and remove stand off tabs. Note:
Two tabs on R1!
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 13 of 29

Wing Construction Cont.
☐Center W10 over rib R1 and bond to W1b and
bottom of R1.
☐Bond part W8 (3/16 in. square laser cut
basswood stick), to rear spar between ribs R2
and centered to rib R1
☐Align and bond W7 pushrod exit to recess in
bottom of rib R1.
☐Use one of the ply fuselage doubler parts to
reference the proper profile for the leading
edge.
☐With a razor plane and sanding block/bar
shape the leading edge until the proper airfoil
contour is reached.
☐Using 400 grit sand paper finish sand wing,
squaring trailing edge and rounding wing tips.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 14 of 29

Wing Construction Cont.
☐From the 3 in. length of 1/8 in. dia. nylon
tubing cut two 1-1/4 in. lengths. Install cut
tubing centered within each of the two
channels in the center of the left wing tip.
☐Optional. To move CG aft for better stunting,
battery may be mounted in the wing, install a
6 in. length of 1/2 in. wide velcro at this time.
Velcro strap is installed through slots in ply
support from top of wing.
☐Fasten strap to itself to keep it out of the way
while covering the wing. Strap may be easily
removed later, but can not be installed after
wing is covered.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 15 of 29

Bellcrank Installation
The following steps may be done after covering,
however, some may find it easier to install the
lead-out wires through the bare framework before
the covering is applied. Refer to Flight Control
Setup instructions for information on adjusting the
sensitivity of controls.
☐Prior to finishing leadouts, cover left wing tip
of model with your color choice of high quality,
light weight, model aircraft film such as
Stevens AeroModel’s AeroLITE or AeroFILM.
☐Install E/Z Connector [DUB845], 3/8 in.
machine screw, washers and nut as shown...
...one washer on each side of the control
bellcrank. Do not tighten nut - it will snug
down on final installation.
☐From provided 3/32 in. O.D. aluminum tubing
cut four 1/4 in. lengths to create crimp tubes
for lead-out wire. Tip: score tubing at cut
length with a sharp blade then snap off
length.
☐Install one crimp tube to provided 4 foot
length of wire, then thread wire through
outside hole in bellcrank as illustrated.
☐Loop wire back through aluminum crimp tube.
☐Make a second loop through the tube.
☐Now, tighten loop as illustrated (leaving no
more than 1 in. of excess length). Using
round nose or fine needle nose pliers place
two crimps in tube and secure with a drop of
medium CA at each end of crimp.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 16 of 29

Bellcrank Installation Cont.
☐Use wire cutters to trim excess wire length.
☐Feed wire though holes in ribs and lead out
tube in wing tip. Then feed wire back through
the other lead out tube and rib holes, and
connect to opposite hole in bellcrank using
technique described in previous steps. Place
a drop of CA on each crimp to secure.
☐Put a drop of thread locker on machine
screw and mount bellcrank on W6. Gently
snug down screw until bellcrank is free of
wobble but rotates smoothly.
☐Cut leadout wire at end of loop as shown.
Note: To prevent leadout wire from falling
back into wing, place two tabs of masking
tape around wires as illustrated.
☐Finish lead-outs by crimping loops in the
same manner as the bellcrank attachments,
leaving at least 2-3 inches of wire beyond
wing tip. Note: with bellcrank centered wire
leadouts should be of equal length.
☐With leadout wires properly installed, cover
the remainder of the wing using your color
choice of high quality, light weight, model
aircraft film such as Stevens AeroModel’s
AeroLITE or AeroFILM.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 17 of 29

Fuselage Construction
☐Fit and glue Cockpit to fuselage F1.
☐Fit 1/4 square hardwood Fuselage Stiffener to
Fuselage F1. Tip: For the strongest bond,
lightly sand bonding area along balsa part F1
to smooth and remove laser cutting residue.
☐Measure and cut to length, leaving 1/8” to
1/4” extra to be trimmed off later.
☐Bond Stiffener to F1 with thick CA on top of
flat work surface. Lightly sand fuselage after
bonding.
☐If desired, Ply parts may be covered or
painted at this time.
☐Dry fit two motor mount parts M1 to fuselage
doubler F2 (left). Ensure that the etching on
F2 (left) faces up. Tabs in M1 will extend
proud of backside of F2 (left) by 1/4 in.
☐Dry fit motor mount M2a to M1’s and F2 (left).
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 18 of 29

Fuselage Construction Cont.
☐Test fit M2b to face of M2a then bond motor
mount assembly with medium CA glue.
☐Dry fit motor mount assembly to fuselage,
then, covering back side of motor mount
assembly at F2 (left) with thick CA, bond/
laminate assembly to fuselage. Ensure that
1/8 in. dowel hole and wing saddles in
parts match.
Note: Rear tabs on M1’s will protrude slightly,
allowing doubler F2 (right) to key in place.
☐Fit and laminate/bond doubler F2 (right) to F1
with thick CA. Ensure that 1/8 in. dowel
hole and wing saddles in parts match.
☐Revisit motor mount joints on both sides of
fuselage applying a fillet of medium CA.
☐Trim excess hardwood and sand to match
shape of fuselage at nose.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 19 of 29

Fuselage Construction Cont.
☐Cut notch through hardwood doubler with
razor saw to match pre-cut notches in F2 (left/
right) parts. Creating a slot to receive landing
gear wire.
Further clean up and open landing gear notch
with a small file, just enough to allow landing
gear to fit snugly.
☐Dry fit right and left horizontal stabilizer parts
H2 to H1 and bond.
☐Lightly sand fuselage components, including
horizontal and vertical stabilizer, to a smooth
finish with 400 grit paper in preparation for
sealing or covering.
☐Seal fuselage components with clear lacquer,
dope, or cover with your color choice of high
quality, light weight, model aircraft film such
as Stevens AeroModel’s AeroLITE or
AeroFILM.
☐Sand a 45 degree bevel to the leading edge
of elevator in preparation for tape hinge
method (see diagram below).
☐Assemble Vertical fin (V) and Rudder (R).
Lightly sand a bevel trailing edge of vertical
fin to produce 3/8 in. right offset to rudder
when bonded to vertical fin (Refer to picture
below). Match rudder vertically along fin
using “SA” logo etching as a positioning guide
and bond using medium CA glue.
RingRat 250 © 2010 Stevens AeroModel all rights reserved. Page 20 of 29