Mountain Models Boomer EX 2 User manual

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Boomer EX 2
Builder’s Manual
Thank you for purchasing the Boomer EX2. The Boomer was designed with love and dedication by Mike
Baker to be an easily assembled and fun entry level discus launch glider (DLG).
Specifications: Mountain Models
Wingspan: 33.5” 465 D Street
Wing Area: 318.25 sq. in. P.O. Box 762
Weight with 2/3 370 NiMH batteries: 5.5-6.5 ounces Penrose, CO 81240
www.mountainmodels.com
Phone: [phone]
Required Equipment
! 2 Channel radio with elevon mixing
! Micro receiver
! 2 Micro servos
! 370mAH 2/3 AAA 4cell NiMH or 2 CR2 Lithium Camera Batteries
Parts List
2 ea – Foam wing cores
2 ea – 1/8” Balsa elevons
2 ea – Ply control horns
2 ea – Ply launch pads
1 ea – Carbon Fiber tail boom
1 ea – Ply tail boom anchor
2 ea – Wire L-bend pushrod ends
2 ea – Wire Z-bend pushrods
1 ea – Heat shrink tubing
2 ea – Carbon fiber tape
2 ea – Plastic pushrod tubing
2 ea – Tails
1 ea – Packing tape
Items required to complete your Boomer.
Spray adhesive (Most spray adhesives can melt the foam if used in excess so it’s wise to experiment on
scrap foam)
220-grit sandpaper
5-minute epoxy
Thin CA
X-acto knife

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Assembling the wing
1. The first step is to shape the wing tips and clean up any residue from the hot wire cutting. Be
careful with the difference between EPP and EPS foam as they are of different consistencies and
respond to sandpaper differently. Using the wingtip guide at the end of these instructions, trace
the wingtip curve onto the wing tips and cut out the shape with a sharp xacto knife. This is a good
time to put a new blade in your knife.
2. Now round the wing tips equally. Try to maintain the general airfoil shape. Go very slowly when
you transition from the EPP to the EPS foam.
3. Install the throwing pads by holding the wing you will be throwing from, carefully, thumb
underneath, index finger up front at the wings' leading edge, middle and ring finger on top. If you
are right handed then it would be your left wing, left handed then the right wing. Position the pads
under your fingertips with the points facing towards the root and note the positions. Epoxy the
pads there.

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Color and tape
1. If you wish, you can now paint your plane with acrylic or latex paint or good old magic markers.
It’s wise to test whatever method you choose to use on scrap foam. Another point worth
mentioning is that the Boomer is rather happy inverted so it is wise to be able to differientiate the
top of the wing from the bottom so you can orient from the ground, so ensure that you make a high
contrast difference top to bottom.
2. If you want to make your Boomer really light, you can tape only the leading and trailing edge of
your Boomer. This is hard to do, as you will need to mask off the areas you won’t tape to keep the
spray adhesive off the foam. It also makes your Boomer easier to damage. The tape adds a lot of
strength.
3. Take the spray adhesive that you tested on scrap foam as many adhesives can melt foam if used
in excess and carefully, lightly spray the top of one wing section. Note that adhesive such as
3M77 Spray Adhesive will melt the foam if you spray too close, but if you lightly spray from 18”
away, it will work well. Always test first to be sure and follow the directions on the can.
4. Apply the packing tape the length of the trailing edge (TE) leaving ½” over the TE. See picture on
next page Continue applying packing tape towards the front of the wing leaving 1/8th to1/4”
overlap to include the leading edge (LE) of the wing. Wrap the excess tape around the edges. To
get the tape to wrap around the curves, you will need to slit the tape at the curves.
5. Now do the same to the bottom of the wing and tape the other wing in the same manner.

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Elevons
1. Align the 1/8th” balsa elevons to the TE (Trailing Edge) of the wing’s outside edge and ensure that
they are 3/8” from the wing center. Adjust as needed so that the tail section will fit.
2. Sand the bottom of the elevon from the bottom of the LE (Leading Edge) to the top of the TE to a
point. It is normal to end up with the elevon curved as shown in the diagram. This is fine. Sand
the front of the LE of the elevons to a 30-degree angle to the front top. This bevel is to allow the
elevon to go down and not interfere with the wing.
Leading Edge Trailing Edge
3. Glue the control horns to the inside edge of the elevons with CA or epoxy. Make sure you glue
one control horn to the left side of one elevon, and the other control horn to the right side of the
other elevon to make a right and left elevon.
4. Align the elevons to the wing leaving a 1/32nd” gap and set with scotch tape or something similar
and then tape the full length with packing tape. Flip the elevon over to the top of the wing and
place 2” lengths of packing tape at the ends and the middle of the elevons to reinforce the hinge.
Ensure that the elevons move freely. You may have to flex them a bit to break them in.

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Installing radio gear
Note: You have the option of installing your gear from the top of the wing or inside. The inside
mounted gear is cleaner but the top mounted is easier.
1. Temporarily tape the wings together.
2. Position your battery and receiver on top of the wing opposite each other as far forward as you can
comfortably install them. Place the servos behind the batteries and receiver opposite each other
and check your center of gravity (CG). The CG should be 4.75” to 5” behind the very front of the
wing. Chances are that you’re very close. If you are tail heavy, leave enough room in the nose for
a little lead. Note the position of your radio gear on the foam.
3. Take your time and cut out the foam just enough to install your gear. If you choose to mount your
gear inside the wing then you will mount the servos so that the control horns are positioned down.
Remember that the servo horns will need room to move.
4. Use a straight edge to make a straight line from the servo control horn to the elevon control horn.
Cut a slice into the foam to install each pushrod.
5. If you use a long antenna cut a shallow slice to imbed it into the length of the wing opposite the
throwing pad side.
6. You will need some sort of switch to turn the radio on and off. We use switchjacks.

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Installing the pushrods
Note: Ensure that the servos are centered. Plug the servos into the receiver, turn on the
transmitter insuring that the trims are centered and plug the battery into the receiver. Adjust
the servo control horns so that they are positioned 90 degrees to the servo.
1. Take the music wire with the Z bend and install it into the servo control horn.
2. Slide the plastic guide tube over the wire. Ensure that the guide tubes don’t interfere with the
movement of the servo control horn.
3. Position the guide tube and cut to length so that it is 2” in front of the elevon control horn. Do the
same in the opposite wing.
4. Slide the 1” heat shrink tubing over the wire.
5. Install the L bend wire into the elevon control horn.
6. This is important! With the servo centered, ensure that the wing is flat and use a piece of 1/16th”
balsa to raise the back of the elevon. You should hold the wing down securely while taking the
next step.
7. Position the pushrod wire on the opposite side of the elevon control horn from the L bend wire and
slide the heat shrink over both wires to capture them. Shrink the heat shrink tubing with a
soldering iron or, if you’re brave, a lighter.
8. Carefully place a drop or two of thin CA down the heat shrink tubing to secure the wires. Don’t let
the CA touch the foam or get in the yellow tubing!
Installing the tail
1. Sand the tail so that the front (with the slot) is rounded and the rear comes to a point.
2. Cut the 2.25” carbon fiber into four strips of equal width. Do the same for the 3.25” carbon. Two
of each size will be used on the tail, the other pieces are for the spare tail.
3. Glue a 2.25” strip behind and in line with the slot, using thin CA and wax paper to hold the carbon
down. Glue the other 2.25” strip to the other side. See photo on the next page.
4. Glue a 3.25” carbon fiber strip across the bottom of the tail, about ½” from the bottom. Let the
strip overhang the front and back of the tail. When the glue is dry, trim the strip to the edge of the
tail with an xacto then glue another strip to the other side of the rudder. Ensure that the second
strip lines up with the first.

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5. Slide the slotted end of the carbon fiber rod into the slot in the tail and adhere with epoxy. Don’t
use too much, epoxy is heavy.
6. Lightly sand the bottom of the carbon rod in front of the tail.
7. Position the plywood mount to the bottom of the rod at a 90-degree angle to the tail and epoxy in
place.

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8. If you wish, you can add micro balloons to the epoxy to save weight.
9. Tape the wing halves together with packing tape down the middle both top and bottom.
10. Turn the wing upside down and place the tail over the bottom of the wing and note the position of
the rod.
11. Cut or sand a groove into the wing STRAIGHT down the middle of the wing to attach the tail.
12. Ensure that the tail is straight with the wing.
13. Tape the tail to the bottom of the wing with strapping tape or packing tape.

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Flying
1. Check the CG, it’s 4.75” to 5” behind the very front of the wing. Add weight to the nose as
needed. Check the lateral CG – wing tip to wing tip. If it’s unbalanced it may cost you. Add
weight to the lighter wing, I use a quarter slid into a slot I cut into the wingtip. Check that the
elevons are in the same 1/6th” up position. Insure that your elevons move in the correct direction
and are not reversed. Grab the throwing pads and throw it out and up at a 45-degree angle with a
half arc.
2. Remember to hold it gently. If your Boomer noses up on launch then give it a click or two of
down trim. If you nose it right to the ground then a click or two of up trim might be in order.
3. This is a hard plane to hurt so enjoy the process and relax. This is fun!

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Wingtip Guide