Instructions

EA Australia - Maxi Cub

As noted in the post on Thingiverse, these instructions are to be used as a guide only.

While every endeavour has been taken to ensure they represent the model as constructed,

variations in build sequence and method are easily conceivable. All persons using all or part of this

information do so at their own risk.

Please note to follow appropriate health and safety guidelines when cutting and drilling foam and

carbon fibre parts and when sanding ABS plastic parts.

There are two derivatives of the design with a PS foam nose and tail section, and the second using

printed parts. The ABS parts add over 200g to the AUW, but do not affect the motor or propeller

selection.

The donor fuselage for the foam sections is from a HobbyZone mini super cub, which costs around

$15 for a bare fuselage.

Step Notes

Print Settings (Feed rate / travel rate /

layer ht / shells / infill)

Parts - 2x wing joiners – 5 degree cant. 4 x wing spars each side plus the left and right wing ends. 6mm square hollow carbon rod, glued with epoxy 3mm carbon tube, fitted and drilled to suit Overall length 840 mm

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Fit balsa nose strip, cover edges with 1mm balsa sheet, sand and fit.. super glue works well for this application, but you do use a bit of it.

Cover and seal with adhesive heat shrink film.

Print and assemble fuselage sections, threading parts on from smallest to the largest. Spacing between sections going from the rear to the front are approximately 65, 65, 69, 95, 88mm. I tried to thread the sections on so that there was no apparent stress on the rods. Print and fit the tie down brackets at 131mm centres. Some drilling of the tie down bracket holes is required to suit the angle of the fuselage tubes. I have used 4mm solid CF rod, 4mm tube would easily work as well. Fit sections of 8mm square balsa between the fuselage sections and the tie down brackets to fill the gap between the wing mount and the CF rods. Sand to fit after printing the wing mount pieces.

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Print and mount the battery and electronics holder in place before securing fuselage sections. There is no external support required for this part if printed in the orientation as saved. There will be some small tidy up required as the inner edge of the upper surface will sag. This is not material to the performance of the part and cuts down print time significantly.

60 / 80 / .2 / 2 - 3 / 30%.

Cut the last 85mm from the donor foam fuselage and fit to the end fuselage section. Be sure to leave an overhang of 4 – 5mm from the edge of the tube / rod. Cutout sections to accommodate the fuselage rod, glue in place with epoxy, drill and sleeve for fitting of the servo control rods.

Alternate – print the ABS tail section, drill the guide holes for the control rods, sleeve the openings with plastic tube and glue in place. Notes: This will increase aircraft weight by over 50 grams when compared to PS foam. Be sure to fit this part with an angle of incidence between 2 – 4 degrees to the main wing. An easy way to do this is to locate the fuselage on a level surface, using your iPhone measure the angles of incline for both the tail plane and the wing mounts.

60 / 80 / .2 / 3 / 20%

Print and fit the tail wheel bracket. I have used the same 15 mm sheet metal fasteners with washers. The wheel and axel are from the front landing gear of the HBZ mini super cub. Fit the axel and retain with a touch of super glue. The wheel is nominally 32mm dia.

40 /40 /.2 / 4 / 20%.. is a fine print.. set speeds to very low.

Print tail fin bracket... shown here printed in red and fitted to the tail section, with tail fin inserted.

60 / 80 / .2 / 3 / 20%, with raft and external support enabled.

Cut and fit the nose section to the fuselage section as shown. The foam nose section is nominally 69mm long. Fill the gap as shown with a piece of the donor fuselage, glue in place with foam safe glue or epoxy. Sand with a Dremel or similar.. small dia sanding bit makes an easy job of it.

ALTERNATE – print the ABS nose section, drill and trim to fit or mould a balsa block, cover with tissue and dope then drill and mount to suit. This design needs to be trimmed (ie sanded), on the engine mount face to get a 3 – 5 degree downward and left cant on the motor.

80 / 100 / .2 / 3 / 30%. Increase HBP temp from 115C to 117 if lifting occurs.. the part will start to burn if you set to 120C.

Print the landing gear and landing gear retainer block. Drill out the axel holes as required. Increase in the shells from 2 to 4 required for these parts. Fix with 15mm hex head screws after coating the foam nose with carbon or fibreglass tissue.

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Mark and cut out the space for the landing gear retainer block and epoxy in place.

Secure with 4 x 15 mm metal screws after drilling pilot holes. Cut and fit a single piece of CF rod to your desired wheels and secure with axel collars.

Print the engine block mount. Before fixing with 15mm hex head screws with washers, fill the void behind the engine mount with epoxy or hot gun glue to avoid flex or cracking from the increased weight and stresses in flight.

60 / 80 / .2 / 4 / 80%

Drill the tie down brackets out to suit 5mm CF rod. Thread and glue in place. Print the tie rod ends, drill out to fit and spot glue with super glue.

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Print the wing mount pieces, drill and glue CF rod in the forward hole and insert tube for the aft brace. Overall width, 61 mm.

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Print the stabiliser sections, plate and join top and bottom faces with 10mm x 1mm CF plate. Glue with epoxy in this case, as it has a higher elasticity when dry than super glue. Sand the edges of the CF plate as well as the leading and trailing edges of the stabiliser. Cover with adhesive plastic film, cellophane and spray glue or heat shrink adhesive film. Create a hinge with plastic RC hinges or hinge tape. I have also loaded a Version 3 design of the stabiliser, control surface and matching rudder (pics below), with

80 / 100 / .2 / 3 - 4 / 20%

slightly larger surface area and a more aerodynamic profile. Note: Thin long sections like this don’t retain their shape well when heated, as such an alternate build method is also included below.

FURTHER ALTERNATE.. Print either the left or right stabiliser sections and use as a template for a 3mm foam board parts... this will save approximately half the weight to using the ABS parts (+30 grams), reinforce with diagonal 2mm CF rods onto the ASB tail fin. Cover with adhesive plastic film as desired.

Version 3 stabiliser and rudder set, print settings unchanged. For use with both the control horns feeding from underneath the stabiliser. A further option is to use the tail fin, rudder and stabiliser sections which come with a Hobby Zone mini super cub.. these parts can be ordered as a set. Is light weight, light duty and should be diagonally braced with 2mm CF rod. Assemble the tail fin, rudder and stabilisers, add control horns, thread 1.2 – 1.5mm steel rod through the tail section and adjust servos for zero loading at the neutral position.

80 / 100 / .2 / 3 - 4 / 20%

I located the ESC on top of the extension piece on the battery holder and the

Mount the motor and electronics using a combination of adhesive Velcro and hot melt glue. Test for

receiver underneath to give clearance for the pushrods from the wiring.

correct operation and freedom of movement. Secure the battery by threading a Velcro strap through the slots provided in the housing.

Print and glue the battery cover and mounting blocks in place after trimming / drilling as required. Use the locking catch from the donor fuselage battery cover to secure this battery door. Drill a 1.5mm hole in the fuselage section adjacent the unhinged end of the battery cover and secure screw with super glue.

For the mounting blocks - 40 /40 /.2 / 4 / 20%.. is a fine print.. set speeds to very low. Increase feed rate to 60 / 60 for the battery cover.

Next steps, (if the gear I ordered nearly a month ago ever arrives) is to coat the nose cone with CF tissue and seal with polyurethane. Same for the tail section and the wing tie downs to secure them as well as possible to the CF fuselage rod. Next, cover the fuselage with adhesive heat shrink film.

Second last step is the fitting of the wing mount bracket and secure with a cable tie over the aft cross brace onto the fuselage section. Mount the wing onto this matching profile and secure with rubber bands, placed diagonally and longitudinally from each corner.

Lastly, weight and balance. The COG of the wing is in line with the 6mm square carbon rod... balance the wing tips on your finger tips (or two dowel sections taped to food cans) at this location on each side and test. The nose should be pointing slightly downwards when finished... add lead weights as required based on the configuration you have built.

Motor selection

New to all of this, motor selection seems to be a bit of a black art, there are apparently several

correct answers to any question.

Based on the style of aircraft, the AUW and the desired flying time I have, (with a little help along the

way.. thank you Garry from the HK discussion blog), chosen the following motor as a good balance

for this model.

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=24529

D2830-11 1000kv Brushless Motor (AUS Warehouse)

D2830-11 1000kv Brushless Motor

Kv (rpm/v) 1000

Weight (g) 52

Max Current (A) 21

Resistance (mh) 0

Max Voltage (V) 15

Power(W) 210

Shaft A (mm) 3.17

Length B (mm) 30

Diameter C (mm) 28

Can Length D (mm) 14

Total Length E (mm) 45

The rule of thumb for a trainer is that you need 50W – 75W per pound. A model with an AUW of

530g it would require around 100W of power.

As per the prop selection options below, this motor gives you sufficient power to get going at low

speeds and has good up side to increase the prop size and speed as skill levels increase. Unlike the

high kV motors (2000 plus), the throttle response will be more gradual and controllable.

8 x 5 Current Draw 9amps, Power 100w.

9 x 5 Current Draw 12.5amps, Power 138w.

10 x 4 Current Draw 14amps, Power 155w.

For a weight of 520 to 740 grams (with ABS nose and tail sections, instead of foam), I am using a 9 x

5 inch electric slow fly prop, (720 grams = 1.6 pounds x 75w per pound = 115w required)

Servo – any 5g micro servo will suit this application – 2 required.

Update to the wing design to follow with a further 2 servos required to operate the ailerons.

Battery – For this application the following battery works well.

Spec.

Minimum Capacity: 800mAh

Configuration: 3S1P / 11.1v / 3Cell

Constant Discharge: 20C

Peak Discharge (10sec): 30C

Pack Weight: 75g

Pack Size: 57 x 29 x 21mm

Charge Plug: JST-XH

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16735

Additional guides....

These are pieces on information I have gathered over the past 12 months which may assist if like me

you are new to most of this.

Applying Heat Shrink.

Film is convenient to use, and adds more strength to the structure than tissue or silkspan.

This covering is commonly used over balsa wood, although it can also be used over

fiberglass, and even foam (low temperature film only). There is some skill to applying heat

shrink plastic well, and this photo tutorial will help you develop that skill.

First, you will need a part that has been sanded smooth. I prefer 800 grit sandpaper as the

final finish. If the final finish is not smooth it will show after covering, do not think that you

can hide it! A good sanding job is a critical piece of getting a good covering job.

Second, make sure to remove that sanding dust. The dust particles get trapped under the

covering and result in imperfections and bubbles. You will also need to remove dust from

your work area, or perform the covering in a cleaner room (e.g. unused guest room in your

house).

A tack cloth from the hardware store is essential for cleaning the balsa airplane parts. Wipe

the whole airplane down with the cloth; get into all the crevices that you can. Also use a

vacuum cleaner with a brush attachment to remove dust. The wipe with the tack cloth again.

You will also need to wipe down your work surface and tools. It's also a good idea to wash

your hands before after cleaning the model and before starting to cover. You get the point:

the cleaner, the better.

OK, now you're ready to cover! You'll need the covering material, scissors, a sharp blade, a

covering iron, heat sock, and a metal ruler to cut trim pieces. Our demo piece is an outer

wing panel. Place the panel on the table, and measure and cut a piece of covering at least 2

inches bigger than the part.

For wingtips, make the excess about 4 inches, as you'll need to hold on here during the

wingtip sealing. Don't forget to remove the clear plastic protective backing from the film!

The covering will first be tacked down at a few places around the frame, then it will be

sealed at all the edges, then shrunk tight. The recommended sequence for tacking is shown

below on the left.

Click on any of these thumbnails to enlarge.

For a wing or other flight surface, you'll generally cover in two pieces, bottom first. For a

fuselage, four pieces work well. Look closely at the numbered sequence of covering pieces,

and at the overlaps.

These overlaps should be around 1/8 inch. This sequence will help ensure that seams are less

visible. When covering the fuse, if you need to use multiple pieces along the length, start at

the back of the fuse and work your way forward, so that the seams face to the back.

A word on the covering iron temperature. These films have an adhesive that is activated at

one temperature. A higher temperature is required to shrink the film after tacking it in place.

The covering iron has a dial with generic settings. For the old Hobbico iron and Ultracote

covering in these photos, 1.25 works for tacking and 2 works for shrinking.

Of course, this will vary from iron to iron and covering to covering. Read any directions that

came with your roll of film to see what temperature they recommend. You can purchase a

covering iron thermometer, but you could just estimate the correct temperature this way: cut a

small piece of the covering, place it adhesive side upwards, on the face of the upturned

covering iron.

If it begins to change color slightly, that's a good temperature to start tacking. It the film

wrinkles a lot, try that setting of the iron for shrinking. If the films melts or vaporizes, that's

way too hot!

With your iron at the lower temperature, begin tacking the film. Use the tip of the iron to

tack a spot about 1/4 to 1/2 inch diameter at one corner of the frame (labeled "1" above).

Let the corner cool for a couple of seconds, then gently pull the covering towards the

opposing corner ("2"). This pulling is essential to make sure that the covering ends up

moderately tight, minimizing the shrinking that is need later. Don't pull so hard that you

break the airframe! After tacking at corner "2", proceed to pull-and-tack around the airframe,

till all eight (8) labeled spots are tacked:

Note that if you don't like how a certain spot is tacked down, you can reheat that spot and

gently pull the covering up, then reposition and stick it back down again with more heat.

There are lots of wrinkles at this point, but that's to be expected. Now seal all the edges

except the wingtip. The best way to do this is tack at the midpoints between all the

previously tacked 8 points, e.g. halfway between 1 and 5.

Then seal the entire length between 1 and 5. Repeat the rest of the way around the frame.

Don't seal over the edge of the frame yet, just on the surface.

Now you're ready to tackle the special case of the wingtip. It's special because it has

compound curves, i.e. curves in more than one direction at once.

To make the film go around these curves, the film has to become very stretchy, so we must

apply more heat.

Turn up the covering iron temperature to the "shrinking" setting. Pull the covering tight

over the tip, and begin to iron it in place. Work slowly from the center to the front, then from

the center to the back.

Move along just a few millimeters at a time. Stick the covering just over halfway up towards

the topside of the wing.

The middle photo below shows the covering pulled tight where the tip meets the leading

edge, note the wrinkles. The next photo shows the same are after the covering is ironed is

place, note the lack of wrinkles.

It's the iron's heat that allows this to happen. If you find yourself exerting a lot of force on the

covering (and risking a break in the airplane structure), then turn up the heat!

Here is the tip after the covering is completed ironed around it. We'll trim the excess

covering with an X-acto or single-edge razor blade:

Now turn the iron back down to the lower tacking temperature, and let it cool for the next

steps.

We'll start to trim the excess film.

First use a blade to remove right-angled pieces from the corners of the frame. Then start to

trim along the edge, leaving enough to overlap as in the "wing section" diagram above. Rest

the cutting hand on the edge itself, use that as a guide as you cut.

If you work slowly you can get a fairly straight line (it does not need to be perfect, as it will

be overlapped later). For the trailing and leading edges, overlap a bit more more than half the

thickness of the edge. See the photos on the right below:

Now seal the overlaps to the wood. Go over the entire structure, making sure that it is

completely and securely sealed: leading edge, trailing edge, wingtip, and inboard edge.

Now cover the topside of the wing, using the same procedure. Again trim the overlaps using

the frame as guide; this time, put the blade itself on the frame, using the frame as your ruler

to get a straight cut.

Now that both bottom and top are covered and all the edges sealed, it's time to begin

shrinking the covering. Put the heat sock onto the (cool) covering iron.

You will be running the iron over the entire surface of the covering, and the surface will have

small scratches if not protected. Turn the iron on, and let it heat up to the "shrinking"

temperature.

Now start gliding the iron over the bottom surface. Do not press down onto the wing! The

iron should be barely touching the surface. Start the iron at one end of the structure and

move it in slow circles. As a guideline, move in 2 to 6 in circles, about one circle every

couple of seconds.

The speed that works will depend on the iron temp and the covering brand. Do not leave the

iron over one spot, as you can burn a hole in the covering! You'll see the covering change

color slightly, wrinkles will form and disappear as you move the iron. As one area begins to

look tight, drift slowly downwards to the adjacent area.

Keep moving down the entire wing until the whole bottom covering looks tight. You will

probably need to go back to a couple small areas and re-shrink. When the bottom is done,

flip the wing over and do the top side.

And now we're DONE! Also check out our 'how-to' on making multi-color trim schemes

from heat shrink covering.

Motor selection guide

motor selection.pdf

With thanks and all credits to the original authors of these documents.