Category Archives: Model Airplane Building

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Tower Hobbies Ultimate Bipe GP/EP ARF – Build and Flight Review.

The Ultimate Bipe from Tower Hobbies is certain to turn heads with it’s bright red and yellow color scheme!

Early in the flight season this year I was certain I wanted to add a biplane to my ever growing fleet of radio controlled planes.  When I saw that Tower Hobbies was going to release an Ultimate Bipe in a 45″ wing span I was certainly interested.  Having had good experience with Tower Products in the past (Kaos 40) I was certain this would also be a quality product – and deliver a quality product they did!

I decided to purchase the kit after Tower Hobbies had this particular ARF on sale.  I decided to outfit the plane with their  recommended equipment:  Rimefire 55 Motor, 16×6 or 16×8 prop, Castle Creations ESC, and the Tactic TS25 Servos.


The ARF arrived packaged very well and every part was wrapped in the usual plastic bags secured with tape in the shipping container.  I removed each part one by one and inspected it by hand looking for any defects or broken pieces.  Everything looked perfect.  The covering was done very well and only a minor wrinkle here or there was found.


The Tower Hobbies Ultimate Bipe comes with an easy to follow and heavily illustrated instruction manual.  Starting with the wings, you have the option to use either two or four servos for the ailerons in the wings.  I opted to go the four servo route (for my particular setup I used an eight channel receiver) since my radio allows me to setup the necessary mix to operate this many servos each on their own channel.

If you are using four servos, the manual provides directions on where to cut the covering on the top wing to allow you to install the additional servos.  The kit also includes two extra servo mounting plates for this purpose.  The kit also came with enough hardwood servo mounting blocks for the extra servos.  I cut the blocks down slightly for a better fit and then one by one mounted them to their plates using thick CA.  I drew a reference line with a pencil to help ensure accurate positioning of the servos.  This is a tedious step so it is best not to rush this process!

Once the servos are mounted, the servo wires and any extensions you’ll need can be routed through the wing with the provided guide string already built into the wing from the factory.  (NOTE: In the photos it shows I used a servo extension, later I removed these extensions in favor of a direct solder connection… to help reduce any possible fail points within the wire.)

With the servos completed and installed in the wings, mount the bottom wing to fuselage. The bottom wing is used for alignment of the horizontal stabilizer.  Fitting the stabilizer requires centering it left to right and making sure it’s parallel to the bottom wing.  Follow the direction in the manual to align the stabilizer front to back. Only minor sanding should be required to get the alignment perfect.  Once that is in place I used 30 minute epoxy to secure it to the fuse. Don’t forget the elevator joiner wire should be put in place at this  time as well!


Next, the vertical stab is installed in the pre-cut slot provided in the fuselage. Use 30 minute epoxy and secure in place while it dries.

Another nice touch with this ARF kit, is that the ailerons come pre-glued to the wing and the hinge slots are already cut for the elevator and rudder!

 Once the horizontal and vertical stabilizers are in place, you can install the elevator and rudder control surfaces using the provide CA hinges. With the pre-cut hinge slots everything should fit together nicely!

At this point, the build really starts to progress quickly!  With all of the control surfaces glued in place you are now ready to install the motor and ESC.  In the back of the manual they provide a drilling template for the Rimfire 55 motor and instructions on where to mount the Castle Creations 75 amp ESC to the motor box.  For the ESC you’ll have to make a battery lead extension.  I added a few inches to the recommended length in the manual to make connecting the battery a little easier to handle.

Another nice touch with the Tower Hobbies Ultimate Bipe is the battery mounting plate included with the kit.  This battery plate bolts in place with a single 1/4-20 bolt and blind nut. This makes battery changes and getting the CG in the same place during battery changes much easier!  Tower certainly receives an A+ for that handy little feature!


Next, you can begin mounting the servos for the rudder and elevator.  Controls rods are provided with the kit.  You’ll have to locate the exit holes and make a small slit in the covering for the control rod exits.  Be sure to consult the manual for which side is for the elevator and which side is for the rudder since they are in slightly different locations. While mounting the rudder and elevator servos you will be working on the plane upside down.  (NOTE in the manual they include an addendum instructing you to install some filler wood strips because the servo slots are a little too wide.)

Wood filler strips and mounting plate for RX

Wood filler strips and mounting plate for RX

 With all the servos in place you can now install the servo control horns if you have not already done so.  There is a hard ply mounting location for the control horns in each aileron which I was pleasantly surprised to see! Harden the screw holes with thin CA.

With the plane nearly finished at this point I moved on to mounting the canopy.  One thing I didn’t like about the canopy was the noticeable gap at the front where it mounted to the removable hatch.  I created a paper template and used some of the extra covering included to seal the edge around the canopy.  See photos below for details.

Mounting the Cowl:
Tower included several hardwood mounting blocks for the cowl.  Align the cowl to provide enough clearance for the spinner back plate if using one.  I also like to visually align the cowl to make sure it is centered left and right and up and down while looking down the propeller shaft.  Once satisfied with the alignment, secure the cowl in place with blue painters tape and begin to drill holes for the mounting screws one by one.

That’s pretty much it!  This was one of the quickest ARF builds I’ve done and was easily accomplished in a few evenings!

 Just a few additional notes:
Plan on using a fairly large battery for this Ultimate Bipe as you will need the extra nose weight in order to achieve correct CG.  I’m getting seven minutes of flight time on a 4500 mah 6S pack with a lot of sport flying and several full throttle bursts!

I setup my control throws using the low rates in the manual for the maiden flight.  However, even the low rates on ailerons felt way to responsive.  I found my self cutting those back to around 1/4 to 3/8 of an inch of throw up and down.  I dialed in around 30% expo for the maiden flight as well.

One issues to note with the landing gear is that the landing gear studs do not appear to be long enough to allow the nylon lock nut to fully tighten.  I used blue thread lock to remedy that situation.

Nylon locking nut does not fully tighten.

Nylon locking nut does not fully tighten.

The Rimfire 55 motor provides plenty of thrust and vertical power using a Xoar 16×6 prop.  In the manual they recommend a 16×8 for ultimate (pun intended) performance.  I’ve pushed the plane pretty hard with the 16×6 prop and the motor hardly reaches above room temperature.  The Tower Hobbies Ultimate Bipe had plenty of air flow and is also aided by the spinner I’m using from Gator RC. NOTE: the motor mounting template appears to show the motor mounted off center – this is normal as it accounts for the amount of right thrust built into the firewall.

Finally, I decided to use the Castle Creations 10 amp BEC since I was powering six digital servos.


Flight Review
The main purpose of this article was to focus more on the build aspects of the plane but I do want to share a few notes about it’s flight characteristics.  The Tower Hobbies Ultimate Bipe will easily lift off the run way at a little above half throttle.  This particular plane can be flown nice and easy or full on 3D if you wish!  It will handle anything you can throw at it.  It seems to roll as if it’s on a string – staying precisely in it’s track and responding only to your inputs.

When setting up the CG location at home before your first flight be sure to not make it excessively nose heavy as you will end up having to dial in so much up elevator.  The Tower Hobbies Ultimate Bipe tends to like it CG location to be where the fuselage is level with the ground.  With the CG correct it should take very little elevator to maintain level inverted flight.

Landing the Ultimate Bipe is also a pleasure.  You are able to ease it in with a little throttle and gently set it down with a slight nose up attitude to bleed of some of the air speed on final approach.

Knife edge flight did not produce any coupling or any unwanted characteristics.

Overall the Ultimate Bipe is a clear winner from Tower Hobbies!

Equipment Used:

  • Rimefire .55 Brushless Motor
  • Tactic TS25 Digital Mini Servos (6 or 7 needed with glow)
  • Futaba R2008SB 8 Channel RX
  • Pulse 4500mah 6S 45C LiPo
  • Castle Creations 75 amp Edge ESC
  • Castle Creations 10 amp BEC
  • Xoar 16×6 Beachwood Prop (the Xoar prop was a direct fit with the included prop adapter with the Rimefire .55 motor – no prop reaming required)
  • Gator RC Electric Spinner – size based on preference.
  • Deans plugs for battery connections.

Some Additional Photos

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Sig J-3 1/4 Scale Cub Build Series – Part 12 – Wings and Wing Tube

Since the Sig Quarter Scale cub is an older kit I decided I wanted to “modernize” the wing design by incorporating a bolt on fuselage center section, wing tube, and a two piece removable wing. The original design called for the center section to be permanently attached to one of the wing halves. I did preserve the functional wing struts for this build however.

To begin the wing design I had the plans scanned at my local UPS store so I could work off an image of the plans using a program called DevWing. Many builders in this hobby are familiar with the “Profili” program offered by the same company.

DevWing is a great program that allows you to completely design a wing with spars, wing tubes, dihedral, servo boxes, and even multi-part wings just to name a few of the features! I started by basing the design off of the scanned sig plans and drew in the positions for the aileron and spar locations. I also used some basic trigonometry to build in 1.75 degrees of dihedral into the wing. (A little dihedral in a cub is a good thing giving stable flight characteristics and also prevents the wing from looking like it’s “drooping” in flight compared to a completely straight wing with no dihedral.)

DevWing also allowed me to specify the wing tube locations and it automatically accounts for the dihedral I had specified. I decided to make the first three ribs incorporate a wing tube from TNT Landing Gear. I used their 5/8″ by 30″ long aluminum tube with a .049 wall thickness and socket.

Another thing I decided to do was build in two degrees of washout into the wings. DevWing allows you to configure this and builds the washout into the building tabs it creates for each rib. This allows you to build the wing on a flat surface without the need for a wing jig! Washout will prevent the wing tips from stalling as quickly as the center of the wing toward the fuselage – helping to reduce the chance for the dreaded tip stall. (NOTE: the test flights with this built into the wing have been extremely stable and without event. Landings and take offs are very graceful and smooth!)

DevWing also allows you to lighten the ribs by automatically generating cutouts into the ribs. This really helps to keep the weight down and doesn’t compromise strength. It also serves to make running servo wires much easier. With the DevWing program you have complete control on how much material the program is allowed to remove. I used 3/16 balsa – which is a little thicker than stock. Using the thicker ribs will make up for an deficit in strength and wider balsa is easier to work with while building the wing on the bench!

Once the wing is fully designed (you can preview a 3D view of the wing from any angle as you build so you can get a good idea of what is looking like) DevWing provides an export feature allowing you to take your parts to the nearest CNC machine for cutting. (A couple of years ago I invested in one of the eBay CNC machines – so far it’s been reliable and has worked really well! You’ll have a lot of fun with all the precise parts you can make!)

Once all the parts were cut out I began the building process on my magnetic work bench. I’ll spare you the detailed description of building the wings since the process is the same for most wings. Just remember that the flatness and straightness of the building surface will determine how straight and precise your wings are.

I normally start by laying down the bottoms spars in place and securing them with magnets to keep them from shifting around. Next I start by placing the ribs in one by one – dry fitting them to ensure a good fit before any glue is added. Once the ribs are in place I’ll glue them with CA making sure to use a square next to each one to make sure it’s perpendicular to the spar and lines up properly on the plans. With the ribs securely in place I’ll put on the leading and trailing edges. Finally I top things off with the top spars. Once that is all dry I then add in the shear webbing which greatly increase the strength of the wing at this point. Once the spar webbing is dry I sheet the top and bottom using the traditional D-tube construction method. Once the sheeting is in place the wing is very stiff and strong – just the way we want it!

Here’s a gallery of photos of the building process!

I will write a separate post showing some screenshots from the DevWing Program.

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Sig J-3 1/4 Scale Cub Build Series – Part 11 – Cutting Cowl for DLE 40 Twin

In part 11 of the Sig J-3 Cub Build series we will take a look at cutting out the cowl for the DLE 40 twin.  (NOTE: At this point, the cub is actually finished and has already had it’s maiden flight both off land and water!  The DLE 40 Twin Engine is a great match for a 25% size J-3 Cub – balancing out the plane out perfectly!)

The DLE 40 engine is a larger engine and will require you to cut out a significant portion of the cowl on each side.  Also note that the cylinders are offset from one another so you will need to measure and mark out each side as needed.


Glue the two cowl halves together using the provided plastic strip and thin CA.  Roughen up the inside of the cowl where the bead of glue will be applied helps the CA glue adhere much better than on a smooth surface.

Next, determine where you want the prop hub to come through the front of the cowl.  Use a hole saw to make a nice clean hole.  Clean up the edges by hand and some 120 grit sand paper.

One each side of the cowl I placed a few strips of masking tape and using a ruler and a square I marked out the approximate cut lines of the shape of the cylinder and muffler locations on each side of the cowl.  Be sure to take into account how much the cowl will “overlap” onto the nose of the airplane!

With the locations roughly marked out, I used a jigsaw to rough cut the cowl on the marked locations.  The cutouts were quite rough but using a Dremel with a sanding drum you can smooth the edges quite nicely.

The paint used to paint the cowl was from a spray can called VHT.  This is an automotive based enamel paint that you can get in a spray can form.  It sprayed nicely and evenly!  This paint is heat and fuel resistant and has held up nicely so far! They have it available in a number of colors.  The white color seemed to match fairly closely to the white covering I used on the rest of the plane.  I also used their “bright red” color for the floats (covered in part 14 of this series)

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Sig J-3 1/4 Scale Cub Build Series – Part 10 – Cabin Access Door

In part 10 of the Sig J-3 Cub Build series, we will be taking a look at adding an access door on one of the  fuselage sides.  This will allow easier access to the inside of the cabin when bolting on the wings and connecting servo wires.

The window outline comes as part of the printed balsa sheets included with the kit.  Cut this out using a band saw or tool of your choice.  Instead of gluing this directly to the cabin formers, we will hinge this to the rear-most cabin former.

Start by tracing the shape of the hinges on the cabin window. Then, remove the material in the traced area to the same depth as the hinge thickness.  This will allow the hinges to set flush with the inside of the material.  For added strength, the hinges should be pined in place.  I used toothpicks for this and epoxy.




Mark the locations for the hinges on the rear most former and pin and glue the hinges here as well.  Make sure to get the placement correct as not to cause binding.


The access door can then be secured in place during flight using magnets or a latch. I intend to use a small neodymium magnet for this purpose which will be installed later in the build.


The hinged area can be sanded flush with the side of the fuselage for a nice fit! Leave some extra material for final finishing and fit.


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Sig J-3 1/4 Scale Cub Build Series – Part 9 – Fuselage Strings and Cabin Floor

In part 9 we will take a look at installing a miscellaneous items such the fuselage stringers, some additional window framing and also the nose flooring.

Included with the are a number of 1/8 x 1/4 long balsa sticks  for use as strings.  Reference the included place for their orientation and placement along the fuselage.  One helpful tip to make sure you get the stringer that is placed in the middle of the fuselage is to use a long straight edge as you glue it in place.

With the strings now in place we can turn our attention to the window framing that needs to be done. These are included as balsa sticks so you will have to measure and cut these as needed.  They will be a bit over sized and stick out over the sides of the fuselage, but they will be sanded smooth later.  Part of the metal bracing that secures the nose to the main former gets in the way of the 5/16 stock.  See the photos below for how to shape the stock so it fits nicely around the metal bracing.

To get the curve I just placed a small piece of sand paper over the wire and ran the 5/16 stock back and forth several times until it had carved out the center of it as shown below.

The fuselage flooring pieces are included as printed balsa parts that will need to be cutout at a band say or hand saw.  Also there is a large piece of balsa that will be used for the cabin floor, this is cut over sized and will need to be fitted as shown in the photos below.  I used a number of clamps here to make sure the glue joints will be strong.  I also added some additional triangle balsa inside the nose to help further secure the floor pieces.

Once everything is dry, the cabin floor can be sanded to match the shape of the fuselage!

Sanding the main floor to match the rest of the fuselage shape.

Sanding the main floor to match the rest of the fuselage shape.

In Part 10, we will look at installing and fitting the cowl around the DLE 40 Twin motor!

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