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Sabre F5K Build Instruction

Sabre F5K Glider Build Instructions

Sabre is an F5K glider that takes a new approach to the airframe design.

The science involved in creating the main wing is unique, and so is the flight performance.

Its low-drag design uses a thin wing profile, special curved wing tips, and a thin and narrow fuselage.

Sabre F5K is available in two main build options:

  1. Receiver-Ready, where you will need to add only your receiver and battery, or
  2. As a kit, and finish the servos, motor installation, and control linkages on your own.

In case you prefer the second option, this article is just for you 😉

Below, you’ll find a step-by-step instruction on the Sabre F5K build with tricks & tips to help you finish it hustle-free.

For even more information on the build options and setup, check the dedicated Thread on RCGroups.

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Order Sabre Receiver-Ready

Before Starting Sabre F5K Build

Since Sabre is designed to use some specific components, make sure to prepare the following to use during the build:

  • A pair of KST X06 servos for the fuse and a pair of KST X06H for the wings
  • T-Motor F1507 or F1806 motor with M5 threaded shaft
  • Matching ESC 20A+
  • M5/25mm Spinner with matching folding prop blades

You will also need some of your favorite tools and supplies to make the build easier, we recommend at least the following:

  • Medium and thin CA
  • Epoxy resin
  • Masking tape
  • Diamond files
  • Tweezers
  • Pliers
  • Flathead and Phillips-head screwdrivers
  • Sandpaper
  • Rubbing alcohol
  • 2.5mm shrink-tube
  • Soldering iron, solder, and flux
  • Kapton tape, or the other sticky tape that you prefer.

Part 1. O-Ring For A Canopy

Getting a kit, your canopy will not have any “security” system to hold it in place while flying.

We find it both the easiest and the most reliable to use an O-Ring for this purpose, especially when it is so easy to make.

Even if your kit will have a latching system, the O-Ring will act as a fail-proof system.

For a detailed instruction please, follow the steps described in the video below:

Part 2. Motor Mount & Tail Servos

Next, let’s move on to the fuselage and install your motor and tail servos.

Prepare a supplied motor mount, your power set, and mounting bolts
When using a power set, make sure that your ESC slides in the slot in the motor mount. Extend it for a loose fit if needed
Screw a motor to the mount, make sure to use the screws of a right length not to damage the motor coils
Prepare your spinner & prop, scrub the outer surface of the motor mount where the glue will be applied
Push motor & mount sandwich into the fuselage, facing ESC to the bottom of the fuse
Slide it forward to reach the motor shaft in front
Mount your spinner on with a moderate force
Use prop blades and spinner to position motor mount inside the fuse. Leave ~1mm gap between the back ring of the spinner and the front edge of the fuselage. Fix the prop blades to a fuselage with a masking tape, and apply medium CA or epoxy between the motor mount and the fuselage walls from the inside of the pod. Leave it like that until your glue cures
Next, prepare two KST X06 servos with standard mounting tabs
Mount the servos to the provided servo frame
Scrub the side surfaces of the servo frame, put it into the pod and slide backwards under the wing saddle. Position it in place and fix with epoxy or CA
Prepare tail servo arms. Trim them down leaving only the 1st hole – the one the closest to the hub
Center your servos and install servo arms in a position that is the cosest to the 90° relative to the centerline of the fuselage. Fix servo arms with the M2 bolts from the accessory bag

Part 3. The Tail Surfaces

Mask out the area around the control horn slot on the elevator
Using the mounting holes as guides, draw a center line and measure the lenght of a future slot based on the control horn length and thikness
Cut through the top skin where the masking tape is applied and remove the foam from the inside. Leave the skin on the other side untouched
Remove the masking tape, round the sharp corners on the control horn, scrub its sides where the glue will apply. Double-check the fit
Install the control horn in place and fix it with CA (the core is a CA-friendly Rohacell) or epoxy resin
Repeat the same steps for the rudder control horn
Next, prepare the thin music wire from the kit acessory bag
Bend these in C-shape approximately 60mm long
Install you C-shaped springs into the tails pushing the legs into the opposite sides of the hinge slot of both tail surfaces. Make sure to put one leg right next to the control horn to prevent bending the control surface under load

Part 4. Tail Control Linkages

Now you can make connections between the tail servos and you tail control surfaces.

You will need a servo tester or just your radio and Rx to center and adjust the neutral position of your servos in the process.

Thin pliers with a side cutter will come in handy to.

Mount tailplane to the fuselage
Make sure that the slot in the boom is wide enough to allow a full down travel for the elevator
The full down deflection should rest the elevator on the boom
Prepare your pull-wire and the crimp tubes
First of all, make a loop through the crimping tube
Then, push the tail of that cable through the tube one more time, creating another loop from the other side of the crimping tube
Make the second loop as small as possible and crimp the tube. Apply thin or medium CA to the both sides of the crimping tube to secure the joint
Pull the wire with the loop you just made though the boom
Hook the loop to the elevator control horn
Pull the other side of the pull cable through the crimping tube first
Next, pull the cable through the servo arm and then – back into the crimping tube. Connect the elevator servo (down on the pic) to the servo tester to keep it in the neutral position while crimping
Trim the length of the cable in the boom to set the elevator to neutral position, and crimp the tube to fix the needed length. Secure the joint with two drops of CA on both sides of the crimping tube
The elevator need to be in this position when the servo is centered, or as close to it as possible
Next, apply the masking tape on the side of vertical fin pylon, to the front part of it
Drill a small hole in the boom close to the base of the pylon, approx 7-10mm back form the leading edge
Remove the masking tape and thread the cable through this hole and all the way to the front, where the servo tray is located
Next, pull the cable through the crimping tube, the servo arm, and back into the crimping tube
Crimp, trim the excess wire, and secure the joint with a few drops of CA
Install the fin in place and make a loop on this side pulling the cable through the crimping tube and back
Set the rudder servo (up on the pic) to 90° to the fuselage centerline even if it’ll be slightly off the servo center. Leave the servo connected to servo tester (or Rx) to hold position while crimping the other side
Hook the loop to the rudder control horn and trim the length of the wire to set the rudder in neutral position
Crimp the cable and cut off the excess
Add a few drops of CA on both sides of the tube to secure the joint

Part 5. Aileron Servos And Linkages

Sabre’s wing is designed to use 3D-printed frames for installing KST X06H servos.

Sabre Wing servo frames for KST X06H

The process of using frames is described in the build instruction for Joy F5J.

However, you can get away with using X06 or X06N servos as well w/o using a printed frame, but gluing the servos directly into the wing.

The only difference in these options is potential maintenance and replacement of the servos.

But in case you are not planning to crash too often, you should be good 😉

Your choice of either or doesn’t change the overall process, so please, use the following steps as a guide for building your wings.

Remove the foam from the inside of the servo bay to reach the top skin of the wing from the inside. Be careful, not to produce any damage. Flathead screwdriver might help
Use 2mm round rod or file to make a channel in the foam core for the pushrod
Your channel should align with the sidewall of the servo bay
Here, we’ll use KST X06 servos with standard mounting tabs and will glue them directly into the sing bay
Wrap aileron servos with masking tape. Cut off the servo tabs before wrapping (Optional)
If using servo frames from the kit, install your X06H servos into the frames before proceeding istead. DO NOT glue these yet
Trim the servo arms leaving only the first hole – closest to the hub. Center the servos and install the arms as close to 90° to the servo body as possible. Fix the arms in place with the provided bolts
Make a twisted Z-bends on one side of the 0.8mm music wires provided with the kit
Install pushrods into the servo arms
Insert pushrods into the channels in the wings and position your servos (with or w/o frames) inside the servo bays. Fix them permanently applying CA or Epoxy between the masking tape and the top skin of the wing from the inside of the servo bay
(Optional) Add 2x1mm carbon fiber tubes to the wires for stiffer linkage. length of ~48mm works best
(Optional) Install these tubes as close to the servo arm as possible, leaving enough naked wire for proper servo arm travel. Test the travel before proceeding
(Optional) On the other side, the tube should have around 2-3mm gap to the control horn. Fix the tube on the wire with a drop of CA from both sides
Connect your servo to a servo tester and set it to the full UP position
Fix the aileron in the full UP position as well using a strip of masking tape. Dry-fit the control horns and mark where you need to make an L-bend on the wire
Set the servo to the full DOWN position to release more pushrod length to work with and make your bends at 90° towards the control horns
Cut off the excess wire, round the sharp corners of the control horn, and scrub its sides for better adhesion. Install the control horn onto the pushrod wire
Set the servos to the full UP position once again & fix the ailerons respectively. Then, install control horns into their slots in the ailerons and apply CA or Epoxy to glue the control horns permanently
Cut off the unneeded servo wire and solder it to the pigtail in the wing, matching the Ground, Power, and Signal lines respectively. Isolate the connection with a thin shrink tube
Pack the wire inside the servo bay making sure it doesn’t interfere with the pushrod or servo arm travel
Cover the servo bay with covers provided with the kit, and fix these in place with a sticky tape

Expert’s Advice

In case your pushrod connection has a slop, it will create issues while flying.

To eliminate the slop, put a drop of CA on the moving connections of the pushrod to the control horn, and the servo arm. Literally, glue the pushrod into the control horn 😉

Let it sit, and move the control surface slightly.

The CA fillet will slide on the wire, filling in the harmful gaps, and making your pushrod connection more precise.

Get Ready For Maiden

Sabre F5K at the field

That’s it!

Now, it’s time to install your Rx, and battery, check your CG-point, and set up your radio.

Please, follow our basic settings recommendations mentioned below:

Sabre F5K Control Throws and Camber Settings
CG 64-62mm from wing leading edge
Rudder +/- 15mm
Elevator “Touch-the-boom” down & “Touch-the-rudder” up
Ailerons 10mm up & 12mm down (optional negative differential)
Brakes 16-25mm down
Launch 1-1.5mm up
Cruise 0mm (aligned with the root) to 2mm down
Min Thermal 4mm down
Max Thermal 10mm down

With nothing else to say…

How would you rate this build?

Please, let us know in the comments below.

2 thoughts on “Sabre F5K Build Instruction”

  1. Eric

    amazing Instructions! Thank you very much!

    Reply
    1. Evgen

      Doing our best 😉

      Hope it helps

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