YF-12 RC RG Instructions

The YF-12 RC rocket glider kit

 

The YF-12 RC Rocket glider kit is designed after the prototype interceptor version of the A-12/SR-71.  It comes with  white BMS tubing for the body and engine nacelles and Depron wing and tail surfaces.   You will need two 8-11 gram type servos, a receiver, and a small 500mah single cell lipo battery and an 18″-20″ servo extension.  You will need a transmitter with delta or elevon mixing.   Foam safe CA+ is the only correct glue to use for all construction on this model.  Any other adhesive will add weight in the wrong place, and reduce flight performance.  Please refer to the General instructions for all kits tab above, then read these instructions completely before starting assembly.   ​Wingspan 21.5″, length 40″(about 1/32 scale) weight 12.5-12.75 oz rtf.  High quality cut vinyl decals available Here

This kit is more of a builders kit than my others, but still not complicated if you follow the directions.

CG location for rocket flight:  1″ behind the the front of the nacelle tubes.

 

Unpacking your kit:

The kits are packed to protect them in shipping, but the contents are fragile so unpack carefully.  Carefully cut the tape holding the tubes in the box, then unwrap/lightly cut the plastic wrap to free the tubes, the spar may be packed in the tubes and the baggie with the little parts and nose cone will be in the tubes as well.  Carefully cut the tape holding the cardboard wing protector in the box and carefully remove it, don’t pull hard or bend it.  Then carefully cut the tape holding the cardboard top piece to the bottom.  There may be some sticky tape holding the cardboard to the bottom cardboard piece, carefully peel it being sure not to bend anything.  Once the top cardboard is free you can see the foam wing/tail parts, there are little fragile pieces in here, so unwrap carefully.  It may be best to use an exacto to lightly cut the plastic wrap and carefully remove it without cutting into the foam.  Make sure everything is free before you remove the pieces to avoid breaking anything.  Kits contain one or two scrap pieces for repairs if you damage anything in construction or flight, just cut and patch in a spare piece of the foam if needed using foam safe CA+.  The tubes may look a bit smudged or have some gray marks, this is due to the aluminum angle I use for cutting the slots, if it bothers you you can use a soft eraser to remove it, but since it will be painted black, it won’t really matter.

Welcome to the world of rocket boosted radio control gliders.  This is not a model for a novice RC pilot, but anyone who is comfortable with RC flying of an aileron controlled medium speed model should be fine.  Read through the instructions, look at the photos and be sure you understand the step before commiting to cutting or glue.

Identify all pieces, the kit should contain:

1  wing  taped together

2 vertical stabilizers

2 2.5″ long foam strips.

2 body tubes with rail buttons installed

1 nacelle tube(will be split and used for the right and left nacelles.

2 control horn​s w/pushrods

Velcro(for battery and rx/bec attachment)

3M blenderm tape

Nose cone

2 intake cone lower plates

2 intake cone upper plates

Intake cone paper wraps

2 foam cockpit pieces.

motor tube with clip

long and short carbon spars.

Lead weight

Spare foam (for testing paint, glue,  and sanding the edges to see how it behaves)

Download of small foam parts in case you lose or damage them, you can cut from the spare included with the kit.

YF12smallparts.pdf

Assembly:

  1. Look at all parts and understand what pieces go where.
  2. Unfold the main wing and glue the taped joints.  The forward joint is taped only on half of the cut so that it can fold to fit into the box.
  3. Glue in the two spars into the premade slots on the bottom of the wing and then tape over with blenderm tape.
  4. You may use 320 grit sandpaper and a sanding block to round the edges of the foam before further assembly.  Round all edges of the wing at this time except for the flat part where the intake cone will be mounted. Go slowly and take your time.  Round the leading and trailing edges of the vertical stabilizers at this time as well.
  5. Once the sanding is finished wrap blenderm tape completely around the forward horizontal  wing joint near the neck, it will help support and hide the joint.
  6. The body tubes are  pre-cut for the wing slot except for where the coupler is glued, they are shipped with foam inbetween to keep the slot open, the tube tends to flatten a bit once cut, leave the foam in place till ready to glue the wing in.  Glue the two body tubes together with the foam safe CA+.  The body tube is marked with an arrow, make sure you align the two tubes so that the arrows are aligned so that the marking wing slots are correctly aligned.
  7. Once the glue is set, carefully using multiple light cuts slowly cut the body tube slot through the tube and coupler to make a complete slot.   You can do it freehand, it took a little bit of time but if you go slow and make multiple passes a little at a time will yield the best result. Test fit the a spare piece of foam into the slot to make sure the wing will install easily.
  8. Test fit and slide the wing into the body tube slot making sure it is centered and the rail buttons are on the same side as the visible spars(on the bottom)  Once centered, glue fully along the body tube top and bottom to secure it in place. It’s better to place the model upside down and glue the bottom part of the tube first so that the wing and tube are supported flat, then flip the model right side up and glue the top making sure to keep the wing/tube flat. The tube tends to flatten once it is cut so you may need to pinch the tube slightly as you glue and use accellerator a bit at a time to make sure it stays round in the middle and makes contact with the wing.  Flip over and glue the top tube starting with the neck section so it is supported by something flat.  Since the rail buttons are in place you will need to be careful when you glue the top rear that you do not deform or bend the wing as you glue.
  9. Glue the two pushrods/control horns in the bottom of the wing in each control surface in the pre-punched holes using CA+. Apply CA+ to the top of the control surface on the prongs from the control horns to capture them in place.  Set with accelerator.  Note in the picture how the control horns face, the flat part of the control horns faces forward so that the holes that the pushrod go in are even with the hinge line.
  10. Your radio needs to be configured for Delta mixing, this means that the servo arms will move the same direction during elevator stick movement and opposite for aileron stick movement.  Connect your servos to the receiver one in the aileron connection and one on the elevator connection and apply power.   Use a servo arm at least 9/16” long and with holes small enough that there won’t be slop with the pushrod wire when installed.  I use the hole furthest out on the servo arm, to maximize movement. On some servos there are a long two-ended servo arm, you can use this arm and trim off one end.   Zero out any trim settings on the transmitter.
  11. Connect a servo to each pushrod.  If the pushrod is too tight, you can use twist an X-Acto knife in the servo arm hole to make it larger, but be careful and do not make it too large.  Note that the servo arm will be facing the center of the model so that the pushrod comes to the servo at a 90 degree angle from the hinge line.  Once connected check control surface direction.   Flip the model right side up and look at it from the rear.  Moving the transmitter stick back(up elevator) should move both elevons up.  Moving the transmitter stick to the right should move the right elevon up and the left elevon down.   If you can’t get the servo reversing to give you the right polarity try swapping aileron/elevator inputs to the receiver or turning the servos over and swapping the servo arms to the other side of the output shaft.  If that is correct insert the screw to hold the servo arm in place.
  12. Flip the model upside down.  The servos may be attached to the model using double back servo mounting tape(not included) or by directly gluing the servo to the wing with foam safe CA+.  Double back servo tape can loosen over time and with exposure to heat, I prefer to glue the servo in place.  With the radio still on, put a moderate amount of glue on the servo, being careful not to get any near the output shaft, and set it in place on the model  next to the body tube and keeping the control surface centered.   Do the same to the other side.  Make sure the glue is set before continuing. Note**  The servo electrical wire should point toward the front of the model.   See the photo for an idea of how it should look. Unplug the servos from the receiver.
  13. Attach a servo extension to each servo long enough so that it will go the full length of the body tube and out the front to allow you to connect it to the receiver.
  14. Cut a 1/8″ by 1/2″ long slot on each side to allow you to route the servo wire forward to the front.  Tape over the slot once the wires are fully inserted.
  15. Glue the two foam 2.5″ long strips onto the motor tube on the two pencil lines that are opposite each other.  Note how they are on opposite sides and the motor hook is at a 45 degree angle to the strips.  This to allow the motor hook to have clearance when you slide the motor tube in place in the rear of the wing.
  16. Test fit the motor tube in place, sand the two foam strips a little at a time till the tabs will fit into the rear of the model with the tabs straight up and down.  The sides of the motor tube are centered in the cutout in the wing. Note the motor hook is glued and taped at the front, make sure you slide the motor tube in so that the motor hook can move to release the motor, apply foam safe CA+ from the rear to secure it in place.  The motor tube doesn’t need a lot of glue to hold it in place, the thrust of the motor is against the rear of the wing and the hook just keeps the motor from falling out after burnout.
  17. Glue the lower intake cone foam piece to one of the the longer upper intake cone strips so that the cones shapes are aligned.  Cut out the paper intake cone shroud.
  18. Glue one end of the paper wrap onto the side of the foam triangle shaped piece so that it is flush with the bottom and notch aligns with the notch/step between the two pieces at the rear.  Glue so that the glossy side without printing will be visible.  Gently wrap the paper around and glue to the other side making a half cone and glue to the other side.  Run CA on the inside corners and tip as well. Trim the foam tip at a slight angle if there is any excess to make it look clean. Repeat for the other side.
  19. Glue the intake cones on each wing, so that step is flush with the front of the wing and the cone is approximately 1/8″ from the marked nacell tube wing line so that the nacelle tube can fit over the cone.
  20. Find the short 2″ diameter pre-marked body tube with the slots pre-cut.  Carefully cut the tube on both sides on the long pencil marks to make two halves using an exacto making multiple light small cuts, take your time.  Using an exacto or scissors cut the rear angles as marked in pencil, these are needed to clear the elevon.  Note the angles are not symmetric because the elevon is angled and the two sides need different angles.
  21. Lay one side of the wing on a table edge and supported so that it is flat.
  22. Look at the two pieces of nacelle tubing.  There is a left and a right.  They are marked on the tubes and the slot on for the vertical stab will be inward.  If you have these swapped the elevon won’t have proper clearance to move.
  23. Glue the correct nacelle tube in place.  The font of the nacelle tube is even with the front of the wing and the rear must allow the elevon to move fully.  There is a line on each wing half for gluing the nacelle.   IT IS CRITICAL the first edge is glued on the line otherwise the nacelles may not be straight and the vertical stabs will have an undesired rudder angle built into them!!  Glue the other edge in place.
  24. Repeat for the other side.  Use accelerator to set the glue as you go.
  25. Glue the two vertical stabs in place in the slots.  The stabs angle inward, it isn’t critical the absolute angle just try to get both sides approximately the same.  Reinforce the joint on both sides with a CA fillet on the inside and outside of the tube, use accellerator to set the glue before proceeding.
  26. Glue the two cockpit pieces together.  Sand the sides/top to a pleasing round shape.  Wrap sandpaper around the front of the body tube and sand the bottom of the cockpit so that it will conform to the tube.  Glue in place so the front of the cockpit is even with the front of the tube.
  27. Re connect the battery to the receiver and the servo extensions to the receiver and make sure everything is as expected.  You can mount the receiver in the front of the body tube recessed into the pre-cut notch in the front of the wing with velcro.
  28. The nose cone needs to be washed inside and out and lightly sanded so that paint will adhere better as well as the nose weight.
  29. Attach the flight battery using velcro to the inside of the nose cone.
  30. Paint the model using ONLY testors or model master enamel spray paint. This is the only paint  I recommend.  I’ve used testors and model master flat black.  Mask off the rail buttons and the servo output arms to prevent paint from getting on them.  Do not spray too close to the model. Use many light coats and do not spray heavy.  I apply a coat to all the edges of the foam first since it tends to soak into the sanded exposed edges and look lighter, then apply light coats till the model is covered.  Paint adds weight, use just enough to get a nice even finish.  I used slightly more than one can of flat black to complete each prototype, and that added exactly 1/2 ounce to the model.
  31. You can use a silver sharpie to add panel lines or accents if you wish.  The real YF-12 had a white cross painted on the bottom of the aircraft during the speed record runs for visibility, you may use vinyl trim or paint to do the same to help with orientation.
  32. Install your loaded motor.
  33. Support the model at the balance point indicated for boost.   Add weight as required to balance into the nose.  Hold it in place with a good epoxy.   Do not try to fly the model too nose or tail heavy.  Remember, a nose heavy model flies poorly, a tail heavy model flies once.  My prototype requried about 1.1 oz weight.  To do this I left the shot in the baggie and stuffed it into the nose cone, removing weight till it was slightly tail heavy, then mixed that shot with a little epoxy and installed it into the nose taking care not to get any epoxy on the velcro.  Once set I checked that it was slightly nose heavy, adjust if needed.  Do not just use all the shot included or you will be nose heavy most likely.  If you are worried about the epoxy not sticking to the cone plastic, you can insert a small nail or screw into the underside of the nose that the epoxy can lock into and prevent it from breaking loose.
  34. Set up your throws and trims:  The model uses approx 5/8-3/4″ up and down elevator throw and 1/2″ left and right aileron throw.  It is quite roll sensitive on boost so you may tone this down as needed.  For boost I used zero control trim but you may need some depending on how your model is built, and for glide I’m using about 3/16 of up trim or a slight bit more. I put this trim onto my flap switch so that I can go from boost to glide trim with the flip of  a switch.  Make sure when you launch you are in boost trim or it will be a very short flight.

Flying:  Be ready on the first few flights to keep the model straight till you have the trims set perfectly for boost and glide.  Try to do initial flights in dead calm conditions.  You need to be ready to react quickly to keep it boosting straight up or slightly away from you.    Keep the wings level.  Count to 7 and start to push the model over level as the motor burns out and it slows down.  Then click in the up trim.   Avoid drastic bank angles which cause you to lose altitude and make it easy to lose orientation.  Gently fly around, and set up for landing into the wind when about 100′ high.  The model will rock the wings if you start to get too slow, if this happens push forward on the stick slightly.  The decent rate is very predictable,  keep some speed up so you don’t stall, and keep the wings level as it decends and gently flare just before touchdown.  Try not to flare early and stall the model.  

Photos may show the SR-71/HABU kit parts a some assembly steps are identical.