ChopperAddict's Hints & Tips

CHOPPERADDICT SPECIALISES IN THE BUILDING, REPAIRING & 
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HOW TO - Replace the boom on a Belt CP

Many new pilots who are just learning too fly have the problem of the boom getting bent in a crash, and have no idea how to replace it.  So here is the easiest way to do it.  These instructions are aimed at the plastic tail, but will work equally well for CNC tails

1 - Remove the two screws that hold the vertical fin (king pin) to the tail assembly.

2 - Remove the three small screws at the very back end of the tail drive

3 - Remove the screw(s) that hold the silver tensioner pulley into the tail casing.

4 - Unclip the plastic link on the tail control rod from the control ball on the tail control rod.

5 - Carefully pull the left hand side of the tail casing away from the right hand side.

6 - Carefully pull the right hand side away from the boom, and then release the toothed belt from the drive gear.

7 - On the inside end of the main drive shaft in the assembly you have just removed from the right hand side there is a small plastic belt holder that can and will slide of the shaft, so remove it now before it gets lost by sliding it of the shaft.  - NOTE the way it goes on, with the flange in towards the gear itself.

8 - Put all those parts to one side carefully.

9 - Undo the two screws the hold the horizontal tail stabilizer and remove it from the top of the boom.

10 - Remove the two screws on the side of the bracket that held the horizontal stabilizer, and slide that bracket of the back end of the boom (or wait till you can do so from the front of the boom if the bend is behind it.)

11 - Unclip the tail control rod from the small clamp it slips into halfway along the boom. then disconnect it carefully from the servo and lay it to one side.  Loosen, but DO NOT REMOVE the screws that hold the servo mount to the boom (not the servo to the mount screws) so that it can be slipped off the front of the boom when we are ready.

12 - Pull the small plastic strip that tightens that bracket on the boom, and then slide it off the boom if possible

13 - Move the very back of the main frame, where the boom goes into it, and you will see 4 screws, one in each corner, that trap the boom in place  Loosen (don't remove) all 4 of those screws.

14 - Pull the boom backwards out of the frame.  You may need to wriggle it around a little, but don't twist it too much as there is a slot in the boom that slides over a plastic ridge to stop it rotating.  The drive belt will also pull down and out of the boom.  If the damage is to much to let the belt pull out, use a small screwdriver or similar to lift it off the drive pulley just behind the mainshaft, and pull the boom off with the belt in it.  You can then cut the boom as necessary to remove the belt afterwards.

If you couldn't slide the brackets off before, slide them of the front end.  If the boom is bent on both sides of them, use a hacksaw to cut it so that you can remove them more easily.

The boom is now fully removed from the aircraft

Fitting the new boom is basically a reversal of the above procedure, with a few other things you need to do, such as feeding the belt into the boom carefully so that it doesn't get twisted, and setting the belt tension.

1 - Pull the belt through the new boom. The best way to do this is to use a bit of old piano wire or similar.  Make sure that it does NOT get twisted as you pull it down.

2 - Pull it out of the back of the boom only far enough to let you tape the belt to the boom using some electrical tape or similar. This will stop it twisting at the back.

3 - Slide the servo mounting bracket and servo over the front of the boom, ensuring it is refitted the correct way around.

4 - Pull all the rest of the belt out of the front of the boom, and push it into the hole the boom is going to push into as far as possible.  

5 - Slowly push the boom into the hole.  Make sure that the slot in the new boom is on the left hand side at 9 o'clock so that it will engage with its guide.  Push it in as far as it will go, ensuring it fits on the guide.  Lightly pinch all 4 securing bolts/screws 

6 - The belt should now be visible, so use a pair of swan nosed pliers or similar to lift it and drop it over the tail driven gear.  Make sure you don't twist it any more.

7 - Before we go any further, slide the control rod hanger and then the horizontal stabilizer bracket over the boom from the back.

Then complete following steps 10 onward (in reverse)

Job done.