Phase 4 - Tail mounting and alignment

The FireFly has the stab mounted to the bottom of the boom, and because of the novel wing mount the tail cannot simply attached to the boom before attaching the boom to the pod. As a result you need to be careful and take this step slowly as everything must align perfectly fiirst time around.

1. Prepare your boom for the stab by sliding the vertical onto the end of the boom and marking the position of it's LE. The stab needs to be mounted as close to the vert as possible and this marked position will help you align it's back end so the gap between them is very small.

2. Attach the pylon to the stab with it's screws and then temporarily glue 2 shaped blocks of scrap balsa to it's centre line. These blocks can be glued with paper glue and their shaped points should be aligned with the centre line and furthest edges of the stab. Their height is important - they should be slightly shorter than the pylon.

3. Use the wrap and line technique in the photo to mark the centre line of the boom on the underside with thread.

4. Place the pylon/stab on the boom in the position it should go and mark the area where the pylon will sit with tape. Use the string centreline and the vert mounting mark in conjunction with your scrap shaped balsa to get it about right. Having marked the position, fully mask it off and sand the boom in that area to prepare it for good joint when mounting the stab.

5. Set up the jig shown in the photo on a large flat board, table or floor. It is very important that the cups are heavy and are at equal distances from the planes centreline - this will ensure your wings are level. Once you have the wings aligned, tape the cups down and to the wings. This will hold everything in place when you mess with the stab.

6. Move the stab into position and align using the centreline string, marks and scrap balsa. If you have a dentists mirror (see photo) use that, if not place a mirror under the back of the boom to help stab alignment. In any case placing a firm flat piece of foam under the stab (black in photo) will help ensure it is not damaged when you set it in place.

7. Ensure the stab is aligned in all three axes - the balsa and centre line should help in the horisontally and laterally, the flat board/cup jig should keep you in line with the wing. Once you are happy, triple check everything (e.g. are you definitely in front of the Vertical mark?). Finally, carefully pin it down around the edges (not through the Stab!) to hold everything in place while you glue.

8. Lift the boom carefully away from the stab/pylon and support it with something (yellow tape in photo). Take some chilled a from the fridge (you do keep it there to prevent it going off don't you?). Chilled CA will cure far slower and give you time to recheck alignment. Then place CA on the pylon and carefully lower the boom back into place. Quickly reheck all your alignment marks and then press down firmly (not too firmly or you'll break the stab) and hold for 5mins while it sets (Yes I know CA says it sets in 30-60s but do not skimp on the 5mins). When done check the bond - it should not require wrapping with CF or glass.

9. Now to set the Vert, which is cambered so needs careful alignment - the camber is put on there to prevent it stalling during launch, but this means it needs to be set at a small angle. The camber/curved side should face the thrower/wing blade and it's flatter side should face away. The first thing to do is to set it up normally and ensure everything is square using the centreline on the boom.

10. Now to set the small angle in the Vert so it is at a negative AoA (it's zero lift line) there are two techniques (use both). First sighting from the back of the boom, adjust the Vertical so that you can see equal amounts of airfoil on each side of it's trailing edge (it should now be angled ever so slightly away from the thrower/wing pylon). Next to fine tune I use a portable wind tunnel made from a hair dryer and straws (see photo). Hang the plane from the ceiling and then sight up down your "wind tunnel" and boom before turning on. Adjust the Vertical slightly until zero rotation occurs (i.e. the plane stops turning on the string). Do this last step carefully as you need to be aiming exactly down the boom with the hair dryer.

11. Double check everything again for alignment and then first spot fix the Vertical in place with foam safe CA. Recheck and then fully fix with the CA. Finally, once cured apply a light glass cloth patch on both sides of the boom wetted out with CA to hold the Vertical securely.

That's it - next step...throwing blade!

Album info