Building Boards

My building board is knackered (for those not familiar with English slang, just read "unuseable"). A good building board is an essential piece of kit for the free flighter. The requirements are simple, it must be:

• flat
• easy to pin and grip pins well
• big enough for your needs - long wings, bigger board

Some people are lucky enough to find a suitable fibreboard, blockboard, soft timber board or other ready made sheet in their local DIY shop or hardware store. I searched all over and could not find anything suitable. So I decided to make my own and here is the build sequence. It did not take long and cost me less than £10.




I used hard 15mm balsa planks, 4" wide mounted on a flat chipboard backing (an old bookshelf).

The planks and the chipboard were evenly coated with contact adhesive.











After 10 minutes, the planks were glued down to the chipboard. In addition to the contact adhesive under each plank, PVA glue was used between the edges of each plank. The excess PVA was wiped off with a clean damp rag.








The whole thing was weighted down overnight while the glues set.












Here is the finished board, trimmed and sanded flat. It takes pins well with good grip.


Now, what shall I build on it....?

Model gliders - all Chuck Gliders - Old and New

Here is a photo of 4 hand launched model gliders. In a way, they represent many decades of aeromodelling between them. Anti-clockwise from the top right:

• 20" span vintage HLG by Bowers from the 1930s. This is the oldest polyhedral design HLG that I'm aware of. This one has a drinks can aluminium side flap dethermaliser (DT). Build information is shown elsewhere in this blog. Since then, I've maxed it (>60s) a number of times.
  

• 14" span vintage HLG from a range of books entitled Newnes Pictorial Knowledge. This seems to be from the 1940s and is a good basic all balsa design. I found it in a SAM35 year book.
  

• 8" span HLG based closely on Kevin Moseley's excellent LET'S ROLL design (bamboo "kebab skewer" fuselage instead of carbon fibre and dihedral angles are slightly different). This one flew out of sight on its maiden flight (literally the first hard throw). It was found months later many miles away - always write a mobile phone number on your model! When I picked it up the wing was fine and it still flew, but the tail needed replacing.
  

• 36" span tip launched glider LIPZOID. Its design and build is shown in this blog below. It follows the recent discus launch developments and I suppose represents the modern era of chuck gliders.
  

DLG Plan: Part 6, Finishing the glider

This photo of the finished glider - LIPZOID - was taken just before its maiden flight. See the video in Part 5 below.

Parts for the left side of the fuselage. From the left: 1/16" ply, 3/32 balsa (the hole is for the DT viscous button timer - I modify the basic cheepo buttons available from Flitehook for £1.50) and 1/16" balsa. Edges were sanded so that the surfaces blend together smoothly.

After the front of the fuse is finished, I cut out the wood boom block (pine) and measure out and cut the rear of the fuse.

I ca'd a bit of thin clear plastic to reinforce the rear of the fuselage, as this will come into contact with the spruce block when the boom is up. This was then trimmed and cleaned up.

This is the pine boom block ready for gluing with ca. Then it was glassed with the cloth running round the 5mm carbon fibre tube.

Ready for drilling. It was quick and easy to drill the pine boom block first. Glued one 1/16" ply cheek and when dry, marked and drilled it. Then did the same for the other ply cheek.

Wing being glued to fuselage. I simply sanded the top of the fuselage flat to mate with the wing underside. However, because of the upsweep under the LE, I also made a small wedge shaped balsa piece to match the space between LE and fuselage.

This is a close up of the wedge under the LE.

Close up of the finished boom block socket.

Glass cloth was applied to wing joints - two 2" squares, one over the LE and the other over the TE, plus a strip top and bottom. Lightly tacked with a spray glue, ready for resin to be sparingly brushed on. In addition, the left wing was given extra reinforcement in the form of oval patches in the middle of the joint on both surfaces (not shown in this picture). The centre wing-fuselage joint was also reinforced in a similar manner.

Detail of rear of fuselage. The gf cloth reinforcement is visible as is the nylon hing bolt. I used two transparent hair bands around the boom (Lark's Head knot) looped over a bamboo peg in the middle of the wing. The yellow band is thinner pole elastic for the timer.

Detail of the boom arrangement. Pink band is 1.6mm pole elastic, tied (Surgeon's knot) to the thinner yellow elastic. The yellow is tied to nylon fishing line with a small loop tied to the end. The loop is hooked over the timer arm. Coaxing it to operate reliably (one turn of the arm should take about 1 minute) is good fun and surprisingly easy. Under the wing the pink elastic is tied to a steel pin head and run round two cocktail stick pegs. Also, you can just see the adjusting screw for decalage.

Glider with boom in the up position. Just numbers (BMFA and mobile) to apply. The finished model without ballast was 83 g, a bit heavier than I would have liked. I definitely overdid the glassing, especially on the tail. On the other hand, it's pretty strong and I reckon it will need to be because it's going to get a good bashing!

I enjoyed this design and build process. It is always amazing to see one's model fly. LIPZOID seems to be fairly stable with hardly any trimming effort so far. My tip launching was not very consistent, but thankfully, the model recovered from most of the scary attitudes. There was one very heavy landing, but just a minimal repair to the right wing was needed (I knew that was going to happen because there was a natural softer spot in the wood there). I'm now waiting for good weather to have a decent trimming session. I'd like to try increasing the decalage and perhaps moving the CoG more forward. It's at 50% at the moment.

DLG Plan: Part 5, Sneak preview Video!

I will continue the build posts, but in the meantime, here's a sneak preview of the glider LIPZOID in flight today on its maiden outing. It dived off the top of the launch, but stabilised nicely in a wide right turn. Lee Hines commented on a forum somewhere that CoG at 45-50% and a fair amount of decalage works well for him. From the brief flying that I've done so far, I'd agree with that. LIPZOID is not trimmed yet as I only had a bit of time to fly today. The sky was beautiful, but it was getting dark.

DLG Plan: Part 4, Wing breaks and fuselage

Photo left is just a reminder of where I had reached at the end of Part 3 in this build. The wing high point is just visible as a dotted line and both wing and fin have denser wood LE reinforcement.











After cutting at the breaks and sanding, the photo right shows what the aerofoil looked like. The walnut LE shows up nicely. The TE is thicker than I would normally finish a HLG. However, I'm nervous about strength and kept the TE at just over 1mm thick to provide some surface area for the glue and to preserve some rigidity in the wing. Quite close to AG03.

Photo left is the wing drying. Glue is Araldite Precision slow setting epoxy. It's all standard HLG building so far. 109 mm under each tip (the convenient height of a tomato tin!) .

While the wing was setting, I glassed up some 1/32" (0.8mm) marine ply using medium glass cloth and two part epoxy. This will make the wing break reinforcing braces - it's cunningly sized to fit exactly within a tenon saw cut. I may also use it for the boom hinge plates (or 1/64 ply - haven't decided yet). Poly bag below and above, then weighted down with books overnight while it set. This is the first non-standard HLG bit.




A closeup of what the glassed ply looked like when dry. Probably too much resin this time. However, job done and it's much stronger and not significantly heavier than without the glass fibre.












Also while the wing was setting, I cut out the fuselage parts. Very simple: 6mm square spruce, a carefully selected coffee stirrer (thanks Starbucks!), and 1/4" (6mm) balsa 18mm wide. Glue these together with PVA and rubber bands, with the spruce butting against the coffee stirrer.



Then apply 1/32" (0.8mm) ply cheeks to reinforce the central part. This was standard marine ply, not the glassed stuff. Again, glue with PVA. The ply cheeks also act as the locator for the carbon fibre boom.










After cleaning up the glassed ply, and sawing the wing along the high point line from the underside with a tenon saw, test fit the glassed ply wing break reinforcer. Mark with a pen above and below the wing and trim.













Cut off the excess and lightly sand up the glassed ply brace. This is what it looks like - a sort of chevron. When happy, I glued it in place with Araldite Precision .













This is what the underside looks like after the glassed ply brace has been glued into the saw cut.


I hope it's strong. So far, this is easy and relaxing building. But will it fly, or is it destined to crash into the ground with a sickening crunch?....

DLG Plan: Part 3, More work on wings & feathers

For aerofoil section, I am trying to follow the AG03 by Mark Drela. He developed it for the Apogee RC hand launched glider. Unsurprisingly, it is remarkably like conventional HLG aerofoils. Walnut works well with plane and sandpaper - I would use it again.

The high point was marked with a fine felt tip pen dotted line. It is 28 mm from the front of the LE running parallel and then curving to the wingtip centre line. Use the wing tip template to draw it.

The sanded fully shaped wing weighs 40.8g. I've kept the TE at >1mm for strength.

The stab was given very little work. Just rounded off the LE and sanded the rearmost ~ 1" of the top in a taper to the TE (but not too thin, because I want to preserve some strength). A thin strip of bass wood was glued and rubber banded to the LE of the fin, wrapping it a little around the bottom edge.

Photo left is a close-up of the bass wood LE of the fin, after the bands had been removed and a bit of cleaning up with sandpaper.

Next, wing breaks, or shall I start the fuselage instead?

DLG Plan: Part 2, Cutting out the flying surfaces

At long last, I had a chance to put scalpel to balsa today and cut out the wing, stab and fin. Wing is from 1/4" (6 mm, ~ 6.5 lb/ft3), stab and fin from 1/16" (1.6 mm, ~ 8 lb/ft3). The first step was to print ellipses of the right size on to thick paper and cut them out to use as templates. In keeping with the design objectives, I will not be sanding the stab and fin to aerofoil sections, but will round the leading edges and lightly taper the trailing edges.

In the photo, hardwood strip has been glued to the leading edge of the wing with waterproof PVA. I use rubber bands and masking tape to clamp it while the glue sets. Normally, I would use spruce or bass wood for LE reinforcement, but this time I used walnut D strip simply because it was there and it was long enough - I used one piece for the whole LE. The walnut bends well using steam from a kettle and the dark colour makes a nice contrast to the balsa. Should be strong too.

Thanks Stevie B for the encouragement!