MoonBug SAL/DLG

lightning bug

A while ago now I built a Lightning Bug DLG by Carl Dowdy. It was the first time I’d built a balsa model in a long time and although it came out okay it did have some flaws.

 I only really got a few flights out of it before a particularly energetic launch exploded the fuselage and split the wing. I was never really happy with how it flew so I didn’t repair it. The tail boom was very flimsy and I had a LOT of twist in the tail surfaces. It came out VERY tail heavy (a flaw others have noted) and required a big block of lead in the nose.

The chances of me getting a decent flying DLG were slim but a recent interest in built up gliders got me thinking… Could I build a new fuselage in a more traditional style and revive the design? This is what I came up with…

MOONBUG

The inspiration came from the Leprechaun vintage glider. A sleek, HUGE glider suited for slope and high-start launches.

leprechaun

Constructed almost entirely from 3mm balsa strip it should be a straightforward build. I am guessing I will need to put in some diagonal bracing to stop the fuselage from deforming but otherwise I reckon I should give it a go.

Balsa Stripping

Master Airscrew Balsa StripperIf you are planning on doing any sort of building using balsa then this little tool is a must-have item!

This one I got years ago from Master Airscrew so I’m not sure if they still make them. Simple to use, you just adjust the screw to suit your width. A couple of minutes work and a relatively inexpensive sheet of balsa can be turned into a whole bundle of sticks for building. Get one, you won’t regret it!

Moonbug construction
Constructing the first fuselage side

Building the first fuselage side was an enjoyable process. It was so easy to work with the 3mm balsa. Of course, it takes longer than using foam board but the result weighs only a few grams and looks awesome. Here’s a few things I found useful…

  • CNC machine – those shaped parts were cut on the CNC for accuracy
  • A sheet of foam board stuck to MDF makes a great building board. Laminating film over the plan keeps it clean
  • Those single sided scraper blades from Bunnings are razor sharp! They go through balsa like a hot knife through butter
  • 3D printing is great. I printed those tiny set squares to help with jigging the fuselage

The fuselage came together really nicely. I found I had to add diagonal bracing to add rigidity to the structure but it was really easy to do.

moonbug fuselage
The nearly completed fuselage

Old School Finish

I’m a cheapskate, but I’m also fascinated by the old rubber-powered free-flight models you see around. Tissue and dope is a technique as old as the hills but “proper” modelling tissue and dope is hard to find and expensive. A bit of research found me a forum post where someone suggested attaching the tissue to the frame using a glue stick, shrinking with a 50/50 water/isopropyl alcohol mix and then sealing with hairspray!

Another search discovered that I could get packs of wrapping tissue for next to nothing from Officeworks. It comes in big sheets and even in different colors – I had to give it a go!

Tissue covering on the finished model

It is so easy to apply tissue to a model in this way that it is almost too easy! I’ll do an article about it in the future but suffice to say I was very happy. The one downside is that this covering is VERY fragile. The hairspray sealer may be okay for free-flight models but I need to find something more hardy for larger models. I’ve heard rumors that thinned PVA glue or polyurethane varnish works well.

An Element of Control

I’d embedded two nano servos in the nose along with a small 2S LiPo and DSM-2 Rx. Those tiny little Matek voltage regulators are great here as they convert the 2S pack into usable 5v power.

I’d spent ages trying to work out how the heck I was going to run light enough control rods/snakes to handle the rudder and elevator and then a video on micro DLGs appeared in my YouTube recommendations that suggested “sprung” hinges.

Torque springs and nylon cables

The idea is you use a tape hinge on one side of the surface and then bend a spring from fine wire that deflects the surface away from the control cable. The springs in the picture were far too heavy and I ended up using 0.14″ fishing wire to get the correct tension. The cables are nylon fishing line, crimped at the servo arm and then fed through the hole of another servo arm cut down to be a control horn. I then used a split fishing weight to lock it in place. The resulting hing is very accurate and totally slop free!

Into the Air

I finally got everything finished off and headed for the field. It took around 25g of lead in the nose to balance it out properly but the total weight is still next to nothing.

I did a couple of test throws to check that everything worked and was pleasantly surprised. I got a little video and to be honest that is about as far as I have got at the moment. The wind started to get up and I decided to call it a day…

Conclusion

I think that this will be a lovely little glider for flat field (if I fit a tow-hook) or light-wind sloping on low dunes.

The tissue covering technique, whilst great for small free-flight gliders and rubber-powered models, just isn’t up to the task for R/C. I have already punctured the fuselage multiple times as it is so fragile. I think I will soon be recovering this model in film just to give it some strength and longevity.

Was it worth it? Possibly. I’m not sure how much sloping I will get to do but the build process was fun and that is just as important

Until next time…

Update!

Newly covered in film

I’ve completely recovered the MoonBug in film now and it feels much stronger than before. I’m even considering putting the peg back in to the wingtip for some DLG launches…

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