We’ve had an awful run of bad weather in this part of Australia over the past few weeks. If it isn’t raining, it’s blowing a gale. Today it was doing both. Little time for flying but plenty of time for designing and building.
The Foam Board Discus Launch Glider Project
I’m fascinated by Discus Launch Gliders (DLG). It looks fun, challenging, maybe even a form of exercise. I’d love to give it a go but it’s the price of the gliders that puts me off. The best price I could find on HobbyKing for an airframe was $64 for the Apollo. The most expensive was the $182 Versus. Of course none of these even come close to a proper competition model, which would set you back nearly $1000 for all that carbon fibre loveliness.
So the challenge was on to see if it is possible to build a functioning discus launch glider from foam board – the cheapest modelling material around. Of course, I would need to steer clear of carbon fibre to keep the cost down. This immediately excluded all of those pod & boom designs that I’ve seen. The model that caught my eye eventually was the Dreamflight Alula. This bird-like flying wing is an all foam design and, if the videos are to be believed, not too bad in the air.
I had an idea then, and some inspiration for a design. On with the drawing…
It didn’t take long to get some basic plans drawn up and transferred onto the foam. The biggest decision I made was to use the KF Airfoil with a symmetrical step. Although this is supposedly a good airfoil for flying wings I already know it is going to come back to bite me with below average gliding performance. It is however a very quick and easy way to build and perfect for this “proof of concept” design.
Remember, I said functioning DLG not high-performance DLG…
The weird nosecone design…
The nosecone is designed as a foam board box. In hindsight the “A Fold” (or is it B-Fold) technique was a bit pointless as there were so many score cuts on both sides of the foam the paper just fell away in the end.
What this complex cutout did create however was a very strong box that is a perfect push-fit onto the wing. I did realise fairly quickly that those lovely tapered edges at the back would have to go as they would obstruct pushing the nose over the receiver and battery.
Building the airframe
To be honest, it will take considerably longer to type this than it did to build the airframe. The parts were cut in half an hour and the build took only a matter of minutes. Even if the KF airfoil doesn’t work you have to love it for speed building!
The completed airframe feels plenty light enough to fly but with enough weight to allow for a good discus launch. I still haven’t decided how to attach the launch pegs but that will come later!
Installing the gear
In fact, before I installed the gear I took a bit of time to bevel and sand the leading edges of the wing to make then nice and round. I also decided to treat this bird to a light polyurethane coating to protect it from getting too damp.
I had a couple of BlueBird 3.6g sub-micro servos sitting around from another project that I thought would work well here. Slotting them in next to the fin, behind the step is perfect as the step almost completely shrouds their depth. As usual, a little hot glue fixed the servos in place.
The wires from the servos feed nicely into the nosecone, where they meet up with an OrangeRX 6ch receiver. The size of this couldn’t be better as it sits perfectly on the underside of the small tray that forms the center of the nosecone. The will be joined shortly by a small capacity LifePo RX battery to complete the installation.
…and that’s it so far. I am keeping my fingers crossed for better weather over the next week so I can get out and try this out.
Watch this space for more on the foam board discus launch glider and possibly also our first design competition…