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Foam Board DLG

by | Aug 20, 2019 | 0 comments

One of the earliest builds I ever tried was a foam board discus launch glider (DLG).

It was an utter failure! It was a heavy KFm3 wing with not enough wing area and a weak nose section. It flew like a brick and broke like a twig.

That plan and project has been lost to the forgotten archives but I remember that it was based on the Dreamflight Alula – a foam glider that I have always admired but am too cheap to go out and buy.

A new-found interest in gliding along with a continuing desire to spend as little cash as possible has found me revisiting the idea with some better design skills. Yes, since the original project foam board DLG designs have proliferated somewhat but I still yearn to create a version of the Alula that I can piece together from sheets of foam board and a hot-glue gun.

This then will be the story of that project…

Drawing up the plans was simple enough. I had a couple of sheet of 3mm foam board that I thought might make the wings a little slimmer and lighter.

I imported the 3-view of the Alula into Sketchup so I could get the rough dimensions and then set about creating a shape that would be easy to cut and fold. Rather than get complicated with the fusalge I evenutally opted for a simple sandwich construction with a bay cut into the nose which would house the receiver and a small 2S LiPo.

After printing out the plans I soon realised that I had made the fuselage profile quite curvy and difficult to cut out. Fortunately I still have the CNC so it only took a few minutes to transfer the outlines to the CAM software and produce some cutting files.

I should really build myself a drag knife (or buy a laser) as using an end mill does produce some furry edges that have to be sanded off.

Still, the results were satisfactory for a quick build so I cut the wing panels from the 3mm foam and hinged the ailerons and leading edge.

Remember, Australian foam board is a lot denser than Flite Test foam so all fold lines have to be scored and creased to get a good fold.

The build was really straight forward. A few squirts with the glue gun and it was together.

A little 4ch DSM Rx and 450mah 2S LiPo went into the nose bay with a Matek Micro BEC. This was then sealed up with the outer cheek plates.

Of course, I forgot to check various things before I sealed up the nose. First of all I discovered the battery connector had broken off the BEC. So I had to cut into the nose to repair that. Then I realised the ailerons were reversed but elevator wasn’t. In OpenTX this isn’t a problem but with the Spektrum you have to manually swap the connectors over – for which I had to cut the nose open once more!

By the time I had it all working it was nowhere near as pretty as it had started…

Flying

The weather was going a bit downhill when I finally had the DLG ready so I decided to try a test glide out the back of the house.

“The thing glides like a brick and lands like… another brick”

First throw was horribly tail heavy. I had guessed the CG and obvioulsy my guess was way out as it fluttered to the ground like an oversized leaf. So I cut another chunk out of the nose and taped in a big sinker then went out again. This time was better but the resulting nosedive crunched the already weakened foam even more and separated one of the wings from the fuselage.

I fixed that and dialled in a little fake-reflex to see if that helped. It didn’t really – the thing glides like a brick and lands like… another brick.

By now it was getting very crunched up and the other wing was loose so I brought it in for the day.

I just can’t seem to get it right with this design. I think it is too heavy to ever glide nicely. I’ll give it a few days and then have another look…