Global trend to anti-drone restrictions got me thinking about designing a new ultralight under 250 grams FPV plane. Also it should have become more compact and portable compared to my existing crafts to fit into hand luggage bag. And certainly this plane should have had good range, speed, stability, glide ratio and agility. While thinking about project i have found quite interesting way to design and make relatively accurate and complex shaped foamies. For this tech you need free OpenVSP software, Blender and 2D CAD. First step is designing and testing aircraft's shape in OpenVSP.
Then you need to slice it and export cross-sections to Blender. After some changes you just need to import it to 2D CAD and print these templates. 
After that you need to make foam segments with hot wire and glue them together
. This way you can get beautiful streamlined craft with correct airfoils. After learning OpenVSP I designed and made drak-style tailless bird
. Howewer flight test results were disappointing - prototype was fully destroyed due to multiple design errors - plane was too underpowered with 2S Li-ion battery, roll stability was close to zero, thin fuselage skin was destroyed very quickly. After changing battery to 3S engine torque caused plane to roll after take-off and crash into the ground. That was total failure. Second prototype had modified winglets and fins to improve roll stability. 
Howewer I had to make not collapsible wings to save weight. It flew very nice. Howewer since few weeks it was destroyed in crash. It was possible to repair, but in this case total weight would increase dramatically. This fail got me thinking about building a simplified version - and several days later I tested F16XL-style delta.
It flew great howewer it was too big to fit into standard bags. So I started to design 3rd prototype of this challenging plane. I returned detachable wings and fins and changed center section's airfoil from NACA 4 series to laminar 16 series to optimize internal volume. On the "Bycicle Day" I successfully tested this bird even with not suitable large and heavy motor. 
Total weight was 314 grams, so wings could flex even with carbon tubes inside. Almost 3 months later I decided to install new powerplant - small 10g engine, ultralight ESC and 2s 800 mah battery. Total weight decreased to 204 grams with FPV system! Tests were very successfull - plane could easily fly 1 kilometer away from launch site and stay in the air relatively long time. 
Plane is a little bit underpowered (0.55 thrust to weight ratio), so take-off and ascent may be not very fast and easy. Glide ratio is rather high (18 in OpenVSP) so sometimes I use spirals and s-turns before landing. Fully disassambled it easily fits into the small hand luggage bag even with controller, FPV ground station and chargers.
I think this plane achieved all planned performances. It's very compact and smoothly flying FPV plane that absolutely legal in many countries. I also plan to convert F-16XL-like delta to small 30mm EDF jet. I hope you enjoyed my article and that interesting technology.
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