Hot wire cut FlyingFoam Nurf (ish)

[iwan_canobi]

Ever since I saw the Drak I've really liked the look of forward swept wings, and I spotted the flyingfoam Nurf a while back. It looks cool and video footage from it seems really nice and stable. I figured that it would make a good replacement for my Z3 which has been nosed in 1 too many times now and is ready for retirement after a short life. I also have been meaning to try making a hot wire bow and had some perfect foam blocks I'd kept from a dining table packaging.

Nurf -

https://flyingfoam.com/product/nurf/

So I finally got round to assembling the hot wire bow. My first attempt was using PVC piping I had, I made a simple bow using 90 degree adaptors I 3D printed, and I used a guitar E string for the wire, connected to a brushed ESC and servo tester so I could vary the voltage. Straight away though I realised that the PVC was too flexible, so I just couldn't get enough tension in the wire to make it work. So V2 was made from some wood strips I'd kept from an old wardrobe (hoarding FTW!). This worked much better, and I used some screws with an electrical block connector to attach the wire. This allows you to tension the wire by just unscrewing the screw a bit, and there's no faffing with solder if you break a wire.







The Nurf has the plans available as open source, so I used the plans to make templates for the airfoils, and cut out some plywood templates:

These were then fixed onto the foam blocks using some nails to hold them in place. I want this to be able to fit in the back seat of the car easily, so I reduced the wingspan down to 60cm per wing (original is about 80cm I think). I also guestimated the amount of forward sweep just by eyeballing it, but it looks close enough. You can tell that I'm not doing this as an exact science! :P





Then came the time for this first cut! It's a bit of a learning process but I think it came out ok. You can see a kind of wave where the wire tension catches up with itself, I think I need a bit higher voltage than 3S to get it a bit warmer, but the ESC can only take 3S max. So I was probably pulling too quickly, but it did work. The ripples easily sand out anyway. I did the cut in a few passes but it came out pretty reasonably for a first go!





The foam is a decent density, but it does get quite thin towards the trailing edge. I have some balsa elevons to go on and I will be laminating it as well, so it should be pretty firm after that. I repeated the process on the second wing with similar results, then cut the trailing edge so both were even.

Then came the spar, I'd bought a couple of 5mm spars which are ideal, and I used a technique of sticking an allen key into my soldering iron and running it down the wing, it works a treat!



I'll glue these in later once I'm happy. The next part was to start thinking about the fuse. The foam I have isn't thick enough to do in one piece, so I'd need to join 2 bits to get the depth. This got me thinking about alternatives. I may get some depron sheets and just make up a long box type fuse, and 3D print a nose with camera cutouts in semi flexible filament. Whilst I was thinking I also remembered I have a boxed X6 sitting doing nothing....forward swept X6 anyone? :P



Whilst this looks cool, the X6 fuse is huge and probably too big in comparison to the actual wing area. But maybe it would work? I dunno.

That's where I am just now, I'll take my time thinking about the fuse but I'm happy with how the wire cutting ended up! I'll update the thread and I'll try and do a full build video as I've been recording some footage as I go along.

[Jake Bullit]

I like the nerf too,looks like it should fly well.

Like your work so far Euan.

Andrew Newton does a good tutorial on foam wing cutting:

! No longer available

I think David Windestal does a good tutorial too.

[iwan_canobi]

Cheers Jake, ah yeah, I watched that one a while back! Looks like he is just using 4S straight onto the wire, might give that a go as mine definitely didn't cut anywhere near as fast as his! Also his wire looked a lot tighter, which resulted in his looking amazing and mine looking crap next to it! :P

I did jump in at the deep end, cutting a symmetrical airfoil would have been a lot easier!

[philf]

The Nurf floats my boat too......I looked into buying a kit from FF but they don't ship to UK unfortunately.

[iwan_canobi]

Some small progress on this, cut out the center straight section of the wing and mocked up the spar arrangement. Hopefully this should give it enough strength.



I think for the fuse I'm going to go simple and just get some depron and make a box tube style fuse like on the VAS Spectre. Then I can make it removable and just use bands to hold it on.

The plan is to use the electronics from my Z3, but I'm wondering if the standard size servos and massive motor will be too big for this build. Not really sure at this point, may need to look into some calculations on the wing loading.

[BlueFlyer]

I like the look of this nurf... I've also seen a similar airframe called the gaugans (I think that's what it was called). looked great.

[BlueFlyer]

Graugans... that's it.

[iwan_canobi]

Yeah I saw that a while back, I actually thought it was the Nurf and that's what set me off researching it, the graugans seems to be a total one off with no plans available I don't think. Looks like it flies awesome though!

[beesleyboy]

That's a great video,  it always amazes me how thay keep the reception over those hills.