Nurf Flying Wing Design

Coby February 23, 2013 at 5:25pm

A few more changes:

- Thrust line adjustment to account for moving motor up

- Switching to a .188" CF rod for vertical fin retainer (untested as of yet), as the spring canopy pins are a bit pricey and can be hard to find.

- Switched to balsa elevons as it makes the wing easier to build straight.

- Switched to 1.3# EPP for fuse as the 1.9# was overkill.

- Switched to .188 CF spars top and bottom in case someone wants to do outside loops. Actually it makes the wing easier to build straight too.

Hope to have the updated plans done in a few weeks. Test units ship next week to a few brave souls. Should have their feedback incorporated and kit ready early April.

Nurf v5 got gear - wheels and then skis once we got enough snow. Nurf is designed for hand/bungee launch and belly land but we figured we would test it with gear anyway. I've always wanted to fly something with skis. The vertical shift in CG with skis hanging on on the bottom made it pitchy. No surprise. Could be tweaked but the skis are not really a permanent fixture for this one.

Coby January 27, 2013 at 8:42am

Nurf V3 has been built and flown. We cut back the nose with a band saw and added a GoPro for this model. Might fall into the "so ugly it's cute" category. James wants to call it Fruit Bat. Whatever you call it, so far so good...

Airfoils have been tweaked for better stall recover and it's now at 72" span. Also completed our tests for tool free wing joiner and it's working well. One more prototype before it's ready to kit. We want to tweak the thrust line and make sure we have ground clearance for a 9" prop. It can handle up to a 12" prop but you would be best off with a folder once you get by 9".

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Vladimir "Lazy" Khudyakov January 14, 2013 at 10:14pm

Coby, I flew with Paparazzi AP.

Coby January 14, 2013 at 6:19pm

I understood. However, for clarity, when you say AP are you suggesting that tailless does not fly well with AutoPilot in general or ArduPilot specifically?

It sounds like you are suggesting gains needed to be adaptive/computed/dynamic depending on the situation. I think there may be instances, such as big changes in DA (density altitude) or wing loading, in which any design may benefit from dynamic gains. Not sure it's been addressed as I have not followed ArduPilot dev very closely the last year.

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Vladimir "Lazy" Khudyakov January 14, 2013 at 8:41am

Coby

You not understand me as well. :)))

I say nothing about you design. It's flew, and flew well, I believe.

But we talking about tailless with AP.

Coby January 14, 2013 at 8:36am

Vladimir,

Not ready to give up on tailless just yet. Considering there are successful flying wing designs out there we will press on with your feedback in mind. The Nurf is about our 6th flying wing design in the last few years. James and I have had some good success and spectacular failures with some prototypes during that time. Almost all failures can be traced back to poor CG location, which lead to pitch instability. After we started favoring 15% MAC for our stability margin things got much better in pitch. You are correct they can be a handful in pitch, but so can any aircraft if you get outside of proper CG range. Flying wings just tend to be less forgiving. Again, it's all about trade-offs for what we think is a more rugged design with fewer moving parts/complexity.

It should be noted that James and I do not claim to be engineers. I never took the test and James has taught himself more about low reynolds aero than I ever learned from school. But we have managed to make some funky things fly:

- Mercury is basically a bucket that flies

- Gemini is a delta wing that can hover

- Joker is an R/C flying wing design that can do knife edge

So Nurf is not our first rodeo as we say around here. However, we open our designs to get feedback and allow other people to make it better. I know it's not as good as it could be by any stretch. But it does fly well right now.

While I am waiting for our maiden flight video to upload to youtube I thought I would address your comment about the tail being too small. You could be right, but the flight tests do not show it. That tail area was a SWAG and I would not mind making it bigger. Part of the bonus of a forward sweep is you really do need a big vertical stab since it's usually shortly coupled. It's a bonus in my mind because I have a very hard time seeing a delta wing when it turn profile at a distance. The fuse and tail of the Nurf help the operator see the thing at distance. Just an example of form and function coming to together. As I mentioned before, we could take say a Drella designed glider and tweak it for our needs, but it would not matter if it's not usable in the context of a general purpose DIY UAV.

R,

C

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Vladimir "Lazy" Khudyakov January 12, 2013 at 12:11pm

Not a roll...Basically, FW is stable on roll axis. Problem began, when you start to tune pitch/throttle loop. All FW is a single mode aircraft, I mean - it's flew nice in limited speed/trust range. Add a 100 g weight - welcome to the hell. Wind? Yes, re-define all again.

AP not a human pilot. It's execute a programm, not work with associative automatism.

Coby January 12, 2013 at 12:03pm

Thanks again. We hope to have some time after I get back from the expo to try an ArduPilot in the Nurf. What issues were you having with tuning? Too pitch/roll sensitive?

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Vladimir "Lazy" Khudyakov January 12, 2013 at 11:46am

Coby, look in my blog...

I build something similar. Flew like a dream, land almost no hand, strong as stone...But I lost one season to tune AP in this plane. And finally I buil classical plane, with tail. :)))

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