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Old Sep 18, 2012, 03:52 AM
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steve are u going electric with this build?
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Old Sep 18, 2012, 05:03 AM
Kiwi in Australia
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Australia, NSW, Carlingford
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Yep - looking at around 600W for the power system - 2x 4 cell batts I think pushing a 11-13 inch prop.
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Old Sep 21, 2012, 04:15 PM
Joe_Crash
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United States, MD, Gaithersburg
Joined Oct 2010
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Wire cuttting

Thanks for including that video of you cutting your wing cores. Just wondering how many amps you're putting through the wire - the kerf seems a lot bigger than the few foam cuts I've been doing. What type of wire too?
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Old Sep 21, 2012, 04:30 PM
Joe_Crash
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Really nice thread! Lot's of info on bagging wings - about how much would it cost in hardware (times a whole lot bigger I'd bet!) to get started bagging wings like you're doing? What kind of vacuum pump are you using, and at what psi? (is it psi with a vacuum?)
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Old Sep 21, 2012, 08:39 PM
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Quote:
Originally Posted by joe_crash View Post
Thanks for including that video of you cutting your wing cores. Just wondering how many amps you're putting through the wire - the kerf seems a lot bigger than the few foam cuts I've been doing. What type of wire too?
Quote:
Originally Posted by joe_crash View Post
Really nice thread! Lot's of info on bagging wings - about how much would it cost in hardware (times a whole lot bigger I'd bet!) to get started bagging wings like you're doing? What kind of vacuum pump are you using, and at what psi? (is it psi with a vacuum?)
hey joe when i use 15v my power supply limits is 5amps when i use slightly higher voltage 16-18volts it lowers my amps i use a simple laptop power supply and 40lb fishing wire trace also for the vacuum bagging u can use a fridge compressor pump i bought a new one for $50 just to vacuum bag
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Old Sep 23, 2012, 06:09 AM
Kiwi in Australia
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Australia, NSW, Carlingford
Joined Mar 2012
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Thanks Joe - the bagging gear is not too expensive but a little niche in terms of where to find it. I get most of my bagging stuff from the states but the glass, epoxy and foam I get locally. The expensive bits are generally the foam and epoxy. Like Gazza said, the pump is pretty inexpensive. It doesn't need to pull much, in fact too much pull can cause damage to your cores.
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Old Sep 23, 2012, 06:17 AM
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Australia, NSW, Carlingford
Joined Mar 2012
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Got a fair amount done this weekend but unfortunately my attention span is similar to that of a goldfish and I got distracted by some older cores that I had lying around. I had cut some out for a motor glider based on a slightly modified Drela airfoil and decided that I should do something with it... More on that in a little bit.

First - on the Kahu:

Added a single layer of uni-directional glass to stiffen the winglets. Again as these are flying winglets I can expect some torsional forces at the root (in toward the centre of the wing) so it's fairly important to make sure they don't shift or break off. The glass was applied on the inside and outside then covered with peel ply so that I don't make myself too much work when it comes to finishing.





The other thing I did was cut out the notch (loosely used term, it's more of a big wedge) from the centre and trailing edge. My reason for doing this is that the motor is not terribly light and I don't want to be adding too much ballast in the nose. Ideally the two 3300 4S batts should do the trick but I don't know till I've mocked up the install... I also need to order the parts.



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Old Sep 23, 2012, 06:22 AM
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Australia, NSW, Carlingford
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Second - just briefly. The idea behind this wing is for it to be a discus launched wing which I think are not that common. It has a span of 1490mm and has carbon spars top and bottom with carbon bi-directional on the wingtips - it ain't pretty but she's strong and fairly light. If the DLG idea doesn't work I'll go for High Launch.



All up I'm roughly expecting the flying weight to be around 650g or 23oz which should give me a wing loading of 7.485 oz/sq ft. To put that in perspective an AXN Floater has a wing loading of around 8.6 oz/sq ft and they float around quite nicely. It does leave to be seen though if it will actually have any real pitch stability!



I really need to finish one of these planes... I've told myself that I'm not allowed to start any more until I finish one first!!!
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Old Oct 08, 2012, 06:32 AM
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Australia, NSW, Carlingford
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My weekend ended on a Monday night - turns out it's brilliant for getting work done!

Since I have basically been pandering to my rather flighty (sorry) need to engage in building whatever comes to mind, and subsequent need to reign myself in, I thought that an extra day of building would do me some good, and good it did!

First on the books was getting Kahu a good coating of micro to smooth out her top surface. It's a laborious task but the ends results are worth it and it only adds a small amount of weight. Having said that I've started getting a little concerned about her potential AUW and decided that only the top will be getting this love... so far...

Micro on:


After the micro goes on, it's the usual story of biffing the plane in the tent to cure quickly although this time I used the fast epoxy hardener so it went off in 2-3 hours which is all good.

Once out of the tent I gave it a quick going over with the sander and then hit it with some black rattle can paint to provide a good high and low point indicator for the initial finishing sanding.

After working up a pretty good sweat we've got what is really not too bad a finish.




I had hurled a bit more on the leading edge and used some more micro to fill in some bubbles that had formed on the surface during curing.
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Old Oct 08, 2012, 06:33 AM
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I shifted over to the DLG flying wing I had dreamed up a couple of weekends ago and after doing some CG calculations decided that I had no choice but to add a pod to it. The other option is to load up the leading edge with lead but that kind of negates the purpose of a glider...

I grabbed a likely bit of scrap and marked out a shape based on what I kind of had in my minds eye. The initial design had a square taper at the back which I wasn't too happy with.


I planned to use the 'lost foam' technique to build this which is why it's covered in packing tape.


After deciding that the square end was both ugly and very poor from a aerodynamic perspective, I peeled all the tape off and worked a nice taper into it. Colour me happy!


I cut out some bi-directional glass from scraps to go around the mould and laid them out within easy application reach.


Turns out that laying out glass on something that small is a proper pain the in proverbial especially around the ends where it tapers in. The glass I used was pretty heavy weight because I wanted it to be pretty sturdy when I accidentally dart the poor thing into the ground, but heavy glass doesn't like tight curves. Still after much swearing and glass manhandling I managed to get the little sucker into a vacuum bag! My hope was that the bag would make up for all my layup inadequacies.


In the interim I attacked the tail. I had done a flat glass layup the night before and it turned out quite nice but seemed a bit too flexible for my liking. I turfed it in the oven to heat treat it, commonly known as a post cure, and it takes a little of the elasticity out of the layup. It still wasn't enough so I had some carbon fibre strands lying around (this stuff isn't cheap so I even hold onto the individual strand groups that pull out sometimes!) and used that to provide some added stiffness.

I cut the tail out and then cut a slot into it for the CF rod to go into leaving a little guide 'flange' at the back and then just used some two part 5 min epoxy to glue it on. After that had set I grabbed the CF strands and some very lightweight glass and used some quick curing epoxy to stick it on. I was going to leave it at that but it kept lifting off the CF rod (grrrr). Enter panic mode and chucking the tail into the bag with the pod (yeah not a great idea to open the bag halfway through the cure but I had little choice).

END RESULT! Yay! Not bad at all!
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Old Oct 08, 2012, 06:34 AM
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Having used the DLG flying wing as an excuse to procrastinate (albeit a productive procrastination) I got back to Kahu and drew up a motor mount.


Drilled the holes cut it out and bent it with a vice and a soft mallet... success! But I forgot to take a photo... woops... yeah got distracted again...

The pod came out really nice! I cut out a rough shape for where the fuse would sit over the wing saddle.


Now this is the fun bit - where you 'lose' the foam. I used a generic paint thinner and it seemed to do the trick. Woo melting!


Halfway there and I've freed up some of the packing tape lining.


And it's all out! Yeah I know what it looks like... yes my mind is in the gutter...


Chucked a little bit of micro in the nose both as added ballast and also to strengthen the nose. I also used a little to smooth out the surface a bit.


And it fits!


Next is the tail boom hole... I hate cutting into these things. It gives me the willies but it had to be done. This is my rather elaborate way of making sure I get the hole straight...


And finally all sitting together! You'll notice that the nose is a little dirty. I couldn't resist taking it outside for a glide test so I put what electronics I was expecting to have in the pod plus some washers and of course the first thing it did was a lawn dart impression. DOH! Extract the washers... ah success! It had a rather nice drifty glide, happy days. However this is without the servos and elevons cut in so the washers may well have to go back in. Still the AUW at this stage is looking at around 680g which is still pretty good and still within thermalling wing loading.
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Old Oct 08, 2012, 06:34 AM
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Australia, NSW, Carlingford
Joined Mar 2012
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Since I had the 'hacking into things' bug I took to Kahu. This was going to be a puzzler because with wings like the Zephyr II the foam cores have no real structural requirement, that all comes from the glass fiber and carbon spars that you glue in. The skin on Kahu does the same job, the down side of this is that if you hack a whole bunch of big holes in it you are steadily reducing it's structural rigidity. This is bad...

Ah well - to it! First Battery bay (you can see my nice motor mount in the background there)




Second battery bay




Motor mount slot


Electronics bay and the battery harness inserted. I forgot to take a photo of the harness but it's nothing to write home about. It took such a rottenly long time to shove the thing in that I didn't want to pull it back out again. I ended up tunneling all through the foam to run the wires. I still need to consider cooling for the ESC as well... having said that I won't be pulling the full 70A that it's capable of so I'm not expecting it to get too hot.


And finally cutting an elevon




I've bought the wing home with me so I can keep working on it over this week. I really want to be getting onto the flight test stage and I'm not going to be able to get to the hangars over next weekend so it's going to be a little while. On the positive side I should be able to get the elevons and wiring all finished. She should be flight worthy the next time I'm out there.
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Old Oct 08, 2012, 07:26 AM
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hey steve i like your pod what weight cloth did u use and how many layers?

also do u have zero degree on your motor mount?

top job
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Old Oct 08, 2012, 07:02 PM
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Australia, NSW, Carlingford
Joined Mar 2012
245 Posts
Hey Gazz, it's pretty heafty actually. I think it's something like 8oz bi-directional cloth laid out at 45 degrees and I've used two layers (but there is a fair amount of overlap with two 1.5 inch strips of unidirectional glass wrapped around the fuse at 2 points for 'hoop' strength. It's come out really solid. In terms of the motor mount, it's at a 90 degree angle at this stage but that might change depending on what the flight characteristics are like. I was really hoping to get the maiden in this weekend just gone but I ran out of time. The electronics bays ended up taking a really large amount of time.

Thanks for the comment Gazz, it's great to have someone actually pipe up every now and then I thought there might've been a little more interest but there you go.
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Old Oct 09, 2012, 12:38 AM
One Powerball
Australia
Joined Dec 2006
163 Posts
Lots of interest, but we are just silent and in awe watching this build... Totally awesome!

Brian
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