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Posted by Cats Eyes | Mar 23, 2007 @ 08:42 PM | 13,154 Views
Shot Getter Build thread

This will be my build log for my version of Real Ira's Shot Getter. I was waiting for Doug at Mountain Models to come out with his new AP ship, but it appears that project has been shelved. So I figured it was about time to get my feet wet and do a scratch build. I'm a slow builder, so this will probably take many months. Heck it's taken me about three weeks of fooling around on the computer to come up with the design in a CAD package.

First, a disclaimer. Read Ira's Shot Getter thread in its entirety first! Ira has decades more experience than I have in building and designing aircraft, the original design is his, and he has been steadily refining and improving the design over time based on real-world flying experience. I am making quite a few modifications from the original Getter design to suit my own requirements, building style, availability of materials and components, etc. etc. which may or may not be improvements over the original. If you wish to incorporate any of the changes I am making here, you do so at your own discretion and risk.

List of Materials

I am building this list as I go along, so obviously it is not comprehensive (yet).

[table 1 3 1]
2^Qty.|Item/Material|Size|Notes
2|White foam|2" x 12"x 32"|Foam wing blanks
1|White foam|2" x 24"x 2 1/8"|Foam for fuselage
2|Aircraft grade plywood|3/32" x 12" x 6"|Fuselage sides etc.
1|CF Rod|1/4" OD, 3/32" ID x 36"|...Continue Reading
Posted by Cats Eyes | Mar 05, 2007 @ 09:35 PM | 14,744 Views
OK, this is my new attempt at wing cutting, this time with a longitudinal cutter with about 36" of wire. This will allow a fully-formed airfoil wing, as opposed to the "chisel" wings that I tried previously.

The wing is for Real Ira's Shot Getter and I am building it as per his specifications and instructions. Well, for the most part anyway.

After some initial power supply problems, the wire bow is now working well. I found a massive old 120 VA Hammond transformer with a 50V secondary. I have a light dimmer in the primary circuit and the secondary feeds the wire (see figure 3). As per Ira's instructions, I crank up the dimmer until the wire glows red, back it off until it no longer glows, then back it off "just a hair" from there. That seems to work well.

The wire was salvaged from an old hair dryer that I picked up at a thrift store, see Figure 1. The pink thing is the housing for the motor and fan and the heating elements are on top of that. The pic shows about half of the wire removed (it was in two sections, presumably for "high" and "low" heat settings). I have only removed one section, which ended up being 115" long, enough for three wires.

Here's a tip. What I did was stick the tightly-wound coil on a screwdriver (shown at the left of Fig 1), put the screwdriver in a vise, then just pulled the wire off. That removed the tight coil and I ended up with the wire just loosely coiled (figure 2), which makes it much easier to work with and less likely to "kink".
Posted by Cats Eyes | Dec 09, 2006 @ 06:00 PM | 14,690 Views
This was a mount I had designed for my old Great Planes Spectra, which has been gathering dust for a few years. I decided to resurrect it, and stick on an AXI 2212/26 that I had floating around. I think it might be a little underpowered with this motor, so I wanted the mount to be bolt-on and easily removable.

I had designed the mount already in MS-Visio thinking I would cut it out on a scroll saw. However, just about this time a fellow modeller, Roman, announced he had a CNC router up and running and was looking for projects. It was the sheerest of coincidences that I had the mount designed, but had not yet started cutting wood. I converted the drawings to DXF and emailed them to Roman.

Long story shortened, he cut them out with his new CNC router and sent them to me through the mail. He has documented that part on his site at http://www.cncwings.com/Router.html. I was very impressed. The pieces are like the precision of laser-cut, without all the black stuff!

I finally got the mount glued together and installed it on the plane today. Here are some photos of the build and the results.

--...Continue Reading
Posted by Cats Eyes | Sep 14, 2006 @ 09:44 PM | 17,155 Views
After many long months, I have finally gotten past the "design" phase of this build -- all those pesky things where I have decided to deviate from the stock plane and go my own way. It should be a fairly straightforward build from now on in. This is the really fun part, watching it all come together, and I thought I'd share it with a blog.

A partial list of mods is:
  1. Camera mount. This is a protective mount surrounding the camera (Nikon Coolpix 5200) with a 1/4" layer of foam on all sides. The mount will pivot through about 160° under servo control, allowing a view from 10° below the horizon on the left side of the plane, through straight down to 10° below the horizon on the right. Hopefully.
  2. Landing gear. I began designing an alternative LG in a sort of half-assed way, but somehow managed to lose the supplied aluminum LG mount, so had no choice but to continue. The wheels are 3" Du-Bro "Lite", mounted on a 3/32" music wire "V" shape, which can pivot out the side of the plane. It is held in check by a spring, which should allow some "give" on a hard landing and avoid breaking anything. So goes the theory.
  3. Covering. All fiberglass. I have done this before with a non-AP Magpie and it works very well. When I'm done with the physical build, I'll paint the fuselage with artist-grade acrylic paint (gives a more opaque and even coat than the cheap stuff from Michaels or the dollar store) and cover with 0.75oz fiberglass. The
...Continue Reading
Posted by Cats Eyes | Feb 12, 2006 @ 11:08 PM | 16,983 Views
Here's an update with pics of the wing cutting operation and results.

As I noted in previous entries, the straightedges are 1/2" aluminum bar screwed to the foam with 1/2" wood screws. They have held during the cuts very well.

You can see the "ridging" in these pictures as a result of either wire too hot or moving too slowly or not evenly enough. At one point the wire was stopped by one of the screws, which I'd put in the wrong place, and "burned" a groove in the foam. None of this is a problem -- easy to fill. Since making these cuts, I've gotten a lot better at knowing how fast to move the wire. It seems to find a "natural" speed on its own just by keeping a steady pressure on it. I made the same cut on the other piece (which will become the wing tips), and it came out almost perfect.

There is a three-inch "hump" that I put in the middle of the panel that is thicker at the back than the rest of the panel. This is supposed to be a support for the elastics that hold the wing on the plane. I also have a 2 1/2" "hump" under the leading edge, which will attach to the piece that will sit in the wing saddle (which I have yet to design).

I had the 12 thousanths wire break on me -- twice. It wasn't where you'd expect it either, at the ends where it is held, at the contact points, where it slid over the straightedges or inside the foam while cutting. No, it was in the middle of the wire out in free air. I'm...Continue Reading
Posted by Cats Eyes | Feb 11, 2006 @ 10:30 PM | 17,204 Views
Design complete. I mean, nothing's ever complete until it's complete, but I've decided to just build the thing and see how it flies, then correct what doesn't work.

Over the last couple of days I've finished the centre section of the wing. I have no way of making long cuts with nice edges, so I cut it with a utility knife part way through and just "broke" it the rest of the way. Fortunately, I had an extra quarter-inch, so I made the edge "nice" by using the hot-wire to remove the last quarter-inch. While the foam is nominally 24 inches wide, it actually has a ridge that sticks out an extra half-inch that fits with a cut in the next panel (if you're using for it's original purpose, i.e. insulation). Since the TE of the wing fits in the extra notch, that means I actually have 24.5 inches to work with, hence the extra quarter-inch per panel.

To make the straightedges for the cuts, I drilled holes every 6" in some 1/2" aluminum bar I had floating around. The thickness is something odd, but roughly 3/32" for rough figuring. I then just screwed them to the foam with 1/2" wood screws. Made small holes in the foam, of course, but I can fill them with Micro-Fill later. I've filled in much worse!

The first couple of cuts didn't go awfully well for some reason. I mean they worked, and are OK, but are kind of "ridged". I was not able to keep the wire moving smoothly for some reason. I've gotten better with subsequent cuts. At...Continue Reading
Posted by Cats Eyes | Feb 06, 2006 @ 10:11 PM | 17,731 Views
Scratch the SS#3 idea. Too much work. The Slow Stick is a nice plane as it is, without too much modification. If you're going to go to the trouble of re-engineering it, might as well go with a whole different plane. I'm still thinking of that twin-boom pusher idea...

I am also re-thinking this idea of increasing the wing area that much. The current design is over 40% larger. I've modified it now to be only 15% to 20% (depending on how you measure it) more area. I shouldn't then have to modify the tail feathers, except perhaps to increase the throws. So the wing will just sort of replace the stock wing but not improve on it much except to make it portable. I don't have major complaints about the stock wing.

Over on the Pink AP1 thread, CrazyHerb suggested going with a thinner foam -- 1" or even ¾". In the interest of getting on with it, I'll keep this in mind for future projects, but keep with the 1½" stuff for now.

I got some 1/8" plywood for the joiners at the LHS today. Also picked up a Sombra Labs Shadow 7 receiver (was surprised that they're keeping them in stock now). Made in Canada, eh?

Onward and upward.
Posted by Cats Eyes | Feb 05, 2006 @ 08:38 PM | 18,359 Views
I got some great feedback from Dark Overlord on my Slow Stick replacement wing thread. I have made a number of decisions now.
  • The joins will be made with 1/8" ply screwed together with nylon bolts as per Dark Overlord's thread Wing build for SSV2 Dedicated AP aircraft.
  • I've modified the wing profile a bit. Joe was of the opinion that the "winglets" would produce a smaller force than a polyhedral wing. For some reason I thought the force would be proportional to the height above centre and independent of actual area. Come to think of it, I've never seen a wing with that profile, so there must be a reason. So, the current design has 25% of the wing area for each "winglet" (50% total) and 50% on the centre flat section. The angle of the winglets is now 15°, down from 30°.
I was at Home Depot today and picked up a 2' x 8' sheet of 1½" pink foam. I also found that they have a good selection of nylon screws & nuts, which kind of surprised me as I have head a hard time finding them up till now. I got the 1/4" X 20 Nylon bolts and nuts for the wing joiners. I'll pick up the 1/8" ply at the LHS tomorrow.

Another bit of advice I got was that the increased wing area might require lengthening the fuselage and/or increasing the area of the tail feathers. So my current plan is to "retire" my old Slow Stick (SS#1) and use the parts to build a new bird with longer fuse and larger tail feathers (SS#3). SS#2 will remain my "workhorse" AP ship while the new one gets built. For the tail feathers, I could use balsa if I feel like being old fashioned, but I'm itching to give Depron a try. I think there's a Canadian supplier here somewhere....
Posted by Cats Eyes | Feb 04, 2006 @ 01:58 PM | 18,386 Views
As you can see from the posting dates, the entries below were not entered on the date shown. Actually these were copied from another blog source and I thought I'd try this out to see if I like it better. I do, so I will be dropping the other blog.

I posted a question on the AP Forum on a new thread, Design for Slow Stick replacement wing. We'll see what responses I get...

The Slow Stick replacement wing design continues apace. The stock wing is around 500 in² and I'm thinking of bumping it up to about 700. I don't know yet if I need to increase the tail feather areas or increase the fuselage length. Please post any ideas you might have in this area on the replacement wing thread. I have an old Slow Stick (sp400, NiMH) that I can always reconfigure for the new wing (and upgrade the power system) if necessary.

I'm planning on hitting the local Home Depot tomorrow to pick up some foam. Below is the current state of the design...
Posted by Cats Eyes | Feb 04, 2006 @ 11:47 AM | 18,699 Views
Below are some photos of the completed hot-wire cutter.

It's currently in an old hacksaw frame. I made a little wooden joiner piece that insulates one end of the wire from the hacksaw frame, and allows the wire to be tightened by turning a bolt. The bolt turns in a nut which is inserted in a cut-out in the joiner. A screw in another part of the joiner holds the wire.

So far the tests were done by just putting alligator clips on each end of the wire, but I guess I should make something a bit more elegant...

Back to designing the Slow Stick wing...
Posted by Cats Eyes | Feb 04, 2006 @ 11:40 AM | 18,433 Views
Tonight I tested out the three wire sizes I got yesterday.
  1. The 20 thousandths -- the transformer (6.3V, 2A nominal) dropped to about 3V then recovered to about 4V. (As compared to 3V for the 25 thou. stuff.) Wire seemed hotter. Test cut went well, seemed to cut more easily than the 25 thou. Less "angel hair."
  2. The 12 thou. -- transformer dropped to about 4V then recovered to about 5V. Cut went well, a bit better than the 20 thou. Almost no "angel hair".
  3. The 9 thou. -- transformer dropped to about 6V then recovered to about 6.3V. Cut went well but more slowly. Almost no "angel hair."
From these tests, I would conclude that the 9 or 12 thou. work well with this transformer. I will probably stick to the 12 as it cuts a bit faster and I'm less likely to break it! The 20 thou. is a tad cool and draws down the transformer voltage a bit much for my liking.

The "quality" of the cut seemed to improve with each test. But I think maybe I'm just improving with practice!

I noted that the wire seemed to lengthen when the power is applied, i.e. went slack as it got hotter. I was glad of my little insulated spacer gadget that allows me to just do up a bolt to tighten it again.

Now, I just got to get that wing designed and go buy me some foam.
Posted by Cats Eyes | Feb 04, 2006 @ 11:36 AM | 18,575 Views
Roman had some suggestions about power supplies, and also gave me the name for the residue that's left behind when you're cutting wire is too cool: "Angel hair!"

Angel hair!!! ROFL. Yeah, I got lots of angel hair. But that don't make me no angel!

I stopped by Metro Music on Bank St. today to pick up some steel guitar strings. $0.90 apiece! Interestingly, they give the thickness on the packaging. I got some 9 thou., 12 thou. and 20 thou. That covers the range of what the guys suggested.

I am keeping the chopped (PWM) power supply idea in mind, but I hope I won't have to go to all that trouble. I'm hoping that I can select the right gauge of wire and match it with one of the transformers I have floating around. The current setup works fine. Even if there's lots of that "angel hair" it shouldn't affect the result adversely. If I can improve the cut, so much the better.

I'm not planning on doing full longitudinal cuts. I'm going to be starting with "Chisel" Airfoils as you can see shown in this post and described here.

The idea is to approximate an airfoil with line segments, cutting laterally the length of the wing. More drag than a perfect, smooth airfoil, but then drag has its advantages sometimes. Can hardly be more draggy than the stock Slow Stick wing, eh?

I'm putting together a little wire holder gadget tonight so I can tighten the wire by turning a bolt. It'll be mounted on an old hacksaw frame. Epoxy will have to set over night, so it'll be tomorrow before I can do some testing. I'll let you all know how it goes.
Posted by Cats Eyes | Feb 04, 2006 @ 11:32 AM | 18,755 Views
I posted a question on the OREO group about hot-wire foam cutting and got some responses back. DougB (webmaster at All Electric Flite) wrote back that he has used .020" stainless steel wire, which one can get from "a boat yard or ship chandlers." Not that such things are exactly ubiquitous in Ottawa.

RomanG, who has a CNC hot wire setup (see cncwings.com) and did a Clark-Y Slow Stick replacement wing for me, wrote back that he uses .009" stainless steel. He has used guitar strings in the past, but found them to be too short. He mentioned that Home Depot has both pink and white expanded polystyrene in thicknesses up to 2.0". I will have to give them a try this weekend.

I happened to see some steel wire at the Buck or Two at Billings Bridge today and picked it up. It's a tad heavier than I wanted. I don't have a good means of measuring it directly (of course the package didn't say), but using my flatbed scanner as a "microscope" it appears to be somewhere around .025 to .027".

I found an old 6.3V centre-tapped transformer and ran one half of the secondary (3.15V) through a 12" length of wire. I tried a test cut using the foam left over from Roman's wing. Seemed to work fine, but very slowly -- about 15 seconds per inch of cut (and I was only making about a 2" cut). Also it seemed to leave behind a bit of a residue which I hadn't seen on Roman's cuts. I concluded that it was a bit cool.

I tried a second cut at the...Continue Reading
Posted by Cats Eyes | Feb 04, 2006 @ 11:28 AM | 18,804 Views
After hearing about these things for years, I finally decided to jump into the foam cutting racket after hearing about a fairly easy way to do it. As described in the thread Pink AP1 - Designed around camera (Nikon3700) (on the Aerial Photography forum).

As noted, apparantly steel guitar strings work well in this application. I will also have to find a good local source for foam (white and pink)...