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Nov 02, 2007, 08:06 PM the skies...
Cats Eyes's Avatar
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Build Log

"Cat's Eye 1" - Home-brew AP plane

OK, guys. Here we go. I've finally shaken off the jitters and started building a plane of my own design (sort of), the Cat's Eye 1. Since this is my first design, I'm being rather conservative and mostly re-using stuff I've used in the past and I know works well. This basically takes my "Long-Nose Getter" (a version of Real Ira's Shot Getter) and moves it forward. The Long-Nose Getter is a ROG vehicle and I wanted a hand-launch belly-lander for more flexibility on flying locations (if there isn't a handy runway around). Although much of the design follows from existing planes, I think it is sufficiently different that I feel justified in giving it my own name and claiming it's my own design. My appologies if the name is rather obvious, but I couldn't think of anything better.

For some background on what I'm trying to achieve, please visit my Cat's Eye 1 overview page. I also have some drawings available, and information on the Long-Nose Getter.

I will be describing most the features as I go along, but I'd like to just mention a few things to start.

First, as you can see from the side view below, the wing is situated much further back from the camera bay than on the Getter. The black "X" marks the location of the CG (centre of gravity). The pilot should thus be able to cradle the rear fuselage in his/her palm and launch it by pushing on the back of the fuselage on either side of the boom.

I will be starting with the tail feathers. Unlike the Getter, on the Cat's Eye the servos will be mounted directly to the assembly containing their control surfaces. I.e. the elevator servo will be mounted directly on the horizontal stab and the rudder servo will be mounted on the vertical stab. Both of these assemblies will be removable from the boom.

The "exploded" view below shows the boom, horizontal assembly (horizontal stabilizer and elevator), and vertical assembly (vertical stabilizer and rudder). Two 1/4" nylon screws will hold it all together and the only thing to attach will be the servo leads.

The servos selected are Hitec HS-65MG. These seem to have the right tradoffs between light weight, high enough torque, and not too great current demands. I will be using a ParkBEC, so the current demand shouldn't be an issue, but I've had trouble with some servos in the past. Mainly the concern here is low weight and moderate torque.

If you have any comments or questions, please feel free to post away. Any and all input is greatly appreciated.

-- Kevin
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Nov 02, 2007, 08:16 PM the skies...
Cats Eyes's Avatar
Thread OP

Tail feathers

I have completed as much of the tail feathers as I can without the actual servos, which are on order. The control surfaces are all 6mm (~1/4") Depron.

The horizontal stabilizer is a simple "slab". I have used a .057" x .177" Carbon Fiber bar at roughly the centre for stiffening. There are three holes "drilled" (i.e. a drill bit twirled by hand) through the centre. The two outer holes are for the mounting screws that hold it all together. The centre one has a short piece of dowel glued into it, to keep the Depron from being crushed when it's screwed together.

The plywood piece on the top of the horizontal stab will hold the elevator servo. Two short ply rails will be glued to it to hold the servo. I haven't glued these in as yet as it will be much easier to do once I have the actual servo.

As with the horizontal stabilizer, the vertical stab has a length of .057" x .177" CF glued in for stiffening. The rectangular hole at the bottom of the vert stab is where the rudder servo will go. At the bottom of the vert stab is a 3/32" ply piece with 1/4" holes 1" apart which will screw onto the horizontal assembly and the fuselage boom.

As I mentioned, the completion of the tail feather assemblies will have to wait until the servos arrive. In the mean time, I've started working on the fuselage, which I'll report on in a future post.

If you're interested, I have drawings here.
Nov 02, 2007, 08:40 PM
I fly low, I'm in high demand
birdman11787's Avatar
Nice ........ I have been following Ira's design as well. A good design always goes thru many iterations. Its interesting a good design can reach a point and then split off and run in different directions. Everytime I fly and take photos I drive home dreaming about the ultimate ap design. Ira's design work encompasses many things on my wish list. Your direction ...... to be able to hand launch and belly land is high on my list. I have gone to heavier landing gear and would love to lose that extra weight with a belly lander. Looking at what you have so far and wondering how to protect horizontal stab and boom, one idea might be to add an additional piece of shaped foam to the bottom (like a belly hanging down) and maybe a strip of packing tape on that to serve as a skid, that would elevate the fuselage up and add the needed height. It could be faired in nicely with the nose by extending that lower profile and carring it back past the camera before sweeping back up and meeting the boom some where before the aft plywood section. That way you would still be able to push there on launch.

Nov 02, 2007, 08:56 PM
Not THAT Ira
Real Ira's Avatar

That ROCKS!!!

As I mentioned at the get go I could hardly wait to see what other people came up with to improve the basic concept and what you have done is awesome!

The one $00.2 worth is to hand turn the prop so a blade is as close as it can get to the boom and then hand flex the boom to it's max to assure there is no way it can flex into the prop in rough air or if for some reason the prop is turning during a rough landing.
Probably needless advice. I'm sure you would have checked that.

What do you expect for an AUW?

Nov 03, 2007, 12:25 AM
Gwelan's Avatar
Cool design ! I especialy like the indentations in the liteply for the vertical shots.

I would like to know your method for transfering the 2D data into Sketchup. I always had a hard time with that part.

BTW, I'm thinking about something like that on my own:
- frontward looking camera situated at CG (very Beastlike)
- tiltable tubular pod made of soft materials like Noodleboard or EPP
- oversized rings on each side of the camera tube that act as a protector for the camera lens barrel and as weels on landing...
Last edited by Gwelan; Nov 03, 2007 at 12:41 AM.
Nov 03, 2007, 01:32 PM
I fly with my little eye
Swanlander's Avatar
Looking good Cats Eye Kev!

I hope you don't mind some constructive criticism:
Your CAD model suggests your tail might be prone to landing damage.

I also like the hand launch and belly land principle, as used on my


Note that the angle of my tail boom means that the horizontal tail never contacts the ground, even when the plane is at rest with a wingtip grounded.
This has worked well for me thus far (18 months and 1000s of pics!)
The other advantage is that the tail is located near the centre of the prop wash, which keeps pitch response positive when maneouvring at low airspeed with a bit of power on.

Good luck with the cats us the progress!


Nov 03, 2007, 08:23 PM the skies...
Cats Eyes's Avatar
Thread OP
Originally Posted by birdman11787
A good design always goes thru many iterations.
Yes, I expect there to be a Cat's Eye 2, 3, 4... Apart from the portability issue, that is one advantage I'm hoping to get from the "modular" approach. If a particular part is not working out I can re-design it and keep the rest of the plane as-is. Both you, Ira and Swanlander have mentioned that the horiz stab might need some protection -- if I find that to be the case I can perhaps replace the tail feathers with a V-tail as Ira has done. Your solution with the foam under the fuselage sounds like a great idea too.

Ira -- thanks for the tip re the prop clearance. I obviously checked the clearance in the CAD model, but neglected to think about the boom flexing. I will give it a try as you suggest. The motor mount is designed for adjustable downthrust and the least clearance occurs with no downthrust. With a few degrees of downthrust, which will probably be necessary, the prop will have even more clearance, so I think I should be OK.

Originally Posted by Gwelan
I would like to know your method for transfering the 2D data into Sketchup. I always had a hard time with that part.
Sorry, I don't understand the question. What 2D data were you referring to?

It is interesting to see how different people have different requirements. I think it is largly what you're used to. I have always mounted the camera facing sideways and now prefer it to a front-facing position. And most of my camera mounts have some kind of in-flight tilt adjustment and I find I miss it when I don't have it. Many people find it superfluous. To each his own.

Swanlander -- I am always looking for constructive criticism. That's why it's here and not on my web site, so I can get feedback. Thanks for your input.

I will report on the progress of the fuselage as soon as I grab some more pics, but in the mean time I am happy to report that I just saved 2 oz. I ordered a 3.3V regulator from Dimension Engineering and the Nikon Coolpix 7600 runs perfectly happily off that! That will save 2 oz worth of battery. Current drain is about 200mA (from the 3S LiPo) average/350mA peak, or about 600mA avg/1 amp peak to the camera (this is an efficient switching regulator, so a step-down in voltage means a step up in current). Now I just hope I don't have to put the batteries back in just to make the plane balance!

Thanks everyone for your input. More soon.

-- Kevin
Nov 03, 2007, 09:28 PM
Gwelan's Avatar
Originally Posted by Cats Eyes
Sorry, I don't understand the question. What 2D data were you referring to?
-- Kevin
I was wondering how your CAD drawings were transfered to Sketchup to make the 3d rendering of your plane.
Nov 04, 2007, 07:10 AM
Hogster's Avatar
Very impressive CAD work and what looks like the start of a very clean build! Subscribed

Nov 04, 2007, 08:28 AM
Hi Kevin,

Nice work on the cad and working things out before the build starts.

If the airfoil in cad is a good drawing of what you're using, I tend to think you might have a cg problem. If it truely works out that way it's easy to fix - nose ballast.

Notice the wing's upper surface curvature. The X appears to be just behind the thickest point of the airfoil. I believe that you want your X to be at or just slightly ahead of the thickest point of the airfoil.

To see how the X and thick-point relates, run an imaginary line straight up from the X to the under surface of the wing, then try to take that imaginary line out toward the tip kinda parallel to your black lines on the undersurface. And then go straight up to the upper surface. (all this because the view point is from near the trailing edge and the X-relative-to-thickpoint is distorted)

I'll be curious to see how it works out in flight.

Last edited by skymind; Nov 04, 2007 at 01:58 PM.
Nov 04, 2007, 10:09 AM
Professor of Wood
kd7ost's Avatar
It looks very well thought out Kevin. Nice work.

Nov 04, 2007, 08:49 PM the skies...
Cats Eyes's Avatar
Thread OP
Gwelan -- sorry, I'm not using Sketchup. I'm using Solidworks, which is native 3D. In other words, the design is done in 3D and the 2D drawings are derived from the 3D model. The "rendering" is just the native view in the software (downsampled by Irfanview to save some space).

Tom -- Thanks for the heads-up. The CG is supposed to be the same relative to the wing (i.e. the same percentage back from the LE) as my Long-Nose getter, since I'm using the same airfoil (Clark Y). However, maybe I slipped up somewhere. I will double-check it all again. Note the airfoil in the CAD model is just an approximation, a spline fit through a small subset of the points that define the foil, so I can't vouch for it being all that accurate.

Thanks guys for your kind words and encouragement.

-- Kevin
Nov 04, 2007, 08:56 PM the skies...
Cats Eyes's Avatar
Thread OP


OK, here we go with the fuselage.

I was going to make the sides from a single piece of 3/32" plywood, but ran into a snag. For some reason my LHS only stocks 6 x 12" sheets. I also wanted to try and leave pieces left over that were approximately square so as to be able to use them for other parts, so I came up with the idea of making the sides from two pieces, a "U"-shaped pieces at the front that would go around the camera bay, and a straight piece that sticks out the back and forms the rest of the wing saddle. I made the brace from the back of this piece to the lower end of the rear of the fuselage out of 1/8" CF rod. This has used up much less material and left more useful-sized pieces left over (I'm so cheap!). I don't think it has sacrificed strength.

I also had the same kind of problem with the bottom piece, and so made this out of two pieces glued together as well. I have updated the list of drawings to include the fuselage and motor mount pieces.

The boom is 1/4" CF tube, which is inserted into 5/16" OD plastic tubing (you could use aluminum tube here as well), which is held down to the bottom piece by the vertical ply pieces and short aluminum hold-downs which are screwed to the bottom piece by 4-40 screws. They are also glued in to prevent rotation. The CF boom slides into the 5/16" plastic tubing and is held by a single screw at the front.
Nov 04, 2007, 11:17 PM
Not THAT Ira
Real Ira's Avatar

Sure didn't take you long to master the scroll saw.

This is going to be a very fun build to watch!

Nov 05, 2007, 09:25 AM
Here's something for all you stick-boom guys. At many local hobby shops in the park-flyer section, they've got a nice carbon square-boom part for a slow-stick-like plane. Don't know the name. It would seem to be superior in terms of construction and flight performance over the carbon rods. I've got me a couple for my next project. I comes with some other parts already mounted which you can remove.


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