Design & build of Pencam-class photo platform

Karl B²

I've been working on & off for the past 5 months on a design that will replace the Slowstick for me when operating out of all but the most cramped LZ's. Two months ago I reached CAD stage, and for the last two weeks the balsa scraps and glue have been flying.

WS: 48", just under 400 sq. in.
Airfoil: modified E-193
Power: geared 300-400 class
Control: R/E/T/Shutter
Payload: 3 oz max

CF tailboom, pull-pull controls inside boom, surfaces & fuse built-up balsa/ply, wing built-up balsa/ply w/CF tape spar doublers, quick-release wing (NO RUBBERBANDS! )

Ideas for larger next-gen: 6-8 oz payload for larger CCD/AF, pitch leveler for camera, left-down-right aim on aux. channel, flaperons.

Karl

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Karl B²

Tail items:

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Karl B²

last for now:

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RMihara

Hi Karl,

Very nice design there. I am wondering if you will be incorporating any dihedral in the main wing? The self leveling properties of such a design would be a plus. Of course if you wanted maximum lift then keeping the wing flat would be a better design no?

I like the angled rudder surface, has this helped in reducing the turning radius of the plane? I'm still learning the basics of plane design so please bear with my questions.

BTW, 0.02 on your self-leveling thought. You could attach the camera with a simple two-axis gimbal, that would not only give you pitch correction but roll as well.

Regards,
Roger

Karl B²

Hi Roger,

Thanks for the comments. Wing will have a constant chord 24" center section, with two 12" double-taper polyhedral tips. The taper and tip design on the tail uses a modified TLAR method called ILILT (I like it like that). The fuse including the boom will be over 40", with a tail moment arm of about 26".

Angling the rudder hinge line effectively adds a bit of up pitch, so that when holding a slow turn, the pitch angle (hopefully) won't need much adjustment.

I built up a gravity leveler (pendulum) test rig with a small RC car damper (shock minus spring, 1/2" stroke), and found that the pencam needed to be suspended about 4" to swing free with the damper working at about an 8:1 reduction using 10w silicone oil. Shorter length requires less damping, and 8:1 is about the geometrical limit with a simple extension strut.

A viscous suspension would certainly be simpler than struts, especially for a two axis stabilizer. At any rate, that would be for a larger craft, and using a commercially available optical wing leveler/copilot (FMA?) might be the simpler solution once weight is less critical.

Back to work,
Karl

RMihara

The wing sounds like a winner and I like your 'modified TLAR' method

Here is a drawing of the gimbal mount I mentioned. Given that the camera would be exposed to the elements (namely open air velocity - buffeting), I really like your approach using a damper based system. The single spring in this design could be modified (single-dual rate, coil dia., wire thicknes) to account for this effect but would not allow for self leveling as the spring rate increases...
I suppose I could increase the distance of the cameras moment of inertia away from the pivot point to account for any change in spring stiffness.

Back to (work) the drawing board.

Roger

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RMihara

Oops, your plane shows the camera mounted in 'portrait' orientation...

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Karl B²

I've GOT to get into 3D cad. I have DesignCAD 3D, not sure of the version, for Win 95. Just haven't installed it yet.

Yes, I'm using the Pencam SD, which takes landscape shots with the body horizontal. I'll be mounting it as shown in the attached pic. An electronic switch or remote servo-actuated switches would reduce the dimensions to be rotated.

I'll always need easy access to the USB port, SD memory cam, or batteries, and I went with the passively faired "notch" for simplicity. I may go with a thin sheet of ABS held with magnets to fully fair the cam.

Karl

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Karl B²

Fuse construction started with a crutch of 1/32 ply with balsa & ply boom mounts.

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Karl B²

Fuselage frame 95% complete. I have the upper portions sheeted with 1/32 balsa, and once I install the motor mount and LG hardpoints the rest of the sheeting will go quick.

Karl

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Karl B²

Sheeted..

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Karl B²

View of the wing saddle showing the battery platform. Also visible is the right thrust built into the front former. Wing will have either a dowel or tab in front to engage a hole or slot, rear will be retained with either a latch or internal rubber bands.

Running out of excuses to put off making the wing...

Karl

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Karl B²

First mockup:

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Karl B²

Another view:

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