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Old Dec 09, 2014, 04:13 PM
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7car7's Avatar
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Best plane design to tow behind another plane for video.

I'm interested in making a depron plane to tow behind my other planes. This towed plane needs to be very light, and very simple. I want to mount a key chain camera on the towed plane.

I'd like to hear some thoughts on plane design for this job.

My thoughts so far include these -
Lots of dihedral
Maybe a canard
VERY light and small as possible

I'm just concerned mostly that it will want to pitch up or down at take-off, and try to bring down the front plane, so, that's where my thoughts of small and light as possible come from of course.

I think I saw a vid once where the tow plane was shaped like the stereotypical paper airplane delta.

Thoughts?

(oh, and if my searching missed a good thread on this, please let me know of it.)
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Old Dec 09, 2014, 05:32 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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I would suggest that you don't want a plane like object. Instead you want more of a weight stabilized drogue like thing to mount your camera onto. Any sort of airplane like towed craft will buck and flit all over the place. But a stable drogue will just sit back there and let itself be towed around with very little reaction to changes in the airflow direction.

You'll want SOME lift so that it doesn't hang too far below the airplane's flight path. But really you're after more of a kite like deal with a towing bridle and a hanging harness with a stabilizing weight on the end. It should be pretty small so that the airplane doesn't get pulled around by the kite. Besides you only need something the size of a half sheet of printer paper to give the sort of lift needed to hold up a keychain camera.

In fact half way through writing this I did a google for "camera drogue" and found this video along with others of the drogue in use.

Quick overview of my camera drogue (0 min 34 sec)


Note that he mounted the camera up in the middle of the tube then had to add ballast along the bottom. Instead of doing it that way I'd suggest that the camera be mounted down low to aid in establishing a stable setup with a little less ballast.
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Old Dec 09, 2014, 07:42 PM
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Maybe a small annular wing kite would work, once the tow hook is properly positioned? Something a bit like this paper plane:

Not a lot of control, but very stable and should not really wander about too much.
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Old Dec 09, 2014, 08:21 PM
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Zurich
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I can suggest a symmetrical cone with pointy-end forward, having an effective axle down its length [can be 2 stubs front & back] and a "U" or staple shaped wire free to swing with the camera on the bottom, or the camera on top with a longer weight hanging down.
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Old Dec 09, 2014, 10:10 PM
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The 'Wack, BC, Canada
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You mentioned a "folded paper dart" like airplane.

A tow drogue based on the dart like paper plane would likely not be bad at all. You'd still want the lifting and vertical keel/fin to be up high with the camera and likely a ballast weight for stability hung below the "dart". And I'd suggest that it be a little more span so it's a bit less dart like would be appropriate. Like a 60 degree leading edge sweep from the center line. Which would leave the two leading edges sitting at an included angle of 60 degrees. The keel/fin would not need to be quite as big.

For a key chain or similar size and weight camera it won't need to be big. An 8 inch wingspan with a 3 inch deep fin keel might even be too big. But it would be a good place to start. The camera should be down about 4 to5 inches below the structure on a wire pylon. The tow line would need some testing to get it right but I'm thinking that it should be located at some distance below the drogue. And possibly on a V bridle that locks the angle of attack in so it only lifts enough to sit at or slightly higher than your model. Some testing will be needed to get it to sit just right and tow well.
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Old Dec 09, 2014, 10:23 PM
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The paragliding community use a very simple device (http://www.wingmancam.com/Home.html ) or a derivative of it.

It is not as simple as it seems to be stable: it needs the right amount of drag, creates as little as possible lift in pitch and yaw, been well balanced (mechanically and aerodynamically) around its attachment point as well as as light as possible.

When all of it is achieved it gives the right damping for a stable video, the key for a good shot.

NOTE: it is critical to have a hollow tube, any fairing at the front will result in unwanted sinusoidal type undamped motion in pitch, yaw and, eventually, roll.
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Old Dec 10, 2014, 03:08 AM
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Basically ... a windsock.
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Old Dec 10, 2014, 12:59 PM
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Great thoughts here guys, I appreciate that. Not sure how soon I'll get on this, so, for now just collecting ideas. Maybe over Christmas break.

I also found that vid after I posted, and it didn't occur to me to use the word drogue until I saw that.

There are certainly no shortage of ideas out there once you use the right word for a search!

One idea I'm having at this point is this - whatever design I end up with, I am thinking about a vertical section at the nose that has several holes to adjust the tow line. It seems that many of the vids out there show the drogue to be quite a bit under the tow plane. Maybe with a bit of adjustment to the tow attachment point, we can get a bit of lift without having to rely too much on elevator adjustment.

Another idea I'm having is about the tow line itself. It seems some out there are much heavier than need be. I'd bet a nice nylon sewing thread would be plenty.
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Old Dec 10, 2014, 01:40 PM
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Zurich
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the more lift it gets and the more it starts to fly, the more problematic wiggle-waggle zig-zag .... which can then of course be solved with servos and stabilizing accelerometers ["AS3X"]
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Old Dec 10, 2014, 03:48 PM
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The 'Wack, BC, Canada
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Maybe the high strength "carpet" thread. But don't discount the snap that occurs when the line goes slack then tight all of a sudden. The G forces with even a seemingly gentle snap can be VERY high.

A fishing line swivel on one end of the tow line would be a grand idea. A lot of lines want to spin with changes in tension. And even if they don't it's nice if the line can unravel itself easily. I'd go for one of the slick ball bearing ones. They are pretty cheap from anyplace that sells fishing gear.

The multiple attachement points is pretty much a given so you can adjust things. Or if you are using a line bridle then some way of slipping the line snap so you can adjust the relative lengths does the same thing.
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