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Old Nov 06, 2001, 01:32 PM
Crashez-vous sans stress!
Dan H.'s Avatar
Chicago
Joined Nov 2001
374 Posts
Tapping Zagi mod experience

I'm building minor mods into my Zagi 400. Any advice on the following would be appreciated:

1. I picked up a 1/4" CF (graphite?) shaft from a kite store for a spar. Install bottom or top of wing? Exactly on the 8" CG? Do not extend even a bit into the EPP leading edge? In the 400X directions, Jerry recommends Super77 to save weight, or epoxy to save time. I'd like to use a thin bead of silicone caulk to seal the channel after spraying the spar with 77. Too heavy/flexy? I could also use ProBond, the miracle glue.

2. I have ordered an 8-cell 800AR pack for the future. I assume the Zagi 14 ESC can handle the draw with that pack and a cobalt motor, but should I not even try running the stock can motor with that pack, lest all the smoke escape?

3. What's a good prop to run with the 800AR pack and a cobalt motor or Turbo 450 or Mag Mayhem, and a good source for props and prop nuts (I assume a pressure-fit Guenther is inadequate for high RPM/megawatt setups).

4. What's Ohm's law again, W=VxA? (Just kidding--what's a good R/C e-power primer covering current draw, load, RPM, prop pitch, heat, and matching components?)

Thanks for any help. This is a terrific forum.
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Last edited by Dan H.; Nov 06, 2001 at 03:22 PM.
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Old Nov 06, 2001, 03:54 PM
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UK
Joined Jan 2001
466 Posts
Okay then,

1) The spar should go on the 8 inch c.g. line so as not to interfere with balance. You shouldn't cut into the EPP foam, stop the spar just short of it. That would make the spar about 21" in length, I think.

Have you already stuck the wing cores together? If not, you could install the spar with no glue at all (like I did) - installing it with epoxy adds quite a lot of weight. See my post here for instructions on how to install it without glue. I've had no problems with this method, and I'm flying it on the T450 upgrade.

2) The Zagi 14 ESC will be marginal. The stock S400 motor draws ~14A with the stock prop on the 800AR pack, and anything else will most likely draw far more than 14A (the T450 draws 17-18A, for example). I would suggest buying a Jeti 350 ESC or similar (I know it sounds way overkill, but it's a great ESC, and you can always use it again in another plane).

3) The best prop by far on the T450 is the Aeronaut Carbon 6.5 x 4. I'm not sure about props for the MM or the cobalts. The Gunther will not physically fit anyway as the shafts for the larger motors are 3.17mm as opposed to the 2.3mm of the S400 shaft.

4) Actually Ohm's law is V=IR, although W=VA is another important rule. You should really check out the FAQ (link at top of the page) before anything else. It is a wealth of useful information.


Hope this helps,
Ben C
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Old Nov 06, 2001, 05:05 PM
Crashez-vous sans stress!
Dan H.'s Avatar
Chicago
Joined Nov 2001
374 Posts
Thanks for the reply Ben, and the spar tip. I have not joined the halves yet, so I will give your method serious consideration when planning for AUW considerations (ideally I'd like the wing to be flyable in the weaker 7-cell, Speed 400 stock configuration, but also strong enough to handle a T450 or MM and heavier packs).

My spar rod is an Avia hollow shaft--yours was solid. Any reason to think it wouldn't work as well?
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Old Nov 07, 2001, 01:08 PM
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UK
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I think that the Zagi 400x comes with a tube spar as opposed to a solid one, doesn't it? (I'm not sure because you can't buy the 'X' version over here, only the standard 400 version).

If so, it would suggest that a tube spar would be fine. Perhaps someone else could tell us the diameter of the 400 'X' spar?

Fianlly, how strong is your spar? You say that you got in a kite shop?


Good luck,
Ben C
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Old Nov 07, 2001, 03:16 PM
Crashez-vous sans stress!
Dan H.'s Avatar
Chicago
Joined Nov 2001
374 Posts
It's a pretty stiff tube; seems to be about 1/4" or 5/16" o.d, inner diameter is small (walls are fairly thick), about 30 " or 32" long (I'll be cutting it down), has "Avia Sport" stamped on it in gold ink.

I don't have any hard data on its stiffness/strength, but it "felt right" when I flexed it with moderate pressure to simulate what I estimated would be an average 2 or 3-G load on a 24 oz. Zagi. Only flexed a few degrees, but felt like it would give a little more, if it had to, before breaking.
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Old Nov 08, 2001, 08:35 AM
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staten island new york
Joined Sep 1999
829 Posts
As I think is the case, archery is popular in England wrapped or pultruded carbon arrow shafts can be used. In looking at my friend's 400x I think that's what they are. I've used both fiberglass (much cheaper) and carbon arrow shafts from Walmarts. The only advantage I see in using wrapped tubes for kites isthat some of them by Avia (?) ar large diameter and thin walled which makes them much stiffer for the weight.
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Old Nov 08, 2001, 09:42 AM
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Joined Mar 2001
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I’ve been using “Dave Brown Products” fiberglass pushrods for spars. They appear to be the same material as the stock 400x spar, side by side, I can’t tell the difference. The good thing is you should be able to find them in most local hobby shops and for around $8 you get 2- 36” x ¼”rods.
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Old Nov 08, 2001, 10:20 AM
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So Cal
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I have used both carbon arrow shafts and tubular Avia kite spars and for a given diameter, a good carbon arrow shaft is about half the weight of the latter.

Steve
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Old Nov 08, 2001, 03:28 PM
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Kings Park, New York, USA
Joined Sep 2001
813 Posts
Carbon fiber arrow shafts

Carbon Fiber arrow shafts work fine. They cost a bit though.

Want some for free?

Go to an archery range, prefer. indoors, many large sporting goods places have em, and garbage pick the broken ones. Usually only 1/2 inch or so is bad.

The guys hat em cause they have to bust em up to fit in trash. Ask and you may find a nice guy to save em for you.

Ron Parigoris
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