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Adding weights elegantly

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Old 07-30-2002, 08:01 AM
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rajul
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Default Adding weights elegantly

I have always had diifficulty in balancing my planes with lead weights. The real difficulty is not in the balancing act itself but in figuring how to attach the lead weights to the plane. Do I stick them on or do I cut a hole and drop them in and patch the covering, etc. I just would like to find out how you guys do this. Is there a good and convenient way to do this without damaging the aesthetics of the plane (and aerodynamics too) or it is more practical to just stick or screw them on ? Hope to get some thought and ideas from you folks out there..............
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Old 07-30-2002, 09:42 PM
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Default Adding weights elegantly

Nose heavy isnt as bad of a problem because you can add a heavy hub or put the weights behind the firewall. For the tail, it gets harder. Sometimes you can drop the weights down the fuse, untill it balances out, and then dribble some epoxy down there. What works really well is peeling up a seam of the covering so that you can seal it down again without a patch. You just do that, and cut a hold in the wood and drop your weights in.
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Old 07-30-2002, 09:52 PM
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Default Adding weights elegantly

Thanks Jack. I am facing a situation now with my avistar where I need to add weight to the tail, about 100g. The tail (below the horiz stab) is made of balsa block and it is not possible to drop any weight there. I can drop in weight fore of the balsa block but that will mean that I have to add more than 100g due to smaller distance from the cg. I thought of just screwing in lead weights into the balsa block (my 7g lead weights have screw holes) but that will kind of ruin the looks, but then again only if you look below the horiz stab. Another option is to drill several 3/8" holes across the black and insert cylindrical lead weights, but I have a concern of causing structural weakness to the tail. Any idea how to do this better ? Thx...........
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Old 07-31-2002, 05:02 AM
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Default Adding weights elegantly

Lead melts very easily, as you probably know. What about melting up enough lead to make the plane balance and then using it to replace a portion of the balsa block under the stab. Shape roughly with a knife, attach with epoxy and blend with sandpaper.

Lead sinkers for fishing work very well for this, and are quite cheap.

Have you tried moving other stuff around to make the plane balance without adding so much weight? 100g. is a lot of lead... There is nothing wrong with putting the battery in the rear, a 600mah pack weighs about 100g. and placed toward the back can go a long way in reducing the amount of "non-functional" ballast needed.
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Old 07-31-2002, 05:15 AM
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Default Adding weights elegantly

Hi digger, I'll probably need a 24-inch extension wire to move the batt to the rear. Do you think the wire resistance will cause a serious voltage drop to my receiver and servos ?............
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Old 07-31-2002, 07:50 AM
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Default Adding weights elegantly

The extension (heavy guage!) may not be a bad idea...
That balsa block at the tail can be drilled... Then you can get the lead in under it. (go to a gun store and get lead shot... pour in and dribble in the epoxy... )

Avistar normally turns out tailheavy. What engine are you using?
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Old 07-31-2002, 08:03 AM
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Default Adding weights elegantly

Hi FHH, I am using a OS46FX with CG at 3.25 inch. It would have been easier for me if it is nose heavy ! I don't think I assembled anything wrongly except that with the clamp-on type engine mount, I had to push the engine as far back as possible to get 1/2 inch between the spinner backplate and fuselage front. Will that be too much ? I definitely can't get any closer. I know that 1/4 inch is better but that's as near I can go..........
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Old 07-31-2002, 09:40 AM
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Default Adding weights elegantly

Are you using the stock muffler? If you are, then a MACS pipe might be a good way to lighten it up. It will give you more power too. Another way is to put a Tru-Turn prop hub on it. Get the aluminum one. It should be lighter, and it wont wear out like a spinner would. Plus it's all you need to remove when you change the prop. Just remove it, and the prop comes off. These two things wont completely fix your CG, but they will reduce the amount of weight you need to fix the CG. Also, I'd put your RX as far back as you can too, even if it is in the tail. Dont use any extensions on it except the aileron. That way it will reduce the length of the extension needed. If you have already mounted the switch then it wont matter, so just leave your RX where it is. If you havent mounted your switch, then you can move your RX, switch, charging jack, and battery to the back. If you do that, you might not even need an extension.
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Old 07-31-2002, 09:59 AM
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Default Adding weights elegantly

the spnner backplate being 1/2 inch forward of the cheek cowls... the engine's still further forward than any I've seen on the Avistar. The .46 FX is also heavier than the LA .40 that everyone else 've seen has used, and that's probably where the problem is.

If the CG is 3.25 inch back from the LE wth no ballast... fly it. Its not that far nose-heavy to be a problem, especially for training. The CG in the instructions is the aerobatic location. Up to 1 inch forward of that is acceptable for use as a trainer. Even if you are more advanced... getting used tothe pane with a forward CG, and mving it aft (slowly... 1/4 inch or less at a time) later won't be a bad idea.
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Old 07-31-2002, 04:39 PM
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Default Adding weights elegantly

Hi FHH, the recommended cg is 3.25". The actual cg position now (without ballast) is way way forward. Sorry for the miscommunication !

With the battery in the original batt compartment, I need to add 3.5 ounces to the tail. With the batt push rear into the fuse, I still need to add 1.5 ounces. Anyway, even if I add 3.5 ounces, will the additional wing loading cause any problems, given that I have a powerful .46 instead of a .40 ? Thx...............
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Old 07-31-2002, 07:42 PM
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Default Adding weights elegantly

The additional wing loading probably wont even be noticed, but a lighter airplane is always better. Your extra power will help the takeoff, but no matter how much power you have, a heavy airplane wont land or fly as well as a light one.
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Old 07-31-2002, 09:34 PM
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Default Adding weights elegantly

Adding lead less than half the fuel tank capacity is usually OK. (a simple guide to knowing when you have excess ballast) The Avistar has a 10 oz tank if I remember... (at least 8, maybe 12) So up to 5 oz ballast won't significantly harm its performance.

While every ounce you can reasonably save is a good thing... You don't need to worry too much, as long as you don't exceed the listed max weight on the box the plane came in. I tend to come out several ounces under the low weight listed... even after making modifications to improve strength. (because of many years of experience in how to save weight.)

You don't say how far off the CG is now that you've moved things back as much as is convenient... the plane will fly fine with the CG 2 1/2 inches from the LE, and might even be easier to handle as a trainer at that far forward a CG location.

Also... you are ballancing with the fuel tank empty... aren't you? Full fuel tank can move the CG forward over 1 inch. If you ballance with full tank... and get the CG to that 3.25 inch back from LE location... when its out of fuel, it will be uncontrollable.
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Old 08-01-2002, 03:57 AM
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Default Adding weights elegantly

Hi FHH, yes the cg was measured with empty tank, GP cg machine, no wind, and both my kids out of sight !! My two little boys can really cause quite a bit of "turbulence" with them whizzing around !! I am still cracking my head as to how to secure the batt in the fuselage in a way that allows me to remove it easily. The batt needs to go pass two plywood formers and I need to find a clever way to position the batt with some foam around it and properly secured in position. Phew !...
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Old 08-01-2002, 08:39 AM
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Default Adding weights elegantly

Well, how much are you going to remove the battery? Just glue the foam to the plane, and zip tie the battery to the foam. Or velcro works wel.
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Old 08-01-2002, 09:32 AM
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Default Adding weights elegantly

Got 2 convenient places to put in mini cup hooks? Then you could strap it down with a rubber band. Slick trick I learned from a used plane I bought. When doing this... you rubber band a foam wrap on the battery, then strap it in. Works for the RX too.
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Old 08-01-2002, 09:58 AM
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hmmmm................sounds viable. I'll look into this one. Thanks...
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