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Adding weight

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Old 03-15-2006, 10:22 AM
  #1  
MK7
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Default Adding weight

Ok, I'm doing my first balancing job. I have to add weight to the nose, but it seems like an aweful lot of weight to add. It comes down to about 6 oz. which is not alot in reality, but seems to me to be alot in added weight. It is a KMP AT-6 Texan with a Evolution .061. Am I out to lunch or is this normal? Thanks
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Old 03-15-2006, 11:06 AM
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Default RE: Adding weight

It isn't huge, but adding any weight is a pain. Can you shift anything forward to reduce the unwanted addition?
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Old 03-15-2006, 11:30 AM
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Default RE: Adding weight

If you move things as Britbrat suggests, since it is an AT-6 possibly add a heavy prop nut to help out some.
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Old 03-15-2006, 02:47 PM
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SamD
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Default RE: Adding weight

6 oz is not a a lot? It's plenty in my book; heck, it's a decent size battery pack. Double check where your CG is then figure out if you can move existing weight within the airplane to mitigate the CG problem. It's an AT-6 so you're limited by the cowl how far forward the engine can go but if you can move the engine forward withing acceptable limits, move it- it's the biggest chunk of weight out front with the biggest moment arm (forward of the CG, that is) so small movements will have a greater effect than moving stuff that is more closely located to the CG. I'm not a Warbird expert- but minimizing the wing loading is a plus on a typical warbird with high wing loading.
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Old 03-15-2006, 02:58 PM
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Default RE: Adding weight

As others said, shift stuff forward if you can, but don't feel bad about adding 6oz to a Texan.

Hell, I just added 22oz to the Nose of a seaplane to make it balance.
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Old 03-15-2006, 04:19 PM
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Default RE: Adding weight

My KMP corsair came out way tail heavy. It is not uncommon to add nose weight, try moveing the battery in the cowl if possible! Or a bigger cell battery. I had to add almost 2 pounds to the nose of mine. hope this helps
Greg
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Old 03-15-2006, 05:23 PM
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Default RE: Adding weight

You might want to get a bigger book. 6 ozs in a 3 lb airplane is a lot, in a 10 lb model not a lot, and in a 25 lb model nothing at all, I have one that took 10 lbs to bring it to the proper cg but spread out over 2700 plus square inches it is not so bad.
And you are right holding the wing loading on a warbird is important but cg always trumps wing loading.
ORIGINAL: SamD

6 oz is not a a lot? It's plenty in my book; heck, it's a decent size battery pack. Double check where your CG is then figure out if you can move existing weight within the airplane to mitigate the CG problem. It's an AT-6 so you're limited by the cowl how far forward the engine can go but if you can move the engine forward withing acceptable limits, move it- it's the biggest chunk of weight out front with the biggest moment arm (forward of the CG, that is) so small movements will have a greater effect than moving stuff that is more closely located to the CG. I'm not a Warbird expert- but minimizing the wing loading is a plus on a typical warbird with high wing loading.
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Old 03-15-2006, 07:35 PM
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Default RE: Adding weight

Where possible, I put the throttle servo & battery under the cowl & shift the rudder & elev servos forward to use the vacated space left by the throttle servo.
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Old 03-15-2006, 11:15 PM
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Default RE: Adding weight

1st try shifting your battery and receiver as far forward as possible - also consider a larger battery. You may also want to investigate a larger (heavier) engine and heavier wheels. If you have to add weight [] , make it "useable weight" whenever possible.

In addition to Higley's Heavy Hub, DuBro sells "crankshaft" weights. They go under a spinner and are used in place of the washer under the prop nut. SIG also sells weights with holes drilled in the center of them - great for attaching to the motor mount. Just use a longer engine mounting bolt.
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Old 03-16-2006, 03:00 AM
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Default RE: Adding weight

Don't forget to see if there is anything you can reduce at the tail, i.e. lighter tail wheel, mount and axle, anywhere you might be able to add lightening holes (obviously recovering required in those places). It takes a lot less weight change way back on the tail to accomplish an equivalent c.g. shift done with a larger weight change on the nose. Every little bit helps.
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Old 03-16-2006, 03:10 PM
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SamD
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Default RE: Adding weight

The issue of added weight vs. overall weight isn't something that's lost on me; that's self evident- to me, anyway- it's a ratio, after all. That CG trumps wing loading isn't difficult to understand or accept either. What is difficult to accept is adding weight to an airframe if there are other ways to accomodate the CG requirements. Adding dead weight isn't something I'd choose to do if simply moving some existing components was a viable option to meet the CG requirements.

It's interesting to note people's reaction to adding weight to an airframe and the common feeling that "it isn't really that much weight". This approach is deceptive, seductive and, without a doubt, an easy trap to fall into. Pretty soon, 6 oz. turns into 10 oz, then it turns into 16 oz. and so on. Pretty soon, you have an airframe that's over its design weight, the wing loading creeps up and it doesn't perform in the fashion you might expect it to. I can feel the flames right now on my back regarding this issue of weight. There are a few people 'round these parts that seem to like heavy planes and feel they fly better. That's fine and I'm not going to argue about it- ya' gotta' run what you feel good about.

That said, it would be tough to find a commercial aircraft manufacturer that would like to add weight to their airframe design(s) unless it was absolutely necessary. Further, it's a rare Pattern/IMAC/TOC person you find loading bricks into their airplanes and commenting that "a little extra weight won't hurt".

Still, if strapping a brick on to the nose is the only way to get the CG where it needs to be, get to strappin'!

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Old 03-16-2006, 03:28 PM
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Default RE: Adding weight

You'll get no flame from me. Well said and so true. I'll exhaust all other alternatives before adding dead weight. There are times I do want a heavy plane for purposes of cutting through high gusty winds or high wind slope soaring for example. But even then, I would rather make the added weight useful weight rather than just dead weight. But most of the time lighter is better. Take a 10 lb plane and cut it to 9 lbs and you'll think you put a bigger engine on it not to mention how much better it flies. It's just common sense really.
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Old 03-16-2006, 03:41 PM
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Default RE: Adding weight

On a T-6, the c.g. is THE major thing to consider!
Move the receiver battery up into the cowl.. use a heavy prop, a heavy hub... if one exists for that plane..
And bevery careful on the elevator. It can't move much. These things snap-roll at every opportunity, so proceed cautiously with elevatot throw.
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Old 03-16-2006, 04:00 PM
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Default RE: Adding weight

But you also must understand that there is only so much you can do to lighten a plane! Then you make choices, Bigger motor Bigger battery, pack move all sevo's forward.. Try lightening up the push rod's go with carbon fiber. I done all the above and still added nose weight. But what else could I do?
Greg
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Old 03-16-2006, 05:02 PM
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Default RE: Adding weight

Hi!
SamD you are absolutely right, adding weight is no good .
You can do so much before adding something. You can take the Dremel drum sander and start sanding away most heavy structures in the fuselage...people doesn't seem to understand that most formers and other stuff is just not needed.
Use light foam wheels, light battery packs...why use heavy old fashion Nicad:s when there is lighter NiMh cells available, 950mA NiMh cells weight the same as old 250mAh Nicad pack. In a small model 300-400NiMh cells could be used and those weighs half of an old 250mah nicad pack.
Remove servos and place them as much forward you can, don't use standard servos 4-10g servos could be used as throttle serv and Hs 80-85 on elevator and aileron.
Use pull and pull fishing wires, thats the lightest possible stearing system...or 2mm carbon rods also good.
I never place any unnecessary weight in my airplanes, never! I rather rebuild the complete airplane than adding weight because I know from experience that adding weight is going to make the airplane a bad performer and going the easy route, adding weight is simply just ain't worth it...

Regards!
Jan K
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Old 03-16-2006, 06:46 PM
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Default RE: Adding weight

Minnflyer -

Hell, I just added 22oz to the Nose of a seaplane to make it balance.
Perchance a Northstar? I've taken to hollowing out the nose cone and pouring molten lead in there before final attachment. It's reduced the amount needed.
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Old 02-14-2010, 08:55 PM
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Default RE: Adding weight

You added 22oz to the nose of your plane? How did it handle? Im in the same situation with my KMP T-6. Wont balance @CG. Moved what I could as far forward as possible. Will have to add about the same amount of weight to my plane.
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Old 02-14-2010, 09:50 PM
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Default RE: Adding weight

There were a number of pattern planes that were designed to be heavy, I have one of the old designed Daddy rabbits that was designed to come out heavy just to compete in different wind conditions. Adding extra weight isn't the best idea but in most planes that had a rotary engine they are going to come out tail heavy every time. I have built Bipes that left no choice. Sometimes you just have to bite the bullet and grab the lead even after you have moved all your gear up front. You do what you gota do.
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