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Man are you fat!

Old 02-11-2007, 08:06 PM
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Kevlar
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Default Man are you fat!

OK, had to get your attention. I need to add some weight to the a** end of my GP RV-4, as the OS .61FX seems to be a bit much. How much weight is to much to add before it's start to comprise any possible flight characteristics.

I did a rough balance and it drops, not quickly, but it will need some in the tail....I haven't even put the tank/batteries/or receiver in yet. I know, I know, I can always move those behind the wing, but just wanted to know how much weight you've had to add to get your bird to balance.

Thanks much.

Wiqar
Old 02-11-2007, 08:24 PM
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obo
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Default RE: Man are you fat!

The best way is if you have a cg machine , is to put the plane on it then add weight as needed. Then you can adj it a little at a time ,but I would put the tank & battery in first.
Old 02-11-2007, 08:27 PM
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theradioflyer
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Default RE: Man are you fat!

Yeah thanks, I've already been told that I'm fat. Oh, BTW, Move your stuff as far back as possible. The more weight you add the worse your plane will fly. Lite planes fly the best and trim out better. Take a penny and drop it. Did you notice how fast it dropped? Now think of the wing area and speed it would take to keep that penny in the air and multiply that by how many pennies it takes to balance your plane. If you can, don't add any weight. I've put batteries in the tail of my planes before useing extentions.

Good-Luck and God Bless,

Jay
Old 02-12-2007, 02:49 PM
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DaveCFI
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Default RE: Man are you fat!

I am battling the CG and balance thing right now too. I just built a 4 Star 40 that is quite nose-heavy. I thought of moving the battery to the rear instead of adding weight. Can I use a servo extension lead on the battery so that it will reach? I have a JR 24" servo extension. Can I use that?

Thanks,
DaveCFI
Old 02-12-2007, 03:09 PM
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jaka
 
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Default RE: Man are you fat!

Hi!
Add as many extensitions you like(within reason).
Never ever think of adding weight to model airplane.
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Old 02-13-2007, 04:22 PM
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Default RE: Man are you fat!

on a long extension for the battery huse heavier gauge wire to prevent voltage drop.
Old 02-14-2007, 08:23 PM
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DaveCFI
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Default RE: Man are you fat!

OK...I stripped the covering off the turtle deck of my newly built 4* 40. I can recover that easily so I figured that would be the least intrusive way to get some weight shifted. The plane balances out almost perfect if I put the battery back as far as I can get it. Right behind the F5 fuselage former. The battery is wedged between the fuselage side and one of the nylon push-rod tubes. (The outer tube, not the push-rod itself.) There is no room to wrap the battery in foam like I was hoping to do. Will it be ok just like it is or should I figure out something else? This way I will not have to add any extra weight and it balances out to about 1/4 inch ahead of the main wing spar. (Recommendations are CG on the main spar.) This is my first kit build and I just don't know how I should handle this issue. With the battery up front I have to add about 4 ounces of weight to the tail. However, if I put the battery back there and need to get at it later I have to tear my plane up again to access it. I have included a picture so y'all can see for yourselves. Advice would be greatly appreciated!

DaveCFI
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Old 02-14-2007, 08:45 PM
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Live Wire
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Default RE: Man are you fat!

Dave
Do you have a pic of the front where you have your motor mounted. Some times you can move the motor closer to the fire wall or use a lighter motor mount to change the CG.
Old 02-14-2007, 08:55 PM
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DaveCFI
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Default RE: Man are you fat!

I am using a Hangar9 universal mount. There are 4 bolts that hold it on with metal plates to sandwich the ears on the motor. The ears are against the back bolts as far as they can go. As it is, the back of the spinner sits about 1/4" ahead of the fuselage "cheeks". The prop is about 9/16" ahead of the cheeks.

DaveCFI
Old 02-14-2007, 09:11 PM
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Live Wire
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Default RE: Man are you fat!

Sounds like you have the metal alum. mount and they are heavy the Sig or GP mounts are a lot lighter. You could remove part of the cheeks and drill the mount back further not using the hold down plates.
Putting the battery back in the tail might cause problems if you have to service it or have a rough landing[:@]
Old 02-15-2007, 06:57 AM
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Default RE: Man are you fat!


ORIGINAL: Kevlar

How much weight is too much to add before it's start to comprise any possible flight characteristics?
Regardless of how much weight you need to add, you will never compromise flight characteristics by properly balancing your plane. A heavy, balanced plane will fly better than a light, poorly balanced plane.


ORIGINAL: theradioflyer

The more weight you add the worse your plane will fly. Lite planes fly the best and trim out better.

Jay
Sorry Jay, but this simply isn't true.

Light planes need less engine power to fly, and light planes 3-D better, but light planes do not "Fly" better, and they are also much more subject to windy days.

Your analogy of the penny is a bad one. A penny is not aerodynamic.

Wad up a piece of paper the size of a baseball and throw it. How far did it go?

Now throw a baseball.

A baseball will fly faster, smoother, and it will go farther than a paper ball because it is heavier.

So a lot depends on what type of plane you are flying. An RV-4 shouldn't fly like a Piper Cub - it shouldn't fly like a 747 either, but adding any required weight is not a no-no.

Case-in-point, Last year I needed to add 22oz of lead to the nose of a GP Seawind to get it to balance. That's almost a pound and a half to a plane with a 676sq in wing.... It flew great!
Old 02-15-2007, 11:14 AM
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Default RE: Man are you fat!

I think I've made my decision. I will simply add the 4 ounces of weight to the tail. This will alleviate my battery decision and still balance the plane. This is a Four-Star 40 and I have a Super Tigre 45 in it. It will undoubtedly be plenty enough power for this plane and I would much rather have the flexibility of easy battery access. I have some self adhesive weights but I figured I would epoxy them in the plane so I don't have to trust the adhesive on weights themselves. Is this adviseable or is the adhesive sufficient by itself?

DaveCFI
Old 02-15-2007, 11:21 AM
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MinnFlyer
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Default RE: Man are you fat!

I find thos stick-on weights will work well if they are stuck to something like clean covering and away from grease. A tail is a good location for them, a firewall is not. As far as putting them internally, they would be stuck to ply or balsa - I wouldn't trust that - go with epoxy or screws
Old 02-17-2007, 11:02 PM
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Default RE: Man are you fat!

I'm having the same problem with being nose heavy. I really don't want to stick lead weights to the bottom of the stabilzer. What's a good way to conceal it?
Old 02-19-2007, 01:53 PM
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MinnFlyer
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Default RE: Man are you fat!

I usually just stick weights to the bottom of the fuse just forward of the tail wheel.

Another option is to cut a hole in the bottom of the fuse, Epoxy the weight in place, and then cover the hole with covering.

If you're feeling ambitious, you can make a hatch there for future access.
Old 02-19-2007, 02:00 PM
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Kevlar
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Default RE: Man are you fat!

Minn - How much wieght is to much to add? What's the most you've put in the tail to get it to balance?

ORIGINAL: MinnFlyer

I usually just stick weights to the bottom of the fuse just forward of the tail wheel.

Another option is to cut a hole in the bottom of the fuse, Epoxy the weight in place, and then cover the hole with covering.

If you're feeling ambitious, you can make a hatch there for future access.
Old 02-19-2007, 02:48 PM
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Default RE: Man are you fat!

Believe it or not, I have been playing with a delta wing plane lately that has over a half pound of lead in the tail and it's still nose-heavy.

But usually 2 or 3 oz will do the trick

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