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help on balancing low wing planes

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Old 11-03-2012, 10:17 AM
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jetdeck
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Default help on balancing low wing planes

i have a 90 size glow f4 phantom, and 2 nitroplanes foam jets, one is a f4, the other is a f16, both are edf, my question is should i i balance them upside down or right side up?, and whats the difference? i have the measurement, are using a greatplanes cg balancer, i know about high wing balancing, i want to know why you have to balance a low wing plane upside down, if its on the stand upside down, and you want it a tad nose heavy, would the nose be pointing toward the cieling, or toward the floor? ive asked guys where i fly but really couldnt get a good answer, anybody help me
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Old 11-03-2012, 10:27 AM
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Default RE: help on balancing low wing planes

Upside down and the nose pointing towards the floor.
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Old 11-03-2012, 10:40 AM
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jetdeck
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Default RE: help on balancing low wing planes

hey greybeard , thanks 4 responce but why upside down? IF IT WERE RIGHT SIDE UP it would be showing tail heavy, that is my dilema why upside down
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Old 11-03-2012, 11:00 AM
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Default RE: help on balancing low wing planes

Why to balance it up side down? Because most of the weight needs to be below center. If it was above center and you slide the pane it will roll all the way over and fall off the machine. Kinda like: Have you ever played "don't spill the beans" game? It's the same principle.
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Old 11-03-2012, 01:50 PM
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Default RE: help on balancing low wing planes

Theoretically, both sides up should balance the same distance back. It's just easier to do when the CG is actually lower than the two points holding the plane.

What you're trying to discover is where the vertical plane (pun intended) of the CG cuts through the wing. The CG is in two different planes (at least), vertical and horizontal. Since we balance our planes horizontally, and are trying to find the vertical plane, how we do the task has an effect on how hard it can be, but still should show the same thing.

If the actual location of the CG is not on the horizontal plane of the wing (which is what our fingers or CG machine is working against), when it's above it, you'll have a real balancing act ahead of you. When it's below it, not so much.

A low wing airplane's CG is probably going to be above the wing. Turn the sucker over, and taa daa...........
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Old 11-03-2012, 01:56 PM
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Default RE: help on balancing low wing planes

BTW, if your model's wing is really high, or really low, it's a good idea to balance the plane as level as possible and find the CG. If you want to insure you've got more nose-heavy stability, then simply move the CG so your balancing act proves the CG is ahead of the one you're basing your effort on.

When the wing is really high or really low, "slightly nose down" could give you one heck of a safety margin. Truth is, you won't have any idea on any model unless you balance it level. Could be close, could be far. Why not slide the sucker around a couple seconds more and know exactly.
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Old 11-03-2012, 02:37 PM
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Default RE: help on balancing low wing planes

As stated turn a low wing plane upside down to balance as it's the center weight that will make it hard to balance on a typical balancer . On some planes once you have it balanced correctly upside down, turn it right side up and see what happens to it on the balancer ...probably won't be balanced any longer.
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Old 11-03-2012, 03:12 PM
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Default RE: help on balancing low wing planes

It should still balance , right? (although will be tipsy if off center)
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Old 11-03-2012, 04:49 PM
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Default RE: help on balancing low wing planes

Balancing a low wing right side up is kinda like pushing a rope....very hard to do and probably won't be good......
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Old 11-03-2012, 05:20 PM
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Default RE: help on balancing low wing planes

Some people drill a small hole on each side of the fuse at the balance point, you then glue in a piece of decent 1/8th ply inside where the hole is.. now redrill the holes. You take some piano wire bent like a letter L, stick one in each side and let the plane hang on the balance point,, works pretty good if you don't mind the small holes.. its also nice because you will be able to find the cg again without looking it up online later
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Old 11-03-2012, 06:45 PM
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Default RE: help on balancing low wing planes

Another trick is to find the dead centerline of the fore/aft of the plane, and the CG and put a hook there, then hang it from a string. You can then balance all axis at once.
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Old 11-03-2012, 06:45 PM
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Default RE: help on balancing low wing planes

G'day Mate,
As has been said, balance upside down, & don't think of it as the CG, or Centre of Gravity, It is the Balance Point, of the wing, & that is why you must balance low wing upside down,
& high wing right side up.
The actual Centre of Gravity is a point somewhere above or below the wing, depending on where the wing is, high or low.

Cheers.
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Old 11-03-2012, 08:56 PM
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Default RE: help on balancing low wing planes


Quote:
ORIGINAL: foodstick

Some people drill a small hole on each side of the fuse at the balance point, you then glue in a piece of decent 1/8th ply inside where the hole is.. now redrill the holes. You take some piano wire bent like a letter L, stick one in each side and let the plane hang on the balance point,, works pretty good if you don't mind the small holes.. its also nice because you will be able to find the cg again without looking it up online later
What a great idea!!! I have never heard or thought of it. I have balanced by hanging and using a plumb bob to locate the CG but this sounds too easy! I do have a number of small bubble levels I tape along the datum line over the CG to see how well the plane is balanced but this sounds easier then putting a plane on a CG machine. Thanks for the tip, I will give it a try. Nice to learn something new.
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Old 11-03-2012, 11:01 PM
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Default RE: help on balancing low wing planes

Isn't the whole idea of balancing a plane is to see if it handles well? Why all the fuss to determine exactly where the CG is? And once you go to all the trouble, now what? HOW DOES IT FLY? Get the CG close, go fly it, and decide then whether to move it forward or aft, regardless of where "exactly" it is.

Kurt
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Old 11-04-2012, 03:58 AM
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Default RE: help on balancing low wing planes

Hi Kurt , I would somewhat agree , however one of the main points of balancing is to be able to fly twice lol , a tail heavy plane may not make it back in one piece .
I have been on 737 commercial flight with tons of "road miles on them " the pilot knows exactly how they fly , and passengers are moved around on empty flight to make sure the plane flys at the optimum safe balance with the load that is on baord .
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Old 11-04-2012, 04:14 AM
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Default RE: help on balancing low wing planes


Quote:
ORIGINAL: LDM
I have been on 737 commercial flight with tons of ''road miles on them '' the pilot knows exactly how they fly , and passengers are moved around on empty flight to make sure the plane flys at the optimum safe balance with the load that is on baord .
You can bet the farm they aren't moving anything before rollback in order to be safe. Nowadays most every major airline uses a weights and balances program that assures a safe balance wherever the passengers move about the cabin. They may profess the desire to have an optimum balance, but the heavy loadings are positioned for absolute safety. Where the passengers are really can't make the balance unsafe.

There were computer weight and balance applications in use back in the 70s. They most assuredly considered the safety aspect of the task with absolutely adequate safety margins. The goal was the most flight efficient balance, but the aircraft are designed such that no matter where the passengers were for whatever reason the aircraft would be reliably safe.
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Old 11-04-2012, 07:09 AM
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Default RE: help on balancing low wing planes


Quote:
ORIGINAL: jetdeck

hey greybeard , thanks 4 responce but why upside down? IF IT WERE RIGHT SIDE UP it would be showing tail heavy, that is my dilema why upside down
Since you don't seem to have responded in this thread anymoe I hope you udnerstand that balancing upside down or right side up still has a nose heavy plane pointing DOWN to the floor and a tail heavy plane pointing UP. What happens if you do it right side up is that when the CG is above the fulcrum the plane will fall over and be next to impossible to find the actual balance point. This, by the way, also makes if very difficult to balance a mid-wing plane if the "horizontal plane" as someone used above is on the denterline of the wing. No matter which way you do it the fulcrum point is always below the horizontal plane because of wing thickness. I had fits with a Yak54 because of this.
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Old 11-04-2012, 08:10 AM
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Default RE: help on balancing low wing planes

Nice explanation rgburrill. My corvalis is that way. It must be right on the centerline because it's tricky either way you do it.

I still say that the "don't spill the beans" game is key to understanding this.

ps. If we were to add some weight very low below the balance point on a plane of this type it may make it easier to balance , it wouldn't "fall off" the machine. The extra weight would have to be well below center and exactly on the balance point, right?
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Old 11-04-2012, 08:29 AM
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Default RE: help on balancing low wing planes

You can balance any plane, low-wing, high-wing, or mid-wing, right side up or upside down, with a Vanessa rig. You can make one out of stuff you've probably got or can buy for $5. Do a search. Works great, no risk of dropping the plane, and if you get the urge to get a cup of coffee while you're in the middle of the job you can go get one and then come back. When you're done you can lift it up to the ceiling where it will be out of your way until you need it again.
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Old 11-04-2012, 08:54 AM
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Default RE: help on balancing low wing planes

The plans for the Vanessa rig are here on RCU if you do a search. I printed them out some time ago and still have them in my things to do pile. Another cool item. Worth the search.
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Old 11-04-2012, 10:54 AM
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Default RE: help on balancing low wing planes

to all my good friends here on this forum who have responded to my question on balancing a low wing plane, i would like to give my heart felt thanks to all of you, you have given me a wealth of information that i can apply to my hobby, i never expected such a great number of responces, you all are very knowledgable and talented people, thank you again my friends, if i need any further help with a question i will post it here. jetdeck
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Old 11-04-2012, 03:58 PM
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Default RE: help on balancing low wing planes

One last tip. To avoid any holes or dents in your wings, make a couple about 2 inch squares of 1/64 ply. I mark the cg range on it and draw a line usually a little past 1/2 way point and nearer the rear cg limit on the plans as that is where i like to start. Tape the ply squares to the wing with blue painters tape. Now use your balancer as above.

I usually write the planes name, the CG range and have a line on it marking what I used for the first flight. Just save in a drawer and you can always have the CG at your fingertips.

For heavier jets I used a trapeze method: 32 lbs Byron F-15.
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Old 11-04-2012, 07:28 PM
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Default RE: help on balancing low wing planes

This has worked for me without fail. My aeronautical engineer buddy uses this method. Just place a bubble level on the horizintal stab to check that the airplane is level. It can be used for high wing, low wing or biplanes. Make sure your hook is strong enough to hold the weight.

Bob
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Old 11-04-2012, 08:17 PM
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Default RE: help on balancing low wing planes

Does it really matter if the plane is level?

Kurt
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Old 11-04-2012, 08:39 PM
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Default RE: help on balancing low wing planes

Well it matters if you use a Great Planes C.G. Machine. They give you a bubble level with the product.

If it's not level, it is out of balance. That's the purpose of the whole process, to find the balance point. The moment arm on each side of the balance point must be equal. If it points up or down, it is not balanced.

Bob
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