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Old 07-01-2014, 11:00 AM
  #1  
gphil
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Got a Stick 60 it is called a Dragstick from Texas RC I am now in finishing stages and her is what i need answers to . ....... The manual says the balance point is 4 1/8 inches from the L.E. My plane will balance at 4 1/2 inches back. Might need just a touch of wt. to make it perfect. Now do I go ahead and put the balance point where advertised and add wt. to the nose or leave it alone. It has battery installed, tank. If I move the point fwd from mine it will be tail heavy and need wt. added. So there it is. With fuel no telling where it will go. Ok professionals go for it ,,,...... Check back later and thanks guys. My gut says it will be fine but my mind says make it like the manual says. gphil.
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Old 07-01-2014, 11:53 AM
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JohnBuckner
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OK I am going to be very straight forward especially since your airplane is so simple with a rectangular wing and no sweep. First lets start out with it is normal for our airplanes ready to be flown but with no fuel in the tanks. Yes of couse CG will move forward with a full tank but protocol is to always express where the cg range or point should be flown with the Tank Empty.

Now if the manual says to balance the airplane at 4 1/8th aft of the leading edge and your airplane actually balances (with no fuel) at 4 1/2 then absolutely do not fly it there if you can,t move anything the yes use the lead. Often the guys will put the battery at the fornt wing bulkhead. If not put it forward directly behind the engine firewall. Along side or above, below the tank. Tank to big? get a smaller one.

If you suspect the manual information. Its so simple with your airplane to just measure the distance from the leading edge to the trailing edge and divide this distance by four and that will be the distance back from the leading edge of the wing that is the very best point to make your first flight and the airplane will be a buttercup hand down. This is also know a 25% MAC or in some circles the Quarter Chord.

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Old 07-01-2014, 02:49 PM
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gphil
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Excellent John,,,, That was and is my thinking also. Just for some reason afraid of doing something incorrect with these guys. They obey the same rules as the biggies. I have misplaced the manual and
These figures came from a web search. I hope they are correct. I figure the plane is much like the others , Stick, the tail feathers are different but basically looks the same. I got the control throws from the web also and hope they are ballpark. If you know of them post please for like you I want spot on figures. Thanks for what you posted. I have never seen (1/8) for instance. gphil
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Old 07-01-2014, 07:28 PM
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52larry52
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gphil, JohnBuckner is spot on correct with his advice to balance @ 25% of the MAC. One other thing to keep in mind as you assemble/build ARF's and kits is that many,many times the printed C.G. spec in the instructions are incorrect. It happens for a variety of reasons but is not uncommon. Always calculate the C.G. yourself and then compare it to the what the instructions say. You will be surprised how often there is disagreement. Go with your calculated 25% of MAC.
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Old 07-01-2014, 08:56 PM
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speedracerntrixie
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While I agree that 25% MAC is a great place to start I will disagree that this is the optimum setting for most airplanes. If you find that the airplane required a fair amount of up trim and/ or lands on the fast side odds are you can safely move the CG back some. Contrary to popular belief a nose heavy airplane is not easier to fly then one that has the CG correctly adjusted. Of course a tail heavy airplane is just miserable and short lived.
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Old 07-02-2014, 05:54 PM
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52larry52
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Speedracer... is correct that the 25% MAC may not be the optimum C/G for all planes and all pilots, but it IS the right spot to start. The general rule of thumb is to balance a plane between 25% and 33% of MAC. In general, the closer to the 25% number the easier the plane will be for a less experienced pilot to fly, and the closer to the 33% number the more responsive the plane will become requiring a more experienced pilot. There is not a set % number for all planes and all pilots, you have to experiment moving the C/G between the 25-33% to find what is comfortable for you with a given aircraft. If you go past the 33% you are in "no mans land" and the plane may not be flyable by anyone. Been there and done that! Start @ 25% and move it back as you feel comfortable doing. Right in the middle @ 29% will still be a good flying Stick airplane but move it only after you have flown the plane awhile and know the plane.
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Old 07-02-2014, 07:42 PM
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I don't mean to muddy the waters here, but "more responsive" and "less responsive" with respect to CG isn't really the issue. Yes, going back does increase the sensitivity of your elevator. But you can also turn your elevator throws down as you go, keeping the responsiveness the same. Assuming that one is adjusting the control throws to keep the feel he wants, the difference as you go back with the CG becomes some more subtle things. First, the way the plane stalls changes. If you are gliding in with a nose heavy plane, you tend to get a smooth mush forward as it stalls. If you do that at altitude, the plane will pick up speed as the nose mushes and most sport models will self recover. As you go back though, the mush goes away and the plane starts to stall more suddenly. Beginners who use the elevator to control their descent on landing (the wrong way to do it) will find that a nose heavy plane bounces, but a tail heavy plane pancakes in from about 6 feet. The former embarrasses you; the latter costs you. Second, moving the CG rearward changes knife edge flight, vertical lines, and inverted flight. Generally, the closer you get back to the neutral point, the straighter your knife edges and verticals will become and the less down elevator you'll need to maintain inverted flight.
Overall though, unless you are setting up an aerobat, the "right" CG location is the one that gives you an obedient plane. You don't want the plane dropping its nose in a glide or snapping in weird ways. For most sport planes, the sweet spot will wind up being 27-28% assuming that everything else is right. So start at 25% for your first flight or two, and expect to move it back just a little at a time until the plane develops an obedient feel that makes you comfortable as the pilot.
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