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Old Oct 14, 2012, 11:39 PM
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United States, AZ, Camp Verde
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Originally Posted by Scott Morgan View Post
It shouldn't take any weight to balance at all. I think you are the first person to mention this. You might want to check where your measuring your cg from again. It should balance with a 4 cell 2200 somewhere close to the center of the battery tray, or slightly foward of that with no extra weight needed at all.
That is exactly where my 2200 4 cell sits, in the middle.

Terry
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Old Oct 15, 2012, 09:32 AM
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United States, IL, Champaign
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When picking it up at 75mm back from the leading edge of the upper wing, without that added weight the tail hangs low and with it the horizontal stab is horizontal. I'll have the guys at the field second check the CG for me. I'll check it tonight at the LED channels.
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Old Oct 15, 2012, 04:03 PM
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Clarksville, MD
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Originally Posted by jwellsy View Post
When picking it up at 75mm back from the leading edge of the upper wing, without that added weight the tail hangs low and with it the horizontal stab is horizontal. I'll have the guys at the field second check the CG for me. I'll check it tonight at the LED channels.
I think the Dynam recommended 75mm CG is way off the mark! If you do a goggle search on determining CG of biplanes, you can get some easy directions to follow. Some of the references are here on RCG.

Using the guidance provided in the various references, I think it is more like 90mm give or take a few mm behind the upper wing LE. That is where my plane balances with the battery in the center of the battery compartment and that is where I will start with the maiden flight.

The recommended 75mm behind the upper wing LE makes the airplane extremely nose heavy.

Ken
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Old Oct 15, 2012, 08:35 PM
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United States, NM, Espanola
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Originally Posted by jwellsy View Post
Another thing no one has talked about is how much weight it took to balance their Dynam Waco.

I used 4 oz of lead bound together and shoved as far forward in the battery compartment as possible, and a 4c 2650mah battery wedged and velcroed in behind that. The CG is ready for the maiden flight when the fall winds ever cooperate..
I'm using Turnigy 5s 4000mah batteries standing on their sides and pushed to the front all the way! Balances great there
Dan
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Old Oct 15, 2012, 08:36 PM
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Terry, Scott, Ken, Dan you guys are all over this CG flub up. I appreciate the help. I found a good article on finding a biplane CG at http://www.modelairplanenews.com/blog/2011/04/12/balancing-biplanes/

Using their Center of lift method I came up with 100mm as the Center of lift.

Using their Mean Aerodynamic Chord method I came up with CG range of 76-100mm.

The LED channel runs 77mm from the LE until about 6" from the fuse, then it angles back to 120mm where it exits the wing.

So given all this, the 75mm in the book is wrong.

I've got to go pull some weights out and see where I'm at.
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Old Oct 15, 2012, 08:37 PM
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Originally Posted by krazyman View Post
You had better remove the lead. The battery doesn't need to be all the way forward. I balance mine just in front of the slots for the led wires for the wing tips. If you put all that lead in there you will be very nose heavy, I speak from experiance.

Terry
I really don't think any two of these planes balances at the same point!
I have two flying buddies who also have this bird and not one of our's is the same... go figure
Dan
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Old Oct 15, 2012, 08:48 PM
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Originally Posted by poziovahim View Post
I really don't think any two of these planes balances at the same point!
I have two flying buddies who also have this bird and not one of our's is the same... go figure
Dan
I think that the next time I fly this plane I will move the battery back to the rear of the battery compartment and see how well it flys. Right now I have it in the middle of the compartment and have to give it a little up elev to make it fly level at 50 to 60% throttle.

Terry
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Old Oct 15, 2012, 09:44 PM
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I removed all lead weight and with the battery installed it balances at 97mm from the top wing LE. The best way to describe this location is that it is even with the back edge of the front windshield.

My 2650mah battery only fits in the front half of the bay without cutting any foam. It doesn't seem to make much difference weather the battery is as forward as possible or as far back as the cutout in the cover allows. It balances nicely with one finger above the rear edge of the front windshield.

I think I'm in the right ballpark now, thanks to you guys. I ordered this plane from killerplanes.com and had them instal their max crashproofing kit in it which is like 43 additional carbon fiber rods in strategic places. So mine probably will balance a bit differently than every one elses.
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Old Oct 15, 2012, 11:31 PM
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Originally Posted by jwellsy View Post
I removed all lead weight and with the battery installed it balances at 97mm from the top wing LE. ...
I think that's a good starting point. I used the Mean Aerodynamic Cord (MAC) method for my estimate and came up with a range of approximately 79mm to 104mm based on a MAC of about 12.5 inches. I got the 12.5 by adding the top cord of 8 inches to the exposed bottom wing cord of 5 inches but I reduced it by 10% to 4.5 inches to account for the fact that the bottom wing span (and area) is about 10% less than the top wing.

So the math gives: 12.5 x 2.54=31.75cm or 317.5mm MAC.

0.25 x MAC=79.4mm & 0.33 x MAC=104.8mm.

So the initial CG should be somewhere from 79.4mm to 104.8mm back from the top wing LE. I picked 90mm as a nice round number in that range.

Ken
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Old Oct 15, 2012, 11:33 PM
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Are you using any kind of hinge tape? I've got some 1" Gorilla tape that I'm tempted to use on my hinges.
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Old Oct 15, 2012, 11:45 PM
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Originally Posted by jwellsy View Post
Are you using any kind of hinge tape? I've got some 1" Gorilla tape that I'm tempted to use on my hinges.
I used the DuBro stuff which is actually 3M blenderm tape repackaged on all control surfaces.

http://www3.towerhobbies.com/cgi-bin...?&I=LXJGT1&P=7

Ken
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Old Oct 16, 2012, 12:14 AM
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Originally Posted by jwellsy View Post
Are you using any kind of hinge tape? I've got some 1" Gorilla tape that I'm tempted to use on my hinges.
Blenderm rocks! I use lots of it, so I order it from medical supply places online for a couple bucks a roll instead of paying $5-6 a roll for "Hinge Tape"

I order it here http://www.medicalsuppliesshop.com/p...each-roll.html

Norm
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Old Oct 16, 2012, 07:56 AM
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Originally Posted by Norm62 View Post
Blenderm rocks! I use lots of it, so I order it from medical supply places online for a couple bucks a roll instead of paying $5-6 a roll for "Hinge Tape"

I order it here http://www.medicalsuppliesshop.com/p...each-roll.html

Norm
Work at hospital so I get all the short roll I need!
I have seen some of the small foamy guys use foam tac for hinges and had a thought about using on Big Birds. I wonder if you spread thin layer on hinges after flexing to remove stiffness if it would work. Thought are to hold surface in one extreme direction while applying and wait for foam tac to dry, then do opposite side? Foam tac would fill the "cracks" from flexing and remain flexible same would hold true for canopy glue my other favorite foam glue.

Tim
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Old Oct 16, 2012, 08:42 AM
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Two questions has anyone had control surface failure at the hinges? I have looked at the hinges and they appear to very good, I have flown many hours with these types of hinges Parkzone Multiplex and have had no problems.
Has anyone flown at the 90mm CG?
Thanks
Ken Smith
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Old Oct 16, 2012, 12:52 PM
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Quote:
Originally Posted by Ken Smith View Post
Two questions has anyone had control surface failure at the hinges? I have looked at the hinges and they appear to very good, I have flown many hours with these types of hinges Parkzone Multiplex and have had no problems.
Has anyone flown at the 90mm CG?
Thanks
Ken Smith
Never had a failure.... I've just always used the blenderm for insurance since the foam hinges always "look" like they're breaking. I'm going to try 85-90mm CG this evening.
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