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Old Feb 03, 2013, 10:46 AM
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United States, CA, San Juan Capistrano
Joined Feb 2013
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Here it is with 10% Static Margin




5% Static Margin



So, anywhere from 3.14" to 3.41" from the LE... I should be flying control ably?
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Old Feb 03, 2013, 05:34 PM
ARFs make me BARF
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United States, MI, Roseville
Joined Dec 2000
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No substitute for good math

Now you'll see why we say disregard the root chord as a point of reference for most planes.

Now , I have some that fly well at 30%, while others, like my Avatar clipped wing P63, was EXTREMELY tailheavy at 28%..it's now at 21%.
Some fast,heavy types like a forward CG. I know of a GeeBee flown by a reputable modeler that flies well at 17%, and even an F104 at 0%!

In general (and I hate saying that), most sport types are safe to start around 25-28%, and work forward or rearward from there. I dial it in until it needs about 1/4 or so down stick when inverted on semi-symmetrical wing types. On aero types, I like to get the knife edge flight so that it requires no cheating of mixing in ele to stay in a decent knife edge.
If it tucks under, I'm carryin down trim for a tailheavy model....if it tucks toward the top, I'm carrying up trim for a nose heavy model, and I adjust CG accorgingly.
This doesn't work for all models, but for an aerobatic type, its gets the CG dialed in nicely.
Mark
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Old Feb 03, 2013, 07:32 PM
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Palmdale, CA
Joined Oct 2000
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Took down the HOB T-6 which has been hanging up for a while...(this is the only way to have an old T-6, BTW)... washed off the dust, and here's the c.g. on that airplane. Any further aft is unflyable!
When it was competing with the others, OS 25 FP...
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Old Feb 03, 2013, 07:39 PM
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I was going to say something about warbird tapered wings also, but TMI.
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Old Feb 03, 2013, 11:58 PM
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United States, CA, San Juan Capistrano
Joined Feb 2013
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So, to get the CG where Sparky Paul has his set up... I need to input a Static Margin between 22% and 30%.

My plane with no weights or anything sits with a CG 2 3/16 from the LE. To get this # from the calculator, I have a 27% Static Margin.

If this sounds like a good place to start from... I'll charge up some batteries and get things ready for its maiden voyage ( at least for me ).
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Old Feb 04, 2013, 01:23 AM
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Australia, ACT, Kambah
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Dcope17,

were you able to figure out which flavor of AT-6 yours is, eg the Herr Engineering, or another?
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Old Feb 04, 2013, 01:33 AM
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I think it would fly fine for first flights 15% from LE at the fuselage? 20% is good also. Make sure you don't have too much elevator travel to start with.
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Old Feb 04, 2013, 02:23 AM
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Also, I don't think anyone picked up on this. You will probably crash the heck out of this plane. This is probably one of the 'more harder' planes to fly. It looks like a warbird, and will handle the same. It probably has a lot of quirks. If you're asking for advice about CG, it would be better to stow it away for a year or two. It's possible you will fly it well, let us know how it goes.
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Old Feb 04, 2013, 02:47 AM
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Here is a link to the website for the Herr Engineering/Sig AT-6 Texan.

http://www.sigmfg.com/cgi-bin/dpsmar...nuF.html?E+Sig
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Old Feb 04, 2013, 02:55 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia / UK visits
Joined Jan 2010
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Quote:
Originally Posted by Dcope17 View Post
So, to get the CG where Sparky Paul has his set up... I need to input a Static Margin between 22% and 30%.

My plane with no weights or anything sits with a CG 2 3/16 from the LE. To get this # from the calculator, I have a 27% Static Margin.

If this sounds like a good place to start from... I'll charge up some batteries and get things ready for its maiden voyage ( at least for me ).
Maiden ? I would put it back on the shelf and get a Trainer ....

Nigel
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Old Feb 04, 2013, 03:26 AM
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Australia, ACT, Kambah
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Quote:
Originally Posted by solentlife View Post
Maiden ? I would put it back on the shelf and get a Trainer ....

Nigel
He picked it up used. He and this model have flown before, just not together
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Old Feb 04, 2013, 10:17 AM
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United States, CA, San Juan Capistrano
Joined Feb 2013
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My RC fleet includes a 40 size trainer, parkzone typhoon, Blade 400 heli, century .46 heli and an x-cell fury expert. I know heli setup but airplanes are new. The trainer, I put everything it and it flew. Never checked anything. Typhoon just assemble and fly as well.

I like this plane and it looks a bit more tempermental to fly. I want it to survive my plane setup learning curve.

If you guys think this is bad... a friend gave me his 98% finished .91 motor size F4U Corsair. I will be going through that and everything will be perfect before that engine ever fires up. It has robart air retracts and all. Is done kinda cheap with 1 servo on the ailerons and one on the elevator. I want to split them up and run 2 Rx so if one dies, I can control one side of the plane still... this one is several months off before tinkering.

Also, I don't know what brand this little plane is.
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Old Feb 04, 2013, 07:50 PM
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Alright then, 1st.. flight tomorrow after work with 2 3/16 CG from the LE. ( which is a 27% Static Margin ) I'll let you all know how it goes.
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Old Feb 05, 2013, 10:06 AM
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I like to fly my planes at 28-30%, but no further back. 25% is OK, but I tend to run out of pitch authority when flaring for landing. Also, these are numbers for a tailed airplane. A no-tail plane like a Stryker uses different factors and should be 15-25%.

I always use a CG calculator, because most wings are not just bar shaped, and sweep angle can change the MAC position a lot.
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Old Feb 05, 2013, 02:07 PM
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Aberdeen
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Quote:
Originally Posted by ChillPhatCat View Post
25% is the general rule of thumb regardless of what plane (for traditional non-swept monoplanes). 35% is technically unstable, best to leave to only the most hardcore 3D machines.
Nope, 35% back does not necessarily make the plane unstable. I've had freeflight gliders that fly very stable with the CG at 60 or 70% of the wing chord.

The thing that's often missed is that the biggest influence on where the CG needs to be for stability is the tail. A plane with a very large tail and a long tail moment can balance way back and still be stable. In fact it's perfectly possible for the CG to be behind the trailing edge of the wing and the plane still be stable.

The fact that the tail is so important to CG position is why any rule of thumb based on wing chord alone and totally ignoring the tail is little more than a guess.

Steve
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