Plane CG... where should it be? - Page 5 - RC Groups
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Feb 06, 2013, 04:45 PM
Registered User
New pilots, fly smoothly, maintain some speed, usually half throttle or more. Avoid full elevator or abrupt elevator movements. Avoid sharp hard turns, especially if you are flying downwind. Watch the nose of your plane, climb gently, when you are landing, make sure the nose of the plane is either level or pointing downward slightly. Maintain some throttle as you make your landing approach (maybe 1/4). As you get over the runway, level out, maintain light throttle. Gradually cut the throttle and allow the plane to settle onto the runway. As you fly, think of the wing as knifing through the air, leading edge first. Abrupt and big elevator movements will cause the bottom (or the top) of the wing to move through the air, killing lift.
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Feb 06, 2013, 08:40 PM
Co-heir with Christ
Dcope17's Avatar
After the wing calculator results... says a 20 MPH stall speed. I wasn't going over 30MPH with about an 80 deg. bank in the corner. I can float my trainer and Typhood 3D plane through anything... I knew this bird would be temperamental.

Next time I will fly smoothly up and higher then I'll try things out and see what it can and can't do.
Feb 08, 2013, 11:46 PM
Registered User
cold wombat's Avatar

GuanLi 955mm J3 Cub COG.

Sanity check time...

I've got the Guan'Li 955mm J3 Cub (as supplied by HK- Blue & White or Invasion stripes), but the included instructions are for the RTF version (which assume you're using the supplied battery) and don't give the COG. I've plugged the numbers into the COG calculator (at 10% static margin) and it's saying the COG should be about 55 ~ 57mm from the leading edge (depending on how I muck around trying to 'square off' the tail measurements). This is around 38% of the root chord. Does that sound right?
Feb 08, 2013, 11:58 PM
darn you, kakka carrot cake.
derpron's Avatar
Originally Posted by scirocco
When you stop posting poor advice based on what, 5 1/2 months experience ( people will stop criticising those posts.

Your desire to contribute and help is admirable, but you're dealing with people's effort and money when you provide advice in these forums, and it needs to be backed up by sound knowledge and experience.

Fortunately one of the benefits of an open forum like this is that bad advice tends to quickly get moderated or corrected. Consider it part of your learning process.

Feb 11, 2013, 08:31 AM
Registered User
wombat, A J-3 Cub CG should be at about 28% for good flying. I would not go beyond 33%. The wing is a bar shape, so just multiply wing chord * .28 and that is the distance from the leading edge (LE) that it should balance.

Many of my ARF manuals have incorrect CG.
Last edited by tclaridge; Feb 11, 2013 at 06:29 PM.
Feb 11, 2013, 08:50 AM
Registered User
flypaper 2's Avatar
Just a bit of history. We old pharts used to call them plank wings as opposed to tapered wings. Now I feel even older

Feb 11, 2013, 09:46 PM
Registered User
cold wombat's Avatar
Originally Posted by tclaridge
wombat, A J-3 Cub CG should be at about 28% for good flying. I would not go beyond 33%. The wing is a bar shape, so just multiply wing chord * .28 and that is the distance from the leading edge (LE) that it should balance.

Many of my ARF manuals have incorrect CG.
Thanks muchly tclaridge. I was a bit nervous at the number the calc was giving me. I'll play around with it and see if I can work out why. Just out of interest, should the wing width be measured from the aircraft centre line or the side of the fuselage? The diagram on the calc suggests using the CL, but I'm not so confidant that is right.

My only radio kicked the bucket the other day and I'm away from home for now, but once I've sorted those two issues I'll give it a try at 28% and see how it goes.
Feb 12, 2013, 06:02 AM
Senile Member
Lnagel's Avatar
Center line.
Feb 12, 2013, 07:45 AM
Registered User
cold wombat's Avatar

Thanks Lnagel.
Mar 17, 2013, 08:51 PM
Co-heir with Christ
Dcope17's Avatar
Alright, I've been busy and its been over a month... flew the Texan today trouble free.
I didn't do a pretty fix ( it was a good fix, just not smoothed out or covered, no cowl either ) Once i get 2 more flights with it without crashing, I'll make a place to hang it in the garage as it will then be a more permanent bird in the fleet.

I flew in a huge open flight field, kept the speed up and flew great. Landed and actually floated better than I thought after cutting power to a nice smooth landing.

Thanks for all the help everyone.
Mar 18, 2013, 04:36 AM
Learn to build with wood.
Tucci's Avatar
Please post a pic of your plane on a CG machine. I have the same one. I balanced it using the numbers from one of the calculators and it was too far back...
Mar 18, 2013, 01:12 PM
Co-heir with Christ
Dcope17's Avatar
Will do, give me a day or so and I'll get it checked.
Mar 18, 2013, 01:28 PM
Yea, I fly dusty planes..
zeezee's Avatar
The main spar is a good start, always worked for me. ZEE
Mar 18, 2013, 01:54 PM
Registered User
E-Challenged's Avatar
Best to try maiden flight with some nose-heaviness and move battery pack aft (etc.) in small steps as you get familiar with it's habits. Check for wing tip washout and add some if possible by twisting and reshrinking covering. Let model lift off on it's own when ready at 3/4 throttle and keep climb angle shallow while you or a helper adjust up/downelevator trim as needed. Good tail dragger take-off and landing technique are needed. Nice looking model!! Land on the mains with some power and raise elevators to prevent nose over when rolling slow enough.
Mar 20, 2013, 10:12 AM
Co-heir with Christ
Dcope17's Avatar
Prolly not getting a pic soon. Working too muck and my buddy has the CG machine so I can't just run out in the garage and do it. There are a couple posts in this thread saying CG no more than 2 1/2" from the LE. Mine was 2 3/8 on its first flight and when I rebuilt it, I put everything back the same. Didn't check CG though. With possiblt a little more weight in the front because of the repair. Mine is likely 2 1/4 - 2 3/8 from the LE.
If your patient, I can check it... just not till the weekend or so.

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