Propwash in Pa

Does anyone know the CG for a 100” Antares? Just put the radio in last evening and am hoping to fly it this weekend.

da Rock

Get out your yardstick and go to this application.

http://www.geistware.com/rcmodeling/cg_super_calc.htm

Do the 9 (easy to do) measurements they want and plug them in.

Pick a margin of 10%, and click the compute button.
Read out the CG location.
Change the margin to 20% and click the button.
Read out that CG.

The two CG locations give you the CG range for your airplane.

This works with just about everything we fly, and works excellently well. It's unbiased and accurate as hell. It beats the heck out of sound byte expertise, btw.

BTW, it doesn't take me another 30 seconds to plug in a margin of 15% and get that CG location. I've used this application on everything I've built for the last 15-16 models, and it's been deadly accurate. And I've found that the 15% CG is an almost perfect starting point for my models and the way I want to fly them. I didn't find the application until I'd already plugged together a couple of ARFs that had less than good CG suggestions. I should have done the math, but figured the ARF manual wouldn't be wrong. Wound up having to move stuff around inside since the recommendations made for lousy flying. Wished I'd known about this application then. Or been less lazy. Sometimes the mfg's manual isn't very good for some of our ARFs. Nowadays, I always run a new airplane's measurements through this application. I used to do the same with CL stunters years ago, but had to do the math myself. That taught me how good those formulas work. Now we don't have to do the math.

bkdavy

My Feedback: (1)

Also read Gordy's Balancing System. I had never heard of this until last week. Following this guidance, I've removed about 4 oz of lead from the nose of my GP Spirit, and the handling has improved significantly.

You can google it or just read it at http://www.slnt.org/articles/gordys_articles/1%20Gordy's%20Ballancing%20System.PDF

Brad

kzimmerm

I've used this method and it works! ............

Kurt

Propwash in Pa

Thanks All.

Kurt, did you fly the Antares? If so, any pointers or overall comments?

da Rock

Gordy's system works great for gliders. It really ought to be called "Gordy's Glider Balancing System".

And, btw, for all the newbies........... Gordy's guidance isn't just to snatch the nose weight out first thing. But he does suggest ignoring the mfg's suggested balance point and starting at a certain location for the CG. Truth is, this does work for basically straight wings like gliders have, but there really isn't much reason to work to place the CG at any magic starting place if the glider is already rigged as suggested in the manual or you've setup the CG based on reliable computation. Because his proceedure is going to work no matter where the CG starts. And sometimes the suggested CG is the best start location.

Gliders almost always have very straight wings.

da Rock

BTW, it's RCU's policy that posts not have advertisements in them. There is an entire marketplace here at RCU that works great for selling your stuff. And RCU asks that forum posts not contain sales ads or want ads.

kzimmerm

No I never flew one. I was planning on building one but don't have time.

Kurt

mocgp

Just looked at the plans, the CG measures 3 3/16" back from the LE, which happens to also coincide with a line drawn straight down from the back edge of the wing rod.

Propwash in Pa

Thanks, I built this plane about 10 years ago and could not find the plans. Did you ever fly one?

mocgp

Yes, I built one a couple years ago as a test bed for a 4-servo wing installation that I was planning for a Lovesong kit that I had started. It was a nice looking plane but it had some nasty habits. I had flown a Windsong for several years prior so I knew how to handle a full-house ship but I could never seem to get any washout twisted into the wing tips, so the thing would tip stall at the slightest provocation. Otherwise, I think I would have enjoyed it very much. It's on the scrap heap now that I have the Lovesong on line.

soarrich

My Feedback: (98)

Boy this brings back memories. I flew one for a while, if you slow down the ailerons just about stopped working, then you put more throw in and tip stalled it. This cured it:
Put a trip strip on the tips at 25% of the wing, I glued on some very thin string 1/64 inch tall on the outer 18 inches of the wing. the handling improved and it didn't affect it's thermaling ability. Not really a great plane or airfoil, I think it was a 205 top on a 193 bottom, the Windsongs ate them for lunch.

Propwash in Pa

Rich,
Can you describe what you did in a little more detail? Were the strips installed on the top of the wing, 25% back from leading edge? I am interested in leaning more about this type of flying and will probably move to a different plane if I am not satisfied with this one. I love all aspect of flying from Senior Pattern like Dirty Birdi's, modern aerobatics like the Extra and Edge, right down to 3D Harrier and classic war birds. Soaring is now in my blood and I joined a soaring only club. What sailplane (not a composit) would you recommend for next keeping in mind that I send tuition checks to multiple universities?

Lastly, I appreciate the comments from all.

John