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Parkzone Radian: Battery size/weight and placement.

Old 09-25-2011, 04:22 AM
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Where is your CG? with battery in? Is it at manufactor suggested location? If its right on the number, I would add weight to the tail section. I use a quarter taped to the tail. Is your battery sliding around in the cockpit? It should be velcroed in place.
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Old 09-25-2011, 05:08 AM
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Default Parkzone Radian

Thanks for the reply. I moved the lipo rearward and it was tail heavy. I usually have the lipo about one half inch forward. I have not had any problem flying the glider before this happend. I can recheck the CG per instructions. I could add a 2100 MA lipo but it might make it nose heavy.
Usually when I climb to altitude and shut off the motor the airplane immediately stops in mid air and goes nose down. It dives then suddenly climbs, stopping and repeating the process. I have added up trim it doesnt stop down trim caused it to dive. It dove fast I thought the wing would come off and I was quick on the control to pull it out.

I fly alot of other airplanes with ailerons and am a experienced pilot with RC aircraft. Not alot of glider flying. I just wanted to try this sailplane due to its floating ability and thermal and slope soaring ability where I live in PA.
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Old 09-25-2011, 05:45 AM
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Ok, good to know. I would secure the battery in place. Check CG. The Radian usually..is nose heavy. I use a Gforce 1500 2 cell, its five inches long. So, there is a lot of battery forward on mine. I taped a quarter to the tail section. I have my rudder centered, and I trim slightly down on elev during launch. When I reach my height, I back off throttle, and trim elev slight back from neutral. The nose is going to drop when you back off power, just be prepared to bring the nose up once power is reduced. Then trim the nose back until she flies flat. You will learn to do this with a glider all at once in that transition after a while. Your getting progessive stalls when the nose goes up and then down and back up again. Another method I use before launching, hand throw the glider with no power, not a hard throw..just a straight good toss. She should flatten out on her on and land smoothly. if your having to fight the elevator your CG is wrong. There are alot of good threads on this sailplane, many pilots have different ways of setting up CG and methods after power is reduced. Take what you read and tweek your own method. I have a few videos of the radian on my youtube site, with onboard cam...you will see the nose drop just about on all of my launches, but back stick and trim will smooth her out very fast. you can see these on youtube "615thaerosquadron"
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Old 09-25-2011, 09:44 AM
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Originally Posted by ChrisFlysRC View Post
I had the battery 1/2 inch out of the battery compartment. The airplane after power was shut off would drop the nose and suddently climb, then stall and drop the nose and repeat the process. It did this at high altitude but I pulled back the stick and it corrected the problem. I applied up trim and it continued to do that manuver and I almost lost the airplane. Any suggestions?

This is is called porpoising and is usually indicitave of a nose heavy plane. Becuase it is nose heavy you have to apply up trim to support that heavy nose.

You fly too slowly and the plane stalls. The nose drops and the plane dives and picks up speed. That speed interracts with excessive up trim and the nose comes up .... and you stall again and the nose drops and it repeaths over and over.

If you are using the stock Radian battery it should be all the way into the battery compartment.

Push it back, put in 2-3 clicks of down trim and try again.

If it contineuse to porpoise, add down trim till it stops.

My fully stock radian has a couple of nose area repairs. I have a quarter taped on the tail to shift the CG back.
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Old 09-25-2011, 05:05 PM
Rockin Robbins
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Chris, the battery location is much less important than where your center of gravity is. The location of the center of gravity is measured from the leading edge of the wing. I use a square to make sure I'm accurate.

Parkzone says the factory center of gravity is 62mm behind the leading edge. Mark that on both wings. Label it 62mm so when you change it later (you will) you can keep track of where you are compared to the factory setting.

The producers of the planes tend to give you a CG that is more toward the stable end of the spectrum than working for ultimate performance. Don't worry about it for now, it will fly great.

I measured my CG by drilling two spaced holes in the styrofoam of the shipping box, and using two pencils with the chisel tipped erasers. Works great and it's part of your box. I used my box for transport too, so everything was always together.

Assemble the entire plane and balance it with the chisels lined up on your 62mm CG line. I used clear packing tape over the line so the erasers didn't bore into my wing. It should balance level or very slightly nose down on those two lines. Move your battery back or forth to make her balance.

You see, there have been some differences in the weighting of individual planes so one may run with the battery position in one spot and another with the battery in a different position, although their CGs were in the same spot. If we just talk about battery position we'll never get anywhere in getting your plane to fly right.

Now, as to ultimate CG position. This is subjective. In order for the plane to have neutral trim and highest responsiveness the CG and center of lift (CL) would have to be coincident: the same spot. Unfortunately at that point the plane loses all inherent stability and you cannot fly it.

But as you approach that point your stall speed decreases and your plane responds more evidently to thermal activity. As a result, you have to make more and more control inputs to keep the thing in the air. It cannot fly itself any longer.

So what we do is, as we become comfortable with the plane, we move the CG back, a little at a time and fly it that way until we're comfortable with that. The further back your CG moves, the greater effect tiny changes in the position will have.

As a result of discussions here, I moved mine back to 72mm. The plane was darned scary, in part because I moved it right back there from stock position, 10 mm forward. I found pitch stability in launches to be terrifying as I was jockeying throttle position continuously and elevator the same way all the way up, never exceeding half throttle. Then when I shut the motor down I found turns were were incredibly scary. The plane just didn't care which direction it flew. It didn't crash but my inexperience could have crashed it if I weren't very careful in flight. Don't repeat my mistake!

Then I moved the CG forward to 70mm, only 2mm! The plane was transformed. NOW it felt directionally stable TO ME (your mileage may vary! Don't just go for 70mm and expect a miracle), I could calm down on the inputs and the plane was mine again. But the stall speed seemed like half of that of the stock 62mm CG position.

When the plane did stall, I didn't get that 20' dive to regain enough airspeed that the elevator could regain enough authority to force the nose level. The plane kind of mushed and came down horizontally. When I blipped in some down elevator, she lost a couple of feet and resumed flying! My sink rate was cut by an amazing amount. It was plastered to the sky, capable of flying at unbelievably slow speed and just didn't want to come down.

I'd recommend flying her absolutely stock until she's YOUR plane, doing exactly what you expect and you know the difference between overcontrolling and "just right." Resist the urge to tinker and just enjoy the plane. It's plenty good right where they recommend.

When you're ready, I'd make marks two mm apart back to 64mm, labeling in a way you can read it easily. Then moving the CG back 2mm to 64mm, fly her that way for awhile. Feel the difference. Get very comfortable with that in multiple flights and days.

Then my movements would be to 66, then one mm at a time, slowly making changes, giving yourself time to get comfortable with each step and knowing for sure what the difference is from your change.

Eventually you'll find a spot where you just aren't having fun flying the plane. That's a danger sign. Move back to the previous comfortable position and fly there for a long time.

Every once in awhile you can try moving back again. As your skills improve you will be able to fly comfortably with a less stable plane.

The pros, who have the ability to fly at insane CG positions, still realize that as you move the CG back you need to make more and more control movements to fly the plane. At some point these induce enough drag to hurt your glide duration. They'll move it forward based on their still air flight duration, not their flying ability. Maybe Ed is at that point, but it's completely out of sight for me. 72mm scared me to death and I'm sure lots of people fly there with no problem.
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Old 09-26-2011, 02:36 AM
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Default Park Radian CG Problems

Thanks for all the CG information with the Radian. I moved the lipo to the front a half an inch. Slightly adjusted the trim. I located a CG point where the holes are to see the carbon tube holding the wings together.

It flys good in a slight wind. The glider flys good without wind. It's a good powered glider. It is one of the best flying gliders I have flown. Its a good glider for slope soaring and is the 480 motor is good power to take it to altitude for flights up to an hour.
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Old 11-13-2011, 05:43 AM
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Regarding CG position and Radian mods to improve performance. Just thought I'd pass along the link to Paul Naton's Radian modification blog. Paul has been building, tuning, and flying fun and competition RC and full scale gliders for many, many years. He also produces some awesome RC (and full scale) flying videos.
Paul tuned a Radian, moving the CG back 1+ inches and corrected the horizontal stab decalage by a few degrees. Everyone who's followed his suggestions has noticed remarkable improvements. I only did those two suggestions and it does fly better as a motor glider. Before you "dis" on it, try it, and check the videos of the after flying ability.

See it at Glidefast My Parkzone Radian Modifications and Set Ups

There's links to his youtube videos Stupid Parkzone Radian Glider Tricks and the followup Radian Acro Practice
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