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Old Jun 03, 2014, 02:33 PM
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Help!
Lanyu Phoenix evolution 2.6m glider. Nose heavy = bad?

I recently purchased the Phoenix evolution glider for FPV and I didn't seem to get it to fly right.
It seemed to be way nose heavy. I was constantly fighting it with up elevator and it would stall and begin that porpoise thing.
I had the cg set to be slightly nose heavy, as I was taught that was always better then tail heavy.
The manual says cg at 70mm.
Does anyone have experience with this glider who can give me ideas?
I know it was heavy due to the fpv gear. But it didn't seem to fly well even when I traded the 2200 battery for a 1300.
I have the fpv video showing me struggling with it if it'll help anyone.

Thanks
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Old Jun 03, 2014, 03:57 PM
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Hi, scribble. I don't have a Phoenix but I have some thoughts.

1. Regardless of cg "that porpoise thing" is almost always caused by trying to simply fly too slow. Everything that I have read about the Phoenix suggests that it likes sufficient air speed. My general advice for planes that porpoise is to trim the plane for maximum lift to drag rather than slowest descent. Think in terms of covering the most ground rather than staying up for the longest duration.

2. How nose heavy is "slightly nose heavy"? Some planes are more sensitive to cg than others. 2-3mm can make a big change in handling.

3. Extra weight and drag will exacerbate the problem.

Here's my suggestion. Take out the FPV gear, set your cg at the recommended position, and fly it around in the glide, rather than with power, until you achieve steady flight. Find the cg and trim that gives you nice, level, gliding flight. Don't add the FPV gear until you have the plane sorted out in stock configuration. When you add the FPV gear keep the cg at the same place. If you suffer a degradation in glide, assuming you are mounting stuff externally, your problem is caused by the drag.

Cheers!
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Old Jun 03, 2014, 04:13 PM
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Thanks for the reply.
Taking out the fpv gear was my next step.

The only external things are the horizon hd camera head on the top of the canopy. Which is pretty aerodynamic. And the video tx mounted just iron of the tail.
I'm not sure how far off the cg is. I will check that tonight.
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Old Jun 03, 2014, 04:22 PM
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I'm always happy to (try to) help. I'm pretty sure that you will be able to sort it out once you get rid of the extra weight and find the best glide angle and speed. With a sailplane; even small cg errors and increased drag can really screw things up.
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Old Jun 03, 2014, 04:53 PM
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Can you explain your first point a little more?

Trimming for maximum lift to drag?

Do you mean go as fast as it can in unpowered as level as possible flight?
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Old Jun 03, 2014, 06:18 PM
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Yes. Maximum lift to drag, or L/D, means you want it to go as fast and far as possible in level flight.

Maximum lift and drag is achieved with the nose high. Minimum drag is achieved with the nose low. But? Increased speed also creates more lift. The trick is to find a happy medium between the two extremes.
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Old Jun 03, 2014, 07:13 PM
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Ok so here's what I'm working with..Name: uploadfromtaptalk1401840413102.jpg
Views: 15
Size: 91.5 KB
Description:

Removing the canopy, which the camera is glued. With the 2200 3s as far back as I can get it. With the vTX still attached. I can balance the aircraft on the tips of my fingers on the tiny line you see there on the bottom the wing next to the cutout by the servo. The bottom of the wing is parallel to the ground.

With the camera/canopy on. I can achieve the same with a 1300 3s moved as far back as it will go. (I glued the frsky antenna in as you can see. To get the diversity and lessen the drag was the goal.

Step 2 is I think there is far to much weakness in my tail control surfaces, I can move them to almost full deflection without it moving the servos..

*edit
Why did it upload the same photo so many times...?
trying to fix it...
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Last edited by scribble007; Jun 03, 2014 at 07:19 PM.
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Old Jun 03, 2014, 08:03 PM
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Fingers work, to a point, but one can make a more precise balancing rig very easily and cheaply. Simply grind off a couple pencil pencil erasers and ram them into a bit of foam or wood. This will provide a more precise result. Check the picture for my simple balancing rig.

I'm not sure what you mean about the "weakness" in the elevator control but I can tell you that too much elevator movement can really ruin your day. I would suggest reducing your elevator throw to the manufacturer's recommendation, with either your transmitter or by changing the linkage, before going any further. If you don't have a transmitter that will accomplish this task then you would move your connector towards the servo, on the servo arm, and/or away from the elevator on the control arm. That just might be the only correction needed.

Cheers!
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Old Jun 03, 2014, 08:33 PM
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I will give that balancing rig a shot.
Elevator throws are fine. I'm using the taranis. Adjustments are endlessly possible.
Ill try and make a rig and take a few photos.

By weakness, The rudder is the biggest culprit to the weakness. I mean that if the rudder servo is centered, I can manually move the rudder 20 degrees in either direction, before the servo will "catch up"
So its making me think that with air resistance, if i were to give it full rudder, say a 30 degree deflection normally. The rudder may only be holding a 10 to 15 degree deflection during flight..

Hope that makes sense
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Old Jun 03, 2014, 09:23 PM
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OK. So, that balancing rig, easy enough. Got my stand that has served for a parrot toilet for who knows how longhttp://www.nitroplanes.com/79p-8002-foamstand-blue.html. some holes.
Pencils.
With the 2200 Lined up to a repeatable spot (looks like slots in the front tray for that extra metal weight) No canopy/camera, Vtx still on the back. And the center of the eraser head exactly on my 70mm CG point. She is level. Without the Vtx. I fear that I wouldn't have enough front weight. (which is probably why they included this 1.5x 2 cm metal cylinder)

With the 1300 3s and the canopy/camera, I would need some weight on the tail to balance out.
So I'm gonna see what I can do to move some weight around to under the servo tray under the wing. Such as the receiver, current sensor, and vario.
I will be happy if I can use my 4s 1800 and FPV gear with a proper CG.
Because it really needs the 4s. To gutless.

Pics to follow once my phone charges.
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Old Jun 03, 2014, 09:47 PM
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It's a bit late for me and, to be honest, I have become a little bit drunk. Let's pick it back up tomorrow and we'll get it sorted out.

Cheers!
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Old Jun 05, 2014, 12:25 AM
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So this is what I've come up with.
Moved as much stuff around as I could. Wish I could move a bit more. Like the frsky current sensor. But with the full fpv/frsky gear and a 1800 4s, which is what I want to be running.
I think the CG is about prefect.
But I have almost no wiggle room. Everything it'd pushed as far back as it will stay.
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Old Jun 13, 2014, 11:37 AM
SKSS Delaware AMA 1010092
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If your still nose heavy? there is a 44g weight under the battery mount board just behind the motor
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Old Jun 13, 2014, 11:54 AM
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Quote:
Originally Posted by Little_Eddie View Post
If your still nose heavy? there is a 44g weight under the battery mount board just behind the motor
Mine was never installed.
I found it among my parts bags.
I think I got everything sorted out. Ill know for sure tomorrow.
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Old Jun 27, 2014, 03:20 AM
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I find this glider flies very well on 78.5 mm cog.
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