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Old Apr 30, 2001, 11:54 AM
Registered User
Omaha, NE
Joined Apr 2000
566 Posts
What is wrong with my zagi?

Okay I have been flying this zagi for a while now and it has always flown fine but now it has a strange charactaristic. It has had some horrendous crashes but the airframe looks fine. First here are the stats:
RS 1600
Permax 480 with 5.5X4.5 APC prop
weight 26.5oz.
CF Rod across the bottom of the wing at the CG. Which I have at 8" back where I like it.

Here is the problem. Now when I enter a dive it gets steeper and steeper fast. I have to use almost all of my elevator to pull it out as it screams toward the ground and even with full elevator it takes what seemss like a lifetime for it to be effective. It has been so bad lately I have not been flying it as it can get out of control fast. This is my third zagi and I have been flying for 10 years and I have never had a plane I could not at least diagnose. Any ideas?

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Old Apr 30, 2001, 03:13 PM
I'm disoriented!
ChrisD's Avatar
Mt. Laurel, NJ, USA
Joined Aug 2000
948 Posts
Ray,

What mt-100 said. I added 1 oz of weight in the nose this past weekend, and the Zagi flew much better than it ever did. Tail heavy, it was squirrelly. Slightly nose heavy, it's smooth.

Also check your elevon linkages. Are they tight or sloppy? Any slop in your hinge? Are your servos loose in the foam??? Try deflecting "full up" (on ground) and try to pull the elevons down by hand (carefully). Does the servo pull out any? That's all I can think of. Make sure the pack is secure and doesn't shift.

Chris
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Old May 01, 2001, 12:10 AM
I have no friends
United States, MI, Holland
Joined Dec 1996
3,363 Posts
Go to Northeast Sailplane Products web site and read the article about dive testing.

Here is a link. http://www.nesail.com/centergravity.htm

Basically, you are tail heavy. Read the article and I think it will help.
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Old Feb 23, 2002, 12:02 PM
Registered User
Trabuco Canyon, CA
Joined Mar 2001
28 Posts
My zagiclone has the same problem as yours. The CG was not the problem, as I moved that so progressively forward that I did not have enough elevator throw to pull up. Basically you are flying against the up elevator needed to keep the plane flying level. If you move the CG back the plane flies much faster and nicer in level or slow controlled flight. But pull up for a loop and it does the wildest snaps you could imagine. I found a few things so far that could contribute to the problem but haven't gotten back to "the way it was" yet:

speed control was flakey - didn't always work right, would start out and then drop the motor power. It just died - and in the dead mode one servo kinda worked, the other didn't. This made me realize that perhaps the voltage regulation for the servos and receiver was faulty causing flakey control of the servos.

One servo was slower than the other. I took the actuator arm and moved it back and forth on both servos - one had more resistance to movement than the other. I took that unit apart and didn't find anything wrong with the gears so I took the wires off the motor and ran it with a power supply. First it was drawing noticable current and then it dropped down to next to nothing. After that the actuator arm moved faster like the other servo.

I also had the servos right against the receiver. I'm thinking maybe EMI from the servos may interfere with the receiver so I'm moving it away from them.

I mounted a coroplast tray as a base for the servos and putting another corroplast sheet across the top - so the darn things better stay put!

I had the elevons mounted with hinges of strapping tape. They allowed some play that may contribute to different action one from the other. So I'm going back to some kind of linear tape attachment close to the original clear mylar scheme. My elevons are 4mm coroplast. They hold up much better in crashes but I think the balsa ones had less flex.

I'm also wondering about the biasing of the servo actuator - whether it should be centered with the stick centered and with the actual arms vertical or slightly back(?).

I also have servo savers installed. I need to check them to see if they are working right. Maybe one lost its spring or something.

Barry
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Old Feb 25, 2002, 09:38 PM
Registered User
Fremont Ca.
Joined Jun 2001
94 Posts
mine did

A while back mine did some strange things some of which involved pulling out of a dive and strange roll characteristics. What I found was the hinge tape out near the tips was pulling away fron the wing just from the trailing edge forward about 1/4 inch. I then tried a thin hinge tape that I had and the roll issues were still there. When I went to the thick Zagi tape all problems went away I feel there is some dampening from thick tape out near the tip where the ailerons can flutter due to the distance from the control horn. Just thought I would put my 2 cents worth in.
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Old Feb 26, 2002, 01:17 PM
Registered User
Trabuco Canyon, CA
Joined Mar 2001
28 Posts
Where can I get more of that type of tape? Didn't see it at Home Depot or Staples.... I tried strapping tape and it improved things but I was talking with a guy that does slope combat and he says guys tried coroplast and went back to balsa for the elevons because it is stiffer. So I made new balsa ones, covered with red packing tape, and then am using clear packing tape to adhere it to the plane. Trying it in 15 minutes.....
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Old Feb 26, 2002, 01:32 PM
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Sparky Paul's Avatar
Palmdale, CA
Joined Oct 2000
13,466 Posts
Tape and MonoKote hinges can use help in the form of the figure-8 thread hinge to keep the surface centered and eliminate the tape stretching and pulling away from the wing and surface.
Surfaces with the control horn at one end, such as rudders and rudder-vators on vee-tails can use the extra support.
Makes an easy field repair when needed also..
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Old Feb 26, 2002, 03:31 PM
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hardlock's Avatar
Joined Aug 2000
2,536 Posts
One thing that wasn't mentioned that might be a possible is that from repeated crashes, the nose tends to compress and curve (downward from my experience) adding more camber at the root.

Normally this shouldn't hurt much except in a high speed dive where the down pitching moment this causes can overpower the reflex in the airfoil maybe?

If the elevons have a loose tape hinge (loose as in able to push the LE of the elevon up/down at the hingeline), this can override the control effectivness as well and maybe reduce the control leverage and reflex effect also.
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