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Apr 10, 2002, 09:05 PM
Registered User
cfossa's Avatar

Zero CG Questions for GWS4CEO


GWS4CEO,

What c.g did you guys test the Zero (300 version) with? I set mine up with the cg about 55-60 mm back from the leading edge as recommended in the manual. I'm using 600 mAh NiMH packs that weigh about 3.5 oz, and the plane weighs 10.5 oz (total flight weight just over 14 oz.)

The plane had a tendency to climb at full throttle, and seemd a bit unstable .. as if it was tail heavy. I fed in a bunch of down elevator trim, and that did not solve the problem. Slowed doen to about 2/3 throttle and it seemed to fly straight.

I've seen some other posts recommening moving the cg to about 45 mm.

Any updated cg recommendations now that the Zero is out and flying? Is anyone else seeing this tendency to climb with the cg at 55-60 mm?

Thanks,

Carl
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Apr 10, 2002, 09:10 PM
Registered User
russ6421's Avatar
The new CG is now 45 to 50 MM back from leading edge.
Last edited by russ6421; Apr 10, 2002 at 09:19 PM.
Apr 10, 2002, 09:26 PM
Registered User
joemi's Avatar
ahh.. that must be it... Mine was climbing so much with full throttle, I had to give full elevator down just to keep it from climbing so much. I thought it was my thrust angle becuase I had just remounted the motor (after breaking it off), but after taking a closer look, the motor and mount look fine. I'll see if I cant move the CG up a bit for the next flight.
Apr 10, 2002, 10:14 PM
Houng-wen Lin
GWS4CEO's Avatar
Sorry, GWS Zero in our test is by suing Sanyo 600mAh AA Nicd at 7.2V. at EPS-100C for the original. When EPS-300C equipped, the powerful speedy flying will make climb tendncy obviously, need to move CG a little forward. 5~10mm.

When you use AAA getting light again, need move CG even more forward.
Apr 11, 2002, 12:21 AM
Our Daddy and Heli Junkie
Fred Bronk's Avatar
I think you need some downthrust. I built it into mine, and alittle up aileron to stop the snap roll !
Apr 11, 2002, 10:19 AM
Registered User
cfossa's Avatar
Fred,

You may be right about the down thrust. I taped a quarter in the battery compartment and got the c.g. to 50 mm with an 8 cell 600 mAh NiMH pack. I took off, and the plane still wanted to climb. I added a bunch of down elevator trim and eventually got it to fly straight and level ... still seemed to want to snap a bit in turns though.

I had flown about 6 minutes, and the batteries were getting a bit weaker. I'm not sure what happened, but the plane nosed up and stalled. It started coming down and I pulled hard on the elevator ... but she didn't pull out. It went in nose first hard

The good news is that the Zero took the crash well. I broke a prop, the battery busted through the firewall, the wing bolt plate tore out, and the fuse cracked on one side just behind the trailing edge of the wing. It's all epoxied back together now and will be good as new ... with a few battle scars

I checked out the controls after putting it back together, and it is no wonder I couldn't recover from the stall. The bunch of down elevator trim to keep the plane flying level had made it so I had almost no up elevator movement .... didn't really notice because I was just flying straight and level.

Before going up again I'm going to move the c.g. forward even more. I plan to tape 1 or 2 quarters inside the cowl and try to get the c.g. to about 40-45 mm.

I may need down thrust too, as you suggest, but I'm pretty sure I have a c.g. problem here. The plane was very "squirrelly" in the air and wanted to tip stall in turns ... classic symptoms of being tail heavy. Not sure how I'd add down thrust now w/o damaging the fuse trying to get it apart.

Hopefully moving the c.g. will help. I'll post another message after I try again .

BTW, my plane (pre-repairs) weighed in at 10.5 oz, and the NiMH pack at just over 3.5 oz. If you are using similar wieght batteries, I'd seriously consider moving you c.g forward before your first flight.

Carl
Apr 11, 2002, 11:11 AM
Houng-wen Lin
GWS4CEO's Avatar
If you are welling to add down thrust, add right thrust too. Since your over cells add on more prop thrust will make slightly left turn when take off.
Apr 11, 2002, 05:16 PM
jah
jah
BALD MEMBER
jah's Avatar
I flew yesterday for the first time at 55mm CG. I had built in down and right thust, had the ailerons slightly reflexed up. Did not fly to well. Here is a post detailing the first flights yesterday:
https://www.rcgroups.com/forums/show...5&pagenumber=1
Today I put the battery far foward, actually into the cowling, almost against the cowling, and got a CG of 47mm. Trimmed down the elevators, and........
TOTALLY different aircraft. AWESOME

Thanks GWS, just wish the manual had the correct CG for the IPS300 planes.
Apr 11, 2002, 06:09 PM
Registered User
cfossa's Avatar
JAH,

I just read your first flight report, and it sounds just like mine! Glad to hear that moving the CG seems to have solved your problem. I did not build in down thrust and I think it is too late at this point. Hopefully just moving the CG will solve my problems.

I flew the Zero today with a CG of about 50-55mm. It wanted to nose up and roll left. A bit of right rudder trim solved the left roll easily. But, it took a bunch of down elevator trim to get it to fly straight. Still wanted to nose up and stall in turns, and finally did one stall I couldn't recover from. Nose down straight into the ground!!

Turns out I had so much down elevator trim that I had almost no up elevator movement .

I glued the front of my battery compartment back in, so can't try you method of sliding the batteries into the cowl. But I did tape three quarters inside the bottom of the cowl and I now have a CG of about 40-45 mm. I also have decided to jam some foam in behind my batteries so they can't shift in flight ... the crash loosened things up a bit

Once the wind cooperates I'll give it another try. Hopefully it will be better than today! I'll post a post flight report.

Like you, I wish the manual had the right CG and/or thrust angle for the 300 motor system. Might have saved me some epoxy

Carl
Apr 11, 2002, 06:54 PM
jah
jah
BALD MEMBER
jah's Avatar
Carl, good luck on your flight. Yeah adding the down thrust after the stick is glued into the fuselage is a real puzzle. Maybe you could shave it down and add a little wedge of balsa to get it right. In my thread Lefty and Louie posted a great pic of the correct measurements to get it right. Check his website, the link should be in my "Captured Zero" report.
good luck
Later on
Jerry
Apr 11, 2002, 07:22 PM
an earth bound misfit, I
Basketcase's Avatar
If you really need to dig out the stick to change it you can glue it back in with some ProBond whipped up and it'll be stronger than original and lighter. Don't have a Zero but it worked great on my moth. am using a EPS on my SB.

BC


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