Weight snd balance

[kblaswich]

Well, my-o-my, it seems that I've been flying right at the aft cg limit ever since I bought the plane.I managed to get a copy of another Gull 2000 airworthiness documentation that had an arm chart for the whole Earthstar line, and it seems that the JT/JT2 arms for nose, pilot, fuel, and mains are different than for the Gull 2000. So much different that is about 4.5"different, and my numbers were for the J/JT2. I did some on-line research, and it seems that aft cg does indeed make an airplane faster, but less stable to gusts and turbulence, and the heavy weather drivers keep the cg more forward to make the plane more stable at the cost of speed. Now I have to go out and get new flight numbers. I did do a test flight yesterday, and indeed the nose feel heavier, but when trimmed flies off and flares just fine and did seem to be less prone to bumps, but that may have been that I was so excited to get back in the air after 6 months of rework (yes, I'm slow).
kb

[cossitt.alan]

Great to hear, I know Mark told me the best CG was just a bit aft of center
of the CG range. There are enough variations in these airplanes (I found
out my JT2 was a slight variant from the standard line, designed for more
cargo space) that I would recommend doing your own measurements with a
plumbline and use those for your CG calculations.

-Alan

[blaswichk]

I used a plumb line to verify that my was built as a Gull 2000 using that arm chart, and it is. Mark calls out for the datum line to be 12.5” ahead of the nose wheel (axle?), and 10” for the J/JT2. I assumed the datum line at 12.5”, which was about 3/4” ahead of the actual nose, and I used that figuring that each plane could have the fiberglass slightly different as the builder attaches the fuselage shell to the airframe, and how closely it fit. The datum line is referenced to the airframe and axles which is jig welded and should all be the same.
I just took it up for another flight after my lengthy winter project, and oh what fun. I probably only added 7-8 lbs of fiberglass and foam, but the plane feels more solid at higher speeds now and still goes like stink. Now for more polish.

[cossitt.alan]

Thats great Kess! Glad to hear you are out having fun.

In my case, I found out much later that Mark had two jigs for the JT2 and
that I wasn't using the standard one. I'm glad, since this version has
more space. My situation is different since I didn't have ownership of the
airplane from its beginning and thus didn't realize which jig was being
used.

[wsweidemann]

Interesting that folks are re-figuring their weight & flight range. This is something I did with my Odyssey as well. When I first bought it and flew a few hours I realized I was using great amounts of trim for the whole flight from takeoff, cruise & landing. Upon weighing and using the work sheets it showed my flight range was way aft and I needed more weight in the nose, so I strapped 17 lbs of divers weights in the battery box in the nose (about the right amount called for to get it within limits). Now (flying solo) I do not generally change trim at all during takeoff, cruise and landing. (I actually do make very minor changes during level flight.). An important factor in my case is that the former owner had removed the battery from the nose and installed one behind the student seat instead (don't know exactly why....other than it is a big job to fit a battery in the nose).

Skot
Odyssey N159BS, HKS 700E

[blaswichk]

Interesting to see that an owner moved the battery location, and didn’t leave a documentation trail in the log book. My thought is that a heavier than normal (?) pilot/owner might have had to remove some nose weight to get the cg numbers in range. I just went flying with my friend Don who has a JT2 with 40 lbs of lead in the nose, and at first I thought that was excessive until he told me that before the weight was added (by our local A&P friend), He couldn’t get the nose to lower as he got in the plane until he gave the throttle a blip. No wonder he had landing difficulty’s with his new (to him) plane. I now know that you can’t just jump into somebody else’s plane if you don’t weigh close to their weight, and 50-70 lbs different in the seat does make a difference in cg. I too am an owner of a prior owner built plane and the 3rd owner with a sketchy paper trail of things done.