Earthstar Forums

I just went through W&B with my eGull. One less variable (battery instead
of varying fuel tank), but still important to get right.

The exact zero point for all the moment arms is not important, only that
all arms are measured from the same point.

My eGull's steel tube cage is as close to stock as they come, so I used
Mark's moment arms for nose wheel (12.5") and mains (87.5").

I weighed the empty plane (on 3 scales), and repeated with me in it (both
per Mark's instructions with the nose wheel 3" down, as it will be in
flight). Comparing the two gave me my weight (duh), but also the pilot's
moment arm (55.5"). CG came out to 78" from the nose or 19" from the wing's
L.E., right at the rear limit of the allowed range.

Then I ran a few what ifs: to move the CG forward 1" requires either
- move the pilot forward 3.5"
- install 9 lb ballast in the nose
- remove 5 lb from the horiz. stab
- gain 29 lb weight

I had already removed 2.6 lb of lead from the stabilizer (to better balance
my rather light, Oratex-covered stab) - another 5 lb would be impossible. I
am 6 ft tall and would not be comfortable with the seat moved forward from
the rearmost slot. I worked hard at losing weight and do not want to gain
it back. The only practical solution was to install ballast in the nose. I
got 10 lb of brass blocks and secured them on the battery tray. I now get
17 lb on the nosewheel (empty), which should work fine according to Mark.

I am currently building a cargo box that will be installed on the floor
between the rudder pedals, as far forward as possible. This will hold tie
down stakes and rope, wheel chocks, maybe a fire extinguisher, and anything
else heavy (the box has a latching lid). I am hoping that flight tests (any
day now, right Mark?) will show that I can remove some of the ballast.

A ballistic parachute in the nose would have helped get the CG forward, but
I opted to install the charger in that space (which weighs much less).

Just be careful that the weight removed from the stabilator does not cause
it to become unstable (flutter) in flight.

-Alan

Hi Alan
Martin kept enough weight for the stab to balance. He used oratex, lightweight covering so he could remove more weight from the balance weights.
Happy Flying
Mark

Sent from my iPhone

What method are you using to do your CG calculations? Pencil/Paper or software? If software… which are you using?



Thanks,



John

I use my GPS and record my airplanes W&B arms on the GPS and in my
maintenance logbook. -Alan

Cool, good to hear, Mark. Nice technique to use if your airplane is tail
heavy. -Alan

Thanks… I am using an excel spreadsheet… without much success I might add.

http://download.cnet.com/Aircraft-Weigh ... 08028.html

http://www.aopa.org/News-and-Video/All- ... lance-apps

http://mattsaviationblog.com/tools/tool ... nce-sheet/

http://aeml.tech.purdue.edu/airframeimages/c172w&b.xls

http://www.kitplanes.com/magazine/misce ... 274-1.html


Perhaps one of these will help.

-Alan

Thanks Alan.

I mentioned about my nose-wheel to nose measurement, and at 12.5” from the axle to the datum point is about 1 1/2” forward of the actual nose, then all the other reference stations came out correct. I also would be hesitant about putting extra weight with supplies between your legs, as that will constantly change your cg. When I bought my Gull, it showed 8 lbs on the nose-wheel scale empty/no fuel, and now with the correct arms and my few added lbs, I had to add about 10 more lbs to the nose. I used plastic covered heavy fishing weights that have a nice loop to pass a bolt through. By the way, the parachute weighs 23 lbs.