Diet plan for skymasters?

[rrice]

We recently acquired a 1968 337c and I could not get the W&B numbers to work my way. After going through the updates from years past I found a mistake - a big one. Someone miscalculated the new CG (moved wrong way) based on fuel remaining in tanks during a weighing procedure. Check your old numbers carefully

[JAG]

Some great advice here already. The only thing to add, is sometimes the scale error (if you weigh) can also add some weight. Last time I weighed an aircraft at a shop (part 145 authorized Cessna Service Center), we went through 3 sets of calibrated scales until we found ones that were accurate (at least to my liking). It was quite interesting to see the difference in weight between these calibrated electronic scales.

My '66 was never weighed at the factory - the weight was calculated.

Jeff

[JAG]

Just for info:
my 1966 empty weight was calculated and was 2,746.5 pounds
8 years later (1974) it was weighed after autopilot added and VOR upgraded, it was 2,886.5.

Result in 8 years, aircraft put on 140 pounds of weight. I think you all can see the trend - the aircraft are never as light as we think they are...
Jeff

[Learjetter]

Where do we keep the "crow pie" around here?

Last summer, I reported in another thread on this board that my 77 NA G model had a calculated empty weight of 2957 lbs. Folks expressed some surprise that it was so "light." I was confident in those numbers. I also wrote that we'd be weighing the aircraft this fall.

Over the years, the various mods (avionics upgrades or adds x4, VGs, gear door delete, MT props, new paint and interior x2, etc.) had resulted in a calculated BEW of 2957. I checked all the math over the 44 years of logs and it checked out.

I was certain it was going to check out closer to 2960 (or less!). Just posting to lend credence to the theory that airplanes tend to run a little heavier than their calculated weights.

Weighed it twice, to be sure, with reset on the scales in between. Followed the procedures in the service manual and POH. Readings nearly identical both times.

History:
Left the factory in late 1977 at 2992 lbs CG: 140.15 Useful load: 1638
All calculations leading up to Summer 2021 values of:
2957 lbs at 141.3 CG Useful load: 1672

Imagine my surprise when the scales settled on:
Lt Main 1285
Rt Main 1283
Nose 422

Total: 2990 CG: 139.6 Useful load: 1640

Now, this these are numbers I can have some confidence in.

Aside: jacking a skymaster is a stressful experience.

[patrolpilot]

With the addition of the cargo pack, my airplane was reweighed at the last annual:
3,006 @ 140.3

The mechanic and I both did the... "that cannot be right." So, we weighed it again the next day, were careful with the setup, and came out to the same numbers.

I read about the accumulation of debris and fluid traces in the hull over time, and what looks like nothing amounts to something. Mud daubers are a big thing in many locations; we pulled about 130 lbs of mud nests out of the wings of my patrol plane. I kept one because it was so perfect!

[patrolpilot]

I learned about the debris and fluid accumulation in 121 and 135 operations to include corporate jets maintained to a 121 standard. Aircraft are required to be reweighed every 36 months. No physical changes to the plane, but they always gain weight. Our 337s are +/- 50 years old.