Unknown item in W&B

JAG · #1 07-13-20, 08:58 AM

Thanks Jim,
Interesting to see your W&B from Cessna from 1969. Mine is about 5 pages, and it is similar in the sense - but it also includes the whole equipment list for all 1966 aircraft, then and 'X' or 'O' depending on if it was installed.

I was worried about the same on my my aircraft - for the last 30 years the W&B had been amended, but I was concerned about the actual weight and CofG. My reweigh went well, and right about where I thought it would be. I removed a lot of old stuff, but added a bit with a lot of soundproofing/insulation in the cabin. Nose scale was 390 lbs, LH main 1249 lbs and RH main 1243 lbs = 2882 lbs. I weighed with fuel empty, but oil full.

Cof G is 140.2 inches.

Jeff

TomM · #2 07-13-20, 03:54 PM

Its interesting how the static wicks are negligible but post lights are worth weighing and calculating moment arm.........I cant imagine the post lights weigh more than the static wicks....

hharney · #3 07-13-20, 05:00 PM

My empty CG is 141.39

https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a64682a24c2ce51086257ed700622c0f/$FILE/A6CE_Rev_41.pdf

JimC · #4 07-13-20, 10:24 PM

Mine was 137.08 at one point. That's a massive difference for similar model airplanes. I've surveyed 6 owners and I haven't found anyone farther forward than about 139.7. Most are 140 to 141.

137.08 has to be an error. I'll know by the end of next month. Until then, I'm loading it with a load that is in c.g. for both 137.7 (my current c.g.) and an arbitrarily picked 141.0. It just generally means throwing a bunch of extra stuff behind the rear seats. That way I'm safe whether it's wrong or right.

JAG · #5 07-15-20, 08:54 AM

Hi Jim,
I just looked back at your other thread, and one thing I noticed is the measurements you had for calculating the CofG.

When I measured my points, I came up with:
A (front face of Fwd Firewall to main wheel centers) = 87.8 "
B (Nose Wheel center to main wheel center) = 93.7 "
I took a great deal of time doing the measurements using a plumb bob, tape on the floor, large straight edges, etc. Still easy to mess it up though...

The last W&B on my aircraft had the following measurements: A=88.5" B=94"

You indicated in your last post that they had 96" for B. That may be an error (I am only guessing), and a larger number for that measurement will move the C of G forward.

I would hope all of our early model 337's have the same measurements, but it can change a little (1/4" maybe) depending on who measures and how tight the rigging is on the gear.

Let us know how the next weighing goes and what you find out. One last thing is to move the scales around when you weigh it. When I weighed mine, I jacked the aircraft to set it on the scales. Even though they were calibrated scales, I weighed it a second time (jacked it back up and set it down again) after moving the scales to a different position, just to make sure there was no difference in how they read.

Hope this helps.

Jeff

JimC · #6 07-15-20, 06:11 PM

Quote:

Originally Posted by JAG

When I measured my points, I came up with:
A (front face of Fwd Firewall to main wheel centers) = 87.8 "
B (Nose Wheel center to main wheel center) = 93.7 "
I took a great deal of time doing the measurements using a plumb bob, tape on the floor, large straight edges, etc. Still easy to mess it up though...

[...]

Hope this helps.

Jeff

It helps tremendously. All I know at this point is that it's very likely wrong. Knowing where it's likely wrong will help me sleep at night. I figured the linear measurements were off - there was no effort made to record a precision of less than one inch. Also, the the weight of my front tire was recorded as 500.0 lbs, exactly. Is it possible? Yes, but I think it's more likely they were using a substandard scale with a precision of 10.0 lbs. Combine that with substandard measurement and you have my W&B.

What REALLY shocks me is that this has been the reference W&B for 30+ years! Either
a) nobody checked c.g. or
b) nobody thought having two 170 lb pilots throw the plane out of c.g. was unusual!

JimC · #7 06-16-21, 06:02 PM

Well, it took almost a year - but I had my plane accurately weighed. As expected, I gained 60+ lbs of useful load and the c.g. moved back almost two inches. I'm still trying to figure out why the c.g. is slightly forward more than the fleet average - I'm at 139.38.

This error has been in the paperwork of the plane for over 30 years!