I recently purchased a PA-22/20-150 (actually a former PA-22-160) and the weight and the most recent weight and balance paper work completed when it was recovered in 2003 appears to be a mess.

At that time, the tare weights on the scales were:

Left Main = 555 pounds

Right Main = 543 pounds

Tail = 74 pounds

So far, pretty normal numbers. However the arms are where things go south.

Rather than using "0" for the arm for the main gear and +178" for the tailwheel arm (and then adding 60" ahead of the LE to the imaginary datum line in the W&B) who ever did it did this instead:

Main gear arm = 61.5"

Tailwheel arm = 255.5"

I *presume* he leveled the aircraft per the hole in the door frame and center punch point in the seat cross tube, and then dropped a plumb line form the spinner to measure the distance to the center of the main gear axles, more or less getting lost in the weeds and missing the whole point of an arbitrary datum line at the aircraft nose to make the math easier - after the aircraft has been weighed.

However, I cannot figure out where he got the 255.5" "groundline" he refers to in the W&B diagram. Per the TCDS, 178" is the distance from the center of the mains to the center of a Scott 3200 tailwheel. If I add the 61.5" arm that he used for the main gear, I get a total arm of 239.5" form the point where he apparently dropped a plumb line from the spinner. However that indicates 16" error in the arm used for the 74 pounds of weight at the tailwheel.

The CG calculations using his numbers:

1,098 x 61.5 = 67,527

74 x 255.5 = 18,907

1,172 86,434

86,434 / 1,172 = 73.74

CG = 73.4 - 60 = 13.7 aft of leading edge(Yes, he switched from 61.5" to 60" for the datum line to reflect the normal 60" distance from spinner to wing leading edge, with no adjustment of the total moment to reflect the 1.5" change.)

He then calculated a "most forward" W&B:

Empty CG: 1172 x 73.7 = 86376.4(note the confusion on significant figures here, where he's rounded the 73.74 down to 73.7, but then goes to ".4" in the moment.)

Fuel 12.5 gallons: 75 x 84 = 6300

Pilot (front seat): 170 x 81 = 13,770Weight =1417 pounds, Total moment = 106,376.4

CG= 75.1 - 60 = 15.1 aft of leading edge

He then calculated an "alternate most forward CG" with half fuel and two 170 pound front seat occupants with a CG of 15.9" and a weight of 1620 pounds. (I'll spare you the math.)

Finally he calculated a "most rearward CG" with a 170 pound pilot, two 170 pound rear seat passengers full fuel and 100 pounds of baggage:

Empty CG: 1172 x 73.7 = 86,376.4

Fuel 12.5 gallons: 216 x 84 = 18,144

Pilot (front seat): 170 x 81 = 13,770Rear passengers: 340 x 109 = 37,060

Baggage: 100 x 127 = 12,700Weight =1998 pounds, Total moment = 103,492

CG= 84.1 - 60 = 24.1 aft of leading edge

That's 1.1" aft of the 23" aft CG limit for a PA-22-160, and 0.1" aft of the 24" limit for the PA-20-135. And he was apparently ok with this.

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If I use the same scale weights, but use a 60" datum line consistently and use 178" as the difference between the mains and tailwheel I get results that appear to be more logical and acceptable:

Left Main = 555 pounds

Right Main = 543 pounds

Tail = 74 pounds

Main gear = 1,098 x 60" = 65,880

Tailwheel arm 74 x 238 = 17,612

Empty Weight = 1,172 Total moment 83,492

Empty CG = 71.2 aft of datum, and 11.2" aft of wing leading edge.

The most forward CG is then:

Empty CG: 1172 x 71.2 = 83,492

Fuel 12.5 gallons: 75 x 84 = 6300

Pilot (front seat): 170 x 81 = 13,770Weight =1417 pounds, Total moment = 103,562

CG= 73.1 - 60 = 13.1 aft of leading edge

The most rearward CG is then:

Empty CG: 1172 x 71.2 = 83,492

Fuel 12.5 gallons: 216 x 84 = 18,144

Pilot (front seat): 170 x 81 = 13,770Rear passengers: 340 x 109 = 37,060

Baggage: 100 x 127 = 12,700Weight =1998 pounds, Total moment = 165,166

CG= 82.7 - 60 = 22.7 aft of leading edge

Both of those appear to fall within the allowable CG envelope for both the PA-22-150/160 and the PA-20-135.

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It gets worse of course as the last documented W&B I can find is the one done after the 2003 recover and it does not include the 2016 addition of Sullivan wingtips, nor does it reflect the removal of a whole bunch of avionics.

Consequently, I'm going to have it re-weighed anyway, but I want to make sure the basic numbers as I've calculated them are properly done in the interim.

I also want to confirm that I should still be using the PA-22-150/160 CG envelope.

Thoughts?