gross wt.
 

Does anybody know what changes were made to the skymaster to up the gross wt. through the years?

Thanks,
Howard

I have often wondered this myself
 

I have asked many folks this question and for the most part have always gotten a simple and short explanation: A: "Nothing".

The empty weight got heavier over the years as they added more interior bits, made changes to fuel system set up etc, some change to gear power and associated plumbing, but to my knowledge the structural part of the airframe never changed much at all (some change early on to the chord length of the elevator and trim tab size and travel as well). Also some change to the flap operating range.

As far as I can tell, all the changes to the model appear to have added empty weight and as they went up with that, so did the gross weight (certificated). Of course power has always been 210 HP each end for the NA machines. This leads me to believe that the lower gross weight of the early models is purely a paper issue (ie this is how they were certificated). I have heard folks who have flown lots of different skymasters (not me) express the view that the early planes climb better (I guess if both a later and early plane were both operated at their respective gross, this would make sense). It seems to support the view that structurally the machine is the same through the years.

Don't take this as the definitive word, though, because I am no expert. Don Nieser at Commodore Aero has taken many of them apart over the years, so maybe he knows for sure.

Something to keep in mind is the rational behind the higher gross weight aircraft. In 1971 the 337 gross weight was increased to 4630 lbs but the landing weight remained at 4400 lbs. The 336 at 3900 lbs had less horsepower (190 HP) engines and the A & B model 337's lacked the full 4400 (4200 & 4300 respectively).

From Aviation Consumer article 2005:
During its years in production, the 337’s gross weight crept up, starting at 4200 pounds and eventually making it to 4630 pounds, but max landing weight was limited to 4400 pounds. (The P-337, with its 30 extra horsepower, had a takeoff weight of 4700 pounds and max landing weight of 4465 pounds.)

It was common for Cessna to increase the gross of their airplanes based on newer models until they reached a threshold for landing weight. The best useful load of any model is the normal "F" model at a published 1,935 lbs, lowest was the Turbo "D" model at 1,485 lbs. The average that most of us are familiar with is about 1,575 lbs. There are STC's that have increased the gross up to 5,200 lbs. Most of us know that these airplanes can really carry a load.

My recollection of discussions with Micro-Air prior to ordering my micro-Vg's (which are great by the way) was that the gross weight limitations on the 337 are essentially locked up becuase they/Cessna did not want to drop test X number of them to re-certify the gear at a heavier weight. So it's not so much what the aircraft can lift, but what the gear can withstand.