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...Still "Scary" and VERY expensive
Ray,
Notwithstanding your excellent no-doors kit for the Skymaster, which we have installed on our '77 P337, I believe William D. Thompson, one of Cessna's lead engineers on the 337 project, would find some exception to your statement that, "... the only difference between a P337 and a non "P" 337 is one additional frame at the pilots side window and about 20 lbs of tank sealant."
In all fairness, that is not quite an accurate summation, as the P337 does have a beefed up airframe with heavier gauge and more numerous bulkheads throughout the cabin structure and a rather monstrous rear firewall, as compared to the other 337's, so as so withstand the high cabin pressure loads, even though the cabin pressure is design limited by sonic venturis installed aft of the turbos which limit the maximum pressurization differential to 3.35 PSI.
Anytime you punch a hole into the pressure vessel -- especially one the size of a baggage door -- you're just opening up the possibility of more problems down the road, especially since this baggage door mod relies on a 'BLOWN' seal, unlike the main cabin door seal, which is designed with tiny holes spaced around the door frame opening that allow pressurized cabin air to enter into the seal and inflate it against the door molding. (And woe to the A&P mechanic I saw one day trying to patch/fill those small holes --so as to help "improve" the door seal! -- obviously this guy didn't have a clue!)
Obviously, if Cessna felt the needs of its customers would have warranted adding this feature and they could have justified the additional costs, they would have included it in the original design. That they did not speaks of their concern for the integrity of the presure vessel. As you know, an explosive door failure while pressurized was one of Cessna's main concerns, as such an event could suck out the co-pilot, but their final design has resulted in no such event ever happening with the airplane.
As I've remarked before, access to the rear of the airplane -- even across the sliding bench seats in our '77 -- is no big deal. It's even easier with the 1973 through 1975 models. Both variations have their pluses and minuses. Besides, if you're going to carry that much junk, the belly pod is the only way -- or leave it at home!
So, my take is that the integrity of the airframe comes first. If you really need a baggage door, buy a normally aspirated Skymaster or a turbo non-pressurized unit that already has one... and save $25,000 and a lot of heartache if things go wrong, which they will, if Murphy's Law intervenes.
By the way, William D. Thompson, one of Cessna's main Skymaster design engineers, passed away last year. He was 81. Some of his wisdom is preserved on this website under the heading "History".
SkyKing
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