Did any manufacturers experiment with "slightly" pressurized aircraft?

[RussR]

I've been flying pressurized light twins a lot recently (Cessna 340/421, Beech 58P). These aircraft have maximum differential pressures of somewhere around 4 psi. This allows about a 10,000 ft reduction in cabin altitude, so cruising at FL200 with a cabin altitude of 10,000 is possible. Obviously with this level of pressurization the fuselage and windows have to be stronger, there is additional complexity in the systems, etc.

I was wondering if any manufacturers ever experimented with lower levels of pressurization - like, say 2 psi, or something like that, where maybe it wouldn't require as much modification of the airframe, but still yield useful results.

I figure a 2 psi difference would mean about a 5000-foot reduction in cabin altitude, so cruising at 15,000 or a little higher would be easily obtainable without oxygen. Or make cruising at any altitude more comfortable on a long flight. Maybe just attempt to seal up an existing non-pressurized airframe as cheaply as possible. Create a P-Comanche? A P-Bonanza?

This seems like the type of thing that might have been tried in the 60's or 70's. I'm aware of the Mooney M22, but that's a little more modification than I'm asking about.

I'm not asking if it's a practical thing to do, just wondering if it was tried.

 

[Clip4]

The P210 would maybe fall into the slightly pressurized category. 3.35 PSI provided with 23k the limit and 19 more realistic. Just pressurized the skin and some seals.

 

[SoonerAviator]

I'd think that most of the stuff you'd have to do to get it to seal at 4psi, you'd have to do at 2psi. I mean, maybe not the windows, but the rest of the door/cabin seals/outflow valve would likely need to be done. Not sure how much savings that would net.

 

[midwestpa24]

The P-Baron comes to mind, a non-pressurized aircraft that was later converted. From outside there aren't a lot of differences noticeable right away. Looks like is still is 3.7-3.9 psi cabin. The P-210 is very noticeable due to the smaller windows.

Like SoonerAviator said, there probably isn't much difference from a design standpoint between 2 psi and 4 psi, and the effort to build a 2 psi airplane probably doesn't net enough benefit to be worthwile.

 

[Doc Holliday]

The P210 would maybe fall into the slightly pressurized category. 3.35 PSI provided with 23k the limit and 19 more realistic. Just pressurized the skin and some seals.

Thicker different windshield, thicker different side windows, different door and latch design, plus many other changes to accommodate pressurization.

 

[Cluemeister]

It would be great if a light pressurization could work up to 18,000, and get you below oxygen requirements, an effective 12,000.

 

[Tarheelpilot]

I would consider a 4 psid to be a lightly pressurized

 

[Pilawt]

The Mooney Mark 22 of 1965 claimed a 4.0 psid, "the equivalent of 11,000 feet (3,400 m) at the aircraft's operational ceiling of 24,000 feet (7,300 m)."

 

[3393RP]

Thicker different windshield, thicker different side windows, different door and latch design, plus many other changes to accommodate pressurization.

And a vent window with a latch from a '64 Impala.