Air in the wood and air freight

[Tom Bender]

Another post mentioned this and I'm intrigued. Air freight could quickly reduce air pressure to 5 psi. Air in the wood could then be trying to get out with 10 psi of force. Small bubbles would not act over much area individually and would probably be contained by most ridged finishes. Oil might get surface bubbles. Most glued joints should be ok but laminate might get lifted.

Anyone have experience?

[Curt Harms]

No experience but I don't know of any cargo aircraft that are unpressurized except small propeller aircraft that mostly operate below 12,000 feet. Air pressure at the altitude is about 9 psi according to an online calculator I found. Sea level is around 14.7 psi I believe. A related bit of minutia - the top of earth's atmosphere is about 60 miles high. So where is the half way atmospheric pressure wise? I always thought it was about 30 miles but nope, air pressure decreases at a logarithmic rate. The halfway point is about 18,000 feet, there's as much air below 18,000 feet as there is above 18,000 feet up to 60 miles.

[Bill Dufour]

Surplus military sealed storage cases often have air breather port to equalize pressure but keep out water.
Bill D.
POS the medical chest is a nice size for home storage of camping gear. No more rats in my sleeping bag on the shelf.

https://colemans.com/medical-transport-chest-u-s-g-i-aluminum

[Wes Grass]

IIRC, airliners are pressurized to 8k ft altitude. Roughly 4psi lower than SL. Reduces the stress on the fuselage. Cargo is included, takes the load off the cabin floor.

Remember the issue years back with cargo doors blowing off? I think the floors caved in on those.

[Tom Bender]

No experience but I don't know of any cargo aircraft that are unpressurized except small propeller aircraft...

Really? Seems like a plane carrying freight would be more efficient if it didn't carry all that air in the cargo compartment. I'll take a stab at some math. (10' x 10' x 50') / 10 cubic ft per pound = 500 pounds. Well that's not a lot. Never mind, just an engineer rambling.

[Wes Grass]

As an engineer consider the stress on a pressure vessel, one a round tube, the other a 'D' profile. Yeah, you could put a big corner radius on it, but then the window seat passengers wouldn't have any leg room.

Something leads me to think the floors 'float' as well, to let the fuselage stretch in diameter and length under pressure.

Remember, aluminum doesn't have a fatigue limit ...

[Curt Harms]

Really? Seems like a plane carrying freight would be more efficient if it didn't carry all that air in the cargo compartment. I'll take a stab at some math. (10' x 10' x 50') / 10 cubic ft per pound = 500 pounds. Well that's not a lot. Never mind, just an engineer rambling.

A lot of freighters are converted passenger planes, some are purpose built. I doubt it would make economic sense to certify an aircraft with pressurized cockpit and the rest not pressurized. It costs a LOT to certify a new jet transport.

[Greg Quenneville]

Conventional airliners (including civilian freighters) are typically pressurised to 8 psi. Which yields a cabin altitude of around 8,000’. I spend around 900 hours a year up there, and if your boards did too they would be as wrinkled as I am.

The 787 and the Airbus A-350 can tolerate a higher pressure differential due to their carbon fibre construction. Cabin altitude on those is around 5,500’ which is significantly more comfortable for passengers and likely green wood boards too.

Greg

[Lee Schierer]

Other than Red Oak and a few others, most wood, particularly green wood don't contain a lot of air. If you apply a stain or finish on red oak you don't want to set it in the sun to dry. The air and finish down in the pores will expand and push up through the surface producing bubbles. On the other hand you can place a piece of maple with the same finish in the sun as the pores are much smaller and less likely to bubble the finish.

[Bill Dufour]

You can always fill the box with helium to reduce the weight and shipping cost.
Bill ,D

[Alex Zeller]

You can always fill the box with helium to reduce the weight and shipping cost.
Bill ,D

Have you priced helium lately, lol.

[Bill Dufour]

Have you priced helium lately, lol.
And that use would contribute to the looming worldwide Helium shortage that will soon raise the price astronomically
Bill D.

[Randall J Cox]

What lee said. I once (many years ago) finished a piece and set it out in the sun to dry. Yup, bubbles in finish from wood heating up and oxy expanding in wood. Never did that again! Randy