can you survive only using rich mixture, say 70%-80%, of oxygen in your cabin which is not presurized at high alt? Or if I wear oxygen mask, can I fly FL 300 without presurization?
You can read all about the different oxygen systems in the Pilots Handbook of Aeronautical Knowledge.
1. You can't simply release O2 in to the cabin of a unpressurized aircraft, it would just leak out and not help increase the O2 absorption in your lungs.
2. Yes, with the correct O2 system and mask.
Pilot and crew must wear O2 if above 12,500 for more than 30 minutes; all the time if above 14,000; above 15,000 it must be availible to your passengers.
I think it depends on the country? In the UK I had a flight lesson and was told that we can't go above 10,000 feet without pressurisation (in a Piper PA3😎.
Let me clarify the questions:
1. How high can you fly without cabin pressurization and without an oxygen mask?
In the US to be legal, as described by SamIntel in his post above. It's recommended above 10,000 ft. daytime and 5,000 ft. nighttime.
2. How high can you fly without cabin pressurization with an oxygen mask?
High powered aircraft such as the P-38 Lighting and P-51 Mustang are not pressurized and can exceed 40,000 ft. with the pilot wearing an oxygen mask. At an altitude of about 60,000 feet your blood will boil, SR-71 and U-2 pilots wear pressure suits that are similar to the ones worn by Astronauts.
3. Can you survive using 70-80% oxygen in a cabin that is not pressurized?
Only if the 70-80% O2 is at a sufficient flow rate into a mask and only to an altitude that the flow rate (liters/min) will maintain your blood O2 percentage to an acceptable level. Releasing O2 into the cabin would be pointless. 🙂