A little while back I obtained a Mountain High Oxygen system. This was primarily motivated by having a very bad headache after a long day of flying at 8500 feet. I also like flying at night and while this time of year nightfall comes quite late once we get into the fall there will be more night flying. Your night vision degrades above 5000 feet without supplemental oxygen and I often like to cruise above that point so a portable O2 system makes sense (especially for a flatlander like me).
I haven’t had a chance to try out the system yet since most of my recent trips have been short legs. I had the evening to myself tonight and so I decided I’d take the Cardinal up to a higher altitude and test out the O2 system. Armed with a pulse oximeter to verify my blood oxygen saturation I took off from Nashua and climbed out VFR on a west heading.
I put the oxygen system into “Night mode” which means it will immediately start delivering O2 rather than waiting until a preset altitude. This system is a pulsed-demand controller which means that on each breath in it delivers a meters pulse of gas through a canula (or a mask above 18,000 feet) instead of continuous flow. This is a bit more sophisticated but conserves oxygen so a smaller bottle is needed. As you climb the pulse of gas at the beginning of each inhalation gets longer.
I stayed on the west heading and kept the climb speed relatively high to keep the engine happy in the thinner air. With a normally aspirated (not turbocharged) engine the amount of power the engine makes is reduced as it climbs. This is offset by reduced drag in the thinner air but eventually a ceiling is hit and you cannot climb any higher. While temps in the climb are more of a concern in a turbocharged engine that can make more power higher up I was still monitoring closely. Soon I was well above altitude of the lower few clouds and you could see the raked evening sunlight hitting the tops of the clouds and making them pink.
The outside air temperate had dropped considerable and around 11,000 feet it was below freezing outside. The air temperature didn’t drop too much after this point. At this altitude the engine manifold pressure (vacuum) with the throttle wide open was around 16″ – barely above a power setting I would normally use for descending on final approach!
As I got close to 15,500 feet I was struggling to maintain more than a few hundred feet per minute of climb. I decided to head back down. Since I was still maintaining an airspeed somewhat above “best climb” I could have climbed higher but I didn’t want to slow down and be rough on my engine. I leveled off briefly at 15,500 feet, let the engine temperatures stabilize, and turned back.
I had a headwind on me west heading and so as I turned back the headwind turned into a tailwind. This gave me almost 200 knots of ground speed in the descent! Since this was just an out and back I had to make a few turns to avoid overshooting Nashua without an ear bending descent rate. If I was cruising at 15,500 on a real XC trip to take advantage of tailwinds proper descent planning is quite important. A descent starting a hundred miles out would be a more optimum profile.
As I descended (and did a circle or two to burn off some altitude) the sunset was simply fantastic. Words cannot do the pictures justice so I will just show you them…
I managed to avoid being distracted by the sunset in front of me and executed and reasonable nice landing back at Nashua. You can view the full set of photos and larger versions over on my photo site. Enjoy!