Notes on High Altitude Wave Flight

For flights below 28,500 ft, I use the standard Mountain High (MH) O2D1 pulse-demand oxygen system. Below 18,000 ft I use a standard cannula, above this I use the MH ALPS mask.  This is a great system, easy to use and its effectiveness to keep blood oxygenated has been carefully researched and discussed in Dancing with the Wind (Jean-Marie Clément.)

On 17 Dec 2020 I was able to attain an altitude of 36,630 ft (OLC trace) using a more complex oxygen system.  To go above 28,500 ft I used an A-14 pressure breathing diluter-demand regulator (available from Fluid Power, Inc (Hudson, Ohio), part number 1550, contact: Kevin Morgan, k.morgan@fluidpowerohio.com, lead time for fabrication is 16 weeks.)  The A-14 is mounted on the side of the glider near my right hand (see photo.)  This regulator is sufficient for flight above 40,000 ft (more on this below.)   I initially tried to find an existing, older A-14 and then send it to Fluid Power for refurbishment but this turned out to be not viable; Fluid Power will not work on regulators which are too old, and some older units have radioactive radium paint and are classified as toxic waste.  Purchasing an old A-14 on eBay or elsewhere seems to be not a good path.  Given the difficulty to find a unit which can be rebuilt, and the essential life-support role of this equipment, I decided to have a new unit built.  I could imagine a club having a couple of these regulators to support wave flights.

The A-14 has a connection to an indicator called a "blinker" which shows oxygen flow during suction for each breath; this is very reassuring to see during the flight.  I mounted this on the glare shield of my DG303 and routed a 4mm plastic tube (from MH) under the cushion which my right leg rests and then to the blinker connection on the A-14; the pressure in the blinker connection is ~10psi.  This could definitely be improved and I think using a small (1/8" OD) solid wall tube (copper or stainless) would be a better way.

I used a Mountain High gas regulator (00REG-2101-04) on a 22 cu-ft oxygen bottle, filled to 1800psi (see my comments below about the failure of the Mountain High regulator at low temperatures).  I removed the high pressure gauge on the regulator and use this 1/8" NPT port to access the high pressure oxygen which is routed to the input of the A-14 using flexible high pressure stainless steel hose. The low pressure output of the MH regulator is used for a fixed-flow system which was a back-up in the event the A-14 failed.  I moved the high pressure gauge to be visible during the flight, however I am not sure how the MH gauge is effected by the extremely low temperatures (-70F at 36K ft, -80F at 40K ft).  For instance, does the zero of the gauge calibrated at 70F change when it is cooled to -70F? (This is an important question if you want to know how much more O2 remains during the flight.   I will replace this gauge with one rated for -65F and a larger 2.5" face which should give more accuracy and confidence during the flight (Perma-Cal, part number 123NIM13A01-Z ).   Remaining O2 is such an important piece of information during the flight.

The MH gas regulator seals onto the high pressure bottle with a CGA-540 fitting using what appears to be a buna-n o-ring (good to -30F).  I have replaced this with a fluorosilicone o-ring which is rated to -80F (7/16" OD, 1/16" width, 5/16" ID, McMaster-Carr part number 8333T121) and will use these in the future.

For high pressure hoses and fittings, I use these flexible stainless hoses from McMaster-Carr (part number 4552K201), and stainless steel Swagelok NPT fittings (Swagelok fittings are made to higher tolerance than those I find on McMaster-Carr which are really super crappy.)  Joints with NPT are made leak tight with Teflon tape.  Flexible stainless steel hoses allow for installation and removal of the system without risking kinking or crimping of solid metallic lines; a good idea especially if this system will be shared in a club.  

Advice for novice plumbers (which I give to my new PhD students in the lab): do not use unnecessary intermediate fittings to get from A to B; order the correct fittings which minimizes the number of joints.  Your goal is to create the most reliable and leak-tight set of connections possible.  By adding unnecessary joints (simply because that is what you had laying around the day you decided to make the circuit) makes your system less reliable and more prone to leaks and in this application, makes the system more dangerous. Think through what you actually need and order the correct set of fittings.  Also, try to minimize the use of dissimilar materials. For instance, using hoses with stainless NPT fittings, connected to brass NPT fittings risks the fitting becoming loose due to differences in thermal contraction.

I used a MBU-20/p mask which I found in nearly new condition on eBay.  I use a Bonehead Composites carbon fiber helmet (model Comm-it) with J-mount oxygen receivers.   This is essential to hold the mask tightly to the face during pressure breathing.  This helmet works well with the standard bungee visor for an HBU-55/p helmet (I found my visor on eBay.)  It also adds very little height above the head which is critical given the tight fit under the glider canopy (HBU-55/p would not fit in my glider, if it can, there are many on eBay and is far cheaper than a new Bonehead helmet.)  To properly interface the standard microphone in the MBU-20/p to a standard microphone input in a civilian aviation radio, I use this amplifier from Gibson-Barnes, PA-101 Amplifier.  It is essential to have working communications while the mask is in place.

I use a CRU-60/p to connect my mask to the output of the A-14 and to my fixed-flow (secondary system) and to the bail-out bottle, (tertiary system.)  The CRU-60/p is attached to my parachute harness using a standard mounting plate.

As mentioned above, I installed a fixed-flow system as a backup in the event that the A-14 failed, but the main O2 tank is good. I routed the output of the MH regulator (specified above) affixed to the main O2 bottle,  to a 1/4 turn valve and then a MH flow meter MH-4.  The output of the MH-4 is then teed with the bail-out bottle and connected to the CRU-60/p.  This has the advantage that one can switch to the fixed-flow system by simply turning a valve.  The down side of this is that feeding a fixed flow into a MBU-20/p (or MBU-12/p) mask, one finds that inhaling the oxygen is OK, but exhaling is very difficult as one has to overcome the pressure on the input line, which becomes pressurized by the fixed-flow devices.  I was surprised by this behavior and am glad I tested this on the ground.  I can imagine the distress being unable to exhale after the stress of a failing A-14.  I contacted both Gentex who produce the mask, and an experienced military pilot about this behavior.  They both confirmed that this is normal behavior and suggested simply putting a finger under the mask when one needs to exhale.  I feel that this is a better, less risky solution than attempting to switch to another mask if the A-14 failed.

I use a 2 cu-ft bail-out bottle strapped to my left leg, Aerox Aviation Oxygen Systems, EMT-3-1, and routed to a MH flow meter (so that I could see oxygen flow) and then to the bailout connection of the CRU-60/p using low temperature compatible rubber hose (McMaster-Carr part number 5543K41, gum rubber rated to -70F).  This same hose type is used to connect the fixed-flow system as well. To connect the rubber hose to the bail-out port on the CRU-60/p, one needs a connector (Puritan part number 118040, I found a couple on eBay). The bail-out bottle was to be used in flight if the main O2 tank failed, or in the event of bail-out.  The size of this bottle is sufficient for ~15 min of breathing.  During the flight to 36,000 ft I was able to descend 20,000 ft in 13 min; more rapid descent is possible.

I monitor my blood oxygen saturation with a finger sensor: I used this one by Wellue.

Good places to find parts for a flight helmet, oxygen mask, hoses, and other parts are Flight Helmet and Gibson-Barnes. 

I fabricated a frost shield using 1/16" thick polycarbonate (Lexan) sheet (McMaster-Carr part number 8574K81), cut to size such that it would spring against the canopy support structure, and the gap sealed using standard foam weather stripping.  This was to avoid the buildup of frost from moisture from exhalation. 1/16" thickness is thin enough to cut easily with tough sheers and to bend easily, but thick and rigid enough to hold its position with spring force inside the canopy and to compress foam weather stripping. The MBU-20/P mask has an exhaust port on the right side of the mask, and I did observe frost growing on the inside of the unprotected part of the canopy near the exhaust port.   One might be able to fabricate (3D print?) a connection to the exhaust port, to route the moist exhalation to the back of the glider, or to outside the glider.

I use a Patagonia Capilene 4 Onesie one-piece with attached hood for my base layer. This was good; my head and core keep sufficiently warm.  Over this I wear a CWU-64/P cold weather flight suit (found used on eBay).  The pockets and heavy weight is good.  I have experienced cold air coming up the legs (especially when flying with high airspeed and ultra-cold air was squirting up the leg.)  This could be fixed by adding an elastic cuff at the ankle, or possibly some down insulating pants.  I had a tailor sew straps on the left leg to attach the bail-out bottle.  I wear wool socks and insulated WaveRidge shoe covers.  My feet do get cold, but not terrible or distracting; some heated soles would probably be sufficient.  I use mittens which open up to allow my fingers to be exposed for touching screens.  I think a down mountaineering suit, a down ski suit, or a snowmobile suit would also work well.

I wore (very nerdy) glasses rather than contact lenses.  Bob Harris described the effects of the extreme cold when he reached 49,000 ft, which included his eyes tearing and the tears freezing.  I was concerned that my contact lenses might freeze and come off my cornea.

A flight helmet is very beneficial for wave flying for a few important reasons.  As mentioned above, the helmet provides the mounting points for the oxygen mask, which must be sealed against the face  when the oxygen regulator is applying positive pressure at higher altitudes.  The head protection is important in the event of bail-out: two recent bailouts resulted in the pilot being knocked-out or dazed by impact of the canopy or hitting the glider when exiting.  Lastly, wave flights will have have high surface winds.  Landing by parachute in high winds is hazardous and has resulted in serious injury due to being dragged.   

I recorded my flights on both a ClearNav Vario and an OUDIE IGC, both calibrated to 60,000' by Paul Remde at Cumulus Soaring, Inc.  IGC rules require this calibration to be done every 5 years if this data is to be used to make a record or award claim.  I fly with a Trig ADS-B OUT transponder; a transponder is required to fly in class-A airspace of R2508.

During the flight to 36,000 ft,  I experienced the flight controls becoming very stiff and nearly frozen at ~30,000 ft: the pitch trim was completely frozen and inoperable.  I was able to control the glider's pitch and roll with the stick by applying a larger force.  After discussing this behavior with more experienced pilots, freezing of the grease used in the mechanical control circuit between the stick and the control surfaces is suspected.  For the joints which are accessible, I intend to remove the white lithium grease applied during the manufacturing of the glider in 1996 with low temperature compatible grease, Molykote 33 which is rated effective to -100F (this is the minimum temperature of the troposphere I have observed in skew-T plots at 40,000 ft; above this height the temperature is constant (tropopause) and does not continue to drop.  The temperature grows as one goes even higher (defining the stratosphere) due to absorption of UV by ozone....interesting! )

Update (4/5/21):  Together with my A&P we took a look at the DG303, looking for where on the mechanical circuit it can be relubricated.  The DG303 is fabricated in a way which makes almost all of the mechanical circuit totally inaccessible without cutting into the fiberglass structure.   After some thought, my current plan is to find and configure a SGS 1-34 for this type of flying.  More experienced pilots at Inyokern have flown this model in the Sierra wave; the Boulder soaring group had a 1-34 for wave flights as well.  

Advantages of the SGS 1-34

• metal: no gel-coat damage due to low temperatures
• mechanical control circuit accessible: lubricate properly with low temperature grease
• roomy: lots of room for oxygen gear, clothes, large instrument panel
• terminal velocity dive brakes: will not over-speed in vertical dive
• robust: rated to  +5.5g / -3g
• large useful load: 270 lbs for fixed wheel model
• inexpensive: ships currently flying are sold for $15-20K

Together with Stewart Ayotte, we have purchased an SGS 1-34, N7595.  This ship was fabricated in 1970 and has flown over 3700 hours(!)

What I described above is the oxygen system I used in December of 2020 to FL366.  I have been thinking a lot about how to make an oxygen system which is compatible with the low temperatures encountered at and above 40,000'.  When one looks at the design of the Mountain High regulators (posted on their website), one sees internal o-rings.  I suspected these could be a problem at low temperatures (viton for instance is rated only to -15F) due to loss of elasticity and cracking.  I discovered that failure of the Mountain High regulators was indeed observed during low temperature testing of the oxygen system for Perlan II; unregulated high pressure gas rushing out of the low pressure port.  Perlan heats their Mountain High regulators to avoid this failure.

I also learned that the A-14 from Fluid Power is tested at -65F after a long cold-soak at -80F.  The A-14 is designed to work at low temperatures encountered at high altitude, and each is tested during certification after manufacture.  This is an excellent mil-spec product and you can now see why they cost $1800 each.

As a result, what I believe to be the safest design is a direct high pressure connection from the main oxygen bottle to the A-14 regulator, with no side branches feeding a constant flow system.  I will have a constant flow system supplied from a second 4cu ft bottle which also serves as a bailout bottle (Aerox.)  

To connect to the blinker, I am using 1/8" copper tubing and compression fittings.  I have tested the polyurethane tubing which Mountain High sells at -100F and found it to be excellent.  At these temperatures the tubing is very stiff, but not brittle.  I dipped this tubing into liquid nitrogen (-321F) and did not find any change: stiff but not brittle.  However, connecting to this tubing is with the one-touch fittings which use o-rings, squeezing around the OD of the poly tube. I have decided to minimize all polymer materials and gaskets, switching to the copper tubing and compression fitting to avoid any issues of thermal contraction, embrittlement, ect. 

I also have read research papers which describe how to mitigate the occurrence of decompression sickness which is likely to occur at these altitudes.  Pre-breathing pure 02 for an hour, including 10 min of exercise to 75% VO2 max is show to be effective.  To arrange this, I have purchased a surplus A-14 regulator (eBay) and secured this to a large O2 bottle to use the hour before a flight.