How not to black out
or die in the suit
Everything on this page is a way the suit kills its pilot, followed by the physiology, the number that matters, and what the MK-I design intends to do about it. The physiology is published science; the design responses are intent, not tested capability. If a requirement on the systems page exists, it traces back to a line here.
G-LOC
Blood leaves the brain. Vision greys, then goes, then you do. 12 s out, 15 s confused, no memory of it.
Hypoxia and cold
Above 3,000 m the brain slows and you feel fine about it. Above 4,500 m the air is 40% thinner and −14 °C before windchill.
The dead zone
Between 3 m and 120 m there is no parachute and no survivable fall. Only redundant thrust and a controller that re-trims fast enough.
Fire, heat, CO, noise
Five kerosene engines strapped to a body. 700 °C exhaust, carbon monoxide next to the mouth, 125 dB at the ears.
Spatial disorientation
Your inner ear lies above 2 g and in any turn you cannot see. Pilots fly perfectly good aircraft into the ground every year.
The pilot shows up wrong
Dehydration, a hangover, four hours of sleep or a cold each cut G tolerance by a full g. Most accidents are decided before launch.
G-LOC: the one that takes the pilot and the suit together
What happens
Under positive G (head-to-foot, +Gz) the heart has to push blood uphill. Eye-level blood pressure is normally ~22 mmHg lower than at the heart; every additional g costs another ~22 mmHg. Around +3.5 to +4.5 g relaxed, the retina starves first: peripheral vision narrows (greyout), then colour goes, then all vision (blackout). The pilot is still conscious and can still fly by feel for a few seconds. Past +4.5 to +5.5 g, the brain follows and the pilot is gone.
G-LOC is not a nap. Absolute incapacitation averages 12 s (range 9–20 s). Relative incapacitation, where the pilot is awake but confused, uncoordinated and often convulsing, lasts another ~15 s. Most victims do not remember the event. At 200 km/h that is 1.5 km of flight with no one home.
The three things most people get wrong
- Onset rate matters more than peak. The cardiovascular reflex takes 6–10 s to compensate. A gradual pull gives greyout as a warning. A rapid pull (> 1 g/s, easy for a thrust-vectored suit) can go straight from fine to unconscious with no visual warning at all.
- The push-pull effect. Any negative or sub-1 g exposure (a push-over, a dive) dilates the vessels and resets the baroreceptors. The positive G that follows is tolerated 1 to 1.5 g worse. A dive-then-pull is the deadliest manoeuvre a suit can make.
- Orientation is everything. Humans tolerate chest-to-back acceleration (+Gx) far better than head-to-foot. Reclining a fighter seat 30° buys about 1 g. Lying prone, the way the MK-I cruises, converts most of the load into Gx and roughly doubles usable tolerance.
| +Gz, relaxed, no protection | Effect |
|---|---|
| +2.0 | Heavy limbs, hard to lift arms. Fine. |
| +3.0 to +3.5 | Greyout begins. Peripheral vision dims. |
| +4.0 to +4.5 | Tunnel vision, then blackout. Still conscious. |
| +4.5 to +5.5 | G-LOC. Unconscious. |
| +9 | Trained pilot with G-suit, AGSM, reclined seat, ~15 s max. |
| −2 to −3 | Red-out, severe headache, vessel damage risk. MK-I limit −2. |
| +12 to +17 Gx | Chest-to-back, tolerated for seconds by astronauts and crash-test volunteers. The direction we want. |
Consequence for the design: a standing pilot in a suit is the worst possible G geometry: upright, no seat, legs full of blood. Every protection fighter pilots have must be designed in, and the suit must fly prone whenever it is going fast.
Countermeasures, in the order they are worth
Prone cruise (Gz → Gx)
Above 60 km/h the controller rotates the pilot horizontal. Thrust and turning loads then press through the chest instead of pulling blood from the head. This is the single largest safety gain in the program and it is free.
Anti-G straining manoeuvre (AGSM)
Tense legs, glutes and abdomen hard, as if lifting a car. Take a breath, close the throat and strain against it for 3 s, then a quick exhale-inhale (under 0.5 s) and strain again. Done well it adds up to 4 g. Done late it adds nothing. The controller counts the cycles through the chest strain gauge and cues the rhythm in the pilot’s ear.
G-suit
Five bladders over calves, thighs and abdomen inflate from 3 g, squeezing blood back toward the heart. Full-coverage designs (Libelle-type fluid suits, ATAGS) do better. The MK-I bladders are driven by a 70 kPa compressor on the arc core, pre-pressurised the moment the controller sees a pull coming.
The controller envelope protection
The pilot cannot command more than 6 g upright or 8 g prone, nor more than 3 g/s onset, nor a push-pull sequence. From 4.5 g the controller softens inputs; at 7.5 g it unloads to 3 g in one second regardless of what the hands are doing. Eye-tracker fixation loss or pupil lag triggers the same unload earlier.
Hypoxia and cold: the ones you feel good about
Oxygen partial pressure falls with altitude. The brain is the first organ to notice and the last to admit it: hypoxia produces euphoria, confidence and bad arithmetic. Pilots have narrated their own hypoxia on the radio, laughing, until they stopped. Time of useful consciousness (TUC) is how long you can still fix the problem.
Two things make the suit worse than an aeroplane. Under G, the lungs and brain are already short of oxygen, so the controller turns oxygen on above 2,500 m if any manoeuvring is expected. And the pilot is physically working (AGSM, arm thrust), which raises oxygen demand.
Cold: the standard atmosphere loses 6.5 °C per 1,000 m. At the 4,500 m ceiling it is −14 °C on a 15 °C day, before a 200 km/h wind. Exposed skin frostbites in under a minute. Hands lose fine control first, and the hands are on the throttles. Every square centimetre is covered; gloves and base layer are heated; the visor is sealed and heated against fogging.
Rules: O2 armed above 2,500 m, flowing above 3,000 m, hard ceiling 4,500 m unpressurised. Pulse-ox on the earlobe (fingers read wrong under G and cold). SpO2 under 90% is a warning; under 85% the controller descends.
The dead zone: where an engine failure has no recovery
Helicopters publish a height-velocity diagram: combinations of altitude and speed from which an engine failure is not survivable. A flight suit has one too, and it is uglier because a suit cannot autorotate or glide.
- 0–3 m: a fall. Airbags (motorcycle-vest type, 80 ms inflation) at neck, hips and knees plus the armor shell make it a bruise. Every early hover test lives here, over foam.
- 3–120 m: no chute will open, no fall is survivable. Only remaining thrust saves you. This is why the MK-I has five engines arranged so that any one failing still leaves hover thrust and a controllable moment balance for the controller to re-trim within 50 ms.
- Above 120 m: a rocket-extracted ballistic recovery chute (the kind that has saved hundreds of light aircraft) opens in ~1.5 s and brings suit and pilot down at ~7 m/s. Armor and airbags take the landing.
Operationally: The controller keeps every climb and descent through the 3–120 m band short, fast and with forward speed, so that at the top a chute is available and at the bottom a run-on landing is. It never loiters at 40 m.
Also in this category: fuel exhaustion (The controller lands with 2 minutes of fuel no matter what the pilot wants), a flameout from ingesting the exhaust of another engine (nozzle placement rule: no intake downstream of another nozzle in any attitude), and foreign-object ingestion on dusty pads (intake screens, paved pads only).
Fire, heat, carbon monoxide, noise
Five kerosene micro-turbines on a body. Each hazard has a number and a design response.
| Hazard | The number | Design response |
|---|---|---|
| Exhaust temperature | 650–700 °C at the nozzle, > 300 °C a metre downstream | Nozzles angled away from every limb in every flight attitude. Titanium heat shields on calves and lower back. Thermocouples on the shell; The controller warns at 60 °C skin-side. |
| Fuel fire | Jet A-1 flash point 38 °C; 20 kg aboard | Crash-resistant bladder tank with breakaway self-sealing fittings. Fuel shutoff solenoid per engine, auto-closed on tilt > 90° on the ground, on impact, or on the ABORT button. Nomex base layer. Fire crew with foam at every test. |
| Engine burst | Turbine wheels at 100,000+ rpm | Kevlar containment wrap on every engine. Engines mounted so the burst plane never intersects the pilot’s torso or head. |
| Carbon monoxide | Warn 25 ppm · abort 50 ppm (OSHA 8 h limit is 50) | CO sensor inside the helmet. Visor sealed with positive-pressure filtered air from an intake forward of all exhausts. Hover in own exhaust is the worst case; The controller limits ground-effect hover to 20 s. |
| Heat stress | Core 38.5 °C warn · 39.0 °C land · 40 °C heat stroke | Liquid cooling garment (Apollo-style) removes ~350 W. Core temperature from an ingestible pill or tympanic sensor, not skin. AGSM and arm thrust are hard work; summer flights are shortened. |
| Noise | ~125 dB at the ears unprotected; 115 dB is a 15 min/day exposure | Foam plugs plus active-noise-reduction helmet: ~35 dB reduction. All audio by bone conduction. Hearing checks in the medical. |
| Vibration | Five unbalanced rotors | Elastomer engine mounts, balanced at build, vibration sensors feed the controller’s engine-health model. Rising vibration is the earliest warning of a bearing failure. |
Spatial disorientation
The inner ear cannot tell acceleration from gravity. In a sustained turn it reports level flight; roll out and it reports a turn the other way (the leans). Tilt the head in a turn and the Coriolis illusion makes the whole world tumble. In cloud, at night, or in the first second after a visor fogs, pilots fly into the ground convinced they are climbing.
Response: the MK-I is day-VFR only (visual conditions, daylight) for its entire first program. The controller holds attitude; the pilot commands intentions (climb, turn, faster), not angles. The visor always shows an artificial horizon and the controller ignores a pilot input that would roll past 60° while vertical speed and vision disagree.
The face
At 200 km/h air pressure on the face is ~1.9 kPa; eyelids cannot stay open and tears stream. A sealed, heated, anti-fog visor is a flight-critical system, not a comfort item. Visor failure is a mandatory immediate landing. Bird strike at cruise is 2.4 kJ into the face: the visor is bonded polycarbonate rated to motorcycle standard and the helmet shell spreads the load.
Lightning, rain, gusts above 15 kt, and any visible moisture are no-go for the first program. Weather station at the pad, the controller refuses launch outside limits.
The pilot standard
G tolerance is not a fixed property. The same person varies by 2 g from one morning to the next.
Medical, once
- Cardiovascular exam with ECG and echo; no history of syncope, arrhythmia, hypertension.
- Normal haemoglobin, no anaemia, no anticoagulants.
- Vision correctable to 20/20, no retinal issues, normal fields.
- Spine and neck imaging; a 3 kg helmet at 6 g is 18 kg on the neck.
- Hearing baseline. Vestibular function test.
- Not pregnant. BMI 19–27. Age 21–45 for the test program.
Training, before first free flight
- Centrifuge qualification: 6 g for 15 s upright with AGSM and G-suit, with no greyout. Repeated every 12 months.
- Hypoxia awareness: altitude chamber or reduced-oxygen breathing device, so the pilot knows their personal symptoms.
- 50 hours tethered hover, 20 hours simulator with controller failure injections.
- Egress and chute drills in the suit on a drop rig.
- Fire drill: fuel-fire escape in under 15 s.
Every day · what moves your number
| Dehydration (2% body mass) | −1 g |
| Alcohol in last 24 h | −1 to −2 g |
| < 6 h sleep | −0.5 to −1 g |
| Skipped a meal | −0.5 g |
| Fever, cold, flu | −1 g, no flight |
| Hot shower, sauna before flight | −0.5 g (vasodilation) |
| Good AGSM, trained | +2.5 to +4 g |
| Strong legs and core | +0.5 to +1 g |
Pre-flight pilot self-check
0 / 0Suit and pad pre-flight
0 / 0Abort criteria · design intent: automated landing, pilot opinion not required
- Any engine EGT, rpm or vibration out of band, or a thrust asymmetry the controller cannot trim in 200 ms.
- Fuel for less than 2 minutes at hover power.
- Helmet CO > 50 ppm, SpO2 < 85%, core temperature > 39.0 °C.
- Heart rate > 180 or an arrhythmia on ECG. Eye-tracker fixation lost for > 1 s under load.
- No pilot input for 3 s while the controller expected one (incapacitation test), or incoherent inputs.
- Visor fog or crack, cooling loop failure, G-suit pressure loss.
- Geofence or altitude ceiling breached. Wind at the pad above limits. Telemetry link lost for 5 s.
- The ABORT button. Either grip. Or the ground crew’s.
Planned pilot-incapacitation protocol
- Detect (< 1 s): eye-tracker fixation loss, head slump on the head IMU, limp throttle inputs, ECG pattern. Any two of four.
- Unload: acceleration to 1 g, wings level, airspeed to best-endurance. G-suit to full pressure, oxygen to 100%.
- Hold: straight and level for 30 s. Most G-LOC victims recover within 30 s. Audio and visual prompts to the pilot; a response within 30 s returns authority gradually.
- Land: no response, or any vital still out of band: The controller picks the nearest pre-surveyed landing site, flies the approach, lands at 0.5 m/s, shuts down the engines, inflates the airbags, broadcasts position and vitals to ground crew and emergency services.
- Never: hand control back mid-approach to a pilot who has been out. Authority returns on the ground.