7.5G Centrifuge Qualification
Before flying the T-38, Air Force pilots must complete high G-force training in the centrifuge at Wright-Patterson Air Force Base. This training prepares pilots for the physical stresses experienced during flight in the T-38 (or any fighter type aircraft) by exposing them to G-forces in a controlled environment.
The T-38 has the third highest G-Induced Loss of Consciousness (GLOC) rate of fighter aircrew across the Air Force. Thus, it is imperative that the pilots flying this jet have consistent and effective Anti-G Straining Maneuver (AGSM) mechanics to protect themselves from GLOC.
Allowing pilots to experience high G-forces on the ground greatly reduces the risk of GLOC in the air, as pilots are able to develop an effective AGSM, recognize their susceptibility to GLOC, and receive real time feedback from highly educated and experienced aerospace physicians and physiologists (G-force subject matter experts). I recently had the opportunity to go through the 7.5G qualification prior to flying the T-38. In this post, I will share a few valuable lessons I learned and talk about my overall experience.
For the T-38, A-10, F-15E, and F-18, pilots are required to undergo a 7.5G for 15 seconds centrifuge qualification. For the F-22, F-35, and F-16, and F-15C, pilots are required to qualify at 9Gs for 15 seconds.
For the 7.5G rating, the sequence of G-loading is as follows:
Measurement of resting G-tolerance, apply AGSM when gray out or vision loss begins, rest as required.
5 Gs for 15 seconds, rest as required.
6 Gs for 10 seconds, rest as required.
5 Gs for 30 seconds, rest as required.
7.5 Gs for 15 seconds, rest as required.
Simulated Air Combat Maneuvering
7 Gs for 10 seconds, immediately followed by…
3 Gs for 5 seconds, immediately followed by…
6 Gs for 5 seconds, immediately followed by…
3 Gs for 5 seconds, immediately followed by…
7 Gs for 10 seconds, rest as required.
Repeat G-loads as required for AGSM development.
GLOC is a brevity term for the physiological response that results from a lack of sufficiently oxygenated blood and or/pressure in the brain. GLOC causes visual impairment, degraded cognitive function, hypoxia, and absolute/relative incapacitation. A majority of the time (90%), GLOC is caused by an ineffective AGSM. However, attention management, G-suit awareness, dehydration, nutrition, and fatigue can all play a role in a pilot’s instantaneous and sustained G-tolerance.
The best part of attending this training was receiving the knowledge and education that our instructors provided first hand. All of my classmates were able to improve their AGSM technique and G-tolerance simply by applying the strategies they enforced. In order to have a proper AGSM, it is necessary to have a relaxed upper body, effective respiratory component, and intense lower body muscular contraction. A good analogy is to think of the body during the AGSM like a tube of toothpaste that is running low: if the top of the toothpaste container is rigid, liquid from the bottom will not be able to flow upwards. Keep in mind that as the load factor increases, the only thing that should change in the AGSM technique is the intensity of the lower body strain. The upper body and breathing remain the same.
Below is a brief description of the three components of the AGSM:
Relaxed Upper Body
Allow the upper body to melt downwards. From the chest up, the body should be loose as a goose!
Keep as relaxed a face/jaw/neck as possible before, during, and after G-onset.
Effective Respiratory Component
Breathe from your diaphragm. Inflate your diaphragm when you inhale.
Take a proper preparatory breath - about 0.5 seconds before G-onset. A proper prep breath should be 70-80% of your maximal inhalation.
Make a short/crisp air exchange every 3 seconds. Many people recommend using the ‘Hook’ or ‘Letter K’ sound at the top of every air exchange. What matters isn’t the sound, but the quality and speed of the air exchange.
Lower Body Muscular Contraction
Perform lower body exercises in the gym to increase power, strength, and mass.
The AGSM requires intense lower body straining. Ensure you are adequately conditioned so you do not risk pulling/tearing a muscle.
The proper leg position for the AGSM is to drive your heels into the ground, with your toes pointed upwards.
As you begin the muscular contraction, drive your knees inwards (using the adductor muscles) and towards you. Engage your glutes (like a hip thrust) by pushing your hips against your safety belt.
Take a quick preparatory breath to brace the core moderately (like you’re bracing against a weight belt).
Sustain the lower body and core contraction, while allowing air to be exchanged every 3 seconds.
The AGSM is very technical, but with proper coaching and with enough practice, the AGSM becomes instinctual. The proper sequencing of events when flying the aircraft is to set your lift vector, allow about 0.5 seconds to AGSM, and then pull back on the stick. If you load up the aircraft before your body is prepared for the G-forces, you are at a significantly higher risk of GLOC (this phenomenon is called “Getting behind the G”).
Below are a few common mistakes that pilots make when performing the AGSM:
‘Bearing Down’ is a brevity term for being too tight/tense/rigid with the upper body and face. When performing the AGSM, you want your upper body and face to be as relaxed as possible, allowing the skin on your face to droop and your shoulders to sink downwards.
Inadequate Leg Strain
Without question the most important part of the AGSM is having a rock-solid lower body. Even pilots with poor breathing mechanics and a tight upper body can fight their way through 9Gs simply by having a solid foundation in their core and lower body. Squeeze your legs proportional to the Gs you are pulling. The heavier the G, the more you need to squeeze your legs.
Make a rapid breath exchange every 3 seconds. Don’t allow your breathing to break down when the Gs hit you. One of the biggest mistakes I made in the centrifuge was allowing the wind to get knocked out of me and then gasping/gulping for air. Take a solid prep breath, and keep it in your belly. Do not allow the air to be knocked out of you during the G-onset. The air you inhale from the prep breath is what will sustain you for the 6-15 seconds you are under G.
Pulling Gs (especially in the centrifuge) is VERY physically demanding. However, with the proper training just about anybody can learn to sustain G-forces. Don’t forget this when you have light loss, gray out, or feel overwhelmed by the power of the centrifuge/aircraft. I know several people who have experienced GLOC/ALOC solely because they did not believe they could sustain the Gs! They second guessed their G-tolerance. The most important part of sustaining Gs is desire. Ultimately, having the will to maintain consciousness, despite maximal light loss and intense physical exertion, is what will get you through the program. No amount of physical fitness, nutrition, or rest can prepare you for G-forces. It is all about having the will to win!
I am often asked what the most challenging part of the centrifuge was. While it varies from person to person, I found that the hardest part was feeling out of breath. As soon as the Gs hit me, I felt like the wind was knocked out of my stomach and I was gasping for air. Finding the right quantity of air to inhale during the prep breath was something that took me several attempts. To improve my AGSM going forward, I will combine lower body and core isometrics with breath hold training to increase my tolerance for oxygen deprivation and improve my body’s oxygen delivery. With regards to weight lifting and resistance training, I will focus on properly inflating the diaphragm when performing any compound lift, especially barbell squats, leg press, and hack squats.
While necessary to maximize performance in the aircraft, going to the centrifuge is not something pilots necessarily look forward to. G-forces do not discriminate against anybody, and will humble even the fittest of athletes. To prepare for the centrifuge, I recommend strengthening the core and lower body, increasing VO2 max, and improving heart rate variability.
If you’re interested in training or experiencing the centrifuge but have no plans of becoming an Air Force pilot, the 711th Human Performance Wing and USAF School of Aerospace Medicine in Dayton are always looking for volunteers to get spun at up to 9x the force of gravity! For more information please contact the 711th Human Performance wing at 711HPW.HSP@us.af.mil.
Thank you for sharing, and stay grinding!