G axes, jolt & turbulence loads
G (TC AIM AIR 3.15):
- Acceleration: a force with a direction (3.15.1).
- Affects every pilot, in every aircraft.
- Gravity: g = 32 ft/s² (3.15.1).
G described in three planes relative to body (international convention):
| Direction of acceleration | Resultant | Vernacular | Code |
|---|---|---|---|
| Headward | Head to foot | Positive G, "eyeballs down" | +Gz |
| Footward | Foot to head | Negative G, "eyeballs up" | -Gz |
| Forward (chest to back) | Transverse | "Eyeballs in" | +Gx |
| Backward (back to chest) | Transverse | "Eyeballs out" | -Gx |
| To the right | Lateral | "Eyeballs left" | +Gy |
| To the left | Lateral | "Eyeballs right" | -Gy |
Axis tolerance (only Gx and Gz matter to civilian pilots):
| Axis | Matters to civilian pilots | Tolerance | Effect |
|---|---|---|---|
| Gx (transverse) | Yes | Well tolerated; up to +50 Gx for short intervals without tissue damage | Disorientation is most significant effect; breathing impeded |
| Gy | No | Not a significant problem in current aircraft | - |
| Negative G (-Gz) | Yes | Poorly tolerated | Blood pressure in eyes and brain increases, giving red-out (red haze in vision) |
- Unqualified "positive"/"negative" G means Gz (TC AIM AIR 3.15).
Non-steady loads (TC AIM AIR 3.15.2):
| Load | What it is | Effect |
|---|---|---|
| Jolt | Rate of change of acceleration; short, sharp accelerations | Can cause serious spinal injuries |
| Turbulence | Brief alternating positive and negative Gz forces | Serious problem for light aircraft in hot weather; interferes with precise flying; potent source of fatigue |
Trap: unqualified "positive"/"negative" G is Gz. Name the axis for Gx or Gy. Turbulence G alternates between positive and negative Gz, not one-way G. Jolt is not G-LOC (loss of consciousness).
References
- TC AIM AIR 3.15