An experiment has been performed to study the loss of charge from a high velocity probe as it passes through a high‐pressure, low‐density plasma generated by a flame. Charged projectiles are fired through the flame and the loss of charge is measured as a function of the flame density and the projectile speed. Expressions are derived for the charge loss based on the thin sheath, thick sheath, and the field‐limited/sheath convection models normally used to describe the behavior of Langmuir probes. For a low‐density flame plasma, the sheath conduction turns out to be field limited and the exponential function describing the charge loss has been verified experimentally. The charge loss from the ballistic probe is used to compute the electron density profile of the flame. At the sound velocity in air, the residual charge after passing through the flame suddenly drops to near zero, suggesting that the sheath conduction mechanism changes radically as the velocity passes through the transonic region. This result may have far‐reaching implications for the use of Langmuir probes at transonic and supersonic speeds.