Para hélices, existe uma distância mínima ao solo de acordo com as Regras de fácil acesso da AESA para aviões normais, utilitários, acrobáticos e de passageiros (CS-23):
CS 23.925 Propeller clearance
Propeller clearances with the aeroplane at the most adverse combination of weight and centre of
gravity and with the propeller in the most adverse pitch position, may not be less than the following:
(a) Ground clearance. There must be a clearance of at least 18 cm (7 in) (for each aeroplane with
nose wheel landing gear) or 23 cm (9 in) (for each aeroplane with tail wheel landing gear)
between each propeller and the ground with the landing gear statically deflected and in the
level, normal take-off, or taxying attitude, whichever is the most critical. In addition, for each
aeroplane with conventional landing gear struts using fluid or mechanical means for absorbing
landing shocks, there must be positive clearance between the propeller and the ground in the
level take-off attitude with the critical tyre completely deflated and the corresponding landing
gear strut bottomed. Positive clearance for aeroplanes using leaf spring struts is shown with a
deflection corresponding to 1.5g.
(b) Aft mounted propellers. In addition to the clearance specified in sub-paragraph (a) an aeroplane
with an aft mounted propeller must be designed such that the propeller will not contact the
runway surface when the aeroplane is in the maximum pitch attitude attainable during normal
take-off and landings.
So 18cm parece ser a distância mínima ao solo para hélices na maioria das aeronaves (por exemplo, ATR-42).
É difícil provar um negativo, mas a seção sobre turbojatos e motores turbofan não lista um mínimo.