6i 



CHAPTER VI. 



GROUND PERFORMANCE. 



General. Apart from the performance of an aeroplane in the 

 air it is often necessary to know how it will perform on the 

 ground. Thus, for instance, in connection with the size of aero- 

 drome required, the distance required for the machine to come to 

 rest on landing and the length of run to get off the ground are 

 sometimes laid down in a specification : also before the trials of 

 a new type, the pilot may ask to be told these figures. 



Again, aeroplanes are often launched from and landed on the 

 decks of ships, so we must calculate the length of deck required 

 in each case. 



These matters are dealt with in the present chapter under 

 the general heading of " Ground Performance". 



Getting Off a Deck. Dynamical problems involving relative 

 motion are full of traps for the unwary. It is therefore advised 

 that the line of investigation here given be not departed from, 

 since to do so may give results different from those here found 

 and leave the investigator faced with some fallacy which may be 

 very difficult to locate. The method here given is accepted by 

 those who are competent to judge and gives close predictions of 

 the results obtained in practice. 



In launching a machine from a deck, it will probably be 

 arranged to do its run at about its angle of attack for minimum 

 resistance, and then be "hoiked" up to its angle of attack for 

 maximum lift at the end of the run. 



Machines specially designed for deck work often have their 

 propeller shafts inclined so that the propeller slip stream meets 

 the wing at a larger positive angle than is ordinarily the case : 

 this is done in order to reduce as far as possible the minimum 

 flying speed under full power. 



Let v m be the minimum flying speed of the machine under 

 full power in feet per second. The method of finding v m for any 

 particular machine will be given later on page 69. 



At air speeds between zero and v m the horizontal component 

 of the thrust of a propeller on full torque, i.e. on full throttle, is 



