NO. 5 STABILITY OF AEROPLANES HUNSAKER AND OTHERS 37 



and damped to one-half amplitude in time, 



/= -^ =o.ou4 second. 

 7-3^ 



For most aeroplanes, this first factor corresponds to a short oscilla- 

 tion SO heavily damped that it is of no im]:)ortance. Indeed, it could 

 not be observed on the actual aeroplane in flight. 

 The second factor, similarly, reduces to : 



Z)=-.o85±.i8i/. 



P= ,, = >4-7 ."^econds, 

 .i8i 



t= —/ =8.1 seconds. 

 .085 



This is a longer oscillation but heavily dami)ed. The period of 34.7 

 seconds for the motion is great, and at high sjieed this aeroplane if 

 left to itself after an accidental longitudinal disturbance should follow 

 an undulating path with rising- and sinking of the center of gravity, 

 together with ])itching- and periodic changing of forward speed. 

 There is an oscillation in u, iv, and B. In 34.7 seconds, the aeroplane 

 runs 3900 feet, which is the distance from crest to crest of the flight 

 path. In one period the ampHtude of the undulation is almost com- 

 pletely damped. It is unlikely that this motion wpuld be uncom- 

 fortable to the pilot even if the initial disturbance due to a gust or 

 other cause were severe. 



At high speed, this aeroplane is very stable compared with other 

 machines which have been tested. The natural period of the Curtiss 

 JN2 is aljout 34 seconds, damped 50 per cent in 11 seconds, according 

 to calculations made by us. A Bleriot monoplane model tested by 

 Bairstow had a period of pitching of 25 seconds, damped 50 per cent 

 in 15 seconds. 



There 'is no other i)ublished data of this character. It appears that 

 great statical stability or large AUv will give a stiff machine with a 

 rapid period. Such a machine, though very sta])le, may be so violent 

 in its motion as to lead the pilot to pronounce it unstable. The design 

 tested here appears to have as easy a period as the Curtiss and Bleriot, 

 both considered very satisfactory in flight, together with greater 

 damping. 



High speed and a long tail tend to damp the pitching. What we 

 aim to secure — namely, steadiness in flight — may better be obtained 

 by large damping factors rather than by strong righting moments 

 (statical stability) . It is well known that the French monoplane pilots 



