602 TRANSACTIONS OF SECTION G. 
4. Catastrophic Instability in Aeroplanes. 
By F. W. Lancuester. 
Attention was called to a form of instability of a kind not previously 
investigated. The author bases his investigation (which is of a preliminary 
character) mainly on observations made in the course of his previous experi- 
mental work and mentioned in his ‘ Aerial Flight,’ reading these in the light 
of some modern experiments on the pressure reaction of aerofoils, more 
particularly tests made in the National Physical Laboratory. The author 
takes as his starting point the ballasted plane, it being shown that this type 
of glider (in common with some other types) has a certain ambiguity in its 
flight path, its whole peripteral pressure system being liable to reversal as the 
results of aerial disturbances of quite minor degree. It was pointed out that 
types of gliding model having this property are unsuited to the purposes of 
aerial navigation, since in the event of a ‘reversal’ taking place an immediate 
and accelerated descent results of a character that can scarcely fail to bring 
disaster. 
The conclusions formulated are that, although in absence of knowledge the 
design of a machine might easily be such that this form of instability would 
show itself, the avoidance of any danger is not difficult; briefly, the following 
points require to have due consideration :— 
(a) The tail should be a directive rather than a weight-carrying organ, the 
construction of existing machines being criticised in this respect; 
(b) The aspect ratio of the tail-plane should be high; 
(c) The influence of the ‘ wash’ as affecting the angle and behaviour of the 
tail-plane to receive proper consideration. 
It was further pointed out that amy model or machine that, with a single 
setting of its directive organs, is capable of flying either way up is liable to 
exhibit catastrophic instability, and must be considered dangerous. 
In conclusion a few remarks were added on the subject of the flexibility 
of the sustaining and directive organs as bearing on the main subject of the 
paper. 
5. Domestic Electric Cooking, Heating, and Lighting. Results of One 
Year’s Working. By Professor J. T. Morris. 
6. Note on Frictional Losses in Steam Pipes. 
By Crciu H. Lanper, M.Sc., Assoc.M.Inst.C.H. 
The loss of pressure in a steam pipe is usually estimated by an expression of the 
form 
Wig ibeafleh 
i Ny as 2 gd 
in which different values of the constant f are used for different diameters of pipes. 
More accurate determinations referring to the flow of fluids carried out under more 
general conditions have shown that the exponent of the velocity is less than 2 and 
in the neighbourhood of 1°8. 
The formula obtained from the theory of dimensions and deduced by Osborne 
Reynolds is 
dp = Kqd"-3 pon p” -1,2% dl 
where dp is the drop of pressure along an element di of the pipe, d the diameter, 
u the viscosity, p the density and v the velocity. From this the following formula 
may be derived 
pie — pit — BEE (: = om) 
(d*”) Qw 
where A = actual weight of steam condensed per sec. per lin. foot of pipe - 
w = weight of mixture flowing through pipe in unit time. 
S = Constant. 
