THE " HD-4." 1 
A 70-MILER WITH REMARKABLE POSSIBILITIES DEVELOPED AT DR. GRAHAM 
bell's laboratories on the bras d'oR LAKES. 
By William Washburn Nutting. 
[With 9 plates.] 
One of the most interesting of the many strange things that have 
come from Dr. Graham Bell's laboratories is a weird-looking glider 
that recently has been tearing about the peaceful Bras d'Or Lakes at 
the rate of 70 miles an hour. 
The HD-'Ji. is not a hydroplane in the usual sense of the term. It is 
the successful development of the idea, by no means new, of lifting 
the hull clear of the water by a system of submerged planes not a 
part of the hull itself. In other words, it uses the denser medium to 
obtain the lift and takes advantage of the low resistance to pro- 
pulsion offered by the air. An ordinary hydroplane, of course, 
utilizes the lifting principle and dodges much of the resistance of 
the water, but it is still comparatively inefficient in that it uses only 
the lower and by far the less important surface of the plane. 
A number of years ago Cooper-Hewett experimented with the idea 
of superposed planes and Forlanini attained some success with this 
principle in Italy. It is an alluring idea as the patent office records 
w^ill show. But the HD-^J^^ although she is only in the stage of de- 
velopment of the aeroplane of 10 years ago, is much more than a 
successful application of principle of lifting the hull clear of the 
water. You will notice from the detail pictures that the steel planes 
are arranged in sets like the rungs of a ladder and graduated from 
large ones at the top to small ones at the bottom. The faster the 
craft travels the more of the planes rise out of the water until only 
sufficient surface to carry the load remains submerged. 
This automatic reefing of the supporting surface is one of the 
important features of the IID-J). and one which, I believe, never has 
been attempted in an air craft, in which there is but one economical 
condition of speed and loading, a disadvantage particularly notice- 
able when taking off and landing. 
» Reprinted by permission from Motor Boat, Vol. XVI, No. 20, Oct. 25, 1919. 
205 
