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to resistance and high maximum lift with the same section. A good ratio of lift to resistance necessarily means a low value of maximum lift while a high value of the lift co-efficient means a low value of the lift to resistance ratio. The Hendley Page Company hoped to realise the combination of both by putting in this variable device which will admit of two different effects of the resulting air flow. It is to effect this combination that the new design known as the slotted plane was devised.

     The experiments with the De Haviland 9 show an approximate increase of forty per cent of the lift coefficient with the alot opening. The second machine was a cantilever type plane. When tested out in the wind tunnel this second machine gave a maximum lift coefficient of .77 absolute units unslotted and 1.035 when slotted. The full size machine was loaded to 11 pounds per sqaure foot, and the machine landed at 45 miles per hour, corresponding to the lift's coefficient of 1.17 in absolute units. This high lift coefficient with the high lift wings, proves, according to Mr. Handley Page, that model results still hold good as with wings of thimer sections. In this machine the opening and closing of the slot was carried out by means of the vibration of the

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