English grammar

O. H. Kabir, Dhaka
There are five vowels a, e, i, o, u in English language. It is said that no word is complete and meaningful without affixing any one of the five vowels such as cat, met, inn, run, black, elder, injure, open, urge etc., etc. But what about words without any one of the five vowels like sky, dry, slyly, try, why, fry etc? So, for cogent reasons, why should not English language have six vowels a, e, i, o, u and y instead of five? May I humbly request our learned English language experts to enlighten us on the matter?