Quenya did not tolerate the vowel combinations [ae] or [ao], and these generally became [ē] or [ō]. These sound changes explain the somewhat peculiar rule that the genitive form of nouns ending in -a was -o, for example:

• ciryo genitive of cirya “ship” (LotR/377).
• calo genitive of cala “light” (PE17/143).
• Eldo genitive of Elda “Elf” (PE21/77).

This is because -aō > -ō > -o. Tolkien discussed these phonetic developments in the Outline of Phonetic Development (OP1) from the 1940s:

In case of ae, ao contraction occurred: quality depending on length. ā + ĕ, ā + ŏ > ā; ā + ē, ă + ē̆ > ē; ā + ō, ă + ō̆ > ō (PE19/63).

Thus, ae, ao > ē, ō unless (a) the ā was long and (b) the ĕ, ŏ was short, in which case: āĕ, āŏ > ā. This sound change took place after [ɣ] from [g] vanished (PE19/63) and thus applied to all cases where a was or came to be in hiatus with e/o.

Conceptual Development: Tolkien described a similar set of sound changes in the Qenya Phonology of the 1910s:

ā̆ē̆ gave ā (aḗ); ... ăō gave ō; ā̆ŏ gave ā (PE12/14).

At this earlier stage, the default was ae, ao > ā with the exceptions ăō > o and apparently ăḗ > ăḗ. However, the only clear example of this sound change in the 1910s shows ăŏ > o (with presumably long ō > ŏ before the consonant cluster):

• ᴱ√TAHA > tahorme > taorme > ᴱQ. torme “mountain peak” (QL/87).

Thus, Tolkien may have flipped the default developments for ao early on. In the 1930s Tolkien first wrote: “Also ae > ā, ao > ō” (PE19/63 note #165) before deleting this and replacing it with the rules given above. Thus in the first draft of OP1 the combination ae still showed the Early Qenya development to ā before Tolkien revised this development to ē. There are no published examples of Quenya words containing ae at any conceptual stage, so analyzing Tolkien’s thoughts on this combination is difficult.