HEE-licopter

[Dale Coye]

I don't have time to look it up further than my handy MW10, but the root word
there is not Gk helix, but heliko (maybe they're related? my Gk is
non-existent) but Latin and Gk words of two syllables with a single consonant between
the syllables have long vowels, hence HEE liks, but three syllable words with
stress on the first syllable are short, regardless of the original length of the
Latin or Gk word.   So on historical grounds (for what it's worth) HELL ih
copter is the better choice.   Maybe  this lawyer, who looked about 50 was an
old navy man.

Dale Coye
The College of NJ.