HEE-licopter

[sagehen]

 My old family dictionary, a New Century edition, IIRC, 1928 (the front
pages have disintegrated), gives only "hel-i-cop-ter" with a short /e/, but
"HEE-licopter" was the usual pronunciation I heard in the '30s & '40s in
Nebraska, at least.  HEE-li-o-copter, also occasionally, but considered
substandard.
I've never heard /helix/ pronounced with anything but the long /e/, but the
spiral wires with which we assembled innersprings in the mattress factory,
in which I worked in the '50s, were always and only called "helicals,"
short /e/.
A. Murie