These quotes below(of which I have removed some info I felt to be non-pertinent were made on another thread.
Originally Posted by
Dropp the Pilot
Training for positive rate/climb identification is based on teaching pilots to recognise a positive V/S trend and increasing RA."
Two wrong statements in less than twenty words
Neither of these things are "positive rate". A V/S trend is a measure of vertical acceleration. It will happily read a positive vertical rate with both main gear planted on the runway with say, a gross error in take-off performance calculations or wind shear. RA is valueless for rate as the reading which the pilots see is a product of an algorithm of pitch attitude and gear tilt and is by no means a direct reading of actual height.
The ONLY measure for positive rate is a sustained and progressive increase in the altitude displayed on the altimeter.
Should you doubt any of this, consult any FCTM from a company called Boeing. They've been doing this stuff for quite some time.
Originally Posted by
silverstrata
Well said.
In addition to your reasoning, inertial vertical speed indicators will show a false positive rate of climb, on rotation.
Silver
Subsequently I found a note mine for a particular modern aircraft that says.....
VSI indication comes from the IRS, therefore when the nose is raised, there will be a positive climb indication even though the main gear is still on the runway.
So would most agree that the VSI is not a good instrument alone to use a determining a positive rate of climb for gear retraction after rotation and that the positive rate indication is initially due to the IRS moving upward.