Back in 2001, we were talking (in a more erudite fashion, I might ad
) about this:
http://www.pprune.org/tech-log/9523-...eed-aztec.html
.. and again in 2003:
http://www.pprune.org/dg-p-general-a...n-trouble.html
Multi-engine aircraft are divided by FAR 23 into two weight classes - above and below 6000lbs, and those below 6000lbs are divided into two classes depending on Vso (stall speed in the landing configuration) above and below 61 knots CAS.
Only those twins that weigh more than 6000lbs or have a Vso higher than 61 knots need to demonstrate any single-engine climb performance at all for certificaion, and the requirements are pretty meager. Basically the regulation says that these aircraft must demonstrate a single engine capability at 5000' (ISA) with the inop engine feathered and in a clean configaration.
The only requirement for an aircraft less than 6000lbs, and with a Vso less than 61kts (like the Aztec) is that its climb performance (positive or negative) be determined.
There is nothing in the FAR which says an aircraft must fly while in the take-off configuration with one engine inop.
Talking about rotation, manufacturers tend to have a philosophy about this that shows up in in the aircraft design, wing incidence and gear positioning.
Piper recommends that most twins be rotated at Vmc, Cessna on the other hand suggests a lift off at a speed much higher than Vmc and very close to best single-engine angle of climb speed. In the case of a C-310, Vmc is 75 knots, recommended rotation speed is 91 knots and best single engine angle of climb speed is 94.
Try and hold a Seneca or Aztec on the ground much beyond Vmc plus 5 knots (zero flap) and the aircraft will begin to wheelbarrow! Cessna twins (and most cabin class twins) will happily stay on the ground for much longer than that.
A Navajo for instance (stretching the old memory) will happily go by road, if you don't positively rotate it - you hardly have to "force the aircraft on the runway well past VR and until a few knots past Blue Line"!
I would rotate a light (FAR 23) twin not below Vmc+5 (or the recommended rotate), and I pull the gear up just after getting airbourne, then climb at the best all engine climb rate (which is faster then blue line) until clear of obstacles in the area.