Well, that is, on official ships that even have obvious impulse engines. There are more than one where there is no exhaust at all which leaves many to speculate, (myself included) that the exhaust area we see is not intrinsic to the propulsive abilities of the engine. Rather than being a high tech rocket, it is actually a field drive much like a warp engine. This is in direct opposition to the various tech Manuals which explicitly state that the impulse engines are just fancy rockets, but this non-Newtonian model actually satisfies the on-screen evidence more. For example: Rockets don't have reverse gears. Impulse Engines do. Rockets need to be mounted along an objects center of mass. Impulse engines do not. Rockets are firing only when providing propulsive force. Impulse engines are on all the time. Rockets generate velocities well below light speed. Impulse engines have been shown to be able to move faster than light. (See Enterprise in "Where No Man Has Gone Before" (TOS), the Romulan Bird of Prey in "Balance of Terror" (TOS), the Enterprise saucer in "Encounter at Farpoint" (TNG) et al.) No one says you have to agree with this in your own Star Trek universe, but as far as this design goes, the position of the impulse drives is the least of our worries. --Alex
One thing is for sure... Star Trek is consistently inconsistent about stuff like that... For example, has anyone besides me noticed that only Federation designs even HAVE a main deflector...?
Oh I noticed. Believe me.. I noticed. That's the funny thing too, is that there are plenty of Feddie ships that lack one too but people get all up in arms about making sure there's one of some sort or another on their fan-designs. Oh well. --Alex
I did to use them for 'Cage Era' and 'Early TOS' period ship designs. I figure that at some point, they just said 'screw it' and tied the deflector to the shield grid for most ships (particularly smaller ones) and had done with it.
Personally, I prefer the notation in the Franz Joseph plans that it is the Main Sensor. This implies a suite of instruments mounted on ships that engage in exploration/science missions (either exclusively or in addition to military missions). This also implies that many (but not all) Federation designs would have it, and could explain its near total absence on the warships of other powers...