Realistically, this thing will be crawling off the rod. By the time the 3rd stage lights, it'll be lucky if it's not already pointing back at the ground. While the forthcoming E12 will no doubt be an improvement over the E9 in terms of lifting ability, it's still not a high-thrust motor (comparatively speaking). Yes, an E12-0 booster will be better than an E9-0 booster. And I will surely buy and fly them. But they're still only moderate thrust motors. Yet they're still quite heavy motors. So the the two upper stage motors will present quite the payload challenge to the 1st stage motor, even in an otherwise very light rocket.
Flyer beware
Doug
Well, the Comanche (or a Comanche-3E variation) is, for the E motors, a minimum diameter 3FNC -- not a huge chunky thing like the Saturn V or the Maxi V-2 (to name a couple rockets which have had E9 launch problems).
https://www.nar.org/SandT/NARenglist.shtml
According to NAR, there will be an E12-0 (as well as a -4, -6, -8)
Also according to the present data, max recommended liftoff weight for the current D12-0 is 13.9 ounces. I would guess the max liftoff weight of the E12 will not be less.
The listed kit weight for the C-3 is 2.1 ounces. (In addition a 'Comanche-3E' would not have the interior motor mounts in Stages 2 and 3 that the 'stock' version does, only thrust rings, so total vehicle weight would be slightly less).
Current E motors weigh about 65 grams (2.3 oz) at ignition so if you went all-up with 3 E motors at 2.3 oz each makes 6.9 oz, add 4 ounces for the rocket (allowing some extra weight for sloppy building), all-up weight should be something around 11 ounces (of course it's also possible some extra nose weight could be needed too since we're sticking heavier motors in the rear end. You'll also have to mess with Stages 1 and 2 to accommodate the longer E motor casings).
We will have to see exactly what the time-thrust curves and total impulse of the E12 turn out to be. My guess is a Comanche-3E would chug somewhat slowly off the pad, but once it starts picking up speed should be fine.
As you note the E12 will not be a "high-thrust" MPR motor (certainly not compared for instance with the AT E30) but it will have a good deal more kick than the current E9. My wild guess is the liftoff characteristics will probably be pretty similar to the current D12 (with a longer burn of course).
Unless you have dramatic problems with rod whip/tip-off my guess is the rest of the flight would be OK. After you drop the first stage your rocket weight is down to about 7.5 oz and lift capacity and airspeed/stability should be no problem any more.
But getting that third stage back could be a problem unless you're launching in the desert. My bet is the odds of SECOND-stage recovery are about 20 percent. That is gonna be a teeny-weeny stage dropping off from way way up. When second-stage burnout occurs the stack will have been under thrust for something like 5 seconds. Not to mention, the second stage in the current Comanche kit is held on by friction-fit tape on the motor -- if you are launching this sucka E12-E12-E12, by the time you get midway in the Stage 2 burn, the drag forces on the fins are going to get pretty stiff and be likely to peel that thing right off of there unless your "friction fit" has the holding power of industrial welding.
Once the actual E12 thrust data is out, somebody will have to RockSim it (I don't have a current version) but I would guess by the time you get to Stage 3 burnout you could be in mach-busting or speed-of-balsa territory. After 7.5-some seconds of thrust that third stage is going to be going like a BOOH.
This would definitely be a roll-the-dice project, probably about $25 of motors going up in a $30 rocket, with a good chance of something going wrong, but it would be fun to watch if somebody can pull it off.
But yeah.... Flyer beware!!
:y: :y: