Jeff, I quite like where you're going with this. Nice big tail and rudder for single engine controllability. Big engines for single engine performance. It needs to be so good on one engine that the saying "second engine takes you to the scene of the crash" doesn't apply.
If we're sticking de-ice systems on this plane, then it needs big engines to keep performing when the icing gets bad too. The turbo UL520 sounds wonderful.
4 seats though, need the seats.
Would it sell? Would people build it? I'm guessing not many. Same problem as described the 6-seater thread. The plane would simply be too big and complex.
Yep, I agree with you David. I understand the Derringer had pretty good engine-out performance. Like you said, big engine, big tail, and you also need to be lightweight (read: high HP to weight ratio) to get good single engine performance. To help out on the S.E. performance, just don't load up with fuel and payload and stay light if you're worried about an engine-out scenario (mountains, night, etc.). Once you're out of the "danger zone" you can land, tank up and fly heavy, with a lower S.E. service ceiling.
That's one of the main reasons I said to have huge fuel tanks. So that even with half full "main" tanks you still have good range in the aircraft. You're going to want to have around 180 gallons total fuel capacity with this aircraft. 30 gallons in the outboard tanks (each tank) and 60 gallons in each inboard "main" tank. The UL520T typically burns 8-11 GPH so full tanks should give you about 9 hours before you're a glider. That's a LONG flight!!! With 30 gallons in each main tank, you're talking a 2 hour flight with a 45 minute reserve. The Derringer supposedly had a 184 kt cruise speed. I would expect with the more powerful engines you would be going faster but this still gives you about a 350 nm range with a 45 minute reserve. That can get you past a lot of "bad" territory.
Maybe a compromise on the seats would be to do what is done on the Sportsman 2+2. You have two, full size seats in the front and two aft facing seats in the back. The aft facing seats share a common seat back that can be easily removed via four bolts to make room in the back if you want to pack the back with cargo. The rear seat "bottoms" are attached to the seat back via piano hinges and are removed with the seat back (it's all one big assembly). The piano hinges allow you lift up the seat bottoms to store small items under the seats when they are installed. It's a really nice setup. The seats in the back can easily fit a couple of kids or small adults. Plus, they work great for tossing baggage on them. Just Google "Sportsman 2+2 aft facing seats" and look at the images. Some people had forward facing seats in the back but the head room was limited as was the allowable load due to C.G. concerns.
The aft facing seats have some good qualities to the design.
1) It keeps the C.G. close to the front seats when you put people in the back.
2) You get more head room for those in the back since the fuselage has a larger cross section there.
3) Both the front and rear seats, seat belts, headset wiring, etc. tie into the same bulkhead. You don't need to make two, relatively heavy, complex bulkheads with this arrangement.
Let's face it, most of the time you probably won't be flying with someone in the back seats. If you do, they will be facing backwards. Some people won't like facing aft during the flight. For them either put them in the front seat or leave them on the ground...
Would it sell? Yeah, I'm sure it would sell a few. How many? Who knows. A lot of people talk. Very few take action unfortunately... If Van's had something like Glasair's Two Week To Taxi (TWTT) program, then you'd probably get more takers. With the TWTT program, you're essentially trading cash for time. Also, the people who would most likely be purchasing an aircraft like this have the cash but not the time. The people who don't have the cash for a TWTT program wouldn't be purchasing an aircraft like this anyway.
It would be nice but again, I don't think Van's would do this. Maybe someone else will...
Jeff