Man I love 680Fs and FLs. I really hope you end up in a nice one. But you shouldn’t, you really shouldn’t.
I mean, unless your neighbor has one and the shop has it all figured out. Or at least your mech is already maintaining a couple of igso Lycs. Which is not the case.
I think I’ve mentioned how much I admire your internet sleuthing skills. I’ve been down all the same alleys you have, scouring for every bit of info on the big engine Commanders. Pretty much reached the same conclusions you have. And yes, if I was rich and retired, I would pursue an igso powered plane to compliment my 500. Turbo are great airplanes, but they just don’t interest me.
I can tell from your writing that you already know the following, but you want to push ahead anyway and enjoy the ride.
1 - It is going to be more expensive and less reliable than you are planning for.
2- Comparing book figures (I own the same manuals you have) with the very limited amount of real world reported performance by people like Popeye who are actually flying the planes - these manuals were published back when everybody knew that performance was overstated by 10 percent and fuel burn was understated.
When shopping for my plane I went on a demo flight in a 560F. I expected it to be a real performer. I still have the notes from that flight. No front door, no interior (crew seats only) 160 gallons of fuel on board. It really didn’t accelerate or climb better than my 500. Less rip from the props. I mean the engines sounded great! The speed was well below book. 22” and 2600 rpm at 1500’. Should have been truing 170kt on 25 gph. I saw 150 kt on 34 gph. About 5 kt faster than my shrike but burning 50% more fuel.
If fuel totalizers were correct left was burning 15 but rh would not run smoothly below 19gph. Maybe there was something wrong with the engines. Wait, what am I saying. With unsupported engines from this era you’re always living with “something” wrong.
My initial thought when you were suggesting that 680 FL takeoff and climb to 1000’ might be comparable to a 690A was a head shake. However I do remember, as young corp pilot getting a rude awakening in Denver my first “ hot high” takeoff in a -5 690A. So maybe a long wing igso could outperform -5 short wing at high DAs.
Let me take a different tack. While saving for your -10 powered TC is it possible that a little investment in the 500 could meet your needs?
You didn’t say what you need the extra space for but on our adventures, we are packed to the gills carrying 4 people and gear. It would take two Barons to do the job.
1- A front door makes a big difference in how much junk you can take with the couch out and two or three pax.
2- Getting rid of aft cabin trim with access to baggage compt. Makes loading more easier.
3- baggage compartment. Extensions.
4- A nice 500U that I looked at had a mod that moved the battery down, and gave nice compt at battery door with room for all the oil, step ladder, etc you could want.
