I love the D5 motors, but I tend to lose rockets on them due to having only a 500 foot radius around the pad for guaranteed recovery.
I had a bunch of them, actually still do. A great rocket for these on a larger field is a BT-50 downscale of the Blue Bird Zero, that I build specifically for this engine. I've built two of these, and lost them both. Eventually got the first one back (along with camera strapped to it) after 3 months in the trees. The second one is still AWOL (fortunately, no camera attached). The first was BT50 with the D5 motor mount glued in (I used tape wraps as centering rings), while the second was built as BT50 minimum diameter used with an adaptor for D5 engines.
BT55 version of Der Red Max also does well with this engine (mind the nose weight!), and Big Bertha has a fun ride too. Anything more massive may not be safe due to the low initial thrust off the pad. In still winds my full scale Der Big (green) Red Max has a good flight, but after about 7 mph winds, it weathercocks unsafely.
I'm considering a futuristic design using these in external pods. It would be rear-eject, off a central D5-6, (~10 seconds into flight, post-apogee) while the pods would be designed to pop off first using D5-4 engines. There don't seem to be D5-0 booster engines, though there are plugged D5-0s available. These are too weak to be traditional boosters, so no surprise there.
I have an adaptor made from one of the D5 motor tubes / thrust rings, with peeled out BT-20 to BT50 paper rings for centering. Actually, my adaptor is lost with the latest BBZ downscale, so I guess I need to make another one.
Since the bird needs to be lightish, it makes good sense to build for a D5 and then adapt down to B or C engines. I'd say a lightly-built Berta-esque bird would be a good choice. I tend to build heavy so I need to be careful with these...
"If at first you don't succeed, Scream and Leap!"
NAR member 92906