Total impulse [(N-s) max] of an A-sized engine is only 2.5.

Your C does a bit better at 10 N-s max.

D's makes about 20 N-s max total impulse.

The largest you can buy without a Level 1 amateur rocket license are "G" size engines... They have a total impulse output of 160 N-s. That's right.... 1"G" engine = 8 "D" engines all fired at once... or 64 of your A size engines. [>:][>:]

...So get "G's... even if you just use 1.

---oh yeah, it's new tubes for D+, but you know this.