pattern_is_full is essentially right, but overstates the cases somewhat.
I like to compare in terms of
bypass ratio. A typical modern turbofan runs about BP = 4 to 8. A turboprop will be at least double that; Big low-speed prop, small core. This gives lower fuel consumption, better TO performance, and other well-known attributes.
Now put a REALLY BIG fan on it, slow it down and rotate it so the shaft is vertical. They call this a helicopter. Bypass ratio might be in the hundreds, great static thrust, lousy high-speed performance.
OK?
