If the aircraft is designed well, then no.
The yaw stability comes from the vertical stabilizer. It generates a sideways force which gives the aircraft the required directional stability in the vertical axis. As you might already know, all the forces on an aircraft acts through its center of gravity (CG). Thus, the lift force generated by the vertical stabilizer will increase the further away it is from the aircraft CG. A longer aircraft will have its stabilizer placed further from the CG when compared to a shorter aircraft. This will by itself make the shorter aircraft less stable than the longer aircraft in the yaw axis.
However, a shorter aircraft can still be designed to have the same or quite possibly a higher directional stability than a longer aircraft. One way of doing this is by increasing the size of the vertical stabilizer. The larger the size of the stabilizer, the more lift it can generate and hence the more directional stability it can provide. One example is the Airbus A318. Its vertical stabilizer was lengthened compared to other variants of the A320 family (A319, A320 and A321).
The Airbus A318’s vertical stabilizer is 3 ft longer than the other members in its family.
There are also other ways of increasing the directional stability without increasing the length of the aircraft. Some aircraft manufacturers utilize Dorsal fins which are an extension from the vertical stabilizer. This dorsal fins add extra lifting surface to the keel of the aircraft, which assists the main stabilizer to improve the directional stability. Ventral fins are also used and serve the same purpose as dorsal fins. The only difference being the ventral fins are attached below the aircraft fuselage. The advantage of such design characteristics is that it can give stability without increasing the size of the stabilizer itself. This reduces weight and allows the aircraft to be accomodated into tighter hanger spaces.
Dorsal fin on a 737.
Ventral fins on a Lear jet.
Author – Anas Maaz ( Airline Pilot )
