* Models/An-24B.xml: animate propellers with engines/engine[*]/rpm instead
of engines/engine[*]/thruster/rpm. The values of the properties are the
same but only engines/engine[*]/rpm is automatically transmitted over mp.
This animates the propellers over mp.
* an24b-set.xml (help): swap the descriptions of F3 and F4 keys to correct
them.
