That happens depending on where you place the planes on spawn. Obviously you can't have 45 planes take off at the same location. If you start on the air or flying over the base that will work. For Taxi and Takeoff, you need to use the Spawn feature. So first 1-4 planes move and take off then you can experiment how long they take to leave spawn area then the next wave spawns.
You can only use the original Spawn points once. That is an IL-2 feature/limitation. If you try to use a second flight with the same generic spawn point, the planes will explode, bounce or nose down. If you use something like a P-39 or P-38 sometimes it will work but I do not use that in UQMG programming. That is why in the initial flight, they will be at their spawn points, and then for subsequent waves, they will line up in the first taxi-takeoff waypoint.
You can mess around with moving the taxi and takeoff waypoint in the Waypoint editor but that is an advanced technique, if you will.
I recommend going through the Tutorial or loading up one of the 30 or so sample missions I included. Go to the File menu in the interface, and Open UQMG file. There are two folders, one with the Tutorial "solutions" and one with PreAlpha sample missions. 27 if I recall... Each mission has detailed briefing that explains what concept is being explored, and each one suggest ground object settings in the Sector Selector Tab.
Take a look at the included mission below and observe the highlighted areas. That shows you a solution... but there are several ways to do this with experimentation.
Note that the first wave is in the spawning points and all others are in lineup fashion. That is why I indicate in the Map template building guide that thinking location through is important for both spawn points and taxi waypoints.









