Hey Marty,
Ok....Inflight mixture: Most ducted fan engines come with a separate remotely mounted needle that can be controlled by a servo. The advantage of inflight mixture is you can lean your engine out for maximum power at take-off and once airborne richen the engine up to get a bit more lubrication. The ducted fan engines turn somewhere in the 24,000 rpm range, that's a lot of stress on the motor! Since most ducted fans need all the power you can drum up for take-off and climb-out you want to lean the engine to max power but once you have the plane on step you can then back off the mixture, reducing a little power but getting more lubrication to the engine.
Speed Brake: I have attached a picture of my kangaroo with the speed brake half deployed. Here is an easy description of the speedbrake function, I will relate this to turbine aircraft since you really need them more on turbines than D/F. Turbines have what is called turbo/throttle lag, meaning that there is a delay in response time from when you push your throttle from idle to full throttle or any where in between. This delay can be as much as 8 seconds to go from an idle to full power, now to go from half throttle to full power takes considerably less time. The purpose of the speed brake is it allows you to use power on your landing approach but keeping the approach speed as if you were not applying the power. Reason for this is if you had to do an abort on the landing when you apply full power the delay will be minimal from say half throttle as opposed to idle. Catch here is that if you abort the landing you must retract the brake or your acceleration back to flying speed will be affected. As you can see, there is a lot going on when your flying jets. Takes a good deal of concentration to keep up with all the functions.
I remember one incident I had when I first started flying turbines. I made a landing that was a bit on the fast side, was running out of runway quickly and reached for the rudder dual rate to turn my steering back to high to avoid an obstacle at the end of the runway (I always take-off on low rate for steering) I hit the wrong switch in my panic and retracted the gear.....Not pretty but damage was minimal. Point is, you must be able to react quickly to any situation, the more gizmos you throw into the mix the more you can get confused. Be proficient with a high speed aircraft to the point that you don't need to think to fly then you are ready for the added complexities.
Hope this helped, I think I confused myself
Let me know if you have any further questions. Feel free to e-mail me for my phone # if you want to discuss things in further detail.
Regards,
Todd