I would like to know if it is possible to mix roll, pitch and yaw and how that might be done using on board mixers.
I have an F-117, built from a kit offered about 8 years ago by a fellow from a western state. I don't recall the name of his company. It has a 48 inch wingspread and power is a Super Tiger 51, in front, with tractor propeller. It's the plane the kids want to see fly at fun flys.
The problem I have is the design's "failure to rotate" on takeoff. The design relies on the ailerons for pitch control. They are in fact elevons, responding to both aileron and elevator input, via a v-tail mixer on board. However, the elevons are located only slightly behind the center of gravity, and even with full "up", both stick and trim, it takes at least 250 feet for liftoff, and the climb out is very shallow. This presents issues at some flying sites, for example, when a tall corn crop is growing at the end of the runway. In the air the elevons perform well both for roll and pitch.
I recalled that F-18s turn BOTH rudders inward during takeoff, to help them rotate. Because the fins are slanted, there is a pitch component to rudder deflection. (Link below)
I wonder then if I could also mix the elevator input to the rudder servos on my F117, and have the benefit of the pitch component from the slanted rudders? Or perhaps a better solution: Could I mix the flap channel to the rudder servos? The mixing would only be used on takeoff (or also landing if necessary), and that way I wouldn't affect the present good in flight performance.
I presume I would need the ability to reverse the flap input to one of the two rudder servos which currently move the rudders in the same direction. (Thinking about it, I presume that would also have to be done in mixing elevator to rudder.)
I guess this raises the question of whether or not it is possible to mix three inputs, and if so, what would the wiring arrangement be?
I would prefer to use and on board mixer for this purpose, though, by changing transmitter and receiver, I could have flap elevator mixing via the radio.
F-18s rudders inward:
Edit: The link isn't working: Here is the comment from a post on Airliners.net:
[TD]Quoting Brendows (Reply 3):
the rudders are put in this position to help the elevators with pushing the nose up on takeoff.
Brendows is correct. They create a lifting moment on the nose for takeoff. It you were to see the hornet in the picture above a split second later, you would have noticed that the rudders went back to their normal position. They only toe-in when you are on the ground and have the flaps down (1/2 or Full).