So I'm starting to plan out the fuselage and pull together the necessary parts. With the horizontal stab and elevators I made the decision to make them removable and put the servos in the stabs. This will make transport and assembly much easier, but also adds to the weight in the tail. Even with 4 motors up front I still need to be very careful with tail weight on a bomber like this. To keep weight down in the tail the vertical stab and rudder will be permanently mounted, the only plywood I'm planning in the tail will be for the tailwheel mount, and the servos for the rudder and tailwheel will be mounted as far forward in the fuse as possible with pull/pull cables. I have Kevlar thread that should work well for the rudder and steering but that is TBD.
I settled on a retract unit for the tail yesterday and got it ordered. It is a solid Robart unit similar to their pneumatic or electric units, but this one is mechanical and is driven by a standard servo. Like the main gear, I really want to be able to service this myself and a servo driven unit is ideal for that. Plus if I do the linkage right I will be able to install the servo for the retract forward in the fuselage and further reduce tail weight.
Below is a picture of the retract unit. I've ordered it with the right-hand offset rather than the fork in the picture. It will retract a bit further into the fuse than a truly scale unit, but I don't think anyone will notice. I've already got the 2" wheel for it
So... what I'm debating at the moment is how best to hook everything up. Options:
I settled on a retract unit for the tail yesterday and got it ordered. It is a solid Robart unit similar to their pneumatic or electric units, but this one is mechanical and is driven by a standard servo. Like the main gear, I really want to be able to service this myself and a servo driven unit is ideal for that. Plus if I do the linkage right I will be able to install the servo for the retract forward in the fuselage and further reduce tail weight.
Below is a picture of the retract unit. I've ordered it with the right-hand offset rather than the fork in the picture. It will retract a bit further into the fuse than a truly scale unit, but I don't think anyone will notice. I've already got the 2" wheel for it
So... what I'm debating at the moment is how best to hook everything up. Options:
- 3 servos (1 retract, 1 rudder, 1 steering)
- advantage is that I can more easily set individual travel and expo on rudder/steering and linkages will likely be easier
- disadvantage is weight of extra servo and pushrods/cables
- 2 servos (1 retract, 1 rudder/steering)
- advantage is saving servo weight
- disadvantage is steering and rudder must be programmed together and I need to get all 4 pull/pull linkages to one servo horn. Servo placement must also work for both rudder and steering.
- 2 servos (1 retract, 1 rudder)
- So the full scale did NOT have a steerable tail wheel. It would freely caster and then would be locked in place before the takeoff run. I'm considering just using the centering springs on the unit and letting the wheel caster. I won't have brakes on the mains like the real thing but with differential thrust and rudder I may have enough authority to steer on the ground. Advantage is simplicity and weight savings
- Disadvantage is that if I find that I don't have enough authority on the ground it will be a PITA to retrofit with steering linkages.