I'm designing a tandem (push-pull) twin with a conventional (low) wing and a normal-positioned tail, probably t-tail, as for the tail, the Miller-Bohannon comes closest, though still far from similar:
Moving forward from the rear prop, there's the PSRU (mounted about 7" above the midpoint of the fuselage), a conventional or BMW boxer engine, a firewall and then the spar of the fin at 25% chord. The spar is canted backward and for the moment I'm betting at a T-tail to keep the prop at least out of the elevator-wash. The fin is slightly tapered (0.5 to 0.7 root to tip) with an area of around 10 sqft and an aspect ratio of around 2, the elevator has a similar area. Also I'm thinking of sweeping the fin 20 to 40 degrees backwards, for a larger moment arm of the elevator (and thus a smaller elevator) and also for looks.
The main wing is by the way more than 10' before the prop disk so I don't expect any problems there.
I preferably don't want a tail that's protruding underneath the fuselage to avoid the nose digging in during a belly landing. Better break a rear prop than nose-over @ 60 kts.
I'm more than interested in your comments on this. Some random issues:
*Noise. Though the prop turns through only one disturbed part of the wake, being too close at the fin/rudder might still produce a lot of noise, especially with a rudder deflection, though that's barely needed normally.
*Vibrations. Same issue as above, except that this can ruin the rudder or prop (or psru or engine).
*Rudder efficiency. Thinking whether the rudder is more effective or less effective with a lot of power on caused me a hard time. Since there's way more airflow over the fin at low speeds it might be more effective. On the other hand, a prop straigtens flow out, so it might be less effective. Help!..
*Elevator efficiency. Currently the elevator trailing edge is around 10", above and just before the prop. Deflected downwards it's half. How would elevator effectivity and trim be, especially during power changes.
How do you guys feel about this configuration. Would another one (H-tail, conventional tail, inverted or normal v-tail) be better? What kind of clearance between upper/lower fin and propeller disk and between prop and elevator would you recommend? How about rudder and elevator control authority, especially during full and no power? How about trim change?
Moving forward from the rear prop, there's the PSRU (mounted about 7" above the midpoint of the fuselage), a conventional or BMW boxer engine, a firewall and then the spar of the fin at 25% chord. The spar is canted backward and for the moment I'm betting at a T-tail to keep the prop at least out of the elevator-wash. The fin is slightly tapered (0.5 to 0.7 root to tip) with an area of around 10 sqft and an aspect ratio of around 2, the elevator has a similar area. Also I'm thinking of sweeping the fin 20 to 40 degrees backwards, for a larger moment arm of the elevator (and thus a smaller elevator) and also for looks.
The main wing is by the way more than 10' before the prop disk so I don't expect any problems there.
I preferably don't want a tail that's protruding underneath the fuselage to avoid the nose digging in during a belly landing. Better break a rear prop than nose-over @ 60 kts.
I'm more than interested in your comments on this. Some random issues:
*Noise. Though the prop turns through only one disturbed part of the wake, being too close at the fin/rudder might still produce a lot of noise, especially with a rudder deflection, though that's barely needed normally.
*Vibrations. Same issue as above, except that this can ruin the rudder or prop (or psru or engine).
*Rudder efficiency. Thinking whether the rudder is more effective or less effective with a lot of power on caused me a hard time. Since there's way more airflow over the fin at low speeds it might be more effective. On the other hand, a prop straigtens flow out, so it might be less effective. Help!..
*Elevator efficiency. Currently the elevator trailing edge is around 10", above and just before the prop. Deflected downwards it's half. How would elevator effectivity and trim be, especially during power changes.
How do you guys feel about this configuration. Would another one (H-tail, conventional tail, inverted or normal v-tail) be better? What kind of clearance between upper/lower fin and propeller disk and between prop and elevator would you recommend? How about rudder and elevator control authority, especially during full and no power? How about trim change?
