Hi
Probably a silly question, but...

What difference does the tailplane height above/below the thrustline make..?
For example, imagine a Cap 232 with a T-tail...?

Was going to mess about with an Ugly Stik, but thought its a lot cheaper to ask...

Be gentle with me...

Such locations add structure otherwise not needed. both for the added load at the tip, and flutter prevention.
For a aerobat, having as little mass away from the inertial axes of the configuration as possible makes for crisper manuvers. Start easier, stopped easier.

Mostly it's desireable to try to balance the tail area around the line of flight. A high mounted rudder creates a slight adverse rolling action. A low mounted rudder a proverse rolling action. The CAP rudder with it's strongly wider chord below the centerline and narrowing as it rises tends to balance the area so the rudder has a more or less neutral rolling side effect. Pattern fliers play with this aspect a lot in their designs to try to achieve pure control effects with as few side effects as possible. The rest of us don't really worry about it much.

T tails should be avoided unless there is some compelling reason to use one. They are inherently weak & require extra material (weight) to achieve acceptable strength, they sometimes have VERY nasty stall characteristics, if they are out of the prop slipstream (the usual case) they offer poorer elevator response at low airspeeds, and they have high polar moments of inertia.

They are usefull to keep the horizontal control surfaces out of water spray in amphibs & seaplanes (like the Seamaster), they are used to keep the horiztail out of the jet blast on high-wing transports like the C-141, C-5A & C17, & they are used to permit aft-fuselage jet engine installations like in the DC-9 -- not too many genuine model applications.

Thanks guys

T-tails are commonly used on military transports that may need to do extremely short takeoffs/landings. Being so high above centerline they give more leverage than a lower mounted tail.

T-tails were seen on early jet fighter designs to, for the same effect plus it gets the elevator out of any turbulence caused by the rest of the plane. Hans Multhopp (from Focke Wulf) in Germany in WWII helped pioneer them (designed the TA-183).

T-tails were not successful in fighters -- many F-101s, F-104s & Gloster Javelins were lost from abrupt pitch-up due to the tail being blanked in high-alpha maneuvers