A little background:
The subject aircraft is my Harmon Rocket, which is a derivative of the RV-4. The RV has wonderful handling and not surprisingly has a vertical tail coefficient (Vv) of .04 which matches Raymer and other texts guidlines for "correct" sizing. Vv is influenced by wing span/ area and aft fuselage length, both of which are modified in the Rocket. The Rocket mod shortens wing span AND lengthens the fuselage, which should drive the required tail on the Rocket even smaller than the RV if the same stability is desired. However, my particular Rocket has been fitted with a RV-8 tail group which is quite a bit larger than the -4. It appears that I have a lot more vertical than I need.
Plugging in the Rocket numbers to the equation: Vv=Sv * Lv/Sw * b gives me 14.1*11.25/106*21.5 = .069. So that 14.1 sq ft of vertical area is way too big! Working backwards with the 14.1 as X, and looking for a Vv of .04 drives me to a vertical area of 8.1 sq ft.
So two questions: is it appropriate to include the fuselage vertical area directly under the vertical fin as "tail area" (I did, in this calculation); and does my math pass the sanity check? That seems a massive reduction in area.
The subject aircraft is my Harmon Rocket, which is a derivative of the RV-4. The RV has wonderful handling and not surprisingly has a vertical tail coefficient (Vv) of .04 which matches Raymer and other texts guidlines for "correct" sizing. Vv is influenced by wing span/ area and aft fuselage length, both of which are modified in the Rocket. The Rocket mod shortens wing span AND lengthens the fuselage, which should drive the required tail on the Rocket even smaller than the RV if the same stability is desired. However, my particular Rocket has been fitted with a RV-8 tail group which is quite a bit larger than the -4. It appears that I have a lot more vertical than I need.
Plugging in the Rocket numbers to the equation: Vv=Sv * Lv/Sw * b gives me 14.1*11.25/106*21.5 = .069. So that 14.1 sq ft of vertical area is way too big! Working backwards with the 14.1 as X, and looking for a Vv of .04 drives me to a vertical area of 8.1 sq ft.
So two questions: is it appropriate to include the fuselage vertical area directly under the vertical fin as "tail area" (I did, in this calculation); and does my math pass the sanity check? That seems a massive reduction in area.
