Vertical Stabilizer Incidence Angle?

I would definitely build a new mount to get the engine up to where it needs to be.  Since this is not a symmetrical airplane like the Pitts it probably needs the fin offset.

I agree, and plan to make the new engine mount (tubes and washers are on order!).  I'm just curious if anyone else has run into this issue with the Smith Miniplane...

What do you mean by 'this is not a symmetrical airplane like the Pitts'.  What part is not symmetrical?  Are you referring to the wings not being symmetrical?  As far as I know, the rest of the airplane is symmetrical.

The Pitts design  criteria is primarily geared to aerobatics.  The airfoils are symmetrical (with the exception of the S1-C and S1-D) and the airplane is designed to fly inverted just as well as it does up right.  The Smith does not have symmetrical airfoils and prolonged inverted flight was never part of the design goals.  The Smith will perform basic positive "G" aerobatic figures.

I suspect the mount in the picture would cause prop to ground clearance issues.

I measured the prop to ground clearance because I had the same concern.  The recommended propeller per the plans is a 60" diameter propeller.  The distance from the center of the hub to the ground is 46 inches.

I'm still a bit confused about how airfoil symmetry affects the incidence angle of the vertical stabilizer?

It is not the symmetry of the airfoil, but rather the intended use of the airplane.  Some symmetrical aerobatic aircraft don't use fin offset because the off set would be wrong for inverted flight.

I understand now.  Thank you!

Tommy;

Your best bet is to find a "Type Club" for the Miniplane online. Whatever questions you have will be best answered by people who know the type.

As to the fin offset; yes you need it to counteract the torque/spiraling slipstream supplied by the motor/prop. It will keep you from having to bias the rudder to net the same effect if you install the fin with 0* offset. Don't worry about the rig changing when you're inverted, if the motor is turning the same way the fin offset will be the same...

The Smith is a short coupled airframe and will therefore have a more acute offset angle than an airframe with a longer distance from the CG to the surface. All prop driven airplanes have some way of dealing with torque; offset, "airfoiled" vertical fins (low pressure on one side) or a combination of the two.

I once heard of a fellow who decided that zeroing all the incidents out of a Lazer 200 would make it fly the same up, down, left and right and built it that way because it was "logical". The airplane was basically uncontrollable scrap from day one.

My Hiperbipe is short coupled, has a fuzz over 200 horsepressure and has (I think) 4* fin offset.

                                                                                        Hope this helps ya'

                                                                                        Chris

Tommy,

I've seen some airplanes build with an off-set tail fin to compensate for P-factor generated by the engine/propeller.  Other airplanes have an offset built into the engine mount for the same reason.

Jim Faix

Sarasota FL

Tommy yes the S1S has the offset on the rudder for torque too. I believe it is around 1/2 inch

Andy

The vert stab on my Sonex is built exact square on-center.  Then again, the two engine options they offer turn in opposite directions, so we're left to work it out with a trim tab on the rudder.