Does Fin Shape Matter So Much?

It would have increased weight and cost at the time of change, basically when jest came of age, but we’ve overcome those problems now. There would probably be more flutter on a fin with an upright leading edge. The shorter the body length to diameter, the bigger the fin. Lok at A380, that outrageous fin on a dumpy body. If the Body was twice as long the fin would get smaller (If it’s further back from the turning moment it has to do less work).
Single engine prop jobs have a non uniform fin. i.e. in cross section the shape more resembles a wing, with one side nearly flat and one side curved. This counters the shear from the prop. In twins and upwards, the shape is the same at either side of the chord.

Isn’t there an a/c with the fin facing forward? Looks like it’s on backwards?

I think you are referring to the Mooney M20 series of machines where the fin leading edge is vertical and certainly does look like it is back to front. Lovely pitch trim system on them too, the whole tail cone complete with fin, rudder, tailplane and elevators pivots up and down. Never heard of it causing any problems though for all it is an unusual idea.

Most GA fin and tail-plane designs are 2-spar arrangements. The forward spar reacts the aerodynamic forces and moments of the fixed surface and the rear spar usually carries the hinges that react the control surface forces. The hinge prevents moments being transmitted from the rudder to the fin (unless you hit the control stop), these are effectively reacted by the control horn and appear as stick and rudder forces.

The Mooney fin has a vertical forward spar, so minimising twisting forces and fairly neutral elastic stability. The forward sweep on the rudder hinge line doesn’t add any great twisting moment to the fin.

Rearward sweep has a slight performance advantage in moving the centre of pressure of the control surface further aft from the centre of gravity thus increasing control effectiveness or allowing a smaller surface area. Elastically the twisting forces will try to reduce the angle of attack making it more elastically stable, but reacting the twisting forces may incur a weight penalty as it requires a stiffer section.

In high speed designs, sweep also delays the onset of critical Mach number and shock-induced drag.

Torsional stiffness and aerodynamic/mass balance can also affect the onset of flutter.

Structural optimization tends to yield an unswept but tapered design which is typical of what has evolved in most GA aeroplanes.

It’s been along time since I studied all this as an undergrad, but that’s roughly how I remember it.

Bah did this in my FI flight test. Sweepback essentially allows a smaller rudder for a given amount of authority. Can’t remember why 😡

Indeed for much of the history of light aviation the tail shape has served as a brand identity.

Moggy

Single engine prop jobs have a non uniform fin.

I’d be careful about making such a sweeping statement.
While it may be the case with many modern GA types, it’s not the case with most of the vintage SE types I’ve seen.

Isn’t there an a/c with the fin facing forward? Looks like it’s on backwards?

Yes, the Mooney line. Their aircraft have had that tail as a trademark since the first model in the early 50s.

Appearently not to a great extent.
I’d guess (since I’m not an engineer) that at GA speeds, a wink is as good as a nod.

In his excellent book, Cessna Wings for the World — The Single-Engine Developmernt story*, long time Cessna engineer and test pilot, William D. Thompson says when the straight tails were changed to swept units in the early 60s, (purely for marketing reasons) the rudder became less effective which showed itself in reduced crosswind drift correction capability, spin recovery authority, and an overall slight loss of directional stability. It also increased weight and cost.

*1991 Maverick Publishing.
It was followed by a book on Cessna light twins (336/337, 310, 340, 303, and T-37), and then a third book was released dealing with the heavier 400 series of cabin-lass twins.
All three books should be on the shelf of anyone interested in the develoipmenbt of GA aircraft.
It’s a pity more hasn’t been written on the subjecty, there are a lot of good “inside stories” still to be told.

It would have increased weight and cost at the time of change, basically when jest came of age, but we’ve overcome those problems now. There would probably be more flutter on a fin with an upright leading edge. The shorter the body length to diameter, the bigger the fin. Lok at A380, that outrageous fin on a dumpy body. If the Body was twice as long the fin would get smaller (If it’s further back from the turning moment it has to do less work).
Single engine prop jobs have a non uniform fin. i.e. in cross section the shape more resembles a wing, with one side nearly flat and one side curved. This counters the shear from the prop. In twins and upwards, the shape is the same at either side of the chord.

Isn’t there an a/c with the fin facing forward? Looks like it’s on backwards?

Appearently not to a great extent.
I’d guess (since I’m not an engineer) that at GA speeds, a wink is as good as a nod.

In his excellent book, Cessna Wings for the World — The Single-Engine Developmernt story*, long time Cessna engineer and test pilot, William D. Thompson says when the straight tails were changed to swept units in the early 60s, (purely for marketing reasons) the rudder became less effective which showed itself in reduced crosswind drift correction capability, spin recovery authority, and an overall slight loss of directional stability. It also increased weight and cost.

*1991 Maverick Publishing.
It was followed by a book on Cessna light twins (336/337, 310, 340, 303, and T-37), and then a third book was released dealing with the heavier 400 series of cabin-lass twins.
All three books should be on the shelf of anyone interested in the develoipmenbt of GA aircraft.
It’s a pity more hasn’t been written on the subjecty, there are a lot of good “inside stories” still to be told.