Lots of interesting information here.

When thinking about the fuselage size and shape you must remember a few things. The prop makes the a large disk or displacement in the air. Bigger props have a bigger displacement and also have a bigger dead band in the center. Say you used a 16" (only for comparison) you would have a dead center of roughly 20% or 3.2" that was of no use for thrust. (The center area of a prop cannot be pitched high enough and is stalled any closer than 20% of the prop diameter. There for no airfoil is used in this area.)

Also, the prop causes a pulsing disturbance over the fuselage in a swirling direction the same direction as the prop is rotating. So, you cannot make the have get the fuselage to have laminar flow.

Another point to make about the drag of the fuselage. The longer the body the wider it can be without causing any larger drag penalty. Lets say your fuse length is 78" and you wanted a thin low drag body. You would probably chose something around 7%. That would mean you would make your fuse 4 1/5" wide with the Max thickens at 33 to 40% back. This is very low drag when you consider the large prop needed just over 3" to use for a spinner and the transition from the spinner to the wide point of the fuse needs to transition smoothly.

OK Say you wanted to add a draggy fuse... Lets make it fat ad use about a 12% to actually get some drag. Because a 8 or 9% is still kinda normal. That means you would need a 9 3/8" wide fuse to start to get the fuse to slow you down. The faster you go the less drag you make--this is how Reynolds numbers work.

(Coefficient of Drag the higher the number the more drag .9 has more drag than .5)

I ran some fuses through my Desk top wind tunnel program.

A 12% 2 meter fuse at 50 mph had CD of .0071

Now the real fast fuse that's only 7% wide at 50 mph has a CD of .0066.

The fat 12% fuse at 75 mph had a CD of .0067.

So, the real fast fuse at 50 mph matched the drag of the fat fuse at 75 mph...Kind a freaky when you thing about it...

Some other things fall into play here too. Say you wanted a to do a slow downline. The prop will dictate the airflow around the fuse and it will be different from the air just out side the prop disk. In this case the air around the fuse will be slower and there for more draggy. If you wanted a speed plane it would make a bigger and more significant difference. The prop speed will be much faster than the air speed and the drag would be less. Now don't start jumping down my throat with frontal area, parasitic drag and profile drag. Because this is the stuff that makes the smaller fuses on race planes work better...it not the size so to speak, but the actual amount of molecules the plane disturbs as it passes by. So less is always better in the long haul. But we are not talking about the hole aircraft--just the fuse here and were talking about slower speeds too.

Spend time on the fuse to make it handle correctly.

Wana make it slower. Spend more time on the airfoils. Check out the Eppler 474 if you want to see some backward stuff. The faster it goes the more drag you get and the more it will stall. (this is good for Snaps) Slow it down and under 150K Re and will continue to lift even in a deep stall and high Alfa. Pretty nice for landings and 3D stuff. Landing gear, things that disturb the airflow around the fuse to make it look fatter to the air and stuff like that.

Air brakes would probably work the best. (Hence the Name) Set up Flaps on the inboard of your ailerons. When the throttle is set to lower setting the airbrakes would gradually become stronger. And to balance the aircraft so there is no pitching problems. The flaps would come down and the ailerons would go up...Crow or butterfly as it's normally called.

The flaps can be mixed to the ailerons so you don't lose the roll rate.

For lighter aircraft that balloon at landing; you would reflex the TE (Raise the flaps and ailerons.) This reduces the amount of lift you have to get the aircraft to basically drop down without reducing the speed any farther. Also adds twist (washout) in the tips to keep them from tip stalling.

OK, I got a little carried away here--but it's just something to think about when you buy that new aircraft or decide to try something new.