Hi,

I'm looking into installing larger flap skins on my Stinson 108 and I was reading some comments questioning the usefulness of reducing stall/approach speeds with STOL mods and I had to help myself justify all the added work and expense of my fun...

There are some people who don't think a few mph drop in stall speed is "worth it" and they are welcome to their opinion but I just wanted to point out that STOL modifications are not just practical but are also for safety.

A drop in stall speed could save your life in more ways than one. It gives you an added linear stall speed margin in flight but it also gives you an exponential margin on landing. I'm going to use stall speeds for convenience but the same would be true with reductions in approach speed.

Kinetic energy increases at the square of speed so, for instance on a Stinson 108, a set of VGs with a claimed 8% drop in a 61 mph stall speed and consequently, approach speed (4.5 mph) kinetic energy drops over 14%. A Cub that gets a 16% drop in stall (43mph to 37mph) would get a whopping 26% drop in kinetic energy at the lower speed.

Sure, lower stall speeds are great in the air, but ultimately, It's kinetic energy that kills you in a crash so speed reduction yields even greater dividends, exponential ones, where the plane meets the ground. STOL mods save lives. Now... where's my rivet gun?

All true, however there are additional things that contribute to safety and "crashworthiness" that need to be kept in mind in addition to reduced stall speed and energy. How the energy absorbed and so on is also important. Good stuff for discussion and consideration.

Kurt

For most small airplanes, including Stinson 108, the stock airplane is capable of getting in as short as it will get out. Flaps and slats are good. What and where is your touchdown airspeed? It's not a gauged thing, below Vso, but significant.

No free lunch, though. The slower you land, the less crosswind you can handle. Depending on where you fly, there may be more crosswind landings than short ones. There are ways to mitigate that somewhat, of course, but it’s something to think about. . . .

Good point. Angle across will mitigate crosswind for faster 4 place and control completely with lighter airplanes. But you have to fly short final slow. With the extra headwind component, however, slow groundspeed is not a problem. And the controls are feeling better than normal relative wind.

We don't run out of aileron to bank into the wind. We run out of rudder to hold the nose straight down the runway. As the crosswind increases, we move the end of cross runway point closer to the approach end numbers. Yes, we have to control glide (actually power/pitch) angle with power only to touchdown very close to the downwind corner of the runway.

Angle across starts with a modified base to final. We mentally create a new centerline and centerline extended at the desired angle. We already know the rudder would be insufficient to safely go down the painted centerline.