Scudrunners

The impact of stalling in a skid gets beaten into us and I've practised lots of spin entries and recoveries, but I've never stalled a plane in a forward slip. I feel you'd mostly just get some nose drop and maybe sliding to the side, but nothing too scary. The downward wing has the aileron on that side already killing off some lift, but at the same time the upward wing has some of its airflow blanked out by the turbulence off the fuse. If the plane has an appreciable dihedral that also might increase the alpha on the downward wing, leading it to go first, but overall... No yaw rate so no accelerated wing, probably not a lot of difference between the two.



The next time I'm up with an instructor I'll ask, but in the meantime would anyone care to share their experience?

Usually in a slip I'm trying to lose altitude and keep going forward. I tend to drop the nose. Airspeed seems to stay pretty stable. Likelihood of a stall is low I'd think.

I know, I wouldn’t expect to stall in any normal slipping approach. But if one were to provoke the plane a bit...


It’s mostly a mental exercise. I’m trying to understand the aerodynamics of what would happen.

I'm hoping to read some good stuff about this. It's funny how some instructors seem frightened by forward slips. Most like them.

Thinking about it some more… I wonder if the real danger isn’t stalling during a slip, but rather stalling as you come out of it. If you were riding a full rudder slip right at the edge of a stall and kicked it straight violently, you might generate enough yaw to stall one wing and induce a spin.

It's a good setup for a spin.  To understand why consider the following:

In a slip you have crossed controls, (rudder going one way and ailerons going the other).  So this means you are applying rudder to the the same side as the wing with the down pointing aileron (i.e. in a left slip the rudder is pointing left and the left aileron is down).  The down pointing aileron raises the overall AOA of the wing.  If you take a look at a lift vs AOA graph you will notice that once you pass the critical AOA (i.e. you stall) lift decreases with AOA.  You will also notice that drag dramatically increases as AOA exceeds the critical AOA.  When we apply this to the stall in the slip you can see that the higher wing should stall first.  Funnily enough, this is also the side to which your rudder is pointing.  The result is a rapid wing drop and yaw to the side to which you have applied rudder.

That's the theory.  In practice I've found that it only results in a spin 60-70% of the time. 

Found this video that was very instructive

That's some impressive miss use of the foot rests. Where's the colonel? This would be a pretty good place for one of his patented catch phrases.

Considerable mis-handling of an aircraft is required to accidentally
spin.  Full rudder, aided by adverse yaw produced by full opposite
stick, and full back stick at slow speed is not something I often
absent-mindedly do at low altitude, but some people manage to
somehow get there.

Also, it helps if the aircraft has large, powerful flight controls
which still have great authority at slow speeds.  While this might
accurately describe an expensive modern aerobatic monoplane
with enormous full-span ailerons and a giant rudder and elevator,
not so much a 172.

This fatal spin was entered at altitude, with a wildly aft C of G:



Remember in cruise, at altitude, you are unlikely to accidentally
stall or spin because at say 120 MPH, you need to accidentally
load up and sustain +4G.  Not many people do that by accident.

Most pilots are likely to accidentally stall/spin when they are flying
slowly, which occurs at low altitude just before landing or just after
taking off.

It's possible to kill yourself by accidentally stall/spinning just after
takeoff, too.  I knew two guys from Rockcliffe that died doing that.

Fun Fact Of The Day, From Someone Who Isn't Allowed To Hold
An Instructor Rating in Canada Any More:

While keeping the ball centered is nice, it is no guarantee of spin
avoidance for several reasons I can think of.  One is that the wings
are at different angles of attack in descending and climbing turns,
which is nothing mysterious after all - you do that every time you
turn from base to final.  That's before you introduce the prop.

That's ok but, I was hoping for a hearty.

Lower the nose.â„¢

Or maybe a, "Let go of the stick."