OT: Slips (was Re: !Re: Nuke Redmond!)

From: Chris Kennedy <chris_at_mainecoon.com>
Date: Mon Apr 10 10:34:04 2000

allisonp_at_world.std.com wrote:

> As a pilot I figured going into gory detail was excess.

Perhaps, save for the fact that I can use yaw to induce skid just as
easily as slip.

> As a C150 driver and verious gliders, your wrong. Slips allow application
> of the airframe to get drag, thsi is very useful with some planes that
> have marginal flaps (or none at all).

Wrong about what? I wrote:

> > in other words you cross control it. Slips as applied for altitude loss
> > also require the use of cross controls, otherwise there's a tendency to
> > impose large aerodynamic loads for no particularly good reason and the
> > possibility in some high-wing aircraft of partially blanking the
> > elevator resulting in an uncommanded pitch-up moment if done with
> > inappropriate flap settings.

Quoting from FAA AC 61-21A, page 103:

"Assuming that the airplane is originally in straight flight, the wing
 on the side towards which the slip is to be made should be lowered by
 use of ailerons. Simultaneously, the airplane's nose must be yawed
 in the opposite direction by applying opposite rudder..."

That is, cross controlled. You *can* just step on the rudder, but what
you'll get is a skidding turn into the rudder, which, due to the
stability of most airplanes, will eventually generate bank in the
opposite direction, stopping the turn from developing further.

> Even with flaps a slip can be use
> for additional drag or forward visibility enhancement.

Again, from the same advisory circular (same page, even):

"Note: Forward slips with wing flaps extended should not be done
 in airplanes wherin the manufacturer's instructions prohibit
 such operation".

Having just stuck my head in a 150B, 182Q and 210L each has
placards forbidding slips in conjunction with full flaps. For
improved forward visibility during descent flaps are generally
preferred to slips, as most light airplanes have simple plain
flaps which cause the greatest uncommanding (nose-down) pitching
moment when applied. At least that's the current line of jive
from the FAA and what we're required to teach.

> C150 roll rate is not very fast and while the 6/sec degree number is
> likely low i've barrel rolled one and they are slooowwww. Nothing like a
> clipped wing cub or Citabria.

Nor the 300 degrees/sec you get out of a T-28 -- but still fast
enough to get three rolls before running out of energy and
having to trade off altitude to maintain airspeed. :-)

> As to spins, i've done a few, after all it's the only legal acro for
> a C150 commuter of any significant degree. Yes it does roll out easily.

Legal how? It's permitted in any aircraft certificated for and operated
in utility category and not otherwise placarded against. It's listed
as specifically approved in every 150 or 152 AFM I've pulled off the
shelf this morning. The only issue I've ever had doing spins in a 150
is that power-off spin entries to the right don't work all that well --
it seems to want to mush into a spiral. Blipping the throttle once
full rudder has been mashed in generally gets it to roll over, but it's
still lazy -- but a good way to introduce the maneuver, as opposed to
a power-on snap entry which generally scares the hell out of students. :-(


Chris Kennedy
PGP fingerprint: 4E99 10B6 7253 B048 6685  6CBC 55E1 20A3 108D AB97
Received on Mon Apr 10 2000 - 10:34:04 BST

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