Re: Spin recovery vs tail design

On May 11, 10:24 am, "Wayne Paul" <wa...@xxxxxxxxxxxxx> wrote:
"Andreas Maurer" <mau...@xxxxxxxxxxxx> wrote in messagenews:3jjg05hpl4e6hth12gegpo24l4718kv571@xxxxxxxxxx
On 11 May 2009 16:00:06 GMT, Ron Ogden <rogd...@xxxxxxxxxxx> wrote:

I would like to solicit comments on the question: Compared to a standard
tail configuration such as a 2-33 or Blanik L-13, does the initiation and
recovery from a spin vary substantially in  T-tail (ASK-21 type),
all-flying (Phoebus) or V-tail (HP series) sailplanes? Really look forward
to reading and learning.

No significant differences - stick neutral, rudder against direction
of the pin.

Some V-tail gliders require the stick to be pushed fully forward (to
achieve sufficient deflection of the V-tail).

Ron,

Like Andreas, I find no significant dirrerences.  My "V" tail HP-14 doesn't require any special technique.

Wayne
HP-14 "6F"http://www.soaridaho.com/Schreder

I would disagree.

Studies done on exactly this in the early 1960's by NASA at Edwards
AFB did show an effect. To understand the finding, consider how the
airflow moves over the tail at a very high angle of attack as in a
well developed spin.

The flow tends to parallel the swept rudder hinge line on a 2-32 or
2-33. The low mounted tail disrupts or blanks some of the air flowing
toward the rudder. The result is a measurable reduction in rudder
effectiveness which manifests itself in a delayed spin recovery.

Swept tails are undesirable at any airspeed below transonic and are
used merely for styling.

A "T" tail with a vertical rudder hinge is a good solution since the
rudder sees clean airflow and the horizontal acts as an end plate on
the fin and rudder. The one caveat is that the "T" tail shouldn't be
in the wings turbulent wake at any achievable angle of attack - else
you risk a "deep stall" phenomenon.

The second best configuration is a low stab/elevator mounted ahead of
the fin as seen in a BG-12 or K-13 so the free flow has unobstructed
access to the rudder at high angles of attack.

Finally, a separate stabilizer and elevator produces more nose down
moment than an all moving "slab" tail which can stall in it's full-
down position. A stab/elevator can also stall but will nonetheless
produce enough nose down moment to break the stall/spin.

This led to the NACA standard spin recovery technique which called for
anti-spin rudder while holding full up elevator until the auto-
rotation slowed and only then applying down elevator. The reasoning
was that full up elevator exposed more of the rudder to high energy
flow.
.

Relevant Pages

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