HP-11/Sisu Polar

I am told that in the UK and Europe, most pilots have
adopted a 45 deg. diagonal leg between downwind to base in
the pattern some time ago. In the US, most instructors and
most of the gliding texts still teach a rectangular pattern.

A principal advantage is supposed to be that the pilot can
better keep an eye on the touchdown point at all times and
more readily gauge the glide path to touchdown.

Does anyone know if this pattern has in fact reduced landing
accidents, especially during off field landings? Are there
any reliable statistics to support claims of its benefits?

Thanks,

Pete


--

Peter D. Brown
http://home.gci.net/~pdb/
http://groups.yahoo.com/group/akmtnsoaring/

Pete Brown wrote:
UK and Europe 45 deg. diagonal leg downwind to base

Pete.
This has been around for quite a long time (UK) and I found
took some getting used to after a lay off.

I sort of compromised on a "less rectangular" circuit but
no way 45deg. I divert on the 2nd half of the downwind by maybe 15
degrees? any more and the base leg is largely lost and degenerates into
a sort of base/final turn?

Jonathan

Pete Brown wrote:
I am told that in the UK and Europe, most pilots have adopted a 45 deg.
diagonal leg between downwind to base in the pattern some time ago. In
the US, most instructors and most of the gliding texts still teach a
rectangular pattern.

Does anyone know if this pattern has in fact reduced landing accidents,
especially during off field landings? Are there any reliable statistics
to support claims of its benefits?


I don't think anyone could provide statistics on this, though the BGA
accident database is available on-line (I think from www.gliding.co.uk).

From personal experience, flying a square circuit in the US made me
feel quite uncomfortable as I reached the "corner", as I was not in a
position to correct the circuit if I'd misjudged. The diagonal leg gives
you options to start the base leg at any time, and as you're closer to
the airfield it makes judgment simpler.

In practice, especially for off-field landings, the diagonal is really a
series of small adjustments (and if you've got it right, a constant
radius turn as described by Don Johnstone) - though I do like enough of
a base leg at 90 degrees to the approach line to decide whether I'm high
or low, adjust for my precise intended approach line, etc. My model for
achieving this is to maintain a constant angle to my reference point
from the end of downwind to the final turn.

Because you make a series of fine adjustments, rather than one large
one, it seems intuitive to me that this produces a lower workload.