HP-11/Sisu Polar

Does anyone have a decent polar or any type of performance figures for
either an HP-11a or Sisu? All leads are greatly appreciated.

Thanks,
Mike

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.

You are absolutely correct we do teach the downwind
to base as you describe for the reasons you state.
My experience is that it does work and makes it easier
for a low hours student to judge position and helps
to reduce the possibility of getting out of gliding
range.
While I always taught the 45 degree diagonal, like
many other pilots I use a constant radius turn from
downwind to approach which is even better in my opinion.
This is more difficult to teach which is probably why
a compromise was reached. I don't use the constant
turn if by doing so I would conflict with those using
the diagonal.



At 09:00 16 February 2005, 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.

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/

At 20:30 16 February 2005, Chris Reed wrote:
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.

There is opportunity to correct at this corner; just
angle in a bit if you have gone too far, or angle out
a bit if you didn't go far enough. You can also lift
or drop a wing for a quick peek without endangering
yourself if you are carrying a bit of extra speed in
the pattern.

Mike,

I was a kid around Texas Soaring Association whan the Sisu was being
built. The performance was 38/1 as I remember. The speeds and so forth
I have no clue... sorry. I sat in Al Parker's Sisu when it was being
built and made swishing noises. My brother Jessie delivered several to
their owners after building the trailers and most of the glass parts
(leading edges, nosecones, etc.) Unfortunately, a lot of that knowledge
passed with him several years ago. Wish I could be more help.

Jack Womack
wrote:
Does anyone have a decent polar or any type of performance figures
for
either an HP-11a or Sisu? All leads are greatly appreciated.

Thanks,
Mike

Mike,

Feb 1971 Soaring has a Paul Bikle article called 'Flight
Test Performance Summary' that includes data from a
1960 test of the Sisu 1 N7983A performed by Niemi and
Johnston and published in the Feb !961 Soaring. It
also has data from a test of Sisu 1A N1100Z performed
by Roberts in 1963.

The two polars reported were very different. The Sisu
1 at 660 lb + 6.11lb/ft2 was:

Best LD 40.5 at 53knots
Min sink 126ft/min at 48knots
Sink rates:
147fpm at 40knots
128 @ 50
158 @ 60
219 @ 70
299 @ 80
392 @ 90
499 @ 100
A surprisingly good polar for that era!

The Sisu 1A measured at the higher weight of 730lbs
and 6.75lb/ft2 was worse at all speeds:

LD 36.5 at 50knots
Min sink 135fpm at 45 knots
145fpm @ 40knots
139 @ 50
185 @ 60
257 @ 70
353 @ 80
470 @ 90
614 @ 100

Both gliders were reported to have the same span and
airfoil and both had been smoothed and filled. There
is a note 'Sisu performance with flaps below 48knots'
- presumably both gliders.

There is reference to an HP 8 test done in 1958 but
nothing for an HP11

John Galloway



At 07:00 16 February 2005, wrote:
Does anyone have a decent polar or any type of performance
figures for
either an HP-11a or Sisu? All leads are greatly appreciated.

Thanks,
Mike