Johnson Flight Tests have been updated

Willie wrote:
Not all of the reports are Dick Johnson's articles, some
are pilot reports.

Not to negate a fine article by Eric Greenwell, but it is purely
subjective. If someone loaned me a glider to fly, and happened
to live in my neck of the woods, I doubt I would have anything
negative to say about it either.

I was the one who came up with the list of newer articles that were
recently placed on the SSA site. I included some articles not written
by Dick Johnson because information is good. All reports, whether by
Dick Johnson, Eric Greenwell, or someone else, are subjective. It is up
to the reader to decide what weight to place upon them.

Greg, you did a fine job of putting these articles up
and the effort is greatly appreciated. I read them all
and found useful information in all of them.

I was not putting down anyones pilot report.

But...

Give ten pilots the opportunity to fly a new ship and
you will get ten different pilot reports, each will have
his own opinion depending on a variety of things,
including experience, skill or ability, weight, etc.

All of these pilot reports are subjective, Wheras I
believe Dick Johnson's flight reports are more OBJECTIVE.
Backed up by flight tests with measured and recorded
results. They feature polars and numbers relating real
world results.

Over the years, manufacturers have consistantly given
their L/D numbers to be 1 or 2 points higher than was
revealed after Mr. Johnson tested a production craft.
Dick Johnson has established his credibility among
glider pilots by being very independant in his testing.

My issue is with the claimed L/D of the Sparrowhawk.

I was hoping to see an independent review of this
sailplane with polars.

Willie

Willie wrote:
My issue is with the claimed L/D of the Sparrowhawk.

I was hoping to see an independent review of this
sailplane with polars.

The tests have been done, it was discussed at the SSA convention. It
hasn't been published in Soaring, yet, so it is no surprise it isn't online.

Earlier, Marc Ramsey wrote:

The tests have been done, it was discussed
at the SSA convention. It hasn't been
published in Soaring, yet, so it is no
surprise it isn't online.

Hmmm. I was pretty sure I did see it in Soaring. Now I'd better go
check.

Willie wrote:

All of these pilot reports are subjective, Wheras I
believe Dick Johnson's flight reports are more OBJECTIVE.
Backed up by flight tests with measured and recorded
results. They feature polars and numbers relating real
world results.

Even Dick will tell you that a flight test is not exactly "real world
results". How many contests or soaring flights are flown in dead calm
conditions at steady speeds? The early ASW 24 is an interesting example
of this, as it tested well, but did not climb well in mid-afternoon
turbulence. Later models changed the airfoil slightly, showing no change
in flight testing, but definitely improving the climb. Another example
back in the '80s from Schleicher is the ASW 20, which outdid the
Ventus in dolphin style flying, but not in straight steady glides. One
glide suffered separation in pull-ups, the other did not.

Even ensuring these "dead calm" conditions is a major problem, which is
why the Alafliegs use a very carefully tested comparison sailplane to
fly with the glider they are testing, instead of trying to measure
actual sink rates.

Also, as Dick has explained in the past, his results are not based
entirely on objective criteria, but involve some "educated guessing"
about which points to ignore and exactly where to draw the curve through
points that are kept. As you might expect, not all aerodynamicists or
sailplane designers agree with this approach!

The point I'm slowly making is it sounds like you may be giving too much
weight to Dick's flight tests, instead of considering it just one of a
number of ways of evaluating a glider's performance in the _real_ world.
This is definitely more difficult to do with a new glider whose small
numbers mean there isn't much real world flying you can examine.

The people at Windward Performance tell me they believe the calculated
value of 36:1 is reasonable, based on informal glide testing against
several other types of gliders in the 35+ L/D range. I don't know if
this practical for you, but if I were seriously interested in a
SparrowHawk, I'd try to arrange to fly one, or to fly along side one in
glider with the performance I'd want it to have (Std Cirrus? Std
Libelle?). Great Western Soaring might be the place to do this, since
they are a SparrowHak dealer and will have a SparrowHawk there, and
maybe other sailplanes to rent for the comparison. A couple days there
would be money well spent when considering the purchase of a new sailplane.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA