ASK21 --- OR --

Bob,

I fly with Brad Hill, and I'm sure he'll vouch for me. I'll take you
up on the 10 dollar bet. My old club had a Jr and a Puchacz. Both
planes seemed well constructed and gave honest performance along the
lines of their published values. Back in college, I did measure our
clubs Ka7 using the techniques outlined by Dick Johnson. I still have
some of the equipment. Would you accept an independent measurement if
we every get one up here in the Northwest?

Kevin

The only time I've ever used Dr, was back in college when I did some
DJ'ing. I was known then as D.J. Dr. Finkenstein.

On 8 Nov, 03:51, Bob Kuykendall wrote:
On Nov 7, 5:10*pm, KevinFinke wrote:

I don't think 40/1 is remotely unreasonable for the Perkoz...

Ten bucks says that if the Idafliegs do a polar it tops out at or
below 39.

Perhaps, but if Dick Johnson were still around he could stick some
turbulator tape on it and suddenly get 45 ...

Ian

On Nov 7, 11:36*pm, "noel.wade" wrote:
Couldn't the wing use multiple airfoils or varying thicknesses to get
around the need for (as much) washout, despite the moderate taper
ratio? *Those wouldn't be immediately obvious from the visuals or 3-
views... **shrug*

--Noel

Multiple airfoils is a slick way to design the desired tip stalling
characteristics into a plane. I'm not sure if the Perkoz uses this,
but I have noticed it seems to have a good bit of forward sweep to the
wing. Forward sweep can certainly be used instead of washout, as
demonstrated clearly on the Sisu.

Based on independent tests I've seen done on other Polish gliders, I
have no reason to doubt the SZD figures for the 54. The Pols have
always been rather scientific and less optimistic about their polars
and such.

-Paul Hanson
SZD-59 driver, claimed at 40/1 by SZD (wet w/winglets...) and measured
by Johnson at 38/1 (dry w/no winglets...)

At 14:52 08 November 2008, Ian wrote:
On 8 Nov, 03:51, Bob Kuykendall wrote:
On Nov 7, 5:10=A0pm, KevinFinke wrote:

I don't think 40/1 is remotely unreasonable for the Perkoz...

Ten bucks says that if the Idafliegs do a polar it tops out at or
below 39.

Perhaps, but if Dick Johnson were still around he could stick some
turbulator tape on it and suddenly get 45 ...

Ian

Quite the reverse - Dick Johnson tended to find that turbulated gliders
performed better without the tape. He also usually found lower
performance figures than the manufacturer's (and Idaflieg) polars.

John Galloway

On Nov 8, 3:15*pm, John Galloway wrote:
Quite the reverse - Dick Johnson tended to find that turbulated gliders
performed better without the tape. *He also usually found lower
performance figures than the manufacturer's (and Idaflieg) polars.

John Galloway

John -

Actually, it depends. On earlier gliders he started finding benefits
to the turbulator tape - which is why he developed the practice of
sticking it on gliders he tested.... That's because earlier airfoils
tended to have laminar separation bubbles, which could be eliminated
by forcing the airflow to go turbulent (which, while higher-drag than
laminar flow, is usually less-draggy than a bubble).

It went on this way until the airfoils developed for some later
gliders started to reverse the trend. I attribute that to the
advancement of high-end wind-tunnels, CFD, and other computer-modeling
techniques that allowed much better prediction and testing of airfoils
for laminar bubbles and other boundary-layer effects.

However, many of the gliders that are still popular today (and flown
in large numbers) use airfoils that can benefit from select
turbulation.

--Noel