Schweizer 1-35 and other flapped sailplanes

Udo wrote:

Eric Greenwell wrote:
There may also be performance issues related to designing a modern flap
only glider: because modern airfoils use such narrow control surfaces, a
flap only glider might not have enough glide path control. I was
astonished at the difference in glide angle between my ASW 20 and my ASH
26 E, even though they employ the same flap system for landing: the ASW
20 descended much more steeply than does my ASH 26. Even though part of
that is likely due to the higher wing loading on the 26, the flap chord
on the 20 is almost double that on the 26.


True,
I am building a new wing and I was hoping to include landing flaps
only.
The airfoil was not given me the results I desired with the larger
flaps. I had to reduce the flap size to 16% and install spoilers. The
flap/aileron arrangement will similar to the DG800,
May real preference would be the ASW20/26/27 set-up but I decided to
keep it simple
As for surface aerodynamics the spoilers are always past the laminar
transition. Smooth and sealed spoiler boxes have no ill effect.
In my case the max transition on the top surface will be at 66% and
that is where the box will be installed.

Interesting! On my ASH 26 E, the flap chord is 15.5% at the root (root
chord 33 inches), and the leading edge of the spoiler cap is at 48%.


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Eric Greenwell
Washington State
USA

The pressure recovery on the ASW26/27 is a bit more conservative. As
far as I know the transition for your wings if it uses the same
airfoil as the ASW27, would be about 59% in cruise and in climb about
65%. Top surface only.
As I had very good experience with my previous project regarding
pressure recovery and not wanting to use forced transition past the
hinge line on the bottom surface I came up with an airfoil that would
meet my requirement on paper and I think it is a good compromise.
The up-shot is the total wetted laminar flow around the airfoil is
about the same as the ASW27. In cruise it should be at par and in climb
it will have a small advantage and for that I will have to wait a wile
yet,
to see if I am right.
Regards
Udo

Ray Lovinggood wrote:
One question for 'flaps only' glider drivers:

On a cross country aero tow, do you ever feel a need
for some type of draggy things to help keep you in
tow position?

If you need a tow speed fast enough to get you home
before the sun sets but that makes it too fast to deploy
flaps, what procedure do you use, if and when necessary,
to keep the towrope tight?

"Too fast to deploy flaps" might be an overly-simplified statement of
the situation. How fast are we talking and how much flap are we
deploying? It doesn't take much flap to create significant drag. In
other words, it is likely OK to deploy a little bit of flap at high
speeds. Or perhaps just return them to neutral if you had them
reflexed.


Another nice "trick" is the ability to make the towplane more visible.
Cranking in a little flap such that the glider assumes a slightly nose
down attitude works nicely and easily.

Regards,

-Doug

Unfortunately, I just had the opportunity for an aero retrieve in my PIK-20.
8 deg. positive flap made for a comfortable tow at 70 - 75 knots and held
good tension during the occasional "snooze".


"Doug Hoffman" wrote in message
ups.com...

Ray Lovinggood wrote:
One question for 'flaps only' glider drivers:

On a cross country aero tow, do you ever feel a need
for some type of draggy things to help keep you in
tow position?

If you need a tow speed fast enough to get you home
before the sun sets but that makes it too fast to deploy
flaps, what procedure do you use, if and when necessary,
to keep the towrope tight?

"Too fast to deploy flaps" might be an overly-simplified statement of
the situation. How fast are we talking and how much flap are we
deploying? It doesn't take much flap to create significant drag. In
other words, it is likely OK to deploy a little bit of flap at high
speeds. Or perhaps just return them to neutral if you had them
reflexed.


Another nice "trick" is the ability to make the towplane more visible.
Cranking in a little flap such that the glider assumes a slightly nose
down attitude works nicely and easily.

Regards,

-Doug

That seems like a workable plan and well thought out.

But, the 6 allowed spoiler deployment up to redline as I recall so
pulling the spoilers was a perfectly legit operation and resulted in
immediate slowing and increased descent rate. Having the spoilers
sucked out and whistling at close to redline did get my attention along
with the hail coming at me from below.

The best solution is 'terminal velocity' spoilers that once deployed,
prevent acceleration to redline. 1-34 had 'em I think. Nice but not
required.

Flaps are workable, spoilers still seem just a bit better to this pilot.

Bob Whelan wrote:
"Maule Driver" wrote ...

I've never flown an HP. Getting sucked into a cloud seems to primarily
be a strong conditions (e.g. Western US) problem. Happened to me in an
LS6... have no idea what I'd do with a flaps-only ship except exceed
redline. Deploying the spoilers at close to redline scared the stuff
out of me as it was, but it worked.


Short of having the magic fairy wave a magic wand, I've a hard time
imagining anything simpler and safer in glider/cloud-avoidance terms. If -
for the sake of limiting this discussion - we ignore *how* one comes to be
in the situation of realizing cloud avoidance is (thought to be) a
necessity, and consider only the (forced) choices of either a) opening
spoilers at high speed for the first time beneath a cloud AND successfully
staying out of said cloud (e.g. Maule Driver!), or b) pulling on full flaps
at low speed AND unsuccessfully NOT staying out of said cloud (not me!), the
coward in me opts for "b)" in a heartbeat. Even with the Zuni's wimpy
large-deflection flaps, there is ZERO risk of exceeding maneuvering speed
and pulling the wings off in a spiral dive, because one must *hold* forward
stick w. full flaps to maintain flying speed.

I've done it in the PIK. Like everything else, a little flap specific
technique makes it work ok. Spoilers are a bit easier (mindless).

The fun is in reflexing them and pulling into side by side formation
with the towplane... :-)

Ray number ?
Bill in Durham

Ray Lovinggood wrote:
One question for 'flaps only' glider drivers:

On a cross country aero tow, do you ever feel a need
for some type of draggy things to help keep you in
tow position?

If you need a tow speed fast enough to get you home
before the sun sets but that makes it too fast to deploy
flaps, what procedure do you use, if and when necessary,
to keep the towrope tight? Yea, yea, yea, I know:
Fly it properly and you won't need to worry. But
what about when the tuggie snoozes a little and starts
a slight descent and gains speed. (Hey, I'm not even
sure spoilers could help out here.)

Popping spoilers out sure works nicely and easily.

And by the way, I don't like cross-country aerotows.
Sometimes, I think I would rather have the trailer
instead of the towplane.

Ray Lovinggood
Carrboro, North Carolina, USA
LS1-d (No flaps. Spoilers only)

Didn't your stick arm get tired holding the nose down? Mine did as I
recall because you couldn't trim it out. 70 - 75 knots would be nice
but seems like most tow planes in cruise want to go a bit faster.

Glen Kelley wrote:
Unfortunately, I just had the opportunity for an aero retrieve in my PIK-20.
8 deg. positive flap made for a comfortable tow at 70 - 75 knots and held
good tension during the occasional "snooze".

To Bill in Durham:

Bill, I'm still Ray #4.

But when it comes to any kind of racing, I'm Ray #last.

Ray Lovinggood
Carrboro, North Carolina, USA

At 16:24 20 August 2005, Maule Driver wrote:
I've done it in the PIK. Like everything else, a little
flap specific
technique makes it work ok. Spoilers are a bit easier
(mindless).

The fun is in reflexing them and pulling into side
by side formation
with the towplane... :-)

Ray number ?
Bill in Durham

The Glasflugel Mosquito flap/spoiler combo is terminal speed limiting. I
believe that was a requirement until right around 1980?
I've fully deployed the flaps+spoiler on mine and pointed the nose something
near vertical and didn't exceed manuvering speed. The POH says they can be
fully & abruptly deployed at up to redline, but be ready for the 2G
deceleration shock.


"Maule Driver" wrote in message
om...

The best solution is 'terminal velocity' spoilers that once deployed,
prevent acceleration to redline. 1-34 had 'em I think. Nice but not
required.

For Example John Smith wrote:

The Glasflugel Mosquito flap/spoiler combo is terminal speed limiting. I
believe that was a requirement until right around 1980?

It disappeared in the mid or late 60's, which is why the Std Cirrus and
other late 60's - early 70's gliders had relatively weak spoilers.

My ka-6E had terminal speed limiting spoilers, and I enjoyed their
ability.

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Eric Greenwell
Washington State
USA