Flaps and V-Tails of Death

Earlier, Eric Greenwell wrote:

Are there engineering or manufacturing
issues that make spoilers a more
desirable choice these days? For
example, a fiberglass wing might be
more flexible than a metal one, which
would make a 90 degree flap harder
to implement. The early ASW 20 had
problems this way with it's 60 degree
flap setting.

Boy, you picked up on that one quick!

I'm not qualified to address the actual engineering
aspects of this issue. But speaking from the perspective
of a sailplane development pundit:

I think that, absolutely, implementing 90-degree flaps
on a composite wing has complications that you wouldn't
find on a more rigid metal wing. However, the lessons
of the PIK-20B and the Zuni suggest that it is doable.

As you point out, the big problem is bending of the
wing with fully deployed flaps, which tries to bend
the flaps in the plane in which they are most rigid.
I suspect that overcoming this issue requires the right
layup type and fiber orientation. I'd have to do test
sections to be sure, but I think that either aramids
or possibly newer polyethelyne fibers on some sort
of bias orientation would be required. That might give
reasonable torsional stiffness without undue bending
stiffness. It seems to work for the LS-6, which uses
Kevlar (tm) laminates in the flaperons.

Of course, a stiffer wing than the old ASW-20 would
help, too. That, and more hinge points and more drive
points.

Before I tried it for sure, what I'd want to do would
be to test a candidate flap section, and see how close
I can get it to the predicted wing curvature at the
ultimate loading limit. It might turn out to be necessary
to either make the wing stiffer, or to limit loading
to a lower G value under landing flap deployment. Or
perhaps something else entirely. That's what testing
is for.

Thanks, and best regards to all

Bob K.

Wallace Berry wrote in message ...
lots of good stuff snipped...

Geeze, Wally. Thanks! Just a couple of responses through the entire
thread.

Floating down the runway? More flaps. With 90 degrees and the nose
level...she stops pretty close to right now. Might want to make sure
you aren't more than that foot or so above the ground, or you test
Schreder's wonderful shock absorbtion.

Clouds? Full flaps at whatever speed you are going aren't going to put
you up much...and you will come down quite quickly...and out of the
cloud. If you go 90 degrees in my 16, you can pretty much let go of
the stick (at altitude) and it descends quite docilly...well...it bobs
and weaves but it don't scare me much. There is a bunch of drag there.
I should note that I am at the forward limit of the CG.

My biggest concern about the -16 is that it is gonna ruin me for other
gliders. No way will I ever find similar glidepath control. I can
modulate out of pretty much any amount of trouble.

At any rate, Wally, thanks again. I love to share! And I had to fly
tow anyway!!

Jim

"Eric Greenwell" wrote in message
...

Wayne, what's it like to land an HP in a strong, gusty wind? Do you use
a higher approach speed and only partial flap?


Eric,

I am a low time glider pilot and I think more experienced pilots could
provide more insight then I; however, from my limited experience you are
right on target.

Several years ago I purchase a HP-16T (now owned by Brian Case). I search
the web for information and found almost nothing, so I started a web site to
act as a repository of information relating to Dick's designs. The site was
well receive by HP/RS/RHJ owner and article, pictures, etc started arriving.
The result is http://www.soaridaho.com/Schreder The information on the site
reflects the cooperation of HP enthusiasts, not my expertise.

Bob Kuykendall started a complementary service by forming the hp-gliders
news group. (http://groups.yahoo.com/group/hp-gliders). The combination of
the two resources have served Schreder sailplane design owners over the past
five+ years.

After I sold my HP-16T to Brian I purchase a HP-14 which I have been
restoring for the past 3 years.

Here are some relevant landing related articles that I have collected:

Dick Schreder --
http://www.soaridaho.com/Schreder/St...r_on_Flaps.htm
Steve du Pont -- http://www.soaridaho.com/Schreder/Large-span_flaps.html

Bob Kuykendall -
http://www.soaridaho.com/Schreder/St..._HP_flight.htm

Wayne
http://www.soaridaho.com

Bob K wrote..
As you point out, the big problem is bending of the
wing with fully deployed flaps, which tries to bend
the flaps in the plane in which they are most rigid.

If one were to bounce, or land in a rough field, in one's ASW-20, with 45
degrees of flap on, the downward motion of the wings would force the deployed
flaps to move up, thus bending the internal flap push-rods. I would think some
sort of sliding push-rod arrangement might prevent this situation. The Ventus
has a gas strut that will allow the deployed flaps to come back up. Do I have
the Ventus gas strut figured out correctly, you Ventus drivers?
JJ Sinclair

On Tue, 18 Nov 2003 07:47:58 -0800, Eric Greenwell
wrote:

.... text deleted ...

Wayne, what's it like to land an HP in a strong, gusty wind? Do you use
a higher approach speed and only partial flap?
--

Eric, I resisted jumping into this thread, but for what it's worth,
while I no longer fly a PIK, I did own a PIK20B for 18 years and have
something over 2000 hours in this 90deg flap only ship.

Most of the important points on 90deg flaps have already been said.

- they are different, so there is an initial learning curve that is
made more difficult by the lack of 90deg flaped trainers. I often
recommended new PIK pilots to get an hour in a Cessna 150 to get a
feel for high flap deflection behavior.

- once mastered, they can be modulated during any portion of the
pattern with no problem. As has been said before, if you are floating
and can not get the ship down, put on more flap. Once the main wheel
is on the ground, dump the flap (full negative (up)) to plant the ship
on the ground.

- Like any flapped ship, so not get below the flaps up stall speed
during the pattern, until your final flare. This allows you to
modulate the flaps with no concern about pulling out flap and
stalling.

- On the PIK, I recommended new pilots move the PIK flap handle (5
turns total) in full 360deg increments, always stopping at the top of
the circle. This made modulation like normal spoilers, pulling the
handle back from the top position lowered flap, increased drag, just
like pulling back a spoiler handle. And the opposite for pushing
forward from a top position, less drag.

- Relating to your question, the only drawback I found in the 90deg
flaps was landing in very gusty conditions. Here I would limit the
down flap to something like 45deg. Since this only occured with strong
headwind components, I did not need large flap deflections.

- The strong advantage to the 90deg flaps was in short field landing,
where you could point the ship at a spot on the ground and modulate
the flaps to control airspeed. BTW, the only time in all my flying
that I used 90deg flaps was in off-field landings over a tree line,
and for routine practice. Typical landing flap varied between 30deg
and 60deg.

Bob

Bob Whelan wrote:
...
IMHO, about the only situation I can envision where a flaps-only ship IS
worse than a spoilers-only one is that of getting low and slow on the
approach. Is there a spoilers-only driver alive who doesn't take some
comfort in the thought s/he can slam the spoilers shut in that situation and
not distinctly improve things in the near-term future? Get yourself in that
situation in a flaps-only ship and you're essentially out of options. The
GOOD news is that you're much more likely to get low and slow in a ship
having weak landing aids...generally not a problem in gliders having _only_
large deflection flaps as landing aids.
...

Except for the presence of the runway instead of unlandable terrain below
the glider, this is exactly the situation of my question, and so the answer,
as I suspected, is that you are out of options.

When Slingbys tried to produce the HP14 for the British market they ran into
trouble with the use of flaps only for cloud flying. At that time to get an
airworthiness certification the glider had to have speed limiting devices
for cloud flying. It had been proved in test flying that the flaps
certainly limited the airspeed to "rough air max." but the test pilot ( John
Williamson) reported if the airspeed was already high and rising, the effort
required to lower the flaps down to 90 degrees was just too much.

If the sailplane was genuinely going out of control in cloud the flaps would
be useless. Various methods were tried to overcome this including a high
pressure air bottle to actuate pneumatic jacks- unfortunately at high speeds
forcing the flaps down in this manner caused problems with the supporting
secondary spar structure requiring yet further modifications.

DB

The Ventus Strut is pushing up.
Part of the preflight on my Ventus B is to push down on the inboard flap
both sides to feel the gas strut pressure.

Al

"JJ Sinclair" wrote in message
...
Bob K wrote..
As you point out, the big problem is bending of the
wing with fully deployed flaps, which tries to bend
the flaps in the plane in which they are most rigid.

If one were to bounce, or land in a rough field, in one's ASW-20, with 45
degrees of flap on, the downward motion of the wings would force the
deployed
flaps to move up, thus bending the internal flap push-rods. I would think
some
sort of sliding push-rod arrangement might prevent this situation. The
Ventus
has a gas strut that will allow the deployed flaps to come back up. Do I
have
the Ventus gas strut figured out correctly, you Ventus drivers?
JJ Sinclair

"Bob Whelan" wrote in message ...
[snip]
Speed control is important in gracefully landing flaps-only gliders
(spoilers-only too, of course). What I've found - and often seen - is that
gliders' large-deflection flaps essentially 'quit working' as drag producing
devices if landed 'too fast.' True even for HP-16's. Come in too fast and
you _will_ float a long ways in flapped gliders...unless you slowly ease off
on the flaps, in which case the ship will gently settle...
[good stuff snipped]
IMHO, about the only situation I can envision where a flaps-only ship IS
worse than a spoilers-only one is that of getting low and slow on the
approach.
[snip]
Regards,
Bob W.

Hi, Bob and all.

With all humility and with the following caveats, I would like to
mildly disagree and vehemently agree with a couple of your points.
First the caveats: I am not all that experienced, and have only flown
my HP-16 for one summer, I think I am qualified to comment, but by no
means am an expert. The following comments ONLY apply to my HP-16,
N8DC, with 90 degree flaps, standard sized flaps (no flap was
sacrificed to improve the ailerons), and flown fairly CG forward.

Mild disagreement on the too fast comment. I think that the only way
to make my -16 float would be to be going too fast and then roll off
the flaps. 90 degree flaps require an impressive deck angle just to
keep the speed in the 60mph range on approach. If, when I get close to
the ground, I flare, any excess speed, and I mean ANY excess speed is
gone very quickly, and I land. Period. An approach with, say, 60
degrees of flap would indeed float if I had too much speed on, and as
such, one possible corrective action would be to roll off the flaps,
if I had slowed considerably...otherwise, more flaps is usually the
right answer. This airplane will not float with maximum flaps. There
have got to be 6 square feet of aluminum hanging perpendicular to the
airflow...we stop pretty quickly.

A minor expansion on that. It is very difficult to get the airplane to
accelerate with 90 degree flaps...If I should let the airspeed decay
on approach with full flaps, I need to push the nose down to
frightening angles...as in hanging from the straps...to
accelerate...or just roll off some flaps, which is what I do. This
presupposes that we are talking 45-60+ speed range. I would very much
not like to get much below 45 with full flaps. The aircraft's stall
characteristics are quite benign, but recovery requires a fair amount
of altitude with flaps at that level.

Conversely, speed control on appoach is quite trivial. Should I, for
whatever reason, let the speed creep up...more flaps...less speed. It
is amazingly linear...and better than any speed/lift control device I
have used, including throttle.

To agree emphatically on another point: Low and slow with flaps on is
a VERY BAD THING (tm). Too fast is no problem...roll the flaps in to
slow, roll them out to stretch. Too slow, and your options
are...well...gone. So that is an area of the performance curve that I
avoid.

I too went into the -16 wondering about all of the forked-tailed flaps
of doom talk. Turns out that my airplane is an absolute pussycat. If
yer ever planning on being around LaGrange, GA some weekend, drop me a
note. We might can work something out!

Jim

Robert Ehrlich wrote
Except for the presence of the runway instead of unlandable terrain below
the glider, this is exactly the situation of my question, and so the answer,
as I suspected, is that you are out of options.

I think that's rather overstated. Unless you have botched the pattern
so throroughly that you are at 30 degrees of flap and coming up short,
you do exactly what you do in a spoiler-only ship - you retract the
flaps. The difference is this - you can't just retract completely, as
you would spoilers, because retracting that last 30 degrees is going
to cause a transient drop you won't like. However, going from 90
degrees to 45 causes no loss of lift at all, and a huge loss of drag -
thus causing airspeed to increase, which allows lifting the nose and
dramatically flattening the approach. This was certainly the case in
my HP-11, and I can't imagine it would be much different on other
flaps-only gliders.

Michael