Flaps and V-Tails of Death

From: (Kirk Stant)

As far as V-tails go, anything to reduce wetted area
is good, right? ;-P

This is a bit of a myth, I think. You still need the same tail volume
regardless of tail configuration, so you end up with basically the
same wetted area. If you cut down the size of the tails, you start
having stability problems (the Bonanza was originally a bit marginal,
I think), which is probably how V-tails on gliders got their bad
reputation in the first place. HPs apparently got it right from the
start. The theoretical saving is in reduced interference drag due to
fewer intersections (less of an advantage compared to T-tails) and
reduced weight (a big advantage compared to T-tails).

Right. Also, according to Dick Schreder, the V-tail shares the T-tail's
advantage of being up out of harm's way if landing in tall crop. The
conventional tail suffers there. Dick also spoke of the advantage of the
V-tail for the metal home builder, which obviously applies to the HPs. Just
build 2 identical parts, mirror imaged.

-Doug

( "Flaps and V-Tails of Death", you gotta love that subject title)

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.

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

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

Al wrote..
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.

So, what is the purpose of the air strut?
JJ Sinclair

"JJ Sinclair" wrote in message
...
Al wrote..
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.

So, what is the purpose of the air strut?
JJ Sinclair

Maybe it has no real purpose. The Ventus 2bx does not have a air strut on
the flap linkage (at least I have not seen one). Maybe S-H decided that one
was not needed.

Duane

On 20 Nov 2003 00:32:06 GMT, (JJ Sinclair) wrote:

Al wrote..
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.

So, what is the purpose of the air strut?
JJ Sinclair

So the flap pushrod can shorten when you open the brakes. It is much
the same in the Mini Nimbus and Mosquito and gas struts in gliders are
a disaster waiting to happen to you. When they fail it is usually with
no warning. Try getting one while at a contest in the boonies. I found
that the one from the hatch of a VW Golf (Rabbit in the US)fitted.

Mike Borgelt

(JJ Sinclair) wrote in message ...
Al wrote..
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.

So, what is the purpose of the air strut?
JJ Sinclair


I believe the flap / spoiler-drive mechanism on the Ventus a/b is more
or less identical to the Mini Nimbus / Mosquito solution. Last winter,
I and my co-owner, replaced the gas struts on our Mini Nimbus C. After
spending a few hours studying the finer details of this clever
arrangement I dare say that the struts do indeed have a purpose.

There are two struts involved, one of them is (as far as I can figure
out) used to balance out the forces in the spoiler handle and ensure
locking of the spoilers in their in and locked position. This strut
will work against the movement of the spoiler-handle for the first
part of the spoiler deployment, and then change into working to
further open the spoiler. As Mini Nimbus drivers knows, the forces in
the spoiler handle will immediately after unlocking them be very low,
you may even have to hold them back for the first 1 / 4 of spoiler
travel. After this the force will increase as also the flaps will be
deployed. The gas strut will, to some extent, limit the force
variations during spoiler operation. I would assume that this is also
true for the early Ventus models. The spoiler-flap operation on our
Mini was improved after replacing the strut.

The second gas strut is there to push the flaps up against a stop. The
position of the stop is altered with the flap handle. If you push the
flaps downwards, the gas strut is compressed, and when you release it
will spring back against the stop, which is -7 to +8 degrees depending
on flap setting. This is clever! When the spoilers are deployed, they
will after initially opening some 30 degrees, catch on to the flaps
and rotate these to (I believe) 60 degrees. The flaps will during this
operation be pushed away from the stop and the gas strut will be
compressed.

The result, for those not yet acquainted with gliders equipped with
this very efficient and easy to use arrangement, is that for the first
part of the spoiler deployment, only the spoilers will open. After
approximately 1 / 3 of travel the flaps will also start to drop
increasing the effect of the spoiler. When fully deployed, the flaps
will be at 60 degrees, and you will be hanging in your straps viewing
the runway from the same perspective as the HP pilots describes.

Well, this was probably impossible to understand, at least for those
who haven't looked inside a Mini Nimbus, Mosquito or early Ventus.

After flying the Mini for a couple of seasons I really like this
system. The steep approach angles it enables means safer landings over
masks. The only downside is that the glider will float some in the
ground effect if you are carrying to much speed. Not a lot, but more
than say a LS-3 or some other glider with big conventional
Shemmp-Hirth brakes. I would assume that the float effect is still a
lot less than for gliders with only flaps.

We bought our struts directly from Schemmp Hirth, they were not at all
expensive and the delivery was swift. At least one of the struts have
some custom made fittings that will save you some work of you get them
from SH.

Happy soaring
Jan Larsson
Sweden

Ps. The website of my club
http://www.flygklubben.bojn.net/

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

Thanks Wallace ! I love my RHJ-8, though its flaps aren't quite as
effective as the HP-14 I once owned. Note that the HP's (later ones
anyway) are *much* easier to land than some other flapped ships, as
the flaps can produce much more drag. The 1-35 (especially the
models with less flap) requires much more precise speed control
to avoid floating across the aerodrome. Required speed precision
varies quite a lot between sailplanes (different models of 1-35,
PIK, HPs with different flap/aileron lengths, Monerai, C-70), so
be careful of generalizing too much ! Also, forked-tailed-devils
vary a lot (and many HPs have been modified - tail lengths and
angles), so again don't generalize too much...

Best Regards, Dave "YO"

"Wallace Berry" wrote in message
...
Hi all,

I'm here to report that I cheated death and survived a flight in a
glider with the dreaded "Landing Flaps and V-Tails of Death". Jim Harper
graciously allowed me to fly his beautiful HP-16. What's an HP-16 you
say? Well, looks to be just like the HP-18 (or I should say the HP-18 is
just like the -16) except that the -16 has a large and comfortable all
metal cockpit instead of the narrow composite cockpit of the -18.

Jim's -16 is equipped with winglets and, as far as I know, the ailerons
are standard (not with the J.D. Colling mod, correct me if I'm wrong
Jim). Center stick. Tow was behind our 180hp Cessna 175 on a 275 foot
long rope. Started out in -2 flap position, went to + 5 at 40 knots. Had
no trouble keeping the wings level. The bird lifted off level and was
easy to fly on tow. Released and tried slow flight (no stalls), flight
up to 90 knots. Steep turns, etc. Well sealed and quiet. Good rudder
response and easy to coordinate compared to my 301 Libelle. More stable
in a thermal than my Libelle. Aileron response was a little slower than
my Libelle at thermaling speeds, but was positive and more than adequate
for centering thermals. Climbed a few hundred feet in a very week
thermal. Very nice thermalling glider.

Landing was the best part. I stayed high and close in the pattern. I
rolled on some flap on downwind, maybe 30 degrees or so. I was way high
on final so I started rolling in more flaps. I never quite got to the
full 90 degrees mark as I had the nose down at a truly obscene angle
just to maintain 50 knots. Steeper than my 301 with the tailchute and
full divebrakes. Steeper than a Mosquito with everything hanging out.
This was more like parachuting than flying. Nothing but dirt out the
front of the canopy. The horizon was visible more towards the top of the
canopy. I aimed at a target and just kept the nose pointed there. I
pulled back on the stick when I ran out of nerve. The bird settled on
with a slight bump of the tailwheel and a little bounce as the main
dropped on (I flared just a bit too much). I have no doubt that I could
easily put this bird in a tiny field much easier than I could my Libelle
(and that is not difficult at all).

So, I'd have to say that all the bad things I've been told about landing
flaps on gliders and V-tails are definitely untrue with respect to the
HP-16. It is a comfortable and easy to fly glider and compares very well
to my Libelle and also to other glass birds, including my favorites for
handling, the Mosquito and LS-4.