Flaps and V-Tails of Death

(Mark James Boyd) wrote in message news:3fbc8231$1@darkstar...

I was always under the impression that Fowler flaps
reduced stall speed, but didn't think plain flaps
did much other than just add drag. On the
Katana, AA-1 Grumman, and Tomahawk (all power planes)
they seem to do nothing but add drag. Interesting
to hear these experiences, and I'll certainly
look at the next HP I come across more carefully.

All flaps will lower stall speed at small settings - even split flaps.
That's why you usually have a takeoff setting for soft and/or short
fields.

Boy, I havn't flown an AA-1 (the original, American Aviation Yankee,
with the "hot" wing) in a LONG time (32 years!) but I seem to remember
it's flaps didn't do much at all - at least compared to any Cessna.
Sure was a fun little thing to buzz around in, though!

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). Then there is
the rudder-elevator mixer issue...

They do look nicely retro, though. And the Fouga Magister proves that
the V tail can work beautifully in a relatively high performance fully
aerobatic jet trainer.

Finally, let's face it, V-tails were a fashion for a while in the late
40s and 50s (Bonanza, Magister, SHKs, Sisu, HPs, etc.) Now, T-tails
are the "cool" tail - which probably has a lot to do with why the poor
little PW-5 is dissed so much.

Kirk

Kirk Stant wrote:

They do look nicely retro, though. And the Fouga Magister proves that
the V tail can work beautifully in a relatively high performance fully
aerobatic jet trainer.

And I'm told the Salto does quite well as a Vee tailed aerobatic glider.


--
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Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

(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/

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)

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.

Robert Ehrlich wrote
This will work on approach, when you have the nose down attitude
corresponding to the flaps setting but not in the situation of my
initial question, i.e. just after a botched flare, a few feet above
the runnway and no nose down attitude. In this case retracting the
flaps will cause a loss of drag, but no so huge, i.e. the drag will
much more than in zero flaps or zero spoilers configuration

I do not concur. Imagine, for example, a similar situation involving
a glider with approach flaps and spoilers, such as the Blanik L-13.
It is normally landed with full flaps, and spoilers are used for
glideslope control. It is also a common primary trainer, so the
situation you cite comes up with some regularity. The solution is to
retract the spoilers - but you still have flaps hanging out. How is
this any different from retracting Schreder-type flaps to 30 degrees?

and there
is no gain in lift and no change in the stall speed, you don't have
the altitude that you can convert into speed, so I think that you are
going to fall on the ground, with a slighly increased delay compared
to what would happen if you didn't retract some flaps.

Actually, you will fly onto the ground, and if you're not careful you
will float. With the flaps retracted to 30 degrees, the HP-11
certainly had a tendency to float even when brought in at very low
airspeed. In fact, after some experimentation I came to the
conclusion that if my flap mechanicsm were to ever fail with the flaps
at less than 30 degrees, I would need about 2 miles of runway to stop.

Michael

Michael wrote:

Robert Ehrlich wrote
This will work on approach, when you have the nose down attitude
corresponding to the flaps setting but not in the situation of my
initial question, i.e. just after a botched flare, a few feet above
the runnway and no nose down attitude. In this case retracting the
flaps will cause a loss of drag, but no so huge, i.e. the drag will
much more than in zero flaps or zero spoilers configuration

I do not concur. Imagine, for example, a similar situation involving
a glider with approach flaps and spoilers, such as the Blanik L-13.
It is normally landed with full flaps, and spoilers are used for
glideslope control. It is also a common primary trainer, so the
situation you cite comes up with some regularity. The solution is to
retract the spoilers - but you still have flaps hanging out. How is
this any different from retracting Schreder-type flaps to 30 degrees?

and there
is no gain in lift and no change in the stall speed, you don't have
the altitude that you can convert into speed, so I think that you are
going to fall on the ground, with a slighly increased delay compared
to what would happen if you didn't retract some flaps.

Actually, you will fly onto the ground, and if you're not careful you
will float. With the flaps retracted to 30 degrees, the HP-11
certainly had a tendency to float even when brought in at very low
airspeed. In fact, after some experimentation I came to the
conclusion that if my flap mechanicsm were to ever fail with the flaps
at less than 30 degrees, I would need about 2 miles of runway to stop.


OK, I have no experience on this kind of ship, I was just trying to
figure how to handle this situation. What you are saying is that
in the range 30-90 degrees on this ship, flaps work like spoilers
on usual (from my point of view) gliders, i.e. retracting them to
30 degrees brings the drag at a level similar to that of a non-flapped
ship with spoilers closed, without change in lift. So the important
thing in order to be able to recover from the 3 most common mistakes
is to have the flaps at more than 30 degrees when you begin the flare.

Someone mentioned that landing with T or V tail is
better than conventional tail in tall crop.

I'd like to know of someone who has landed
in crop with a conventional tail. Any
stories out there?

It strikes me that the yaw of crop hitting a
wing is the real problem. A conventional tail,
if it grabs the crop BEFORE the wing does,
might actually keep the glider straighter,
kind of a keel effect?

Maybe in 2-3 foot crop this means the
conventional tail is damaged but T-tail isn't,
but in very tall crop, the conventional
tail is damaged and the glider
pancakes in straight in vs. yawing
and rolling T-tail (since a wing hits first).

Any opinions about this? Anyone
have anecdotes? I've wondered
the same thing about high-wing vs. low-wing
water landings in power aircraft...

In article ,
(Michael) wrote:

Imagine, for example, a similar situation involving
a glider with approach flaps and spoilers, such as the Blanik L-13.
It is normally landed with full flaps

It's a few years since I've flown a Blanik, but I've flown 5 different
L-13s a total of 110 flights. I'd estimate that at least 105 of those
landings would have been with zero flap.

-- Bruce

Don't know about conventional tails. But I have been helping rebuild a
DG202 (T-tail) that landing in a tall wheat feild. It caught a wing
tip and turned sideways breaking nearly every part in the fuselage.
(Major Damage) Don't know if a conventional tail would have helped.

Brian