Cross Country Magazine - Bautek Twister
test flown:
"Dennis
Pagen jumps into bed with Bautek's latest, and gets his knickers in a twist!"
Bautek’s
Twister was one of the first kingpostless gliders on the market, but it has yet to grab
much international attention. Bautek has spent little effort marketing outside of
Europe. They have been content to serve the large European market which has
historically formed the nucleus for the global market.
All
that is changing. Bautek has a competitive topless glider in the Twister, and it is aptly
named, as we shall see. Its performance is good and some special engineering renders
it most desirable in terms of safety. In addition, the strong US$ in relation to
European currency makes the price attractive for us Americans looking for a top
performing, safe topless glider.
I took delivery of the Twister at Monte Cucco, Italy where I flew it in the Pre-Worlds
meet. Then the factory graciously let me keep it for another two weeks of peripatetic
flying in the Alps where I tested its mettle in non-competition mode. This report is
the result of some 30 hours of airtime in widely varying conditions and regimes from light
air scratching to high-wind racing.
BAUTEK'S BACKGROUND
Before
we talk about the glider, let me fill you in on the company, Bautek. They have been
in business since 1971, developing parts for airplanes and sailplanes. In 1981 they
designed and produced their first hang glider, the Fafnir. This wing was followed by
the Saphir, Zephir, Pamir, Milan, Milan Racer, Sunrise, Astir and Twister. All of
these gliders except the Milans and the Twister were bowsprit gliders; now you recognize
them!
The Bautek name comes from the German word bau which means construction and technik.
The company heads are the Zimmer twins, Horst and Harald. Horst is the
engineer; Harold is the business whiz. Bautek is near Trier, in the Moselle wine
country of southwest Germany next to the Luxembourg border. The factory is a large
new building constructed specially to build gliders efficiently.
GLIDER
PERFORMANCE
Let
us dispense with performance factors right away, for although performance is of utmost
importance we have many other items of interest to report on the Twister.
My experience on the Twister indicates that it climbs extremely well. Both in the
Pre-Worlds and later free flying (with as many as 50 gliders at Laragne, France) I was
never outclimbed when sharing a thermal. The Twister's thermal climbability is what
I would claim to be its strong point.
At normal glide speeds I was keeping with the tight comp gliders. I maintained the
glider in stock configuration, so at higher speeds I could not keep up with the gliders
with lowered sprogs. But if we were to compare the stock Twister to other stock
gliders, I believe we would find equity.
The Twister handling is also one of its fine points. The glider is tuned without a
lot of sail and batten tension, similar to the Laminar. This setup promotes good
handling and the ability to slow down well in thermals. The VG system has lots of
travel with three long pulls required to go full-tight. The result is the best of
both worlds: good loose VG handling and drum-tight maxed-out glide with a tight VG.
Harold told me they worked for a year to perfect the Twister's handling by altering tube
flexibility, sail tension, tip twist, airfoil profiles, batten tension and crossbar
holdback configuration. The glider has a curved down basetube to let you hang lower
and a keel pylon to make your hang point higher. With all of these factors, Bautek
believes they have found the best compromise of handling, performance and landing ease for
the Twister.
One last point on performance: the Twister was flown this year by factory pilot Jobst
Baeumer in the German Nationals. He won the meet against top pilots such as Bob
Baier and World Champion Guido Gehrman.
THE
BAUTEK FEATURES
Now
comes the fun part, at least for us design buffs. But even pilots who don't know the
difference between an upright and a downtube will find interest here, for some unique
safety features are highlighted.
The Twister has an automatic pitch stability system which is a welcome feature on a
topless glider. Here's how it works: If turbulence unloads your side flying wires,
or if your glider is pitched nose down to the point the side wires off-load, the tip
struts automatically twist upward. This action simulates reflex bridles (found on
kingposted gliders) kicking in or an up elevator control on an airplane.
This automatic twist device, known as the Safety Pitch System, works with a lever attached
to the side cables which is activated by a spring concealed inside the crossbar. When the
side cables go slightly slack, the spring rotates the lever which pulls a cable routed to
the tip struts and configures to tilt them upward. Careful testing has shown the
system to work effectively at realistic flying speeds and weights.
Another system working in a similar manner is connected to the hang strap to activate the
tail on Guggenmos' RCS. The Zimmers tried such a system, but felt that the side
cables are more sensitive to potential pitchover events. You can see the Twister's
tip twisting trick by rotating the glider's nose up and down in the wind. When the
wings lift the twist goes down; when the nose is dropped so the side wires go slack, the
twist increases.
The next item of interest is the crossbar itself. It is not made of carbon as is the
crossbar of most topless gliders. The Zimmers checked with their sailplane
manufacturer associates and found out how critical the construction and inspection of
carbon was. They opted to make a crossbar out of aluminum using a truss system. A
truss system consists of a main compression beam and a series of supports designed to keep
the compression beam in column or handle tension loads. Most bridges that aren't
suspended bridges are truss systems, for a truss is the lightest form of construction for
a given load requirement.
The truss arrangement in the Twister consists of a couple sets of outriggers and cables
that stiffen the crossbar much like the mast of a sailboat. The result is a crossbar
just as strong and light as the cantilever carbon ones at less than half the price.
In addition, this crossbar is easier to inspect for damage compared to a carbon spar and
the Zimmers feel this is an important advantage when it comes to the resale of the glider.
Another interesting feature on the Twister is the upcurved plastic tips. These tips
are similar to those seen on the Stealth, but developed independently. In fact, the
Zimmers called on their friends at the Mercedes factory and used their wind tunnel.
By carving wood tips and trying many different shapes they were able to come up with the
minimum drag design.
Other features on the Twister include the nose zippers which free the Mylar at the nose so
it doesn't get bent when packing up as it does on all other gliders. Next is the
lower surface netting at the tip which relieves pressure and prevents downward inflation
at the tip at high speeds (low angles of attack). This feature renders the glider
more yaw stable. Tests have shown that closing one side makes the closed side create more
drag and lag behind. We have already mentioned the basetube which is about one inch
diameter for lower drag with a nice rubber grip and an internal cable for safety.
Finally we should point out the aluminum keel which is tapered to look sexy and reduce
drag. It also swings down like a kickstand to aid in setup if you so desire.
FLYING
THE TWISTER
We
have previously mentioned the twister's nice handling characteristics, but let us look at
other factors. While free flying I put the glider through some standard tests.
First I tried stalls, both with the VG on and off. In all configurations I
couldn't get the glider to drop its nose as long as I started the stall from minimum sink
speed. The glider would simply mush or go into falling leaf mode. What this
means to flying is the glider may have less tendency to nose in after a landing flare, and
may be less apt to rotate nose down if stalled in strong turbulence. A month after
flying the glider, Bautek told me that they’ve positioned the uprigths 11 cm to the
rear of the keel tube to improve landing further.
Another thing I tried was slipping turns and hands-off turns. The slipping diving
mode was very controllable and predictable. I like to use this feature for landing
setup and it came in handy during a flight in France when I chose to alight in a small
wheat field along the Durance river.
By putting a glider in a coordinated bank and letting go, you can check for a glider's
spiral stability. Most designs are slightly unstable which means that the bank angle
increases. On the Twister the glider slowly leveled out which means that no high-siding is
required in smooth thermals.
I found the Twister to have lots of positive pitch bar pressure. In fact, it was too
much for my taste when diving full-tilt to goal. The factory said the sprogs could
be safely lowered to relieve some of this pitch pressure and this is one topless glider on
which I'd be willing to do so. Again, since reviewing the glider, Harald tells me
that they have optimised their sail tension to slightly lessen bar pressure at 60 km/h.
Takeoffs and landings are straightforward on the Twister. I had no unusual
experiences launching in either calm or strong conditions. The glider is relatively
light (73.7 lb./ 33.5 kg) for those light-wind launches. When landing you'll find
the glider to slow admirably and the only awkward landings I produced were in turbulent
conditions when I flared early.
SETUP
AND OTHER DETAILS
The Twister setup is fairly conventional, so we'll only point out a
few unique features. First is the sprog and tip strut setup. The sprogs usually fall
in place and all you have to do is place a transverse batten (which engages the battens on
either side of the sprog) in the slot at the end of the sprog, then zip up the under
surface. The tip strut is similar: you push it in to slide over a swiveling (up and
down) stud, pop on the transverse batten to hold it in and zip up.
The next interesting matter to note is the tip batten. There is no need to fumble
inside the sail trying to locate the batten on a stud, for it is fixed to the leading edge
and folds in its mid-span. To attach the batten you simply put the outside end in a
loop then straighten the batten slightly past center.
The batten pockets are one side forty-fived, and the lower surface battens were the second
easiest in the business (Airwave's are the best with their forward retainer loop). The
battens have new end plugs with steel springs...
Finally, I wish to mention the nose cone which is the only one I've ever found which I
could put on every time cleanly without pulling the nose down. The nose zippers
allow the Mylar inserts to stop closer to the nose than on other gliders, so the nose cone
can be a bit smaller and it is perfectly shaped.
This nose cone detail is indicative of the attention to detail characteristic of Bautek's
engineering on all their gliders. They make their own upright basetube junctions
which are nicely rounded and faired in. The uprights come with a grip patch for
those sweaty palm days. The rear haulback is a simple ring that loops over a small
block with a recess for the cable thimble. All these little details serve to
satisfy.
Perhaps the nicest detail is the sail. It is made in-house by Bautek and is very
clean. The glider looks sleek with its long smooth lines ending with the graceful
tips. I had many pilots checking out my glider wherever I went. Internally the
sail has three top to bottom straps and two ribs per side to hold the airfoil in shape
(this is a safety factor for negative angles of attack as well).
Finally, the best news about the sail is that your choice of colors comes at no extra
charge (Bautek maintains six leading edge and sixteen lower surface colors). In
addition, you can get a sail with the Bautek wave pattern on the lower surface in your
choice of colors at no extra charge. The upper surface sail comes with Dimension
Polyant's Power LL cloth (you've seen it before, it's the one with the black pinstripe).
I loved the Twister in almost every way. It is one topless glider I would like to
own, if only because of the warm, safe feeling it affords. Of course, climbing above
other gliders also piques the love interest. I would recommend this glider highly to
pilots who want a fun, high-performing topless glider without the worries. The best
bit I have to report is the price: $5000 which compares nicely to other topless gliders on
the market. (By Dennis Pagen) |
's friendly topless!
