Older reviews
LAK-17A feedback from users
John Gonzalez writes..."This is the best sailplane I have ever flown. The controls are light to the touch. Response rate is quick. There is so little required rudder input, it is easy to fly and man is it fast...... This plane will go 110 kts and it feels as though you are going 65-70kts. It is simply awesome.... All together, the plane is a 10+. I cannot glow enough about the plane. I am so excited about this plane's performance and handling characteristics. It is unbelievable...... I believe this company really has something special with this plane.... Like I said, this plane goes like butter on warm bread.... Thank you for making me so HAPPY...."
Bill Bartell wrote to one of the LAK-17A future buyers...
Performance of the LAK17
was equal or better than anything flying in the contest. The
factory has taken my comments about the tail attachment bolt and
the lack of jettisoning the tail ballast in flight and made
improvements. The factory has been excellent at reacting to my
comments. I'm sure others saw some of these flaws and commented
as well. Overall, if I was in the market for a new 15/18 meter
glider, I'd spend the money on a LAK 17. Want to buy my Ventus
2a?
Bill Bartell
www.glider.com
830-591-1769
Jeff Baird
wrote...
"Today I flew a 135nm task with a final glide of about
32nm. With 18m tips, no water save tail ballast, and a blue
hole to glide through all the way, I zeroed the McReady setting
and was told I needed about 4300 feet to arrive at 800ft. I
thermaled to added about 1000ft because I did not believe, then I
arrived at 2000ft. Some glider. The computer said I
made 49:1 at 49kts with 1kt tail wind."
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Dick Johnson's LAK-17A flight evaluation in progress
Draft 10 of the Evaluation
Excerpts from the correspondence
and photos
A FLIGHT TEST EVALUATION OF THE LAK-17A RACING CLASS SAILPLANE
Richard H. Johnson 12/19/00 – Draft 10
Published with permission from the author. The whole article is to appear in the March or April 2001 issue of the SOARING magazine, along with the referenced graphs, tables, and photos (not included here).
INTRODUCTION
The LAK-17A is a new and very modern composite 15-meter/18 meter Racing Class sailplane that was designed and produced by the newly privatized Lithuanian manufacturer Sportinë Aviacija. That is where the LAK-12 (Reference A) and other series of sailplanes have been manufactured for many years. The Genesis 2 production and certification were sent overseas several years ago to the same manufacturer. Dr. Eduardas Lasauskas is the LAK-17A’s wing airfoil section designer and Dipl.Eng. Klemas Juocas is its principal airframe designer. They both show a lot of talent.
The LAK-17 is of a conventional modern racing sailplane configuration, except that its wing aspect ratios (wingspan divided by average chord) are very high. That wing aspect ratio measures about 24.8 in its 15-meter configuration, and about 33 in its 18-meter configuration. In the 15 meter configuration, that high aspect ratio is exceeded only by the ultra slim all carbon 15 meter SZD-56 Diana sailplane (Reference B), which measures at about 27.6. Not only are the LAK-17 wings of unusually high aspect ratio and surprisingly thin, but they are relatively light in weight. Figure 1 is a 3-view of this fine new sailplane.
Sportinë Aviacija apparently accomplished that commendable feat by using extremely strong carbon pultrusion rods, a revolutionary new structural material for the wing spar caps. These rods are about 1/8th of an inch in diameter, and they are manufactured by pulling tightly packed resin soaked carbon threads through a heated forming die. That is a continuous process, and it produces an extremely strong and light structural material. The spar caps are built up by clustering numbers of these spanwise oriented high strength carbon rods and bonding them together with an epoxy resin. A large number of these rods are located at the root of the wing, tapering to but a few near the wing tip. Through extensive use of this most modern structural material, the empty weight of the LAK-17 is relatively light. The wing panels weigh about 135 lbs each. That makes their handling during assembly fairly reasonable, even without special rigging aids.
The LAK-17 has now been in production for over one year now, and at a rate of about 2 per month. I was fortunate in that two members of the Dallas Gliding Association decided to purchase serial numbers 104 and 105, the 4th and 5th production models. Also, that they both were agreeable to my using their sailplanes for testing and evaluation. We performed 27 test flights and thoroughly evaluated Jeff Baird’s S/N 5 in 5 different wing test configurations; all unballasted. Our plans are to test Steve Hundley's S/N 104 in its ballasted condition before we complete this test series..
When both the sailplanes arrived in Texas late last winter, we carefully inspected them in detail and found them to be of high quality. The polished white epoxy finish was excellent and the wing surface waviness was extremely low, well below the .004 inch limit that I believe to be needed to achieve extensive low drag laminar flow on sailplane wings. Its glass and carbon fiber composite construction appeared to be quite strong, and its empty weight fully equipped with 2 batteries and competition instrumentation was about 520 lbs. The details of its construction were very well done. All of the exposed metal fittings were nicely cadmium plated for enduring rust protection. Its retractable main wheel is a well-sized 350 x 135-mm (13.7 inch tire diameter by 5.3 inches wide) unit that is equipped with a standard drum brake that appears to function fairly well. The aft end of the fuselage is equipped with a relatively small but adequate 6-inch diameter pneumatic tail wheel. The tail wheel itself is nicely machined from aluminum alloy and is mounted on sealed ball bearings.
AIRSPEED CALIBRATION
The LAK-17 airspeed system uses a fuselage nose pitot and aft fuselage sides for its static source. Our flight test calibration was flown at indicated airspeeds of 40 to 122 kts. Those test data were used to compute the LAK-17’s airspeed system errors versus indicated airspeed chart shown in Figure 2. The LAK-17 airspeed system errors appear to be generally about 1 kt or less over the entire 40 to 122 kt IAS test range, and that is excellent. They show that the LAK-17 is actually flying about one half to 1 kt faster than indicated.
WING SURFACE WAVINESS MEASUREMENTS
We made chordwise waviness measurements of our almost year old LAK-17’s wing top and bottom surfaces at 7 spanwise stations along each wing using a standard 2 inch long wave gage. The magnitudes of the unwanted waves were surprisingly small. Both the wing top and bottom surfaces showed a remarkably small amount of waviness, averaging only about .0015 inches. That is about the smoothest wing surface that we have ever measured! Those measurement data values are for peak-to-peak magnitudes –from valleys to peaks. Those data are shown plotted in Figure 3.
WING DRAG RAKE MEASUREMENTS
During the initial part of the LAK-17’s flight testing, we installed a Reference C type of wing profile drag measurement rake to its left wing trailing edge, about one meter outboard from the fuselage side. Theoretically we could then determine the optimum flap settings versus airspeed, and even how well the factory-installed turbulator on the wing bottom surface performed.
A high tow was then made in an effort to determine which wing flap setting might be optimum at each flight test airspeed. To do that it was necessary to make drag pressure measurements over a relatively large range of airspeeds with each of the sailplane’s 5 flap settings. A calibrated Rico Drag Meter was used to measure the pressure differentials between the sailplane’s pitot pressure and the rake’s integrated pressure. This is a simplified relative measurement scheme where lowered rake delta pressure indicates a lowered wing profile drag, without having to fully quantify the wing drag magnitudes.
Those drag rake data are shown summarized in Figure 4 for the test with the factory turbulator installed, and Figure 5 shows it with the factory turbulator removed. As the drag data in Figure 4 shows, the L (landing) flap setting provides the least drag when flying below 40 kts, and the +2 thermalling flap setting appears to be best between 42 and 55 kts. The zero flap setting appears to be best when flying between 56 and about 90 kts. Above that airspeed the negative –1 flap setting appeared to incur the least drag. In general, these flap settings were used during the initial performance sink rate flight tests.
At the L (landing) flap position the flap deflection was measured to be about +14.9 degrees; +2 thermalling flap measured +11.3 degrees; +1 flap = +5.4 degrees; 0 flap assumed = 0 degrees; and -1 flap = -5.6 degrees. The handbook referred to an additional –2 flap high-speed setting; however the cockpit flap setting plate in our test sailplane did not include that notch. We placed the flap handle in its full forward position and measured that flap setting to be about –11.9 degrees. Flight measurements with that full negative –2 flap setting were made during Part 2 of this report, but they showed no improvement over the –1 flap setting.
SINK RATE TEST FLIGHTS
A. FACTORY DELIVERED CONDITION
Before we made the sink rate measurement flights, we checked and made certain that the LAK wings were well sealed. Since the flap and aileron hinges were near the wing bottom surfaces, we found that the factory installed bottom surface tape adequately sealed them from vertical leakage. The wing roots were also well sealed because the wing root ribs were solid and the control connections were of a rotary design that allowed very little clearance through which air might pass from the fuselage out into the wings.
Three high tow test flights were then performed with the sailplane in its 15-meter factory delivered condition with the wing bottom surface turbulators installed. The test data from those 3 flights were averaged and plotted in Figures 6 and 7. A minimum sink rate of about 116 ft/min at 42 kts, and a best L/D of about 40:1 at 52 kts were indicated. Those values were a bit lower than expected, but the sailplane climbed well in thermals, and its unballasted L/D at 70 kts was an outstanding 36:1!
B. TURBULATORS REMOVED
Since the wing drag rake data shown in Figure 5 indicated that the wing profile drag might be reduced if we removed the wing turbulators, we did that before the next sink rate test flights. We also removed the wing top surface Mylar seals because they appeared to be unnecessary, and they added noticeably to the aileron control system friction. Also, we added foam plastic sealing to the aft end of the fiberglass main wheel well cover, and that reduced the cockpit wind noise considerably.
Three more high tow test flights were then performed with the sailplane in its 15-meter configuration, but with the turbulators and wing top surface Mylar seals removed. The test data from those 3 flights were averaged and plotted in Figures 8 and 9. There a minimum sink rate actually increased to about 124 ft/min at 43 kts, and the best L/D decreased to about 37:1 at 46 kts.
That lowered rather than improved performance was a surprise in that the drag rake testing indicated that it should have been improved! However, the weakness of our drag rake testing is that it only evaluates the wing profile drag at the one test location, and different readings will most likely occur at other spanwise wing test locations.
In an effort to investigate these anomalous performance results, oil flow test flights were then conducted at both 50 and 70 kts, with the turbulators still removed. The oil flow patterns appeared normal at both those airspeeds, with extensive low drag laminar flows indicated on both the top and bottom surfaces. An airflow separation bubble on the wing bottom surface was indicated by the oil patterns at 50 kts. However, at 70 kts the bottom surface oil indicated laminar flows all the way aft to the flap and aileron hinges, which are located at about .85 chord fraction.
C. TURBULATORS RE-INSTALLED
We quickly realized that we were wrong, for undetermined reasons, about the turbulators being detrimental, and we re-installed them at the same factory location. The leading edges of the Zigzag turbulators were located at about .793 chord over the flap portion of the wing, and tapered to about .729c at the aileron tips.
Four more high tow test flights were then performed with the sailplane in its 15-meter configuration, but with the turbulators re-installed. The test data from those 4 flights were averaged and plotted in Figures 10 and 11. There a minimum sink rate reduced to about 112 ft/min at 42 kts, and a best L/D increased to about 41:1 at 52 kts. The L/D at 70 kts now appeared to be restored to its original 36:1. If our test LAK-17 were fully ballasted to its 999 lb /10.25 psf certified limit, that L/D would theoretically increase to about 36.5:1 at 84 kts.
PERFORMANCE COMPARISON
For polar comparisons, I chose the Ventus 2 because it is currently at or near the top of the current 15-Meter Class contest score sheets worldwide. We had tested Sam Fly’s Ventus 2B N4SF four years ago; therefore we had comparable test data for that sailplane. As shown in Reference D, the Ventus 2 achieved about 44:1 L/Dmax at 56 kts, but only after we installed internal flap and aileron air seals in the wings. Since our Ventus 2 flight test data was shown in Reference D was for a gross weight of 762 lbs, and a wing loading at 7.30 psf, I corrected its polar by the theoretical square-root-of-the-wing loading method to match the LAK-17’s 7.08 psf flight test wing loading.
Those polar data are shown plotted, along with our best 15-meter configuration LAK-17 test data, in Figures 12 and 13. Note that although lacking somewhat in L/Dmax, the LAK-17 polar shows a bit lower sink rate in the 42 to 44 kt range - where climb performance is important. Very important to racing and cross-country flying is the cruise performance above 60 kts. There the LAK-17 appears to have about 3 to 5 kts more airspeed when flying at the same sink rate as the Ventus 2.
The modern day racing and cross country sailplane designers appear to be emphasizing superior cruising performance and not worrying too much about L/Dmax values. Our recent tests of the contest winning Standard Class LS-8 and Discus 2 sailplanes indicated just that. Their L/Dmax values in the low 40s, but really good L/Ds are shown at 70 to 80 kts, even when measured in their unballasted condition. See References E and F for the LS-8 and Discus 2 flight test evaluations.
GENERAL CHARACTERISTICS
Commendably, all of the LAK-17 controls connect automatically upon assembly, although considerable care must be taken to properly align the rotary control couplings when assembling the wings; otherwise the wing panels cannot be fully inserted and locked into position. The cockpit is enclosed by an excellent forward hinged canopy that has good optics. It is well sized and very comfortable. To avoid degrading flight visibility, I placed the seat back in its most forward and upright position. That way I did not to sit too low in the cockpit, and it still provided me with about 1 to 2 inches of head clearance with the canopy. However, my rearward visibility was limited to about 45 degrees aft of the wing tips because of the aft end of the canopy frame.
The design of the recessed rudder pedal adjustment handle on the forward part of the right cockpit ledge is exceptionally good, and the best I have ever seen in any sailplane. It is completely out of the way, yet easily accessible in flight. My 70-inch frame was very comfortable with the rudder pedals adjusted to their next-to-forward location, and that gave me good thigh support against the well contoured cockpit floor. During subsequent flights, I found that I could see about 80% of the towline length while in normal position on aero tow with +1 or +2 flap settings. I always appreciate being able to see the tow line when flying an aero tow because that adds to flight safety. The cockpit sideward visibility is very good, and the forward visibility is much better than with some of the new flapless Standard Class sailplanes that I have test flown recently.
The LAK-17 handles well and is comfortable to fly. Its stall characteristics are surprisingly gentle, with almost no tendency for the sailplane to drop a wing during my attempted stalls. The wing airfoils are reported to be a relatively thin 13% thick LAP 92-130/15 near the root, changing to a slightly thicker 15% LAP 92-150/15 at the wing tip. Perhaps that is where it gets its excellent stall characteristics. The oil flow tests indicated that about all of the airfoil’s potential low drag laminar airflow appeared to have been achieved. The wing panels were initially reported to weigh only about 110 lbs each, but were subsequently "beefed up" somewhat. Our test sailplane’s wing panels weighed about 135 lbs each, which is still not too bad for old backs to lift.
The LAK-17’s double plated wing top surface only airbrakes are very adequate. However, care must be taken to not open them abruptly at high airspeeds. As with most sailplanes equipped with powerful top surface only airbrakes, their rapid extension above about 70 kts causes a strong reduction in wing lift, sometimes sufficient to put the pilot’s head through the canopy –if he is not tightly strapped in. Sailplanes equipped with both wing top and bottom surface airbrakes are much more benign in that respect, in that they do not appear to exhibit any significant delta "G" effects when the airbrakes are extended suddenly at high airspeeds.
+/- 45-degree rolls at 45 kts took me about 4.2 seconds to perform, which is quite adequate. Almost full rudder was required to keep the yaw string centered, but that is normal with most sailplanes at low airspeeds.
Water ballast tanks are installed in each wing leading edge, capable of holding a total of about 180 liters, or about 397 pounds. A tail fin ballast tank holds about 8 liters, or about 17.6 lbs. However, as yet we have not performed any testing with ballast. When the Texas upper air temperatures rise to safe operational levels, we plan to flight test Steve Hundley’s S/N 4 in that configuration.
I was fortunate during the LAK-17 fall test period in that a few strong thermals still existed during several of the testing days, and I was able to make two 100 mile or so cross country flights to evaluate its excellent cross-country capabilities. It both climbed and cruised very well, and was very enjoyable to fly. Dean Carswell performed the sailplane’s flying qualities testing, and he also was favorably impressed with the LAK-17 flight characteristics. He will present his evaluations separately.
SUMMARY
The new LAK-17 sailplane is, in my opinion, an excellent combination 15/18 meter sailplane for advanced high performance soaring. It appears to be of high quality in design, construction, and finish. Its powerful Schempp-Hirth type airbrakes provide very good landing approach control. A favorable exchange rate with Lithuania makes its purchase here quite attractive.
Many thanks go to Jeff Baird for allowing his fine new sailplane to be used for our flight tests, and to the Dallas Gliding Association for providing both the hangarage and the 27 high tows needed to accomplish it. Also to Southwest Soaring’s manager Mike Solano, and his Caddo Mills tow pilots who did the excellent towing. They usually required only about 22 minutes to tow me to 12,000 ft AGL with their powerful Pawnees.
PART 2
The second portion of this report will include additional testing of LAK-17 sailplane with the 18 meter wing tips installed, and also tests with factory winglets installed on the 15 meter wing. Possibly higher gross weight tests with water ballast installed will be included –if our test air temperatures are not too cold.
REFERENCES
PHOTOGRAPHS
Wing bottom surface oil flow patterns near mid-span after a 20 minute 50 kt test flight with the factory wing turbulator removed. Airflow is from right to left. Laminar airflow is indicated all of the way aft to about .82 chord, followed by what apparently is a laminar airflow separation bubble; as evidenced by the excessive thickened brown oil ahead of the wing flap. The tape air seal between the wing and flap obviously was successful in keeping the oil from entering the flap hinge cavity, and the hinge line gap discontinuity apparently caused the airflow to turbulently reattach over the entire chord of the wing flap. No turbulators were installed on the wing during this oil flow testing, but their re-installation later proved to be beneficial to the sailplane’s flight performance.
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Dick Johnson praises the LAK-17A
During October and November 2000, Dick Johnson has been evaluating an early model of the LAK-17A, and he shares his enthusiasm about this glider. He writes that, .."(in the 15-meter configuration) above about 65 kts the LAK has about 3 to 5 kts more speed for the same sink rates as an equally wing-loaded Ventus 2B ...That is excellent! ...."
Dick writes,..."I have made 6
of the test flights so far, and Jeff Baird has made one of them.
4 test flights were made with the wing drag rake, to optimize the
test flap settings. and 3 to perform preliminary sink rate
measurements. I find the cockpit fits me beautifully, and I fly
it very comfortably with both the seat and rudder pedals in their
most forward position, and the tail fin battery installed. All of
the controls are easily reached, and comfortable to operate. The
recessed rudder pedal adjustment handle on the forward right
cockpit ledge is exceptionally good, and the best I have ever
seen! I am 70 inches tall, 77 years old, and provide a cockpit
load of only about 76 kg...."
...."Good news! Yesterday's oil flow
tests on the LAK-17, wing with factory turbulator and Mylar top
seal removed, indicated no separation bubbles anywhere, and
extensive laminar flow on both surfaces. One test flight was
performed at 50 kts/+5 deg flap, and the 2nd at 70 kts/0 deg
flap. At 70 kts the top surface appeared to be laminar back to
about .70c, and the bottom back all the way to the .845c control
surface hinge lines. That is excellent! ...."
...."I just finished plotting yesterday's wing oil flow test summary results, and they look very good. Before the test we had removed the factory installed wing lower surface turbulator tape, and the unneeded (my opinion) top surface Mylar gap seals...."
...."Three more high tow sink rate
measurement test flights were made with the 15 meter LAK-17a on
Thursday, 2 Nov. The wing was configured with its factory
installed lower surface turbulators and Mylar top surface seals
removed. The new performance test results showed poorer
performance than those measured during the three 18-19 Oct test
flights with the factory turbulators and top surface Mylar seals
installed. I was wrong thinking that they should be removed! When
my LAK-17/15M October test results (at 7.07 psf) are compared to
the sealed Ventus 2B polar measured during '96 at 7.30 psf, the
differences are:
1. Above 60 kts the LAK flies about 3 to 5 kts faster than the Ventus 2B, at the same sink rate.
2. Below 60 kts the LAK shows a bit higher sink rates. Perhaps I need to better optimize the LAK flap settings, and I plan to work on that. ..."
...."After reviewing the sink rate
data some more, I think that it might be best to reinstall the
wing turbulators and make a couple more high tows in the 15 M
configuration; then see what we get. I still do not think that
the wing top surface Mylars are needed, but I might be wrong; as
I apparently was about the drag rake data and the turbulators.
The lighter ailerons are nice and we should try to keep them if
we can...."we plan 3 high tows; still in the 15 M
configuration but without the top Mylars. The ailerons are
free'er that way, and hopefully the performance will still be as
good or better than it was initially..."the flight tests
came out well, using the factory wing turbula-tors, but without
the wing top Mylar seals. Above about 65 kts the LAK has about 3
to 5 kts more speed for the same sink rates as an equally wing
loaded Ventus 2B. About the same minimum sink rate, as but not
quite as much L/Dmax.
Aileron forces are noticeably lighter without the Mylar seals, and there seems to be no difference in performance.
18 meter configuration tests are next...."
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Draft 12.17.00
Flying the LAK 17A
by Dean Carswell
Published with permission from the author. The whole article is to appear in the March or April 2001 issue of the SOARING magazine, along with Dick Johnson's Evaluation.
Dick Johnson, in conjunction with his Flight Test Evaluation of the Sportinë Aviacija LAK 17A, was kind enough to invite me to give my impressions of its flying qualities. The LAK is a new 15 m. Racing Class ship designed to JAR 22 specifications. The test aircraft, generously provided by its justifiably proud owner, Jeff Baird, was the fifth production example (s/n 105) which I had the opportunity to fly in unballasted 15 m. (without the optional winglets) and 18 m. configurations. I was delighted to find such benign handling qualities in a state-of-the-art racing sailplane.
Cockpit layout is fairly conventional, with flaps, airbrakes, tailplane trimmer and tow release on the left side, and the gear retraction lever on the right. The canopy is hinged at the front, with a locking lever on each canopy rail. An emergency jettison handle is located in the instrument panel which releases the front, assisted by a gas strut to push up the front end when the handle is pulled. On release, it rotates around a Rüger type lip behind the pilot's head, all without the need to unlock the normal operating levers - a nice feature, especially when time is at a premium. Early production ships are fitted only with a towhook close to the center of gravity (of which more later), but a nosehook is a recent addition to the list of optional equipment.
180 liters of water ballast (approximately 397 lb./180 kg.) can be carried in the wings with an 8 liter (17.6 lb./8.00 kg.) trimming ballast tank in the tailfin to permit the center of gravity to be moved back close to the aft limit to minimize trim drag. On the test aircraft, while the wing tanks can be emptied in flight, the tail tank cannot. This means that a light pilot needs to make a careful CG computation as dumping the wing ballast could cause the CG to be moved behind the aft limit. The current production ships have the ability to jettison tail ballast in flight.
On first approach, the LAK 17 appears slender with its high aspect ratio wings and small diameter aft fuselage - the only modern sailplane I can recall with a slimmer waist is the SZD 56 Diana. These features give a small reduction in wetted area and a little less parasite drag, potentially leading to a performance gain over 'fatter' competitors. That notwithstanding, the cockpit area looks large enough to cater for nearly all comers. Inquiry revealed that a max. permitted gross weight pilot (max. cockpit load is 242 lb./110 kg.) 6 ft. 0 in./183 cm. tall had no difficulty sitting comfortably; however third hand reports suggest that it would be hard to fit a 6 ft. 4 in./193 cm. or larger occupant. Such judgments, however, need to be taken with a pinch of salt as variations in body proportions, especially thigh and leg length, can make a big difference between fitting acceptably and not at all.
Climbing in confirmed the impression of roominess, and with my 165 lb./75 kg. (with parachute) 5 ft. 9 in./175 cm. body there was lots of room to spare. The cockpit has a very deep seat pan which likely prevents 'submarining' in the event of sudden deceleration without the need for a 5 (or 6) point seat harness (Ref. 1) This is a good safety feature, although I like the idea of a fifth strap which prevents the other 4 from slipping up the abdomen from the place they are supposed to be. Leaving aside the theory, the seating position was very comfortable and (although I lacked the opportunity) one in which a pilot could likely spend several hours without suffering fatigue induced by cramped space. Electing to sit as far forward as practicable - seatback in the fully forward position - the rudder pedals felt comfortable set back slightly from their full forward travel. This gave a relatively upright posture, at least 2 in./5 cm. headroom, and the best possible rearward vision, as well as a good view forward. The view towards the back was good with the fuselage only obscuring vision about 30° either side of the centerline.
On takeoff, with flaps in the +1 (+5˝°) setting, aileron control was almost immediately effective in the 15 kt. quartering headwind. This was improved on my second flight (with 18 m. tips) by starting with -1 (-6°) and moving to +2 (+11°)as the ship accelerated. Raising the tail to get the fuselage horizontal during the takeoff roll felt natural. Surprisingly, the close-to-CG towhook did not give the LAK any apparent desire to pitch up as the towplane and glider combination accelerated to climb speed, although prudence stopped me from investigating to see what might happen if some pitch-up were permitted. Trim was set one-quarter back from the full forward position. The controls felt light and sensitive, and this first impression was confirmed throughout both my flights.
Once established in the climb, I found that the instrument console covered up the view of the tail of the Pawnee; however, selecting +2 flap resulted in sufficient lowering of the nose to give a clear view of towplane and towrope for the remainder of the tow. If necessary, setting L flap (+15°) would improve the forward view even more.
Off tow, aileron/elevator harmonization was reasonably good. Later, with the 18 m. tips fitted, it felt even better. At thermalling speed, a lot of adverse yaw was present, a maximum rate roll needing almost full rudder to maintain coordination. That said, coordination seemed to come easily after just a few minutes. Raising (and lowering) the landing gear requires little effort, and the actuating handle clearly shows when it is locked up or down.
As well as investigating low speed handling, in the 15 m. configuration (in which spinning and limited aerobatics are permitted) I tried to aggravate the ship to see whether it could be induced to bite. Stalls were preceded by a rumble and a small amount of airframe vibration - some warning, but not a lot if the pilot were to be distracted doing other things. This, however, turned out to be unimportant as the stalls were all innocuous. If the stick was held back at stall departure, the nose dropped a little without any real break, then nodded back up. The slightest reduction in back pressure on the stick had the ship flying smoothly again. At the +1 flap setting, a very modest wing drop sometimes accompanied this process at 37 kt./69 km. hr. The amount of wingdrop increased a little as flap was increased to +2 and L, but it remained gentle, occurring at 34 kt./63 km. hr. in the L configuration. Stalling from a gentle turn produced similar results. Doing the same with airbrakes open seemed to discourage the wing drop tendency; with L flap, the 'nod' occurred at 37 kt./69 km. hr.
I was test flying at a cockpit load only 11 lb./5 kg. above the permitted minimum of 154 lb./70 kg., the center of gravity was close to its aft limit. Despite that I was only able to induce a spin departure using fully crossed ailerons and rudder - a configuration which should never occur in non-aerobatic flight. The wing dropped, followed by the nose; and as soon as the latter had dropped a few degrees below the horizon the LAK entered a gentle spiral dive. I tried this both ways, using different flap configurations, and was unable to hold in the spin.
Cockpit noise was remarkably low, even with the gear down. With the nose vent and window scoop open, things still remained fairly quiet although, with the low air temperatures on the day of my test, I hurriedly closed them again. There were a few very weak thermals - just enough to climb a couple of hundred feet, or to maintain height for a few minutes - but sufficient to reveal the LAK's pleasant thermalling qualities. Once established, it could be flown hands off, although I doubt that would be possible in stronger conditions.
Getting prepared to return to the field, I experimented with sideslipping. A slip at yellow ? speed (49 kt./91 km. hr.) turned out to be surprisingly effective, generating a goodly sink rate. The double segmented top surface Schempp Hirth type airbrakes were powerful. Opening them at a representative approach speed of 55 kt./102 km. hr. gave a modest pitch down, but nothing else, during which, if not checked, the speed would increase to 60 kt./111 km. hr. Closing them had the reverse effect. At these speeds, there was little tendency for the airbrakes to snatch open - a good feature when it is necessary to transfer a hand from the airbrake to the flap lever on final approach.
With a little time before pattern entry, I experimented with the trim control, which is worked by an internal spring mechanism. In the test ship the springs were fairly strong, requiring a fair push or pull when making an out-of-trim control movement. With my weight, I could trim out stick loads all the way from the stall up beyond the rough air speed (116 kt./215 km. hr. in 15 m. configuration). Doing this left the rear half of the trim travel completely unused. Inquiry revealed that a pilot operating the ship at max. gross never used the last quarter of the rear travel, and one has to question why it is there. I simulated what might happen if takeoff were attempted with the trim lever inadvertently set fully back; the result was a much higher than comfortable stick load to hold the nose down level, emphasizing the need to complete careful pre-takeoff checks.
Approach angle appeared really steep when using full flap and airbrake. Landing was straightforward with good directional control despite a 10 kt./19 km. hr. crosswind component (the Manual quotes a maximum demonstrated crosswind component of 8 kt./15 km. hr.). It was possible to keep the landing roll straight right until the ship came to a full stop, at which point aileron control had just about run out. This was a pleasant surprise as many 15 m. flapped ships appear to have a tendency to head for the hills when full flap is retained in these conditions. The shock-absorbed landing gear made for a very comfortable touchdown. In the test aircraft, the wheelbrake worked, but not a whole lot more.
Most of my comments apply to both 15 m. and 18 m. configurations - the only significant handling difference between the two were, at 18 m., slightly more adverse yaw, roll rate a little slower, and a little better aileron/elevator harmonization.
At a basic price of under $40,000 for the ship in 15 m. configuration without instruments, the LAK 17 is highly competitive in price as well as performance (one placed 2nd in a field of 33 in the US 2000 18 Meter Nationals). Prices are denominated in US dollars, so there is no need to gamble on the future direction of the Euro, as is the case with most ships built in Europe. Lots of bang for the buck!
Summing up, the LAK 17A is a beautifully simple and straightforward sailplane to fly, despite the obvious complication of having flaps; it also displays no obvious vices that I was able to discover. I believe it should prove a suitable mount for pilots of lower experience than would normally be the case for such ships. Conversion should be relatively straightforward although, as always, a careful and systematic approach to this (Ref. 2) will pay dividends and avoid unpleasant surprises.
My thanks to Jeff Baird for allowing me to evaluate his delightful sailplane, to Dallas Gliding Association for donating the tows, and the staff of Southwest Soaring at Caddo Mills TX for providing them.
References:
1. Segal, Dr. Tony: Six Point Belt on Test, Sailplane
& Gliding, April - May 2000, page 20
2. Carswell, Dean: Sailplane Type Conversions, Soaring,
September 1996, page 18.
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NEWS FLASH
LAK-17A proves its phenomenal performance at the 2000 U.S. 18-meter National Championships, finishing second overall!
For five of the eight days of the U.S. Championships, Bill Bartell in LAK-17A was in number one place cummulatively among thirty three contestants. Ultimately, Bill finished a very close second overall.
For detailed results click here (includes
the detailed day-by-day results and statistics)
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by Derek Piggott
(Sailplane & Gliding, February – March 2000, Volume 51, No 1)
I have been looking forward to flying the LAK 17 a since the prototype flew some years ago and was lucky to have a good soarable day to try it out. It is the first LAK 17 a in this country, based at Husbands Bosworth and owned by the importers, Baltic Sailplanes. After only three flights to get used to the aircraft and his instruments, Tony Pozerskis flew it in the 18 Metre Championships at Booker and finished 8th out of 35 competitors.
The LAK 17a is a 15-metre flapped glider with a very high aspect ratio wing, and comes with wingtip extensions to 18 metres. These are inclined with 20° of dihedral. It is largely constructed of carbon fibre with the result that the empty weight is only 4751b. This makes it easy to rig and good for climbing in weak lift. When ballasted to maximum weight (lOOOlb) the loading is 10.251b sq ft (46.2 kg/m2) giving excellent high-speed performance on days with strong lift.
I found the cockpit large, but the seatback, headrest and rudders are fully adjustable and all the controls come easily to hand. On the left are the flaps, airbrakes, elevator trimmer and release toggle; the undercarriage lever is on the right. The canopy is hinged at the front and the instrument panel lifts with it for easier access. It is locked down with two positive locking levers either side, but has a single lever above the instrument panel to be pulled to jettison the canopy, an excellent feature. The rigging is quick and easy, though care must be used checking that the flap, aileron and airbrake connections mate correctly as the wings are pushed in the last few inches. All the controls including the water ballast self-connect and the only loose parts are the two main pins.
A look round quickly convinces you that no pains have been spared to produce a well-finished, smooth glider. This is not a cheap imitation but a well-built modern design. There are one or two surprises: the ailerons are of narrow chord and have no differential in their movement. With full landing flap, the ailerons are both down at quite a large angle. I expected high aileron drag and a lot of adverse yaw and problems with keeping the wings level at low speeds. How wrong can you be?
I landed each time using full flap with airbrakes and found no problem at all during either take-off or landing. I was amazed, since most owners of other flapped machines find they dare not use full flap for landing without risking a possible ground loop.
The LAK 17a has a T tail with a fixed stabiliser and a normal elevator with spring trimming giving a good positive feel to the elevator. Being cautious, on my first flight (with the 18 metre tips fitted) I set minus flap for take off and pulled it to the first positive setting before leaving the ground and for the rest of the aerotow. This is probably unnecessary except for no wind conditions.
The undercarriage locking system is excellent. It is quite obvious when it is properly locked, both up and down. A small plate is clearly visible in a slot when the handle is down against the cockpit side and this acts as both an indicator and an additional positive lock. The lever is well placed and the forces needed to raise and lower the wheel are surprisingly low. The main wheel uses a gas strut for extra shock absorption. Provision is made for nose ballast to cater for light pilots, and the fin holds up to seven litres of water to compensate for the large water ballast tanks in the wings and for heavy pilots. The tail ballast is not jettisonable in flight.
The wings hold a total of 180 litres giving a maximum wing loading of 50 kg/m2. I flew without ballast in the wings and found that using about 40° bank it circled happily at 45-48kt with the flap in the normal thermalling position, a surprisingly low speed (there are two positions of positive flap for thermalling plus the full landing position and neutral, and one position for negative flap). The handling is excellent, with a time to reverse 45° to 45° in about 4.5 seconds at 50kt. I seemed to be able to get down almost to K-6 circling speeds without losing positive control and there was a reasonable stall warning. The stall was very straightforward with a gentle wing drop from a shallow turn. I tried to get it to spin several times but it did not want to spin continuously and spiralled out each time.
It is a delightfully simple machine to fly and about my only criticism was that I had to look closely at the flap lever to tell its position. I expect that you would soon learn to sense it by feel, but it would be nice to have some way of making either the zero or the thermalling flap position feel distinctive so that looking down would not be necessary.
This is one of the few of the new breed of very high performance 15/18 metre machines I have flown and I was very impressed by the performance at high cruising speeds. The manufacturers claim a max L/D of 50:1 at 62kt at maximum weight and this seems reasonable. Only extensive testing and competition flying will establish how it compares with the Ventus 2 and similar machines.Using the full landing flap with the powerful airbrakes, the approach on the LAK can be steeper than many modern gliders.
We then took off the wingtip extensions and I made a flight in15-metre mode. This time I took a winch launch. It was quite straightforward. I found no tendency to zoom up after leaving the ground and got about 1200ft. This was enough to find lift and climb several thousand feet. The handling was, of course, even snappier and I was interested to hear that Tony prefers to fly it 15 metre. The polars show that with full ballast, above about 65kt the performance is better without the tips in spite of the higher performance offered at low speeds with the tips on.
I came down from this flight feeling it must be a good buy when compared with its competitors. Certainly those thinking of ordering a new machine should get a trip in it before deciding what to go for. It is amazing value for money. Think about it: you could use most of the saving on some really good instruments or spend it on a few nice soaring holidays abroad.
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by Jochen Ewald
(Sailplane & Gliding, February – March 2000, Volume 51, No 1)
THE LAK 17a is AB Sportine Aviacija's bid to break into the competitive 15/18-metre market. It has a low weight, 214kg for the 15-metre and 220kg for the 18-metre. The wings will take 180 1iters of water, raising the maximum take off weight to 453kg. The C of G can be adjusted by water in a tail tank, although this cannot be dropped in flight. In 15-metre mode the narrow wing has 9.06sq m of wing area, which goes up to 9.8sq m with the 18-metre tips added.
I flew with a weight of around 300kg and a little water in the tail to move the C of G close to the aft position. On tow it was stable and easy to control despite having only a belly-hook. A flap setting of -1 gives immediate aileron control and, as the tow speeds up, the lever is moved to +1. You need to practise switching flap on the ground as the slots are quite narrow.
As it's light, the LAK becomes airborne after a short ground run with no tendency to zoom in either wing configuration. Control, stability and view on aerotow are good.
Flying in 15-metre mode at around 100km/h with a flap setting of zero, 45° bank changes took 3.2 seconds: in 18-metre mode the figure rose to five seconds. Another system of connecting the outer aileron parts on the wing extensions so that they only operate upwards might improve the roll rate.
Thermalling is easy in both spans, with only a little outward aileron needed. Flying together with other gliders, the lightweight LAK 17a seems to climb excellently. Usually, +1 is the optimum thermalling position, while +2 only seems to improve the climb in 18m mode in calm air.
Stalling is gentle with the 18m wings and +2 flap; a slight shaking can be felt at 70km/h and stalling starts at 67km/h. If the stick is pulled further back, the left wing drops in all positive flap settings. With the 15m wing, the behaviour is about the same, but at 4km/h faster speeds.
Flying fast, the slim wings damp gusts comfortably. The control forces become higher and give a comfortable, safe feeling of stability. For landing, the double-bladed Schempp-Hirth-style airbrakes on the upper wing surface are very effective.
The concept of a lightweight glider with small wing area and high aspect ratio promises excellent performance. Some design details are well thought out, while others are a little behind the times – rigging and fitting the tailplane could be better - but this was only the second model built and it will probably improve. With a price of $42,000 the LAK 17a has a good chance of finding a place in the 15/18-metre market.
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How does the LAK-17A fly?
By Ludek Kluger. Published in "Vztlak", October 1999. Translation by Blanik America, Inc.
In the beginning of July 1999, several glider pilots from the Hosín Aero Club (Ed.: in the Czech Republic) set out on a Slovenian safari. Our contacts with the local clubs (Ed.: in Slovenia) were always arranged through Boris Kozuh, who, besides being a professor at the Ljubljana University, lived with his parents for many years near Split in what is now Croatia, and learned how to fly at the Sinj Aero Club. Despite the fact that he now lives 400 miles from Split, he keeps this aero club alive with a superhuman effort (in my opinion).
We were heading to Slovenia (to the aero club of Bovec airport) because of our desire to introduce the less experienced pilots in our club to mountain soaring, generally known as pretty non-existent in the vicinity of Ceské Budejovice (Ed.: a city near the writer’s home gliderport of Hosín).
This safari was a success: we didn’t wreck our Blanik, and didn’t put ourselves to shame. Additionally, I had a chance - with Boris’ substantial help, with two days of telephoning, a trip to Ljulbana, plus a payment of DM 118 - to get my glider pilot license endorsed for flying also in Slovenia. The reward for me was then to get to fly in Boris’ Jantar Std 3.
The license verification in Slovenia is no easy task. It is necessary, in the first place, to personally visit the appropriate office. (Mainly to find out where it is – if you have never been there before.) Then you need to fill in about three forms and be in luck that the particular clerk is in. (This job is done by a mere one person.) After that you have to locate the nearest post office with a payment form for 11,800 SIT in your hand (Ed.: about 65 American dollars), pay, and then return to the government ministry where you wait for a mere four hours to get your license issued. You can count on two days to accomplish this task - that is, as long as that clerk is not on vacation, because if he is, then you simply are out of luck. The issued license is valid just for one year – so then in 12 months it’s "welcome back" at the ministry.
Nevertheless all bad is good for something, as during the week of our stay I made acquaintance with ing. Matija Znidarsic. He was at Bovec to take a ride in Boris’ LAK 12R (the only flying two-place LAK12 prototype, built for record flights). I found out that he would be receiving a LAK 17A he ordered from Lithuania, and it would arrive in the end of the month of August. At present, I am considering what I could buy for my hard-earned money. (I don’t like the classic VSO10 and I will not be able to afford anything new from the Open class (Nim4, ASW-22) for a long time.) Therefore I jumped at a chance to accept the offered opportunity, to take a ride in the new LAK when it would reach Slovenia.
Act Two took place in August when I called to Slovenia and received the news that the little machine had arrived on Aug. 23 in Ljubljana, and that it would be able to fly after being equipped with basic instruments. Saturday afternoon Sept. 4, I jumped in the car and after driving some 280 miles I was at the location. That evening I spent with Boris sipping the local Sipon brand wine, pouring over brochures of the LAK17A , and hatching plans for the next soaring season at Bovec and Sinj. Reading the Slovenian counterpart of our aviation magazine L+K (Ed.: a Czech aviation fortnightly) that evening, I must also add that I was quite surprised to find out how much more is written there about gliding and general aviation. Well, perhaps the Slovenians aren’t such fans of militarism as are our readers of L+K.
At the break of dawn, at 10 am, after a hefty breakfast, we went to see the Znidarsics’ (about 1/5 of a mile away). We drank a cup of coffee together, I handed over the bottle of liqueur I brought, and I threw myself into the study of documentation and manuals for the LAK17A. The type certification according to JAR22 was completed on August 26, 1999, so the ship truly is a novelty. Znidarsic’s glider has the production number 3. Matij’s son Luka recalculated the center of gravity (I weigh only 121 lbs). Because the weather outlook bode no threat from thermals (but was nevertheless flyable), we jumped in our cars at noon and after about twenty minutes arrived at something I would call the hangout of the Ljubljana aero club. A local philanthropist donated the field, located next to the village Podpec, about 5 miles from the outskirts of Ljubljana. On a meadow with the dimensions (they say) of 2600x83 feet he established an airport of a "lesser category" where instruction is prohibited. On one end, the meadow ended in some local creek, and the other end was protected by about a seven foot tall fence. When we positioned the glider in the 18 meter configuration on the runway, almost seven feet on each side were remaining… but the length of the runway was sufficient.
And then it all started:
The LAK17A resembles in many ways the ASW27, including the outside shape. My first impression was that even some mechanical solutions and construction features (for example the foot controls) were taken over from the AS workshop. The assembly and disassembly is in my opinion easier than that of the ASW27; all is arranged by quick connects and in essence nothing needs to be aligned or prepared ahead of time. What I somewhat did not like was the attachment of the horizontal stabilizer. The fastening bolt sticks above the surface outline after it’s tightened. Then there was an animated discussion about filling with water ballast. The holes are on the lower wing surfaces. No matter how hard I tried I could not figure out a way in which one should fill it. There was nothing to plug the hole with after the filling has been unsecured. There are no plug threads, only a rubber seal around the conical opening. For sixty dollars the manufacturer supplies some assembly so it will probably be necessary to invest in it.
The technological finish of the glider is on a very high level – apparently Lak’s cooperation with the Americans manufacturing the Genesis there leaves its stamp. The Znidarsic also visited the factory in February 1999 and had quite a few pictures from there which testify to the LAK factory’s great in-house development effort. There is a large laboratory of own materials and the factory is several times larger than AS.
I would solve some construction details differently but that is my subjective opinion. I was actively involved in the glider assembly. I must say that this machine is one of a few which, without any considerable effort, a helper and I could put together and take apart. The equipped wing weighs 60.45 kg (133.3 lbs) and the whole ship resembles a toy rather than a glider. The empty weight of this third unit is 221 kg (487 lbs) in the 15 m configuration with winglets.
The cockpit is dimensionally fantastic. It was lengthened by 12 cm (5") over the prototype and it is quite noticeable. With my height of 173 cm (5’8") I had to add a small cushion even after I put the seat fully forward so that I could reach all the control elements. Matija Znidarsic gets in the cockpit without problems despite his 115 kg (253 lbs) and 191 cm (6’3"); Boris Kozuh is a few centimeters taller and even he did not have any complaints.
The controls are positioned in clear view. Unscrewing two bolts and removing the plastic cover solves the instrument access. The forward-hinged, upward-opening canopy may be simply removed for cleaning and cockpit maintenance. I quite liked the location of the tow release on the cockpit left side – the classic ships like Discus, Ventus, etc. always have it somewhere in the area of the sex organs, and if there is an emergency during take-off, it’s a little crisis to quickly find that yellow nipple.
The flap and undercarriage controls location is secured by dropping a protrusion on the lever in a cutout in the duralumin sheet. It should also not be a problem to make one’s own flap deflection stops according to a pilot’s individual preference.
The ship’s owner first asked me what wing span configuration I would find sufficient for the first take off. While personally I maintain a conviction that for me a machine with a wingspan in excess of 25 meters is the right one, they attached the wing extensions on and without delay I stuffed myself in the cockpit. The LAK with extensions is 18 meters, and since I never had an opportunity before to fly anything with between 15 and 20 meters, I was sufficiently charged to see how the glider would respond during take off. The owner did not comment anything to my remark that, since it was manufactured, the LAK had had only 7 take offs and I was its 4th pilot.
Practically right from the first meter of the take off roll, the glider is controllable laterally. The longitudinal control is very pleasant and not tricky. I would not fear entrusting the LAK17A even with the 18 m extensions to a pilot with under 100 hours as his first "glass" ship. One can’t compare it with the VSO10’s properties! The undercarriage wheel is from the L-13 and is partially sprung so the ground roll is no pounding like with, for example the Discus. During take off there is no need for manipulations with flaps, it’s sufficient to set them before start at +1 and then reset them only when you want to speed up during cruising above 160 km/h (85 knots). The trim is a spring-type. Its operation is a little impractical by a lever on the left side of the cockpit, but during flight you practically don’t need it. During the first flight I did reprimand the manufacturer for the somewhat stiffer controls but the Znidarsic family is already planning to relubricate them (the glider is brand new and during the second flight all seemed to me OK). The undercarriage operation is a toy even for those most slender lady pilots.
When I spoke with our glider pilots about the LAK17 in Poland in July 1999, they told me that the biggest problem was the soft wing, which at higher speeds probably would not hold shape and then the glider would lose performance. The truth is I’ve never seen a glider with such a thin profile, and the responses to flap changes with the LAK17A are entirely insignificant compared to for example the ASW20. The wing indeed is somewhat softer than that of the classical German products, but it’s no big deal, and even at speeds over 200 km/h (~110 knots) it decisively keeps shape better than the ASW20. Well, carbon is carbon – and the prototype didn’t have it. The flaps even in the "0" setting are already a little in the plus. Nevertheless, the advertised performance is probably there, because in absolutely calm air the ship really glided and really didn’t drop. What it would take is some precise measuring or side by side comparison. I’ll probably have to talk Mrazejek into taking his "guy" and bringing him to Slovenia.
The view from the cockpit is quite good and there is still one other good property – very efficient air brakes, almost poisonous. Wherever you look around you can put it down there. During landing you don’t need to reset the flaps – the "L" is enough and that’s it. The minimal airspeed without water was somewhere around 68 km/h (37 knots) and one could circle comfortably in the 18 m version below 80 km/h (43 knots).
For the next start I asked that the wing span be reduced to 15 m and thus I made the LAK into a 15m FAI race horse. The lateral agility was even further improved, the take off was additionally simplified and in no time I hung above the slope near the airport at 1300 feet and tried not to fall down. It is possible to circle in the shorter version at 80 km/h (43 knots) without water. But if someone tries to slow down even further, it probably ends up after a while with the total softening of the controls and subsequent settling down of the glider without the tendency to transit into a spin or other flight regime. Additionally, before the fall the glider warns by shaking all its controls. I concluded my about 40 minute flight with a positively-commented-upon fly-by and a landing when I tried to reset the flaps on the ground to the negative values. I must say that then the LAK literally rivets itself to the ground and then you have no chance that it would refloat or something like that. In deference to the owner I did not try any of the aerobatic maneuvers with which the LAK is certificated in Utility (Ed.: airworthiness category).
After the landing I conversed with local pilots who then also went up in the LAK, and engaged in a commercial dealing with the Znidarsic family who from Sep.1, 1999, represents the manufacturer in Slovenia and Italy. In the evening the only remaining thing was to drop in right next to the runway on the 40th birthday celebration of the airport owner’s wife, stuff our faces, partake of a glass of Slovenian wine, and then bounce in five hours via Maribor, Graz and Linz up the freeway to Ceské Budejovice. I still want to thank the owner’s wife by means of this writing for all the care given to us (Boris and me).
In conclusion here is still some information where you can find out more data which I purposely or unwittingly omitted, at www.kiss.uni-lj.si/~k4fs0332/ , or if need be, write in English to luka.znidarsic@kiss.uni-lj.si .
And now all that remains for me is to finish saving up those few ten thousands of dollars, fight the type certification through our favorite ÚCL (Ed.: civil aviation authority) and for the 2000 season – racers watch out!!!
P.S. The total service life is 6,000 hours, with 100 hour or annual inspections done. Ludek Kluger (author).
TRANSLATION BY: BLANIK AMERICA, INC. Disclaimer: Blanik America Inc. assumes no responsibility for the opinions expressed or statements made in this article. The accuracy of any information is the responsibility of the author. The translated text may be freely distributed with credit given to Blanik America, Inc.
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