304CZ and
304CZ-17 Test reports
and article reprints
304CZ and 304CZ-17 Polars
These Polar calculations were complete by Lisa Goodman, owner of ser#20
Using 17.4 meter curve the polar is a=+1.92 b=-3.02 c=+1.71
Using 15 meter curve the polar is a=+1.06 b=-1.04 c=+0.66
This is conservative since this test did not have turbulators installed.
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Polar 15M
Polar 17.43M
Long wings for the 304CZ
The extensions add 0.8m2 area and change the aspect ratio
jumps to 22.8 from 28.4. With a minimally higher empty weight of 0.5kg the slow-flight
characteristics as well as the best glide numbers should get significantly better. HPH has
not released any performance numbers but a L/D increase of at least 3 points is to be
expected.
Once only a 304CZ customer, Peter Marx, 51588 Nuembrecht, Homburger Str. 2 has now taken
over sales for Germany.
A FLIGHT TEST
EVALUATION OF THE 304 CZ SAILPLANE
Richard H. Johnson 11/30/99
The 304 CZ is a modernized version of the 1980s German Glasflügel 304 sailplane that was designed by Martin Hansen when he was employed at Glasflügel . It was designed as a successor to the then current 15 Meter Racing Class 303 Mosquito glass composite sailplane, which was designed and produced by Eugen Hanle before he died (References A and B). The 303 Mosquito was an outstanding design in that all of its controls connected automatically upon assembly, it had a PIO proof parallelogram pitch control stick mounting configuration, an excellent forward hinged canopy, and it also had the super powerful trailing edge airbrakes that was then unique to the Mosquito design.
When the sailplane manufacturing industry in the Czech Republic became privatized during the late 1990s, the HpH company there acquired the tooling and manufacturing rights for the 304 Model sailplane and resumed its series production. When Tom Wescott kindly offered to bring his one year old serial number five 304 CZ all the way from California to Texas for flight testing, we naturally were very pleased to have the opportunity. It was especially attractive in that Tom had just received his new 17.5 meter wing tip extensions, and therefore we could test it in both its 15 meter and 17.5 meter configurations. Figure 1 is an outline drawing of the sailplane, in both its wing configurations.
When the sailplane arrived in Texas, we carefully inspected it in detail. It was beautifully made! Its polished gelcoat finish was excellent, and the wing surface waviness averaged only about .0025 inches, which is well within the .004 inch limit that I believed to be needed to achieve extensive low drag laminar flow on sailplane wings. Its all glass composite construction appeared rugged and somewhat heavy compared to carbon composite sailplanes, but the details of its construction were beautifully done. All of the exposed metal fittings were nicely cadmium plated - for enduring rust protection. Its retractable main wheel is a well sized 5.00 x 5 inch (tire width and hub diameter) Tost unit that was equipped with an internal drum brake; which functioned well. The aft end of the fuselage was equipped with an excellent 210 x 65 mm (tire O.D. and width) pneumatic tail wheel.
The 304 CZ airspeed system uses a tail fin mounted pitot tube for its pitot pressure source, and its static source is from a pair of flush pressure sensing holes located on the aft fuselage sides, about half way between the wing and tail. Before flying the 304 CZ we carefully checked the airspeed system for leaks, and we found two large ones in the static pressure side! One was at a tee under the seat pan where the left and right side aft static lines joined together. Tom had joined a line at the Tee, and possibly he may have been responsible for that leak. The second major leak was found at the Winter airspeed indicator’s face. The “O” ring behind the glass face had slipped out of its sealing groove, thus allowing the instrument static chamber to leak heavily around the glass. That meant that Tom had been flying N304W with essentially a cockpit static for his airspeed system. Since the modern sailplane cockpit static pressures are quite close to those that we measure at the aft fuselage sides, Tom’s airspeed system errors were likely quite small.
We repaired both of the 304’s airspeed system leaks, and then we calibrated the sailplane’s Winter ASI for instrument errors by teeing its pitot port to my calibrated master ASI pitot port, and carefully pressurizing both with a common squeeze bulb while in the hanger. I then made a high tow with my independent master ASI temporarily installed, complete with its Keil tube pitot and trailing static bomb that I deployed out of the 304’s side vent window after I had released from tow. I then compared the 304’s ASI readings to my master ASI indications while flying at 23 different 304 sailplane indicated airspeeds. Those flight test indicated airspeeds varied from 36 to 123 kts; and those test data were used to prepare the 304’s airspeed system errors versus indicated airspeed plot shown in Figure 2.
Note that the 304’s airspeed system errors appear to be less than 2 kts over the entire 36 to 123 kt IAS test range, and that is excellent. The error data shown in Figure 2 do not include the sailplane’s Winter ASI instrument errors, that were small, and that we had previously measured during our hanger tee pressure testing. It is customary to present Sailplane Handbook ASI errors assuming that the sailplane’s ASI has no mechanical error, and that is the case for the Figure 2 data.
Again in the TSA hanger, we made chordwise waviness measurements of the one year old 304 CZ’s wing top and bottom surfaces, at 7 spanwise stations along each wing, using a standard 2 inch long wave gage. Those measurement data are shown in Figure 3. The magnitude of the unwanted waves were mostly very small. Only at two places on the top of the left wing did the wing waviness appear a bit excessive. A little sanding there can easily reduce those waves to a more acceptable .004 inches, but I did not ask Tom if we could do that before we performed the rest of the testing. The 304’s wing airfoil is reported to be an HQ 010-1642 and appears to function well, as our following oil flow and flight testing indicated.
Next, before Tom took off on a 40 minute local soaring test flight, we applied black, well used 10W-40 motor oil to the top and bottom surfaces of the left wing at 6 spanwise stations. The wing was not equipped with any turbulator strips on either its top or bottom surfaces. After Tom landed we took photographs of the oil flow patterns and used a tape to measure the chordwise extent of the indicated low drag laminar airflow on the top and bottom wing surfaces. The top surface oil patterns indicated excellent laminar air flows back to about 60% of the wing chord, followed by a normal transition to turbulent airflow. Those measured laminar oil flow regions are shown in Figure 4.
The wing bottom surfaces showed good laminar air flows back to about 70% of the wing chord, followed by a classical high drag laminar separation bubble! The chordwise location of the leading edge of the bottom surface separation bubble was measured. Those data are also included in Figure 4. Apparently the 304 wing would benefit by a turbulator strip installation on its bottom surface, but we did not have sufficient time in our test schedule to investigate that farther.
To start that testing I would recommend installing several short 3 inch long test turbulator strips, of either a standard dimpled or .5 mm high Zig-Zag type, ahead of the measured bottom surface separation bubble leading edges. About three or four 3 inch long test strips should be mounted in a laterally staggered pattern at each wing test station (see Reference D photos). Place the most aft strip about 8 mm (.32 in) ahead of the measured separation bubble leading edge and the second test strip at about 16 mm, and so on. Then repeat the oil flow flight test to determine the most aft turbulator location that will reliably breakup the unwanted high drag airflow separation bubble. Do that at each of about 6 spanwise test stations on the bottom surfaces of both wings. After those optimized chordwise turbulator locations have been determined, then one can install full span turbulator strips there. After that the sink rate testing should be repeated to determine how much the full span turbulator installation affected the sailplane’s performance polar. That is something that Tom or we can do in the future.
After the oil was wiped off, a Reference C type of wing profile measurement integrating pitot rake was attached to the 304’s left wing trailing edge, about one meter outboard from the fuselage side. A high tow was then made to determine which wing flap setting was optimum at each test airspeed. To do that it was necessary to make drag pressure measurements over a relatively large range of airspeeds with each of the sailplanes 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 8 pitot tube integrated pressure.
Those drag rake data are shown summarized in Figure 5. 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.
As the drag data in Figure 5 shows, the +2 landing flap setting provides the least drag when flying below 39 kts, and the +1 thermaling flap setting appears to be best between 39 and about 44 kts. The zero flap setting appears to be best when flying between 45 and 78 kts. Above that speed it is difficult to see much difference between the –1 flap and –2 flap (full negative) settings until above about 93 kts, where the –2 flap setting appears to be clearly better. In general, these flap settings were used during the following performance sink rate flight testing.
Three high tow test flights were the performed with the 17.5 meter wing tips installed, to measure the 304’s still air sink rates over an airspeed range of 41 to 108 kts. Those sink rate data were corrected to sea level standard atmosphere conditions, as is customary worldwide, and then plotted versus calibrated airspeed in Figure 6. There a minimum sink rate of about 120 ft/min is shown at 46 kts, and a best L/D of about 40.5 at 51 kts.
That performance was disappointingly low for this class of sailplane, so we removed the wings and started looking for problems that would degrade the 304’s performance. That became obvious when we saw that there were no air seals at the wing root ribs. Our test 304 did have spanwise Mylar seals on both the top and bottom wing surfaces over the aileron hinge lines. However, experience has shown that low air pressures on the wing upper surfaces can suck air from the fuselage all the way out to the flaps and ailerons, especially if the Mylar seals are not new and tight. I prefer an internal fabric hinge line seal, such as that shown in Reference D, and no overlapping external Mylar seals, where practical. That is the way Klaus Holighaus/ Schempp-Hirth delivered my Ventus A to me years ago, and it has always tested well. Tightly fitting external Mylar seals do noticeably add to the control system friction, especially to the ailerons.
The second problem that we saw was the lack of internal air seal strip at the airbrake forward lip. That is another place that drag producing air can be sucked out from the fuselage. Schempp- Hirth and Glasflügel had usually cemented a 20 mm wide spanwise Mylar strip inside the airbrake cavity where the forward portion of the airbrake lip contacted its stop (ledge).
WING ROOT AND AIRBRAKE AIR SEALS INSTALLED
We (TSA Members assisted) fabricated and installed conic Ceconite fabric air seals around both the aileron and dive brake pushrods, and cemented the larger end of the conic fabric seals to the otherwise solid wing root ribs. Be careful that those air seals are not going to limit the control rod travel. I usually make the fabric-to-rod interface a sliding fit, and I lubricate the rods with a light grease coating. I usually place a 2 inch long piece of wax paper around the pushrod where it contacted the small end of the fabric seal before I cemented the seal to itself around the rod. That way I did not have to be concerned about the cement (Poly-Tak, Duco Cement, or contact cement all work fine) sticking the fabric seal to the rod.
An attempt was made to seal the open cavity at the wing flap root leading edges by installing pieces of soft open cell plastic foam there. I also installed essentially flat 17mm wide internal Mylar seal strips along the airbrake forward lip stop. However, in the rush I neglected to check them for positive contact with the airbrake flap bottom internal surfaces. That can be done by brushing a light coat of paint or dark oil along the top aft edge of the Mylar strip, then closing and opening the airbrake to see if proper contact is made. That seal does not need a tight fit because low air pressures on the wing top surface during flight will help hold the free aft edge of the Mylar strips against the closed air brake flap internal surfaces.
Tom performed the above recommended Mylar seal contact paint/oil test of my 17mm wide strips after he returned home. He performed that test both on the ground and in flight, and his conclusion was that I had an inadequate seal there with the 17mm wide flat Mylar strips that I had too hastily installed! A wider and/or upward curving Mylar seal appears to be needed. Perhaps a strip of soft open celled weather stripping placed under the aft edge of the Mylar strips would ensure a more positive air seal there.
Also, our wing oil flow testing had indicated that a bottom surface turbulator would likely be beneficial. However, we did not have that available for our Texas testing at that time.
RE-TESTING WITH WING SEALS INSTALLED
After installing the above described wing root and airbrake seals, we reassembled the sailplane and resumed our sink rate testing. Two high tows were made in relatively smooth air with the long 17.5 m tips installed, and those test data are shown in Figure 7. There a minimum sink rate of about 95 ft/min is shown at 39 kts, and a best L/D of about 45 is shown at 56 kts. For some unknown reason the sink rate measured unusually high on both flights at 46 kts. The L/D measured quite high between 56 and 63 kts.
We were pleased to have made a good improvement in the 304’s 17.5 meter configuration by adding a few seals. I have instructed Tom, the owner, on how he might improve on my hurried wing air sealing job. I also recommended that he add a turbulator on the undersides of the wing, and make additional flight tests at a later date.
The final part of our 304 CZ testing was with the wing in its 15 meter wingletted configuration with the above discussed wing seals installed. Two more high tows were made with that configuration to measure its sink rates versus airspeed, and those test data are shown in Figure 8. There we were disappointed to see that the minimum sink rate appeared to be about 122 ft/min at 42 kts, and the best L/D of about 38 at 56 kts. We had expected better performance, but for some reason it did not materialize. The performance will likely improve significantly when a wing lower surface turbulator is installed, and additional wing sealing is added. Perhaps we will test that configuration at a later date.
Looking back, I wish that I had applied some oil to the winglets to see if the air was behaving well there. Possibly the airflow on the winglets was not staying properly attached.
The 304 CZ handles very well and is comfortable to fly. The cockpit sideward visibility is excellent, and the forward visibility is better than with some of the new Standard Class sailplanes that I have flown. I could see about 80% of the aero towline length while towing, and I appreciated that! The 304 CZ’s stall characteristics are surprisingly gentle in both its 15 and 17.5 meter configurations, and there is little tendency for the sailplane to drop a wing during a stall. I was comfortable while thermaling in our weak winter thermals at airspeeds as low as 42 to 45 kts.
The German HQ 10-1 642 wing airfoil appears to perform very well, both drag wise with its remarkable ability to achieve extensive low drag laminar air flows over about 2/3rds of its chord, but also in its ability to provide relatively gentle stalling characteristics. The Figure 4 oil flow summary plot indicates that all of the airfoil’s potential low drag laminar airflow was fully achieved. That occurred even over the somewhat wavy portion of the left wing’s upper surface, where the .006 to .008 inch waves were measured.
The 304’s super powerful airbrakes are superb. My Ventus A (Reference E) is equipped with the same airbrake design, and that is one reason that I have kept that sailplane for almost 20 years! To test the 304’s airbrake, I turned a normal distance final approach pattern at the TSA Gliderport at about 1000 ft AGL (600 ft above normal), then I opened the airbrakes fully. I was not surprised when I had to partially close the airbrake to avoid undershooting the runway.
The other excellent feature of this Glasflügel type trailing edge airbrake design is that when full open with +2 landing flap, the sailplane’s stalling speed does not appear to increase above that with the airbrake closed; nor does the full open airbrake appear to degrade the sailplane’s stalling characteristics. However, when the 304’s airbrake is about half open, the forward portion of the airbrake protrudes several inches above the wing top surface, and the wing flap still remains in its landing +2 setting. I could not stall test Tom’s 304 in that configuration, but later did so with my similar Ventus A, which does not have the 304’s airbrake/flap interlock. I found that my Ventus’s stalling speed increased by about 2 kts when in that half open airbrake configuration. Further deployment of the airbrake simultaneously forces the wing flaps to larger angles, and increases the upper surface flap protrusion height.
The only feature that I did not fully appreciate initially was a hinged rocking bar airbrake/flap interlock mechanism that was located on the left hand cockpit sill, between the flap and airbrake handles. It prevents one from changing flap settings when the airbrake is less than half way open. That is likely a safety feature to prevent the wing flaps from being accidentally retracted while modulating the airbrakes during a landing approach. It is quite likely that if the airbrake were half or less open, and the flap setting changed to a lower deflection angle, the sailplane’s stalling speed would increase noticeably. That is because the initial portion of the airbrake extension only extends its top surface, which degrades the wing’s lifting capability. Because of the cleverly designed rocking bar airbrake/flap interlock mechanism, I was unable to test that; and that is apparently as the designer had planned!
With the long wing tips installed, +/- 45 degree rolls required about 5.5 seconds when flying at 45 kts with +1 thermaling flap. Toward the last portion of those slow airspeed rolls, I would run out of enough rudder to keep the yaw string centered, but not by much. I later repeated the roll rate testing in the 15 meter wing configuration while using +2 landing flap and 45 kts indicated airspeed. Those rolls took about 4.2 seconds, and I do not recall running out of enough rudder control to keep the yaw string centered.
The sailplane climbs well in thermals when using its +1 thermaling flap setting. I sometimes used +2 landing flap setting for thermaling more tightly, and that also worked well. However, until pilots get quite familiar with their 304 CZs, I do not recommend using other than the Handbook recommended +1 flap while thermaling because a higher degree of proficiency is needed to thermal with the flaps in their landing position.
Water ballast tanks are installed in each wing leading edge; totaling about 245 pounds (115 kg). Both the inlets and outlets for these water ballast tanks are located on the wing bottom surfaces. We did not test the water ballast system, but I am told that it works well. However, because the dump outlets are located relatively close to the fuselage sides, there will likely be some tendency for the aft fuselage static ports to clog when dumping the water ballast. To cope with that situation, it is helpful to have an instrument panel mounted alternate static source valve that can be opened to the cockpit, or to an alternate static source. In my past ASW-17 flying days, I found that its otherwise excellent aft fuselage sides static ports had a tendency to clog when either flying in rain, or when dumping water ballast. I solved that problem by using a simple golf tee as a removable plug at the end of a tube teed into my static system line. Removing that golf tee plug would open my static system to the cockpit, and that worked well when needed. An even better solution is to install a commercially available alternate static valve that allows the pilot to momentarily shut off the connected instruments, and at the same time blow pitot system air into the water clogged static ports to blow them out.
The new HpH 304 CZ sailplane is, in my opinion, an excellent sailplane for advanced high performance soaring. It appears to be of very high quality in design, construction, and finish. The nose tow hook option makes it quite easy to fly during aero tow, and its super powerful airbrakes are superb. A favorable exchange rate with the Czech Republic makes its purchase here quite attractive.
Thanks go to Tom Wescott for bringing his fine new sailplane all the way from California to Texas for flight testing, and to Applebay Aviation who fitted the new wing tip extensions during a stopover in Moriarty, NM. Thanks also to the Texas Soaring Association for providing both the hangarage and the high tows needed to accomplish the flight testing, to Dean Carswell who did most of the towing and performed the 304’s flying qualities flight testing, which is reported separately, and to the numerous TSA members who provided assistance during the flight testing.
A. Johnson, R.H., A Flight Test Evaluation Of The Mosquito Sailplane; Soaring- Aug 1979.
B. Carswell, Dean, 1997 Sailplane Directory, pages 60-61, Soaring-July 1997.
C. Johnson, R.H., At Last; An Instrument That Reads Drag; Soaring-Oct 1983
D. Johnson, R.H., A Flight Test Evaluation Of The Ventus 2B 15 Meter Sailplane –Part 2: Soaring-June 1996
E. Johnson, R.H., A Flight Test Evaluation Of The Ventus A Sailplane; Soaring-Dec 1981
1. 304 CZ sailplane with its 15 meter winglet wing tips installed.
2. 304 CZ on TSA’s new paved runway, with its 17.5 meter extended wing tips.
3. N304W ready for a flight test takeoff on TSA’s new paved runway.
4. Tom Wescott approaching for landing at the end of his oil flow test flight.
5. The excellent forward opening canopy is an added safety feature.
6. View of open cockpit, showing instrument panel attached to canopy frame, and Rico Drag Meter is temporarily mounted on left side of canopy frame. Landing gear handle is mounted on right side of cockpit, and the airbrake and flap handles are mounted on the left side of the cockpit.
7. The left wing root spar is of a conservative forked design, providing extra robustness to the wing-to-fuselage attachment.
8. The left wing spar ends installed on the fuselage, with owner Tom Wescott supervising the wing assembly.
9. Well sized vertical fin with automatic elevator connection at the top, and good pneumatic tail wheel at the bottom.
10. Wing top surface oil flow patterns after a 40 minute test flight. Low drag laminar flow is indicated over the forward 60% of the airfoil, as indicated by the gradual thickening of the black oil to that point. The sudden thinning of the oil patterns behind .60 chord indicates that the air is transitioning to normal attached turbulent airflows aft of that point.
11. Wing top surface oil flow patterns on the inboard portion of the wing, showing the airbrake top flap in its closed position. The airbrake was used during the landing approach, therefore the oil patterns behind the airbrake L.E. is not representative of that with the airbrakes closed.
12. Wing bottom surface oil flow patterns near the outboard end of the wing flap after the 40 minute test flight. Laminar airflow is indicated all of the way aft to about .70 chord, followed by a classical high drag laminar airflow separation bubble; as evidenced by the inch wide black band of thickened oil. No turbulators were installed on the wing during our testing, but likely their installation would have been beneficial to the sailplane’s flight performance.
13. Wing bottom surface oil flow patterns near the mid-aileron region of the left wing; showing similar laminar flows and thickened oil airflow separation bubbles. The black oil flowing inboard from the separation bubbles is likely caused by the wing dihedral gravity effect, and some of that obviously occurred after landing,
14. Dean Carswell towing the author above the small cumulus clouds, on my way to 12,000 ft where smooth air and light winds existed for sink rate testing. Note electric vibrator motor unit attached to left side of instrument panel, and its battery pack resting on the left canopy rail.
Additional comments from pilots on flying the new 304CZ
Pilots Notes by David
Welles
FLYING THE GLASFLÜGEL 304 CZ
When Tim Mara asked we to fly this sailplane
in the regional contest at Dansville, N.Y. I knew very little about it. There were photos
and pictures (looked good) and of course there was the Glasflügel history of
designing good products. I finally saw and flew the sailplane for the first time in
Mayville, N.Y. about a month before the contest was to start.
The 304 is the last of the Glasflügel design series. This one dating back to the
early eighties. The aircraft was recently put back into production, now being built in
Eastern Europe. The aircraft flown is the first (new) production 304 CZ to be brought into
this country.
After that first flight the concern became how to get familiar with not only the sailplane
but also the equipment which included the Filser LX5000 flight computer and data logger
among other things as I didn’t want to make this fine sailplane look bad in a
contest.*
This 15M sailplane is equipped with winglets, water bags (a little over 30 gallons
capacity) in the wings, automatic control hook-ups (including the water ballast damp
controls), a forward hinging canopy with the instrument panel moving with the canopy; and
in-flight adjustable seat back and rudder pedal positioning. The tow hook is located in
the nose (the C.G. hook is an option) with the opening serving as the cockpit ventilation
air source. The one-piece horizontal tail attaches like the Ventus (actually a Glasflügel
design adapted later by Schempp-Hirth) with the elevator hooking up automatically.
The only difference on assembly between this sailplane and the current state-of-the-art
designs is the weight of the wing panels, more like the ASW-20 than an ASW-27. But with
the Cobra Trailer the assembly / disassembly chores are minimized and my Schreader trailer
will never be the same.
The two things that were new and different for me were the dive brakes and the wheel
brake. Your heels actuate the wheel brake - you push both heels forward together which
moves the rudder pedal assembly forward and actuates the Tost wheel brake. The manual
recommends resetting the rudder pedals aft before landing to insure adequate braking and
in my case, being 6 ‘3" it was never a problem but I did find it hard to turn on
the landing roll and apply brakes at the same time. The dive brakes are actually a
combination of flap and trailing edge spoiler creating a dive flap with which pitch
changes and / or ballooning or settling normally associated with changing flap positions
are minimized. The only change one experience when changing the dive brake handle position
is a change in drag. The cockpit controls consist of a flap handle and a dive brake
handle. The flap handle can be placed in any of five positions, two of which are positive
(down) for thermaling and two are (up) or negative for higher speeds and neutral.
Typically on take-off the flaps were left in the -2 position (full up) until well into the
take-off roll then brought back to the +1, or +2 position before lift-off. On tow the best
flap position seemed to be neutral or +1 depending on tow speed and ballast load. There is
a "gate" between the two handles so the dive brake handle cannot be brought out
of it's detent if the flap handle is not in a detent and vice versa, (With the divebrake
handle full open the flap position is always the same full down position regardless of
where the flap handle is positioned.)
After a second flight in Mayville two weeks later I brought the sailplane back to Harris
Hill were I could devote the remaining time (3 or 4 days before the start of the contest)
for practice and preparation. The sailplane preparation was minimal, measuring how much
water it would carry and how long it took to dump, and to install a turnpoint camera for
back-up* to the data-logger.
The "Practice" consisted of one three hour flight with partial water ballast on
a day too weak to tempt other club members into flying but exactly the kind of weather one
can expect to encounter at Region 3 contests. It seemed like half of the flight was in
"low saves" to keep from landing at the Schweizer Soaring School in the valley.
I was very pleased with how the sailplane climbed especially late in the day after
dropping the water ballast (When the Soaring School quit for the day.) The only problem
found was on dropping ballast the static ports, located on the sides of the aft fuselage,
would temporally be corrupted by water and the airspeed became unreliable, lasting for
about a minute.
The next day there were clouds and "streeting" and I got to experience some of
the high speed aspects of the performance envelope - seems to run very well. The only
problem is getting comfortable with the Filser Flight computer (easy to use just a
personal matter of trust).*
The first day of the Dansville contest ended up a "no contest day" with everyone
who left the field landing out including yours truly, I landed in a wheat field near
Cohoctan with no problem (other than this is a "first time" with a brand new
sailplane). With the off-field landing behind me now I’m really ready for the contest
to start.
After a couple more non-contest days Wednesday promised to be the day we have been waiting
for and a 150 mile task with turns at Corning and Hanna’s Acre (16 miles North of
Dansville), and Avoca. The optimism lasts as far as the Bath-Hammondsport valley where
reality sets in in the form of an extensive search before an acceptable thermal is finally
located to get me up and going again. Making the turn at Corning the decision is made to
go towards Monterey (90 degrees to the course line) where the clouds still look good.
After another search I’m up and going again, lining up the clouds but not finding
much along the way. Climbs at Hammondsport, Naples and the north end of Hemlock Lake get
me into the Hanna’s Acre turn. No further lift is found and I find myself on the
ground back at the Dansville airport sure that I will be last for the day. I actually
ended up first in I5M that first day (as bad a day as I had everyone else in 15M had a
worse day). I was first again on the second day (by 3 points!) then snatched defeat out of
the jaws of Victory with a slow first leg on the third and final contest day flown.
Saturday was the last scheduled day but it was slow in developing and a no contest day was
declared at 3:00 leaving "SM" (John Seymour ASW-27) in first place by just 17
points ahead of the 304 which ended up second.
So, how does the sailplane fly? The short answer is very easily and very well. The
handling qualities are excellent with a roll rate at typical thermaling speeds better than
any 15M span sailplane I have ever flown (The manufacturer says 3.5 seconds for 45 to 45
degrees.). The spiral stability is good and you can thermal "hands off" using
the rudder to control bank angle similar to the ASW-20. The pitch stability seemed to
strong for me at first (my personal preference is for almost neutral static stability to
minimize trim changes with airspeed changes) but after a few hours had made my peace with
the trim system (Similar to the Libelle, just push and release a button built into stick
grip and you are re-trimmed).
The performance seems to be there, both in climbing and gliding. We worked a lot of
"Trash Thermals" (those thermals that are impossible to center for more than a
turn) and this sailplane seems to have an advantage here. In the strong conditions,
because of the lack of water ballast capability, the ASW-27 has the edge with a wing
loading capability 1 to 1.5 lbs. per square foot heavier. The third day when we were all
carrying water the winning speed was 72 MPH and the 304's speed, not counting the slow
first leg (which was actually pilot error - not the sailplane's fault) was over 70 MPH (63
MPH for the full course).
The sailplane is a joy to fly both from a cockpit comfort point and the lightness of
the control forces. The control stick (elevator) is set up with a parallelogram
arrangement so any vertical accelerations do not induce unwanted elevator movement, which
should minimize "PIO's" during high speed flight. This would be a good sailplane
for ridge running but the safety harness needs the addition of a crotch strap for serious
ridge running.
The assembly of this sailplane, with a single pin and all of the controls hooking up
automatically make this a very convenient (and safe) sailplane. There is a learning curve
associated with assembly as it took us about three assemblies before we found all the
potential misalignment problems but once we knew what to look for assembly was a five
minute task (disassembly was never a problem). I have always liked the assembly tool to
pull the Wings together used with the 304CZ which my sailplane, a Schweizer 1-35, also
makes use of.
In summary, having the use of this sailplane for the contest was a very enjoyable
experience, (in spite of the marginal weather) and I must thank Tim Mara for making it
possible.
David Welles
Tim’s Notes:
Dave is one who is still flying with turnpoint cameras and simple variometers rather than
the latest GPS data-Loggers and expensive flight computers. He did in fact on the final
day of the contest admit that he really enjoyed using the LX5000 flight computer and once
he actually used it found it to be quite enjoyable and easy to use. BTW: Dave took
turnpoint photos at every turn rather than zooming through the center of the barrel and
going on to the next turnpoint, something more experienced GPS logger users have found to
be real time savers in contests, though this didn’t seem to take much away from
Dave’s performance as he won 2 of the 3 days flown during this contest, beating not
only the users of the latest technical gadgetry, but also those flying sailplanes costing
nearly twice the price of the (not so) obsolete Glasflügel !
Good going Dave!
Flying the Glasflügel 304 CZ
Dean Carswell
Tom Wescott's 304CZ at TSA
Dick Johnson invited me, in conjunction with his Flight Test Evaluation, to give
my impressions of the qualities and handling of the Czech constructed 15 meter racing
class [flapped] Glasflügel 304.
The original 304 was the final design produced by the Glasflügel company in Germany
before its demise in the early 1980s. The new HpH-produced model has been modified by
adding winglets to the basic 15 meter configuration, and giving tips extending the span to
17.43 meters as an option. The outcome is a pleasant 15 m/17.5 m flapped ship which, while
possibly lacking the performance edge of the latest state-of-the-art 15 meter sailplanes,
comes at around half the cost, at least of those priced in DM! The 304 is a sophisticated
ship and, as such, requires some experience for safe operation. For that reason I have
used a relatively subjective approach for the analysis rather than the stringent
evaluation criteria I have used on other occasions to evaluate "starter" single
place sailplanes (References 1 and 2).
The 304 is of generally conventional layout, with T-tail and mainwheel located ahead of
the center of gravity. The tailplane has a fixed horizontal with separate elevator. The
latter is controlled by a parallelogram configured control column designed to eliminate
pilot induced oscillations. Elevator trim is accomplished by a stick mounted trim system,
of which more later.
The cockpit is comfortable and roomy although just failing to comfortably accommodate my
token 'large' (6 ft 5 in/196 cm) pilot. He reported both canopy interference with his head
and rubbing his knees on the instrument panel. He described the fit as larger than a
Discus or Ventus, but smaller than an SZD 59. I have seen an independent report that a 6
ft 3 in/190 cm pilot can fit in satisfactorily. The 304 is fitted with landing gear
retraction lever positioned on the right side of the cockpit, and flap and airbrake
controls on the left side. The seat pan is very deep, a good safety feature, which avoids
the need for a 5-point seat harness and prevents "submarining" in the event of a
sudden deceleration. This arrangement was surprisingly comfortable and gave good support
to the thighs, likely reducing fatigue on very long flights. The canopy is hinged at its
front end; and another safety feature was a device holding the canopy at the rear acting
as a Rüger hook when the canopy is jettisoned assisting a clean separation when the front
end is forced up into the airflow.
The cockpit ventilation was good, both from the well placed Mecaplex vent on the canopy side, and from the nose. The latter is controlled by a push/pull knob in the panel, and air delivered by two adjustable "butterfly" louvres located in the left and right corners of the panel. When all of these were closed, cockpit sealing of the test aircraft was shown to be good with very little extraneous noise.
I fitted
my 5 ft 9 in/175 cm frame in a seating position as high as possible while still getting
adequate clearance (1½"/3.8 cm) between my hat and the canopy. At rest with tail
down, and again on tow, this gave an adequate view forward over the slightly intrusive
instrument panel. Some care is needed as getting just a little high makes the towplane
rapidly disappear out of sight - this effect is more pronounced when being towed at the
lower end of the recommended speed range.
Following
the flight manual recommended procedure of starting the takeoff roll with flaps set at -1
and moving to +1 as speed increased on the ground showed no lateral control problems;
indeed on the rollout after landing in a 5 - 10 kt/9 - 18 km/hr wind, I omitted to reverse
the procedure yet the wings could be held level until the glider was very nearly at a full
stop. Operation of the flaps, particularly at each end of their range (-2 and +2) appeared
stiff, although this became a little easier after Dick did some troubleshooting with
lubricant.
Immediately apparent as I took off for the first time (in 17.5 m configuration) was the
control harmonization, or lack of it. The elevator, controlled by the traditional
Glasflügel parallelogram type stick, was delightfully light and high geared. The
ailerons, on the other hand, felt low geared and relatively heavy. I feel this would take
a bit of time to become accustomed to, requiring small gentle movements fore-and-aft while
making large rather deliberate movements from side to side. In the 15 meter fit, the
ailerons felt a little lighter. While on the subject of controls, the Glasgflügel
stick-mounted spring trim system, actuated by pressing the little finger on a button
located near the base of the handgrip, was a pleasure to use, and effective throughout the
practical speed range. It also could be set by moving a small knob mounted on a
semi-circular wheel fixed on the horizontal part of the parallelogram control column just
ahead of the pilot's fingers. Trim position could be checked from the position of the
knob. While failure to set the trim correctly before takeoff is clearly an important
oversight, in the 304 the lightness of the elevator and the consequent small amount of
trim force required to eliminate such loads means that such an oversight could be quickly
and easily overcome.
On tow, the 304 was easy to control. Bringing up the landing gear after tow release was simple, and could easily be accomplished with one hand. Once off tow, good handling qualities were at once apparent. My flights were carried out on two successive warm (75ºF/24ºC) fall days with light southerly winds and moderate instability up to 5,000 ft/1,500 m agl. These gentle conditions clearly demonstrated that thermalling was pleasant and effortless, although the instrument panel once again intruded into the forward view when turning at thermalling speed. This caused me to take a little time to feel comfortable with the nose attitude at 48 kt/89 km/hr and +1 flap. Visibility elsewhere was good although I couldn't quite see the tailplane. Aileron control is fairly good; rate of roll with the 17.5 meter tips was noticeably slower than with the 15 meter fit. Coordination was easy, but it was possible to run out of rudder using large aileron deflections at low speed. The airspeed demonstrated signs of yaw sensitivity - just a little lack of coordination sent the airspeed needle flying back towards zero. A good attention getter to your flying inaccuracies even if you are not watching the yawstring!
The 304
CZ is designed to conform to JAR 22 requirements giving a permitted cockpit load range
between 154 lb and 242 lb/70 kg and 110 kg. My weight of 160 lb/73 kg with parachute put
me close to the rear c.g. position. That notwithstanding, it was difficult to induce a
stall, and only after substantial warning with high nose attitude. The lead-up to the
stall was accompanied by some side to side 'hunting' of the nose. The ailerons remained
effective right down to the stall, and recovery was quick although, particularly from a
turning stall, speed built up rapidly in the ensuing dive. Attempts at spinning (15 meter
configuration only) were almost completely unsuccessful, and a spin only developed after
gross crossing of the controls. Again, recovery was quick.
Approach control is by combination of flaps and upper surface trailing edge brakes which rotate around that edge and up into the airflow. Initial movement of the airbrake lever brings out brakes only; as the lever is moved further back, airbrake action is combined with increasing flap settings. The result is a very powerful system without almost no trim change throughout its range. That doesn't mean that a constant nose attitude can be maintained when the brakes are used - the braking effect makes it necessary to pitch the nose well down to maintain a constant approach speed. Steep, relatively slow approaches and short landings can be easily achieved. One idiosyncrasy which became apparent was the proximity of the flap lever to the airbrake handle - both located on the left side with the airbrake handle between the flap lever and the left cockpit wall. To operate the flap, you must rotate the lever outboard, while to operate the airbrake, you must rotate the handle inboard. This gives rise to the possibility of interference - fingers getting jammed between the two, particularly if gloves are worn.
The wheel
brake is relatively effective, and operated by the heels moving the rudder pedals forward
together. This may require re-siting the rudder pedals closer as part of the downwind
check. Approach and landing are straightforward and unremarkable. The flight manual
recommends an approach speed as low as 49 kt/90 km/h with full airbrake at a weight of 838
lb/380 kg. Below that speed, closing airbrakes suddenly is not recommended, although doing
so at 55 kt/102 km/h gave no apparent sign of a momentarily increased sink rate. A pilot
unfamiliar with the trailing edge brake/flap system may get a surprise at pitch attitude
achieved with full brake and correct approach speed; this again emphasizes the need for
careful monitoring of approach speed.
Despite
my comment on elevator/aileron harmonization, the overall feel is of a pleasant high
performance sailplane which is a joy to soar. In the 15 meter configuration, mild
aerobatics (inside loop, stall turn/hammerhead, and lazy eight) are permitted. While
unlikely to satisfy the desires of an aerobatic enthusiast, the maneuvers are easy to
accomplish and provide a pleasant way of burning off height at the end of a Sunday
afternoon's soaring. That said, however, no aerobatics should be of the self-taught
variety.
Both of
my flights were made without water ballast; it was of interest to note however that the
flight manual states a full load takes 4 min to jettison. Ground launching is permitted as
well as aerotow, and the test aircraft was fitted with a c.g. hook just ahead of the
landing gear doors.
The 304 is a capable 15 meter sailplane, even if apparently lacking the performance generally believed necessary for 15 meter racing class competition at national level. It should have the ability to hold its own in regional contest, and is a natural mount for the sports class with handicap designed to eliminate performance differences between contenders. It is a pleasant and straightforward aircraft to fly, with no obvious vices or serious shortcomings. Accepting the complications of flaps and retractable landing gear, which can be made less significant by thorough briefing, proper use of a checklist and a suitable gear warning device, operation by relatively inexperienced sailplane pilots should present few problems. A couple of flights in a flapped retractable gear 2-place ship would undoubtedly ease the transition. As always, a careful and systematic approach to conversion (Ref. 3) will pay dividends and avoid surprises.
My thanks
to Tom Westcott for allowing me to evaluate his well-equipped sailplane, to Bob Kibby for
being my 'large' pilot and giving his comments, and to Texas Soaring Association for
contributing the tows.
References:
1.Richard H. Johnson and Dean Carswell: A Flight Test Evaluation of the Russia 12.6 Meter
World Class Sailplane, Soaring, March 1995, page 21.
2.Richard H. Johnson and Dean Carswell: A Flight Test Evaluation of the PW-5, Soaring,
April 1997, page 5.
3. Dean Carswell: Sailplane Type Conversions, Soaring, September 1996, page 18.
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