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Nov 07, 2014, 07:06 AM
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Heiko Baumgärtner 1:4 scale L13 Blanik glider part1

When a wing of my ¼ scale Multiplex Ka6e structurally failed just after releasing from too fast a tow during an event in Wey (Germany) during spring 2014, my scale marvel came down vertically from 400meter and was only good for the scrapheap. Either I had to build another model, but that would leave me without large-glider scale-weekends during summer, or I had to buy a ready-to-fly secondhand scale model. I opted for the latter, and after missing a 5m Lunak by a matter of hours (sold by a German to another Belgian), I choose for a rarely used ¼ scale Heiko Baumgärtner Blanik that had been for sale for a while in Switzerland, but not advertised much on popular web places. After a few mails with the seller, I borrowed my dad’s new station wagon, and left early for a 1400km non-stop up and down trip (in one day) to pick it up. I found his house just after noon of the third of July, and after a coffee and chat whilst I ate my sandwiches, we went to the garage where he assembled the Blanik for me. Although similar in wingspan to my Ka6e, it looked twice as big, and was highly detailed and in superb condition.

The Swiss owner demonstrated me that everything worked, and just a look at his garage convinced me that with such a meticulous workplace, the glider must have been assembled with the precision of a Swiss watch. We dismantled the model and stowed it in the back of my car, I paid him close to 1000 euro, and set course North again around 3pm in order to beat the rush-hour around some large enroute German towns. On the Swiss-German border I got pulled aside, and even calling the seller and a thorough inspection of all contents of my car, didn’t convince the five Gestapo/Stasi type German customs people that it was just a hobby transaction between two modelers. It took them many phone calls and typing up a series of customs import papers with everybody’s stamp on it, to allow me to take my latest acquisition into the European Union. I honestly had forgotten that Switzerland still was an isolated island completely surrounded by the European Union. The Swiss customs couldn’t care less, it were the Germans that who made problems importing a German produced model glider back into their country. After losing 2 hours being interrogated as a criminal, and paying 200 euro import duties and fee for not spontaneously declaring the goods, I drove away into the traffic of every town I passed (Schaffhausen, Stuttgart, Heilbronn, Manheim etc), and it was just past midnight when I finally drove through the Netherlands to get to the North of Belgium again.

The previous owner bought the HB kit in 2007 and had equipped it with a side slit behind the nose for towing. The cockpit had been built to scale and nice leather seats had been fabricated to be positioned on top of a flat floor. All electronics and servos (including an expensive Easy-Patch12-2 ZSX dual power supply with microprocessor) were mounted either under the floor, or behind the backseat. The instrument panels were still empty, and a new canopy had been fitted after an unfortunate inverted landing during its maiden flight. I got the pictures of the minor damage of that mishap, and was satisfied of the repair quality. This complete kit radiates quality all over, all control surfaces move into hollow receptacles, the fuselage is made of thick GRP, the wings are super smooth and solid, and joined by a 23mm solid resin spar-key weighing almost half a kilo. Ailerons, drooping (but not sliding out) flaps, and spoilers on top of the wing, help for precise control during landings. Multiplex connectors ensure quick wing assembly on the field. The two separate elevators are detachable and have their own servo. Internally mounted pull-pull Bowden cables connect the large effective rudder to the servo behind the instructor seat. The wingtips are plastic pods, and there only was a plain tailskid at the back, none were protected because the model had always operated from grass. I also received extra servos, pilot safety belts, and detailed documentation of the full-scale Blanik plus pictures of the interior and exterior. The chosen color scheme was that of a well-illustrated Slovenian full-size real Blanik still wearing those markings in 2008, but I have no idea of its present fate.

Setting up for my maiden:
When he sold me the model, he told me that he had changed the aileron servo type because one was erratic, and he also gave me two extra brand-new Hyperion servos to replace the flap servos, but all worked well in the meantime. With the multitude of servos in the model, I preferred to have each one connected to a separate channel in order to allow future complicated mixes, so I installed a spectrum DSMX AR 10000 receiver, and after some difficulty got it connected through the existent dual-power distributor to the servos.

The previous owner had no figures about the CG position, but assured me it flew very well as delivered to me. When I put it on the scale it indicated 10,5kg and the CG was measured to be 85mm back from the root. Through the internet I found that HB recommended 70mm, so I added 350 gram weight in the nose to bring it forward to 75mm for my maiden. After measuring the wing, I calculated the wingload as 92gr/dm2. Its chord was 42cm at the root, tapering to 12cm at the tip of these forward swept wings with a span of 4,04cm. The span being only 30cm more than my crashed Multiplex Ka6e was no yardstick to compare both. Following picture of both wings next to each other clearly show the huge difference (especially in aileron surface).

The living room is the only place where I can work on this large glider and even that is barely large enough to mount both wings. The hobby room is only used to work on dismantled subsystems of my increasingly large models. Size difference between the fuselages of both gliders is also very pronounced in following picture.

Three days after I got the model, I took it to the field for its maiden flight. Benny’s Calypso 62 was on the light side to tow me, but we figured that with a good briefing and instantaneous disconnect if we saw anything develop, we could take her up. I had Phaedra and Benny inspect the model in detail before we performed a range check. As a tow pilot he paid special attention to the towhook, and made a test under load (he uses a calibrated weight spring in between) to see if the disconnect servo was strong enough to pull the pin pack. The servo had trouble doing it at 10kg load, and after that test I discovered that the pin that ran through 2 wooden blocks had forced the blocks to separate from the glider skin. This was the first of many occasions where I found that some things had been glued by strong epoxy, but without previously having roughed the GFK surfaces. Contrary to my habits, I made a quick field repair to allow one testflight before replacing the complete hook system with a proper one. As often before a maiden, I like to have a picture taken of the model before any possible damage.

Carrying it towards or from the runway, I felt how heavy it was, and made a mental note to develop a solution for it to be towed by hand. Everybody else cleared the sky so I could concentrate just on flying for this maiden. After hooking it on the towline, I saw that even with the horizontal tail in a dihedral, their tips touched the ground with one wing at rest on the runway. This was caused by the tailskid being too short, but I couldn’t have noticed it at home because in my apartment I nowhere have sufficient space to allow it to rest on the ground. I thus asked a fellow club member to lift the wing in a horizontal position during the launch from our tarmac runway, and that would also keep the “tiptanks” from scraping our runway during the first meters.

It got airborne faster than expected, and I quickly had to apply down elevator in order not to be too high behind the towship. With all the turning into the sunny sky, it was hard work to correct my position, attempt to trim, and especially to see the glider’s attitude against the nearby high sun. Besides sporting black registration, the color scheme under the wing is the same as on top, and might be highly attractive for pictures on the ground, but silver and sky-blue are very difficult to see against any sky or cloud backdrop. During the most difficult angle of a turn at altitude, my position in the tow must have been wrong, and Benny called for a disconnect when he felt his towship got in trouble. I initially hit the wrong button, and by the time I corrected, Benny already had disconnected on his side, we never found the rope anymore. We didn’t have to recover from unusual attitudes, and must have been above 150 meters, giving us sufficient time. With Phaedra and Benny next to me, we calmly started to fly the test profile we had agreed upon during our briefing, calling out everything we did or felt.

After the release and another hefty portion of down trim (full down trim!), it glided steadily without need for aileron or rudder trim. I gently turned the Blanik around and pointed the nose 30° down. I normally perform the CG dive check with 45° nose down, but a combination of excessive play on the servo arms of the ailerons and flaps (that could lead to flutter), and one of the two elevator carry-through beams being too short and too light, made me restrict the dive angle on this first rapid CG check. As the excessive down trim already pointed to, it wanted to increase the dive, indicating a rearward CG and necessitating a prompt but smooth recovery to level flight. With a CG too far back, this limited the stalls and spin capabilities, and I only ventured a clean approach to stall profile, from which I recovered at the first sign (gentle dip of the nose without wing drop). After a 30° and 45° bank turn left and right, I flew another straight stretch and tried the spoilers, no noticeable pitch change, and after repositioning at approach speed, I lowered the flaps to the first position (about 10° to reduce landing speed or turn tighter in thermals). Having dialed in some up elevator mix, the glider raised its nose and ballooned. I still had sufficient altitude to fly a couple of horizontal eights in both directions, so that I could observe how much rudder I had to apply (very little) to counter the adverse yaw during the reversals away from me. This Blanik flew as on rails, and I timely entered the downwind for a standard rectangular pattern.

Benny had already landed the towship and parked it well away from the runway, and he now took over from Phaedra in assisting me for my first landing. The crosswind forced us to fly a base-leg under the sun, but the model was large enough that I could sufficiently see the “shadow side” to judge the glide slope and direction it took. Having found out that the spoilers had no real side effects, I deliberately came in slightly high with sufficient speed. After rolling out from the turn to final, I lowered the flaps to the first click, and caught the ballooning by opening the spoilers. Having read horror stories of real Blaniks smashing against terra firma with full airbrakes, I made sure to slowly retract them to less than half, about a meter above the threshold. This resulted in the model touching down about one quarter down the runway, and without full flaps nor much headwind component, it rolled to a standstill on the last meters of the tarmac. The silent audience around me started talking again, and I resumed breathing.

I walked to the end of the runway, observed all flight control positions, switched the battery off, and carried the Blanik to the pits again. Benny offered me to tow me up again, but I declined. There still were too many shortcomings on the model, and this short successful maiden had pointed out some good and bad points, and I knew what to correct and how. I didn’t want to push it any further before I had assured myself that everything was perfect. I then noted all trim positions on my transmitter, and dismantled the Blanik for transportation.

Essential fixes:
Back home I made a long list of things that had to be modified or corrected, and here is what I did during the two following weeks. During the preflight inspection before the maiden, I had noticed that the servo arms in the wings moved a lot, and was afraid ailerons and flaps would be imprecise and even dangerous because they had too much play. The flaps had no definite up position, and more than a few degrees play in the down position as well. My assumption that the servo’s wheels were worn out, proved incorrect. Part of the play originated by the linkage being inserted in the wrong servo arm and control horn holes, and after opening up the servo cover plates I discovered that that the servos were only kept in place by that thin cover plate. Inside the cutouts in the foam they still had too much space to move under load. The wooden blocks around the servos were not sufficiently close to solidly encapsulate the servo. At that point I decided to replace the 5,5kg/cm Futaba S3010 servos by the identical size 13,kgcm Hyperion HP-DS20-UMD digital servos with 23kgcm hold power.

This might be an overkill, but with such large control surfaces on a speedy 11kg aerobatic glider, I didn’t want to take risks. After inserting the new servos, I made custom cut aluminum shims, which I inserted between the servos and the blocks keeping them in place. An extra aluminum brace was then bolted on top, so the blocks couldn’t separate under load. To keep the servos firmly down against the baseplate, I glued additional thin layers of balsa on the inside of the cover, so it would press the servo’s down after being tightened flush with the wing.

I also repositioned the arms at better angles, and used the inboard holes to produce the desired maximum torque (closest to the pivot point) and minimizing any angular play. I arranged for the arms to be almost in line with the pushrod with the flaps in the up position, thereby reducing the strain from the flaps on the servo mechanism during positive and negative-G maneuvering. To still get sufficient control throws, I had to cut away some more of the cover plate openings. The previous owner had no throw figures, but I had measured and noted down his throws when he demonstrated all the servo operations. For the ailerons he used 1,4cm up and 1,9cm down, just the opposite of differential ailerons ! He used the flaps 1cm down to turn tighter in thermals. His elevators moved 2,5cm up and down, and his rudder 7,5cm left and right. He flew aerobatics like that, and I used those figures to connect my servo links in such a way that those figures could be attained on the normal full servo range. He had them mechanically connected differently, causing more torque to be necessary on the servo arms, and he limited the deflections electronically on his tx, not my way of doing things.

After applying the aforementioned modifications on the four wing servos, I applied the same link principles to both elevators and the rudder servos, all Hitec 645, which had been tightly mounted in the back of the cabin. I had to modify the length of the Bowden cables to get the rudder servo arm centered together with the rudder flight control.

I then took the easyPatch12-2 out from below the floor and connected my receiver and the servos to the ports so that all servos had individual power and channels. This sound simpler than said, and I ended up having to make a table on which all pins and labels could be traced.

A major problem was that my DX10t transmitter did not have dual-elevator programming in the glider-type options. The right elevator thus moved up and down and had had trimming capabilities, the left one just moved up and down without trimming capabilities, rather annoying considering I also planned to include flap/elevator (through the camber menu) and spoiler/elevator mixes. None of those would move the port elevator, creating an asymmetry versus the starboard one. While at it, I also used the flap function to command the ailerons a bit down with any flaps deployed. On flaps one, the ailerons drooped half the amount of the flaps, and helped augment the camber of the complete wing for better slow speed thermal centering. They stayed that way with full flaps, to help lower the approach speed, without drooping too much and induce tip stall. Furthermore, all these changes ran through a four seconds slow movement timer (on the transmitter).

After disconnecting the wings, the next thing I did was epoxy a shaped 3mm piano wire along the underside of the plastic wingtips. The idea was that at any pitch (ground) attitude, some part of the wire would scrape the runway whenever a wing dropped before takeoff or after the landing. On following picture you can see the that the wire runs along a good portion of the plastic tip fairing, and that the ailerons are now actuated by the linkage in the hole closest to the servo pivot point, and on the most outside hole of the horn. The servo arm is at the 90° angle with neutral servo without subtrim, because I prefer to dial in my aileron differential electronically, and want my aileron droop to happen fully symmetrically upon flap extension.

After removing the old spring hooks from the wings, I stowed the latter in their protective bags, and ordered two longer and stronger 10mm diameter aluminum tubes to join the horizontal tail halves to the fuselage. These now fill the hollow receptacles to both ends, and although apparently strong enough, I still can slide a carbon 8mm rod in the tube to reinforce them even more for aerobatics. The increase in weight at the back could compensate the weight of a lightweight pilot in the front (when installed). I also mechanically adjusted the angle of the left (non trimmable) elevator to coincide with the mid-range angle of the trimmed right elevator between flaps up and down. That way I hoped to minimize asymmetry and ensuing slight roll movements.

To get the tailplanes higher from the ground, I used a strut and wheel from a scrap small airplane, and bent it to lay in a gutter I had carved under the tailskid, the pin then bent 90° up to slide in a vertical hole drilled in the forward part of the skid. Because this was temporary to check the solidity and nowhere like the scale tailwheel (yet), I fastened it by screwing an aluminum plate around the assembly to keep everything in position during the next series of shakedown flights. The complete assembly only added 8grams to the tail (important because of the CG already too far back). The exit tube of the port elevator servo link had been badly damaged during the Swiss mishap, but by gluing the end bit to the fuselage this was at least mechanically acceptable. As with the rest of the works at that stage, none were cosmetic, that would only start after I got the Blanik tuned and perfectly under control.

The major work took place in the front of the fuselage. The badly glued wooden blocks through which the pin of the towhook servo passed along a slit in the lower side fuselage, were eliminated, and the slit epoxied close from the inside. With the whole mechanism including the servo being mounted under the mainly fixed floor (openings under the seats), changing the towhook system to a pivoting hook through a hole in the correct scale position in the nose, wasn’t the easiest of tasks. On the next picture you can see that besides the hook system, I also had reservations about the way the previous owner had blocked (not fixed)metal and lead plates in the nose, around the wooden battery compartment that accommodated a condensed 2x5Nimh2600Mah redundant pack that were connected via short Multiplex leads to power the glider’s electronics . Although it was invisible behind the front instrument panel, I found the setup to be relatively loose, with little space remaining for additional weights to bring the CG forward to 70mm.

I kept the wooden box structure, but removed all the loose side and top weights because there was just too much unusable space forward and around them. I bought a pot with 1500 4,5mm steel blast bullets for air guns in a shooting store, each weighing 0,35grams. I first drilled and Dremeled the hole where the towhook tube had to come out of the fuselage, then put the fuselage to rest on its nose, and filled the nosecone entirely with the steel balls. I did that in layers, each time pumping in 30 minute epoxy that filled the space between the balls and bonded everything solid. I repeated the process further back of the new tow opening, with the fuselage inverted, and in the end worked with a pincer to add single balls into the curing epoxy where I wanted to, leaving just sufficient space to allow the hook mechanism to be inserted from within the fuselage against a solid surrounding of steel/epoxy casing. On following picture, the steel balls in their epoxy soup can be clearly seen through the new cutout for the hook. The former oval slit was much further back, and at a straight angle would have caused many nylon loop cables to wear out prematurely. Resting on top of the inverted fuselage is a proper hook mechanism designed to allow the hook to open with minimal pulling force or friction. The tube had already been sliced away at an angle to hug the angled fuselage upon exit. The wider cone of the hook would rest against the first plywood fuselage former and “ball soup”, thereby forming a strong impassable obstacle even during the strongest of pulls (that sometimes happen after a slack in the cable whilst under tow). In a worst case, if the sleeve with pivot point would be pulled out, the link to the servo would automatically open the hook and release the towline. Just imagine how the force of an 11kg glider, snapping after an inadvertent cable slack, would be transmitted via the original release system through the perpendicular slit. I had chosen for a z-bend connection at the hook because once glued into position, there was no way I could access that area anymore. The link was then fully assembled (soldered and glued) on an approximate length via a quick-link onto the existing arm of the 5,5kg Futaba S3010 servo.

All that had required many dry fitting trials, not an easy task because the complete assembly (including the hook mechanism) each time had to be inserted through the hole of the removed cockpit seat , then underneath the very tight underfloor space, and hooked to the inverted servo arm to adjust the system to (mechanically) work with full servo throw through the most inner servo hole for maximum torque. When everything was finally tight and working, I again rested the nose of the glider vertically on a soft surface (my house slipper) and continued pouring individual steel balls and epoxy until the complete nose was one extremely solid unit, with as much weight as far forward from the CG as possible. I kept the system of fixed plates on top of the battery box, together with the screw, around which additional weights can be affixed, either until the correct CG is found, or to cater for the balance changes if a scale pilot takes place on the front seat. On following picture you can clearly see the towhook servo, connected under the cockpit floor to the aluminum hook just below the battery box, and the amount of epoxy encapsulated steel blaster balls filling every empty space in the nose. A few extra plates are temporarily bolted on the long screw pointing up (in flying attitude)

After reassembly of seats, blank instrument panels, canopy, battery connection tray and complete glider, it was time for another balancing act, first with a dummy in the cockpit to establish the minimum weights to be fixed at the front, and without the dummy to group the additional weight plaques that could be screwed on top of the fixed ones. Thanks to the uttermost forward positioning of the steel balls, total glider weight barely augmented with all those modifications, but I got a much more solid nose and CG at 70mm in the process . When fully assembled on the table, wings and tail are physically very close to walls and furniture, and the only way I can use the Sig balancer is by resting the glider’s tail on chairs, and lift the nose with one hand whilst sliding the balancer under it with the free hand. The wooden Sig contraption is on the limit of its design capacities and on the verge of collapsing under the 11kg weight resting on the two small rubber pads.

Exploring the flight envelope:
My Blanik was now ready to resume flight testing, and shortly after mid-July I made a couple of very successful shakedown flights that proved the worth of the modifications I had made. The CG was perfect, and with the wires under the tips and tailwheel under the skid, I could take off without any help on hard surfaces. The ailerons quickly became effective to lift the wing from its rest position.

After a couple of flights my mixes between flaps, spoilers and elevator became better, and the control surfaces were adjusted mechanically to have zero trim and subtrim for normal flight conditions. The full speed spectrum plus stalls in the various configurations, and clean spins, were explored with no signs of bad behavior. It could be flown very dynamically using its high mass and penetration capabilities (even without the up aileron setting used by the previous owner), or sedately and gracious. Use of full flaps and spoilers gave it the same body angle as a real Blanik in final approach, but contrary to its full size counterpart, this HQ straight profile wing had no tendency to develop tip stalls. I must admit that at this weight, I keep a good safety margin.

Img 3864 crop

After a while I even dared to land it with full flaps and spoilers fully extended, allowing precise touchdown point control. The inertia of this model and lack of wheel-brake cause it to roll-out quite a bit on a hard runway. In a no flap configuration, care has to be taken not to hold it off too long because it could touch down first on the now lower position weak tailwheel.

With the model finally ready, I took it to the BIGGS gathering of Schaffen for its debut. Unfortunately rainfall in the afternoon cut it short, and I only flew it once. The hope getting pictures of having it towed by a period scale PZL Kruk had to be postponed. Two days later I planned to attend a week of towed gliding at Pottes (near the Belgian-French border), and I had no envy to carry around that heavy glider every day. The 21st of July being a national holiday and all stores closed, I gathered various spare plates and a lawnmower wheel from my garage stock, and fabricated an assembly that could be attached by Velcro around a wingtip. A rope with loops at both sides (one in the towhook, the other for my hand) completed the equipment that made it possible to haul my Blanik to takeoff position, and recover it after landing. In Pottes Dutch glider friend Jeff fabricated a nice T-handle on a better rope, and offered that to me. This way of pulling the glider around (instead of carrying it) tremendously relieves my painful left elbow (too many too heavy models lately?).

Although the wind blew force 3to4 during that week, is was in the direction of the slightly upslope runway, and with temperatures in the upper 20’s, it was a superb week where I flew many flight each day, gaining confidence operating the Blanik in stronger winds, and even exploring its aerobatic capabilities. Roll rate was more than adequate, and loops passed well with the inertia. Barrel rolls are very elegant, but stall turns have to be initiated well before the speeds decays.
August was a bad flying month, wind and rain prevented us from flying our models most of the time. Besides preparing a Hangar 9 B25 bomber for its maiden, I spent a week further detailing the cockpit. I incorporated detailed custom made dashboard panels, mounted flap, spoiler and tow release handles, fabricated control sticks, installed a micro, and glued the correct placards in place. It was a major embellishment, but not yet the endpoint. I still had to install the seatbelts and place pilots figures in both seats.

On the 28th we had the annual club day, and although a bit windy and turbulent, I took my FMS B25, Hugues 500 Magnum heli and Graupner EDF Tiger F16 along, and flew 4 flights with the Blanik. The second flight was videotaped and can be seen in the link hereunder. It is an unedited video and contains some other activities, but the Blanik portion starts at minute 2:30
clubdag lvmodelafdeling 2014 (8 min 14 sec)

Rapidly developing troubles:
The third flight started with the first raindrops, and whilst friends of mine moved my other models under the shelter, I completed that flight with a very good landing on a wet runway. After the shower we resumed flying, but my 4th flight was anything but standard. Hooking up, I noticed the only remaining nylon loop was rather thin. When I mentioned that, the others waived away my concerns, so I didn’t argue with those more experienced tow and glider pilots. The wind had completely shifted, and was blowing fully cross into us. Takeoff was normal, but we got blown sideways towards the threes before gaining sufficient height. Benny managed to turn to the right, and instead of staying outside his turn, I panicked for the nearby threes and probably cut the corner too much, causing the rope to slack a bit. Halfway the 90° turn I saw the towship start climbing steeper, so I also pulled up. This probably caused the rope to snap tight, and the thin nylon loop to break.

There I was, less than 10 meters from the ground, into the headwind, and heading towards a three line separating us from a row of houses. I had no other option than to lower the nose whilst turning further right for another 135° to land back on the runway. That plan worked, and to kill the speed for a landing in quartering tailwind, I lowered the flaps and pulled the spoilers when about 2 meters high, approaching the grass adjacent to the runway. Landing downwind I preferred the grass in order to have more friction to stop the glider before running out of prepared surfaces. I was unable to raise the nose quickly enough to break the sink rate, and the Blanik bounced back in the air. Fearing an even heavier second touch, I retracted the spoilers to ¼ to keep her flying instead of falling. Unfortunately that was accompanied by an increasing right bank, causing the Blanik to veer directly towards us. A quick shout from Benny had Chris and me jump away from the flight path while I made frantic inputs to steer left again. The glider impacted a mere 10 meters behind us, in a slight nose-low attitude and some left bank. It came to standstill after half a groundloop around the left wingtip. The side force on the landing gear had caused the strong FEMA 85mm wheel to break in two pieces. I was able to glue both parts of the flange together with 30min epoxy and it held.

At that time most pilots blamed the crosswind for the veering off course, and the ensuing tailwind for the lack of aileron or elevator control. Damage from the impact on the soggy grass was very limited, but the fin and tailwheel were found at the place of the first touch. That puzzled me because if the speed had been too high, the tailwheel even wouldn’t have touched the ground. It was found in one piece, so my tailwheel modification had been strong enough. Traces of grass on the fuselage and the broken-off skid, show that the tail got pushed in the ground. Did I fly too slow? How come it then flew another 80 meters before the second and final touch? If I flew straight at that time, how come the tailskid broke away?

Just bending the leg away from the skid, and epoxying the latter to the fuselage, resolved the problem. Applying a few mats on the inside to reinforce the tail at this critical position would hopefully cater for the increased leverage forces of the tailwheel. Traces on the lower fuselage indicate the shallow pitch and roll angles of the final impact (the first one was wings level). The scale towhook and reinforced nose showed no traces of damage.

A few days later I took the repaired Blanik to a 4-day large-glider gathering close to Bastogne in the Ardennes. I flew my 4m Flair Ka8b until a spoiler problem caused me to land into a fence, grounding that glider until full winter restoration and overhaul. That Saturday I assembled the Blanik and flew it in front of a considerable audience. During the preflight, I carefully checked all the control movements and flap operation, and all were normal. The tow and flight went well, but when I was on a steady final to land, I lowered the flaps to full, and the Blanik pitched down and started to veer to the right, pointing the nose straight towards the pilot-box and public. Whilst some shouted to watch out and run, I was able to reverse the roll and make an emergency pull away from the people.

I even got it lined up with the grass runway again, but again full up stick was insufficient to flare the glider, and it impacted with slightly right bank on its nose. Apart from the tailskid breaking off (again), I could see no damage. Somebody happened to make a picture of the wing digging into the ground a fraction before the fuselage touched in this bad attitude.

Troubleshooting and correcting the problems:
That was it, I grounded the Blanik until the cause of these sudden uncommanded dives and right bank movements could be found. Apparently the first time it happened had not been due to crosswind, but something went seriously wrong when I moved the flaps down. Some had seen flap asymmetry, but I couldn’t see significant differences when operating the flaps after the mishap. I let it rest for a month and used that time to acquire, prepare and tune a second hand wooden slope glider (with towhook for the shakedown flights).

When I finally found the courage to assemble it on the dining table, I first could not find anything wrong with those flaps. The large flaps 100cmx8cm, and 90x8cm ailerons caused those 13kgcm servos to be very noisy when I simulated airflow pressure on them, even to the point of not moving, but when I somewhere let go the pressure, they moved and locked tight with their 23kgcm holding power. With equal pressures on each side, I could see no asymmetry. You might remember that instead of using a flap function, I had programmed 3 different wing cambers through the flap switch. Two of these dropped the ailerons, but because it was not much, it happened a bit erratically. To simplify and prevent possible problems, I decided to eliminate that function for the following check flights, and the ailerons were rigged and programmed to be just straightforward ailerons with 50% electronic differential.

After measuring intermittent and full flap deflections during at least 30 cycles, some of them under various simulated loads, I still could not detect any asymmetry as long as the (airstream) forces were similar on both wings. I thus shifted my focus towards the elevators, and for the first time noticed gross asymmetry and brutal movements during various flap movements and elevator applications. Each elevator being 45x10cm, there was sufficient potential for dramatic pitch and roll inputs. Unable to program my DX10t for 2 elevator servos, I knew my elevator trim only commanded the starboard elevator, but through the slave function of the stick, the elevators worked together, and both also got the mixes with the flap angles (or so I thought). The model being so large, my peripheral vision never caught the elevators when I focused on the flap movements during the preflight checks. A detailed analysis was the next step.

First discrepancy that I discovered, was that a guide for the port elevator pushrod had become loose, causing the latter to just flex under load, instead of pushing the elevator up. That guide had again been glued with epoxy to the inside fuselage, without any sanding. That must have caused it to torn loose at the first impact after the tow failure. Any up elevator thereafter only caused the right elevator to move up, the left one just remained streamlined, but pulled down if commanded to. With little stick input during flap operation, that still didn’t explain the sudden right rolling. That guide was deep into the fuselage and it was very difficult to apply sufficient pressure on the sandpaper through the tip of my finger, to remove the slippery top layer of the inside fuselage polyester surface around that spot. Using 30minute epoxy, I let it rest for 24 hours and it bonded very solidly. In the meantime I decided to give up the twin channel input (one for each elevator), and connected them on a single channel through a Y-cable and servo reverser. I lost redundancy, but gained trim capability on both elevators. Both elevators finally operate in full symmetry (after some mechanical adjustments on the servo arms).
Watching carefully how they moved with various flap commands, I first noticed they had a rather pronounced down position with flaps up, moved slightly up with flaps one, and again seriously down with full flaps. Both movements now happened on a 4sec slowdown to coincide with flap deployment speed (instead of previously slow on the starboard one, but instantaneous on the port one). It were serious deflections of the neutral point, and once down, prevented use of much up elevator (as can be seen on the crash picture). Those sudden down movements must have been the reason that I twice saw the Blanik dive, and the panic up movement on the slick only caused the starboard elevator to go up (the port one remaining streamlined due to the loose support). The result was a right roll, and largely insufficient (one slightly) up elevator area to raise the nose before impact (during both mishaps).

The next accidental discovery was even worse. If I moved the flap switch in one movement (up to full down without pausing through the intermediate position, or opposite, I saw the elevators assume positions they were not supposed to. I then tried to eliminate all the flap to elevator, and camber to elevator mixes, but to no avail. It took me one more hour to discover what caused the inputs. Each wing camber is recognized as a flight mode though that (common) switch, so every mode “remembers” the last trim settings of the selected flight mode, and moves the tail towards it when it changes flight modes (in my case flap setting), but in case you move the 3-postion switch directly from 1 to 3 or vice versa, it moves the flaps to the correct angle, but the elevator trim only to the next angle, hence the brutal pitch movements upon switch actuation, accompanied by uncommanded roll movements during the snappy corrections when the flaps were actuated at low altitude when landing was assured. I had no idea the that the elevator trims were stored for the 3 “flight modes”. I therefore set all 3 trims to zero again, and will not touch them anymore until I find out experimentally what the correct trim setting is for every flap angle at the correct speed. All this will have to be done at altitude, but low enough to be able to visually trim for a correct glide angle.

A step by step mandatory order to avoid another catastrophe, will be to first fly the model without touching the flap level (using only spoilers to control the rate of descend), and mechanically adjusting both elevators in order to obtain a zero electronic trimmed balanced flight. Only after that, will I dare to pull flaps one, and adjust the trim electronically for it, then further down to full flaps, and set that trim again. That way trims with flaps will be electronically correct for minimal stick changes when operating with various flap settings (in this case flight modes). With the flaps up, I will be able to trim the elevators according to the flight speeds I want, without affecting the trim settings when switching the flaps in either extended way.

Another thorough check on the spoilers revealed that during slow retraction, the starboard one also had a tendency to remain slightly deployed (also causing right roll). After disassembly I noted that I had insufficient travel to move the actuator in the mechanical lock position. During my initial setup, I had created a rather simultaneous movement of both spoilers by slaving the second servo on the throttle input, and adjusting it electronically into ranges I would never use for flight controls. Now was the time to correct that mistake. Being unable to reach the servo in the wing, I reprogrammed both channels to standard values, then mechanically changed the length of the pushrods in the narrow slits in the wing, then made final adjustments using servo travel adjusts (within 120% range) to obtain symmetrical deployment throughout the range, and a positive locking push to keep both spoilers flat in their location when not in use. The initial hastily setup used to cut corners had never been looked upon anymore, until after these two rough landings.

I’m glad that after some sober and deep analysis of portions of “succumbed” flight, I was able to find out the various causes of strange behaviors I couldn’t recover from. Sometimes, modern electronics are a blessing, but they have a (logical) mind that only can be understood by their program writers. It takes much time and thorough logical thinking of “traditional” pilots to find out why something doesn’t behave the way your aerodynamic schooled brain thought it should. After resolving those problems, I triple checked all control deflections again before removing the wings and horizontal stabilizers. Next step was again binding the receiver for the new setup, but that is only temporarily, before failsafe settings with new trims can be nailed down. This probably will again take at least more than 5 flights, but this time at ease in my own club, and certainly not progressing from one flight to another without programming well thought off values, step by step, into these electronic gismos.

Continued on part 2 hereunder, story was too long for a single post, besides the last cosmetic enhancements you can read about the highly successful post-repair flights that were made just before winter came.
Last edited by BAF23; Nov 07, 2014 at 11:46 AM.
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Nov 07, 2014, 10:35 AM
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Heiko Baumgärtner ¼ scale L13 Blanik glider Part2

Final interior finish
With minimal chances of flying the Blanik in the windy autumn days, I decided to continue the interior detailing. I had been collecting puppets of various dimensions during the last years, but most proportions of those are too Barbie-like. For the large and wide Blanik I therefore wanted to install a more representative pilot. The quality Axel pilot figures were just too expensive for me, even secondhand. Being a two-seater I had choices: having a solo pilot fly it from the front seat, pilot in the front and passenger in the back, or instructor in the back with passenger in the front. I choose for the latter, with a cheap lightweight child in the front (for CG reasons), and an affordable realistic-sized pilot in the back. I ordered a 49 euro Graupner glider pilot because of its approximate scale, but upon receipt was very disappointed about the product. It weighed a lot, arms and legs couldn’t be bent at all and pointed straight out, body and legs were much too long for the shoulder width and head size, and some limbs didn’t stay put well in their joints.

Blanic post crash

After undressing him, I removed his shoes and cut away a portion of one lower leg. To fit the shoe over it required the remaining portion of the lower leg to be made slimmer. Cutting some of the thick latex away with a knife worked well, and gave me the idea to seriously reduce the pilot weight, and create some bending capabilities for the limbs by cutting away more than half the thickness of the material. I then also cut away a ring of his too long torso. It took me a few hours, but the pile of removed material amounted to 65 grams, and I could bend his arms to hold the stick and spoiler levers. When nude, he now looks very anorexic, but once dressed, you don’t notice his skinny arms and legs anymore. After gluing the torso and shortened neck together, and forcing the limbs into their pivot points, I dressed the pilot and he tipped 220grams on the scale, not exaggerated considering he sits almost under the CG.

Post crash 3

Just as in the real Blanik, I made the crew wear (foam) parachutes for correct position. To keep him in his seat, I used a 4-point harness that was fixed to the seat, making it possible to remove the complete assembly in one piece (for maintenance in the back of the cockpit or fuselage) by simply removing two bolts at the front of the seat, and his left hand and spoiler lever from the fuselage. I didn’t like his beard but couldn’t eliminate it because of the mold. I discarded his heavy 20gram hat, and painted his facial hair (now with moustache) with mainly grey accents (older instructor). Sunglasses also got a bit of paint, and I detached every finger from the adjacent one so his hands could be gripping the stick and spoiler handle in a more realistic manner.

Blanik post crash 4

In addition to a parachute, the young guy in the front got seated on a home-type cushion to bring him up a bit. That body was one of a strong man, but with a much too small head. The latter was therefore exchanged for a younger head about twice the size. I had to melt his legs so they could be bent at a proper angle. He got the same seatbelt treatment, but his torso can bend forward about 20°, together with the back of his seat, so I can gain access with my finger on the power switch, and visually check the lights monitoring the power status and voltage lights.

Post crash 7

Hardware repairs:
I then turned the model upside down and replaced the repaired (glued) wheel flange by a new one. Finding nothing but a 90mm FEMA wheel, it would have been extremely tight in the wheel cutout, but both use the same flanges, so I just mounted the old 85mm tire on the new wheel flanges. At the back end of the fuselage, I unscrewed the tail cone. After seeing a serious crack of about 2 inches where the skid had broken away, I decided to try another approach to fix it. When using hard epoxy bonding, upon impact the fin with tailwheel obviously passed the forces straight through to the fuselage. The fuselage then squeezes temporarily from a circular into an oval shape, leading to separation of the rigid epoxy bond with the skid. In order to better absorb touchdown forces, I decided to glue a nylon mesh mat inside the lower aft fuselage in a liberal bed of Tec7 bonding/filling material. Before it dried, I used the same Tec7 to glue the skid to the lower fuselage (all traces of epoxy had been removed by knife and sanding both surfaces). I hope this will allow some degree of elasticity to also absorb the lateral forces during a groundloop after unfortunate landings. The skid assembly might still get torn away, but at least it will happen sooner and probably prior to fuselage deformation or cracking.

Back on its wheels, I mounted the seat/pilot assemblies in their spots, and wished to add the two sliding ventilation windows to the port lower canopy Perspex. These were quarter scale assemblies but were much to small when compared to the pictures of the real aircraft. Larger ones were ordered before tackling that very visible modification. The back/seat/instructor plus seat combo weighs 360gr total (seat alone is 95gr). The student pilot with his cushions weighs only 70grams.

Post crash 11

Mounting vent windows in the canopy:
The 1:3,5 scale vent windows ordered from Lindinger (Austria) looked much better, but also had those 6 tiny 1mm screws in the bag. Are those so expensive that they cannot add one or two extra because it is easy losing them during assembly. Not wanting to ruin my nice canopy, I decided to make a trial installation on the remains of a spare canopy I had received from the previous owner. The way to assemble those vents is to first hand-drill 0,8mm holes in the guide rails, then position the bottom one behind the Perspex and hand drill a 1mm hole in front of the middle screw opening. Use a 1,5mm drill tip to make the countersunk so the screw will be flat with the Perspex, then insert the middle screw but not tightening it yet. The bottom rail can still pivot, allowing it to be moved out of the 1mm drill path once it has been pinpointed on the back of the rail. Failing to do so might widen the hole in the rail and making it impossible to tighten the screw in it. With screws of only 1mm, there is no tolerance whatsoever to drill the holes, because there is no way to compensate even for the tiniest misalignment. Next we do the same with the front hole, but to pivot the guide out of the way, the back screw has to be removed again. With the 3 bottom screws in position and tightened, you now can slide the window in from behind, in the open position (back). The top rail can now be held in position over the window, and the middle hole drilled. Then the same scenario as for the bottom rail, but moving the sliding window to check for correct alignment when drilling the outer holes.

Be very careful not to lose those 1mm copper screws. I found out that minimum risk was achieved by not working on a table (crews can easily slip away, bounce on the ground and never be found again), but on a uniform colored floor. If by accident a screw goes haywire, it can relatively easily be spotted on the floor within half a meter of where it impacted. I also found it easier to keep the tiny crews in a bottle cap, and only remove and position them one at a time with small pliers. Only when they are in their hole, I swap the pliers for a very tiny screwdriver, making sure not to damage the minimal slit during tightening or unfastening. I recon I frequently used a serious magnifying glass during the assembly of these vent windows, and have been lucky so far that I haven’t lost any screws, because I have no idea where I could purchase spare ones.

That was the easy part, and I kept it that way on my former Ka6e. It looked like a window, was sliding, but there was no real opening for air, just the aesthetics of a vent window. On the Blanik I wanted it to be functional (also to allow some ventilation in the large greenhouse when resting between flights. The Perspex being circular and glued to the canopy frame, doesn’t make it easier to be cut. Either I had to mark the cutout and then remove the assembly again to attempt to make the window opening with power tools, or I could attempt to cut it with a knife. That is where the spare canopy came in handy, and keeping the complete assembly in place with the vent hole on the forward closed position, I used a sharp knife to make a groove on the canopy, following the lines of the inside of the sliding window underneath. I then slid the vent window fully back (future open vent position), and carefully deepened the groove with multiple knife passes in it, the rounded corners being the most difficult whilst avoiding any slips (that would be very visible). That 1mm Perspex is much tougher than you think, especially when you have to cut completely through it and have only one try to get that rounded cornered rectangle out without slipping and ruining your nice canopy.
I admit I had a few slips on the spare canopy, but that gave me practice on how to do it flawless on the actual HB model canopy. I then removed the vent assembly from the spare, and repeated the process on the scale Blanik. I did it without slipping, but the complete job of the spare and actual canopy took me more than 5 hours. Trouble is that the Blanik is a two-seater, but I that had already been so concentrated and delicate work, that I preferred to do the backseat a day later.

The result is not only stunning, but also fully functional. Following picture illustrates from left to right: front vent window in closed position, completely flush with the canopy, plastic bag containing additional vent window and 6 screws, finger resting on carefully cut out portion of the rear canopy, finger pointing at the tiny screws which have to be bolted through the Perspex into the two guide rails, under that the kit provided window with minimal surrounding flap to prevent it from passing through the Perspex. Tools are a 0,8mm drill, 1,5mm drill with plastic around so it can be hand twisted to make the countersunk crater in the canopy, 1mm drill in finger drill tool, cutting knife for careful multiple passes on the shape of the inside vent window on the Perspex, and pliers to insert each screw in its fabricated hole before using a mini screwdriver to tighten it flat with the Perspex. The back window is already cut out with the 6 holes drilled and ready to accept the rails. Good luck.

Blan fin coc 6

Finally in the air again:
With everything into place, again, I got the Sig balancer out and proceeded with a new weight and balance check. It now weighs a hefty 11,5kg, and that calculates to 101gr/cm2 (more than any of my powered aircraft!). About a week later (early November 2014) came an unexpected good weather day and the availability of Benny’s Calypso62 towship. That gave me the possibility to make a couple of flights to validate the behavior after all my modifications, repairs, and reprogramming. The first tow was as normal as could be, but after I released, I had to click through half the up-trim range before it flew at a sedate scale-speed. As planned, I didn’t touch that trim anymore during the two flights because I wanted to see what happened at the various flap and spoiler positions. With all the mixes removed from the transmitter, I expected serious side effects, but to my surprise, only when moving the flaps further down, did I get some momentarily ballooning, but after a few seconds it flew along fully trimmed about a slightly steeper glide path. Spoiler extension caused no pitch nor trim change whatsoever. I landed cautiously with full flaps and full spoilers deployed (there was very little headwind). I let it settle at too high a speed, causing a momentarily light runway scrape along the forward lower fuselage shell. It just took the paint off from about a square centimeter, but luckily none of the plastic. I’ll gradually lower the approach speed and augment the flare pitch change as I gain confidence flying the Blanik. The full size Blanik has a protruding square protection plate at that position, and now I know where to place it on my model (all depends on the angles and seize of that single wheel. On the real Blanik this main wheel is semi retractable but the glider can be landed with it in the up position, even recommended under certain circumstances.

That first very successful post repair flight had been mostly about configuration changes, and because the setup seemed good, I didn’t touch anything and immediately made another flight. With that elevator trim setting, the Blanik got off the ground by itself in only 2/3rd of the first ground roll, and settled much higher behind the towship. When I pointed that out to Benny, he assured me he felt no problem with that, and even suggested I stayed there instead of forcing it lower. That tow was super stable again, and upon release I had expected a serious pitchup, but that didn’t materialize. My clearing turn absorbed the extra speed, and after rollout 180° further, it settled in a steady comfortable glide. I then did some approach to stalls in the various configurations to assure it displayed no vices after I took out the aileron droop feature. I did not feel the need to explore the full stalls nor spins, that had been done months ago, and as I had not changed anything drastic aerodynamically, moved on to the CG dive check. As I anticipated due to the up-trim, it recovered more rapidly than it should have, which confirms a slightly too forward CG, which could be corrected by removing one metal plate at a time from the bolted ones in the nose (trouble is that I each time have to remove the front dashboard assembly to reach it. I continued with more turn reversals away from me, to verify the 50% aileron differential setting, but that proved adequate and required just a tad of rudder as per real glider. Although I intercepted the final at a lower altitude, I still needed full flaps and spoilers to get it down on the first half of the runway. That large heavy glider really has excellent gliding capabilities, and next year I might slowly augment the flap deflection (but will have to buy a Hyperion servo programmer to do so) and droop some ailerons with it to augment the drag for landing.

On the third flight, the sun was so low that we had to fly a different tow pattern. I released early because I thought there was slack on the cable after rolling out of an almost overhead turn. As we were high enough, I took no risks and pulled away. Being only half the height I had counted on, I nevertheless was able to dive and execute a looping, an aileron roll, and a barrel roll, which confirmed my control throws were adequate for mild aerobatics. All throws were measured at the inboard side of the surfaces. Elevator was 3cm up and down on 80% dual rate and 25% expo, rudder was 9cm each direction with 100% dual rate and 30% expo, ailerons moved 1,5cm down and 3,5cm up with 100% dual rate and 20% expo, flaps moved down 1cm for thermal (I call that takeoff flaps) and 3cm in landing mode.

Holding it off a bit longer before touching down, ensured a touchdown with the body in a level attitude (despite full flaps). Without flaps, risks are high that de delicate tailwheel touches first, and I certainly don’t want that to happen. After these flights, some who hadn’t seen my Blanik in the air before, commented how stately it looked, and how faithful the flight image appeared. For me, those 3 flights tremendously boosted my confidence with that model (after the 2 consecutive mishaps). Back home I glued a protection plate under the nose (as per real Blanik), took away 85gram of lead plate from the nose, and reduced the uptrim to ¼, that probably will be pretty close to a better CG. The year 2011 Sanyo NiMh batteries still have plenty of power, and with the redundancy of the double 6v system with visible light indicators on the control box, I feel confident to use them for another season. The Blanik can hibernate and is completely ready for a better 2015 season.

Post blanik crash 12

Recap and reflections:
Has it been wise to quickly buy a so called “plug and play” second-hand quality-glider to continue flying with the “BIGGS” circus during summer, without time to properly set it up? I don’t think so. I don’t regret the purchase nor the custom fees, they definitely were worth the looks and flying qualities of this historic glider, certainly compared to the looks of the omnipresent white “Tupperware” models of ASW, Cirrus, Fox, Pilatus B4, Arcus etc… I can best compare it with showing up with a 1967 Mustang coupe on a parking lot filled by uniform looking modern Audis, Fords, Opels, Hyundai, Toyota, etc, where you have to look at the badge to read what it is. A Blanik is a classic that is instantly recognizable, and made for the amateur just like a Ford Mustang , mass produced at a reasonable price, but whatever the timeline, standing out of the mainstream in a positive unique charming way. Some designs are timeless, and the Blanik glider definitely belongs to that list. With close to 3000 of those aluminum gliders, it is the most produced glider in the world, and one of the most versatile ones. It was the instrument to teach students from all over the world (even the USAF used it) how to fly gliders, but was also a performing glider with excellent aerobatic capabilities, and very robust until limited by metal fatigue after decades of aerobatic torturing.
Dec 25, 2014, 02:56 PM
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A christmas present for my Blanik

Having permanently into view because due to its seize I have nowhere else to stow it but on a dresser in my living room, the young guy in the front cockpit didn’t seem to fill neither the bill nor the cockpit. The possibility of changing the batteries with him in his seat wasn’t outweighing the penalty in overall appearance. For his Christmas I decided to offer my cherished Blanik a full size pilot and removed the young chap and his seat belts. After a change in clothing he will most probably find its place in a 3m55 span WIK Twin Astir II as a Belgian air Cadet undergoing tuition (restauration project temporarily shelved until I find a new clear canopy for it, in anyone can help I would appreciate a mailing). For some reasons beyond my comprehension, most affordable pilot figures on the market sold for a certain scale, rarely match the size and proportion of a same scale model (except for the very expensive Axel figures). Through a friend of mine I accidently bumped on the offerings from Topmodel France. In their wide assortment I discovered a few full pilot figures that looked very good for a reasonable price, and with the dimensions on those pages decided to try the 1:3,5 scale pilot Peter. When I got it delivered he looked superb in his box, and I couldn’t believe how light he was. It therefore must be the biggest rip-off on the model market, 75 euro for 40 grams foam! 2 euro per gram of polystyrene. On the other hand, it is the cheapest most realistic proportionate and accessorized pilot available, being hand painted and delivered wearing a hat, sunglasses, a wrist watch and reasonable fabric seat belts with plastic buckles.

The only drawback was that you couldn’t change his stance because of the rigid material. I would have preferred him to sit more upright instead of having a posture more adapted to modern gliders, but I could live with that. Installing him in the front seat for fit, I discovered its size to be perfect (for a quarter scale glider), but there was no way I could get his right hand around the stick. His upper legs prevented the his right arm to be further lowered to grab the stick. I got around the problem by increasing the stick length at the bottom (completely hidden from view through the soft bag around the base, and changing the arm angle. When I put the knife in between his sleeve and arm, I was surprised it came off so easily, but that was because I had by chance made the cut at exactly the place the separate polystyrene parts had been joined by use of a toothpick (the head is mounted the same way and can therefore be oriented better by varying the neck angle). After cutting off a triangular slice of his arm, I could reposition the toothpick and glue the arm to the sleeved part at the correct angle so the hand fitted nicely around the stick. The triangular slice was used to fill-up the join void, and the picture shows the result before painting made the surgery almost invisible. Some glue between his arm and leg made everything rock solid.

Pic pilot change 3

I glued a small strip of Velcro to his derriere, which allows him to be very easily removed for battery change or access to the main power switch when his seatback is folded down. His small mass of only 45 gram and minimal head to canopy clearance ensure the little bit of Velcro plus his hand slit around the stick, are sufficient to keep him in in place even during aerobatics. Because of his body to leg angle I had to leave the back parachute out, but retained the cushion he is seated on, this brings him to the correct head height as per full size Blanik glider pictures.

Pic nyflying18

I choose not to modify his left arm for it to grab anything, this would only complicate the frequent pilot extractions or installations. In this position it looks like he is fully ready for a start and is looking at his watch for that towship to be finally ready to take him airborne. That is also the reason why I turned his head slightly to the left, then allowed expanding glue to drip down his neck to firmly secure the head to the body. With only the toothpick holding both together it was not possible to take the pilot out by his head. The overall aspect of the front cockpit got a major improvement by that pilot change.

Pic front pilot change 4

Pilot and instructor now appear very realistic and scale. Replacing the back seat instructor could be a future option, not so much for size, but it would save 180 gram total weight Without affecting the CG. I could then use those heavier pilots in gliders that have a need of additional ballast at the front. I still hesitate because I probably would have to modify the face of the guy in the back so it doesn’t look like identical twins flying around in the same glider.

To compensate for the 30 gram weight save of the front pilot, I decided to install the much needed small plate at the underside of the front fuselage (as per real Blanik). Most people don’t realize, but a Blanik had a (semi) retractable wheel. You can clearly see on pictures of the real glider that the wheel is only half visible under the fuselage (takeoffs are mostly performed with the gear up so it doesn’t leap off prematurely in the air when towed by its low position towhook in a higher alfa ground stance. For landing, the gear is normally full down for additional ground clearance (wheel totally exposed is not caused by extended oleo spring). On the fixed gear model, the wheel is fixed at just over half an exposed wheel height. With my model being on the heavy side, it has to be landed at a rather high speed. Combine this with the lower body angle due to the full flap extension position, and the front part of the belly comes dangerously close to our highly abrasive tarmac runway (I already had it scrape momentarily at touchdown). In order not to cause permanent damage to the belly, the real model got equipped with a replaceable (wooden?) cushion-like appendix at the spot where the fuselage could touch. The solution I found most practicable was to mount a slick grey Teflon plaque normally used under chairs to make them slide silently over floors. As a last aesthetical enhancement I added the standard real world piece of tuft with adhesive to the windscreen. This is used by the pilots as an indicator to apply the necessary foot pressure on the pedals to keep refrain gliders from sideslipping during turns, the minimal deviations being much more pronounced when the piece of tuft deviates from the middle, than from looking at the ball on the instrument panel. The latest frontal look with the vent windows half open, the red tuft on the windscreen, and friendly happy pilot looking at you before consulting his watch, is just stunning.

Pic front pilot change 9
May 18, 2016, 05:10 PM
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Minimal flying in 2015

As described elsewhere on the blog, in 2015 I made the switch from Spectrum to Taranis/FrSky electronics. During Summer it was the turn of the Blanik to get the update and I chose to install two X6R receivers under the cockpit floor, together with a high precision vario/altimeter for the telemetry smart port. For redundancy I opted for each the dual elevator and each dual aileron servo to be mounted on a separate receiver (hopefully allowing sufficient control for an emergency landing). To avoid dramatical asymmetrical conditions, both spoilers were hooked on one receiver while both flaps were together on the other receiver

The post june 2015 configuration comprises following electronic elements:
-Spoilers: 2x Robbe Futaba S3001 2,5kgcm
-Towhook: Futaba S3010 5,5kgcm
-Elevators: 2x Futaba S3010 5,5kgcm (eventual to HS5645MG?11kg)(HS645BB/MG 9kg)
-Flaps and roll : 4x Hyperion HP-DS20-UMD dynamic 13kgcm , holding 23kgcm
-New Graupner battery packs: 2x5 NH 6V2600 mah in pack 7x5x3cm 300gr
-FrSk: 2x X6R + high precision vario
-EasyPatch 12-2 dual battery feed and connectors

Blanik 2016 reinforced 4

Needless to say, the programming on the Taranis transmitter was completely different but thanks to the excellent Open Tx Compagnion feature on the PC, I could visualize every control deflection on the screen, thereby avoiding the nasty surprises I encountered with the Spectrum flight modes versus flap -elevator mix. For the flight-test I hooked up behind Benny's Calypso 62. Because we had to wait for a landing glider, his engine ran idle for a long time and although up to liftoff the acceleration was normal, the engine then had a very long power loss instead of rapidly clearing the hiccup. As we couldn't climb any more and both risked ending up in a tree-line about 300m from the runway end, I decided to release and attempt a 180° turn. Just after the separation his engine picked up and all pilots and spectators watched in awe how I barely avoided the trees during the turn that was performed at no more than 3 meters of altitude. Thanks to the tailwind I was able to stretch the glide back to abeam the runway but elected to touchdown in the grass instead of landing on the tarmac because the drag was higher and allowed me to stop abeam the point I had initiated the takeoff roll.

I can assure you that I was rather shaken by the occurrence, who would want to perform such a critical maneuvers with an 11kg untrimmed model you hadn't flown since 10 months? Luckily the second flight that day was uneventful and a CG dive check was performed as well as an evaluation of the flap-elevator mix. After the landing I left all the trims in their flight positions so back home I could make the mechanical adjustments to further refine the glider around the zero trim positions.

Bad weather and a lack of sufficiently powerful tow aircraft prevented me from flying my Blanik till some late Indian Summer days during November. Due to a too short tow-loop the deeply buried hook could barely be engaged and around 80m altitude it got disconnected. I started getting used losing the Calypso62 during tows, but this time at least it happened at a comfortable downwind altitude so half a pattern later I touched down early on the tarmac with full spoilers and stopped just before the end. A longer nylon loop solved the problem and during the second flight I tried to keep up with a couple of 6m span pencil shaped gliders but I fell through and again recovered with a super-smooth albeit fast landing, again using full spoilers at touchdown. It was only after I dragged my Blanik back to the startline that I reflected not having used flaps for landing on this almost wind-still day.

During the third flight I thus made no attempt to catch the very weak thermals but started straight with partial and full-flap cycles to get a feel of the necessary elevator inputs on top of the still intermediate flap-elevator mix. No correction was needed for movements up to takeoff flaps, but a pronounced ballooning had to be manually compensated between the takeoff and land flap range. In baseleg I lowered the takeoff flaps and after rolling out on final I selected full flaps and pushed the nose down to maintain the glideslope. In short finals I slowly added spoilers and all seemed super steady and on the groove with a normal speed for a perfect touchdown. About 5 meters from the threshold at an altitude of about a meter, the left wing abruptly dropped and caught the grass, causing the model to spin around and stopping dead on the track with the impact of the starboard wingtip and elevator in the soft grass just a meter short of the runway.

As I recovered the model I noted the tailwheel skid had separated and the plastic tailcone was dangling due to broken wood tabs, the right tiptank showed multiple fracture lines, and the stbd elevator pointed more down than the port one. For the rest the Blanik looked intact, a tribute to the sturdiness of Heike Baumgärtner models. Other pilots had seen the mishap and all were surprised about the stall at what seemed like adequate speed at that time. It is only then that I realized that due to the very little flying after the receiver change, I still hadn't performed stalls with the now increased full-flap deflection angles, and close inspection also revealed the port flap to be a tad more down than the starboard one when fully extended.

Back home the detailed inspection revealed no other structural damage so I started the straightforward repairs. The stbd elevator must have impacted pretty hard because I had to remove the piano hinge of the hollow pivot to get things in place again, which automatically aligned both elevators again. Epoxy was used to glue the splinted stbd plastic tiptank together, and after some filling, sanding and priming, it got a new paint job and passes visual inspection well. I electronically reduced the maximum flap deflection angle and following the recommendation of our most experienced club glider pilot, I mixed up-ailerons to the full flap deployment to reduce the tipstall probability. As this might also compensate for the ballooning, I didn't dial-in elevator mix. I also made adjustments to the towhook mechanism and used a flashlight to check the rigidity of the long pushrods in the fuselage. As the model flew perfectly in the thermals and pattern, I kind of reverse balanced it and found out that the CG was at 72mm from the leading edge, so I made a permanent mark of this on the fuselage. Flight ready weight was measured at 11,2kg and the wing load therefore calculates at 98gr/dm². That figure also explains the need to maintain speed on final until touchdown.


Unavailability of strong towships and suitable weather caused the first 2016 flight of the Blanik to be made at the Biggs gathering at Tongeren, my second club in which I hadn't flown yet except for the maiden of my Piper Super Cub. With only a couple of flights in 2015, my currency and confidence for the Blanik were at an all time low. The wind blowing fully cross at force 3 during the 4 days of the gathering wasn't helping much either. Once the ice had been broken I managed 5 uneventful flights needing less than half the runway to land with various flap configurations. I was very glad to discover that my reprogramming of the flaps, ailerons, elevator mixes and crow function for full flaps, produced the desired results and after some more elevator mix refinements, finally produces a super steady glide angle that doesn't need any pitch changes whatever flap or spoiler deployment I select. Another experienced club member suggested me to fly the Blanik faster at altitude and that made it really rock solid in the thermals. It is a huge model that makes large turns at speed, but I soon will start exploring the possibility of tighter turns using takeoff flaps. My confidence grew with every flight, but all that refining left little time for catching the rare good thermals, and none for aerobatics. My recent purchase of that expensive 30cm Shambeck outrigger wheel proved its worth, this was much more handy and wouldn't cause further damage to my wing surfaces.

On day 2 when after an excellent landing I had to quickly vacate the runway because 3 other large gliders were also dropping back in. I ran to the Blanik with my outrigger wheel and tow leach, hooked it all up, looked in final and saw I still had the time to cross the runway. Unfortunately, pulling the glider 90° away from its landing direction with the leach, caused the tailwheel and lower fin to again separate from the aft fuselage. I put it in my pocket and that meant end of flying session. After turning the Blanik upside down and inspecting the damage I got some club members offering me the help into first preparing the surface (some of the lower fuselage was still hanging solidly on the fin), then mixed very strong UHU glue which we kept it under pressure for about 10 minutes before leaving the repair to dry in the hot sun for 3 hours. That repair held well but back home I removed the tailcone and saw that the cause of the recurring break-offs was that I used a wheel that increased the leverage that the thin aft fuselage underside couldn't cope with (see pictures on previous entries).

I decided to keep the exterior repair, but scraped away all previous attempts to reinforce the interior walls, plus carved a 1cm thick balsa block to hug the fuselage bottom. I then applied a liberal amount of PU glue on that block and stretched a polyester cloth over it. After a bed of PU glue was laid down in the fuselage, I pressed the block and cloth into it and held it with clamps during the drying. Triangular balsa sides were then added between the top of the block and the walls to further spread any lateral forces over more than half the circumference of the delicate aft fuselage.

Blanik2016 reinforced 2

The assembly is now much more rigid than before and lateral forces by the wheel don't bend and crack the vertical thin vertical aft fuselage anymore. It still isn't perfect, but I want to first evaluate the results after a few fore flights before going any further. I also added to my checklist to raise the tail during sharp turns on the ground. On previous picture you see copper tubing, this had nothing to do with the tail, but are the remains of a much bent 6mm tube that had been installed (straight) by the builder between the aft wing pins to serve as a hold to maintain correct wing incidence , but also as a an anti-compression aid if the wings got aft forces during impacts. I remember having straightened out the copper tube after trying to push the wing pin in while not lined up correctly. This probably forced the the copper to bend in between the liberal carbon fiber applied by the builder around the extremities. A forward compression obstacle had never been installed because it would interfere with the scale cockpit above the back seat.


In this picture you see how the 43cm long wing root is held tight against the fuselage. From left to right: the forward incidence pin only penetrates the copper guide for a mere centimeter. The cg mark at 72mm (but remember the forward wingsweep), next the hole through which the wing fastener is inserted and screwed from within the cockpit. Then the round carbon tube through which the wingspar joiner slides. The next round hole has no use. The rectangular hole is where the green Mpx plug sits after the wings are in position. The last hole by the trailing edge is the one where I removed the copper tube from. Note that that hole is 33cm (more than a foot) from the canopy opening, and the vital structural plywood former at the CG limits access to the aft fuselage even more.

I nevertheless realized the importance of a strong compression crossmember between the aft wings in case I would hit something again. Those forces now had to be absorbed solely by the GRP fuselage, with an unacceptable risk of fatal cracks. I therefore took a 10mm hardwood dowel and cut it to length to fit between the vertical GRP walls behind those aft holes. I also drilled 5mm holes in the wood extremities to accept the wing pins. Getting rid of the clumps of polyester that held the copper tube in place was impracticable from the inside due to the depth. A first attempt with the Dremel grinder proved dangerous and lots of chances to hit thin places that had to be left intact. I thus used a regular 3mm drill that I inserted from the outside at various angles through the existing 5mm aft holes to slowly punch away the material behind the hole. It was a tedious job but I got it done. Trial fitting of the dowel hurt my hand scraping everywhere on the inside fuselage, but proved the concept worked. After taking it out I applied a liberal amount of PU glue on its extremities before pushing it back into its final place. I trial fitted the wings before the glue dried so I was sure the holes for the pins lined up correctly. With the dowel only 15gr compared to the 13gr for the copper tube (not counting the polyester lumps), my solution adds tremendous compression strength spread over a larger surface of the aft inner strong wing ribs, at little or no weight increase. Following picture shows the wooden dowel glued in position between the remains of the polyester on the left and the cleaned right (of the picture). The fact this is 33cm deep into the aft fuselage does not show well, but the limited space for my hands through the first frame does.

Bl2016 reinf 5

Whilst everything settled and the aft pilot and seat was out of the fuselage, I took the opportunity to check all the connections of my aft 6 channel receiver (another one sits under the front seat), the telemetry and the variometer, all being completely hidden under the floor under normal conditions. A check was also made to confirm the very long (140cm) tube-in-tube Sullivan Nyrods were still rigidly attached over their complete length (the 2014 disaster was still in my mind). Another solidity problem I tackled was the canopy that only held on one side by two hinges, and on the other side by the single closure lip. The front and back of the 35cm long canopy at the port side therefore had lateral play just sitting loosely on the flat rail, all the burden fell on that single lip. I decided to add two 2mm pins that I glued in the canopy corners (as can be seen on the picture of the wing root, and engage into two holes that were made in the fuselage part. The previously incorrect geometry will slowly (by time and heat) be corrected but in the meantime it needs some pushing through the vent windows to allow both pins to engage the holes. When everything is closed and latched, the canopy now is flat with the front and back bows and has no more play. This provides me more confidence for performing stall turns and not losing the canopy during incidental spins, both maneuvers causing significant side forces to such a large canopy.

My Blanik is now ready and fully trimmed for the 2016 season. So far lack of confidence (in myself and the model) caused me to only fly it under ideal circumstances. The recent flight experience and work hopefully will allow me to fly longer trouble free periods under more diverse weather conditions. It still is an eye catcher on the ground at every show I attend, I hope to soon be able to perform some elegant maneuvers closer by, in the air as wel.

In June I drove to Wey in Germany where they had a week of towing. That is where I really developped confidence and proficiency in my Blanik. I made about 8 flights with it, one of 28 minutes during which I regulary had to perform aerobatic maneuvers in order not to bust the strict 300m altitude limit and from which I landed prematurely due to a verbal clash with a local member.. I couldn't believe how wel that heavy Blanik thermaled. Whatever the wind, I always made good landings with whatever flap settings. The tailwheel also held wel. Later in the week more and more pilots came to the event and I left because of the crowded very limited airspace and unrational authoritarian behavior of the "flugplatz fuhrer".

I also got ired of mounting and dismantling the 3 models every day so they fit in my camper. I actually had to sleep carefully next to wings and fuselages whilst I saw others stowing their models in large garages of more recent campers. Such large gliders definitely require adapted transportation so a camper change was initiated a week later.
Last edited by BAF23; Jul 05, 2016 at 08:31 AM.
Apr 30, 2019, 11:25 AM
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2019 Mid-Life Update

During 2016, 2017 and 2018 I often flew my Blanik at various airfields and it always was a pure joy, for me and for the bystanders. The more I flew the model in 2018, the more I lost faith in the (even replaced) NiMh battery setup, mainly because of the heavy servo load and the lack of reliable capacity measuring. As after the season I had to also replace all my receivers (because I finally switched to an EU LBT transmitter), I decided to throw everything out of my Blanik and replace it with state of the art electronics. I first removed both seats, both instrument panels, the canopy, the old expensive dual-power distributor that was limited to 5,5V, the antenna’s, the variometer and its wiring, all the removable lead, all the wiring specific for the old power-box. The battery box in the nose being completely surrounded by solidly fixed ballast, limited the use of replacement batteries. After much searching I finally found a pair of LiFe batteries that fit exactly into the space of the old NiMh packs.

Although these batteries came with regular green MPX plugs, the balance plugs were incompatible with the rest of my plugs or boards and had to be altered. These new batteries had to be inserted one behind the other but as the wires then were at the sides, I had to make a slit for them to allow easy insertion and extraction under the instrument panel. One of the battery balance cables is connected to a loose mini voltage sensor and then stuffed with a battery connector cable behind a simple gravity type lip that keeps the anything from creeping out of the box even under serious acceleration and climb angles.

Pic 4888cr

As I had removed the instructor pilot from his back seat (to use in my Göppingen4-3 glider) I decided to install a Graupner PRX-5A-HV stabilized receiver dual power supply discretely along the back seat but under the floor, with only the operating switch protruding and the 2 control leds hardly visible to unalerted lookers. This was much easier to operate than the previous system that each time required me to take the front pilot out and pivot the seat-back to operate the battery switch. The 6,6v of the LiFe batteries are now reduced to 5,9V (due to servo-voltage being limited to 6v) and each separate output cable is connected to separate receivers. The primary being an vario-integrated FrSky G-RX8 commanding the right elevator, right aileron, rudder, hook, right and left spoilers. The secondary a simple XR6 operating the left aileron, left elevator, left and right flaps. That setup should provide sufficient redundancy for failure of individual systems.

The new setup was incompatible with the old wiring so new wires had to be cut and plugs soldered on. This could only be done correctly after the MPX plugs in the wing had been removed to notice how it had been wired internally during the initial build. Next I copied the pages of old Taranis transmitter setup and adapted all settings for the newly distributed 10 channel setup with all it’s complicated mixes, plus max allowable throws for the powerful servo’s. The new EU-LBT transmitter was then manually programmed, hours of work. After binding both receivers and connecting them through S-bus, I labeled all the servo wires and connected them to their respective receivers. After all wires were routed, the receiver’s antenna’s were slid into the pre-glued plastic tubes that had been installed at 90° angles.

Pic 4883

Wings and horizontal tailplanes were then mounted so a full check of the system could be made before reassembly of the forward compartment. Due to lighter batteries and no more power box, I had to augment the lead ballast from 175 to 325gr. Total weight decreased to 10950gr and wing load to 96gr/dm². It took me 33 hours to perform that midlife update but I end up with a model that I trust a lot more than before.

A first post-update flight was first conducted at Pampa but the real fine-tuning flights were made during the following days at my club in Tongeren and at the BiGGS meet at Odoorn, the latter under very windy conditions operating from a 64m grass cross-runway. Even performing aerobatics and fighting the turbulence, my battery consumption was less than a quarter after an hour’s flying. That was a huge improvement over the previous setup with the NiMh and the powerbox. I experimented a bit more with the CG until I found the sweet spot which allows me to complete the rest of the season in full confidence.

First landing at Odoorn under strong wind, hence the takeoff flaps and relatively high speed
Pic odoorn 194
Jun 02, 2020, 07:59 AM
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Thread OP

Technical recap for my HB 1:4 Blanik

Dimensions: L:218cm (215 with tailcone pivotted) , span: 406cm, height: 57cm, single wing lengths: 193cm
Ballast: 415gr: batteries: 2x98gr 2S1700 LiFe
Total weight including ballast for 68mm CG: 11040gr
stab: 390gr (total incl keys), Fuselage: 7000gr , left wing: 2108gr, right wing: 2110gr
CG: final 68mm
My final throws: Ail: +40 mm -25mm, Ele: + 50mm -45mm , Rud: 95mm L&R
Servos: Elevators and rudder: 3x Hitec HS645 MG.
Ailerons and flaps: 4x Hyperion DS20UMD digital
Spoilers: 2x Futaba S3001
Hook: CYS-S0150 analog 15kgcm
Mixes: 10% down mix on elevator only when flaps at takeoff position
30% up mix of ailerons when flaps selected fully down (reflex crow)
Expo: Rudder: 30%, Ailerons: 20%, Elevators: 20%
Last edited by BAF23; Jun 02, 2020 at 11:58 AM.

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