Bidirectional Differential Balanced Control

BDBC or Bidirectional Differential Balanced Control is similar to hang gliders because of its control of center of weight, thus the angles of pitch and attack.

            During vast outside disturbances or during landing, I work symmetrically with both semi wings and that’s why landings are like with hang gliders.

            The new thing, unlike hang gliders or CAGE is the ability to control each semi wing separately.

            The newest thing is that we found the “tunnel” (or fluger) turn – rotating the bars around their vertical axis changes the angle of attack of wing tips ( sideslip angle for the whole wing is AoA for the wingtips because of its arc shape ) and it appeared to be quite effective way of turning. The standard paragliders have similar effect by the use of small rings at the trailing edge, which convert the downward brake lines pull into sideways inward pull increasing the drag (like a pocket) and wingtip profile curve, instead of working with the entire AoA of the wing tip as we do.

            It was quite turbulent on landing during my first cross-country flight from Bekleme to Moskovets. I tried to use the classic paraglider brakes then but didn’t find them much effective. So far, BDBC didn’t made powerfull selfindiced overshoots leading to a collapse, so I didn’t have to stop something with brakes, but working only with bars for increasing of angle of pitch was enough.

Maintaining low angles of pitch and attack by pushing the back part of bars up for long time is tiring, so I have to add something like a speed bar operated by the legs. It’s inspirational to be able to control the whole flight with your whole body, with every bit of muscle, not just a fat ass as baggage.

The idea of BDBC came entirely from the Master (Nikolay Tsarov), as his other numerous experimental models, which he made to test the theory we work on (not looking for a superwing).

By the way, flying BDBC made me understand and fly better the standard paraglider…


30/05/2019  :


In the launch brake, when it became too strong for students, I managed to do my second cross country flight with BDC.

A classic trip to Ravnets and back with low cloudbase and nice thermals. BDBC was stable without any collapses. No self-induced overshootings – it seems that the double triangle or the probable S shape from the decreased profile curve worked well.

It was interesting to feel how the push of the thermal travelled along the chord. Despite the bars hardly moved, I felt the difference of force in their frontal and rear part. It’s like flying by holding the wing chord in your hands.

The most effective thermalling technique so far is with outer wing induction and inner wing tunnel/fluger turn.  Further on, I should develop a technique for further tighter turning of narrower and evil thermals. Tight flat turning with a standard paraglider brakes is in semi stall mode and probably with increased sink through the air. It will be difficult to apply this with the BDBC because its idea is to fly further away from stall and slow flight.

The direct speed control is very pleasant, because a passing gust, when using classic paraglider brakes, we have this annoying loss of airspeed, drop and waiting and waiting for self-recovery of airspeed and you cannot do anything about it. With the BDBC, you can dive and accelerate after the gust and with a surprisingly little height loss you continue forward. I’ve flown around good hang gliding pilots and I wondered how they managed to deal with difficult thermals, despite their higher speed and radius of turning. And now with BDBC I start to grasp their technique and advantages.

My landings also become more like hang gliding type. Yesterday, wind suddenly switched to NE on landing and by using a deep turn I managed to accelerate and achieve a nice long round out and hold on. Probably my last year gliding experience had its role.


30/05/2019   :


Smooth evening flying after work ;-)

First entering inside the mountain, first cloud flying, first triangle.

Tests: when converging the back part of bars (rotation of 50-60 degrees), there is a light increase of airspeed from 34 to 37 km/h. When diverging them, the speed decreases to 32 km/h.

As the axis of rotation is somewhere between the front and back part of bars, then, when rotating their noses outside, the inner A’s loosen and outer A’s tighten and vice versa.

Nice pitch and rolls.



02/06/2019   :


The first flirt between BDBC and CB and lamb soping at Pevtsite restaurant. The cloud was growing lazily over Karlovo, but when cumis poped up under the main cloudbase I thought how much more impudent should I be.  I couldn’t figure them out, but once I saw the rain curtain over the middle of the flats, I understood that the machine is on. A billow of rolling clouds formed under the main cloudbase, connecting Stara Planina mountain and Sredna Gora mountains, which made me withdraw diplomatically westward, where the orographic cap was visualizing falling north winds. This kept me calm because falling winds suppress cloud production. Still, it was better not continuing toward Klisura, as I would had been trapped at the end of the valley and later the cloud quickly came and re-developed there. The CB gust front combined with the falling north wind (the geostrophic for the day was moderate NE). Then I landed vertically within the falling north wind and 2 minutes later, the gust front hit from East. Then heavy rain with hailstone, but my bro came first.

            I didn’t have much worries throughout the flight, because I judged well that the speed of the rolling billow cloud (and the corresponding gust front bellow) is slower than my ground speed ( I think that Cb’s coming from East are held and fed more by the terrain and accordingly slower than the CB’s coming from West). This particular Cb had many cells in its frontal part and early stage and again I understood how important is to keep calm when you enter stronger and stronger climb, until you lose nerves and start spiraling there. The embedded cells of instability were big and distinct, so you can go back in the previous weaker climbs or to fly around and find other weaker climbs where to spiral. Otherwise, you won’t stand the G-force long, if you spiral in strong lift. The G-force is a function of time. You can stand 10 G, for a fraction of a second, but if you need to spiral for minutes, even 2 G is enough to blackout.

            Additionally, I didn’t have worries, because yesterday I made my first BDBC controlled spiral. The Master is again right, as for years he was telling me about the role of pitch for spirals. So, for the first time I managed to control a spiral by the pitch and unlike brake control, which goes through secondary processes, the BDBC produced direct and very precise control over the spiral and the G-force. May be we still don’t aware what treasure we found.


06/06/2019   :

video from the second flight. A nice spiral with precise tangentor control ;-) and landing in light drizzle


07/06/2019  :


Humid and turbulent conditions with torn thermals and ragged cloudbases:



09/06/2019  :

 - climbing in front of the rain under the rotor clouds in front of take-off. It was turbulent after the take-off, but further out the moisture stifled the things and there were nice climbs triggered by the falling winds and nearby rain.  


 - simulation of collapses. The frontal didn’t happen, because the range of pull was small and restricted by the short A riser. On my second attempt, the left wingtip collapsed and stayed like this for a while, which is a sign that it worked at lower angle of attack and had lower pressure and air mass inside. Harder pulls and real collapses are needed to check better the front collapse behavior.

            Asymmetric collapses tend to be bigger than what I usually pull and enters a spiral, which I have to stop (unlike standard paragliders, where there is more drop than turn), probably because of bigger freedom of the system. There is also a tendency the collapsed side to enter and cravat into the lines, because the space in between them is bigger from the whole BDBC construction itself.


 – a landing with a view from behind. There was a wind gradient (0 at ground and 4-5 m/s at 30 meters above), but I didn’t felt it because of the ability to accelerate the wing with the BDBC system i.e. I didn’t go through a speed loss and had the next classic hanglider style of landing.


13/06/2019 :


It’s harvest time!

It turned out that I can fully use BDBC during my paragliding work – except when pilots which I guide are too picky and fussy. I even rose their interest and they didn’t mind to compare each other in thermalling.

But my cross-country flying was too fast for thermalling comparison between BDBC and standard paragliders. Still, I managed to fulfill my duties and guide them to the fish restaurant and with the extra height I got there I tried this or that.

In kiting and in flight, the pull of A risers for collapse causes distinct acceleration of the whole wing forward, which hinders my simulation. I had to pull harder, but even then I didn’t reach a clean frontal collapse, but something like 70% asymmetric with a spectacular throwing of my body sideways and a beautiful recovery. I don’t know how further should I pull, but I feel I’m close to the twilight zone and I don’t have a second rescue, a cup of water underneath or at least a juicy forest. 

The acceleration of the wing forward when pulling the A’s confirms the preservation of speed when entering a thermal – unlike some standard paragliders, which ricochet in it, lose airspeed, drop down and after a proper entry in the updraft, they bite the flow and go forward. The previous 2 days I flew with my Omega and indeed, the BDBC sharpened my senses and understanding of flying with a standard paraglider, which is a clear gain – even if BDBC doesn’t turn into a super wing, it is beautiful and suitable as a learn to fly device. As I flew the Omega in weak conditions, I noticed how much efforts, attention  problem, but I wish tighter and flatter turns.

At the outermost 3-4 brake lines I connected an additional line in order to work only with outermost wing tip (I removed the inner 1/3th of brake lines of my Omega and this is quite good for thermalling. The rest 2/3rds are enough for stopping symmetrical overshooting forward. I recommend you to get rid of wing’s brakes and brakes in life as well. Or at least from part of them ;-) It turns out that the combination of a tunnel (fluger) turn with inner bar and outer wingtip brake is so efficient, that it directly enters the wing into a spiral (it takes time to develop with standard paragliders). The reason is that the wing works fully and there is no killing of speed by brakes like with standard paragliders.

So, I grab with full hands and there is something new every day. I try to use the humid conditions at maximum and gain experience, as I don’t know how easy BDBC will be in dry and evil thermals later. And soon picky groups are coming, so I don’t know if I’ll have time for experiments.

I feel how flying the BDBC leads to accumulation and awareness of the flight, but their meaning will come with time. The more I know, the more I realize how little I know :-)p - thermalling - thermalling - gliding, a side view – light twists – trying of tunnel (fluger) turn with inner bar + wingtip brake (a side view) – pitch up and pitch down (side view) – frontal, asymmetric, stall, spiral, slalom – pitch up and pitch down (side view) – landing – side view



13/06/2019 :


On my second flight, I managed to thermal with another pilot with Advance / Epsilon 7. It was weak, but we managed to take a climb to the cloud base from 150 m above the center of Vasil Levski village. Despite the lack of vario, I managed to out climb the Epsilon and catch up with Christo above, but it might be because I’m slightly lighter on my wing. So, more comparison flights are needed to confirm or reject that the BDBC is more efficient in thermalling than standard paragliders.

            When Christo managed to fly above me, he confirmed that there is a noticeable wrinkle over the D line, which is logical if D lines are loose with about 3 cm. This wrinkle and the rise of the tail are signs of S-shaped profile and this is the possible reason for the pitch stability when encountering a thermal. Later on I may remove the wrinkle to see if there is a change of the wing behavior. I still suspect, there won’t be change because the longitudinal self-stabilizing is more because of BDBC work itself.

            Over the fish restaurant, we made a nice sincro spiral with Christo.

            Video from the landing. It was in wind gradient and I overdid the acceleration:


14/06/2019 :


My most dramatic BDBC take off, just before the coming of north wind on take-off. It lifted me up with the rising of the wing and threw me sideways toward the cable lift. I thought it was a dust devil and let it carry me along the flow, but also managed to direct it outside the mountain. Then upward, upward and upward. I don’t know how it didn’t collapse. I didn’t know if I did something to help or it was just my holding of the bars (working like a damper). I was either lucky or the BDBC somehow has a high resistance against collapses. Still, from the collapse simulation before, I understood that they can be serious. I can have tens of beautiful flights and still there might be a beast sleeping on my shoulder, which can wake up in a very specific situation. Meanwhile, I imagine the future of paragliding toward a partial autopilot system, which can enhance safety and performance by working the micro and macro outside disturbances… similar to those robot shells, which amplify the movements of the human operating them from inside… but here, the pilot continues to act as a pilot, but the system takes care of the things he doesn’t sense or understand…

            After I moved away from the mountain, conditions calmed down. Over the center of Karlovo, I climbed in a linden blossom smelling thermal and found out that the pilots I guided, had already landed, so I flew back to Sopot. It was turbo again there because of the falling winds. I wanted to land next to the railway station, but the north wind broke through , the factory was vomiting thermals and the down sloping terrain additionally was turbolizing them. From time to time I was being blown back. Even with a classic paraglider, the landing wouldn’t be comfortable, so I turned and nested myself in the heart of a bigger and more aggressive climb and drifted downwind with it toward the calmer air further south.

Later I had a muscle fever in my shoulders. Hang glider pilots also complain about shoulder pain in bumpy conditions, despite that here we’re in a more comfy sitting position. At one point I even got tired to fight with the conditions ( I even though as a joke isn’t it better to throw my rescue, to have less job and fear recovering the wing from this or that) and continued to control only with one hand, only the tunnel turn. Now, I understand why at the beginning of aviation, the pilots, except smart also had to be physically strong. But as I continue thinking, it might turn out that the fight is only with myself, only in myself. BDBC gives so much options for control, for a full participation in the flight, that the pilot might be super busy, more than acro, speed and base jump guys. At the same time, if the inherent stability is studied and understood, then the pilot can be relieved to control everything and still keep a full participation in the flight.


27/07/2019  :

First BDBC top landing and first out and return flight (to the fish restaurant and back).

Despite the slow crossing of gorges (I still need to find time to install something like a speed system) it turns out that I still can do my paragliding guiding job with BDBC and even out climb some pilots in the thermals. I had time to speak on the radio, though I’m less relaxed compared to a classic paraglider. I suppose it’s a matter of time until I got tired of fear. BDBC gives much more opportunities for control and this requires a lot of concentration.

The goals of this flight were to see BDBC behavior in strong summer conditions and compare its thermalling with classic paragliders.

I had 2-3 asymmetric collapses of 20-30%, but without going into a turn. There were not overshootings forward, probably because of BDBC construction itself or/and because of (S-shaped) profile because of separated attachment points.

I felt an increased resistance against frontal collapses, which is confirmed by the collapse simulations during a previous flight.

During thermalling I managed to outclimb Godfrey with the BiBeta 6 tandem and another pilot with a pod harness and EN C paraglider, but I don’t know if it’s because I know local thermals, because I have better thermalling technique, because I’m at the bottom weight range of the wing or because of BDBC itself. I need much more comparison flights before I reach any conclusion.

I miss those tight flat turns, like with the standard paraglider. My landing approaches also require slightly more space, because I cannot play with the stall and turn tight. Instead of tight flat turns, BDBC makes bigger turns and always with some bank. In big thermals I’m competitive, but I suppose in tight thermals and cores a standard paraglider will climb better. Still, thermalling is a pleasure – as I see the out wing to lag behind, I push it forward and reacts instantly. Also, when I see that I drop off from the core, I turn the inner wing with a tunnel (fluger) turn and it turns the whole wing tighter. Like a director, which conducts the whole orchestra – I just point somewhere and music comes back (vario music, wind, accelerations :-) When an ex-student saw the BDBC, he supposed to name it “marionette”. One day I may get promoted to “Master of puppets” rank.

And the best thing in thermalling or gliding is the ability to restore decreases of airspeed. In hairy thermals and turbulence, there are no more those annoying drops and waiting for the paraglider to start working again and move forward. This, except the efficiency of the whole wing (lift force and maneuverability) will allow me to harvest the onion flakes.

Have you noticed when gliding, that sometimes a light push of the speed system makes the wing accelerate unusually well for a long period? How it glides faster and better, than with the same amount of speed system in calm air. I think that the air is more flaky and grainy than we think and sliding (surfing) a certain layer gives noticeably better speed and performance, compared to gliding few meters higher or lower? This flakiness/layerness exists not only during glides, but also in thermals themselves and BDBC is the way to move along the fluid streamlines.


29/07/2019  :

A good turning in strong thermals, which kicks would consume the speed of a classic wing, but BDBC kept gliding forward or obeyed my commands. The good image of thermals I’ve developed through experience was very useful for avoiding their turbulent edges.

On landing, the wind surprised me and I landed with about 1 m/s tailwind. The ground was coming fast, but accelerated the wing even faster to produce a good flare and after a sharp slide through the grass I landed well. Still, it’s better for experimental flights in future to use good boots, instead of my cross-country sandals.


Take off:  ,

Passing by:



06/08/2019  :


Another good BDBC performance in strong summer Sopot conditions and juicy clouds. This time I was with a pod harness – Impress 2, which increased my trim speed with 1-2 km/h.

Again, good thermalling and outclimbing other wings. I had few powerful and long lasting climbs of average 4 m/s and it was pleasant to sense uninterrupted speed and maneuverability. Often, in such strong thermals with a classic wing, I have the feeling the wing stops flying forward but goes up as a piston in a cylinder; maneuverability decreases and you can easily drop out from the thermal, despite its significant size and strength.

It was the first time I started crossing Dzhendema (Hell) with such low height (around 1600 amsl), but the conditions were generous and the BDBC managed the complex climb. Further east, toward Tazha roseberry fields I lost height and noticed some minor deficiencies – BDBC is still less maneuverable than classic wings with brakes, so I couldn’t turn that tight to avoid sink. Also, the slower speed of BDBC was reducing the search ability of bubbling lift. In zero’s and weak climbs I wish it turns flatter, because its turns are always banked, while classic wing with brakes and opposite weight shift allow for small radius turns with minimum sink. In this particular case, the bubbling lift with around zero climbs was big enough and I managed to reach the cloud base again. 

Another adventure were the hills between Kalofer and Vasil Levski, where I was nailed down by a – 4 m/s and head wind and at one moment I realized that, it will be hard to do precise landings on handkerchief size meadows inside the forest i.e. the reduced maneuverability and play with the stall will restrict my landing options and thus mine insolence my roaming and searching for thermals here and there.