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Thread: FPV for 7 hours thermal soaring

  1. #1
    Forum Member
    Join Date
    Aug 2014

    FPV for 7 hours thermal soaring

    Hello colleagues,

    As I was able to enhance my personal best to more as 7 hours during practicing of thermal flying, I would like to share with you story of the Fascination to this flight time, including my mistakes and failures – mostly stupid.

    First idea of thermal flying FPV has come with the legendary flight of Roberto Montiel in 2012, in same time when type of full-scale glider I was flying in club had been grounded by EASA. In job I was busy too and was not able give all my time as slave of weather to full scale gliding. Therefore at that time I was searching the possibility to fly similar as full scale, Roberto Montiel has proven, that its possible.

    The selection of airframe was relative simple: local supplier, fair price, proven airframe – Fascination from TopmodelCZ.
    In order to do not „invent a wheel “, I had started with „copy and paste “, or if you wish learning from experienced, thanks god for FPVlab and RCG.

    My setup was similar to Roberto Montiel:
    Powertrain: AXI 2826/12, Aeronaut CC 14/8, Castle 40A, Li-Po 3s 8,4Ah/20C
    Controls: 1xHS85MG, 1xHS65MG, 4xHS82MG, 1xHK180
    RF-Link: EZUhf 8ch div. 2x custom build dipole
    600TVL Sony, Partom 800 VTx, Circular Wireless-SPW1.2
    Vario: L1D

    Have been flown it for few years occasionally, enjoying thermal flying, learning link and video stuff and doing something totally different too :-). Sometimes I had mounted Mobius HD camera – not for duration because of drag and noise on 433 MHz. Flight time reached with this setup was 2 hours 39 minutes. Testing of range hat brought me to ca. 20 km + with helical, without issues.

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    During the approx. 60 flight hours I had found 3 main weaknesses in system that should be tuned up on next build:

    Stiffnes of airframe: Fascinantion is made for F5J style of flying, where high speed ability is not required. During FPV I had come in situations (sometimes “brown pants moments”) where the speed was over 130 kph – the wing was on the limit where the aeroelastic behavior known as flutter had taken place. The only solution was different type of wing construction – I have started build of F5J-RayX - competition full molded carbon/Kevlar plane.
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    RayX – future sporty FPV thermal soarer

    Autopilot: FY41AP is very reliable autopilot, with great readable OSD. On other side there are missing some important data and the OSD is not fully configurable. Further the size and weight AP components was too high in comparison to new systems available on market. Solution for that was change to proven Vector from Eagletree – uV. Benefits are wide configurable OSD with graphical variometer, tiny size and weight of not only AP but sensorics too and relatively good customer support.

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    Ply "mainboard" with FY41AP

    Juice: 3S Li-Po was not optimal because did not give stable 12V for 1.2GHz video gear for whole flight. On video input was less than 12 volts already after first climbs by searching for thermal bubble. Secondly huge 8,4Ah Li-Po takes a lot of room, and square shape was not much “glider friendly”. The energy density is lower as Li-Ion cells too. Solution for that was to go to 4S Li-Ion with switching stabilizer.

    Because the build of new F5J glider on hold because of searching of solution how to handle carbon fiber, I had come to decision, make a minor update on Fascination just for practicing. In middle 2017 I had replaced the 3S Li-Po by 4S3P made of Sony VTC6 cells. VTC6 can give relatively high current (30A) by higher energy density as Li-Po. Due to higher voltage I had to swap the propeller to 12x6,5. At same time I had changed the RF link to TBS Crossfire and build repeater for connection to Jeti DS14. With that setup I could reach 3 hours and 36 minutes.

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    Initial layout development of Ray and Jeti/Crossfire repeater

    As the build of RayX was long way run, I had been thinking about placing of more juice onboard. I was able to push 5 slim 4S sticks from Li-Ions in nose of the Fascination. Further I wanted HD footage too. Therefore the Sony had been replaced by Runcam Split V2. Initial dry tests were successful, therefore I thought that Fascination is ready for 2018 season… had thought… and then had the rebuild nightmare started.

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    First version of electronics in RayX and comparison Sony 600VTL to module of Split

    Unfortunately I had found the gap between spinner and fuselage too big (2mm) therefore removed the washers under screws of AXI and tuned gap to 0,5mm. Unfortunately, as many before me had experienced, the screws without washers come too long and had come in contact with stator wires… result was well known magic smoke shortly after start of motor test run. AXI, CC Castle had burned out, power module of FY41AP had smelled as hell and could not be trusted anymore… all because of gap on spinner that was more optical disturbance as aerodynamical problem :-(

    As I did not wanted to invest in FY41AP which was planned to replace, I had made decision of quick but full rebuild to micro Vector. RayX was too far from finish and I did not wanted to waste the whole season.
    Then current setup had been made as follows– generally at end of the day only servos and few cables had stayed on place:
    FY41AP replaced by uVector
    Power unit of FY41AP had been replaced by Matek PDB-XPW for current measurement
    VTx have separate power from MICRO BEC 5V/12V-ADJ
    AXI 2826/12 replaced by AXI 2814/28 with 12x9 Aeronaut – because of lower KV
    CC ICE45 replaced by CC Talon 35 – BEC used for servo power
    4S3P SONY VTC6 replaced by 4S5P of same Li-Ion
    Runcam Split V2 – powered by separate Matek MICRO BEC placed in canopy

    First of all, I wanted to make the electronics clean as possible to avoid spaghetti chaos on board and to open the possibility of HW upgrade of system. Therefore uV had been placed on PCB same as by build of molded glider. Method same too – Excel / laser printer / iron / hand engraving.

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    First layout trials of components with 4S5P

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    Main PCB with BEC and low ESR capacitors on lower side

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    Main PCB with uV and Crossfire Rx on upper side

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    Matek PDB-XPW with current sensor and connection board to harness to main board

    Then all seems to be ok already to maiden before start of season. Maiden flight was absolutely terrible, CG too far back, Fascination extreme unstable, a lot of throttle had to be applied and finally on approach to landing the motor gave up and I had to go in emergency landing in corn field about 400 meters far away. Thanks god for CC Talon that has thermal and current protection. Motor was overloaded by too big propeller and had burned out. Motor had been replaced, added aluminum cooling plate to Talon, CG moved forward by removing of ballast in tail.

    Again dry testing with thermal camera in nose, motor hot, therefore I had made further holes in spinner. Repeated dry test with fan in front of plane had shown higher temperature of motor, but seems much better as without holes. Had made new maiden by relative calm weather – all seemed OK, flight time practically without thermal about 2 hours 15 minutes, flight much more stable. Unfortunatelly by first attempt with thermal, there was no picture in goggles – for absolute unknown reasons had been shorted 12V power to video line. Had measured every wire in wing middle section but had not found the reason - the main board of Split, microVector and VTx were garbage.

    Because all had been working if connected directly to connectors on main board, I had decided that the old cable harness in wing must have some failure and cannot be trusted anymore. Therefore I had to tear up all the cables from central section. Some had been already glued with epoxy under frames for flap servos… pretty nasty job with high risk of breaking the wing somewhere. After two days of work was all back, under the flap servos were connection boards and under wing was new connector to main board. All cables shielded by protection mesh. Very carefull measurement of each component and connection – and dry test – seems all OK… again. Maiden had taken about three hours, without any big problems except the instability – the CG had to be corrected again – all Li-Ions about 20 mm forward.

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    Connection boards under flap servos and Li-Ions moved fully forward for CG correction

    The Fascination was then ready for purpose of initial idea – practicing of thermal flying not in beginning but at last quarter of a thermal season. First local, before going somewhere to cross country. Extreme hot temperatures and sharp sunlight were bringing relatively fair amount of energy in land… at 26th of August was the forecast for thermal interval for 6 -7 hours, cloud base about 1700 – 2200 meters. The meteorologists were right. Had started shortly before 12 and the thermal activity was till 6pm. Last hour I had a chance to test the Li-Ions during discharging them to 3,3V per cell. Had worked flawlessly till landing shortly after 7pm.

    Weakest point was recording on the ground, but the new ground station is already in preparation, to be ready before next thermal season starts. Hopefully there will be enough time to finish the RayX too.

    Last edited by zlutyslamak; 3rd January 2019 at 04:00 AM.

  2. #2
    Forum Member
    Join Date
    Mar 2011
    Fountain Valley, CA 92708, USA
    Good write-up.

  3. #3
    Forum Member
    Join Date
    Feb 2012
    Great idea with the connection boards.
    My Videos:
    --> https://vimeo.com/user2421484/videos
    --> https://www.youtube.com/channel/UCTlLcJj_WboUDre8JmfKg4Q/videos[/url]

  4. #4
    Forum Member
    Join Date
    Apr 2014
    Nice write up and thanks for the build tips.


  5. #5
    Forum Member
    Join Date
    Aug 2014
    Quote Originally Posted by LVSloper View Post
    Nice write up and thanks for the build tips.

    Thanks Mike,

    Good luck with build and if you will need any further help, just let me know ;-)


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