The K8J project

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Arfang, Sep 14, 2018.

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  1. Sep 14, 2018 #1

    Arfang

    Arfang

    Arfang

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    Good day all,

    I think it's time to finally present my project. It's a jet conversion of a Ka8B glider.

    The goal from the get-go was to make a jet-powered conversion as inexpensive and simple as possible while being compliant with the french ultralight regulations. Also important was keeping the number of unknown factors down, focusing on having a flying airplane, improvements can always be added later.

    The requirements for a single-seat ultralight were:

    MTOM: 300 kg (661 lbs)
    Vstall max: 65 kph (35 kts)
    max engine power: 80hp

    My personnal additional requirements were:

    A minimum climb rate of 1.5 m/s (295 fpm) and enough fuel to gain approximately 3000 ft AGL in order to have enough altitude to switch to ''soaring mode'' before the engine runs out of fuel.

    The choice of a glider airframe was motivated by the relatively high LD and low weight of this aircraft type, allowing good enough performance with only a small engine, reducing the cost. That and the fact that there are plenty of airworthy old gliders for sale at reasonable prices.

    So I ran some numbers, compared several types of gliders and bought a Ka8B.

    IMG-20180511-WA0001.jpg

    Now to the ''build log'', note that not everything is mounted in place yet, I still need to do the engine installation and wiring, probably this week-end.

    Added a nosewheel on the bottom of the skid, like on the Turbine 1-26. http://csanders2775.wixsite.com/turbineschweizer126
    Chad Sanders was very helpful and provided more information about his nosewheel installation than I could ask for.

    20180902_170302.jpg

    Replaced the cockpit floor and seat, replaced the instrument panel with a custom one to accomodate the ''throttle'' and FADEC display.

    20180914_193828.jpg 20180903_200340.jpg 20180903_200326.jpg

    Designed an engine mount to install a 310N thrust engine on it. It's not retractable to keep the installation as simple as possible. The mount also holds the fuel pump and FADEC. The triangular structure on the left drawing is located on the left in the last image.

    20180914_200136.jpg 20180914_193647.jpg 20180708_163003.jpg

    3D printed fairings will slide over the mounts to cover the cables and fuel line.

    20180914_194827.jpg

    A 2.5 US gal fuel tank is located beneath the engine mount. I still consider making a custom one and I'd like to thank the HBA members who helped me but for now the goal is to keep it simple.

    Removed several unnecessary elements like the second vertical speed indicator, second thermos bottle and tow hooks. The airframe ended up at the same weight as before the engine installation.

    The airplane has now received a temporary permit to fly, if I'm not mistaken it will be the first 3-axis jet-powered ultralight under french UL regulations. It's also probably the cheapest private jet in the world.

    First test flight will take place hopefully before the end of the month.
     
  2. Oct 10, 2018 #2

    Arfang

    Arfang

    Arfang

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    Update on the K8J: The test flight had to be postponed due to me not being able to find a suitable trailer. Fortunately, I found one for sale last week, so everything is now ready.

    I decided to use those two weeks to make some improvements, I replaced the engine mount fairings with a lighter version and added an aluminium plate to better support the fuel tank straps.

    20181010_182034.jpg 20181010_182045.jpg 20181010_182058.jpg 20181010_182237.jpg

    Also added some thermal protection to the top fuselage and tail:

    20181010_182510.jpg

    I noticed that a small portion of the fabric is slightly loose under the tail section, maybe someone more qualified than me could give me some advice on that.

    20181010_183411.jpg
     
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  3. Oct 11, 2018 #3

    Chilton

    Chilton

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    Loose fabric generally means something underneath has moved, possibly just fairing strips but may be structural, can you get at the inside for a look in any way?

    I once rebuilt a PA15 which had a very similar start to that, but the owner decided to just shrink the fabric down, result went from one cracked longeron to both, plus the upper longerons bent when he landed!
     
  4. Oct 11, 2018 #4

    Arfang

    Arfang

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    Thank you, I'll see tomorow if I can see something from the inside. Is there something specific I should look for? I slid a block of foam under that area a couple of days ago to better distribute the weight, maybe it has something to do with my issue.
     
  5. Oct 12, 2018 #5

    Chilton

    Chilton

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    As it is probably 20 years since I last okkked at a K8 I cant remember if there is wooden fairing structure there or just the main longeron, if there is fairing theere it has probably pushed something out of position or cracked a strip, in which case not a biggie, if a longeron it is a bigger issue but mainly what you are looking for is anything which has moved.

    To be honest if the fabric which has slackened is aagainst the main structure I think you will have to cut it open to check what has caused the movement but if it is only fairing pieces you should be able to make sure it does not interfere with controls and be good.

    Fingers crossed it is fairing!
     
  6. Oct 12, 2018 #6

    cluttonfred

    cluttonfred

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    No comments to offer except that this is a very cool project and thanks very much for sharing. I hope to see pics and video of your K8J in flight sometime soon!
     
  7. Oct 12, 2018 #7

    lr27

    lr27

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    You've probably already thought of this, but if not, it might be a good idea to use a bunch of temperature sensors while taxi testing to make sure you're not overheating anything on the fuselage that's downwind of the jet.
     
  8. Oct 12, 2018 #8

    Arfang

    Arfang

    Arfang

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    I have bad news, the structure underneath the fabric is in fact a longeron and it is bent.

    20181012_145651.jpg

    I have two options now: either find someone who can repair the structure and the covering or buy a new Ka8 to test the conversion now and repair the first one this winter.

    Either way the K8J project is not over. I'll find a solution and keep you informed. Thank you all for your feedback.
     
  9. Oct 12, 2018 #9

    Chilton

    Chilton

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    Ah nuts, I was really hoping to hear it was a fairing! Hope you get it fixed soon, really looking forward to hearing how it flies.
     
  10. Oct 12, 2018 #10

    cluttonfred

    cluttonfred

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    That does not seem to be a big deal to repair...where are you?
     
  11. Oct 13, 2018 #11

    addicted2climbing

    addicted2climbing

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    You have picked my all time favorite sailplane. I have wanted to own one of these for years but at 6'4" and 230lbs I was usually outside the max pilot weight on any but the lightest version without any repair history. I do know I fit if it has the large canopy and not the Ka6 type. Looks like yours has the smaller KA6 type canopy. I will be following your progress.
     
  12. Oct 13, 2018 #12

    addicted2climbing

    addicted2climbing

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    Where in France are you? I have family in the GERS (Samatan) and visit every year. Would be cool to come see you once its flying.
     
  13. Oct 13, 2018 #13

    Arfang

    Arfang

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    I live in Switzerland, the airplane is currently there but will be flown and stored in the Doubs.

    My next step is to contact Alexander Schleicher for advice and the local vintage glider association to see if they can help me.
     
    sotaro likes this.
  14. Dec 1, 2018 #14

    Arfang

    Arfang

    Arfang

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    The K8J made its first flight today in Pontarlier, France.

    Here are some picture of the airplane:

    20181201_132607.jpg 20181201_132624.jpg 20181201_141054.jpg

    Everything went well and the aircraft seems to perform like predicted, more test flights will follow.

    I'll post more informations and videos later.
     
  15. Dec 3, 2018 #15

    Arfang

    Arfang

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    As promised, here's a video of the taxi and take-off sequence:



    Unfortunately I was unable to fit my camera mount inside the cockpit. I also need to work on a removable tailwheel to make taxiing easier.
     
    Last edited by a moderator: Mar 20, 2019
  16. Dec 3, 2018 #16

    addicted2climbing

    addicted2climbing

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    Wow Congrats. Wish the video showed more of the flight. How did it go?
     
  17. Dec 3, 2018 #17

    Arfang

    Arfang

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    Regarding the flight:

    Takeoff from the concrete runway at 70 kph after approximately 11 seconds, the vertical speed indicator showed 1m/s and reached 1.5m/s when I got up to 90 kph. I felt some turbulences on the crosswind leg due to the Jura mountains nearby. Then finished my climb and set the engine to idle mid-downwind at about 900ft AGL. Landed on the grass runway like a normal glider, touchdown speed was about 60kph. After landing I was met by two police officers who saw ''an airplane going down trailling a lot of smoke'' and came to see if I nedded any assistance.

    Takeoff speed and climb rate are close to my predictions.

    Regarding the aircraft:

    The K8 behaves superbly, I can't wait to fly it next summer in better weather conditions.
    Some minor improvements could be made this winter: completely removing the steel plate on the skid to shed some weight and installing a bigger fuel tank. The 2.5 gal I'm using now was almost empty when I landed. And of course I need to find a way to install a camera on board.
     
    Vigilant1, Pops and cluttonfred like this.
  18. Dec 3, 2018 #18

    jedi

    jedi

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    How do you explain the "Lot of smoke"? I would not have expected it to smoke at idle or if shut down unless there were a fuel source with no fire.
     
  19. Dec 3, 2018 #19

    Arfang

    Arfang

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    There's always some smoke when the engine is running and even more at the start of the cooldown phase, that's probably what they saw.
     
  20. Dec 4, 2018 #20

    hole in the ground

    hole in the ground

    hole in the ground

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    Or they might just have wanted an excuse to see what the noisy glider was about :)
     

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