The K8J project

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

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  1. Jan 21, 2019 #41

    Hot Wings

    Hot Wings

    Hot Wings

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    There is a reason the English voted for Brexit ;)

    Your turboprop plans may end the same way. We have an expression here in the US "It is often easier to get forgiveness than permission". It didn't work for you the first time around. :depressed
    If you can afford the time and money to build the turboprop version, knowing that you may meet the same end, it may be the best option?
     
  2. Jan 21, 2019 #42

    Arfang

    Arfang

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    That was my point. It's the same here, UL pilots don't need endorsement for turbine/jet engines.

    A google search took me to the REAA forum and to a page with CAD renderings but I found no Wankels on this website, what exactly should I look for?

    I would also like the bureaucracy to bureaucrexit.

    Are you suggesting putting the turboprop without telling anyone? There might be no need to do that, some measures have been taken but I can't give more details for now.
     
  3. Jan 21, 2019 #43

    Hot Wings

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    No. If the path looks to be reasonable according to the French regulations*, AND you can afford to ultimately be rejected, then build without consulting the EASA for their opinion. Getting permission or approval from the EASA may be a long and expensive project.



    *or some other path that you may already have found but don't care to share right now - which is completely understandable.
     
  4. Jan 22, 2019 #44

    proppastie

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    Not part 103 (I think)
     
  5. Jan 22, 2019 #45

    proppastie

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    Good luck
     
  6. Jan 28, 2019 #46

    ypsilon

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    In all fairness. This time it isn't the EASAs (EUs) fault. They just told the french authorities, that this machine isn't EASA business, which it clearly isn't under regulation 2018/1139. It's the french authorities that messed up here. Sometimes the EU is more reasonable than our national governments.
     
  7. Jan 29, 2019 #47

    jedi

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    The jet powered Mitchel wing was operated under USA FAR 103 but was limited to 5 gallons of fuel. It was barely enough for two short circuits of the ultralight strip at Sun-n-Fun.
     
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  8. Jan 29, 2019 #48

    BJC

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    It didn't go far, but it arrived in style.


    BJC
     
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  9. Mar 8, 2019 #49

    Arfang

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    Unfortunately, no answer from the aviation authorities or even from the ultralight federation. The K8J will not fly again. However, the engine supplier accepted to replace the turbojet with a turboprop transforming the K8J into a K8T.

    It's a KingTech K-100TP producing 13kW, spinning a 4 bladed 26x22 propeller.

    20190308_170336.jpg

    The engine will be mounted in the nose. Above the nose actually. The pitot tube will have to be moved under the propeller arc, where the tow hook is currently located.

    Here's a rough idea of the engine installation:

    K100TPmount080319_1.jpg K100TPcowling080319.jpg

    It would be made out of steel sheet and welded to the fuselage. The idea is to use the engine mount as part of the cowling. It's still work in progress at this point.
     
  10. Mar 9, 2019 #50

    Topaz

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    I was about to ask if you were sure the nose structure could handle the thrust loads. But "glider" with "tow hook". Duh. :roll:
     
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  11. Mar 9, 2019 #51

    Arfang

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    As you wrote, the structure is designed to react to 'tow' loads. However I can only get an estimate for thrust since no propeller data is available.

    Using formulas from Simplified Aircraft Design for Homebuilders, I was able to estimate a thrust force of 112lbf at 32kts, taking into account a 10% power loss due to cooling drag. 120lbf without power loss. Eta P was 0.75, Advance Ratio was 0.569 and the Power coefficient was 0.078 in both cases.

    Using J.C. Debreyer formulas I got an Eta P value of 0.57 at a max cruising speed of 75kts. Using that value of 0.57 the thrust goes down to 88lbf at 32kts. Those numbers could be off though, I'm still at the beginning of the learning curve. I'm thinking about using the highest thrust result to calculate the thrust loads on the structure and the lowest result to calculate the flight performances.
     
  12. Mar 9, 2019 #52

    Grelly

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    Somehow I am very late to this thread, but had to chip in. I have many happy memories of flying the K family back in the late 70's, early 80's. I learnt to fly in K13's and K7's and graduated to K8's, K6's and K18's. I lost interest in gliding when the club I belonged to sold the last of their rag-and-tube gliders and went all K21's and K23's. For me, the glass machines didn't have soul the way that the earlier gliders did.

    Good luck with your project.
     
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  13. May 4, 2019 #53

    Arfang

    Arfang

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    Quick update on the project:

    The engine mount design is done, the engine will be located over the main spar instead of the tractor configuration presented earlier. The reason for that is to be able to remove the mount in the case I want to install another engine or operate it as a 'normal' glider. Also, it's a tried setup used previously on another motorized K8:

    [​IMG]

    Here's my design without the cowl and fairings for comparison:

    [​IMG]

    Also, the airplane has been re-registered as a K8T by the authorities, thus allowing me to perform flight tests.
     

    Attached Files:

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  14. Jul 5, 2019 #54

    Arfang

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    Engine mount and cowl are done. The air intake will be printed next week, after that we'll be ready for engine tests.

    20190705_155729.jpg 20190705_160057.jpg 20190705_162329.jpg
     
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  15. Jul 5, 2019 #55

    bmcj

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    Given the high exhaust speed compared to the flight speed, would a thrust augmenter tube give you more overall thrust?
     
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  16. Jul 6, 2019 #56

    Arfang

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    Why not, although I didn't find anything about thrust augmentation on turboprops. Do you have more information on the subject?

    What I could do is add curved exhaust pipes to direct the exhaust flow backwards.
     
  17. Jul 14, 2019 #57

    Arfang

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    We performed the engine tests this afternoon, just a few details to adjust and she will be ready for her test flight. IMG-20190714-WA0002.jpg IMG-20190714-WA0010.jpg
     
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  18. Jul 25, 2019 #58

    Arfang

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    The powerplant unit is now complete with fairings and air intake, all 3D printed. The intake alone took 72 hours.

    20190725_223914.jpg
     
  19. Jul 28, 2019 #59

    pwood66889

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    It looks very impressive for 17 HP. Thank you for posting your progress!
     
  20. Aug 11, 2019 #60

    Arfang

    Arfang

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    The K8T flew today for the first time:



    Everything went well, the performances were close to what was predicted.
     

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