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  1. #926

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    The humming is from the nose gear bay. The thin fiberglass edges are making the humming when it's getting onto speed approximately over 160-180mph. It's no a flutter. Mine does it all the time as I have a 140N size engine. Mike
    Global Jet ARF PRO, Air-C-Race-Germany, CNC-Italy, Feibao, Der Jet, Jet Legend, Flying Legend, Xcalibur, Skymaster & more - globaljetclub.com, we keep our members flying

  2. #927

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    I've only been flying jets 2 seasons now but I got to say, I would NEVER pull my jet that hard out of a loop. That video you showed, that was a very tight loop at the bottom. I've seen this happen a few times on "*** crashes".


    In terms of CG I dont think that should matter. A hard pull is a hard pull If you had to pull hard enough to snap it you were pulling too hard and didnt have enough room to do the cuban 8 IMO.

    Some delta wings can take these hard pulls but this jet will snap. I snapped it on take off once when I had to pull up hard due to a fence coming up and too long of grass. I climbed out inverted, which to me says once you letup on the elevator it will stop.

  3. #928
    VF84sluggo's Avatar
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    Quote Originally Posted by essyou35 View Post
    In terms of CG I dont think that should matter. A hard pull is a hard pull..
    True statement.

    The CG location will affect pitch sensitivity and stability/instability, but will have no bearing on the actual aerodynamics of the wing and the stalling angle-of-attack. Pull hard enough to exceed the critical angle of attack, regardless of speed, attitude, loading, cg, etc., and the wing is done 'flying.'

  4. #929

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    the noise used to be created by the air catching the wheel wells and causing a humming noise , are your wheels open in the wing or are they fully enclosed by doors? MK
    Aviation Design USA

  5. #930

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    Didnt mean to sound condenscending in my post. I have almost lost my jet as well, 5 times actually. This is my lucky jet for sure and that may be the difference between me and the guy who crashed his in the water.

    1) Hard snap on take off due to grass too long, pulled out inverted

    2) Bouncy landing in a heavy cross wind, tipped onto the wingtip but landing on its wheels. It still has the scar on the wingtip.

    3) One time forgot to put a wing bolt in. Fortunately I always put a 2" strip of tape on the front of the wing. Mine is the older version with only 1 wing bolt. I have a gap at the front of the wing between the fuse and the tape gets rid of the gap. People laugh but tape will hold your wings on if the plane is designed right, and this one is.

    4) I did a high speed pass on the rear hatch blew off the jet, and hit my tail hard. It actually bent the metal pins in the front of the hatch. That is bad design, the pins should be in the rear not the front. I havent fixed but the hatch gets a piece of tape too.

    5) turbine flame out, the tygon on the pump started sucking air around the nipple on the OUT line, so past the UAT. The turbine was "pulsing" but I kept going. Knife edge pass, and lots of white smoke. I landed a bit hard and the front pin in my front gear is bent. The design of that is bad as once the pin bends it can be impossible to get it out of the trunion. I pounded it out and straightend the pin. Interesting thing is that thought the pin bent, the flex plate did not even crack! Ironically the main flex plates crack on mine just flying from grass. I make talk to to GJC and get a new trunion but it would be nice if they made a pin with a collet on the trunion end so the pin can come out either way.

    I'm not perfect but I also dont pull my jet hard either. 3 feet knife edge passes, yes I do them. But there is little risk of snap using the rudder on this jet, I crank the baby all the way almost into a knife edge loop.


    Tape, a fix it for everything?
    Last edited by essyou35; 03-14-2014 at 09:04 AM.

  6. #931

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    Thanks guys, good to hear that the humming noise is normal on this plane. i think the humming came from the 4 wing bolt holes and not from wheel wells. I had the comp arf kangaroo with open holes for landing gears and it didn't make any noise.

  7. #932

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    Here is a video I made with a couple of Jet legend Vipers in it. They fly so great. www.youtube.com/watch?v=8AgkBrbuFMM

  8. #933
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    If the humming is coming from the edges of the nose gear bay, has anyone noticed any cracking at the corners of the bay? I would think that high freq vibes here would eventually lead to cracking.

    I'm wondering if beefing up the inside area of the bay edges with some extra fiberglass cloth and resin might be a good idea.

  9. #934

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    I have 300 flights or so and not a single crack anywhere except on the rear hatch near the pins from where it blew off.

    Also I dont have any type of buzzing/humming. I do get a nice howl though. That is definately due to the HUGe intakes letting in too much air. That is probably why my back hatch blew off too much air getting in there with nowhere to go. I plan to build some clear inserts to taper the intakes.
    If noise is coming from anywhere it is from the rear hatch due to the excessive air going in with no way for it to escape except out through the seams of the hatch or in the small spots between the pipe and the fuse.

    A couple NACA ducts out the back would be nice. Or better yet smaller intakes, too big even for a 140N turbine. I think they did that so EDF was an option but dont know of anyone going that route.

    No body's viper has blown up yet and probably wont ever but I bet there is a lot of pressure back there.
    Last edited by essyou35; 03-19-2014 at 02:51 PM.

  10. #935

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    Has anyone tried a P180 SX in this plane?

  11. #936
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    Quote Originally Posted by LarsHoi View Post
    Has anyone tried a P180 SX in this plane?
    Wow. A P-180. Mike Lin flew his Viper at Tucson last weekend with a 140 and was as fast as anyone, had unlimited vertical and as much or more thrust than he needed for ANY maneuver. Why would you put a 180 in this airplane? BTW, my Viperjet was maidened at Tucson with a Kingtech K-80 and did just fine at 3/4 throttle. True, not a speed demon, but a 180?
    Regards,
    Gus
    AW Extra 260/ZDZ Super 80; Elan/K-100; GJC Viperjet/K-80; YA F-15C/K-140

  12. #937

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    I have a P180RX and it would physically fit. However that is newer smaller turbine. The old P180 is huge. I am not aware of an SX version so I dont know how big it is. If it is big like the old 180 it wont fit easily.

    If its all you have I would get a larger viper jet instead, otherwise you are risking it not fitting or it ripping the tail off.

    Gus congrats on the maiden.

  13. #938

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    Sorry it is a new P180 RX not SX
    I'm corently flying the Viper with an P80 SE, but I can use the P80 in another plane.
    The weight is the same from P80 to P180. I will change max RPM so the thrust will be at max 120 or i will be very care with the throttle.


    I know the plane is'nt build for high speed. Just want to know how big turbine/thrust people have used in this model.

  14. #939
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    Hi folks, my viper is due to arrive next month. Still on the look out for a decent turbine. I've read entire thread...very informative and came to conclusion, I want a 100N of some sort.
    Last edited by fredo; 03-20-2014 at 07:11 PM.

  15. #940

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    A P80 or P100 is good match for this plane. I have a K80 and it's perfect. From 3/4 power to full has little performance difference, no noticable speed difference or handling improvements. Over power this airframe too much may destroy it

  16. #941

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    Does anyone have first hand experience using JL's own brand servos in the Viper ? I would like to have folks opinion on these good or bad, cheers

  17. #942

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    Mine has the factory servos. No problems and have been reliable. Have over 90 flights is far. Mike
    Global Jet ARF PRO, Air-C-Race-Germany, CNC-Italy, Feibao, Der Jet, Jet Legend, Flying Legend, Xcalibur, Skymaster & more - globaljetclub.com, we keep our members flying

  18. #943

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    Quote Originally Posted by mikedenilin View Post
    Mine has the factory servos. No problems and have been reliable. Have over 90 flights is far. Mike
    Thanks for your comment Mike.

  19. #944
    VF84sluggo's Avatar
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    Quote Originally Posted by fredo View Post
    Hi folks, my viper is due to arrive next month. Still on the look out for a decent turbine. I've read entire thread...very informative and came to conclusion, I want a 100N of some sort.
    My Kingtech K100G pushes this jet around just fine.

    Sluggo

  20. #945

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    Im using the Spark T 12 engine, flys the jet very nicely.

    I have one of the first engines they built. I sent it back for a ECU upgrade, ever since the engine has been faultless. Perfection.

    The plane was designed around this engine. Recommeded.

    Matt

  21. #946

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    I personally think that a 100N size turbine is the best fit for this Viper. I fly mine with T12 but I cranked it up to 140. For experienced pilots, the raw and unlimited vertical power from any 120N + turbine make this Viper fun and exciting, but it can be a bit challenge for novice pilots or pilots with limited eyesight. This plane can disappear quickly when It goes full throttle in a few laps. 100N gives the most comfortable speed and thrust. Mike.
    Global Jet ARF PRO, Air-C-Race-Germany, CNC-Italy, Feibao, Der Jet, Jet Legend, Flying Legend, Xcalibur, Skymaster & more - globaljetclub.com, we keep our members flying

  22. #947
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    Thanks for the response guys, I will get Kingtech 100.

  23. #948

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    Does anyone has problem with the main wheels. My main tires only lasted 3 flights. The front tire is solid, so no problem but the mains are hollow and not inflatable. On the ground, it was ridding on the rim. I have a Everthing Included option from GTC. I took my plane out last week to try a new CG but couldn't get off the ground. Both my tires sheered off during taxiing. Does anyone knows where to get a solid tires to replace. I don't know if the airpower solid tires will work.
    Also, I noticed the humming noise on the ground too but very faint. I think it came from the vibration on the fuse skin.

  24. #949

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    could you send some photos of your damaged tires to info@globaljetclub.com attention Jose and Mandy. We can help you work with the factory to find out what's the best solution.

    If they are not properly inflated then, like regular car tires, the rims will shear off the tires. There is an inflation port on the side of the rim that looks like a tapped screw hole. You just need to press an airline on to it and inflate some air into it until it's stiff enough. JL wants to keep the landing gear system light so it only needs minimum pressure to retract the gear. On the other hand, the solid tires provide longer service life which is what I prefer as well.

    Mike

    Mike
    Global Jet ARF PRO, Air-C-Race-Germany, CNC-Italy, Feibao, Der Jet, Jet Legend, Flying Legend, Xcalibur, Skymaster & more - globaljetclub.com, we keep our members flying

  25. #950

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    Thank you Mike, I didn't know the mains are inflatable. I'll contact Jose.


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