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Apr 10, 2013, 06:30 PM
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DukeDiablo's Avatar
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Help!

HK ParkJet MKII Problems


Dear Forum-

I searched and found quite a bit of information, but even implementing that knowledge... I'm still hopeless here:

I purchased a second hand (read, well crashed) ParkJet MKII from a local guy and took my time going through it and making sure everything was solid and functional. I installed my own 40amp esc, a 9x receiver, and a 3S 1000mAh battery, and 4x4 prop. The previous owner had already beefed up the motor mount and installed possibly another out-runner, but I'm not sure if it's the original or not.

I setup my elevon mix on my 9x, and everything seems to work correctly.

I've got the CG set around the front edge of the finger/hand holds on the bottom of the MKII.

So I thought I had everything correct and tried to fly it today for the first time.

Complete failure. Tried numerous different hand launch approaches, all did exactly the same thing:

Just after release, the MKII snap rolls to the right and lawn darts into the ground.

I tried no throttle, 30%, 50%, and full throttle... with absolutely no difference except the velocity at which the MKII struck the ground, haha.

I also tried to launch it similar to how Josh Bixler did on the FliteTest review video... and had similar results as my original approach.

The only time I actually got the ParkJet to glide for a second or two was after it rolled and seemed to settle into an inverted flight before grounding.. so I was nearly able to fly out of it upside down! The thing just acts like it's top heavy and wants to fly upside down.

I have tried throwing a bunch of left aileron trim to it, but I'm still unable to stop the roll.

The ONLY time I was able to get it to glide, was an experimental toss after I snapped a prop saver band. So there was no propeller on it... but everything else was fine.. and for some reason it floated level and landed on it's bottom. I felt like I tossed it just like before... but something must have been different, or random.

I don't have any problem flying my Multiplex EasyGlider Electric, and I know this isn't as easy a plane to fly, but if I could get the thing to glide for about 2 seconds, I'm fairly certain I could handle it.

I've checked the "tweak" (my R/C background is in 1/10th scale oval) by laying it on a flat surface, and using a long handle screwdriver to slowly raise the rear from the center line... and it's pretty close to neutral... I set my electronics over to the left to try and compensate for the roll too... and that hasn't helped. So I don't see any weight bias that is causing this.

I've got it back looking pretty nice again after 15-20 launch crashes today with the help of some hot glue... and I would just love to be able to get something close to an actual flight in someday.

Thanks for any help/advice and have a great week.

Sincerely,
Jim
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Apr 10, 2013, 11:38 PM
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Had the same issues until reading this thread, lowered motor similar to post 125 & no more problems.
https://www.rcgroups.com/forums/show....php?t=1345323
Apr 11, 2013, 06:16 AM
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DukeDiablo's Avatar
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Thanks RanWell, I didn't see that whole post, so I'll read through and give it a try.

I saw some "magic motor mount" variants for sale online, but was unsure if any of them would be a good option for the ParkJet?

What mount did you use... or did you fab your own?

Also, maybe I'm naive to think that I can judge if the plane will track straight by looking at it... I mean, all the control surfaces look square and the elevons look trimmed correctly, but maybe I should try some extreme left aileron trim at launch as well.

Thanks!

-Jim
Apr 11, 2013, 10:03 AM
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cytochrom's Avatar
how is your cog
Apr 11, 2013, 04:50 PM
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DukeDiablo's Avatar
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I originally used a CG point about 5-10mm in front of the hand/finger holds... but I've since changed to more front of the finger/hand hold wells.

Since I haven't been able to get the thing to float... it's been hard to tell if I'm too tail heavy.

Any advice on purchasing a good mount... or making one? I need to take a picture of this franken plane to give you an idea of what I'm working with...haha.

I think I'm going to run out to the field and try throwing some major left trim to it and see if that will give me a shot at a flight today. I suppose I'll plug in the hot glue gun before I leave so it will be ready for the carnage when I return...haha.

-Jim
Apr 11, 2013, 08:15 PM
Registered User
Quote:
Originally Posted by DukeDiablo
Thanks RanWell, I didn't see that whole post, so I'll read through and give it a try.

I saw some "magic motor mount" variants for sale online, but was unsure if any of them would be a good option for the ParkJet?

What mount did you use... or did you fab your own?

Also, maybe I'm naive to think that I can judge if the plane will track straight by looking at it... I mean, all the control surfaces look square and the elevons look trimmed correctly, but maybe I should try some extreme left aileron trim at launch as well.

Thanks!

-Jim
I just glued the round (disc) part of the original motor mount straight to the foam & it's been fine, COG at front of finger holes about half throttle & should be good to go.
Apr 11, 2013, 08:27 PM
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DukeDiablo's Avatar
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Thanks RanWell,

I tried it again this evening and with a ton of left trim it actually began to roll left instead of right. Then I began trimming it back to the right and I think I was just about to get to a level hand toss when I broke the nose off again.

So, on the positive side, I decided to take everything off the plane, and re-do the motor mount as recommended... then give it all a try again after some boiling water and hot glue madness.

Thanks for all the help and considering it needed that much left trim to get close to level glide path... there must be something seriously wrong with this plane.

-Jim
Apr 12, 2013, 11:54 PM
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kushal_22's Avatar
Mine did the same thing. I ended up going nose heavy and slowly worked it back.

Mal
Apr 13, 2013, 08:48 PM
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DukeDiablo's Avatar
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Thanks Mal,

Once I get it back together again, I'll try working the CG forward a little at a time and see if that helps.

Have a good week.

-Jim


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