Parkjet advice?

[Hans_Svetty]

Hello,

I have read a lot about this HK Parkjet model here. Built the kit yesterday. I thought I could launch it, but no luck.

The motor is mounted on a metal mount from HK, (aluminium, black, goes on end of the wooden stick.)

Do I need to give it thrust offset as designed? (Top of prop if vertical is slightly forward.)

Is the CG critical? Perhaps my guess that I was at the front edge of the fingerholds was not precise enough.

Forgive my asking these tired questions, but I was drowning in the many many posts about this plane trying to find the answers, and thought to ask these questions on a 'clean sheet of paper', so to speak- do please ignore me if annoyed.

Thanks,

Hans

[stuart]

i feel your frustration on launching the pkj. bungee launches are best and cg is important! a little down thrust is recommended and it sounds like you've got it right. you didn't state what your powering the pkj with so i can't say what the torque is during your launch. mine with the 3000kv 4cell is wicked on launch....thus the name of the motor from dons rc "wicked is appropiate..lol.

[Hans_Svetty]

I used the AX 1806N 2500kv Brushless Micro Motor (19g) from Hobby King. 4.75x4.75 grey prop, stiff. I have never used a motor of this size, being more used to Eflite 450 motors.

By downthrust, I would like to confirm that the bottom of the motor would be pulled back a degree or two, relative to an imaginary line drawn horizontally through a cross section of the fuselage. (Would more of this downthrust possibly help me to launch it? That I imagine would have the effect of pushing the aft end of the airframe down a bit when launching, to get more of a nose up tendency.)

To describe my crashes, I had a sort of power stalling/flop crash, no tracking with enough airspeed to get control. Repairs next. I have learned that my carbon fiber reinforcements need to be extended past the cabin vent hole to strengthen the nose section.

Do I balance at the very forward edge of the finger holes? Or in the center of them?

Is it even possible to hand launch this thing? Building a catapult would be a bit of a comittment.

Thanks,

Hans

[Hans_Svetty]

This has me thinking- Lots of down thrust?

"HobbyKing ParkJet EPO - successful hand launch" (see on YouTube)

[CHELLIE]

Originally Posted by Hans_Svetty

I used the AX 1806N 2500kv Brushless Micro Motor (19g) from Hobby King. 4.75x4.75 grey prop, stiff. I have never used a motor of this size, being more used to Elite 450 motors.

How is this to be mounted properly? Tiny little self tapping screws passing through holes drilled in the mount to match the three very small holes on the included motor base?

Is there a better way perhaps?

By downthrust, I would like to confirm that the bottom of the motor would be pulled back a degree or two, relative to an imaginary line drawn horizontally through a cross section of the fuselage. (Would more of this possibly help me to launch it? That I imagine would have the effect of pushing the aft end of the airframe down a bit when launching, to get more of a nose up tendency.)

To describe my crashes, I had a sort of power stalling/flop crash, no tracking with enough airspeed to get control. Repairs next. I have learned that my carbon fiber reinforcements need to be extended past the cabin vent hole to strengthen the nose section.

Do I balance at the very forward edge of the finger holes? Or in the center of them?

Is it even possible to hand launch this thing? Building a catapult would be a bit of a comittment.

Thanks,

Hans

you can use a hi start used for gliders to take off with, you dont need the rails, lay the plane on the ground and have someone let it go for you, make sure the numbers on the prop are faceing towards the front of the plane, a little down thrust will help like about 1 to 2%, CG is Critical, make sure its right on the money, the rear of the motor where the prop is at will be pointed down a tad for down thrust Hope that helps, Chellie

http://www.hobbypeople.net/index.php...tube-5006.html

[Hans_Svetty]

For the hi-start launch idea that you have described, it is on the ground for the launch, the motor is not on, right? So the rubber pulls it up and you hit the throttle when airborne?

Could you share details on the launch attachment you created for the airframe?

Did you use a small parachute for the launch line?

[Hans_Svetty]

This fellow gives us slow motion, diagrams, and a picture of his motor stick modification for lots of down thrust. Reflex on the elevons is also used:

http://www.youtube.com/watch?v=eG9D2iuiXMc

Does this approach make sense?

[stuart]

cg....if you have your fingers on the front edge of the holes your good to go. finger in the center of the holes would equal nose heavy.

i highly recommend if you can''t get a bud to throw the pkj power off into a glide that you throttle up slow so not to torque roll into mother earth,that you try the Frisbee type toss that the guys on "testflight'reviews show. you hold a wing tip and throttle up and give it a side toss. the video you show of that guy throwing it that way could equate to a trip to urgent care and a bunch of stitch's.

i have 2pkjs setup,a funjet,and a stinger edf so the bungee launcher get plenty of use once set up....but i must admit to being less motivated using it when the field is crowed with other pilots.

as far as down thrust goes,i found using the stick supplied in the grove made for it was the correct down thrust for the pkj,you will notice the correct angle of the motor similar to the diagram the guys video showed but not nearly that extreem. hope this helps. i am only just get back to flying from a hybernation in the man cave building so the fast birds will have to wait till the thumbs get warmed up to the sticks again...lol.

[Hans_Svetty]

Does one pull the rubber tight, Set reflex trim on, Release, then throttle up?

[stuart]

i can't picture letting the pkj attached to the bungee scooting along the ground till get flight speed up. the rails on my launcher allow me to power up a little and it leaves the rails very fast getting airspeed up crazy quick. heres a vid of a launch....

• 

the first 1 1/2 mins was trimming flight.

[Hans_Svetty]

Thanks. How does the plane actually launch forward? I could not see how that worked on your video...

[Hans_Svetty]

Could you share details on the launch attachment you created for the airframe?

[Hans_Svetty]

On Youtube,

http://www.youtube.com/watch?v=dP2MAH5evNM

I noticed this comment about launching the Parkjet:

Meister Jazz 1 year ago
If you mount the motor high above the thrust line, then it must have the shaft 'looking at' the CG. Else, mount it right in the center behind like the funjet, with 0 thrust angle. Launch at 60 percent throttle, hold by the left wing (with left hand) then gently let go at 30 degree angle to top. No matter what, the shaft of the motor must point at the CG. I crashed mine many times to learn this. I don't use the supplied mount, it's useless.

[stuart]

3

pkj3 4850kv cell 50amp esc. the one thing i like with this vid is the other plane flying normal speed to help give perspective of the pkj...lol.

[Hans_Svetty]

So there is some sort of trigger. And a hook on the plane.

[stuart]

yes,theres plenty of designs for launchers using PVC pipe,real cheap to build. as far as the hook goes,Nigel and i experimented and the location is good here as pictured. note,if you over power the pkj for speed you should review the carbon fiber or bamboo stick reinforcements or she'll breakup and the wing and eleverons will flutter.

reread the need for speed thread and all the answers are there,also go to rcg and find a thread there with tons of info....i leave you with the best video i have of pkj3.......do post us some pictures of your pkj and perhaps some vids. sorry i don't have music on my vids...pretty boring.



4:56

[Hans_Svetty]

I will glue it back together and share photos.

[rcers]

I am not at all fond of bungee launchers. They are such a pain IMHO. I have watched many crashes from improper setup. I have watched the rails come in contact with servo arms and strip them causing a crash.

I just use reflex a good toss and zero throttle on launch. Zero issues with my light setup. It takes practice and good launch technique. Good launch does not mean 40 degrees of up either. Too many want that and is bad. A good firm flat toss is always best.

Mike

[fhhuber]

Practice tossing... aim the plane about 50 ft out at the ground.

If you can do a good launch it will glide out a bit further.

If you can't toss it hard enough to get a glide its probably be a bad idea to hand launch that model. (you probably already know if you can toss it hard enough before tossing)

There are some models that are just too heavy to hand launch. For them some form of catapult, or maybe a takeoff dolly, have to be used if you don't want to "bolt" landing gear on.

I think that most of the small "jet" style models that are too heavy for hand launch would perform better on lower power. You can bolt in so much power that the airplane is SLOWER because of the weight.

[Hans_Svetty]

Thanks for the new advice Mike and Huber. I find this model to be very challenging. I like the looks of it a great deal.

I think your suggestion is to try gliding it without power, so as to see if it is at all controllable?

I am not sure If I can get enough airspeed to establish a proper glide from a strong flat toss and still get my hand on the controls to power up and make trajectory corrections quickly enough, but it will be interesting to try. I suspect that CG location is critical, as I have read.

Will the Parkjet not glide if nose heavy?

Mine seemed to dive on the first tosses, then was just power stalling without sufficient airspeed to fly and crashing randomly until broken.

May I ask Mike, How much reflex? (I have never set this up before on my Dx6i transmitter.) Do you use a particular switch for convenience?

[rcers]

Originally Posted by Hans_Svetty

I think your suggestion is to try gliding it without power, so as to see if it is at all controllable?

I am not sure If I can get enough airspeed to establish a proper glide from a strong flat toss and still get my hand on the controls to power up and make trajectory corrections quickly enough, but it will be interesting to try.

I am not sure if that was his recommendation - but it is NOT one I would follow. While I do launch with no power for safety I get right on the throttle. These are not gliders after all.

Originally Posted by Hans_Svetty

How much reflex? I have never set this up before on my Dx6i transmitter. Do you use a particular switch for convenience?

I use about 2-3mm of reflex (Up of both elevons) in the ParkJet. I do program that to a switch on my DX18 but can't assist you as I no longer have the DX6i. I use flight conditions and conditional trim with two different launch settings but again that isn't something the dx6i supports.

You could post in the forums and see what others do on your TX.

Mike

[Hans_Svetty]

I will try to post a photo.

[Hans_Svetty]

[Hans_Svetty]

[rcers]

What is your all up weight (ready to fly)?

Mike