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Old Feb 12, 2013, 03:57 AM
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A good tip for those who still are about to build their parkjets. Besides the 6mm carbon fiber rod reinforcement along the wings, you could glue a 3/8" plywood strip along the lenght of the battery bay. This will make your fuselage more resistant to deforming in case of a crash.
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Old Feb 12, 2013, 11:25 AM
Reap the wild wind
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Bristol,UK
Joined Feb 2007
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Quote:
Originally Posted by m_ark View Post
I would love some ribs to make a 3mm depron airfoil of it.
Dave Reap had done some more work on the plans for the Parkjet but needs a decent side on photo to work from. It's dark here already so can someone in sunny climes take a decent picture and post for Dave on the KF thread. Here is the link to his latest work http://www.rcgroups.com/forums/showp...postcount=5505
Andy
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Old Feb 13, 2013, 01:33 AM
ICrashRCs
United States, TN, Memphis
Joined Jun 2011
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Quote:
Originally Posted by sonnydc View Post
A good tip for those who still are about to build their parkjets. Besides the 6mm carbon fiber rod reinforcement along the wings, you could glue a 3/8" plywood strip along the lenght of the battery bay. This will make your fuselage more resistant to deforming in case of a crash.
See the pics linked below.
I used 3 flat carbon strips standing up.
The pic with the 2 strips would now show a 3rd strip in the center and running a bit further back than the other 2.
I also put strips in the canopy sides. The canopy tends to self destruct when nosed in.
PJ2 survived a full speed nose in with zero damage.

http://www.rcgroups.com/forums/showp...postcount=1053
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Old Feb 13, 2013, 02:12 AM
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Thats also also good idea. There's just one thing I don't like about cf, they tend to shatter upon impact.

On my first parkjet, I did the same thing but instead of carbon strips, I inserted bamboo barbecue sticks. After several bad take-off's and landings, the fuse already came bent and would always torque upon launch. That's when I thought of placing a sheet of 3/8" plywood with the the same width and lenght of the battery bay. I also spread some thin c/a on the wood to strengten it. Seems to do the job in keeping the fuse straight.
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Old Feb 14, 2013, 07:24 AM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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Originally Posted by sonnydc View Post
Nigel, I saw the twin on the other forum. That's wicked!
She's sitting there with :

2 x 3000kv motors
2 x 50A ESC
4S 1600 or 3S 2200
4.75 x 4.75 props, contra to reduce any torque tendencies

Launch is to be by catapult bungee - deadstick till she clears the rails ... then it's TRY and ease in throttle .... too quick and I think she'll flip head over tail ....

NO reflex on take-off for good reason - again the flip over ...

All calculations indicate a possible speed in excess of 265kph ... but we all know what theory is !!

Here's the original 3800kv motors that drew over 100A and blew my LiPo !!

PKJ twin power-up (1 min 27 sec)


Here's the replacement 3000's that now have a reduced draw on the LiPo and hopefully shouldn't destroy my battery inventory !!

PKJ(T) 2623 3000kv motors test (5 min 12 sec)


The baby ready to go :





PLEASE don't tell me props are back to front - I KNOW !! and that's all sorted ! I fitted quick just for photos and vid !!

The servos have been changed and elevons set up properly now.


Nigel
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Last edited by solentlife; Feb 14, 2013 at 08:15 AM.
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Old Feb 14, 2013, 08:01 AM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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Modifications for Speed !

We see many modification recc'ds for this baby and I would like to now list my personal ones :

a) Elevons are flimsy to say the least and unsuitable for anything other than sport flying ... any hard manouevring or speed and they will soon let you know. On my first PKJ that hit 222kph - I did as many - used CF rod running span of them. But that soon proved to fail as the foam let the epoxy go and the rods starting to exit the grooves ... So I looked for alternative that would also be better cosmetically. Thin 1/16th balsa sheet epoxied to the underside of the elevons gives a nice smooth and strong stiff form. The balsa can be sanded to regain the trailing edge. The epoxy in the 'sandwich' really does stiffen it up.

b) The fuselage especially at wing joint and at rear where channel is cut for motor leads etc. is weak. So my remedy again is balsa but in form of 1/4 sq beams. 2 of them parallel set into the underside from just about where the airscoop hole is back to mid wing position. These not only are light - but with epoxy again are stiff ... they also provide anchor for stitching to hold the Velcro inside canopy for battery hold downs.

c) On the twin - the channel cut at rear of fuselage is filled in with pink foam to make more rigid.

d) Servo rods and horns on top of wing ... servo still fitted underside. 9gr used instead of the smaller recc'd. The stock control rods are fine and never given trouble.

e) Canopy hold down is by two bolts and blind nuts. The blind nuts are pressed into the underside of fuselage and the bolts go down through the side ;pieces of the canopy ... via holes in fuselage to the blind nuts. This makes sure that canopy becomes one with fuselage and helps stiffen it up. There is no chance of canopy ever 'flying off' in flight !! At over 200kph - it needs serious hold-down !

f) On the single motor PKJ - the motor mounts are fragile and my answer was a L furniture bracket drilled to fit motor ... the bottom part of the L then set into a slot below the wood beam and set in with epoxy. A single self-tapper then through bracket and up into the wood beam. This steel bracket enabled bending to desired thrust angle if required.

g) On the twin - I use plastic RCTimer beam mounts to 10mm sq beams epoxied alongside the fins and to the fuselage. These plastic mounts are more forgiving than metal.

h) Battery retention is by two Velcro straps as sold for 450 helicopters ... I first cut in half to i) remove the buckle, and ii) flip one round so they fasten together. Second the strips are epoxied into bottom of cockpit area and BEFORE epoxy dries - carpet thread is sewn down and through the balsa beams in underside of fuselage and back up ... tied of. Knots have a drop of CA applied to make permanent. My Velcro straps this way have never lifted !!

i) Once all done - I then smear a thin layer of epoxy along the centre fuselage underside to give some protection for landing.

I do not add anything to the wings - I keep to the original kit CF rods and that's all. The foam wing is thick and has proven more than strong enough.

I will mention glue joints though. The foam used is not so happy with epoxy without a little work done. It needs to be roughed up a little ... if left smooth - the epoxy cannot 'grip' and over time will 'let go' ... So scoring of the glue surfaces to give a good key for the epoxy to sink into and 'grip' cures that.... this applies particularly to the wing to fuselage joints.

So - nothing overly fancy in my mods ... simple, easy and seems to work.

Nigel
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Old Feb 14, 2013, 08:09 AM
222 km/hr Parkjet flyer
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In addition to my above 'modifications' post just now - once I get home and start the renovation of my record breaking PKJ ... it is in sorry state !... I shall photo and possibly video its re-birth.

I intend to put her back in the air and maybe get her up to speed again !

Well - with no more PKJ's on sale - what else can you do ?? maybe it will get more people to re-birth their broken PKJ's ??

Nigel
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Old Feb 14, 2013, 08:10 AM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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Quote:
Originally Posted by sonnydc View Post
A good tip for those who still are about to build their parkjets. Besides the 6mm carbon fiber rod reinforcement along the wings, you could glue a 3/8" plywood strip along the lenght of the battery bay. This will make your fuselage more resistant to deforming in case of a crash.
Maybe check out my post about various mod's ...

Nigel
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Old Feb 16, 2013, 01:42 PM
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United Kingdom, England, Bisley
Joined Oct 2010
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First stage toward making my parkjet faster.
I bought a 4.75x4.75 prop and fitted it to the stock motor but it vibrated so much it nearly shook the fins off.
So I bought a new motor with a larger diameter motor shaft 3.17mm.
It is shorter too which helps reduce vibration and has bigger bearings.
Let's hope with a shorter prop I wil get more revs and higher top speed.
Still just running a 2s battery for now.
The motor is a rc timer 2805 14t rated at 2840 kv.
.
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Old Feb 16, 2013, 10:55 PM
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Quote:
Originally Posted by solentlife View Post
Maybe check out my post about various mod's ...

Nigel
The balsa rod reinforcement under the fuse is really good. I also use the GWS plastic mount which has proven its toughness vs alloy stick mounts which tend to bend and brake during crashes. I use velcro to stick my canopy to the fuse. Much better than using magnets.

Just changed my motor into a TP 450-Size 2415-09T Brushless Heli Motor 2700kv from Hobbyking paired with a 30A red brick esc and 4.75x4.75 prop.
With this setup, my parkjet can handle a Zippy 1800mah 40c battery and It flies faster too even with all that added weight.

Awaiting your Parkjet Twin flight reports Nigel.
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Old Feb 16, 2013, 11:46 PM
BLANIK213
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United States, NY, Phoenicia
Joined Feb 2008
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Hey Nigel Nice to see your twin come together,looking forward to the maiden.
How many Mah is your 4s battery and what c rating .Running a twin setup with 45c 3000 mah you will be sure to hit some serious speed and safe gaurd the life of your battery and 3600mah would be even better at keeping your voltage from sagging during the flight. Nice work .
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Old Feb 17, 2013, 09:16 AM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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Quote:
Originally Posted by ledzep76 View Post

First stage toward making my parkjet faster.
I bought a 4.75x4.75 prop and fitted it to the stock motor but it vibrated so much it nearly shook the fins off.
So I bought a new motor with a larger diameter motor shaft 3.17mm.
It is shorter too which helps reduce vibration and has bigger bearings.
Let's hope with a shorter prop I wil get more revs and higher top speed.
Still just running a 2s battery for now.
The motor is a rc timer 2805 14t rated at 2840 kv.
.
Rc Timer - I like their motors ......

mmmmmm just looking at the motor mount ... with an L bracket mount - I fitted my horizontal UNDER the beam into the foam. Enbedded with epoxy - it made for a super strong fixing.

The vibration may have been due to the mount being as it is only fixed by a narrow section ... and what looks like tape between the mount and beam ? For the stock and the motor you have - I would prefer a proper beam mount - RC Timer do excellent plastic beam mounts - my Twin uses 2 of them ...........

Nigel
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Old Feb 17, 2013, 09:26 AM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by blanik213 View Post
Hey Nigel Nice to see your twin come together,looking forward to the maiden.
How many Mah is your 4s battery and what c rating .Running a twin setup with 45c 3000 mah you will be sure to hit some serious speed and safe gaurd the life of your battery and 3600mah would be even better at keeping your voltage from sagging during the flight. Nice work .
the problem here is weight ............ all was set-up to take a 2200mAh 3S at 200gr ... so I have to keep to same weight in 4S ... which means a 1600mAh 35C ....

The amps draw combined is just under 50A ... so the 4S is gonna puff up when speed runs made .. but I'm willing to trade that for getting the speed.

35C x 1.6 = 56A technically capable ...

I haven't decided what pack will be in for test flight ... probably the 3S ... (note my 222kph was with 3S - never got to 4S as PKJ1 suffered bad crash with first trial of 4S .... ). I expect the 3S to produce similar 220 mark ....

Voltage sag ... flights are only going to be very short affairs ... I'm 57yrs old and I worry about my heart !! More than 2 mins in air with the twin I reckon will test my adrenaline The 4S pack even to full discharge is barely 2 mins ... the 3S at 35A is 3.8 mins. I think volt sag is least of my worries !!

Looks like I may be home before end this week ...so hoping that weather is OK for weekend.

Nigel
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Old Feb 17, 2013, 11:35 AM
BLANIK213
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Joined Feb 2008
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Nigel I hear you loud and clear about the adrenalin rush ,dry mouth and sweaty palms,I am 62 and flying my twin( Aurora) at 4.6lb's with 3800 watt's on hand is a scary blast, I am excited before I even get to the field.This season I'll be using a 4s 5000mah 65c Nano tech battery. Building a new Aurora that will use 5-6s 4000 mah 65c. I am sure they will come out with the next jump in battery technology by this summer 85 or 90c rated stuff
and lighter still.
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Old Feb 17, 2013, 12:41 PM
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Joined Oct 2010
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Nigel, my beam is gorilla glued in, I like gorilla glue as it has good grab on the epo only problem is when it expands it can leave a foamy edge. The mount is ply wood screwed and glued with epoxy with a 1/4" balsa rib for extra strength. It is all strong enough I assure you.
If the weather is good I will fly it tomorrow and see how it goes. I plan to remove the lumps under the wing as they were to protect the servo arm that now sticks up. Maybe clipping the wings a little will release some more speed. My aim is to go as fast as possible on a 2s battery.
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