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Old Feb 17, 2013, 08:21 PM
BLANIK213
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United States, NY, Phoenicia
Joined Feb 2008
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ledzep76 if you want to go fast on 2s a higher KV would help ,2840 on 2s might get you 80 depending on what prop is used. Scorpion makes a 4400 KV motor that would do the job on 2s .
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Old Feb 17, 2013, 08:48 PM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
8,391 Posts
Quote:
Originally Posted by ledzep76 View Post
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.
Photo's are always deceptive .... I wish you great speed !!

mmmmmm the lumps under wings ... doubt they make much difference - iof you fit the plastic bits over that are supplied - they are streamlined and smooth ... As to clipping the wings - don't forget this model is extremely torque happy ... and reducing span could increase that ...

The KV motor you are running is less than stock ... i would suggest going up from stock ... there are plenty of 250 size Heli motors out there ... 3500 ... 3800 ... 4000 and more KV ... even a 450 heli motor like my 4400kv from Hobby King would generate good speed and be able to turn a high pitch prop ...

2850kv .... 2s ..... 4.75 .... gives theoretical as per my test data sheet of : 57mph / 92kph .... (i have a spreadsheet that I devised based on tests of my PKJ's ... logging calculated vs actual in terms of RPM / Speed etc. - motors I've run have been from 1800 up to 4400kv ... 3S ... 4S .... and props from 4.5 up to 5 pitch etc.)

Nigel
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Old Feb 18, 2013, 01:19 AM
Note to self, put on pants.
Jayman72's Avatar
Australia, VIC, Frankston
Joined Mar 2012
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Quote:
Originally Posted by ledzep76 View Post
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.
This motor could fit the bill although would look unusual.
http://www.hobbyking.com/hobbyking/s...r_55_64mm.html

Only 50 odd grams and has a 3.0mm shaft not the 2.3mm shaft of 250 size motors. At 4200kv should be good on 2 cells if you can source the current.
I've chopped a couple of props to get the specs i want such as a 7x6 down to a 4x6 just to get the pitch speed and take the load of the motor for higher rpm. Where did i put that 8x9!
Jamie
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Old Feb 18, 2013, 01:31 AM
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Australia, VIC, Frankston
Joined Mar 2012
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They say the load rpm is 37040 for 3 cell. But dont say what load. 2 cell would be 24693 rpm
Pitch peed for this on 4.75 prop is 178kph if current draw is in check and can run a 4.75x4.75 prop. Even a 4.5 pitch is 169kph
Jamie
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Old Feb 18, 2013, 05:41 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
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Quote:
Originally Posted by Jayman72 View Post
They say the load rpm is 37040 for 3 cell. But dont say what load. 2 cell would be 24693 rpm
Pitch peed for this on 4.75 prop is 178kph if current draw is in check and can run a 4.75x4.75 prop. Even a 4.5 pitch is 169kph
Jamie
Jamie ... one of the first things that happens with the PKJ as we extend up into the power regions ... is pitch speed goes out the window ! well actually real speed vs Pitch Speed.

I have a Spread sheet that I enter calculated, theoretical based on average of real vs calculated ... etc. In the lower kv / power bands the real vs calculated is pretty constant - but as soon as you get into extremes - the rules fall apart.


2200kv
4S
145W
32560kv/volts
19200rpm actual
5 pitch
154 pitch speed MPH
248 pitch speed KPH
93 theoretical speed MPH
149 theoretical speed KPH
84 actual speed recorded MPH
135 actual speed recorded KPH
54% calculated speed vs actual.

My record breaking 222kph results :-

3700KV
3S
520W
41070kv/volts
32000 actual rpm
5 pitch
194 pitch speed MPH
313 pitch speed KPH
117 theoretical speed MPH
188 theoretical speed KPH
138 actual speed MPH
222 actual speed KPH
71% calculated vs real

See my point ?

I'm truly waiting to see what my twin results will be ... this is the theory results :-

3000kv x 2
4S
over 700W combined
44400kv/volts
38000 rpm
4.75 pitch
300 pitch speed MPH
482 pitch speed KPH
180 theoretical speed MPH
289 theoretical speed KPH

Actual unknown at present ............ but I reckon she will hit about 275kph ...

Nigel
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Old Feb 18, 2013, 02:42 PM
Note to self, put on pants.
Jayman72's Avatar
Australia, VIC, Frankston
Joined Mar 2012
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Yes i agree Nigel. Its pie in the sky stuff. Same with most planes. But its was a base line for a 4200kv motor compared to the 2850kv for 2 cell. Starting from a better place so to speak. Of course other factors such as drag and prop efficiency come into it. And drag goes up exponentially with speed. Just actually bought that motor to try out. It cheap enough to try a fastish 2s plane.
Jamie
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Old Feb 18, 2013, 02:48 PM
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United Kingdom, England, Bisley
Joined Oct 2010
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Hobbyking parkjet on 2cell. (6 min 24 sec)

Interesting motor, I guess I could try it. I got one flight in at lunchtime today and found that after I raved about gorilla glue my launching handle under my parkjet came adrift on landing.
I had even cleaned all the epo parts of my parkjet with surgical spirit to get rid of any mold release agent.
Anyway I did a video today. Its a bit long but does show some passes in both directions ( although most are into wind the wind speed was only 5 mph).
I fly from a small park about the size of a rugby pitch, for the passes I was diving toward the trees at the end and flying at about 20ft off the deck for the length of the field. Video is a bit poor as it was done on my phone.
Can anyone Doppler this please and maybe we can pool our results.
Personally I think I have made my parkjet a little slower than a stock one.
.
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Old Feb 18, 2013, 04:21 PM
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Australia, VIC, Frankston
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Ledzep
One of the things i do with foam and gorilla glue (Love the stuff) is using a skewer, poke holes in all directions in the foam for the glue to expand into. She grabs good them. Tip i picked up on here somewhere. What prop are you using on the 2850kv? I have the emax version of this motor which unlike the rctimer version has poor windings but a good basis for rewinding. I have the stock amount of turns but using 24awg 'real' copper. Rewinding is a tedious job but you can get the kv you want by altering the turn count. These are wound dLRK. This may also be an option for you. Are you wanting the plane to be fast but still be light and floaty or as fast as possible regardless of weight?
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Old Feb 18, 2013, 04:43 PM
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Joined Mar 2012
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Ok guys, finally finished my parkjet. 9 months after i bought the kits. Intention was too keep this one close to stock and make the 2nd kit the speed machine, but not sure now that the machine is nla. Scratch built clone for a speed machine maybe.
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Little changes are rewound stock motor, 30a esc, xtra carbon, big old hard drive magnets and carbon pin for canopy holding, servos on top, stick mount to keep motor as sleek as possible. will be running 850 3s
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Old Feb 18, 2013, 06:11 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
United States, MN, Hermantown
Joined Dec 2008
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This is for you, ledzep76


Say NO to Vertical Videos,Vertical Video Syndrome (2 min 42 sec)
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Old Feb 18, 2013, 11:41 PM
BLANIK213
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United States, NY, Phoenicia
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Thanks for the late hour laughter CoolerByTheLake.
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Old Feb 18, 2013, 11:56 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
United States, MN, Hermantown
Joined Dec 2008
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Glad to be of service!! A fellow in the scratch build edf forum posted a video just like that, someone else did the honors.
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Old Feb 19, 2013, 01:10 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
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One format that you would have a field day with ... Keychain cam at an angle ... I attached one to my Cessna wing strut for an onboard .... Only did it one time !!

Cessna 182 In-Flight keycam 10 july 2011 (5 min 22 sec)


Catch that one !!

Nigel
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Old Feb 19, 2013, 02:33 AM
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United Kingdom, England, Bisley
Joined Oct 2010
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That's hilarious!
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Old Feb 19, 2013, 03:33 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
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Quote:
Originally Posted by ledzep76 View Post
That's hilarious!
I didn't really understand Movie Maker then and thought I could trim the window to square it up !! No - all it could do was to rotate so horizon was level !

I now mount the keycam on top of wing to one side by tie-wrap through the wing. It only needs two very small inconspicuous holes for tie to pass through. When not carried - you don't notice the holes at all.

Nigel
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