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Pusher Park Jets For all pusher jets and jet-like models.

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Old 01-23-2012, 10:40 AM   #51
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Originally Posted by stuart View Post
solentlife,why not just order a few props from value hobby? i have a bunch of 5.5's 4.5's 4.75's,and am waiting on two 4.1x4.1 for the parkjet. emp e props.also the emax mg servos.

i would think to large a prop on the parkjet will torque roll it to much. but I'm new to this pusher jet stuff,and hooked on experimenting. lets face it,the 800watts with a 4cell in the park jet is equal to a lead weight with wings....i think it should fly fast...but i better not loose control or someone might get hurt[or worse].
My biggest problem is supply of anything RC related as I live in latvia ... a vacuum for gear.
The PKJ is spec'd on it's stock sytem as 5x5 ... so i will stick with that having ordered a few props in the box with the model.

As I said earlier - one of the benefits of cutting back a larger prop is rigidity of the prop ... and as I'm looking to push the speed to max and flex of props may be an issue. I agree that torque effects are going to be a factor to cover ... which I think staying with pitch but cutting back diameter is way fwd ... to keep potential speed up but torque down.

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Old 01-24-2012, 01:18 AM   #52
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thats pretty cool cutting down a prop. i have a bunch of 7x6 apcs that aren't getting used. i know nothing about cutting the shape of props to be messing with them. i always thought a props tips played an important part but shaping new tips shouldn't be an issue ,and a good balancer is a must i would guess.

wish i could mail stuff to you in latvia......i'll have to check a map to see where in the UK you are. when you get the hkpj going i hope you'll post your finale setup. thanks for sharing.

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Old 02-07-2012, 01:07 AM   #53
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update on the hkpj#2....on Saturday i went to maiden it,a friend was willing to toss it and i was going to use 1/2 throttle during the toss,this would have insured a good launch.

we were on the flight line and i was just about ready when he says"ready" ,i say "wait" only to watch my bud throw the park jet really hard...lol...i almost got it under control as it did a rocking roll before hitting terrafirma....

broke into 3 large pc's and looked pretty bad caked with dirt,wash off the dirt and epoxied the pc's back and shot a coat of paint to make it look nice again.

these pictures are of the gws stick mount which is way better than the custom ply mount that broke on impact. the motor is higher off the fuse than the first setup but thats the way hk designed it to be. i epoxied the stick in place but to be sure it is secure,i used a thin stip of ply with screws to insure it's not going to pull away from the fuse under stress.so heres hoping the weekend proves successful. at least it's no longer considered a maiden...lol...


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Old 02-08-2012, 11:44 AM   #54
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Originally Posted by stuart View Post
thats pretty cool cutting down a prop. i have a bunch of 7x6 apcs that aren't getting used. i know nothing about cutting the shape of props to be messing with them. i always thought a props tips played an important part but shaping new tips shouldn't be an issue ,and a good balancer is a must i would guess.

wish i could mail stuff to you in latvia......i'll have to check a map to see where in the UK you are. when you get the hkpj going i hope you'll post your finale setup. thanks for sharing.
Way to cut back a prop :

Clear a nice piece of bench ... stick wide masking tape from bench edge at 90 degrees at more than length / width of prop.
Measure and mark prop blades at length you want. Cut ONE blade.

Now put prop boss against bench edge and mark on tape end of prop. Cut other blade. Check they both match mark on tape.

Shape blade tip one only. Get it to desired .... then put back on tape and draw round.

Shape other tip to match tape marking.

Then chamfer the tip edges thinner ..... making sure you keep both same.

balance and bingo.

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Old 02-14-2012, 12:44 PM   #55
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Data for the following :

HK parkjet >
3700KV Heli motor rated for 6 to 8" props ... with a 5x5 Prop .... 3S 1300mAh 25C pack.

I had problems with a 35A ESC basically not being smooth in strat-up and throttling. Changed to Red Brick HK spare ESC I had ....

Connected wattmeter ...

Slowly ramped up throttle ... 5 .. 10 ... 15 .... 20A ..... and stick is still way down !! 30 ... 35 .... now I'm waiting for ESC to go pop ! ... 40 .. 45 ... 50 .... 54 Amps ! 540 Watts !!!!

Amazingly the motor remained cool .... but ESC / LiPo was warm - not over hot - but warm.

To maiden the PKJ with this ?? I'd limit throttle back to maybe 200W mark ... but honest answer ... I'm extremely wary of it .... and the run time by calculation is only 1.4 mins ......IF the ESC etc. holds out that long.

Now have to decide what I'm going to do as I cannot install a LiPo of sufficient size to give reasonable run-time ..

I need a high KV motor 3500 or more, but lighter so that it doesn't need the amps to drive it. Hopefully stays within the 15 - 25A~ range ...

Hobby King / Ebay suggestions please as I live in Latvia and USA shops are not supplying here ...

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Old 02-15-2012, 12:13 AM   #56
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increase the c rating and mah a little and try her out for a 2 min flight. but certainly go to a 60amp esc and open the rear of the canopy to increase air flow over the esc.

the helie motors arn't direct drives,they are geared to the helie prop shaft if i'm not mistaken. gears would reduce the wot draw in a helie?yes? i don't have any helies to attach a wattsup meter to check this out. did this helie motor pull 540watts in the helie?

solentlife,are you calculating your flight times as full throttle all the time,cause these type birds need glide time to keep things cool.so some added air time is shooting up high and floating down to the next screaming run with bone chilling high speed turns and shooting back up to cool down again..........i would average 4min flights with hkpj 1.but am waiting for another stick mount like yours to arrive. those alum mounts look great,way nicer than the plastic one i have on hkpj2.

so watts your plan for your power now?

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Old 02-15-2012, 01:42 AM   #57
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Originally Posted by stuart View Post
increase the c rating and mah a little and try her out for a 2 min flight. but certainly go to a 60amp esc and open the rear of the canopy to increase air flow over the esc.

the helie motors arn't direct drives,they are geared to the helie prop shaft if i'm not mistaken. gears would reduce the wot draw in a helie?yes? i don't have any helies to attach a wattsup meter to check this out. did this helie motor pull 540watts in the helie?

solentlife,are you calculating your flight times as full throttle all the time,cause these type birds need glide time to keep things cool.so some added air time is shooting up high and floating down to the next screaming run with bone chilling high speed turns and shooting back up to cool down again..........i would average 4min flights with hkpj 1.but am waiting for another stick mount like yours to arrive. those alum mounts look great,way nicer than the plastic one i have on hkpj2.

so watts your plan for your power now?

You Chuck Yeager speed demons amaze me. Dying to see a vid of the souped-up HK Park jets screaming by on a low pass Whats' not to like? I'm still flying like granny.

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Old 02-15-2012, 03:42 PM   #58
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No way I'll try the heli motor as a maiden on the PKJ ... Later - yes once it's set-up and I know what its like in the air.

I changed the motor to a 1800kv 2805 motor ... yes - I know its a hell of a drop back from the 3700kv motor ! but this one takes a 4S ok !!

I have 920mAh 4S packs from my EDF that give me 11A and 150W on the motor. This initially sounds low and unsurprising ... but look again ... 1800kv on a 14.8V pack ... AND still using a 5x5 prop ... so speed should still be reasonable.

I have a 3800kv motor on order that should be more reasonable on amps draw ....

I'm no expert in this - but in my mind speed is related to how fast you can get the prop to turn ... and pitch. Most i read CUT BACK props when increasing power ... mmmmmmmmmmmm well - I'm looking to get not only a boost from increased power / kv ... but also pitch.

I also a 5000kv motor sitting waiting .....

Biggest problem we have here at moment - is the northern winter .... short days, snow everywhere, freezing temps ....

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Old 02-18-2012, 02:37 AM   #59
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getting ready to install a new motor in the hkpj#1 mounted on a stick with a plastic motor mount from headsuprc,it angled to be mostly neutral with slight down thrust. i also couldn't help but shoot a fresh coat of orange paint tonight...lol.

this lil birds taking serious abuse and is so easy to repair.

.......................................
this is a very serious discovery on my part and must be shared for all.

i made custom plywood motor mount that even impressed pilots at my field. the simplicity and strength was all there and so cheap. the last time i hit terrafirma with this bird i put her back together with this new motor and screwed it to the ply mount. bench test to see how much thrust i could feel while holding the pj by the nose....

not to bad!!! i could tell by the force it will fly pretty fast if i prop up...ran the motor up wot just for a few seconds each time before shutting it down.......,that when with a slight touch the ply mount broke offand after initial annoyed moment i realized if the mount failed while doing wot test i would most likely be telling everyone how many stitch's i got.

moral to the story is this....if you think its good enough...do it even better,and don't fabricate things that other wise will hurt you if it fails. i am embarrassed by my discovery but happy to share my error so others don't have to make the same mistake. thanks,stu
........................................

pictures are of the plywood mount i'll never build again,and then the repaint job before reinstalling the motor saturday.








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Old 02-18-2012, 03:50 AM   #60
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Whew ! Close call Stu ! Thanks for sharing this with us.

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Old 02-18-2012, 08:16 AM   #61
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Stu ... sorry to say this but a single vertical plate like that ? with couple hundered watts shoved against it ? Not so bad if the thrust is into the beam and model - but its acting like a lever on the joint.

Reckon if you'd fitted side panels going forward as the CF light mount does - it may have been ok.

Me ? I'm sticking with the beam mount in alloy ... only way that will come away is if the beam itself breaks out of the model.

Today - I try with the increased power plant and EPA ... 25A / 280W / 21,060rpm .... and I have optimistically fitted my Eagletree speed sensor ...



readable through canopy ...



Wish me luck !!

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Old 02-18-2012, 11:48 AM   #62
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Details :
18 Feb 2012
Ventspils open field Latvia
-5C and light easterly wind

HK Parkjet stock kit
Wester 3700kv Heli motor
1300mAh 25C 3S LiPo
30A Red Brick ESC
Throttle EPA set to keep full throttle to max 30A
5x5 Eprop

FlySky Radio
FrSky Module + Rx

Eagle Tree Speed Sensor with onboard display.

>>>>>>>>>>>

First Launch was disaster as previous.

Second launch with more power - she got away and started to fly but trim was so far out despite all surfaces being aligned before flight ... needed assistant to trim as I couldn't let go sticks ! Got her trimmed and she flew dead straight ... on rails ........ incredible manouvreability ....
3 minute flight and a beautiful gentle glide to a few feet from me ....

We all knew she had been fast ... I could hear the guys behind me all quoting various numbers .....

I picked her up ................ took her to back of car to try and get to warm !! Hands shaking and adrenaline still flowing ....

Called guys over and we read the sensor display :

222 km/hr or 138 mph

No joke ..... video of reading available. Unfortunately the SD card didn't like the cold and the flight vid was corrupted.

Motor / ESC and LiPo - all came down well within reasonable temps.

Note I still have throttle left to use ... but only if I up the ESC ...

222 km/hr !! Who's going to be first to top that ?

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Old 02-18-2012, 03:05 PM   #63
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nigel,....first off,you don't need to appolgize for commenting on that motor mount,from now on you are to consider yourself as having a very good friend in nj usa! the mount and pusher flyers are all new to this ol pilot ,and i'm glad to share mistakes with good friends....lol..i consider everyone here at wattflyer as such. the hkpj's are using plastic stick mounts and won't be breaking away any time soon.




secondly,i'm sorry to have to tell you this about your 130+ flight.............










congradulations!!!!!
outstanding good news to hear of this my friend! you have set the bar for the speed to be beat. i am positive the 2700kv with 4 cell will beat your speed,but i have to get the nuts to give it a go without having been at the field much. so today i'm charging batts to fly the newly rebuilt rv-4 40 and also will take the airfoils yak. i need to spend time putting the motor back on hkpj#1 and will use it to warmup before flying pj#2.....better warmed to the speed sticks then sorry to the walk of shame...lol[like 2 weeks ago]. besides,i'm going to have to beat a very fast pj record here at wattflyer.


nigel,that speed checker looks very cool!!! nice job!! lastly i will video todays flight of the rv-4 and airfoils yak,and possibly the funjet ultra maiden, i'll have to rely on dopler to record speed on the pj & funjet as no one has a radar gun at my club.

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Old 02-18-2012, 03:53 PM   #64
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Stu ... you DEFINITELY have a pal over here in Latvia ....

2700kv with a 4s ..... I think you'll be slower ............ even if you hit theoretical rpm ... you are still 2k short of my combo ........ AND I use a 5x5 prop.

I also have the 5000kv motor sitting in the wings to fit ... shaft adaptor on way from HK ....

AND I have a 4S that fits nice ..................... I am DETERMINED to get max out of this amazing machine.

So I am setting benchmarks based on 3700kv motor :

3S power : 222 km/hr

4S power : (once I have better ESC will set this mark)

THEN I will set the marks on the 5000kv .................

OK - lets get back to reality - the PKJ is a dream once you get the trim set .... but it is SO sensitive to trim ..... and is why I couldn't get it to launch before. I was amazed when I shut down throttle and it appeared to just hang in the air and glide so sweet ...... unlike any delta I have flown before.
The surface movements I have are too much in all honesty. I'm lucky that I took your advice and added stiffening to the elevons. I reckon a simple way to stiffen these - make a slot along the length and fill with epoxy. No need for CF or anything else. The Epoxy alone would be enough and also you can smooth of nicely with a damp finger ....

Parkjets rule !!

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Old 02-18-2012, 04:59 PM   #65
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Before actually getting this machine to fly ... and to get such a fantastic result on its maiden ... 222 km/hr .... I can now without reservation say to some who advised against such a power set-up ............. it works !! Plus I still have power reserve to call on ............

I was told the motor would burn up .... ESC would fail .... model would never fly as it would torque roll out ...

I agree that it is a real handful to launch and get going - BUT it flies ... once it settles out - it flies on rails ! amazing machine.

I like to experiment and prove things possible..... so many things are supposed to be impossible.

I am now looking to see others push my speed aside and do better ......

???

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Old 02-18-2012, 05:31 PM   #66
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Here's reading the sensor ....

http://www.youtube.com/watch?v=bADB0...1&feature=plcp

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Old 02-19-2012, 12:26 AM   #67
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that thing is excellent! i didn't know it was a numerical readout. i thought it would flash twice fast and space the next number of flashes to give the second # of the speed...ect..ect...but to read those numbers is great.


i came home from a bad day at the field only to combine 2 planes into one...lol.rv-4 40,and airfoils foam yak together in the same garbage bag.


but to ease my pain,i finished the pj1 with a simple set up to use for warming up.it a 2000kv,30amp esc,and 3cell. its pulling 277 watts and 27 amps using a 5x5 e prop. i will hopefully will be trying the pj2 soon. i can't believe this,but my order from hobbyking of another parkjet arrived already. not even 2 weeks this time and used regular shipping. i have to wait to build it so i can see how the 5000kv motor you have works out.

nigel,i would consider adding structural support for the wing and fuse if your exceeding 140mph. foam failure is imminent with the g forces we hope to put these birds through. the eleverons may even be better replaced with a more solid material,they will flex and twist at high speeds,but we'll just have to experiment with this bird. like you said...folks will say it can't be done,but we'll prove them wrong...


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narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 02-19-2012, 12:48 AM   #68
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Nigel, what do you think it would do with a 5x3? Hurry back from the land of sand so you can break more barriers!

All of my landings are three point landings if you count the spinner, too
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Old 02-19-2012, 12:51 AM   #69
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Stuart-we are putting solid control rods into those Fly Skys you sent us. I'll send a vid when we get them in the air. Thanks, again!

All of my landings are three point landings if you count the spinner, too
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Old 02-19-2012, 08:45 AM   #70
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My thoughts are to get light finishing scrim cloth and epoxy glass the underside completely. I did this years ago with a FW190 that was without wheels. It took so much abuse without a mark. The weight penalty was small. It will also allow me to fix the battery velcro strap - which has failed again. I can then "stitch" right through the fuselage and back up to lock the velcro strap down.
Elevons ......... thoughts there are to replace with balsa section which will be straight and no need to CF at all. A thin grain filling base coat - then spray paint to match.

5x3 ? That's reducing the pitch a lot ... I think a better move would be to keep pitch up and reduce diameter ? I have an excel file that calculates pitch vs distance travel unloaded and actual ... which relates to speed. So far the 5x5 has EXCEEDED the calcs ............

If I fit the new motor coming from HK ... a 3800kv - then a reduction of diameter is likely needed.
The 5000kv EDF motor I want to fit once I get a suitable adaptor - also in same order from HK ... again diameter may be the issue.

I reckon I can push this baby over 150mph with only a small change - even on present set-up if I risk overloading the ESC ......

YES Stu - it's story of my life - proving experts wrong !! I love it !! Especially when they go very very quiet !!

Rock on !!

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Old 02-19-2012, 01:06 PM   #71
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thats his way of saying"hey stu! take a pill!" lol.that post earned 3 laugh smilies...lol +1.

I GUESS WE KNOW WHERE TO BUY SPEED NOW!!!!to funny!

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 02-19-2012, 01:15 PM   #72
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good morning Nigel and friends,i think Nigel has 2 ideas here that will work together. add 2 thin skewers or in my case carbon fiber rods i the fuse ruining front to back and go ahead and glass the bottom of this pj all over the bottom with the Velcro strap recessed in the bottom of the fuse for the battery as you described earlier.edit:other changes are alloy motor mount,a dowell/screwed down canopy as nigel also showed but modified to use a plactis thumb screw in the rear.

now that will secure the battery and support the overall build. it's funny you mentioned glassing. yesterday at my clubs field a friend who has a funjet glassed the top of his wing and elerverons,he also added a strip of carbon fiber from to back on the bottom and only glassed over that area to protect the bottom and secure the rod. this bird of his has been clocked at 168mph and he will wot down the field and pull straight up at wot and go around with super g forces on the wing ...rolls whipping fast turns.....the bird stock would break without a doubt.

so now I'm looking to make a list Nigel,and your discoveries are paramount to the ultimate design for future hkpj's!!! special note: the funjet of my friend is flying a motor on 6cell,2 3 cells in series. the weight of his plane is very heavy,so if speed and weight play a factor over speed and strength,some one would have to explain to me how that bird flys,it is a rocket,and the fastest plane at our field.

at least for now....lol heres a video i took of his funjet doing 140mph[dopplered using a phone app]

funjet 145+mph video
stuart


cool,i just copied my post from your thread and moved it here! how easy.

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 02-19-2012, 02:59 PM   #73
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Here's the stress marks in paint I mentioned ..





Ok ............ first mod made while packing bags for next assignement !

Measure and cut balsa 1/4 x 1/4 spars to insert into underside :



Soldering iron to melt grooves for spars to sit into ...



Epoxy spars in ...



Sand to section





Spread epoxy thinly all over whole modification to give added strength .. then mask up .. spray ...



Finished job ...





Now I just wait to have paint dry ....... then epoxy / screw the velcro strap into place.

I was going to use pine spars ... but then balsa is lighter ... with epoxy can provide a good screw hold ... plus if it does a lawndart - the balsa is not so strong that would cause greater damage !
I can say the fuselage is now stiff ...


I hope that my and others bits and bobs can help others to enjoy this baby ...
Even though some of it appears to compete with convention !

It's going to be a long frustrating time at work for 3 weeks with no PKJ to play with !

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Old 02-19-2012, 06:58 PM   #74
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I'm sorry if some find my obsession overpowering .... but I am on a road to find the max we can take this baby to ...........

I wish others would join in and add their mods / ideas to the pot.

At present I am running the stock advised 5x5 prop .... this is probably at or near max speed on my set-up ... much more and I reckon it will start to actually decline in performance...

So question is what happens if I cut back a higher pitch prop ... ie a 7x6 cut back to 5x6 .... problem of course will be to keep tip aerodynamic for the tip speeds we are in. Second the amps draw on the ESC / LiPo ...

Before than though there are other avenues to go for ... higher kv ... higher amps ... 4S ..... plenty of scope to play with yet ...

Here's a few photos from the day ...

Dusted of after first failed launch .... ready to try again ...



Vilnis waiting for the GO signal ...



SUCCESS !!



She's away ... but trims are in dire need of help !!



She's up and on rails ...



...........

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Old 02-19-2012, 10:38 PM   #75
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I think for more speed, you should reduce pitch. Instead of a 5x5, try a 5x3 (if there is such a thing). I find the difference in speed between a 6x4e and 6x3e to be pretty dramatic on my modded Wild Hawk. 6x3e blows the pants off a 6x4e!

Obviously, going up in diameter is going to draw more amps. Don't know what your esc and motor can handle.

All of my landings are three point landings if you count the spinner, too
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