RC India

Dear All,

I am using this forum for long time yet I have not contributed any thing to this community. So, here I am putting my effort to build a electric J3 cub that I am building for my friend. Plans are from RCG, a profile plan, I am building as full fuse.

Specification:
Fuse- 3mm, Coro 31"
Wings- Foam cut, 52" (planning kind of back packable)
motor - Turningy 1450kv motor ( suspecting not sufficient)
Prop - 8 X 4
ESC - 18A
Servo- 4 x 9g (2 aelleron+1rudder+1elevator)
Battery - 1000mah,3s

Targeted weight was 550g, now i feel it heavier than i planned. i may have to reduce some weight on fuse (Coro). Suggestion for reducing the model weight is appreciated

some more pics

wing halfs

Looks GORGEOUS.

What is your AUW ?
If your weight (in gm) and Watt of Motor (Volt x Amp x η x t)
where η = system effeicency , and t = throttle (Let 75%)
and if you get 10-15 gm/watt, your plane will fly beautifully from power point of view.

Your 1000mA 3S (Hope 20C minimum) can deliver 20A Max Safely.
So, power = 11.1 x 20 x η x 0.75 = 120 watt minimum at 75% Throttle.
So, you can go upto 1000 gm AUW (All Up Weight).

Just search some previous thread where AUW and power calculation in details given.

Thanks

Firstly a great build!

Are those Aluminium strut landing gears? may be u can substitute it with a wire type?

also you can use a Carbon fiber or a Glass fiber rod instead of that beading ?

Hope to see her maiden soon!
 Happy Landings! :)

Congrats Boss! You are now tempting me to start assembling my HK J3 Cub!

Very beautiful profile on that wing. Nice build, just needs a cowl for the stubby nose :)

Attractive build msri21  :thumbsup:
@KALYANPRODHAN: which motor + prop you suggest for this model, assuming average AUW of 1000grams?

Thank you all for your comments.
@Kalyanprodhan: as per spec, with this prop it should give 550gm thust( 150w). i feel the model should be now 700gm.
@Jataya: ya it is a aluminium sturt, made using aluminium strip(25rs) purchased from commercial street. i had am option of using steel spokes( 10 gauge) very much suitable for this purpose. felt it will be heavy. this is a budget model of my friend 5.5k all.
@VC: thanks
@sunlikestar: i was not able to make proper cowl. coz my motor is limiting.
Hope I'll maiden this weekend.

very nice build msri21.
have a great maiden and pl do share the video

p.s: in fuse 4 .jpg it looks like the tail is bit twisted. Cub is very sensitive to this.. watch out!
ashta

some more pics with wings, wings servo mounting is on progress

@ Ashta: that photo was taken before glueing the tail

is the wing span more than 4 feet?

 Yes 4.3 feet

Beautiful aircraft. {:)} {:)} {:)}

All the best for the maiden.

msri21

For her size, her track is less, consider wing skid

Hi Augestinev. i do not understand the concepts you are talking about, can you brief a little please. I mean track and wing skid

weight is 700 grams with the electronics?

it is not only the longitudinal distribution of weight that matters, vertical wt distribution also matters, in a high winger the CG is sitting pretty high compared to a Mid or a Low Winger, so as a thumbrule your track should be atleast 1/3 of ur wing span or more for a high winger to prevent it from doing Ground Loop , cart wheel or wing touch and damage the wing, even then since the chances of wing touch is more for a high winger, so you put  wing skid to avoid wing tip damage

Also high CG affects during rolling and combination of manoeuvres, that's why most aerobatic aircraft have CG along the centre of the fuselage ,neither above nor below

Thanks for that beautiful explanation, i never know this fact. I will try to better it by widening the wheels so height will also come down. 

Its gr8 at alll.  can anybody suggest me how to shape such foam in airfoil shape? i tried once same as we do on balsa  -

not succeed :banghead:

using sand paper you can achieve the shape

hmmm, but  i was not able to make it smooth.... may be the foam or sand paper i am using is differnt from you are using. can you say about it more? :headscratch:

@PiyushI: this is a foam cut wing. Very simple i took 2inch thermocol. Made two aerofoil shapes out of cardboard,very easy to shape. Fix these two pieces on either end of thermo.  using hot wire foam cutter drawn along the aerofoil. Slightly sanded over for finishing

there are sand papers of different fineness.... try using a finer one than the one you already have
@msri not everyone has access to a hotwire cutter

exactly, the method was same, tool was differ :o. i didn't yet used hot wire cutter. I will try to find how to get that tool.


you are right, Rajiv.

 :help: CAN anybody show how to prepare hotwire cutter or from where it can be purchased?

you can see how to make the hotwire foam cutter here:-
http://www.instructables.com/id/Hot-wire-foam-cutter/ (http://www.instructables.com/id/Hot-wire-foam-cutter/)
more than 1000 :Rs: !!! :o

@rajiv
 :thanks:

Did the maiden today, model was heavy and under powered. Hence planning to change the power system. And reduce some weight on coro side. She had a short fligh and nose dived. Feel every thing is fine except power. Will do that this week.
@PiyushI: hot wire cutter is very simple to make search in the forum. Already threads are available. I myself made using that information.

http://www.youtube.com/watch?v=GWF1XwrgjD4&feature=related (http://www.youtube.com/watch?v=GWF1XwrgjD4&feature=related)

try making the fuselage with 1 cm styro sheets cut with the help of hot wire cutter. Use coro to give strength to the landing gear, wing attachment and motor mount area.

hi,

here is my piper J3. made from 3mm coro. All up wt is around 2.8kgs.

flys with a 5s lipo and a 650kv motor turning a 12x6 prop.

@sbajare.. what are the dimensions? Looks fab