|May 11, 2012, 06:48 PM|
Rainy day RBC balsa MicroJet build
I found this interesting kit at a swap meet a couple years ago and have debated with myself on what power system to use.
As the rain was falling today, I decided to pull it out and give it some thought.
Here are the specs..
CNC cut wood built up with rib/frame and full balsa sheet wing
WS 475mm, 18.7"
Flying weight 500g
The model was designed around the year 2000 and flew on a 6v speed 480
and wemotec fan.. and a bunch of heavy batteries.
I have choices at home here ranging from edf to various outrunners.
The edf unit was pulled out of some foam jet. At over 80 grams complete, and drawing over 30a, it adds up to a heavey system for my mission. I know it would be cool though.
I want a parkflyer type plane that is quiet, light, and efficient, while demonstrating great power to weight and respectable speed range.
I am thinking of a light outrunner with small 3s, 400-800 mah,
and flying weight of 6-8 oz. 170-226 grams.
I have an Eflight "park 280" 1800kv 22g that swings a gws 6x5rs quick enough to go quickly and have better than 1.5/1 thrust to weight.. assuming I meet my goals. Sounds nice but..
I have these pretty little Microdan motors.. at 34g, they dont look so little hovering over the plans. 1845kv is the slowest one and would still be 70mph+ with a 6" apc or Graupner prop.. or 90 plus on a little 4s lipo. Forget the 2535, or 2900kv.
Not bad, but I was thinking of just entertaining the "Park" not scaring it. Having a slower and quieter wing will expand my close to home flying site options.
Not to mention, very enjoyable to fly because of being light and powerful.
That means a light esc (10-12a) and a motor that does it's best work at around
Still havn't settled on a motor but I saw this in the case at the LHS..
I think it would bridge the gap between the motors I have and give me a new flavor of power for my special build, if not at a bit of a cost.
I will start tonight by cutting loose the parts (they have large holding notches)
and weighing them. Stay tuned, should be a nice one..
|May 11, 2012, 09:26 PM|
Why would you need a 6" prop on a 19" plane? That's a torque roll death waiting to happen.
You could run one of your higher Kv MicroDANs with a ~4.5" prop and still have a ton of power on tap, but even that would be a little sticky as far as practical weight. One of those popular 10g outrunners would be a good match on three cells... Maybe you could go even smaller.
|May 12, 2012, 10:33 AM|
I have considered torque on this small model and am prepared to go smaller on the prop, or do what it takes.
A 6x5.5 at 15k sounds much quieter and performs better than any of the fast (19-23k) turning gws I run on the Microdan.
You will see as I build this that it is not as small as 19" would suggest.. It flew great back in the day at 500g. (not a "micro")
I will post a pic beside a baby Stryker to illustrate.
The separated cut wood pieces, planks, and sticks total 170g.
How much is left behind and how much is gained in covering?
I figured 4-5 oz airframe with a 2-3 oz electronics is about right.
6-8 oz total is really light considering this design will fly fine at over 1lb.
I like the idea of Microdan but it only musters 6-7 oz thrust on a 4.5" and 10 on a 5".
I can change a motor/esc/battery in minutes, so I do not have to settle on one system.
|May 13, 2012, 02:18 PM|
Since this is a discontinued long-ago kit, I am just going to post the highlights.
This is a builder's kit that requires careful measurement of both weight and dimension of the skin panels. I found out the hard way having to backtrack and re-draw a few things.
It took about 5 hours to get to the point were I need to spend hours carving and sanding.
It is built like a tank at a full 142g (5oz), but I see alot of carving and rounding so take off 1 oz.
Add a firewall, some carbon, glue, and clear orange covering with trim.
I think the goal of 5 ounces minus electronics is realistic.
Keeping under 8 oz will be a challenge, so I will be satisfied with under 9.
|May 15, 2012, 03:28 AM|
Thank you Rctrainerplane.
Here is the latest after another 4 hours of firewall/motor installed, ailerons hinged but not glued in, and further sanding.
I must say that this has been a very difficult build.
There have been so many considerations in how and what to sand as one has to visually interpret a 2D plan into a sanded 3D wing with taper and washout.
The new Park 340 was chosen and comes with a mount perfect for this application.
Almost ready to cover...
|May 15, 2012, 10:10 AM|
|May 16, 2012, 04:09 AM|
My phone camera doesnt capture the real color, but it is officially clear orange monokote.
Coverite checker is some serious high quality film, and they know it... $25 a roll!
The center has a clear monokote top, that will reveal the not yet installed electronics.
10 ounces AUW.
340 motor has a unique 5.1x4.5" "paddle" prop installed... have others to try.
Mad Dog12a esc and D47 servos complete the package.
Looks like fun!
|May 16, 2012, 10:06 AM|
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