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        Discussion "Lucky 13" - A sport/aerobatic plane

#1 V-Man Jan 19, 2013 06:17 PM

"Lucky 13" - A sport/aerobatic plane
 
2 Attachment(s)
Back in the 80s, when I was a teenager, I used to buy R/C magazines like RCM and Flying Models. I only flew freeflight (mostly Guillows), because that's all I could afford. Besides, no one I knew flew R/C, and good luck learning without a simulator back then!

A couple of years ago, I finally hit on the right combination of free time, interest and spare cash, and I got my first plane (and a sim). Now my current fleet is up to #12, most of which are still flying. All of it so far is foam of some kind, because it's simply cheaper and more forgiving. At the end of last season, I decided I'd gotten good enough that I can now risk more hours in my aircraft. So, it's back to my first love, balsa!

Though I have several projects on the board, the first one to go is the appropriately named thirteen airframe. I've decided to base myself on a design from a mid-80s issue of Flying Models, called the Just-4-Fun. It's originally planned for a .20-.25 four-stroke engine, with a wingspan of 51". I wanted something a little more "park-flyerish," so I scaled down the blueprints to a more manageable 40" wingspan. I'm also modifying the outline, adding different wheelpants, nose, built-up and skinned tail, etc. The goal is to learn and practice as many techniques as possible. The plane will fly on electric power, the exact motor will depend on the airframe's final weight (I want around 100-125W/lb).

Pictures below show the original design by Ron Farkas and Hank Stumpf, from the pages of Flying Models. It's the November 1987 issue, if you want to order the blueprints yourself.

#2 V-Man Jan 19, 2013 06:27 PM

6 Attachment(s)
While I was cutting out fuselage parts, I decided to get started on assembling the tail group.

The original design called for a solid 3/8" balsa sheet tail, but that's too heavy. I made patterns from foam and I bent some wet balsa strips to make outlines (a technique I'd never used before). Once these were dried and sanded, I added some structure inside.

I glued the top skin on: it's 1/16" sheet, which will be sanded down to a slight airfoil shape. Before I close the bottom, I will reinforce as required for the hinges and horn mounting points.

#3 V-Man Jan 19, 2013 06:34 PM

3 Attachment(s)
The fuselage is basically a balsa sheet box. The blueprints called for 1/8" liteply, which I'm sure I required for a four-stroke engine. In this case, though, I'm using 1/16" balsa with some doublers and internal reinforcements. I have a similar-size plane made of 6mm foam sheet, and it flies just fine.

Once the doublers were dry, I glued on the main formers, making sure they are square to the sides. Then I added the rest of the formers. The plane is already taking shape! Got to start thinking about a hatch somewhere to change the battery without having to take the plane apart...

#4 Charles B Jan 19, 2013 08:13 PM

Quote:

Originally Posted by V-Man (Post 23865503)
Back in the 80s, when I was a teenager, I used to buy R/C magazines like RCM and Flying Models. I only flew freeflight (mostly Guillows), because that's all I could afford. Besides, no one I knew flew R/C, and good luck learning without a simulator back then!

A couple of years ago, I finally hit on the right combination of free time, interest and spare cash, and I got my first plane (and a sim). Now my current fleet is up to #12, most of which are still flying. All of it so far is foam of some kind, because it's simply cheaper and more forgiving. At the end of last season, I decided I'd gotten good enough that I can now risk more hours in my aircraft. So, it's back to my first love, balsa!

Though I have several projects on the board, the first one to go is the appropriately named thirteen airframe. I've decided to base myself on a design from a mid-80s issue of Flying Models, called the Just-4-Fun. It's originally planned for a .20-.25 four-stroke engine, with a wingspan of 51". I wanted something a little more "park-flyerish," so I scaled down the blueprints to a more manageable 42" wingspan. I'm also modifying the outline, adding different wheelpants, nose, built-up and skinned tail, etc. The goal is to learn and practice as many techniques as possible. The plane will fly on electric power, the exact motor will depend on the airframe's final weight (I want around 100-125W/lb).

Pictures below show the original design by Ron Farkas and Hank Stumpf, from the pages of Flying Models. It's the November 1987 issue, if you want to order the blueprints yourself.

Yes you'll like that Plane. My has a 50.5 inch wing and 34 inch Fuselage. We got it from some one 4 years ago. It is one of our best fliers. We couldn't ever find out the name of the plane .
Ours is electric it uses a SK3536 910 kv its run a full power of 240 watts with a
Prop a 9 * 6 APC and a 3S 2200ma Lipo. Flight time is well over 20 minutes.

It has no bad tip stall even at real slow speeds.

It flies upside down as well as right side up.
If you look at my Blog you'll see mine.

We run off of grass runway an use 2.5 inch wheels. It handles wind up to 20mph with not to much problem. Ours come in at 2.5 lbs.

Good Luck

Charles B.

#5 V-Man Jan 19, 2013 09:40 PM

Quote:

Originally Posted by Charles B (Post 23866390)
Yes you'll like that Plane. My has a 50.5 inch wing and 34 inch Fuselage. We got it from some one 4 years ago. It is one of our best fliers. We couldn't ever find out the name of the plane .

What are the odds? :D It's a 25-year old design, not even kitted, for a specialized engine.

Quote:

Ours is electric it uses a SK3536 910 kv its run a full power of 240 watts with a
Prop a 9 * 6 APC and a 3S 2200ma Lipo. Flight time is well over 20 minutes.
Good to know. Mine is about 3/4 the size, so I'm planning on using 1000 mAh packs.

Did you have to put the ESC and battery very far forward? I'm trying to figure out the hardware location right now...

Quote:

It has no bad tip stall even at real slow speeds.
It flies upside down as well as right side up.
If you look at my Blog you'll see mine.
We run off of grass runway an use 2.5 inch wheels. It handles wind up to 20mph with not to much problem. Ours come in at 2.5 lbs.
Awesome! Thanks for the tips!

#6 V-Man Jan 19, 2013 09:47 PM

1 Attachment(s)
I finished skinning the tail group, it's drying under weight right now. Before I glued the skins on, I made slits for the hinges and generally made sure everything was supported correctly (had to add a mounting plate for the elevator's control horn).

Now that the fuselage's sides are together, I started to figure out where I'm going to put my equipment. I was considering having the entire front deck lift off as a battery hatch, but I'm stumped at how to do a clean job of it. Might do two hatches, a service one forward for access to the motor and ESC, and one for the battery. Not sure. :confused:

I also realized that because of the spinner and nose shape, I should really get the motor in place to ensure everything is straight before I shape the forward fuselage. Being blocked there, I started work on the rear turtledeck. The bottom will remain open for pushrod installation.

Then I'll put the wing together, I guess... and an order for motor and ESC.

#7 Charles B Jan 20, 2013 09:23 AM

1 Attachment(s)
Quote:

Originally Posted by V-Man (Post 23867100)
I finished skinning the tail group, it's drying under weight right now. Before I glued the skins on, I made slits for the hinges and generally made sure everything was supported correctly (had to add a mounting plate for the elevator's control horn).

Now that the fuselage's sides are together, I started to figure out where I'm going to put my equipment. I was considering having the entire front deck lift off as a battery hatch, but I'm stumped at how to do a clean job of it. Might do two hatches, a service one forward for access to the motor and ESC, and one for the battery. Not sure. :confused:

{ See attached picture ]

I also realized that because of the spinner and nose shape, I should really get the motor in place to ensure everything is straight before I shape the forward fuselage. Being blocked there, I started work on the rear turtledeck. The bottom will remain open for pushrod installation.

Then I'll put the wing together, I guess... and an order for motor and ESC.

Here is a close up of my plane .
The ESC is on the right just behind the fire wall.
The battery is in the same area.
Please note the CG location on the wing. At the top square spar.
Also note that we have a large plastic spoon cut into for a air scoop.
Don't forget you need a exit for that air that's twice the size of the air inlet.
The air exit is on the bottom just behind the TE of the wing.

My battery is 105mm long if any longer they would get in way of the AIL servo movement .
Make sure that there is no screws on the firewall that can touch the battery.
A sharp screw can cut the battery on a bad landing . Don't want a fire . LOL

#8 V-Man Jan 20, 2013 04:28 PM

2 Attachment(s)
Quote:

Originally Posted by Charles B (Post 23870268)
Here is a close up of my plane.

Thanks for the picture, much appreciated. I was hoping to have the battery above the wing but looks like it will have to go much more forward.

Today I completed the sheeting of the tail group. I'm sanding a slight airfoil shape in for looks, aerodynamics and to save a gram or two. :D

#9 V-Man Jan 20, 2013 04:35 PM

3 Attachment(s)
Works continues on the turtledeck. I preshaped the balsa sides by wetting and wrapping them around a broom handle. Once dried, I applied glue and used tape to get the skin in place.

The fit looks fine but there are slight gaps where I didn't sand enough of the top stringer. Hopefully it won't show once the turtledeck is sanded to the final shape. I might use 1/32" balsa strips to reinforce the joints between the side sheets. Can't hurt the rigidity of the tail, and I'm okay on weight so far.

I test-fitted the tail group and everything lines up correctly and square. Just need a touch of sanding at the bottom of the rudder.

#10 V-Man Jan 20, 2013 09:21 PM

1 Attachment(s)
I've been sanding the tail group for the past few hours, I think my arms are about to fall off. But it now has a nice airfoil-ish shape, and is a gram or two lighter to boot.

I'm done for the weekend, so I slapped the parts together for a picture. Not bad for two half-days' worth of work. The wing is next -- it will have the most changes compared to the original design, so it should be interesting. :popcorn:

#11 kenh3497 Jan 21, 2013 08:46 AM

It's starting to look like an airplane. I bet ya it'll never fly, I betcha, I betcha :rolleyes:;):p:p:D:D

You are a much faster builder than I and I'm just jealous you'll finish this before I even think about finishing one of mine. LOOKS GOOD:cool:

Ken

#12 V-Man Jan 21, 2013 11:52 AM

Ordered a Turnigy D2836/8 motor (336W on 4S, on 3S should get 200W) and 40A ESC from Hobby King before going to bed last night. Hopefully they will ship before the Chinese New Year! I need the motor to finish the forward fuselage. I just hope the included prop adapter will fit my spinner. :confused:

I also need to start sketching up the color scheme. The bottom will be a yellow and black checkerboard (had this on my Funbat and it's super visible), the top will be green, probably with yellow trim and/or markings. I want to go with a "luck" theme, maybe a cloverleaf pattern. If you have any example to suggest, please do!

#13 V-Man Jan 21, 2013 10:20 PM

Had a little time tonight so I prepared the wing skins and started cutting ribs.

#14 V-Man Jan 26, 2013 04:52 PM

1 Attachment(s)
Ribs were cut this week, now I just need to sand them and make the notches for the spars. Note the color variation -- I used lighter balsa for the ribs on the outside of the wing. Saved maybe a gram or two, but why not?

Now I need to sand the wing skins and mark them for the ribs and spars. Not sure whether to make the openings for the servos and landing gear mounts before or after I assemble the wings, though.

#15 KOMET 44 Jan 27, 2013 06:12 AM

You did such a nice job on the tail feathers with building a outline frame work.Why would you want to cover it up and add more balsa? I would have left the open frame work.You'll be adding DEAD NOSE Weight:( to balance the plane.But looking nice so far.Have fun,
stefanP


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