FTFC20 Carl Goldberg Electra designed by Corbarrad

[Corbarrad]

This is my entry for the FTFC20 Classic to Modern Forum Challenge!
(in the hopes that opening a thread will help me get my butt in gear...)

The Subject is the Carl Goldberg "Electra", an electric powered glider from the late 80s/early 90s

The Electra was my first powered rc plane and, at the time, a bit of a disappointment.
Running a Mabuchi 550 brushed motor with an 8x4 prop on a 1300 mAH 7 cell Nicad this thing was not only underpowered and struggled to climb but the added weight made it kind of a pig in the air once you gained enough altitude and tried any kind of soaring.
I was told the plane made an excellent glider once you removed the battery and prop but my high start attempts proved less than successful
After I crash I ended up shelving the plane, along with RC flight for the best part of the 90s and 00 years until Flite Test and some gentle coaxing from a few friends brought me back.
I still have the fuselage that I cobbled back together from the splinters I picked up at the field and the wing which is mostly undamaged at home.
In a bout of nostalgia I also bought an unbuilt kit off of my local hobby shop a year or two back, So I got the original plans to work off of.

Design brief is as follows:

• I will mostly be using Flite test building thechniques since the boxy fuselage and square-ish wing lend themselves to it.
• The plane will be RET, as was the original.
• The FT alpha I built for Flite Fest this year will be the donor for the F-Pack used to power the plane although I'll be going for 9 gram servos for the control surfaces.
• A folding prop might be in the planes future but for now it'll be the 6X4.5(?) that came with the F-pack.
• The goal is to have as little exposed foam as possible
• As with the original Electra the Battery will be located right under the CG so you can up the capacity for longer powered flights and reduce it for better soaring performance without too much hassle.
• I'll be going with 3D-printed FT-style hardware for control horns and the like. [Link to the original creators thread/thingiverse will be included here in the future]

My plan is to first build a roughly 60" Version as proof of concept and then maybe scale up to the original 80". This will hopefully let me get half a wing onto a single sheet of foam.

Caveat: I've been known to start projects that I never finished, mainly by overcomplicating things and then getting distracted by the next shiny thing.
Here's to hoping that doesn't happen this time...

 

[Corbarrad]

Progress 09/01/2019:
Instead of dragging my 20+ year-old build plans through my scanner I managed to download a build plan off of outer zone:

After converting it to a bitmap I slapped it onto my Fusion360 workspace and started drawing the wing. Let's see what tomorrow brings...
Update 09/08/2019:
Sadly nothing tangible happened this weekend, but I should have a wing by the end of the week.

 

[Corbarrad]

In the face of my abject failure to produce anything presentable over the weekend (I went flying instead, not too bad of a trade, really) I want to at least share some of my plans for the build.

• The wing will be built in two parts each half being the full length of a sheet of foam board (30").
  • The root profile will be modelled FT style as close to the original profile as I can get.
  • The top plate will be folded as per the root profile for the full length
  • The bottom plate will extend the length of the inner wing panel and then taper to meet the top surface of the wing giving a gently increasing amount of undercamber up to the tip of the wing. This will also strngthen the outer with panel in the absence of a spar.
  • A notch will then be cut at the joint of the outer and inner wing panel to allow the outer panel to be swivelled backwards.
  • The back of the outer wing panel will then be cut flush with the back of the inner panel. This will cause the outer panel to have some amout of washout, just like the original Electra wing had. (I hope this works out...)
• The fuselage will be built from three parts with the middle section being the battery compartment
  • The battery compartment will be double walled with tabs extending from the inner box to attacht the front and rear bit
  • The tail section will start as an open section built with the bottom on the bulding board
    • The horizontal stab will be put on next, angled slightly downwards to compensate for the amount the back of the fuse will be lifted once installed.
    • The Vertical stab with attached rudder will be dropped on top of that, estending all the way down to the bottom plate. It will also run the length of the fuselage for a bit as a means of reinforcing the tail and as a mounting pont for the servos.
    • The top will be closed out once the servos are installed. (and tested hopefully)
  • The front section will be a rounded U-shape, tapering towards the nose.
    • If possible I'd like to do some sectioning on the top to emulate the curve of the canopy but in a pinch I think the taper alone will do...
    • The holder for the power pod will be attached to the left wall of the fuselage to give some right thrust and a bit of down angle (tbd), then braced against the left wall to stiffen up the nose
    • The nose will be closed up from the bottom. This plate will include the hatch that closes out the battery compartment.
• The electronics will be comprosed of a power pack F and two 9g servos.
  • The power pod will be straight with the angles being dictated by the mounting bracket in the fuselage
  • The Servos will sit in the tail, glued to the vertical stabilizer. That will keep the linkages short and open up more space in the battery compartment. (and eliminate the abomination that ist the threaded rods glued to the balsa push rods)

I will probably have to play around with the length of the nose and tail a bit, since my plan is to be able to fly with a variety of batteries.
(A light loadout for improving soaring capabilities or a heavier one to increase powered flight times)

 

[rockyboy]

That sounds like a good plan to me! Might consider using something like a fiberglass arrow shaft as a wing spar to make sure she doesn't do the "taco" pulling out of a loop.

 

[Corbarrad]

That sounds like a good plan to me! Might consider using something like a fiberglass arrow shaft as a wing spar to make sure she doesn't do the "taco" pulling out of a loop.

Wouldn't that be considered keeping true to the spirit of the original?
Not to worry, I have a contingency plan should the wing be prone to failing. Now, first I need to build one of them things.

 

[rockyboy]

Wouldn't that be considered keeping true to the spirit of the original?