freeCAD and fuselage creation

I am currently out and about doing steam trains - (Severn Valley Railway and the Dean Forrest Railway thus far) and enjoying feeling 8 years old again instead of just shy of seven decades....  

And I saw a video about a new curve tool in FreeCAD which looks like it would take a lot of the faffing around creating printable wings and perhaps fuselages. I previously had taken a sketch of a Clarke-Y and for a tapered wing I calculated the scaling for each rib. For my explorations of LW-PLA I took the Clarke-Y and used scaling manually to come up with sections to 'loft' the wing from.  Lots of notes and faffing, especially if I wanted a wing that tapered in chord as well as thickness.

The link below is to a fellow building up a wing (he chose a rather silly wing shape but only to demonstrate the process). The curve tool allows you to take a sketch of a wing section as well as the plan layout and the thickness and it does the hard work.  You tell it how many intermediate sections to create and it scales them and turns it into a solid.  He also shows how to patch the fiddly bits if you don't like the wing tip.  I learned a lot - haven't tried it yet.  Once you get the hang of it it probably would take less time than the video to do.


 

Some time ago I made a post about a small printed part intended to prevent shorting of motor connectors. I am unable to locate the post which is a pity as it generated a bit of chatter.

It looked like below.  The trouble is that it takes space, the 2g it weighs is less of an issue.  It was meant to be Velcro-d to the side of the fuselage. 

 

The LW-PLA fuselage in the Dragonfly2 is tight. I still worry about those exposed bits of brass in confined space. And then it came to me a much simpler device which is smaller and lighter.  Takes less than 4 minutes to print,  less than 1g. It is composed of three merged 5mm lengths of hollow tube (in the CAD tool) sized for the shrink-wrap on the bayonet coming from the ESC. 

 

 

If the upload works I have zipped up both the freeCAD file (so you can resize as needed) plus the STL file.

 

-Jon

 

jon
Neat but I am not sure you have the shrink wrap insulation correctly positioned.
The pin and socked shrink wrap insulation should look like this.
 
The socket which could be live is completely covered at all times.
The insulation on the pin, which is only live when connected, is arranged so there are no exposed areas when the pin and socket are fully connected.
Works for me on my motor wires..

  

I think the shrink-wrap creeps a bit with each re-connect.  Yes, I should have thought to just put some new shrink on (rather obvious once said).  

I do like having something to keep them tidy none-the-less.

Point taken on the components being swopped less frequently.  I got a few receivers from Tony that I can devote to specific models now.

The connection that is increasingly frustrating for me is the battery connection to the ESC. Those T30s have a finite life and what with bending the battery or ESC wires each iteration I find myself replacing those connectors and having to re-solder.  

I am thinking about my next wing.  The foam and printed PLA rib Dragonfly original has a rectangular plan form but needs work as the servos for the ailerons have detached.  

Given that I find heat-forming the leading edge of a Clarke-Y rather tedious in foam and the trailing edge difficult to make nice and shape I thought those might benefit from printing.

However, the tension cracks I find in LW-PLA wings is a bummer.  So I am thinking about a different kind of hybrid - with printed leading and trailing edges and the balance made up of a foam skin (with tape covering for colour and tension) and with LW-PLA ribs and CF spars.

The prior wing had a constant chord of 5" and a 1m span so 190 sq inch area. I found the taper plan I used in the LW-PLA wing to be rather fun but there were comments that it might be better to shift the taper from mostly at the trailing edge.  So I opened up the aero toolbox site and looked at what I might get with 190-200 sq inches and different sweep angles.

The first with a 3 degree sweep would introduce complexities at the leading and trailing edges and design of the ribs. An aspect ratio of 10 should limit drag.
 

I tried some variant sweeps to shift the taper to the leading edge which simplifies the aileron and trailing edge. I can have a perpendicular-to-the-fuse trailing spar.  
 

Question - should the main spar be perpendicular to the fuse or follow along the sweep of the chord?

If I decrease the desired wing area I need a bit more sweep and end up with a bit more taper.


If I drop the span a bit I get a chunkier wing with less taper and a similar aspect ratio as my recent LW-PLA wing.


My thought is to design the printed leading edge to ~12.5 % of the chord (where most of the curve happens). And the ailerons along about 2/3 of the trailing edge and ~20% of the chord. I would 'print' the ailerons and the equivalent non-aileron bit of the trailing edge.  Ribs would be LW-PLA at ~60mm intervals and tab into the leading and trailing edges.

Anone have pointers and preferences about these shapes?

Thanks for mentioning swept and tapered wings.

AND there were a couple of questions in the post - if the leading edge is swept should the main CF spar also be swept?

And why try a hybrid printed and foam wing? - Well it is a combination I have not tried.  It might be an interesting mix using the better bits of prior designs.

I have been sketching possible cross sections.  Certainly a head scratcher in places. It would force me to learn some new CAD tricks.