freeCAD and fuselage creation

Thanks for the STL. I am not yet convinced about a linkage without a Z. I might scale it a bit wider. Have to think about that....

I decided to return to my smallest and lightest Clarke-Y wing (the 700mm x 123mm 123g one) and see if I could get the model weight down.

I created some light printed platforms for the wing and the motor which are, effectively sleeves with a flat section on top with slots for velcro to pass through. I then got hold of a 10Amp ESC that weights much less than the usual 20A ESC.



I tried various arrangements of the components on the motor platform (see below). There were two likely batteries that I might use - a 450mAhr 3-cell and a 650 version. The first is short and fat, the 2nd thinner and longer. I could mount the receiver behind and the ESC on the side of the battery. Being exposed and with a season of wet grass looming I wanted to create covers to fit both battery types.





A QUESTION - I have tied the ESC to the side of the battery - is that likely to get me in trouble? The design should allow copious air flow under the protective cover (I hope).

As those who know freeCAD know - there are rituals involved in creating flowing forms which one forgets. It took me a bit to re-discover the workflow. What I wanted to create was a simple thing and I thought there is no better time to record the whole process - from sketch through all the steps of creating a cover including setting up the PART primitives (circles and ellipses), lofting them, adding thickness and then using the boolean slice-apart to dump the lower section of the loft and the preview and print it.



The finished beastie held in place with a velcro strip with the battery monitor trailing.



It came in at ~10g and is just flexible enough to slip over the components easily.



Here are the primitives in freeCAD. Note: these were all created within the PART workbench - I didn't need to create sketches!



This is after the cover has been lofted and a vent opened up in the top. The image is for the larger battery variant. It fits. The tie-down is ad-hoc. As opposed to the earlier 'oval' fuselage this combination has reduced the weight by ~30g.



Next steps....
I have ordered a new set of carbon fibre tubes which should save another 15g off the carbon fibre arrow shafts that I am currently using so the that should further improve things.

I created a 13 minute video - yes I know that some folk will run away but it is hard to capture the 'rituals' of freeCAD via mostly static images (I include a few below). But for those who are shy about 'lofting' or have never seen it happen it might be good information.

Here is the link....



-Jon

Thanks for the video jon.
It answered a number of questions I had.
I can imagine creating the primitives I require but positioning them to give the lofted profile I am after is another matter.
Some more learning required.

Glad it was helpful.

Looking back over all the great comments folk have provided for me in my journey to flight I wanted to give something back to the community.

Lofting - simple lofts can work and at random moments it just produces something that is ''art" but which is not what was intended.
Small steps, save often.

freeCAD lofts seems to respond better if there are more primitives than fewer and small changes between them if the X-section is going to be changing a lot.

I suspect you might want to do a loft that joins two inlets to a single duct - most of the examples I have found on YouTube do not include a branch example - might be something out there. It might be an iterative process of trying some simple branchs to find the magic path.

Here is a link to a site that goes over quite a few options for lofts... Several others about additive and subtractive lofts.
Lofts in freeCAD


-Jon

I think I found a tutorial that might give clues for more complex lofts. A fellow is creating an engine exhaust manifold - so the case of a single duct diverging into several. I did not follow it to the end. The good stuff starts about 4 minutes in.... -Jon

Given the wetness I decided to re-visit the oval fuselage but to build it around some new carbon fibre tubes. They came 800mm long and I thought to see if I could use that to save 15g. To balance I re-printed the front section of the oval 30mm longer. With the 1m x 120mm Clarke-Y it does seem to me to be rather dragonfly-ish.



The extra length allows some choice of battery but I decided to go with one of the bulkier 605mAhr 3-cells. The REC and a 20A ESC and battery monitor fit nicely behind. There is just room for the T30s to connect but I can see that it will eventually stress the wires.

What I really want for Christmas is a T30 shaped adaptor that includes a switch. The only ones available seem to be for T60 and they weigh 20g!

Ready to fly it was 440g (178g for the wing 60g for the 3-cell, 25g for the ESC). I am amazed how much weight wiring adds! The wiring in the wing is almost the same weight as the servos.



I took it out to a new section of the local park that has a much more even surface and better drainage. It was slightly smaller in extent and bounded by trees so I wanted to keep well clear. The alternative open space was quite boggy and also would require launching down-wind which seemed problematic for a maiden.


I balanced it between 25% and 30% COG. There proved to be a breeze above ~50ft. I started with a 50% expo on all control surfaces. The aileron servos already included a mechanical differential I didn't need to do much to limit the down angle. 50% throttle to launch, into the wind 40% throttle and probably would have been happy in calm conditions at 25%.

It took a few flights to get a feel for the beastie but not really enough to get it dialled in and be comfortable at altitude. It was very grey out so the red and yellow tape was not all that great a help, especially if it was skirting the perimeter trees or flying directly along the line-of-sight. It does have a rather minimal X-section so I should not be surprised.

I gathered sections of those flights and an overview of its bits in a short video.



I noticed the elevator seemed undersized - difficult to level off after climbing as well as get the nose up a bit in the last few metres of landing.


I printed out an elevator extension and look forward to trying it out in the next few days.



If anyone wants the CAD files or STL's let me know. -Jon

My next project is a slightly bigger oval fuselage to match the 920x170 Clarke-Y (resized wing platform, slightly bigger cross section an a bit more length).

jon
Looks quite flyable but I wonder if the tail plane itself is a bit under size rather than the elevator. It is after all the fixed part of the tail plane that provides the stability.
In fact a small elevator on a generous fixed surface has the advantage that it also gives a 'built in' expo as small movements have only have a small effect but larger movements up to 45 degrees still work well.
Just a thought.

I will have a think about the tail plane - it was scavenged off a prior model. I had thought that the longer boom would amplify the limited surface area of the tail. I can certainly upscale the tail surfaces and give that a try.

I was just out again with it in a rather stiff breeze and mostly it was coping but quite a battle and was being tossed around. A couple of times as it was turning to go down wind it was like a great shove. And running perpendicular to the gusts was also fraught catching the up-wind wing and flinging it up. High enough to recover but clearly a whole subset of skills waiting to be honed...

My view of FreeCad is that it doesn't matter how far down the tunnel you explore the light at the end never gets any nearer.  Made worse by the fact that at my age I tend to forget how I got that far down the tunnel in the the first place!