Wanted to keep this reasonably light, not perfect scale, but looks close enough when done. I can always change it! Mounting is with 2 M4 screws.
The seat is built from 6 alu strips going front to back and 7 crosswise. Sort of like in this test. I need to think about this a bit, the center one going to the rear will have to be somewhat special.
Not much to add, just another leg..
Lots of inspiration comes from: Achim Engels, build your own Fokker plane.
And another one: Kerry Ann’s Piper.
Again on close inspection you recognize so many of the tricks that are used in the SA-750. If some construction detail is not clear, check here!
Another great source is Biplaneforum.com . To view everything it wants a donation, but it is worth it when you are building.
The first leg is the easiest, the second has to match, which is far more work. However, I’m quite pleased with the weekends work. Total weight of the leg is 118 gram. I also added all the pilot seat tubing, giving a total fuse-weight of 1148 gram. (still hoping for a less then 2 kilo RTF fuse.)
I started with the main pipe, angled forward 8 degrees. Followed by the cross-way pipe to which the bungy-cord attaches. Next the support for that, so that the triangle is complete. Next the rear support to lower main leg. Then the bit between front and rear support, and finally the cross between rear and bungy-cord pipe.
Note to self: Need to make a 4+ mm bushing to fit snugly into the 5 mm fuse attachment tube. With a 4+ mm bushing and 3 mm bolt to secure the bushing, all will be perfect!
Closeups of my handywork. After sandblasting I ‘ll reheat the joints to make them flow a bit more and fill any voids leftover. This will be for cosmetical reasons only.
The plans call for square tubing for mounting the wings, but you guessed it, not available in the size I want, not even close. Here I have to deviate from the plans and make something that will look the same, but is something I can make. At stations 31 and 51 I added the normal tubing cross bracing. Then I made some solid steel supports that look like the original. I use short pieces of steel. Later I will put a false ‘square’ cover over the visible bits in the cockpit area.
I’ve always been reluctant to start milling steel, but actually, if you take it slow, it goes quite well! (surprising myself here.) This stuff is plain cheap ironbar, I will have to try stainless steel as well, but that is probably a different game. Time will tell. (Note to self: This was done with a 2 mm bit, @300 mm/min, 0,1mm layers. Probably can go larger on the layers, but I need to do something about cooling, since WD40 is not that great as cooling liquid.) Looking at the parts you see that the toolbit vibrates, it creates an uneven surface. However, using a 2 mm bit is really pushing things. I will need to study this subject a bit more!
While I was at it, I also made the support for the LG-front attachment point. By using 2 mm parts I get enough strength, and I can easily cover the gap between the supports with a 0.2mm strip. The rears support consists of triangular gussets. Again a milled part will be the real support, gussets will/ might be added to make it look nice.
As you can see, the new shipment of tubes has arrived. Visible progress is made again today. Overall I’m happy with the result, there are always little things that do not quite turn out as intended, but since this is all about learn as you build, it’s not a disaster. (So far I have not had to scrap anything)
The outline of the rudder is not 100% accurate, I went more along the route of TLAR. I might have a couple of square inches more rudder area, which never hurts. Most of the rudder was build freehand. I pre-bend the outline of the TE as much as I could, then stuck the front of the tube in the top rudder tube, soldered the main post, and added the ribs as I went, keeping a nice smooth shape as I progressed.
Again, 2 bottles of sand were blasted into the atmosphere. At 8 bar air pressure, the ribs do deform, better use 5-6 bar and take longer. Nothing drastic, but keep it in mind.
I found out that stress was present in the construction (surprise) which causes a slight bow in the rudder post. The balancing part of the rudder is now to close to the rudder part. Nothing that can’t be fixed, but it goes to show how much tension develops in the parts after cooling down. I could of course stick everything in an oven @600C for 24 hrs. Only problem is I don’t have one.
Just a relative quick job tonight: making the fin. The only noteworthy item would be that after installing the ribs, I still had to drill a hole for the bracing rods. I decided to simply cut a slit with the Dremel and enlarge it to fit the tube. Seems to work well, and since it will be hidden, it’s good enough for now. Consider this a practice run for the elevators.
Given that it is difficult to find the right size streamline tubing, I better go ahead an make some. With the open-scad script I found I made a handful test pieces. The idea at the moment is to attach the plastic with a layer or 2 of 25 gram glass cloth. That should fill the little grooves in the printing and provide enough strength. Obviously this has to be done after the brazing.
I also tested the deflection in the motor mount once it is attached to the frame. Can’t move it. This is a comforting thought.
I did say undercarriage? A whole new can of worms just opened. I had hoped to be able to use a normal streamline tube as offered by various vendors. However, can’t find anything close enough to what I want.
I could make my own from round tube, just like friend Achim , but that’s a major effort. Many say that deforming a round tube introduces cracks, and therefore failure waiting to happen. Don’t need that.
How about adding some plastic and cover with some glass, a bit of sanding and no one will see? Time for a 3D print job.
A quick search for airfoil scad scripts turn up something useful. This is the first idea. Ideally there should not be a round nose, but given the rather short length of tubing and the ample power of the engine, I think I can forget about the added drag of not having a perfect airfoil shape.
Most streamline tubing has a more rounded TE, we need to fix that!
So this would be glued to the back of a round tube. I’m sure it will look right 😉