[79FT]: Building Things
done..! Well, almost
|On:||Aug 12, 2014|
|Tags:||CAD, lower wings, ailerons, control system, fittings, fuselage|
Ahh.. Finally. One week for a business trip, nothing done. One week and three days for Oshkosh. Nothing done (or rather, other stuff done :) ). And many more hours of fighting Solid Works; I finally have something to log! :)
First, the incidence. Last time, I was trying to figure out how to deal with vertical fittings having to align with spars angled at 1.5 degrees up (incidence). A good discussion on the Forum ensued, and I figured (aside from me having to buy a +/- .0001 Precision Axe), to drill the hole at 1.5 degree angle in the front fitting, and forget about the little gap that shows up there, and weld the rear fitting in place. So something like this (you're looking at the fitting pair from the side, the CL is the hole centerline).
A pair of fittings, with the hole drilled at an angle
Gap that shows up when fittings are vertical, and hole is at an angle.
Note to self: When building / finish welding, I might reconsider and bend the tops of that fitting 1.5 degrees back to make everything flush. I probably will.
Next item on the list was bellcrank-to-aileron pushrod, which is tricky. See, if it's straight, it doesn't clear all the hardware.
Pushrod is not clearing hardware if straight
So it had to be slightly bent to make the bellcrank side rod-end a bit more "horizontal", if you will, while not "horizontal" enough to hit the spar above.
This sounds easy; and probably is -- but tweaking splines, checking, re-checking and tweaking again while checking for full range of aileron's motion took up most of the time here.. I think I spent a good 10 hours or so just tweaking that one pushrod... And finally, here it is -- notice a slight bend in it. Just a touch less bend and it hits the washer under the bellcrank side rod end, just a touch more, and it gets dangerously close to the spar.
Aileron pushrod, tweaked to fit
Finally, I was able to move the aileron linkage on the wing model and check the idler - bellcrank pushrod for ribs' verticals clearance. It clears! There's another clearance issue though - by the looks of it, it won't clear the compression struts (3/4 x 3/4 inch struts go in the middle of the ribs, forming wing bays along with drag/anti-drag wires) by the looks of it. So struts and wires it is, next, amongst other things..
Control system looking from the wing butt: won't clear the compression struts
For some reason, Solid Works gods decided to start hating me here. Remember the note about angled hole in the front wing fittings pair? Assuming that pair is mated to the fuse (lower longeron); front spar butt hole (ha.. ha ha.. haha..) mated to that angled hole in the fittings' pair should produce correct incidence; and dihedral can be set with wing spar centerline mated to, say, one of the fuselage's crossmember's centerlines, at required 1 degree angle? Ha! Yes; that worked -- but for some reason, would cause all kinds of shenanigans the moment I would make the SWX assembly flexible (== allowing me to move control surfaces of the wing sub-assembly as a part of the overall assembly).
Yeah-right. -3 hours of my life until I gave up.
Instead, I made a virtual "jig" -- another sub-assembly containing planes at correct dihedral and incidence angles. Wing's "Top" plane would mate to the "wing" plane of the "jig"; latter ("wing" plane) would be at 1.5 degree incidence / 1 degree dihedral. That worked.
The virtual "jig" made of planes.
Dihedral of the lower right wing
That same "jig" assembly contains fittings mated to the wing spar -- and then, that "jig" subassembly is mated to the fuse via fittings - to - longerons mates.
That, for whatever reason, worked. After that, 10 more minutes of making one final pushrod connecting idler to Actuator Arm on the Torque Tube, and..
Control system all hooked up and working!
Happy me, making virtual airplane noises moving virtual torque tube moving virtual control system actuating virtual ailerons... Who says CAD isn't fun? :)
Now, back to those compression struts, only to find out that the pushrod does NOT clear... Le sigh.
A helicopter is a collection of rotating parts going round and round and reciprocating parts going up and down - all of them trying to become random in motion.
in search for missing bends
|On:||Jun 17, 2014|
|Tags:||CAD, fuselage, lower wings, fittings|
Today, ended up messing around with putting the lower wing and the fuselage together...
Lower wings are set up at 1.5 degree incidence, 1.0 dihedral.
Started with that I realized that I mis-positioned the hole on the front spar and gear fitting. Simple fix :)
Next, came a lot of thinking and reading. Here's the problem.
The plans position fittings perpendicular to the longeron.
Fittings on the lower longeron
Holes are co-linear, and incidence is achieved because of the stagger in the attach holes on the spars. Airfoil chord, tilted up 1.5 degrees make these holes come together.
The problem is that spar sides then become non-coplanar with the fittings' faces; possibly introducing bad fit, play, misalignment, and whatever problems I can't think of.
Here's how the spars go 'into' the fittings. I circled the rear spar, since Ill use that for illustrating the problem.
Spars on fuse (rest of wing hidden from view not to obstruct
Now, looking at it from the tip of the spar towards the fuselage, you can see the angle between the fitting and the spar. That's because of 1.5 degrees of incidence.
Angles don't match == no fit.
This problem caused about an hour and a half worth of research with no results...
Firebolt and Pitts plans explicitly state either bending, or welding fittings to longerons at correct angles. Not Skybolt though...
Ended up posting on the Forum. Let's see what the folks say....
On a more positive note; I can see an outline of an airplane in this now ;) Made some virtual, mental airplane noises :)
If God had wanted me to fly, he would have made me flush riveted.
cleanup, and more bending
|On:||Jun 16, 2014|
|Tags:||CAD, fuselage, torque tube, control system, ailerons, elevator, lower wings, fittings|
For starters, cleaned up the torque tube; added all the hardware (thanks cwilliamrose again for AN hardware models!) and proper mates. Was a nice warm-up, and came out real well.
Torque Tube, Cleaned Up with HW
After that, added the lower wing front fittings to the fuse. Piece of cake! :)
Lower wing front and gear rear fittings
... and zoomed in.
Notice on the above picture how they interfere with the tubes of the fuse truss (geometry penetrates one another). There are a couple ways to fix that; plans just call for 'trimming in place'. Note to self: figure out if the weld should only be around the bottom longeron; or if to weld the top of the fitting to the vertical too?
The cool thing about SW is that I can "cut" in place; add a bit of margin on the real pattern for the fitting, and make it to fit without constant trial and error.
And then, lower wing rear fitting.. that one is tricky due to the way it's dimensioned on the plans (it makes sense plan-wise, since it maintains clearances between longerons and spar butts, etc; so hole positioning takes metal thickness into the account). Can't believe it took me 2 hours and a few tries to figure out how to model this right. Learning curves be damned :)
Lower wing rear fitting
Now, the reason for all that trouble is that getting the flat pattern out of that is just 1 mouse click!
Lower wing rear fitting
I think this was a great day. :)
If something hasn't broken on your helicopter, it's about to.
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