Long ago I had a Yak that I had to retire because of a wing-tube that approx 3 degrees dehidral (too many snaps I guess). Anyway, I usually keep all the good parts of a retired air-frame. So I had the actual bracket for the wheel. I had a single nice looking wheel, and a bit of carbon. An old wheel axle provided the new bearing for the part.
The result looks good enough for now. The wheel axle needs changing to something steel (brass won’t last long) but that is a later job. The hideous bolt on top will also need hiding at some stage.
And yes, I want to add the weight now, so that later-on I will not have any CG surprises!
Funny enough, Probuild still caries these tail-wheels! (I got mine sometime 2002 I think, when I used to live in Trowbridge/ UK.)
The panels for the access to the rear end are made from 0.3 mm stainless steel. The main challenge was working out a method to fit the panels with screws as per full size. After the inevitable ”not fit for use” parts, I think I worked out a method that I can use at the front as well, without adding too much weight. I am using 2 mm steel strip, partly drilled and cut at the locations I want to keep. I use the panel for alignment, and when the first 2 point are soldered, I remove the panel and solder the remainder. Afterwards I cut of the bits no longer needed. Once the lugs are prepared, they are tapped with 2 mm. At present I am still working on the cutout for elevator, but already it looks great.
In hindsight I should not have followed the plans for locating the tabs. It would have been better to place one or 2 at different locations, i.e. I now need to add 2 extra to hold the front part of the cover and an additional one to hold a filler plate above the hole for the stab. Hey, it’s a Homebuilt!
It is always a good thing when the magic red lines end up where they should..
Making the bottom bracing means you have to get everything lined up properly. You don’t want to start pulling this out of whack. Since I went through all the trouble making the clevises, I might as well use them. Officially the stab side is made by drilling a hole in the flattened streamline tubing. Guess no one will know except me (and you). It is also easier at the moment to make them that way, so that I can slip the streamlined ABS tubing over the 3mm rod.
In order to give the plastic some time to cool down and to provide some stability, I print a ‘cloverleaf’. The ends are barely touching, it comes apart very easy. First trial looks good. The texture looks quite rough here, but a small amount of sanding smooths things out in no time at all. I still want to add a layer of glass, and tidy the ends to make it all look very much like ”scale”.
Also made a slightly different version, this one has a tapered front section. It looks nice too. I only flattened one side, where the screw goes, that leaves a bit more flesh for the thread on the other side. In the picture above I drilled it for a 3 mm bolt, reduced the bolt-head to 3.9mm, so it sinks into the top bit. Anyway, 3mm is too big for a 6mm rod, but the idea is good. (Since I now have the lathe setup better, the results are better too. Not good, not machinist good, but hobby good enough for the job. I drilled the 3mm screw with a 1.5 mm hole, in order to put a locking pin through. Yes, too much work. I agree (for now)
Just so I remember the sequence of work next time around.
Make sure you have the proper radius tool to make the nose radius. I had to make my own, which was not as hard as it sounds. Just take you time with the dremel. This was an old tool that I (ab)used for this purpose.
Drill a square piece of alu/brass or whatever with a 6 mm hole so that you can securely put the brass rod in the tool holder. Since I don’t have a 4 way chuck, mine was drilled off-center but that does not matter. Tap a few holes for M4 bolts to hold the brass rod. The are other methods to do this, I simply show what I did, not because it is the best method.
Cut a piece of 6 mm brass approx 20 cm, that way you can make ca 10-12 pieces at the time.
Drill the 6mm rod with a 2.5 mm drill, at least 20 mm deep. This will be tapped to M3 later. (If you have a 2.4mm drill, you should use it, 2.5 is slightly oversize if I remember correct)
Round the nose with the specially radius-ed tool. You need to do this before cutting the slots. Believe me, this will work better.
Next transfer the rod to the aluminum holder. I want to cut ca 10 mm on both sides, so make sure it sticks out ca 12 mm.
Now comes the trick: make sure the outside of the blade lines up exactly with the outside of the brass piece. You only want to cut a saw’s width off the sides. Run lathe at a fairly high speed, and feed slowly. You really want the blade to cut. Repeat on the other side. Next eyeball the blade in the middle and make a 6-7 mm deep cut.
Insert the rod in the chuck again, and reduce the backend to ca 4.5mm.
Use a bit of fine sandpaper to rub off and smooth any bits that don’t look good. When done and happy, part at a total length of 17mm.
I tapped the holes with M2, and will install proper steel bolts when all is done.
These few bits took you all day? Yeah, but I did disassemble and clean up the lathe as well, There was some play in the cross support that was hard to get rid off. It’s all good now 😉 (look at mini-lathe.com for guidance)
AcrodusterComments Off on I did not like the clevises …
..so fiddling around I managed to make a better one, that looks more scale like. I did have some thin saws from the pound shop so here we goes. Those things are undoubtedly not made for what I use them for, but as always, go slow and be careful. I tapped a hole in a 12mm rod I had lying about, and fitted the blade. Clamp a 6 mm brass rod in the support and go slowly. The design is basically copied from Dubro 4-40 rod ends. I have a few of those, but they are tapped for 4-40 thread, with is approx 2.8 mm. Not enough flesh on them to tap a M3 hole, and I don’t have any imperial taps/dies lying around to make the rods. Hence the ‘need’ for DIY.
Next step is make a handful more, and get the streamline tubing for the bottom braces. Stab side of the tube will be flattened with a hole drilled through (easy), the other side is adjustable like above. In fact, this adjustable one goes on the fuselage side, but that does not matter.
So, 4 in total for the bottom, m3 threaded. 8 for the top, solid with a hole for the bracing wire.
AcrodusterComments Off on The smaller the parts, the longer it takes to make them.
There must be a law for that! Anyway, at the moment of writing I have half the brackets done. Most challenging part is cutting without cutting meat-ware. So far all fingers are present. Material is 0.8 mm stainless, not the easiest to work with. I had some nice clevises from Pete Tindal*, they look good and do the job just fine. They were meant to be used with glue and a 3 mm carbon rod, but cutting a 4mm thread in the hole works great. Cutting a 4 mm bolt to size and drilling a hole for the wire seems to work. I might tidy up the bolt end, it does not look to grand. ( *only people of a certain age will know Pete)
Servo needs to be hidden under the seat, so I built some bits to do just that. All overkill of course. I also remade the pivot of the control stick. The washers I has used had an internal diameter of 3.2mm. The bolt was 3mm. Very sloppy! Same with the link at the bottom. It took some time, but now it is all slop free!
Update: did not like the crossbar, it interfered with full up. So changed things a wee bit, still same servo position.
Need to get from the (future) servo under the seat to the back-end in an orderly fashion. I’m using the full size method as guide. Main part is the reversing bar behind the seat. It has to be zero play. No play, whatsoever. After the usual fiddling around for a while, I got it sorted. It’s a once you install it, you can never change it construction. Failure here is no option. The bolt at the bottom prevents the assembly sliding out of the bushings. It does not support anything. The 2 little square supports were reamed out to provide a zero play bushing.
Next will have to be the construction of the stick assy, and the mechanical interface to the servo. Lot’s of fun ahead!
I am only installing the main stick, front seat is ”occupied”. Not sure yet if I am going to use a separate servo(s) to drive it. Separate seems safer, since there is a reasonable mass in this contraption. Might build a pilot with power arms 😉
The stick has to be fixed with AN4-22 bolt, 4 washers, AN310-4 nut and a AN380 1-2 cotter pin. Yup, M3 bolt and nut will do fine! (for the curious: AN4 is 1/4 ” = 6 mm. So 2 mm would be scale. Since those 2 mm bolts are usally quite soft, I won’t waste my time installing one, they will rattle loose in no time at all. The nut is a castle nut so you can put a cotter pin through the bolts hole to stop it going awol. I know you wanted to know all this.
..many times you have to make parts before the other parts that need to go on before the parts that you need to fit to get the job done. This was one of them. Needed to make more hinges. Not difficult, just fiddly, and a bit dodgy, since I try to cut them on the lathe, with a dodgy china cutting wheel going full speed. However, hats of to the china-folk, I have not had a single one fail on me. So far I have used approx 20 odd discs on this project.
After checking the tail, I noticed the main spar was bend. This appears to be almost inevitable when you heat bits. I decided to simply cut the middle, and add a sleeve. Problem sorted. My metal working skills don’t go so far that I can predict how much distortion I will get. Of course I could make very expensive, very heavy jigs. yup, I could..
A bit of a showoff.. Starting to look like it wants to fly!
Just one more weighing session. 1569 grams as seen here. Good stuff!
And I am calling it a day. All in all it does not seem much, but I am happy with it! The section above weighs 300 gram. As a comparison: the ”light” elevator from my 2.5 meter Extra weighs also 600 grams. Ok, there’s 2 servo’s included in that figure, but still..
Finished the rest of the elevators today, another milestone reached! Also bolted the motor back on to get a feel for the CG. At the moment I am still slightly nose-heavy, so things are good! I don’t expect to have to add any of the grey gravity stuff.
The rear stabilizer mount consists of a single bolt, as per original, the front is made up of a few gussets. I probably simplify that part. Not sure how, but simpler as original. (too many small bits that fall apart when you heat things up, is the main reason)
AcrodusterComments Off on Lets make some tail bits.
The plans call for square tube at a few locations. I don’t think it will be a problem to use round tubing. As usual, use what you got! I also don’t think I have enough space for the 2 central bearings, another fudge expected there.
My template has a more rounded outline at the outer elevator. Might have to redo it, since the big one has a smaller radius.