AcrodusterComments Off on it’s getting serious now..
A good day was had, is the saying. Over the last week or so I have been bending the cap-strips. It is a time consuming job. First you soak them for a few days, then clamp them in a jig, then let dry for at least 24 hours. Repeat.
Since there are always minor variations in the construction, my plan is to route the outline to final shape once I have enough ribs done. That would make them all exactly the same, which is the whole purpose of all this effort.
If in doubt do it the Paolo way 😉 . Success guaranteed!
The full size cap-strips for the ribs are 1/4 x 1/4 pine. Scaled down that translates to 2.12 mm square. That is just too small for my fingers.
The plywood I have (that lite-ply) is 2 mm. I have nice 2 mm mill bits. (Not great for wood, but it works). Some time later, I have found The Way to Do it.
Mill a groove in the 11 mm strip, offset from centre (don’t ask where I got 11 mm, that’s what it is, came from some “Imperial” country. Supposed to be 1/2″), turn it around, same again, and last, run a deeper groove in the centre to cut it into 2 halves. Bingo, nice cap-strips.
Next I probably need to make a jig so I can glue the cap-strips on the ribs. (40 odd ribs.) en in general get busy. Once the glue dries, I can (if needed) sand the cap-strips down a bit, looking for no more then 3 mm wide. I’ll leave the height for now as is, it will give me some room to play with during the final assembly.
The vertical rib stiffeners are just scrap, probably do them in thinner ply. Joining the mains and aft spar requires triangular pine blocks, again, by the time you scale things down, they are small. I think I have a cone bit somewhere, I will try to make the blocks the same way as the cap-strips, mill a groove and chamfer the side..
Ouch, almost got myself in trouble. The cap-strips run all the way from LE to TE !! Even though the nose section of the wing is covered with plywood! Good to check, and check again. Which means I have to make the ribs complete, and slide them over the spars. No problem, but it shows you got to pay attention.
With the wing spars ready, it’s time to start thinking about the ribs. On these wings, nothing is straightforward, every rib looks different. (which gives it those nice wings 😉
Luckily the designer was smart enough to keep all the ribs up to the aft spar the same, so the only difference is the rear section of each rib. Which means, after I sorted the profile, I decided to make some test ribs to see how it all looks.
These are really just for testing, the wood is something called lite-ply, which to be honest is pretty useless. It’s as light as balsa, but warps by just looking at it. Been carrying it around for 20 years, so time to get rid of it!
The profile is approx 13%, I might thin it down slightly, I think 12% will still fit. It’s roughly a NACA0013, so 12 will do just fine. Or 12.6, or something.. I’ll think about it. Have to make sure the servo’s fit as well!
At some stage, after laminating the wing spars, I needed to bevel them at 4 degrees for the forward, and 6 degrees for the aft spars. Could have done it by hand, but this was quicker. (After spending 2 hours thinking about it, and trying to mount the planer. ) Only do this under adult supervision. You’ve been warned. Count fingers. Keep them.
Anyway, looks good. The main spars cut to length came at 97 grams each. That’s the great thing about wood, if it is too heavy, sand some more, until you get to your target.
There are some small errors in the laser-cut parts, but nothing that I can’t fix quickly. If I remember right, at one stage I thought that I needed a bit more material around holes, so added 0,5mm to the outer contour. Should not have done that, stuff is strong enough as it is! The rear attachment point is now a bit tight, but as I said, easily fixed.
AcrodusterComments Off on Nothing like a good plan..
After many thinking’s and deliberations, I came to the conclusion it would be better to build the bottom wings first. The mounting points are already fixed to the fuse, so their alignment is hardwired into the frame. When the bottom wings are done, I can align the top a bit easier.
I had planned on making the spars from sticks I have saved for 15 years now. They are vintage, but appear to be in good straight shape. These were once destined for a Waco project that never took off. There’s enough of them, and laminating thin strips gives a nice strong spar. Rear one is approx 26 x 7mm.
I hope that having wings will make other parts easier. (famous last words.) The wing structure is going to be per full size, the hard way. The spars are what carries everything, and fore/aft stiffness is provided by 1″ alu tubing. The stuff that would be available is actually heavier then stainless steel, so I am going to use that. Which means I also need to make brackets for those tubes. And when I am at it, do all the other bits I need as well.
Glueing strips together is not that exiting, but this is the result.
And for the rest, a bit of sanding and shaving to get to the correct size. I love the smell of pine!
Today was officially the first day we were allowed out again. Corona has not disappeared, but is becoming less of a problem. Technically, when the infection rate stays below 50/100000 people, the hospitals can cope. So it’s not over, it’s manageable.
I made 2 trips to the field so far. The only thing I need to look at is getting at least one, better 2 mirrors, to see what is going on behing my back.
I got a nice envelope of Bling last week. The process of getting from the parts I drew to something in my hands is not that complicated. Submit a dxf file, receive a quote, say yes, wait a few days, done. And the good part is, it is not breaking the bank!
The one thing that I had to learn is that a ‘part’ is a single dxf file. What you see here is a single file. Why is this important? The handling and preparation fees deal with single parts. There appears to be no limit to how complicated the parts is (apart from obviously the amount of time the laser needs to cut).
To keep it simple, stick as many individual bits together as you can, to produce as large a part as possible. That gives you the cheapest part. Unless of course you want a 1000 of each individual bit, but then we talk something else.
All I had to do is cut the bits apart, do a bit of filing and sanding an you’re done.
So next is doing some trial fitting, and start building the center section of the top wing. Once that is done, the cabane structure etc. At the moment there is a build thread on biplane forum, at just about the right stage. I’ll add some of these here for comparison
This is the first trial fit for my new bike trailer. I still need to do something on the rear so that there is less change of anything hitting the nose or prop. Wings fit too, and even I can squeeze on the bike. All in all happy with progress.
Update 30 April: There was no easy way to properly secure the connecting pin to the saddle post. (If only I could weld). Most of the bike frame is alu, and I did not want to chop up too many things. The solution is what can be seen here. I also added some bling lights to the rear of the trailer, and 2 batteries for charging plane batteries. (2 x 13Ah)
Update 1 Mai: Went for a short drive, just to test road stability and handling. If it was a plane, I would think it works as designed, don’t touch it!
With the added mudguard and wheel bearings and other small bits, the Hitec 645MG is struggling to get the gear up. There is a point halfway between up and down, where max force is needed, it’s just how the design of the gear works. In theory I could redesign everything. (Yup, maybe sometime soon). Or I could add another voltage regulator to give it it’s own supply, 6V would work (most of the glider runs on old 5V gear), or solve it for now with slightly more powerful servo.
I found a SAVÖX 1256, which has probably twice the torque of the Hitec, so will strap that in for now.
Of course with the way I wired things up, that’s easier said then done. Since I installed a 9 channel Rx in the plane, and needed an extra channel for the Flashy Lights, I came up with the cunning plan to use a single channel for multiple things.
In short, gear up or down is only 2 positions. Light on/off same thing. So why not do a bit of mixing and send the resulting servo signal to an Arduino-Pro-Mini, and let it drive the LG servo and Lights. I cooked that software a year ago, knowing it was a quick fix for a self imposed problem. (That’s what this hobby is all about, if you don’t have a problem, make one!)
Anyway, long story short, the pulse that the servo needs for up or down is hard coded in the software. No biggy, but it means it’s not very convenient when you change servo’s.
Oh, it’s sooo much fun. With the aid of my little magic ToolkitRC.com M6 I measured the output pulses to the servo. 1000-2000mSec. Perfect, but the servo only rotates 90 degrees and a bit? (By the way, there is an software update for the M6, V1.31 dated 23 March 2020)
Oh dear. Now what. Time for a rethink, and do remember in future that you really want a 180 degree servo!
After some reflection and relaxing in the sun, I remembered that I used to convert servo’s to 180 degrees by adding a few resistors to the feedback pot. That triggered of course the thought ”did I maybe modify that servo?”.
And the answer is yes, I did! Funny enough I posted that same fact on 3rd Dec 2016 on my Facebook account. Oh where would I be without my facebook memory. Scary..
Well that sure was a fun exercise for a locked-down Saturday. So next question is: Am I going to modify the Savox? The answer is below. Same trick, 2 * 1.5kOhm resisters either side of the potentiometer will do the trick. Funny this servo is rated to produce 4096 steps. It never stops to amaze me how you can get that resolution from a cheap 5k pot. But they work, so I’m not counting! by the way, there are no wires in this servo, which should make it more reliable (cheaper). But it does mean some sort of skill is required to remove the pcb!
And while at it, might as well try to sort out the wiring mess a bit. I’ve got some space at the top of the fuselage, out of sight.
By the way, that stepdown converter acts as a current limiter as well. Max current the chip will produce is 4 Amps, stall current for the servo is 5 A. Should be safe. And since it is only ever used for up and down, it is not likely to get warm. And if it does, it will disconnect, saving the battery. In theory this is what is supposed to happen. Real life might work differently.
So, that’s enough for Corona-Easter-2020. Left’s hope and pray the world will not have to repeat this ever again!
Corona, DG800Comments Off on What a difference a month makes.
To say we have never experienced anything like this lock-down is an understatement. We are lucky to live in a nice place, with lots of space, so we should be ok. Even if this madness takes a lot longer then the official guestimates that our gov’ment now spreads, I will keep myself entertained.
Saying that, I managed to mess up my back (again) which sorta restricts my movements at the moment. Hence the lack of stories.
I have finished drawing the metal parts for the SA-750, and are waiting for the nice laser people to cut them for me. Obviously my parts are low on their list of things to do, they likely have other more immediate pressures on their business. Never mind, lots to do.
Last year I hardly flew the DG800, mostly because our field was dry, so unbelievable dry, that the stake I use for the bungee did not hold. I once had that metal spike flying in my general direction, and that was once too many times. I’ll try to think of a better solution for tying down the end of the rubber. I probably need at least a double stake, and most likely longer and heavier. And that’s the pita I want to avoid, I don’t want to drag all that stuff to the field. I’ll have a think about it.
At the moment the field looks fine, I could use the single stake, but you guessed it (or not if you read this in years to come) we are closed for business due to the Corona virus. Sad as it is, we are a sport, and all outdoor and indoor sports have been banned. It does not seem logical to us, but the gov’mnt does not have the time to look at each sport in detail to see if it makes sense. So, everybody stay at home, no exceptions.
So, do some maintenance. I knew I had a flat tire. Sorted that by inserting a length of silicone tubing inside the wheel. (I know, I could have bought a new one. No Fun). Then, since I have them, added some bearings to the wheel, that never hurts. I also wanted to make a mudguard, just to see if I can.
The plan is to print the form (positive) slap on some fiberglass and see if it looks like something I want to use. Right now the vacuum pump is doing it’s best to maintain -0.6Bar. I lost the manual for the little thingy that decides when to turn on and off, but it seems to work, so will look for that later.
I would be better off giving the walls a slight angle, so that it is easier to pop of the form. With this version I had to split it to get it to loosen. But in the end, no harm was done, and it looks good enough for now. If it survives, and this lockdown continues, and if I am getting bored, I’ll do another one. This one is approx. 8 layers of 25 gram and one of 225 gram. I have miles of the thin stuff, I use it to get a nice surface. (It was nice until I had to split it in half to release form the form 😉