Seems like it took forever for Saturday to get here, despite being off work on Easter Monday.
I decided to pull out the fuel tank side for the right wing and start test fitting the finger strainer. Fuel tank assembly will have to be done soon. If you recall from when I made the tank sides, I made sure to mark the location of the fuel outlet hole. Shown below is the outside of the tank wall. The flange on the tank actually faces outward for welding:
The finger strainers I was given are actually the large size, the plans call for small or regular size. This doesn't change anything with regards to operation, the fuel lines will still be the same size.
I placed the finger strainer directly over the outlet port mark and it will fit fine (it's facing the wrong direction in the picture, the mesh goes inside the tank):
Here is a better look after I flipped over the tank side (now showing the inside of the tank wall):
The welding flange that the finger strainer screws into is too wide to fit and keep the strainer close to the bottom edge of the tank.....
Here the complete assembly roughly laid out. The strainer screws in through the threaded mount flange from the other side with just the mesh inside the tank:
If I trim off a bit on the bandsaw I can get it even closer to the bottom of the tank and still leave enough for welding and threading in the strainer. This will be done when I get the rest of the fittings for drains, etc., and I can assemble the tanks for welding.
Picked up some new ratchet straps and started the process to wrap the nose skins:
This is a very familiar process which i used on the horizontal stab, flapperons and slats. Long boards help spread the wrapping force equally across the skins:
I still need to figure out how I'm going to cut the slots in the nose skin for the slat brackets. The one at root is exposed so I'm going to use it as the example and copy the measurements across to the other three moving outboard from the root. It will take some time, but I'm confident it will work.
This was my first chance to see if the template I made for the outboard nose skin matched up to the wing tip. Here is a look at the wingtip in place. The curving edge of the nose skin fits very well!
I still need to trim the upper skin still and the trailing edge to match properly. Again, the template I made is a great help:
I still need to finish drilling the nose skin at the spar, but the outboard double ow of rivets on the spar tip is done to A3. I also have the first rivets in the nose ribs along the nose skins. I have enough in there now to release the ratchet straps:
The long boards will stay in place for now until I finish drilling out the nose skin/ribs and at the spar. But it looks even more like a wing now!
More to come! Thanks for following along!
Couple of hours in the shop today, continuing on fit up of the wing tip.
First up, I wanted to trim the wing tip a bit smoother. I marked the extent of the trimming out with masking tape and cut the line carefully with the Dremel tool, including some minor trimming at the trailing edge taper. Clamping it to the bench with wood screws and scraps of shim worked well. I put a container of clecos behind it to prop it up a bit:
I don't have some after pictures, but once trimmed back to the tape, I used some sandpaper to smooth everything out:
The plans ask for some standard L to be attached to the end of the spar tip and rear channel. I wasn't happy that would be wide enough to support the wing tip, so I made a custom wide L from some scrap 025 I had: Drilled the A3 pilot holes in the L:
Then I used finger clamps to hold it in place and back drilled through the spar tip, then upsized them to A4
The L's support the back of the wing tip.
The rear channel area is a bit tight and I mis-drilled the L at this location. It needs to sit more proud of the channel than shown below, so I made a new one (not shown). I also had to grind a bit off the tip of the rear channel so it could be inserted inside the wing tip far enough:
The wing tip now sits in the correct position. I was concerned that the nose skin would properly wrap around the nose of the wing tip, but everything measures up correct, so it should be good. I'm not final riveting the wing tip in place until the top skins, trailing edge and nose skins are complete.
I laid out the rivet line across the outboard lower skin and pilot drilled the holes to A3. I also roughly scribed a line across the inside of the upper outboard skin. This will need further trimming, but I've been fighting with it a bit when putting the wing tip in an out.
Knowing the outboard nose skin will fit correctly once it is wrapped around, I finished off the spar and nose rib rivets in this section:
I left the last outboard rib and spar rivets un-done in case I need to slip the outboard main lower skin out of place. These will get done once the wing tip is in final rivet:
The wing tip looks real nice in place now that both outoard skins a trimmed closer to what they will look kine. I still need to trim the trailing edge both lower and upper to match the wing tip. Before I drill the rivet holes for the wingtip, I want to back it somehow to prevent the pulled rivets from cracking the plastic. I was thinking some small flat washers on the tail side of the rivet, but I think instead I'll run a narrow strip of 016 aluminum along the inside and drill through the plastic and the strip as a backer. I also think this is a good spot to use a hand puller instead of a pneumatic gun:
I mentioned yesterday, I wasn't entirely happy with the grip length of an A5 rivet in this hole. I drilled out the A5 and will replace it with an A6 which has a longer grip length.
My testing of the 10 PSI pressure transducer that I ordered is going well, however I found the resolution of the 0 to 10 PSI sensor to be to large a range for what I need. I found some 0 to 1.5 PSI ones online last week at a "decent" price so I pulled the trigger and ordered a couple. I'm looking forward to testing them as I believe this will be the solution I'm looking for to measure fuel tank levels.
Next up, some final work on the lower surface of the right wing, including some cleaning of the aluminum. Then the wing gets flipped right side up for nose skin wrapping and trailing edge set up.
More to come this week.. Thanks for following along!
Easter weekend is here already. This CoVid BS is getting real tiring, but at least the nicer weather is here.
Spent a "Good Friday" in the shop, working on the right wing. I was going to leave the rear root doubler clecoed in place and finalize it later, but I decided the fuel routing can still be done with it in place. I staggered the clecos and pulled the last of the A5 rivets in the rear channel face:
I final riveted the root nose rib into place and added the splice plate. I also final torqued the spar pick-up plate bolts:
I added and final torqued the wing strut attach angle bolts top and bottom where they go through the spar caps. The first picture shows the A4-7 bolts that hold the spar pick up attachment that are yet to be installed (I put them there to remind me they are coming up soon):
With the bolts all installed along the fron spar, I reattached the lower skins in preparation for final rivets, including the freshly primed wing stiffeners -I won't be rolling the lower skins anymore, this is final assembly on the wing skeleton:
Couldn't resist adding in the wing tip again to see how it's going to look and also figure out the trailing edge:
I'll have to do some more thinking on how to trim this up. There is a large bulge at the trailing edge that will need to be trimmed away, but it's hollow so I want to make sure trimming it way isn't going to compromise it's integrity going forward or lead to cracking:
It's extra work, but I like to put clecos in any holes along a line of rivets that need to wait for a rivet. It's a good reminder to think twice before pulling a rivet too soon in the process that would have to be drilled out later:
All the rivets along the rib lines and wing stiffener lines are done. I left the perimeter of the skin at the main spar and along the trailing edge joint open as well as anything close to those as I may need the flexibility to reinstall the trailing edge where it tucks under the main skin.
Next up were the nose skins. These need to be attached permanently as all the front strut attachments are riveted through them, the skins and the spar.
Strut support angle clecoed in place. The hole where the strut pickup comes through the skin was already deburred at this point (I forgot to erase my Sharpie note). This is a complicated joint which takes some thinking about order of operations to ensure rivets are done while the holes are exposed.
I clecoed the strut doubler in place and I got the two A4 rivets and the A5 spar rivet in the support angle done before adding the strut pickup and several others towards the rear. Those two just in front of the spar line would be impossible to reach if the strut pick-up was bolted in place as well as the A5 on the angle to the left of them:
I slid the strut pick-up through the skin from the outside and had to carefully curl the skin back with a piece of twine to provide the work room to add the pick-up bolts. The topmost bolt in the picture needs to feed the other way through the hole, otherwise the nut and tail of the bolt won't clear the skin when it lays flat. These were then torqued to spec:
With the skin laid back down and riveted to the spar, I realized I should have done the other A5 rivets close to the spar pick-up. It's way to narrow to get any rivet puller in there:
Only two A5 rivets had this issue, so I pulled them in the opposite direction. Not ideal, but perfectly acceptable solution (I'll mark that down so the other wing looks the same!). I also pulled the single A5 rivet just below the strut pick up hole - I think it might need to be replaced, I'm not sure it's long enough for a complete grip, maybe I'll up-size the hole to A6 here:
Really happy how this assembly turned out- tight and just like the plans describe.
The slot I cut in the trailing edge to go over the rear strut pick-up worked perfectly as well, but is a real pain to to slide over the rear pick-up AND tuck under the main skin - it's just to tight to do easily. I think I will be permanently attaching the trailing edge as well. Adjustment up and down can be made when the top side of the trailing edge is tucked under the top skin. There should be enough room to work in there from above for the fuel line routing as well:
With the nose skin in place, I can add the front jury strut pick-up:
Finished of the spar line rivets:
Pulled the A4 rivets on the lower side of the nose skin into the nose ribs where I could.
The wing is really starting to feel solid! The front lower corner in the picture is where the wing root nose skin will reside. It will be done after the top of the wing is completed.
I've decided to hold off a little longer on the outboard skin and the outboard nose skin until I can get a better idea on the trim and finish of the wing tip. I still need to trim the outboard end of the trailing edge skin to match as well.
Overall a mostly productive day, inching ever closer to the point I can flip this wing back over the way it should be and start the final processes to close it up for storage.
Thanks for following along, more to come over this long Easter weekend.
My second Monday night session at the shop was a productive one. Three uninterrupted hours of build time and I got some good stuff done.
First up, I decided to go ahead and rivet the flap arms in place. The three outboard arms follow the standard rivet head on thinnest material (in this case the ribs):
The inner-most flap arm sits inside the fuel tank bay. In order to allow clearance for the fuel tank, the rivets are pulled with the head on the thick side of the joint here (the flap arm):
Rivet tails on flap side:
Rivet heads on rib side:
Fuel tank bay is opposite - rivet heads on flap arm side of joint:
All rivets double checked for correct pulled form. Lots of strength here:
I decided it was time to start trimming up the wingtip and cut it out of the moulding material.
I tested the Dremel cutting wheel on waste edge first, it makes quick work of cutting out the wingtip from the form:
Here it is, rough cut out:
Careful use of the Dremel trims it down to the flat flange edges that will eventually tuck under the wing skin tips:
There are a couple of spots where the flange narrows around the point of the nose and at the trailing edge. I was careful to leave lots of extra for fine trimming later:
I removed the skin stiffeners that were clecoed in place on the inside of the upper skin. I can't believe how much drill debris (called swarf) that can fin it's way into the little spaces between parts.
A quick vacuum with the ShopVac and a soft brush attachment cleaned up most of it.
With things cleaned up, I slid the wing tip onto the end of the spar and rear channel. I still need to make the support angles for each, but really happy how it's shaping up!
Neither the picture above or the one below capture how slanted the wing tip is. The is on purpose and is for aerodynamic reasons (more on this in a future blog):
Finally tonight, I finished deburring the upper wing skin stiffeners, cleaned them and primed them.
They will go back on the upper skin once the wing is right-side-up. For now, I'll leave them off until the upper skins are deburred, primed and not rolled up for storage.
Overall a good night. Back on Wednesday for more.
Thanks for reading :)
Full and productive day in the shop yesterday, but not a lot of pictures to share.
Started taking the nose and lower skins off the wing in preparation for deburring and priming. If I'd only known how many holes there would be to deburr, I wouldn't have drilled so many! Just kidding, but man there are a lot of holes to clean.
Lower outboard wing skin, deburred and primed. This section is small enough to store flat, so I deburred, primed and riveted the skin stiffener in place.
Inboard nose skin deburred and primed. I found it convenient to leave it on it's edge on the floor and roll along on the stool with the deburring tool. Primed the areas using a sheet of newsprint held behind. The lower edge shown will be primed later (didn't want to get primer on the carpet runner):
Lower wing skin removed and flipped over for deburring. Very pleased to see all rib holes are centered on the rib flanges and I don't have any elongated holes - bonus! Once complete and primed, I rolled it up for storage until ready for re-assembly.
At this point I can begin the final riveting of the wing skeleton. Removed nose ribs from the spar, deburred them and the holes in the spar and final riveted them to A5:
Next I finished the final rivets on the wing tie down ring (not pictured) and the rear channel, including the channel to ribs and the rear strut pickup. This joint has seventeen A5 rivets and an AN3 bolt on the face of the rear channel alone - plus another eight A5 rivets once the skin is in place. It's one heck of a stout assembly once it's in place:
Final riveting of the flapperon arms might wait until I have the lower skins on, or I might rivet them first. It's probably better to do them now while I have unfettered (today's big word) access, so I'll do that before I rivet the skins on.
I'm getting closer to fitting up the wing tip. I'll need to cut it out from the blow mold process that it is made from. These are the ones I picked up in 2019 when Dad and I went to Montreal-St Hubert
I'll probably cut them out rough with a Dremel cutting wheel and leave enough of an edge that can be trimmed, sander later. It will be easier to fit up with the wing upside down on the bench:
Still a bunch to do, but the wing is essentially ready for the skins to be added back and final riveted to the skeleton. I need to add the support Ls at the spar and rear channel tips that support the wingtip. Before I rivet the skins though, I also need to vacuum out all the drill and deburr debris so when I flip the wing over it doesn't get into any areas I won't be able to reach.
I'm also close to fuel line routing decision. I can't add the trailing edges in permanently until that gets finalized and installed, which can't happen until the tanks are fabricated and the rear channel root doubler is dilled and deburred for the fuel line passthrough. Need to start looking for grommets for that to0.
Blog posts in the coming episodes will likely be shorter but more frequent. Thanks for following along! More to come.....
Got the inboard and outboard trailing edges fit up and pilot hole drilled tonight.
The fit up was fairly easy and straight. I'll need to close up the trailing edge angle a bit before fitting up the topside. I can't rivet the bottom side until I route the fuel lines.
Notched the inboard edge at the rear channel. I'm going to wait to trim the trailing edge taper for now.
A3 pilot holes along the rear channel. Outboard half of the wing will be upsized to A4, inboard to A5
Outboard trailing edge will get trimmed to match the wingtip. I'll need to get it out of storage and prep it for fitting too.
Not a huge update tonight, but progress is progress.
Stay tuned for more, thanks as always for following along.
Although I've read it many times, watched and listened to other successful builders state it many times, one of the truisms I have really realized the value over the past couple of weeks is consistent shop time. Not leaving so much time between shop sessions leaves previous work accomplishments and next steps fresh in mind, saving tons of re-thinking everything each weekly visit.
To that end, I'm planning on adding 2 nights a week to the full Saturdays I'm currently spending in the shop. Some nights, I might be only a couple of hours, some more. The point is I need to keep at it if I ever expect to get this project done. Blogs will be more frequent too. Tonight was my first evening session.
I decided to get the strut support section done.
Like the jury strut brackets, I found the scaling of my original templates lacking some accuracy, so I did up a new template on cardstock. I left the lower end a little wider than the plans call for - that give me room to trim it after I bend the flange over to match the strut pick-up.
Found a nice piece of 063 perfectly sized for this - nice to find in scrap bin!
Bending this bracket took a fair amount of figuring out. The point of the curve needs to mate up to the curve of the strut pickup. I measured three times and used a cut-off piece of 063 as a proof piece first to establish correct angle and bend line:
Trimmed the lower flange to match the upright flange of the strut support angle - perfect fit, glad I took the time to measure thrice!
Seven measured A3 (small bit) pilot holes in the lower flange:
Some small C-clamps hold everything in place nice and tight and even:
Match drill the bracket to the angle. This is challenging, but easily do-able with a very long A4 drill bit and 90 degree air drill.
Match drill the 3/8 strut bolt hole in the support bracket by back-drilling (BIG bit) through the strut pick-up:
A5 (big bit) rivet hole as per the plans, drilled through both:
Everything comes apart, bracket to angle rivets are upsized to A5 and deburred. Scrub down with Scotchbrite and prime (I did the front jury strut brackets at the same time.
As the title says, every bit counts. More to come.
I can't believe how much work I got done in the past 3 weeks. Progress has been so good, I've been neglecting my blog in favour of keeping up the momentum on the right wing. I was off work this week for annual holidays, so was able to get four solid days in the shop this week alone.
I wanted to start on the trailing edges. Like the tops skins, they are made of two sections which join at the mid-way point of the wing in the same area as the strut pickups.
Cut the inboard and outboard trailing edge skins to width and length then I marked out the inboard edge where the trailing edge tapers and has a cutout to match the rear wing channel.
On the bender, I used the the 1/8th "shoe" to creat the trailing edge:
With all the top skins fitted and keeping the wing skeleton square I was finally able to release the spar from it's screw-down clamps and flip the entire thing over on it's back. At this point it makes sense to elevate everything up on square steel tubes:
I've temporarily added the required skin stiffener "L"s in each of the wing bays. The upper skin will need to come off for deburring later so I haven't final riveted these yet - that way I can roll the skin for storage if needed.
With the bottom side open for work, I could have a good look at the alignment of the flapperon arms in comparison to the rear channel and each other. The mid-wing joint at the rear channel and strut attachment point is quite a complex piece of joinery!
All four flapperon arms mount up correctly and line up close to perfectly. There is a bit of twist in the wing induced by the roundness of the upper wing surface, so I'm happy where the arms are at for now.
The lower inboard skin is the largest part I've made from of aluminum sheet so far - almost 3 metres long and 720mm wide. I rolled a full sheet of 020 out and made the necessary cuts - it was A LOT of cutting with shears, but at least it's a rectangle to start with before trimming the tapered inboard edge. Layout is marked on the sheet, including the areas for the cut-outs at the spar and rear channel whoch will allow access to the wing mounting bolts:
It even looks longer in the photo! No way in our shop to cut that other than by hand. We'd love a CNC or waterjet cutter for stuff like this, but where would we put it!
The wing skeleton is bolstered from below to bring the spar perfectly vertical again. With the spar both vertical and level from end to end, The lower wing skins can be added. It all begins with the first dill hole at one corner, then squaring it all up before adding more holes down the spar and rear channels:
With enough clecos to hold the skin square to the skeleton, I laid out the rib rivet lines and the lower skin stiffeners:
The skin was removed again and taken to another spot in the workshop (the floor!) to drill the A3 pilot holes as laid out. The skin is returned to the wing skeleton, re-attached by clecos and pilot holes are drilled throught the skin into the ribs, working from rear edge to front spar:
Man, there is a lot of holes to make and secure! A quick peek once in a while through the spar lightening holes confirms the rib holes are in the centre of the rib flanges and not near any rib fluting.
Eventually, all the rib line holes are upsized to A4. The spar and the rear channels remain as A3 until the nose skins and trailing edges are added. I've constantly checked the level of the wing across the spar and the rear channel, so far so good - it get better with each cleco I add as the whole assembly stiffens up:
With the skins drilled to A3 at the rear channel and the ribs brought up to A4, I removed the skin again and pilot drilled the spar. Then I re-attached the skin -again- and used the strap dupplicator to complete the skin holes at the spar up to A3:
With the inboard lower skin now firmly in place and square, I cut out the outboard skin and starting fitting it up in positiion, again using the strap duplicator where this skin overlaps the inboard one and at the spar:
The outboard skin has a very subtle curved edge on it which I was able to trace using the cardstock templates I created:
Looking ahead to the fuel line routing, I marked and pilot drilled where the fuel line will exit the rear channel - it's hard to see in the picture, but the pilot hole is just left of dead centre in the image below. This will be upsized to the required diameter once I figure out fuel lines and grommet sizes for the hole. There will also need to be holes in this area for wiring - but that can wait for now.
Next skin I prepared was the outboard nose skin. This has a very complex curve to match the wing tip insert once it is wrapped around the nose ribs. Another cardstock template I created from the plans is used here to trace the curve described in the plans:
The inboard nose skin is almost as long as the inboard lower skin, but only extends from rib number 1 to rib number 5. I cut it out from a sheet of 016 and laid it temporarily on top of the clecos to get a better idea if the length was correct and it was. According to the plans, it is a rectangle shape to start before it is wrapped around the nose ribs:
I notices in the assembly drawings however that the pictured skin they show was a triangular tab running between the 1st nose rib and the root rib (outlined in yellow on my picture):
My plans don't reference this at all. My plans do not show any rivet line layout in this location (which there would need to be) nor any dashed line to indicate this tab:
After some head scratching and discussion, both Ron and I feel a full root nose skin from top of the spar to bottom of the spar will be correct (as shown in the plans). Everything is covered, this isn't a structural piece and the plans version is actually cleaner aerodynamically, At the end of the day, the plans are always the final answer.
The procedure to fit the nose skin is multi stepped. First the skin is slid between the main lower wing skin and the spar:
Now the lower skin holes at the spar are used to back drill through the nose skin:
The same is done for the outboard nose skin:
Once all the holes are drilled along the spar of both nose skins, they are pulled out and cleco'd on top of the lower wing skins - this will be their final orientation.
I removed the outboard lower skin and using the strap duplicator, I created the A3 pilot holes in the spar tip. Eventually, there will be two rows of offset A5 rivets here (the flange die is keeping the skin flat to the nose rib below as I drill them out):
I re-attached the outboard lower skin, sliding it below the outboard nose skin - this too will be it's final position. The three clecos at the spar hold everything square, but I'll wait to drill the second row of A5 rivets where nose and lower skins overlap once I have the wingtip trimmed and in place:
Speaking of wingtip, you might recall I decided to wait on trimming the outboard top wing skin until the wingtip is in place. I decided to trial fit the cardstock template and although still in very rought layout, it looks promising!
The yet to be wrapped overhanging nose skin doesn't leave a lot of room between the workbench and the counter!
To give myself (and Ron) some room to work, I sued a couple pieces of twine and tied the nose skin loosely down and out of the way. This gave me the room to work I needed to layout and pilot drill the nose ribs:
Next up is the strut support angle. This is a piece of 032, bent in an L shape which helps transfer the load of the wing strut back and across the wing rib and wing structure.
In the picture below you can see the lateral skin stiffeners temporarily mounted on the outside of the lower skin. The eventually will be inside the wing, i just have them there to help keep everything firmly in place while I was pilot drilling the rib holes. Perpendicular to that is the strut support angle which mounts on the outside of the wing. According to the plans, the support angle is supposed to only go as far back as shown, about 40mm short of the the lateral stiffeners - this makes absolute no sense to me. Why would they leave it short of the lateral support? I double and triple checked the plans and it clearly shows it short like the picture below..... strange choice by the designer.
I decided to deviate a little here. I'll extend my support angle back to meet the lateral supports. It adds more strut support with very little work or weight penalty and I'm not adding any new holes or rivets in doing so:
Once bent, each end of the 032 strut support angle is tapered:
Before adding that support angle to the lower wing surface, I'll need to know exactly where the strut support protrudes through the wing at the spar so I can fit them together properly. So until that was done, I set it aside for the moment and focused on the jury strut angles which needed to be attached.
Jury struts are diagonal braces that run between the middle point of the main wing struts and the wing. That triangular structure adds even more rigidity to the wing structure. The jury struts attach to the wing with simple (so I thought) 025 brackets. I made the ones I needed way back when I had some scrap 025 metal cut-offs from the wing rib blanks (that was a couple of years ago - jeez time is flying by). They are the ones on the left below.
Turns out the scaling I calculated back then was skewed and the original PDF cardstock templates I created was incorrect. I tried using them and bending them as per the plans and made several bad ones before deciding it was time to re-do the templates new (shown on the right). The CriCut Maker does this so much better than manually scaling a PDF to print on cardstock!
Below, the proper size front jury strut brackets, match drilled, one pair for each wing.
One set of rear jury strut brackets get match drilled holes as well:
A pilot hole drilled in the centre of the lower flange:
Mounted in position on the wing at the main spar. The other two pilot holes are made using the strap duplicator (not shown):
A long A3 bolt is used to help line up the second bracket where i mounts on top of the lower one:
Matching pilot holes drilled from below through the upper bracket and secured by a cleco for drilling of the other 2 pilot holes:
Secured to the wing. The bolt is not the correct one that will be used here, it was only temporary to help align things:
Next up was the tie-down ring and how the nose skin needs to be trimmed at the number 5 rib to allow it to protrude below the wing (sorry about the crappy picture):
I measured the distance from the spar forward to where the tie-down ring would pass through the skin and marked everything out on the skin. The tie down ring has not been riveted yet to the rib, it is only clecoed in position for fitting at this point, that can be done later from above:
Using a Dremel wheel, I cut out the slot a little at a time until the tie-down ring fit nice and snug:
I used the same methods for the wing strut pick-up pass through point:
Now I can fit the strut support angle as I know where it meets the strut support laterally. Again the duplicator is very handy here:
I'll need to create new 063 strut support brackets which mount under the strut attachment plates. I don't show it above, but I ran into the same issue where the part I made isn't correctly scaled. More to come on that.
Next up was the flapperon arm slots at the rear channels. This time I measured and used a 1/8 drill bit to create the upper extend of the slot and used metal snips to create the slot up from the trailing edge of the lower skin to the hole. That worked very well.
The skin and fapperon arms are very well supported on both sides here - four A4 rivets in the rib and four more A4 rivets in the flapperon support angle on the opposite side of the arm:
This wing is really getting close to be ready for final debur and riveting of the lower skins. Next up is trailing edge skins and maybe a trail fit up of the root nose skin.
When not at the shop, I'm still tinkering with a way to use an Arduino and a pressure transducer to measure fuel quantity in the tanks. I picked up some fittings and some 3/8 diameter poly pipe to use for simulating a fuel tank level sensing device. I'll need to make a decision soon if this is going to work like I expect it to. I think I'm going to need a lower range sensor, bt have found a decently priced source for them online. More on this to come.
Well, I've been hacking away at this blog well past my bedtime. I'm exhausted be very happy with what I got accomplished since my last post.
Thanks for following along.
Productive day at the shop today.
First order of business, sorting the parts we ordered from Aircraft Spruce. Some hardware machine screws, lock nuts and castle nuts for Ron. I also ordered 4 drain valves for the wing tanks (2 for me, 2 for Ron). I wish this pandemic was over. I hate paying shipping when I could drive to Brantford to get stuff - probably cost more in gas than shipping, but who doesn't like going to an aircraft parts store?!?!
One of the appealing features of the 750STOL is the visibility from the cockpit. Most high wing airplanes have a wing spar/structure that carries through the top of the cabin or the cabin roof itself is solid. Look at the roof between the wings on this stock photo of a Cessna 172:
Compare that to the 750 which has a clear panel roof - the visibility from the 750 cockpit is amazing:
How does the 750 design accomplish this? The wings taper sharply at the root, but the curvature of the upper wing surface creates a very complex curve. To make this work, the root skins need to a way to mount at the varying taper angle from the tank rib to the root laterally and from the main spar to the rear channel as well. I needed to make a root skin support angle out of 025. I started with a piece of 025 strip and bent it to a 30 degree angle along the length of it.
I marked the angle 400mm up from the end and used the dead blow hammer to flatten from the end to the mark. The goal here is to go from completely flat near the rear channel to a full 30 degree angle at the 400mm mark. It went easier than I thought.
Next I marked the location for fluting bends between rivet locations on the tank skin. It takes a bit of tweaking to get the flutes just right, but eventually the angle starts to get close to the curve required and I could tuck it under the tank skin to get the first rivet in near the reach channel:
The strap duplicator is used to match drill the holes in the tank rib:
Continue to massage the flutes and work the angle until it matches the top of the nose rib:
It took a lot of fussing with flutes, adjusting here, tweaking there to get the angle to lay straight and flat. I soon realized the cleco I used on the taper side at the spar doubler was preventing me for properly adjusting the flutes. Once I removed that one cleco, it was much easier. Unfortunately that misaligned the hole slightly, but I can recover from that when I upsize the holes in final drilling.
Rivets across the angle and into the nose rib. That's better:
Root angle, looking forward:
Sometimes it's easier to take the plans out of the binder and put them beside me on the floor cutting mat instead of walking back and forth to the bench.
With the root skins laid out on 016 sheet, I used the bender as a straight edge and cut the templates out:
First fit up of the root skin looks promising. The instructions aren't very clear on how this interacts with the nose skin, but my measurements look good. The root angle also seems correct:
Laid the skin back on the bench and used the template cut out on the CriCut maker to lay out the curve that sits inboard and will match the curvature of the roof line and the offset of the root rib:
Finger clamps at the rear channel and spar, along with some wide masking tape to get the first cleco in the rear channel:
With all the holes drilled and clecoed along the rear channel, the skin appears to be fitting well:
Happy with how the root skin is fitting up, but I got a bit or work yet to do on it, including rivets along the root rib and the root angle.
Progress is progress. I've got some more hardware for the fuel tanks, and I expect the pressure transducer I ordered online to arrive this week so I can begin testing it's suitability for fuel quantity measurement. Soon I'll be able to flip the wing over on it's back and work on the bottom skins.
Thanks for following along - more to come soon!
Continued working on the right wing. Got the upper outboard skin mostly matched drilled to the ribs. I've only pilot drilled the skins at the spar and rear channel as I will need to fit the nose and trailing edge skins first, the right size them as a group.
first thing was laying out the rivet spacing on the upper surface as per the plans:
On of the keys to good rivet spacing is knowing where the rib fluting is. Marking it out ensures two rivets between each flute. I marked the distance of each rivet back from the spar centre-line so I can easily transfer the same measurements to the other ribs which are the exact same:
A3 holes clecoed before right sizing to A4 across the top of the wing chord. This really makes the curve of the wing apparent:
With the ribs confirmed as right size, the rear channel is drilled out to A3, waiting for trailing edge skin:
Next up was the upper inboard skin. This makes up the panel that covers the fuel tank. It's installed much the same way as the outboard skin. I'll wait to drill the rear channel here too:
finger clamps help to keep everything straight for pilot hole A3 clecos. Again, I'll wait to drill these up to A4 when I'm ready to add the upper root skin as there is a root angle to attach at the junction of the two skins that help form the taper to the root:
The main upper skins are now complete:
After cutting the 2nd fuel tank skin, I roughly laid out the tank ends and some other parts I needed on 025 for the fuselage. Minimal waste is the goal:
The next steps are joining up the two halves of the fuel tank form template and the two halves of the tank end aluminum templates:
Confirmed the templates match the measurements of the plans. This is very similar to the templates and forms of the wing ribs:
The form template fits well on the outside of the inner wing rib and this confirms the extended tank will fit in the wing bay as I expect. Kinda cool to see it work :)
With that confirmation, I laid out the aluminum templates on the pre sized 025 section. Then I used the centre punch to mark the relief corners:
I also punched the inboard tank ends where the plans show the out-port of the fuel tank. I've yet to completely decide on how this will look on my system with regards to the fittings, lines etc. But the out-port will be here:
To remind me where I made punch marks, I circled them as I went. Always drill and debure the holes before making relief cuts - so much easier
All four ends laid out for the fuel tanks - one left, one right:
Templates cut out, awaiting final relief holes and corner cuts:
Seeing as I only have four ends to make, I decided some pine boards would be just as easy to use and much cheaper than expensive 3/4 inch plywood pieces.
Stacked two boards and traced the form template on the top one. Screwed the boards together.
Cut the template line out on the bandsaw. Fresh pine getting cut smells real nice :)
Once I sanded the edges to the correct size, I marked the edges for rounding off on the router:
Both sides of the form, edge rounded and beveled on the sander for springback allowance on the aluminum blanks:
The rest went the same as the wing ribs, except the forms needed to be clamped around the periphery as there are no tooling holes to use like the wing ribs. Holes in the fuel tanks are not welcome here for obvious reasons! Next step will be start laying out the bends for the wing tank skins.
Before I move forward on the tank construction, I need to finalize what needs to be built into the tanks, including fittings for the filler neck, the out-port where the fuel will travel to the engine via the fuel line and where the quick drains will be mounted (more on this later).
The other thing I need to decide is how to monitor fuel tank levels - this is the kind of stuff I love to figure out, but also keeps me awake at night. The plans call for a float type fuel level sender similar to what you have in a car fuel tank. Essentially it's a float on an arm connected to a sweep contact that changes electrical resistance or voltage in the fuel sensing circuit, which is fed to a gauge on the dash similar (simply) to this:
The drawing above is simple enough, however there are two flaws for this to work in my airplane. There isn't room between the top of the tank and the upper wing skin for the the sliding contact/arm pivot. Second flaw, related to the first is the plans call for the same float arm system, but mounted in the side of the tank. All I can think of is why would anyone want to cut an unnecessary and large hole in the side of the tank? That's just asking for trouble with leaks and the builders forums are chock full of stories regarding just that.
So, like the trim control and lighting, I'm going to create my own Arduino solution. I've been doing some research on other methods to measure liquid quantities (the level) in a container (the tank) without being invasive (cutting holes).
My challenge is to find a method that can provide accuracy over 190mm of fuel tank thickness (top of tank to bottom) at it's thickest point and not require holes in the sides or bottom of the tank where it can leak fuel.
There is some limited information on the interwebs about using ultrasonic sound waves to measure the distance from the sensor to the fuel, but that requires a large range between full and empty to be accurate and again would require a sensor at the top of the tank, something I'm trying to avoid. The math to make this work and the shape of the tank doesn't make this easy.
I briefly thought I could make something like this I found on Amazon. It uses a float that slides up a column open/closing magnetic reed switches as it rises/falls, but it would still require a hole and mount on the top side of the tank and a bunch of circuitry to complicate things:
I've decided to try something like these. A pressure transducer that measures the weight of the fuel in the tank inline with the fuel out port via pressure. These transducers are fuel proof and output proportional voltage in a linear ratio to the pressure sensed - solid state, no moving parts and maintenance free They come in various pressure ratings and configurations, but most importantly are threaded the same size as my planned fuel fittings.
The outputs from the transducers can be read and interpreted by the Arduino microcontroller and with some simple programming the Arduino can output a signal for a readable gauge in the cockpit (one for each left/right tank).
What I want for gauges is really up to me as they can be displayed on a LED panel by simply programming whatever images I want to use as the display.
I could go with something simple such as the traditional automotive gauge on the right, but I kind of like the sweep/ribbon style on the left. The numbers in this example represent percentage, but could be made to show litres/gallons as well - it's all customizable in the programming.
I started to play with LibreCad to make my custom display. I created the sweep and used Microsoft paint to colour each section of the arc. Each arc represents a reading correlating to what the Arduino is reading, giving me a moving gauge as fuel is consumed.
The LED display uses low resolution bitmaps for display, but they can be in colour. I plan on green for anything more than 1/3rd full, yellow between 1/4 and 1/3rd orange then flashing red for anything less than 1/4 to draw attention to it. I might even have the programming sound an aural alarm as well.
A simple animated GIF shows what a declining tank would show (with an added funny at the end):
Progress is leading to more thinking and I love it. It's the true core of what this adventure is about.
Next up, flipping the wing over and fitting the bottom skins and mocking up the fuel tanks for welding and fittings.
Thanks for following along.
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.