Fuel lines and fittings have arrived. Stainless braided Auto-Flex line and Swivel Seal fittings. Expensive but the peace of mind this provides is worth it. This is one area of the plane I refuse to compromise on. Very impressed with the quality of Earl's Performance products. With these in hand I can start laying out the fuel tank plumbing.
I've been wanting to figure out a way to measure the fuel level in the tank that requires no internal sensor - less holes in the tank means less chance for leaks. There are several stories on the builders forums about tank sensors mounted through the sides of the tank leaking or being terribly inaccurate, hard to service and generally failing.
I wondered if there was a better way, and I originally came up with the following. A very sensitive presssure transducer (the chrome unit with yellow label below) that will measure the "head" pressure of fuel in the tank via a "T" in the fuel line next to the tank. In theory this should work using an Arduino microcontroller to read the sensor and output a value to a gauge. Here is the assembly mocked up on the bench. From right to left - finger strainer (inside the fuel tank), tank fitting (through wall of tank), threaded adapter, threaded "T", coupler and pressure sensor), fuel line fitting elbow.
Testing of the system has proven difficult. I've been unable to get consistent readings from the sensor in a static set-up. The programming of the Arduino works fine, I'm just not happy with the accuracy of the output due to the very low spread between empty tank head pressure and full tank head pressure, which given the depth of the tank is about 1.5 PSI. I'd hoped a programming algorithm within the Arduino to amplify the input values and stabilize the readings would work, but it's become too much of a tail chase to get it right. From there I'd still need to figure out how to smooth the values to account for changes in atmospheric pressure (fuel changes "weight" with changes in altitude) and aircraft attitude - banking towards the sensor increases head pressure, banking away reduces head pressure.
In an effort to focus on the build getting moved forward, I've decided to abandon this concept in favour of a top mounted float sensor. Yes, this means another hole in the tank, but if mounted from the top, the risks of leaks is minimized and the ability to service the sensor if needed is much easier. More on this later.
So removing the pressure transducer from the fuel line leaves just the tank strainer, the tank fitting and the elbow. I'll need to order the fitting that goes between them, but they are inexpensive and easy to obtain.
The tank fitting is a one direction NPT thread. This picture shows the fitting as it looks from the outside of the tank.
These fittings were gifted to me by another builder. They are actually the larger style, so I need to modify them slightly to fit the tank side rib so the strainer sits nearest to the bottom of the tank as possible. Trimmed them using the bandsaw, then cleaned them on up the disc sander.
The smaller diameter of the fitting needs to fit through the tank rib from the inside. I don't have a drill bit this size to make the hole, so I had to improvise.
I confirmed the fitting was trimmed enough by laying in on the outer face of the tank rib:
I drilled a pilot hole equivalent to where the centre of the fuel strainer will be on the tank:
Used a large step bit to create the general shape of the hole almost up to full size in the tank rib:
Laid the fitting centred over the hole on the tank side of the rib and traced the final size/shape:
Clamped the rib to the bench elevated on some blocks, then used the Dremel tool with spiral cutting bit to carefully bring the hole close to size using the trace lines as my guide:
Filed the hole to final size to ensure a tight fit:
Here is the fitting in it's final position looking from the inside of the tank rib.
On the outside of the rib, the fit is really good:
With the finger strainer in place
Bending the tank skins can be tricky. It is paramount to ensure the bends are as tight as possible to the corners of the tank ribs to reduce any gaps that will need to be filled when the tanks are welded.
I wrapped and finger clamped one of the ribs with the seamstress measuring tape (very handy long ruler for any project) to get a general measurement of where the corners of the tank skin will be. This picture is of the second tank taken later in the day (left tank had already been through this process and I forgot to get a picture for the blog):
The throat depth of the wide bender isn't deep enough to get to the middle tank skin bends, so I needed to use the heavy bender. To allow full access we moved it out into the open floor area, rather than roll up the paint booth curtain (Ron is painting currently).
First I laid out the 025 skin and marked the approximate location of the first bend. Like the slat skins, order of bending is important here, working from middle out to ends. I've left the skin a bit long at each end to make sure it doesn't come up short once it is bent to shape:
The heavy bender allows for material to pass through, giving full access to the middle of the sheet:
First bend complete, next was measuring the second bend closely to make the corners tight
Finger clamped the ribs in position to get a good measurement where the next bend would be:
Second bend line laid out (note the little circled "2" I used to remind me of the bend order):
Back on the bench, I discovered the second bend was slightly overbent and the process on the bender had opened up the first bend as well.... I corrected both before moving forward, but swapped the bend order on the second tank which prevented this from happening again.
Left tank skin rear corners corrected and test fit shows good:
Marked out the location of the fuel filler neck:
Front side of the tank skin bent up to meet the top skin and close off the tank:
The front side of the tank skin needs to have a 5mm flange bent forwards to create the seam for welding. I puposely waited to bend this flange as I didn't know where the bend would be until I mocked up the tank:
I tipped the tank forward on its nose and clamped the forward tank skin onto a piece of aluminum angle at the bench edge:
Using a deadblow hammer I caefully bent the 5mm flange forwards to match the top corners of the tank ribs:
Reassemble the tank and use Cleco vise clamps to hold it together. Some final tweaking of the rib flanges squares it all up - very happy with the final shape! The extra material overhang on the top side of the skin will be trimmed back to match the flange.
Marked out the fuel tank drain location which is directly below the fuel line fitting. This is the lowest spot in the tank once it is mounted in the wing. It is from here that fuel is drawn during pre-flight to check for contaminants such as debris or water:
The right wing tank went faster now that I have the benefit of a process from the first. Fuel outlets are on the opposite side of the left tank (the face inwards towards the fuselage:
I drilled and sized the fuel line fitting for the right tank after creating the tank so we could move the bender back out of the way. The process for the fitting was the exact same as the left wing, just the opposite side of the tank:
Picture of the top front of the left wing tank. I've laid out the location of the top mount fuel tank sensor and the fuel filler neck.
Both tanks clamped together, resting on top of the wing and awaiting parts for the fuel filler neck and fuel level sensor. These will be fitted before final weld-up.
Very pleased at how the tank assemblies turned out, hopefully welding and subsequent leak testing goes as well. Getting ready to order the fuel filler necks, fuel caps and the parts needed for the fuel level float sensors.
This doesn't fit under either the engine or avionics category, I guess it is part of the wings? Maybe under other......
Thanks for following along, stay tuned for more.
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.
Busy couple of weeks since the last blog update, but lots to share.
I continue to assemble the wing spars and gather the remaining materials and make parts for the wings.
With the spar webs cut, it's time to layout the lightening hole locations along the web, and cut the spar cap angles. These form the top and bottom of the spar. It starts with a centre line along the length:
Measuring outboard from the root edge, I made a hatch mark for each of the lightening hole locations:
With the locations laid out, I stacked one spar web on top of the other, secured them with clamps and drilled pilot holes through both - this means all lightening holes in each spar are in exactly the same location.
Next up was cutting the bottom and top spar cap angles using the chop saw. I left them a couple of mm long to allow for filing and sanding the ends smooth as the chop saw cuts fairly rough..
Here are the first pair, roughly laid out on the right spar web. You can see in this picture I've marked up each of the webs with a Sharpie so that I keep everything straight as to which way is up/down/fore/aft and a rough idea of the lightening holes. This is important as I want to use the factory edge on each of the spar webs on the bottom edge of the spar and as my reference for measuring the height of each assembly.
With the lower spar cap lined up with the factory edge and clamped in place, I laid out the rivet lines on the spar cap angles. These holes will eventually be filled by A5 solid rivets. I measured and double/triple checked the layout to ensure everything matches the plans. It's easy to be off a couple of millimetres at the beginning that translates to being off several millimetres at the other. The rivet pitches also vary a bit near the middle of the spar too where the spar web doubler and strut pick-ups are located so those have to be carefully considered too.
Drilling all the A3 pilot holes in the spar caps left a LOT of swarf!
At the bottom of the spar at the root I only drilled one pilot hole to begin the process of lining up the spar cap angle. There are several holes and bolts needed here in the spar cap angle, but I have more components to add including the spar root doubler and the spar root pickup. It will be easier to back drill from the opposite side - pilot holes for spar root pickup will be laid out and drilled on the drill press for accuracy and ease.
To start the process of matching up the lower spar cap to the web, I used a straight steel block. The web sits on a board to back up the drill bit, tight against the block and under the spar cap angle. The spar cap angle is exactly even with the end of the web, forming a perfect corner. Drill through the pilot hole to A3 size - this hole will eventually drilled out and filled with an AN bolt.
I secured the inboard end of the lower spar cap with a cleco, then used the same steel block to line up the web and lower spar cap again moving outboard. A clamp kept everything straight as I drilled the next holes:
Every tenth pilot hole was drilled though the cap and web. A long piece of HSS square tube confirms everything is remaining straight as I go:
With the spar cab and web confirmed as straight and true, I finished drilling the rest of the holes between, checking for straightness each time:
I left the section un-drilled between each end of the spar web doubler location (shown as red angled lines). I'll wait to confirm fit of the doubler and the front strut pick up angle once they are made and fitted. I may back drill these like the spar root depending on how the fit up goes.
With the lower cap in place, i started to layout where the top spar cap will be on the web and the associated rivet lines. yes those are my red Crocs.... don't judge.
The upper spar cap is initially cut long enough to overhang the web where it tapers. This will be trimmed off later to match the doubler which gets added here at the root (more on that later). The rivet layout at this corner is non standard, so for my first hole, I chose the first standard rivet spaced on along the cap. I used a ruler underneath everything to make the spar height exactly 209mm as per the plans and secured it:
Pro Tip: Be careful your pilot hole isn't over top the ruler when you drill through the web! Better that than a finger I suppose!
With the spacing between spar caps confirmed and triple checked, I used a carefully cut wooden spacer to make each of the subsequent holes along the upper spar cap exactly parallel to the bottom one. I started with a wooden block close to the length needed to fit between the caps, squared the ends on the band saw, then slowly sanded each end until it fit snug but perfectly between the two.
I copied the process all the way along, doing every tenth rivet and double checking the spar height each time. The caps are perfectly parallel and the spar height is bang on 209 mm. I finished of the rest of the holes to A3, skipping over the section where the spar web doubler will be. All the holes, top and bottom are A3, eventually will be up sized to A5 for solid rivets. The whole spar assembly as it sits now is already very strong.
Flipping the whole assembly over, I checked the rivet lines and confirmed the spar height as correct. I also started to formulate a plan for the spar root assemblies, spar web doublers and how to trim the upper cap angle taper effectively.
Next up is the spar tips. Made from 025, I bent these a while back when I was working on some 025 sheet work. They too have lightening holes, which I laid out and completed with the fly-cutter on the drill press.
Both tips with lightening holes cut and ready to be flanged. These holes are exactly the same diameter as the ones that will be in the spar web, so I marked the cutter with a flag note stating it was already set. Once I get the spar lightening holes cut, I'll flange them at the same time as these.
To ensure the spar tips are perfectly square and parallel to the spar, I flipped the spar back over and clamped a spare piece of angle to the bottom spar cap angle, measured exactly where the tip should overlap the spar end and marked it for pilot holes.
The red line on the left is the rivet line for the spar tip where it attaches to the spar web. The red line on the right is the rivet line station for the outer wing and nose ribs. It has a different rivet spacing, so I'm leaving that alone until the ribs are ready for installation. This will allow a small adjustment to compensate for any variance on the pickups in the slats, which will be installed on the wings later.
Four A3 holes evenly spaced between the spar caps. These will eventually be A5 pulled rivet holes.
Flip the spar back over. Layout the rivet holes in the ends of the spar caps as per the plans. Clamp it all together. I found it helpful to extend the whole thing over the end of the bench for this.
Back drill through the spar caps through the spar tip and secure with clecos:
Extremely happy with everything so far. The spar is dead straight, dead on 209mm tall throughout it's length and distance from root to tip is exactly as in the plans. Straight and rigid enough to stand on it's own! I'm waiting to pick up some aluminum sheet and flat stock later this coming week to make the spar pick-ups, the spar web doublers and front upper strut fittings..
I had a couple of hours for the shop one morning, so I decided to start modifying my wing rib templates. I've had these made for many months and now that I'm ready to start forming wing ribs I wanted to re-visit their layout. I'd experienced some issues forming the slat ribs and thought I could address this on the Wing ribs. I marked the location of flute relief on both the left and right side templates. This will eventually make forming the curves on the bottom and top of the ribs easier.
I started cutting the flutes using a small drum sander on the Dremel tool. It worked really well (more on these later).
Back in the shop the next evening, I started to form up the 032 spar root doubler. It was relatively easy to make as I had experience from installing a missing one on the 701 wing repair (click here for that part of my story).
It starts with bending a flange on the outboard end, then trimming the doubler to match the taper of the spar web, leaving enough width to bend a second flange to match the taper.
With the doubler bent correctly, I laid out the rivet lines for the upper perimeter and back drilled through the web out to A3, using the bottom spar cap angle as a guide to keep everything straight. (it's hard to see it here as it is underneath the inboard spar web):
Flip the spar over and lay out two rows of rivet lines, 5 rivets between spaced between the spar caps:
With the spar doubler drilled, clecoed and and confirmed as correctly positioned as in the plans, I removed it again in order to better see where I need to trim the upper spar cap angle. I marked a line on the angle using the web as my guide.
The next part was quite challenging - using the chop saw to make the accurate angle cut on such a long and un-wieldly piece of angle. I managed to get it close enough, but boy the chop saw makes ugly work of the cut:
The black line represents everything actually left to trim back for a perfect match to the spar taper. I used an angle grinder to gently remove more material using the spar doubler as a guide until it was perfect:
As I got close, I switched to a hand file, taking it down until it was perfectly level. Some final sanding to round off the sharp edges and it is complete:
Putting it all back together, I began laying out the rest of the root doubler rivets and drilling them out to A3. The plans here are kind of lacking about the spacing, but I believe I got it close to what is intended. These will be A5 rivets and the spacing I've left between them it well withing tolerances. I've written what I've used for measurements on my plans so it will be the same on the left spar.
I upsized these to A4 with the exception of the 3 at the tip. I'll leave these as A3 until I can align the inboard root rib and nose rib. This assembly will only get stronger with the addition of the root attachment plate.
As per the plans, I added two standard L angles on the back of the spar at the required location. These add more torsional rigidity to the spar assembly as a whole.
First I marked the centre line of where the angle attaches at each location on the spar:
I cut and deburred two pieces of L to 209 mm long, then used the rivet holes in the spar tip as a guide as they are the same layout (4 rivets between the spar caps):
It doesn't show here, but I drilled pilot holes in each of the L pieces, then used the layout line on the web to align the L in each of the spots and drilled it out to A3. They too will become A5 eventually.
Ron had a look at the flutes I cut in my rib forms and suggested I widen and soften the edges a bit. To do this I used a hand file.
The file was very effective but left the flutes a bit rough.
A little hand sanding of each and they cleaned up nicely.
Both the wing and the root rib bottoms taper slightly up from the front bottom corner. In order to lay out the lightening hole and tooling hole locations correctly, I set up one of the forms on the bench and used a scrap of angle and a carpenters square as a straight edge for measuring against. As this is my first go at using these forms, I decided to do the two root ribs first in case I discover procedural issues. Better to change plans now if needed, but I think this will work.
The four vertical lines measured laterally from the square end. The tooling hole locations measured vertically up from the straight edge provided by the angle. I drilled the four holes out to 15/64ths diameter, same as the bolts I will use to clamp the forms together when bending the blanks into ribs. Left to right, the first 3 holes are also the centre of the lightening holes, the fourth is a tooling (bolt only) hole:
Flip the stack over, clamp the forms together straight and use the new holes to back drill though the other half of the forms, ensuring both left and right rib consistency.
With the forms and templates ready, I start to stack them and a blank together. From top to bottom in the picture below - right side form, left side form and wing root rib blanks. The blanks don't have holes yet and the stack is now pointing in the opposite direction (left to right - tooling hole, and 3 lightening hole centres).
Line up the root rib blank on one side of the form......
.... followed by the other form, lined up directly over top the other. Normally this alignment is accomplished via the bolts and holes. My blanks don't have tooling holes as I wanted the holes to first match on both forms otherwise what's the point?
With everything lined up exactly where it should be, I clamped the sandwich to the table and using the form holes drilled pilot holes through the blank:
This results in perfectly located holes - all four will initially be bolt holes for forming the rib.
With both root rib blanks having their tooling holes complete, I can bolt it all together and put it in the vise for forming:
Gentle and firm blows with the dead blow hammer, bends the flange over the sides of the form. A piece of hardwood dowel rod helps direct the forming blows, massaging the aluminum into the flutes, taking up the extra aluminum from the curve of the form and creating the desired shape across the top and bottom of the rib:
The flutes really help make the rib nice and straight, but it also make is tougher to remove the form. Not bad enough to avoid the flute work! Once out of the form, fluting pliers can be sued for final adjustment. Once flat and out of the form, the 3 forward bolt holes become pilot holes for the fly cutter.
Knowing the procedure works as I intended with the root rib, I repeated the hole alignment procedure for the wing ribs and it turned out perfectly. I'll get to pilot holing the rib banks soon in preparation to form the ribs..
The nose ribs of the 701 and 750 are close enough that I can use Ron's forms. I remembered this while looking for my nose rib forms - that's why I didn't make them for myself! Ron and two other builders were making their nose ribs at the same time, so they bolstered their form with a metal plate close to the nose. This absorbs and backs the small tinsmith hammer blows required to get the thin nose flange rolled over much better than the wood alone.
Ron's forms are already drilled for tooling and lightening hole centre, so the process changes only slightly. This time, I laid a nose rib blank on the drill backing board and centred the form on the blank.
With it clamped in place, I drilled out the holes, using the form as a guide. Then I repeated this step 11 more times for a total of 6 left and 6 right rib blanks.
Ron's forms do not have flutes cut in them, but Ron says they had no issues forming their ribs without flutes. I will need to know where the flutes need to be crimped using fluting pliers, so I marked out 6 left and 6 right for future forming:
A couple of parts I've yet to make are the front upper strut fitting and the spar root fitting (2 of each, one set for each wing). These are substantially thick pieces of aluminum, each a 1/4 inch thick.
One challenge scratch builders have is a good reference of materials needed for a build. Kits come with everything already cut and mostly bent. To make scratch building affordable, one needs to purchase materials in complete sheets then cut them down to size. Buying in bulk saves major bucks.
Thankfully, I received a really good spreadsheet from another scratch builder early on in my build process, which has been invaluable in giving me some idea of the materials needed.
I've been following along pretty closely to the spread sheet of material, but it sometimes has a bit discrepancy compared to the plans. But as we all know, the plans are king.
My spreadsheet states the spar root fitting is 38mm wide by 240mm long - this coincides nicely with the spreadsheet and can be made from 1-1/2 inch x 12 thick aluminum bar stock perfectly (38mm is 1.49606 inches, close enough for me!)
My spreadsheet also states the front upper strut fitting is 40mm wide by 203mm long. This means I'd need bar stock just over 1-1/2 inches wide (1.5748 inches). This sucks because the next width in bar stock is 2 inches, meaning a bunch of wasted material if I have to cut it to width.
I spent too many hours thinking about this and trying to figure out if maybe I'd be better to order some 1/4 inch plate and cut them all out from that, which means more work and chance for error. It was then I looked again at the plans and realized the spreadsheet is wrong. Both are 38 mm wide, meaning I can make all four from a single strip of 1-1/12 wide bar stock. Cool! (I've adjusted my spreadsheet!)
So the 1-1/2 inch bar stock has been ordered along with some 063 to make the spar web doubler and some 0.188 plate for the wing attach brackets on the cabin/fuselage. It pays to shop around, these materials are about a quarter of the total cost ordering it from Aircraft Spruce and 8 hours closer too! I'll pick it up this week from the supplier. I'll probably get them to quote some 020 that I still need for the wings and fuselage skins.
One material that is cheaper to get at ACS are aircraft grade hard rivets. What you see below is way more than I need, but it's good to have extras. $68 something including tax and the time to go get them. I was going that way anyhow to pick up something for Ron, so it saved us both a little on shipping too. The picture below is what I got for the money. The writing on the label is the weight in pounds, not the cost per rivet.
Another consideration I've been pondering is fuel capacity and what that means for my build. Will the standard size fuel tanks be adequate for my expected fuel burn and range? I need to think about this as it affects how and where the fuel tanks get installed in the wing.
I reached out to William Wynne, the Corvair guy and he advises I can expect to flight plan for an average of 6 gallons per hour fuel burn at normal cruise speeds. Looking at the specs from the Zenith website, standard dual wing tanks are 24 US Gallons (2 x 12 gal.) - meaning not including unusable fuel in the lines and any reserve I can expect about a 4 hour range on average.
The extended tank option from Zenith (plans sold separately?!) increases this to a total of 30 US Gallons (2 x 15 gal.) - an increase of about an hour of endurance. The tanks are essentially a little bigger but still fir in the same wing bay.
Some have added a second standard tank in each wing, meaning a total fuel capacity of 48 Gallons!
That sounds great, but there are some serious pros/cons to consider. Extra range and fuel is always a good thing. But how long do I want to a leg to be - i.e. will I need to stretch/pee/eat before 4 hours? It also costs more to make larger or dual tanks, and it complicates the plumbing of the fuel quite substantially. There is also the consideration it may decrease the usefull load (how much can I take in baggage and gear - fuel weighs a lot) and that it costs fuel to haul fuel.
I'm all for the extra range - it never hurts to have more fuel than I need. I'm just not sure it meets my mission and if I eventually plan to put the plane on floats, then what? That has impacts on gross/empty weight on it's own, without considering the extra weight of fuel.
I don't have to decide yet, but will have to soon. Maybe I'll reach out to Jeff Moores in NewFoundland - he has a 705 Cruzer on floats and see what his experiences are. I'm leaning towards the middle option for a slight increase in range without complicating the plumbing.
So.... long blog today. I hope you are enjoying following along. More to come soon including some decisions on fuel tank size.
I worked this week on getting the elevator trim channel installed on the elevator skeleton. I went over the plans several times to visually ensure I was adding the trim to the correct side of the elevator (remember, I'm building it upside down to take advantage of the flat upper surface of the airfoil).
Again, the plans have to be interpreted correctly - in this case the position of the channel is determined relative to the trailing edge of the elevator. But, that can be difficult without the elevator skin installed as the fold of the skin at the trailing edge extends past the tail end of the elevator rear ribs.
To solve this, I made a small narrow strip of 020 aluminum and bent it exactly as the elevator skin would be - it looks rough but it is exactly the right length to simulate the trailing edge:
I placed the strip in position and clamped it with clecos to the spar as if it was a complete skin. Measuring back from this temporary trailing edge, gives me the position of where the elevator trim channel should be but gives me room to to see my work.
Even with the measurement confirmed, I was having a hard time getting the trim channel to fit correctly, until I got a look at the build pictures that come with the plans. Turns out the kit supplied channel has been joggled at the end, allowing it to sit inside the tip and inner elevator rib.
Once I joggled my channel (that sounds bad as I type it), it fit in the ribs where I needed it to. This automotive body panel air tool is very handy for this:
The middle elevator rib gets trimmed down to fit between the spar and the trim channel. It's attached to the trim channel by an appropriately sized L bracket.
With everything squared up thus far, a quick check of the elevator alignment to the horizontal stabilizer shows extremely close to the plans, so my measurements, cuts and bends are very good and accurate. Very, very happy.
Next step is to start cutting the skins. These are fairly large in size and the bench is pretty crowded at the moment, so I rolled out the 020 sheet and traced out the skin on the floor, leaving it a couple of millimetres wide and long - it can always be trimmed back once I have it fitted to the tail skeletons.
First up is the horizontal stab skin. Making it fit correctly is challenging as you have to make holes AND account for the curvature of the skin across the top (bottom) of the airfoil as well. A kit skin would already be trimmed and holes cut for the front and rear stab brackets. As a scratch builder, this isn't a luxury we benefit from, so we have to come up with a workaround. Time for a template!
First step I did was to mark the location of the front brackets on the spar:
In order to transfer these measurements to the skin, I made a template from scrap 020. I cut out the space needed for the rear bracket, keeping in mind the overlap that is required by the real skin past the spar (15mm):
I removed the front brackets and with the template now in place (clamped) where the skin will be including the curve, I drew a line with a straight edge to represent where the back of the spar is - the goal here is to simulate where the final skin will sit in relation to the brackets. It's better to make mistakes on the scrap than on the full skin!
Knowing where the brackets come through, I was able to measure-mark-create the matching holes in the template and gently open the holes a little at a time with a Dremel tool until the brackets can be reattached where they will protrude through the skin:
I'm very happy how this template fits and I'm very confident it will transfer the positions of the holes to the real skin. I'll use the template to cut the slot for the rear stab bracket before final fitting the skin, but for now I placed the skin across the stab skeleton to check the fit - perfect, nice and square with the outer tip ribs and has the correct overhang of the spar.
Now I've reached a decision point. Do I fit the skin on top first and tighten it down with straps across the flat bottom or vice versa? Both have advantages. I can work form the rear bracket at the spar, fit the skin over the front brackets and pull the skin tight across the nose. Or I can start at the spar on the flat side, secure it and draw the skin tight around the nose, over the curve of the top - essentially working in the opposite direction. I've read that drawing skins tight over a curve is easier, but that means fighting with the brackets.
Either way, the skin will need to be pre-bent at the line that defines the tightest curve first - at the nose with a 27mm radius. The plans show a 90 degree bend in the skin prior to wrapping it around, so I need to get that done first.
I flipped the skin over on the bench to mark the centre of the bend line as per the plans (checking very carefully to mark it in the right spot - right and square:
A long piece of factory edge aluminum clamped down with wood blocks makes a great straight edge:
With the scribed line, I slipped the sheet under the stab skeleton to where it overlaps behind the spar 15mm and the bend line coincides where it should.
The next step will be pre-bending the skin, but I'll need to obtain something close to 27mm radius and more than 8.5 feet long so I can clamp it to the bench. I was thinking a piece of 2 inch ABS plumbing pipe might work, but it may not be stiff enough laterally, so maybe a piece of steel pipe. Unfortunately, Ron doesn't have anything that long in house, so I guess I'm going shopping :)
Thanks for reading, more to come!
Been away from the shop a bit. Christmas with the family, shopping, work etc. There are important things in life besides airplanes I suppose :) That doesn't stop me from doing reasearch. Okay, you can call it browsing if you like.
I wanted to share a website I found called experimentalavionics.com
One of the biggest decisions to be made with my build is what avionics I want in my panel. This of course is guided by the three points of mission, cost and simplicity in that order, although they aren't mutually exclusive either. Simplicity generally leads to lower cost. Mission needs vs wants can also directly influence cost up or down. With a bit of work, the following items can be built very inexpensively, with off the shelf parts and instructions found online.
My aircraft mission is simple enough. I don't need to go fast or high (the Zenair 750 isn't pressurized nor is it a speed demon) and I won't be flying IFR (instrument flight rules). I do want good communications (it's actually what I do for a living!) and the ability to navigate outside the normal ATC coverage areas to some of those good fishing/camping spots.
I'm using a converted Corvair automobile engine. Instrumentation for this is simple too.
The idea of building my own EMS (Engine Monitoring System) from open source electronics/software fits both my budget and interests in learning. I have learned enough electronics skills over the years to build it (thanks to Mom and Dad for starting my learning in basic electronics by buying me this when I was a kid). Whether this becomes my primary engine instrumentation or a back up to the traditional analog engine guages will be decided later after I do some more research. It might look something like this:
A nice, easy to read display suitable for the 6 cylinder Corvair engine. The bonus is how much panel space I'd save and the ability to datalog the information for testing mods or diagnosing trends. Alarm annunciators (flashing warning lights or audio) can easily be added for any parameter that goes out of range. Cool!
The other panel items such as primary flight instruments (altimeter, VSI, etc) require more thought. I like traditional instruments for their familiar simplicity. For the same reasons as the EMS, a EFIS (Electronic Flight Information System) has an intriguing draw, but I'll likely have something like this as my backup instruments:
Again, easy to read, simple and space saving. 6 instruments and a clock all in one place.
A couple of cons that I'll need to consider are temperature operating range and failure modes. It gets real cold where I'll be keeping the plane when it's built (unless I win the lottery, then it's heated floor hanger all the way!)
As for failure modes, how comfortable am I putting all indicators in one place, where a single failure may result in losing everything at once.
The website that I linked above also includes preliminary discussions on intercoms for pilot/passenger communication and a WiFi based AHRS (Attitude Heading Reference System) that could link wirelessly to a tablet for navigation. Perhaps someone will adapt the AHRS to be an inexpensive ADS-B out module!
Lots to think about...
Happy New Year everyone :)
The Google search bots are really going to love my posts now!
Remember my fellow Corvair engine builder Jeff Moores of Newfoundland (see previous post "time-to-get-back-at-it")? While at the Zenair Open House we talked over lunch about the struggles I had been having with head studs and Jeff reassured me that my issues were common issues in both his previous builds. He offered to send me some extra head studs that he had lying around his shop to replace the bad ones from my core. They arrived via mail on Tuesday and they are brand new! All for the price of shipping via snail-mail.
The more I continue pursuing a Corvair as my choice of motor, the more I'm starting to realize the value of getting to know other Corvair builders, both for their experience and generosity. This is the kind of group I want to associate with, not some faceless foreign owned engine maker that just wants my money and couldn't care less about my mission to learn. Thanks Jeff!
Next steps, dealing with the 3 stud holes that need to be fixed (see "progress-sort-of") . I've decided on using TimeSerts which are a threaded barrel insert repair that is accepted in the conversion manual. Definitely more expensive than Helicoils (another possible repair method) but I believe worth the piece of mind. Corvair automotve parts warehouse Clark's Corvairs rents the TimeSert installation tool kit and also sells inserts that are the proper length and a blind nut tool for proper torquing of the head studs. I think I'll order those now and get the repairs done soon in preparation for some case machining work I'm planning.
It's been a while since I had anything to post. Between my paid job, a weekend camping with my daughter's Scout Troop, horse shows and Thanksgiving hikes with the family time has flown by the last couple of weeks.
Found a day free in the schedule on Monday so popped into the shop for a bit. Ron and Donna had been away the previous week so Brenda and I were watching over the shop and property. I was pleasantly surprised when I arrived Monday to see that Donna was kinda enough to put my plans set into a binder for me:
Ron and I had a good chat about my build plans. Comparing the 750 plans to his 701 plans we realized that they shared even more DNA than either of us thought. Obviously we knew that the 750 is the evolution of the 701 design but we are both struck just how common the airfoil (wing shape) and internal structures are. It's easy to see where improvements were made over time and how Zenair has evolved in their kit manufacturing processes (introduction of CNC production of kit parts and CAD drawings). Ron's group of builders are scratch building their 701 planes and have made all the forming blocks for the 701 parts. In other words, rather than buy the kit pieces, they are making (read bending) everything themselves from bulk aluminum sheet and other stock. Time consuming? Yes. Cost savings? Huge (the cost of individual kit pieces from Zenair is in the manufacturing, not the actual materials).
Ron seems to think that his 701 forms are almost exactly the same as those needed for the 750, perhaps with a bit of tweaking. Comparing the plans seems to back up this theory too. So the question becomes one of time vs. money. Scratch building takes time but saves money. Enough money of course always saves time. I'm caught somewhere in the middle, but if I can save some money without too much investment of time there is opportunity there. What makes it better is all the work of the making the forms is already done.
I'm going to defer this decision for now and perhaps order a couple of wing ribs from Zenair. I'll compare the 750 kit pieces with Ron's 701 forms and see just how close they are or what modifications need to be made. From there the decision should be easier. If it turns out the forms aren't appropriate, at least I'm a couple of pieces closer to the end....Ha!
So, onto Monday's task - start stripping the paint off the wing skins anywhere new skins will be overlapping. This ensures good strong joints and provides a clean aluminum surface for anti-corrosion primer.
First, apply the chemical stripper. I'm thankful to have a workshop space that isn't in the basement of my house - this stuff is strong!
After letting it sit for a while, a plastic scraper works fantastic to remove the layers of paint:
I didn't take any final pictures yet as I still have some clean-up to do with acetone and Scotchbrite pad. It's not pleasant work, but I learned the work involved if I change my mind about what colour paint I want for my airplane! While I waited on the stripper to work, I also reworked that rear channel I made that had cracks developing at the corners..... always keep busy.
I'm away next week on a work assignment (near the Zenair Canada factory!) so shop time will be limited again. I wonder if I can order those ribs and have them in time to pick up while I'm in the area? Hmm....
First off, I ordered my plans set today! Hopefully it won't take long to be shipped from Zenair. Once I have them, I'll have my very own serial number and I can start going down the road of endless inspection paperwork that needs to be on file with Transport Canada. I'm trying to decide if I want to reserve a good registration (call letters) or wait and see what they assign..... but that's a bit premature.... ha!
Four more hours in the shop today. Continued to open up the salvaged 701 wing. Wasn't too surprised to find damaged structure inside. This is the top of the wing at the root where it attaches to the fuselage. It likely got twisted back from the impact out on the tip of the wing. Lots of rash damage, probably from improper handling after the crash.
Flipped the wing over and with some drill effort, off comes the wing root fairing, fuel cell inspection cover and lower wing skin. Whomever built this wing wasn't much of a craftsman (or craftsperson). Lots of rivets where they shouldn't be, and lots of rivets missing from where they should be. We also discovered the rear spar channel is way under gauge from what the plans call for. Seems like someone decided to take a shortcut.
Next step was to drill out the rivets holding in the incorrect rear channel:
It came out easy, but it too has holes in all the wrong places.
Easy to fix/replace, but after seeing this, we are truly wondering what else we are going to find.
Next up, straighten the inboard main wing rib (on the left in the above picture). It will require another strip of aluminium (called a doubler) to reinforce the damaged area after we straighten it.
I just two afternoon sessions, I've learned a ton thanks to Ron but I've got a ton more to learn yet!
Had a real great afternoon today speaking with and working in the shop of my new friend Ron. As I've stated before in my blog, the prime motivator of building my own airplane is about learning.
Ron is a long time builder and re-builder of aircraft, both certified and homebuilts. He has a very deep knowledge of all things in recreational aviation and most importantly wants to teach me some of what he knows.
Ron's current projects include rebuilding a Cessna 170, a short wing Piper and several Zenair projects. His thinking is to have me assist his group of builders repair a Zenair 701 as a very first step to learning metal aircraft construction. Perfect! What a fantastic way to get an introduction to building skills.
He gave me a quick tour of his workshop and we immediately went to work on removing the skins off a salvaged Zenair 701 wing that was badly damaged by a previous owner. This wing is being rebuilt.
We started by assessing the wing to determine the best course of action. We discussed what was salvageable as is, what could be patched and what would need to be cut away completely. As you can see in this picture, the damage is substantial.
After making some marks on the wing of what needed to be removed and a quick demonstration of the procedure required, I was drilling out the rivets. As you can see, there are a ton of them:
We also removed the lower wing skin closest to the wing root that was crinkled really badly. Again, a ton of rivets to drill out:
I wish I took more pictures, but I was having too much fun drilling rivets. Obviously today was just a tiny taste of what's to come for learning and building, but I'm hooked!
As we worked, Ron and I talked at length about my plans for building a Zenair 750 STOL. I explained my plans to put a Corvair engine in it and he was very interested in the combination.
Use of Ron's shop and taping into his experience building Zenair aircraft definitely confirms for me that this 750 STOL airplane is a do-able project that I can accomplish, and that by making some of the parts myself from raw materials (called "scratch building", as in "from scratch") I have the opportunity to save a bunch of time and money.
So after some weeks of debate, tomorrow I'm sending in my order to Zenair for a complete set of builders plans for a 750 STOL aircraft. Once I have them in hand, Ron and I are going to sit down and discuss a build plan.
I haven't posted anything to my blog for a couple of weeks because I've been busy doing the other things in life that keep our family hopping at this time of year. Vacation, two birthdays, two anniversaries, the end of the school year, fireworks shows for Canada Day (another hobby of mine) and some camping. All this happens in the span of 14 days. But it's over again for another year.
Of course my mind hasn't strayed too far from my project and I'm starting to narrow down my decision on what airframe I want to build. In my post from last year "So Many Choices" I describe my thought process in this regard.
Just before I started vacation, I managed to meet up with Ron, a local home builder who has vast experience with building aircraft from scratch, from kits and rebuilding damaged airframes for others. He is currently working on a Piper Pacer, but he has offered me a spot on his build team and more importantly, the opportunity to assist him and another guy in building a Zenair 701. You can't ask for better chance to learn from someone that has "been-there-done-that". Ron is also keen to see a Corvair installation process, perhaps for future build of his own.
So, after much debate and thinking out the pros and cons I've decided 99.9% that I'm going to begin the process of building a Zenair 750 STOL (Short Take Off Landing). This aircraft has the best of everything I'm looking for:
One thing I really like about the home building movement is the willingness of others to share what they have learned and help others get started. It's a tight knit group of individuals and it's great having that support network when working through a build.
During my vacation, I got a call from another Corvair builder named John who is putting a Corvair in his Zenair 650. His engine was built for him by William Wynne and he is close to flying his 650 for the first time. He reached out to me after seeing I was also in Ontario in hopes of having another Corviar builder to bounce ideas off of (again, that built in support network is great). He also offered to put me in touch with yet another Corvair builder who is doing the same 750 airframe that I'm interested in.
I told John I was planning on heading to the Zenair open house being held in conjunction with the Midland RAA (Recreational Aircraft Association) fly-in being held this past weekend. We agreed to meet up in person and that's exactly what happened yesterday.
I arrived at the Midland Huronia Airport sharply at 9am Saturday morning. I was hoping to meet the Zenair staff before the crowds got too busy. I had the opportunity to speak directly with brothers Michael and Nicholas Heintz, sons of Zenair aircraft designer Chris Heintz. I explained my goals and mission and they answered any question I had. When I mentioned I was planning on putting a Corvair engine into the airplane, they were very positive about the combination which is extremely encouraging.
Michael advised me that a builder from Newfoundland by the name of Jeff Moores was coming that day to look at purcashing a Zenair 750 and was a Corvair builder as well. I've had conversations with Jeff via the Corvaircraft forums, as he has already built a Corvair for his Merlin ultralight, so it was great to meet him and his wife Dale in person. Shortly after, John walked over and introduced himself.
Jeff, John and I talked at length about each of our plans and how we are at substantially different phases of the build. having built both a 2.7 litre and 3.0 litre Corvair engin, Jeff offered some great insight to the differences and advantages of each. Considering none of us had ever met before in person, it amazed me how quickly we became friends - guess that's all part of being a builder.
We took a tour of the production facility where Michael explained the evolution of Zenair kits and how advanced the CNC production has become, even just in the last few years. The 750 kits are considered state of the art and are "match drilled" meaning all the holes in the pre-formed aluminum parts are already drilled for the builder, saving substantial time in assembly. It was clear from the tour that the kit quality is top notch, and I came away from the tour feeling very confident that this is a great project for an amateur builder like me.
As the morning progressed, each of us were offered a flight in the factory 750 demonstrator with Nicholas Heintz. This one is actually the 750 Cruzer model, which has a somewhat cleaner airframe (no slats, different wing, etc) resulting in a somewhat faster cruise speed than the STOL model, but the cabin dimensions and "feel" are the same. The demonstrator is equipped with a Jabiru engine (which is has approximately the same horsepower as what a Corvair would:
Now, I'm not sure what my goofy smile was from; the fact I was actually going flying or how pleased I was to experience the visibility this cabin design provides (and I wasn't even in the air yet!) but I suspect it was a combination of both:
A short time later and we were airborne! I was so wrapped up in the flight experience and speaking with Nicholas about the handling characteristics of this Cruzer model vs the STOL version, I didn't get any puictures, but I am really impressed with this aircraft. Smooth, stable and comfortable. The visibility is incredible in all directions and the bubble doors give that extra feel of roominess. One thing I noticed when I had the controls and entered a turn was the really nice visibility through the clear panel cabin roof:
Jeff's wife Dale took some pictures and videos of my flight and when they get a chance will send them to me and I'll post them. Here are a couple of more I took:
So things are starting to pick up speed. I'm definitely in the arena and the game is about to really get started!
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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.