I had hoped to get to the shop last week, but an unseasonably warm weather forecast was causing me some concern at home. With all the snow we've had through January and early February, we had about 3 feet of accumulation on the roof. Rather than go to the shop, we thought it better to remove the bulk of snow before the positive temperatures arrive and make the snow weight too much for the roof. It took several hours, but I got it done. Didn't feel like going to the shop (ok, actually I couldn't lift my arms for a couple of days).
Back to the shop today. Got right to work creating two new wing root spar doublers. These will be installed where they should have been in the first place. Using a template, I traced out the rough shape on the 0.032 aluminum:
I cut out the shape in rough and used a file and the grinder to get the final shape exactly right:
I repeated the same steps for the second one. The process is fairly simple as you can see from the wing root attachment brackets below. From top to bottom, a finished piece from inventory, a rough cut piece to be ground and the template from the plans:
First you trace the template onto the stock, and use (in this case) a bandsaw to cut it out close to the line. Comparing the two after the bandsaw, use a sharpie marker to trace it again, leaving a line showing the remaining material to remove by sanding or grinding:
Next, use the grinder or file to remove the balance of the material as defined by the trace line:
Last step, hand sanding all the edges to a satin smooth finish. Here is the stack of eight I finished (two for this repair and 6 for inventory) and below that the stack of wing root doublers for inventory:
More rain tomorrow, so back to the shop to start working these items into the repair.... and find more things wrong with this wing..... probably :)
Those that know me also know that I tend to stew on things. It's a trait I've always had and as I grow older, I've tried turning the energy that is wasted away worrying about the little things and more towards solving the problem or fixing the mistake. It doesn't always work, but sometimes, with a little thought and time to ponder it does.
I got to thinking about the Rear Wing Root channel that I made the "oops cut" on last week. Looking over the plans, not all is lost. I'd already made the flange end longer than what the plans called for. Beefing things up in this manner is an accepted practice. This larger flange means that I still have room to correct my mistake and salvage the piece.
Here is the damage I did. You can clearly see where the cut extended beyond the relief hole:
By trimming the flange end a little bit narrow and creating a new relief hole, I eliminated the bad cut and still met the requirements for size on both. The corrected mistake is shown on the top in this picture and my second proper length "no damage beyond the relief hole" cut at the bottom:
Once I dressed and deburred the edges of the entire piece, off to the bending brake we went.
Unfortunately, I went a bit far with the lower edge. It ended up with a full 90 degrees of bend, but needed to be less than 90 to match the curvature of the wing skin.
No big deal, I just made up a jig to bend it back a bit (you can't undo bends in the brake). The key is to bend it all at once to maintain a consistent edge on the flange. You can see in the next picture that I placed the channel on the workbench and used a two-by-four and C-clamps to secure it. Ron has an excellent flanging tool just perfect for adjusting things (painted red):
Worked like a charm... my oops is no more!
Fit up seem good. Plenty of room for new rivet location and flange matches top of the rib:
Next I worked on making a new wing root attachment bracket to replace the damaged original. This required cutting thick aluminum with the band saw, a new experience for me (although I've cut wood many times on the bandsaw). It went well. The secret is to cut the piece out slightly larger, allowing room to sand/grind the piece smooth to it's final dimension:
Next up will be to make a replacement forward wing attachment bracket and the new wing root spar doubler that we discovered was missing on the original build. Luckily we have a traceable template for this:
With each repair and new fabrication I'm making, I'm getting the courage up to start bending and shaping metal for my own plane. I CAN do this!
Back in the shop again Monday. I got some more repair work done on the 701, but like home renovations one thing leads to another.
Talked over the latest issues with Ron. We decided we didn't like the original builders efforts on the rear wing attach point either. Damage to the rear root channel is also too much to accept as is, so we'll replace it too.
Drilled out the rivets holding the root rib and the first outboard rib, then started removing the rivets to separate the channel from the wing attach bracket:
With the rivets removed, it becomes easier to see the damage done by whomever drilled the wing root skins. The wing root skin is one of the last things to be fitted during a build and one might understand the desire to "hurry up" and get done, but this is done terribly, even if they weren't in a hurry. None of the holes are measured right and at least one critically damaged the wing attach bracket:
The hole for the wing attach bolt has a few issues too. According to the plans, it should be drilled directly centered in the channel. A random second hole on this attach bracket shouldn't even be there and look how close it is to the main bolt hole. This is a fatigue crack waiting to happen. Corrosion protection certainly wasn't considered either. Regular old white paint ain't going to cut it!:
I spent some time cleaning up the skin edges around the fuel tank bay. This will go a long way to making the skins sit flat. We are also putting L brackets over the top of the ribs and spar web in this area. This has the dual benefit or strengthening the ribs and providing a better place to rivet the tank skin on later - with the proper rivet spacing! These look like Swiss cheese.
The overriding goal of this repair is to learn the fine skills required for my build. I definitely learned one when preparing the new rear channel. I measured very carefully, and made sure to drill the corner relief holes in the correct position. This material is 0.032 thick, something I really haven't cut before with hand tools.
Reminder to self.... when cutting with hand shears, the tool will jump ahead when reaching the relief hole. A cut past the hole is the inevitable and regrettable result, ruining a well measured part:
I originally circled the excess cut and was pretty angry for making this simple mistake. Then I reminded myself the goal is learning. As long as I don't forget next time when cutting towards a hole, making a 2nd replacement rear channel isn't a big deal.
I added the rest of the word "OOPS" as a humorous reminder that life is good as long as I'm learning. I'm going to salvage the majority for other small parts and leave this part propped up on the bench as a reminder.
Back into the shop in a few days. Thanks for reading.
As regular readers will recall, I'm working on repairing a damaged Zenair 701 that shop owner Ron bought as a rebuildable scrap project. Eventually, it will be reinspected, painted and sold to fund other projects. Ron is giving me the opportunity to learn the skills I need for my build by doing this rebuild and it's been really enlightening.
We are both starting to guess that whomever inspected the original build must have either been in a huge hurry or not very aware of acceptable building practices. Through this post, I'll point out some of the more obvious clues. It's lucky no one was killed flying this airplane (I use the term loosely).
These photos were taken over the course of the last couple of weeks, but are generally in order that I accomplished them.
Ron decided that the rear tank channel needed to be moved back to accommodate a bigger fuel tank, so I worked on removing it. This first picture was from several weeks ago, when I was still stripping paint and the rear fuel channel was still in place:
Here is a more recent one. The paint strip is mostly complete and the rear fuel channel is removed. I've also removed the silicone caulking the builder used for "anti-oil-canning":
The channel came out without too much effort. It's in rough shape and covered in the remnants of adhesive from the tank mounting cork, silicone (surprise) and, get this.... crack filling foam! Ron seems to think that the plane at some point probably developed a fuel leak and the silicone and crack foam were a red-neck repair (clue # 1). Ron also let me know that the suspected cause of the crash that damaged this 701 was the plane running out of fuel. More on this later. Here is the removed channel:
As the wing gets thinner top to bottom the further to the rear you move, so does the space where the channel will go. After measuring very carefully considering what size it will be in it's new location, I cut the top edge off. Here is the modified channel, all cleaned up, cut down and straightened:
In order to bolster the strength of the channel top edge, I created an "L" flange out of flat stock using the same thickness as the channel:
Next was a series of trial fits, removal, trimming, fit, removal, and fit again to get the new channel in the right place to ensure the new flange was at the correct height to meet the wing skin. I predrilled the new mounting holes in the ribs at this time. This is where clecos earn their value!
It took some more working of the edge of the channel to remove any interference with the rib lightening flange hole and working around the rib repair piece:
Once I was happy with the fit of the modified channel, it was time to attach the reinforcement L flange. Measure two rivets per section, cleco, drill and deburr:
The new L flange really tightened everything up!
I've put it aside for now to work on the next repair item, the wing attach point.
When this plane crashed into the trees, this wing was ripped backwards, bending the wing attach bracket. No small feat, as these are obviously designed to be stout:
Even if it wasn't bent, it would need replacing anyhow for a couple of very obvious reasons. Look at the shape of that hole! There is no way this was an acceptable mount. It looks to me like someone got lazy and just made the hole bigger instead of rigging the wing properly in the first place (clue #3). Another issue is the lack of corrosion protection at this joint. The aluminum of this wing attach point was obviously in direct contact with the steel of the fuselage frame. Anytime two dissimilar metals are in contact, there needs to be corrosion protection. It's called Galvanic Corrosion, and you can read about it here.
To remove the wing attach bracket is going to take some work. These are installed using bucked rivets, not the pulled rivets I'm used to dealing with. That root nose rib is also really trashed from the accident, so it will also need to be replaced:
To make access easier, I tied back the top of the nose skin with a piece of string, being careful not to crease it. Sometimes it's the simple way that's best!
Using a centering punch and a drill bit, the heads of the rivets are drilled off. After some gentle persuasion, the wing attach bracket came off without much trouble.... hmmm. It shouldn't be that easy, should it?:
Pulled rivets have a hollow core, which means they can be drilled out and removed with ease. Bucked rivets are solid all the way through and what a pain they are to remove even after the heads are removed. Reminder to self - don't screw these up when doing mine!
Next, remove the root nose rib and it's support bracket. This is when I noticed this wing spar is missing the root doubler (clue #4)! A root doubler is another layer of aluminum plate sandwiched to the main spar web to increase the strength and integrity of the wing attach points. This is missing on this build. How it could have been omitted, I don't know. What drew my attention to the issue was the L bracket riveted on the spar web. This doesn't appear anywhere in the plans. The root doubler has this built right in!
As far as I am concerned, this was an accident waiting to happen, all the clues add up. It's a wonder this wing (or the other one as I suspect it's the same) never folded or failed in some way, even on the ground.
Running out of fuel (the actual cause of the accident), probably saved this guy's life and perhaps that of his passenger. I'm not going to even try and guess the reason they skipped such an important assembly, but I guess I'm fixing that too!
I decided to drill out the next row of nose skin rivets, as I'll have to remove everything up to and including the next outboard rib to install the missing doubler:
Next I removed the bent L that supports the root skin at the rib and I removed the slat support bracket. Next was the nose rib and the mystery L on the spar web:
Definately a ton of work (and learning) done and still more to come. I'm really enjoying this process!
During my free time away from the shop I'll continue to get the plans digitized into CAD. I've repurposed an old laptop we had lying around. I installed the Ubuntu (Linux) operating system and the CAD program LibreCad. It's really fun, easy to use/learn and best of all it's free. It's also available for Windows and OSX if Linux isn't your thing:
Back to the shop tomorrow, thanks for reading!
Haven't done much in the shop on my own stuff lately, as I've been helping Ron with his Aeronca Scout rebuild and puttering away on the 701 wing rebuild. I'm gaining confidence in my ability to fabricate simple aluminum channels and web caps and learning the value of measure twice, cut once, fit and debur before riveting. Pictures to come!
I've also been talking at length with Ron and he's all but convinced me that building my 750 from "scratch" (hand make all the parts from raw aluminum stock) rather than via prefabricated kit components from Zenair is not only doable, but really economical. It's what he's done with his 701 and has shown me how easy the process actually is. The monetary savings to be had by forming the parts myself is nothing to scoff at either, perhaps saving upwards of 75% on what Zenair produced parts cost! Sure, there are some things it makes more sense to buy direct (windshield comes to mind), but the more I think about it, the more I like the idea of scratch building (and it means more learning!)
So what does scratch building entail? Basically it means making forms out of wood from the plans which in turn will be used to form the raw sheet aluminum into ribs, channels and other associated parts. Other flat parts (wing skins, fuselage panels) are measured and cut directly from aluminum sheet stock.
The obvious trade off is time, but Ron and I both believe the goal of 3 years building is easily achieved.
In order to determine how much aluminum sheet to order (the Zenair plans unfortunately don't include a comprehensive material list), I'm working on converting the appropriate plan drawings to scale CAD files. In the spirit of money savings, I've found an excellent free online CAD program called LibreCAD that makes converting the dimensional drawings in the plans to CAD files easy.
For example, I can take the drawing of the Horizontal Stabilizer Nose Rib from the plans:
.....and use LibreCAD to turn the information from the drawing to a CAD file, suitable for printing, exporting to a CNC machine, etc:
As you can see from the screenshot above, I'm not including the dimensions on the CAD drawing, as they are just as easily referenced on the paper copy. I've also created the CAD file with 3 different layers; form, aluminum and a label layer. Each of these can be toggled on or off for easy viewing should the need arise.
I am however keeping an Excel spreadsheet to document each drawing that has been converted. Once I have the drawings all converted, I'll be able to place parts of the same material thickness onto a page representing a complete sheet of raw aluminum. This should save material and money as I can nest smaller parts (ribs, channels, etc) among the larger ones, saving material waste.
The spreadsheet also tracks what forms I've got made and what parts are completed and ready for assembly.
I never had CAD available to me as a highschool drafting student, but that part of my brain that knows how to interpret drawings still works it seems! Is this worth the effort? Who knows. I'm just enjoying the journey!
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 :)
So, I got my block/case back from the machine shop. It was worth every penny to have a professional with a CNC milling machine do the work of drilling out the two broken studs. His work was incredible and he went as far as to countersink the holes slightly for the TimeSert barrel inserts. Nice, clean and straight holes, important details:
With that done, it was time today to tackle installing the TimeSert barrel inserts that will make up the replacement threads for the head studs on these two holes. I've spent more hours than I should have pondering this critcal step, but it wasn't nearly as difficult as I allowed my imagination to believe it could be.
TimeSerts are an elegant solution for replacing damaged in-hole threads in a variety of materials. They are in my opinion much better than Helicoil wound wire inserts. I ordered the TimeSert install kit from Clark's Corvairs and the recommended length (0.75 inch) TimeSerts from a local industrial supply shop. The kit contains all the tools you need to install these:
First step, drill out the hole to the correct size. The importance of having this hole straight can not be understated. Although drilling aluminum is easy, best to use a drill press:
The brand new bit that came with the kit was very sharp and made short clean work of the holes.
Next up, the shoulder countersink bit. The countersink the machinist put in was quite deep enough. The bit has a cutter which creates a countersink shoulder for the top end of the TimeSert allowing it to sit flush on the surface. Again, the drill press is the only smart way to do this:
Careful application of preasure on the very sharp cutter results in a nicely formed shoulder.
Next up, threading this aluminum hole with the tap provided in the kit. This tap (also brand new) has four cutting flutes and a flat nose to ensure the hole is completely threaded to the bottom. This is delicate work that is only done by hand, so it was important to make it perpendicular to the case, ensuring straight threads in the hole. I used lots of 3-in-1 oil to ease the tap through and keep the threads clean from debris. The secret is to cut 1/2 a turn, back out 1/2 a turn and repeat:
Once both holes are tapped, it's important to ensure they are cleaned out of any cutting debris. A blow gun and compressor is perfect.
At this point everything looks good. Next up is the insert mandrel.
What makes TimeSerts so effective, is their engineering. The bottom couple of rows of the insert are formed in a way that allows the insert mandrel to cold-roll the threads, pushing them outwards and into the surrounding material, locking the insert in place:
First, a couple drops of oil on the mandrel to ease the insert forming the new threads, then thread the insert partly onto the mandrel:
Once placed in the newly cut holes, the insert threads in easy, up to the shoulder stop. Continue moving the mandrel forward (in) until it bottoms out:
Back the mandrel out and the TimeSert stays in place, now permanently attached to the aluminum walls of the hole. Looks perfect!
Was it really that easy? YES!
After cutting the matching threads on the two upper (long) studs that will be used with these inserts, I test fitted one. A good clean fit that will be made real strong with LocTite 620 as per the conversion manual.
I can't explain how relieved I am to be past this part of the head stud saga. Next steps will be fastening all the studs in permanently with LocTite 620. Before that, I need to clean the block completely as there are still areas that can use some detail attention. The suggestions are to either hot tank the block at a tranmission shop, use varsol with stiff brushes and 3M pads or maybe media blast it. Ron has a sandblasting machine, maybe that would be easiest. More food for thought.
The other task I completed was the removal of the oil pick-up assembly. It is press fit into the aluminum:
A little gentle tapping from the oil passage end of the block witha pirce of dowel, and it came right out:
Overall, a very productive 3 hours. I'm tagging this blog entry as a milestone because it has been bugging me for months to get past it. Barring any further surprises, this will be my airplane engine.
Now back to making other airplane parts :)
Looking back I can't believe it's been almost a month and half since I posted to the blog. I've been busy waiting on some stuff I ordered to take the next steps on the motor rebuild and some travel to visit family in Ann Arbor Michigan took up a bunch of time as well. Well worth it though, we needed a quick family get-away to recharge.
Since my last post, I took my engine block into the machine shop to fix the snapped stud issue. They have a highly accurate CNC milling machine which will make short work of the snapped stud. The process will remove the remnants of the broken stud but this will also mean sacraficing the hole threads. I've now got the TimeSert install kit that I ordered which will repair the damage and create a new set of threads to insert the studs into.
Until I get the block back from the machinist early next week, I got some of the prep work needed for the studs done. The original short (lower) head studs from my core engines are in decent shape, but typically very dirty with some light surface rust. The push rod tubes are similar. Here is the before pic:
The perfect tool to clean these is the bench grinder. This one is a beautiful old school one. I prefer old tools that are made to last:
The wire wheel makes short work of cleaning of the decades of old grime and rust and is excellent for cleaning up the stud threads:
The push rod tubes from the core are really dirty. Under the grime, the tube was manufactured with two coatings on top of the bare metal, as shown in this picture from Google:
I had a go with the wire wheel on one of my tubes and this was the result:
I'm happy with how they cleaned up, particularly around the o-ring area. However, after seeing the picture from Google that I found for tonight's blog entry, I'm not sure if I've just removed the grime, or removed the zinc coating as well. Removing the zinc coating and getting down to the bare steel is what I want to do as this will allow me to paint (or maybe powdercoat) them white as described in the conversion manual. I'll have another look next time I'm in the shop. These may require a bit more work. The one in the picture I copied was sandlasted, perhaps that's what I'll end up doing.
Overall, the first twelve studs all came out really nice and clean - they should paint up real nice. There are some minor tool marks on each. I have a bunch more in the inventory, so I'll clean those up too and choose the best ones for the build:
The other task I've been pondering is cutting new threads on the end of those studs being inserted into the TimeSert holes of the block.
The studs on Corvair engines are made from a very high tensile steel alloy. The original threads at the block end are a proprietary GM thread called 38-16 NC5. These will not fit the TimeSert which are the more common 3/8-16 NC. So, for those holes that I'm installing TimeSerts, I'll have to use a die cutter and rework the threads to be 3/8-16 NC. The head end doesn't need to be altered.
I had a bit of time today, so I took one of the old long (upper) studs that are being replaced with new ones due to corrosion and experimented cutting new threads on it. Best case, I see how easy or difficult it is, worst case I ruin an old stud that I won't be using anyhow.
I clamped the stud tightly in the vise. When I do the good ones, I'll have to remember to put something in the jaws of the vise to prevent clamping damage marks. Here is a picture of the tools I used. I couldn't find where ron keeps his cutting oil (if there even is any), so I substituted a little 3-in-1.
There ins't a huge difference in the GM thread and the 3/8-16 I need to use with the TimeSerts. Carefully starting the die on the threads and using a fair amount of oil, I managed to cut or reshape the threads about under half way down. This involved the time proven method of turning the die down a little bit at a time, and backing off numerous times but it went marvelously well. Here's a close up:
When I got home, I test fitted this stud in a TimeSert and it threaded in real nice. I bit of LocTite 620 should make the repair as good or better than the factory fit. I've been worried about this process for a long time, but I think with a little attention and time, it's going to work out fine.
Next up, prepping the block for stud install.
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.
A couple of more hours in the shop today. Work continues on the 701 wing rebuild.
Stripped off the last of the paint where the wing and nose skins will be replaced. A wipe down with acetone and it comes out real shiny! Next step will be to scuff the aluminium and paint it with primer in preparation for mating the new skins.
While I was letting the stripper soak in for the above step, I finally got up the nerve to clean and trim the nose skin where the damaged piece was cut away. Working from the outside, I wanted to make sure to cut not only straight but well away from the underlying nose rib. To make the task easier, I laid on a piece of painters tape outlining where I was going to cut:
The curve of the nose skin makes this difficult to use hand shears or metal snips. Bring on the power tools! Ron suggested using the air powered saw:
When it's running, the blade on the air saw moves faster than the eye can see. It's fine tooth blade made short and clean work of the skin. The last inch or so I did with metal snips to prevent accidentally cutting into the wing spar (that would be a unmitigated disaster!):
A productive couple of hours.
I've sent off a quote request to Zenair for a complete tail kit of my own, minus the rudder pieces I already have.
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.