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!
Well, my buddy Guy had some progress in getting the last three broken studs out on the 110hp block.
The first one came out fairly easy once centre drilled. Looks like the threads are still intact and should clean out nicely:
Number two, not so much. The centre of the stud hole doesn't always line up exactly with the threads, so he stopped working this one with the end mill until we can decide if we want to re-tap the hole afterwwards:
I tried using a large EasyOut bit but the last of this stud won't come out and I'm wary of damaging the remaining threads. I've filled up the hole with some home-brew penetrating oil and will let it sit for a couple of days to see if it will loosen up before trying again. I think I might be able to use a tap and just clean it out, but I'll wait for now on this one. This is likely the worst of the bunch.
Number 3 was the most interesting result. Using an EasyOut, Guy backed the stud out carefully, but unforuntately it brought most of the aluminum threads with it. It was stuck in there real good:
Now, the beauty thing of all this is that all 3 holes are salvageable. There is enough room left between each of the damaged holes and the cylinder bores to insert either a Heli-Coil or TimeSert thread repair. They each have their strengths and pricing differences and from what I've read they each work well (click the links to check them out). I kinda like the TimeSert method better, just seems more permanent. This will mean cutting new threads on the end of the replacement studs with a sharp die to match the repaired holes, but that is common practice and an acceptable repair for a conversion.
If I can't get the number 2 one out cleanly, it will be easily removed during the drill/tap/insert process of the thread repair.
I'm stoked this is going to work and I can use this block for my engine <grin>.
On another note, I've added a running total time log on the lower right of my blog page:
One of the things builders like to keep track of is the amount of time spent on parts of the project. I've broken things down into basic groups and will try an remember to update it regularly. I considered purchasing a commercially available program like KitLog, but I prefer this blog format. The 25 hours showing under Engine is just a rough guess and doesn't include non hands on time like time I've spent online and in person looking for a core. I might consider breaking the chart down further, but I'm happy with it for now.
Next step, research where to purchase TimeSerts.
Took advantage of some sunny weather and removed the rocker covers and rocker arms.
Like everything else so far, the rocker nuts seemed to be on mostly finger tight, so they were a snap to remove:
Here is the right side heads with the rocker arms removed. A couple of the rocker studs came right out with the rocker arms and that's okay because the studs need to be removed next:
The rocker studs serve 3 purposes. They connect to the lower head studs, they hold down the guide plates to distribute the clamping force over a larger area and proved the mounting stud for the rocker arms. Out the studs and guide plates came, easy:
I know that current wisdom is to leave the head studs in the block as they are, however I have several of the upper studs that have badly seized head nuts on them:
I've been following the advice of others and soaking these daily with a good amount of PB Blaster penetrating oil. As this core has been previously at least partially apart, it looks like they pulled the studs when taking it apart and I'm presuming that is because they either thought they should pull them, or just did because that was easier to do than dealing with the frozen head nuts. Some of the nuts came off without any trouble, some not so much.
The studs that have seized nuts seem to be backing out somewhat easily but I haven't taken them out yet so I don't know what shape the internal threads are in. But I know if they are turning at all it is something to be concerned about.
So, long story short.... I have to figure out if I am better concentrating on removing the stubborn head nuts as they sit on the core, or backing the stud out completely (it's already loose anyhow) and following the procedure others have used involving Locktite adhesive if the threads are okay.
As long as I don't have to deal with snapped studs like on the 110hp core, I'll be happy. I've sent an e-mail to the Corvair conversion forum and to William Wynne for some guidance.
I'm not looking for a shortcut, just remembering my late grandfather's words of wisdom "work smarter, not harder".
Next up, removing the harmonic balancer while I wait for answers on the head stud nuts.
Awaiting arrival of two things in order to take the next steps.
First, my dis-assembly DVD should be in the mail in the next couple of days. Once I have it, I can begin the teardown of the 140hp core motor seen here:
I'm hoping this block is in as good condition on the inside as it appears on the outside. I can't use these particular heads for my conversion, but none of the head studs are broken on this one, saving me the aggravation of trying to replace the three broken ones in the 110hp core. I'll be leaving them in the block as per the suggestion in the conversion manual, something that wasn't followed by the previous owner of the 110hp core. Also, these 4 carburetor heads will be sold to someone else and should (depending on internal condition) bring a handsome price in return.
The second things I'm waiting on is warmer weather. My plan is to mount this block on the engine mount work stand I got with the purchase. Hopefully I can drain any of the old oil that remains in the block before bringing inside to the shop for dis-assembly. Mother Nature can't seem to make up her mind - it's the 3rd of April and we got another inch of fresh snow last night.... sigh.
At least she is giving me the luxury of time to think through my plan :)
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.