After completing the 701 wing repair/extension, I'm anxious to get started on the 750 tail group. It will be really great starting to assemble the parts I've made and have been sitting patiently in boxes at my workshop.
Back in September, I was at the Zenith factory in Mexico, Missouri. I decided to buy the spars for the horizontal tail and elevator. I could have made these myself, but our shop bender isn't wide enough to bend them and I decided the price was worth the value of having factory accurate spars to build around. The wing spar is made differently and can be replicated easily in the shop, where these can not. The purchased tail spars have other distinct advantages which I will get to later.
You may recall from a previous blog, the spars come neatly wrapped from the factory in a very long paper package:
After what seemed forever, it was finally time to open up the package. The staff at Zenith sure do a great job wrapping!
All the spars come pre-drilled from the factory as these would normally be part of a complete kit. As I'll explain later, this makes assembly much easier!
Although 6061-T6 aircraft aluminum is already a very corrosion resistant alloy, most people including Zenith recommend addition corrosion protection be added anywhere metal parts join. It's not the metal part themselves that cause issues, but any moisture that accumulates or creeps it's way in between the parts (and it will!) that can cause issues. I'm particularly concerned about this as I want the plane to be robust against all weather conditions, particularly when it may have to reside outside. In addition, my plans are eventually to get the 750 on to floats, so operating on the water adds to the concern.
To accommodate this, I'll be painting all joints with Cortec latex primer. Cortec comes in traditional primer green or clear. I choose the clear, which paints on with foam brushes as a milky white colour and dries clear. It weighs next to nothing and offers huge advantages over more toxic and smelly spary on primers like Zinc Chromate.
It sounds like a bunch of work to prime all the mating surfaces, but I was able to complete all three spars in about 10 minutes and it cures fully in about 30 to 45 minutes.
While I waited for the primer to cure, I decided I just had to trial fit some ribs - I've been waiting for a long time to see if all the work I put into making the forms, cutting the blanks and bending the ribs was going to pay off.
Although they fit properly within the spar web flanges, something didn't seem quite right. That's when I remembered that I hadn't bent the last flange over where it would connect to the elevator spar. Fit first every time to confirm!
A quick look at the forms also showed me I hadn't yet cut back the end of the form to allow the bending of the spar attachment tab:
I was quickly able to fix the problem by measuring the correct length for the form and cutting it in the band saw.
With the right length on the form, it was then easy to make the rib have the correct spar attachment tab:
With that, all the ribs now fit correctly - very satisfying to know all the work I put into getting the plans from paper to CAD to card stock to forms paid off. Hoping other forms are this well done too.
Before I got to far into it, I decided it would be a good idea to get the spar doublers made - they are the last larger component that I need for the tail group. You may recall from a couple of blog posts back, I broke a rotary bit trying to cut the 040 aluminum sheet. I managed to find replacement bits on Amazon fairly cheap and now that I had them in hand, I could continue to try and use the rotary cutter to finish off these 4 parts.
I got everything lined up again on the bench and proceeded to make another attempt. Unfortunately although I didn't break another bit, the cutter really wasn't working that well with the 040 thickness. It would bind and the cutter would get gummed up with aluminum chips, rendering the cutter useless.
In the end, I abandoned cutting the other two doublers on the bench. It was just easier to use the band saw, even if that meant a little bit of waste cutting the larger 040 sheet down to a manageable size.
Well, that's today's update. More exciting things to come, thanks for reading!
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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.