Jason builds a plane

how did this 701 ever pass inspection?

29/1/2017

0 Comments

 
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:
Picture

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":
Picture
On the top of the left rib, we've created a doubler to address some crack damage to the rib from the accident. It's temporarily held in place with clecos until we get the rear channel fit in it's new spot.
Picture
The original builder thought silicone was the answer to everything I think! It took lots of elbow grease, but it's all clean now.

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:
Picture
Ron's notes, written in red Sharpie marker. Rather than make a whole new channel, we decided to modify this one to fit. This also required some straightening too. Time to learn some tin-smithing skills :)

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:
Picture
This picture also captures the new rear spar channel I created, already riveted in place.

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:
Picture
Cut to length, measured for bending.... off to the bender
Picture
Fresh from the bender

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!
Picture

​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:
Picture
If you look just in front of the channel on the rib you can see two rough cut holes for the fuel line from the tank. This should NEVER have been left sharp like this where it could abraid the fuel line! (clue #2)

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:
Picture

The new L flange really tightened everything up!
Picture

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:
Picture

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.
Picture

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:
Picture

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!
Picture

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?:
Picture

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!
Picture

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:
Picture

​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:
Picture
At least this rib is salvageable!
Picture
Everything out except a few more rivets, ready to begin fabricating the missing (and oh so important) spar root doubler!

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:
Picture

Back to the shop tomorrow, thanks for reading!
0 Comments

HMMM.... THIS IS NEAT (said the geek)!

24/1/2017

0 Comments

 
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:
Picture

.....and use LibreCAD to turn the information from the drawing to a CAD file, suitable for printing, exporting to a CNC machine, etc:
Picture
The CAD drawing appears upside down compared to the plan drawing, but that's just the way the polar co-ordinates show.

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! 
0 Comments

    New here? Try starting at:

    blog #1

    Author

    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.

    Categories

    All
    Airframe
    Airport
    Avionics
    Decisions
    Engine
    Interior
    Keep Looking
    Mentor
    Milestone
    Mission
    Motivation
    Paperwork
    Philosophy
    Priorities
    Scrounging
    Tools
    Ultralights
    Welcome Aboard
    Workshop

    Archives

    June 2022
    May 2022
    April 2022
    March 2022
    February 2022
    January 2022
    December 2021
    November 2021
    October 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    January 2021
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    September 2019
    August 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    June 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    February 2017
    January 2017
    December 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015

    RSS Feed

    build log

    Item Hours
    Engine 31
    Tail 151
    Wings 701
    Fuselage 0.5
    Interior 0
    Controls 4.5
    Avionics 27
    Other 66
Powered by Create your own unique website with customizable templates.