Hello Zenith Builders...

I am looking at the recent offers and completed sales for CH750 STOL projects on this forum.   So I have come here hoping for detailed guidance on how to inspect a project to see if the work is well done. 

Need to have the repairman's certificate and want to finish the build in just a few weeks.   So buying a kit in progress is the solution.   But how to avoid bad news and reworking mistakes??   

I want to put together a proper and well thought out list of details that must be checked.   Your guidance and advice will be greatly appreciated.   

R. M. Moore, CPA


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So I have come here hoping for detailed guidance on how to inspect a project to see if the work is well done. 

That's a tall order!  One could go on forever, assembly by assembly, giving "detailed guidance," but I would think these general principles would work for most:

  1. Spend some time in the model-specific forum on this site - you'll pretty quickly pick up where the problem or difficult areas in the build are.
  2. If at all possible, get an experienced Zenith builder - preferably of the same model - look the project over with you.
  3. If possible, inspect the project in the builder's workshop - the general cleanliness and orderliness of the shop will give you a big clue to how the builder approached the build.
  4. Look for properly-pulled rivets, tightly set against the metal, with the proper domed-head from using the Zenith modification of the rivet gun tip.
  5. Look for properly smoothed and deburred edges of sheet metal.
  6. Inspect in the deepest recesses of the build - use a flexible "snake" digital camera if possible - and examine those areas critically.  If they look good, likely the build is a good one!
  7. Expect a builder's log with lots of pictures documenting the build.

That's what I came up with right off the top of my head - I'm sure others will think of many more things.  IMHO, however, if you expect to pick up a mostly-completed project and have it flying in a "few weeks," then that's likely a project that's 95+% complete (99+%? - those "last little details" can take forever!) and it may be doubtful you would qualify for the repairman's certificate.  You can still do all the maintenance, however, but not sign off the annual. On the other hand, remember the old builder's saying:  "90% done with 90% left to go!"  

Good luck with the hunt!



Thanks John...

All very helpful information.   The rules for qualifying for the repairman's certificate are not based on a percentage of time spent.   I have discussed this with the Honolulu FSDO office.   My understanding is that the Repairman's Certificate is based on sufficient knowledge of the building process and the airframe.   You can have a team of a twenty on the build and any one can be designated as the choice for the Repairman's Certificate.  Your point may be valid in a 99% complete situation but not say.. 85% as with a recent kit that was offered on this forum.    BUT.. let's don't divert this topic in that direction.   I will take up your point and recheck.

Beyond what you have said, what about alignment issues?   Wing incidence, dihedral, sweep, etc?  Which of these apply?   Fuselage square and true??  Are these potential problem areas?  Or does the match hole CNC pretty well cover all that?   

Thanks for the kind assistance.   Much appreciated.


You are 100% correct about Repairman Certificate qualifications.  In my case, it was a joke - the FAA took all of 5 seconds to glance at my builder's log, filled out the paperwork, and that was it!  However, I just meant it as a caution - FSDO's vary wildly in the interpretation of the regs and one could just as likely be told differently.  You've done your homework and sounds like you and your FSDO are on the same wavelength!  ;>)

The match hole CNC (the older kits have matched pilot holes, I think the current kits have matched full-size holes) does help keep things aligned, but AFAIK the holes that determine the wing rigging and strut length, etc. are builder-determined and not pre-drilled, so yes, it would be critical to check all those factors - incidence, dihedral, sweep - since they are set by the builder.  As I recall, the incidence is 3 degrees and most obtain about 2.7 or so due to some limitations, but Zenith is OK with that.  Minor variances in sweep aren't too bad, either - in fact, I know at least one builder had a bit of forward sweep and the engineer at Zenith said it was OK and would in fact probably make the plane even more stable!  (It's plenty stable per plans, however!)

Any doubt about a dimension/angle not conforming to plans, I would call Zenith.  They give full support to those who have acquired projects just as if you were the original builder!


I know you don't want to ID the project, and I'm not asking you to.  However, if you could give us some idea of what *has* been completed thus far, we could give some add'l pointers. John's general guidance below is excellent and spot-on.  If the plane really is *that* complete, I would strongly back-up what John says below about renting/borrowing/buying a small borescope camera (iPhone has compatible units for dirt cheap) to take a look inside structures that have already been closed. As an example, the wing rivets may *look* great and tight on the outside, but what if about 6 ribs inside there's a 1/8" gap between the rib and the skin?  Probably not much of a deal with an occurrence of 1, but as John says, you get a general idea of the care that went into the build.

You're talking about dihedral, incidence, etc.  *Have* the wings been rigged yet? That's typically done very late in a build, and sometimes not even done until the plane gets to the hangar, just for convenience.

Has the engine been mounted?  type?  There are lots of engine-specific areas to check WRT throttle/mixture cable routing, panel wiring, and engine instrumentation wiring/plumbing, antenna routing, etc.

If the plane has been set up with the tail attached, etc., you might check the cable routing to ensure fairleads are in place and nothing metal rubbing the cables, etc.  Take an angle finder and verify that the elevator, rudder, and trim tab all are close to the spec'd range of motion.

Check for presence of a "forest of tabs" type grounding block, or ensure there's some evidence that all grounds terminate at a point individually. You don't want ground tied to another ground wire, and then *that* ultimately get attached to a common ground.

If avionics are in, perform a radio check. Hopefully with the engine running, to see if there's static in the line. If strobe-equipped, turn 'em on to make sure the cables were shielded properly (while on the comm, that is...).

Your hope to get this airborne "in a few weeks" is admirable, but there's usually a LOT of little things to address before you're ready for inspection, let alone first flight, but it sounds like you've considered all of this.

If the plane is *that* complete, does the owner's story align with that level of completion?  I realize family issues frequently alter a completion plan, or maybe the person just likes building and has no desire to fly it.

Hello Carl and also John..

Very helpful.   I would certainly do my best to get someone knowledgeable to inspect.   But it is my nature to provide detailed instructions.    

I began to do as John suggested and plowed through about 13 pages of the forum and bookmarked any topic that dealt with potential alignment, fitting, adjusting, etc.    Lots to digest.  Matches with Carl's suggestions very closely.

I would be looking for a kit that has zero FWF installed.   But if wings and tail feathers are closed, then inspection becomes critical.

Further comments are most welcome.    


Everyone's abilities and available time are different, so I'm just making general comments.  Again, you haven't told us what *is* complete or what engine / FWF you're intending to use, so trying to cover all the bases is a bit like shotgunning it.

If the engine is something like a UL, you'll need to consider using a header tank, usually installed behind the baggage compt wall. You may have to re-plumb the fuel system if this wasn't done. If you're using an O-200 (as an example), do you have one? Going new O-200D, or are you planning on finding removed engine and just installing?  I would advise against that approach unless you personally know the pilot and plane from whence it came to KNOW it's not a prop strike, rod knock, etc. I don't care what an unknown seller says. It's your life.

Other things that will take some time are getting the baffles all set-up. Any baffle *kit* you might find will still need a lot of trial-and-error fitment just cuz there's so many variables.  Then there's the cowl. It's not a bolt-on-and-go situation; lots of finessing.

Engine instrumentation could be challenge - not cuz it's hard, but very detail oriented, and you have to plan it out  beforehand. As an example, on my prior plane, I used an MGL EFIS. The RDAC unit on the engine side, which collected all engine inputs, said to keep the data cable feeding the EFIS well separated by any high current or any antenna wire.  That just required thinking cable placement, etc.  If you're going analog, that would probably be the easiest installation, cuz you don't have to plan as much.

All told, I don't want to discourage you. Any completed kit aircraft is one more ambassador for the E/AB movement. Realistically, unless you're an A&P, or have built a few other airplanes, you're probably looking at 100-150 hrs just on FWF. As I said, everyone's different; I don't like to spend more than 3-4 hrs / day on my Cruzer project, but I have a lot of other "things" on which I spend time; new granddaughter, walking the dogs for both of our health, running errands with my wife, etc.  I and others are always glad to offer suggestions.

Hello Carl...

I responded in the immediately preceding post... "I would be looking for a kit that has zero FWF installed."  Tried to focus the thread on the airframe.   Sorry if I was not sufficiently clear. 

In any event, other readers may find your points on the FWF helpful.   All good.

I do have a personal preference on engine choice and instrumentation.   But I don't want to turn the thread in that direction.   

One thing that surprises me is the lack of a comprehensive database of problems and the various excellent solutions experienced builders come up with.   Similarly, possible modifications are scattered across many years of posts.   Such invaluable knowledge is hard to dig out.   New builders are left to do this individually and repeatedly.   

For a long time I was fixed on the Kitfox.   I spent lots of time researching for modifications.   Read about other builders doing this same long and complicated research.   I came back to the Zenith due to the all metal construction and match hole kit design.  

Each builder is focused on their own issues and a ready pool of all this wisdom and creative problem solving is never accumulated as a ready source.   Obviously, this is not the factory's priority.   But it is obvious to me that Zenith watches this forum carefully and solves problems with their kits.  Outstanding customer care and support is Zenith's hallmark.  

People with experience can assemble these aircraft is amazingly short time frames.   I heard the adage from one such repeat builder that the general rule is 75% of a new builder's time is spent staring at the plans and trying to figure out what to do.   That is the new PlaneCrafter's Two Week to Taxi program's focus.   Kicking up the efficiency to do the 51% in a minimum of time.    I know one person who can build a CH 750 STOL to Phase 1 flight testing in thirty days.   Beats even the factory 400 hour estimate.     

Back to the database idea, maybe someone with the knowledge and sense of sacrifice could put the links to the key threads together in a list by model.   Perhaps then Zenith would allow a new primary forum section for "Solutions and Modifications".   As any of the links age out, they could be tagged as solved at the factory level if that applies.

In the several hours that I spent yesterday, I found about a dozen such very specific threads.  This was John's suggestion which I took seriously.    BUT...very time consuming albeit very worthwhile.   Really wondering why this has not already been aggregated for the benefit of all new builders.

Big thanks.   More thoughts are welcome and truly appreciated.



Response from Brock Butler - Recent buyer of a kit project

Reply by Brock Butler 2 hours ago

Hi Michael,

I didn't pay for the plane until I picked it up.  When you buy a partial kit you are buying the kit, the builder, and the decisions the builder has already made regarding engine and firewall forward accessories.  How experienced is the builder?  How meticulous is his work?  How knowledgeable is he regarding Zenith Aircraft?  The reason you buy a partial build is the money savings.  Regarding the quality of the build, you hope everything checks out but you plan for the worst.  Then you go through the build manual and check every step the previous builder completed.  In my case the previous owner was well known on the forum and had decades of experience.  His shop was immaculate and he had tables he laser leveled using square steel bars (which he gave to me).  The completed fuselage and wings were also immaculate and carefully stored in crates. 

My goal is a light sport CH750 STOL that weighs less than 700lbs with a total investment of less than $30k.  Depending on what I find when I tear down the over-hauled O-200 (original owner died and records lost) I should hit my goal.  I'll keep you posted on my progress.


I think I'd make sure I was pretty comfortable with the plans as well -- by my nature, I'm more comfortable if I can see it in the plans and then look for the item/feature/assembly on the project itself.  Not being an A&P or anything like it, it usually takes me 8-12 hours of lazy thumbing through the plans before I'm modestly comfortable with what I'm look at (size of rivets, locations, order of build/close, etc...)


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