Hangar Flying

Drew,

Oh brother?

What stipulates that addition of VGs on a primary flight surface would be, or not be, a Major change? (Answer to this a bit later...)

My T/C advice to Dave was based on:

1.  Older Ops Limitations

2.  Definition of Major change

3.  My 20 years as an engineer in the airplane biz (currently a Certification Engineer - yes, Part 25 is bigger and nastier, but Part 21 applies all around).  I do airplane Certification & Major/Minor Determinations for a living these days.

The approach I suggested to Dave was conservative.  Addition of VGs could easily be determined to be a Major change, as they can be shown to have an appreciable effect (Appreciable, meaning measurable, for simplicity's sake) on the performance and/or handling characteristics of the airplane.  Dave's operating limitations were of the "older " variety (circa 1988), and thus required him to contact FSDO.  A prudent thing to do, when in doubt, especially for those who did not build their airplane.  The Bill Davenport incident should continue to be a reminder to all operators of experimental homebuilts regarding adherence to Ops Limitations.  Sorry, but playing below the table (i.e. not following your Ops Limitations with respect to making changes to the airplane) is something that can only work against us.  Knowing the the requirements of your airplane's operating limitations is paramount.  To be ignorant of them, or worse, to dismiss them, is bad ju-ju.

Now then, as I counseled Dave, not all FSDOs are created equal.  My put to him is that he needed to find out what his local FSDO would say, based on his situation.  I also gave him some talking points to better poise him for dealing with the FSDO, regarding the VG installation.  In the end, the FSDO called "Minor", and all is kosher.  I certainly would not dare do battle with the FAA and tell them that I was still convinced the VGs constituted a "Major", after such a ruling (unless I got paid for it, like in my day job)...  Other FSDOs could easily say otherwise (if only for an excuse to get some of the inspectors out of the office and looking at some real hardware).

"Shopping for FSDOs" is possible, but as things progess in the FAA, such a practice will become less and less possible.  There are continuing efforts in the FAA regarding what is called "harmonization" - this, driven by the need to make the world's skies a more level playing field, with respect to the various regulatory agencies of the world, and their respective regulations.  This will have a trickle-down effect within the FAA.  I have already seen more standarization between two different Aircraft Certification Offices in the past year, for example.  Fortunately for you FSDO shoppers, this is still a way's out.

Dave has a nice set of test flight parameters detailed by a competent EAA Flight Advisor, in order to test his VG installation in a safe manner.

Cheers,

-Joe Person
EAA Tech Counselor 4418
VariEze N79JN
Bothell, WA  (KPAE)

Tom,

The gent lives in Edmunton, Alberta.  As soon as I hear from him, I will let you know.

Thanks for the assist,

-Joe Person
VariEze N79JN
EAA Tech Counselor 4418
Bothell, WA (KPAE)

OK, I gotta weigh in here.

There was a VEZ for sale a month or so ago on ebay, nice (really nice & sporty) paint job, and a nice-looking airplane overall.  Caveat emptor...

I was asked by an earlier potential buyer almost 2 years ago to review some of the critical details on this airplane.  The airplane was, at that time, located in the Vancouver, WA area.  Before committing to fly down to examine the airplane in person, I asked for some good digital photos of the critical areas (wing fittings, F-22 bulkhead, canard lif tabs, etc.).  Upon seeing the pics, I told the prospective buyer to steer clear.  The wing fitting plates common to the centersection spar had been shimmed between .063 and about .090 inch farther apart than the by-design .375 inch.  The original builder, while a talented finish guy, was obviously ham-handed with his layups - to have to shim these critical structural items the way they were shimmed showed total lack of ability when building the sparcap & shearweb of the centersection spar.  This shimming totally blew the critical geometry of the wing attach fittings, and heaven only knows how the builder compensated for this gross error.  There would be no easy way to fix this garbage, short of building a wholly new centersection spar structure.  Unsafe airplane, until proven otherwise.

Upon seeing this same airplane on ebay recently, I asked the seller if the wing/centersection structure had been repaired/re-built.  The answer I got was far too nebulous for my liking, and shortly thereafter, the airplane disappeared from ebay.  I do not know if it ever sold.  I hope to hell that anyone who might have purchased this airplane would have been cognizant of the history of the airplane.

I have personally examined (many times) another VEZ that was eventually sold on ebay (and untruthfully touted in the ad as, "...possibly the nicest VariEze...").  That airplane was fairly well-rendered, but had several safety-of-flight no-no's that I repeatedly insisted needed correction.  After tiring of the incessant, repeat-questions on how to fix these problems (about 10 hours of my own time wasted...), I gave up and bluntly told the dweeb owner that he needed to hire a good A&P.  The airplane was sold several months later.

Where am I going with this?

Each VEZ, LEZ, Cozy, etc. are ONE-OFF airplanes.  Each has features (good or bad) that are unique to that airplane.  In this vein, those of us who are experienced builders have some responsibility to call "BS!" when indeed BS exists in the realm of the selling of one of these airplanes to the uninformed/inexperienced.  And I'll take this a step further - anyone who enters into the purchase of any homebuilt, with nothing more than the desire to own a "cool airplane cheap" should be counseled, especially when the airplane in question is a plans-built.  As a Tech Counselor and a practicing aerospace engineer, I have seen too many scary things done in the name of building a homebuilt airplane.

If a seller is content to misrepresent any aspect of an airplane, particularly a homebuilt, caveat emptor.  What happens when a buyer thinks he can get his airplane off the runway in 750 feet, when in reality it takes 1500 feet?  What happens when a latent construction error manifests itself at 12,000 feet?  Sorry.  Anyone who thinks we should keep such facts to ourselves and not be a buttinski, is off-base.

Off my "All Temperature Cheer" box & with no apologies,

-Joe Person
VariEze N79JN
EAA Tech Counselor 4418
Bothell, WA (KPAE)

Engineer's (airframe & mech systems engineer) opinion:

Don't ever make a material substitution just because a material seems/sounds "better".  Kevlar is no longer used to the extent it was in the 70's and 80's (in airframes) because of some of it's less-than-desirable properties.  It is hydrophyllic, and moisture ingression was a big problem (and this with advanced, high-temp epoxies with autoclave-cures).  

Carbon fiber sounds dandy, and the physical properties and structural performance seem grand.  Show me those physical properties using our construction techniques (They don't exist when used in the manner we build airframe structires in our garages).  Hand-layup properties (strength-to-weight) of S-Glass are damn-close to hand-layed carbon, and S-Glass is cheaper.  And no, it is not necessary to use S-glass for your winglet attach either.

As Dan Patch mentioned, mixing different composites (with differing modulii & other physical properties) is nowhere near a simple "sum of the parts" exercise.  Avoid such practice for any primary structure, period.

There is absolutely NO need to look at material substitutions in the Rutan airframes.  I am a reasonably-experienced engineer in the airplane biz, and I have no desire at all to charge out and try to make improvements - I don't have the time, money etc to support the engineering effort (which would include all sorts of physical tests to boot, to qualify my re-engineering).  

Keep it safe - do it right (good workmanship and attention to detail) and stick with the plans.  You will be much happier, and dollars ahead, in the end.

...or, you can go for Good and Cheap (inexpensive) - I put my first VEZ into the sky for $9500 US (1990) dollars.  Made as much of the machine myself as possible.  The VEZ, for its overall capabilities (as well as the related compromises), is still one of the the best bangs-for-the-buck around.

-Joe Person

When making material substitutions, especially for primary structure, one must arm themselves with enough knowledge of the new material's characteristics.

Here's my take on using CRES in our construction:

CRES ("stainless steel") resists corrosion via the formation of a naturally-ocurring (i.e. naturally-forming) oxide layer.  Aluminum does the same thing, by-the-way, albeit with a layer that is not quite as robust.

When CRES is machined, bits and pieces of ferrous metal (from the steel tooling) become embedded into the CRES.  These are potential corrosion cells, and if not taken care of, a sometimes insidious corrosion problem manifests itself.

The means to address this situation is via a process known as passivation.  Passivation typically entails treatment in some sort of acid, so as to remove embedded surface contaminants and help form the necessary oxide layer, at the same time.

Nastier still, if unpassivated CRES is potted in or embedded (like lift tabs would be), there is potential for accelerated corrosion internally, and right at the bondline because the bonding surface does not allow sufficient exposure to the environment such that a naturally-occurring oxide layer forms, yet it can still let moisture in via small pores & such at the bond interface.  The mix of trace moisture and ferrous cells in the CRES make for a great corrision scenario.

IF I were to use CRES, I'd, well, not opt to use it.  The beauty of the aluminum tabs is that one can do a great corrosion-preventive treatment for them in one's own garage (as opposed to passivation of CRES & such).  If you absolutely HAVE to use CRES, well, 302 1/4H or 304, 1/4H, with all proper passivation, could work, but I cannot absolutely qualify it's use in such an application (i.e. I cannot make any reccomendation for it's use on someone else's airplane, and I would not use it at all on mine).

I am an engineer in the airplane biz, and I can comfortably state that there is NOTHING wrong with plans-built lift tabs.  I have evaluated many aspects of the composite canard design (strengths, servicability, corrosion prevention, etc.) from an engineer's perspective, and am quite comfortable with my enhancements to the basic design (e.g. Alodine on all aluminum parts that cannot be replaced, use of good primers and paints on metal parts, etc.).  For corrosion protection, a proper Alodine treatment is sufficient for corrosion resistance.  If one is worried about moisture ingression into a glass/metal bonded area, application of a good automotive urethane sealant, or aircraft sealant (e.g. ProSeal) as a fillet seal around the metal will work well.  I have a VariEze, with embedded 2024-T3 wing attach fittings.  I applied Alodine, and after installation, made fillet and periphery seals with ProSeal (BMS 5-95 - Boeing's Spec) around all of the installation, prior to primer & paint.  I am 99.99999...% sure I will not have a moisture ingression and related corrosion problem.  The VariEze wing fittings are far more susceptible to corrosion than lift tabs.

Properly made & installed 2024-T3 works well.  The tabs are good for over 20 g's in a Long-EZ installation.  Your F-22 bulkhead will disintegrate before the tabs go bye-bye.  If one is worried about durability (i.e. being a klutz and bashing around the tabs when the canard is off the airplane), one could "up" the gauge of the tabs to .160.  Note that the Berkut uses .250-thick tabs.  However, I maintain that if your work style is such that you cannot protect critical parts of the airplane from incidental damage, maybe you should stay away from building your own airplane altogether...

Does this help?

Application of Alodine can be done in-situ, but one must exercise caution to ensure the solution does not find its way between surfaces that cannot be disassembled & rinsed.  The Alodine 1200 or 1201 solution (the oft-used "gold" colored mix) is a ferro-chromic acid solution that performs a controlled chemical reaction / oxidation of the aluminum.  The reaction is stopped by removal from the Alodine, and a rinse.  If Alodine wicks into areas where it cannot be rinsed off, a decent corrosion problem can be established.  Think of Alodine wicking up into the canard, on the lift tabs.  One could not remove the Alodine up in the structure, and further etching would occur.

In the field, application of such treatments in-situ is often done with paper towels placed on the area to be treated, and wetted with the Alodine.  It does work, but one still has to be careful.  Any situation where gravity or unwanted capillary/wicking action must be eliminated when doing an in-situ treatment.

For anything on our airplanes that cannot be removed for treatment, I'd suggest applying a good primer (zinc chromate is very good) followed by a compatible enamel topcoat or epoxy paint.  Or, simply use a good primer that is compatible with aluminum and the rest of the airframe, as part of the overall painting effort.  Don't worry too much about Alodine application at this point.  Also, in any areas where an aluminum part penetrates into a glass layup, use a good automotive urethane seal to fillet-seal the penetration.  Do not use ordinary silicone (RTV), as the acids in the uncured mix are probably not good on aluminum.  For completely enclosed inserts (e.g. the hardpoint inserts in the Long-EZ wings & center section spar), I would not worry too much about those rotting away - they are pretty well isolated from Ma Nature's fury.

For my VariEze wing fittings, they have complete periphery seals made from a chromate-based aircraft sealant (ProSeal).  I do not ever expect any moisture penetration into the fitting-to-sparcap intrface areas because of this.  Not everyone can get ahold of small quantities of such sealant (I work for Boeing...), hence the suggestion to use a good automotive urethane sealant (available at most auto body & paint stores).

Hope this helps some.

A simple option:  Rent a 24' U-Haul truck with a liftgate - the main wheels can be rolled onto the gate with the nose pointing away from the truck box.  hold onto the nose gear, raise the liftgate (you need a helper), and roll the fuselage into the truck.  Wings and canard can be wrapped in clean moving blankets and secured inside the truck as well.  Done this a few times.