Steve Innova

Thanks Marc, Gullikson!

We'll know how well I've designed out peel in about 4 weeks, when I do the destructive test of a fuselage cross-section & seatback combo. Should be lots of fun!

-- If I have enough material left over, I'll build a standard plans MkIV shoulder brace & seat harness attach and test that too.

Here's a sneak peak of the seat-back, in it's early phases. (Working with Carbon Fiber BID 282 is just the greatest thing ever. That little bit of stiffness makes it so much more controllable than the fiberglass BID!)

I would like to see you break the flox off of a glass structure without destroying the structure. how much stronger do you need it? never seen the flox come loose, it always stays stuck and takes glass with it. use what you know works or be a test pilot for a new product. thats a no brainer

Under normal flight circumstances, no flox bond should ever be stressed enough that the flox bond could break.

But this is intended to bond a seat frame to the fuselage. The only time I need it to work (that is, stay bonded to the fuselage) is during a crash, when it will be subjected to not-normal loads.

I think that flox is probably strong enough, in large enough quantities. But I really don't want to use 5 lbs of flox to bond the seat frame to the seat-back, fuselage floor, and side walls.

If flox was the best way to do this kind of thing, it would be the only thing that aviation companies use for secondary bonding. But that doesn't seem to be the case.

If I were you, I would build a paegment from both and break it.

 

If I wer me, I'd spend my time making the finished part using flox and move on.

Not sure what a "paegment" is, but whatever it is, breaking won't help me, as I don't have access to the equipment necessary to measure the peel, compression, or tensile strength differences between an flox and Hysol bond.

Let's take this back a step. I'm trying to decide if I should use flox for secondary bonding or use something like Hysol 9430.

(Again, this is for a modified design -- flox has been demonstrated to work "just fine" for the plans applications)

To make that decision, I would need to know what are the properties of an MGS-285 based flox slurry?

The only estimate of flox strength I could find turns out to be from none other than Marc Zeitlin, posted to the Cozy Builders email list 21 SEPT 2008, message titled "Re: COZY: Re: fuel vents":

"Good question. Most of the laminating epoxies that we use, while

having pretty good strength in bending, etc. are pretty crappy bonding

adhesives. I always have a hard time finding info on the bond

strength of the laminating adhesives. But lets say that it's on the

order of 1000 psi - could be a factor of three in either direction,

I'd think."

Anyone else have suggestions on how to compare Hysol 9340 w/ and MGS 285 flox mix?

How many failures of flox joints have there been in the ~3000 flying Rutan derivative canard composite aircraft?

Didn't Yar Gil's flox joint from his nose strut to the nose wheel assembly fail?

If I recall, Velocity uses a separate "structural adhesive" for secondary bonding. Anyone know what they use?

How many failures of flox joints have there been in the ~3000 flying Rutan derivative canard composite aircraft?

Before or after they hit the ground? Joking.

I'm doing a few things differently on my aircraft. One specific change has been seat backs with integral safety harnesses, and I need a way attach these to the fuselage.

I could use flox, but I suspect this will heavier than neccessary.

Also, I'm conducting destructive testing on one seatback & fuselage cross-section. Flox might not have the most consistent characteristics, batch to batch. I don't have the time or money to conduct multiple tests, so I'd prefer to use an alternative commercial adhesive intended for secondary bonding, and with consistent, known qualities.

Blended winglets on a canard aren't entirely new.

I seem to recall reading in CSA that Klaus Savier built blended winglets for his Vari-EZ back in the early 90's, but wasn't satisfied with the results and scrapped them.

Or if you really believe that aircraft engines are the best long-term investment, get together with like minded investors and bid on Superior Air Parts, which looks to go to some Textron company for around $21 million in Chapt. 11.

This is way off topic, and there are arguments for and against. Yes you can pick up great deals at the bottom of an economic cycle, if you have cash to pay for assets. But you have to consider what your "cost of money" is for holding an $20k engine for 4 years. What else could you have invested that money in?

Also, inflation is a given when the economy eventually recovers, so that dilutes your ROI when it's time to sell.

Best advice is still probably, don't buy your engine or avionics until the end, you never know how long your project will take.

in dollar quantity, yes. In value, adjusted for inflation, maybe not as much.

I have entirely abandoned the use of Urethane foam in my aircraft. There are superior substitutes available.

Who cares? Our shops have a tendancy to get crowded quick.

I don't need to bait my own traps.

 

If it works for you, that's great but advice like that is going to cost another builder ...... guaranteed.

Regardless of superstitions, cleaning with acetone is an accepted technique for preparing / repairing fiberglass laminates on PVC foam (e.g. Divincell H45/H100). Here's the Exra 300's tech manual (lots of good info on composites there. Go to Chapt 51, pg 21: http://www.extraaircraft.com/Tech-Manuals/MM300SC/CH51.pdf

If builders can't distinguish between their Styrofoam wings and the PVC fuselage, strakes, and spar, then maybe they ought to select a hobby better suited to their lack of attention to detail.

That said, it's not bad advice at all, that once the wings are on (or exposed) don't use acetone around them.

Do you have research to back up the anti-acetone claims w/regards to damaging Divincell foam & fiberglass layups?

Burt Rutan the designer of these little airplanes we build and fly says it is fine. So I am satisfied with what is presently used. STeve build on

He said MGS was fine? Unlikely.

Here's another technique that another builder is using:

http://www.iconixresearch.com/aircraft/chapter20.html

At minimum, Mike (aka Dust) should have used a higher density foam for the blend, if he's only relying on external skin.

Don't use acetone....

The wing & canard foam is the only material especially susceptible to acetone.

Acetone is fine for working on the fuselage.

I'm with you right up to the acetone part. I won't be doing that.

Then allways wear gloves while handling your parts. Your hands have dirt and oil on them that can contaminate (to some degree) the bond.

This study (conducted by "Orion" from the Homebuilt airplanes forum) compares the effect of surface preparation methods on peel strength:

http://www.oriontechnologies.net/Documents/bonding.pdf

Most of the epoxies we use are primarily intended for laminating (I use MGS 285/287). They generally have low viscocity and high sheer strength.

For secondary bonding (e.g. bonding bulkheads to the fuselage, etc...) our plans have us mix the laminating epoxy with flocked cotton to make a thick paste.

While it seems to work fine, it's heavy, has non-uniform consistency, and and indeterminate (at least to me) bond strenght. I'm not sure it's the optimum use of laminating epoxy.

I've heard that various Hysol epoxies are specifically intended for secondary bonding. Does anyone have any recommendations, pros/cons?

Why take any risks? I peel ply all my parts, then sand them, then wipe them with acetone.

Get yourself a copy of SolidWorks w/Cosmos. Give the landfill a break.

Most of what your talking about can be proven with software. You can weed out the failures without pumping any epoxy or cutting any foam.

"Proven with software" = garbage in, garbage out. FEA is a good starting point for composite design, but what you seem to be missing is that it's not just the theoretical performance of the materials in the design configuration, it's also the material variances and builder technique tolorances.

Remember your canard that came out 10 lbs heavier the first time? You followed the design both times, but somehow ended up with 30% more wieght? I guess that wouldn't have happened if you'd just "proven it" with SolidWorks?

Sure, you can account for the known and and unknown unknowns with a high safety factor, but you're missing the point. Aviation design is about compromises, how to acheive an optimal compromise between strength and weight. Sure, add 20lbs of S-glass to that winglet and it'll hold, no doubt. But that's a big waste of material that you'll pay for in AVGAS for the next 20 years.

If I was static failure testing all my parts that's all I would be doing is rebuilding parts (and I do enough of that now.) This is why we buy plans and incorporate proven designs from reliable/qualified sources.

What you are "incorporating" is not a proven design. If you're only the second person doing it, then that's pretty much the definition of experimental.

I have great respect for Marc's engineering work on Jack's blended winglet, but I'm willing to bet that he would agree that it's impossible to know that it's an optimal design without actually testing it.

I've seen Jack's workmanship and it's high -- I woudn't count on every other builder achieving the same level of worksmanship and safety factor. Maybe it matters, maybe not... You won't know.

Are you aware that Cirrus has tested their wings by deliberately leaving peel ply and other foreign objects in the layups? Just testing the "optimal" design doesn't answer questions about all the sub-optimal executions of that design.

If anyone is real curious .......... send me a check and I'll ship my canard to you. Figure on 30+# for frieght.

Figure on on 170 lbs once you build a crate and packing... I just did this. The canard was 25lbs, box 150 lbs.

Load testing wings & winglets:

This page http://www.cozybuilders.org/Canard_Pusher/RAF_LE-Structural-Test.pdf describes (with pictures) a static load test on a Vari-EZ wing, canard, and winglet.

While the Vari-EZ wing is somewhat different from the Cozy, and quite different from a blended Cozy winglet, this would be a good starting point for learning how to set up and test a modified winglet.

This particular canard failed at only 8.4 g's, which was much less than the often [mis?] quoted 12gs. Why did at fail at a lower limit? Probably builder technique, which goes to show that even if the modified design, layup schedule etc... is good, variances between builders can have a big impact on the strength of the part. I've heard some advice on adding a 2.0 safety factor to homebuilt designs to account for those variances.

But bear in mind -- this is a static, ultimate load test. We simply don't have the equipment neccessary to conduct dynamic load tests on wing structures. That's what the test period is for, I guess...

For those that care, in the next month I'll post pictures of the static load test of my modified composite "A" fram seat-back, which is intended to meet the FAR 23 seat / harness requirements. The test rig is proving to be quite the design challenge -- I've had to re-build a 18" fuselage cross section to attach the seatbacks into. Fun!

If anyone has a line to where I can get lead shot bags cheaply, please let me know!