Varieze Wing Attach

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Offline farnswow

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Varieze Wing Attach
« on: January 04, 2011, 02:54:46 PM »
I am nearly finished with reverse engineering the varieze wing attach fittings. I am interested in finding out what other people have to say about them. I am proposing to build my own, made of grade 5 titanium 6AL-4V. Titanium is stronger than 2024 aluminum, and nearly immune to corrosion. The pins will be made of Inco 718. The bolts will be Inco 718 as well, since cadmium plated steel is not recommended against the titanium. Questions:

1) Is there other things that should be changed, or is the material change sufficient to overcome the problems with the current fittings ?

2) Are there other builders that would be interested in titanium fittings for new builds or replacement of existing fittings ?

Offline Tom

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Re: Varieze Wing Attach
« Reply #1 on: January 04, 2011, 09:20:36 PM »
Forgive my ignorance,,  why would you go to the effort to build titanium fittings?

There is nothing wrong with the 2024 alum if taken care of properly.

-Tom

Offline EZPILOT742X

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Re: Varieze Wing Attach
« Reply #2 on: January 05, 2011, 02:00:13 AM »
The first concern that comes to my mind is; How well do epoxy resins bond to titanium? A dis-bond between the composite spar structure and the attach fitting parts would be a bad, bad thing. I kicked the idea around of building a simple, bare-bones (the way it was designed to be flown) Vari-Eze after I finished my Berk-EZ. If it were me, I'd do away with the attach fittings all together and do a one-peice wing with a carry-through spar.

Chris

Offline go ez

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Re: Varieze Wing Attach
« Reply #3 on: January 05, 2011, 06:03:15 AM »
Bonding to aluminium is actually very difficult, mainly due to the fast (instant) forming oxide layer which occurs immeadiately after any surface roughening, hence use of self-etch primers before painting aluminium.  

Regardless, the bonding of the aluminium or titanium plates to the BID pads of the spar caps is of no structural relevance whatsoever. All the load in the spar / wing is designed to be transferred from the BID pads to the plates in double shear by the 8 sets of 8 AN525/509 1/4" screws.

There was a VariEze structural failure accident cited in the CP notes (CP50 page 4) where a builder was reported to have installed the spar side screws but left the wing side screws out, thus leaving only the epoxy/2024 bond to secure the wing. The epoxy-2024T3 bond held for a while but the wing eventually came off in flight!

I agree that alodining 2024-T3 largely eliminates corrosion issues and titanium seems a bit of overkill and may introduce other failure modes.

One piece spar carrythrough is one way I guess but would restrict transportation to the airport somewhat and off-airport recovery etc too when in service I would have thought.

Regards
Steve

« Last Edit: January 05, 2011, 08:46:55 AM by go ez »

Offline EZPILOT742X

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Re: Varieze Wing Attach
« Reply #4 on: January 05, 2011, 09:49:07 PM »
Great post/reply Steve.. you brought up some interesting points. I wasn't thinking about the screws that compress the al. plates and the BID pads together. (even though I see them every day lol). There are lots of ways to build these things!

Offline Joe Person

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Re: Varieze Wing Attach
« Reply #5 on: January 05, 2011, 11:43:27 PM »
One other aspect associated with the 2024-T3 fittings - the taper pin fit in the bores formed by the fitting plates' stack has to be very, very good.  For "production" VEZ wing fittings (those assemblies made by Ken Brock), the cutting tooling for making the taper pins and the cutting tooling for making the bores in the fitting plates were ground to the desired taper on the same jig/fixture.  This ensured a very good fit, after machining.  Subsequent to the basic machining, the taper pins were lapped into the fitting bores.  Per-plans taper pins are 4130 steel, with a 125 KSI heat treat, followed by cad plating & baking.  With Nickel Alloy 718 & Ti, you'd have to ensure you achieve an adequate pin fit in the bores, without distorting the pins themselves (with modern digitally-base dmachining, I'd guess this is possible).  The 125 KSI heat treat on the per-plans pins, coupled with 2024-T3 for the fitting plates, allowed fine lapping & controlled wear of the aluminum, and little, if any, corresponding wear on the pins.

As noted, Alodine, or similar chemical film treatment of the bare 2024-T3 is satisfactory for the fittings - I have a VEZ in a marine climate (Puget Sound region), and with the Alodine treatment and wing removal every Condition Inspection, I have never had any corrosion problems.  Good marine-grade grease on the fitting mating surfaces, and LPS-3 or Boeshield T-9 on the bolts has served me well. 

If I were to do it all over, I'd stick with 2024-T3, and have a very light phosphoric acid anodize (no other anodizing process) for corrosion protection and epoxy bond.  I'd not do anything beyond a certian type of phosphoric acid anodize, on account of fatigue performance reduction induced by the more mainstream anodizing processes.
Joe Person
VariEze N79JN
Cozy #879 Under Construction
EAA Tech Counselor 4418
Bothell, WA (KPAE)

Offline Bruce Hughes

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Re: Varieze Wing Attach
« Reply #6 on: January 06, 2011, 03:38:13 AM »
To Farnswow (it would be nice if we knew your name...)

Joe Person did not say the following but I know that it is true: 

Joe is one of Boeing's experts on metals.  After work he has
built 2 Variezes.   He is a superb craftsman.  I would listen to
what he is saying.   It is NOT a good idea to make changes
in RAF plans.

I have made a few mods to the RAF plans.  I have changed
almost all of them back to the way it was designed.   :(

Bruce Hughes    :)
Yelm, WA
Longeze N199BH
retired
taught at Maui Community College

Offline farnswow

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Re: Varieze Wing Attach
« Reply #7 on: January 06, 2011, 12:26:59 PM »
Thank you all for your thoughtful replys. My name is Windy Farnsworth for those that want to know. I will be match machining the pins to match the taper in the Ti. There is a man in my EAA club that makes very high precision parts of the same size as the taper pins. Hand lapping is a good idea, but unless the pins are to be placed in the same hole they were lapped in, the utility might be lost. A The parts need to be machined to match at very high tolerance to prevent fretting. The surface finish should be good. I will have to look at the GE design practices for rabbet fits and see what it says.

Windy

(860) 305-7392

Offline Joe Person

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Re: Varieze Wing Attach
« Reply #8 on: January 06, 2011, 01:28:50 PM »
Don't know that I'd be considered one of Boeing's experts on metals/materials, but I was a structures engineer for about 17 years in the company, developing airframe structural repairs, mods, etc. 

As far as changing the plans, you HAVE to know what you are doing (TLAR  - "That Looks About Right" engineering will only be successful in certain situations).  I modifed my Eze a fair bit - one inch wider, re-designed strakes (4 gallons more per-side, which required analysis & testing (computed fuel volume & fuel CGs at different fuel quantities & angle of attack, etc., then, actual testing to validate fuel volume & CGs), and half the as-designed anhedral.  Major changes, but I was able to qualify/validate them through analysis & testing, and with an engineering background, I knew how to analyze & test, and how to ensure the results/data were valid.

Many builders will make changes, and call the changes "good" if things merely appear to work.  Again, you have to understand the engineering principles in play if making changes to structural configuration and materials. 

Ti will certainly work for wing fittings, and they may be the "ultimate" VEZ wing fitting design, as long as all pertinent geometry & other design requirements are met. 

Mis-fit the taper pins in the fitting stack-up, and eccectric loading starts to show up on the centersection spar-side of the joint.  This can overload the sparcaps via localized bending at stress levels associated with less than 4 g's of flight-loading.  Pin fit is critical here.
Joe Person
VariEze N79JN
Cozy #879 Under Construction
EAA Tech Counselor 4418
Bothell, WA (KPAE)

Offline EracerFL

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Re: Varieze Wing Attach
« Reply #9 on: January 07, 2011, 11:21:58 AM »
There are pictures on this site for a different wing attach system for the Varieze.  http://michaeltdrew.com/photo.html

Offline Joe Person

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Re: Varieze Wing Attach
« Reply #10 on: January 07, 2011, 11:57:57 PM »
The "different" wing attach system that was used on Mike Drew's former VariEze (he sold it) was due to the wings being a set of a handful of Jiran pre-fab wings - very few of these wing sets were ever made.  The wing attach system for that configuration is no better/worse than the standard "per-plans" wing attach configuration, with respect to relative complexity, potential corrosion issues, etc., and, working to design that type of wing attach system, adapted to the full-foam-core wing configuration, would entail a lot more engineering, fixturing/jigging, etc., to render.

Joe Person
VariEze N79JN
Cozy #879 Under Construction
EAA Tech Counselor 4418
Bothell, WA (KPAE)

Offline niceez

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Re: Varieze Wing Attach
« Reply #11 on: January 09, 2011, 09:21:18 PM »
Joe,

I think the stock materials are used for a good reason.  I would sure had to try and lap in Ti cups.   :o
If someone really wanted to make a neat change then using a spar and wings built the same way as the LEZ to VEZ size and spec without the anhedral wood work well.  Who wants to sit down and figure out the spar cap schedule?   ;)
Dale Martin
LEZ
Lewiston, ID

Offline Joe Person

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Re: Varieze Wing Attach
« Reply #12 on: January 10, 2011, 02:39:28 AM »
Yes, 2024-T3 was used for good reason - it provides sufficient strength for the required performance, it is easliy machined/fabricated, and it is cost-effective.  Deeper into the design requirements, properly built sparcaps and BID bearing pads, coupled with the choice of materials for the fittings (per-plans) give higher probability of shearout and/or bearing failure of the fittings (at the .125 thick plates) in an overload scenario (i.e. during a crash), rather than failure of the centersection spar buildup itself (thus yielding a better chance of maintaining fuel tank integrity).

There is more to airframe structural design than static strength analysis & testing.  The balance of materials selected & used is dicated (if the designer is a good one) by a host of design requirements, some of which are not evident when applying just basic engineering evaluation/analysis.
Joe Person
VariEze N79JN
Cozy #879 Under Construction
EAA Tech Counselor 4418
Bothell, WA (KPAE)

Offline Bill James

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Re: Varieze Wing Attach
« Reply #13 on: January 10, 2011, 06:22:43 PM »
Please stay on good subject of VE wing attach. But an aside on design ramifications-
Standing by one of dozens of LEZs on the Mojave ramp, someone asked Burt what he thought about not installing the lower winglet.
The answer included quickly sequencing through the installation, but going well beyond the expected considerations. All said to agree with your points Dale and Joe, and also to encourage the discussion-
Bill James, Fort Worth VariEze N95BJ
Downdraft Plenums, QuickCowls
There was supposed to be anhedral?
ATP, Society of Flight Test Engineers

Offline flyoz

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Re: Varieze Wing Attach
« Reply #14 on: February 06, 2011, 02:54:52 PM »
Windy
I would be interested in a set of standard 2024-T3 fittings as suggested in this tread
Flyoz