Lift tabs

[Joe Person]

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.

[Anonymous]

Thanks for the detailed and complete reponse.

ProSeal is readily available...the RV crowd uses it to seal their tanks. Van's has it, and so do the rest of the usual suspects. I think that Van's might have it in very small quantities.

[Charles Davis]

I went ahead and machined mine from (.125) 304 stainless.

What swayed me wasn't so much the strength increase, but the resistance to bending, scratching, and corrosion of 304 vs 2024.

I am trying to be careful about weight inflation by adding "Just a few more ounces" here and there.  This is one area that I chose to tolerate the extra weight and fabrication effort & cost.

[Joe Person]

And the 304 CRES is...

Annealed, 1/4h, 1/2H, 3/4H, Full Hard?

Plain, sulfur-containing, free-machining 304, or 304L?

If annealed 304, is there an understanding that the yield strength is 64% of the yield strength of 2024-T3?

After machining, is there a step to passivate, so as to remove potential corrosion cells (e.g. the embedded ferrous bits intrinsic to standard machining practices)?  

What kind of bolts will be used to attach the tabs to the canard (internally)?

Just curious...

[Tom]

Charles,,


I can only beg that you stick with the plans and make the lift tabs out of the recomonded material. It is clear to me that your not an engineer and you dont understand what your doing..


Sorry to be so blunt, but it is the truth, and I'm sure others will agree.

if you have doubt in the design,, look at the pics here..

http://www.ez.org/cp45-p3.htm


Tom

[Charles Davis]

Thanks for the responses.  If you guys tell me to dig them out, I will.

I used .125" 304 Stainless steel sheet ordered from McMaster-Carr

Part Number: 9785K17  www.mcmaster.com

I picked an area of the sheet with no blemishes or scratches, and CNC machined the tabs so the grain direction of the metal ran in the "long" direction of the tabs (up-down).

The part was to thickness, so all I did was drill the holes and contour the OD.

To finish, I used a fine file on the OD to remove any machining tooling marks.

No other processes (heat treat, etc) were done.

[1 Glider pilot]

Just something to think about
the 304 stainless you selected has a Yield strength of 30,000 psi
The aircraft grade Alum. has a Yield strength of 47,000 to 50,000 psi. The alum. is heat treated to a T4 condition and the stainless is Anealled, thats soft. 304 stainless can not be heat treated, it must be worked to make it harder as in rolling or forming.  The problem that will be forever on your mind as you fly along over the city with your loved one in the back seat is which one of the modifcations to the plans will work and which one will fail. Doesn't make for very fun flying. If you are going to make changes don't just think something is stronger or better , Know it is or Stick to the plans! And have fun building and flying safe.

[Charles Davis]

Where were you guys a few months ago?

That's it.  We're pulling them out and putting in the plans tabs.  Thank you all for the very knowledgeable and honest responses.  You may have well saved my life.  

This is the only structural item where we deviated from the stock plans (other than well documented and proven mods, like the Davenport nose and brakes).

Lesson learned. :oops:

[Waiter]

Where were you guys a few months ago?

CD, Please reread all of the previous posts to this thread.

The stainless is OK, leave them in.  You may be exposing your canard to higher risk by the act of making the change, rather than the materials being changed.

I think the point made from the last several posts, there's a lot more to this stuff than eyeball engineering.  BUT, thats what this is all about, learning.

Waiter

[1 glider pilot]

Learning at whos expense? your loved ones? or maybe your own life? You may want to have an engineer look at the numbers before replacing the lift tabs. Stainless is like carbon fiber, it looks great and strong right up to the point where it goes , Bang. Replacing the tabs is not a hard job, many were replaced many years ago when Brock supplied customers with tabs made of 2024-0 (dead soft ) material and recalled them. Don't make structural parts out of material that you can't identify as the correct material, as printed on the sheet. Watch out for surplus material it may be the incorrect printing on the material that landed it in the surplus yard.  Suppliers make mistakes and the Mtr's ( Manufacturing test reports ) sent with the material can be sent with the wrong material. the guy who filled the order may be the lowest paid employee at the supplier. Those pieces of paper are for the Lawyers not the undertakers to argue over at some to be determined date.  Have fun building and fly safe.

[Bruce Hughes]

Hi Charles and others

If you have decided to remove the SS tabs and have not
yet done so, email me direct at bruce@ywave.com

I just finished (early April) doing that job.   May have a
suggestion or 2.  

It is not hard to do.   Few minutes each day for a few days.

[Gilbert DRIEUX]

I recently weigh my VE, and whith 57lb lest at FS0, read on the nose wheel balance :
             42 lb.
With me at pilot seat 247lb
            186 lb
Nose wheel FS is quite the same as Canard LE FS.

That is to said that in flight the total effort in both tab is :
42 - 57 + 186 = 171lb........, 85lb each = 39 kg ! (sorry, I understand better kg' figures.....!).
Don't change the plans. Tabs are far strong enough!
Concidering 3g acceleration, 85 lb are 255 lb each. Don't need NASA's materials...
Did you pay attention to the engine mount ? :roll:
Do you remember to bind the engine to the fuselage with a chain ? As recommanded, to warrant CG position in "normal" range (and accordingly flight control ability.....) in case of engine mount collapse.... :shock:

I beg your pardon for my poor english practical.... :oops:

[niceez]

I hope you did exactly as your post said and removed them.  I repair composite airplanes part-time and have the engineering background to explain this into the ground as does Joe Person and others that have the technical background.

Rutan has a copy of my tape of the canard load tests.  In that test it shows the steel frame (1/4" steel) failing under all the weight when the canard twisted.  The lift tabs never failed with all the weight and it was well beyond 30 G's.

For Waiter -  No one will never hurt the canard by replacing the lift tabs in the recommended way.  The skin that is removed durring this process does not carry the major part of the load but rather the bottom spar cap (only as a refresher to get the gears spinning ).  The larger top spar cap is in compression and the bottom spar cap is in tension taking most of the load.  Since the cut (1" X 3") is in front of the lift tab there is no weakening of the shear web, top or bottom spar cap that carries the load.

The three new plies of UNI the span over the top to a well sanded surface are in front of the lift taps and is more then enough to re-constitute the strength before the cutting, - as long as it is done correctly.

Thank you for the original poster asking the forum.  You more then likely saved your own life.  You do not know how many times during the repair of a canard airplane I find deviations from the plans.  It just cost the owner money for me to put it back to the way it should be.

Dale

[Charles Davis]

Yes, we are definitely replacing them.

I didn't quite understand the implications of changing this material.  People tried to tell me in earlier posts, but I wasn't listening.

That's why I really appreciated the blunt talk and solid facts regarding the stainlesss vs. aluminum tabs.  

That's what it took for it to really register with me.

Thanks again everyone for helping me.