NEW V/S Modification video Anti-Splat-Aero

[sblack]

I have a coup,e of comments after reading this rather strange thread. I am an aero eng with over 20 yrs experience.

For those who scoff at engineers, van is an engineer and without that skillset there would be no RVs. Period.

We are not talking about an over load issue here. It is a cracking issue so it is fatigue. Fatigue analysis is at best a rough estimate as every airplane is built and flown a bit different. The designer is always walking a fine line between keeping it light and providing adequate fatigue life.occasionally a week spot shows up after many hrs on many aircraft. This is the case for all aircraft including Boeing, Airbus and any military or recreational aircraft. So this is not an indictment of Van, it is a normal occurance. That is why we do inspections. And Vans aircraft have had several of these situations on various models.

AC 43.13 is an Advisory Circular. An AC is an acceptable means of compliance, not a mandatory standard. Mfgs can and do deviate if they can show justification. A mandatory instruction is an Airworthiness Directive.

This SS beefup from ASA is not to increase the static strength, which is adequate in the initial design, it is there to increase the fatigue life. And the designer is not stating that this is the critical load point on the Vstab. It is simply a location where cracks are known to form for the reasons stated above.

So you can inspect and repair as per the AC or you can take these conveniently made parts and increase the fatigue strength and most likely never have to worry about cracks forming and it will involve less work than a repair. Or, you might put 10000 hrs on your airplane and never need it. It depends on where and how you fly, how much power you have up front etc etc.

As for all the other surface mounting points, if there has been no service history of cracks forming there would be no need for any modification. So suggesting that installing a beefup on the vstab mount is the same as beefing up every other part of the airplane just doesn't make any sense.

This part has been offered as a service to the community in good faith and we are all free to take it or leave it.

[rjbob]

Scott Black,
EXTREMELY good post...thank you.

[rvbuilder2002]

Originally Posted by sblack

This part has been offered as a service to the community in good faith and we are all free to take it or leave it.

Very good point.

The problem with that is that within this community, 99.9+ % of the people don't have your aero engineering background (or any engineering for that matter), so taking it on faith is about all they have.

Sometimes that works.... some times it doesn't.

[DanH]

Originally Posted by sblack

AC 43.13 is an Advisory Circular. An AC is an acceptable means of compliance, not a mandatory standard. Mfgs can and do deviate if they can show justification. A mandatory instruction is an Airworthiness Directive.

Yes and no. A manufacturer is never required to do anything in AC43.13. On the contrary, AC 43.13 is an acceptable means of compliance only in the absence of manufacturer's guidance. Nothing in it can be substituted for manufacturer's guidance. From the seldom-read very first page:

This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no manufacturer repair or maintenance instructions.

Confirmation was direct from the top, FAA AFS-300 in DC, the office responsible for AC43.13.

This SS beefup from ASA is not to increase the static strength, which is adequate in the initial design, it is there to increase the fatigue life.

Given hard analysis, does it in fact increase fatigue life? Or is it the classic eyeball design beef-up, many of which may worsen or relocate the fatigue issue?

[sblack]

Originally Posted by DanH

Yes and no. A manufacturer is never required to do anything in AC43.13. On the contrary, AC 43.13 is an acceptable means of compliance only in the absence of manufacturer's guidance. Nothing in it can be substituted for manufacturer's guidance. From the seldom-read very first page:

This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no manufacturer repair or maintenance instructions.

Confirmation was direct from the top, FAA AFS-300 in DC, the office responsible

Totally agree. It is Advisory only. I don't see anything in your post that contradicts what I said.

As for a eyeball beefup, if you have a crack and stop drill it and put a patch on it as per 43.13, that's exactly what you will have, an eyeball beefup.

Anytime you beef up an area you are likely going to make some other area fail first. Rare is the structure where every single part fails simultaneously. But as long as all the parts stay within the static and fatigue load envelope you'll be ok.
Suggesting that putting this part on is going to weaken some other part of the airplane is pretty far fetched.

Now if Van comes out and tells you to do something different then that's another story.

[ChiefPilot]

Originally Posted by sblack

Now if Van comes out and tells you to do something different then that's another story.

That is exactly what happened with the horizontal stab, actually. Van says one thing, AntiSplat says "no, that's too complicated - here's another piece of SS to use instead".

[CATPart]

Originally Posted by DanH

Given hard analysis, does it in fact increase fatigue life? Or is it the classic eyeball design beef-up, many of which may worsen or relocate the fatigue issue?

I do fatigue analysis on aircraft structures for a living, primarily for repair work due to things like cracks and shop errors. Dan as usual you make valid points. Yes this is an eyeball design and all it is going to get is an eyeball analysis (from me anyway). I have no dog In this fight, just giving my objective observations. Looking at the damage picture earlier in this thread I think it is obvious that the root cause is as stated, the bracket was bearing on a sharp edge, probably with some misalignment preload caused by improper shimming, causing a crack initiation, further irritated by the typical flight loading. The crack did show up in the right spot from a load path perspective. I honestly don't like the design of the original vans bracket, from an installation perspective, because of the tolerance stackup involved, which leads to installation misalignments that are hard to overcome, especially for more novice types or know it all types of builders. Likewise, the splat bracket is pre-bent and again you are matching angles that are different on every aircraft, causing preload situations unless carefully dealt with. Also the new bracket is dependent upon frictional clamp up to remove loads from the original bracket. I'm not trying to give an answer, just raising the points that a room full of fatigue engineers might raise. There are other points to be made, but I will stop here for now.

As a note, good fatigue analysis requires sound experience, judgment, and often test data that helps quantify loads and unforeseen load paths. I make no claims that I have the experience or judgment to approve or disapprove the design. In my experience, the loads used to analyze a part are developed from a very involved process of instrumentation and test, and correlation of the them with an FEA model. (I mean, putting strain gauges on an aircraft or structures in a test rig, and then comparing the resulting strains with a finite element model). With that you can make more meaningful calculations of fatigue life.

[mr.sun]

So, if I have no cracks in my h/s and I install the ASA patch, AND keep flying the same minimal occasional aerobatics, have I made anything worse?

[LifeofReiley]

It is all Smoke and Mirrors. Leave everything alone.....

[ChiefPilot]

Originally Posted by mr.sun

So, if I have no cracks in my h/s and I install the ASA patch, AND keep flying the same minimal occasional aerobatics, have I made anything worse?

That's really what it comes down to. With the case of the ASA patch, nobody really knows since it's essentially a guess as to whether it actually mitigates a potential issue or simply moves a fatigue problem somewhere else.