What the heck are Blow Out Doors? 14

[cmarinelli]

Hello everyone,

I'm reverse engineering a latch that is used on a "blow out" door of a turbine engine thrust reverser. I like to know exactly what the part's function is, but I'm stumped here. What exactly is the function of this blow out door? Does it simply alleviate an overpressure in the nacelle? Does it operate only in flight, or during thrust reverser actuation? I believe it is located aft of the thrust reverser air stream which makes me believe it is really intended to operate during flight.

Any ideas on this?

Thanks in Advance,
Chris Marinelli
Dynatech Aerospace

 

[MintJulep]

Does this question scare the hell out of anyone else?

 

[Kenneth]

(To MintJulep)

Yes.

 

[monkeydog]

The question doesn't scare the hell out of me. The fact that someone is reverse engineering a component (most likely for a passenger aircraft) without knowing the function or design intent of the component.
This probably happens all the time.

 

[rb1957]

yeah, but is anyone going to be helpful ?

chris, i'd suggest that you start with the airplane's maintenance manual, it should describe the detail function of the door. failing that, possibly looking at the door and how it's attached to the plane will answer some questions ... if there're electrical sensors and systems around (prox. switches, actuators) it then there are going to be complex activation conditions; if there's just a simple mechanical system (a spring or an over-center mechanism) then there's probably only a very simple (over-pressure) activation.

good luck

 

[cmarinelli]

Gentlemen (except RB1957),

I apologize for not being born with an innate knowledge of all aircraft systems. We typically work on turbine engine components, but are branching out into other areas and trying to LEARN before we start Reverse Engineering. We've asked our airline contacts and haven't gotten a thoughtful response.

We don't make anything without thorough knowledge and complete testing of every component. We partner with companies that have expertise in particular types of components. I'm just trying to get a better understanding of the function of a blow out door other than the obvious.

I have looked at the location and operation of the component, and it has no sensors, actuators, or switches, merely a cable that limits the door opening. We are looking at one of the latches that has a definite break-away torque required to open the door provided by a cam/detent and spring loaded roller.

If you have something positive to add, please do. If you only have negative comments, please keep it to yourself so as not to stunt free and open discussion.

Chris Marinelli

 

[patprimmer]

I think that questioning the ability of someone designing aircraft components and asking dubious questions is very constructive.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MintJulep]

We don't make anything without thorough knowledge and complete testing of every component

Where does that "through knowledge" come from? Internet forums? The airlines? The people who KNOW what this component does are the good people at GE, or Rolls Royce, or Pratt and Whittney that designed the engine.

How do you test a part if you don't know what it does or how it is supposed to perform? Besides, "testing" proves nothing. The Pinto was "tested", it still exploded if you ran into the back end because nobody ever though to test that particular situation.

Counterfiet aircraft components are a real problem. Airplanes crash because of them.

I'm still scared.

Is that positive enough for you?

 

[rb1957]

chris,

i'd try to get the component (airplane or engine) manufacturer's open source information (maintenance manuals in particular). i suspect that the flap needs to be rigged in some way to control the opening pressure.

but it sounds like the flap is a simple mechnaical system (a simple input (over-pressure) and a simple response (opening the valve).

as to the other posters ... let them vent, it is their prerogative

good luck

 

[monkeydog]

So, why don't you go to the manufacturer and ask them?

 

[rb1957]

just a thought, but i'd think that the manufacturer isn't going to reveal their hard earned technical data (secrets?) to someone planning on competing against them in the markerplace for replacement parts.

 

[MintJulep]

Unapproved Part definition: A part, component, or material that has not been manufactured in accordance with the approval procedures in FAR § 21.305 or repaired in accordance with FAR Part 43; that may not conform to an approved type design; or may not conform to established industry or U.S. specifications (standard parts). Such unapproved parts may not be installed on a type certificated product, unless a determination of airworthiness can otherwise be made.

http://www.asy.faa.gov/safety_products/unapprovedparts.htm

http://www.faa.gov/avr/sups/standard.cfm

 

[rb1957]

MintJulep,

consider the possibility that this is a part manufactured under a PMA. the intention doesn't have to be misrepresentative or "counterfeit"; there are legitimate ways to manufacture approved parts.

 

[Drej]

> If you have something positive to add, please do. If you only have negative comments, please keep it to yourself so as not to stunt free and open discussion.

Don't agree.

Chris - this is a forum, where every opinion - negative or otherwise - counts for something and is encouraged. As long as it is relevant to the question it shouldn't matter. If what you're saying was true, then we would be saying to all of those junior/other engineers out there: "Oh, that's fine just go ahead and build your proposed design. I won't check it because I don't want to point out the negative aspects of your work." How many aircraft would fall out of the sky if we couldn't point of people's design shortcomings? Lots. Engineering is a critical business, if you don't like negative comments you should be in another industry.

Cheers,

-- drej --


------------
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[MintJulep]

rb1957,

I recognize that there are methods to gain approval of parts.

The original poster has provided no indication that he has such approval, or is even aware that approval processes exist.

 

[WKTaylor]

cmarinelli

Recommend You get a copy of MIL-HDBK-115 “Reverse Engineering”. I think there is also a book with roughly the same title available thru bookstores. I found this document discusses many practical topics/issues/questions that might help You thru the initial engineering process leading to FAA certification.

Also recommend checking the FAA Advisory Circulars at the following website and searching on key-words “parts” and "certification” for appropriate documents relative to FAA certification issues.

http://www.airweb.faa.gov/Regulator...rgAdvisoryCircular.nsf/MainFrame?OpenFrameSet

NOTE: I am assuming that this is for a civilian aircraft… otherwise military “certification” issues would likely be identified in appropriate “JSSG xxxxx” documents.

For the rest of You Guys... MintJulip ... soap-box time…

My favorite intro line(s) for many of the topics I’ve needed to discuss with experts [scientists, engineers, technicians, mechanics, nurses, lawyers, secretaries, waitresses, gardeners… whoever…”] has been:

"I have a dumb question for you"
or
"I need to ask You a (few) REALLY dumb question(s)".

Most folks tend to hear what I am asking [next] in a more-positive/relaxed way… ‘cause I am really saying: “help me understand this so I can be informed/guided by Your experiences”.

If cmarinelli was a student “doing a homework problem”, or a non-engineer asking an “engineering 101” question, then I’d say “red-flag him and good riddance”.

HOWEVER, DO NOT denigrate a fellow engineer asking a “dumb question” like this. He appears to be a sincere, competent engineer asking a “dumb question” because he has a REAL need to understand what the function of a cowling blow-out door is, and any subsequent implications, so he can deal with it and do the assigned work, FAST. He may eventually realize it is too complex/subjective a topic and NOT worth pursuing… he but also he might gain appropriate insight and excel at this tasking.

I have been stuck in some pretty awkward positions [“challenges”] in my +26-yr career… and have had to dig to the root of a topic [problem] FAST to be effective. In doing so I have asked a pile of direct “dumb” questions and been given a gold-mine of understanding in return. OK, I try to do my homework in advance… but that has [undoubtedly] left me realizing what I really DO NOT know about the topic. That’s when I have turned to others asking “dumb questions”.

What amazes me about aero engineering is the relatively vast sum of knowledge out there that is NOT easily accessible or documented… but is available, IF You just know where to look. Getting a peek at a wide/unique variety of topics, thru the eyes of others, has been an invaluable starting point, and on-going practical training, for me.

As for taking on an engineering task in unfamiliar territory... as an old/famous [departed] aero engineer loved to say, when asked why he risked his career/fortune by designing a popular homebuilt aircraft... “A turtle only makes progress when it’s neck is stuck out”.


Regards, Wil Taylor

 

[MintJulep]

Ok, my turn on the soap box.

Counterfeit parts are a real and serious issue. That is why the FAA has an entire department dedicated to the subject.

Aircraft in flight are intolerant of engine failure. There have been two recent crashes with fatailites in the New York City area that both appear to have engine failure as the initiating event in the crash.

The original poster may very well be a sincere and competent engineer, and the company that he purports to work for does actually appear to be a legitimate aerospace firm. However, his responses to being challenged have not convineced me that he is aware of the existing requirements and processes for what he is attempting to do.

Furthermore, asking a "dumb question" on a topic with potential life-safety and legal implications in a public forum such as this does not serve the interests of the industry well. If the poster is legitimate it certainly seems that he should have a better network of contacts to pose questions to than anynomous names on an internet forum.

Taking risks is easy when it's not your neck that is sticking out.

 

[FredGarvin]

"Counterfeit parts are a real and serious issue."
This is true.

"Aircraft in flight are intolerant of engine failure."
This is not necessarily true. There are many situations where in flight shut downs occur safely.

"Furthermore, asking a "dumb question" on a topic with potential life-safety and legal implications in a public forum such as this does not serve the interests of the industry well. "
The OP was in reference to reverse engineering A LATCH on a cowling door. I think you are a bit on the melodramatic side here. The OP was not looking to redesign the cowling or the door itself. If anything I think he is doing right by trying to understand the environment that the latch is operating in.

"However, his responses to being challenged have not convineced me that he is aware of the existing requirements and processes for what he is attempting to do."
I would assume that you are refering to his management and quality reps as well who also shoulder that burden.

"Besides, "testing" proves nothing."
That has got to be the most asinine statement I have ever heard. Bad or improper testing proves nothing. Testing is one of the most important things that can be done to assure safety and proper operation.

 

[Sparweb]

Mr. Marinelli seems to have been given a very narrowly defined problem. Looking for the bigger picture was the right move, but he could have phrased the question better, and shouldn't have published the company name on his post. I think he's subsequently made himself clear and we can now get on with the answer.

Firstly, which kind of TR is this stuff for?

or

Since you're branching out into new areas, you could try visiting your "airline contacts" to visit their facilities and see the aircraft for yourself, on the ramp, in the shop, and in pieces on the table.



Steven Fahey, CET

 

[cmarinelli]

I must say I regret asking a question and starting this thread.

Thanks to rb1957, wktaylor, FredGarvin, and SparWeb for understanding why I might ask such a question.

My company has obtained many dozens of FAA-PMA's, and are mindful of FAA regulations governing certification of the same (Order 8110.42A, FAR 21.303, etc.). Our ACO has commended us on the professionalism and thoroughness of our PMA applications. We take flight safety very seriously, and know that lives potentially hang in the balance. Although PMA's may not be held in high regard, there are some out there that are doing what they're supposed to. It is up to the FAA to make sure everyone meets the same standard.

We use MIL-HDBK-115 as a template for our reverse engineering methodology as well as our experience developing (via R.E.) dozens of parts for the US Army, supported by 150 hour engine tests. We scrutinize and document the reasoning behind every dimension, fit, finish or process and perform a failure mode and effects study on every part, no matter how simple.

For every certification project we perform a preliminary design review to evaluate the feasibility of pursuing a particular PMA. Wktaylor hit it on the head in that I was trying to quickly obtain insight into an area I am not familiar with.

SparWeb is correct in that I am only interested in a Latch with a spring loaded cam/detent overpressure configuration. It is on a CF6 translating cowl TR which may very well be the lower picture of SparWeb's post. It is essentially a spring-loaded roller attached to a small bracket that rides on a cam with a notch. The roller 'cams out' of the notch when sufficient torque is applied.

I've visited OH shops in AirCanada and SW, and am scheduling a visit to Lufthansa and possibly Delta. Unfortunately, it is difficult to get significant time in the shop as the technicians need to get their work done.

Thanks again to everyone for sharing their two cents.