600115-005 intake duct

[Shadrach]

8 hours ago, cliffy said:

Just a thought -

Has anyone assessed the deflection with impact ice on the inlet air filter thereby lowering the pressure inside the duct due to this ice restriction to air flow ahead of the duct? Both the C and E model ducts (they are different)  could/would be susceptible to this event.  

Failure analysis probably should include this possibility/probability.

As a long time A&P I would still have to fall back on "what is the approved data that was referenced to make this part", before I would consider installing same and signing it off. 

Don't take this wrong, no disrespect meant but-     How many here promoting the making of this part through OPP in a way that is "different " than the original (even if better than original)- How many of you actually hold an A&P and would sign your name to the log  book? That is a true test.

Also remember each owner who "designs" an OPP part shall sign HIS name to the log book signifying that he was the one who participated in the design.

BUT ultimately it comes down to an A&P being willing to put this part on the airplane; 

The question remains - How do you get around the "approved data" requirement in OPP?

A challenge-

Someone needs to go the their local FSDO and present this idea and ask about its legality rather than just guess as is being done here. That's what they are there for. 

Why waste your time if its not going to fly. 

 

 

I’ll speak for myself only.  I supported making an OPP part to the exact dimensions of the OEM duct out of equal or better material. When it was mentioned that McFarlane is seeking PMAs to add to their portfolio, I suggested that improved design and materials would be welcomed. Aeromotors has made a number of design changes and material improvements to the Dukes pumps under a repair station certificate, surely a company like McFarlane could refine the current design.

[N201MKTurbo]

Everybody keeps talking about making it out of better material. It seems the material they have been made out of holds up pretty well. 
 

The easiest way to get a PMA would be to build an exact duplicate of the current design using the current material. The PMA process specifically allows that.

[MikeOH]

30 minutes ago, N201MKTurbo said:

Everybody keeps talking about making it out of better material. It seems the material they have been made out of holds up pretty well. 
 

The easiest way to get a PMA would be to build an exact duplicate of the current design using the current material. The PMA process specifically allows that.

EXACTLY!

If I were to undertake this, I would be analyzing the material and construction, documenting that, and producing as close to an identical duplicate to the original as I possibly could.

[Shadrach]

9 hours ago, MikeOH said:

EXACTLY!

If I were to undertake this, I would be analyzing the material and construction, documenting that, and producing as close to an identical duplicate to the original as I possibly could.

In my experience, these ducts are susceptible to both age and use.  I am on my 4th in 22 years and 1600hrs. If that qualifies as robust, our standards are quite different. It could be that more short hops wear it out faster as I think startup and shutdown are hardest on the duct. By the time a failure is externally obvious, there’s a good chance it’s been sucking unfiltered air for a while. Do you decowl your plane and inspect before each flight?
 

There are lots of things we did really well in the sixty’s, wood fabrication, metallurgy and machining to name a few. However, in the case of precision made, lightweight, flexible ducting, design and materials have come a long way.

[EricJ]

14 hours ago, Allen_D said:

@EricJ

If we can establish that the new part is at least as strong as the original – and even stronger – it should inherently be capable of withstanding conditions such as a backfire. The aim is to not just meet but surpass the standards set by the original design.

Absolutely.    Just thinking of ways to demonstrate that it meets or exceeds the expected performance.   Without a "new" copy of the existing design to compare against (perhaps even destructively), it's going to be somewhat of an exercise to figure out what's "good enough" to do that.

 

[cliffy]

 

14 hours ago, Allen_D said:

Recognizing the legitimate concern surrounding A&P sign-off, the local FSDO is conveniently located less than a quarter mile from my hangar. I plan to seek their advice once I have a tangible prototype. Their endorsement could prove influential in persuading any hesitant A&P.

BINGO!!!! Problem Solved!!!

[cliffy]

19 hours ago, EricJ said:

I was entertained to discover, in the words of the FAA guy making the presentation I attended, that the whole purpose of VARMA is to educate IAs that keep making people remove stuff from airplanes that is actually okay to be there.   VARMA is essentially just a mechanism by which the FAA can provide an official letter for an owner's records saying, "Yes, that starter relay that he bought at NAPA is perfectly legitimate to be installed on this particular aircraft", so that some future IA won't make them take it off.

I attended the same VARMA webinar. BTW  It seems to me that VARMA is a path to "replace" approved parts with other than approved parts on a like for like basis and not to "manufacture" a different part altogether.  And for "non-important" parts much like NORSEE approvals  As was the battery relay shown in the program. 

[N201MKTurbo]

32 minutes ago, cliffy said:

I attended the same VARMA webinar. BTW  It seems to me that VARMA is a path to "replace" approved parts with other than approved parts on a like for like basis and not to "manufacture" a different part altogether.  And for "non-important" parts much like NORSEE approvals  As was the battery relay shown in the program. 

My impression of VARMA is summed up by:

If you know that the voltage regulator on the old Piper is a DELCO model 1XXX, it is OK to use the DELCO 1XXX from the auto parts store. The same with fan belts and wheel bearings. It has nothing to do with manufacturing new parts.

[N201MKTurbo]

3 hours ago, Shadrach said:

In my experience, these ducts are susceptible to both age and use.  I am on my 4th in 22 years and 1600hrs. If that qualifies as robust, our standards are quite different. It could be that more short hops wear it out faster as I think startup and shutdown are hardest on the duct. By the time a failure is externally obvious, there’s a good chance it’s been sucking unfiltered air for a while. Do you decowl your plane and inspect before each flight?
 

There are lots of things we did really well in the sixty’s, wood fabrication, metallurgy and machining to name a few. However, in the case of precision made, lightweight, flexible ducting, design and materials have come a long way.

It reminds me of a seminar I attended about fuel tank bladders. 

The presenter ran a company that makes bladders, mostly for twin Cessna's. He told the history of fuel bladders and how they were invented during WWII. They were originally made from cotton reinforced butyl rubber. During the 80s they changed to more modern materials, mostly polyurethanes. After about 10 years in service, the urethanes got brittle and fell apart. They tried a few other materials with similar results. He said that today all bladders are made from cotton reinforced butyl rubber. 

[MikeOH]

5 hours ago, Shadrach said:

In my experience, these ducts are susceptible to both age and use.  I am on my 4th in 22 years and 1600hrs. If that qualifies as robust, our standards are quite different. It could be that more short hops wear it out faster as I think startup and shutdown are hardest on the duct. By the time a failure is externally obvious, there’s a good chance it’s been sucking unfiltered air for a while. Do you decowl your plane and inspect before each flight?

Well, based on your experience let's call it a five year life.  So, how long does a battery last?  Seems like about 5 years and, these days, it's a $500 problem.  I paid $600 for my new intake duct; if it was few hundred why would that life be so unacceptable?  For myself, I've owned for 6 years and am now on my first replacement.  No idea how long the old one was in the plane but it wasn't in horrible condition; just a couple of small tears in the pleats.  And, yes, I inspect the duct every oil change.

Sure, we'd all like parts that last forever but I'm not convinced 'miracle' new materials will dramatically increase life.  And, absent convincing life testing data I'm not just ready to accept the 'argument' that new materials are better for this application.  Refer to the example above with the fuel bladder material change.

I usually have an open minded attitude to parts substitution when the application is not critical.  E.g. the starter relay...the NAPA part fails and you can't start the plane; not gonna kill you.  A new design intake duct collapses or folds over and blocks the engine intake...no thanks!

Valid test data, especially meaningful life testing, is NOT easily obtained.  This intake is now very hard to get and expensive.  I'm just cautioning not to get recklessly excited over an available, presumably lower cost, alternate without sufficient convincing evidence that it is really an equivalent or better part.

[Shadrach]

7 hours ago, MikeOH said:

Well, based on your experience let's call it a five year life.  So, how long does a battery last?  Seems like about 5 years and, these days, it's a $500 problem.  I paid $600 for my new intake duct; if it was few hundred why would that life be so unacceptable?  For myself, I've owned for 6 years and am now on my first replacement.  No idea how long the old one was in the plane but it wasn't in horrible condition; just a couple of small tears in the pleats.  And, yes, I inspect the duct every oil change.

Sure, we'd all like parts that last forever but I'm not convinced 'miracle' new materials will dramatically increase life.  And, absent convincing life testing data I'm not just ready to accept the 'argument' that new materials are better for this application.  Refer to the example above with the fuel bladder material change.

I usually have an open minded attitude to parts substitution when the application is not critical.  E.g. the starter relay...the NAPA part fails and you can't start the plane; not gonna kill you.  A new design intake duct collapses or folds over and blocks the engine intake...no thanks!

Valid test data, especially meaningful life testing, is NOT easily obtained.  This intake is now very hard to get and expensive.  I'm just cautioning not to get recklessly excited over an available, presumably lower cost, alternate without sufficient convincing evidence that it is really an equivalent or better part.

You've done an excellent job of articulating your position. You keep talking about a collapse that chokes the engine to failure.  In the history of the fleet, there has been one incident of a hastily repaired duct that resulted in an engine failure. I have not seen the failed unit but given my experience with the duct, I would bet that the engine failure was very likely caused by whatever materials were used in the lousy repair being sucked into the torn intake and creating an immediate blockage and or pressure drop that may have collapsed the whole mess. The failure would have likely never happened had the duct been left alone...even if it was a torn mess. 

Have you ever replaced one? I am sure there are folks that are faster and more competent than me, but it's kind of a PITA to R&R. You either drop the cowl or finesse your way around the exhaust and intake tubes. 10 bolts in close quarters 4 of which need to be safety wired.  Is it a big deal? no...would I rather not have to replace it every 5 years, you betcha.  Aviation maintenance expenses come in many forms. The big ticket items...I have one engine overhaul, one engine IRAN, a case OH and 3 prop overhauls under my belt (just off the top of my head). And the smaller items...I have 3 generators, two starters, an oil cooler OH,  a new prop governor. Several vacuum pumps, mag OHs, tank repairs, instrument OHs, exhaust OH, gear blocks, shock discs, tires, brakes, etc...etc.  It's the "death of 1000 cuts" analogy. I have not tallied the outlay for "small" expenses over the last few decades, I don't really want to know, but I can say with certainty that it's enough to want to minimize a "cut" when I can.

[cliffy]

On 2/8/2024 at 1:02 PM, Shadrach said:

 

http://www.velocolutions.com/FAA-owner-manufactured-part.pdf

There seems to be a disconnect between an OPP part FOR A PARTICULAR AIRPLANE ((by N number) which is what the OPP regs allow and having an owner design and build a part per OPP AND THEN OFFER IT TO THE PUBLIC for sale.

Any owner can make HIS OWN part but he can't then go out and sell it to the general public even if he designed it and qualified it for his own airplane by OPP. 

The above referenced article is clear on that subject. 

The problem remains - How are you going to get the part available to those who need it  without either an STC or a PMA.?  There is a way but I'll leave it there. 

[MikeOH]

1 hour ago, Aviationist said:

It seems Mr “oh” is not really capable of considering anything other than a specific thing he is fixated on at the time. In my short time here I've seen this from him many times, most notably in the ADSB thread and this one. 
 

I

Why should I need to focus on more than one specific thing….when that one thing can end up causing an engine failure?

 I’m also unimpressed with the argument that the old design has had but one known catastrophic failure. Uh, that’s my point: we’ve got zero data on the new design. So how, exactly, is pointing out how the old part is reliable means anything regarding a new part.

 The animus towards my point just seems like you all are looking for excuses to bury any criticism so you can feel good about embracing a new shiny object with blind confidence because, hey, it’s made of ‘new materials’ so it’s just better! And, with zero data! Maybe that’s the new Boeing standard for engineering?

[Shadrach]

4 hours ago, cliffy said:

There seems to be a disconnect between an OPP part FOR A PARTICULAR AIRPLANE ((by N number) which is what the OPP regs allow and having an owner design and build a part per OPP AND THEN OFFER IT TO THE PUBLIC for sale.

Any owner can make HIS OWN part but he can't then go out and sell it to the general public even if he designed it and qualified it for his own airplane by OPP. 

The above referenced article is clear on that subject. 

The problem remains - How are you going to get the part available to those who need it  without either an STC or a PMA.?  There is a way but I'll leave it there. 

There’s no disconnect at all. Sending my old boot to someone that I know to have expertise in the fabrication of custom rubber ducts is no different then sending a part to a machine shop for duplicatation.

[Shadrach]

This thread is starting to take a turn for the silly. No one here is obligated to use an OPP. No one here is required to sign off on any OPP. There is lots of guidance on this issue. It’s a free country and no one is forcing anyone to participate in the process.

[lithium366]

6 hours ago, Shadrach said:

You've done an excellent job of articulating your position. You keep talking about a collapse that chokes the engine to failure.  In the history of the fleet, there has been one incident of a hastily repaired duct that resulted in an engine failure. I have not seen the failed unit but given my experience with the duct, I would supposition is that the engine failure was very likely caused by whatever materials were used in the lousy repair being sucked into the torn intake and creating an immediate blockage and or pressure drop that may have collapsed the whole mess. The failure would have likely never happened had the duct been left alone...even if it was a torn mess. 

Have you ever replaced one? I am sure there are folks that are faster and more competent than me, but it's kind of a PITA to R&R. You either drop the cowl or finesse your way around the exhaust and intake tubes. 10 bolts in close quarters 4 of which need to be safety wired.  Is it a big deal? no...would I rather not have to replace it every 5 years, you betcha.  Aviation maintenance expenses come in many forms. The big ticket items...I have one engine overhaul, one engine IRAN, a case OH and 3 prop overhauls under my belt (just off the top of my head). And the smaller items...I have 3 generators, two starters, an oil cooler OH,  a new prop governor. Several vacuum pumps, mag OHs, tank repairs, instrument OHs, exhaust OH, gear blocks, shock discs, tires, brakes, etc...etc.  It's the "death of 1000 cuts" analogy. I have not tallied the outlay for "small" expenses over the last few decades, I don't really want to know, but I can say with certainty that it's enough to want to minimize a "cut" when I can.

I don’t get why it is ok to leave 6 remaining bolts without safety wiring at the cowling side. Is it like - if it does not fall off then it is acceptable?

[MikeOH]

50 minutes ago, Aviationist said:

some people should not fly airplanes. Judging from what I have seen in this group, you are one of the most short sighted, arrogant, unimaginative people I’ve come across on the internet, and unless your online persona is some sort of game or joke, you are absolutely one of those people. 

WOW! A tirade of personal insults is your idea of a cogent argument to my concerns??

I've been civil and have presented reasonable concerns that are certainly open to debate.  Not sure where your anger is coming from.  I have in no way indicated I want @Allen_D to stop what he's doing in developing a replacement.  I, too, would benefit from a low cost alternate. Perhaps as soon as 5 years based on @Shadrachs experience.

[Shadrach]

25 minutes ago, lithium366 said:

I don’t get why it is ok to leave 6 remaining bolts without safety wiring at the cowling side. Is it like - if it does not fall off then it is acceptable?

Nor do I. It may be something as simple as a general requirement that all servo hardware be safetied?

[DCarlton]

Since this thread has gone on for so long, could some of the experienced mechanics please explain how other aircraft manufacturers have solved this intake duct design problem?  Are all the designs similar using similar materials?  It’s a tough problem; it seems reasonable to brainstorm all the possible failure modes.  

[Shadrach]

 

8 hours ago, DCarlton said:

Since this thread has gone on for so long, could some of the experienced mechanics please explain how other aircraft manufacturers have solved this intake duct design problem?  Are all the designs similar using similar materials?  It’s a tough problem; it seems reasonable to brainstorm all the possible failure modes.  

Most of the manufacturers use some sort of flexible boot/coupler. Hyper Cherokees have a somewhat larger rubber accordion style made of a similar material to the Mooney’s. Some Cessna  utilize what looks like a thin silicone material reinforced with fabric. None of them are squeezed in to as tight of a space the E/F model. Some twin Cessnas use round silicone duct IIRC.

[cliffy]

I wonder it the original manufacturer of the C and E ducts is still in business?

I further wonder if they are in a position to help with an OPP order (best solution) much

 like McFarand does with throttle cables?

They may have an exclusive deal with Mooney but if Mooney is not interested in supplying the part

and because the follow on business is now in reality a dead issue that company might be wiling to

break any deal with Mooney

[Shadrach]

9 minutes ago, cliffy said:

I wonder it the original manufacturer of the C and E ducts is still in business?

I further wonder if they are in a position to help with an OPP order (best solution) much

 like McFarand does with throttle cables?

They may have an exclusive deal with Mooney but if Mooney is not interested in supplying the part

and because the follow on business is now in reality a dead issue that company might be wiling to

break any deal with Mooney

Hat tip to Clarence for the info…

https://www.thermoid.com/wp-content/uploads/AERODUCT-Aviation-Ducting-and-Hose-Products-Catalog.pdf
 

[EricJ]

10 hours ago, DCarlton said:

Since this thread has gone on for so long, could some of the experienced mechanics please explain how other aircraft manufacturers have solved this intake duct design problem?  Are all the designs similar using similar materials?  It’s a tough problem; it seems reasonable to brainstorm all the possible failure modes.  

On a J model, and many airplanes, the inlet is not part of the cowl but is open to the cooling inlet for the engine.   This means it can move with the engine and is isolated from the cowl, so it doesnt' need any kind of accordion duct.    The accordion ducts are a pre-J model problem. 

[DCarlton]

45 minutes ago, EricJ said:

On a J model, and many airplanes, the inlet is not part of the cowl but is open to the cooling inlet for the engine.   This means it can move with the engine and is isolated from the cowl, so it doesnt' need any kind of accordion duct.    The accordion ducts are a pre-J model problem. 

That would be the practical way to do it.  I’d like to take a look at a J if I get a chance.  

[EricJ]

1 hour ago, DCarlton said:

That would be the practical way to do it.  I’d like to take a look at a J if I get a chance.  

You can see the air filter here just in front of the #2 cylinder.   The air box can be seen behind it and going down below the starter to where the fuel servo intake is.   I have some foil tape on the the cover from the ram air delete kit where that air used to come in.