One piece belly owner produced part?

[isaacpr7]

  On my last annual inspection it took me a few hours to take all the screws off the segmented belly. I started to do some research on the one piece belly but as I am sure all of you know it is very expensive. I was wondering if anyone has ever heard of a one piece belly made out of sheet metal. The fiberglass type adds about 10 lbs to the aircraft weight so I started to ask myself, is there anyone who has made an owner produced part out of sheet metal? I was thinking about overlaying some contractor's paper on the belly and drawing the outline as a template in order to transfer into a sheet metal piece. Does anyone know of this owner produced part being created in the past?

[Hank]

I thought owners could produce replacement parts, not new assemblies . . . Maybe I'm wrong, but I don't think that we as owners are empowered to do whatever we want with our non-Experimental aircraft.

Note that changing from several panels to just one requires different methods of support across the middle, and the number, size and placement of peripheral screws is different, too. The one-piece belly is an STC available through different companies at different prices, depending on material, number & size of screws/dzus fasteners.

[Sabremech]

You could make the original panels as an owner produced part, but going to a one piece belly will require you to buy one that is STC'd or do a field approval with your FSDO. Since they are available as an STC, I doubt any FSDO will do a field approval.

David

[Mooneymite]

Everytime I do an owner assisted annual, I am amazed at how many screws have to be removed for the inspections/lubrication and how inconvenient even the simple tasks are.

 

While I admire the thought that went into making a Mooney a great flying plane, apparently no one at Mooney ever thought the airplanes would be worked on by humans.

 

Good thing the hangar faries don't get aches and pains when they assume impossible positions to complete  the various routine tasks.

[isaacpr7]

I watched Mike Busch's video on owner produced parts and this is what I got from it:

 

Owners may produce parts on certified aircraft, so long as they are involved in the design and production process. They may not produce a part for sale to other aircraft. This is the video below. Maybe someone can watch it and help me interpret what I thought was right or wrong:

 

http://www.eaavideo.org/video.aspx?v=1105297993001

[isaacpr7]

I thought owners could produce replacement parts, not new assemblies . . . Maybe I'm wrong, but I don't think that we as owners are empowered to do whatever we want with our non-Experimental aircraft.

Note that changing from several panels to just one requires different methods of support across the middle, and the number, size and placement of peripheral screws is different, too. The one-piece belly is an STC available through different companies at different prices, depending on material, number & size of screws/dzus fasteners.

Hank,

 

I thought about the screws supporting the middle as well. What I was thinking was drilling holes in the exact location where the panels are supported but making these flush instead so that I could have less dragg.

[Hank]

Hank,

 

I thought about the screws supporting the middle as well. What I was thinking was drilling holes in the exact location where the panels are supported but making these flush instead so that I could have less dragg.

 

Going by memory, there are five small screws around the nose wheel well, and two to each side reaching the corner. Don't recall if the back has 4 or 5 across the width. There are many down each side, and I think three rows that go across the fuselage, "Y" shaped on each side [2 inside the outer perimeter, then two more in a straight line; there are four matching screws on the other side; there are three sets like this]. The total is 52 screws, I've counted them more than once. Seems that there are sheet metal supports hanging down for these rows of cross-wise screws, with ~½" flange for the screw. Somewhere I have a picture of the belly panel by itself, but it won't be off again until the end of the year for annual.

 

Since it came with the plane, I don't know if it's a factory part or not, but it's definitely fiberglass. You should price out Bill Wheat's carbon fiber belly with dzus fasteners if you think the fiberglass one is costly!

[Sabremech]

You can produce the exact part that is on your aircraft by having the drawings or reverse engineering and it must be equivalent or better than the original. It can't be different in the form you would like in a one piece belly panel. What you want to do is an alteration which will require a 337 Field approval or an STC.

I currently manufacture owner produced parts, FAA/PMA parts and hold an STC while currently working on 2 more STC projects. I'm familiar with the processes.

David

[isaacpr7]

You can produce the exact part that is on your aircraft by having the drawings or reverse engineering and it must be equivalent or better than the original. It can't be different in the form you would like in a one piece belly panel. What you want to do is an alteration which will require a 337 Field approval or an STC.

I currently manufacture owner produced parts, FAA/PMA parts and hold an STC while currently working on 2 more STC projects. I'm familiar with the processes.

David

David,

 

How possible do you think it would be for me to go through the process of obtaining a 337 for this type of alteration I am trying to do? Do you have any tips you could give me?

[Sabremech]

Hi Isaacpr7,

I think the chance of getting a field approval 337 is slim to none since there is at least one STC available for this. No FAA inspector is going to want to put their name on this field approval without a whole lot of data which will probably cost you more than buying the STC.

The best advice I can give is to either buy the STC or keep the panels you have and use the money to buy avgas.

Thanks,

David

[isaacpr7]

Hi Isaacpr7,

I think the chance of getting a field approval 337 is slim to none since there is at least one STC available for this. No FAA inspector is going to want to put their name on this field approval without a whole lot of data which will probably cost you more than buying the STC.

The best advice I can give is to either buy the STC or keep the panels you have and use the money to buy avgas.

Thanks,

David

David,

 

Thanks for the education. Sorry for the ignorance but, can you elaborate a bit more on the difference between a field approval and an STC? How do I buy or apply for an STC?

[jetdriven]

David,

Thanks for the education. Sorry for the ignorance but, can you elaborate a bit more on the difference between a field approval and an STC? How do I buy or apply for an STC?

An STC is a supplemental type certificate, basically a modification (Major Alteration) developed by someone who is then granted approval to sell this mod to others. The stc holder grants you a license to use the STC on your plane. They prove to the FAA that the mod is safe when installed and used per the directions. The STC data is considered "approved data". If you wish to pursue a 337 field approval you must basically do what an STC applicant did, which is supply acceptable data to the inspector who then approves your (Major alteration) mod. Basically a 337 Field Approval is a one-time STC for your own plane.

Minor alterations require no field approval. Minor and major alterations and repairs are spelled pretty clearly in the FARs but it is vague enough for some mechanics and IAs sometimes may call a minor alteration, a major alteration. IDK WRT a one-piece belly panel but it smells like a major alteration.

[Sabremech]

Byron described it well. Nothing for me to add.

David

[N601RX]

The belly has a compound curve which is probably why Mooney made it out of several pieces of aluminum instead of one. Another advantage of the 1pc is that it gives you access to the rear of the main spar and a few other areas anytime it is off.

[isaacpr7]

Once again, thank you all for the education. The only other question I have would be, how would I collect this data for submition to the FAA? Will I have to obtain approval to create and install the part so that I may test it in order to collect the data?

[jetdriven]

Vacuum bagging a mooney one piece belly panel from carbon fiber would be pretty easy. The real work is fitting all the rails and Camloc receptacles to mount it. We has one in the shop for a prebuy last month and I felt like a fool for not looking at the belly structure more closely to see how it was done. FWIW that 1977 M20J with a 9/7 P&I, 400 hour-8 year old overhaul, fiberglass belly, and 430W/KFC-200 combo sold for 74K. Shocking.

[Sabremech]

Hi Isaacpr7,

For a project like this, you'll most likely need to hire a DER (Designated Engineering Representative) who can help you determine if you want to proceed with this project and what his costs would be. Personally, this is a project I wouldn't pursue because there are already parts available (STC's) and I know It would cost more than buying an existing STC.

It would be an education for you and definitely lighten your wallet as well as trying your patience.

David

[carusoam]

I'm guessing engineering, designing, building and testing are expensive.

This type of work is required to keep from accidentally hurting somebody.

When you cut out the expensive part, what's left...sheet metal and fasteners?

Do you have sheet metal shop or machine shop experience?

Price of aluminum $1.12/lb

Price of aluminum assembled into a new Mooney approximately $200/lb

It would be a great project to model and build your ideas. You will want professional help prior to putting it on a plane and flying with it.

Having it become partially dislodged in flight could be disastrous!

Can you see the gravity of the idea?

Best regards,

-a-

[scottfromiowa]

Vacuum bagging a mooney one piece belly panel from carbon fiber would be pretty easy. The real work is fitting all the rails and Camloc receptacles to mount it. We has one in the shop for a prebuy last month and I felt like a fool for not looking at the belly structure more closely to see how it was done. FWIW that 1977 M20J with a 9/7 P&I, 400 hour-8 year old overhaul, fiberglass belly, and 430W/KFC-200 combo sold for 74K. Shocking.

Good grief...I wish I was buying now...what a great deal!

[isaacpr7]

I'm guessing engineering, designing, building and testing are expensive.

This type of work is required to keep from accidentally hurting somebody.

When you cut out the expensive part, what's left...sheet metal and fasteners?

Do you have sheet metal shop or machine shop experience?

Price of aluminum $1.12/lb

Price of aluminum assembled into a new Mooney approximately $200/lb

It would be a great project to model and build your ideas. You will want professional help prior to putting it on a plane and flying with it.

Having it become partially dislodged in flight could be disastrous!

Can you see the gravity of the idea?

Best regards,

-a-

carusoam,

 

I don't have a machine shop or experience; however, my MX does but he has never produced a part and was not much help when I asked about the process. You guys have been awesome at answering all my questions and giving me a lot to think about. Thanks.

[Marauder]

Isaac - I hope everyone didn't discourage you, but the reality it is easier to land a man on on the moon than it would be for you to gain the experience and knowledge to navigate the STC/PMA gauntlet. It is a regulated environment with a ton of requirements. If the new proposed law is enacted, perhaps there would be more flexibility in what can be installed on our planes.

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[KSMooniac]

If you're still interested in pursuing such a project, you can call up your local FAA Aircraft Certification Office and ask for an appointment to talk with one of their engineers or project managers.  To date, I don't believe anyone has made an STC'd one-piece belly out of aluminum, so you would very likely be breaking new ground and thus they might "have" to listen to you vs. telling you to go buy one already STC'd.  It used to be that a person/company could submit designs and analysis to prove them directly to the FAA for approval, but nowadays it is common for the FAA to just tell the applicant to go hire a DER to get them approved, which really sucks.  You'll find DER's will cost $100/hr or more for their services.

 

Before you do that, use google and learn all about the steps to go through the STC process, and later, the production approval process leading to PMA approval to actually fabricate the parts.  There is plenty of info out there.

 

in this particular case, the belly panels are not structural per se, so that removes a LOT of the burden in substantiating the engineering design for the new part.  You could show equivalent strength for the attachment design compared to the original configuration, and the FAA might buy that.  It also doesn't affect the handling or control of the plane, so there would be little to prove in that arena as well.  Thus it would be one of the easier STC's to obtain, compared to something like a new nose gear truss like LASAR developed long ago, or a replacement aileron.

 

It is possible, certainly, but it will require a lot of time and effort, even if you just want to make one for yourself.  If you do it, it would make sense to plan to sell them to others.  

[carusoam]

It may be helpful to know/understand why Mooney made it out of several smaller pieces originally.

1) What has changed (sheet metal technology) to allow making it out of one piece?

2) what can be improved (fastener technology) to make removal and replacement better?

3) is there an aerodynamic reason for going to one piece?

I went with new stainless hardware and a powered screw driver. Two new technologies that were not available in 1965...?

Best regards,

-a-

[KSMooniac]

With a big enough press, an aluminum version could be formed easily enough, but would still need some additional internal structure to make it viable where as the carbon fiber or fiberglass versions might not.  Of course the tooling costs for a 1-pc aluminum would be too high to justify, and few of us have access to a press either.  I bet one could be designed, however, and built from smaller pieces of aluminum and assembled into a big piece that replicates the easy access of the later model designs.

 

I've never read any claims that the factory 1-pc belly improves anything aerodynamically...just makes for easier maintenance.

[OR75]

why is the segmented belly such a pain to take off and put back ?

because over time, mechanics just force in whatever will keep the panels in: machine screws, sheet metal screws, tinnermans, oversize the screw , who cares, just need to close the panels as quickly as possible !

find a long weekend to take off the panels , clean them well and put the right screws, tinnermans, etc ... as per the parts catalog .... do not over tighten , snug is all you need.

the next time you have to take the panels, it will be a breeze. just make sure you tell the mechanic you want the panels put back as they should be.

personally , i had rather putt them back in myself.