Reverse Engineering

[drawoh]

I have just been looking at a job ad for an aviation supply/manufacturing service. One of their activities is the re-engineering of aircraft components to be manufactured and installed in aircraft.

How feasible and safe does this sound to people out there? I don't know how much information the re-engineer would have as they prepared the CAD model and the drawings. It would be nice to see the part in place, and understand how the rest of the aircraft interacts with it.

--
JHG

 

[rb1957]

it depends (!?).

It is very difficult to replicate an OEM part (what we call a PMA), 'cause you don't have OEM data.

It is however very easy to make a part similar enough to the original part that you can claim it has the same strength, etc. But now you identify the part with your own number, and use an STC (an LSTC is even easier) to put it on the plane.

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

rb1957... good advice!

drawoh... not to scare you, but to enlighten you..

Be very careful regarding materials and fab processes substitution! Use/specify similar raw stock as the original part when ever You can. Determine existing alloy/temper/finishes etc from whatever means/methods possible.

When an equivalent original raw-stock material, or finish or fab process does NOT exist... IE: sheet/plate, extrusion, casting die, forging, etc... then You start getting into a mine field very quickly.

NOTE.
FAA AC43-18 Fabrication of Aircraft Parts by Maintenance Personnel attempts to define in 'FAA-eze' just how critical spare/repair parts fabrication is... and limits parts fabrication to specifically trained mechanics with materials and processes knowledge. Airworthiness can be affected by a multitude of factors that are NOT obvious to all.

I do this type engineering on a daily so this is all old news to me**... but is really hard for non-materials oriented liaison and design engineers to grasp. MY BIG piece of advice is to work closely with a competent Materials and Fabrication Processes engineer at every stage of the reverse design process.

NOTE.
I constantly have mechanics who need to replace a 'casting'... when in-fact the part they have to replace is a highly loaded flight critical machined die forged fitting, shot-peened, anodized and drilled-reamed to match existing structure on installation. Grrrrrrrrrrr.

** my second job at my first aircraft factory was as a liaison engineer for the fabrication division... I got to work with 'gray-hair' M&P engineers who explained every phase of parts manufacturing and fab-processes... and specifically how strength, durability, corrosion resistance, distortion, embedded defect detection [NDI], heat treatments, finishes [mechanical and coatings], etc/etc, could affect airworthiness. The possible ways to screw-up something were dizzying to me.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[berkshire]

Drawoh,
I have a friend of mine who just got a PMA for a replacement set of pistons for a Warner Scarab radial engine. These were CNC machined out of bar stock because the original castings were NLA. It took him 18 months of tilting at windmills with the feds.
That stuff is not for the faint of heart. However if the company you are looking at does it for a living, they know what they are getting into. Are they working on STCs or do they just get PMA approval for existing parts?
B.E.

You are judged not by what you know, but by what you can do.

 

[drawoh]

berkshire,

The company works closely with some aircraft manufacturers. They specifically mention reverse engineering. This is as opposed to taking the manufacturer's drawings and specifications, and taking over the contracting process. All of WKTaylor's remarks kick in at this point.

I can inspect a part and take measurements accurately enough to work out nominal dimensions. If I know how the part works, I can sort out the accurate tolerances. Figuring out the exact material without the cooperation of the original manufacturer is a challenge. I have no experience with forgings. This could be very, very interesting, in the Chinese curse sense.

--
JHG

 

[rb1957]

You don't know as much as the OEM, drawing tolerance-wise; so you don't know where this part is in the OEM drwg tolerance band. So you could guess (use typical), or go very tight on the part you do have.

Finishes may be tricky to "know" so you can assume normal industry standards.

Material may not be as hard as you think. You can get close by weighing the part, if steel you can do a hardness test on it (to determine strength); you could cut tensile coupons from the part and test.

Forgings adds another level of complexity to the problem.

another day in paradise, or is paradise one day closer ?