Progress

[Alfred Scott]

The machining of the P/N 520 Gearbox Housing has been held up slightly by a rush of work for the machine shop caused by COVID-19. But it is due to start shortly, and I’m holding up a big FBL to be able to show this part, which will look like a piece of jewelry.

Plane crash yesterday in Middlesex County in a Bonanza but it was not Ed Fisher who owns a Bonanza and also a Falco built by Buzz Glade years ago. However Ed did have a nose gear collapse while landing at our Rosegill Farm airstrip. Repairs are now in progress. No injuries.

Lots to report.

Alfred

[Alfred Scott]

We are now in the process of machining the gearbox. There is a full description of the process on the website

05Parts1.jpg (141.37 KiB) Viewed 37184 times

http://www.seqair.com/skunkworks/Landin ... gGear.html

Alfred

[Dvale]

Alfred,

It was very interesting to see the photos and comment on the progress of the new gearbox's. So much so that I forwarded the link too my son who is a lead design engineer at APPH http://apph.com specialising in landing gear design. I am a medical scientist and not an engineer so I am fairly ignorant in this area but my son's comments were somewhat alarming and may need some explanation as I am sure there are logical reasons why he may have drawn the wrong inferences from the photos etc.
1.) T6 temper aluminium is a big no no! And not used by Apph and others due to it being highly susceptible to stress corrosion cracking!
2.) A drop hammer does not give it a T6 temper, that would be heat treatment.
3.) No shot peen!
4.) No sulphuric anodise.

I do not need a new gearbox, but if I did then I would like to feel comfortable that what I installed is not likely to give me a nasty surprise in a few years. I know it is in a fairly non-corrosion environment and therefore the corrosion aspects may be less significant but corrosion from condensation especially between different metals is still I guess possible. I would also guess that in the U.K. this may need LAA approval as the originals are I believe cast.

[Alfred Scott]

David,

That’s all just silly.

Of course, T6 is a heat treatment process. The part is in the dead soft annealed condition when poured as a casting, then work-hardened by the drop hammer. That’s what T6 means. 6061 is the aluminum alloy.

This is a gearbox housing that sits on the aft face of the main spar thus not subject to the elements. Strength and stress is hardly an issue. All this part does is provide location and support for the bearings which locate the shafts and gears in relation to each other.

For an important exterior structural component for the landing gear of a jet fighter you would use a different material.

Alfred

[Dvale]

I think the response was more of emotional quick response rather than reflection before answering. I do not want to get into a pissing contest but the photos and dialogue imply that a soft block of aluminium is taken in the first photo and then it has the shit beaten out of it to produce a T6 condition with no mentioning of annealment etc that is required in the process.

The taking of the corrosion aspect as compared to jet fighters is somewhat extreme. The same principles of material selection are also used for civilian whether they are commercial or not, and even applied to small UAV's operating on aspirated Lycoming powered at low altitude. Corrosion from condensation is evident in internal structures. In flight even flying at altitudes of 5000 ft in cold air for an hour and then descending to lower altitude can easily produce condensation. We are not all fortunate to live in regions of predominately low humidity. In addition an aircraft lives most of its life in a hangar if it's lucky. I cannot believe even those living in a low humidity have never experienced a cold hangar with a warm front producing condensation. It's a very regular occurrence to those of us not so fortunate.

As for its strength, I am sure this is more than totally adequate for its purpose in everyday use but there are numerous examples of condensation corrosion causing stress fractures and then causing catastrophic failures. Take note, Falco's endure and have lifespans somewhat more than the average microlight, let's keep it that way. Both Piper and Cessna are not immune to the problem of internal T6 conditioned aluminium and condensation corrosion.