Bottom Cowl on BC12D

[Robert G. Hamm]

I have a totally messed up bottom cowl on my BC12D. The lovers seem to be backwards to me. They are formed inwards with the cut up forward. Can someone send me a picture or tell me how they are supposed to be?

[Robert Lees]

Re: Bottom Cowl on BC12D

I've seen lots of varieties on bottom cowls on BC12D models, and to be honest, I don't know what is the "correct" version.

If the photo below helps, this is what I have on mine.



It's difficult to show the louvres...perhaps the attachment below helps...just imagine the firewall 18" above the carpet.

[Robert G. Hamm]

Re: Bottom Cowl on BC12D

Thanks. Maybe my louvers are correct. Super looking sheet metal work.

Bob

[Hank Jarrett]

Re: Bottom Cowl on BC12D

Kripes Robert, If my cowl looked that good my wife would want it for a coffee table!
Hank

[Robert G. Hamm]

Re: Bottom Cowl on BC12D

Mine has patches on top of patches. The last ones are made of steal plate to stop the crack in the first patch. Hope the new one turns out something like Robert’s.

Bob

[Larry Lyons]

Re: Bottom Cowl on BC12D

We are in the process of making new cowl and hood for the long mount for Tims 46 Rob. Hope ours look as good as yours when done. L

[Hank Jarrett]

Re: Bottom Cowl on BC12D

I am going to need to make new top cowls for the 41 (I HATE those cowl bumps for the long plugs). What are you using to make yours? Do you have drawings or are you just using the old ones as a sample? My old ones are pretty bad. They fit terrible and have a couple of piano hinge in the middle. I have managed to make a nice set of front and rear hinge ends and a nice set of the inter-curled hinges (there MUST be a name for those "wound into each other" hinges), but I need to start thinking about making the flat sheet metal parts and the stiffeners.

For anyone interested, DO NOT think about trying to make those goofy hinges! They were a RIDICULOUS amount of work and I am lucky to still have ten fingers. If you don't get them PERFECTLY straight and shaped "just right" they jam and tear apart. Another of those little things that are JUST NOT WORTH trying to do yourself. There HAS to be someone with the tool to make them somewhere. Whatever they want to make them, PAY IT!

We all need to post some pictures of what we make to help each other get them right.

Hank

By the way, there is more than just the short and long lower cowls. Some of the early short ones were NOT made from flat sheet. They were worked on an English Wheel or draw formed with a distinct "bowl" shape to the bottom. The shaped ones looked really nice.

[Marv]

Re: Bottom Cowl on BC12D

Check the site out below. Could these possibly be the correct hinges. They have them in steel or stainless steel whith mounting holes and without. http://www.hardwaresource.com/hinges...inuous+Hinges/ Whatever they cost it would be better than making them. Marv

[astjp2]

Re: Bottom Cowl on BC12D

If you want to stay legal, you need the MS hinge. Its not that expensive that you cant afford to buy the real $dit. http://www.gen-aircraft-hardware.com/
I use 3003H-14 .032 for the top cowl, I then use a shrinker on the front to raise it to clear the REM37BY plugs. The aluminum is abour 50.00 per sheet. Tim

[Hank Jarrett]

Re: Bottom Cowl on BC12D

If you are looking at the MS-20257 it may be a MS part, but it is NOT the original used from the factory. You can't just change from an original part to a different one (even if it is an MS one) without approval. Maybe I am looking at the wrong part number. Which number are you saying to use?
Hank

[astjp2]

Re: Bottom Cowl on BC12D

If you are looking at the MS-20257 it may be a MS part, but it is NOT the original used from the factory. You can't just change from an original part to a different one (even if it is an MS one) without approval. Maybe I am looking at the wrong part number. Which number are you saying to use?
Hank

You are wrong on that one Hank, its hardware and you can substitute hardware as a minor alteration. I used the smaller one, I like the extruded hinge, it seems to last longer....Tim

[Hank Jarrett]

Re: Bottom Cowl on BC12D

I think we need to hear from an FAA guy on that. I have NEVER heard you can substitute a part just because it has an MS part number. There are MS hinges designed for different loads and conditions just like there are lots of different fasteners, all with MS numbers that are not all interchangeable, even if they fit. Different standard parts may be made from different materials and heat treats. Substituting another part that fits, but is made from a softer or lower heat treat could be disastrous! We can get away with a lot on our planes since the loads are pretty low and most parts are not stressed to anywhere near the ultimate strength of the material, but as an example, there are aluminum, brass and steel hinges that are all MS parts. If you put a brass or aluminum hinge in for a steel hinge that is actually designed for a critical load that requires steel, that part WILL fail. The original hinges on the top cowl were rolled interlocking aluminum, so a steel piano hinge isn't going to be understrength, but I am betting that changing to the piano hinge is NOT LEGAL, even if it is perfectly safe. You are deviating from the original design, and the FAA requires analysis to do that.
I DO agree that the extruded steel hinge is stronger, safer, and will last longer than the original rolled interlocking hinge, but that does NOT make it legal to change it without approval. I would need to look at the wording for a minor alteration, but I would bet you have to have AT LEAST an A&P and probably an IA sign it off. It's a pain in the a** to have to go through it, but the regs are conservative (sometimes in the extreme) to protect owners from themselves. I have seen some really dumb substitutions used on light planes. Even with MS numbers on the parts.
Hank

[Hank Jarrett]

Re: Bottom Cowl on BC12D

Tim,
I did just look you up and see you ARE a certified mechanic, not just an owner. That does make a difference, but when you change the design, aren't you deviating from the original configuration? Doesn't that require analysis and approval? Is an owner allowed to make that determination or do you need an A&P, IA or DER (and how is it supposed to be documented)? Where is the line between maintenance and modification? When are you no longer in conformity with the original TC?
Not saying you are wrong, but I am from the engineering side and I know I don't have the authority to change the design. How much can a maintenance professional change before he needs approval from the manufacturer or the FAA?
I think we can both agree that an OWNER can NOT make configuration changes like this (outside of the normal parts list) without approval (even though a lot of them do).
Hank

[Robert Lees]

Re: Bottom Cowl on BC12D

Here's a couple of photos of the hinge in question:

[Robert Lees]

Re: Bottom Cowl on BC12D

I reused my hinge, because it waas in good nick.

My whole cowl rebuild / replace story is here for intersted parties.