dzeleski Posted September 2, 2020 Report Posted September 2, 2020 Hi all, Got my plane back from an unrelated maintenance item that most likely required these access panels to be removed. When I got the plane back I noticed a slight amount of extra elevator control friction and when outside the airplane I heard a rubbing noise and then eventually saw the entire belly pan flexing down as the elevator was moved. After some digging I found out one of the small access panels forward of the rear most belly panel near the foot step had a screw that was too long. It appears the screws are different lengths and this was not noticed when they were re installed. I dont see any major damage to the tube other then paint missing, but I wanted to get some opinions on what to do going forward. Is there a specific paint I can use to touch this scratch back up? I assume the scratch isnt so bad that the whole tube needs to be replaced? Thanks, Dylan 2 Quote
PT20J Posted September 3, 2020 Report Posted September 3, 2020 The paint looks like it might be epoxy primer applied for corrosion protection. Epoxy primers require mixing with a hardener and then they have a pot life of several hours. You can clean up the area with some Scotchbrite and then brush on two or three coats of primer. Often mechanics keep some around for just such repairs and can mix up a cup for you. You might try the shop that made the goof and see if they'll fix it for you at no charge since it's their mistake. Failing that, you could go to an auto paint supply store. Some NAPA auto parts stores have paint departments. Skip 2 Quote
carusoam Posted September 3, 2020 Report Posted September 3, 2020 Great pic! Have a serious discussion regarding the screw length interfering with the aircraft control system... At least be aware yourself... That is a scary pic. often, errant screws pass into and through things that shouldn’t get holes, or jams.... PP thoughts only, not a mechanic... Best regards, -a- Quote
David Lloyd Posted September 3, 2020 Report Posted September 3, 2020 And thank you for posting that picture. It explicitly shows what can happen using the wrong length screws. 2 Quote
Bartman Posted September 5, 2020 Report Posted September 5, 2020 That happened to me many years ago. No telling how long it had been that way or when it was done because I had not had the plane very long. We had to replace the tube. Quote
0TreeLemur Posted September 5, 2020 Report Posted September 5, 2020 This was avoidable. Good on you for paying attention and catching the error quickly. That's an unfortunate error. Using random length screws really shows ignorance at best and negligence at worst. Almost every part on our planes is specified and described in the parts manual. In the wings for instance, the parts manual calls for S4 length machine screws in the smaller oval inspection panels with 8 ea, and S5 length for the larger rectangular panels with 10 ea. screws. I know this because I just removed the SS ones that were in there and getting sticky with new cadmium plated ones. The ones I removed were all uniform of S6 length. 2 Quote
dzeleski Posted September 8, 2020 Author Report Posted September 8, 2020 I did call the shop that did the work and let them know it happened. I have never touched that panel since buying the plane last December and it was never a problem so its obvious something was done wrong when the work was completed. I ended up having to cut down a screw as none of them were short enough, I think all the screws got put into a big bag and then smacked back into the plane without paying attention to sizes. I then smeared some grease over the scratch so it doesnt rust and ill find some epoxy paint in the next few days to properly get it coated. I did not realize until this happened that screw length on these panels matters quite a bit so now im tempted to check all of them and make sure they are correct.... Thanks for the comments all! 1 Quote
carusoam Posted September 8, 2020 Report Posted September 8, 2020 Dzel, You can do yourself and your machine a favor... All the proper fasteners are listed in the parts catalog... about 98% are easy to figure out... Trading out the old random screws for similar identical proper length screws is a good idea... Most MSers doing owner assisted annuals get this figured out before starting their second annual... You will also recognize the quality of design your Mooney was constructed with... Parts don’t get extra strength, extra weight, or extra volume... So... if you find an extra long fastener... it weighs more, takes longer to re-install, and doesn’t give any more benefit... In this case it gave a random hazard to flight... Stainless screws can make things better... Some nylon washers can be beneficial in certain locations... Rounded tipped sheet metal screws are better for your skin than sharp pointy screws... PP thoughts only... things my M20C taught me. Best regards, -a- Quote
0TreeLemur Posted September 8, 2020 Report Posted September 8, 2020 2 hours ago, carusoam said: Stainless screws can make things better... After some research in general, I voice a cautionary opinion regarding the use of stainless steel (SS) screws on aircraft. SS screws will cause cathodic corrosion in aluminum when wetted. See table here for compatibility of different metals: https://www.accuratescrew.com/asm-technical-info/material-compatibility-selection-data/ Letting your aircraft sit outside in a storm is all it takes, particularly during that weekend trip to the coast which adds a little salt to the mix. Another issue with SS screws stems from their tendency to spall in high-shear dynamic situations. Shear might be caused by incipient corrosion or using a screw gun where friction heating causes thread interference. There are places for SS screws, especially in connecting chromium steel parts. But they shouldn't be used in contact with aluminum. As I discover them, I'm replacing all the SS screws on my aircraft that are in contact with aluminum with cadmium plated steel screws. They won't cause corrosion. Before installing, I give them a bath in Corrosion-X, which will help with removal and keep water out. There are folks on MS who swear by SS screws. I swear by science, which suggests against using SS in contact with aluminum to minimize the probability of corrosion. I also do occasionally fly to the gulf coast. If you live in Montana or some such place this is less of a concern obviously. Another threat with interesting material on this topic here: https://mooneyspace.com/topic/34824-panel-screws/ Quote
dzeleski Posted September 8, 2020 Author Report Posted September 8, 2020 I ended up ordering the SS screw kit from Spurce last week. I have the multi piece belly and dozens of the screws are completely mangled so I need to replace most of them anyways. Keep in mind adding any kind of coating changes the torque spec of the fastener. I would probably consider using anti seize for mixed metals over anything else, but you are correct SS and aluminum do not mix well. Quote
carusoam Posted September 9, 2020 Report Posted September 9, 2020 9 hours ago, 0TreeLemur said: After some research in general, I voice a cautionary opinion regarding the use of stainless steel (SS) screws on aircraft. SS screws will cause cathodic corrosion in aluminum when wetted. See table here for compatibility of different metals: https://www.accuratescrew.com/asm-technical-info/material-compatibility-selection-data/ Letting your aircraft sit outside in a storm is all it takes, particularly during that weekend trip to the coast which adds a little salt to the mix. Another issue with SS screws stems from their tendency to spall in high-shear dynamic situations. Shear might be caused by incipient corrosion or using a screw gun where friction heating causes thread interference. There are places for SS screws, especially in connecting chromium steel parts. But they shouldn't be used in contact with aluminum. As I discover them, I'm replacing all the SS screws on my aircraft that are in contact with aluminum with cadmium plated steel screws. They won't cause corrosion. Before installing, I give them a bath in Corrosion-X, which will help with removal and keep water out. There are folks on MS who swear by SS screws. I swear by science, which suggests against using SS in contact with aluminum to minimize the probability of corrosion. I also do occasionally fly to the gulf coast. If you live in Montana or some such place this is less of a concern obviously. Another threat with interesting material on this topic here: https://mooneyspace.com/topic/34824-panel-screws/ I was highly skeptical as well... Then I didn’t check how well the original steel screws reacted with aluminum... The machine screws are going into something other than aluminum... what are those threads riveted in place? The other thing the sheet metal screws screw into are spring steel clips... Lots of paint between the screw head and aluminum... So many interactions are possible... Best regards, -a- 1 Quote
PT20J Posted September 9, 2020 Report Posted September 9, 2020 Area effect comes into play here. https://corrosion-doctors.org/Corrosion-Forms/area-effects.htm In the case of stainless screws and aluminum skins, the area of the anode (aluminum) is so much greater than the cathode (screw) that the corrosion is negligible. 1 Quote
0TreeLemur Posted September 9, 2020 Report Posted September 9, 2020 The SS screws that were installed in our C weren't in there more than a few years and I was starting to have trouble taking them out. SS is softer so the heads are easier to strip. Cadmium is a "slippery" metal when used as a plating. This is an experiment. I'll see if I start having trouble with the cadmium plated steel screws in two years. If so, I'll go back to SS. Quote
PT20J Posted September 9, 2020 Report Posted September 9, 2020 FWIW, every screw that I've had to drill out has been cad plated. Part of the problem is that the cad plating wears off after a few cycles. I've been replacing any questionable screws with stainless steel, simply because it was easier to buy a kit of screws than to figure out what individual screws I need, and the kits all seem to be stainless. I haven't had any issues with the stainless but I'm careful to tighten by hand so as to not over-torque them and I soak them in WD-40 (or ACF-50, or Boeshield if you prefer) before installing. Skip Quote
Hank Posted September 9, 2020 Report Posted September 9, 2020 4 minutes ago, PT20J said: FWIW, every screw that I've had to drill out has been cad plated. Part of the problem is that the cad plating wears off after a few cycles. I've been replacing any questionable screws with stainless steel, simply because it was easier to buy a kit of screws than to figure out what individual screws I need, and the kits all seem to be stainless. I haven't had any issues with the stainless but I'm careful to tighten by hand so as to not over-torque them and I soak them in WD-40 (or ACF-50, or Boeshield if you prefer) before installing. Skip No electric screw guns on my plane! I use this: 1 Quote
francisg Posted September 10, 2020 Report Posted September 10, 2020 Thanks to all, as usual MS has the final word, in this case, no mater which screw material, use a hand screwdriver only (and maybe some antiseize)... Quote
EricJ Posted September 10, 2020 Report Posted September 10, 2020 In my experience most fasteners can be removed with power tools, like electric screwdrivers, or impact wrenches on lug nuts or whatever (for non-aviation machinery), but stuff should be fastened by hand. Pulling panels for annual inspection goes a lot faster with an electric screwdriver. Setting the torque low prevents stripping stubborn ones, which you can address as needed by hand or blowtorch or whatever. 1 Quote
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