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Thread: Project 5 build thread

  1. #21
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    Default Re: Project 5 build thread

    That's actually a damn good question. SB38 can be found on the kitfox web page. Apparently I have been hallucinating because I just read through the entire thing and the material type isn't mentioned anywhere.

    Possibly I've read what others did, or possibly it's because I happen to have some 0.016" stainless.

    Astute readers will observe that the SB lists the Vixen but it is tribal knowledge that all model 5s and on need reinforcement.

    The SB states that the kit with parts will be provided free of charge but it is a Skystar document and I don't feel like it's the McBean's responsibility to fill that order.

    I made two paper doll iterations before arriving at what I think will be the ideal flat pattern.

    Interested to hear what material others have used

  2. #22
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    Default Re: Project 5 build thread

    Quote Originally Posted by airlina View Post
    Alex., do you have the name of that two part epoxy primer in a spray can? I wasn't aware of it either and would be nice for small jobs that I have. thanks Bruce N199CL


    Bruce
    That's the stuff right there. Check with your local auto body store.
    963A425A-B5B3-480B-9BE3-4BFA6C25866C.jpeg

    IMG_20200612_150247.jpg
    I left one of my non Puka pedals with the paint shop so he could match my custom rattle can. One of these two pedals was used for a test and the other came out of my tub of parts I'll never use. I would say I'm pretty happy with the results

  3. #23
    Senior Member Delta Whisky's Avatar
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    Default Re: Project 5 build thread

    The reason I asked about the material choice was because I once had a really bad experience with SS welded to mild steel. I don't know how a SS to steel weld would behave in the long term on the pedal assembly but I would hazard a guess that the pedal is made with 4130 and would recommend that you stick with that. Additionally, some SSs are too malleable to be strengtheners on 4130 and I'd be concerned with .016 not being up to the job in any event. Just one opinion and it is worth exactly what you paid. Maybe there is a metallurgist on the forum and will weigh in.

  4. #24
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    Default Re: Project 5 build thread

    Ah. It's not welded. It's riveted and bonded with structural adhesive.
    I'll see if I can find a good visual aid.

    Edit:. This is from the service bulletin

    7FEF5D76-17DE-4848-8065-2D9DD9D85F58.jpeg
    Last edited by alexM; 06-12-2020 at 08:57 PM.

  5. #25
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    Default Re: Project 5 build thread

    thanks for the photo of the primer cans Alex. And also there was a recent thread on the rudder pedal issue and i posted some pics of how I handled it on my Series 5 without welding with SS , rivets and scotchweld (3m version of hysol) . Bruce N199CL

  6. #26
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    Default Re: Project 5 build thread

    One step forward and a few steps back

    I’m sure I’m the first person to experience setbacks while building an aircraft. After doing the alodine treatment of my rudder pedal brackets I had one of those forehead slapper moments when I realized that the previous builder had installed the flight controls into the fuselage at one point – which means that they match drilled the (dimensionally incorrect) brackets to the steel channels in the fuselage. That in turn means that my new brackets are unusable unless I have the holes in the steel channels welded up and I re-drill them. More on that later.
    I took advantage of father’s day to spend my day working on my Kitfox. Knowing that all of the following steps are a dry run, and that I’ll be removing all of this at least one more time before final torque values are applied, I installed the control column assembly (the contraption with the sticks) into the fuselage, installed the bell crank for aileron control, and then installed the push-pull tube which goes between that bell crank and the flaperon mixer.
    I installed the flap handle and the push-pull tube which goes to the flaperon mixer for flap control. I set the center console in place and verified that the flap detents work with the flap handle (works perfect).
    IMG_20200621_163235.jpg

    I installed the small intermediate elevator bell crank (I think it has a different name but I can’t remember it right now. It’s sort of a pendulum thing) near the back of the seats, installed the elevator push-pull tube from the control column to that intermediate bell crank, and hooked up the forward end of the long elevator push-pull tube used in the model 5. I found that I was missing the sleeve bushing that goes in the tail cone and sent an inquiry to Debra at Kitfox to see if those are even available. They are, and I now have one on the way.


    I loosely installed the rudder pedal assemblies and sure enough the previous builder’s match drill efforts resulted in the rudder pedals aligning very well. I was hoping they would be wrong so I could justify welding/re-drilling. Still more on that later.
    Of course I had to take advantage of the moment and actually sit in the aircraft. Thank the maker for bubble doors. Occupant comfort will be “sufficient” and not much more, but I’m okay with that. I learned to fly in a C152 and find the room pretty comparable. I would have said the Kitfox was easier to get in and out of until I installed the sticks.
    While sitting in the airplane I boxed the controls a few times and felt friction in the ailerons. Part of it was caused by me sitting in a seat which was flexing quite a bit, a result of not having any hardware retaining it. Contributing was very limited space under the seat from the aileron push-pull tube.
    While sorting parts recently I put my hands on the various push-pull tubes to identify them all. Two of them have a slight bend in them. The KF 5 manual doesn’t say anything about the bends, but the KF 7 manual does. Using the dimensions in the KF 7 manual I was able to identify one for aileron control and the other (longer) one for flap control. The manual says the short end of the bend on both tubes goes aft, so I labeled the parts and installed them that way.


    I wondered if maybe the KF 5 used straight tubes originally but mine are powder coated red the same as the rest of the fuselage, and once installed I don’t see how straight tubes could possibly have worked. So I think it was just a shortcoming in the KF 5 manual that it doesn’t tell you how to deal with the bent tubes.
    The loosely assembled aileron bell crank came with a stack of washers so I knew there was going to be adjustments needed. I quickly discovered that this bell crank needed to be biased as high as possible between the fuselage mounting tabs in order to keep the aileron push-pull tube from contacting the fuselage tubes as it moves. I got it to clear but just barely. Eventually I found the sweet spot for orientation of the bend in the aileron push-pull tube so that it would not contact either the fuselage tubing or the bottom of the seat (even with the seat flexing because of my gravitational impact).
    IMG_20200621_162155.jpg

    My other side project was to incorporate the Service Bulletin to address the cracking issues in the rudder pedal torque tubes. I used the SB (found in the technical section of the Kitfox web site) to create a mylar template. I thought I would be able to send my CAD file to a couple of places that could make the parts for me but I was no-quoted both times. I guess working with thin stainless wasn’t their favorite thing to do. So I ordered some 0.020” stainless shim stock from McMaster-Carr. I used the cut off wheel on my die grinder to make one part before I realized it was pretty crude for the process, not to mention having consumed an entire 2” cut off wheel for one part.
    So I obtained some aviation tin snips (both left and right) and practiced some more. I used my cut off wheel to slice the remaining shim stock into 2” strips, giving me 6 parts where I needed 4. I’ve been in the business long enough to know I would probably need those extras.
    I guess Dykem layout die is not as popular as it once was. We can thank CNC machinery for that. I couldn’t find any locally, so I improvised by dusting the stainless with some self-etching primer, then got to work with a carbide scribe and a spring loaded center punch. The tin snips worked very well for cutting the shapes out. I drilled one hole in each end of the parts and used clecos to hold them all together. That allowed me to use the 3M discs on my angle grinder to get the periphery of the parts closer to the same. And finally, I used my drill press to drill the other four holes with the parts stacked together. They’re not perfect but they’re not terrible (and yes, they are intentionally asymmetrical)

    IMG_20200623_183028.jpg

    Welding

    Now I’m at a cross road. I have three areas where I could use the services of a skilled welder, and I could theoretically avoid all three – but do I want to? While going down the path of creating the stainless straps for the rudder pedal torque tube Service Bulletin I kept going back to the possibility of finding someone to weld the triangle gussets employed by the factory currently. Where I initially had concerns that the gussets would difficult to dodge the rivets on the outboard pedals, I am now equally concerned about being able to pick up the three holes common to the existing rivet pattern and translating them to my stainless straps. It is going to require some luck and possibly those two extra parts before I declare success.

    Upon further review, if I go the welded gusset route I would have to drill out the existing rivets anyway, and the only ones which would be difficult to access for reinstallation would be the two up on top that would be between the gussets. I have verified that I can reach the most inboard one with gussets in place and may be able to reach the outboard one. If not I could just add another rivet where ever I can to meet the design strength.
    The second application of welding is the one I referred to for rudder pedal mounting brackets. Again, I could go either way and just get over it but I would always know I let a discrepancy slide. Not a safety issue, just an OCD thing. And I’m not very OCD.
    Lastly, I have read recommendations to beef up the tailwheel support at the back of the fuselage. The link I followed yesterday shows it is just a doubling up of the existing plate, which should be cake for any welder.
    I’m prepped as far as primer and paint goes, so at this point I can deal with some welding. It will require that I load up the fuselage and take it to the chosen welder, or that they be mobile. I’m going to seek quotes today and decide. If I employ a welder at all, I will be going with my new rudder pedal brackets.
    IMG_20200622_172639-01.jpg
    The other thing I did was buy a new 1/4" drive torque wrench of much higher quality than the harbor freight crappy one I have used to strip two AN3 bolts with already. This new one is very small and cheerfully applies as little as 10 inch pounds.

  7. #27
    Senior Member bbs428's Avatar
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    Default Re: Project 5 build thread

    Time to invest in a small mig welder and get some OJT. My millermatic is essential piece of gear out here in the country. I'm self taught and not the best welder but .023 wire will allow me to make some nice stitch welds on thin tubing.

    My fix was to the rudder pedals Port side only. Was a bit dicey as the tubing is so thin. Glad it's done and over. Prior to welding I was wishing I'd just riveted the darn thing! lol. A screw up here would not be good.

    All the best and Keep up the great work!
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  8. #28
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    Default Re: Project 5 build thread

    Learning to weld has actually been on my "to do" list for decades. The pieces have never fallen into place for that, but that might have changed yesterday afternoon. I looked on my local craigslist for welding services offered and found an ad that said all the right things (TIG, 4130 and that he's an A&P). So I called him up and we had a nice conversation. Not only is he a qualified welder he flies a King Air and he teaches the A&P curriculum at a local community college.

    We discussed the three potential applications for welding on my Kitfox and he asked me questions about wall thickness and the type of filler material. I got a brief education on preheating and stress relief - both of which should be of minimal concern with the thicknesses involved here. I've got some measuring to do for wall thicknesses, and I need to figure out how thick the triangle gussets need to be and also the reinforcement for the tail wheel. He mentioned ER70S-2 instead of 4130 filler (confirmed now that I've read up a bit), but it also looks like ER80S-D2 could be used.

    He told me he has no problem teaching me and letting me practice on some scrap material and then supervising while I do the actual welding. I'm to obtain the 4130 and filler since he doesn't have any on hand (says almost all the welding demand he has now is for stainless and aluminum). Then we'll coordinate me trailering my fuselage to his shop. I'm thinking that when the welding cools off I'll bring it to my garage to do the primer and paint fixes and complete the installation of flight controls so the fuselage is ready to cover.

    For the rudder pedal reinforcement I will be doing both sides since I will be flying from the right seat quite often (possibly most of the time).

  9. #29
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    Default Re: Project 5 build thread

    I'm anticipating my elevator push-pull tube bearing from Kitfox any day now, along with my latest aircraft spruce order. That order will contain my usual fistful of hardware and the 4130 sheet metal, welding rod etc.

    I took the opportunity to deconstruct the rudder pedal torque tubes by drilling out the rivets. Back in my 20's I drilled out hundreds of aluminum rivets when I had a job at a place that sold sea kayaks. Except that these are steel, not aluminum so it was much slower going.
    I started out using some Harbor Freight (supposedly) HSS TiN coated still bits I already owned. I swear I've eaten pasta that is tougher. So I ditched that plan and used one of the bits I ordered through Kitfox recently. Much better. I spent part of my life as a CNC programmer and took pride in learning the proper feeds and speeds for various materials (and wow is it a wide range). With a decent drill bit and proper lube I was able to drill out every single rivet and still have a sharp bit when I was done.
    IMG_20200701_185306.jpg

  10. #30
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    Default Re: Project 5 build thread

    I keep catching blurbs from someone building a CH701 with the line "something every day". Well I can't claim to be doing something on my Kitfox every day but I finally got a major task complete and that was taking my fuselage and rudder pedals to the welder. From where I'm at now I need to do some light grinding, sanding, primer and lastly my color matched red. Then I can make some progress installing flight controls, floor boards, seat etc - all of which I've read ahead on many times.

    Before I get long winded (which I know is about to happen because I've already typed it) I'll say that the three thing welded were the triangle gussets on the rudder pedal torque tubes, filling the outer holes for the rudder pedal torque tube brackets, and reinforcing the platform for the tail wheel leaf spring.

    When my Aircraft Spruce order showed up I got to work fabricating triangle gussets. I wanted to make them 1.75x1.75 so I started by cutting 2" squares out of the 2x36" strip of 0.032" 4130 stock with my tin snips. I took my time and made some very accurate 2" squares. I scribed lines for the finished long edge of the triangle and rough cut the triangles, then came back and cut to the line. Maybe someone out there can follow an exact line on the first pass but I can only get "pretty close" and I don't like the results as much.

    In the end I was pretty happy with my very uniform 1.75" triangles, so I deburred them with a 2" scotchbrite wheel, cleaned them with acetone and set them aside without touching them.

    I also made a reinforcement piece for the leaf spring mount at the rudder post. The example I saw doubled up the thickness of the flange and then bent almost 90 degrees to form a sort of triangle gusset attaching it to the rudder post. I don't have a press brake and as much as I'd like to have one, the ones I can afford are good to about half the sheet thickness I needed. In the end I made a gusset flange out of 0.125 4130 and it's welded to the existing flange quite solidly. For that piece I accurately laid out some thin scribe lines, then laid some masking tape exactly on that line. Next I took a sharpie pen and made a big fat line along the tape edge. Pulling the tape off I then had a nice thick, very clean edge to follow with my 3" cutoff wheel. I got lucky and my first one was right on the dimensions after deburring.

    I'll edit later to insert some pics, but I coordinated with the guy that would do the welding and went to rent a trailer or possibly a truck at U-haul. The only thing they had that could possibly do the job was a 26' truck.

    I took one of my sons to the airport and loaded up the fuselage. He pulled the tail up the ramp and I duck waddled the front of the fuselage until I could get the mains into the truck, then I secured it from moving. I'm guessing there won't be too many trips with this plane that will be this easy.

    I get up the next morning and see that the outer dually is flat (the bead was loose). Blah, blah and U-haul roadside assist came through and we're on the way. The welder was a super nice guy who was stoked to be working on a plane. A lot of his business is race cars.

    He put me and my son to work using 2 and 3 in scotchbrite wheels to remove the powder coating where the welding would be done. The first thing he did was fill the holes where the rudder pedal brackets mount to the fuselage channels. Easy job.

    Then he moved on to the tail reinforcement. Once he had it welded to the tail post and front edges we rolled the fuselage up on it's side so he could complete a nice bead on the outer corner. He also discovered a weld in the most acute inside corner at the very back that wasn't welded well so he fixed it (I'll note here that I have a Skystar fuselage, not a current build Kitfox)

    I was able to practice a few inches of TIG welding with the equipment. I learned pretty quickly that my bifocal glasses were all wrong for the welding helmet because the auto dimming window was perfectly positioned for the distant portion of my glasses. If there's a next time I'll dig up my single vision glasses I hardly wear but would be perfect for this.

    I probably should have destroyed the evidence of my welding prowess but I didn't start the place on fire or get to smell myself burning so I'm marking it down as a win. Needless to say I let him do the gussets. It was apparent that we should have sanded the powder coating off further from the weld than I did. Again, 2" scotchbrite wheel removes everything back to clean metal and feathered into the good powder coating.

    Today I picked up some 2" sanding discs so I can blend the filled holes to make them invisible after paint. I did not have him fill the holes for the center bracket or brake master cylinder bases since they were all correctly located.

    Then we trucked the fuselage back to the hangar. Since I had the truck, I picked up the crate with the new spars and extrusions and took it to my garage.

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