Bearhawk Construction Log Section of

I called Bob today and asked him about the AN210-3A vs -3B pulleys. He said either would work just fine.

I also asked him about the braided fuel line, which is something I’ve been waffling about for a while. The issue is that the current fuel lines are braided stainless lines instead of solid 3003 aluminum lines. The braided lines are popular with the race car crowd, but they are about much heavier per foot than the same size of Aluminum wire. In fact, the weight difference of 40 feet of 3/8′ is 1.76 pounds for the AL vs 5.8 pounds for the stainless. I don’t have any doubts that the stainless tubing is up to the task, since the pressure ratings and chemical resistance are great. I am worried about the longevity of the rubber line inside of the stainless tube. Is this concern well-founded? Probably not, but I really don’t know. By using these lines does it mean that the fuel system will only last 132 years instead of 250? or does it mean that the fuel system will only last 5 years instead of 50? Racecars aren’t built for the long term- they are built to be reliable for short periods but not for long periods- but that doesn’t necessarily mean that the fuel line won’t still last for as long as I need for it to.

I have consulted several expert opinions about the tubing, so I figured I might as well ask Bob what he thought. To summarize, he said that it should probably be fine, as long as the resistance to auto fuel was good (which I would say it is). He added that it was much more expensive and much heavier and thus couldn’t imagine why anyone would use it instead of the AL. Richard’s point was that it was much easier to install than the AL tubing. If I were starting from scratch I would have stuck with the AL tubing, but since the stainless is already paid for, cut to length, and installed, I will probably stick with it for now.

Today I continued my hardware patrol.  I have been through the entire fuselage and the control stick and have replaced and/or noted what I’ll need to get to continue.  I can definitely justify the expense of a drilling guide since I have lots of bolts that are good candidates for drilling for cotter keys.

I changed the bolt on the trim wheel to one with a hole in the shank and feel much better about it.  I removed the doors since the hinge bolts were a little bit too short.  Rather than just swapping the bolts I just took the doors all the way off so that I could get in and out easier.  I made a few bolt changes on the elevator and flap controls to account for length and/or drilled bolts.  I also went through the landing gear bolts and installed the ones with the correct grip length, now that I know how to do that.  I didn’t have the proper drilled bolts on hand but I’ll have the gear off several other times and can replace them next time.

Using the torque wrench for the first time on the Bearhawk

Comparing the M4 to the Bearhawk

This morning started out with a morning of Young Eagles flights.  I got to see Buck’s Maule M-4 for the first time.  He flew 8 of the 31 kids, which was pretty amazing considering that he only had 2 seats.  He said that the max gross weight is 2300 and the useful load is about 800 pounds.  He has the same engine that we will use, though we probably won’t have the same Hartzell CS prop.  His airplane is certainly beautiful, and I can’t wait to finish ours since it will be a very capable young eagle hauling machine.  For now I just helped out with the paperwork and logisitics.

Filing the Brake Pedal to fit between the tabs

In the last entry I was starting to install the right side brake pedals when I realized that I was going to need to relocate some tools from the clubhouse.  I loaded up my home-made work bench and took it over to the hangar, complete with an assortment of tools that I will hopefully not need in the clubhouse as much as I will need in the hangar.  I had to file the attach side of the pedals a little bit so that they would fit between the attach tabs.  

I started to mount them but realized that I didn’t have the right bolts.  I have several little boxes of bolts but was surprised that none of them were the right length!  Actually, I did have several that were the right length, but they were not drilled.  Since the brake pedals and cylinders are subject to rotation, 43.13 states that they must not be secured with self-locking nuts- that means a drilled bolt with a cotter key.  Since I knew that I was at least going to need those bolts, I figured I might as well go through the rest of the airplane and see what else I will need.  Shipping from the aircraft hardware stores generally isn’t free or even cheap.

"Reserving" the hardware anywhere that I can

I also started to notice that some of the bolts that I had were already comitted to parts and assemblies that were temporarily removed from the airplane.  For instance, the bolts that hold the flight control cables onto the control horns were not on the airplane, but were presumably in some of those little boxes of bolts.  I made a sweep of about half of the fuselage, adding missing hardware as a way to mark it as “reserved.”  In the process, I also saw some hardware that was not installed the way that I would have installed it, so I also resolved those minor conflicts.  For instance, the rudder stop bolts weren’t really quite long enough to stick through the nylon lock nut, so I switched them out. 

The longer bolts with 1, 2, 3 threads showing.

This was the case in several areas, and I also saw a few “subject to rotation” applications that I would have prefered to use with castle nuts and cotter keys.

This bolt should have a castle nut and cotter key per AC 43.13.

This bolt is too short since it doesn't have a thread protruding through the nylon.

I worked for 3 hours today and made notes of which hardware I was definitely going to need, which included a few small pieces, and a few big ones, like the engine mount bolts.  I was somewhat surprised to see that I didn’t have any of those, since I figured that they would have been part of the Wicks hardware kit.  So, I went to the Wicks hardware list to look and see if they were originally included.  There on the list are some AN6-46 bolts, which are about the right length and in the right quantity (5).  So either the wicks list has changed, I have the bolts somewhere else, or I don’t have them.  I repeated this same process a couple of other times, referencing the Aircraft Spruce catalog for the grip length of each AN bolt, measuring what the grip length needed to be, and sorting through drawers to try and find the right stuff.  All the while I was making a list of things to buy so that I can make one order and get most of what I need.

I have several bolts that are the right size but undrilled, so I might try and find a bolt drilling jig.  For example, I have enough -6 bolts for the landing gear that I will probably not need anywhere else.

I also noticed that on the plans Bob calls for a pulley as AN210-3A, which is equivalent to MS24566-3A.  Yet, the wicks kit included only -3B pulleys instead of the -3A’s listed on the plans.  So far I haven’t resolved this discrepancy.  The Aircraft Spruce catalog says that the -a and -b pulleys are the same dimensions but have a different type of bearing in the center.  I suspect that they are interchangable but will probably have to call Bob or someone else to figure that out for sure.  The funny thing is that in a case like this I picture an attorney questioning a witness.  “Why didn’t you use the pulley specified in the plans?”  Maybe that’s an idea for the next episode of Law and Order.  I know it’s terrible to think of it that way, but that is the image that comes to mind in this case, and also quite often at work.

Some folks say that building airplanes isn’t as hard as people make it out to be.  This is quite likely true, and an experienced airplane builder can certainly separate a harmless or seemingly meaningless discrepancy from a major or life threatening one.  That is one certain difference between a new builder and a seasoned veteran- knowing what is worth fussing over and what isn’t that big of a deal.  Without the benefit of that experience, I have to chase down even the smallest discrepancies to learn which category they fall under.  The pulley difference is certainly just the first of many.

I also took some time to scratch my head and figure out which tabs went to which flying wire on the tail surfaces.  I used the front view on page 1 of the plans to note the angles of each of the flying wire attachments and to notice that the bottom of the diamond shape uses attach points that are welded to the fuselage.  With that information it was easy to sort out the remaining 6 tabs, after which I labeled them with a sharpie pen and set them aside with their associated hardware.

I think the process of “reserving” hardware by attaching it where it needs to go is going to be well worth the effort.  This should keep me from double-booking a particular bolt and not realizing it until final assembly.  I still need to do the same thing for the rest of the fuselage and the wings.