I have mentioned before that one of the interesting things about building the RV-3 is the fact that you really, really, REALLY have to know how to read the drawings and cross-check the information between the various sheets. It is simply not enough to find a part (or an assembly) on a single drawing and figure that you know enough about how to make it. Frequently, the information is all there, but simply doesn?t register until you see a different view of the same area (or a related area) on another drawing that makes a light bulb go off in your head. Sometimes, that light bulb is a little slow to go on?.and sometimes, it is surprising to find that little warning bells have been going off along the way, but it takes a few chimes before we put the pieces together and recognize our mistakes.
Today, for instance, I felt the ?click? as the bulb came on for something that I did over a month ago! Fortunately, I have adopted a policy of healthy suspicion on just about everything we do, never calling anything ?complete? or ?final? until we have no other choice than to drill, rivet, or close it up. Frequently, we?ll do a job, and as we move on to other things, I?ll be perusing the drawings and learning a little more about the overall assembly when those little bells start ringing. The problem part today was the lower forward stringers in the fuselage ? they form the lower corners of the fuselage from the center section to the firewall, and set the geometry of this critical relationship, as well as providing a strong structure to transmit engine loads to the wing.
I had framed this portion of the skeleton up awhile back, using the side view drawing of the forward fuselage. Looking at this area, you see the longerons, the lower stringer, and a diagonal brace stringer, all of which look alike in side view. The longerons are ?? x ?? heavy angle, as is the diagonal brace. And, if you look at the lines on the drawing, this appears to be the case with the lower stringer as well, so that was how I built it. All looked just fine, and since the longerons matched the lower corners, it seemed to make sense.
But then a few days ago, I started to install the lower forward floor skin. There is a cross-section drawing a few pages back that show the details of this and the two triangular ribs that help to support the firewall where the engine mount intermediate pads bolt on. This area also has some angles to support the rudder pedals, and says that you might have to put those angles up on to the ?1? x 1? angles??. Hmmm, what 1? angles are they talking about? I looked closely, and the cross-section showed the corner angles with the rudder pedal support angle sitting on top. Well heck, those corner angels are 3/4??.couldn?t be talking about those! (Warning bell!!!) I went on to something else, but came back to this drawing for another detail later on. Sure enough, it still said the same thing ? the rudder angle might have to go up on top of the 1? angle.
Well, we spent a couple of days doing some skin riveting on the aft fuselage, but I kept thinking about this little incongruity. Any time I get different answers to the same question, I get suspicious ? and the warning bells keep going off. Sure enough ? today, I put the pieces together ? if only due to an unlikely circumstance! We were cleaning up the hangar for an RV gathering, and as part of the clean-up, I was putting away some long angle stock that had been lying on the office floor. And?I came across this five foot length of 1? x 1?x 0.125? angle stock. Well, we?ve used up most of the big angle stock by this time?.what the heck could this be for? And suddenly, the alarm bell went off loud and clear ? along with the brilliant light bulb of illumination!
I pulled out the drawings again, and sure enough, there on the original side view was the thing I?d missed. While the three angle piece were all DRAWN to the same width, the note pointing at the lower one said 1? x 1? x 0.125? angle stock, whereas the top and diagonals were shown to be ??x ???..Fooled by the drawing! I expected that since the three looked to be the same size, they must be the same size ? and missed the note.
Fortunately, it was a very simple fix to remove the floor skin and the two incorrect angles. It only took about an hour to fabricate and match-drill the two new pieces. And I was right back where I was, ready to proceed with skinning the forward fuselage. But once again, I learned to read the drawings with just a touch of suspicion, to look deeper for what they are trying to tell me ? and to listen to those little warning bells that are telling me that something just doesn?t add up?.
Paul
Today, for instance, I felt the ?click? as the bulb came on for something that I did over a month ago! Fortunately, I have adopted a policy of healthy suspicion on just about everything we do, never calling anything ?complete? or ?final? until we have no other choice than to drill, rivet, or close it up. Frequently, we?ll do a job, and as we move on to other things, I?ll be perusing the drawings and learning a little more about the overall assembly when those little bells start ringing. The problem part today was the lower forward stringers in the fuselage ? they form the lower corners of the fuselage from the center section to the firewall, and set the geometry of this critical relationship, as well as providing a strong structure to transmit engine loads to the wing.
I had framed this portion of the skeleton up awhile back, using the side view drawing of the forward fuselage. Looking at this area, you see the longerons, the lower stringer, and a diagonal brace stringer, all of which look alike in side view. The longerons are ?? x ?? heavy angle, as is the diagonal brace. And, if you look at the lines on the drawing, this appears to be the case with the lower stringer as well, so that was how I built it. All looked just fine, and since the longerons matched the lower corners, it seemed to make sense.
But then a few days ago, I started to install the lower forward floor skin. There is a cross-section drawing a few pages back that show the details of this and the two triangular ribs that help to support the firewall where the engine mount intermediate pads bolt on. This area also has some angles to support the rudder pedals, and says that you might have to put those angles up on to the ?1? x 1? angles??. Hmmm, what 1? angles are they talking about? I looked closely, and the cross-section showed the corner angles with the rudder pedal support angle sitting on top. Well heck, those corner angels are 3/4??.couldn?t be talking about those! (Warning bell!!!) I went on to something else, but came back to this drawing for another detail later on. Sure enough, it still said the same thing ? the rudder angle might have to go up on top of the 1? angle.
Well, we spent a couple of days doing some skin riveting on the aft fuselage, but I kept thinking about this little incongruity. Any time I get different answers to the same question, I get suspicious ? and the warning bells keep going off. Sure enough ? today, I put the pieces together ? if only due to an unlikely circumstance! We were cleaning up the hangar for an RV gathering, and as part of the clean-up, I was putting away some long angle stock that had been lying on the office floor. And?I came across this five foot length of 1? x 1?x 0.125? angle stock. Well, we?ve used up most of the big angle stock by this time?.what the heck could this be for? And suddenly, the alarm bell went off loud and clear ? along with the brilliant light bulb of illumination!
I pulled out the drawings again, and sure enough, there on the original side view was the thing I?d missed. While the three angle piece were all DRAWN to the same width, the note pointing at the lower one said 1? x 1? x 0.125? angle stock, whereas the top and diagonals were shown to be ??x ???..Fooled by the drawing! I expected that since the three looked to be the same size, they must be the same size ? and missed the note.
Fortunately, it was a very simple fix to remove the floor skin and the two incorrect angles. It only took about an hour to fabricate and match-drill the two new pieces. And I was right back where I was, ready to proceed with skinning the forward fuselage. But once again, I learned to read the drawings with just a touch of suspicion, to look deeper for what they are trying to tell me ? and to listen to those little warning bells that are telling me that something just doesn?t add up?.
Paul