Warning Bells?..

Ironflight · #1 02-21-2010, 06:32 AM

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

plehrke · #2 02-21-2010, 07:50 AM

Quote:

Originally Posted by Ironflight

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.

Ahh, the lost art of reading an engineering drawing. I marvel at the shop guys in the past that could build a complex 3D thing using only a 2D drawing created by someone they never talked to. Today with all the 3D modeling, animations, trimetric views, simplified work instructions you forget the past. We have made great strides in removing the "skill" from the manufacturing process by simplifing and improving the visual aids. This has reduced the cost of most items we buy but also has allowed many things to be made by unskilled labor (and thus shipped overseas).
Once in a while I pull out some of the old drawings of past airplanes (F-4, and even the F-15) just to marvel at the "art" of the designer and the "skill" of the shop workers.

aeronut · #3 02-27-2010, 11:29 AM

WOW that was really well written and very pertinent; good job.

RV3Bob · #4 06-15-2010, 01:47 PM

The 1X1 angles are a different angle. Not 90 degrees. This angle really helps when trying to tie in the firewall angles.

KatieB · #5 07-09-2010, 08:12 PM

I just heard my first warning bell/ reminder to put brain in gear, get out the binoculars and see what's ahead.

Looking at the NEW horizontal stab photos Louise put up today, I noticed that the builder of Paul and Louise's tail used flush rivets for the first 3 spots outboard of the centerline to hold the HS-307 rear spar doublers in place. I wondered aloud, why? Then Ben said "Oh S*^%. The -8 is like that. Look at where the stab attaches to the fuselage." I see the brackets that come up from F-310 intersect the front web of the rear stab spar in that area. Of course the HS drawings mention NOTHING of this potential conflict!!

Question: I just riveted my spar last night with universal head rivets (like it said to do on the plans). I can drill out the AN470 rivets in that area and countersink AN426 rivets into the front of the spar so the bars can sit flush-- no biggie. But what if the mount bolts need to go too close to the side of a rivet hole? Is there enough wiggle room to move the stab mount bars so there's proper edge distance for such important holes, or did I just screw myself over??

http://picasaweb.google.com/lh/photo...eat=directlink

The empty holes are reserved for the root rib.

Ironflight · #6 07-10-2010, 06:23 AM

Quote:

Originally Posted by KatieB

But what if the mount bolts need to go too close to the side of a rivet hole? Is there enough wiggle room to move the stab mount bars so there's proper edge distance for such important holes, or did I just screw myself over??

I was worried about the same thing when we did an initial fitting, but once we got serious about lining things up, there was adequate room between the rivets for an AN3 bolt while still maintaining edge distance to the vertical attach bars. Note I said "adequate" - not generous. It should work out, but it will be close.

Paul

rv9aviator · #7 07-10-2010, 06:52 AM

I've spent my whole working life building injection molds using mostly 2D drawings of the part the mold produces. I've seen some of the worst drawings you can imagine and to make it worse I have to build everything in reverse. So if anyone sees an RV-9A flying upside down and back-wards you know it's me.

Reckon that will hurt the resale value?
BTW, Vans drawings are great compared to most.

apkp777 · #8 07-10-2010, 07:49 AM

What a relief! I thought I was the only one that did things like that. Half my build I felt like Tommy Boy.

KatieB · #9 07-10-2010, 09:23 AM

Quote:

Originally Posted by apkp777

What a relief! I thought I was the only one that did things like that. Half my build I felt like Tommy Boy.

Hehehe... Tommy Boy...

I figured if it was a good idea to junk the spar, I'd like to do it now rather than wait til the **** skins & ribs are riveted together... but I think we can make the best of it.