After some sweating and swearing, I made the forward ends of the F-315 seat ribs, including their 3/4" angles, fair to the spar bulkhead side plates.
Getting the 3/4" angles to joggle was a real pain. Even getting them to have a simple bend, as the SK-45 sketch shows, was a real pain. What happened was that these angles are 1/6" thick compared to the 1/8" thick angles for the lower longerons, and these would buckle. I tried various things to prevent that before it dawned on me that even SK-45 allows a flute there. A flute is another word for a pre-buckled section, so I accepted the buckle and continued.
This form block pair didn't work. It's oak. It has a slot so that the upstanding flange won't buckle. It would have taken more force than I could generate to form the 3/4" angle with these since the upstanding angle, which needed to be formed too, didn't. And when I removed it from the form blocks, that upstanding flange buckled.
I ended up doing it pretty much the way I'd done the forward lower longerons, using shorter spacings, though. I think the spacings were 1/2" for the tension bend, 1" for the gap between bends (that might have been 1 1/4", I don't remember) and 3/4" for the compression bend. Once the tool is in place and the angle seated and clamped, I'd give the upstanding compression flange a decent whack with a round bucking bar right in the middle of the compression bend so that it would know which way to flute itself.
Sure wasted some extruded angle getting here, though.
After that, it was time for the aft end of these angles, which need similar but milder treatment. Here I was faced with an interesting issue. When the unbent end of a 1/16" angle is considerably less than 1 7/8", if I tried to bend the angle, the part held by the vice actually shears through the thickness of the flange. It does that before there's any chance of actually bending. If I wanted to, it would have been possible to actually calculate how long the unbent part would need to be to allow for bending, but I didn't bother.
Instead, I slotted the angle and made the bend from the slot. The length of the slot was governed by the F-377 flap mounting blocks which get bolted to these angles later - always got to look ahead a bit on an RV-3B.
After that, I turned towards my mis-drilled tailwheel mount base, and replaced the original AN3 bolts with AN173 bolts, which are slightly oversize. These were not fat enough to fill these holes, though, so I took some advice and tooled up to install taper pins. The appropriate pins are AN386-1-7 and these use an AN975-2 cup washer. The reamer is a Brown & Sharpe #1. Shop around because various companies sell the reamer. I found that Aircraft Spruce was a very good place to buy the hardware.
I successfully reamed the first hole and it wasn't too difficult. I'd been warned not to go too deep and the result was fine.
While reaming the second hole, though, the reamer didn't follow the original hole nicely at all, and I ruined the entire assembly.
Parts on order....
Worth mentioning is that Van's Support checked the assemblies on hand and found that they are all loose there. Evidently they all got mis-drilled like mine in 2012. I ordered separate parts rather than the assembly, and will have to drill them to the tail spring myself.
The photos are also hosted here, here, here, here, and here.
Considerations for the Mixer Mount
1. The length is designed to pick up the spar bulkhead's angles that are riveted on to the aft face and extend aft to the F-304 bulkhead's side flanges.
2. The spar angles are short to allow for the insertion of the spar splice plates, above and below the angles. If the mounts extend into those openings, it'll be more difficult to get the splice plates installed.
3. The large lightening holes in the seat ribs are centered roughly 1/2" forward of the mixer bearing center.
4. If the mixer bearing is too low, the mixer's elevator pushrod fork will interfere with the floor.
5. The bearing in the mount bracket is closer to the free edge than the flange edge. If the mount bracket flange is on top, it might interfere with that splice plate opening. There's less likelihood of that if it's upside down, so that's the way I'm doing it.
6. The seat ribs spacing is such that the mount brackets are slightly too wide for the mixer itself. This will vary as the bearing is placed inboard or outboard of the bracket.
I bonded a 3/16" thick spacer between the bearing and the mixer, on each side, on the left side and 1/8" on the right side. This appears to fill the gaps. This shows one of the shims glued on. The glue with some microballoons added to control bond-line thickness provides galvanic separation between the steel and the aluminum.
7. The beads on the seat ribs are on the outboard side of the rib. Clearing these adds to the width of the mounting bracket spacing if the brackets are attached outboard of the seat ribs. If they are on the inboard side, the bracket's flange will interfere with the mixer itself.
8. The lightening hole's bead is just slightly thinner than the thickness of the bearing flange. On my left one, I needed a .063" thick spacer between the spar bulkhead's angle and the mounting bracket, and at the aft end, I needed a .12" thick spacer between the web of the seat rib and the mounting bracket.
For the right one, I didn't use a spacer at the spar angle's flange, but used a .063" spacer at the aft end. I may need to adjust these slightly.
Here are the mixer brackets with the spacers getting glued on.
I looked towards the tail cone bulkheads and as expected, the slots for the lower longeron will need to be adjusted. I used a small laser on a tripod to establish a straight line.
The photos are also hosted here, here, and here.
Recently, I got to see a remarkably well-built RV-3B under construction and was treated to what amounted to a one-day seminar in advanced techniques. The builder, David Howe, has previously built an RV-4 and then a Rocket. The Rocket is flat-out beautiful, and it looks as if the RV-3B will be at least as good. Its fuselage skins are so smooth and fair that you almost can't see the rivet lines.
I'm not going to go into specifics because those are, in many cases unique, and I think that it's up to him to show what he's developed. So this is an abbreviated report mostly describing my field trip. It amounted to a one-day seminar in advanced construction techniques.
He made a number of professional-looking tools. These include everything from custom wing supports to bucking bars to rivet sets to jigs for a single-use operation. Typically, I use wood or aluminum for my tooling, as you've seen in the photos. He'll weld up some steel and he's not afraid to go stout. Since stoutness means stiffness, and stiffness helps precision, this all adds to the quality.
One thing he's been doing is bonding his skins to the frame. The main reason he does that is to use the bond as a variable-thickness shim. He also uses shim segments of aluminum to reduce the bond-line thickness. The bond serves another purpose as well, in that it holds the skin in place while riveting. Extra work but the results are superb. We went into some detail on this and I might do something along these lines on my plane.
One thing that as an engineer, I really appreciate, is that he tests virtually every non-standard thing he does. He has his own pull-tester, for example. And he's cycle-tested the end attachment to a push-pull cable that he built.
Some of the changes he's made are strictly to enhance the utility of the airplane. One example is a built-in, easily removable toolbox that fits in one of the few unused areas in the RV-3B cabin area. Normally, you'll never know it's there, yet it's easily accessible when needed.
I've been putting in flutes to straighten the bulkheads and ribs in my plane. We all do that. He has a shrinker/stretcher pair on a stand and corrects them that way. I'll be getting a set of those this week. Incidentally, he pointed out that you don't need just a shrinker, but both, because otherwise you'll always be changing jaws from one to the other, after slightly over-doing it one way and needing to go the other way just a bit.
He's made some fittings that look a lot like those standard blue AN fittings, same blue anodizing, same general sizing, but which have custom configurations for a particular need. Looking at these on the plane, they're very easy to overlook, never guessing that they aren't standard AN fittings.
He'll have redundant fire sensors and a fire-suppression system in the plane. Race-car equipment, and readily available.
His plane abounds with cool little ideas for the RV-3B. I'm not going to steal his thunder on these here, but I might steal some of the ideas and incorporate them in my RV-3B. I do have to admit that here and there, some of them do add a bit of weight, but not all of them. Here's a view of the baggage floor rails with flanged lightening holes. He made the hole flanger tool, of course.
Dave, I'm just perusing your thread for the first time, and it's been a month since you were working on juggling your angles, so this might be too late, but I thought I'd share what I ended up with in case you found the idea useful.
Mike, that was roughly the idea with the oak blocks above. Not having a press, I used a decent vice, but no joy there.
One of the first things I did on the plane once I got back home was spend a couple hours with a machinist friend putting in the tapered pins in the new tailspring assembly. We did it on his Bridgeport mill. For those of you unsure of the relative precedence of this venerable tool, it's something like this:
Hand-held drills are good.
Drill presses are excellent.
Bridgeport mills are significantly superior.
I refrain from calling them "perfect" only because there are newer, more heavy-duty mills these days, with additional capability. But if you say the word "Bridgeport" to any machinist, he'll know what you're talking about.
Bridgeports are large tools and to be effective, will need a large investment in cutters and holding fixtures. You can get digital devices to assist you and probably even CNC add-ons, and I'd expect that you can rapidly drain your tool budget and outrun your own capability before you even cut a piece of metal. You can look them up if you're interested. They remain solid, reliable mills even today.
Anyway, we lined up the parts and went to work. And I got home that day with the tailspring ready to install -- until I realized that although the pins are fine, one of them is not in its proper place. New parts on order. And I might have to beef up the floor of the Attic of Shame, where all ruined parts go.
The next step was to glue the two F-311 aft-most bulkheads together. The plans only specify one of them but the RV-4 uses two and I was advised to follow that example. Mine are back to back. I did some tweaking to get a better fit and glued them together overnight. Now the masking tape is off and I've got a single-piece assembly to install.
I'd checked the fit of the flap weldment to the plastic F-377-1 flap mount blocks. They were very snug. I spent some quiet time with strips of crocus cloth, and now the flap blocks ride smoothly on the flap weldment.
One tool that I saw on my field trip was a shrinker/stretcher pair. It looked handy so I bought a set from Harbor Freight. It's now assembled in my shop.
Of course I had to grab a small piece of angle and give them a try. First thing I found was that .12 thick flanges simply wouldn't fit in. But .063 fits fine. The process leaves grooves, not all that deep but there they are. In a stressed part I'd certainly need to clean these up. I understand that more expensive stretcher/squeezer pairs have smoother jaws.
And this was after I'd taken out a bit of one of the bends.
I haven't decided yet if I'll replace the seat rib angles. You'll remember that I put in a joggle in one end and a slot in the other. I think that I can use this tool to bend the angles if I choose without any joggle. Might be worth a try.... something to decide. It would let me make those angles out of 1 x 1 x 1/16 angle and narrow them down except at the flap blocks, might be worth it -- but probably not necessary.
Floor Stiffener Joggles
Let me know how they work out for you!
When I left off, the second tailspring assembly had been ruined. The third set of parts arrived and my friend Charley dove in. This was pretty amazing considering that he had a deadline in his company that he should have been working on. After a couple hours, I took the new tailspring assembly home. It's acceptable.
Here are all three sets in order, with the most recent on the bottom. You'll probably notice that the mounting fitting on the top set has been trimmed; the stock tailspring mount doesn't fit the RV-3B aft bulkheads because the mount is from the RV-4. In the middle one, I had started cutting it down before I realized that it was mis-drilled. I have not yet touched the bottom and newest one but I should.
Charley also fit the brass bushing into the control stick for the mixer bolt and now that assembly feels like it's on jeweled bearings. There is zero perceptible free-play in those parts now.
One curious thing that I need to address is that my digital level has decided that the world is about 3 1/2 degrees out of kilter. Well, it's no doubt correct that the world is awry - this is an election year, after all, but none of the bubble levels agree with that assessment. I'm inclined to rely on both my own sense of things and the combined opinion of all my bubble levels. Let's just say that the judges have voted and the digital level is off the project.
Looks like I'll be using my iPhone for the near term.
While I was waiting for the tailspring to get finished, I went ahead and added a few holes to the welded rudder pedals. I think that this saved something like 1/2 or 3/4 of an ounce, definitely worth going after.
I've been playing with using the shrinker/stretcher to put a joggle into those seat angles. There is no question now that it can be done. The only question is whether I am willing to sand off about .002 to about .0025 inches on each side of the flange (total .004 or .005 inches) that I shrink or stretch (or both) to clean up the marks from the tools.
The photos can also be seen here, here, and here.
The new seat angles are fabricated. They went relatively smoothly. I had to work on the flanges to remove most of the roughness from the shrinker/stretcher, which does leave a mark in 6061-T6.
In both pictures, the top one is the new one and the bottom one is what I'm replacing.
It leaves less of an impression in 2024-T3. I used it on the flanges of the F-306 bulkhead to flatten it up while I was fitting the baggage floor rails.
There were fewer marks in the 2024 bulkhead flanges but then of course I was using it more gently. I've decided: the shrinker/stretcher is a good tool and worth having.
By the way, when I started fitting the baggage rails to the F-306 bulkhead, the bulkhead was about an inch aft of it's proper location, clamped to the aft face of that aluminum rectangular tube on the jig (the one that it is now clamped to the front face of). It fit well there, except for the baggage floor rails, which weren't long enough. I moved the bulkhead forward so that the rails would fit, but then the bulkhead was inside the longerons. I hadn't glued this bulkhead yet since I had a feeling it might need tweaking. I unclecoed one side from the other side and spread them apart slightly and clamped them so that they fit to the longerons. Then I reclamped them where they joined in the middle.
I'll have to add splice pieces but it's not a big deal: about .10 inches at the bottom and about 1/2" at the top, more or less.
I'm glad I thought about doing that.
The tailspring mount is clecoed nicely in between my F-310 and F-311 bulkheads where it belongs. Both of these bulkheads are now glued together - you'll remember that I doubled up both of these.
The F-310 bulkhead is riveted, too, to the stabilizer mount bars.
The photos are also here, here, here, and here.
The side-clamps holding the bulkheads to the longerons finally got themselves replaced by clecos. It was fun drilling holes for a change after all that measuring and tweaking and flange straightening.
One of the things that was necessary to do was see if all four splice plates would go in after the fuselage was all riveted together. As received from Van's, they are bare steel, covered in oil. I cleaned them up and lightly primed them.
There are two different styles. Two of the splice plates have square edges and the other two have one rounded edge. It was pretty clear that the rounded edges fit against the lower flanges on the spar bulkhead, and that the square edges fit on the top of the spar bulkhead. The splice plates are marked "fwd" and "aft" and there were one of each style for both locations. I was glad to see that since it meant that I didn't have to worry about which went where.
The aft splice plates went in to their positions nicely, even with the mixer in place, although I removed it for the photograph.
The forward top one went in easily. Unfortunately there's no way that the forward bottom one will fit after the fuselage is riveted. I'll have to have it in place during that operation. Since there are some serious rivets going in close to that splice plate, this might get tricky at that time.
Please remember that I changed my F-312 firewall reinforcement pieces to be more like the RV-4 and pick up both top and bottom splice plates. The stock F-312 pieces provide ample room to fit that splice plate without much drama. I tried to allow for clearance for this but it's just not going to happen.
The photos are alternatively hosted here, here and here.
Here is a photo of the brackets that attach my firewall to spar bulkhead replacements of Van's F-312 ribs. The brackets are attached with a couple of AN3 bolts so that if it's ever necessary, I can remove these to remove the spar splice plates.
There might be some photos earlier that showed these with holes for rivets; I decided to follow the sensible RV-4 scheme and make them removable.
The bolts are hardware-store bolts and will be replaced when the wings are permanently on.
A short editorial:
If you haven't already sent in your donation to support VAF, please do it now. I rely on VAF for a great deal of my support, and beyond that, to host this log of my construction. I wouldn't be building this airplane were it not for VAF. You can do it here. Thanks!
The photo can also be seen at an alternate hosting site at Imagebam.
|All times are GMT -6. The time now is 11:43 PM.|