Wings « Matt's RV-7 Project

Archive for the ‘Wings’ Category

Pneumatic plumbing

Thursday, July 20th, 2023

The pitot tube, to be useful, has to be plumbed all the way to the panel… a long journey through a lot of unhelpful structure. I used 1/4" black nylon tubing for pitot pressure and blue for AOA:

Looking up through the access panel at the plumbing:

This area is difficult to see or photograph, but the tubes loop around to connect to the previously installed fittings:

I used a longer bolt and an adel clamp to keep the tubes from fouling the aileron bellcrank:

Running the tubing all the way through the wing and into the fuselage was only barely doable! I need a skilled helper with both flexible availability and flexible arms:

The tubes take an S-turn that's impossible to photograph, then enter the fuselage through the same bushings that allow the wire bundles to pass:

I secured the tubes out of the way of the aileron pushrod, and ran them aft through a protective 3/4" plastic conduit:

The conduit runs aft under the seat floor, then up the forward face of the F-705 bulkhead:

Another adel clamp keeps the conduit out of the way of the rudder cable:

The pitot and AOA tubes, along with the white static tube, pass up through the armrest through a set of plastic bushings. Don't ask me why I chose to use three separate 1/4" bushings here rather than one single larger one. The pitot line (black) goes all the way to the panel, while the static and AOA tubes are cut short here:

I wrangled the pitot line through a piece of 3/8" conduit, along with two 1/8" tubes for static and AOA. I didn't really want to have to use this tiny tubing size, but due to the space available to run the conduit I had no choice but to use small-diameter plumbing here:

In retrospect I wish I had finished the pneumatic plumbing prior to riveting the center section cap strips. Snaking this conduit over the top of the center section and around the rollbar bolts, without being able to get my fingers on it, was very tough:

The reducer fittings that convert the static and AOA tubing from 1/4" to 1/8" will be hidden behind the interior panels, aft of the pilot's elbow:

Forward of the panel, the plumbing conduit terminates at an adel clamp screwed to the bottom of the subpanel, and the various tubes branch out from there:

This photo is looking up at the bottom of the subpanel, with the nose of the airplane towards the bottom of the picture. I had previously done most of the under-panel plumbing prior to riveting on the forward top skin, but in my haste neglected to document it. Tee fittings are screwed to the subpanel flange with little brackets I made from scrap, and an adel clamp or two keeps everything constrained. To this I zip-tied the AOA tube, adapter-ed back up to 1/4" interface with the #2 ADAHRS:

One branch of the plumbing brings pitot and static to the G5 backup instrument, as well as connecting to the alternate static port:

The #2 ADAHRS lives underneath the radio stack, and is difficult to photograph, but it now has all three of its pneumatic ports plumbed:

I have no good way to leak-check any of this plumbing, but I did apply lung pressure to the pitot tube and suction to the static ports, and confirmed the expected results on the cockpit displays. So that's good enough for me to call the instrumentation air plumbing complete.

Posted in Electrical/Panel, Fuselage, Wings |

Flap pushrods

Sunday, June 25th, 2023

After trimming the flaps to fit nicely to the fuselage, the next step is to finish the mechanism that operates them. The RV-7 plans have you make a pair of pushrods by tapping the ends of some fairly skinny aluminum tubing, but I decided to follow in the footsteps of others and use the beefier hex stock normally used by the RV-9. Since the RV-7 uses shorter pushrods, the easiest way to do this was to simply buy the RV-9 parts and cut them to the correct length:

Real machinists are cringing at the unsupported length in the above photo, but since I didn't have a good way to support these pieces while facing the ends, I just took light cuts and worked carefully. Here's a finished pushrod with one rod end bearing installed:

The most challenging portion of this part of the project was cutting the holes that allow the flap pushrods to pass through the fuselage bottom and sides without binding. I'm told that these are prepunched on the RV-14, which must be nice, since they have to be a strange 3D shape that can only be determined iteratively. I didn't take any pictures of the process, but there was a lot of tedious test-fitting, marking, and grinding until I achieved a satisfactory result:

Here's a view of the same hole from the inside looking down. I still need to clean up the mess of aluminum dust and sanding-wheel particles from inside the fuselage:

I must have installed and removed this pushrod a hundred times before I got the shape of the hole right. Here you can see that there is adequate clearance all around when the flaps are in the full-down position:

Finishing the first first hole took me an entire day and then some. Instead of starting from scratch on the second hole, I used a piece of manila folder to make a rough template that would give me a head start:

Here's the second hole, which only took me a half-day to finish. The blue line indicates where the flap bottom skin ends, showing that the hole will be completely hidden when the flaps are up:

I have to say, this whole pushrod-hole situation seems like a real afterthought to the design, and the way they have you grind your way through the corner of fuselage is pretty barbaric. And I'm not just saying that because I slipped with the sanding drum and scuffed up the fuselage skin:

The plans list the flap travel limit as "40-45 degrees maximum", which is less than precise, but I don't think there is actually much adjustment possible with this mechanism – you just have to take what you get. In my case I am right at 45 degrees at full-down, which is acceptable. I haven't hooked up the flap positioning system yet, so this may be reduced slightly in the future.

I don't want to install the flap mechanism permanently quite yet, and I don't want to damage the flaps while crawling in and out of the fuselage carrying tools, so I removed them from the wings and set them aside for now. While I have improved access to the lower rod end bearings, I removed and reinstalled them with lock washers and blue Loctite in accordance with the plans:

Still some work to be done before the flap system is truly finished, but it was neat to be able to hook up a battery and watch the flaps go up and down.

Posted in Flaps, Fuselage |

Flap fitting

Friday, June 2nd, 2023

I got the flaps down from the attic and installed them on the wings to see how they fit:

As expected, the inboard ends needed a little work to properly fit the fuselage. The flap skin was rubbing on the fuselage in places, and the gap was generally unsightly. The plans don't specify how much clearance you need here, but I've seen numbers anywhere from 1/16" to 1/8" mentioned. I decided to split the difference and shoot for a nice consistent 3/32" gap.

Instead of using a sharpie, I painted each flap skin with marking fluid and then scribed a line along the fuselage side with a 3/16" brad-point wood drill bit. Result, a perfect 3/32" line. (click for the big version to see it)

From there it was a simple matter of cutting and filing up to the line. After a couple iterations I was able to achieve a nice even gap that looks pretty good:

Posted in Flaps, Wings |

Installed and rigged ailerons

Sunday, April 9th, 2023

I brought the ailerons down from the attic and cleaned off the worst of the dust – but not before being perplexed by the critter tracks I found. Let's hope that happened during the time I had them stored in a neighbor's hangar:

One of the steel hinge brackets had developed some rust, and though I could have cleaned it up and repainted it, I decided it was easier just to replace it with a new one:

With all that cleaned up, I proceeded to hang the ailerons on the wings:

I made the required hinge spacers on my little lathe, which is great for this kind of job:

This is what the hardware stack-up for the outboard hinge brackets looks like. (Note: many of these photos taken during the test-fitting process show loose fasteners and non-aviation hardware. I'll fix everything up properly when I'm done fiddling with things.)

I made a set of alignment tools out of hardware-store aluminum and bolted them to the tip rib. It helps to put some spacers between the angle and the rib (I used the lathe again) to prevent it from being bent by the outboard hinge bracket. That would throw off your aileron alignment and lead to problems later. You can also see here how I am holding the aileron in place with a strip of scrap aluminum and some cleco clamps:

This is an easy way to solidly hold the ailerons in the right orientation (tip aligned between the blue lines) while I work on other parts of the flight control system

This photo is looking up through the outboard access hole in the left wing. The W-818 pushrod runs from bottom to top on the left side, and the W-716 pushrod goes off to the left. Visible in back is the W-730 alignment jig holding the bellcrank in the right position. The idea here is that you use jigs to align the bellcrank and the aileron, then adjust the W-818 pushrod to connect them.

Although I fabricated my W-818 pushrods using the dimensions shown in the plans, they ended up slightly short. Judging from the many similar forum posts I've read, this is a common occurrence – it would be best to make them 3/16" or even 1/4" longer, material permitting. I solved the length problem here by switching the jam nuts to AN315s, which are 1/16" thicker than the default AN316s (a modification approved by Vans customer support). This ensures that no matter how the pushrod tries to unscrew itself, the worst-case rod end bearing will still have more than the minimum amount of thread engagement.

Inside the cockpit, I built a temporary jig to align the control sticks vertically, using a collection of woodworking squares which are screwed to a board clamped to the spar:

I maneuvered the W-716 (transverse) pushrods into the wings, adjusted them to fit between the control sticks and the aileron bellcranks, and then got a rude surprise. Although I built them exactly to the length specified in the plans, they are way too short, and will allow the rod end bearings to unthread themselves – an obviously unacceptable condition:

Judging from the many forum threads on this topic, this is another well-known plans error that has caught plenty of other builders just like it caught me. How incredibly aggravating. So now I'm on the hook for $100 worth of parts and the time required to build a new set of pushrods. At least nowadays I'm close enough to the factory to save on what would otherwise be the exorbitant cost of shipping long pieces of tubing. The new parts will be 7/16" longer than the plans dimensions:

These aluminum pushrods are trivial to build, but they end up taking a while due to all the priming required, especially in the winter. I flooded the interior of the tubes with 7220 spray primer and allowed them to dry for several days, then suspended them on strings and primed the outside:

Finally I riveted on the end caps, inserted the bearings with their jam nuts, and slid the new pushrods into the wings. The result is a perfect fit that can't possibly come undone. In retrospect I could have made these 3/8" longer rather than 7/16", but this will work fine. This photo shows that there are still plenty of threads engaged in the worst-case condition where the other end is screwed all the way in:

With the left and right ailerons finally connected together properly, I was able to fabricate the control stops. The plans call for a set of aluminum angle pieces riveted to the hinge brackets, but I wanted to try the popular method of using plastic bushings on the pushrod attachment bolts instead. I happened to have some black Delrin stock on the shelf, so I turned a pair of 1/2" diameter bushings with an aluminum spacer in the middle to handle compression:

This is what the aileron stops look like when installed – the black Delrin ought to be good for UV resistance:

It turns out that – for my airplane – the 1/2" diameter stops are an ideal size. To check the aileron travel I aligned the ailerons with the tip jigs and set my digital angle gauge to zero with the ailerons neutral:

The ailerons on both sides hit the up-stop just shy of the 32º maximum limit specified in the plans:

Similarly, the amount of down-travel is well past the minimum and just under the 17º maximum:

This also gives me my first chance to evaluate the total movement range of the control sticks inside the cockpit. Happily, neither stick comes close to hitting the throttle quadrant, which had been a concern:

Similarly, opposite aileron travel provides plenty of clearance between the sticks and anything nearby. I'll still have to trim these shorter to accommodate my stick grips, but it's good to know what I'm working with:

I haven't torqued all the fasteners yet, as I will probably have to remove the sticks at least one more time, but for now all the primary flight controls are hooked up and usable – a great milestone:

Posted in Ailerons, Fuselage, Wings |

Fuel system plumbing

Monday, March 6th, 2023

Having finished all the electrical tasks in the lower-forward fuselage that I can conceive of, I should hopefully not have too much more crawling under the panel in my future, so there's no reason not to install the fuel plumbing for good. I retrieved the fuel pump/filter unit from storage, touched up the paint on the selector valve plate, and installed the whole assembly in the fuselage with screws:

Next I fabricated the remaining fuel lines that go between the wing tanks and the selector valve. I'm really glad I decided to make these in two pieces, with a bulkhead fitting in each F-783B cover support rib, because it would have been a nearly impossible task to fabricate these lines as a single piece. As it was it was still difficult – even though it's a pretty simple component, the lack of access and the fact that you have to bend and flare it in situ results in a fairly challenging job.

At each outboard side I used zip ties and a piece of rubber fuel hose to prevent the wiring bundle from chafing on the fuel line:

The plans call for a block of styrofoam to support the line that runs forward from the fuel pump to the firewall. I started with some craft foam and a hot-wire cutter:

I split the foam in half and cut out a groove for the fuel line. I like cutting foam with this tool, much less mess than traditional cutting tools – just try not to breathe the fumes.

Fuel line and foam support installed between pump and firewall – the foam block is held together with a strip of clear packing tape:

Out in the wing roots, I fabricated and installed the 1/4" vent lines that run from the tank to the fuselage, snaking around the tank attach bracket in the process. In the background you can see the 3/8" line that goes from the tank outlet into the fuselage:

As a final step in finishing the fuel system, I removed the plastic plugs from the bottom of tanks and installed the fuel quick drain valves:

It's kind of wild to think that, in theory, I could probably fill the tanks and start the engine almost any time I want. Well, a set of working brakes would probably be good first. Still, feels like progress.

Posted in Fuel Tanks, Fuselage, Wings |