Author Archives: admin (Richard)

Under the Cowl – Work Goes On

With a bit of study and suitable periods of procrastination, I was able to rework the newer of the cabin heat shroud parts to fit the muffler. Knowledge and experience gleaned from my work with the heat valve duct was transferred to the outlet duct for the muffler shroud.

I got a start on the oil hoses and fittings. I’ve elected not to use any of the hose and a number of the fittings supplied with the FFW kit for the oil system. Rather than struggle with a vice to clamp fittings and attempting to push the hose onto the barbs – by hand – I picked up a Koul Tool. Not cheap, but it works ever so nicely – if, that is, your 90 and 45 degree fittings have a shoulder. Some of the FFW kit fittings don’t have a shoulder. I’ve replaced those with Aeroquip AQP AN8 fittings. I’ve also gone with matching high temp Aeroquip oil hose. All very nice stuff. Each hose I’m making has swivel fittings at both ends to make an entire system of modular components. Admittedly, I’ve deviated slightly from the plans and supplied parts here, but in a good way. I’m building as experimental in the USA, so I can tweak some things without a big hassle.

Now seemed like a good time to get the radiator and oil cooler secured to the lower cowl with the factory-supplied Sling 2-specific brackets. I’m using Camlocs instead of the kit-supplied Dzus fittings. They’re just better.

Cowl fitting continues, this time with a minimal cutout to clear the exhaust pipe. Eventually, I’ll be bonding reflective fiberglass heat shield to the inside of the cowling where needed.

Windscreen Bonding

Bonding the windscreen is a critical milestone. It isn’t nearly as glamorous as mounting the engine or powering up the avionics, but it means a great deal to the overall aircraft structure and final outcome of the project. It’s a make or break moment.

Surface preparation of the bonding surfaces is very important. Various special primers promote adhesion. Accurately locating the about-to-be-bonded windscreen while things are battered with jet-black SikaFlex polyurethane marine adhesive, onto the frame and fuselage, is aided by reference holes and locating pins. Masking and protecting areas where adhesive does not belong, makes it just possible to get the assembly together without too much of a mess. Gentle, even clamping keeps the windscreen in place while the adhesive cures.

Minimum working temperature for the adhesive is 50ºF. At that temperature it will take up to 12 days to cure and it will be all I can do to keep my workshop warm enough though the winter days, here in Pacific Northwest Washington. Time will tell.

All in all, it seems like I’ve pulled it off! Looks like a good fit, no Plexiglass cracks and plenty of nice adhesive in the right places. Now I just hold my breath for a couple of weeks. Whew! Glad to have this step in my rearview mirror. What a relief.

Windscreen – Trim to Fit

Having put this off as long as I could, I’ve summoned the courage to trim the windscreen until it fits. I absolutely do not want to crack it and I cannot afford to over-trim. It has to be done, just so. If ever there was a time to apply, measure twice, cut once – this is it!

Along the way, I take comfort in and from small stress-reducing distractions. Testing out my fancy new lithium battery charger yields a few moments to gather myself. The charger has a feature that can supply up to 10A of current to power the avionics and allow for extended sessions of testing, configuration and familiarization – ok, play! There’s a lot to learn and it’s going to take quite a bit of play time.

Canopy Latch and Exhaust System

The canopy latch is inset within an oval area that must be carved out of the top front of the canopy plexiglass and underlying composite frame and held in place with blind M5 rivnuts and screws. Let’s just say that this is a challenging and nerve racking set of tasks. And – that’s a major understatement. But, with patience and a good bit of careful work with my trusty Dremel tool, I was able to achieve what I deem, at this point anyway, a satisfactory result.

The latch mechanism is an over-center affair with a hook engaging a latch pin that mounts to the top underside of windscreen support arch. Four 3,2 x 10mm CSK rivets attach the pin and it’s mounting plate to the arch, along with whatever additional security is afforded by a dollop of JB Weld epoxy. Where exactly to position the pin is an exercise left entirely to the discretion of the builder. Good luck with that.

I think by the time I get the weather seal in place, the latch will pull the canopy closed – firmly and without gaps. We’ll see. All of this latch fitment has happened before having the windscreen and support arch bonded in their forever positions. I’ve got my fingers crossed. Time will tell.

The exhaust system has been languishing in a box and it seemed a good time to see how well (if) it fits with the engine and airframe. It looks… maybe not so bad. Good!

There’s going to be some work needed to get the cabin heat muffler shroud assembled, because I don’t have a part that actually fits. So far, I’ve gotten 2 different parts (and part numbers) from the factory, but neither part matches the mounting rings on muffler. Argh. I’ll have to adapt and/or fabricate something. But, at least it seems the exhaust pipes and muffler do fit. Hooray for that.

Windscreen and Canopy – Initial Fit

Rivets, wires and avionics are friendly territory for me, compared to where I’m headed now. Fitting the windscreen and getting it bonded in position are tasks I’ve been apprehensive about – extremely apprehensive.

Manipulating clear acrylic sheet – Plexiglass and Perspex are brand names – that’s been molded into compound curves of unusual size, is just asking for trouble. I don’t like trouble. Dealing with this stuff is tricky, all by itself. Don’t even get me started about cutting or drilling holes in it. Eventually, I’m going to add sticky gooey pitch black marine adhesive caulk to the mix. That could easily lead to – yes, you guessed it – super trouble!

The time has come. I can’t avoid it any longer.

Because I opted for a factory quick-build kit, it came with the main canopy already trimmed and bonded to its painted composite frame. That’s fortunate because it may well have spared my frazzled nerves just enough to be able to deal with the windscreen.

The initial canopy placement seemed easy enough. Screw holes in the frame aligned with the ones in the slide assemblies. Countersinking of the frame will be needed to correspond with the short M8 stainless steel CSK mounting screws.

The arched windscreen support frame was fitted and match-drilled to align with M5 rivnuts that were installed at the factory. I made cardboard templates for left and right sides because they’re different. (They shouldn’t be – but that’s how the factory built it.)

The trial fit reveals that the rear edge of the windscreen will have to be cut back by at least 4 or 5 cm to align with the arched support frame. The lower rear edges (corners) of the plexiglass will just barely be under the fuselage top skin when it’s riveted in place. Precise positioning of the windscreen is going to be extremely important to avoid any unsightly gaps between the aluminum skin and the plexiglass.

A latch mechanism has to be fitted into the canopy. I inventoried the latch parts when I received them, but I could not have detected that the supplied spring was not correctly formed. I checked with the factory and confirmed the situation. They’re going to send me a replacement spring.

Windscreen cutting, drilling and bonding comes next.

Glareshield/Dash and Instrument Panel

I’ve been working hard to finalize work behind the instrument panel before I permanently close up the area and bond the windscreen in place. Once that happens, any work behind the panel will have to be done though the openings where the GDU 460 displays go. I could possibly remove the whole panel from the dash, but it’s really and truly so nestled into place that I don’t want to disturb it. Disconnecting it, reconnecting it, pulling it out and fitting it back seems more challenging than I want to contemplate — or actually deal with. Get everything right before it all gets locked down – that’s the plan.

Instrument Panel Powered Up with Engine Information System (EIS) Displayed

The fuselage top-skin on my factory QB came partially riveted in place. I removed it. I also dimpled the skin and the rib to accept 3,2 x 10mm countersunk rivets. The parachute compartment cover skins will eventually go over the countersunk rivets, to be held in place by just a few domed rivets and slotted “fingers” at the edges of the cover skins. I’ve put the top skin back into position with clecos. The dash has been positioned and match drilled with the skin to accept 3,2 x 8 mm domed rivets. The lip of the dash is bonded to the skin with very sticky double-sided tape – supplied with the kit. The next step is to pull the rivets on the lip of the dash.

Once the dash lip is riveted, it’ll be time to fit the windscreen. The windscreen has to transition from outside to inside. The dash does the same thing. The windscreen needs to go between the dash and the skin at the edges. It’s going to be tight. I probably won’t rivet the skin until, or even perhaps after, I do the bonding process for the windscreen with Sikaflex adhesive.

Before bonding, the windscreen and support arch must be fitted with the canopy. The windscreen will almost certainly need to be trimmed along the rear edge of the arch. It’s all going to be very delicate and require great care. If I crack or otherwise damage the plexiglass windscreen it would likely be many months before I could get another one.

At this point, I’ve managed to get the panel and dash positioned and connected to the harness. The wiring looks crazy. Ok, it is crazy. But, it’s pretty much the nature of the beast. This is a custom plug-n-play harness that’s essentially one piece. I laid it into the CF like a sleeping octopus. There’s extra craziness because of how much stuff I’ve got to connect. I think the only way to make it any neater would have required building the harness on the airplane. That just couldn’t happen. As it is, I’ve got all of the various “tentacles” dressed and secured about as naturally and as stress free as they can be. I’m very happy with it, even if it looks rather wild. There’s a lot there.

I’m delighted to report that once again, the panel has life. This time, the Engine Information System (EIS) is active. The sensors seem to be working. There are still things that aren’t connected yet. But for the things that are, it all looks great and my confidence is high.

So far, working the flap control, hearing the actuator run and seeing the indicator change is my favorite thing. The VP-X Pro and the G3X Touch integration seem nice. Working the radio frequencies and the remote audio panel is very cool. Both radios transmit and receive. The headset jacks are working, but I haven’t been able to try the LEMO connectors yet. Navigation, position and strobe lights work. Cabin lighting works. Oh so nice.

I’ve got to say, it’s more than just a little exciting. Build on!

FFW – Wiring and Fuel System Tasks

As I’ve mentioned before, the fuel system is just short of outrageous. It’s not bad. It’s just that there are plenty of bits and pieces to fit in awkward places, along with the ever present mandate of ensuring the robust integrity of every aspect of the system.

The Sling KAI provides guidance. Careful reading and understanding of the Rotax 912iS Installation Manual is a must. Let’s certainly not forget AC-43.13. All of the information lines up pretty well, yet there’s a lot left to the discretion of the builder.

I’m incorporating all of the fuel system features that appear in the KAI and the Rotax manual, with the exception of a fuel selector bypass check valve for the fuel return line. This valve appears in the Rotax fuel system schematic, but not in the KAI. The purpose of the check valve is to relieve pressure (of residual fuel in the system) to a fuel tank if one or both of the fuel pumps get turned on while the fuel selector is set to off. For now, I’m just going to be careful. But, after 20 years of maintenance experience with my Piper Warrior, I know that I’ve switched on the electric fuel pump [and started the engine] with the fuel turned off. Return pressure is not an issue for the Warrior, but the potential condition of fuel pump on and fuel selector off is common to both airplanes and I’ve already done it – more than once.

Also, as I’ve mentioned in other posts, I’m adding AN6 flare fittings in several places where only barbed fittings were provided with the kit. Key reasons for elimination of the barbs is to avoid awkward conditions for crimping the Oetiker ear clamps and to somewhat modularize sections of the fuel system. To my mind it seems advantageous to have separable pieces that can be unfastened and refastened with wrenches instead of having to cut and then crimp metal clamps. Adding bulkhead fittings for the supply and return lines pretty much demanded flare fittings. Being able to service/replace the fuel filter is another place where swivel fittings seem like they’d be somewhat more conventional and convenient.

The great majority of the fuel fittings are aluminum with just few brass NPT elbows at the fuel selector. Ahead of the firewall, steel fittings are often used, but for experimental applications anodized aluminum fitting are quite common, and as far a I know – not unacceptable. I’m not certain about the metal fuel lines themselves, but Piper put exclusively aluminum fuel fittings behind the firewall and in the wings of my ’84 Warrior II.

The kit provided a big fuel filter with barbs. The engine came with a Rotax part that pretty much everyone that’s building a Sling uses. Me to. The filter really needs to be secured in a suitable location. The sensible and popular location for the Sling 2 seems to be near the battery box. I designed and fabricated a bracket and clamp system.

Another consideration has to do with where to put the fuel pressure sender. Some builders have voiced concerns about making sure that the wet/pressure port faces down, to prevent pooling of fuel in the sender and orifice. I don’t know how big an issue that really is, but I found a place to put the sender and keep the port facing down. More AN6 fittings are involved. I designed and fabricated a bracket and attached the assembly to the engine mount with a cushioned clamp.

One of the things I’ve done is to upgrade the fuel hose. The kit provided SAE J30R7 hose for low pressure fuel supply and return lines. SAE J30R9 fuel injection hose was provided for the high pressure lines between the fuel pump an the engine. I’ve replaced all of the R7 hose with R9. The R9 hose has low permeability and resistance to methanol. There’s also R14 hose. It seems to be somewhat more available, but samples I’ve found are noticeably stiffer than R9 and I believe the pressure rating of the R14 is about half that of the R9. The R14 hose would probably be adequate, but I’ve gone exclusively with the R9.

I’ve built several of the short lines with connectors and firesleeve. I found push-lock fittings specifically for 5/16″ hose. Assembly with those fittings is easy. The ear clamps are solid.

The 5/16″ hose and and several of the fittings – especially the 1/8″ NPT fittings – are a bit on the narrow side. So franky are some of the barbed fittings supplied with the kit. I’m under the impression that the small variations I’ve made will not introduce inadequacies in the feeding of the miserly 912iS, even at full power. If it were a 914 or 915iS it would be a different story. From what I can see, I don’t think I’ve changed the game. I’ll test carefully, you can bet on that.

The fuel system also incorporates a tiny pressure relief channel between the supply and return lines that allow the high pressure side to bleed down into the return circuit when the [engine and] fuel pumps are turned off. Rotax shows this before the fuel filter, but the Sling 2 KAI shows it after. After lots of consideration, I think I’ll go with exactly how the KAI depicts it, using the T-fittings that were provided. I did however, purchase a clever manifold part from Lockwood Aviation that I’d seen on another builder’s blog. Since then I’ve seen the same part used on several Sling builds. The part incorporates the orifice for pressure relief, NPT threaded input and output fittings for pressure and return lines, and also a place to attach the fuel pressure sender, but all at the cost of more fittings that, in close proximity with the fuel filter and another check valve, presented an awkwardness that I don’t care for. I’ve decided not to use the Lockwood part.

Dealing with firewall penetrations is a subject with seemingly endless discussion. It’s a good topic, I’ll admit. The kit came with a big hole in the firewall and 2 halves of a cover plate. This is where avionics power and engine management cables go. The KAI makes a brief mention of the plate and setting some rivnuts, but not much more. I ended up making a sort of gland out of scrap silicone engine baffle material. My Warrior has the same thing where throttle and mixture cables penetrate the firewall. I replaced those cables some years ago. Piper used a paper-like material, but it had seen better days. The silicone material proved to be an excellent replacement for the Warrior. I’ve used the same material here. I’m not done with. It still needs to be sealed. But, it’s basically what I think I want.

While I’m working to get the FFW tasks finalized, my priority is getting the glare shield/dash, forward fuselage top-skin and windscreen done. I want the panel in final position and completely working before I do that. For confidence testing, I’m connecting up all of the power and grounds for the fusebox and engine.

Fuselage Tasks – Cables, Wire and Lines

For an E/A-B project there’s a seemingly endless list of small tasks. Some things are simply items in the KAI. Other tasks are things that come to mind as you think about how its all going to come together. Task creep just seems to happen. As long as it doesn’t get out of hand – it’s a good thing.

There is a daunting amount of wiring to support the avionics I’ve elected to squeeze into this airplane. Frankly, I’ve gone overboard. On the other hand, I’ve got all of the makings for a technologically advanced airplane (TAA), extremely well equipped for IFR training and cross-country adventuring. Finding good ways to dress and secure the wiring bundles is important. I’ve put a lot of thought into it and determined that an extra bracket will help me keep the harness up and out of the way. I designed and fabricated one.

Many things have to be squeezed into available space without undue conflict. Wiring, fuel lines, pneumatic lines, brake lines, valves, linkages and such. While there are plenty of best practices for how to do things in airplanes, finding ways to apply them to all of the situations that present themselves is what keeps this amateur builder scrambling for ideas. There’s always something new to learn. It’s fun. Challenging, but fun. Yes. It is. I think.

The fuel-injected Rotax engine has a somewhat complex fuel system. The fuel lines have a fuel supply circuit and a fuel return circuit. When you add filters and a duplex fuel selector and physical considerations, the plumbing details border on outrageous. How I do it is up to me. The KAI supplies only general information. I’m also introducing AN6 flare and push-lock swivel fittings in several places where barbs and ear clamps were originally called out and supplied. Figuring out where and how to mount and connect many of the fuel system components is ongoing.

Some tasks just need doing. Then they’re done. Cutting coax cables to length and adding connectors is straightforward enough. Done. The Rotax 30A Regulator B needs a heat sink that calls for the regulator to move from the fusebox to a nearby location on the engine mount. Done. There are a couple of GPS antennas for the PFD and G5 flight instrument that found homes on top of the GAD 29, above the center avionics stack.

Brake lines need to be routed. The time to do it was now. One line goes from the brake fluid reservoir, through the firewall, to just under where the throttle and brake quadrant is located. From there, another line originates at the pressure side of the master brake cylinder an runs to a compression T-fitting under the console compartment. Two other lines run from the T-fitting, down the main gear legs to each wheel. The combination of the 3 lines and the T-fitting were challenging to place. I should have done it earlier, when access was better. It’s done now.

I received some [evidently] old-style mounting hardware for the parachute activation handle, so I ended making a small bracket to secure the activation pull-handle to the back of the instrument panel. It’s nice. It’s done. My design turned out to be a slightly improved version of a bracket I eventually saw in a photo from the factory. Great minds think alike.

It was time for pneumatic lines to go in. I found a really nice way to route them from the left wing root, though the center console and up behind the instrument panel. Because I’ve seen that the Sling TSi documentation now shows 2 static ports, I added a second one in front of the LH fresh air NACA duct. Both of the equal length static port lines arrive at a push-to-connect T-fitting at the center console. A short line runs from the first tee to another T-fitting that provides two more equal length lines to the the G5 and to the GSU 25C ADAHRS unit. The pitot line has a single T-fitting that also splits between G5 and the GSU 25. The AOA line only goes to the GSU 25. All done.