It took some time to get back to my “Showplanes Cowl with A/C left hand inlet plenum problem”, but this week I finally unleashed my new 3D printer on the problem, and the result was great.
This is a complex part, and I evaluated several different slicing applications to figure out how to do the necessary support structures. I wound up using Cura, because of its “Tree” support capabilities. It generates all sorts of weird tree trunk/branch constructs to support the part while it is being printed. This results in less interference between the support and the part.
It took 4 days 16 hours to print the part in ASA, using a bed temperature of 100 deg C and a 0.4mm nozzle at 250 deg C. I did gear up to use a dissolve-able filament (HIPS) between the support and the part, but decided for the first trial to simply use the one extruder. As it turned out, the support was easy to rip away with a pair of pliers, so I’ll stick with the single material process to save time and complexity.
There were a few areas where the support came slightly adrift, causing rough regions on the part. I need to fix this by manipulating the support to have better adhesion to the bed. It takes about 5 hours to render the model, another hour or so to “repair” the STL, and about an hour to slice the result and generate gcode for the printer. Although the part as printed is certainly usable, there are areas I can improve on. Since each printed part is a 5 day exercise from start to finish, and comes with a filament cost, I won’t be spinning revisions too often.
There are some new materials around, Polyamide with Carbon Fiber filler, which are stronger and have higher operating temperatures, up to 180 degrees C. I can print these materials if I install a hardened nozzle on the printer, but I’ll hold off on this until late in the build because the filament is expensive, and there are new products hitting the market all the time.
For now, I have the entire process under my own control and I’ve been able to print a perfectly acceptable part – mission accomplished for the inlet plenum, finally. Now I can finish the front baffles in this area.
How many hours have I spent on this? A lot, between assembling the printer from parts, calibration, printing test parts, evaluating slicer software and monitoring the printing of the plenum. None of this is really direct work on the air frame, so I’m going to simply log 1 hour for this activity, knowing full well that it was many times this.
Starting the inlet plenum print, layer 1
A day in, and a long way to go
A bit over half way
Nearing the end
Print complete!
Support rips away quite easily
Complete part less support
Installed - and a perfect fit!
2 inch connection is for heat muff SCAT tube
Room for A/C connections
A/C line connections will work OK
Air filter fits inside here, fits into standard Showplanes system
I got an E-mail from someone wondering why I stopped posting.
I’ve been steadily working the project, but having reached the “90% done, 90% to go” stage, it’s been hard to progress many tasks through to completion. Winter down in Tassie was long and cold as usual, and the short days tend to slow down workshop hours. Thankfully that’s now behind me for the year.
The inlet plenum 3D printing work reached a stalemate. After many Covid delays, I received the second prototype and it was damaged in transit due to poor packing. I worked with the vendor and insurance to have it replaced, and after yet more Covid delays the replacement arrived, also smashed in shipment. I was able to tape together enough pieces from the two parts to decide that the shape was going to be correct; however, I lost faith in the high temperature epoxy material – it was clearly too brittle. The correct material is ASA, but the quality of the first prototype was not good enough. In order to compete in online 3D printing services you need the lowest price, and there’s a big difference between how this first prototype was printed and how I would want it done. I talked to a few vendors in Australia, and it was clear that the cost would rapidly escalate into the thousands of dollars, for each printing, and I might want to do more adjustments yet. I decided to shelve the work, and ordered a commercial grade large form 3D printer. After months of delays, some again due to Covid-19, this thing will arrive here next week. The only problem is it arrives in 8 boxes and I have to assemble it. Once I get it up and running, I’ll be able to print the plenum as many times as I care to, with the quality I want, before calling it right.
I designed all the overhead panels, some auxiliary panels for headset connections etc, and settled on the replacement lower panel arrangement for the Aerosport 310, which was previously incorrect. I worked with AFS to get these designs finalized and the panels are being cut and printed at this time. In the meantime, I made some cardboard replicas and used these to do most of the overhead wiring. I’m not willing to post a photo of that.
I’ve been doing the wiring, which is a big job for an RV-10 made bigger by my choice of 2 batteries, 2 alternators, a 3 screen panel, A/C and SDS EFI. The wiring is about half done overall, and currently looks like a disaster. I started out wanting to simply do the wiring behind the baggage bulkhead and through the overhead, so that I could finish up the tail and put the final skin on. This plan rapidly devolved into an acceptance that I had to do all of the wiring, there are too many interactions to lock up one part before all parts of the puzzle are solved.
Associated with the wiring are some custom electronics. These pieces are:
Backup EFIS power. The backup EFIS power nominally comes from the second battery/alternator supply. However, what is the action in the case of an electrical fire and smoke starting to fill the cabin? It has to be “both masters off”, there’s no time to figure out which system is the problem. The engine will keep running because the EFI system is separately powered, but in order to keep minimal EFIS functionality, the regular backup battery must be used. So, I designed a board which will supply backup power to the AFS system, which will come from the secondary battery/alternator system if it is running, otherwise will come from a backup battery. Changeover is automatic, and the functions are ground tested as part of the runups.
SDS EFI power. Although the ignition systems, the two fuel pumps and the two ECU’s are on physically redundant battery+alternator systems, there is only one set of injectors so I needed what some would call an “essential bus” to run the fuel injectors. Any place physically redundant systems have to come together is a problem so I’ve applied some effort to this which I’ll post more about in a few months time.
Monitoring and logging. Between the extra TFT display on the panel, the EFI power system, the battery backup system and the A/C there are various sensors and data monitoring that I wanted brought back to a central non-essential point. A small embedded computer system sits under the pilot’s seat and has various communication methods to collect data and present information on the extra TFT display. This may eventually be a last resort backup EFIS, but not initially. I needed a set of interfaces for this embedded system that went beyond what is commercially available, so I’ve done a board for that as well. The prototype worked OK with a couple of jumpers and I’m re-spinning the board now.
In between all these activities, I found I was missing various miscellaneous/low-cost parts, which I’ve procured on a slow track with a few consolidated shipments from the US, again affected somewhat by Covid delays.
Reading through all of the above, it’s clear that I’ve done quite a bit over the past few months, but haven’t managed to actually finish anything. When I finally do manage to finish something, I’ll put up a celebratory post that will include some photos.
I have no idea how many hours I’ve spent on the above over winter – quite a lot – but I’m just going to log 100 hours because I really haven’t kept track of it all.
I bought my A/C kit quite a few years ago from Airflow-Systems. I was shipped a so-called “Australian” evaporator, which is actually a product called a Monster Trunk System, part #685000-VUY from https://www.vintageair.com. There was a collection of metal parts and adapters in the kit, with no obvious way to set up the air flow and no instructions for this evaporator unit. The evaporator contains a 3 speed high volume scroll blower, which is ill suited to pressurizing the overhead console. Several other builders have supplemented this evaporator with an inline blower which is more capable of pressurizing the overhead console. Yet another technique has been to forget about the overhead, turn the unit around and fit enough ducting to blow air straight into the cabin – see here.
I was already committed to a conventional mounting position, having done the inlet ducts and cutout for the overhead several years ago. What I needed to do was complete the evaporator outlet ducting, including an inline blower to suitably pressurize the overhead console, cabin flood air ducting, and a means to use the rear NACA vent air, via the Aerosport products NACA vent valve. This exercise is complicated by the fact that there isn’t a single right angle anywhere in the system, and it all rapidly turned into a 3D modelling exercise. First though, here’s a description of the evaporator inlet system I put together a few years ago:
The F-1006 bulkhead attachment for air to pressurize the overhead is a difficult area. In order to get enough air volume, a significant cutout is required. This mandates a doubler plate, and there is not much room to fit one. Edge distances, strength, clearances, Aerosport overhead console flange dimensions and screw positions for the rear baggage bulkhead all come into play. I wound up using both a shim plate and a doubler, in order to tie the doubler in with the rivets which secure the top of the F-1028 baggage bulkhead channel. Rivets for the doubler are flush on the rear side (where the manufactured heads are inside the overhead console air space) and flush on the front side where the baggage bulkhead overlaps the F-1006 flanges. I lowered and moved the normal position of the baggage bulkhead top screws, in theory they should have landed right in the middle of the Aerosport overhead lower flanges, in practice they are a little above this point but still easy enough to install.
This whole area is so busy, it is difficult to find a good way to “attach” the required air duct(s) to the bulkhead. It’s also not reasonable to have hard attachment points between the bulkhead and the evaporator/shelf, due to vibration and cracking. The idea of this design is to use a 3D printed bulkhead attachment block to achieve the following:
It can be fitted to the F-1006 bulkhead after the top skin is riveted on, sealed with some form of gasket material, and brings the air duct attachment plane clear of the bulkhead.
Two long #6 screws act as locating pins for the flange of the main attach duct.
A thick/soft gasket or manifold can be used between the rear of this bulkhead attachment point and the main duct, to seal airflow and provide vibration isolation.
If (when) the evaporator arrangement changes, a new 3D duct can be printed to mate with the existing bulkhead attachment point.
I use only one hole for airflow into the overhead, the side with more area (the F-1028 is offset from the center). Manifolding air into both sides complicates things and is pointless – what matters for overhead air is pressure, not volume. I wanted electrical connections into the overhead as well, so these are on the right hand side of the bulkhead, and will be sealed off in the overhead.
Cutout for overhead air feed, with shim and doubler plates
Holes for electrical conduits into overhead, with doubler plate
3D printed template for bulkhead attach block, to verify it clears all obstacles.
3D printed ABS bulkhead attach block, bulkhead side.
Bulkhead attach block trial fit. Installation can only happen after top skin riveted on.
A/C evaporator on shelf, with 3D printed inlets.
3D printed inlets are contoured to match the curved front surfaces of the evaporator.
Production inlet parts, made from tough epoxy, to replace the ABS prototypes
Production inlet parts in place
Cutouts done, nutplates in place
I added a stiffener to the front face
Fitting a rubber seal over the original evaporator inlet
Cover plate in place, screwed on. Rubber pads on front of inlets, riveted on and sealant applied
Cutout in evaporator shelf for receiver/dryer
Clamping shroud for receiver/dryer
For the evaporator outlet, I designed a manifold which caters for the following requirements:
Fits onto the two irregular shaped outlets on the evaporator, with a simple rubber seal and some screws.
Provides an outlet for the inline blower. I used a 4″ blower, because it fits. A 3″ blower would probably also be adequate.
Provides a pair of outlets for cabin flood air. These should probably be 2.5 inches each, I used 2 inches because that’s the attachment size I have room for on the front (top) bulkhead.
Provides a pair of inlets for the Aerosport NACA vent valve, to feed vent air from outside into the system
Provides a place to mount a temperature probe
Can be assembled in-place, or if necessary by lowering the rear edge of the evaporator shelf (after removing the support).
The following pictures show what I came up with. I had the prototype fabricated in tough epoxy, and it fitted fine except for an indentation on the top that I made to clear the top stiffener. For some reason my measurements were off, and the indentation missed the stiffener by 20mm. I fixed this up and made some other improvements, and just ordered the final version which should arrive here in another week or so.
The 4″ blower just fits in the required space. I’m mounting it to a metal bracket that will be riveted to the cover plate I made up for the evaporator inlet. Also mounted on this cover plate are three relays (for the scroll fan) and a pwm controller for the inline blower. A wiring harness for this can be seen in the pictures, not properly laced up or secured yet. A high side pressure sensor, and evaporator air outlet temperature sensor, are included. The system controls will be on the overhead, except for the master “A/C on” switch which is on the front panel, pilot’s side. Turning the A/C off (before rolling) will be on the pre takeoff checklist, if necessary it can be re-engaged at some point during climb out. Part of the wiring includes a connector that could be used for a micro-controller that would be capable of climate control, if the rotary switch in the overhead is set to the “auto” position.
The final duct is to go from the outlet of the axial blower to the overhead. I printed some prototypes for this on my own consumer grade 3D printer using a flexible material. Once the shape was correct, I decided to order the production part in SLS Nylon. This will be very strong, but will still have enough flex to effectively detach the evaporator/blower assembly from the airframe. Although I will be assembling all of the final components with the top skin still partly open, everything is designed to be removable and reassemble-able after the skin is in place. It won’t necessarily be pleasant working back there in the hell hole, but it can be done. For assembly, I’m going to take advantage of the skin being off and will cheat as follows:
With everything in the tailcone finished, and with the evaporator/shelf removed, cleco the top skin on in its entirety. With Rosie outside on the rivet gun, and me inside, we’ll rivet the holes across the front and towards the rear on each of the three stiffeners.
Remove all the remaining clecos, allowing access from each side.
Fit the bulkhead adapter and the (flexible) duct from the inline blower outlet to the bulkhead. This can’t be done until after the (above) rivets are set.
Install the evaporator, shelf, outlet manifold, inline blower, NACA vent valve etc, using the access from each side to make the job easier this first time.
Fit the remaining refrigerant hoses etc. and charge the system. I plan to use an electric motor with a grooved pulley and a long serpentine belt as a means to run the compressor for this step.
Check for leaks and proper operation.
Cleco the skin back up, climb inside and finish riveting on the skin.
Evaporator outlet manifold
Top view
Bottom view
Right side view
Left side view, small hole is for temperature sensor
Construction work has been spotty for the past few months due to some work commitments. Time to catch up on a few posts.
I received the prototype 3D printed inlet plenum, after a very long delay caused by Covid-19, a shipment lost in customs, reprinting a replacement, more shipping delays etc. This part was printed in ASA material by a vendor in Sweden. Quality is good apart from some areas where the wall thickness should have been greater.
The part fitted perfectly around / through the compressor, the air filter shroud mount etc. The inlet ramp was also good, perfectly horizontal and lined up with the opposite side (standard Showplanes fiberglass plenum) within 1mm, which is good enough for me. The front edge of the inlet ramp is too far forward, requiring me to trim too much of the cowling. While it would work, it doesn’t leave as much of the cowling inlet hole as I’d like, to get nutplates and some sort of overlapping seal in there. This is one of the areas where the wall thickness is also a bit low. Clearance on the bottom side to the cowling is good, a bit over 1/8″ at the closest point. The rear scat tube connection for a heat muff is also good.
Overall, close to a hole in one which I’m relieved about given how complex the part is. I can now proceed to finish the front of the baffles and around the governor. I’m going to need to address the wall thickness issue and trim back the front edge, which means re-printing the part. These are simple adjustments but I’m going to also look at whether any better alternatives exist than the ASA material I’ve used.
It’s really hard to see much from the pictures, because the 3D printed part is black, but they show the general idea.
Prototype inlet plenum in place
A/C fitting clearance OK
A/C fitting clearance OK
Prototype inlet plenum in place
Good fit around A/C and into air filter shroud
Good fit around A/C and into air filter shroud
Horizontal, and about 1mm below right hand side plenum - good enough
Since I didn’t use the Skybolt flanges, I needed to drill out both the cowl and the custom built flange holes that I’ve been cleco’ing so far for holding the cowl in position. I used a step drill to take a section of holes out to 15/32″, removed the cowl, and drilled the flange holes further to provide enough clearance for the retainers. A tapered hand reamer is handy for touching up the 15/32″ cowl holes slightly to fit the rings.
I used floating retainers for the lowest position on each side. These allow a bit of up/down movement, not sure they were necessary but I put them in anyway as they were part of the kit.
While waiting for the 3D printed inlet plenum, I went back to complete a few cowling jobs.
The hole that I cut out of the lower cowling to clear the A/C compressor needed to be filled in. To do this, I taped a 1/4″ thick cardboard spacer in front of the A/C compressor, then applied play-doh to build up a shape that looked aerodynamically reasonable. I applied more masking tape over this, and then packing tape to act as a release agent. I then took the bottom cowling off, and applied two layers of fiberglass cloth over the taped off area. Once this cured, I pried it off, trimmed the excess, and scuffed the resulting shape all over.
After removing the tape and packing, I epoxy’d and cleco’d the shape piece in place, turned the cowl over, applied thickened epoxy to fill the gaps around the cutout, and then applied two layers of glass cloth over the entire inner area. Once cured, I applied a layer of micro to the outside, and sanded it back to form the final shape. There were a lot of crater sized pin holes and these will have to be filled, apart from this the A/C compressor bump on the lower cowling is done.
I also did the oil door. I stiffened the door with a piece of 0.063″ Alclad, bent into shape by hitting it with a rubber mallet. In retrospect, I should have either drilled some lightening holes in it or perhaps 0.032″ would have been OK, the door is quite heavy. I used a pair of Cessna KM610-64 Camloc’s for the catch, building up the button area with thickened epoxy to match the oil door thickness.
I also fitted the Aerosport RV-10 emblem covers to the cowling halves. Just follow the instructions, being careful not to epoxy the cowl halves together anywhere except where you intend to.
Taped 1/4" cardboard spacer in front of A/C compressor
Essential materials
Building up the shape
Taped up with packing tape
Two layers of glass cloth
Trimmed shape in place
Applied two layers of glass cloth to inside cutout
After one round of micro, needs more work
Oil door and stiffener plate
Alclad plate to stiffen oil door
Setting stiffener plate in place
After epoxy set
Drilling oil door hinge
Drilling holes for release catches
Release catch buttons built up with thickened epoxy
Release catches in place, roughly sanded
Release catches in place, roughly sanded
Stainless steel catch plates in place
Almost completed oil door
Glassing in Aerosport templates
After curing, with holes drilled and template punched out
A couple of months ago I bought a pair of long stroke 3000kg hydraulic jacks, because I knew that “soon” I was going to have to jack the fuselage to finish some jobs on the main gear and do the wheel spats. After that I would need to be able to safely jack the entire aircraft for ongoing repair and maintenance. I reviewed a thread on VAF that contained various pictures of how builders had made Jack Stands, to provide stability for the Jacks and reduce the chance of a disaster.
I also bought some Jack Pad adapters from Bogert Aviation, these screw into the wing tie down points and provide a non-rigid jack point. The Jack Ram adapter didn’t fit on my Jacks, the adapter was larger than the Ram diameter, but there were a pair of grub screws to secure it.
I asked my eldest son – who works in industry and has done a lot with metal – if he might have some scrap plate lying around that I could make a few base plates from, and showed him the pictures on VAF. He said “leave it with me”, and some time later came over and picked up a Jack.
The other day he brought over the most awesome pair of Jack Stands I’ve ever seen, complete with routed out base plates, welded supports and a two section collar that bolts together to retain the Jacks. He also had a pair of adapter rings, which perfectly fitted the Bogert Jack Ram adapters to the Jacks.
I’m now all set to Jack the airframe. What else can I say?
Over the past month I’ve had to deal with something that was always going to stop the project dead in its tracks – sorting out how to mount an Airflow Systems A/C compressor inside a Showplanes cowl. The main problems are:
The A/C compressor doesn’t fit – it smashes into the cowl
The A/C compressor occupies almost all of the space normally used for the left hand air inlet plenum
I’ve seen other build efforts that range from leaving out the left hand induction air plenum entirely, to an A/C compressor mount position that occupies a good part of the area of the left hand inlet duct – in turn compromising the cooling air for cylinders #2, 4 and 6.
Recent efforts in Australia, such as this one, use a longer arm on the A/C mount to drop the compressor down low, and make a bump on the bottom cowling to suit. Armed with the latest mount kit from AFS, I proceeded to test mount the A/C compressor, and immediately ran into quite a bit more trouble than I had expected.
Tensioner wheel, bracket
The supplied drive system simply didn’t work. The tensioner (idler) wheel, using the supplied bracket, hits the starter motor. I can see that with the previous “short” arm, the system would swing up higher and that would free up enough room for the idler wheel to swing past the starter motor. I sent feedback to AFS about this but received no reply. After consulting with the Australian builder referenced above, it turns out the solution was to:
Add spacers, for a total of 7/16″ of spacing, to the engine mount. This moved the entire compressor assembly “away” from the starter motor by 7/16″.
Machine a replacement idler pulley, which was the same size as the AFS supplied pulley, but without the ridges on each edge – saving around 1.5mm of edge distance.
Make a longer arm, even longer than the “long” one AFS supply
I started making up additional spacers (AFS supplies three 0,063″ spacers), using 0.063″ Alclad, but I was only able to add two of these before I ran out of threads on the engine studs used for the A/C mount. I didn’t want to replace these studs, and I didn’t want to switch over to low profile lock nuts – the A/C compressor is quite heavy. So, my spacing limit without resorting to these measures was 0.3″.
The guy who did the VH-BKK installation referenced above graciously had another idler pulley made, and sent it down to me. Armed with this, I still needed to change the position of the idler mount, which means I have to build a new idler mount bracket. I’ve ordered some 6061-T6 plate to do this, in the meantime I drilled a new hole in the existing bracket (rendering it structurally unsound) just to prove I have the hole position correct. This is shown in the following picture, along with the new idler pulley. The clearances everywhere around this are very small, but this is typical and they will be adequate. The idler pulley can now swing up past the starter motor with about 1.5mm of clearance.
I also had to change the Serpentine belt, for this arrangement I fitted a 4PK1130 belt, rather than the 4PK1113 belt provided with the kit – just 17mm longer.
It is necessary to cut out a section on the front of the Showplanes cowl and fiberglass a bump in place to provide adequate clearance for the front of the A/C compressor. There’s nothing hard about this, and one good thing about the Showplanes cowl installation is that the Serpentine belt does not overlap the inlet at all (unlike with the Van’s cowl) – so there is no air leakage associated with treatment to clear the Serpentine belt, and no compromise to cooling air inlet area.
New location of idler hole (dimensions in mm)
Modified tension pulley position
LHS Inlet Plenum
I had expected to solve this problem with various cuts and balloons etc. to the existing inlet plenum. After looking at the problem, I didn’t even attempt it because (a) this was going to beyond my fiberglass skills, and (b) this is probably beyond anyone’s fiberglass skills. There simply isn’t a clear enough path through the maze to make an adequate shape, and unless I could turn the plane upside down, gravity was always going to work against me.
After some soul searching, which included consideration of leaving the A/C system out, I decided to go ahead and create a 3D model of the entire system as a means to 3D print a replacement inlet plenum. The top end is identical to the Showplanes system, using the lower 1/3 of the circular inlet hole for induction air. The plenum has to step down and change shape, wrap around the bottom of the A/C compressor while clearing the bottom cowling, and then join in to a replacement shroud around the existing Showplanes air filter system. Here are some screenshots which include various early prototypes and the final model, which includes an air takeoff to account for the standard Van’s 2″ scat tube outlet for air to a heat muff.
Early model - rear view, showing heat muff scat tube attach point
Early model - Front view, without compressor
Early model - top view showing heat muff air inlet - slot is for Van's supplied mesh screen
Early model - left side view showing heat muff air inlet - slot is for Van's supplied mesh screen
Early model - Induction air inlet, detail showing clearance for Serpentine belt and A/C compressor lug
Early model - Rear view with A/C compressor model in place
Early model - Top view with A/C compressor model in place
Early model - Right side view with A/C compressor model in place
Early model - Front view with A/C compressor model in place
Inadequate clearance for botton A/C fluid connection (early model)
Prototyping with small sections taped together
Prototyping with small sections taped together
Location of A/C cutout in Showplanes cowl
Final model
Final model - Serpentine belt and A/C compressor lug clearance
Final model - Rear air takeoff for heater SCAT hose
Final model - Air filter shroud, note drain hole provision at bottom
Final model - Viewed from bottom front
A/C clearance (note: not fully rendered)
A/C clearance (note: not fully rendered)
Bottom showing fluid connections (note: not fully rendered)
View showing clearance for fluid connections (note: not fully rendered)
Separate shape under design for attachment around Governor
The inlet plenum as shown can be 3D printed in one piece. It is secured at the bottom by three screws in the LH air filter shroud, using nutplates, same as the standard Showplanes arrangement. Around the compressor, two places mount to the A/C compressor lugs using Buna-N rubber spacers, AN3 bolts and washers. The vibration-damping spacers are rated to 200 degrees F which should be adequate. At the top, a flat Alclad plate which extends down from the existing #2 cylinder mounting flange is secured across the heat muff air inlet area, and at the very front of the inlet, using #6 countersink screws with nutplates on the underside of the inlet plenum. One of the front positions uses a low profile nut, embedded in a hex shaped hole, instead of a nutplate.
For the plenum material, the choices are currently between UV resistant ASA, or the more expensive UV resistant tough resin. Both have high glass transition temperatures and adequate chemical resistance. The plenum does not extend back too close to cylinder #2.
To prototype the system, I printed the plenum in sections on my cheap consumer grade 3D printer, using PLA, and taped the parts together. It takes about 100 hours of printing time to do the complete model, and I’ve made several revisions to refine the design and fix up the various maths mistakes I made along the way. It’s been a laborious process but I’m happy enough with the end result. It takes a high end desktop platform 15 hours to render the model in suitably fine detail, and a bit of repair processing to derive the final STL file. I uploaded the (64MB) STL file to http://www.craftcloud3d.com and was quoted just over U$200 to print the model in Black UV resistant ASA, with 40% infill.
Just today I pulled the trigger and ordered the final article, it’s being printed by a vendor in Sweden, and will be delivered here within two weeks. There is still a chance that the final piece will require some small adjustments. There’s a limit to how far I can go with taped together sections, and how many times I can re-measure everything. The final model is way more complex than I had expected, and has consumed far too much time, I’m tired of fretting about it so it’s a relief to get it off my desk.
In the meantime, there are a few other, much simpler pieces I can design to help with the baffling around the governor etc. I’ll complete these, but mostly I’ll be getting back to actual, real, physical work on the project – there is a lot still to do.
In order to use SDS EFI &/or ignition products, it is necessary to modify the ring gear to insert magnets for timing sense. This is a straightforward procedure, but not commonly done for dual pulley ring gear as used when an A/C compressor is fitted to the engine.
My ring gear (flywheel) was supplied by Airflow Systems as part of the A/C kit, and uses a serpentine belt for the A/C compressor drive. The magnet insertion points wind up in the middle of the serpentine belt area, which changes how things need to be done compared with the standard procedure published by SDS. Here’s what I did.
My flywheel had timing marks on the front side only. This confused me for a long time because the timing marks didn’t line up with the tooling holes as described in the SDS procedure. It turns out this was all because of my ignorance about Lycoming engines. When timing marks are on the front side of the flywheel, the TDC #1 mark lines up with the small hole at about the 2 o’clock position (viewed from the front) of the starter motor. When timing marks are on the aft side of the flywheel, the TDC #1 mark lines up with the vertical split at the top of the casing. So, with the flywheel lined up at TDC #1 (which I confirmed by looking at the #1 piston through the top plug hole), I marked the rear TDC #1 mark, and the tooling holes then matched up as described in the SDS instructions.
There is a difference though – the tooling holes in the Airflow Systems flywheel are 3/16″, whereas those in the standard flywheel are 1/4″. Ross at SDS kindly made me a drilling jig to suite the flywheel I have.
I then went ahead and drilled the flywheel exactly as per the SDS instructions, using a new #29 cobalt split point drill and plenty of cutting fluid. By sheer good luck, the holes wind up exactly centered in one of the grooves for the serpentine belt – see the pictures. This is lucky because it means it isn’t necessary to rebuild the “crest” of the grooves on the flywheel, just fill in material that has been removed inside the groove.
I tapped the holes #8-32, again as per the standard instructions, and carefully de-burred the sides of the holes in the micro-V groove using needle files, sandpaper and a magnifier. I then cleaned out the holes thoroughly with acetone. At this point though, it is necessary to deviate from the SDS procedure.
There isn’t enough depth to insert two grub screws as well as the magnet, only one grub screw will fit. Here’s what I did:
Each hole contains the magnet, and one grub screw. I soaked the grub screws in acetone to remove any grease or oil, then set the four grub screws aside on a clean, dry tray.
For each hole, I picked up a grub screw with an Allen key, applied red loctite (these aren’t ever coming out) to the grub screw threads, and inserted the grub screw to a bit short of the right position from the outside, leaving the Allen key still in place.
I then mixed up some 5 minute epoxy, filled the hole per the standard instructions (the plastic shaft of a Q-tip with the head cut off works well for this), and inserted the magnet from the inside. The magnet gets pulled in and smacks against the grub screw.
Now carefully wind the grub screw further in, until the magnet is at the desired position, just inside the inner surface of the flywheel. Remove the Allen key. Wipe off the excess epoxy with some acetone on a clean rag.
Clean off the red loctite from the serpentine pulley groove with acetone. I used a piece of paper towel with acetone, and a clean feeler gauge to get right down to the bottom of the groove. Then I used a Q-tip dipped in Acetone to get down and clean the loctite out of the threads in the hole, above the grub screw, while holding the flywheel so that the acetone would run out of the hole rather than down around the grub screw – so as not to displace any loctite around the threads.
Do one hole at a time – go back and repeat steps 2-5 another three times, making sure to get the magnet orientation right. Then set everything aside for a few hours or overnight for the epoxy and loctite to cure.
Now it is necessary to “rebuild” the damaged groove. I used a product called Devcon Titanium Putty to do this. It’s an expensive product and you only need a small amount, I was able to borrow some from a friend that is a commercial user. There are other metal repair products around that would also be suitable.
Mix a small amount and force it down each hole so that there is a continuous layer of putty around the top of the grub screw out to the bottom of the groove, and use a fine knife to roughly shape the two sides of the groove, ensuring the threaded hole is fully filled up to the top of each side of the groove. I then let the Titanium putty cure for 3 hours. Don’t let it go much longer – after about 6 hours it gets a lot harder to work.
Three hours after applying, I used a combination of tiny needle files and various fine grades of sandpaper to rebuild the groove in each of the four hole positions. I started with the files, then switched to 120 grit paper to get each position nearly done. I wore a magnifying headset to do this, so that I had good vision for this micro-surgery. When I got close to the final result, I set the flywheel aside for another few hours for the putty to harden a bit more.
After about five hours total, I did some further sanding using 240, 400 and finally 800 grit paper to polish each side and the rim of the groove to complete the rebuild. The Titanium putty is well secured by the threads of each hole – see the final picture. The job is done when each side of the groove is smooth and flat, and you can run your fingers across the top of the groove with your eyes closed and not be able to tell when you run across where the hole was.
#29 hole drilled in Airflow Systems dual ring gear
With the two outer cowl halves fitted, the next step is to fit the bottom cowl center support structure. This comes in two halves, that have to be trimmed to fit around the front gear leg/fairing. A long time ago I fitted nutplates to the bottom fuselage to hold the rear fairing, so it was fairly straightforward to make the slots necessary to allow the two halves to fit around the gear leg.
Then you fit the lower cowl, and match drill the support structure with the lower cowl. I am fitting eight skybolts, four each side of the gearleg, to fasten the lower cowl to this center support. I found that the support extended into the honeycomb’ed area of the lower cowl, which is no good since it is supposed to be flush against the solid part of the cowl, so I trimmed the nose of the structure and will close it in with a layup after I fit all of the skybolts. With that front section temporarily open, people now mistake it for some sort of air scoop!
Next I started on the intake plenums, which come as a kit from Showplanes. The lower third of each intake hole is used for induction air. Each intake plenum channels induction air down to a center combining section, which supports an air filter each side with drain holes for water, and mounts on the throttle body.
The right hand intake plenum actually intersects with the #1 cylinder head and #1 exhaust pipe, so it is necessary to trim the plenum and do layups to provide the necessary clearance. First though, the two intake plenums need to be trimmed and fitted to match the lower cowl intakes. The VAN’s front baffle ramps need to be cut out and new ones made to suit the Showplanes cowl. The support angles in front of #1 and #2 cylinders are used as a reference for locating the intake plenums, by means of a temporary metal bracket, clamping the plenums into place while epoxy’ing fiberglass supports in place.
I purchased this intake kit before Showplanes made one available for the SDS 80mm throttle body, so my center section had a 3.5″ hole in it. Once the intake positions were set up, I had to extend and reduce the throttle body connection to match. I protected the throttle body with masking tape, and coated the inlet connection point inside and out with PVA release. Then I used a balloon to bridge between the throttle and existing moulding, with everything supported in place, and wrapped several layers of fiberglass cloth to make the adapter cylinder. Once cured, I was able to pull the assembly straight off the throttle body and clean everything up. I decided I needed a bit more extension so I scuffed the outside surface, used packing tape around the throttle body, set it up vertically with the center moulding on the bottom, and applied another two layers of fiberglass. After this cured, I was able to make a nice straight cut in the end and a hose clamp applied enough pressure to the moulding to hold it securely onto the throttle body.
Next I finalized the cuts around #1 cylinder head, packed around the head to establish the required gap, and applied packing tape. I fiddled with the alignment of the entire assembly and decided I wanted to change the direction this plenum took so that I don’t have to modify the assembly to clear the alternator. So I cut around almost the entire section as well. With a balloon in place, I applied fiberglass cloth around the plenum cuts (allowing enough excess to be stretched into place), and carefully “smooshed” the plenum in place, which pushed the balloon inwards in the necessary places while establishing a smooth transition between the original shape and the modified sections.
Next job is to do the same around the #1 exhaust pipe. After that, I need to modify the left hand inlet plenum because of the A/C compressor, but that’s another story.
Center fairing protrudes too far
Trim line Showplanes front center fairing
Trimmed Showplanes front center fairing
Showplanes center fairings
Positioning Showplanes intake plenums
Positioning Showplanes intake plenums
Positioning Showplanes intake plenums
Essential equipment for fiberglass work
Setting up to extend intake plenum around throttle body
Completed intake section extension/reduction
Modifying right intake plenum
Ready for layup
Ready for layup
Right intake plenum layup
Right intake plenum layup to clear #1 cylinder head
