Engine Sensors and FT-60 Placement

Time: 1.5 hrs

I purchased most of the engine sensors needed for the Rotax 914. The engine comes with a few, but there are also a few that needed to be purchased separate. Here what I ended up purchasing:

VDO 323057 – Airbox Temp, not absolutely necessary but nice to have.

UMA N1EU007D – Fuel Pressure, Reads differential pressure between the fuel and airbox so it has both a wet (fuel) and dry (air) side to the sensor.

Electronics International FT-60 (Red Cube)– Fuel Flow, Inserted between fuel regulator and right carb to measure fuel flow.

UMA N1EU70A – Manifold pressure, Taps off of manifold tube. There is a Kavlico sensor that is viable with the Garmin GEA24 Rotax kit, but it’s very difficult to find from another supplier. The UMA was listed as an alternate to the Kavlico. You could probably use other absolute pressure sensors as well. (Still waiting for this sensor from Aircraft Spruce)

IM-927 EGT TYPE K – Exhaust temperature, As far as I can find I only need to install 2, though you could technically install 4. They typically are mounted on the rear cylinder exhaust (I believe 100mm from the cylinder). These have a nut attached and mount to the exhaust by removing the hex bolt and using the hole that hole so no need to drill a hole for the bayonet. (still waiting for these sensors from Aircraft Spruce)

So now on to the real headache. One of the goals I wanted to meet was to reduce the amount of rubber hoses used in the engine compartment since Rotax mandates (though it is not mandatory for experimental aircraft) to replace all rubber hoses firewall forward every 5 years. With that in mind I wanted to use PTFE (teflon) steel braided hoses for the fuel lines. In my Googling I came across Aircraft Specialty that has a full kit for the 912, but I didn’t see anything for the 914. I emailed Steve a few weeks ago and he was eager to want to put together a kit for the 914 and even help figure out how to plumb up a few of the fuel related sensors. Steve is builder and pilot and is extremely knowledgeable about the Rotax engines. He shipped out some parts for me to try a day or two after I first spoke to him and now that the Rotax mandatory service bulletin issue has been sorted out I wanted to get back to working with Steve to come up with an offering for not only the 914, but also some things that might make the Sling 4 build a bit better.

The FT-60 install was the first area I wanted to see if it could be improved. TAF has you cut and solder copper hose barbs onto the existing hard line between the fuel regulator and the right carb to insert the FT-60 into the fuel line. Steve felt like this could be better done with flexible lines and AN fittings, so he shipped me out some fittings to try. The space between the regulator and carb is maybe 5-7″ of straight fuel line and once you put the 1/4″ NPT to -4AN fittings on the FT-60 it doesn’t leave a lot of space. The FT-60 install instructions also impose a few restrictions: 1) Mount the sensor with the wires point up, 2) Don’t allow the fuel line to drop immediately on the output side of the sensor, and 3) Orient the sensor so fuel flows to the Inlet and out the Outlet (duh). So with that in mind I came up with a few install scenarios that I will run by Steve. I fabricated a quick bracket just to give me an idea of how I might mount the sensor. After the position has been finalized I’ll make up a proper bracket and Steve can build the hoses. BTW the fittings and hoses he sent are really top quality all stainless steel.

There really isn’t a whole lot of space to install the sensor. At the bottom of the photo (cut off) the hose drops down to the carb and only has room for a 90 degree fitting which the manual says you shouldn’t do. Plus mounting the sensor becomes an issue because there’s not a whole lot of places to mount anything.

Scenario 1: I figured I could get some room by turning the sensor 90 degrees to the fuel line run. I liked this arraignments where I could even put the fuel pressure sensor on the same bracket. The fuel regulator is to the right side of the photo, right carb is to the left. There is a tee fitting that Steve provided that would feed the FT-60 with a 90 degree fitting and a straight hose could be used to feed the pressure sensor from the bottom (using a 90 degree fitting on the pressure sensor).

So the issue with this scenario is that I have to move the FT-60 about 1 inch forward to accommodate a 90 degree fitting to feed into the sensor, plus this connecting hose is pretty short. But it may still be a viable solution.

Scenario 2: This arrangement moves the sensor further forward and a bracket could be mounted over the ignition boxes. The tee is removed from the regulator and moved to the input of the sensor. Since the sensor gets moved forward the out to the carb has a longer hose and no immediate drop. The draw back here is the out to the pressure sensor kind of is in a weird place. I suppose the tee could be put back onto the regulator which I’ll have to try.

Scenario 3: This arrangement kind of combines the previous two. By moving the tee to the in of the sensor allows a bit longer hose and flexibility in mounting height between the sensor and the regulator. The out to the pressure sensor is pointing aft which would work well if I mount the pressure sensor on the firewall or on the engine mount. On the output side a 90 degree fitting could be used or even a straight fitting with a bit longer hose run to get a gentle bend to go down into the carb. I’m kind of thinking this may be the arrangement to do, but I will see what Steve thinks.

Scenario 3 using a long hose run on the out and a straight fitting.

Sensor input side with the tee facing aft. The sensor can be mounted a little lower and the hose is a little longer then scenario 1. The run to the pressure sensor would be about 1.5-2 feet so a bit longer then expected but I don’t think it matters too much.

NOTE (1/1/2019): After speaking with Steve he thinks Scenario 3 will be the best solution. I will need to make a more proper mounting bracket and then I can mock up the hoses with some cheaper rubber or vinyl hoses. I then send them back to Steve so he can make the hoses.


Charge System Finish Up and Turbo Servo Install

Time: 3hrs

Today I ran some wires for the engine sensors and also bolted down the turbo servo. I also fabricated a simple bracket for the air that runs from the servo to the waste gate. Additionally I torqued down most of the electrical terminals (M6 terminals are torqued to 35 in lbs (5NM) as per the Rotax manual) and connected all the remaining connections for the charge system. I realized as well that I had use some nylon lock nuts on to hold the adel brackets together. Pascal remained me that you’re not supposed to use nylon locking nuts in the engine compartment because the nylon can melt and the nut will loosen. I will need to switch them over to AN363 all metal lock nuts with AN3 bolts instead of the M5 socket heads that I’m using right now. The funny thing is the nuts on the engine mount bolts (supplied by TAF) are nylon locking nuts so I wonder if I should get some M10 all mental locking nuts for those as well.

I was looking all over for the connector pin outs for the small connector on the back of the alternator. And as I sat there staring at the alternator the answer presented itself. The connector pin outs are printed on the alternator.

External alternator wiring done. After speaking to the guys at Torrance TAF I think I will wait on installing the capacitor for the external alternator. It seems like they don’t install one and don’t have any issues. It’s easy to install later since I can just tap off one of the terminals on the fuse holder.

I ran some 2 conductor shielded cable out to the Cylinder 2 and Airbox temperature sensors. I originally ran a single conductor wire, but it seems like the practice is to ground the wire at the engine side. There are grounding points near the cylinder temp sensors on both sides, but it looks like the oil temp sensor ground is a little far from that sensor. I couldn’t finish the wiring for these because I want to try to us the terminal covers I bought for the 250 Faston connectors, but I don’t have the correct Faston connectors for this size wire (22 gauge). I order some and will post after I have those wired up. Typically you just use the PIDG Faston connector and leave the metal of the connector exposed, but I was hoping to make it a little nicer. Another idea would be to find small terminal boots that would cover the terminal and the top of the sensor.

Connected up the internal regulator and capacitor.

I made up a simple bracket to hold the turbo servo cable. It will attach to one of the fuel line fittings with 9/16″ nut.

Turbo servo is installed on the firewall. There’s plenty of room between the servo pulley and the sound proofing on the firewall. I think I ended up is about a 1 1/2″ spacer there and a bit longer AN4 bolts then originally used. I need to paint the bracket so I’ll finish installing tomorrow.



Not much to report on any progress on the plane, but a HUGE relief today. I went into Torrance TAF today and Jean said a new mandatory service bulletin was release from Rotax today. I thought oh man what now? He said they updated the serial numbers of the engines affected by the exhaust valve issue and it looked to be a smaller range then previous so we checked my serial number and to our absolute amazement my serial number was no longer on the list of affected engines. So thank you Rotax for a great Christmas present. Now I can continue to work on wiring up the sensors and permanently installing things for the engine.

The only other item to mention is that I received my loaner prop extension and spinner flange from AirMaster. I fit it on the engine and will start fitting the cowling soon. I need to finish up some of the engine wiring and also need to order the cam locks. The other good news is it fits in the garage with the extension and flange on.

3.75″ prop extension and 10.3 spinner flange (for the AP332) from AirMaster. They were nice enough to loan this out so I could fit the cowling. Actual price is around $1000, this is a used one and I have to return it when I’m done. Thanks again Jean for the help.

Firewall Pass Thru

Time: 3hrs

I fabricated a stainless steal split pass thru for the main wiring between the cabin and engine compartment. I got the idea from an EAA article that combines a split design to cover the larger hole and then grommet covers to cover the wire grommets. You’re technically supposed to use silicone (red) grommets for the high heat resistance, but the synthetic rubber ones will do since I couldn’t get the silicone ones in the sizes I needed. The main plate is made from 1/8 stainless steel plate which is a pain to cut. The design allows you to pass large connectors, etc through the firewall and then cover the hole and reduce the exposure to fire and fumes from the engine compartment. The grommet covers are fro Aircraft Spruce and cost about $8 each. I still need to enlarge them a little since I’m using slightly large grommets then they were designed for (1/2″ ID, 1 1/16 OD and 9/16″ ID, 1 1/16 OD).

Original pass thru cut by the factory. I had to extend out the edges a bit to fit the grommets.

I made a silicone gasket to seal up the space between the firewall and the pass thru plates.

Half of the pass thru on.

And pretty much the final product (still needs some fine tuning). The top part of the plate was a bit of a pain to get one, but a little finagling got it on.

Charge System Wiring (Part 2)

Time: 4.5hrs

I finished most of the charge system wiring. I still have to torque done some lugs, rerun the starter wire, wire up the capacitor for the external alternator, and clean up the cabling a bit. I’ll have to find some larger terminal covers because tithe ones I have done for over 2 6awg wires. So until I get those I can’t install the wires on those lugs. I also need to find something the wrap the wiring. I was thinking maybe like the corrugated plastic with the slit in it, but a little nicer. I’ll have to look around.

The wire to the starter is a bit too short, it works but I’d like a little slack since the engine will move. I’ll rerun it and put a small twist in to give it some room to move. I also don’t want to finish any wiring to the engine yet because I’m not sure if it will need to be pulled off and sent back (Because of the mandatory service bulletin work needed).

I’m pretty happy with the MAXI fuse holders. They’re better built then I expected. From what I can understand in the specs they’re fire rated for like 10 minutes. I suppose that even if they completely melt the metal connections will still be maintained, though it could short to something. The only issue I had when I mounted these is that one is slightly lower than the other (should have mounted them before putting the engine in). It’s just cosmetic, but it bugs me 🙂

I tried to divide up what is mounted to each of the power lugs (on the master and starter solenoids). I went back and forth with if I should put both alternators on the same lug. I may move the ALT2 (internal generator) to the starter solenoid since if the master solenoid lug came off I could still get power to the VPX. Either way I’d lose charging to the battery, but that’s not a big deal in flight.

I’m thinking of mounting the large capacitor for the external alternator on the firewall and tapping off the fuse holder lug. So far I haven’t seen anyone actually install the cap for the external alternator so I can’t find any photos of what other people did. The one on the internal generator I mounted next to the regulator, but it doesn’t seem like I can mount the external alternator one near the alternator itself because I’d have to mount it on the engine and the heat and vibration may be an issue. Maybe I’ll ask Jean about it.

Photo of the master and starter solenoid and fuse holders on the right.

ALT1 and ALT2 holders. I mounted these on M5 rubber mounts so I didn’t have to cut away so much material on the firewall blanket. These are made by BlueSeas and seem to be pretty good quality holders. I had originally wanted to use inline fuse holders but you have to mount them somewhere anyways so might as well just use proper holders and mount to the firewall.

Cable run to the alternator. I need to pull through a little more cable and also install an Adel clamp to hold the wire to the pipe that connects across the manifold.

I mounted the ALT2 (internal generator ) relay to the engine mount with some adel clamps and a rubber stand off. I’ll need to safety wire the bottom section to the relay so it can’t slip off even though it’s on very tight.

Control Stick Grips Engraving

I got my control stick grips back from Midwest Sky Sports with the engraving done on them. I’m really happy with the way they came and and am thankful to Steve O’Connor from Midwest Sky Sports for getting it done and also for Kevin from Tosten Manufacturing. There’s a special plastic that is needed in order to do the engraving and I had already purchased my grips with the soft touch plastic about 6 months ago. Steve contacted Kevin and Kevin told be to just send the grips in and he swapped the plastic out for free. He also sent them over to Steve so he could do the engraving. So not only does Tosten make some cool control stick grips but their support is great as well. I like to support companies (and people) that are helpful and willing to work with you so if you’re thinking about which grips to buy definitely check them out first at www.tostenmanufacturing.com. Steve is also very active with the other Sling builders and has some good experience with the Slings. I believe TAF at Torrance has been working with them to build some panels so they’re a good resource to hit up if you need some custom wiring done or engraving done.

A few photos of the grips. These are the MS style grips and I added the side thumb switch which will be my AP Disconnect. The trigger is PTT. I’m not using the left/right hat switch and the small front button by the trigger. Steve recommended using the left/right hat switch for frequency swap who seemed like a good idea, but I don’t think I’d every use it and I’d have to do more wiring so I decided not to do that.

I also received my prop extension and spinner flange from Airmaster so I should be able to fit the cowling soon. I want to finish up the charge system wiring which I’m almost done with, just waiting on some terminal ends for the 6 AWG wire. Since I haven’t bough the propeller yet Jean worked with Airmaster to get me what I needed to fit the cowl (Thanks Jean).


Charge System Wiring (Part 1)

Time: 1.5hrs

Well I was going to post all this once it was all done, but the parts are taking a bit longer then expected so I’ll post what I have so far.

I purchased a crimp tool for the large 6AWG cable so I was able to make up a few of the larger gauge cable. The crimp tool is a simple hammer crimper, not a squeeze crimper and seems to do a pretty nice job. The hand crimper does a better job because they form more of a hex shaped crimp, but they cost around $200. This one cost about $9 from Amazon and does a good job. I was thinking of maybe soldering the crimps as well, but I’d rather not because that can cause the wire to getting brittle which could lead to it breaking. I’m using 6AWG Tefzel for the bulk of the high amperage connections. A smaller gauge wire like 8 or 10 would have worked as well, but there’s no drawback to using the heavier gauge wire other then weight really and there’s not that much of it. And minimizing the different size wires make it a bit easier and cheaper in some ways.

I need to work on what I’m going to do for the firewall pass thru. There are a few things on Aircraft Spruce but because there is already a large 2″ hole in the firewall it makes it difficult to simply go with what you like. What I’d like to do is use 2 stainless steel pipe pass thrus (one for high voltage wires and the other for the engine sensors). However, I don’t want to make another large hole in the firewall. What I’m leaning towards is a split stainless steel flat pass thru that uses silicone grommets. I’m thinking I might be able to fit 2 grommets side be side and pass them through the large 2″ hole. The pass thru is made for 3 grommets so I’d have to cut the pass thru down to shorten it up. I had purchased a large stainless steel flange that would work, but it’s pretty heavy so I’m going to look for something else.

This is the crimer I purchased. I found that one good hit with at 1lb hammer tightens the terminal so you can get the wire situated. Then 3 more hits seems to finish the crimp.

Not a terrible crimp and the wire is very secure in the terminal. This is the first crimp I did. The next ones were actually a little better.

I purchased some Molex and some AMP terminals and I like the AMP/TE ones better. They have some ridges inside that should hold the wire very well.

I purchased these 2 size terminals from onlinecomponents.com. The 1/4″ (TE part # 321598) fits the 6mm terminals on the start solenoid OK, a little loose and the 5/16″ (TE part # 33466) is for the master solenoid.

Some photos of the master solenoid. I roughed in the cables to the battery. I have the SR560 Schottky Diode installed on the solenoid to reduce reverse current from going through the master switch when you switch it off. The starter solenoid has the same, but it’s wired a little different. I’m waiting on a terminal so I can wire that one. The ground lug passes thru to the Faston terminal (in the cabin) for the avionics grounds.

Some wiring run to the starter solenoid. I have to divide up the connections on the switched side of the battery solenoid so some things will connect to the starter solenoid (batt solenoid side). I’m trying to keep wiring neat as I run it because it’s getting confusing. I purchased some reusable zip ties to help keep wires bundled. There’s a 1k ohm 1 watt resistor wired into the cable that goes to the VPX for the starter annunciator.

This is the ALT2 regulator connector that I wired up a few days ago. The regulator is mount ed inside the cabin. The left side has a ring terminal that connect the large capacitor and the right side will connect to the ALT2 relay out on the firewall. I purchased some large Faston connector so I could crimp the 2 12AWG wires into one connector. The Faston connectors are a bit special in that they have a small tab on the back so that they click when inserted in to the connector. I suppose you could just us the PIDG type and then push them directly onto the regulator and not us etch connector.

I will be mounting the MAXI fuse holders on the firewall as well. I had purchased some Littelfuse fuse holders which I really like, but I don’t like how the terminals crimped on. I don’t have the correct tool and I’m not going to spend $300 on it just to crimp 4 connections. You also can’t just buy the terminals so I’d have to spend another $30 a pop on the holders if I want to redo them. I have some Blue Seas Systems fuse holders coming which use ring terminals. I’ll see how these work out. I have to mount them side by side on the firewall so it’s gong to take up some space. I also need to figure out where to mount the ALT2 relay.