ASP FS61AR CDI Conversion - Q regarding Rich Midrange.
 

Hi,

I've been playing around with an ASP FS61AR of late. It was sitting for near on 10 years and needed a new set of bearings through it (and a couple of other parts) to make it new again given the rust and gum from me forgetting after-run oil on the last run. The liner, valves and rod bearings were all in perfect condition It was otherwise barely run-in, probably 8 flights, so it's pretty much a new engine again.

During the bearing swap I couldn't bear to see the rough edges in the intake manifold and the step from the bore used to make the intake port into the head, so it got a bit of a cleanup with a ball end carbide bit in a die grinder. I'm now pretty happy with the intake air passages.

I also drilled a couple of 0.8mm holes in the crankcase from above the cam followers into the cam case to let the oil mist flow up the pushrod tubes and a 0.7mm hole from the intake valve bowl into the rocker area to let the engine draw the mist back into the engine, that way the breather hole can be plugged and the blowby oil ends up back through the engine.

After flying an Evolution 10GX for a while I was really keen to try spark ignition on the engine, so picked up an RCXEL ignition module, 1/4-32 plug and the hall sensor.

For the trigger magnet, I found a 1mm diameter, 5mm long Neodynium magnet on Ebay and drilled a 1mm hole in the prop driver, gluing the magnet in place with epoxy. It's barely visible on the prop driver and works quite ok - the range to the hall sensor is up to about 3mm with an axial range of the sensor (front-back) of about 2mm. Not nearly as much as with a larger magnet but plenty enough to get a realiable spark without being too precise.

While the bearings were out I drilled and tapped a couple of M2.5 threads on the front bearing housing to hold the hall sensor braket, which I make from a section cut out of some 25mm thin-walled aluminium tubing, with the sensor glued to that with acrylic 2-part adhesive.

I've been experimenting with running the engine on E85/oil blend (currently at the usual 20%/1:4 ratio).

I have no issues at full throttle, it's spinning a 13 x 6 Schimitar Master Airscrew at 9800-10000 RPM static and mixture is more sensitive than methanol, maybe 1/5 turn from losing RPM Rich to losing RPM lean.

Idle is also able to be adjusted nicely, it's happy to tick along at 1950-2050 RPM for minutes on end and then pick up happily after that.

What I am finding though is that the mid-range is all over the shop. Moving up from idle the RPM rises comfortably to about 3.6-4krpm. Opening the throttle further, the mixture gets progressively richer as the throttle is opened further, until the engine is sputtering rich at about 3.6krpm (yes, the revs drop as the throttle is opened at that part of the travel). further opening the throttle the mixture stays rich and sputtery but with the revs increasing until the throttle is opened enough to reach maybe 7.5krpm, where it starts to lean again until it's perfect at full throttle.

I'm not running exhaust pressure at the moment as I found it was worse with it connected and would wander around more (perhaps as the exhaust pressure was breathing in and out of the tank at different load points).

I did think it might have been that the carby-manifold O-Ring had lost its seal but that was replaced without any change to the behaviour.

Given that this engine runs a low-speed needle running in a metering tube with a metering slot cut into it, it seem that an option would be to massage the metering hole profile to tame the midrange. I'm tempted to give this a go but thought I'd see if anyone out there has tried this before and if so what method was used and whether it was successful? It seems like one of those things that could go either way really easily given the small size of the fuel passages.

Any other suggestions on ways to reduce fuel in the midrange? Another thought I have is to have a mixture control servo and map that with the throttle setting, that was I could have different maps for different fuels as well.

Given that the engine is not a particularly expensive unit, I don't know it's worth to pick up another caby for it (the NGH 9cc carby looks the goods but I haven't seen one under USD$85 which is probably what the engine is worth if I'm lucky)..

Just as a final note, the engine did run Ok on 4:1 Methanol with spark ignition (and with Exhaust pressure connected), the midrange was still rich but not nearly so much as on E85, So it seems that it's tied in with the different mixture requirements for the ethanol/gas blend as compared to methanol.

Cheers,
Duncan

Hi Duncan,

No idea if you allready found a solution to your problem, but in case you haven't: the overly rich midrange on a glow carb using alternative fuels, can be remedied by altering the "camprofile" of that slanted groove that makes the throttle barrel move sideways.

I know it sounds a bit crazy to grind away in a carb part, but I have done a ton of conversions in the past 6 years and have stopped using glowfuel altogether (my personal choice of juice is gasoline, but to each his own, of course).

The change is not too difficult and not too critical either and can be done freehand with a Dremel.
I wanted to post a YT link in here, but I am not allowed to since this is my first post in RCU.
Search for channel "rigididiot" video title "grinding a carburettor barrel"

Sorry for the less than optimal video quality, I'll pop in a pic of the desired endresult later (not on my private device right now) EDIT; you'll have to wait for that, apparently pics are also off limits below 10 posts...
The use of muffler pressure really helps a lot in making this mod less critical.

It might be necessary (but at least strongly recommended) to place a stronger spring behind the throttle barel, to prevent it from moving under the intake vacuum, which would upset midrange mixture even more. If no stronger spring availlable, I usually simply place two springs in there, harvested from old carbs. The springs as sold by RcExl (for better contact in the plugcap) usually work well here too.

Brgds, Bert

Efi
 

Thanks for the info on the carby mods - That would have been my next step..

In the end I have put together a fuel injection system for the engine and have it running well :).

The Fuel injector was a 140cc/min motorbike injector with 9 of the 10 holes covered with solder to end up with a 14cc/min flowrate.

I used a gear fuel pump that was originally from a jet engine, controlled by PWM.

The timing signal is taken from the CDI module - the connection used for the tachometer.

I used a 32 bit ARM Microcontroller to accept the SBUS signal from my receiver to take the throttle, mode and some trim inputs (pump pulsewidth and mix trim).

fuel pulsewidth is interpolated from a table with values based on RPM and Throttle position.

I have fed fuel from the pump directly to the injector and it works well - interestingly the mixture is not particularly sensitive to the pump voltage setting.

With a “she’ll be right” first hack at the fuelling table I was getting good performance (13x6 prop at 10kRPM on petrol/20% synth oil). The idle is comfortable at 2kRPM, could go a bit lower but it sounds less happy the mechanically. With a bit of a tidy up it will be spot on :).

Hi Duncan

The less happy mechanical sounds could very well be because of an excess of oil, and your oil transport bores might be insufficient to discharge all the blow by past the ring. Especially when you are mixing 20% (4;1).
Mix yourself an oil ratio of 10:1 (9,1%) and it will run quite a bit better, I can assure you. 15:1 (6,25%) would still be OK, although personally I would not go leaner than that. That is, assuming pump gas (E10 over here). On Ethanol, I am not sure what the best ratio would be, but I ran my fourstrokes with spark and methanol on only 10 or 12% oil.
My best advise would be to either run regular pump gas or possibly this alkylate stuff for chainsaws (with the proper amount of oil of course).
Personally, I do not recirculate the oil back to the intake. I have the original crankcase discharge rerouted through the rockercover, and from there discharged to air, like this:
Attachment 2271048
the bend in the middle is to clear the cowling of the plane it is in.
Works like a charm, very minimal oil from there, but inside the rockercover everything is drenched with oil and valve clearance is as stable and constant as anything...

Say, that's a lot of work, making an injection. How did you end up weight wise and consumption-wise, and how did you create the tables?
My solenoid system weighs in at 25 grammes max, and draws less than 130 mA as a peak, but usually a lot less current than that... It simply uses a programmable curve in the transmitter. It can be upgraded with a barometric pressure and temp sensor to correct fuel delivery for air density. Not necessary, but a noticable improvement. No RPM data used for fuel delivery, no fuel pump, the engine itself is perfectly capable of drawing that stuff in itself, and its self-regulating properties (if RPM increases, so does fuel draw and muffler pressure therefore fuel flow) are more than sufficient to make things work.

Initially I was planning to run the engine on E85+Oil given that it's a bit greener and that there's a power advantage compared to straight Gas. Unfortunately, during the development work on the hardware I had left the pump primed with fuel and after 3-4 days sitting there was a light cloud of rust discharged from the pump when I ran it. It may be that the fuel had absorbed some water but in any case I don't want to destroy the pump *that* way.. I have been using a 98 octane pump gas (no ethanol) mixed with oil.

I pulled the backplate off the crankase yesterday and saw plenty of oil in there - not a big pool but definitely more than needed - so I was already planning to reduce the amount of oil in the fuel. I'll try 10:1 - that will save some money on oil and should end up with the right amount in the crank case. I'll check it again after some runs at that oil ratio. The oil looks quite clean in there (just a slight gray tinge compared to what I mixed with the fuel) so it's otherwise going well. All the valve gear at the top is nice and wet with oil as well so I don't think there's any issues getting the oil to the top and back into the intake. I really like having the engine run clean so don't want to vent the oil other than through the intake and out the exhaust, but I will keep an eye on the oil quality in the moving parts to make sure that it's not getting any dirtier with a lower propotion and may reconsider later.

I didn't notice any power change between the E85 and the 98 octane straight Gas so will continue with that in future.

Regarding the weight of the injection system, the injector is about 25g and the pump maybe 30g. I have kept the standard carby as the throttle body for now (with the needle closed off fully) but could save a little weight by making a dedicated throttle body (and if so would put a throttle pos sensor on it or even make it motorised an do away with the throttle servo). The electronics are just prototype for now on a 100mm square of matrixboard with the microcontroller on a plug-in board - it probably weighs 50-60g at the moment but there's more on there than needed, I think I'll be able to get it down to 10-20g on a dedicated board with UBEC, pump control, Injector driver, CDI power switch, Microcontroller and plugs for everything. One advantage is that then the fuel tank can be at or close to the CG since the pump pressure will preclude any fuel delivery sensitivity.

Overall, the weight is probably a little more than I'd like for a 61 sized engine but given the plane is light won't be a problem. It would be trivial on a bigger engine.

Overall current consumption for the system is around 800-850mA at full throttle, falling to maybe 350-400mA at idle. Pump current is around 1A but at only 3v so from the 2 cell lipo around 300mA, the injector is around 500mA when powered but runs at max 80% duty cycle at full throttle so 400mA max (and dropping significantly at lower speeds). CDI Consumption I haven't measured but is maybe 100mA at full throttle.

Setting up the table was based on running the engine fully manually. I set up extra channels on the Tx rotary pot channels, one for pump PWM control, one for Injector puslewidth and one for pwm compensation with the injector open (to maintain pump speed with the injector open). It was possible to run the engine by making all the settings manually and manipulating them as the throttle was moved. I kept track of the adjustments for different settings and then filled in a table with throttle percent along the top (columns) and RPM in the rows. The next step (which I am in currently) is to set up the Tx pots as Fuel Pump PWM (as before) and a second as pulsewidth trim (80-120%) and go through the throttle points, noting how much trim is needed at the various points then massaging the table to correct the issues. As it is now the throttle response is good and full throttle great but the idle is a touch rich (smooth but slowly bogs down after 20-30 seconds). I do plan to put in closed-loop idle speed control, basically have the code manipulate the throttle servo to maintain a set idle speed with the throttle stick at 8-12%. Throttle 0 will shut off the system and anything over 13% will revert to direct stick control of the throttle servo.

At present the table is hard-coded into the firmware. I plan to put it in EEPROM and set up a windows program (and possibly an IOS app connected via Bluetooth) to enable it to be edited real-time.

it's a bit of a process but something I find fun. Honestly, I wasn't expecting such a broad range of acceptable mixture levels, it's actually quite a range between the rich misfire end and the lean misfire end.

My end-game is to have three inputs channels to the module, the throttle stick, a switch with three positions and a trim. switch is engine off (no spark/fuel), auto pump (pump runs only with the engine spinning) and prime mode (pump runs continuously, injector open if throttle at 99-100%). The trim will allow for mixture adjustment in-flight..

On the injector - I mounted it into the side of the intake tube so it runs across the back of the engine (parallel with the engine fins. I used a dremel to make a hole just big enough that the injector end slid in then used epoxy resin reinforced with carbon rovings to hold it in place. The fuel squirts against the opposite side of the intake tube. The end result is that with the injector fitted the assembly is not significantly longer than without the injector. I would have liked to be able to direct the fuel into the port but there's not enough space for that at this point in time. The epoxy/carbon is quite tough and so far at least is holding up perfectly.

When the engine shuts off after a run, the injector is fairly hot (it is getting the hot air from the engine blowing over it) and when the pump shuts off the fuel almost instantly vapourises in the injector, expanding out into the supply tube. On restart, it very quickly compresses back to liquid again so the pump pressure appears high enough to avoid vapour lock. With the fuel being that hot, and sprayed against the hot intake tube, Evaporation should be near complete by the time combustion takes place.

Unless I interprete your description wrong, the "grey tinge" is worrysome. I do not know what oil you use, but in my engines, the oil colour varies with mixture (not oil/fuel, but air/fuel) and is either as clear as it came from the bottle, or in increasingly dark from soot, but never grey. Grey is a sign of metal. I see that occasionally when breaking in an engine, but otherwise not.
My sincere fear is that your oil is not escaping fast enough, causing it to spend too much time in the crankcase. Those 0,8 mm bores are awfully small for a viscous liquid like oil and alternating positive/negative pressure pulses.
You don't want that oil to stay in the crankcase too long, restricted outflow is bad for lubrication.
FWIW: the .90 in the pic above, running 10:1 fuel/oil ratio, has an oil discharge from the rockercover of about 0,1 ml/minute @6000 RPM, and that really is negligable in flight, and attaching a discharge hole to get the oil down to the landing gear does not seem to affect things at all: there is a good gas exchange and enough passage for the oil droplets to escape. It also means, that it takes about 15 minutes to completely refresh the oil in the crankcase.

I run a modulating solenoid (in itself not all that different from a PWM controlled injector) on a fixed frequency of 25 Hz. I set the main and idle needle slightly rich, and modulate the fuel flow via a separate channel with curve, linked to the throttle channel.
That allows me to run the engine virtually stochiometric over the entire throttle range, without any feedback loops or anything. The rising/falling muffler and intake pressures compensate largely for the loading and unloading due climbing or descending in flight (which is a few hundreds or RPM at best anyway).
I was initially unaware of the "fattening up" effect of altitude: Every 100 metres or so in altitude, pressure (and thus air density) drops sufficient to warrant about 1% less fuel. Since a few months I have a pressure and temp sensor installed in the plane, that via telemetry sends a corrective signal to the transmitter, correcting the fuel curve as needed. Believe it or not, but that extremely small correction has led to a visually cleaner oil discharge from both crankcase vent and exhaust, to the point where I do not see ANY traces of black anymore after flight.

I cannot place the tank in CoG, but I don't need to in this size of plane. I do not see any noticable influence of nose attitude on the running of the engine as you would see with glow... Absolutely nothing. There HAS to be some, I'd say, but fact is, I cannot detect it. And that has nothing to do with the solenoid or the electronics, it was allready like that when it was "just a modded glow carb with natural fuel draw"
Believe it or not: that is no pump, no pressure regulator, no electronics, no nothing. Just a carb modded as described in post 2, and regular 95RON gasoline (and oil of course).
The carb mod worked well, but was not precise enough to my liking, hence the solenoid, that I now use in all my conversions.
Strangely enough, the solenoid I am using is closed when energized (which is good because if it fails, it fails to open and the engine continues to run (rich) on the still active needles) so current draw for the fuel system is lowest at full throttle, but still at best 100 mA roughly at idle.

I am impressed by what you did making this injection system, but the current draw is awfully high IMHO. That needs a big battery to get a decent flight time. My smallest engine/plane combo (5 cc fourstroke) has a single 4,8V 2000 mAh NiMH, that supplies CDI, RX, servo's and fuel valve all at the same time, and I am getting easily 90 minutes of safe flight out of it.

Would appreciate seeing a vid of your engine running.

I have experimented with in-flight trims, but the difference between an engine running rich enough to turn the oil and exhaust residue black, and one running stochiometric, are not audible by ear, so there is no point in in-flight trims: You cannot adjust what you cannot hear.
When you can hear the engine go rich, it is WAY too rich, and when it gets lean, it simply stops like hitting a switch. That's a very thin line, and the only way is to sneak up on it: stay high, go through the throttle range, and as soon as it quits, take a mental note of the throttle position and correct that point on the curve/table after a succesful deadstick. Otherwise, repair plane first :D :D :D

I think your injector does not get hot from the cooling air, because that air is not all that hot (highest I have ever been able to measure, was less than 15 deg over ambient in an engine with a cooling duct. In freely exposed engines, I never saw more than 5 degrees elevation), but from heat conduction through the header. I had to thermally isolate header and carb because of vapour lock, because the header gets awfully hot. Easily 60~70 deg C despite the cold air and the fuel rushing through it. Even then, I had issues with lack of proper evaporation with the normal spraybar, because of the fuel entering in a continuous stream. The intermittent supply from the solenoid forces the fuel to break up in much smaller droplets, and as far as I can tell, I have fairly complete evaporation. The tell tale is black oil from the exhaust. It is caused by the oil still containing dissolved fuel at the beginning of combustion. When the residue from the exhaust starts to clear, you have good evaporation.

Further Progress
 

A bit further on now - the engine is in the plane I want to power and I have gone through the fuel map (throttle x rpm => injector pulsewidth) and got it running pretty nice. It's still a little hard to start - I expect that I'll need to add in a cold enrichment mode, for now I've been using a fuel trim control and starting at about 20% throttle (~3-3.5kRPM) but at the field that's a little more revs than I'd like while starting.

Running a 13x6 ASP prop on 10:1 fuel:oil mix I'm idling comfortably at 2000 RPM but it will go down to 1800 without threatening to stall. Full throttle is about 8900-9000RPM static a little lower than with the MA Schimitar prop I was running. From the ASP tables that's around 1HP.

The engine is fitted about 40º clockwise from inverted (to get the muffler out the bottom of the plane) and I was curious about the oil behaviour, so popped the rocker cover off after about an hour of running (takes some time to work through the map calibration). On the positive side, there was heaps of oil, meaning that 10:1 is more than enough given no roller bearings on the crank. The inside of the crancase is damp with oil but no standing oil. On the negative side, there was heaps of oil (in the rocker cover), so the bleed into the intake valve bowl is not capturing much if any of the oil from the top end with the engine inverted. For now I'll drop the rocker cover after a day's flying, or be sure to fly inverted regularly (Thinking about the implications of that - I may not need a smoke system on this plane...) Long term I'll likely need a bigger vent in the rocker cover to get rid of the oil overboard rather than through the intake. It's a little sooty (not surprising since I was running dead rich and tuning back from there) but certainly nothing to be fussed about. The oil I'm using is 2-stroke synthetic Kart oil, I have some cool power blue oil on the way which should be a whole lot cleaner looking.

Initially on the plane I couldn't get the pump to stay primed - it's getting warm here (was over 30ºC today) and the petrol mix is evaporating in the fuel lines, along with the bubbles that are always going to be present at least initially. I added a tee after the pump and used a needle valve from an old OS 10 FP to bleed a little fuel back to the tank, mainly to let air bubbles through but also to keep the fuel in the lines a little cooler. The fuel bleed has been (so far) a complete success. If any air bubbles come through, they go up to the needle valve and back to the tank and there's no vapour lock issues at the injector pressure. An in-tank fuel pump would be the proper solution (that's how it's done normally) but I don't really want a brushed 180 motor sitting in my fuel tank sparking away (with the fuel slowing the motor and dissolving the winding insulation), so I'll go with the bleed for now.

I had to do a bit of a hardware hack, the receiver I was using during the initial tests was throwing SBUS out with 5V signal levels and working fine, I replaced it with a Futaba receiver which outputs 3.3V SBUS and my optoisolation was running a bit under spec, noise errors and no servo data was the result.. A resistor change solved that one.

The remaining issues before flying are purely mechanical. The first is that the prop driver has excessive runout - with the prop fitted as normally would be for hand starting (~1:30/7:30 at start of compression), one blade was about 1.5mm closer to the plane mid-span than the other. I've ordered a new prop driver to see if that's the issue (it's a little bruised around the bearing surface) but otherwise I'm going to have to pull the motor down and make sure I got the bearing properly seated on the crank (my first bearing swap so not going to swear I got it right). The second issue is that I'm using a GRP engine mount and it's pretty flexible. Wasn't an issue with the 2-Stroke but with the 4 stroke the engine is bouncing around like the kids at a trampoline park. Given that the fuel is mapped based on the throttle servo (and therefore throttle barrel) position, any engine movement is not going to help the cause. Plus it looks sketchy. I have an aluminium mount that I'll put it on over the coming days.

The ECU controls the pump and injector obviosly, but also has a switch for enabling the CDI, has 4 servo outputs (throttle plus 3 others) and take an SBUS signal from the receiver. I'm using a few channels at the moment for trimming the various parameters while tuning (+/- 30% on fuelling and for the fuel pump voltage), not sure yet if I'll need the others.

Using an injector calibration mode on the ECU the injector was run through a couple of pulsewidths at a couple of battery voltages (3ms and 20ms, 8 and 7v) to get an idea of the flow rate and opening delay. The opening delay was around 1.2 ms at 8v and 1.7ms at 7v (running well below design voltage in this application) and the flow rate around 10cc/minute at the pump pressure used for the testing (not measured but based on a pump voltage input of 3v). Full throttle pulsewidths are in the order of 5ms (so 3.8ms fuel + opentime), so if anything the injector could even flow less than this and be fine on this engine. OTOH, 5ms allows engine revs upwards of 15kRPM with 80% duty cycle so this could work on a 2-Stroke engine as well. The injection pulses are every 4 strokes with the cam timing inferred from the difference between the speeds of the consecutive magnet passes.

I'm a few posts short of being able to post images it seems - this is one more towards the target...