Engine failures at full aft throttle? Lycoming 363i

[hawgdrvr]

I'm surprised at how many FX-3 owners I communicate with that are or have experienced engine failures with the throttle full aft (on the ground). The POH guides us to maintain 1000 RPM such as for ground ops but the one time we have the throttle full aft is coming in for landing. I learned from another FX-3 owner watching his YouTube videos where he does a full aft throttle pull after run up to ensure the engine will remain running with the throttle full aft as he's experienced this issue. I don't know if this is an idle mixture issue or an idle stop issue, such as RPM too low. The AMM says the 363i idle RPM should be 500-650 and recently in discussing with a friend affected by this Lycoming says 800-1000. I know of 1 or 2 that had an issue that the engine would quit after touchdown. Moral is this is more widespread than we think and I'd like to learn more about it and hear from anyone that's experienced this and why it's happening.

I bring this up to raise awareness to do a full aft throttle pull on the ground to make sure your engine will run in this condition, again where we find ourselves in this condition is only when on the final stages of landing. Do we need to raise the idle RPM?

In discussing this with an experienced cub owner he has concerns over vapor locks due to the fuel pump location directly behind the engine in the FX-3 and also suggests use of a cooling shroud on the engine drive fuel pump.

https://www.aircraftspruce.com/catal...clickkey=47037

I'm not about to second guess the engineering done by CubCrafters in cowl design and cooling or running any other scat tubes taking airflow from something else but is the fuel pump location, even though behind a heat shield, a concern? I did a search about this type of device as discussed quite a bit on the Van's forum as to whether or not it's needed and don't really have any conclusions. I defer to the experts.

[Andy]

I'm surprised at how many FX-3 owners I communicate with that are or have experienced engine failures with the throttle full aft (on the ground).

Yes, I experienced an engine stop during landing rollout but data review showed abnormally high fuel flow at low power settings before entering the landing pattern. This engine stoppage was caused by an injection servo malfunction and has not happened again since the servo was removed and inspected.

Just a few comments based on my experience with my FX-3:

The engine will not idle as slow with the light composite prop as an O-360 will idle with a heavy aluminum prop.

The AVStar fuel servo is extemely sensitive to adjustments of the throttle stop and the idle mixture control link. 1/8 turn of the speed screw makes the difference beween too fast and too slow. 1 click on the mixture control link is all it takes to make a detectable difference in the idle mixture.

700 rpm seems like a reasonable "on the stop" idle speed. I have manged to get it stable as low as 620 rpm with a small lean rise but, at that speed, the idle is very sensitive to ambient conditions.

The main reason for a slow idle is to reduce landing distance. The FX-3 can be landed so short that I see no reason to go much slower than 700 rpm "on the stop" idle.

I have recently found that the increased fuel pressure of the electric boost pump causes the idle mixture to richen. Now I know that I shall ensure that any idle speed/mixture adjustment is always tested with electric fuel pump on and off. I am hoping I can reduce the electric pump pressure so this does not happen.

Servo adjustment is not difficult but it may take a few attempts to get it right. The servo idle speed and mixture adjustments are far more sensitive than any carb I worked on.

I'll be interested to hear what stable idle speed other EX-3 and FX-3 owners have set.

[hawgdrvr]

Good info Andy, I hadn't thought about the fuel boost pump affect on idle. My point remains, this condition is not one we test, it's one we end up in during flight. At runup we are not in this condition, with throttle full aft if doing a "pull test" at runup, we're not in this condition. It is good to test this configuration you pointed out. Otherwise as stated, the first time we are in this configuration is coming in for landing and I've heard others having the failure on roll out.

The sad fact is three CubCrafters aircraft have experienced engine failures in the last 30 days and are on the FAA list of accidents. One is a close friend (FX-3 owner) that I'm very familiar with but we don't have answers and won't for some time until inspect and repair is performed. So that's a 363i failure on short final, the other appears to be a EAB XCub with loss of oil pressure (393i), and just recently an EX-2 went down with no details and had issues years ago with fuel starvation. In the Air Force this would likely be a safety standdown so I take this as "engine awareness month" for us all to think through what's going on and learn from these incidents to check ours to prevent any further incidents.

I reached out to Lycoming asking them about idle RPM stating the FX-3 AMM states "500-650" and the tech's response was:

Thank you for contacting us. We recommend going with the manufacturer’s recommended idle RPM setpoint. That being said, I’ve personally observed that our four-cylinder engines seem to idle contentedly in the 600-700RPM range.

Edit: In trying to learn more there seems to be concern about the electronic ignition setup, some don't talk so highly of it, some have mentioned there is a concern about a fused solder situation between sensor leads (flywheel to coil). I know nothing about this. Just hoping things remain stable.

[Narwhal747]

Good info Andy, I hadn't thought about the fuel boost pump affect on idle. My point remains, this condition is not one we test, it's one we end up in during flight. At runup we are not in this condition, with throttle full aft if doing a "pull test" at runup, we're not in this condition. It is good to test this configuration you pointed out. Otherwise as stated, the first time we are in this configuration is coming in for landing and I've heard others having the failure on roll out.

The sad fact is three CubCrafters aircraft have experienced engine failures in the last 30 days and are on the FAA list of accidents. One is a close friend (FX-3 owner) that I'm very familiar with but we don't have answers and won't for some time until inspect and repair is performed. So that's a 363i failure on short final, the other appears to be a EAB XCub with loss of oil pressure (393i), and just recently an EX-2 went down with no details and had issues years ago with fuel starvation. In the Air Force this would likely be a safety standdown so I take this as "engine awareness month" for us all to think through what's going on and learn from these incidents to check ours to prevent any further incidents.

I reached out to Lycoming asking them about idle RPM stating the FX-3 AMM states "500-650" and the tech's response was:



Edit: In trying to learn more there seems to be concern about the electronic ignition setup, some don't talk so highly of it, some have mentioned there is a concern about a fused solder situation between sensor leads (flywheel to coil). I know nothing about this. Just hoping things remain stable.

As a data point my FX3 idles right around 500 RPM on the ground now that I have about 300 hours on it. When it still only had about 100 hours it would idle closer to 600 RPM; sea level, standard temp. I always check this at the end of the pre-flight runup as I have had some issues in other airplanes (specifically an O-470L powered C182 that would die at idle, eventually traced to a loose mixture adjustment screw). In the air at 60-70 MPH it will spin at 1100 RPM with the engine at idle.

I do know that my mechanic found an intake leak in the #4 cylinder which was likely caused by me accidentally touching the intake pipe with a socket while changing spark plugs. I cannot blame anyone but myself for that but be advised that the gaskets for these cylinder intakes seem to be quite fragile and are worth checking for leaks regularly. The engine's operation definitely smoothed out quite a bit and the ground idle was more consistent and smooth at about 520 RPM after the repair. Before it would stutter/stumble a bit at idle, but keep running. THere was also a 150 degree increase in idle EGT compared to the other cylinders on the #4 when the intake was leaky.

Here is a test video I did back when the engine had 100 hours, not claiming it's anything authoritative or useful, just me screwing around for fun:

[Andy]

As a data point my FX3 idles right around 500 RPM on the ground now that I have about 300 hours on it. When it still only had about 100 hours it would idle closer to 600 RPM; sea level, standard temp.

Thanks for that. My FX-3 hasn't been anywhere near sea level for 3 years and has the 80 inch prop. Both of those factors may influence how slow it will idle.

What rpm rise do you see with throttle on the idle stop and slowly moving the mixture from full rich towards idle cut off?

[Andy]

My FX-3 hasn't been anywhere near sea level for 3 years and has the 80 inch prop. Both of those factors may influence how slow it will idle.

Prop diameter does not seem to be a factor. I had a look at the data logs from before accepting the aircraft and found two flights with stable idle below 600 rpm before engine shutdown:

5/28/2020 log_20200528_100325_KYKM.csv 580 rpm, 13.5 MAP, 0.4 gph, OAT 25.7 C, DA 2366 (factory test flight)
6/18/2020 log_20200618_115823_KYKM.csv 580 rpm, 13.4 MAP, 0.5 gph, OAT 25.4 C, DA 1780 (delivery to Hermiston)

There was delivery center adjustment to idle close to the end of phase 1 flight and I have no record of what changes were made. I do have a complete record of all adjustments made after that.

[Narwhal747]

Thanks for that. My FX-3 hasn't been anywhere near sea level for 3 years and has the 80 inch prop. Both of those factors may influence how slow it will idle.

What rpm rise do you see with throttle on the idle stop and slowly moving the mixture from full rich towards idle cut off?

Finally got a chance to test this as the weather has been very cloudy and rainy. Shutting down from 1000 RPM I get about a 20 RPM rise at shutdown. It is barely noticeable. Pulling throttle to idle on the ground results in a bit of roughness in the 510-530 RPM range before it stabilizes at 540 RPM. This was today which was 55 F and at sea level 29.80" altimeter.