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Anomaly During Hot Engine Takeoff

D-Dubya

D-Dubya

Well Known Member
I am seeking insights on an issue with my RV-7 that's equipped with a parallel valve IO-360 engine. Specifically, when the engine is hot and at full power during takeoff, there's a sporadic 'pop' or 'miss'. This is perceptible through the rudder pedals and stick and confirmed by ground observers anytime I takeoff when the engine is hot (like during a second takeoff or go-around).

My first hunch was that everything was getting heat soaked after slowing down for landing and it may be experiencing a vapor lock issue. So I tried keeping the power at cruise settings all the way through a descent in smooth air, then applying takeoff power at 1000’ before arriving in the pattern. It’s the same thing; still the pop/miss at WOT & higher RPM.

Key Observations:
- Occurs only under three concurrent conditions: hot engine, full throttle, and full RPM
- Reducing power to 25” MAP or RPM below 2550 eliminates the issue
- Issue persists regardless of mixture settings
- Higher CHTs (usually under 405 degrees F) observed during second takeoff, but cooling quickly upon power reduction
- No issues during first takeoff or at high altitudes
- Fuel flow decreases from 17.5 GPH with a cold engine to 16.7 GPH during second takeoff with a hot engine
- EGTs are similar during first or second takeoff (approx. 1330 degrees F)
- Magneto timing confirmed with both at 23 degrees BTDC

Maintenance Checks:
- Regular borescoping of cylinders shows no concerns
- Performed In-flight LOP Mag Check, Mixture Distribution Test, and Induction Leak Test with no clear issue
- Compression tests show all cylinders in the mid-70's
- Servo levers' range of motion confirmed stop-to-stop

Engine Details:
- ECI Titan IO-360, 185 HP by Barrett Precision Engines
- Experimental version of RSA-5 fuel injection servo
- Cylinders 1-3 have 0.028” fuel injection nozzles, 0.029” for #4
- Bendix magnetos with G3i ignition interface, Champion REM40E spark plugs
- Whirlwind 200RV constant speed prop, forward-facing cold air induction, custom plenum

Although it went undetected during Phase I due to single-takeoff flights, this issue is concerning since I don't know what it is. I am the original builder and seeking suggestions for further diagnostics or experiences with similar issues. More information is available, but I was trying to keep this post somewhat brief.
 
D-Dubya said:
I am seeking insights on an issue with my RV-7 that's equipped with a parallel valve IO-360 engine. Specifically, when the engine is hot and at full power during takeoff, there's a sporadic 'pop' or 'miss'. This is perceptible through the rudder pedals and stick and confirmed by ground observers anytime I takeoff when the engine is hot (like during a second takeoff or go-around).

My first hunch was that everything was getting heat soaked after slowing down for landing and it may be experiencing a vapor lock issue. So I tried keeping the power at cruise settings all the way through a descent in smooth air, then applying takeoff power at 1000’ before arriving in the pattern. It’s the same thing; still the pop/miss at WOT & higher RPM.

Key Observations:
- Occurs only under three concurrent conditions: hot engine, full throttle, and full RPM
- Reducing power to 25” MAP or RPM below 2550 eliminates the issue
- Issue persists regardless of mixture settings
- Higher CHTs (usually under 405 degrees F) observed during second takeoff, but cooling quickly upon power reduction
- No issues during first takeoff or at high altitudes
- Fuel flow decreases from 17.5 GPH with a cold engine to 16.7 GPH during second takeoff with a hot engine
- EGTs are similar during first or second takeoff (approx. 1330 degrees F)
- Magneto timing confirmed with both at 23 degrees BTDC

Maintenance Checks:
- Regular borescoping of cylinders shows no concerns
- Performed In-flight LOP Mag Check, Mixture Distribution Test, and Induction Leak Test with no clear issue
- Compression tests show all cylinders in the mid-70's
- Servo levers' range of motion confirmed stop-to-stop

Engine Details:
- ECI Titan IO-360, 185 HP by Barrett Precision Engines
- Experimental version of RSA-5 fuel injection servo
- Cylinders 1-3 have 0.028” fuel injection nozzles, 0.029” for #4
- Bendix magnetos with G3i ignition interface, Champion REM40E spark plugs
- Whirlwind 200RV constant speed prop, forward-facing cold air induction, custom plenum

Although it went undetected during Phase I due to single-takeoff flights, this issue is concerning since I don't know what it is. I am the original builder and seeking suggestions for further diagnostics or experiences with similar issues. More information is available, but I was trying to keep this post somewhat brief.
Click to expand...

You mention egt of 1300 during this phenomenon. What is typical 75% peak EGT. My guess is a mixture issue.
 
It would seem that you have an intermittent cylinder miss fire when hot. That cylinder has an issue with fuel delivery, ignition or air supply/compression.
Things I would do:
Perform the simulated take off at 1,000 feet again but do it on one mag and then the other. This should eliminate any ignition issues, if it checks out with the same miss.
Clean injection nozzles, flow divider and lines from the divider to the nozzles. This should eliminate any problems with fuel delivery to an individual cylinder. Not sure why the fuel flow drops almost a gallon an hour when hot, at takeoff, but cleaning the nozzles, lines and flow divider should help with that if an issue with them that is causing that decrease.
If that doesn't provide a cure, I would do a thorough inspection of the valve train on all cylinders, looking for broken valve springs, checking cold clearance etc. If nothing shows there, I would replace the lifters/hydraulic units either all at once or two at a time.
Maybe give Barret a call and see what they think. It's their engine.
Good Luck!
Merry Christmas,
Mahlon
 
Charts please

dump the data from the g3x, upload to Savvy, post links or images of CHT, EGT, rpm, MP, FF, OAT...
 
Do you take off with your auxiliary pump on? If not, try that. Could be a fuel delivery issue related to vapor lock.
 
Phase 1 stumble

During my phase 1 testing, in the middle of summer, during run up and takeoff, I would get a stumble. I contributed it to vapor in the lines. Once vapor forms in the fuel line, the only way to get out is through a cylinder. In the hot months, I would do an extended runup with the electric fuel pump on so it would stumble on the ground and not during take off.

Before next summer, during conditional inspection, I plan to shorten and heat shield all the fuel lines fire wall forward. It may not eliminate the fuel vapor in the lines, but would allow the vapor to get out during a sorter run up . JMHO
 
I'll respond to what I can so far...

Yes, takeoff is with the aux fuel pump on. Have tried it with the pump on and off--the miss still occurs.

I was having some issues with the SD card recording complete flights lately, but I think that's been resolved. I will see what info I can gather. I may have an older flight on the Savvy site that I'll try to upload or link. I'm over 60, so I may need to get a buddy to help doing that. :rolleyes:

And I thought I may have eliminated the vapor lock issue by keeping the power in and doing a simulated takeoff at 1,000'. The fuel was flowing at 9-10 GPM and the engine was running smoothly the whole way prior to applying takeoff power again. The power was pulled back at the onset of the miss and the engine ran smoothly for the duration of the flight.

Last week, I did some tests at 7,500' (the SD card didn't capture it) and ran through LOP and ROP several times. I recall peak EGT was 1515 or 1520 degrees F. The G3X was showing over 70% power, but I don't recall exactly what % it said. Pretty sure it was around 75%. It was a cool day and TAS was 184 knots running ROP. Ground speed was 200 knots, so that's why I took a picture of that.
 
D-Dubya said:
Last week, I did some tests at 7,500' (the SD card didn't capture it) and ran through LOP and ROP several times. I recall peak EGT was 1515 or 1520 degrees F. The G3X was showing over 70% power, but I don't recall exactly what % it said. Pretty sure it was around 75%. It was a cool day and TAS was 184 knots running ROP. Ground speed was 200 knots, so that's why I took a picture of that.
Click to expand...

so, if all of the EGTs were sitting around 1330 during this event, it seems unlikely that mixture is the cause. There is a slim possibility that 1330 on one of the cylinders is 200* LOP instead of ROP, but the data should have shown that progression. The drop in fuel flow is a bit concerning. Fuel flow at WOT should be directly tied to RPM,MAP, air temp, baro pressure and airflow volume; however volume should be consistent for any given RPM/MAP/altitude combo, excluding issues occurring with the valve train. If vapor lock occurred, it should reduce fuel flow and the FF would change substantially and would also see significant EGT changes due to the leaner mixture.

The fact this heat induced, I would be looking more closely at valve train issues. If one of the plugs stopped sparking, you should see a spike in EGT, due to the retarded timing. However, with so much going on, this could be easilly missed.

Two EMS plots with a lot of data would help a lot. One with the cold TO and another for the hot TO.
 
Last edited:
Savvy Plots

Okay, let's see if I can make this work. This hopefully will link to a flight a few weeks ago where I took off and flew someone around the area, then landed and repeated the same with another person. The G3X stayed on during shutdown, so it recorded the two flights as one. The first landing was around the 30 minute mark, the second run-up was around the 35-36 minute mark, and the second takeoff with the hot engine was around the 37 minute mark. It made the miss/pop on that second takeoff.

https://apps.savvyaviation.com/flights/shared/flight/7596100/9cfee517-01a6-4e51-b40f-382a1b17c4e0
 
Ohm out your spark plugs.

https://www.championaerospace.com/assets/technical/SL74-20-001.pdf

O-320 D3G 160HP carburetor, Bendix mags w/shower of sparks.
I had a new tempest fine wire spark plug give me similar issues at high power settings. Tested at 17,000 ohms and failed during pressure testing in spark plug tester. New plug with only 70 hours on it. Not under warranty.
Not saying this is the cause of your problem. Although I have to wonder how often spark plugs are ohm tested when removed on a condition inspection.
 
All plugs were tested at the last annual condition inspection in May. They were all cleaned and tested in a Champion plug cleaning rig. I also tested the resistance and if it was higher than 2K ohms, I tossed 'em. At least I think that's the value that Vic Syracuse recommended. I have Vic's books and my spark plug inspection records at the airport or I'd confirm that number.
 
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