Carburetor STC

[C.J.]

3 minutes ago, hammdo said:

Interesting, I’m in Texas and that is what I see with 100°+ temps. If I’m near max load, CHTs are 400°+ before I get to cruise climb…

-Don

@hammdo Well, here in sunny & humid North Carolina we haven't seen triple digits yet, thank God, but most of my summer flights are at OATs between 88 - 94*F at density altitudes between 2500' - 3000' and it's just me in the plane tipping the scale at no more than 2200 lbs. My doghouse is super tight & I do have the LASAR cowl fairing (don't know if it contributes much, but it is there). 

C.J.

[hammdo]

Good to know! Our DA today @ Mesquite was 4500’. So I’m flying @ night time a bit more. `

-Don

[philiplane]

dumping excess fuel through an engine is not the fix for high CHT's. Most baffle systems need work, especially at the front of the engine where air is just diving under the engine instead of cooling the cylinders.

[Shadrach]

15 hours ago, philiplane said:

dumping excess fuel through an engine is not the fix for high CHT's. Most baffle systems need work, especially at the front of the engine where air is just diving under the engine instead of cooling the cylinders.

In my experience with various carbureted and injected Mooneys, C and G models always have hotter CHTs than E and F models despite having slightly lower C/R.

IO360 operators start get concerned when their CHTs climb to levels that many O360 operators would be tickled with.

The factory jetting appears to sub optimal, especially on the earliest models. No one cared before engine monitors. However, now that we have them, it easy to make comparisons between models. I don’t know that it translates into more frequent cylinder work for than the carbureted models.

Everyone has been conditioned to be uncomfortable with CHTs >400°. There are many C model owners that have put lots of time and effort into their baffles and seals but still struggle to keep CHTs < 400°.  Many have take off EGTs in the 1400s. With a CR of 8.5:1, all take off EGTs really should be no higher than about 1300° and preferably less to be rich enough. 
No matter how perfect the baffles and seals, any cylinder that is < 200° ROP at full power in the climb is going to run hot. If it’s running < 150° ROP, it’s going to run really hot.

 

 

[Pinecone]

Dumping more fuel is not the answer, unless you are not supplying enough fuel in the first place.

The rule of thumb I have heard is for max power, you want to be over 1 GPH per 10 HP.   

The fuel flows in the maintenance manuals are MINIMUMS, not maximums.

[Shadrach]

2 hours ago, Pinecone said:

Dumping more fuel is not the answer, unless you are not supplying enough fuel in the first place.

The rule of thumb I have heard is for max power, you want to be over 1 GPH per 10 HP.   

The fuel flows in the maintenance manuals are MINIMUMS, not maximums.

The recommendations I have read online for FF/HP are all over the place. Including in Mooneys own POHs and operating manuals.  Prior to 1968 Mooney did not give FF numbers for full throttle, max RPM, full rich operation in the M20C POH. The 1968 POH calls for SL 18.2GPH @ 2700RPM and 28.0 inHg.  I would treat that as a minimum for any C model.  I think many C models come up well short of this number. 

What's more interesting is the staggering difference in FF numbers between the POH for 1966 and 1968. 1966 only gives numbers for 2600RPM and starts at 2500MSL (Std. Day). Comparisons below.  I continue to believe that the early C models do not get enough fuel even if they have excellent fuel distribution (which they don't). Given the distribution characteristics of carbureted engines, some cylinders are likely running at max ICP.  Noting take off EGTs is a good start to understanding the problem. Those of you that continue to that believe Raw EGT numbers don't tell anything are free to continue believing in the face of contrary evidence, but I'd not recommend it.

2500'

1966 - 2600RPM 27inHG and 14.4GPH

1968 - 2600RPM 26inHg and 16.5GPH

Difference of -1inHg and 2.1GPH

5000'

1966 - 2600RPM 24.5inHg and 12.9GPH

1968 - 2600RPM 24.5inHg and 15.7GPH

Difference of 2.8gph

7500'

1966 - 2600RPM 22.5inHg and 11.8GPH

1968 - 2600RPM 22.5inHG and 14.4GPH

Difference of 3.6GPH

10,000'

1966 - 2600RPM 20.25inHg and 10.6GPH

1968 - 2600RPM 20.2inHg and 9.2GPH

Difference of -.05inHg and -1.4GPH

[philiplane]

3 hours ago, Pinecone said:

Dumping more fuel is not the answer, unless you are not supplying enough fuel in the first place.

The rule of thumb I have heard is for max power, you want to be over 1 GPH per 10 HP.   

The fuel flows in the maintenance manuals are MINIMUMS, not maximums.

ABSOLUTELY INCORRECT. You would be flooding the engine, degrading the performance, washing the cylinder walls and scuffing the pistons, and trailing black smoke like an old B52.

The max power fuel flow recommendations are .088 GPH per HP for normally aspirated engines, and .11 GPH per HP for turbocharged engines. These come from extensive piston engine R&D beginning in the 1930's at Pratt & Whitney in East Hartford CT, and continued today by George Braly of GAMI in ADA Oklahoma. Hundreds of thousands of research hours over the past 80 years. 

Carbureted engines have two fuel flows built in. One through the main jet, and a second through the economizer valve when the throttle plate is at the full open position. This is why full throttle is recommended for climb, rather than pulling power back to some lower level like 25 squared. 

Most pilots don't understand the relationship of fuel flow to spark ignited piston engine power. More fuel is not better. Once you're outside the stoichiometric ratio you have to make compromises for either longevity or performance.

If the engine fuel flow is set correctly, and you have excessively high CHTs, you either have a baffle problem, or advanced timing. Advancing timing from 20 to 25 degrees for example will raise CHT by about 15 degrees, and the EGT will decrease. Advancing from 20 to 30 degrees will increase CHT by about 20 to 25 degrees. We're also seeing this effect in engines with electronic ignitions that have timing advance.

A Lycoming's CHT's in the climb can be up to 450 degrees without any concern. In level flight below 80 percent power, you want to have CHT in the 330 to 400 degree range with oil temperature at 185-210 degrees. Obviously at 65 percent or less the max temps will be lower as a function of power output.

Everyone forgets that all the temperature expectations are based on a Standard Day. So don't expect to have the same results on a 95 degree summer day. You have to compromise with a higher speed, shallow climb to ram more of that hot, thin air through the cylinder fins, than you would on a 60 degree day.  That's why you don't need to worry about a 400 to 450 degree climb CHT for a few minutes on a hot day. So long as you're below 400 in cruise, preferably closer to 350, there's nothing to worry about. Extensive research finds that staying below 380 continuous is key to longevity, and short excursions in the climb aren't harmful. 

For the most part, fuel injected Lycomings don't need any special tinkering regarding the fuel flow. It's automatic. Continentals are another story. Carbureted engines are already set to the correct specs if the correct carb for the application is used.

Virtually every "cooling problem" on any airplane is due to faulty or insufficient baffles, advanced timing, or climbing heavily loaded on hot days at slow speed. More fuel is not only the wrong solution, it will harm the engine in short order.

Baffles are more than the rubber seals. The metal parts holding the seals, and the intercylinder baffles, are often overlooked. In many planes there are large gaps around the starter and alternator. More air can be lost there, than if you had no rubber seals on the rest of the engine. 

I'm the guy who can make a Turbo Aztec climb at 85 percent power from sea level to FL250 with the cowl flaps closed, and no CHT over 400. Those planes are notorious for running hot because they weren't perfect from the factory, and years of inadequate maintenance worsens the cooling system performance. A carbureted Mooney is simple in comparison.

Stop dumping excess $$$$$ fuel through your engines. It's not the answer.

Edited August 29, 2023 by philiplane

[Shadrach]

1 hour ago, philiplane said:

ABSOLUTELY INCORRECT. You would be flooding the engine, degrading the performance, washing the cylinder walls and scuffing the pistons, and trailing black smoke like an old B52.

The max power fuel flow recommendations are .088 GPH per HP for normally aspirated engines, and .11 GPH per HP for turbocharged engines. These come from extensive piston engine R&D beginning in the 1930's at Pratt & Whitney's Willgoos Lab in East Hartford CT, and continued today by George Braly of GAMI in ADA Oklahoma. Hundreds of thousands of research hours over the past 80 years. 

 

Is it your contention that a naturally aspirated P&W 1340 with a compression ratio of 6.1 to 1 has the same FF/HP ratio requirements of a naturally aspirated O360 with a compression ratio of 8.5 to 1?  I agree with everything you've said conceptually.  However, at a more granular level, the general numbers you've given are just that, general. They must be fine tuned by application as the range of configurations of both NA and Turbo Charged engines vary significantly.

Look at Mooney's apples to apples HP/FF ratio specifications in 1966 and 1968 for the same engine...

1966 M20C POH - 2600, 26inHg 90% (162HP) 13.4GPH= HP/FF ratio of .0827

1968 M20C POF =2600, 26inHg 91.2% (164.1hp) 16.5GPH = HP/FF ratio of .1005

Lets look at the specifications for F model IO360 with near perfect F/A distribution.

1968 M20F POH 2700, 28.4inHg 99.9% (198.8hp) 18.6GPH - HP/FF ratio of .09309

You cannot possibly believe that there are no other factors besides Turbo Supercharging and normally aspirated associated with FF, CHT and detonation margins? Do you think we can just throw thermal efficiency (HP/per unit of fuel) and the associated increases in ICP and reduced detonation margins out the window for a 1 size fits all for NA engines and a one size fits all for TSO/IO engines with a range of C/Rs, Piston speeds and boost levels?  All of those variables affect CHTs and detonation margins.  Fractional differences in HP/FF ratio have a profound effect on power, CHT and detonation margin but more so at the extreme lean and rich edges of ignitable mixtures.  According to a widely published graph by P&W, best power mixture (highest ICP) is at .08. and too rich to ignite is at .125. According to P&Ws own graph the engine (assuming NA) will make full HP from ~.08 to ~.094.  

Help me understand how raising the FF of a 1964 O360 M20C from the HP/FF ratio of .0827 shown in it's POH to the FF/HP ratio of .105 shown in the 1968 POH for the same O360 M20C will cause cylinder scuffing?  

Lycoming and Continental have their own graphs mixture graphs and while they are conceptually identical to the P&W graph, the numbers are not.

[hammdo]

 

;o)

[Shadrach]

12 minutes ago, hammdo said:

 

;o)

I'll admit to not realizing when others are poking fun at me. Is that what is happening here?

[hammdo]

Lol, it’s all in fun. I just feel I’m from another planet with all the competing statistics…

-Don

[Shadrach]

17 minutes ago, hammdo said:

Lol, it’s all in fun. I just feel I’m from another planet with all the competing statistics…

-Don

Not stats but specifications.  One must get used to contradicting numbers if one is going to examine decades of factory technical data...especially POH data.

[philiplane]

3 hours ago, Shadrach said:

Is it your contention that a naturally aspirated P&W 1340 with a compression ratio of 6.1 to 1 has the same FF/HP ratio requirements of a naturally aspirated O360 with a compression ratio of 8.5 to 1?  I agree with everything you've said conceptually.  However, at a more granular level, the general numbers you've given are just that, general. They must be fine tuned by application as the range of configurations of both NA and Turbo Charged engines vary significantly.

Look at Mooney's apples to apples HP/FF ratio specifications in 1966 and 1968 for the same engine...

1966 M20C POH - 2600, 26inHg 90% (162HP) 13.4GPH= HP/FF ratio of .0827

1968 M20C POF =2600, 26inHg 91.2% (164.1hp) 16.5GPH = HP/FF ratio of .1005

Lets look at the specifications for F model IO360 with near perfect F/A distribution.

1968 M20F POH 2700, 28.4inHg 99.9% (198.8hp) 18.6GPH - HP/FF ratio of .09309

You cannot possibly believe that there are no other factors besides Turbo Supercharging and normally aspirated associated with FF, CHT and detonation margins? Do you think we can just throw thermal efficiency (HP/per unit of fuel) and the associated increases in ICP and reduced detonation margins out the window for a 1 size fits all for NA engines and a one size fits all for TSO/IO engines with a range of C/Rs, Piston speeds and boost levels?  All of those variables affect CHTs and detonation margins.  Fractional differences in HP/FF ratio have a profound effect on power, CHT and detonation margin but more so at the extreme lean and rich edges of ignitable mixtures.  According to a widely published graph by P&W, best power mixture (highest ICP) is at .08. and too rich to ignite is at .125. According to P&Ws own graph the engine (assuming NA) will make full HP from ~.08 to ~.094.  

Help me understand how raising the FF of a 1964 O360 M20C from the HP/FF ratio of .0827 shown in it's POH to the FF/HP ratio of .105 shown in the 1968 POH for the same O360 M20C will cause cylinder scuffing?  

Lycoming and Continental have their own graphs mixture graphs and while they are conceptually identical to the P&W graph, the numbers are not.

Spend some time at GAMI's test cell, talk with George, and you'll find what I said is current and accurate. You can find all the pertinent articles online as well. I did not claim that an old radial has the same BSFC as a flat motor. I said that the knowledge base began there, and was picked up and further developed over the past eight decades. And yes you will find very narrow windows of fuel ranges to produce rated HP for N/A and for turbo engines. It's related to the BTU available in each pound of fuel. There's less variety now since we essentially only have 100LL in wide use, which has 112,500 BTU per gallon. 

Increasing max power takeoff fuel flow beyond what's needed to maintain detonation margins dilutes oil on the cylinder walls. In one case, I've got borescope photos from an annual inspection, and then a week later the owner and an advocate of crazy fuel flows decided to increase from 28 GPH to 32 GPH because they'd heard the 1 GPH per ten HP and decided to try it. Two months after that, the owner called me and complained about black oil and high consumption. It only took them one hour to ruin six cylinders. He didn't tell me at first what they'd done. I figured it out from the engine data. They made an $18k mistake based on internet ramblings. 

I've tuned well over a thousand engines in the past 25 years. Everything from M20C to Bravos and Ovations, big and small Piper singles & twins, anything Lycoming from the O-320 up to the IO-720, AEIO-580,& TIGO-541, and every Continental that Cirrus uses. Changed over 300 cylinders too, and only as a last resort. Also highly experienced in FADEC, aftermarket electronic ignitions, aero-diesel engines, pro gas drag engines, and I have patented engine dual-fuel control systems. No significant experience with Wankel engines though...er 

A flat four aircraft engine has pretty narrow fuel needs. The compression ratio also has little bearing on the fuel flow. It does change the thermal efficiency of the engine in part throttle operations. This is why the .088 gal per HP works on a 150 HP 7.5:1 CR Lycoming four cylinder, and a 310 HP 9:1 CR fuel injected Continental six cylinder. 

Below you'll find the formula to start the fuel/air ratio calculation before putting the engine on the dyno for fine tuning. You can find further info in SAE White Papers but you'll have to join to get full access. NASA also did some studies that I used as reference material during the patent application process.

Edited August 29, 2023 by philiplane

[Shadrach]

2 hours ago, philiplane said:

Spend some time at GAMI's test cell, talk with George, and you'll find what I said is current and accurate. You can find all the pertinent articles online as well. I did not claim that an old radial has the same BSFC as a flat motor. I said that the knowledge base began there, and was picked up and further developed over the past eight decades. And yes you will find very narrow windows of fuel ranges to produce rated HP for N/A and for turbo engines. It's related to the BTU available in each pound of fuel. There's less variety now since we essentially only have 100LL in wide use, which has 112,500 BTU per gallon. 

Increasing max power takeoff fuel flow beyond what's needed to maintain detonation margins dilutes oil on the cylinder walls. In one case, I've got borescope photos from an annual inspection, and then a week later the owner and an advocate of crazy fuel flows decided to increase from 28 GPH to 32 GPH because they'd heard the 1 GPH per ten HP and decided to try it. Two months after that, the owner called me and complained about black oil and high consumption. It only took them one hour to ruin six cylinders. He didn't tell me at first what they'd done. I figured it out from the engine data. They made an $18k mistake based on internet ramblings. 

I've tuned well over a thousand engines in the past 25 years. Everything from M20C to Bravos and Ovations, big and small Piper singles & twins, anything Lycoming from the O-320 up to the IO-720, AEIO-580,& TIGO-541, and every Continental that Cirrus uses. Changed over 300 cylinders too, and only as a last resort. Also highly experienced in FADEC, aftermarket electronic ignitions, aero-diesel engines, pro gas drag engines, and I have patented engine dual-fuel control systems. No significant experience with Wankel engines though...er 

A flat four aircraft engine has pretty narrow fuel needs. The compression ratio also has little bearing on the fuel flow. It does change the thermal efficiency of the engine in part throttle operations. This is why the .088 gal per HP works on a 150 HP 7.5:1 CR Lycoming four cylinder, and a 310 HP 9:1 CR fuel injected Continental six cylinder. 

I did not say Compression ratio had  bearing on the fuel flow. Compression ratio drives thermal efficiency and ICP. Peak vs mean ICPs are affected by fuel flow. 
 

You’ve said a lot there that is conceptually correct but avoided ringing in on the different Factory FF specifications for the same model from its inception until its discontinuation.
Given your experience, I’m sure they’re quite a few early C model owners who’ve exhausted their efforts sealing baffles and replacing seals that would love to have someone solve their CHT issues.  

[Greg Ellis]

@philiplane A question for you and I am serious with this.  If you have too much fuel that is diluting the oil on the cylinder walls as you mentioned in your previous post, would fuel show up in the oil analysis?

I am one that searched for help on cooling my CHT's.  I have the doghouse style baffling that was replaced with a brand new one quite some time ago back when Airforms were making them for the older Mooneys.  When installed the mechanics said it had tighter tolerances than original and fit perfectly.  Anyways, I always struggled with high CHT's even after the new baffling.  I went around and around until someone looked at my fuel flow and said that 15 gph was too low.  So I went with the richer carb and got about 18 gph fuel flow and my CHT's never touch 400 even in the Texas summer (they come close though but no where near as high as before).  I was one that as @Shadrach says, exhausted my efforts sealing baffles, etc...

[philiplane]

5 hours ago, Greg Ellis said:

@philiplane A question for you and I am serious with this.  If you have too much fuel that is diluting the oil on the cylinder walls as you mentioned in your previous post, would fuel show up in the oil analysis?

I am one that searched for help on cooling my CHT's.  I have the doghouse style baffling that was replaced with a brand new one quite some time ago back when Airforms were making them for the older Mooneys.  When installed the mechanics said it had tighter tolerances than original and fit perfectly.  Anyways, I always struggled with high CHT's even after the new baffling.  I went around and around until someone looked at my fuel flow and said that 15 gph was too low.  So I went with the richer carb and got about 18 gph fuel flow and my CHT's never touch 400 even in the Texas summer (they come close though but no where near as high as before).  I was one that as @Shadrach says, exhausted my efforts sealing baffles, etc...

fuel dilution does show up in oil analysis, but mostly as a product of people stuffing cowl plugs into a hot fuel-injected engine. Then the fuel boils from the lines and ends up in the oil pan. For simple over-rich operation, you will see lower viscosity, and abnormally black oil. 

People focus on the rubber seals, when the problems are usually gaps in the metal to the engine itself. There are large gaps near the oil pressure regulator and the engine isolators. And gaps between the front metal baffles and the engine case, and sometimes there are gaps that allow air to flow under the front cylinder fins.

Also, any ram air getting into the lower cowl upsets the pressure differential. You want high pressure on top of the cylinders, and the lowest possible pressure below the cylinders. Depending on your lower cowl, or any cowl inlet closures, you may have many points where ram air is getting into the lower cowl. Such as around landing lights and front mounted oil coolers. The area around the prop, starter, and alternator need to be sealed as completely as possible.