LOP with carb

Hi All,

Last night on a flight from LLR-PAO I did a little more experimenting with running LOP.

I've got an O-320 with 9:1 pistons and EMag/PMag, Catto 3 blade

While leaning, eventually the motor will start to die, but it doesn't ever run rough.
21" MP
2500 RPM
131 KIAS
10 degrees C
7620' MSL
EGT range 1275-1300
CHT range 350-355
Fuel flow - less than ROP (no flow gauge yet)

When running ROP with the hottest EGT at 1300, the coolest will be 1200 or less. Also, CHTs will often run around 400.

So, the EGTs are more closely grouped and the CHTs are lower running LOP. I'm not sure why the EGTs come together for LOP, but that seems like a good thing.

I don't know my fuel flow yet. Next trip I'll run LOP both directions to get an idea of consumption.

Also, I generally cruise at 135 KIAS - IAS is a good indicator of power. I don't have an "official" power schedule for my engine, but I estimate that to be a bit over 65%.

Next time I'll bump the power up to get 135 KIAS running LOP

Hi Steve,
When you say LOP do you mean all cylinders are LOP? At part throttle I can get the back two cylinders to go LOP but not the front two before the engine starts to run rough/dies.
When you get your fuel flow have a look at Curve #13380 (Fig 3-16 in my 0-320 Operators Manual). It may be of use calculating your HP.

Fin
9A, 0-320, C/S, 9:1, LS Plasma III and mag.

Need more data

Finley Atherton said:

Hi Steve,
When you say LOP do you mean all cylinders are LOP? At part throttle I can get the back two cylinders to go LOP but not the front two before the engine starts to run rough/dies.
When you get your fuel flow have a look at Curve #13380 (Fig 3-16 in my 0-320 Operators Manual). It may be of use calculating your HP.

Fin
9A, 0-320, C/S, 9:1, LS Plasma III and mag.

Click to expand...

Good question. I have a single EGT gauge with a 4 position switch. Difficult to simultaneously monitor all 4. On the next flight I can also diddle the mixture some while monitoring each cyl to see which way it moves.

It may be flawed, but here is my logic:
If the EGTs and CHTs are well balanced at a reasonable temperature, and the engine is running smooth, it doesn't really matter if all the cylinders are on the same side of peak.

Someone feel free to jump in if I'm thinking wrong.

I use this formula to estimate power:
(RPM/2700) x (MP/29.92) / (OAT/288)

OAT is in Kelvins (C + 273). Basically it proportions current engine conditions with that of a "standard" sea level situation at full throttle, max RPM. It assumes that torque is very flat, and over the narrow 2400-2700 RPM range it is pretty flat.

When MGL rolls out their round gauge infinity series in a few weeks, I'm planning to get some 4 channel temp gauges and maybe a fuel flow gauge. That should shed more light on my actual operating conditions.

Also, when I try this up higher at full throttle I may get a completely different results.

Steve Brown said:

I use this formula to estimate power:
(RPM/2700) x (MP/29.92) / (OAT/288)

Click to expand...

On the Lycoming Aircraft Engine Performance Data curve 13381, they show about a 1.2" drop in MAP relative to static pressure. That means in your formula you should ratio MAP to 28.7" rather than 29.9"; that will give you about 4.2% more power at 25" MAP than you think. Also, if available, you should ratio induction absolute temperature rather than OAT to 288K, or, if not available, use OAT(C) + 273K, which is what I'm sure you meant. C.F. Taylor says that the maximum temperature drop from gasoline converted to a stoichiometric ratio is 44F, but the more typical drop is 24F. However, you must allow for the stagnation temperature rise above ambient occuring in your manifold, which is 7.2F at 200 mph TAS. This is given by (TAS,mph)^2/5521. So it might be a little more correct to use (OAT(C)-9C+273. That might give you about 3.1% more power than what you thought at 25C. Taken together, that would give you about 7.4% more power at 25C, 25", 200mph TAS than you originally thought. N'est-ce pas?

Steve,

My setup is very similar except I have 8.5:1, one E-Mag and a Slick. There are several throttle positions where I can run LOP very well. These aren't so much MAP dependent as just throttle position, how far I pull the black knob. One gives me a very nice cruise at somewhere around 65% power. My rpm is lower than yours, however. My fuel flow is off right now, so I won't quote fuel burn, but it is good. EGT's mid 1300's, CHT's 340ish. I find I can stay LOP better if I pull carb heat, also. I can get my EGT's almost equal. Downside, at full throttle, #1 EGT is quite a bit higher than the others, ROP of course. Compressions are all above 75. And yes, I can pull the mixture and just slow the engine down without it running rough. I think you have a good setup!

Bob Kelly

Finley Atherton said:

When you get your fuel flow have a look at Curve #13380 (Fig 3-16 in my 0-320 Operators Manual). It may be of use calculating your HP.

Click to expand...

I forgot you have a F/P prop so thus curve may not be of much use to you. I THINK this curve is based on low rpm such as 2000 rpm below 65% and 2,200 rpm 65% to 75%.

Fin
9A Flying

videobobk said:

Steve,

My setup is very similar except I have 8.5:1, one E-Mag and a Slick. There are several throttle positions where I can run LOP very well. These aren't so much MAP dependent as just throttle position, how far I pull the black knob. One gives me a very nice cruise at somewhere around 65% power. My rpm is lower than yours, however. My fuel flow is off right now, so I won't quote fuel burn, but it is good. EGT's mid 1300's, CHT's 340ish. I find I can stay LOP better if I pull carb heat, also. I can get my EGT's almost equal. Downside, at full throttle, #1 EGT is quite a bit higher than the others, ROP of course. Compressions are all above 75. And yes, I can pull the mixture and just slow the engine down without it running rough. I think you have a good setup!

Bob Kelly

Click to expand...

Hi Bob,
Sorry to repeat myself (post#2), but is your LOP with all the cylinders LOP? My understanding is that when the guys with balanced injectors talk LOP they mean all cylinders are LOP. I have seen many carb guys say they can run LOP but I am never sure if they mean all cylinders are LOP.

Fin
9A Flying

LOP - All Cylinders

Hi Fin,

I have a 9A carb -320(8.5) Dual EI. I run LOP - all cyl most of the time. Here she is at high cruise:

WOT/full carb heat - All cyls LOP - I am at 10,500 here and about 145-150KTAS/5-6GPH over Chicago. Same speeds and less GPH up at 12,500 or 14,500

Here I am low and slow. Sorry for the pic quality. 98KTAS/3.3GPH, 1100+ Mi range.

I run carb heat when running LOP most of the time - you lose a bit of MP, but mine runs smoother. YMMV

Pete,
Great stuff. A lot of good information to think about. I am particularly impressed that you get all cylinders LOP at part throttle settings ( second photo). As I stated earlier, at part throttle I can only get two cylinders LOP. I will try carb heat at part and WOT and see what happens.
Thanks
Fin

Initial Analysis

Fin,

Here is the the thread where I did my initial analysis with the help of Alex P and George.

http://www.vansairforce.com/community/showthread.php?t=12968&highlight=lop

I went from hopeless to "Hey, this actually works." I run LOP every flight now. Cool and smooth - cheaper, too.

I really think EI with advance plays a big part in it. Sure, well tuned FI is better, but I don't have it - and this works pretty well.

Pete,
Your photos inspired me. I couldn't help myself, I jumped in the 9A went to about 11,000 ft DA and played around with the knobs. WOT and carb heat brings all the EGTs closer together and I can now get 3 cylinders to peak (only two before) and the forth peaks just after the engine starts to run rough so there is a good chance that I might get all of them to peak before roughness if I play around with the throttle/carb heat. I am still not convinced about the fuel consumption benefits of LOP. I think the biggest benefit would come from having all the cylinders peak in a narrower mixture band and that being able to run then all near peak would give similar fuel flows per hp as having them all running LOP??
I can verify your TAS/Fuel Flow figures are realistic. I did a run with carb heat on at 20.2" mp and 2210 rpm manually leaned to rough then in to smooth and got a fuel flow of 5.5 g/h at 146 kts TAS (verified by a 4 leg GPS run) so my speed and fuel flows are close to yours in photo #1.

Fin
9A

Good Show!

Fin,

That is great news. I just played with it until I found places where it would work. I do think it saves fuel, but the other nice benefit is that the engine runs cooler. Temps really come down LOP. I'll probably get blasted, but I think cooler is better for engines(within reason of course).

Keep working (playing) with it. Darn, have to fly to get more data

Finley Atherton said:

Hi Bob,
Sorry to repeat myself (post#2), but is your LOP with all the cylinders LOP? My understanding is that when the guys with balanced injectors talk LOP they mean all cylinders are LOP. I have seen many carb guys say they can run LOP but I am never sure if they mean all cylinders are LOP.

Fin
9A Flying

Click to expand...

Yes, all cylinders. It is only at a narrow range of throttle positions, and that range is wider with carb heat pulled. The EGT's get VERY close if I work at it and the CHT's do come down compared to ROP. Since it is a comfortable speed (~155 mph) I use that for most XC work (hey, I'm to old to be in a hurry!) It also works down around 110 mph, but I don't fly at that setting all that often. Will have to play with it more.

Bob Kelly

O-320 w/carb power settings...

You guys have discovered the settings I have been using since June 2005. I spent a lot of time in the 10,000-12,000 altitudes during phase 1 testing and then on long cross-country flights. This first photo was taken June 19, 2005 in early phase 1 testing at a "lower" altitude. I would generally adjust the power settings for nearly balanced EGT's. The highest CHT on the engine monitor is reported at 383 F.


Here is an instrument panel shot from July 31, 2005 cruising home from Pennsylvania after my trip to Oshkosh, The Great Lakes, NJ, NY, and RI.

This one shows the Dynon D-10A showing 143 KNOTS on true airspeed. The EGT bar graphs are nearly equal above the 2320 RPM indication. Manifold pressure at 12,500 MSL is only 18.9 inches at WOT. Fuel flow is at 5.6 gallons per hour. The engine is an ECI 0-320 with carb, one Light Speed Plasma III ignition and a Slick mag on the other side.

Carb heat, WOT, etc

Obviously I'm not the only one able to operate LOP with carb. Looking at this and other threads, there seems to be some debate as to why carb heat helps.
Heat or turbulence?
Partial verses WOT results seem to point to turbulence. On the other hand, power settings appropriate for LOP operation tend to happen higher where it is colder.
This may be a dumb question, but if it's a matter of heat, how about heating the fuel before it gets to the carb?
I'm having a hard time buying the turbulence argument because carb heat or not, the air (in my plane) goes through the air filter afterwards. I think the air filter is going to dominate the way the air flows.

Great Question

Heat makes more sense to me as it would make the fuel easier to vaporize and a gas would flow more evenly to each cylinder than atomized fuel droplets.

What confuses me (one of many things in life) is that I fly from 100degF to 0degF here in Minne and the carb heat trick still works - pointing to airflow.......

I suppose a guy could set up a test with the carb heat door in place, but the heat muff not connected, to eliminate some variables, but cowl air is warmer than ram air, so not perfect.

I have often thought that heated ram air (anti-intercooler?) might be a nice way to run LOP without losing that bit of MP with the carb heat door closed - same effciency and temps, more speed (and fuel)

Back to pivot tables..........

I just flew a bit trying to get some useful info but had to get so high (14,500') that I was getting cold. The one thing that came out of this flight is that when I leaned at around 13,500' my fuel flow was about 2 gph less than my takeoff mixture at the same altitude (Field elevation 6840').

This number is just approximate due to the need to average what I see on the RMI engine monitor but it is clear that if you don't lean properly, you can waste a lot of fuel.