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Fuel flow on takeoff

s24789

Well Known Member
Patron
Looking for other's experiences. On take off we are seeing 13.5 max fuel flow in our carburated o-360 and fixed pitch prop in our 7a. We are also seeing no fuel coming out of the fuel drain in our gascolator mounted on the lower right firewall. We do get flow when we turn on the boost pump. Has anyone else experienced this issue. I am wondering if a vent restrictions keeping us from both seeing fuel at the gascolator drain and also restricting our fuel flow.

Thoughts ?

Thanks
Phelps:confused:
 
Looking for other's experiences. On take off we are seeing 13.5 max fuel flow in our carburated o-360 and fixed pitch prop in our 7a. We are also seeing no fuel coming out of the fuel drain in our gascolator mounted on the lower right firewall. We do get flow when we turn on the boost pump. Has anyone else experienced this issue. I am wondering if a vent restrictions keeping us from both seeing fuel at the gascolator drain and also restricting our fuel flow.

Thoughts ?

Thanks
Phelps:confused:

What you are seeing in regard to fuel flow and the gascolator is normal.
 
I agree with Sam on the Gascolator - you won't get any flow unless you have the pump turned on.

For your measured fuel flow - have you calibrated the fuel flow system yet? The factor "constant" is oftentimes off by 20%, and you have to play with it by measuring how much fuel you put in after a flight, then tweaking the constant. It is an iterative process, and can take awhile to nail it.

Paul
 
.1 gph per hp at max power full rich fuel flow

The rule of thumb of .1 gph per hp at max power full rich fuel flow seems to be pretty accurate.
 
I agree with Sam on the Gascolator - you won't get any flow unless you have the pump turned on.

For your measured fuel flow - have you calibrated the fuel flow system yet? The factor "constant" is oftentimes off by 20%, and you have to play with it by measuring how much fuel you put in after a flight, then tweaking the constant. It is an iterative process, and can take awhile to nail it.

Paul
Hi Paul thx, yes we have calibrated the red cube. Using Mike Bush's plotting website we generally see 410-420 F at sea level 90 F take off and around 14-15 gph Wf in take-off. After a couple thousand feet with WOT the CHTs settle down. Still wondering if we are not getting enough flow for takeoff. Thoughts?
Phelps
 
My set up is O-360, Fixed Pitch, field elevation is 614 ft.

Seems about what I am seeing. Take off run is 13GPH, WOT RPM starts at 2130 and increases as the ground run speed increases. Red cube installed between gascolator and carb.

To drain any fuel out of the gascolator, I have to select one of the tanks using the fuel selector valve. No fuel flows if the selector is in the OFF position.
 
Kevin

Aside from fuel system anomalies and measurement errors, the following is not negotiable in general terms, +/- 5%.

Fuel flow at sea level and ISA is HP/10 in GPH, in your case I assume 18 GPH.

With a fixed pitch prop you may have 85% rpm thus 85% fuel flow, so around 15-15.5 GPH.

CHT on take off should be in the 350-375 F range, if not get your fuel flow right first, then fix your baffles.

Any questions, please ask.

David
 
15.1 to 15.3 gph at Takeoff

I've just checked the digital records of my RV-7a with a 180 hp Mattituck IO-360 M1B. I have a Hartzell constant speed blended airfoil prop. On full throttle takeoff at my fuel flow ranges from 15.1 to 15.3 gph. My airport (KLVK) is at 400 ft msl and the temperatures I looked at ranged form 48 to 90 F. My fuel red cube fuel flow device is pretty well calibrated (usually well within 0.5 gal at fillups).

This seems to be more than than +/-5% off of the range of 0.1 gal/hp.
 
My -9A (IO-320 160 hp - Hartsel) reads 17 gph on climb out. EGTs 1340's, CHT 380's. An -8A I recently flew (IO-360 / Hartsel prop) reads around 17-18 gph also. I think the 13-15 gph folks are running on the lean side...
 
I've just checked the digital records of my RV-7a with a 180 hp Mattituck IO-360 M1B. I have a Hartzell constant speed blended airfoil prop. On full throttle takeoff at my fuel flow ranges from 15.1 to 15.3 gph. My airport (KLVK) is at 400 ft msl and the temperatures I looked at ranged form 48 to 90 F. My fuel red cube fuel flow device is pretty well calibrated (usually well within 0.5 gal at fillups).

This seems to be more than than +/-5% off of the range of 0.1 gal/hp.

You have something not right, either fuel flow measurement or your fuel flow.

One or the other. Either way get it fixed.

18GPH please +/- 0.5 GPH is the aim. If it gets to 5% you need to tweak.
 
You have something not right, either fuel flow measurement or your fuel flow.

One or the other. Either way get it fixed.

18GPH please +/- 0.5 GPH is the aim. If it gets to 5% you need to tweak.

That works out to 0.6 pounds/HP-hour for a 180 HP engine assuming avgas at 6 pounds per gallon. Is that based on a rule of thumb, empirical data or Lycoming data or something else?
 
It is from demonstrated data.

Oddly enough, from the factory my IO540 and most others achieve this.

It is a rule of thumb, however ths rule is in keeping with well established data. Oddly enough TCM recently have found themselves releasing SB's.

You can bank this rule of thumb, it is not an OWT :)
 
With a fixed pitch prop turning 2100-2200 for take off, the engine is not developing anywhere near 180 HP, it 's more like 135 HP. At that power level the fuel flow is about right.

What is the fuel flow at WOT in flight where the rpm is nearer 2700 and the engine is developing more like 180 HP?
 
It is from demonstrated data.

Oddly enough, from the factory my IO540 and most others achieve this.

It is a rule of thumb, however ths rule is in keeping with well established data. Oddly enough TCM recently have found themselves releasing SB's.

You can bank this rule of thumb, it is not an OWT :)

It seems high to me, but then I don't have any data immediately available (and couldn't find any with a quick search) showing specific fuel consumption at wide open throttle, and presumably full rich mixture. I'm accustomed to seeing and using 0.5 lb/hp-hr for calculations, but maybe that's closer to stoichiometric? In any case, using 0.5 translates to 15 gph, which is closer to what some here have observed. Too lean on takeoff?
 
Fuel Flow

To add another data point. I have a 200 hp engine with a constant speed prop and at sea level, it will trip my fuel flow alarm (set at 20gph) occasionally on take-off.:eek:
 
Lars,

I agree with you. I think the your value of 0.5 lb/hp-hr is just about right for my IO 360 with the Hartzel blended airfoil prop and Lasar ignition.
Bob Cowan
 
As Dave has said, your takeoff RPM (horsepower) has everything to do with resulting fuel flow. So does what carb you have. JT and I have exactly the same engine (ECI O360 Titan with 9:1 pistons, built by the same engine shop, but with slightly different carbs. mine has a richer power enrichment set-up at full throttle than Jon's and I see up to 20 gph at takeoff (2700 rpm), about 3-4 more than Jon. At cruise at the same airspeed I see a slightly less FF than he does - verified at fill up. I don't think you are seeing anything unusual with your setup. As long as your other engine indications are normal (CHT, EGT, expected power/climb rate for the RPM) you are in good shape.
 
.51 is a good number leaned out....

The IO360 I had with the 7A was a Barrett engine and it came off the dyno with a BSFC of .51 lbs/hr/hp. I believe that number was derived at best power mixture.

At take off with mixture full rich the number is higher for sure. If it is .60, the 13.5 gph with a fixed pitch prop computes to 135 HP which is about all that can be expected. RPM is in the 2200 range and the fuel flow is about normal.

It is impossible to develop 180 hp at 2200 rpm with a normally aspirated engine. If fuel flow were 15-16 gph at 2200 rpm, that would be a problem.
 
Folks, the info I have provided already is proven good data.

As some have shown, the IO390x is about 20GPH, funny enough for 200HP engines at 2700 RPM full rich at ISA, thats HP/10 :)

On the rich side of peak EGT the HP is determined by MAss Air Flow, so in rough terms if you have a fixed pitch prop and get 2200 RPM on a ISA day (15deg C and 1013/29.92) you should see 146 HP and a fuel flow around 14-14.5GPH.
 
Folks, the info I have provided already is proven good data.

As some have shown, the IO390x is about 20GPH, funny enough for 200HP engines at 2700 RPM full rich at ISA, thats HP/10 :)

On the rich side of peak EGT the HP is determined by MAss Air Flow, so in rough terms if you have a fixed pitch prop and get 2200 RPM on a ISA day (15deg C and 1013/29.92) you should see 146 HP and a fuel flow around 14-14.5GPH.

And in "rough terms" 13.5 gph is in the ball park. :)
 
I'm sitting here looking at my G3X data log for the last flight and the fuel flows talked about on this thread seem right on the money for my setup, O-360/FP/Carb/Mags. When my RPM's are down around 2250 or so I see about 13.5-13.8 GPH and as I flattened the climb a little the RPM's went up to 2450 or so and the fuel flow went up to 15.5, so the RPM/Rated Power vs. Fuel flow argument holds. The OAT was 77F and the hottest CHT peaked at 399.

By the way, be careful reducing power during initial climb with a carbed engine. At WOT the mixture is a lot richer than just below WOT. If you pull the throttle back just a little you will do more harm than good.
 
Quote:
Originally Posted by RV10inOz
Folks, the info I have provided already is proven good data.

As some have shown, the IO390x is about 20GPH, funny enough for 200HP engines at 2700 RPM full rich at ISA, thats HP/10

On the rich side of peak EGT the HP is determined by MAss Air Flow, so in rough terms if you have a fixed pitch prop and get 2200 RPM on a ISA day (15deg C and 1013/29.92) you should see 146 HP and a fuel flow around 14-14.5GPH.
And in "rough terms" 13.5 gph is in the ball park.

David, seek further advice if you wish, but I would say that 93% of optimum is not in MY ball park.

YMMV :)

rvsxer

Your data quoted is incomplete to all parameters, however I am confident that your flow is not in the desired range. I fly Jamie Lee's RV7A with a O-360 FP from time to time and his RPM is 2250 static and fuel flow is more like 15GPH. So should yours. At 2450 RPM you would expect closer to 16 - 16.3 GPH

Cheers

DB
 
It should be a little higher than this

Lars,

I agree with you. I think the your value of 0.5 lb/hp-hr is just about right for my IO 360 with the Hartzel blended airfoil prop and Lasar ignition.
Bob Cowan


Best power would be around .48 to .50 but we normally take off full rich so it will be well above .55 pounds per HP per hour.


And since I have a FP prop I agree that you can't compare it to a CS prop on takeoff or climb because if it is pitched for proper cruise it can't reach more than about 2200 rpm, roughly speaking.
 
rvsxer

Your data quoted is incomplete to all parameters, however I am confident that your flow is not in the desired range. I fly Jamie Lee's RV7A with a O-360 FP from time to time and his RPM is 2250 static and fuel flow is more like 15GPH. So should yours. At 2450 RPM you would expect closer to 16 - 16.3 GPH

Cheers

DB

I would agree except for the following: My CHT's are well within my comfort range, even in the steeper, 2250 RPM climb. Any additional fuel will only cool the CHT's further, which is a waste. Futhermore, this engine has 1000 hours SMOH and wear is going to erode power output a bit. This will lower the "hp" value in your equation so my figures look even closer to your "norm".

You've been asked several times for data to back up your thinking and I realize it's pretty involved. However, the guys I listen to closest are not the "data" guys. They are the people who've seen thousands of engines come through their shop and the conditions in which they operated and the shape the core is in at overhaul. We have a flying club here on our airport (KSGS) that has about 30,000 hours on Piper aircraft. Their engines always go to TBO and beyond and look great when torn down. They don't have any of the EM systems we take for granted and they are flown by hundreds of pilots. Sometimes I wonder what we're all fussing about. I am seeing recommendations on these threads but I have yet to see a reply to the affect of "I agree, I had a cylinder that ran XXX degrees CHT and it failed". That's another guy whose input I'll take into account.
 
Mike, the data is around, it started back with the Spirit of Saint Lois, the Doolittle raiders, NACA tests, Wright, Pratt & Whitney, TCM and Lycoming even have it. In most recent times the only continued work in this field has been done by GAMI in Ada OK, and they have proven the old stuff and further more have refined the knowledge on a lot of what was once believed because they have the only engine test stand in the world like it. Nobody else has bothered.

Your CHT's may be fine, thats great, but if your position is taken on that, it is like saying well I have never worn a seat belt and I am still alive. But you have not had a big accident so thats why you are alive, despite the fact that if you do the seat belt might just matter.

Please yourself. But some other data point which is not public is the results at APS classes from the mechanics, those who are not pilots either and have no experince playing with an EMS in flight to see what happens. Initially they score the lowest by far in the initial mini quiz. By the end of the weekend they are often all over it.

I have said before, be wary of advice, go get educated yourself. Then when you have a really good understanding, you will know how to interpret the engine guy, the hangar buddy or even some nut case from Australia on an internet form! :D

If you were to take your fuel flow advice from someone who can stand the test of scruitiny call up John-Paul or Tim at GAMI on Monday and ask them. I think you should not be wasting their valuable work time and you could search this elsewhere yourself, but you could. Call Bill Cunningham at Powermasters, or Don at Airflow....

Or just believe me I am not here trying to sell you fuel.

By the way fuel does not cool.....another OWT. And no I am not going to try to explain this in detail here, DR will run out of bandwidth and the site will be lost forever or something worse :D

hevansrv7a
indeed! :) you are correct. My typical full rich sea level ISA day rate is 0.593 to 0.597 lbs/hr And that is exactly as Mr Lycoming and Mr Precission Airmotive set it up to be. Recently serviced by the best engine shop in Oz at Riverina Airmotive.

I would believe they have it pretty much under control.

You can lead a horse to water, you can't make it enjoy the view!:cool:
 
How rich is rich enough

Hi All,
If you look in the Lycoming IO-360M1A 180hp 8.5:1CR manual (pg20), it says that at full throttle and 2700rpm at sea level, you should expect an 87lb/hr fuel flow, or 14gph. My density altitude is a little higher than sea level (800ft) and I am seeing 176hp on takeoff according to their performance charts, and if leaned to best power I should be seeing 13.9gph. With a full rich mixture, 28.4" MP and 2700rpm, I am observing 15.1gph via my FT-60 (mounted between the fuel servo and fuel spider) and I guess my question is, how rich is rich enough to provide adequate detonation margin? If 14gph for a Lycoming IO-360 at 100% power wasn't safe, why would Lycoming publish this in a chart? I see people talking up to 18gph on takeoff for an IO-360, but this seems like you would be squirting fuel out the back end.
The reason I am asking this is because I am seeing CHT up to 440degF just after takeoff, although a closer look at my baffle rub points on the cowl today indicate that this may be part of the problem, and not so much my low fuel flows compared to others.
Tom.

2zxw9vm.jpg
 
I run about 17 gph on takeoff with the same engine, at 2700' field altitude, and you're right, it's slobbering rich but it runs cool. At about 500' off the ground I pull the RPM back to 2500, leave the throttle all in, and start leaning it for the climb. I keep it just rich enough to hold CHT's at 400 or less and life is good, that's about 14.5 gph or so initially and dropping as I go up of course, and I go LOP once I level from the climb. I think if you run another 1-1.5 gph on takeoff you'll see your CHT be much lower.
 
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New O-360A1F6, Hartzell C/S prop with the old F7666 blades. Field elevation of 387'. Depending on OAT I see flows from 16.5 to nearly 18GPH on takeoff with the prop spinning up to 2690RPM. CHT's seem happily below 400F on a reasonably aggressive climb-out. Push the nose down for another 10kts of airspeed and I can see 10F drop in CHT.

Per the Lycoming power chart, these fuel flows are pretty much spot-on, or at least as close as one is likely to get when reading that squinty chart!
 
Listening to folks insist on fat mixtures for cooling may be Earth's closest equivalent to Vogon poetry.
 
I've contacted Avstar directly to get their recommended values. Will fill you in once I have the details.

Tom.
 
Listening to folks insist on fat mixtures for cooling may be Earth's closest equivalent to Vogon poetry.

I?m with you on that one Dan - especially for those of us living at high density altitudes! Don?t Panic......
 
After speaking to Avstar they directed me to the test report that came with the engine. Sure enough, my engine is on the low side of the calibration limits. The highest fuel flow test was performed with an airflow of 1004 pph. The 180hp rated power test was at 1116.59 pph airflow. Therefore the rated power test was 1.112 times the AF-1000 test. Multiplying the fuel flow in the AF-1000 test by 1.112 gives 93.75 pph, which equates to 15.6gph, which is still slightly above what I was observing during the takeoff run via my FT-60 fuel flow meter.
Going back to the chart and applying the same 1.112 ratio to the lower and upper fuel flow limits, this gives a lower limit of 92.6pph or 15.4gph, and an upper limit of 102.63pph or 17.6gph at 180hp rated power for the IO-360M1B. Thus at an FT-60 reading of 15.1gph, it appears I am below the lower limit. Keeping in mind that I am at a 500ft elevation and have calculated that my full throttle maximum power is 176hp, applying a ratio of 176/180=0.978, this would make the lower limit of the fuel flow 15.06gph, pretty much smack on what I was reading from the FT-60. I have not calibrated the FT-60, so who knows, even that may be incorrect. All we do know for sure is that during the AF-1000 test, the engine was 1pph richer than the lean limit. I'm still going to work with Avstar to see how possible it is to adjust things so they are closer to the midrange, however in the interim I have continued work on my baffles to try and ensure every scrap of air is being put to use.

Tom.

jkudrs.jpg
 
Richer than 3 feet in a cow's back end

Listening to folks insist on fat mixtures for cooling may be Earth's closest equivalent to Vogon poetry.

As Dan said a few years ago "There are better ways to cool an engine than mixtures that are richer than 3 feet into a cows back end."

What Dan was trying to draw attention to with some good humour is that if a Lycoming in an RV is cowled and baffled and ducted properly CHT's will NOT reach 400F in in a FULL power climb in air that is over 100F.

See the full story here:
showthread.php


Or else go to the traditional engine section and read the sticky "Engine Cooling"
seen here: http://www.vansairforce.com/community/showthread.php?t=163788&referrerid=13191
http://www.vansairforce.com/community/showthread.php?t=163788&referrerid=13191


Michael Robinson has done a lot of good work with the pay off as quoted below:

"OK, its now six months later and I had a chance to really check this mod out today. I left Phoenix at noon with the temp passing through 105. On my normal stair step climb to the west staying clear of the class B sections, the CHT often runs right past 400 on a few cylinders within minutes, but not today. I maintained WOT and best power EGT for the entire 15 minutes it took to get out from under the PHX airspace and I never saw anything hotter than 385. Once to 8500 feet and LOP, the temps settled to 325 -350.

I know that 1 data point does not make a trend, but my first "hot" flight of the season sure went well.

Soon, I will try a climb at VY all the way to altitude and see how it behaves.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
 
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Hi All,

I received the following response from Avstar last night:
"I reviewed your data with my engineer and we both agreed that enrichment of your top end fuel flow for lower CHT's would be beneficial for your engine life."

In a nutshell, I'm removing my servo and sending it back to them for a little enrichening. I'm not looking at this thing draining the middle east of liquified dinosaurs everytime I push the throttle to the firewall, but I think something closer to their midrange of the recommended flow values would be more ideal, especially given that I'm seeing up to 440degF CHT's on cool springtime days even with shallow climbs. I've tweaked the baffle seals a little, but I can't see how I can improve them any further.
Tom.
 
I received the following response from Avstar last night:
"I reviewed your data with my engineer and we both agreed that enrichment of your top end fuel flow for lower CHT's would be beneficial for your engine life."

Did you discuss full throttle, full rich EGT in relation to peak EGT?
 
No Dan, we haven't discussed EGT. The EGT at takeoff was around the 1350degF mark, 1250degF in cruise and the highest recorded was 1450 during the engine runup process. I didn't pull the mixture back at all during the flight. Given that the fuel flow was 11.1GPH at 24 square, which is about what I was going to lean it to anyway, and given my higher than expected CHT both in the shallow climb (420-440degF) and cruise (approx 365-385degF) I thought I should leave the mixture full rich. I'm open to whatever information you have to help resolve the issue.
Tom.
 
No Dan, we haven't discussed EGT. The EGT at takeoff was around the 1350degF mark, 1250degF in cruise and the highest recorded was 1450 during the engine runup process.

Tom, do yourself a favor and forget about fuel flow. You're trying to determine mixture at full throttle. Without a mixture check, both you and the Avstar guy are guessing.

More later, but just from the above, your servo is probably set correctly.
 
Thanks Dan. Avstar are pretty keen to get this servo back, however I won't take it off until I hear back from you. Thinking about the whole detonation and pre-ignition deal, which is my ultimate concern, if my understanding is correct, with a mixture richer than stoichiometric, the excess fuel is simply providing evaporative cooling, so there should be no reason why this task can't be provided by cooling air over the outside of the cylinder. It leads me to also thinking that so long as I am running the recommended octane values and staying below the 500degF published CHT limit, that the detonation or pre-ignition should be a non issue. I did build a row of nutplates into the lower firewall flange so I could create a Dave Anders inspired outlet ramp if I ever needed it. Sounds like I may need to execute this concept. 12 year screwing wind turbines into the ground, and a lifetime of operation basically only electric or diesel equipment means that my spark ignition knowledge isn't where it needs to be.
Tom
 
Thinking about the whole detonation and pre-ignition deal, which is my ultimate concern, if my understanding is correct, with a mixture richer than stoichiometric, the excess fuel is simply providing evaporative cooling, so there should be no reason why this task can't be provided by cooling air over the outside of the cylinder.

Evaporation makes only a very small contribution to cooling. An excessively rich mixture delays peak cylinder pressure and lowers combustion temperature. The overall result is a power reduction.

The other big factor is mass flow, as noted way back in the pre-WWII NACA papers. The previous paragraph can be considered a "per cycle" reality, while mass flow translates directly to RPM, i.e the number of those heat generating cycles in a given time. One of the easiest ways to drop CHT is to simply pull the prop back a little.

And yes, heat transfer to the air is the best of all.

It leads me to also thinking that so long as I am running the recommended octane values and staying below the 500degF published CHT limit, that the detonation or pre-ignition should be a non issue.

Add OAT, ignition timing, compression ratio, RPM, and manifold pressure to the list. High intake air temp, advanced timing, and high CR are pro-detonation. Reduced RPM combined with high MP is pro-detonation.

Given enough octane, a stock engine, stock timing, and basic adherence to the power chart, yes, you're safe. It's why the manufacturer did a detonation survey.

Gather basic EGT data. Climb to 3500 or so, and allow CHT to settle to a cruise value, which I assume to be well under 400. Now lean to a stable peak EGT on the cylinder of your choice. Record the value. Push mixture to full rich, again allow EGT to settle, and record the value. Report back.
 
Ok, the rest of the story...

This is a classic Lycoming document with a few added notes at the bottom. Note the temperature scale at the upper left. It is certainly possible to lower CHT by adding fuel. The question is "Where are you starting from?" If it's to the left of the best power gray stripe when full rich, it's way too lean. If it's already to the right of the stripe, more rich just means you can't make rated power.

Leaning%20Relationships.jpg


Gas temperatures. F/Fc is variation from stoich, aka "equivalence ratio". Note how gas temperature drives CHT.

Mean%20Gas%20Temp.jpg


And here's the basis behind the test, previous post.

270028AF.JPG


245024AF.JPG


Note that although the absolute numbers change (peak 1600 vs 1540, for example), the delta between peak EGT and the EGT for any given FA ratio does not.

Fuel flow will not tell you FA ratio:

270028.JPG


245024.JPG
 
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Gather basic EGT data. Climb to 3500 or so, and allow CHT to settle to a cruise value, which I assume to be well under 400. Now lean to a stable peak EGT on the cylinder of your choice. Record the value. Push mixture to full rich, again allow EGT to settle, and record the value. Report back.

Thanks Dan. If the weather behaves I should be able to gather this data tomorrow. I was speaking with another builder here that suffered the same issue. Lower than "expected" flow on takeoff and 420+ CHT in the climb. He too thought he would have to get the servo recalibrated, but after 5 hours of operation, he noticed a significant drop in the CHT, to the point it no longer passes 400degF in climb, so he never adjusted the servo and is now happy with its operation.
I'll report back shortly with data.
Cheers,
Tom.
 
Thanks Dan. If the weather behaves I should be able to gather this data tomorrow. I was speaking with another builder here that suffered the same issue. Lower than "expected" flow on takeoff and 420+ CHT in the climb. He too thought he would have to get the servo recalibrated, but after 5 hours of operation, he noticed a significant drop in the CHT, to the point it no longer passes 400degF in climb, so he never adjusted the servo and is now happy with its operation.
I'll report back shortly with data.
Cheers,
Tom.

BTW Tom, note the "detonation onset" black tic marks on those plots. They are located on the rich side of peak, between best power and peak EGT.

Most engines make maximum power on mixture leaned to just a little short of detonation. You can see it on the 2700/28" plot.

On the 2450/24" plot here, detonation onset move closer to peak. The commonly quoted figure for high risk is 50 ROP, pretty much the case with this IO-540 test engine.

Look scary? Remember, (1) this test engine (IO540K) is considered to be among the most detonation prone in the Lycoming fleet, and (2) the dyno operator is purposely running the subject cylinder at max CHT (475F), 100+F inlet air temp, max oil temp, etc. The point to remember is that (hopefully) nobody is dumb enough to run it like that when airborne.

Still, you have a hot cylinder problem, and you're worried about detonation. To do the mixture test, a fella might not want to slowly lean through the pro-detonation range to find peak. I think the risk is very low given stock compression and ignition timing, but what about the guy with high CR pistons or jacked up timing? How to find peak and feel comfortable while doing it?

No problem. After settling in at the test altitude, pull the mixture until it is obviously way past peak. It should run fine there, maybe a little rough if nozzle balance ("GAMI spread") hasn't been tweaked on a new airplane. There is little chance of detonation on the lean side of peak EGT at 2400/24". After temperatures settle, find peak from the lean side by enriching very slowly. You can sneak up on peak without risk.

245024AF%20w%20notes.jpg
 
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Data

Righto Dan, here's the data.

Measurements were taken at 2400RPM, 24" MP and 3500 AMSL (2825' density alt., OAT 36degF)

I first ran some cruise runs at the above engine settings, resulting in 162KTAS at 11.1gph. CHT's were in the 360degF range. EGT's ranged from 1245 to 1280degF.

I did the big mixture pull, then started slowly enrichening to approach the peak EGT. Cylinder 1,2 and 3 peaked at almost the same time at 1460, 1430 and 1440degF respectively. I continued enrichening and cylinder 4 peaked about 10 seconds later and 0.1GPH more at 1450degF. In that time period, the other cylinders had dropped 5degF.
The difference between the full rich EGT and the peak EGT for cylinders 1, 2, 3 and 4 were 180, 180, 195 and 180degF respectively. The fuel flow at peak EGT was 8.8gph, giving a speed of 163KTAS.
The takeoff CHT's were much better this time. There were a number of contributions to this including the few "waves" that I rectified in the baffles, a reduced climb angle, being faster to set climb RPM after takeoff, and the 6degF reduction in ambient temperature compared to my first session. I only once reached 421degF, and if kept my finger on the pulse, I could keep the CHT below 400 on climbout.
I'm getting the feeling that things are moving in the right direction and I won't need to pull that servo afterall.
Cheers,
Tom.
 
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The difference between the full rich EGT and the peak EGT for cylinders 1, 2, 3 and 4 were 180, 180, 195 and 180degF respectively.

Perfect.

The relationship between delivered mixture and delta-to-peak is entirely reliable. You're right around 0.085 F/A, or 11.75 to 1 air-fuel, richer than max power. You can plot it yourself on the charts posted previously:

Leaning%20Relationships%2011.63%20AF.jpg


245024AF%2011.75%20AF.jpg


Or there are charts like this one, an oldie from Lycoming:

EGT%20vs%20FA%20Ratio.jpg


Spend your effort working on baffling and sealing.
 
Thanks Dan for pulling together all this info for me. So it's Ops normal by the sound of things.
This may be a little thread drift, but I'm also presuming that by a CHT spread this tight (between 0.1 and 0.2GPH, as the resolution is limited to 0.1GPH increments), there's no point in adjusting injector restrictor sizes? Keep in mind that this is at partial throttle settings (2800' density altitude 24" square). The weather looks good to be back in the air for some testing on Wednesday where I hope to better validate the data and perform some sustained climbs to 8,000' where I can gather some wide open throttle data.
Tom.

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This may be a little thread drift, but I'm also presuming that by a CHT spread this tight (between 0.1 and 0.2GPH, as the resolution is limited to 0.1GPH increments), there's no point in adjusting injector restrictor sizes?

That's a nice tight spread. Do the same check at 8000 or where ever you like to cruise, and if the spread remains that tight, leave the restrictors alone.

Note that all mixture checks should be done with verrrrry slow knob movement, or in 0.1 GPH increments with pauses to allow EGTs to stabilize before moving to the next increment.

Do a liftoff at full throttle, full rich, and note EGTs immediately after liftoff. Are they the same as the previously recorded full rich values (1280, 1250, 1245, 1270), or slightly less?
 
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That's a nice tight spread. Do the same check at 8000 or where ever you like to cruise, and if the spread remains that tight, leave the restrictors alone.

Note that all mixture checks should be done with verrrrry slow knob movement, or in 0.1 GPH increments with pauses to allow EGTs to stabilize before moving to the next increment.

Do a liftoff at full throttle, full rich, and note EGTs immediately after liftoff. Are they the same as the previously recorded full rich values (1280, 1250, 1245, 1270), or slightly less?

Slightly more. The following data sample is pretty consistent with my other takeoffs and was recorded with an OAT of 55degF at 400ft density altitude. The first row of the data is immediately after liftoff, with a 1325-1350degF range, then it continues to climb for the next 20 seconds or so to 1335-1390degF, even after I have pulled the power back. It peaks at this point, then starts dropping as I continue to climb and steadies out in the cruise at that 1250degF average. Looking at the fuel flow chart below however, the full power peak power fuel consumption should be 14.5GPH (87PPH) but I am running at 15.1-15.2GPH, so I have a .6 to .7GPH margin, which should put me on the rich of the danger zone. I'm guessing the only way to validate this is to do another lean test at 2700RPM and full throttle down low?
Tom.
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Slightly more.

Sorry, brain fart, meant to ask slightly more, not less; returning to the examples (post 41), again note the absolute EGT values change, but the relationship between delta-from-peak and mixture remains consistent. Put another way, the whole scale moves upward with higher power production.

The following data sample is pretty consistent with my other takeoffs and was recorded with an OAT of 55degF at 400ft density altitude. The first row of the data is immediately after liftoff, with a 1325-1350degF range, then it continues to climb for the next 20 seconds or so to 1335-1390degF, even after I have pulled the power back. It peaks at this point, then starts dropping as I continue to climb and steadies out in the cruise at that 1250degF average.

The rise for WOT in the posted examples was about 60F. Your initial rise is more like 80, which is fine, and rises a bit more given a bit more MP. Fuel flow mirrors MP reduction in the late entries, so perhaps you unloaded the prop a little with a push to higher airspeed?

BTW, what are the time intervals here?

Looking at the fuel flow chart below however, the full power peak power fuel consumption should be 14.5GPH (87PPH) but I am running at 15.1-15.2GPH, so I have a .6 to .7GPH margin, which should put me on the rich of the danger zone. I'm guessing the only way to validate this is to do another lean test at 2700RPM and full throttle down low?

Not recommended. I might do such a test, but I can maintain much lower CHT at full power. Bad idea given high CHT, with low value given other indications. Work on sealing and baffling.

I should note that your reported EGT delta suggests you're at the lean end of the certification range, which Don Rivera has previously reported as equating to 185 ~ 230 ROP. The fuel flow for certification is based on the worst case operating conditions of the detonation survey...plenty of margin with everything very hot. That's not quite the same as a practical range where performance is of more interest. Sending the servo to Avstar for enriching remains an option, and like all else in EAB, your call.

Again, I'd make a data-driven decision. Go back and look at the Lycoming leaning relationships chart. It says a change from 180 ROP to 230 ROP would move CHT about 5C, or 9F....not much in return for reduced power and increased fuel cost. Cooling air is free and clean.

You pick. The key here is that you are no longer guessing.
 
Thanks Dan. They are 1 second data samples pulled out of the G3X.
I did some sustained climb testing today. If I hold it at 130ktas in the climb passing through 5000' I'm getting CHT's in the 378-362degF range and still managing an 1,100fpm climb rate, which I'm pretty happy with (2 POB and near full fuel). Admittedly this was with an OAT of 34degF, but in the defense of the engine, it's still running on break-in oil and only has 4hrs on it including the hour in the test cell. If I bring the climb speed back to 120ktas, I can do a sustained climb at less than 400degF.
I took it up to 8300ft and ran some leaning tests again. WOT 21.9"MP 2300rpm, 8500' pressure altitude (7700' density altitude due to the -8degC OAT) I did the big mixture pull then richened to peak EGT and was seeing 7.9GPH at 164ktas, and CHT in the 340-350degF range with EGT's in the 1365-1390degF range. The power readout from the G3X said 65%, but I've been told to take this with a grain of salt. Either way, if I interpolate between the published 55% and 75%, this puts me smack on the Van's speed numbers, which I'm pretty happy with, just with a 0.4GPH less fuel flow based on the Lycoming charts, which I suspect is due to the PMAG's variable timing doing their thing. Looking at the data, as I was enriching the mixture, I see a sweet point at around 20degF LOP, where there is no sacrifice in speed, but a further saving of around 0.3GPH.
In light of everything we have covered in the past few days, I'm going to leave things as they are at least until I've got another 10 hours or so on the engine. I've still got that card up my sleeve of putting an outlet ramp on the firewall flange to clean up the exit air if I need it, but elsewhere on the baffles I'm struggling to improve things further. I took it to a maintenance shop here today on my test trip, and had the boss look at the baffles and he couldn't see how I could improve them further and told me to just keep breaking in the engine before I did anything crazy. That said, my oil temps are running on the cool side of normal (160-175degF) so I'm thinking about taping off some of the cooler to force more air through the cylinder head fins instead.
Good times. I think I've learnt more about operating air cooled engines in the past week than I have in the previous 20 years. Thanks again for your help.
Tom.
 
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