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Max Fuel Flow on Takoff/Climb

Aiki_Aviator

Well Known Member
Hi All,

I was wondering what people are getting out of their IO-540 D series engines for Max Fuel Flow on take-off.

I just want to confirm that mine is running in line with others on the forums.

Thanks guys.
 
Depends on altitude and temp but with the AirFlow performance system I see arounf 25 gph at sea level +1K'.

Vic
 
25.5 GPH at sea level. (260 HP )
This is a very important number and ensures that your fuel system is
properly set up for maximum performance on take off and in climb.
Some of that fuel is required for cooling to keep the CHTs in an acceptable temperature range.
 
Documents verifying this number

So looks like consensus is 25.5. Can anyone point to the documentation having this as the Fuel flow for this engine?

All I can validate is the Lycoming Operations Manual setting 21.5 for the D series.

Thanks.
 
Aiki: Many of these engines are experimental and don't fit the manual. Mine is an IO540-K1G5 (heavy crank and case) with lightweight ECi parallel valve cylinders, running an AFP 200. With 9.5 to 1 pistons, it pulls 27 to 28 gph on take off. If I leave it at full throttle, I can climb all the way to 10,000' + running plenty cool all the way.

When I spoke with Don Rivera of AFP about it, he said that was not too much fuel at all. I'm cooling with fuel during the climb at full power, of course, but it climbs like crazy and works like a charm. I end up at (say) 10,500' in a big hurry, still burning about 17 gph, leave the throttle wide open and just manage the engine with the mixture. Pull it back to around 2,200 rpm and at or about 13 gph and your doing 190 ktas or just under 220 mph over the ground in still air.

Good luck...


Lee...
 
For takeoff from sea level you should see about .9-1.0GPH per 10HP. If your engine is a stock 260HP -540, then you should see in the 24-26GPH range. As others have said, this keeps the EGT's low to help keep the CHT's low. I like to see EGT's well under 1300 for takeoff. After I pull back to 25 squared for climb I lean to low 1300's.
 
My rv10 have a fuel flow 25 gallons At take off on a 2700 ft AirPort. Anyone At this altitude to confirm?
 
The excess fuel is not cooling anything. It is merely lowering combustion temperature, and delaying peak pressure, much like retarded timing.

Lycoming data lists what they consider to be the minimum fuel flow for rated power, which includes a detonation margin. Power output is fairly flat in the region richer than optimum, so it is possible to run richer without huge power loss. Setting up the fuel control to be richer than the minimum required for rated power adds additional detonation margin. Recall that best power mixture is about 100F ROP, and we like to see the fuel control set up for 200 ROP at full rich, maybe 250. Some like it even richer, but that's just an expensive way to make less power.

BSFC (pounds of fuel per HP per hour) is a fine guide to fuel flow, IF you know power output with some accuracy. For example, my IO-390 manual says minimum fuel flow is 105 lbs at 210 HP, for a BSFC of 0.50. A 260 HP engine at 0.50 is 130 lbs per hour, or 130/6 = 21.66 GPH. The consensus 25.5 would be a BSFC of 0.588.

Here's a useful chart from the FAA dyno, an IO-540-K. Lots of interesting things to observe, but in the context of this discussion, note the BSFC and fuel flow at max power mixture; 245 HP at 112 lbs per hour, for a BSFC of 0.46, or 18.6 GPH.

 
I have the IO-540 as well. Do not recall the exact number, but it seems like its around 22gph on take off. 500MSL airport in south texas. KCOT
 
Ok, my servo in the bench has 132 pph in 26". But in my airplane it has 25 gal at 26" manifold and full power. For that I send my gauge for a check, but it was ok.
My engine seens to be rich, at 2000 rpm leaning misture knob I have a rise of 100 rpm. Checking mags with this leaned misture at 2000 rpm, drop is 120 - 110 rpm.
Here the problem, at 2000 rpm and misture full rich it drops 190-200 rpm....
Mags with 500hs inspection, new sparkplugs (rem40e) and cables.
That's why I m asking about gallons; I m thinking my engine is very rich and this is the cause of excess of drop in my mags.

Opinions ?
 
The excess fuel is not cooling anything. It is merely lowering combustion temperature, and delaying peak pressure, much like retarded timing.

Lycoming data lists what they consider to be the minimum fuel flow for rated power, which includes a detonation margin. Power output is fairly flat in the region richer than optimum, so it is possible to run richer without huge power loss. Setting up the fuel control to be richer than the minimum required for rated power adds additional detonation margin. Recall that best power mixture is about 100F ROP, and we like to see the fuel control set up for 200 ROP at full rich, maybe 250. Some like it even richer, but that's just an expensive way to make less power.

BSFC (pounds of fuel per HP per hour) is a fine guide to fuel flow, IF you know power output with some accuracy. For example, my IO-390 manual says minimum fuel flow is 105 lbs at 210 HP, for a BSFC of 0.50. A 260 HP engine at 0.50 is 130 lbs per hour, or 130/6 = 21.66 GPH. The consensus 25.5 would be a BSFC of 0.588.

Here's a useful chart from the FAA dyno, an IO-540-K. Lots of interesting things to observe, but in the context of this discussion, note the BSFC and fuel flow at max power mixture; 245 HP at 112 lbs per hour, for a BSFC of 0.46, or 18.6 GPH.



Dan, Interesting stuff here! I would be curious to see and compare the same sweep at a reduced ignition timing.

Caleb
 
Ok, my servo in the bench has 132 pph (22 gph) in 26". But in my airplane it has 25 gal at 26" manifold and full power. For that I send my gauge for a check, but it was ok.

Offhand, I can think of two possible explanations.

Although the flow sender (red cube or Floscan) may be perfectly accurate, installation location and operating condition can increase indicated flow. For example, does the 25 gph indication vary with electric pump on or off?

Uneven or turbulent airflow into the fuel control can drive it rich or lean. On the flow bench it is checked with a standard bellmouth fastened to the inlet. All kinds of inlets are seen on airplanes.

My engine seens to be rich, at 2000 rpm leaning mixture knob I have a rise of 100 rpm.

That tells you that full rich is somewhat richer than best power mixture. You can estimate how much richer by comparing full rich EGT to peak EGT. Go to an altitude that offers perhaps 22" at full throttle (low MP provides detonation margin). Allow temperatures to stabilize at full rich, then record all EGTs. Now lean slowly to find peak EGT for each cylinder. The difference should be 200 to 250F.

Here's an older Lycoming chart, courtesy of Airflow Performance. Peak EGT is 0.065 fuel/air, or 15.38 air/fuel. 200 ROP is 0.086 fuel/air, or 11.63 air/fuel.




Go to the previous FAA chart. Plot peak EGT and you'll find it equates to an air/fuel ratio of about 15.2. 200 ROP is about 11.4. Both values agree closely (within 0.2 air/fuel) with the old Lycoming chart. Best power is about 125 ROP, and plots in the classic 12.5/1 air/fuel ballpark.


 
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This is all very interesting data and for sure it is as it should be in the real world.

The issue is how does Joe Pilot have this information on hand every day especially for take off considering the vagaries of temperature, pressure altitude and humidity.

I tried using a A/F ratio meter in my Lycomjing (Superior clone). It tells a good story of what is going on at the moment. Problem is it did not work because sensor gets clogged up with lead. It worked great with Subby and lead free fuel.

Fuel flow is important anytime. But is it practical to be messing with mixture during take off roll to set an optimal flow? Not without a second person doing it like in old days with a flight engineer.

So we do the best we can with all this theoretical information - push the throttle up, go fly and don't lean it too much too early. :)
 
Hi Dave. Sorry about the tardy reply.

The issue is how does Joe Pilot have this information on hand every day especially for take off considering the vagaries of temperature, pressure altitude and humidity.

There's really not much to remember. First, establish that you have 200~250F between peak EGT and full rich EGT, per the previous post. I said 22" or so, but with a stock Lycoming, doing the check at any setting 75% or less should be fine.

Now note full rich EGT at full throttle on your next takeoff roll. Just one EGT will do; no need to memorize all four. This value becomes your target EGT, and it's the only thing you need to remember, just like you remember a normal oil pressure. Your home airport is close enough to sea level that the slight bit of enrichment due to altitude won't make any difference.

Ok, on some future date you're departing an airport at a higher altitude. At full throttle and full rich, the displayed EGT for the target cylinder will be lower than usual. At whatever point you feel comfortable (on the runup pad, on the roll, or sometime after establishing climb), just pull mixture until the subject cylinder reaches your memorized target EGT. You're now pretty close to the fuel/air ratio you previously established as a bit richer than necessary, but perfectly safe...200~250 rich of peak. Exact isn't necessary; best power is 100~150 ROP, and full throttle detonation is leaner yet. You're inside a big buffer zone, with power only a little less than optimum.

The target EGT method also works after a a power reduction. For example, you might pull the prop to 2500 when MP falls off to 25" or less, as cooling demand is directly related to mass flow (i.e. RPM). Displayed EGT will immediately drop; just pull mixture to return to your memorized target EGT, and continue to do so throughout the climb.

...we do the best we can with all this theoretical information - push the throttle up, go fly and don't lean it too much too early. :)

Some like to know why, not just how. Others want step-by-step instructions, with why being a matter of faith in their adviser. Neither is wrong, but in general, the pilots operating on technical background are probably more comfortable.
 
Reviving Old Thread

I flew with a friend today to help troubleshoot a couple of issues with their plane.

They are experiencing high CHT's, especially on the rear two cylinders. Not terribly unusual on a 10 and they are working on improving the baffles and baffle seals. They have air conditioning and it's tough to seal up the area around the belt and compressor to avoid air spillage into the lower cowl.

The one thing that jumped out on me was the high EGT's on takeoff and during the climb. I know that probe placement can make a difference in indicated EGT, but I was seeing 1400's on takeoff. Attempts at leaning once leveled off, the EGT's were in the 1500 range and the engine was not smooth. It was also surging a bit on climbout - not enough to see anything on the engine instruments, but enough to feel it in your seat.

As a reference point, my RV-10 has EGT's in the mid-to-high 1100's on takeoff and initial climb. I have SDS, they have an Airflow servo. They indicated their red cube was calibrated, but I don't want to rely on that yet for fuel flow numbers.

My gut tells me they are running too lean at full power and this is contributing to the high CHT's.

What is the opinion of the experts out there?
 
My gut tells me they are running too lean at full power and this is contributing to the high CHT's.

What is the opinion of the experts out there?
It sounds like he is running lean. Actual EGT numbers, according to current wisdom, doesn’t mean much, but it all RV-10’s I have gotten flying, the EGT’s at takeoff were around the low to mid 1200’s. Fuel flow should be about 23-24 at takeoff, but it often reads high when running the electric fuel pump. We have had very good experience with the accuracy of the red cube, which should be set as a k-factor of 68,000 to start with, which rarely needs to be adjusted. There is an idle mixture adjustment on the fuel servo that also does some adjusting of higher power mixture. I would Richey that up and see if it makes a difference.
 
I flew with a friend today to help troubleshoot a couple of issues with their plane.

They are experiencing high CHT's, especially on the rear two cylinders. Not terribly unusual on a 10 and they are working on improving the baffles and baffle seals. They have air conditioning and it's tough to seal up the area around the belt and compressor to avoid air spillage into the lower cowl.

The one thing that jumped out on me was the high EGT's on takeoff and during the climb. I know that probe placement can make a difference in indicated EGT, but I was seeing 1400's on takeoff. Attempts at leaning once leveled off, the EGT's were in the 1500 range and the engine was not smooth. It was also surging a bit on climbout - not enough to see anything on the engine instruments, but enough to feel it in your seat.

As a reference point, my RV-10 has EGT's in the mid-to-high 1100's on takeoff and initial climb. I have SDS, they have an Airflow servo. They indicated their red cube was calibrated, but I don't want to rely on that yet for fuel flow numbers.

My gut tells me they are running too lean at full power and this is contributing to the high CHT's.

What is the opinion of the experts out there?

Those EGT's seems high but doesn't mean much without knowing the PEAK EGT for that setup. Pretty easy to figure out what that is. What was the fuel flow? Lycoming says best power at 2700/29" is 21.5 GPH for the 540 D series.. Most desire to run richer than that for detonation margin. I and amny experts recommend 150-200* Rich of peak EGT for take off. Some like a lot richer to make up for cooling inefficiency (highly variable across the fleet). I tend to lean towards best power during the climb, but some consider that crazy. I also sometimes climb LOP when not in a hurry or stretching range.

Surging could be from being lean, but also could be other things, like a gov issue. High EGTs can also come from one ignition not firing and that would also create light roughness, but usually drops CHTs. In flight mag check in order.
 
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