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  #1  
Old 02-07-2021, 11:38 AM
bsvantho bsvantho is offline
 
Join Date: Oct 2012
Location: Rochester Hills, MI
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Default IO-540 Takeoff EGT is around 100F ROP

I have seen that full-rich full power takeoff for Lycoming engines has the EGT typically quoted around 200-250F ROP.

I typically see only about 100-120F difference from the takeoff EGT to peak EGT. I suspect I am running a bit lean at takeoff, though the fuel flow value does not seem to be unusually low. CHTs will jump slightly above 400F if I maintain a full power climb without rolling back MP a bit. Engine has about 125hours. I am trying to determine if an adjustment should be made.

I have a Thunderbolt IO-540 with AFP FM-150 and 1 Surefly + 1 MAG ignition.
Injectors are balanced - spread is usually .3 GPH at peak EGT.
At takeoff (full-rich) Fuel flow is 22.8GPH, RPM 2690, MAP 28.2", OAT 25C, field elevation 980ft.
EGTs are 1315-1365F - peak EGT is around 1450-1460F.

Take off at time 14:25, peak EGT at 22:44 -
Actual Engine Data
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  #2  
Old 02-07-2021, 12:55 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Do you have .025 or .028 injector nozzles? I have the former and see similar fuel flows and EGTs at those ambient temps. With the .025 nozzles, you will see a bit lower flow rates than other who have the stock .028 nozzles. AFP recommends the 025 nozzles for the 540, so suspect that is what you have. The high CHTs can come from many factors, not the least of which is advance levels on your EI.

Best power is around 80-100 ROP and anything more is just wasting fuel, assuming you can keep the CHTs in line and keep the advance curve at 25* or lower during T/O. IMHO 250 ROP is too fat. Wastes gas and reduces power output.

Larry
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Last edited by lr172 : 02-07-2021 at 01:04 PM.
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  #3  
Old 02-07-2021, 01:15 PM
bsvantho bsvantho is offline
 
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Location: Rochester Hills, MI
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Quote:
Originally Posted by lr172 View Post
Do you have .025 or .028 injector nozzles? I have the former and see similar fuel flows and EGTs at those ambient temps. With the .025 nozzles, you will see a bit lower flow rates than other who have the stock .028 nozzles. The high CHTs can come from many factors, not the least of which is advance levels on your EI.

Best power is around 80-100 ROP and anything more is just wasting fuel, assuming you can keep the CHTs in line and keep the advance curve at 25* or lower during T/O. IMHO 250 ROP is too fat. Wastes gas and reduces power output.

Larry
My nozzles vary between .0245 and .255, so yes that makes sense my flow would be a bit lower.

I think I answered my own question though. The reason my spread between full rich EGT and peak EGT is small is because I am comparing takeoff power setting full rich EGT with cruise power setting peak EGT, which is not valid. I reviewed the AFP manual and they say to pick a power setting like 2400/24" and check the EGT at full rich and peak without changing the power setting. I suspect I will see closer to 200F spread with that test.

Yes the advance is the engine fixed timing of 25 BTDC for T/O on the Surefly. That is a good point though. The peak EGT at cruise power will be somewhat lower since that is where the ignition advance should be greater than 25.
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  #4  
Old 02-07-2021, 01:30 PM
BobTurner BobTurner is online now
 
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Quote:
Originally Posted by lr172 View Post

Best power is around 80-100 ROP and anything more is just wasting fuel,
Id suggest caution with a blanket statement like that. Many aircraft engines are set up to run overly rich at 100% power, to provide detonation margin.
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  #5  
Old 02-07-2021, 02:02 PM
sailvi767 sailvi767 is offline
 
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Quote:
Originally Posted by bsvantho View Post
My nozzles vary between .0245 and .255, so yes that makes sense my flow would be a bit lower.

I think I answered my own question though. The reason my spread between full rich EGT and peak EGT is small is because I am comparing takeoff power setting full rich EGT with cruise power setting peak EGT, which is not valid. I reviewed the AFP manual and they say to pick a power setting like 2400/24" and check the EGT at full rich and peak without changing the power setting. I suspect I will see closer to 200F spread with that test.

Yes the advance is the engine fixed timing of 25 BTDC for T/O on the Surefly. That is a good point though. The peak EGT at cruise power will be somewhat lower since that is where the ignition advance should be greater than 25.
I also have the Surefly with a IO540. I think I have the opposite problem and am running a bit rich. I see 28 GPH FF with a airport elevation of 840 MSL. I am running 9.5 to one pistons and a CAI. Keep in mind that pulling power may not help with cooling and with the Surefly in advance mode might hurt. The Surefly will only advance the timing once the manifold pressure is below 25 inches. If you maintain full power that will happen around 6000 feet.
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  #6  
Old 02-07-2021, 10:18 PM
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akschu akschu is offline
 
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Im not an expert, but I do have some thoughts about what I would try.

By certification an aircraft engine cannot be harmed with the red knob when below 65% power. So Id figure out what fuel flow makes 65% power in the lycombing docs then climb to whatever altitude restricts power to 65% then lean to peak at WOT and see if the fuel flows line up. If they do I would note the EGT as the max EGT for my airplane.

If the full rich/full throttle EGT was 150* or more colder than that number you get at 65% then Id be happy with that. You are basically 150 cooler than max which gives some detonation margin.

Id also call Don to confirm my plan....

Schu
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  #7  
Old 02-07-2021, 10:51 PM
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RV10inOz RV10inOz is offline
 
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Brendon,

At your elevation and with the MAP & RPM you quoted your takeoff fuel flow should be 24USG/Hr, or not far from it.

So first of all, get your FCU sent back and flowed correctly.

To add credence to this, you EGT's are backing up this. Given you have an EI which will always have more advance than a magneto, this will create a lower EGT, and normal EGT for a correctly timed IO540 is 1300dF (nominally). The advanced timing should yield 1250-1275 range, and yet you have mid 1300's. This confirms too low a fuel flow.

I would also knock out two degrees of advance from the EI.

Happy to help if you need more.
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  #8  
Old 02-08-2021, 12:20 AM
scsmith scsmith is offline
 
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I think your fuel flow is too low too, but perhaps by even more than suggested by RV10inOz. My IO-360-A (200 hp) pulls almost 20 gph at sea level takeoff power, 150F ROP.

So if you have a 260 hp IO-540, I would suggest your take-off fuel flow should be about 26 gph. I suppose if you have the lower compression 235 hp, then something around 24 gph would be about right.

I see you have an FM-150, which I think is a bit small for a 540, and may be somewhat restrictive. In that case, your fuel flows will be lower, cuz your airflow is lower too. Still, something around 24-ish.
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  #9  
Old 02-08-2021, 03:56 AM
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cderk cderk is offline
 
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Quote:
Originally Posted by scsmith View Post
I see you have an FM-150, which I think is a bit small for a 540, and may be somewhat restrictive. In that case, your fuel flows will be lower, cuz your airflow is lower too. Still, something around 24-ish.
My Thunderbolt IO-540 came from Lycoming with an FM-150... I doubt they are installing things that are a bit small. I questioned it too and both Lycoming and Don say its fine.
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  #10  
Old 02-08-2021, 06:50 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by bsvantho View Post
I typically see only about 100-120F difference from the takeoff EGT to peak EGT. I suspect I am running a bit lean at takeoff, though the fuel flow value does not seem to be unusually low. CHTs will jump slightly above 400F if I maintain a full power climb without rolling back MP a bit. Engine has about 125hours. I am trying to determine if an adjustment should be made.
Do the 24/24 check and I think you'll leave it alone. Slightly above 400 in continuous climb at max power mixture is better than average for RV-10 installations.

You have a T-bolt. Dig out your documents. Does supplied data identify fuel flow at a max power, and the resulting BSFC?

In general, minimum fuel flow for a lycoming at rated power is about 0.50 BSFC. We can't know how much mass you're pumping at the reported point (a function of density, VE etc), so the flow of 22.8 can only be treated as a ballpark indicator. Ballpark, 22.8 x 6 x 2 says it's enough fuel for 274 HP given standard sea level conditions, or a little rich with altitude gain.

Can you pour on more fuel? Sure. The power vs mixture curve is not steep, so you won't lose more than a few percent. You'll lose a few feet per minute, then probably try to climb at a lower IAS to compensate, which will reduce dynamic pressure, which will push CHT back up...

Concern with detonation margin has a practical side. Dyno data puts detonation onset at about 50 ROP, with some variation for ignition timing, CR, and octane. However, that data is taken under worst case conditions, like 475 CHT and max oil temp. Most of us have good instrumentation and would never allow that worst case. And anyway, a steady "slightly over 400" indicates you have normal combustion.

The FM 150 flows a little more air than an RSA-5, the old norm for a 540. Good choice for an RV-10.
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