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Low fuel flow takeoff power, high cht.

M

mmcelrea

Member
Hi.
I have been getting high cats during takeoff and the fuel flow indicates 15.8 gph. During the cruise the chts are fine and I've seen other threads stating similar results.
The engine is an IO360 with an RSA-5 vertical induction and Vans fab setup. I have been wondering if the problem may be caused by the airflow into the servo being too turbulent as it is not ducted or corrected in any way inside the fab, its basically a flat plate bolted to the bottom of the servo. This could then cause the impact tubes to read incorrectly thereby altering the mixture and making he engine run lean on wot.
Would a small trumpet or intake duct inside the fab help?
Thanks
 
I seem to recall fuel flow is about right for takeoff on a 360.. I think I get 16 gph on mine.. so I don’t think you are too low.. are you sure the mixture is hitting the full rich stop on the fuel servo? What IAS are you climbing at? What are your CHTs? Standard mags or electronic? Are your baffles 100% sealed and verified with a flashlight in a dark hangar to look for possible leaks?
 
It’s a standard parallel valve engine, slick mags timed at 25 btdc. All baffles look to be sealing very well. The chts rise so quickly I need to reduce the power at a couple of hundred feet. Accelerating doesn’t reduce them but will slows the rising. I’m using a cs hartzell composite so it accelerates quickly. Bringing the rpm below 2500 seems to have the biggest influence.
 
Tom asked some good questions and you answered most of them. If you can answer his few remaining questions, maybe we can help see what's going on.

BTW, I have the same engine and fuel servo, except I have horizontal induction. My fuel flows on takeoff are usually between 17 and 17.5 GPH.
 
Baffles all appear to be sealing well and the mixture does hit the stops. Been head scratching for so long now I’m not sure what else to look at. I don’t know if the servo has an enrichment jet so that’s the only other thing I can think of.
 
I would check the timing. If more than 25 deg full power, CHT will rise quickly.
Do you see a difference with electric fuel pump on ?
Fuel filter, inlet screen on fuel servo ?

Good luck
 
If you have an oil cooler door, you can also close the door for the first few minutes of climb out.. they may increase the delta P across the cylinders before the oil starts to really warm up. Dan H also talks about measuring the pressure above and below the cylinders for a more scientific approach. Since increasing the airspeed doesn’t control the CHT rise, I suspect you are leaking somewhere through the baffles.. maybe some pictures would be nice to see..
 
Timing has been checked a number of times. I always take off with the electric due pump on, filters etc all clear. The chts rise so quickly I don’t know what they would top out at as I’m reducing the power and accelerating to around 100-120 kts before that. They can approach 440 though. I’m in the uk so ambient temps aren’t high.
 

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My RV7 has an updraft parallel valve 180hp IO-360. On climb out, here in Indianapolis, my FF is 15.8 GPH. My timing is @ 23 degrees advance. If I climb out WOT and 2600RPM CHT will touch 400 unless I shallow my climb and use something above 115 KTS.
 
Something isn’t right.. I’m in Las Vegas and my O-360 holds steady WOT on 110 degree days at 380 CHT on climb out. I can climb continuously without throttling back or step climbing..I think you need to measure the delta P like Dan H talks about.. if your FF is 15.8 GPH, timing set, and baffles are sealed, there’s something else going on.. do you have baffle material on the lower cowl to intake ramp area? What about the air filter inlet.. is that leaking into the lower cowl area? Has it always been like this or is the plane new to you?
 
Miller

Looking back through your previous posts it seems like you’ve had quite a history of issues with your setup. Problems idling/ fuel pressure fluctuations and a cracked prop blade.
To start, I note that the snap shot you posted of the temperatures and settings show what looks like a wide open throttle with 2380 rpm. Normal practice is to reduce manifold pressure before rpm.

I would take a good look at the baffle arrangement. Do you have plates in front of the front cylinders? If so, maybe remove them to start. Check that air can’t escape through the ramps on the top cowl.
Take a good look at the inside of the top cowl and you’ll quickly see where there is a good seal with the baffles. Attention to detail on any holes on the baffles all around the engine case will pay dividends.
Even sealing the inter cylinder baffles to engine case.
Check all the cylinders for flashing left between fins and use a file to clean up if needed to ensure good airflow through the fins.
A good seal around the filtered air box to cowl, otherwise high pressure air can be feed into the lower cowl.

Looking at the data you posted the egt’s don’t look excessively high. But I read in earlier posts were you said you hadn’t been able to set the idling mixture because it never idled smoothly?
Mine will be a bit lumpy on after a hot start on a hot day but normally smooths out if I use the electric fuel pump. Basically a bit of vapour due to sitting hot.
If it’s more than this it might be worth while checking to make sure you have no fuel leaks that could introduce air into the system under suction.

There are a few rv’s in northern island have you had any other builders look over your setup. A second set of experienced eyes cannot hurt.
Once the engine is broken in you should be able to climb at full power without the need to use high airspeed.

Feel free to send a private message or email

Peter
 
Thanks for all the replies so far.
One thing I am wondering is how can engines have a range of acceptable full power fuel flows from 15 to 18gph? The manual for my engine states that it should be getting around 18gph at 2700rpm at sea level yet its only getting 15.7.
What would cause this to be so low when cruise fuel flows are fine and how do I adjust it?
 
Hard to make quantitative comparisons without knowing the ambient temp but even on the ground yours is running so much higher than mine it makes me wonder if there could be a measurement error. For instance if type J thermocouples were connected to an instrument expecting type K thermocouples you would see 250F when the CHT was actually 203. At 340 the actual temp would be 270. It gets more pronounced as the temperature increases.

Mine does indicate 17.5 GPH at takeoff but I can climb 4000 feet at WOT at 2500 RPM leaned to 15 GPM at 100 MPH and not exceed 390F on a 70F day
 
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Not sure if this helps, but my YIO-360-M1B (180 HP parallel valve engine) flows 16.9 GPH at takeoff (Full Rich, WOT, 29.2" MAP, 2690 RPM, 957' DA).
 
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Avanza said:
Rated fuel consumption 180 hp is 87 lb/hr or 14,7 USG/hr.
Click to expand...

Those Fuel Flow (FF) numbers appear to be for a Best Power mixture setting for the injected 180 HP engines at 2700 RPM, according the the Lycoming Operator's Manual. I could not find a comparable Full Rich Mixture FF number, which would be the mixture applicable for takeoff.

However, another chart in the Manual for a carbureted 180 HP engine shows the FF with a Full Rich mixture at 2700 RPM and 180 HP at approximately 16.4 GPH, with a Fuel Consumption Tolerance of +/- 4% (so roughly between 15.7 GPH and 17.0 GPH). I assume the injected engines and the carbureted engines would have similar Fuel Flows at a Full Rich mixture setting.
 
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Take a look at the Airflow Performance manual section 5-4 for checking FF using EGT.
 
Thanks guys. We have looked at all the potential issues mentioned and none have shown up anything untoward.
My biggest issue is that I can't do a full power climb without risk of cooking the engine.
I've seen a lot of threads on this issue already and many are accepting and working around it by flying faster, reducing power etc. I just don't think that is an acceptable answer.
The rsa5 manuals mention that some servos have an enrichment jet installed.
Should this be the type of servo installed in RV's?
 

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To rule out (or confirm) the possibility that you have the wrong type thermocouples, run the engine up on the ground with the cowling off and use an IR temperature gun with a laser pointer to measure the spot temperature near the CHT probe. We've done this before to check for defective CHT probes. If you're uncomfortable doing this with the big decapitator running next to you, shut the engine down after the temps have come up a bit. If the IR gun doesn't match the CHT reading in the cockpit within a few degrees, then you've got to figure out what's going on there first. If the temperatures do match, you may next want to contact Don Rivera at Airflow Performance. He's pretty well acknowledged as THE expert on fuel injection systems and can possibly point you in the right directions or hook you up with some parts if needed.
 
BoydBirchler said:
If you want more fuel flow at TO power you can increase it easily!
The arm that links the throttle plate arm to the servo arm has a little wheel, turn it one way it lengthens, the other way it shortens the length of the arm. It's marked which direction leans or richens. Give it 2 clicks richer, fly it, see what it does.
Click to expand...

Isn't that the idle mixture adjustment wheel?
 
What are the fuel flows of engines with high cht issues?
What are the fuel flows of those that don’t and does the servo have an enrichment jet?
 
Some more questions/thoughts:

- Is this a new problem that did not exist before?

- Was the mixture still full rich at the point of the snapshot?

- It would be helpful if you could post a picture which also shows altitude and MAP, noting if it is a first flight of the day or not.

- Was the flight data you posted from a cold start or was it a hot start? Even if it was a hot turn the cht's of 350 before takeoff seem not likely (as someone already posted).

- Airspeed is very slow to rise on this flight, about 30s+ to go from what appears to be liftoff at about 70 up to 121kias. This appears to be a very steep climb.
 
Todays departure

IMG_4972.jpeg

61 ltrs = 16.1 US gal.
Engine has about 550 hours. Superior IO-360 with cold air induction
 
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Five or more years ago I communicated with Bobby Looper, ECI Titan guy (now Continental). I was asking about proper fuel flow on my IOX-360 because of cooling issues.

He said : "The correct fuel flow for your engine (if you have 8.5:1 compression ratio) Is 16.5 gph.at 2700 rpm x 28.5”hg at sea level. This should give EGTS’s of 1250*-1300*F at sea level. The EGT’s will be richer if above sea level (example 1100*-1200*F)."

When I said I had the 9.1:1 compression ratio 191HP version he recommended 17.5 GPH

I hope this helps.
 
I have an RV-6, IO-360 CS, Bendix RSA-5, that had similar CHT issues. When I had the FI rebuilt by AFP I specifically requested they increase the WOT fuel flow from 15.8 to 18.0 GPH. Fixed the high CHT problem.

mmcelrea said:
Thanks for all the replies so far.
One thing I am wondering is how can engines have a range of acceptable full power fuel flows from 15 to 18gph? The manual for my engine states that it should be getting around 18gph at 2700rpm at sea level yet its only getting 15.7.
What would cause this to be so low when cruise fuel flows are fine and how do I adjust it?
Click to expand...
 
data point

Another data point: takeoff FF on my IO-360 with AFP FM200 RPM-limited to 2500 RPM is 17.2 GPH at sea level (29.4" MP that day). I feel this is a bit rich, and pull back on the red knob shortly after takeoff to get it down to about 15 GPH.
 
rv8ch said:
Another data point: takeoff FF on my IO-360 with AFP FM200 RPM-limited to 2500 RPM is 17.2 GPH at sea level (29.4" MP that day). I feel this is a bit rich, and pull back on the red knob shortly after takeoff to get it down to about 15 GPH.
Click to expand...

OT --

Mickey, is that a propellor limitation?
 
bjdecker said:
OT --

Mickey, is that a propellor limitation?
Click to expand...

No, I've set it to 2500 RPM to comply with stricter noise requirements in some European countries. In an "emergency" I can push hard on the prop lever and get 2700 RPM.
 
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