ROP vs LOP

[Shadrach]

On 5/5/2017 at 8:47 PM, Brian Scranton said:

I was helping my A&P with a 231 today--he installed a new fuel pump and was adjusting the aneroid to get the right flow (25.5 gph at max)--trial and error is the name of the game on that one. Also, made me realize that I really need to invest in a FF gauge. I tried to run LOP again today. I get to that 4th cylinder (the richest one) and the engine feels like she's about to die--I guess I have to get some GAMIs too! 

I'd bet on manifold leaks before an injector issue.

[Shadrach]

On 5/5/2017 at 3:02 PM, cnoe said:

Shadrach nailed it above. I fly out of an airport with a field elevation of 25 msl and generally see 19.1-19.3 gph at takeoff (IO360-A3B6). I think it may be just a TAD rich but I'd rather be rich than lean during takeoff.

Here's a blurb from a really good AVWeb article:

• For a normally aspirated fuel injected engine designed to run on 100-octane fuel (8.5-to-1 compression ratio), takeoff power fuel flow in GPH should be roughly 9% of the engine's maximum rated horsepower.

The entire article can be viewed here:

https://www.avweb.com/news/savvyaviator/SavvyAviator_65_WhatsYourFuelFlowAtTakeoff-199805-1.html

9% is a good base number. Remembering that the angle valve engines are 8.7 to 1, there would be nothing wrong with seeing 20gph or slightly more out of a 200hp Lyc IO360.

[Brian Scranton]

2 hours ago, Shadrach said:

I'd bet on manifold leaks before an injector issue.

Intake manifold, right? Interesting--cuz the RayJay adds quite a bit of complexity to the intake aspect. Not even sure how I'd go about identifying that! 

[carusoam]

9% of 310, is 27.9 gph

According to the STC, 27.2 gph is the max FF at 0 MSL.

Pretty close in round numbers.

Bes regards,

-a-

[Shadrach]

3 hours ago, Brian Scranton said:

Intake manifold, right? Interesting--cuz the RayJay adds quite a bit of complexity to the intake aspect. Not even sure how I'd go about identifying that! 

I would think the only way to do it would be to affix a sealed coupler with a Schrader valve to the compressor inlet housing. Pressurize the manifold, spray it down with soapy water and look for bubbles.

If there is an easier way, I'd like to know.

[carusoam]

Hooking up a vacuum cleaner,

• running in reverse, as a blower...
• to pressurize the air intake...
• where the filter has been removed...
• consider the alternate air as a potential location to add air pressure or have a leak...

Then soapy water, looking for bubbles...  just remember there will probably be at least one intake valve open during this exercise. Make sure nothing comes out of the hose but air.

Sound familiar?

Fuzzy PP memory of something I read along the way, somewhere....

Best regards,

-a-

Edited May 26, 2017 by carusoam

[Shadrach]

30 minutes ago, carusoam said:

Hooking up a vacuum cleaner,

• running in reverse, as a blower...
• to pressurize the air intake...
• where the filter has been removed...
• consider the alternate air as a potential location to add air pressure or have a leak...

Then soapy water, looking for bubbles...  just remember there will probably be at least one intake valve open during this exercise. Make sure nothing comes out of the hose but air.

Sound familiar?

Fuzzy PP memory of something I read along the way, somewhere....

Best regards,

-a-

That would likely work, but do consider that everything upstream of the compressor is not designed to be under pressure.  Your method may cause leaks that didn't previously exist.

Edited May 26, 2017 by Shadrach

[Brian Scranton]

9 hours ago, Shadrach said:

That would likely work, but do consider that everything upstream of the compressor is not designed to be under pressure.  Your method may cause leaks that didn't previously exist.

Or I could just run ROP!

 

[Shadrach]

7 hours ago, Brian Scranton said:

Or I could just run ROP!

 

Yes, using the term loosely! . If your spread is as bad as you describe, then you've got four separate, single cylinder engines running in very loose formation connected by a common crankshaft. Not optimal for fuel economy, power or engine smoothness. 

As a data point, when my IO360 is run at high MP (down low in the winter I use what ever I can get, say 27.5 to 29) it will go to ~80 LOP or more before it gets rough enough for a passenger to notice. It starts missing north of 100LOP.

If I were you, I'd fly with someone really familiar with running these engines to ensure that you are seeing what you think you are seeing. Once you've verified that your spreads really are that wide, then you can readdress why.