IO 360 M1B FF at T/O full power

[RV10inOz]

Originally Posted by Walt

As a data point I just went down this road with a Glasair II, Superior IO360/CS and silverhawk FI. Customer complained of high CHT during climb with associated higher than normal EGT's (1300 + T/O), FF in 14 GPH range, airplane had this issue since new.

The shop that checked the servo said it looked like it was flowed for a 320, after calibration customer can now do unrestricted climb, CHT down by 50 deg, FF in the 17 GPH range, EGT's in the low 1200's.

BINGO!!!!

This is EXACTLY what I suspect is happening. What is more i have found this exact same issue on an Avstar setup as well. It is only in recent times. If anyone cares to search my posts there are some other threads with this same comment.

Thanks a heap Walt...... some days it feels like being a solo pioneer

[gazznsw]

David
I recently purchased an RV6A Superior O 360 A1A C/S, Lasar Ignition, and I am having C/H temps of 420+ on take off. We have tried everything we can think of without success. Fuel flow seems the final option (14.5 GPH Full Throttle) , I need some advice on where to get the right info on diagnosing the problem. I live in Albury NSW.

[RV10inOz]

Email sent

Unfortunately finding the right people is hard, closest to you is in Adelaide.

Call me as per email.

[rzbill]

Just putting my datapoint out there.

2000 ft DA this past Saturday and I saw 16.8 gph

[RV10inOz]

Follow up to this thread.

My concerns about recent delivery (last 2 years maybe??) engines having far too low a fuel flow are continuing to be proven. This is for Precission and Avstar by the way.

The last week or so I have seen similar results to those in this thread and when the FCU was removed and sent to Andrew Denyer at Riverina Airmotive in Adelaide, he found the flows low.

Once set to the correct flow, which is the upper end of a small tolerance, and reinstalled, the very next flight, all the flow, EGT and CHT numbers were exactly as I predicted.

You can't argue with the laws of physics, they apply equally to all men and machines (except the F22 ).

So guys, if you have data showing anything different, get it fixed.

Happy to take questions or offer guidance if you think yours is affected by this.

[DanH]

Originally Posted by RV10inOz

Once set to the correct flow, which is the upper end of a small tolerance, and reinstalled, the very next flight, all the flow, EGT and CHT numbers were exactly as I predicted.

You can't argue with the laws of physics, they apply equally to all men and machines

Let's consider the physics. Enriching increases burn time, which moves the point of peak cylinder pressure some additional degrees after TDC, which in turn lowers CHT. Same effect (delay) for very rich or very lean.

David, I assume you have seen unedited GAMI data. When running the trusty 540 dyno mule, 100 additional degrees ROP moves peak pressure how many degrees?

BTW, just to be clear, I'm asking specifically about the 540 at WOT. We've already seen the generic school chart:

[RV10inOz]

Flying all day today and that will take a fair amount of time digging through some files. Remember in the several (maybe 10's) thousands of hours of dyno work, I have only a few to draw direct data from.

The next point is the engine, matters not. The fuel does not know who made the cylinder or piston. Which 540 do you want????

I gather you are actually wanting to know the Delta for an extra 100dF ROP from a properly set up Vs a not rich enough engine? If so I can probably just surf through some data and look for a sample close to that.

[DanH]

Originally Posted by RV10inOz

I gather you are actually wanting to know the Delta for an extra 100dF ROP from a properly set up Vs a not rich enough engine?

Yes. Let's illustrate the physics, the actual reasons why adding fuel lowers a problem CHT. Retarding peak pressure is one probable contributor, the question being how much contribution as compared to other factors.

The generic school chart doesn't indicate peak or stoich, and it is generic; not sure the values can be taken as specific values. Some actual data (F/A ratio vs pressure peak in degrees ATDC) from a cylinder similar to the majority of RV installs would be nice. Given it's the foundation of APS engine management philosophy...

[RV10inOz]

Retarding peak pressure is one probable contributor, the question being how much contribution as compared to other factors.

It is the retarding of the peak, that means a lower peak value that is the factor.

If you want some values I can pick some off the dyno run for illustration purposes. I am out of town again today...sorry for the delay!

Given it's the foundation of APS engine management philosophy...

No. It is the foundation of the science. Long before APS was around.

[RV10inOz]

OK, Just had some time to look at various engine runs and no this is not your IO360 or 320 in the majority of RV's but the science is the same. It was a 540 set to 30" though.

I did bit of interpolation and when it all boils down to it the spread from around full rich to say 75-100 ROP was in the order of a Delta thetaPP of 5 degrees, but most importantly the greater the degrees the bigger the effect as the volume is not directly proportional.

In other words the first 2.5 degrees of change with increasing mixture has an effect but the next 2.5 degrees has a much bigger effect.

The points of the data I used were at power settings (ROP and constant) and fuel flows that varied in the range of 15-20%.

I am refraining from issuing specific data points as all that will do is start a riot with arguments over this setting that setting this engine that engine. It matters not.

What it did demonstrate to me however the picture above is not just generic and is rather accurate!

Bottom line is this. If the full power fuel flow is not enough, fix it!