Red box

[Bob - S50]

Yes, CHT. Wrong abbreviation. I'd like to know if flying in cold air really does lower CHTs to the point that they would not correlate with ICPs. This is where the direct indication would be nice. I don't think there are any studies or any way to prove at what temperatures CHT no longer provides an indication of pressures both on the high and low side. 

I'm sure someone will correct me if I'm wrong but...

 

I believe CHT is the best indicator of ICP we have in the cockpit regardless of the OAT.  However, a specific CHT does not mean you have a specific ICP.  By that I mean a CHT of 380F does not always mean an ICP of 700 psi (or whatever number).  However, I believe peak ICP will occur at peak CHT, or close to it, regardless of the OAT.  In the summer you may reach peak ICP at 390F.  In the winter with the same power settings you may reach the same ICP with a CHT of 360F (just picking numbers out of the air, not reality).

 

Bob

[Bob - S50]

What is the best way to perform the GAMI test? I probably need the engine monitor first, right?

Yes, you'll want the engine monitor first.  At a minimum you'll need the ability to read the EGT for each cylinder and fuel flow.  If you don't have and don't plan to get an accurate fuel flow indication then don't worry about the GAMI test.  If all you have is EGT for each cylinder, just watch the EGT's as you lean.  if they all peak and start to drop, you are LOP.  If you can get LOP on all 4 cylinders and the engine is still running smoothly, you probably don't need new injectors.  If you cannot get LOP without engine roughness, then GAMI injectors will probably make the difference.

 

teejayevans posted a link above to a page that explains three ways to do a GAMI test.  You won't save installation cost by doing the injectors at the same time as the monitor so you might as well have the monitor installed, learn how to use it, then run the GAMI test.

 

Bob

[DS1980]

I'm sure someone will correct me if I'm wrong but...

 

I believe CHT is the best indicator of ICP we have in the cockpit regardless of the OAT.  However, a specific CHT does not mean you have a specific ICP.  By that I mean a CHT of 380F does not always mean an ICP of 700 psi (or whatever number).  However, I believe peak ICP will occur at peak CHT, or close to it, regardless of the OAT.  In the summer you may reach peak ICP at 390F.  In the winter with the same power settings you may reach the same ICP with a CHT of 360F (just picking numbers out of the air, not reality).

 

Bob

Hi Bob,

No corrections needed, except best power mixture will give highest ICPs. But the question is at what temps does CHT accurately reflect ICP? I'm sure there is a range, but is it a narrow range or a broad range with only very hot or very cold air causing additional heating/cooling? It seems the folks with concerns over low CHTs are taking values at cruise. My theory is they unknowingly have a superior baffling system or some other issue not related to cooling air. I don't believe in shock cooling, so I'm more leaning towards the broad range. Hard to say, and it would take a wide variety of flying conditions and an engine with an ICP gauge to get accurate data. Truth is we simply do not accurately know the ICPs, which is why the red fin graph is good to know.

[David Brown]

Hi Bob,

No corrections needed, except best power mixture will give highest ICPs. But the question is at what temps does CHT accurately reflect ICP? I'm sure there is a range, but is it a narrow range or a broad range with only very hot or very cold air causing additional heating/cooling? It seems the folks with concerns over low CHTs are taking values at cruise. My theory is they unknowingly have a superior baffling system or some other issue not related to cooling air. I don't believe in shock cooling, so I'm more leaning towards the broad range. Hard to say, and it would take a wide variety of flying conditions and an engine with an ICP gauge to get accurate data. Truth is we simply do not accurately know the ICPs, which is why the red fin graph is good to know.

 

Darin,

 

CHT will reflect ICP, as ICP is the driver of CHT. As you change the ambient the raw value of CHT will change, but the general relationship remains, until such a point as it is so cold that considerable ICP change seems to be immeasurable.

 

Just a small correction if I may, best power mixtures are around 75-80dF ROP, where as the peak ICP is found at 35-40dF ROP. Not much in it, granted, but you are someone who likes to be accurate, so I hope this helps.

 

You are 100% correct in that the ICP in the cockpit is not readily available, but the data contained in the APS Red Box graphic or the Mike Busch Red Fin is all the pilot needs. Anything more is like the effect of a fairy tap dancing on a pin head.

 

Cheers!

[DS1980]

Darin,

 

CHT will reflect ICP, as ICP is the driver of CHT. As you change the ambient the raw value of CHT will change, but the general relationship remains, until such a point as it is so cold that considerable ICP change seems to be immeasurable.

 

Just a small correction if I may, best power mixtures are around 75-80dF ROP, where as the peak ICP is found at 35-40dF ROP. Not much in it, granted, but you are someone who likes to be accurate, so I hope this helps.

 

You are 100% correct in that the ICP in the cockpit is not readily available, but the data contained in the APS Red Box graphic or the Mike Busch Red Fin is all the pilot needs. Anything more is like the effect of a fairy tap dancing on a pin head.

 

Cheers!

There are times where CHT does not correlate with ICP, whether or not that's taught in APS.

 

Everything you say is contradicted by the graph provided by GAMI. You say best power is 75-80 ROP? GAMI says 75-100. Peak ICP is found at 35-40 ROP? GAMI says peak ICP is a best power.  I'll go with GAMI since these values are taken directly from an engine on a test stand. I just can't see how anyone can argue with a gauge. Just tap on it until it says what you want it to read.

[KSMooniac]

GAMI/APS told me and few hundred others in the live course that best power is indeed 75-80 ROP, and Peak ICP around 40 ROP, which is why 50 ROP is such a terrible compromise power setting.  After they told us that, they showed it to us live in the test stand, with measured ICP data.

[DS1980]

Interesting. Was this graph in error? It makes sense that peak ICP comes at peak power.

[KSMooniac]

Interesting. Was this graph in error? It makes sense that peak ICP comes at peak power.

No it doesn't... it has to do with the kinematics of the piston/rod/crank relationship and the timing or speed of the combustion event.  At peak ICP the combustion event is quicker, and the piston is higher up in the cylinder when the ICP peaks, so the volume is smaller and the mechanical advantage is reduced.  The result is less power output compared to a slightly longer combustion event that makes more power later in the stroke.

[MooneyCFII]

Wow! Lots of people here who understand combustion! This is a pleasure to see. Usually I am the one trying to explain the operating areas that are hard on the engine (red box) and why LoP operation is actually good for your engine. 

 

I tend to pretty consistently run 60%-65% power. I think the engine lasts longer that way and the extra power really doesn't buy much in terms of speed. OK, I may give up 10 knots but I save a boatload of money on fuel. The way I look at it is that I may get there 20 minutes later but I save enough on fuel to pay for dinner and the rental car.

 

So, here's my standard engine operating practice:

 

Get GAMIjectors. Use 250F RoP for climb (typically about 90% power), make my power reduction (turbocharged) or climb high enough that your power is going to be under 70% anyway (NA), do the Big Pull on the mixture control, and run 25F-40F LoP. Don't loiter with the EGT between 150F RoP and Peak EGT. If I want to fiddle with finding peak EGT I do it from the lean side, not the rich side. OTOH, I know what my power setting and fuel flow are going to be so that makes doing the Big Pull pretty easy. 

 

Also, after using the lean-find feature of the EDM-930 I find that TIT is far easier to use for setting LoP operating point than are the EGT indications in the turbocharged engine. For the NA engine I know which cylinder is the last to peak so I use it to find  peak EGT from the lean side.

 

BTW, I am open to suggestions as to how I can do this better.

[MooneyCFII]

Interesting. Was this graph in error? It makes sense that peak ICP comes at peak power.

Not necessarily. Combustion rate changes with charge and with mixture. Therefore as the charge and mixture changes, peak ICP may occur at a different crank angle. You can have a peak ICP that occurs too early or too late to transfer as much mechanical power to the crank so in that case peak ICP will not occur at best power. Changing ignition timing lets you move the peak ICP to the proper crank angle to extract maximum power for a given RPM. This is why an electronic ignition with MAP and RPM sensing can extract more power from that same amount of fuel burned. It changes the ignition timing to get the peak ICP to coincide with the optimum crank angle for maximum power transfer.

 

If only we had a proper ECU to properly manage mixture and ignition timing. <sigh>

[MooneyBob]

We are of like mind, Brian. After several years of seeking maximum aerodynamic efficiency by flying at Carson's speed,I have now settled on 60 to 65 percent power (8 to 8.7 GPH LOP) as the optimum compromise between speed and efficiency in my Mooney. One nit to pick, though. There is no need for GAMI injectors for many of us IO-360 drivers. Most run fine sufficiently LOP without them. Welcome aboard!

Jim

Jim,

What is your speed at this setting? And what altitudes you usually fly?

[DS1980]

CFII,

You stated in a previous thread that you have run several engines through TBO using ROP, but only a few running LOP. Is this because you've only ran a few engines LOP, or are you finding your engines wearing faster due to LOP?

[aaronk25]

7.5gph at 13000ft gets me 142-144kts true in my J. With 02 on 7.3gph trues out at 146-148kts at 17,000ft at 2700rpm 40rop.

These aircraft are pretty impressive!

When I go to fun and sun I'm gonna try to do it non-stop from MN. At 7ish GPH and a slight tail wind up high we will be in good shape.

[MooneyBob]

7.5gph at 13000ft gets me 142-144kts true in my J. With 02 on 7.3gph trues out at 146-148kts at 17,000ft at 2700rpm 40rop.These aircraft are pretty impressive! When I go to fun and sun I'm gonna try to do it non-stop from MN. At 7ish GPH and a slight tail wind up high we will be in good shape.

Is it like 900nm and 6 1/2 hours?

[testwest]

Brian (CFII) asked what he could do better on his engine management.....how about reading the three articles here on the Vz climb, spark plugs and efficient flight planning. Target EGT tells you where to put the engine, Vz tells you where to put the airplane.

 

http://www.openclip.net/Benchmark/IntroducingVz.pdf

 

http://www.openclip.net/Benchmark/AOALog2012SummerSweetSpot.pdf

 

http://www.openclip.net/Benchmark/AOALog2011SpringTwoSparks.pdf

 

Shameless plug:  http://www.seqair.com/benchmark/Howell/Norman.html

[MooneyCFII]

Thank you Norman. Very interesting. I am planning to fly my M20k around the world and one of the things I have been thinking about is the most efficient climb profile and selection of flight level to optimize fuel economy for a particular leg-length. Looks like you have done some of my work for me. I have started reading your treatise on Vz. Good stuff. Too bad you didn't continue it to FL240. :-)

 

My assumption has always been to operate the airplane very near best L/D in climb to achieve the greatest efficiency. That produces the greatest amount of excess HP. 

 

But it is interesting because I have been working on stretching the range envelope for various aircraft for many years. 

[aaronk25]

Is it like 900nm and 6 1/2 hours?

It's actually longer it's 1086 miles and my best guess is I can do it on 56 gallons. 7.5 hours at 145kts (no wind).

That's right at my max as I always want to land with at least 8 gallons (1 hour) left and for whatever reason my J has 33.5 usable per side even though the book says 32 usable a side. I've ran both sides empty several times, so I know what I got.

Any headwind or weather will have me stopping enroute somewhere.

Aaron

[MooneyBob]

Ok. Good luck and report back how it went ( or from wherever you will run out of gas) .

[mike_elliott]

Jim,

What is your speed at this setting? And what altitudes you usually fly?

I know you asked Jim, but as a data point, I get 158 kts @8.2 GPH at 8 or 9K in an 84 J (pics verifying previously posted), and 145 kts @8.4 gph 8k in my 1970 F 

The J is definitely slippery, much more so than most J's I have flown. My F is about on par with most, as it doesn't have the J cowl or windscreen. Non the less, the F is the weapon of choice for most missions because of how well she is "accessorized"   

[MooneyBob]

I cant wait to get my engine monitor installed and start to tweak my settings and flying habits to get most of the bird.

This weather in NJ drives me crazy BTW.

[aaronk25]

Ok. Good luck and report back how it went ( or from wherever you will run out of gas) .

Or look for me on a major freeway with my thumb up and gas can

And I was sand bagging the cruise numbers a bit too. I can run about 3-5kts faster than I published on same fuel I just back off a bit to be conservative. At 11,000ft 2600rpms at 9.2gph yeilds 157-159kts at peak egt.

[mike_elliott]

Your F is within 5 knots of my '78 J, then, Mike, but my J is hardly optimized aerodynamically, so I find this quite believable.

Your '84 J, on the other hand, is truly exceptional to obtain that speed at only 8.2 GPH. It has to be one of the cleanest in the fleet.

 

I wish it were my J, I am just the caretaker for it. I have yet to fly in a faster J, but am sure some with LoPresti's will whoop it. I wont use cleanest to describe it, but certainly slippery will. It has a 1700 hr engine and needs some new paint, but otherwise TAS verified on the ASPEN and GPH verified on the 730, right over CEW in your neck of the woods, Jim.

[David Brown]

There are times where CHT does not correlate with ICP, whether or not that's taught in APS.

 

Everything you say is contradicted by the graph provided by GAMI. You say best power is 75-80 ROP? GAMI says 75-100. Peak ICP is found at 35-40 ROP? I'll go with GAMI since these values are taken directly from an engine on a test stand. I just can't see how anyone can argue with a gauge. Just tap on it until it says what you want it to read.

 

 

 

Darin, I am not sure how well you know or work with the guys at GAMI, but lets get something straight, the numbers are fuzzy numbers, and you are wanting to split hairs. But lets shall we.

 

 

 

GAMI says peak ICP is a best power.

 

No they do not.

 

The rest others have already explained.

[MooneyCFII]

Brian (CFII) asked what he could do better on his engine management.....how about reading the three articles here on the Vz climb, spark plugs and efficient flight planning. Target EGT tells you where to put the engine, Vz tells you where to put the airplane.

 

http://www.openclip.net/Benchmark/IntroducingVz.pdf

 

http://www.openclip.net/Benchmark/AOALog2012SummerSweetSpot.pdf

 

http://www.openclip.net/Benchmark/AOALog2011SpringTwoSparks.pdf

 

Shameless plug:  http://www.seqair.com/benchmark/Howell/Norman.html

 

Back from my first MAPA fly-in. (I suspect I met some of you.) It was great.

 

Norman, I read more. Excellent! Great work. I have been doing this in a slightly less analytical fashion for many airplanes for quite some time. Climbing high, allowing the aircraft to operate below Carson's speed and closer to CAFE speed, will often result in shorter flights because it will allow me to skip a fuel stop. Not having to descend, land, fuel, and take-off again, makes up a LOT of time for the slower TAS. 

 

Here is the thing: when it comes to airplanes, fast almost always means efficient. So I don't see the Mooney as a particularly fast airplane, but rather as a particularly EFFICIENT airplane. Horsepower doesn't buy you speed because IAS varies as the cube-root of excess horsepower. Want to go twice as fast using horsepower? You need 8 times the power! In reality speed comes from aerodynamics, primarily from reducing parasite drag. The Mooneys, and especially Roy Lopresti, knew this. So you can slow down, overfly a fuel stop, and get there sooner, burning a LOT less fuel.

 

Using these techniques I discovered I could operate my Aztec, a not-particularly-efficient twin, substantially more efficiently. I used to fly between Puerto Rico and Florida regularly and learning to operate most efficiently allowed me to do the trip non-stop. Not only did I not have to buy expensive fuel in the Bahamas, I was also able to avoid having to deal with Bahamian and US Customs. Talk about saving time and money!

 

So my engine settings almost always end up to be 60%-65% power, 40F LoP, and then picking the altitude that results in the greatest average ground speed (including climb). It means my 231 isn't going nearly as fast as it can but I usually save enough money in a day of flying to pay for my dinner and motel.

 

OK, on longer trips you have to pee in a bottle. Sorry. 

[bonal]

OK let's clear the air. The more I read this post the dumber I get. If I run WOT 2450 to 2500rpm leaned out to smooth of rough Cht around 380 to 400 degrees and any where from 6500 to 10500 am I in the red or not?