Aircraft | Blackstone Laboratories

40 Years of Testing Aircraft Oils

This summer marks our 40th year in business, so we thought it would be interesting to have a look back at our history in the field of aircraft oil analysis and how we got to where we are now.
Jim Stark (my father) was first introduced to flying as a teenager by getting a ride in a surplus P-51 owned by local legend Denny Sherman – talk about a fantastic Young Eagles ride! After that
ride, Dad was hooked, but it wasn’t until the early 80’s that he actually started chasing the dream of getting his pilot’s license.

Shortly after he got his license, he was fired from his job working with a local diesel fuel additive company and started working on Blackstone that same day. The funding for this company came entirely from debt, which meant he had to work hard to make ends meet with the family, and all non-essential expenses went right out the window. So long, 1972 Jaguar XJ6 with a bad head gasket, so long kids’ college fund, and so long flying.

Still, he had the flying bug and decided right away that Blackstone would support to aviation community by testing aircraft oils, not to mention he really needed the revenue. There are a lot of oil analysis labs out there, but only a handful test aircraft oils. There is a certain amount of knowledge you must have to test these oils correctly and deal with the challenges that come along with handling samples that are chock-full of lead. Along with being passionate about aviation, Dad had graduated from Purdue University with an Aviation Technology degree and A&P license, so the knowledge part came as second nature. He figured he’d learn how to deal with lead on the job.

Early Years
In the early years of Blackstone, we really didn’t test many aircraft oils—two or three a day if we were lucky. He made sales calls to FBOs in the area, but sales were slow. He had a lot more
success focusing on industrial factories and diesel truck fleets, but he never stopped trying to crack into the aviation market. Since this was well before the days of the Internet, they had to get
creative in figuring out how to tell aircraft owners and mechanics that Blackstone even existed. One of his early sales efforts was a sample kit mailing program. He bought a list of aircraft owners in Indiana, Illinois, Michigan, Ohio, and Kentucky from the FAA and sent one sample kit to everyone on the list. Another sales idea he had was the EAA airshow at Oshkosh Wisconsin. The funding to get a booth like we have now was out of the question, so he and my Uncle Bob (company Vice President at the time) decided to drive up to the show. Then they jumped a fence to get in (again, times were tight) and set an oil sample kit on the wing of every airplane they could find. As you can imagine, this type of “shotgun-marketing” didn’t result in a major influx of samples, but considering the fact that we still have customers today from these programs, both can be deemed a success, just a long time coming.

Enter Howard Fenton
We didn’t really hit it big in the aircraft market until 2002. That was when Howard Fenton called us up one day out of the blue and wanted to sell his company to us. He had first heard about us at
Oshkosh when some joker set a Blackstone sample kit on the wing of his Grumman Tiger, not knowing that he also owned an oil analysis company called Engine Oil Analysis (EOA).

EOA had been in aircraft oil analysis since the 1970s and was well respected in the aviation community. He sent in a sample to us to see what we were all about and decided he liked how we reported the results, so when it came time to retire from the oil analysis side of things, he called us to see if a deal could be made.

Jim and Howard hit it off right from the start. Both had worked for Dana for a lot of years and both were pilots, so Jim made a quick trip to Tulsa, Oklahoma to visit Howard, and the deal was done. Howard didn’t actually own a lab, he just contracted a local environmental lab to test his oil on their spectrometer. When they were done, they would give him a text file with the results and he had to hand-enter the data into his database reporting system. So basically, the only thing we bought from Howard was a client list, a bunch of historical data from the samples he tested, and all the goodwill the EOA name carried with it. Fortunately, Howard had roughly 3,000 happy customers, who trusted Howard’s judgement in choosing us as a replacement, so the transition for his customers to our service went smoothly. Blackstone was now a major player in the aircraft oil analysis field and we’ve never looked back.

40 Years of Growth
There were growing pains associated with taking on such a large chunk of business. The actual testing of the oil really hasn’t changed much over the years. We still offer the same standard
analysis as we did back in 1985. That includes the spectral examination, viscosity, flashpoint, and insolubles test. Spectrometers have improved significantly since 1985 in their reliability and ease
of use, but the accuracy of those old machines is comparable to what it is today, at least for our purposes, which means rounding to the nearest part per million.

As a lab, we needed to learn how to handle not only the large jump in aircraft samples, but the significant amount of leaded waste oil that goes along with it. Since a lot of the waste oil (including most of what we produce) in this world is burned for heat, and there is a limit to how much lead can be in your waste oil, it became obvious that we needed a separate lab just to handle the leaded oil, so we built one.

We also needed to develop a way to train new report writers. One of the things our customers like about our service as the comment section. It takes people to write those comments and the people we hire don’t tend to know anything about engines, so the training program we developed was extremely important in helping us expand and grow.

After Howard sold us EOA, he created a new company called Second OilPinion. Its focus was to inspect aircraft filters. We had never really wanted to get into the filter testing business. It was our
opinion (and still is) that this is something owners and mechanics can and should do on their own, but that doesn’t diminish the fact that Howard had a lot of people who were sending their filters to him for his opinion on what metal was showing up.

After Howard passed away in 2018, we decided to support the customers he was serving and developed our own filter analysis program. This program has come a long way over the years and we’re working on more improvements like developing a way to determine what alloy of metal is present when we do find a large chunk in the filter.

So, that’s a little history of where we’ve been. In thinking about the future, I am really looking forward to the widespread use of unleaded fuel. I believe this will be a boon to aircraft engine owners from a maintenance point of view. Leaded fuel is dirty fuel and the blow-by tends to be corrosive in nature. Once 100LL is safely eliminated, I predict a lot of problems like fouled plugs and stuck valves will fall by the wayside. From a business side of things, we won’t be able to use lead as a judge of how much blow-by is getting into your oil, but on the plus side, we won’t need to have a separate lab just to test aircraft oils anymore.

This past year we did have some major challenges processing samples in a timely fashion, but those have been addressed and our current turn-around time is back to 5 days. Thank you for sticking with us. We’re looking forward to a great 2025 and beyond.

By Ryan Stark|2025-03-14T15:02:04-04:00March 14, 2025|Aircraft, Articles|Comments Off

Finishing the RV-12

For those of you who have been reading these newsletters, you’ll know that I have been in the process of building a light-sport kit plane made by Van’s Aircraft called the RV-12. Last year I chronicled the progress and mentioned that I was getting close to the end. Well, thankfully the end has come, though I have to say it took quite a bit longer than expected.

Excitement/Burnout

We moved the project from the garage here at the lab to a hangar out at Fort Wayne International Airport in early July 2019. The days following the move were a time of excitement and hope, though that feeling wouldn’t last. My wife and I have been working on this project since the summer of 2016 and we were both kind of getting burned out.

However, actually being at the airport and talking with the other owners there helped keep our enthusiasm for the project going. In talking with the other homebuilt owners, it became apparent that even after it’s flying, there is always something to work on, but we didn’t worry about that much. We still had a lot of work to do just to get ours in the air. This was the part of the building process that’s a running joke among homebuilders — 90% done, 90% left to go!

Ironing Out the Details

Soon the prop was installed and the final fitting work on the cowling was done. We ironed out some bugs in the electronics and communication systems, most of which were mistakes we brought upon ourselves. Before too long, we came to the point where there was nothing left to do in the building instructions.

Next came a thorough checkout of all the systems. Van’s provides what they call the production acceptance procedures, which is a very helpful document that tells you how to go through all the systems to make sure they are set up and working properly. It includes things like “Move the control stick to neutral and measure the right aileron drop, it should be 1/4 to 1/2 inch.” Sounds easy enough, until you realize that just about every step requires some type of filling or adjustment on your part.

The Fuel Flow Blues

After a few months of work, we got to the fuel flow test. That’s exciting because right after that you get to start the engine for the first time. We had built the fuel tank about a year and a half earlier and up until then, it had not had any fuel in it. I was dreading putting fuel in for the first time, and for good reason, because as soon as I did, it started leaking out of a return line fitting.

That was a pretty dark point in the whole process because it meant I had to pull the fuel tank, open it up, fix the leak, and reseal it. Anyone who has ever worked with fuel tank sealant knows this is not fun stuff to work with, and it’s even less fun to try and clean it off parts. It’s also the point at which I realized that I had spent a significant portion of my life building something that would only fly about 120 knots max (with a tailwind) and wouldn’t even be able to haul my whole family while doing it. And to further sour my mood, this was mid-October and I knew at that point there was no way I’d be able to get it done in 2019.

Starting the engine for the first time!

Trying Again

So, after a good pity party and some time off, we got back to work. The fuel tank was fixed and reinstalled, though by that time it was too cold to get any serious work done at the hangar. That was okay though because it was also time to start the paperwork.

As some of you know, I inherited this project from my father and I can say for sure that the paperwork part would have been what he hated the most. Still, if you keep plugging away, eventually it all comes together. I was able to obtain a N-number (on my second try) and by the time spring rolled around, we were ready to test the fuel flow again and start the engine. As you might imagine I was fairly nervous about this whole process, but the fuel tank held up, the fuel flow test went well, and on May 3, 2020, our Rotax 912 fired up for the first time since it left Austria.

But is it Airworthy?

With the motor running and fuel tank sound, I was starting to feel a lot better about this project, though I still had the airworthiness inspection to deal with. This is generally the last step before you can fly and was a big unknown in my mind. It was also a little tough to get scheduled because not only did the FAA switch to a new and confusing online application process, the Indianapolis office had been closed since mid-March due to Covid-19.

They were just starting to reopen in mid May when I contacted them, but they were facing a serious back log of work that needed to be processed before they got to me. That basically left me with the choice to either wait until they got time to send someone up (for no charge) or I could contact a DAR (designated airworthiness inspector) and pay to have them take a look. Not wanting to delay this project into 2021, I chose the DAR and scheduled an inspection. Surprisingly enough, the actual inspection was painless and lasted just three hours. At the end I found myself wanting to show the inspector more of my airplane, so he could see the safety wire on the gascolator that I redid three times. Or admire the beautiful fiberglass work on the cowl that took several weeks to sand to perfection.

A successful first flight

Airborne!

With all the paperwork done and my airworthiness certificate on board, I was finally able to make my first flight on Monday July 13th. It went well, the wings stayed on, and the airplane showed no tendency to do anything crazy. As you can imagine, I was relieved. Now, on to some flight testing, as soon as I can get my transponder to report altitude… ahh the joys of homebuilt ownership.

By Ryan Stark|2025-02-06T15:38:44-05:00February 6, 2025|Aircraft, Articles|Comments Off

The Price We Pay to Soar

How does flying in the Air Race Classic affect engine wear?

Let’s start this story with a question.

Mark has a truck – let’s say it’s a red F150. Mark consistently runs the engine 70 MPH on the highway every day on a commute to work with nothing in the bed.

Mark’s buddy Dave lives next door, and Dave also has an F150 (this one’s blue), with the same engine, and he works in the same place as Mark. So the two guys have the same exact commute, except Dave constantly hauls 8 kegs of beer to and from work, and he always pulls a trailer that’s loaded up with about a thousand pounds of dumbbells and free weights.

Which engine looks better in oil analysis? Mark’s, right? His engine sees much lighter use—no heavy loads in the bed and no towing, so he’ll have less metal in the oil. That makes sense. The same thinking goes if you compare driving 50 miles on the highway vs. 50 miles on the race track: track use is harder, and it’ll make your engine wear more. And indeed, the data backs this up.

But is that true for airplane engines?

We don’t see quite as many samples from aircraft engines that are run harder than others to be able to determine whether there’s a difference. Either you’ve got an aerobatic airplane that does mostly aerobatic flights, or you’ve got a trainer that sees everything from countless touch and go’s to multiple cross-country flights on every oil run. Maybe you’ve got your business plane or transport plane doing mostly long-haul flights and not much else (imagine doing aerobatics in your family hauler, with the kids strapped in the backseat). So while we naturally expect harder use to result in more metal, that’s a little harder to quantify in the aviation world than it is in the automotive world. But then there’s Joelene.

Joelene
Joelene is a close friend of mine who has been sampling her 1978 Bonanza’s Continental oil with us for several years. She keeps her IO-520 active enough that corrosion has never really been a problem. Joelene does a nice mix of cross-country flights from the Midwest down to Texas, has the right instruments to keep her current and proficient, and she’s not shy about helping with Young Eagles flights at nearby airports. Overall, most of the flying she does is relatively easy cruising without a lot of hot/cold cycles, and she’s got several pages of nice, stable trends to back it up.

The Air Race Classic
A couple years ago, Joelene got into racing her Bonanza. In 2022, she participated in the Air Race Classic, a ~2,200 nautical mile, four-day race for teams of two (or more) women pilots. The race traces its roots back to the days of Amelia Earhart and her contemporaries, when women weren’t allowed to race with men, so they started their own cross-country race.

This past summer, I was her teammate in her Bonanza. Our race started in Carbondale, Illinois, and ended in Loveland, Colorado, with stops in Indiana, Michigan, Ohio, Minnesota, Missouri, Oklahoma, and Kansas along the way. All told, we traveled 2,269 nm in just over 19 hours, going full-throttle the entire time. This was a little different than the normal kind of flying Joelene does.

Looking at the Numbers
After her first race in 2022, Joelene and I looked at her engine oil test data to try to figure out how much “damage” was inflicted on the engine parts by participating in the race. The biggest thing we had noticed was that make-up oil had gone up from 2.5 quarts in 27 hours to five quarts in 34 hours. There was a little more nickel, too, but nothing noteworthy. Realistically though, one data point isn’t exactly enough to come up with any hard-and fast conclusions about the engine.

Guess we better keep racing.

So after being a part of the Air Race Classic this year, she now had two sets of data to compare to her normal trends. When I asked Joelene if I could use her data for this article, she replied, “Yes! As long as you don’t tell me I can’t race my Bonanza anymore!” We would never.

Non-Racing vs. Racing Wear Numbers
Joelene has a total of 19 samples on file with us over the last five years, and two of them are the race samples. It isn’t a huge sample size, but it’s worth taking a look at.

She averaged a typical 32-hour oil change interval over her 17 non-racing sample. While racing, the average interval is 29 hours. Metal counts are in parts per million.

Aluminum, chrome and iron inched up a bit, copper and lead both managed to improve, and nickel doubled. So, in this case (lead and copper being the exceptions), racing does cause a little more wear for Joelene’s Bonanza. Enough to stop Joelene from racing next year, or raise any red flags on our end? Nope, it’s not that significant. Keep in mind we’re still talking about microscopic metals in parts per million, so we’re not talking about a lot of metal overall—the harder use does affect the engine, but not to the extent that she needs to change what she’s doing.

Why did copper improve? We don’t know. Lead, on the other hand, is a bit more explainable. It comes from 100LL fuel blow-by, which tends to read higher when flying at higher altitudes and lower at lower altitudes. With less air pressure on the crankcase at higher altitudes, more blow-by escapes past the rings, and you end up with more 100LL in the oil.

As part of her racing strategy, Joelene tends to fly quite a bit lower than normal so that she doesn’t spend as much time climbing at slower groundspeeds (since you don’t often make up a lot of speed with tailwinds on shorter legs). Most of the legs of our race were flown at the absolutely lowest FAA minimum safe altitude during the race, which was quite a rush! And also, that means lead, from blow-by was a little lower.

Still with us? There’s just one more factor to note.

Oil Consumption
One of the biggest things Joelene noticed when she’s racing her IO-520 and running wide open the entire time, compared to when she’s flying a bit more tepidly, is that her engine consumes a good deal more oil. How much more oil? When Joelene isn’t racing, her engine burns an average of 1 quart of oil every 25.7 hours, or 0.04 quarts/hour. When she is racing, oil consumption increases to 1 quart every 4.8 hours, or 0.17 quarts/hour. She has a 12-quart sump, but she keeps the oil level at about 10 quarts — anything above that just ends up on the belly on the plane.

So, when Joelene is racing she’s roughly refreshing 50% of the oil during a given run, which means the metal counts we provided above would essentially be diluted by about 50% at the end of the run.

To get the exact dilution factor we’d have to figure out how many hours into the oil run she added each quart of oil, then figure out how much time that oil spent in the engine, and do a whole lot more math. Suffice it to say, the additional make-up oil is making her racing numbers look better than they actually were. It potentially doubles the wear rates over her non-racing samples. I won’t put those numbers here, so Joelene doesn’t have to look at them in black and white (and since the numbers, technically, would be just an estimation anyway), but you can imagine what they’d be: 50% higher.

Conclusion
Did the engine make more metal? Require more make-up oil? Yep, it did. Makes sense, right?

Joelene only gave me permission to write this article and use her data as long as I didn’t tell her she couldn’t race her plane anymore. You’re reading this article, so the conclusion is that I’m not going to be telling Joelene not to race her plane anymore. And rightfully so.

Even with all the data and trends, the metals we’re reading are microscopic, in parts per million, so the increased wear rates aren’t significant enough to suggest we’re looking at part numbers or any serious engine damage. The wear rates are a little higher than average, but that’s nothing compared to all the fun she has racing—the challenge, the excitement, the camaraderie, and the memories. Worth it!

When we have automotive customers whose engines wear slightly more than average because their engines are used for off-roading, or hauling, or even a lot of idling, we remind them that the metal is probably just the small price you pay for all the fun you’re having. And that’s the same thing we’d say to Joelene with confidence: yes, your engine wears a little more on the races, but not nearly so much that we think you should stop racing. Besides, it’s better than *not* flying your airplane and letting it corrode from the inside out. Might as well fly it!

We’re excited to cheer on Joelene (and the rest of those amazing ladies) in next year’s race, and we are looking forward to seeing that little sample bottle of black gold to see how the engine fared.

By Amanda Callahan|2025-01-14T14:48:45-05:00January 14, 2025|Aircraft, Articles|Comments Off

Landslide!

Imagine the awesome event of a landslide. There’s no doubt it’s a brutal force of nature. If you’re unfortunate enough to be caught in one, you might not survive. A landslide is gravity pulling terra firma down a slope with such force that it takes all things, natural and manmade, with it. The very earth that supports us unmoors from its surroundings, changes shape, and becomes destructive. While it may not be obvious at first glance, this landslide can help us understand oil analysis.

Take a picture

Back to your mental image of the landslide: it starts off with a few pebbles rolling down a hill. Those pebbles strike others, and the dirt slide gains momentum. The process escalates and the mass of the movement increases. Larger rocks and patches of earth are dislodged, and the process continues until the whole hillside is involved, taking trees, boulders, and anything else in the way. Now stop: Take a mental picture of the landslide in full force. Step back and look at the frozen picture. Everything on the hillside that started off peacefully and at rest is in the process of roaring toward the bottom of the slope.

If you looked at your picture of the landslide from afar, you’d see a cloud of dust and dirt at the front edge of the sliding mass, and lingering far behind it. The dust cloud itself would actually hide much of the larger detail of rocks and trees crashing along the slope. Without looking at the larger debris contained in the mess, could you determine the makeup and extent of the landslide from the dust cloud alone? For the most part you could, and that’s how oil analysis works.

Normal vs. abnormal

One of the limitations to oil analysis is that we can only tell you about the wear metals that we can see with the spectrometer, which are between about 1 and 15 microns in size. (How big is a micron? One-millionth of a meter. One inch contains 25,400 microns. The period in this sentence is about 615 microns.)

If you have a mechanical problem with your engine, the oil filter should collect the larger metallic particles (usually those larger than 40 microns). These are the boulders in the landslide. There is also a wide range of rocks and stones present in the landslide that don’t become airborne. They still ride the slide to the bottom of the hill, but they don’t hang suspended in the dirt cloud. These are the particles that fall out of suspension and don’t make it to the lab with your oil sample.

Then there’s the dust cloud. We compare the “dust” we see in an oil sample to what is average for a particular type of engine, transmission, differential, etc. We expect all mechanical machines to produce wear in the course of normal operation. But there is normal wear, and there’s abnormal wear. When we find abnormal wear in your “dust cloud,” we may be looking at a potential landslide in your engine.

Avoiding the trees

Fortunately, we don’t have to wait for a landslide to occur before we can determine what’s going on your engine. While the dust cloud accompanying the slide is a one-time occurrence, we can repeatedly analyze the oil from your engine and see trends developing. One snapshot gives you a look at whether the dust we find appears normal or abnormal. But a series of snapshots gives us a clearer picture of the condition of the engine. By trending the results from one oil change to the next, we can see whether the dust cloud is growing or subsiding. If it’s growing, eventually there will be boulders and you’ll need to take action to save the engine.

Occasionally we are asked about the dust: How much is too much? In other words, when someone has a particular metal that’s reading high, they often want to know how high it needs to be before they really start to worry. The answer is, there’s no single answer.

Lots of things affect the amount of wear we find — the type of engine it is, how it’s driven, and what conditions it’s operated in. What’s more important than the level of wear is the wear trend that’s developing. Someone who routinely races a Subaru 2.5L engine in Las Vegas is probably going to find higher wear on a routine basis than a person who uses the same engine to mainly go to work and the grocery store in Minnesota. If the racer’s wear is always high, and it always reads at about the same high levels from sample to sample, we’d probably consider it normal for that particular engine. If the grocery-store engine was producing low, steady wear, and then wear suddenly jumped up to the racer’s levels, we’d worry. That’s why it’s important to establish wear trends for your particular vehicle, and why we can’t always say, “Okay, when iron gets to X level, it’s a definite problem.”

Avoiding the full-on, catastrophic landslide is not hard to do if you practice routine oil analysis. To keep the boulders and trees out of your engine, pay attention to what you find when you change the oil or have it changed. Some metals are normal in new engines, but once past 10,000 or 15,000 miles, you should not be normally finding any metals that you can see. If you do find metal, it’s probably not too late to stop the slide — but it’s better to avoid it in the first place, if you can, through the trend analysis of your engine’s wear.

By Jim Stark|2024-09-19T09:01:39-04:00June 12, 2024|Aircraft, Articles, Gas/Diesel Engine|Comments Off

Blackstone and the Post Office

(TL;DR: You can use the labels that are on your kits now, but if you’d like new ones, you can print one here.)

“I am FED UP,” said the customer on the phone. “Do you even have my sample? I mailed it a month ago.” I looked up his tracking number and he wasn’t exaggerating – he mailed it September 15, and we had just received it that day, October 15. Sound familiar?

Why is it taking so long for samples to arrive? And what are we doing about it? Read on, Blackstone fans. Have we got a story for you.

The Post Office makes some changes

“I think the post office isn’t charging us enough.” Ryan Stark, Blackstone’s president, and my brother and business partner, said to me one day last November after reconciling the checkbook. He’d noticed that for the last few months, the amount we were paying in postage had dropped significantly.

Stick with me, this is all going to tie together.

Last summer, just as we were all realizing the pandemic was not simply going to disappear, I learned the post office was ending their Merchandise Returns program. Because our samples came back to us on MR labels, we needed to create a new one, so I had my printer start working on it.

A major part of that process is getting approval from the USPS at various points along the way. And that’s where the process slowed…then slowed down some more…and then, like molasses on a winter sidewalk, came to a creeping halt.

We called USPS. How’s the label going? No reply. We emailed. How’s the label coming along? Nothing. Time passes. Months go by. Sometimes we’d get a reply – “We should have an answer for you soon!” But then…nada.

Back to the money

Meanwhile, the issue of not paying enough postage was still a problem. What do you do when you think the USPS isn’t charging your business enough? You call them – so I did.

I first contacted my local post office – the ones who deliver us samples every day, the ones who know who we are and what we do. “I think we’re not being charged enough,” I explained. “Nope, that’s not me,” she said. “They take care of that in Indianapolis now.” She gave me a number, so I called down to Indy. “Huh,” the Indy person said. “Let me look into it.”

Reader, you can see where this is going.

I got nowhere in November, so I called again in January. “Hey!” I said. “I still don’t think we’re getting charged enough!” “Hmmm” said the voice on the line. “Let me ask my supervisor about that.”

Time marches on. After calling and emailing various USPS representatives throughout February and March, I got fed up in April and sent an email blast to every single USPS contact I had, including the ones in Washington, D.C.

That one got some attention.

They started looking into what was going on, and to make a long story short, the issue culminated in a conference call with several USPS bigwigs. “Well,” said Bigwig #1, “you owe us (insert a huge amount of postage here. Nope, it was more than that).

It turns out that when the USPS stopped their Merchandise Returns program, our local post office stopped charging us for our incoming samples. We were still being charged for outgoing mail, but we hadn’t paid postage on incoming samples since the MR program ended in August.

After much gnashing of teeth and some heated words on my end (would they ever have caught the problem if I hadn’t kept after them? We’ll never know), we settled on a plan to pay the outstanding postage.

As part of this reconciliation, one of the USPS Bigwigs suggested we have samples returned to us in a Tyvek envelope, to help catch spills. Well, oil spills aren’t really the problem with getting samples delivered, but I tucked the idea away for the future.

Back to the labels

Meanwhile, the new label still had not been approved. And people still needed kits. While all this was going on, we continued to print and send out hundreds of thousands of old labels on kits. What choice did we have? Now those old Merchandise Return labels are now on kits that are sitting in garages, hangars, and marinas all over the country.

So when did we get it resolved? We officially started printing our new, USPS-approved labels more than a year after the old label was officially discontinued. The thing is, the post office reassured me that it would be fine to continue to use our old label – we would just have to pay more when people returned them.

Which is fine. Fine, fine, fine. Except, for some post offices, it’s not so fine. Most of those old, Merchandise Return-labeled kits get here no problem. But occasionally, a post office will hold on to it and not deliver it because it’s the old label, even though they said we could keep using them.

At this point, there’s nothing we can do about the thousands of old labels that are in circulation except try and get the word out. So that’s why you’re reading this. If you have old labels on your kits (they say Merchandise Return right on them), click here to ask for new ones. We really do want to receive your samples. And we don’t want you to have to wait for a month to get your results.

But wait, there’s more!

So while all of that was going on, Travis – a long-time Senior Analyst-turned-coder – had an idea. “What if,” he said to me one day, “we do a test to see if putting samples in a Tyvek envelope helps with the return postage time?” Because although oil spills aren’t a significant problem, it does seem to be a problem that the mailer is 1) small, and 2) clearly headed for a laboratory. Putting the oil into a Tyvek envelope might solve both issues. So we started a test – for one month, we sent all outgoing kits with a labeled Tyvek envelope for returning the sample to Blackstone.

The results were immediate and striking: this was a winner. We didn’t even run the test for the full month. The data Travis put together showed that return times were cut in HALF (from an average of 8.74 to 3.48 days) when samples came back to us in the Tyvek envelope. (See the sidebar.) We stopped the test and immediately started including Tyvek envelopes with each kit order, for return samples.

USPS supporters

Despite the problems, we are proud supporters of the United States Postal Service. No other carrier offers service to every single part of the US, no matter how remote. Lots of people don’t have access to UPS or FedEx, though if you want to use them to send in your samples, that’s absolutely fine.

The changes we’ve made to our label and the return package are already paying off in getting samples to us in a timely fashion. If you need new return envelopes and labels for your kits, let us know – we’re happy to send them out!

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Update! The Post office has discontinued their First Class Return labels (my new mantra: change is good…change is good). We are now using Ground Advantage labels. All the same things in this article still apply. You can use the First Class return labels, but your sample will arrive faster with a Ground Advantage label. You can print one off right here.

By Kristin Huff|2024-09-19T10:15:59-04:00July 19, 2023|Aircraft, Articles, Gas/Diesel Engine, Industrial, Marine|Comments Off

Protecting from Corrosion

Considering the relative inactivity of much of the general aviation fleet, it’s not surprising that corrosion is a hot topic. It’s also fodder for aviation oil makers to claim their oil is better than others at protecting engine parts from corrosion.

The frustrating thing when you can’t find the time to go flying is, your beautiful bird is languishing alone in a dark hangar accumulating rust on its parts and dust and bird doo on its wings. What to do?

If you can’t fly it, you don’t want to just ground-run the engine since it’s pretty well accepted that doing so may cause more harm than good. In the end, the path most often chosen is to “leave her sit.” But that’s the maddening part. You just know that corrosion has begun at the cylinders, cam, and lifters, as well as all the other parts that are parked above the engine’s oil level. “Dammit! Maybe I should go out and shoot some landings.” But you don’t. So the question still stands…what to do?

We get a lot of questions about which oil protects aircraft engines best from corrosion. If there were a sure answer as to which oil is best, someone would surely have come up with it. Since they haven’t, perhaps we should reconsider the question. Maybe what we should be asking is, “What can I do to prevent corrosion in my (not flown frequently enough) aircraft engine, regardless of the oil I use?”

Turned around that way, there may be an answer.

Water orbs

Oil and water don’t mix at the atomic level. Since there is no such thing as dry oil — both hot and cold oil suck moisture from the air like a sponge — the only way these dissimilar types of matter can coexist is for the moisture to ball itself up into minute spheres, so tiny that they can exist in suspension. If the water orbs get large enough they will precipitate, that is, fall out of suspension. But there is almost no limit to how tiny they can be. The longer the oil sits undisturbed, the more water it will accumulate.

Oil routinely has some moisture in it, usually at levels between 40–400 ppm. In amounts greater than that, it can start to make your oil look like chicken gravy. Once moisture sets in, heat and/or pressure are the only way to get it out. If you go out and fly for an hour, the oil temperature and agitation will dismiss the moisture droplets like unruly elementary students. The moisture accumulation process will start all over again once you pull idle cut-off, but at least you have the satisfaction of knowing that, at least for now, the fine film of oil clinging to the metal parts is not heavily populated with tiny balls of water.

Fighting corrosion

After you lock the hangar door, the dry (well, reasonably so) oil film doesn’t last long on all those parts that are parked about the oil level. If your engine is a dry-sump type, none of the parts are parked in an oil bath.

If you can’t fly, you might consider using a pre-oiler once a week to rebathe all the parts in oil. The oil from the pre-oiler will reach all parts that see oil pressure during engine operation. It would require only turning on the master and the oiler switch for a short while, no longer than it takes to check the lights and flaps during a preflight, a few minutes at most. The oil should reach all the way up into the rocker boxes and then drain to form a brief pool over the tappets and cam, parts that are notoriously prone to corrosion pitting in all but the most active engines.

After the pre-oiling dose, you could get out and pull the prop through a few blades (normal direction of rotation, of course) to ensure all moving parts rotate through a couple of full cycles. Further, you will be giving all the rod bearings an oily trip through the sump reservoir, for wet sump engines. (Some people are queasy about touching the prop, so running the starter is an acceptable alternative, if you have confidence in the integrity of the battery.)

Cold dousing all oil-wetted parts isn’t nearly as good as an hour’s flight, but it seems far superior to the ground run-up, or the more often chosen “letting her sit.”

By Jim Stark|2024-09-18T13:48:37-04:00July 18, 2023|Aircraft, Articles|Comments Off

Pre-Ignition and Detonation

The information (and harrowing pictures!) that follows is reprinted courtesy of the FAA.

Pre-ignition. Detonation. Both can be deadly. But what’s the difference? And how can you avoid them?

This engine is from a Beech S35 Bonanza’s fatal accident. The #6 piston was eroded and began to melt. The rings and piston skirt were compromised by thermal expansion and metal transfer. Note the deep pitting and erosion of the piston face. This caused combustion gases to bleed into and over-pressurized the crankcase, forcing engine oil out the breather. The connecting rods then failed due to the lack of lubrication and smashed holes in the crank case, causing loss of power and engine failure.

Normal combustion vs. pre-ignition

Normal combustion is an orderly, progressive burning of the fuel-air mixture in the cylinders. The gasses within the cylinders are ignited from the top. The flame then travels down in an organized way. This combustive force, equally applied to the piston in a stable manner, pushes the piston down. The downward motion of the piston is then mechanically transferred to the propeller. This makes pilots very happy.

In a pre-ignition event, combustion is abnormal. It happens when the air-fuel mix ignites before the spark plug fires, while the piston is still moving up in the compression cycle. The ignition can be caused by a cracked spark plug tip, carbon or lead deposits in the combustion chamber, a burned exhaust valve, an ignition system fault, or anything that can act as a glow plug to ignite the charge prematurely.

When this happens the engine works against itself. The piston compresses and at the same time the hot gas expands. This puts tremendous mechanical stress on the engine and transfers a great deal of heat into the aluminum piston face damaging the piston. Engine failure can happen in minutes.

Detonation

As the name suggests, detonation is an explosion of the fuel-air mixture inside the cylinder. It occurs after the compression stroke near or after top dead center. During detonation, the fuel/air charge (or pockets within the charge) explodes rather than burning smoothly. Because of this explosion, the charge exerts a much higher force on the piston and cylinder, leading to increased noise, vibration, and excessive cylinder head temperatures.

The violence of detonation also causes a reduction in power. Mild detonation may increase engine wear, though some engines can operate with mild detonation. However, severe detonation can cause engine failure in minutes. Because of the noise that it makes, detonation is called “engine knock” or “pinging” in cars.

High heat is detrimental to piston engine operation. Its cumulative effects can lead to piston, ring, and cylinder head failure and place thermal stress on other operating components. Excessive cylinder head temperatures can lead to detonation, which in turn can cause catastrophic engine failure. Turbocharged engines are especially heat sensitive.

Some causes of detonation include:

improper ignition timing
high inlet air temperature
engine overheating
oil in the combustion chamber
carbon build-up in the combustion chamber

A combination of high manifold pressure and low rpm creates a very high engine load, which can also cause detonation. In order to avoid these situations:

When increasing power, increase the rpm first and then the manifold pressure
When decreasing power, decrease the manifold pressure first and then decrease the rpm

Pre-ignition and detonation results

The explosion of pre-ignition and detonation is like hitting the piston with a sledge hammer. The automotive term for the sound it makes is “ping” (something pilots cannot hear in aircraft). The ping sound is the entire engine resonating at 6400 hertz. It sounds like a ping, but it is an explosion with enough power to make the engine resound like a gong.

Both pre-ignition and detonation put tremendous mechanical stress on the engine and transfer a great deal of heat into the piston deck. This can cause the piston to melt (EGT is 1600 degrees; aluminum pistons melt at 1200 degrees). The force of these explosions can knock holes in pistons, bend connecting rods, overcome the lubrication film in the rod bearings, and hammer the babbitt out of rod bearings. Engine failure can happen in minutes.

The bent connecting rod at the start of the article is a good example of the damage pre-ignition and detonation can do.

These cylinder #2 spark plugs are packed with melted piston material.

Here’s what happens

This is a cylinder head showing signs of pre-ignition or detonation.

The carbon coating that normally lines the head dome is knocked off. There is melted piston material in the head and the cylinder sleeve is scored by the overheated piston.

This is the same piston , but note that the piston deck is eroded.

The rings are broken. The piston skirt is scuffed from rubbing on the cylinder wall. A piston in this condition allows combustion gases into the crank case. This over-pressurizes the crankcase and blows engine oil out of the crank case breather — all of the engine oil, in minutes.

Soon after the engine oil departs the connecting rods try to make a break for it, resulting in giant holes in the crank case.

How do I detect pre-ignition?

A rough-running engine can be the first sign of pre-ignition or detonation. High EGTs or CHTs can be a sign of a problem so be sure to keep an eye on that if you can.

Below are common indications of detonation. You should have increasing oil temperature, not pressure. The top left gauge is RPM. The top right is manifold pressure.

What do I do when it happens?

Since excessive heat can be so damaging, your main priority is to cool the engine:

Reduce power
Increase airspeed
Enrich the fuel mix
Open the cowl flaps.
Land immediately!

Preventing Pre-ignition

Do not take off unless the run-up is perfect
Maintain the ignition system
Pay attention to cylinder compression tests
Use the proper heat range spark plugs
Make sure cooling baffles are in good repair

Preventing Detonation

Lean the engine per the flight manual
Keep engine load to a minimum
Do not over boost
Use only the recommended fuel grade
Make sure engine timing is properly set
Make sure cooling baffles are in good repair
Be wary on hot, dry days
If in doubt, run rich

By Kristin Huff|2024-09-18T13:48:58-04:00July 18, 2023|Aircraft, Articles|Comments Off

Aircraft Problems: Should I Be Worried?

One of the main purposes of oil analysis it to find problems that might be developing in an engine, and after doing this for a lot of years, I can say without a doubt that it works. However, some problems are more urgent than others, and part of our job is to determine if a problem is a major one or not. Most engine problems start out minor but if left unchecked can lead to major issues, which eventually result in an engine’s demise.

Minor problems

Abrasive Contamination

Dirt getting past the air filter will cause a lot of problems in an engine, and piston scuffing is the primary concern. Fortunately, most air filters do a really good job even when they are dirty. If you change your air filter on a regular basis, then this type of problem is pretty easy to avoid, but remember, it’s also important to check the whole air induction system down-stream of the air filter to make sure no cracks or other problems exist that could be letting dirt in.

Fuel dilution

This generally includes any fuel level between 1.0% and 3.0% that keeps showing up again and again. This is not a normal situation, but it doesn’t necessarily cause an engine problems in the short term. Still, since fuel is a contaminant, it will cause the oil to oxidize faster that it normally would. That typically causes problems like stuck oil control rings, which leads us to our next minor issue.

Oil Consumption

This one isn’t really a problem at low levels because all engines are designed to use some oil. What you really want to watch out for is a change in how much oil is being burned. If you always use 1 quart every 10 hours and it suddenly jumps to 1 quart every 3 hours, then you know something has changed. That’s part of the reason we ask about oil added between changes. If you’re not losing oil due to a leak, it’s either getting past the rings or the valve guides. Granted, you can buy a lot of make-up oil for the cost of a top overhaul, but there will probably come a time you’ll have to bite the bullet and fix the issue.

Corrosion

If you fly around 5 hours per month, that should keep this minor problem off you mind, though we all know that life doesn’t necessarily allow this. Still, if corrosion is minor it should easily disappear once the engine is back to flying regularly. If corrosion gets so bad that it causes pitting on the parts, that’s when the problem elevates to major status.

Major problems

Cam spalling

This one is often directly related to corrosion getting out of hand, though it can also be related to oil starvation on things like cold starts and high RMP starts. It takes time for that thick oil to get circulating through the engine and if it doesn’t get to the cam and followers fast enough, metal-to-metal contact happens. Problems of this nature won’t necessarily cause an engine to fail, but can lead to loss of some power, which might be needed to clear that 50’ obstacle at the end of the runway.

Excess Heat

This is really a pretty broad category and is often due to operational factors, though it’s almost always avoidable if you are paying attention to your cylinder head temperatures. If those are getting too hot, then maybe the cooling baffles aren’t quite working like they should. Maybe you have a crack in an air induction tube. That could allow abrasive dirt into the combustion chamber, but would also cause that one cylinder to run leaner than others (due to extra air being sucked in) and likely hotter. Excess heat causes the parts to expand more than they were designed for and that’s when wear starts getting heavy.

Stuck or Burned Valves

Abrasive contamination, fuel dilution, and oil consumption will all contribute to this type of problem. Sticking valves can be identified by things like morning sickness (not necessarily in the morning), intermittent rough running, and high mag drops (not due to a fouled spark plug). Burned valves are usually pretty easy to spot with a borescope though might not necessarily cause major operational problems until they burn to a point where compression has significantly degraded.

Detonation

This issue develops in an engine when the combustion process is not completed correctly, usually when an engine is under a heavy load and producing a lot of heat. It can easily burn a hole right through the top of a piston, resulting in all of the oil in your engine being pushed out the breather tube and oil starvation (see below). If your engine had a good muffler, you would hear a ticking or pinging noise, but since those don’t exist in general aviation, this problem can often go unnoticed without the help of oil analysis and/or engine monitor data. If this problem exists, running a richer fuel/air mixture to keep the engine cooler should help.

Instant failure

Oil starvation

Whether it’s caused by oil consumption left unchecked or severely worn bearings not letting oil get to all of the parts, this type of problem will cause an engine to fail in short order and it’s usually accompanied by the worst sound your engine can make — silence.

Spun bearings

When the babbit is worn off your bearings, either due to hard use, abrasive oil, or lack of oil, you will start to lose oil pressure. If the problem gets severe enough, the spinning shaft will actually weld to the bearing itself and spin in place. Once this happens, the engine is pretty much shot, though amazingly enough it might still run (but not for long).

Outside causes

Of course there are lots of other things that can cause instant engine death — see the first cartoon on this link for an example, or, although it’s not a plane, this picture of my flooded MINI. Unfortunately, outside factors probably take more engines down than anything else.

It’s pretty rare for engines to fail suddenly due to minor issues, so when we see something going on, that doesn’t necessarily mean you need to get out the wrenches or head straight to the engine builder and demand a repair. Usually, you’ll have some time to see if the problem persists or is getting worse. Once that has been established, then some action will likely be required to keep the engine going, but the cost should be minor compared to the hassle and expense of having to replace the whole engine. So test your oil every now and then. Chances are good your engine will look perfect, but if it doesn’t, you’re better off knowing about it sooner rather than later.

By Ryan Stark|2024-09-18T13:49:41-04:00July 18, 2023|Aircraft, Articles|Comments Off

Sudden Landing? Remember TWIT

Aviation is fraught with acronyms. There are so many acronyms that it is humorous to think the government still thinks they are a memory solution instead of the problem. I hate to add one more, but TWIT is one that may cause an unfortunate event in your life to turn out to be a good story instead of a tragedy. It is the word to remember should your (single) aircraft engine quit. You know, when the heat pump stops heating, when the cooling fan stops cooling, and/or when the roar of the engine that has always been your security blanket leaves nothing but silence ringing in your ears, uncovering your naked fear.

More than twenty years ago I was viewing the remains of an upside-down C-150 in a bean field with a couple guys from the Sheriff’s Department, when a civilian turned up. He was a lanky guy in a black suit with a camera slung across his shoulder. He asked me if I was the party that had left the airplane in this condition, and I admitted that I was the culprit. He said he was not only the undertaker in Paris, Illinois, but the newspaper photographer too, and when he gets a call like the one he got this morning, he didn’t know if he’d be taking pictures or measuring the body. With a grin, he pulled out a tape measure. “Looks like its only pictures this morning,” he said.

The saving grace of TWIT

I’ve had a long time to think about that and decided your early “engine out” training, as good and thorough as it may have been, could be improved upon with TWIT. Any engine out practice is good because if and when it really happens, you don’t need the tension of suffering the sensation for the first time. Few of us do first-time experiences well. So it is nice when you find yourself gliding around up there, sans engine, to have done it a few times before.

Everyone knows the first thing to do, which is to trim best glide speed. Don’t know it? Well, anything in the vicinity is okay. The idea, of course, is to give you the most time aloft for the altitude you are carrying. The reason that is important is that some prayers take far longer than others to complete. And if you happen to be one of those people who feels the need to pray with your eyes closed, well, you don’t want to waste all the glide time left with your eyes closed. It is a good idea to take a look at the terrain.

Trim

So the first letter to TWIT is for Trim, which hopefully gets you somewhere in the neighborhood of best glide. Your airspeed will be about 65–75, depending on the airplane. Our father…

Your flight instructor thought the next important thing to do was find a field to land in. With all due respect, that may not be the best idea. If you can hit a particular field from 5,000’ you are a better pilot than I am. You may pick the best field in your range of vision, but actually being able to hit it from altitude takes a lot of practice that we don’t generally work on. (Well…maybe the astronauts.)

My experience is, you will pick a field, and then see a better one as you get lower, and then a better one when you get lower than that. What makes it good is your ability to land on it, not its humongous size. It only takes a few hundred feet to land an airplane and you will find most fields at least that long. It is far more important to be landing into the wind so that length of field works. It is also nice to land without hitting anything. It is cheaper to buy a quarter acre of corn from a farmer than have to pay for his custom and recently rebuilt outhouse, which his insurance company will value in the tens of thousands of dollars.

Wind

So the second letter of TWIT is Wind. The first of the two turns you are going to make is the turn to base. You need to be adjacent to the wind. You probably know the wind direction, at least generally. If it is, for example, south, then turn east or west. If it is west, turn north or south. Which direction you turn will be decided on which direction has the best fields and the least structures. You don’t need much of a field, but when it comes to choosing one, the more options you have, the merrier.

If you are headed for a town or city, use some of that glide time to make a 180. A long walk out is better than hitting an unmovable object. Hopefully this is going to be the longest base leg you have ever flown. It will give you time to check your drift and verify the wind direction and speed. You might even stumble across a landing strip, if your GPS hasn’t already found one for you. If the wind is left, you are on a left base. If the wind is right, you are on a right base.

Initiate

You don’t pick your field until you see one that fits your sight picture for turning final. Few of us could hit a field from 5,000 feet, but all of us can hit the runway when turning final (well, almost all of us). If you are on left base, you are looking for the field on your left. If you are on right base, you are looking right. When the sight picture is what you are used to seeing, make your turn to Initiate the landing, which is the third letter to TWIT. It is time to get your flaps and wheels down if the wheels are retracted. (Shame on you if you did either of these things on that long base leg glide you were on.)

Talk

No second guessing at this point. It is time to congratulate yourself on getting from way up there to way down here without having done anything foolish, and you can already hear yourself telling a story about your successful off-field landing. Now that you are kicked back and gliding to final, it is a good time to call ATC, FSS, or perhaps your Maker, and let them know where they may find you, while you still have a little altitude left. You may have already done this earlier when you tuned your transponder to the emergency code, but it wouldn’t hurt to call in again, just to prove you can still talk without stuttering. I can speak here from experience — the last thing on your mind when your engine quits will be the radio. That’s why TWIT ends in Talk. You may be comfortable enough, or have enough presence of mind, to actually talk with someone other than yourself, once you have the field made.

Next time your engine gives up the ghost and you have already run through all the nasty words you can think of, try yelling TWIT to yourself. It may help you get down to terra firma safely.

By Jim Stark|2024-09-18T13:59:14-04:00July 18, 2023|Aircraft, Articles|Comments Off

EGT Myths Debunked

Reprinted with permission from the author, Mike Busch

Pilots still seem to have a lot of misconceptions about exhaust gas temperature (EGT). Let’s see if we can clear some of them up.

These days, pilots of piston-powered aircraft seem to have fixated upon EGT. Scarcely a day goes by that I don’t receive a phone call, email, or support ticket asking some EGT-related question.

Pilots will send me a list of EGT readings for each of their cylinders and ask me if think they look okay, whether I think their EGTs are too high, what maximum EGT limit I recommend, why their EGTs seem to be higher in the winter than in the summer, or why the EGTs on their 1972 Cessna 182 are so much higher than the ones on their friend’s 1977 model. They’ll voice concern that the individual cylinders on their engine have such diverse EGT readings, worry that the spread between the highest and lowest EGT is excessive, and ask for advice on how to bring them closer together. They’ll complain that they are unable to transition from rich-of-peak (ROP) to lean-of-peak (LOP) operation without producing EGTs that are unacceptably high.

Each of these questions reveals a fundamental misunderstanding of what EGT measures, what it means, and how it is interpreted. Let me attempt to clear up some of this confusion by asking you to forget everything you thought you knew about EGT and start at the beginning.

What EGT is not

The absolute values of EGT are not particularly interesting for a number of reasons. The most important is that indicated EGT is not a “real” temperature. To understand what I mean by this, I’d like you to conduct a thought experiment: Imagine that you’re an EGT probe, located in an exhaust riser between two and four inches from the exhaust port of a cylinders, and think about what you would see.

You’d see nothing much for two-thirds of the time¾during most of the intake, compression, and power strokes, because the exhaust valve is closed and so no exhaust gas is flowing out of the exhaust port and past the probe. During the one-third of the time that the exhaust valve is open, you’d see a constantly changing gas temperature that starts out very hot when the valve first opens but cools very rapidly as the hot compressed gas escapes and expands, and then ultimately is scavenged by cold induction air during the valve overlap period (at the end of the exhaust stroke and the beginning of the intake stroke) when both intake and exhaust valves are open simultaneously.

Now, all these gyrations are happening about 20 times per second, and you (the EGT probe) cannot possibly keep up with them. You wind up stabilizing at some temperature between the hottest and coolest gas temperature you see, and you dutifully report this rather arbitrary temperature to the panel-mounted instrument, where it is displayed to the pilot as a digital value accurate to one degree. The temperature you report to the pilot is not exhaust gas temperature (which is gyrating crazily 20 times a second) but rather exhaust probe temperature (which is stable but related to actual exhaust gas temperature in roughly the same fashion as mean sea level is to high tide).

To make matters worse, numerous factors can affect indicated EGT besides actual exhaust gas temperature. These include probe mass and construction (grounded or ungrounded), cam lobe profile, lifter leak-down rate, valve spring condition, and exhaust manifold topology, among others.

For example, the two front cylinders (numbers 5 and 6) on the left engine of my Cessna T310R always indicate lower EGTs than the other four cylinders. The exact same phenomenon also occurs on the right engine. This is not because those front cylinders produce cooler exhaust gas than their neighbors (they don’t), but because the exhaust risers for those cylinders curve aft while the other four risers go straight down. Thus, the gas flow past the EGT probe is different for the front cylinders than for the others, and their indicated EGT is lower. This temperature anomaly is quite obvious on my digital engine monitor¾and also quite meaningless.

What EGT means

Even if indicated EGT accurately reported actual exhaust gas temperature (which it doesn’t), it’s important to understand that exhaust gas temperature does not correlate with stress on the engine the way cylinder head temperature does. In fact, many things that increase engine stress (such as advanced ignition timing and high compression ratio) cause EGT to go down, while things that reduce engine stress (like retarded ignition timing and low compression ratio) cause EGT to go up.

Remember that CHT mainly reflects what’s going on in the cylinders during the power stroke when the cylinder is under maximum stress from high internal temperatures and pressures, while EGT mainly reflects what’s going on during the exhaust stroke after the exhaust valve opens and the cylinder is under relatively low stress.

High CHTs often indicate that the engine is under excessive stress, which is why it’s so important to limit CHTs to a tolerable value (no more than 400°, preferably 380° or less). By contrast, high EGTs do not indicate that the engine is under excessive stress, but simply that a lot of energy from the fuel is being wasted out the exhaust pipe rather than being extracted in the form of mechanical energy.

For instance, a 1972 Cessna 182 with an O-470-R engine will typically have indicated EGTs that are 100 degrees hotter than those seen in a 1977 Cessna 812 with an O-470-U engine. The -R has a relatively low 7.0–1 compression ratio because it was certificated for 80-octane avgas, while the -U engine has a much higher 8.6–1 compression ratio because it was certificated for 100-octane. Because the high-compression -U engine is significantly more efficient at extracting heat energy from the fuel, it wastes less energy out the exhaust and this its EGTs are cooler (despite the fact that the -U engine is much more highly stressed than the -R).

High EGTs do not represent a threat to cylinder longevity the way high CHTs do. Therefore, limiting EGTs in an attempt to be “kind to the engine” is simply misguided.

Diff versus Gami spread

Right behind the “high EGTs are bad” myth is the “identical EGTs are good” myth. Many pilots believe incorrectly that a flat-topped graphic engine monitor display (with all EGTs equal) is the mark of a well-balanced engine, and that unequal EGTs are a sign that something is wrong. This common misconception tends to be reinforced by digital engine monitors that display a digital “DIFF” showing the difference between the highest and lowest EGT indication.

As illustrated by the earlier anecdote about the front cylinders on my Cessna 310R, difference between absolute EGT values are both normal and benign. It is not uncommon for well-balanced fuel-injected engines to exhibit EGT spreads of 100 degrees, and carbureted engines often have spreads of 150 degrees or more. In fact, as shown in Figure 4, EGT spreads are usually smallest near or just rich of peak EGT (the worst place to operate the engine), and often significantly greater at leaner or richer mixture (that are much kinder to the engine.

The mark of a well-balanced engine is not a small EGT spread (“DIFF”), but rather a small “GAMI spread”– defined as the difference in fuel flows at which the various cylinders reach peak EGT. Ideally, we would like to see this peak be no more than about 0.5 gph (or 3 pph). Experience shows that if the GAMI spread is much more than that, the engine is unlikely to run smoothly with LOP mixtures.

It’s all relative

The only important thing about EGT is its relative value: how far below peak EGT and in which direction (e.g., 100 degrees ROP or 50 degrees LOP). Absolute values of EGT (e.g., 1,475 degrees) are simply not meaningful and are best ignored. There is no such thing as a maximum EGT limit or redline, and trying to keep absolute EGTs below some particular value¾or even worse, leaning to a particular absolute EGT value¾is simply wrongheaded. Don’t do it. If you must fixate on those digital engine monitor readouts, fixate on something important, like CHT.

By Mike Busch|2024-09-18T14:00:14-04:00July 18, 2023|Aircraft, Articles|Comments Off