Paul's Down-Home Page

Good news for this update, or at least some of it is. I found a serviceable crankshaft and it has been shipped to the engine shop. With any luck the engine build will start going full throttle next week.

The treasure hunt

In my last update, I’d mentioned that the left engine crankshaft was unserviceable, and that I’d have to find a new one. Before that post, I had already called a dozen or so places that I thought might have one, but I struck out. On a whim that afternoon, I decided to call one of the engine shops that I did not use for the overhaul. They have a good reputation for stocking a lot of various parts and I thought maybe I would get lucky and find that they had one on the shelf. The next morning, and mind you this was a Saturday, I got an email from them. They had a factory-new crankshaft! I was happy.

The following Monday while I was at lunch I got a phone call from that shop. It turns out that the box was marked as containing an IO-470-L crankshaft. When they opened it, it turned out that it actually contained an IO-470-D crankshaft. This may seem like a small difference but in terms of mechanical compatibility it is huge. I went from being elated to have solved my crankshaft problem to being depressed that my last attempt had struck out and I resigned myself to having to wait a few more months to find one on the shelf.

The next morning I saw a post from someone on BeechTalk looking for a pilot to fly a pressurized Baron 58 for a maintenance check flight. I couldn’t do it, but I sent the poster a private message to suggest someone who might be able to help. We struck up a conversation and he ended up referring me to Nagle Aircraft, a maintenance shop in Massachusetts that I had never heard of. I called and spoke to Joe Nagel and he could not have been more helpful. He referred me to a gentleman named Tim Hess who runs the engine shop at the same airport. Tim was equally helpful and said, “I don’t have any, but here are a list of three people who might.” I struck gold on the second of those three, a small parts shop called ENParts in Lancaster, Texas, run by a lady named Eileen McGough.

The funny part was that if I had done a little more research I probably would have run across ENParts sooner because they are a well-known reseller of pieces and parts for situations like this. They have a primitive website, but other better-known websites like CSOBeech mention them. So the lesson I learned was that being more diligent about researching parts suppliers might have saved me some unnecessary angst. After a few back and forth phone calls, we established that the crankshaft Eileen had would be usable, but that would require new connecting rods for the upgraded pistons that I am installing. That matter was all settled relatively quickly, and the crankshaft is now on its way to its new home in my left engine.

During this process, I got a note from the shop that pointed out another opportunity to spend money something that needed to be considered while the plane was down for the overhauls.

Baffles

If you know how car engines work, then you know they are typically cooled by water or coolant that circulates through a radiator. Air passing over the radiator cools the fluid, which is then pumped through channels in the engine assembly to keep it cool. Very few airplane piston engines are liquid cooled. Instead, they tend to be air cooled, but not with the same forced air mechanism that cars use. Drag increases with the square of the surface area, so if you make a big enough opening to force air in, you’re going to multiply the amount of drag disproportionate.

Instead, most piston engines use what’s known as pressure cooling. Air enters the front of the engine cowling, sure, but a system of baffles and seals blocks the air’s free flow so that a higher-pressure zone is created over the top of the engine. The passage of air over the lower part of the nacelle creates a low-pressure area that draws the hot air out and down. There are baffles between each cylinder, and there are multiple baffles that go between various parts of the engine installation and the cowling. In the image below, the blue stuff is the flexible baffle material that forms an air-tight-ish seal against the cowling; it’s riveted to a support bracket that holds it in place. You can’t see the inter-cylinder baffles well from this angle.

My baffles were installed new when the engines were overhauled in 2004. Some of the rubber materials were cracked, as were some of the attachment brackets. The best time to install new baffling is when the engine is out, because otherwise it’s tough to get the inter-cylinder baffles in place properly.

The supply chain rears its ugly head again

As it turns out there are basically two places to get baffles for a Baron 55.

One is from a company called McFarlane that has what the FAA refers to as “parts manufacturing authority,” or PMA. PMA means that you have their permission to produce parts that are functionally identical to what came from the original manufacturer. They don’t necessarily have to be made using the same process or out of the same materials, but they have to work the same way and meet the same standards for durability and so on. The other is from a company named D’Shannon Aviation, which makes a variety of really nifty upgrades for various Beechcraft airplanes. I have a D’Shannon windshield, vent window, and vortex generators and have been very pleased with them. Their modifications are made available through a different mechanism known as a supplemental type certificate, or STC. Why it’s called that, and what it means, are topics best left for another post.

There should be no functional difference between the two and McFarlane’s parts were about 20% cheaper than the ones from D’Shannon. That might make it seem obvious which one I should choose. As it turns out though, McFarland has a minimum 60 day lead time whereas D’Shannon has baffles sitting on the shelf ready to ship. made the decision dramatically easier. Scott and Heather, the owners, were incredibly quick and helpful in processing my order, with the bonus that they were able to break the kit into two subassemblies; the parts that go on the engine are going to the engine shop, and the parts that go on the airframe are headed to New Smyrna Beach to be installed. The screenshot below from D’Shannon’s baffle kit documentation shows all of the pieces and their relative locations (although note that mine are blue and not red!)

…and now, back to waiting

I’d budgeted for the possibility that I would need one new crankshaft. I didn’t budget specifically for the baffles, but I did keep some contingency money aside in case something like this happened. From a budget standpoint I am not too badly off. From a time standpoint the delay in getting a crankshaft added a couple more weeks to the schedule. But at this point it’s hard to act like that matters too much given how long this is already taken. I am hopeful now that all of the parts are in the correct places. That the engine build itself will go smoothly…but I am mentally preparing myself for some other kind of unexpected delay at some point. We shall see.

Since my last update, essentially nothing has happened.

Poplar Grove has disassembled the engines and done preliminary checks on the parts that will be reused. It looks like the crankshafts are in good enough shape to be reused, which is good, as IO-470-L crankshafts are hard to find right now. The visual and dimensional inspections were OK, but the crankshafts still need to have a “magnetic particle inspection,” colloquially known as a “magnaflux” test. In this test, the tester magnetizes the part using a big ol’ electromagnet and coats the part with iron particles to look for incipient or actual cracks. The shop needs to do that before signing off on the crankshafts, so until that’s done I am not 100% confident that I won’t get stuck waiting for replacement for one or both crankshafts.

As of two weeks ago, the last time I checked, my engines were #19 and #20 in Poplar Grove’s build queue. With luck, they’ll complete the magnaflux tests before the 4th of July and then, assuming they pass, the build can start. Steve tells me that maybe he can shave a couple of weeks off the initial timeline estimate of 25 weeks, which would be nice.

It’s official: I’m pulling both engines on N421BJ. This is not unexpected, but it means I won’t be flying for a while. The timing isn’t great but the great aviation circle of life meant I didn’t really have a lot of choice. The engines I have now were built in 2004 and have accumulated about 2650 flying hours… which is a lot.

Here’s what’s going on.

Crack(s) is whack

During my routine annual inspection, Curtis and the gang at Baker Aviation reported lower compression on a few cylinders than I’d like to see, along with some uneven wear on some valves on the right engine. These things are curable… but do you know what’s not curable? The cracks in the top of the left engine crankcase.

Continental’s Service Bulletin M90-17 lays out the rules: depending on the location and size of the crack, you can either adapt “watchful waiting,” weld the crack, or replace the crankcase. My cracks were in a non-critical area, but one of them was leaking oil (as opposed to seeping it), which basically means the case was done.

Because of the way these engines are built, you can’t do the welding without removing and disassembling the engine, and by the time you get to that point, you may as well rebuild it.

The thing about aircraft engines

I’ve written before about the basics of how aircraft piston engines work (part 1, part 2), and things haven’t changed much since then. Aircraft engines are still complex and expensive for what they do, and there’s no realistic alternative given the way that certification works.

Now, the manufacturer’s “time between overhaul” (TBO) of 1700 hours for these particular engines is a suggestion, not a requirement, if you’re flying under Part 91. My engines have performed flawlessly, a testament to Bill Cunningham at Powermaster. If you closely monitor the engine’s health and condition, you can safely fly well beyond TBO… but not with cracks.

The right engine is also past TBO but running fine, with no cracks found on its case. So the immediate question was: do I fix just the left engine and keep flying, or take the opportunity to address both engines at once?

One lump or two?

It made no sense to even consider just repairing or replacing the case given that the guts of the engine were so old. That left me with the decision of whether to only do the left engine or to bite the bullet and do both at the same time. There are various pros and cons to swapping both engines at the same time.

Doing one engine means lower up-front costs, but it also means that, at any time, the other engine could fail in some expensive and/or dangerous way. That means potentially twice the downtime, with no savings. Doing one engine also means I can’t upgrade the engines.

Doing both engines is more convenient but more expensive. It’s the same amount of initial downtime, but there’s an added risk.

See, in both cases, we have to contend with the fact that aircraft engines exhibit a classic “bathtub curve” failure pattern: the failure rates are highest in the first 100-200 hours, then taper down before increasing again as the engine ages out. Putting in two engines increases the risk of having two failures– not necessarily at the same time, but still within that initial “infant mortality” window. Part of the advantage of a twin, of course, is that having both engines fail at the same time is rare, and I decided the small additional risk within that initial window was outweighed by the increased performance of upgrades.

The Cygnet upgrade

Here’s the twist that changed the whole project. My Baron came with a Cygnet Aerospace IO-470-MOD STC — a supplemental type certificate that allows you to install IO-520 cylinders on an IO-470 crankcase. It’s a well-proven conversion that’s been flying since the 1990s, popular with Baron owners who want more power without a full engine swap. The added displacement adds about 25 horsepower per side, which is nice, but the bigger improvement is in single-engine climb performance and single-engine service ceiling. Since I live in the hot, humid southeastern US, OEI performance on a hot day is pretty important to me.

I’d had the STC sitting in the logs but didn’t originally plan to use it during this overhaul. I wanted to, but if I was only going to replace one it wouldn’t work. After speaking to Chris Szarek at Cygnet, I did some more research and found that the cost premium for the Cygnet conversion runs about 25% total. That’s not nothing. But given that I expect these engines to last the rest of my flying career, and that I wouldn’t feasibly be able to go back and add the upgrade later.

I was waffling, still, until I learned that the left engine case was cracked and would almost certainly need replacement. To install the bigger cylinders, the case must be machined to accept them. The IO-470-L and the IO-520-E have identical internals; the 520-E case is bored for the bigger cylinders, but it’s dimensionally identical otherwise. So the easier route was to get two IO-520-E cases and use those, which also necessitates the 520’s bigger oil pump.

Given that, either way, I’d be buying at leats one new case, the Cygnet conversion looked a lot better, so that’s what I decided to plan on.

Shopping for an overhaul shop

I solicited quotes from five shops and quickly learned that comparing engine overhaul quotes is like comparing cell phone plans — everyone bundles things differently, and the headline number never tells the whole story.

The shops I looked at:

AirPower is the only place you can buy a factory engine, whether rebuilt or new. Straightforward, but at a premium — their factory rebuilt price was roughly 15% more than the most competitive overhaul quote, and factory new was about 30% more. They run a 14-20 week lead time, and you can pay an eye-watering $7500/engine to skip to the front of the line. Not surprisingly this was the highest-total-cost option.

Certified Engines Unlimited (CEU) in Opa-Locka, Florida. Competitive pricing, fast turnaround, and my local A&P at Revolution Flight recommended them based on past experience. The downside: their warranty uses a “phantom usage” calculation that assumes you’re flying 30 hours a month whether you actually are or not. At my flying rate, the warranty calendar would expire well before I hit the hour limit.

Pinnacle Aircraft Engines in Silverhill, Alabama. Solid reputation, the best warranty of the bunch (three years to TBO, transferable, no phantom usage), and new Superior cylinders standard. The catch: Alabama sales tax adds about 9% to the bill, which is a significant hit that erases most of their competitive pricing.

Poplar Grove Airmotive in Poplar Grove, Illinois. This is where things got interesting. Steve Thomas and his team have a strong reputation in the Continental piston community, and critically, Chris from Cygnet referred me to a happy customer. Illinois exempts aircraft engine overhauls from sales tax, which is a meaningful advantage. Their warranty — two years or 500 hours, no phantom usage — is solid.

A couple of other options fell through early. To my regret, Powermaster (my first choice) couldn’t take on the work because of their backlog, and Western Skyways couldn’t either.

Financing

A dual-engine overhaul with the Cygnet conversion is a six-figure project. I’m financing through Dorr Aviation, who specialize in aircraft loans. The structure is a refinance of the existing airframe loan plus the overhaul cost, with the post-upgrade aircraft value supporting the loan-to-value ratio. I got quotes from both Airfleet and Dorr, and Dorr had better rates, a better term, and a better LTV ratio for the loan. I’ve used Airfleet in the past and been happy with them, but I chose Dorr when I bought this plane the first time and again for the refi.

What’s Next

The plan’s in motion: financing and insurance paperwork are done (I need better insurance because the re-engined airplane is worth roughly 2.5x what it was with the geezer engines), Steve has sent shipping crates down to Florida for the old engines, and Curtis’ team at Baker Aviation will start pulling the old engines next week. Meanwhile the new IO-520E cases are headed for rework to move the oil filler necks.

I’ll document the process as it goes — I’ll have plenty of time since I won’t be flying the plane for 4-6 months. Send thoughts and prayers.