Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater

Sun, 14 Aug 2016

Building a Biplane: Picking the Engine

In the previous entry, I discussed the considerations that went into choosing a biplane model to build. In this one, the next most important consideration: what engine to use?

There are a huge variety of engines that can be used in this class of aircraft, from a glorified chainsaw motor through a gigantic WWII era radial that produces hundreds of horsepower and swings a 9 foot prop. A list of candidates might look like this, in no particular order:

Some of these engines are off the table from the get-go. The automotive conversions, though some have been successfully flown, are generally regarded as "very experimental" and not suitable for a first project if there's any way you can afford a dedicated aircraft engine. The Warner, although a wonderful, well-proven design, has been out of production for decades, and the parts supply is finite and shrinking.

This leaves the certified Lycoming, and "everything else:" the Rotec, the Verner, and the LOM. I'll discuss the everything else category first.

The Rotec R-3600 is the most viable of these engines. It is gorgeously made, and there are a relatively large number of them flying. The Hatz Classic powered by a Rotec is a huge inspiration to me, and their installation has been very successful from what I can tell. Hatz even includes an option for the Rotec in their plans.

The engine itself seems to be well received, but it has a large number of strikes against it. The first one is that it's hideously expensive: I could install a brand new 160 HP Lycoming O-320 for less (not a lot less, but less). The Lycoming doesn't inspire the same reverential vintage feeling, but it has many other positives going for it, which I describe later.

The next issue is that, at some point, it's going to break. Everything breaks, and that's fine, it's part of life. However, when this engine breaks, spare parts are half a world away: the Rotec is made in Australia, and there are no parts suppliers in the US, that I'm aware of. Regardless of how good their support is, it's still a minimum of many days' shipping away, which could potentially leave me stranded somewhere for several weeks between shipping waits (assuming the part is in stock) and finding a mechanic who's willing to work on such an uncommon engine (or who will lend me their tools to work on it myself).

The final big issue is another "it's so uncommon" problem: I'd have to engineer the installation myself. With a more common engine, there are many resources from which I can draw for help with the firewall-forward installation. I'd have to figure out the engine mount, the fuel system, the electrical system, the exhaust system, the cowling, and whether the combination is viable from a cooling standpoint once it's all cobbled together. To be honest, that sounds like both blessing and curse -- I would greatly enjoy solving all those problems, but they would potentially also add years to the build, and I'm already looking at a decade of build time.

The Verner Scarlett 7Si has an advantage that the Rotec R-3600 doesn't have: it's made by a company that has been designing engines for a long time. The Rotec is made by a pair of Australian brothers who decided, with no real engine design experience, to build an engine in the late 1990s, and have made a good success out of it. The Verner factory had been making aircraft engines for decades by the time the Chernikeiff brothers cast their first piston. The Scarlett shows it, too, with design choices that are perhaps less beautiful looking, but more practical, such as the oil filter mounted on the front of the engine, where it's as simple as possible to service, or the direct drive crankshaft instead of using a reduction gear system.

However, the Scarlett 7Si model was just introduced. As in, last year. It is, as far as I can tell, completely unproven. By the time I get to where I have to make a choice on the engine, it may be viable, but right now it's a huge question mark.

The Scarlett also suffers from all the same problems as the Rotec: I will have to engineer the whole installation; parts only come from the Czech Republic; price is unknown, but likely to be high, at least as much as installing a professionally rebuilt Lycoming.

Couldn't find a bigger picture, sorry

The LOM 332A/AK/C is an interesting engine. The Bücker Jungmann, upon which the Marquart Charger is based, used an inline engine like the LOM. It would be thematically very appropriate. The inline configuration also means a smaller frontal area, which means lower drag, always a good thing. (The radial engines, on the other hand, have the highest drag of all the choices.) The LOM engine also seems to be highly regarded among those who have access to it.

However, from what I can tell, people in the US aren't in that group. It appears to be somewhere between problematic and impossible to get a LOM engine here. It may be that I haven't asked the right questions (and I haven't gotten on the phone with anyone yet, which is sometimes required in the airplane world -- not everyone has a website).

Thus the LOM suffers from the same problems as the other unusual engines (engineering challenge, parts availability, maybe cost, but who knows), plus they're difficult to acquire. This presumably also extends to part availability, making it even worse than the others. The LOM is probably not a practical choice.

Which leaves us, conveniently, with the Lycoming O-320. There are about a zillion different versions, but it boils down to the fact that they make between 150 and 160 HP. They have been installed in about a zillion different Pipers, Cessnas, Beeches, and the majority of the other small planes in the world.

The list of positives is long, longer than the negatives of the other types: parts are available everywhere; every mechanic at every airport in the US knows how to work on them; used engines can be bought for less than $5000 and rebuilt for less than $10,000 (assuming I do the work, which I am eager to do); millions of flight hours have proven them to be very reliable and problems are well-known where they exist; the installation instructions are right there in the plans; I can choose to rebuild myself, have a core rebuilt, buy overhauled, or buy new depending on how well I've saved my pennies; cowling parts (such as the nosebowl) are readily available.

The downside of the Lycomings is primarily that they're a very, very old design: the first boxer engines of this type were flying before (probably well before) WWII, and the first O-320 was certified in 1953. Compared to modern engines such as you might find in your car, Lycomings are heavy and inefficient, with little scope for improvement. However, they're also a well and truly proven design for light planes, which is something that basically no other engine design can offer.

A brand new O-320 costs between $30,000 and $50,000 depending on where you look. An overhauled one is in the low $20,000 range. A used one, as mentioned earlier, can be as low as $5000, or as high as you can be suckered into. It's not unusual to see run-out but rebuildable engines on Ebay for under $4000.

Critically for me, the engineering to install a Lycoming in a Marquart Charger has largely already been done. There's still a huge domain of problems that will have to be solved, but the big, oops-my-engine-just-departed-the-plane engineering is already done, and done well.

Ultimately, it's this combination of factors that inclines me toward using the boring old Lycoming for my build. I would love to mount a shiny Rotec on the front of my plane, or figure out how to get the sleek LOM faired in, but I think the advice of my biplane elders is best: stick with the plans, young man. I'll leave my crazy plans for plane #2, should that ever come about.

Still... I wouldn't be entirely surprised to read this entry over in about 5 years, and wonder what the hell I was thinking, with my blingful Rotec freshly unpacked from its crate.

Posted at 22:49 permanent link category: /charger

Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater