haiqu
Well-Known Member
Two cylinder automobile engine seem to be a dying breed. A stalwart of the European car of the 50s and 60s, they now hold such rarity that finding and using one in a homebuilt aircraft could see the builder with an orphaned design. Engines used in the past include the Lloyd LP600, Citroen 2CV, DAF 600/750 and many others.
The greatest problem with these can be summarized as rarity. In most countries finding one is difficult enough, but then microcar collectors will outbid you for them anyhow. Even if you manage to finally get hold of one it will need a full rebuild and spares are scarce.
As an engine solution for a single place minimalist aircraft they are fairly ideal, especially since they are air cooled and light. Unlike a v-twin or inline twin the job of baffling them is avoided, just let the jugs hang out the sides. This also accounts for the popularity of half-VW conversions, but again these engines are now extinct unless you build them from new and expensive after market parts, which means buying everything from the USA. The beetle has been declining since the mid-70s and few were made in the past 30 years.
With the small Rotax engines reaching end of life - the 277, 377, 447 and 503 are now gone, thanks to worn out manufacturing dies - a replacement needs to be found. About 10 years ago I did a survey of what was available with a view to powering a Quickie, which was designed around an 18hp Onan industrial engine that turned out to be quite unreliable, and some would also say under-powered for that application. I eventually focused on the new industrial v-twin engines targeted at the farming market, since they will be available in any country at reasonable prices into the forseeable future.
When you look at Briggs and Stratton, Kohler, Honda, Subaru-Robin and all the Chinese clones with a magnifying glass, only the Subaru comes out as ideal, with Honda and Kohler also being viable alternatives. The remainder have small bearings and tiny journals, limiting their time between overhauls and opening up the possibility of a broken crankshaft. I eventually settled on the 28hp EH72FI fuel injected model, but unfortunately it hadn't yet been released at that time, so I gave up.
These can now be had for US$1,800 or so off the shelf. Not quite Harbour Freight prices, but after all we are talking about flying this thing so a few extra semolians up front is a wise investment. There have been several B&S and Honda conversions done and the work to convert the Subaru should be lower due to the already strong bottom end and fuel injection. They can also be bought with a tapered shaft, which is ideal for aircraft usage.
What other alternatives do we have? Well, for the scale warbird nuts there's a small radial, once Verner eventually releases their Scarlett Mini series. And some brave companies are making miniature Wankel engines, although their prices are astronomical and these start-ups seem to disappear as fast as they arrive. There's one company making little boxer engines from Piaggio motor scooter parts. Some people have tried - and mostly failed - to use the 2A042 6.5hp military surplus engines.
Finally, there is always a two-stroke made for small aircraft, such as the Simonini designs. While I like two-strokes for their weight the low TBO, poor reliability and the requirement to train owner/pilots on how to care for them all leaves a lot to be desired.
I have excluded engines in the realm of 40hp and above, such as BMW or Ural, since this is all about small aircraft. Once you get above this size it's a two seater, unless you're built like a tank and 6' 4" tall, and that makes you special so solve it yourself and don't bore the rest of us. For the majority, a small industrial v-twin is looking pretty good.
The greatest problem with these can be summarized as rarity. In most countries finding one is difficult enough, but then microcar collectors will outbid you for them anyhow. Even if you manage to finally get hold of one it will need a full rebuild and spares are scarce.
As an engine solution for a single place minimalist aircraft they are fairly ideal, especially since they are air cooled and light. Unlike a v-twin or inline twin the job of baffling them is avoided, just let the jugs hang out the sides. This also accounts for the popularity of half-VW conversions, but again these engines are now extinct unless you build them from new and expensive after market parts, which means buying everything from the USA. The beetle has been declining since the mid-70s and few were made in the past 30 years.
With the small Rotax engines reaching end of life - the 277, 377, 447 and 503 are now gone, thanks to worn out manufacturing dies - a replacement needs to be found. About 10 years ago I did a survey of what was available with a view to powering a Quickie, which was designed around an 18hp Onan industrial engine that turned out to be quite unreliable, and some would also say under-powered for that application. I eventually focused on the new industrial v-twin engines targeted at the farming market, since they will be available in any country at reasonable prices into the forseeable future.
When you look at Briggs and Stratton, Kohler, Honda, Subaru-Robin and all the Chinese clones with a magnifying glass, only the Subaru comes out as ideal, with Honda and Kohler also being viable alternatives. The remainder have small bearings and tiny journals, limiting their time between overhauls and opening up the possibility of a broken crankshaft. I eventually settled on the 28hp EH72FI fuel injected model, but unfortunately it hadn't yet been released at that time, so I gave up.
These can now be had for US$1,800 or so off the shelf. Not quite Harbour Freight prices, but after all we are talking about flying this thing so a few extra semolians up front is a wise investment. There have been several B&S and Honda conversions done and the work to convert the Subaru should be lower due to the already strong bottom end and fuel injection. They can also be bought with a tapered shaft, which is ideal for aircraft usage.
What other alternatives do we have? Well, for the scale warbird nuts there's a small radial, once Verner eventually releases their Scarlett Mini series. And some brave companies are making miniature Wankel engines, although their prices are astronomical and these start-ups seem to disappear as fast as they arrive. There's one company making little boxer engines from Piaggio motor scooter parts. Some people have tried - and mostly failed - to use the 2A042 6.5hp military surplus engines.
Finally, there is always a two-stroke made for small aircraft, such as the Simonini designs. While I like two-strokes for their weight the low TBO, poor reliability and the requirement to train owner/pilots on how to care for them all leaves a lot to be desired.
I have excluded engines in the realm of 40hp and above, such as BMW or Ural, since this is all about small aircraft. Once you get above this size it's a two seater, unless you're built like a tank and 6' 4" tall, and that makes you special so solve it yourself and don't bore the rest of us. For the majority, a small industrial v-twin is looking pretty good.
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