Ever looked at the blown, nitromethane-guzzling 9000 horsepower engine of a Top Fuel Dragster and wondered, could I slap that thing in Beechcraft and break the sound barrier? Well, if that’s the case we’d advise you to lay off the cough syrup and stay out of airports, but the principle is sound – engines from road-going vehicles often prove to be good for powering aircraft. Today, RideLust profiles a few of the legendary (and infamous) auto engines that have taken enterprising pilots into the sky.
Porsche PFM 3200
The Porsche FlugMotoren (Porsche Aero Engines) was either sort of a disaster, or a total disaster, depending on who you ask.
Derived from the road-going 911’s 3.0 liter flat six, you’d think the PFM would make the planes it flew in seem like P-51 Mustangs. Instead, it was the answer to a question that no one asked: can someone build a heavy, complicated, expensive, and unreliable engine for my light plane? Despite making decent power for a plane engine – 217 HP @ 5300 RPM, this was a dud.
Unreliable on the road means you break down on the side of the highway and call AAA. In the air … well, there’s gravity and all that. The last strike against the PFM is that a major advantage of road-derived airplane engines is theoretically interchangeability. The PFM shares almost no parts with a road-going Porsche. After they ended production, Porsche allegedly determined that the liability exposure on these motors was too great, stopped making spares, and campaigned to buy them all back so they could destroy them. If that ain’t confidence inspiring …
So the PFM, ultimately, is the not-so-flugmotoren. It’s not really a good choice to put in anything, let alone an airplane. Surely there is some nutcase who would defend this engine, but since they don’t allow computers in most mental care facilities, it seems like they’ll miss this unflattering treatment.
VW “Type 1″
Lightweight, aircooled, and extremely simple, the VW “Type 1″ engine was well-suited to experimental aircraft use. It was/is famous for powering the Beetle, and is available in a wide variety of sizes and configurations.
Some are highly modified with magnesium cases and the like, but most are just rebuilt and converted. The power ranges from 25 or 30 HP in the lightest applications, to up to 70 or so for heavily modified motors. Of course, larger “Type 4″ VW engines from the VW Bus (Transporter) can be used for more power as well. The list of planes that use VW-derived motors is huge, as is the list of places that build them up.
And that might be the Type 1’s greatest advantage – virtually every part is still manufactured and you can get engines that are completely brand new. Used motors are common. Aftermarket parts are infinitely numerous. And you could swing a dead cat around a parking lot and be able to hit someone who could work on a Type 1 motor. They’re just simple, simple engines. It’s like MacGuyver – give a VW mechanic a shoelace, three bobbypins and a piece of Laffy Taffy and they could probably rebore a cylinder. Or cause a really cool explosion that would allow them to escape from a sticky situation. (Don’t you just love MacGuyver?)
As for applications, the Evans VP-1 Volksplane just seems so freakin’ cool. It looks like a WWII scout plane. Get a scarf and goggles and take to the sky. Awesome.
Unlike Porsche and VW, Subaru’s parent company Fuji Heavy Industries actually built planes in a previous incarnation as Nakajima Aircraft. This Ki-43 Hayabusa “Oscar” fighter was a light Army fighter, built in large numbers towards the beginning of WWII.
After the war, Nakajima became Fuji Heavy, and their Subaru division began producing cars, turning its little 2-cylinder horizontally opposed motor into a 4-cylinder boxer by the 1960s. And so you might notice a theme here. So far, all of the engines mentioned have been horizontally opposed designs. Coincidence? Not really – the boxer motor, as it is sometimes known, offers a ton of advantages.There’s small frontal area (reducing drag), smooth running due to the pistons’ motion balancing out, and short length. So it’s a very common choice for small aircraft, where most of the automotive engine conversions are used. All Subaru engines are boxer motors, like the VW and Porsche, but with the important difference of being water-cooled, allowing for finer tolerances in the engine internals but requiring a radiator. From the early EA81 and EA71 engines, to the popular EJ-series, and even the modern 3.0 flat-six motors, all are popular with builders. As an example, the all-aluminum, OHV pushrod EA81 is an extremely popular choice. In 70 HP trim they are virtually unbreakable, and they weigh 185 lbs dry. That’s quite impressive.
Plus anyone choosing a Subaru motor has the advantage of a huge and rabid fanbase for these engines, a large and reliable supply of rebuildable cores, abundant parts, and relatively low prices. Possibly only the VW Type 1 engine has as much of an advantage in this regard.
Subaru’s rally heritage and experience with turbocharging their motors means that forced-induction is definitely an option, and there are lots of folks putting EJ257 engines from Impreza WRX STis into aircraft service. Stoutly built, the motors respond well to aftermarket air filters and exhaust and can handle a lot of power without expensive internal modifications.
Many of you know about Mazda’s rotary engines, but when you discuss rotary engines in an aviation context, you might find yourself baffled when you come across the Gnome rotary engine.
To be very clear – the Mazda/NSU/Wankel rotary and the Gnome rotary are completely different engines. Early in aviation history, when planes were covered with cloth and topped out at 60MPH, the Gnome was one of the finest engines you could put in a fighter. While pretty much every other engine has a fixed engine block, with internals that move around in some fashion or the other, the Gnome rotated around a fixed crankshaft (click to see an animation of this insanity). So, in case your mind failed to grasp that amazing notion the first time (like ours did), the entire engine, cylinders, heads, and all, rotated around a fixed crankshaft at the same speed as the propeller. The damn thing had a total-loss oil system, using castor oil injected into the motor with the fuel. Absolutely bonkers.
That was a long diatribe but we hope you appreciated how cool that was. Is the Mazda rotary a let-down after the Gnome? Probably not, and here’s why. Rotary engines make an absolutely astonishing amount of power from a miniscule package, especially when you factor in forced induction (supercharging or turbocharging). As an example, the Mazda 13B-REW (found in the last-generation RX-7) had dual sequential turbos. With this setup, and with only 1.3L (that’s 79.8 cubic inches for any domestic car fans in the audience) it officially made 280 HP, but likely exceeded that figure. In aviation trim and ready to bolt right into a plane, the non-turbo 13B engine weighs about 325 lbs and makes around 200 HP (compare that to a Subaru EA81, making 70 HP and weighing 185 lbs uninstalled and without liquids or accessories). Again, this is from 1.3L. Because the power potential is huge and the weight is relatively low, you can see why this might be a good choice.
Why does the engine make so much power? We’re glad you asked. The reason is that the rotary contains triangular rotors, each with (obviously) 3 faces. As the rotors turn, each face becomes a combustion site. So for every single rotation of the rotor, you get 3 combustions and their accompanying power pulses. Furthermore, there’s no reciprocation – they just spin. No fighting momentum each time the piston changes direction. That means less moving parts to fail, a huge advantage in an aircraft. Of course, there are drawbacks. The tips of the rotor have a hell of a time sealing properly, and early ones wore out pretty quickly. They’ve pretty much fixed it by now, and 13Bs get about 100k miles in real-world auto use before needing a teardown. The Mazda rotary has become a well-respected option for many kitplane builders.