Radial and Rotary

Rotary (Traditional)

Classic Aero Machining

For those seeking the ultimate, authentic, full-gyroscopic WW-I rotary experience, New Zealand-based Classic Aero Machining has spent several years developing a brand-new-build Gnome Monosoupape engine. It is a faithful continuation of the Gnome used in many French, English and German aircraft just prior to and during WW-I.

Besides the challenge of fully learning the nuances of this 100+ year old design, CAM, who started by using original plans, is dedicated to improving the Gnome while not detracting from its authenticity. A recent example is a pre-start oil priming system (CAM found it had been taking 20 seconds for pressurized oil to reach the engine internals). Another improvement is lengthening the lower portion of the cylinders for improved piston support. Also the induction ports are now angled, promoting in-cylinder swirl for better fuel atomization and reduced plug fouling, a big help there. The in-cylinder motion is further aided by CAM’s fuel pump (the originals relied strictly on gravity). Purists may decry it, but CAM also has an electric starter for their rotary—it must be the first non-hand-propped rotary ever—but the engine runs cleaner and smoother than ever, and CAM has raised its power rating another 5 hp to a muscular 125 hp and nearly 600 pound feet of torque while whirling at just 1120 rpm.

CAM emphasizes these engines are viable, reliable, real-world choices for WW-I replicas and that they’re in the rotary business for the long term. They certainly are the only new engine capable of delivering the true early bird rotary experience, which might be a little more performance oriented than first imagined. CAM reports their rotary has a Sopwith Pup replica going 110 mph straight and level, plus 1000 fpm vertically. If you want to inspect a CAM rotary or need an airframe to match your new Gnome, Kip Aero in Dallas, Texas, works closely with CAM to build continuation WW-I Sopwiths.

CAM is part of the burgeoning replica and restoration scene in New Zealand and has a well-established business replicating various warbird parts, especially P-40 items. At our deadline they were assembling another batch of four Gnomes, making seven running engines to date.

Motorstar NA

Probably the most piston power you can buy, few homebuilts can take all the muscle a 620-cubic-inch M14P radial can dish out. But hang-on-the-prop sport pilots sometimes need all they can get. For them, the Romanian-built M14P provides the huge torque and long-prop compatibility they’re looking for.

A venerable design, the M14P is still well supported in Romania and through dealers in the U.S. New engines built from NOS parts are available, but no one buys them short of third-world governments due to cost. Instead the M14P market is an overhaul market, which is where Coy Aircraft Sales in Swanton, Vermont, comes in as they are also the M14P distributor for Motorstar NA. They offer a $23,000 flat overhaul rate on these engines. All work is done at the Romanian factory, so the price includes all rebuild work, test run and warranty, but not shipping. Coy says air freight is currently an elevated $4000 round trip to the factory, but this changes with the worldwide logistics situation (currently a mess).

Typically when an M14P is overhauled, it goes from the base 360 hp to the 400-hp M14PF upgrade as the price isn’t that much greater. Another option is dressing the rebuild for use in Nanchang CJ-6s with their different plumbing. Other sources for these robust Russian-designed radials are Jill Gemerzke’s M-14P, Inc. in Kingman, Arizona, and Barrett Performance Engines in Tulsa, Oklahoma, who specializes in hot rod versions with electronic ignition and Airflow Performance fuel injection.

Rotec Aerosport

Naturally slow-turning and geared, Rotecs provide the sound and long-prop looks popular with builders looking for a vintage appearance and experience. The Australian company offers two nearly identical radials, the smaller R2800 measuring 172 cubic inches and the larger R3300 with 220 cubic inches. There are no changes to either engine for 2022.

The 110-hp R2800 was released in 1997 and uses seven cylinders; the R3300 employs nine of the same cylinders and was first offered in 2005. It is the better selling version, no doubt because it’s just a little larger and heavier but puts out 150 hp at 2350 propeller rpm (both engines use a PSRU gearbox). Neither engine is supercharged, and while the R2800 is well paired with a 76-inch propeller, the R3600 can handle 90-inch props.

Standard Rotec induction is a simple Bing slide carburetor, but Rotec’s own—and still simple—TBI Mk 2 throttle-body fuel injection is optional. Its main attraction is staying on the job during aerobatics, and besides fitments for their radials, Rotec offers versions of their carburetor for everything from VW conversions to Rotax, Jabiru and even Lycomings.

Rotec sells direct, so it’s necessary to plan ahead to account for shipping time even under normal conditions. With the snaggled shipping environment this year, even more time is necessary, but at least shipping isn’t impossibly expensive. Typically Rotec estimates $600 to ship an engine to the U.S.

Verner Motor

Czech engine maker Verner Motor began in 1993 but has been making radials only since 2011. Newer yet to the U.S. market and having sold only a few engines here (more have been sold in Europe), it has nevertheless garnered a good reputation. Sam Watrous, the main U.S. dealer, pointed this out when saying, “It’s easy being a Verner dealer these days.”

Well, somewhat easy. The challenge is making enough engines to meet demand. The full Verner line includes five radials ranging from three to nine cylinders. The first two, the Scarlett 3VL and 5VL have been put on an indefinite production stop so the Czech factory can concentrate on the in-demand 5S, 7U and 9S. The numeral denotes the number of cylinders. Furthermore, all engines are fitted with S&S Super G carburetors, the optional fuel injection system also being set aside for the moment. Interestingly, pricing for the basic engines has not gone up, but the accessory pricing (starters, alternators, etc.) has doubled due to shortages.

Delivery times were eight months at our press time, with the dealers hoping to get that down to four months sometime in 2022. The dealers are Scaled Birds, Myers Aviation and Brahn Sport Aircraft.

Much of the Verner’s appeal has to be its very radial-like growling rumble. These engines use generous cubic inches and no gearbox to produce relatively modest horsepower for their size along with a sonorously muscular exhaust note.

As expected, the Verners use the same two-valve, 3.62×4.02-inch cylinder, but fit five, seven or nine of them as power needs rise. Designed to run on 93-octane U.S. or 95-octane European premium mogas, these Scarlets have a 32-inch diameter and a TBO of 1000 hours. Experience shows some lead fouling on a steady diet of 100LL fuel, but this responds favorably to lead-scavenging additives or simply by running mogas. The TBO is expected to rise as experience is gained with higher-hour Verners. So far the company has sold about 150 engines worldwide.

Rotary (Wankel)

American Rotary Engine/Auto PSRU’s

We’re combining these two very separate companies under one heading because they join to offer a Mazda 13B rotary engine conversion package. American Rotary builds the Wankel engines while the Auto PSRU’s makes the propeller gearbox. Their long-standing offering is a 200-hp firewall-forward fitment for the RV-7.

We’ve already introduced Auto PSRU’s in this guide under our Inline and V Four-Stroke heading; American Rotary Engine is the aviation sidebar to Atkins Rotary, a hot rod shop up to their necks in modifying and supporting Mazda Wankels for auto racers.

While American jokes that customers all want a “500-hp engine that weighs 30 pounds,” they offer up to 200 hp, naturally aspirated and turbo-normalized packages, and will support Reno racers. An aviation-specific development of theirs is a spring-loaded pop-off valve set to 4 pounds to avoid overboosting after descents or on go-arounds.