Air Trikes: Engines and Conversion Kits.

World Champions fly our trike with Suzuki G13BB engine.
Do you want the same engine for your aircraft?

General information.

Interest in 4-stroke auto-moto engines converting for Light Sport and Ultralight aircraft is growing all over the world. We know that popular 2-stroke Rotax 503 and 582 are not certified aviation engines but variations of snowmobile engines with all 2-strokers' problems. Prices of certified 4-stroke aviation engines are quite high. The active development of aviation piston engines has stopped more than 60 years ago with the jet age beginning. The same time, cars become more and more perfect. Modern auto engines are light, have high reliability and life time. Electronic ignition and fuel injection with microprocessor control system, low gas consumption and flight hour value, simple and inexpensive maintenance with attractive unit price, these features usually distinguish current-technology converted auto engine from its "real aviation" brother.

I started to use 4-stroke Auto-Moto engines for aircraft in early 90-th. These engines have never been �alternative� for me. Many people interpret that to mean weird, more complicated or lesser way for builders who cannot afford to buy �good & proven Rotax 912S". I never considered them only as "cheap" way of aircraft engine development. Automotive companies spent hundreds of million dollars for their new engines. We all know about serious competition in this industry for the last decades. As a result, even being less expensive because of mass production, modern auto engine is way more advanced. It is a pleasure for me to design new conversion systems and fly them.
There is a lot of experience in converting of Subaru, Honda, Chevy, Nissan, Kawasaki, Yamaha, BMW and other engines but light and small GEO-Suzuki G10, G13 and G16 are the most interesting engines for me as Weight-Shift control aircraft (trike) designer, builder and pilot. G10 with stock fuel injection has about the same HP as popular Rotax 582 model. Trikes with G10 have good flight performances with significantly lower flight hour cost. G10 Turbo, G13BA and G16B have about the same power as Rotax 912, 912S and 914. But my favourite engine for trikes for the last several years is G13BB. Different trikes were built and supplied to customers with these engines. I test fly every one by myself. Years and hundreds of flying hours without major problems.
The GEO-Suzuki has its advantages, as does the Rotax 912. My opinion as an aviation engineer and pilot, and the opinion of many builders and pilots who have tried both Air Trikes conversions and 912 engines is that our GEO-Suzuki conversion in many aspects is the preferable choice. For example our 2-place trike with Suzuki G13BB is a winner of Russian National Championships 2015-16-17-18-19, as well as FAI European and World Championships 2016-2019. It is simply flying better than competitors with Rotax 912 engines!

Our engines are used not only for trikes but for PPC, Airplanes, Auto gyros, Airboats, Hovercrafts etc. More my and my customers' videos at video page. Air Trikes Enterprises supply ready to install engines with gearboxes, propellers, motormounts, control systems, mufflers etc. We also supply gearbox conversion kits and parts for other (Suzuki, Subaru, Honda, BMW etc.) engines. More information below.

Suzuki Power Group (SPG)-3 and 4 gearbox conversion kits:

These gearbox conversion systems were designed as modifications of a popular SPG-2 system (was in production from 2000). They are intended for aviation conversion of 2 and 4-stroke engines and using them with propellers for NOT SERTIFIED experimental light aircraft, hovercraft, airboats etc. SPG-3 has the same gear pair as SPG-2 but lighter and easier to install-remove. Recommended for up to 130HP engines. The available reduction ratios are 1.8, 2.03, 2.34, 2.5. SPG-4 has higher gear module and width, a little bigger body, about 2LB heavier than SPG-3, RR up to 3.16, recommended for up to 180HP, high torque engines. There is a German (BMW) rubber damper between the gear box and the engine. Centrifugal clutch can be used as an additional option (recommended for example for 2-cylinder BMW R series moto engines). The propeller moment of inertia up to 9,000 kg/cm2. Rotax-style propeller hub, hollow propeller shaft so it can be used with variable pitch prop or for glider towing. It is possible to use these gearboxes for both (tractor and pusher) layouts. The gearboxes can be installed up, down and any degrees left or right on the bellhousing. It allows to install the engine not only straight up but inclined or laid flat.

The body consists of 2 bolted down parts:
1) gearbox with the gear and oil inside + damper housing
2) mount plate (bellhousing) and crank-damper coupler.
BMW damper and hardware included. Bellhousing and coupler are different for different (Suzuki, Subaru, Nissan, Honda etc.) You can see SPG-3 sets for GEO (left) and Subaru (right)

More than 2500 SPG gearbox conversion systems have been made to the end of 2019 year. The gearbox expected life time is 2000+ hours (depends on the engine power and the prop moment of inertia). Manufacturer�s warranty 5 years or 500 hours for metal parts (body, shafts, gears, bearings). High proven reliability and efficiency, simple maintenance. Mechanical part of the engine conversion is simple. SPG-3(4) instruction with step-by-step conversion pictures HERE. Click and look - nothing difficult to convert your auto engine using this gearbox bolt-on conversion system.

We supply complete gearbox conversion kits for different engines � Suzuki G (10, 13, 15, 16) and K series, Subaru EA (71, 81, 82) EJ (18, 20, 22, 25), Honda D and Fit (L15), BMW R series, Toyota, universal gearbox kits, bellhousings, spare parts. We also can design and make mount plates and adapters for other engine conversions.

SPG-5 gearbox and gearbox conversion kits:

This gearbox was designed for powerful up to 350-400 HP engine conversions (for example Honda Odyssey-Pilot engine) and big diameter heavy multiblade propellers. Widely used for heavy-speedy airboats and hovercrafts. The available reduction ratios are 2.03, 2.34, 2.4, 2.5, 2.6, 2.8. The prop shaft was modified to absorb more thrust, additionas thrust bearing added. Rotax 912 style propeller hub, hollow propeller shaft. It is possible to use these gearboxes for both (tractor and pusher) layouts. The gearboxes can be installed up, down and any degrees left or right on the bellhousing.

The gearbox life-time is 2000+ hours (depends on the engine power and the prop moment of inertia). Manufacturer�s warranty 5 years or 500 hours for metal parts (body, shafts, gears, bearings). High reliability and efficiency, simple maintenance. Ask questions if you have them. Pictures and technical data below:

Dimensions and weight data:

SPG-3 Metric Imperial
Offset (dimension between crank and prop shafts) 80mm 3.15"
Gearbox length (no bellhousing) 240mm 9.5"
Engine-prop flange dimension* 300mm 12"
Propeller hub Rotax standard**
Gearbox weight 7.5kg 16.5Lb
Full conversion kit weight* 11kg 24LB
*For Suzuki-Geo G10 and G13, can be a little different for other engines.

SPG-4 Metric Imperial
Offset (dimension between crank and prop shafts) 90mm 3.55"
Gearbox length (no bellhousing) 230mm 9"
Engine-prop flange dimension* 290mm 11.5"
Propeller hub Rotax standard**
Gearbox weight 8.5kg 18.7Lb
Full conversion kit weight 12kg 26.5LB
*For Subaru EJ, can be a little different for other engines.

SPG-5 Metric Imperial
Offset (dimension between crank and prop shafts) 101mm 4""
Gearbox length (no bellhousing) 250mm 10"
Engine-prop flange dimension* 350mm 14"
Propeller hub Rotax 912 standard**
Gearbox weight 14kg 30Lb
Full conversion kit weight*
*For Honda K20 and R20, can be a little different for other engines.

**SAE prop flanges and adapters can be ordered for other propeller hubs
Conversion kit weight data provided for the complete bolt on kit consists of gearbox, damper, bellhousing and hardware. The data can vary slightly during the production and depends on the engine model.

Suzuki engines G (GEO) and K series converted with SPG-3:

This is one of G13BB engines converted with SPG-3 and installed on a trike. The standard engine for our trikes from 2005 (Suzuki G10 were standard before). Trikes with our engines have the same flying performances as similar trikes with Rotax 912S engine, with better fuel efficiency and faster throttle response. Short takeoff, maximal airspeed with 14.5m2 wing up to 176kph (108+mph), climbing up to 1600 FPM. The average fuel consumption around 2 GPH, minimal can be as low as 1.5 GPH. We use 87 octane autogas. Average static thrust of G13BB with 2.5 ratio gearbox and recommended prop 500+ LB (around 370 LB for G10).

The engine is 16 valves, full injection, with double ignition coil pack and DENSO computerised injection and ignition control system. The mixture is prepared based on intake pressure sensor data, so altitude compensation is automatic and the mixture is always optimal. Throttle body heating is a standard feature so we never had problems with icing. The engine block is not modified; the stock water outlet with thermostat is used. This makes the engine very thermo stable. I heard a lot about overheating problem from people using conversions with modified water cooling system but have never had it even with a small radiator closed by BRS system. It is well balanced, low level of vibration at all range of RPM, from 800 to 6000. Soft and pleasant sound. The engine is a little heavier than Rotax 912. With all our improvements, the real difference between 912S and G13BB made by Air Trikes Enterprises is around 20LB. As we know, the new injection Rotax 912is is heavier than its carbureted version so the weight difference between these injection engines is even less. The inline G13BB engine (installed correctly) has smaller mid-section than the same HP opposed type engine like Rotax 912S. Its aerodynamic drag is less. I don�t want to make a full comparison of these engines. Just my opinion based on my education as aviation engineer + my real experience as light aircraft builder and pilot � it is possible to use correctly converted and installed Geo-Suzuki engines instead of Rotax 912 with a very good end result.

All conversion parts for Suzuki like mufflers, motormounts with rubber silent blocks, engine control systems, control gauges, light alternators and starters, light aluminum pulleys, radiators etc. are also available with our GEO-Suzuki engine conversion brochure. Every part of the conversion was redesigned and improved based on hundreds of flight hours. "Small" improvements are in reality not so small. For example a set of 3 light (crank, water pump and alternator) aluminum hard anodized pulleys is not only weight saving. Increased alternator pulley diameter makes alternator running slower. It allows to avoid alternator overwork (usually we fly higher RPM than drive cars). This is not only a little bit more of available power but (more important) less possibility of alternator bearing failure. Our light alternator set saves 2.5-5lb of weight comparatively with the stock alternators.

Air Trikes Enterprises, our clients and partners have made a lot of different engine conversions for the last 18 years. We can state - Air Trikes Geo-Suzuki is not just an alternative engine or �project� but well proven and efficient engine. We provide not only conversion kits but also ready-to-install powerplants based on GEO-Suzuki engines + SPG conversion kits. This is our standard package G13BB engine with SS muffler, cooling system options (expansion tank, radiator) and KOOLprop. Typical powerplant for pusher config; tested, crated and ready to go to. Used for experimental aircrafts, hovercrafts, airboats, snowplanes and even wind blowers for movie-makers.

Types of Suzuki G series engine available:

A) Throttle-body injection (TBI) G10 with DENSO Electronic Control Module (ECM) - 62-65HP
B) G10 Turbo with MPI, resonance intake, turbocharger � up to 92HP (intercooler & knock sensor can be used)
C) G13BA 8 valves SONS naturally aspirated � up to 80HP
D) G13BB 16 valves SONS about 100 HP naturally aspirated
E) G13GTI 16 valves DONS 110+HP naturally aspirated
F) G16B 16 valves SONS NA about 115HP

These are 2 engines - G13BB and G16B crated and ready go. They are very simular, the same 16 valve SONS head, oil and cooling system. G16B has longer stroke and 1mm more diameter pistons. Every engine comes with SPG-3 gearbox, motormount, starter and alternator, light aluminum pulleys, fuel and ignition system, high pressure fuel pump, engine computer and wiring harness. Muffler (regular or stainless steel), intake filter, cooling system, KOOL propeller and spinner are options of your choice.

G serie engines are light. G10 standard package weight is about 65kg (145LB), G13BB 82kg (180lb), G16B is 7kg (15lb) more. Pictures of these converted engines on the scales: click PHOTO G10+muffler, PHOTO G13BB and PHOTO G16B

SPG gearbox kit for new Suzuki K series engines has been designed and made in 2015. The first K14B was converted, tested and sent to an airboat company for enduring tests.
We are ready now to supply conversion kits for Suzuki K12B and K14B. Maybe the same kit can be used for K10B as well. We also can supply new converted K14B engines for airboats and aircraft.

Different GEO-Suzuki converted with SPG-2(3):

There is an opinion: straight installed inline engines like Suzuki G with gearboxes are not very suitable for tractor style planes. It is not really true. There are WW1 replicas, Jenny, round engine cowling planes with enough space inside. I decided to show the project ULTRA (Unlimited Trainer) designed and built as full aluminum light acrobatic trainer. It has GEO-Suzuki G13 engine installed straight with SPG-3 gearbox. The first prototype was built and started to fly summer 2015. This project is not ready for serial production yet, but flight test results are very promising.

Air Trikes sells SPG-3 and SPG-4 conversion kits for Subaru EA and EJ:

It is a nice looking and perfectly flying Zenith 750 Cruzer built by Michael Hulle in Australia. The enine of this affordable flying "family car" is 160 HP Subaru EJ-22 converted with SPG-4 gearbox kit and SDS control system.
Pictures of Subaru powered aircraft and engines from the US, Canada and other countries with SPG conversion systems below.

GEO-Suzuki engine conversion brochure

Information brochure about converting Geo-Suzuki G series engines for Homebuilt aircraft and other air propeller driven craft is available for your order. The price is 99USD paid with PayPal to info@airtrikes.net E-mail address. This price included 4% PayPal fees, print and Canada Post regular mail cost. Do not forget to include your mail address. We send only printed version, no CD, no download. If you want more information about it, to see Content or read Introduction/Conclusion - CLICK ON THIS LINK.

If you can't use PayPal and wish to send 95USD by check, or have other questions about ordering this brochure, contact us.

Honda Fit and Civic engine conversions

Compact and light L-series engine came to North America under the hood of subcompact Honda Fit in 2007. It is well known in Experimental aviation, affordable and easy available.
It is 16 valve SONS. L13A engine has 2 sparkplugs per cylinder but these engines are not available in USA-Canada. L15A has approximately the same power as G16B - 109-117 HP. New versions are more powerful, L15B up to 172HP and L15C 183HP
Positive moments of this engine comparatively with Suzuki G series - timing chain instead of belt, 4 stock sparkplug-on coils (one for each cylinder).
Negative moments - more complicated motormount, bulky intake, more complicated stock control system (VTEC, electronic throttle control).
The gearbox conversion kit for Honda L-series has been designed and tested in 2011. Available for your order.

STOL CH-750 and Kitfox type airplanes with Honda L-15 engines and SPG gearboxes:

Aluminum welded compact intakes and stainless steel mufflers can be ordered with Honda Fit gearbox kits:

Honda Civic engines are widely converted and used for aircraft and airboats. These engines are highest quality and reliability. They have stock carburated version with a distributor. We have a complete gearbox conversion kit for Honda Civic (D series) engines.

BMW R series engine conversions

What about motorcycle engines? BMW 2-cyl boxer looks attractive for aero conversion. Everybody knows highest BMW quality, but not all know BMW company was one of the pioneers in aviation engine industry. I and II World War fighters and bombers fly with BMW engines. Light and compact air-oil cooled BMW boxer looks much more "aviation" than most sertified aircraft "steam-age" piston engines. We sell a special edition of SPG-4 gearbox kit for aviaconversions of BMW R1100, R1150 and R1200 (R1200GS) engines. 2 short videos below - weight-shift aircraft flying with BMW R series converted with SPG gearbox kit:

2 types of bellhousing different for 1100-1150 and for hexahonal head 1200GS. 3.0 and 2.58 ratios. A centrifugal clutch is strongly recommended for this type of the engine. BMW R series conversions are well known and popular in Europe. Regardless the high price (about the same as Rotax 912), hundreds of light panes fly with BMW conversions. BMW R1200GS converted with SPG-4 + KOOLprop and installed on AC Tanarg trike below.

BMW R series engine is easier to instal under a cowling of most tractor type planes than most 4-cylinder inline engines. These are pictures of CH-701 and Skyranger. BTW, this Skyranger is used in remote areas of Syberia with luck of maintenance, minus degrees Celsius air temperature, snow, ice, short runways and very hard flying conditions. The owner is proud to fly this small but tough ultralight.

Many Aeros trikes have been built with BMW R series engines. More pictures of BMW R engines converted with SPG gearbox system on weight-shift aircraft.

BMW R1100 engine with SPG-2 gearbox. It was installed and tested on Eagle trike.

There are 2 pictures showing SPG-3 gearbox installed up and down at R1100 engine. We can supply gearbox conversion kits for BMW R series, as well as converted engines. The last picture is BMW R1150 assembled weight with SPG-2 gearbox (no clutch), exhaust pipes, motormount L-bars. As you can see, it is around 72 kg or 158 LB

Can SPG gearboxes be used for other engines?

Simple answer YES! We sell universal gearbox kits for people who wants to do their own conversion. Here are videos and pictures of Yamaha Genesis 3-cyl snowmobile YG3 engine converted with SPG-4 gearbox and KOOLprop. The autogyro is in production in Russia, several of them are flying with hundreds of hours accumulated. Another one is Super Petrel amphibian biplane with YG3 made by Kurt Hansen Norway. The plane had 120 hours on it before it was sold to another owner:

You see RagWing Stork RW-20 with Corvair engine converted with SPG gearbox and 73" KOOLprop. This conversion was done by Murray Green from Rosetown Sask. Canada. He noticed increasing of all performances comparatively with direct drive he used before. From his letter to me: "I couldn't be happier. The gearbox and prop seem to be made for the Corvair engine. A wonderful combination."

Interesting variant of BMW K1200 engine converted using a universal SPG-4 gearbox kit and custom made adapters:

This is a Chinese variant of Suzuki engine converted in Florida USA in 2012. They used SPG-3 gearbox and installed it on a flat aluminum plate. The simplest way of adapting SPG-3(4) gearbox to a new engine.

I decided to make a new page with addresses and feedbacks from some people using our products (including engines and SPG kits) for their aircraft. Look FEEDBACKS PAGE HERE

You also can see more pictures of airplanes with SPG converted engines at my "Simple" photo gallery. I hope they can help you to create your own design. CLICK HERE if you want to see them.

Two-Stroke Engines

General information.

Converted motorcycle and snowmobile engines are also very popular. It is not a secret for example that Rotax 2-stroke UL engines are conversions of Ski-Doo and Sea-Doo motors. A lot of ultralight or hovercraft builders all over the world use such conversions. A lot of redrives exist for them.

5-V redrive system is designed especially for snowmobile engine conversion. This classical system consists of two 6061 T6 aluminum pulleys for 5 V-belts, eccentric shaft with heavy-duty closed ball bearings, motormount plate and all machined parts, rubber elements and hardware necessary for engine installation. It can be made at most of machine shops. I used this redrive with licensed Rotax 640 from 1998 like a powerplant for my "Frigate" trike. It has been installed now with Rotax 503 on my "Eagle" trike. This system has a lot of advantages comparatively with other redrives:

a) Very reliable. Will be working with 4 or even 3 belts. You don't have to be so worried about your belt condition like with your single belt drive.
b) Very light and less expensive comparatively with gearboxes.
c) You can use not only provision-type Rotax but also non-provision. You don't need to convert the engine itself.
d) Spare belts are easy available and not expensive (Car Quest XL serie).
e) Reduction ratio can be easy and smoothly changed by changing the pulley diameter.
f) The engine can be installed head-up or down.
g) This system can be easy adjusted by changing some installation dimensions to almost any project.
h) Quick (a couple of minutes) and easy adjustable belt tension.
i) It is a whole conversion unit included a motormount plate and 4 metal-rubber silentblocks. You need nothing but muffler and prop for your engine installation on a trike or UL plane.

This system is available now as a set of drafts (12 sheets plus description).

We have multi V belt redrives for provision type Rotax and similar engines available for sale. Reduction ratios 2.3, 2.6, 3.0. Offset 140mm 5.5", weight (2.6 ratio) 5kg or 11lb. Can be purchased with a propeller.