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Yamaha Apex YG4i Powers Highlander to EAA AirVenture 2018 STOL Competition Sweep and LSA Grand Champion Award


In 2017 Mohawk Aero fabricated the world's first Yamaha Genesis 4-cylinder (YG4) adapter to mate a Rotax C gearbox PSRU to awesome 150 HP EFI Apex snowmobile engine, and sold it to Steve Henry.  Steve installed it on his "Yee-Haw" Highlander STOL airplane, flew it from Idaho to Oshkosh, and won every STOL drag race competition at Air Venture 2018 - beating out even the amazing "Draco" turbine-powered Wilga.  When all was said and done, he even flew home with the coveted "Lindy" award for best-in-show (LSA). 


Steve had competed at Oshkosh in previous years with another adapter on an RX1 engine and won a few STOL races.  He also returned again in 2019 with a 300 HP turbo-charged Apex built by Edge Performance in Finland, costing tens-of-thousands of dollars more than his 2018 Apex with MAC Rotax C adapter, and won a race or two but overall the race results were less than expected as he got beat by a 160 HP Rotax 912 Turbo.  


The point is that no one - not Steve Henry, nor anyone before, nor since  - has ever been known to swept every STOL competition at Air Venture.  Throw the Grand Champ plaque on top of that and you have something that will most likely never happen again.  No Rotax, Lycoming, Continental, and certainly no Viking nor any other conversion engine.  No turbine, no radial, no engine of any shape, size, might or make. 


This stands as an irrefutable, public testament to not only the amazing craftsmanship and piloting skills of Steve Henry, but also to the help Mohawk Aero provided him with the prototype design and fabrication for this first-ever power plant, a 150HP Apex Yamaha-powered aircraft with Rotax C PSRU.  It is well worth mentioning that Steve's addition of NOS boosted this set up to a whopping 190HP on take-off! 



Greg Mills (MAC) built the world's first ever Yamaha Genesis 4-cylinder, 4-stroke, aircraft conversion in 2012, the Air Command gyrocopter on the home page here.  It was flawless from its first flight, and is still in Greg's possession and flying today from Columbia's KCUB with several hundred hours on it. 


MAC is credited with the world's first successful Apex aircraft conversion kits starting in 2017, including engine, adapter, a variety of PSRU options, clutches and shaft couplings, and the all-important wire loom. 


Then in 2019 the world's first YG2 (80 HP) Phazer aircraft conversion kit was sold by MAC in May 2019 to Gil Audibert of New Orleans for his Quicksilver float plane.  Here's a short video clip of Gil's plane:










In June 2020 we saw yet another first:  Greg completed and flew the first YG4 Apex EXUP (valved-exhaust) aircraft of any kind, another tandem Air Command gyrocopter which became the world's most powerful normally-aspirated Yamaha aircraft flying, at a truly awesome 165 HP.  Geoff Resney owns and flies it in northern Indiana these days, and it has become affectionately known as "Godzilla".  

Greg flies his own, semi-enclosed, tandem Air Command YG4 rotorcraft (shown on top of the home page of this website) out of KCUB airport in downtown Columbia, SC.  If you ever want to take a demo ride in a Yamaha YG4 rotorcraft, email and make an appointment :) 

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