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YAMAHA APEX (EFI) 150HP 118# Engines


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Posted (edited)

 

Yamaha APEX (EFI) engines, adapters, and complete FWF kits are now available, any type PSRU you want. 

GT4 RAM and GT5 CAM clutches are now available, fits all Rotax C box installations, Air Trikes SPG4, and other PSRU types.  This is a direct swap-out replacement for the troublesome, high-maintenance RK400, Air Trikes BMW, and other centrifugal clutches sold for experimental aircraft conversion engines. 

Both the GT4 and GT5 are self-aligning, pre-lubricated, double-sealed, and self-supported/self-aligning by means of precision deep-groove ball bearings.  No more shoes wearing out in 12-120 hrs.  No more filthy shoe dust all over the PSRU.  No more broken springs.  No more drum attachment screws coming loose and falling out.  No more impossible alignment headaches.  No more tinny, irritating, “minibike clutch” rattle on idle.  GT4 comes with a LIFETIME guarantee, GT5 comes with a 1000 hr TBO, and a 500hr/5yr guarantee.   Both clutches are rated at 6 times the torque of the YG4 engines for 1 million start-up cycles. 

The Yamaha Apex fuel injected engine replaced the RX1 carb engines for model year 2006 when they discontinued the RX1.  As availability of good, low-mileage RX1 engines (2003-2005) wanes, Apex engines have only become more available (2006-present).  The 140 HP RX1 was an awesome engine, but refinements that came with the Apex line  made the original YG4 even more desirable.

EFI improves ease of starting, instantaneous air density adjustment (altitude, heat, humidity) and allows precise metering of fuel delivery which allowed Yamaha to go more aggressive with ignition timing curves and cam profiles; which resulted in a 10 HP increase across the entire power band of the original RX1.  The Yamaha engineers didn’t stop there.  They reduced weight from 125# to 118# with the absence of carbs, a slightly lighter crank, and some reduction of case material.      

Mohawk Aero Corp has been successfully fabricating adapters and installing Yamaha 4-cylinder engines on aircraft since 2012.  With an eye on the future for power enhancements such as turbo and superchargers we designed and fabricate a universal adapter suitable for use with just about any PSRU available or imaginable which could easily handle such tremendous HP.  We successfully engineered, fabricated, installed and tested our own Hy-Vo Silent Chain PSRU which bolts directly up to the crankcase with no other intermediate adapter whatsoever.  This unit reduces vibration significantly, includes a prop strike protection friction plate clutch, reduces installed weight, and reduces overall length by 2-1/2” over Rotax C and 3-1/2" over Air Trikes SPG4 gearboxes. 

Please contact us at:  INFO@MohawkAeroCraft.com

Visit our website at: Mohawk Aero Corps

Visit our YAMAHA AIRCRAFT ENGINES Facebook discussion group at: https://www.facebook.com/groups/1251356951570824/?ref=bookmarks

 

Edited by Mohawk Aero
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Posted

Hello Greg,

I see a description on the FB page that these two GT clutches are sprag type.

Do you have pictures of these two clutches (GT4 and GT5), and a description of how they would be installed in a C gearbox?

And since the RK400 runs in a "dry" location, I am wondering how the GT clutches are lubricated (I assume they must be if they are sprag clutches)

Also, the RK400 is designed to fit the shorter PTO taper of the rotax 2 strokes, wheras the Yamaha has the same taper angle but a smaller starting diameter.  Use of the RK400 requires a small amount of grinding on the pto shaft to allow the bolt to press the RK400 onto the shaft.  If the GT clutches are a direct replacement for the RK400, then does the Yamaha shaft need to be shortened?

Thanks.

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Posted (edited)

The GT4 RAM is a roller ramp clutch, see below.  The GT5 CAM is a cam, or sprag clutch.  Both units require lubrication, and both of the Mohawk Aero units are filled with grease and sealed.  The Yamaha taper is identical to the Rotax taper, and is longer.  Hence the smaller Yamaha minor diameter at the end while the major taper diameter is the same as Rotax.  RK400 was designed for use on Rotax, and later applied to Yamaha.  The GT4 and GT5 are both a swap out for the RK400.  With dozens of Yamahas running ground down, shorter shafts to fit the RK400 clutch we have designed our clutches to retro-fit the shorter shafts.  We also have our clutches available for no shaft grinding, to take advantage of the full length of the Yamaha shaft with an eye to the future of our development of the 200-300hp turbo charged YG4iS. 

In the distant past, Arrow Engines in Italy used a 1956-1968 Chevy Hyrdaflow transmission sprag in their aircraft PSRU which bolted directly to the engine and crankshaft of their 500cc and 1000 cc 2-cycle boxer engines.  When overrunning, the sprags require 2-3 GAL of oil pumped into them.  When overrunning, you want the outer race running and the inner race stationary.  This prevents the cams from coming in contact with the stationary race.  If you do it the other way around centrifugal force makes the cams rub against the stationary outer race, causing wear.  Sprags do very well on vibration-isolated powered shafts, they don't do well with a lot of pounding like you get from a piston engine.  The 1000cc Arrow boxer 2-cycle fired two pistons at once, every 180 degrees.  That's a double-whammy sledge hammer banging on the crank, sending massive shock waves hard-coupled to the gearbox and on up to the sprag which was mounted on the prop shaft - design flaw number one.  When the engine was shut down, the inner race spun the cams against the stationary outer race - design flaw number two.  Initially the gearboxes had no way to move oil into the sprag cage - design flaw number three, creating the perfect storm which doomed these internal gearbox clutches to early failure.  Word got around and sprags got a bad reputation in the gyrocopter world which used these engines extensively on tandem trainers in the '80s-'90's.  Arrow corrected the oiling problem with a centrifugal pump, and these later clutches lasted past 1000 hrs TBO. 

With sufficient oiling, the proper overrunning design application, and isolating engine harmonics, sprags are excellent clutches and will easily last far beyond 1000 - 2000 TBO hr.  

GT4 RAM clutches use a totally different technology, and unlike the sprag which has a cage that engages all the cams together, ramp clutch rollers act individually.  You could conceivably have one or more individual rollers fail to engage and the clutch will continue to transmit torque flawlessly. 

Both of these Mohawk Aero clutch elements are rated at 6 times the torque of the Yamaha for one million cycles, or put another way 6 million cycles.  These ratings are for 100% starting torque like you see with electric motors, and since a piston engine has very little torque at start up then the lifetime of the clutch is actually up 8 times longer than that.  However, with any piston engine you reduce lifetime by a wear factor of 4.  With a vibration-isolated application like the Yamaha 4 with its internal harmonic damper, the reduction factor is only 2 - 3.  Conservatively speaking you're looking at a life of 3 - 7 million start up and shut down cycles (not how many times the pistons fire, as some folks have wondered and asked).

Hope this was interesting and enlightening.  I've spent ten years flying and researching sprags, cause of failure, why the Arrow clutches didn't last, and what would make them reliable for use on experimental aircraft engines.  The GT4 and GT5 clutches are the result of hundreds of hours of digging and reading, and then design engineering and now a product we are proud of. 

GT4 RAM Clutch element.png

Edited by Mohawk Aero
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Posted

This shows the sprag element used in the Mohawk Aero GT5 CAM clutches and explains a little about how they work.

GT5 CAM Clutch element.png

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Posted

Great info!  Thanks!

Any pics of the GT4 and 5?

I am also trying to picture how these clutches mount up in the c box.  I'm guessing you bolt the entire clutch to the engine pto taper, but then how is it attached (and power transmitted) to the gearbox?

Also, what are your thoughts on the hardy disk.  It seems like rotax engineered the gearbox to run with that rubber dampener.  Any concern about the GT4 or 5 transmitting vibration and "sharp" undampened positive loads straight to the gearbox?

Thanks again for helping move forward options for Yamaha conversions... and now for a new option for the c gearbox!

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Posted (edited)

The GT4/5 clutch hub bolts to the engine shaft.  Threaded studs (shown) are attached to the PSRU drive flange.  These slide into the three holes on the drum of the GT4/5 clutch.  The hub, clutch element and bearings, and drum are all press-fit together (you can't seperate the inner from the outer parts without special equipment, or else damage to the bearings and clutch will result).  Removal from the engine is by means of a special bolt that threads into the hub face, shown on the left in the photo below.  We recommend the GT4 for longer life with non-damped engines like the Rotax 582 etc., although we still gaurantee the GT5 on those engines for 500 hrs/5 yrs,and it has a 1000 TBO expectancy.  We have a design which incorporates rubber-damped stud sleeves in the hub to improve wear characteristics on the PSRU for 2-cycle engines, but that hasn't been rolled out yet.  As you may know, we are primarily vested in the Yamaha engines.  Our focus has always been on the YG4 with its harmonic damper, which alone, in and of itself, places Yamaha in a class all by itself far and above all other conversion or purpose-built engines for experimental aircraft in the 80-250HP category. 

IMG_2488.JPG

Edited by Mohawk Aero
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Posted

I have been looking for an engine and have found a 2004 RX-1 and a 2007 Apex. The Apex is a little more money but both are a good price. I know one engine is carbureted and the other is EFI. There are more options out for the RX-1 but I feel this will soon be fixed as more people start using the Apex. Can someone tell me what additional considerations I need to take for installing an Apex verses a RX-1. I'd like to know about wiring, fuel system and mounting differences. Thanks

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Posted (edited)

I agree, the apex motor is "the way of the future"  (quoting the movie "The aviator" ):)

 

Greg mills at mohawk makes an adapter and gearbox for the apex but I dont think he has an apex motor flying yet?  Update us please Greg.

I hear Steve Henry (wild west aircraft) just got an apex motor mounted and has tackled the wiring conundrum.  He will have one of the first efi aero adapted yamahas flying in the USA (a few in norway are flying).

 

Edited by MN Kitfox 2

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Posted (edited)

.... oh, and IMO the "real" way of the future will be the sidewinder motor!  (Little ecu tweak and 200+ HP good to altitude) 

That would really open a big market for a ton of other EAB guys (Rans, Lanceair, Bearhawks, Glasair, ect)

As always, gonna take someone waaay smarter and more talented than me to get that motor to fly!  :)

It's totally crazy talk.... but wouldn't it be cool if Yamaha started an aero division!

(No, wait...  then it'd cost as much as a new Lycoming :lmao:)

Edited by MN Kitfox 2

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Posted

Here is an assembled production run GT4 RAM clutch ready to install on Kurt Carleson's Yamaha RX1-powered single place Air Command Gyrocopter, which is currently in my hanger in Savannah, although he lives way over yonder, t'other side of Atlanta. 

Here's a Youtube link of him flying his gyro with the Yamaha installation I did for him last year using the Mohawk GTA adapter and Arrow 2.58:1 gearbox with internal sprag clutch. https://www.youtube.com/watch?v=CFEKoIa0S48

Kurt decided he was ready for more (one of those former biz jet pilot guys who needs a fix) climb thrust, and asked me to install a 3:1 ratio PSRU.  I had a beefy new SPG4 redrive on the shelf I wanted to try out on the awesome YG4 powerplant, but decided I would make my own clutches instead of going with centrifugal clutches like the RK400 or Air Trikes BMW. 

Steve Henry's APEX is running, it is mounted on a stand and he has all the wiring sorted out.

IMG_2244.JPG

IMG_2245.JPG

IMG_2246.JPG

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Posted

Time to update this thread!  Mohawk Aero's 2018 GT4 Roller ramp clutches are coming out very soon. I am done with the drawings, and converting them for CNC machining as of this writing.  Updates (should I go with geek-speak and call this the GT4.2 update?) include, among other things:             

  • Dual idler bearings (front & rear)
  • (Steel-sleeved) rubber-bonded drive-stud pockets to damp vibration and allow for minor misalignment in all directions: radial, axial, and angular.  Kinda like merging "the rubber donut" with a clutch!    

 

 

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