How ironic is this: before I brought to his attention the fact that the RK400 guys require a tear-down inspection of their clutch every 75 hours, Teal didn’t know anything about it.
This is a fundamental issue and concern for anyone making comparisons when considering available choices to hot-rod their aircraft by installing a Yamaha beastie.
Teal has designed and fabricated (2014) one thing, and one thing only, to date: an RX1 adapter which fits a Rotax C gearbox; which requires either a Rotax Hardy Disk (flex shaft coupling) or an RK400 aftermarket clutch designed specifically for use with this gearbox.
I designed and fabricated the first RX1 adapter (2012) two years earlier, which I used extensively with first an Arrow gearbox with internal sprag clutch, then an Air Trikes SPG4, more recently the Mohawk AK7 (based on the SPG4), and a single, lonely, solitary Rotax C in all of my 6 years of production of Yamaha adapters.
Then in 2015 I designed, built and flew the pants off my Hy-Vo chain Silent Drive, with a prop-strike protection clutch no less. The chain and gears have been field tested to over 300 HP. It was perfect right off the bench, and remains so to this day. It even suffered a prop strike, and the engine was saved, as was the PSRU!!! That is not just a victory, it is HUGE, and I have bragging rights that no other PSRU builder known to man to this day can claim as a result of this major, accomplished work let alone a guy who has built and sold but a single design anything in the same period, to date.
There have been other, successful, PSRUs using Hy-Vo chain. There have been other, successful PSRUs built with prop strike protection break-away clutches (Rotax 914 option $1300.00) but no one has ever put the two together before, let alone successfully.
That PSRU is attached to the Yamaha RX1 engine in the same, exact manner that my adapters are. Not only that, it (because it is a prototype) was put together in sectional layers – FIVE OF THEM!
AFTER A PROP STRIKE OCCURING AT 7000 ERPM DURING A FAILED TAKE-OFF ATTEMPT NONE OF THE LAYERS MOVED ON THE PSRU OR THE ENGINE ONE IOTA!
Six years, unknown hundreds of hours, 100% perfect track record with ZERO evidence whatsoever to support the imaginary crap that Harvey the invisible rabbit dreamed up regarding adapter alignment and slip. Someone is blowing smoke, and it is not me. The ONLY advantage of a Skytrax one-piece adapter that can be proven by anyone in this room is that a one-piece adapter coming hot off a CNC table is ready to go. Teal doesn’t have to do one more thing to it when it arrives in his hands from the sourced shop. My collar-and-plate adapter requires several days of water-jet, milling, and aligning and pinning everything together. Once that is done, anyone at all can install it, aligned correctly and reliably, just like a Skytrax adapter.
The only discernable advantage in a Skytrax adapter is to the seller himself, not the customer. It does look pretty, so two points to Slytherin for aesthetics. However, any advantage at all is lost to Gryffindore because the adapter is strictly limited to use of a Rotax C box and it’s associated shaft couplings which are proven beyond any doubt, by any yardstick, to be inferior to what can be bolted to a Yamaha using a Mohawk adapter. It's all about choices, guys, and not being forced into a corner by your vendor.
I don’t know how many Skytrax adapters have been sold/installed, and could care less. Neither do I know or care if Teal has ever purchased for resale any RK400’s to go along with the sale of one of his adapters, and a gearbox. No one can argue that one way or another RK400 clutches have been a topic of detailed discussion that Teal has been aware of and engaged in, often and long enough such that by now, at this late date, he has had more than ample opportunity to have done his homework and thoroughly familiarized himself with this unit which is so integral and crucial to his product sales - a component which is a primary, basic device required by nearly all of his customers from day one.
With only one thing to do and sell for the last 2-3 years, how could this not be part of his knowledge base, how could this escape his attention? The man’s got his agenda, that’s moot: promote the pants off one gearbox, and one gearbox only, to the exclusion of all else. He’s stickin to it, head in sand, that’s obvious.
It has become crystal clear that Teal doesn’t know the first thing about the clutched coupling required for his product – not at least until I told him so last month, and there’s the irony.
Which begs the question: what does Teal know about the only other alternative to the RK400 clutch, the Rotax Hardy disk?
More importantly, what is he willing to tell you about it?
Last APRIL 2017 Teal Jenkins and I were both told by the same source, separately, this account:
This prominent STOL builder/pilot tried to use a Hardy Disk with a 74” Prince prop, powered by a YG4 (RX1) using a Skytrax adapter. After just 12 hours or so, he noticed something wrong and took everything apart. The brand new Hardy disk had ripped through and through – catastrophic failure.
I’ll say it again: HARDY DISK FAILURE AFTER 12 HOURS ON A YG4 YAMAHA RX1 USING A SKYTRAX ADAPTER AND A ROTAX C BOX.
There, maybe now it will return on this forum in a search for HARDY DISK FAILURE connected to a YAMAHA engine using a ROTAX C gearbox.
You see, before I came here in response to someone else already ripping me, I searched “Hardy disk failure” and then simply “Hardy Disk” on here and no news of that failure appeared anywhere.
How many posts has Teal put up here since last April? How much news has he generated in that time to educate you folks on the known dangers of using a Hardy disk in conjunction with his adapter?
I should have posted it here, but I really expected Teal to do and I didn’t want to come off as a prickly, nay-saying competitor bashing inferior equipment.
I did post the failure on Rotaryforum 4/28/17. It got 120 looks, zero replies. I also posted it on my Mohawk Aero Facebook group (Yamaha Aircraft Engines).
I have built an adapter for only one customer using a Rotax C gearbox (RXC). I don’t make enough money off gearbox sales to make it worth my trouble to promote any one over the other, they are all the same to me in that regard.
But I don’t use RXC not because this has anything to do with my competitor here, but rather because they don’t meet my spec - in any category. If they met my spec, I’d use ‘em and sell ‘em till the cows came home, trust me. I was building and selling RX1 adapters two full years before Teal Jenkins entered the scene as my direct competition. No one, by any stretch of the imagination, can ever accuse me of sour grapes due to his intervention in my livelihood - the timeline simply doesn’t add up.
To date, my numerous choices for PSRU (including building my own Silent Drive) have been spot-on and I have been proven right, without a shadow of doubt, exactly 100% of the time with ZERO FAILURES of them in six years.
I say again, for the hard of hearing: ZERO PSRU FAILURES in six years and countless hundreds of hours flying time by myself and my customers.
There have been no less than four documented accounts of Rotax gearbox bearing failure during the same period, at <50 hrs, 200 hrs, 300 hrs and 400 hrs.
Perhaps one of the most esteemed EAB folks in the country has suffered catastrophic failure on multiple occasions using Teal Jenkins’ combination of adapter, shaft connections and RXC. One such failure was explained away as perhaps builder error. I ask you, if a professional builder can’t put the RXC back on his adapter properly, how can Joe the Weekend Warrior be expected to do it every 75 hours?
Teal explained a RXC bearing failure on one of his kits to me this way: The drive gear shaft bearings are so small that if the axial loading due to the helical cut of the gear faces loads only one of the two shaft bearings, that bearing is going to fail 100% of the time, guaranteed.
Other RXC experts and professionals have agreed, saying much the same thing.
The gearbox is an inferior design, plain and simple, for use with a 140 HP Yamaha RX1, let alone a 150 HP APEX. You are required to tear it apart and remove the drive gear, shaft and shims just to install it. Then you run the risk of not shimming the thing right when you put it back together, and that will destroy the bearings because taken alone they are too small to bear the load.
Perhaps you might not know that the gearbox was designed and assembled in the first place made to turn in the opposite direction that our Yamaha engines turn.
There have been countless other RXC failures, but they have largely been kept under wraps by self-serving dealers who fix and sell them. There are so many accounts of RK400 excessive wear, spring failure, dog failure, screws coming loose and falling out that it is pointless to go into all the lurid details and list them individually here. You all know what those issue have been, the risks involved, and you continue to use them anyway.
What I have brought to some eyes – including Teal Jenkins - is the intensive maintenance tear-down inspection requirements RK400’s carry with them. Inspection requires an hour or two of labor, a new RXC gasket, and fresh oil (which needs to be changed anyway) and then WHEN – not if – it needs new shoes it will cost $150 (w/ S&H) for a new set, be that at 75 hours, 200 hrs, or whatever. This is a certain eventuality much as any other friction shoe clutch or brake set requires.
The reason I don’t use Rotax C has nothing to do with Teal Jenkins or his tunnel-vision adapter. My reasoning is/was/has been based on the facts below considered when first exploring various PSRU solutions, and should be the same facts anyone considers when building a high-performance aircraft conversion engine and installation.
First, Rotax C (RXC):
1. Numerous known bearing failures under 400 hours, on Yamaha and other engines
2. not rated for any horse power.
3. rated for prop inertia mass of 6000kg/sq cm. (Check with your prop dealer to make certain your prop is within this spec.)
4. Shaft OD and bearing ID size is 25 mm diameter
5. requires disassembly in order to install or remove it
6. Associated (alternative) RK400 clutch requires tear down inspection every 75 hrs, which requires RXC tear down. RK400 clutch shoes will wear out, and replacement cost is $150. Numerous documented failures when used with Yamaha RX1, though power to the prop has been maintained during flight in most cases.
7. RXC cost is $1625 – 1750. No longer generally available unless you provide a Rotax engine serial number and falsely claim you intend to use it on that, likely due to Rotax becoming aware of gearbox failures when used with Yamaha engines.
8. RXC requires major machining in order to adapt it for suitable use on conversion engines and keep installed lengths to a minimum. Cost for machining at a typical shop $200.00
9. RXC flex shaft coupling is on a 76 mm bolt pattern, and was designed in 1960 for use on small cars producing ~100 HP category, as a half shaft joint. They are intended to be replaced periodically and when they fail they fail completely. They are round in sectional profile, like a donut. Known failures have occurred when used with Yamaha RX1 conversions running 80-85% power in cruise and WOT climb.
10. RX1 adapters available: Mohawk Aero GTA (2012) collar-plate; Skytrax (2014) uni-part
11. APEX adapters available: Mohawk Aero GTI (2016) collar-plate
Comparison: Mohawk AK7 (and Air Trikes SPG4) gearbox
1. No known bearing failures to date
2. Rated and guaranteed by manufacturer to 180HP
3. Inerital mass rating 9000kg/sq cm
4. Shaft OD/ bearing ID 40 mm
5. Gearbox is not disassembled for installation/removal from engine
6. Associated (alternative) BMW clutch requires tear down inspection w/ costs similar to RK400.
7. PSRU cost is ~ $1800.00. Usually in stock, and always available from Mohawk Aero.
8. No machining required, total final cost of PSRU is the same as RXC
9. Flex shaft coupling used is newer BMW part intended for damping driveshaft harmonics on 300 HP autos. Bolt pattern 78 mm. Sectional profile square, giving the part twice as much load-bearing material as RTX “Hardy disk”. No known failures on any propeller drive installations to date up to 200 HP
10. RX1 adapters available: Mohawk Aero GTA (2012) collar-plate and Mohawk Aero uni-part (replaces crankcase cover)
11. APEX adapters available: Mohawk Aero GTI (2013)
In closing, I developed a new clutch in 2017 to be used on my Yamaha conversion kits. On paper, it should see 1000 Hrs TBO. The first design (January 2017) had some flaws. First the seal blew out of one end at WOT. Then the gearbox harmonics forced the clutch roller race to walk on the outer drum and become misaligned after 8 hours at 80% power. I fixed those problems by redesign, and have tested it for over 20 hours without any problems. The earlier failures did not decouple power to the prop at any time, and were easily detected upon simple sound, visual and touch inspection (turning the prop) after shutting the engine down. We will continue to test and put hours on them, and report the total time accumulated and any/all successes or issues.
2018 GT4 Roller clutches are being readied as of this writing, and are expected to be available late December. Of course, as always, all of my products are covered by a 100% money-back guarantee of satisfaction for at least one-year or 100 hours, whichever comes first. That includes all engines I sell with my kits. GT4 clutch guarantee works like a tire warrantee: First year/100 hours 100% satisfaction money back or replacement guarantee. After the first year, for 4 more years or a total 500 hours, value is reduced by useful life wear. Cost is $695. No tear-down inspections required, all pre-flight and inpsection can be done by listening, looking through the PSRU inspection holes, and turning the prop by hand.
Mohawk Aero will not sell GT4 clutches to anyone who has not purchased a gearbox and adapter from us. We originally also sold sprag clutches, and although we have suspended testing and production on them in order to do a better job putting hours on the GT4 we may at some point return to offering sprags for sale at a later date.
All of this being said, here's the bottom line: You might be able to run a RXC with a hardy disk or RK400 and never have any trouble. You might go for 200 hrs and not even have to replace clutch shoes. It all depends on your particular build, maintenance and operation of the aircraft. Some equipment is better than others - there can be no doubt about it, and the choice is left to you to decide what you find most desirable. In the end it is all "Experimental", and that is why we are not flying certificated aircraft. I did not come here to dump on anyone or anything, but in my view some things have been said that are personally damaging and seriously misleading, and other things have been left unsaid which are also misleading as well as potentially dangerous to limb, limb and aircraft if left unknown and unaccounted for. No one can make an informed decision concerning anything if you don't first have all the facts before you, presented in an unbiased manner - to at least some acceptable degree. I hope I have done justice to remaining open-minded here, and that you perceive my long-winded, open letter here as such.
Thanks for reading this. I leave you to consider all viable options now in peace, goodwill and harmony, and sincerely hope you join us on Facebook where we explore the possibilities for the future of Yamaha aircraft conversions and share our builds, to the exclusion of all else. With warm regards to one and all, and may the force be with you...
Yours very truly,
PS: When I reduced chain tension on the Mohawk Silent Drive, it became impossible to start the engine. When I properly adjusted the chain tensioner to remove all slack, it started up just fine. With a gearbox, backlash is not adjustable, and must always be present. You can never get a gearbox to run without it, whereas you always remove all of that slap on a chain drive. I proved that the less slap, the better the YG4 starts, and the more the slap the worse it starts. Two gears is x amount of slap at start up. Three gears is twice as much slap as two, not just 1/3 more. I suspect that Teal is about to find out that his three-gears are going to exacerbate the rough starting we have to deal with when using a 12:1 compression Yamaha thoroughbred. Three gears is twice as much harmonic vibration, twice the noise, twice as much loss of HP due to axial loading, and more weight. Anyone wanting to weigh in on why I chose to build a Hy-Vo chain drive 3 years ago, and then finish and fly it 2015, instead of going with a three-gear solution to raise the prop shaft on a Yamaha conversion kit, be my guest - I'm all ears.