YAMAHA Gearbox: Options & Bearing Life Data

NoWingsAttached

Unobtainium Member
Joined
May 21, 2006
Messages
4,897
Location
Columbia, SC
Aircraft
Air Command Tandem w/ Arrow 100hp; GyroBee w/ Hirth 65hp; Air Command Tandem w/ Yamaha 150hp
Total Flight Time
>350
Attached is the data sheet for ball bearing life, 90% expectancy to last as long as shown. Two sizes are listed side-by-side: First, the 25 mm ID 6205 used in the Rotax C - the only PSRU that can be fitted to a Skytrax adapter, for YG4/ RX1 engines only. Gear tooth angle of contact has accurately been accounted for, though I took liberties with prop and gearbox harmonics as I have no hard data for that.

Next, the 40 mm ID 6208 - used in every PSRU (gearbox or chain drive) by Mohawk Aero to date, to include: Arrow, Air Trikes SPG4, Mohawk Silent Drive, and most recently the Mohawk AK7, which an SPG4 built to Mohawk Aero specs for the YG4 and YG4i.

The datum indicate the Rotax C is an inferior, if not unacceptable, choice for use on any Yamaha 4 powered, carbbed or EFI, experimental aircraft of any type. If is already in use, it should be rebuilt (new bearings) every 300 Hrs.

The Rotax C has no HP rating. The propeller mass inertia is limited to 6000 kg/sq cm, which is 3000 kg/sq cm less than Mohawk AK7, Silent Drive, Arrow, and Air Trikes SPG4 - all rated minimum 180HP or better. Check with your propeller vendor for proper loading spec of your particular prop.

Note that, by design, it is virtually impossible to axially load the two, drive gear shaft, bearings equally in the Rotax C. The gearbox must be disassembled for installation/removal, and therefore the accuracy required to equally load both bearings precisely is impossible to achieve and reproduce, mostly due to gasket thickness changing every time the cases are torqued together, plus micro warping due to mounting to the engine. It is not only possible to load only one of the two bearings fully, but has been shown to have happened even when the gearbox is attached to a one-piece adapter by even the most accomplished kit builders in the country. When one bearing bears the full axial load, it exceeds the maximum acceptable rating for even one hour of use at any speed that could result in flight.

In a perfect world, both bearings loaded exactly the same, Rotax C, 25 mm ID, 6205 bearings, has a 90% probability to last:
  1. 365 hrs at (less than) < 7200 ERPM - minimum cruise speed (conventional setting for light loads and nominal speed).
  2. 310 hrs @ 7200 > 9000 ERPM - fast cruise, to take off, and excellent climb
  3. 270 hrs @ > 9000 - extreme climb
Were only one bearing to bear the full load in any Mohawk Arrow, SPG4, or AK7 gearbox, then there is a 90% probability the bearings will last 410, 365, and 300 hrs, respective to the above listed ERPM. This situation does not apply, however, due to fundamental design and assembly differences between these PSRU's and the Rotax C. With the Silent Drive, of course, there is zero axial loading because it is a chain drive, and all load life calculation is "perfect world" where both bearings share loading equally.
  1. 3300 hrs @ < 7200 ERPM
  2. 2900 hrs @ 7200 > 9000 ERPM
  3. 2300 hrs @ > 9000 ERPM
For further information and copies of NTN, MRC, Timken and SKF bearing manufacturer's data and life formulas, contact [email protected]

MOHAWK AERO IS THE ONLY SHOP ANYWHERE IN THE WORLD THAT SELLS AND DELIVERS EVERYTHING YAMAHA FOR PROP-DRIVEN CRAFT INCLUDING YG3 Nytro, YG4 RX1, YG4i APEX.

Other shops promote and sell but one type adapter, for one type engine (YG4/ RX1), for one type PSRU (Rotax C) - which speaks for itself, in light of the life expectancy life of those gearbox bearings under ideal conditions, let alone worst-case scenario; and at least 3 or 4 accounts found elsewhere on RF of bearing failures reported to us this past season, all under 400 hours, one in a as little as ~12 hrs.

MOHAWK AERO deals, fabricates, services, and sells everything you need to convert to EAB aircraft use your choice of YG3, YG4 and YG4i engines.

For any questions, advice, truly open-minded discussion on ALL available equipment for ALL Yamaha engines, including SALES of stacked adapters, one-piece adapters that replace the crankcase cover, additional vendors' contact info, ROLLER CLUTCHES, centrifugal clutches, hard-coupling flanges and flex shaft couplers, dimensionals & measurements, all known available after-market engine equipment, hard-to-find parts, used parts, new and used engines, after-market turbos & blowers, ECU mods, all the really serious stuff. We are a dealer for Luga, Warp Drive, and Whirlwind props, new aluminum dual-core radiators, Jake-Bilt SS custom exhaust headers, Air Command gyroplanes AND Tango Gyro...with more to come :) If you really want a Rotax C on your Yamaha, we can and will help you out with that, too, NP - just be prepared to rebuild it more often than the other equipment we sell, fabricate and deal in, new and used.

Let us help you build a hot-rod, Yamaha-powered aircraft, cuz THAT'S what we're here for!

Please visit our Facebook group (you don't need a Facebook account to read it) "Yamaha Aircraft Engines" soon.
 

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Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,457
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
The propeller speed reduction unit (PSRU) is certainly a critical part of converting a Yamaha snowmobile engine for aviation use.

What sort of testing has Mohawk Arrow done on the Mohawk Arrow PSRU?

How many hours does Mohawk Arrow have on the test PSRU?

How many hours does the highest hour production Mohawk Arrow PSRU have flying?

How many Mohawk Arrow PSRUs are flying?
 

Gman

Member
Joined
Jul 16, 2012
Messages
471
Location
Joseph,UT/Van Horn,TX
Aircraft
SnoBird Tandem
Greg,
How is an AK7 different from AirTrikes SPG4? Are the modifications something Vassili does or something you change?
 

Jason O

Junior Member
Joined
Jun 13, 2007
Messages
541
Location
Portland
NoWingsAttached;n1127044 said:
Attached is the data sheet for ball bearing life, 90% expectancy to last as long as shown. Two sizes are listed side-by-side: First, the 25 mm ID 6205 used in the Rotax C - the only PSRU that can be fitted to a Skytrax adapter, for YG4/ RX1 engines only. Gear tooth angle of contact has accurately been accounted for, though I took liberties with prop and gearbox harmonics as I have no hard data for that.

Next, the 40 mm ID 6208 - used in every PSRU (gearbox or chain drive) by Mohawk Aero to date, to include: Arrow, Air Trikes SPG4, Mohawk Silent Drive, and most recently the Mohawk AK7, which an SPG4 built to Mohawk Aero specs for the YG4 and YG4i.

The datum indicate the Rotax C is an inferior, if not unacceptable, choice for use on any Yamaha 4 powered, carbbed or EFI, experimental aircraft of any type. If is already in use, it should be rebuilt (new bearings) every 300 Hrs.

The Rotax C has no HP rating. The propeller mass inertia is limited to 6000 kg/sq cm, which is 3000 kg/sq cm less than Mohawk AK7, Silent Drive, Arrow, and Air Trikes SPG4 - all rated minimum 180HP or better. Check with your propeller vendor for proper loading spec of your particular prop.

Note that, by design, it is virtually impossible to axially load the two, drive gear shaft, bearings equally in the Rotax C. The gearbox must be disassembled for installation/removal, and therefore the accuracy required to equally load both bearings precisely is impossible to achieve and reproduce, mostly due to gasket thickness changing every time the cases are torqued together, plus micro warping due to mounting to the engine. It is not only possible to load only one of the two bearings fully, but has been shown to have happened even when the gearbox is attached to a one-piece adapter by even the most accomplished kit builders in the country. When one bearing bears the full axial load, it exceeds the maximum acceptable rating for even one hour of use at any speed that could result in flight.

In a perfect world, both bearings loaded exactly the same, Rotax C, 25 mm ID, 6205 bearings, has a 90% probability to last:
  1. 365 hrs at (less than) < 7200 ERPM - minimum cruise speed (conventional setting for light loads and nominal speed).
  2. 310 hrs @ 7200 > 9000 ERPM - fast cruise, to take off, and excellent climb
  3. 270 hrs @ > 9000 - extreme climb
Were only one bearing to bear the full load in any Mohawk Arrow, SPG4, or AK7 gearbox, then there is a 90% probability the bearings will last 410, 365, and 300 hrs, respective to the above listed ERPM. This situation does not apply, however, due to fundamental design and assembly differences between these PSRU's and the Rotax C. With the Silent Drive, of course, there is zero axial loading because it is a chain drive, and all load life calculation is "perfect world" where both bearings share loading equally.
  1. 3300 hrs @ < 7200 ERPM
  2. 2900 hrs @ 7200 > 9000 ERPM
  3. 2300 hrs @ > 9000 ERPM
For further information and copies of NTN, MRC, Timken and SKF bearing manufacturer's data and life formulas, contact [email protected]

MOHAWK AERO IS THE ONLY SHOP ANYWHERE IN THE WORLD THAT SELLS AND DELIVERS EVERYTHING YAMAHA FOR PROP-DRIVEN CRAFT INCLUDING YG3 Nytro, YG4 RX1, YG4i APEX.

Other shops promote and sell but one type adapter, for one type engine (YG4/ RX1), for one type PSRU (Rotax C) - which speaks for itself, in light of the life expectancy life of those gearbox bearings under ideal conditions, let alone worst-case scenario; and at least 3 or 4 accounts found elsewhere on RF of bearing failures reported to us this past season, all under 400 hours, one in a as little as ~12 hrs.

MOHAWK AERO deals, fabricates, services, and sells everything you need to convert to EAB aircraft use your choice of YG3, YG4 and YG4i engines.

For any questions, advice, truly open-minded discussion on ALL available equipment for ALL Yamaha engines, including SALES of stacked adapters, one-piece adapters that replace the crankcase cover, additional vendors' contact info, ROLLER CLUTCHES, centrifugal clutches, hard-coupling flanges and flex shaft couplers, dimensionals & measurements, all known available after-market engine equipment, hard-to-find parts, used parts, new and used engines, after-market turbos & blowers, ECU mods, all the really serious stuff. We are a dealer for Luga, Warp Drive, and Whirlwind props, new aluminum dual-core radiators, Jake-Bilt SS custom exhaust headers, Air Command gyroplanes AND Tango Gyro...with more to come :) If you really want a Rotax C on your Yamaha, we can and will help you out with that, too, NP - just be prepared to rebuild it more often than the other equipment we sell, fabricate and deal in, new and used.

Let us help you build a hot-rod, Yamaha-powered aircraft, cuz THAT'S what we're here for!

Please visit our Facebook group (you don't need a Facebook account to read it) "Yamaha Aircraft Engines" soon.

Hello Greg,
You have bragged that one of the good things about buying from your company is you keep track of all s/n and you track all items you sell. Instead of all these items you publish which I agree are good if you are in the planning a engine stage and not much good if you have moved beyond the planning. If you are producing goods for the consumer, you should be beyond the planning stage. I have asked you many times (like Vance above), please just publish the numbers. How many engines do you have out there, what is the clutch, what is the gear box, what propeller are they running and how many hours. You have bragged about keeping this info. Instead of using roundabout reasons why other people making parts aren't as good as yours, please just publish your list of hours and engines.

Best
Jason
 

NoWingsAttached

Unobtainium Member
Joined
May 21, 2006
Messages
4,897
Location
Columbia, SC
Aircraft
Air Command Tandem w/ Arrow 100hp; GyroBee w/ Hirth 65hp; Air Command Tandem w/ Yamaha 150hp
Total Flight Time
>350
All truly sincerest apologies for my unbearable shortcomings and personality disorders. Much of the printed content above is/was unnecessary and serves no useful purpose. No point to edit it out, rather let it stand as a testament to my buffoonery for eternity.

Being nice is more important than being right. Until I can live by that rule I'll keep to myself, more or less. I just got home from church, Dr. Jekyl is back, and Mr. Hyde is safely locked away...

With that in mind, here's the best I can do for you with news of the most current, up-to-date info on Yamaha conversions and kits.

2018 marks the final year for production of the APEX YG4i. This is sad, but the YG3 Turbo is blowing everything off the mountain and Yamaha has a business to run and bean counters to satisfy.

YG3 will continue on as the flagship engine for Arctic Cat and Yamaha, with the turbo-charged 180-200 HP version being the highest-powered production sled on the market.

Tango Gyro in Roswell, GA has continued to refine and develop what has become an excellent line of affordable eurotub gyros designed around the YG3 Nytro & YG4 RX1, and using their own adapters and "SPG4" gearboxes built to their specifications, imported direct from Russia. To go with this they have designed and tested their own centrifugal friction shoe clutch with springless expansion slots cut from the hub material.

Same as MAC, Tango had some clutch bugs to work out early on this year, but, also like MAC, they figured out the problems and corrected them quickly and the new updates are performing flawlessly. As an alternative they can provide rubber flex shaft couplings (BMW, 78 mm hole pattern, same as what Air Trikes and MAC resells). These gyros are also available with 912/914 on request. Peach State Rotorcraft Club has been flying the wheel pants tires off of these gyros for a couple of years now, with several units sold.

Skytrax in Arizona offers an excellent one-piece RX1 adapter for use with Rotax C gearbox. As you probably know, Teal is working on a three-gear, Apex, PSRU which will replace the crankcase cover and attach to the engine, with drive gear mounted on the RX1 taper shaft end, no clutch, no harmonic prop nor gearbox damper. In light of his RX1 adapter's appeal, there are great expectations for this gearbox - which may be ready to test early to mid 2018. One question that (literally) jumps out is gear backlash: The more backlash, the more hard-start shock which prevents engine from revving up through to smooth idle. With three gears there will twice as much backlash as in a two-gear setup, so it remains to be seen whether or not this gearbox will ever work at all without some sort of clutch to damp out startup shock induced by prop inertia. An internal sprag clutch is planned in the next-gen prototype at some point later.

An unknown source rumored to be in Oregon attempted to produce for sales a waterjet-cut collar and adapter, no further word on that but we heard it did not line up with the engine mount holes.

It is (unconfirmed) rumored that, sadly, Todd Reick no longer fabricates and sells YG3 conversion kits.

Since 2012, MAC has produced two dozen GTA adapters for RX1 and six GTI adapters for Apex.

In seeking to reduce aircraft maintenance and down time, MAC produced an initial run of 10 roller ramp clutches very early in 2017. All units were sold immediately with the promise of a 100% money-back, satisfaction guarantee, and lifetime replacement of anything that might fail or wear out. That was/is an unconditional guarantee, with refunds offered and paid at all times for any reason at all, to the present day. Several issues were identified in the early examples, and all units were recalled for upgrades to prevent seals coming loose; and clutch race "walk" leading to clutch alignment issues and free-wheeling failure. Since the series' version 1.2 upgrades, no other failures have been found and MAC continues to put hours on the shop's clutch, 30 hours to date. The engine that was being used for testing was sold last month and the replacement YG4 is being readied for installation on the test frame. The 2018 GT4 roller clutches are being fabricated and testing will begin in early January.

MAC continues to fabricate and sell waterjet-cut adapter collars and plates for YG3, YG4, and YG4i (Nytro, RX, Apex) using clutches or donuts, and resells Tango one-piece adapters for RX1 with clutches or donuts.

MAC has used Arrow, Air trikes SPG4 & MAC AK7 gearboxes on customer kits purchased complete with engines; many more kits w/o engines; and has fabricated one Rotax C Apex adapter on special request. Without an Apex engine in the shop, and never having worked with a Rotax C box prior, that adapter was machine with the gearbox holes ~.010" off-center. The customer made adjustments at his end w/o asking for a replacement. The root of the error was quickly identified and a second adapter machined, ready for installation.

Several MAC clutches were ground-tested with this aforementioned customer kit, along with an RK400 clutch currently installed. One of our other customers flying a MAC-installed YG4 with Arrow 2.58 and then 2.72:1 gearbox, then a MAC AK7 and early model GT4, has changed out his GTA adapter with a new Tango one-piece adapter (that replaces the case cover in similar fashion to the Skytrax adapter) and a BMW 78 mm bolt pattern rubber donut. This setup uses a 3-blade 66" Warp Drive prop. No known issues to date, don't know the numbers for flight hours at the moment.

Best estimate of hours for an Arrow gearbox with internal sprag, used first on a 1000cc 110 HP Arrow engine for +unkown+ hrs, installed on a couple of different YG4 kits is at least 400 hrs, so 400 + unkown previous life. No issues, no maintenance to date. Drive shaft bearing load is shared between the engine's shaft bearings on one side, and the PSRU needle bearings on the gearbox side. 40mm shafts and bearings, helical gears.

Best estimate of total time for an Air Trikes SPG4 (most similar kit to Yamaha) on Suzuki is 2000 hrs, drive shaft bearings. It is also in use on a 200 hp snow machine (giant fan), unknown TT. Fleet time for this PSRU on YG4 includes all MAC and Tango, plus many more european one-off builds, dozens of gyros, who knows how many hours at this time. There have been some successes as well as some alignment issues with the private euro builders using BMW conversion centrifugal clutches. No known gearbox or rubber donut problems. Overall fleet time is off the charts, we know that at least 325 of these gearboxes are in circulation over many years.

MAC Silent Drive was approaching 50 hours when it rolled over and had a prop strike. No evidence of failure or damage to the engine or PSRU due to the prop-strike protection break-away clutch that was installed in it. No issues or failures. It had a slow drip leak through a lower bolt hole when it was removed to install a MAC AK7 for testing the GT4 roller clutches, but that started on day one and was not attributable to prop strike.
 

NoWingsAttached

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Joined
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Messages
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Columbia, SC
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Air Command Tandem w/ Arrow 100hp; GyroBee w/ Hirth 65hp; Air Command Tandem w/ Yamaha 150hp
Total Flight Time
>350
No Title

Updates to bearing life info! GOOD NEWS, too. I finally found the exact type of ball bearings Rotax C uses: 25mm ID, P/N 6305. The updated math shows that 90% of the bearings will last to 1000 hrs on a RX1 YG4! Whew. I was really worried there at first, using info for a 6205 gave us some pretty bad numbers, nowhere near 1000 TBO.
 

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Vlad

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Apr 30, 2011
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Location
Moscow Russia, Bulgaria Varna
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MTO3
I m producing tooRX1-1.jpeg....all adapters for SPG4
 

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