Any thoughts on the Yamaha Apex conversion? Verner Radial?

[Cguy]

And if they did (put a feathering prop on it) it'd no longer be LSA legal.

Some, most maybe, of the guys on the Yamaha Facebook site seem to think the windmilling prop is of no concern, I disagree. My last comment on the subject there was along the lines of "anywhere else in aviation it's known that a windmilling prop is much more draggy then a stopped one, except here."

[zkelley2]

I'm not entirely sure that's true. There's some speculation that a variable pitch prop that you cannot access the pitch change in flight would be as legal as any other LSA with a ground adjustable prop. It'd just adjust on the ground a lot quicker. A feathering only in case of engine failure, I'm sure you could make a similar argument.
It would certainly be something you could go look for clarification on. Or, since no home-built is actually LSA (they are experimental Amateur-Built.), just they might fall within the spectrum of what a spot pilot can legally fly you could go with the more generous definition I came up with and if that doesn't happen to by true, so long as you're not a sport pilot, well, it doesn't actually matter, you're not breaking any rules.

[svyolo]

One of the things I noticed about my Yamaha Jetski engine, and the Apex pictures, is there is little structure to the engine to absorb any kind of load other than crankshaft torque and piston bearings. On my Jetski, not even a mini-bellhousing mount of any kind. Just a crankshaft.

Even with a gearbox, the prop loads have to be absorbed by something. It almost seems like the "engine mount" needs to be a gearbox mount, and the engine just running that gearbox like a PTO shaft.

[Roost]

And if they did (put a feathering prop on it) it'd no longer be LSA legal.

Some, most maybe, of the guys on the Yamaha Facebook site seem to think the windmilling prop is of no concern, I disagree. My last comment on the subject there was along the lines of "anywhere else in aviation it's known that a windmilling prop is much more draggy then a stopped one, except here."

Seems that most of the guys running these are competing in STOL drag competitions. Does the extra drag from the prop actually *help* them?

[way_up_north]

One of the things I noticed about my Yamaha Jetski engine, and the Apex pictures, is there is little structure to the engine to absorb any kind of load other than crankshaft torque and piston bearings. On my Jetski, not even a mini-bellhousing mount of any kind. Just a crankshaft.

Even with a gearbox, the prop loads have to be absorbed by something. It almost seems like the "engine mount" needs to be a gearbox mount, and the engine just running that gearbox like a PTO shaft.

Hi everyone...I`m going to post all I know about this Yamaha conversion ....The pros and cons as I see them and try to bring everyone up to speed.....There is an excellent table of contents on the yamaha facebook group that goes deep into all the items I mention here...except for the windmilling prop...

Why I love the Yamaha conversion...

the price.... you can find used engines for $1000...some handy pilots have installed 140hp engines with prop plus gearbox and acssories for $5000 ... Less then 200lbs

Yamaha might have accidentally made one the best aviation conversion engines ever....and then stuck it in a snowmobile...
the starter and alternator are integrated so its very light weight...the engine is designed to pump out electrical power for snowsuit warming...ect...so lots of juice to run your avionics...35-40 amp
on the carburetor version called the RX1 140hp...you just have to defeat 2 limp home modes.....throttle position mode and high coolant mode...ive heard its easy to do and then you have a rock solid CPU and harness...

The carb engine RX1 and fuel injected engine Apex are the same block 1000cc just different years.... earlier years were carberated...latter years fuel injected....the carb years do not have a barometer the fuel injected does have integrated barometer......carb 2003....efi is around 2006....

The fuel injected version 150hp...there is a guy online doing the Yamaha harness for $500 to defeat all all the limp home modes on that engine...

from my reading to this day...they have had very few ....engine outs with the Yamaha engines(I’ve not heard of one)....they just seem to run ...but this part of the problem... since they have had so much success ... nobody is talking about what happens if the engine stops...

the raging success of this engine means that it is now being installed on faster planes... they are close to completion and we’re going to find out soon how valid my concerns are.....


all engines that use a gearbox to reduce the high engine rpms to prop speeds...have to deal with something called torsional vibration...this is because automotive engines make their power in pulses on the downward power stroke ....so these pulses get passed through the gears to the prop and then bounce back to the engine...if not delt with this vibration will destroy the plane...in a matter of minutes....the little bit of play in the gears magnifies this ....so you have to dampen these vibrations...this is done in a variety of ways....

this is an example of how viking engines does it...but this method is common to many gear boxes.....a rubber donut flexes back and forth to absorb the pulses...like an elastic band

Rotax and others deal with it in different ways...using clutch plates that you service ...ect.....all these methods have one thing in common...if the engine stops the prop stops...

maybe someone can correct me...but I dont know of any aviation engine manufacture that ships engines out the door where the prop will windmill(except turbine engines)

BUT...with the Yamaha conversion .....

The most common way that the vibrations are being delt with is with something called a sprag clutch...a sprag clutch is like whats in a helicopter.....engine powers the blades....but if the engine quits...the blades can rotate freely so the heli can auto rotate to the ground...this means if the engine quits on an airplane with this sprag gearbox...you will have a windmilling prop on the front of your plane.

so the engine makes a power pulse...that goes to the prop...but the clutch disengages in a micro second to block the return pulse..then re-engages to alow more pulses to go to the prop......im no fan of a sprag clutch on an airplane...but I have to say the device itself is amazing in what it can do many times a second...

This sprag clutch eliminates all the vibrations completely.....and lets you put a gear box on smaller engines and 2 stroke engines that have been hard to use cause they are vibration prone...

the use of the sprag clutch in the Yamaha conversion is an engineering choice of the company making the most popular gear box ...

we are getting into an unknown area in aviation here....normally a windmilling prop is to be avoided at all costs....but trikes, gyros and some stol planes...have been flying for years with this windmilling prop...and saying there is no problem....

years ago a clutch called the RK400 was developed for the air boat industry on rotax engines...this clutch lets the engine run...but only engage the blades as you power up....great for boat operations....but experimental aviation has been using this clutch on small planes,trikes....for years...with little issues reported...

BUT..... some pilots report there is drag issues with a windmilling props on small planes...with a dead stick situation or engine at idle...and it is known to be a huge issue on larger faster planes like the pilatus...dash 8...planes using turbines...and twin engine operators avoid a windmilling prop as it can be the kiss of death...

so whats going on with the windmilling prop?

it could be that a windmilling prop creates a solid disk only at higher speeds....so slow flying planes maybe get only 5% or 10% reduction...they might not even notice it .....maybe the prop creates a more solid disk the faster it rotates...since windmilling props were avoided all these years... there is zero research just pilots and opinions....

but faster planes...might spin that prop up to high speeds and create a solid disk on their nose...as reported by turbine pilots and high speed twin engine aircraft......

then there is the in between aircraft(faster then a stol aircraft...slower then a turbine)...were the drag is not really known....because maybe the prop spin dictates how much drag it induces?.....its just never been studied so we dont know...we can only comment based on reports...



Then there is the Russians....they are making low cost knock offs of older Rotax gear boxes...for $1500 to $2300 USD....that have the (engine stopped prop stopped) type gear boxes...this might be the way I`m going to go...only problem is the factory does not speak good English and is on the far side of the planet for parts...


if anyone has any questions...Ill try to answer or give a link .....the yamaha conversion face book group is a great resource

[whee]

Is the integral gearbox that is on the Apex and RX1 engine removed? When I was going down this road I was going to use the Nitro engine so that I didn’t have two gearboxes to deal with. I didn’t see a good way to eliminate the gearbox that Yamaha built into the Apex engine.

Sprag clutches are pretty amazing. They don’t completely eliminate vibrations or power pulses but they do greatly reduce the likely hood of the prop/engine combo getting into resonance.

[way_up_north]

Is the integral gearbox that is on the Apex and RX1 engine removed? When I was going down this road I was going to use the Nitro engine so that I didn’t have two gearboxes to deal with. I didn’t see a good way to eliminate the gearbox that Yamaha built into the Apex engine.

Sprag clutches are pretty amazing. They don’t completely eliminate vibrations or power pulses but they do greatly reduce the likely hood of the prop/engine combo getting into resonance.

Good question.... as far as I know... the snowmobile clutch is removed ...this gives access to the output shaft... the gearbox can then be attached...

there is a small yamaha torsion dampener that’s left inside the motor... it does almost nothing to help the torsion issue though... the Yamaha motor does have an internal reduction ratio ....I can’t remeber the ratio.. but it’s very small ... this video goes into in greater depth...

[whee]

Cool, thanks. So the internal gearbox stays in place which probably isn’t that big of deal especially on an airplane. I remember a few guyS blowing them up on their sleds but they were running huge tracks, tons of boost and only blew them up when why came down hard after catching air while climbing a chute. An airplane will never see that kind of load. But I hate the idea of two gear boxes so I’d still probably use a Nitro engine.

[Cguy]

When I do dead stick ridge soaring, there is a very noticeable decrease in drag versus a idling engine, and with the prop stopped. I really can't see why the subject is even up for debate, just ask any motor glider pilot (or turbine pilot) and they will tell you post haste! What IS up for debate I guess, and what most of the Apex builders are so far slipsliding around, is how much of a factor the increased drag will be in daily ops, routine flying, not much is my guess. Deadstick is another story.... What cracks me up about the Apex, is we Rotax drivers have just gotten you legacy engine drivers somewhat used to what we consider normal revs, in my case 3800 to 5200, rarely higher, usually 48-4900, so around 2 K at the prop, one reason Rotax birds are quiet. Then this Apex comes along with insanely higher revs! We Rotax guys are now thinking like the legacy engine guys,"that's pretty high rpm's!" It's a inexpensive, reliable, and powerful engine, Long term viability of the reduction system is still up in the air, for me anyway.

[way_up_north]

When I do dead stick ridge soaring, there is a very noticeable decrease in drag versus a idling engine, and with the prop stopped. I really can't see why the subject is even up for debate, just ask any motor glider pilot (or turbine pilot) and they will tell you post haste! What IS up for debate I guess, and what most of the Apex builders are so far slipsliding around, is how much of a factor the increased drag will be in daily ops, routine flying, not much is my guess. Deadstick is another story.... What cracks me up about the Apex, is we Rotax drivers have just gotten you legacy engine drivers somewhat used to what we consider normal revs, in my case 3800 to 5200, rarely higher, usually 48-4900, so around 2 K at the prop, one reason Rotax birds are quiet. Then this Apex comes along with insanely higher revs! We Rotax guys are now thinking like the legacy engine guys,"that's pretty high rpm's!" It's a inexpensive, reliable, and powerful engine, Long term viability of the reduction system is still up in the air, for me anyway.

Great post

this chart gives you an idea of the RPMs to make HP with yamah RX1 and Apex engines
rx1-dyno2.jpg

[way_up_north]

Seems that most of the guys running these are competing in STOL drag competitions. Does the extra drag from the prop actually *help* them?

You’re asking good questions

im only speculating...

It might depend on the air speed of the aircraft .... when you go to idle or engine quits and the prop windmills....

[zkelley2]

You’re asking good questions

im only speculating...

It might depend on the air speed of the aircraft .... when you go to idle and the prop windmills....

I would say in the STOL drag format it probably helps a lot. In the non race machine that you trailer to race day, I think it's a pretty bad idea.

[schu]

Hi everyone...I`m going to post all I know about this Yamaha conversion ....The pros and cons as I see them and try to bring everyone up to speed.....There is an excellent table of contents on the yamaha facebook group that goes deep into all the items I mention here...except for the windmilling prop...

Why I love the Yamaha conversion...

the price.... you can find used engines for $1000...some handy pilots have installed 140hp engines with prop plus gearbox and acssories for $5000 ... Less then 200lbs

It's possible, but I would at least overhaul the engine because you don't know what abuse it's been through, sleds are like airplanes in that they go through a lot of abuse, then sit for long periods of time.

Yamaha might have accidentally made one the best aviation conversion engines ever....and then stuck it in a snowmobile...
the starter and alternator are integrated so its very light weight...the engine is designed to pump out electrical power for snowsuit warming...ect...so lots of juice to run your avionics...35-40 amp
on the carburetor version called the RX1 140hp...you just have to defeat 2 limp home modes.....throttle position mode and high coolant mode...ive heard its easy to do and then you have a rock solid CPU and harness...

Still one CPU and one harness. But as far as computers go, I agree they are good.

all engines that use a gearbox to reduce the high engine rpms to prop speeds...have to deal with something called torsional vibration...this is because automotive engines make their power in pulses on the downward power stroke ....so these pulses get passed through the gears to the prop and then bounce back to the engine...if not delt with this vibration will destroy the plane...in a matter of minutes....the little bit of play in the gears magnifies this ....so you have to dampen these vibrations...this is done in a variety of ways....

this is an example of how viking engines does it...but this method is common to many gear boxes.....a rubber donut flexes back and forth to absorb the pulses...like an elastic band

Rotax and others deal with it in different ways...using clutch plates that you service ...ect.....all these methods have one thing in common...if the engine stops the prop stops...

maybe someone can correct me...but I dont know of any aviation engine manufacture that ships engines out the door where the prop will windmill(except turbine engines)

BUT...with the Yamaha conversion .....

The most common way that the vibrations are being delt with is with something called a sprag clutch...a sprag clutch is like whats in a helicopter.....engine powers the blades....but if the engine quits...the blades can rotate freely so the heli can auto rotate to the ground...this means if the engine quits on an airplane with this sprag gearbox...you will have a windmilling prop on the front of your plane.

so the engine makes a power pulse...that goes to the prop...but the clutch disengages in a micro second to block the return pulse..then re-engages to alow more pulses to go to the prop......im no fan of a sprag clutch on an airplane...but I have to say the device itself is amazing in what it can do many times a second...

This sprag clutch eliminates all the vibrations completely.....and lets you put a gear box on smaller engines and 2 stroke engines that have been hard to use cause they are vibration prone...

the use of the sprag clutch in the Yamaha conversion is an engineering choice of the company making the most popular gear box ...

we are getting into an unknown area in aviation here....normally a windmilling prop is to be avoided at all costs....but trikes, gyros and some stol planes...have been flying for years with this windmilling prop...and saying there is no problem....

Torsional vibration happens on all engines, and the only way to truly dampen it out is to have the engine vibrate against a heavy spinning mass that is difficult to accelerate and decelerate. In a car this is the weight of the vehicle which needs to be accelerated and decelerated through the drive train.

The problem with torsional vibration on an airplane is that we don't have a heavy spinning mass, instead we have a light weight tuning fork called a prop. If you have the torsional vibration pulses at the same frequency that the prop resonates at (or a harmonic of it) then you are effectively tapping on a tuning fork at it's resonance frequency, and the result is rapid failure.

The rubber donut can change the resonance of the system and dampen the pulse amplitude, but unless it's very finely tuned for the engine, induction system, prop, temp, and load, it can't totally remove the torsional vibration. It simply moves the frequency away from the resonance frequency of the system so that you don't hit a harmonic and have everything fly apart.

A sprag clutch does not eliminate vibrations completely, it can remove the engine induced deceleration portion of the vibration, but it surely continues to tap on the clutch every time a piston goes through it's combustion stroke. I suspect part of the reason the yamaha works well is because it's a very high RPM engine. There isn't a lot of time for things to decelerate before we are back on a combustion stroke due to the 9k+ rpm.

Just like any other system that has torsional vibration, the answer is very plainly to test to find the frequency and amplitude of the vibration, then more testing to see where the system resonates. If the system doesn't resonate in any frequency between idle and redline, then you are good, if it does, then you placard to avoid that rpm.

Because the resonance frequency is determined by the system, the testing above would need to be per prop, and honestly it may change with induction or ignition system.

The point is that the yamaha seems to work, and many people are having success with it, but unless you know where your specific combination resonates at, and know that you aren't operating in that range or a harmonic of it, you are a test pilot. Saying it doesn't vibrate is not true.

Before I forget, it's important to note that these engines are geared down from the factory with an internal chain. By the time the power hits your prop, you have two gear reductions.

I think it's an interesting setup, and I think that more and more people will try it and find where it does and doesn't work, but we haven't completely arrived yet. I suspect Steve is really good at engine out landings for a reason, and I'm thankful for his willingness to be a test pilot and figure out what works.

[Frank]

I've heard it said that the gearbox on the front of a Rotax will protect the crankshaft in a prop strike.

[Cguy]

I believe you are correct. For better or for worse, I know of several Rotax planes that have had prop strikes, and after the new prop arrives and everything eyeballs OK, continue to fly safely for many hours. I know that goes against the old school direct drive engine lore, but the biggest deal with a Rotax prop strike seems to be.....you need a new prop! It's kind of handy really, an unexpected benefit of the reduction drive and it's slipper clutch.

[svyolo]

Rotax's also use very light props, by limitation I believe. I don't think it takes a lot to break a prop that light.

[zkelley2]

Ya, there's a max moment of inertia for the rotax gearbox. It pretty much rules out aluminum props. I think some of the early 80HP engines didn't have the slipper clutch and so you'd still have the prop strike issue with those.

Most of the composite props are designed to fail to save the engine. It's a feature.

[way_up_north]

It's possible, but I would at least overhaul the engine because you don't know what abuse it's been through, sleds are like airplanes in that they go through a lot of abuse, then sit for long periods of time.



Still one CPU and one harness. But as far as computers go, I agree they are good.



Torsional vibration happens on all engines, and the only way to truly dampen it out is to have the engine vibrate against a heavy spinning mass that is difficult to accelerate and decelerate. In a car this is the weight of the vehicle which needs to be accelerated and decelerated through the drive train.

The problem with torsional vibration on an airplane is that we don't have a heavy spinning mass, instead we have a light weight tuning fork called a prop. If you have the torsional vibration pulses at the same frequency that the prop resonates at (or a harmonic of it) then you are effectively tapping on a tuning fork at it's resonance frequency, and the result is rapid failure.

The rubber donut can change the resonance of the system and dampen the pulse amplitude, but unless it's very finely tuned for the engine, induction system, prop, temp, and load, it can't totally remove the torsional vibration. It simply moves the frequency away from the resonance frequency of the system so that you don't hit a harmonic and have everything fly apart.

A sprag clutch does not eliminate vibrations completely, it can remove the engine induced deceleration portion of the vibration, but it surely continues to tap on the clutch every time a piston goes through it's combustion stroke. I suspect part of the reason the yamaha works well is because it's a very high RPM engine. There isn't a lot of time for things to decelerate before we are back on a combustion stroke due to the 9k+ rpm.

Just like any other system that has torsional vibration, the answer is very plainly to test to find the frequency and amplitude of the vibration, then more testing to see where the system resonates. If the system doesn't resonate in any frequency between idle and redline, then you are good, if it does, then you placard to avoid that rpm.

Because the resonance frequency is determined by the system, the testing above would need to be per prop, and honestly it may change with induction or ignition system.

The point is that the yamaha seems to work, and many people are having success with it, but unless you know where your specific combination resonates at, and know that you aren't operating in that range or a harmonic of it, you are a test pilot. Saying it doesn't vibrate is not true.

Before I forget, it's important to note that these engines are geared down from the factory with an internal chain. By the time the power hits your prop, you have two gear reductions.

I think it's an interesting setup, and I think that more and more people will try it and find where it does and doesn't work, but we haven't completely arrived yet. I suspect Steve is really good at engine out landings for a reason, and I'm thankful for his willingness to be a test pilot and figure out what works.

I’m posting the coles notes of my last few months of looking into this engine....

I posted a collection of other pilots opinions and some of my own...there are no facts in my posts.. just opinions...

if it peeks someone’s interest... then a deep dive on the Facebook group will answer a lot of questions and fill in blanks

as of now I don’t own one... never flown behind one...

but you need to start somewhere...sort of like a blind date ....

since aviation is a serious matter.... double check all my information... and as you say...have a professional check over everything