Considering the Rotax 915

[loftus]

I don't think this ought to be a Yamaha vs Rotax discussion. Rotax are great, reliable engines with all the factory support, service advisories etc that go with certified aircraft engines. Fortunately the non-certified engines get pretty much the same benefits in this regard as the certified engines. True Rotax are expensive, technology possibly a little dated and conservative - but again probably related to the logistics of being certified engines.
Lycoming and Continental are the most dated of them all, but still the go to standard in civilian aviation. The more conservative approach suits most of those like myself who are either not homebuilders, or people who would rather use 'stock' aircraft engines in their aircraft and for whom guaranteed factory and dealer support are essential. (Worldwide)
Yamaha not being part of the certified family will appeal to those who are ready to step out of the envelope in order to benefit from things like price, more power etc. But remember that option is available for all engines, including Rotax, Lycoming (clones particularly) etc. Rotax 914 mods for example can provide upwards of 160HP with some racing mods being even higher.
I think if Yamaha were to enter the aircraft market they would definitely be competitive, but are hardly likely to be sold anywhere near to their current prices. Same goes for all the car mods like Suzuki and Aeromomentum out there.

 

[Resasi]

if they ever decide to get into the same aero market niche occupied by Rotax it would spell disaster for the comparatively tiny Bavarian engine builder.

...but they haven’t???

 

[ultracruiser41]

Building an outback version of a naked Tango.....was going to give the Yamahaha a try.....but decided to go with the Honda Viking Engine.....new.....factory fresh engine with a tried and true, heavy duty gearbox. Mounting area for the gearbox on the Yamahaha just not very beefy. Besides.....the Yamahaha is used....no idea how many hours or how it was ran.....old sled harness and lots of unnecessary wires. Looking forward to the Honda.

 

[ultracruiser41]

OutBack Tango project.

 

[DonBishop]

Hey that is not true. I know of at least 2 Yamaha conversion engine outs in trikes alone. I think they were 130 HP (claimed but never materialized).

The STOL guy who broke his 914 enroute and documented it on youtube, had a bastard 914 on his plane. It was his 914 assembled from used parts from parts from various sources and aftermarket parts. Devil is in the details. Its not that 91x series never have engine outs. Its that people in conversion market make claims that are not verifiable or complete fabrications and the fleet size is low.
Can I ask what is the fleet size of your Yamaha based conversions right now and how many hours have the top 5 conversions flown? 100, 200, 500 etc.?

I absolutely hate the fact that some of the Yamaha conversions require a clutch because they shake the hell out of themselves with load at idle.

I have heard that the Rotax 915is has an internal "rattle" at low rpm. That sounds like metal on metal trying to beat itself into failure and operators are "idling" at 2200 rpm to quiet them down. Any idea what that is about? Because, it does not sound like quality to me.

 

[Abid]

I have heard that the Rotax 915is has an internal "rattle" at low rpm. That sounds like metal on metal trying to beat itself into failure and operators are "idling" at 2200 rpm to quiet them down. Any idea what that is about? Because, it does not sound like quality to me.

Its zero degree dogs on the gearbox because somehow the ECU was getting confused with 30 degree dogs in gearbox like 912ULS. Both 912iS and 915iS have zero degree dogs. That rattle is normal and there is an extra oil spray nozzle in the gearbox to keep it super lubricated. It does get better with higher RPM (like above 2200)

 

[Kevin_Richey]

Not having any experience operating one of the Rotax 900 series engines, but is this rattle the same as the two-stroke Rotax gearboxes noise & shaking because anything under about 2,200 engine rpms while turning the prop wasn't smooth?

 

[ultracruiser41]

Not having any experience operating one of the Rotax 900 series engines, but is this rattle the same as the two-stroke Rotax gearboxes noise & shaking because anything under about 2,200 engine rpms while turning the prop wasn't smooth?

Yes

 

[martin-av8r]

Its zero degree dogs on the gearbox because somehow they ECU was getting confused with 30 degree dogs in gearbox like 912ULS. Both 912iS and 915iS have zero degree dogs. That rattle is normal and there is an extra oil spray nozzle in the gearbox to keep it super lubricated. It does get better with higher RPM (like above 2200)

Interesting info about the ECU was getting confused with 30 degree dogs

i never touch the inside of a rotax 915 , i look a bit on some parts diagram for the parts that can cause ecu problem

and it look like he possibly have a 36-2 tone wheel with is 2 crank sensor

i find this kitplane article from Paul Bertorelli

Inside Rotax

It’s really a factory within a factory. The company leverages high-volume recreational engine output to help sustain its aircraft motors. By Paul Bertorelli.

www.kitplanes.com

with this info

Unique to gasoline aircraft engines, Rotax motors have a dual-mode clutch. The ramped structures in the hub form a slipper clutch for torque isolation; the overload clutch is inside the hub. The number 500 refers to the overload torque limit—500 newton meters.
And speaking of dual, the Rotax clutch can be thought of as a dual-mode device. As with the diesel, it’s also intended to isolate the prop from engine torque pulses, but it also has an overload function. As shown in the photos, the clutch hub has three semi-circular ramps or dogs that are held in contact with each other via strong spring washers. The contact surfaces provide a slipper clutch of sorts, allowing up to 30 degrees of rotational slippage during normal operation, so the prop doesn’t feel the engine’s firing pulses. In the 912 iS, by the way, the dog angle has been reduced to zero. Rotax reasons that the FADEC’s firing control over the engine reduces the need for torque isolation.

Both models have the overload clutch, however. It’s similar to an automotive friction clutch design to slip if the prop strikes something hard, saving the crank from damage. The torque limit is 500 Nm (368 ft- lbs) for the carbureted engines and 600 Nm (442 ft- lbs) for the fuel-injected iS engine.

—P.B.

Two versions​

Examples of the Zero degree dog hub (left) and 30 degree dog hub with slipper clutch (right).


The dog is now integral with the propeller gear

Contrails ! Rotax reduction gear

Rotax reduction gearbox : what does it look like inside ?

contrails.free.fr

 

[loftus]

I just completed an Edge Performance EFI conversion on my 912ULS engines. Despite best attempts at balancing carbs, the fuel injected engines run noticeably and remarkably more smoothly at lower RPM's. The previous rattle from the gearboxes noticeable below about 1700RPM are gone, and now the engines idle easily around 1450 RPM. Even on one mag when RPM can drop to around 1000, I'm impressed how relatively smooth they still are. There's a slow motion video somewhere out there of a carburretted Rotax that I've seen that shows just how much side to side movement of the 912 / 914 engines there is at low RPM even with balanced carbs.

 

[martin-av8r]

When i get a look in some parts diagram , i think i recognise the ignition coil brand nology for the efi IS rotax

i dont have one in hand to check the primary winding Ohm's resistance with a meter

carburator rotax ignition is cdi capacitive discharge , normally efi like the yamaha is inductive ignition with induction coil with higher primary Ohm's than cdi , with longer spark duration

1

665613

BOBINE DOUBLE 912 IS

4

378.56

Fig.1 | 665-613 | DOUBLE IGNITION COIL | Cant.4 $339.00

Avirex

avirex.fr

Site is undergoing maintenance

Site will be available soon. Thank you for your patience!

aerosistemasmexico.com

check the dual tower

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High performance nology profire ignition coil for, Harley Davidson, Triumph, Kawasaki, Honda, Yamaha, BMW, Triumph, Ducati, Suzuki, single fire, dual fire.

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BRP rotax dont make coils but BRP can put there logo on the nology coil and you have 1 coil for the price of 4

https://www.cps-parts.com/catalog/rtxpages/rotax-15-09426.php

 

[martin-av8r]

I just completed an Edge Performance EFI conversion on my 912ULS engines. Despite best attempts at balancing carbs, the fuel injected engines run noticeably and remarkably more smoothly at lower RPM's. The previous rattle from the gearboxes noticeable below about 1700RPM are gone, and now the engines idle easily around 1450 RPM. Even on one mag when RPM can drop to around 1000, I'm impressed how relatively smooth they still are. There's a slow motion video somewhere out there of a carburretted Rotax that I've seen that shows just how much side to side movement of the 912 / 914 engines there is at low RPM even with balanced carbs.

Cool ! that you have a better and smoother running motor with your conversion

i think also apart from injecting fuel to each cylinder at the back of the intake valve

you also have a better and bigger intake plenum that receive the 4 intake tube with bell mouth

inside the bigger plenum tube for better dry ( no fuel ) air mixing equalisation per cylinder

i think your kit keep the black CDI ignition box ?

 

[loftus]

Cool ! that you have a better and smoother running motor with your conversion

i think also apart from injecting fuel to each cylinder at the back of the intake valve

you also have a better and bigger intake plenum that receive the 4 intake tube with bell mouth

inside the bigger plenum tube for better dry ( no fuel ) air mixing equalisation per cylinder

i think your kit keep the black CDI ignition box ?

Yes, ignition unchanged, except of course new timing gear and connection to Electronic Control Unit

 

[CLS447]

I miss my 447 & my 503.......WTH is wrong with 2 strokes ? Would have not been able to get into this without them ! Damn Baltimore scored again ! GO GB Packers !

 

[WaspAir]

.WTH is wrong with 2 strokes ?

They have a knack for going quiet at inconvenient times.

 

[BEN S]

Does that mean your 4 strokes go quiet at convenient times?

 

[WaspAir]

Yes, when I pull the mixture at the parking ramp.

 

[wolfy]

I just completed an Edge Performance EFI conversion on my 912ULS engines. Despite best attempts at balancing carbs, the fuel injected engines run noticeably and remarkably more smoothly at lower RPM's. The previous rattle from the gearboxes noticeable below about 1700RPM are gone, and now the engines idle easily around 1450 RPM. Even on one mag when RPM can drop to around 1000, I'm impressed how relatively smooth they still are. There's a slow motion video somewhere out there of a carburretted Rotax that I've seen that shows just how much side to side movement of the 912 / 914 engines there is at low RPM even with balanced carbs.

I have found the trick to a smooth running rotax is not only balanced carbs but also having accurate egt readings to enable exact idle mixtures, then they are like a sowing machine.

wolfy

 

[loftus]

I have found the trick to a smooth running rotax is not only balanced carbs but also having accurate egt readings to enable exact idle mixtures, then they are like a sowing machine.

wolfy

Can you explain how having exact egt readings enables you to have exact idle mixtures on a carburreted Rotax? What is your procedure to adjust idle mixtures according to EGT readings? Do you have EGT readings for each cylinder?
I always thought my 912's ran pretty smoothly, until I installed EFI. Other advantages of EFI are much easier starting even when it's cold and no adjusting throttles (just leave at idle) when starting, better fuel consumption, and a little more power, supposed to be about 5% more.
Personally I am looking forward to never having to balance carbs again, because even if one gets the balance perfect, they don't stay that way. I still think having 1 carb instead of two would have been simpler, eliminated the need to balance the carbs, and not sure what Rotax were thinking with 2 carbs.
And then of course not worrying about floats not floating, needle valve sticking etc. (This happened to me 2 weeks after the 200 hour carb rebuild by Rotax dealer.)

 

[Abid]

Can you explain how having exact egt readings enables you to have exact idle mixtures on a carburreted Rotax? What is your procedure to adjust idle mixtures according to EGT readings? Do you have EGT readings for each cylinder?
I always thought my 912's ran pretty smoothly, until I installed EFI. Other advantages of EFI are much easier starting even when it's cold and no adjusting throttles (just leave at idle) when starting, better fuel consumption, and a little more power, supposed to be about 5% more.
Personally I am looking forward to never having to balance carbs again, because even if one gets the balance perfect, they don't stay that way. I still think having 1 carb instead of two would have been simpler, eliminated the need to balance the carbs, and not sure what Rotax were thinking with 2 carbs.
And then of course not worrying about floats not floating, needle valve sticking etc. (This happened to me 2 weeks after the 200 hour carb rebuild by Rotax dealer.)

The 200 hour carb rebuild by Rotax is a big CYA and usually results in problems because the guy building it is just not as careful. I never rebuild my carbs till I reach close to 500 hours if everything is working. I leave it alone