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Roger Lee

Rotax 915is fuel injected turbo 135 hp

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New Rotax 915is trubo fuel injected  135 hp

 

With an intercooler it will make it a little harder to fit under a cowl and it is a heavier engine. At 185 lbs. this will be more in line with the weight of Cont. and Lycoming.

Will be more likely to see certified aircraft use.

 

 

http://www.rotax-owner.com/en/rotax-blog/item/43-915is

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Yes, it looks like it's targeting the helo and gyro market...it's a small turbo for the low end FAR 33 market and experimental market. 

 

Too large for the LSA market.  Could be a choice for the STOLs (carbon cub) and the RV-10 or the RV-14.  Notice it's built on the 912iS...

 

Side note.  ICON came out with their first production plane and delivered it at OshKosh to it's first paying customer.  The plane is not competitive, priced at $250k...does have a BRS chute, has no glass PFD, but does have the Garmin 796.  100Ktas cruise (the thing is heavy, tiny useful, short range). And the cost of the trailer would cover five years of hangar fees.

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Hi Roger,

 

I note its displacement is identical to the uls at 1352cc, which suggests a lot of shared parts.

 

I have two questions for you, if I may.

 

Are the 80hp ul engine components beefed up in any way to take the extra power generated by the turbo in the 914?

 

And would that answer give any indication of what changes might have been necessary on the uls engine to take the extra 35hp of the 915?

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There are aftermarket mods that increase the horsepower of rotax's engines. Of course, rotax doesn't like them, but people do use them.

 

As for the 912UL vs the 914: if I recall correctly, the dog gears are a different profile, as well as the way some of the engine parts seal and route (carbs and the bowl vent, for example). But in large part, they are the same. I think I recall being told at Rotax school that rotax likes to keep engine parts as similar as possible as it decreases manufacturing costs.

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The intercooler certainly suggests they intend it for continuous operation.

I wonder why they hung the turbo side-saddle. The 914 turbo is directly under the centerline. Are they just feeding it with the exhaust from one side?

They should be at the show Andy, maybe you can pop in and ask.

Also, maybe you can discretely ask about the price. For example, "Will the price increase be roughly proportional to the horsepower increase when compared to the 912is?".

Mike Koerner

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Will be more likely to see certified aircraft use.

And drones.  Thousands of drones.

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And drones.  Thousands of drones.

 

The US military has abandoned the 914 because they want drone engines that run on Jet-A....so this engine will not work for them either...

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Hi Bill,

 

That is true. The military is moving away from the 914 due to fuel. They have some left,, but are reducing inventory. The Rotax engines that the military buy from Rotax are a stripped down model and aren't like the ones you wiould get as a private buyer.

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Also, avoid any used engines that were used in the military. They come cheap for a reason; the military abuses the absolute hell out of them and by the time you get one, there's not much life left in the engine and overhaul would cost more than a new one.

 

This info comes from rotax training at LEAF. They've seen people send them mil engines and they are in bad shape.

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That's a really interesting article.  

 

If they came up with a viable 100hp turboshaft engine it would be extremely small and light compared to existing offerings - and it would be diesel/jet A.  That would change a few things.

 
Here's an innovative drone engine that's recently gone into production in the UK, and one of its variants has just been adopted to power a brand new SSDR aircraft called the E-go.

 
It's a rotary wankel, but it's powered by Jet A/Diesel, yet it's spark ignited.

 

http://www.rotronuav.com/engines/rt-300hfe

 

Very interesting.

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I wonder why they hung the turbo side-saddle. The 914 turbo is directly under the centerline. Are they just feeding it with the exhaust from one side?

 

If you watch the video, you can see all four exhausts leading to the offset turbo.

 

I think that would pretty much have to be the case - otherwise one cylinder bank would have more back pressure as it spun the turbo while the other would have less, leading to a power imbalance and vibration.

 

Right?

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Yep.

 

Still, they could mount a turbo anywhere, as long as the back pressures are equal and the losses are managed.

 

Also, I think that muffler under the engine is being used for noise abatement. I don't understand why it's there for any other reason when they could have just straight piped it out and saved a LOT of room.

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I have a 914 fitted in a Jodel D11. Its a superb engine so much smoother than the 912UL. It has all the chariteristics of the 80Hp which is also a very smooth running engine. If I had a choice I would choose the 914 then the  80Hp in the CTsw.

The 914 has 115Hp for 5mins 5800 rpm   & continuous 100Hp 5500 rpm (up to 15000 ft due to the turbo) . The 914 is expensive near 50% above the 912, The 80Hp is fitted to many CTs in Europe & there is little difference in take off or cruise compared to the 100Hp,( you can go on the European websites & compare the performance of the 80Hp against the 100Hp almost exclusivly fitted to US imports). They are limited to 480Kg MTOW in Europe in the light weight class. It is my understanding that the MTOW is often ignored with aircraft taking off with 1 pax & max fuel.

As a comparison in performance The 914 has a capacity of 1211cc, The 3 cylinder turbo Mecedes Smart motor is 814 cc, it is rated at 105Hp as fitted in the FK9 in Germany. It would appear from that comparison that the Rotax only relies on a low pressure boost & that  it could probably withstand considerably more boost to increase the HP. Fitting the intercooler would in itself give a significant increase in HP.

The Mercedes has a gearbox with a centifugal clutch, on tick over the prop does not rotate. I have travelled over 3000Km in the company of a FK9 with the 3 cyl turbo. At 100Kn the fuel burn was less than 10 Lph. The engine is near silent at cruise. The computer also measures the fuel burn so accuratly that the pilot would know accurately to the litre what was required to top up his tanks after a 3 hour flight.

I suspect with the Mercedes that the centrifugal clutch is neccessary to allow the engine to reach a rpm range where the turbo is producing boost. There may not be enough power to drive the fixed blade prop without the turbo.I would like to know if I am correct in that assumption.

John

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Hi John.

Here's my two cents' worth:

 

I guess that the prop doesn't spin because the complete unit is taken directly from a Smart car without any modification to the moving parts in the engine or gearbox. 

The gearbox is designed to produce very little torque at the output shaft when running at idle speeds due to automotive requirements - when sitting at the lights, for example, you don't want the engine pulling hard.  This just translates to no prop movement when at idle in the FK9.  No real drawback, I think.

 

On the other hand, there is a really huge benefit in not modifying the engine at all, because you automatically inherit the thousands of hours of R&D Mercedes has already done on the unit, and that translates into superb reliability, which is a primary requirement for a successful aero engine.  

 

I'm interested in all the small aero engines being developed and I think this is by far the best one I've seen.  It really would give the Rotax a run for its money and I'm a huge fan of diesel power.

 

Can you give us more info on your experiences and knowledge of the unit?  How does it feel compared to the Rotax?  How many are currently flying?  What do you think of the belt drive? Is the program thriving or struggling, etc. Also, where did you fly in (or with) one?

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I talked to the Rotax guys at Oshkosh...they don't really know any more than we do!

 

I asked about price:  "Uh, not sure since it's a year or two from production."

 

Asked about whether boost is continuously available:  "Uh, not sure, but I assume so."

 

Hmm...sounds like we have a ways to go to obtain reliable information on this engine.

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The engine isn't here yet, not till the end of 2017...and it won't be sold into the LSA market, so unless you are gonna do an experimental, or look at changing to a gyrocopter, or a some kind of strange adaptation to make a slow four-seater  why care at all....

 

Because I care about aviation.  All kinds, not just my little blindered version of it.

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The Mercedes petrol & diesel engines are avaulable from <www.fk-lightplanes.com>. I have flown over 3000 km in the company of the 3 cylinder petrol turbo Mercedes & a number of times in the left seat. The FK9 was originally the demo plane for the importer into Australia & it is now owned by a fellow club member. The gearbox is driven by a very wide (about 75mm) toothed belt which appears to be well over engineered & would be very easy to replace. It may easily absorb more power than gears but because of the ease of replacement of belts & bearings it would be my personal preference to gears.

The first diesel powered LSA  for delivery to Australia is due in the next few weeks & with a bit of luck I will get to fly in her. The diesel turbo has 80Hp & weighs 89Kg installed. The petrol is about 79Kg which is near the installed weight of the 912.
The main benefit would be the economy & availability  of Jet A at 9 litres per hr. The lower fuel burn would more than make up for the extra installed weight of the diesel. There is one other advantage , the core is a standard Smart car engine

which I believe is about  $3500 Au.

I do like the Rotax 912s, love the 914 but for me the Mercedes is a real alternative & my next plane may be powered by a diesel.

johnr

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Hi John,

 

I have to say I agree with you - it's the only alternative to Rotax that I'd seriously consider.

 

The diesel is not listed as an option on the FK website though, so what are you expecting to arrive in Oz?

 

Regarding belt vs. gearbox: does anyone know if a belt would absorb more power than a gearbox?   You'd think it would be the other way round.

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Belts were tried in the 1980's in Ultralight's with poor results. They would always strip teeth if toothed and smooth belts were usually clustered in 4's and 5's, but would still break. They may not want to  go back to that.

 

That said many motorcycles and ATV's are now run by belt and with good success. Even the Rotorway helicopter that had a chain went to a belt.

Belts now days are different from yesteryear.

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