How does Rotax do it?

[Warmi]

Ultimately is not about Rotax being better or whatever ...

One could argue that the reason for the problems with the 737 was that Boeing was trying every way they could to avoid having to re-certify the airplane with a new configuration to properly accommodate the new engines.

Exactly, the whole debacle can be traced not to technical reasons but to attempts to get around overly costly rules and regulations because doing it right way would trigger all sorts of expensive regulatory burdens.
Interestingly, Tenerife disaster similarly can be traced to the pilot in command rushing his way thru to avoid being stuck due to the regulated working hours limits.

 

[Tantalum]

attempts to get around overly costly rules and regulations because doing it right way would trigger all sorts of expensive regulatory burdens

Indeed. And good point on Tenerife. We create rules so people find a way to break them, then create more rules so those can't be broken again, then wonder why innovation died sometime in the 1980s and why everything is so expensive and requires a committee now. Want to develop a new TOILET for a plane, guess what, you'll spend oodles of cash and years on certifying that contraption.. just to create a bowl with a hole in it that people can defecate into

It's a little crazy

My whole point on Rotax, was that somehow someone found a cost-comparable way (to a new Lyco / Conti) to create a modern, turbocharged, electronic controlled, single lever, push button, tiny displacement engine.. when we've been told that for one reason or another the legacy manufacturers were the only option. Obviously a 141 hp engine won't replace most 180 hp applications.. but it's not far, we are a tiny 39 hp away, and, if you are flying out of KTEX in the middle of summer I'd take a Cherokee with that Rotax 915 in it every day over a standard Lyco O360..

We are close... I wouldn't be surprised, especially given the flexible rules of EA / LSA / etc., that in the next decade we will see a 200 hp Rotax

BRING IT!

*Incidentally, I am surprised that there aren't any smaller or more cost effective turbine options out there, the Extra 500 uses a 450 hp tiny Rolls Royce turboprop to power it, and allegedly burns somewhere around 20 gph in cruise.. that's not. And turbines are reliable as all hell, and typically see a TBO well beyond what you see in a piston.. plus Jet A is, in many cases, cheaper and more readily available

 

[Tantalum]

^edit, "that's not bad"

 

[kyleb]

*Incidentally, I am surprised that there aren't any smaller or more cost effective turbine options out there, the Extra 500 uses a 450 hp tiny Rolls Royce turboprop to power it, and allegedly burns somewhere around 20 gph in cruise.. that's not. And turbines are reliable as all hell, and typically see a TBO well beyond what you see in a piston.. plus Jet A is, in many cases, cheaper and more readily available

There are several reasons turbines haven't been downsized. First, they don't scale well - with an 8' fan, a 1/8" clearance between the fan and shroud doesn't result in much efficiency loss. With a 16" fan, the efficency loss from that that gap is much larger. Second, turbines are inefficient at low altitude where GA types fly. Third, cost.

That said, people are working on it and will hopefully come up with good solutions.

 

[mondtster]

My whole point on Rotax, was that somehow someone found a cost-comparable way (to a new Lyco / Conti) to create a modern, turbocharged, electronic controlled, single lever, push button, tiny displacement engine.. when we've been told that for one reason or another the legacy manufacturers were the only option. Obviously a 141 hp engine won't replace most 180 hp applications.. but it's not far, we are a tiny 39 hp away, and, if you are flying out of KTEX in the middle of summer I'd take a Cherokee with that Rotax 915 in it every day over a standard Lyco O360..

The 915 isn’t TCd is it? If not, it should be compared to the non-TCd Lycoming clones then. How do they compare cost wise? I haven’t priced either so I don’t know.

Technologically advanced or not, I’m buying the engine that best fits the airframe and is the most durable. I’d like to think the Rotax is more durable but I don’t think we’re going to know for sure since that data really isn’t collected and even if it was, unless the testing was performed in a controlled environment it wouldn’t be worth much.

 

[Stan Cooper]

Indeed. And good point on Tenerife. We create rules so people find a way to break them, then create more rules so those can't be broken again, then wonder why innovation died sometime in the 1980s and why everything is so expensive and requires a committee now. Want to develop a new TOILET for a plane, guess what, you'll spend oodles of cash and years on certifying that contraption.. just to create a bowl with a hole in it that people can defecate into

It's a little crazy

My whole point on Rotax, was that somehow someone found a cost-comparable way (to a new Lyco / Conti) to create a modern, turbocharged, electronic controlled, single lever, push button, tiny displacement engine.. when we've been told that for one reason or another the legacy manufacturers were the only option. Obviously a 141 hp engine won't replace most 180 hp applications.. but it's not far, we are a tiny 39 hp away, and, if you are flying out of KTEX in the middle of summer I'd take a Cherokee with that Rotax 915 in it every day over a standard Lyco O360..

We are close... I wouldn't be surprised, especially given the flexible rules of EA / LSA / etc., that in the next decade we will see a 200 hp Rotax

BRING IT!

*Incidentally, I am surprised that there aren't any smaller or more cost effective turbine options out there, the Extra 500 uses a 450 hp tiny Rolls Royce turboprop to power it, and allegedly burns somewhere around 20 gph in cruise.. that's not. And turbines are reliable as all hell, and typically see a TBO well beyond what you see in a piston.. plus Jet A is, in many cases, cheaper and more readily available

I wouldn't be surprised to see much higher energy density battery technology developed in the next decade leading to practical electric propulsion for 2 and 4 place GA airplanes competitive with today's airplanes that use internal combustion engine propulsion. By practical and competitive I mean having similar endurance, range, climb performance, and speed combined with better reliability and lower operating and maintenance costs.

 

[Stephen Poole]

The 915 isn’t TCd is it? .

TC in 2017, and has won Engine Of The Year. Or some such.

 

[Tarheelpilot]

... and now you're back to the regulatory aspect. The FAA is not helping matters in GA.

Actually I think they are most of the problem.

 

[Tarheelpilot]

One could argue that the reason for the problems with the 737 was that Boeing was trying every way they could to avoid having to re-certify the airplane with a new configuration to properly accommodate the new engines.

One could also add that the biggest contributor to the pressure cooker focus on that strategy were the people buying the airplanes.

 

[Clip4]

You do realize there are LSA offerings flying with *smaller* Rotax that have far superior performance than what our beloved Lycos give us in the legacy fleet (VL3 climbs at 1200, cruise of 165, <500 ground roll), but this was less praise for this particular engine and more that Rotax is doing what many say is impossible (lighter weight, lower displacement, gear box, full ecu single lever, etc)

The VL3 is an experimental aircraft. To obtain the performance values you list the manufacturer is unable to meet FAA requirements for production airplanes. If you want to make that comparison, we can put a Glassair III @ >240 KTS with an antique Lycoming into the discussion and how the Rotax is not approved for Acro. and the Lycoming is.

 

[Tantalum]

unable to meet FAA requirements for production airplanes

I guess that's part of my point though. The FAA's job is to keep us safe, but if they're stifling advancement... then one could argue they've also stunted advances in safety. Someone up top posted reliability performance comparing Rotax / Lyco / Conti.. and they're virtually equal. And that's knowing that the Rotax are going in home builts with who-knows-what kind of care and standards. Who knows, if a Rotax was babied as much as a typical privately owned Cherokee it might even be superior in reliability

The Glassair III is a great example though.. it *IS* possible to build a small GA plane with a reasonable powerplant that can be optimize for speed, or a certain performance parameter

Safety is critical, and the FAA has a big hand to play in how safe US aviation travel is.. but Part 91 does not have a market that is hundreds of billions of dollars huge, and their agenda is pushing more and more people to EA.. is the net effect of their GA safety push actually less safe ultimately?

 

[ElPaso Pilot]

For those that keep kvetching about only having 140 hp, vs their 180hp lycosaur, for many parts of the country it works out well.

95% of 140 is 133hp
65% of 180 is 117hp

Start with high DA airports,throw in a constant speed prop, and the story gets even better.

Spent a lot of time switching between Thielert conversions and conventional 172s in El Paso; the little Thielert was the preferable airplane to fly from a power perspective.

A 4112 runway altitude turns into 6k to 8k plus DA on a hot day. The Lycomings were downright anemic in climb and cruise by comparison, and the higher you went, the better the comparison got.

If Rotax can get the cost and reliability done right, even this little engine has significant potential.

 

[Tantalum]

A 4112 runway altitude turns into 6k to 8k plus DA on a hot day. The Lycomings were downright anemic in climb and cruise by comparison, and the higher you went, the better the comparison got.

YES!!!

I'd swap the 915 out for the Lyco if I could. I'm willing to bet most people are not getting 180 horse out of their Lyco's anyway with questionable timing on the magneto's, completely manual leaning and a host of other factors that little constant speed with electronic ignition controls is going to be cranking out similar levels of power and give you that power high up well above 10000 ft

 

[Clip4]

For those that keep kvetching about only having 140 hp, vs their 180hp lycosaur, for many parts of the country it works out well.

95% of 140 is 133hp
65% of 180 is 117hp

Start with high DA airports,throw in a constant speed prop, and the story gets even better.

Spent a lot of time switching between Thielert conversions and conventional 172s in El Paso; the little Thielert was the preferable airplane to fly from a power perspective.

A 4112 runway altitude turns into 6k to 8k plus DA on a hot day. The Lycomings were downright anemic in climb and cruise by comparison, and the higher you went, the better the comparison got.

If Rotax can get the cost and reliability done right, even this little engine has significant potential.

Except there is zero reason not to run a 180 HP Lycoming at 75% power/135 HP and a lot of reason not to run a Rotax at 95% power.

 

[kyleb]

Except there is zero reason not to run a 180 HP Lycoming at 75% power/135 HP and a lot of reason not to run a Rotax at 95% power.

I think his point was that if DA is high enough, the turbo'd rotax will come out ahead. True.

But for the 90% of us (or whatever) who live at 1000 MSL or lower, a big bore solution will be superior from the perspective of clearing the runway fence.

 

[Warmi]

The VL3 is an experimental aircraft. To obtain the performance values you list the manufacturer is unable to meet FAA requirements for production airplanes. If you want to make that comparison, we can put a Glassair III @ >240 KTS with an antique Lycoming into the discussion and how the Rotax is not approved for Acro. and the Lycoming is.

VL3 is a light sport plane with stall speed at 30 knots and max cruise at 165 knots ( the retractable version ) - if it qualifies as a Light Sport, which is supposed to be on the safer end of the spectrum , comparing to Glassair is somewhat pointless.
Yes, it is not magic - you get these numbers by making a very light plane and the price you pay for it is rather obvious, especially on bumpy days but still, people are innovating and you can’t do that if , as a small company , you hope to sell maybe 500 or so planes at 100-130k each - the certification process alone would pretty much kill all your profits.

 

[ateamer]

VL3 is a light sport plane with stall speed at 30 knots and max cruise at 165 knots ( the retractable version ) - if it qualifies as a Light Sport, .

Not at 165 knots, and not with retractable gear.

 

[Shepherd]

I have a bunch of time ( >500hrs?) in Rotax powered aircraft and have only had 1 engine out incident caused by a bad carb flooding the engine at 12,600 ft.
While doing pattern work in one of the Cubs I had 5 engine failures while doing 7 landings. The 65hp, wooden prop combination does not like to throttle back in extreme cold.
The old engines, and the FAA requirements to continue using them, are a problem.
I would love a 912UL in a Cub.
Or maybe A Rotec radial?

 

[Grum.Man]

I have a bunch of time ( >500hrs?) in Rotax powered aircraft and have only had 1 engine out incident caused by a bad carb flooding the engine at 12,600 ft.
While doing pattern work in one of the Cubs I had 5 engine failures while doing 7 landings. The 65hp, wooden prop combination does not like to throttle back in extreme cold.
The old engines, and the FAA requirements to continue using them, are a problem.
I would love a 912UL in a Cub.
Or maybe A Rotec radial?

You certainly don't want a Rotec unless they have resolved the gear box issues. If you want a radial go Verner.

 

[bnt83]

Not interested in Rotax, considering that most of the parts for my Lycoming are built by three different competing manufacturers. Don't want to buy a spendy Lycoming crankshaft? Buy a continental one, or buy a superior one...

 

[DaleB]

Not interested in Rotax, considering that most of the parts for my Lycoming are built by three different competing manufacturers. Don't want to buy a spendy Lycoming crankshaft? Buy a continental one, or buy a superior one...

Of course the difference is you won't NEED to buy a crankshaft for your Rotax, at least the ones we're talking about here, during the life of the engine. Or cylinders, or a cam, or magnetos, or...

You WILL need to buy new spark plugs at roughly $3 each, and a mechanical fuel pump every five years or so, and three whole liters of oil every 25-100 hours, depending on how much of the time you burn leaded gas.

 

[bnt83]

Of course the difference is you won't NEED to buy a crankshaft for your Rotax, at least the ones we're talking about here, during the life of the engine. Or cylinders, or a cam, or magnetos, or...

You WILL need to buy new spark plugs at roughly $3 each, and a mechanical fuel pump every five years or so, and three whole liters of oil every 25-100 hours, depending on how much of the time you burn leaded gas.

Well, my engine is 52 years old and never been apart. It has had one cylinder replaced due to corrosion at the exhaust port tho. All the accessories have been replaced of course by now.

I'm just about ready to take it apart and freshen it up a bit.

 

[Skepilot]

Except there is zero reason not to run a 180 HP Lycoming at 75% power/135 HP and a lot of reason not to run a Rotax at 95% power.

I know that's the conventional wisdom with traditional engines. But as I understand it, Rotax says their 915iS engine is rated to operate at 95% power continuously. I recently flew the Sling TSi, and the TAF sales rep said there's no problem cruising at higher power settings, up to and including max continuous power, which is 95%. He says this will not harm the engine or reduce its lifespan, as the FADEC will protect the engine. True, or no?

 

[Tantalum]

I know that's the conventional wisdom with traditional engines. But as I understand it, Rotax says their 915iS engine is rated to operate at 95% power continuously. I recently flew the Sling TSi, and the TAF sales rep said there's no problem cruising at higher power settings, up to and including max continuous power, which is 95%. He says this will not harm the engine or reduce its lifespan, as the FADEC will protect the engine. True, or no?

for some reason there's an active desire on this board to assume that our 1940's engines are the absolute epitome of technology and there is zero room for advancement, and people like rotax, etc are just blowing smoke up our a****

everyone loves to think up of an example of gearbox failure or some dude in a home built that happen to have a rotax crashed. But every time a Lycoming or Continental fails it's just chalked up to a part of life

Of course you can engineer these things to run at 95% Max continuous power..

 

[Warmi]

The only reason I don't run my Rotax at 95% is because of fuel - at around 5200-5300 RPM is the sweet spot in terms of fuel consumption but I could run it at 5500 all day long.

 

[asicer]

The only reason I don't run my Rotax at 95% is because of fuel - at around 5200-5300 RPM is the sweet spot in terms of fuel consumption but I could run it at 5500 all day long.

How's the noise at 5500RPM? 5250RPM?

 

[Clip4]

How's the noise at 5500RPM? 5250RPM?

What did you say?

 

[Skepilot]

How's the noise at 5500RPM? 5250RPM?

Of course the prop RPM is slower due to the gear reduction drive. In the case of the Sling TSi, the prop RPM in cruise is down around 2300. I will say that, when I took off the Bose A20, I thought it was very loud. But then again, I think the SR22 is very loud, too. If/when I fly it again, I'll bring a db meter app on my phone to get a reading.

 

[Sundancer]

Precisely why I ordered a box-stock Lycoming IO-320 for my Experimental. At my current rate of flying, it'll go another 16 years till TBO.

Not positive, but I think the calendar TBO for an O-320 is twelve years?

 

[Capt. Geoffrey Thorpe]

How's the noise at 5500RPM? 5250RPM?

Not much different in my ride. The muffler is pretty good.

 

[Warmi]

How's the noise at 5500RPM? 5250RPM?

Here comes the noise... at idle at first then had to go around at full power because of some dude insisting on taking off while I was landing ....

 

[Matthew Rogers]

I'm just waiting for the day when one can legally swap a Rotax into a Piper taildragger...

There is a Rotax 150 design either EASA certified or close. Constant speed prop and 912

 

[James331]

I find rotax quite underwhelming. Kinda like a grown up ultralight motor

I’ll take a lyc or conti, or if I’m going to be fancy a solar turbine or even some type of auto conversion or a falconer

 

[Warmi]

I find rotax quite underwhelming. Kinda like a grown up ultralight motor

I’ll take a lyc or conti, or if I’m going to be fancy a solar turbine or even some type of auto conversion or a falconer

I am pretty sure you have never flown in one ... but that’s your problem.

 

[James331]

I am pretty sure you have never flown in one ... but that’s your problem.

Flew a sport cruiser, engine seemed to rev sooo high yet make sooo little power, didn’t have mixture or anything, I found it anoying and cheap, I was like huh, so this is probably about what it’s like to fly a ultralight with a modified snowmobile engine or something

Especially when I can get something like this for 10-15k at 150hp

 

[C-1 PILOT]

The only reason I don't run my Rotax at 95% is because of fuel - at around 5200-5300 RPM is the sweet spot in terms of fuel consumption but I could run it at 5500 all day long.

I concur...

 

[SoonerAviator]

Flew a sport cruiser, engine seemed to rev sooo high yet make sooo little power, didn’t have mixture or anything, I found it anoying and cheap, I was like huh, so this is probably about what it’s like to fly a ultralight with a modified snowmobile engine or something

Especially when I can get something like this for 10-15k at 150hp

WTF does that even mean?! 150HP is 150HP, doesn't matter if it's at 5500rpm or 2400 rpm. I don't think people are going to like the fuel burn on a turbine needed to make 150HP running around at sub 10K' altitudes compared to the Lycosaurus/Rotax models.

 

[Tarheelpilot]

WTF does that even mean?! 150HP is 150HP, doesn't matter if it's at 5500rpm or 2400 rpm. I don't think people are going to like the fuel burn on a turbine needed to make 150HP running around at sub 10K' altitudes compared to the Lycosaurus/Rotax models.

Everything with 150 hp is not the same. I wouldn’t want the turbine either unless it was just a toy

 

[Capt. Geoffrey Thorpe]

I wouldn’t want the turbine either unless it was just a toy

"Those who can not remember the past are condemned to repeat it." George Santayana 1906
"Give me Turbines or give me death!" Patrick Henry 1775

 

[SoonerAviator]

Everything with 150 hp is not the same. I wouldn’t want the turbine either unless it was just a toy

I didn't say everything with 150HP is the same, I said "150HP is 150HP", no matter the source in response to "rev so high yet make so little power". If we're talking about revs needed to make 150HP, I don't see what difference is makes what an engine does to make it happen. Now, if the complaint were about delay in spool up, or peaky power bands, etc. then there's a discussion to be had. But I don't see how something can make "so little power" if we're under the assumption that it is making the same HP as any other engine rated the same. The only caveat would be the weight of the powerplant, or HP/weight in the same airframe.