2 stroke expectations

[DDDowney]

Thanks to all of you. This has been very informative for me. I plan to read over them again to try to get in my head what goes on with the engine at different phases of flying so I can think ahead of the engine as to what it needs to be at safe operating for me and it.

 

[RangeRider]

Flew a Kolb with Rotax 503, and a Rans S-12 with Rotax 582. Probably a thousand hours between the two without a failure. Both had oil injection, and ran way over TBO. Nearly every time I saw a 2-Stroke failure when I was flying ultralights, it was induced by some modification to eek out one more horse power. Fly in front of a Lycoming now, difference is $35K and months long overhaul versus 2 beers, couple hundred dollars, and a lazy afternoon.

 

[DDDowney]

From flying a 150 perspective, what types of throttle operations that we use for general maneuvers in the 150 would you NOT use on a 2 stroke? Take offs, descents, landings, if this question makes sense?

 

[Dana]

The big thing with a 2-stroke is you don't to make long fast descents at partial power, or any situation where the airflow is trying to windmill the prop faster than the engine would turn it at that throttle setting. Generally you'd stay at cruise power, then descend at idle. Make sure it's adequately warmed up before takeoff. Keeping an eye on temperatures is more critical than a 4-stroke.

 

[Flatiowa]

Dana nailed it. Only addition I would potentially ad is ZERO ethanol fuel.

 

[Dana]

Dana nailed it. Only addition I would potentially ad is ZERO ethanol fuel.

I used fuel with ethanol in my 2-strokes, because that was all that was available. But it did affect the jetting; ethanol runs leaner so you need a bigger jet. It meant that if I filled up with avgas on a cross country the engine would then run rich. I didn't have to worry about lean seizure, but it would bog a bit at mid throttle settings. At the end of each flying season I would switch to avgas to avoid ethanol issues during winter storage.

And, of course, if you go cross country you have to deal with oil... not a big deal with oil injection, but if you're premixing you need a way to do it. I carried a big syringe to measure the oil and squirt it into the tank halfway through refueling, then shake the plane from the wingtip to mix it.

 

[Cap'n Jack]

Dana nailed it. Only addition I would potentially ad is ZERO ethanol fuel.

I'll note that small 2-strokes, such as model plane engines, run on methanol with the oil pre-mixed. They also contained 5 to 20% nitromethane. Most of the issues with ethanol apply to methanol. It's fine for a model plane, but I don't want it in something I'm riding in.

 

[German guy]

I used to be a big 2-stroke guy for motorcycles, but also for the weight-shift LSA (Rotax 582) we owned back in Germany.

Not a single hiccup over all those years. Then again, I know a lot of people who continuously had (or still have) problems. Without exception, they tinkered with their engines or maintained them poorly. Rotax, Yamaha, or Tohatsu: if left in factory condition, supplied with the proper gas/oil mixture (too much oil actually makes it run leaner), and properly maintained, it will run just as reliably as a 4-stroke.

There is a reason why fishermen, e.g. in the Bahamas, prefer 2-stroke Yamaha outboards even though they have to import them from abroad.

 

[pfarber]

Rebuilding a 2-stroke every 500 hours is a once ever 5 or so year cost... and nowhere near the cost of a Lycosaur.

I'd rather fly and rebuild every 3-5 years for $2k than HOPE a Lycosur makes 2000 hours (which most PPL never do) and have a 6 month down time for parts and a cost of $35k

But its normal to spend $1500+ on magneto's every 500 hours. Or a cylinder or two ever 300-400 hours. 'cause reasons.

 

[pfarber]

Most of the issues with ethanol

What if I told you that the FAA (paid Baylor University) ran a Cessna 150 for 10 years on 100% ethanol and only had to rejet it? That there was minimal wear and none of the issue with lead. Because they did and I can.

Or that there is an STC for 100% ethanol available now?

Ethanol has so many old wives tales that I laugh when I hear them being told like it's poison. It ain't.

 

[Cap'n Jack]

What if I told you that the FAA (paid Baylor University) ran a Cessna 150 for 10 years on 100% ethanol and only had to rejet it? That there was minimal wear and none of the issue with lead. Because they did and I can.

You mean the work by Shauck et al? has anything changed since last year?

Or that there is an STC for 100% ethanol available now?

On the PA-25 airframe, a few models of the O-540, and a few of the IO-540? and the O-235? I'm no expert on STCs but don't the airframe and the engine both need the STC? @Dan Thomas and @Doc Holliday have probably forgotten more about it than I ever knew, although I'm setting a rather low bar. Can I buy said STC?

Ethanol has so many old wives tales that I laugh when I hear them being told like it's poison. It ain't.

Drink too much of it, and it is a poison. Ethanol has about double the vapor pressure of avgas causing a higher potential for fuel line vaporization and vapor lock. Ethanol is also totally miscible with water. We can burn ~50% alcohol in water at room temperature. That doesn't mean the engine will make power with that amount of water. Instead of just looking for water layers when sumping, we would need to measure the specific gravity to verify there isn't so much water in the tanks that the engine won't stop.

 

[AV8R_87]

Ethanol is also totally miscible with water.

And that will corrode aluminum like crazy.

 

[Dan Thomas]

Rebuilding a 2-stroke every 500 hours is a once ever 5 or so year cost... and nowhere near the cost of a Lycosaur.

I'd rather fly and rebuild every 3-5 years for $2k than HOPE a Lycosur makes 2000 hours (which most PPL never do) and have a 6 month down time for parts and a cost of $35k

But its normal to spend $1500+ on magneto's every 500 hours. Or a cylinder or two ever 300-400 hours. 'cause reasons.

The never-ending voice of non-experience. You never give up on those OWTs, do you?

 

[Randomskylane]

My expectation is that they will fail a whole lot more often than standard four-strokes, and I need to be ready for off-field landings at all times.

In a similar vane: Sample size of one-I met a 30 something year old pilot who told me he’d had 27 engine out landings!

So my suggestion is to fly in an area that has some flat/ treeless / etc spots

 

[German guy]

Rebuilding a 2-stroke every 500 hours is a once ever 5 or so year cost... and nowhere near the cost of a Lycosaur.

I'd rather fly and rebuild every 3-5 years for $2k than HOPE a Lycosur makes 2000 hours (which most PPL never do) and have a 6 month down time for parts and a cost of $35k

But its normal to spend $1500+ on magneto's every 500 hours. Or a cylinder or two ever 300-400 hours. 'cause reasons.

Apples vs. oranges, IMHO. Aircraft with 2-strokes are usually flown much less than aircraft with an Conti or Lycoming. Fuel consumption of a 2-stroke also tends to be significantly more, plus you have to mess with 2-stroke oil.

Each type has its applications. All I'm saying is that 2-strokes CAN be very reliable if properly maintained, not tinkered with and if they come from one of the better brands like Rotax or Yamaha.

 

[pfarber]

And that will corrode aluminum like crazy.

Water settles in gas and does the same thing. How is that any worse? Old wives tale.

In 10 years, with 100% ethanol, not one of the tanks corroded 'like crazy'. Or at all.

Ready the study and educate yourself. You're just spouting off random google search results.

 

[pfarber]

The never-ending voice of non-experience. You never give up on those OWTs, do you?

Simple math proves the point. Nothing about certified motors wins when comparing costs. Even when car motors (and even snowmobile) have been in airplanes. Rotax? Diamond?

Why do those always seem to be forgotten?

 

[pfarber]

You mean the work by Shauck et al? has anything changed since last year?

On the PA-25 airframe, a few models of the O-540, and a few of the IO-540? and the O-235? I'm no expert on STCs but don't the airframe and the engine both need the STC? @Dan Thomas and @Doc Holliday have probably forgotten more about it than I ever knew, although I'm setting a rather low bar. Can I buy said STC?

Drink too much of it, and it is a poison. Ethanol has about double the vapor pressure of avgas causing a higher potential for fuel line vaporization and vapor lock. Ethanol is also totally miscible with water. We can burn ~50% alcohol in water at room temperature. That doesn't mean the engine will make power with that amount of water. Instead of just looking for water layers when sumping, we would need to measure the specific gravity to verify there isn't so much water in the tanks that the engine won't stop.

When I spoke with one of the University staff (a woman, forgot her name, can look it up in email) she said that a flight school out west was working on converting their fleet. So the STC is being used. Not that many people know of it sadly.

Depends if the engine is TC'd to the airframe, doesn't it? From the Baylor study the only thing they changed on the Cessna (150 IIRC) was the carb jet. Minor alteration. Field approval. Read the study its highly informative.

Drink to much water and its poison. So what. Again, repeat after me: ALL YOUR OLD WIVES TALES WERE DEBUNKED BY THE 10 YEAR BAYLOR STUDY. ALL OF THEM. EVERY ONE.

Why not EDUCATE yourself rather than regurgitate untrue statements?

If the two wizards of knowledge for it, how do they know it? more inane babble...

 

[Doc Holliday]

When I spoke with one of the University staff (a woman, forgot her name, can look it up in email) she said that a flight school out west was working on converting their fleet. So the STC is being used. Not that many people know of it sadly.

If it’s STC’d, then what’s the “working on it”? It’s not like it takes weeks or months.

What flight school? I’d like to see what they think, how many airplanes are converted, etc.

Depends if the engine is TC'd to the airframe, doesn't it? From the Baylor study the only thing they changed on the Cessna (150 IIRC) was the carb jet. Minor alteration. Field approval. Read the study its highly informative.

Huh? It’s STC’d. What’s the “field approval” for?

 

[pfarber]

Apples vs. oranges, IMHO. Aircraft with 2-strokes are usually flown much less than aircraft with an Conti or Lycoming. Fuel consumption of a 2-stroke also tends to be significantly more, plus you have to mess with 2-stroke oil.

Each type has its applications. All I'm saying is that 2-strokes CAN be very reliable if properly maintained, not tinkered with and if they come from one of the better brands like Rotax or Yamaha.

You mean math? I'm directly comparing costs... what are you comparing?

Please show something that supports your 2-stroke hour data. FUel consumption is higher but so is output. The 2 stroke is making more power at higher RPM. Can't make power without buring gas.

Your also just saying common sense... if you maintain something, it will last. Yes, we agree.

 

[pfarber]

If it’s STC’d, then what’s the “working on it”? It’s not like it takes weeks or months.

What flight school? I’d like to see what they think, how many airplanes are converted, etc.



Huh? It’s STC’d. What’s the “field approval” for?

I just re-read the email chain and its a soaring flight school/club trying to convert the tow planes to enthanol. The tow planes engine (o-540) is covered by one of Baylors STC so I think they are trying to use the approved data as a basis for a new STC.

IIRC only modification of the engine was a carb rejet. So if any required approvals to the airframe would be a minor alteration, which can be done via field approval. Since I cannot get a copy of the actual STC I'm going off the the Baylor study which is the basis for the STC.

 

[Dan Thomas]

Simple math proves the point. Nothing about certified motors wins when comparing costs. Even when car motors (and even snowmobile) have been in airplanes. Rotax? Diamond?

Why do those always seem to be forgotten?

Show me the math that says that Rotex or Austro (Diamond) come out ahead on a hp/hours to TBO basis.

And then include the MTBF numbers (mean time between failures) especially for the two strokes. An affordable engine is not a better deal if it quits on you.

 

[Cap'n Jack]

What flight school? I’d like to see what they think, how many airplanes are converted, etc.

I'd like to know, too

I just re-read the email chain and its a soaring flight school/club trying to convert the tow planes to enthanol. The tow planes engine (o-540) is covered by one of Baylors STC so I think they are trying to use the approved data as a basis for a new STC.

If you have this data, it should give enough information to say a name. If an STC already exists for the engine, they should only need an airframe STD.

Depends if the engine is TC'd to the airframe, doesn't it?

I mentioned this in my reply and that's why I mentioned both the airframe and engine needing to get an STD. I mentioned @Doc Holliday and @Dan Thomas because I know they would correct me if I'm wrong. On airframes and powerplants, they have shown their expertise for some time. The engine, tanks, and fuel lines and valves (such as fuel shutoff valves), and any filters need to be tested together. This is just like the Mogas STC's, where one is needed for the airframe and another for the engine. As an example, see the Peterson Mogas web site: https://autofuelstc.com/

Drink to much water and its poison. So what.

You demonstrating your ignorance is "so what". Drink a pint of Everclear all at once and you won't be able to tell me the outcome of that experiment. Drink a pint of water and you'll only use the bathroom in a little while. You are the one who brought up "poison".

ALL YOUR OLD WIVES TALES WERE DEBUNKED BY THE 10 YEAR BAYLOR STUDY. ALL OF THEM. EVERY ONE.

I obviously did read it. I mentioned the primary author, which provides evidence that I know of the study in more detail than most people. Is the total miscibility or water and ethanol an old wives' tale? Is the lower energy content of ethanol compared to gasoline an old wives' tale? 76,000 BTU per gallon of ethanol compared to 114,000 BTUs for gasoline. It's well known that cars running on E85 get roughly 75% the milage compared to gasoline. So a plane that flies 3 hours with a reserve of 1 hour now becomes a 2 hour plane with an hour reserve.

Why not EDUCATE yourself rather than regurgitate untrue statements?

You haven't shown which of my statements are untrue. I do know something of the properties of ethanol and gasoline.

If the two wizards of knowledge for it, how do they know it? more inane babble...

This reads like babble. What two wizards? Knowledge for what?

 

[UngaWunga]

 

[WJG-GMT-RootBeer]

I am a Private pilot but do not own a plane. The thought of an ultralight something, just always comes to my mind as a way to just fly for the fun of it locally. If I were to learn really how to care for a 2 stroke, are they a dependable for a small plane like a Kolb or Areolite? I have heard of people who never have any trouble with them, and of course shock cooling locked up things. What are some of your experiences from those who fly with them? You know once bitten by the flying bug it never goes away.

Thanks David

I was told, years ago, "friends don't let friends fly two-strokes".

That might have changed over the years, but I'd encourage you to look at certified alternatives as a beginner. Way easier to sell if it does not float your boat.

 

[fast99]

is this the same Rotax that makes engines for Sea-Doo? If so, hope they aren't using the same engineers for anything that leaves the ground.

 

[AV8R_87]

Random 2-stroke thought: would having two plugs per cylinder prevent fouling? The idea being that even if one fouls up having the other one continue to fire would provide the high temperature needed to clean the fouled one.

 

[Dana]

Random 2-stroke thought: would having two plugs per cylinder prevent fouling? The idea being that even if one fouls up having the other one continue to fire would provide the high temperature needed to clean the fouled one.

The Rotax 582 has dual ignition, but for redundancy. Fouling isn't a big problem with the proper mixture and oil ratio.

 

[Daleandee]

The Rotax 582 has dual ignition, but for redundancy. Fouling isn't a big problem with the proper mixture and oil ratio.

Most of the 503's that I flew or were on the planes that members of the club had at the time were dual ignition. One CH2CW had an older single plug 503. FWIW I can never recall anyone fouling a plug on one of these engines (447, 503, 582) but as a group we were quite diligent about maintenance with new plugs, new or rebuilt fuel pump, & new fuel and primer line every year during condition inspection. Use clean, fresh fuel, proper two stroke oil, and set the carbs correctly and the Rotax engines are quite reliable (not as much as a four stroke IMHO) and easy to deal with. Most problems came from those that were always tinkering to make it "gooder" ...

 

[Barrett50]

On two strokes and oil supply. Begin with the statement I have maybe 2 hours total flying a UL with a 503. So, experience in the av-world of 2 strokes is quite limited. However, I have built many 2 stroke MC engines, and worked on enough waverunner/jetski 2 strokes to learn a bit and offer some suggestions on oil supply.

Synthetic vs dino 2 stroke. Don't be fooled, there's a world of difference in how they mix(or don't mix) with various fuels. For those mixing in the tank without an autolube independent pump and injectors, mix and use without long storage, agitate very well, and agitate again before flight. My experience over the years is that syn oil is generally better lube, but tends to fall out of suspension when the pre-mix is allowed to sit over time and temp.

Next, setting the pre-mix too lean is the road to catastrophic type failures. Usually a seizure or a hole in the piston. Going too rich in pre-mix has a similar problem, because there is less fuel, but generally speaking will not be as close to catastrophic failure. A pre-mix 50:1 with syn I would say to stay just on the high side of the oil ratio.

Autolube: Introduced back in the 70s(I think there was a car in EU in 60s that had a 2 stroke engine with autolube, maybe), my vote is Yamaha was the expert in the field. I raced RD-400 twin two strokes and used the autolube with no pre-mix. If one looks at the mixture cam of the autolube pump/delivery, one might see the cam profile is not uniform. When asked, Yamaha service advised that the idle mix is about 65:1, and mid throttle around 45:1, and full throttle is all the way down to 35:1. This goes along with the taper in the carb main jet that richens the mixture as the throttle plate is opened. So, use a needle barrel type carb for land use. Whether this is a good idea for aviation use is an interesting question. But - the autolube should provide a greater volume of oil at higher throttle settings. I love autolube, as long as it doesn't get gummed up. Another vote for syn 2 stroke oil.

I would worry about a 2 stroke that is regularly flown above 5-6000'. I've heard that most aviation type 2 stroke carbs have some kind of altitude compensation? If it doesn't, plan on having a mixture control and fly by CHT and EGT mixture control. Carbs on 2 strokes are also more often exposed to reversion(reversing the flow in the intake and maybe the venturi). depending on the intake runner, and if it has reed valves. Would want a reed valve I think for aviation carb to minimize any reversion at low and mid throttle.

Advances have been made since my days of 2 strokes on ground and water vehicles. The EPA basically put them all out of business in 87--ish, and later for watercraft. With a well designed and engineered aviation 2 stroke, I guess I'd give it a try, with a landing speed down around 25-35MPH.

 

[Dana]

Next, setting the pre-mix too lean is the road to catastrophic type failures. Usually a seizure or a hole in the piston. Going too rich in pre-mix has a similar problem, because there is less fuel, but generally speaking will not be as close to catastrophic failure. A pre-mix 50:1 with syn I would say to stay just on the high side of the oil ratio.

Best not to say "lean" or "rich" when talking premix as it can be confused with rich or lean air-fuel ratio. For premix, best to stick with what the engine manufacturer recommends.

Autolube: Introduced back in the 70s(I think there was a car in EU in 60s that had a 2 stroke engine with autolube, maybe), my vote is Yamaha was the expert in the field.

Rotax has oil injection on some models including the 582. Some like it, others don't trust it and remove it.

I would worry about a 2 stroke that is regularly flown above 5-6000'. I've heard that most aviation type 2 stroke carbs have some kind of altitude compensation? If it doesn't, plan on having a mixture control and fly by CHT and EGT mixture control. Carbs on 2 strokes are also more often exposed to reversion(reversing the flow in the intake and maybe the venturi). depending on the intake runner, and if it has reed valves. Would want a reed valve I think for aviation carb to minimize any reversion at low and mid throttle.

There is a kit to add altitude compensation to the Bing carbs used on Rotax engines, but I've never seen one. Mostly it's the low and slow crowd running 2-strokes.

Rotax engines use rotary valves, not reeds. Cuyunas were piston ported.