Discussion of Sport Pilot June Edition Article Predicting the Demise of Two-Strokes

[Guest davidh10]

I originally commented in the "Magazine" thread about the above referenced article and suggested a new thread to discuss the article's contentions. Turboplanner also thought we should, so here it is..

 

The content and thrust of the article was a contrast to the thread of similar name we had here a while back. The article took a few twists and turns, but was focussed on Rotax two-strokes only. That seemed a narrow perspective, given I've noticed a few other names being mentioned in posts recently by home builders. The key messages seemed to be:-

 

• A rebuilt 2-stroke engine costs almost as much as a new one. Something, to which I guess you can attest. That combined with the much lower TBO than 4-strokes is helping kill them.
   
   
  
• Older models are being discontinued (504), and development seems to have stopped on the 582.
   
   
  
• Two-strokes future seemed entwined with rag & tube due to the power to weight ratio.
   
   
  
• New sales of 4-strokes (912) is dominating, but price is approaching GA levels.
   
   
  

 

 

I'm not sure I agree completely with some of those contentions... we could start another thread or continue the previous "Death of the Two-Stroke" thread if anyone is interested in debating the article?

 

* You really need to read the article. The above key messages provide some context for this thread, but are not a comprehensive coverage of the points put forward in the article.

 

 

[rdarby]

Well I don't have anything to add, but it does have a psychological affect. I am still torn between buying a fancier 4 stroke or going cheap with an X-Air. I find I was going between them and learning as I went, but now I have this bad feeling about 2 strokes, mainly as I now believe, based on the article, that although I can get the X-Air for $15,000, I am going to need to spend that again to replace the engine in a year or two, so I might as well just spend $40,000 (or less) on a 912 powered plane.

 

So psychologically it helps kill the two stroke.

 

Ryan

 

 

[fly_tornado]

what is more unreliable, a high revving four stroke or a rotax 2stroker?

 

 

[Guest davidh10]

...So psychologically it helps kill the two stroke.

 

Ryan

True. Rumour kills markets and manufacturers will only invest to make a profit, but there are several other factors that are impinging on the market forces as well:-

 

• Anti-pollution laws. We've seen it with cars and it's creeping into fuel. pretty soon, we'll all be using PULP in lieu of ULP to avoid the Ethanol. Sooner or later emission laws will impact aircraft engines, but I suspect it will hit motorbikes first as there's a much bigger number of them and getting them off the road or changing the power plant will make much more impact to the amount of pollution than a few aircraft that are flown less than 100 hours a year.
   
   
  
• The development of very efficient light 4-stroke engines.
   
   
  
• The seeming market trend toward "plastic fantastic" recreational aircraft that are heavier and need bigger power plants (most, but not all).
   
   
  

 

 

On the other hand, none of the motorbike manufacturers have stopped offering two-stroke bikes, electric power is in its experimental infancy and we are still seeing new aircraft delivered with two-stroke engines.

 

As also said in the article, parts for the two-strokes will be available for long after production ceases.

 

Your cost evaluation is probably also a major factor in many people's decision making, but sometimes it is a matter of how much can I afford now versus cost of on-going maintenance. That will depend on how many hours per year you fly and there's a big variance, but probably few recreational flyers that are not doing it professionally (instructing), would be doing a lot more than 100 hours per year. It's hard to guestimate before you actually do it. When I bought my aircraft I figured it would be more than 50 but less than 100. Last year was just under 100 and this year looks like it may be a bit over 100. I think I'd be close to the highest hours per year of the local pilots I know, except for one pilot who is retired and often flys twice a day.

 

It will be interesting to see other's views.

 

 

[fly_tornado]

Fuel economy and the TBO is the big killer of Rotax 2strokes. I haven't heard how many Hirth engines have made it too the TBO. Hirth are the only people putting a lot of money into 2 stroke technology for planes anymore.

 

 

[drifterdriver]

what is more unreliable, a high revving four stroke or a rotax 2stroker?

Depends on who makes the engines. I've had a lot more engine failures with 4 strokes from a certain manufacturer than I have in 2 strokes.

 

 

[pudestcon]

For me it's about what can I do now with the money available to me - the overall cost over time is of secondary consideration when the all up dollars are simply not available now.

 

The aircraft in my avatar to the left here will cost me about the same (by the time it flys) as the $23,000 quoted for a 912 4 stroke in the magazine article - and I'm stretched guys!!! Put simply - it's too bloody much to buy an aircraft with a 4 stroke engine in it.

 

Pud

 

 

[facthunter]

You'll get a lot of good service out of your 2-stroke Pud if you look after it. Keep your fuel clean, (always filter it), and freshly mixed and look after your fuel system. Pump, hoses and Carb bowls. The motor should be good for 400 hours and that works out at $20 per hour for the engine life. The problem will be worse in the future, with people trying to breathe life into the "junk" remnants of what is left of them. Even a Lycoming is only worth doing one rebuild (In My View). Don't listen to the smoke and mirrors brigade. Unless someone really knows these engines in a practical sense, just do what Rotax recommend. Wally Rudin had a great feel for the Rotax 2-strokes. Nev

 

 

[Bandit12]

Honda have already ceased production of their two stroke bikes - mostly caused by California banning the sale of new two stroke bikes (both on and offroad) a little while ago. California is I believe the biggest market, and Honda the biggest player by volume.....

 

Personally, I have no issues with the reliability of a two stoke. But you do need to keep an eye on the maintenance. One thing that doesn't seem to rate a mention often is how much a two stroke hates to be left standing and not run regularly. A quick way to kill a two stroke.

 

 

[pudestcon]

You'll get a lot of good service out of your 2-stroke Pud if you look after it. Keep your fuel clean, (always filter it), and freshly mixed and look after your fuel system. Pump, hoses and Carb bowls. The motor should be good for 400 hours and that works out at $20 per hour for the engine life. The problem will be worse in the future, with people trying to breathe life into the "junk" remnants of what is left of them. Even a Lycoming is only worth doing one rebuild (In My View). Don't listen to the smoke and mirrors brigade. Unless someone really knows these engines in a practical sense, just do what Rotax recommend. Wally Rudin had a great feel for the Rotax 2-strokes. Nev

Yeah I reckon I will get good service from the 582 facthunter, and it certainly will not be from lack of loving care and attention. With my lifestyle and where the aircraft will be hangared, I reckon I'll average (long term) about 50 hours a year (1hr or so per week), so 400 hours equates to 8 years of flying for me - enough value for money I reckon.

 

 

[turboplanner]

As I understand it there is a timeline to the end of two strokes in Marine applications due to emission difficulties, and that may flow on to the snowfields where Rotax is a dominating brand.

 

The lowest emissions and best fuel consumptions are coming from diesels, and there are now rules in Le Mans for a diesel class in sports car racing and Diamond Star introduced the first diesel powered light aircraft to Australian in about 2007/8.

 

In the RC world a lot of guys are switching to four strokes, so they can be made light if there's a market.

 

In Formula 500 speedway racing where the Rotax became very popular because it was a low cost of life* two stroke by comparison with some of the more exotic two stroke engines, the Kawasaki four stroke with it's longer life seems to be pulling the costs down.

 

The Recreational aviation business has partly stepped on its own foot going away from localised flying towards trying to achieve cross country flying to around the same conditions as GA, so the aviation demand is drying up.

 

It would be worthwhile studying what's going on in the Skidoo and PWC worlds because it may be that the smaller models will go four stroke for environmental reasons.

 

* Cost of life is the combination of up front cost, servicing cost and repair cost. It's not unusual for the more expensive engine to have the lower cost of life.

 

In any of these engines, aviation use being a constant use is much tougher on the engine than intermittent use, where the engine can cool down.

 

Under load the increased volume of combusted air increases chamber and manifold temperature, and this increase doesn't stop until either the heat is absorbed by a cooling fin or water jacket. If the gas flow doesn't slow down, then engine testing at full load usually requires that at a certain point temperature must remain constant (otherwise engine components would start to distort and failure would follow)

 

We fit into this constant speed category, whereas a motor cycle engine's cooling system can be reduced for weight because it's operation is intermittant. Hence only a few automotive engines have proved reliable for flying, and the reasons for that is because they were over-designed, so suit constant loading.

 

The Skimobile engines hauling a constant heavy load would appear to be ideal for aviation and that's proven to be the case.

 

One factor which can lead to short life (and bad mouthing of the engine) is prop diameter and pitch.

 

The cooling test, where the temperature profile looks like the front end of a gentle bell curve switching to a straight line at the acceptable top temperature can go sharply up if a prop draws more power than the test dyno did, and that will make the temperature line climb beyond the test limit and that will dramatically shorten the life of the engine.

 

The owner will say he hasn't had any luck with that engine, or the engine is unreliable but upper cylinder failures are almost always the result of too much power demand for too long.

 

For this reason, hanging a prop on an engine which hasn't been used for aviation before puts you out in no mans land.

 

 

[fly_tornado]

So does your insurance cover your damages if you have an engine outage past the TBO time?

 

 

[drifterdriver]

So does your insurance cover your damages if you have an engine outage past the TBO time?

Bingo! Particularly in a school.

 

 

[drifterdriver]

I'd have a talk to your broker (and maybe Steve Bell) and get them to clarify in writing the situation but I would be surprised if they didn't see it as an out.

 

Nick

 

 

[facthunter]

There have been some high (for two strokes anyway) hours examples of 582's but you cannot guarantee reliability. The motors have roller and ball bearings everywhere and the end of useful life is not heralded by perceptive "play" always. The hardened surfaces fatigue and the metal flakes off eventually where the loads are highest and the bits of hardened metal can destroy the bearing cages rapidly with complete bearing failure following straight away.

 

Most ring problems are associated with carbon build-up behind the rings which are then forced against the cylinder wall when the piston gets hot and they seize or break and jamb in the exhaust ports, and that is the end of that. The other sudden failure is burning a hole in the crown of the piston. This is invariably the result of LEAN mixtures. ( the real enemy of the two stroke engine).

 

One good thing about a two stroke is that the engine always has oil around it. You can leave it for a while and not worry too much about corrosion internally. The carbs should be run dry at shut-down ( or drained) if you don't use it regularly. The remaining fuel will evaporate out of the carbs and leave an oil residue which can cause the engine to be lean next time it is used. IF the motor has an oil pump this is NOT necessary.Nev

 

 

[fly_tornado]

I don't know why Rotax recommend Castrol 2T when TTS will reduce the amount of ash build up on the rings

 

 

[Guest davidh10]

Is there any regulation that says an overhaul is compulsory in the typical classes we fly? I know I can do what I want in my 95-10 class engine and I think Pud can do the same in his Thruster unless I am mistaken.David

It does indeed seem that some aircraft escape the mandatory maintenance schedules:-

 

• CAO95-10 Sect 5(f)... Must be maintained in accordance with the RAA or HGFA Technical Manual...
   
   
  
• RAA Technical Manual says: For 95-10 and 95-55 paragraph 1.2 & 1.5 aircraft that are "owner operated" the maintenance schedules are up to the owner, however for 95.32 and 95.55 paragraphs 1.3, 1.4, 1.6, 1.8, 1.9 the aircraft manufacturer's maintenance schedule must be followed or in the absence of such, the Technical Manual schedule.
   
   
  

 

 

* The above is paraphrased for brevity and thread context.

 

I must admit, my choice of four-stroke was based on:-

 

• Wanting to do some reasonable cross country trips, hence fuel tank size and consumption (6hrs flying on a tank, excluding reserve).
   
   
  
• My own aversion to two-strokes (Yes, my mower is also 4-stroke).
   
   
  
• Total Cost of Ownership (TCO)... at current rate, over 100hrs p.a., 400 hours would expire in less than four years, plus I bought second hand with 750 hrs on the 4-stroke, so many I have many years till TBO.
   
   
  

 

 

 

 

[pudestcon]

It does indeed seem that some aircraft escape the mandatory maintenance schedules:-

• CAO95-10 Sect 5(f)... Must be maintained in accordance with the RAA or HGFA Technical Manual...
   
   
  
• RAA Technical Manual says: For 95-10 and 95-55 paragraph 1.2 & 1.5 aircraft that are "owner operated" the maintenance schedules are up to the owner, however for 95.32 and 95.55 paragraphs 1.3, 1.4, 1.6, 1.8, 1.9 the aircraft manufacturer's maintenance schedule must be followed or in the absence of such, the Technical Manual schedule.
   
   
  

 

 

* The above is paraphrased for brevity and thread context.

 

I must admit, my choice of four-stroke was based on:-

 

• Wanting to do some reasonable cross country trips, hence fuel tank size and consumption (6hrs flying on a tank, excluding reserve).
   
   
  
• My own aversion to two-strokes (Yes, my mower is also 4-stroke).
   
   
  
• Total Cost of Ownership (TCO)... at current rate, over 100hrs p.a., 400 hours would expire in less than four years, plus I bought second hand with 750 hrs on the 4-stroke, so many I have many years till TBO.
   
   
  

Did you take into account the "opportunity" cost of having that extra (as opposed to a lesser amount if buying a 2 stroke) money tied up in a 4 stroke engine? A bit pedantic I know, but worth considering. What about if you borrowed the money, as has been seen in a poll conducted sometime ago about financing aircraft? Should you take the extra borrowing costs into account as well?

 

Pud

 

 

[fly_tornado]

what about the resale? a rotax 582 with 200 hours won't interest a buyer as much as a hks with 400hours and on a plane purchase $4-5000 premium wont be that big a deal

 

 

[Guest Crezzi]

So does your insurance cover your damages if you have an engine outage past the TBO time?

Unfortunately its an academic question since I doubt you will get any insurance company in Aus to cover a 2-stroke however few hours the engine has.

Cheers

 

John

 

 

[Guest davidh10]

Did you take into account the "opportunity" cost of having that extra (as opposed to a lesser amount if buying a 2 stroke) money tied up in a 4 stroke engine? A bit pedantic I know, but worth considering.

Qualitatively, yes. Quantitatively, no. I recon, like fly_tornado, that the much steeper depreciation outweighs the opportunity cost.

What about if you borrowed the money, as has been seen in a poll conducted sometime ago about financing aircraft? Should you take the extra borrowing costs into account as well?Pud

Yes, if you have financing costs, then those should be taken into account. I didn't, so while I'm foregoing some income, that is partially off-set by paying correspondingly less tax.

 

 

[turboplanner]

I don't know why Rotax recommend Castrol 2T when TTS will reduce the amount of ash build up on the rings

Disclaimer: This is not referring to Rotax policy

 

The Service guys usually get to know the problem customers and the problem oils because they log the statistics and the bad ones show up quickly.

 

So when the programme for the new design starts, they aren't going to be on the list.

 

Faults with the old engine will have been logged, and they try to design them out (sometimes not possible due to tooling)

 

Today they try to design in more fuel efficiency and lower emissions, and only then more power

 

Then they have to change the design because they stuffed up and the new parts foul old parts when assembled, so some compromise occurs (e.g. oil hole diameters if they come out into open air from the new casting to the old casting.

 

The they get a running engine which seizes after an hour on the dyno.

 

That may require some more machining

 

Then they may have to go up the scale with lubricants

 

Then they may find that they may get satisfactory life cycle (5 dropped engines per 100) using say Castrol 2T like Rotax have

 

Then some customer comes along and either extends the oil change intervals or asks his mate what he should use and the mate with 2 hours experience using sump oil and chook manure says that's what I'm using and I'm not having any problems.

 

The mistake they make Fly-tornado is that they don't explain (when it's critical) that the engine failed the life cycle test on everything except Castrol 2T (again I'm not referring top Rotax here), which would communicate to the customer the importance of the correct lubricant. This same principle also applies with grease specifications for earth moving equipment where the manufacturer may specify three types of grease for different areas but the operator pumps it all from the same drum - reliability goes down, R&M costs go up.

 

 

[facthunter]

When a vehicle/ engine comes on the market there will be certain oils available, that meet the specification. Later......better?? oils turn up but the factory never revises the old listings. Later models that are almost identical will recommend different oils which would obviously be OK/better for the earlier models, but no-one makes the connection officially. At least in aero engines oil companies have responded to a need (camshaft lobe corrosion) and produced oils that rectify the problem. Nev

 

 

[fly_tornado]

I suspect that the reason Rotax recommend Castrol 2T instead of TTS is that the modern oils are designed for nikasil plated alloy barrels instead of the cast iron ones that rotax still use.

 

This is a good indication why two strokes are toast

 

http://www.uflyit.com/hks_rotax_cost.htm