Rotary Maintenance??

[Nathan Gifford]

Hello,

 

First post here. I have been following developments on rotaries with great interest. I read one line in Kitplanes that said one of the reasons Greg went to turbine was the maintenance on his rotary.

 

From what I have read so far, rotaries may require somewhat more maintenance than certified engines, but they are not maintenance hogs.

 

What does the group think?

[Jerry Schneider]

Greg Richter has written: If you're going to turn a propeller, I still say the rotary is the way to do it.

 

I don't think Greg switched to turbine for the maintenance. Probably more for the COOl Factor than anything else.

 

From what I've gleaned, the rotary has no more maintenance than the other options out there.

[CBarber]

Please note; there seems to be a lot of bad info regarding the rotary mostly based in ingnorance. I mean that in it true form as "lack of knowledge". As a result, what is not known is condemned. All things being equal, a rotary should require much less maintanance. As you learn more about the wankle rotary, you may tend to agree. FWIW.

 

All the best,

 

Chris

[Nathan Gifford]

Well I come from the old school of process control. Through very expensive problems I learned a lot about what is redundant and what was thought to be redundant (even during the last 24 hours).

 

After reading much about rotaries the reliability seems technically plausible. However, this may not apply in real world situations.

 

In the world of redundancy, 2 engine control computers are not really redundant: one of them is merely a backup to the primary. I like the idea of two engine computers, I just hope when one fails the other can take over without waking the passengars in the airplane!

 

From the comments I have read thus far, maybe Kitplanes overstated Greg's comments about rotary maintenance. I am sure the T58 is great engine except for its next overhaul.

 

I think if I build a Cozy, I would probably want to do a turbo 13B installation. By that time there should be a lot more flying and with more hours some real data may exist to see how reliable these powerplants are. If I were building a Defiant, I would be trying to locate a pair of 13Bs right now.

[Len Evansic]

Please note; there seems to be a lot of bad info regarding the rotary mostly based in ingnorance. I mean that in it true form as "lack of knowledge".

That's why I'm here, to banish my own ignorance. Let me throw out some of my ignorant beliefs here to be smashed. Disabuse me at will (but don't spin through overly rose-colored glasses).

 

First, It is my understanding that many rotary engines tend to have sealing problems that get worse with wear and turbocharging. This is why Mercedes dropped the Wankel and went to a turbodiesel in their C111/C112 cars back in the 70's. I understand that Mazda has done a lot of work to reduce these problems, but I am still worried about them.

 

What is the typical automotive life of one of these engines? 80,000 miles, 100k? 200k? I have no idea, but knowing this would help me evaluate if I want to trust one in an airplane.

 

My mother has had several 250k+ mile Subaru's that never needed an overhaul. I myself had a twenty-year-old diesel Benz that has 190k miles, and when I pulled the head that had a hairline crack, it still had cylinders that look like glass. The anecdotal evidence I've seen does not indicate that rotaries can come close to touching these for reliability.

 

Because of the power to weight ratio, I would like to use a rotary, but I am not convinced of the ease of maintenance or reliability. I am heavily leaning towards an auto conversion, not primarily because of initial cost, but because of the recurring problems that others note with cert. engines. These design-rooted problems tend to cost a lot, which is unattractive to me.

 

-- Len

[Nathan Gifford]

Well, I did have a conversation with my auto mechanic. He's not a run-of-the-mill shade tree mechanic. He is (and his son) one of the finest, skilled, knowledgable technicians I have ever met. Better still he is cheap.

 

I did ask him about rotary reliability. He says they are reliable powerplants today and should have little problem running over 250K miles. Of course he is still using cars as a reference, I do not know how he would feel about them in airplanes.

 

I think one of the pluses about some of the certified wankels being developed, is that the core of the wankel engine technology is the same (maybe not materials or workmanship). Whatever technology is put on these certified engines are probably worthwhile on conversions.

 

What would be really interesting is to see just how much maintenance is actually performed and if someone can give service intervals on beasts.

[David Staten]

 

First, It is my understanding that many rotary engines tend to have sealing problems that get worse with wear and turbocharging.

-- Len

Rotaries have tight tolerances. When new they should meet those tolerances. When rebuilt, you need to mike out everything and make sure its in spec. The factory engines were limited to first 8, then 10 psi of boost. 8 psi is comparable to 45" manifold pressure (speaking in aviation lingo). These limitations were to improve reliability and limit the damage a kid with a lead foot could do to the engine. As with anything, the more power you develop the more wear occurs. The sealing probs are a combination of several things - carbon fouling from poorly burned injection oil causing wear, detonation from using low octane gas for high power performance, disabling turbo boost limiters, etc.

 

 

What is the typical automotive life of one of these engines?

-- Len

The Jspec engines are replaced at approx 40,000 miles (100,000 km), an arbitrary number set by Japan for emissions reasons. American engines with 100,000 miles have been reported to be junk. BUT.. remember.. these are running stock oil systems and the carbon fouling is a major cause of wear.

 

I myself had a twenty-year-old diesel Benz ... The anecdotal evidence I've seen does not indicate that rotaries can come close to touching these for reliability.

 

Because of the power to weight ratio, I would like to use a rotary, but I am not convinced of the ease of maintenance or reliability.

-- Len

Diesels ARE a wonderful thing..durable, powerful and LOTS of torque... but when I went to Oshkosh 2 years ago, Theirlert or SAE or whomever it was there said "our engine wont work on your plane" and Deltahawk was saying "next spring" for the fifth or more summer in a row.. they joke that one year that prediction will come true. Diesels can burn Jet A, which is in NO danger of going away in the near future, and is not as refined as avgas, and not nearly as pricey. he diesels are also being priced in the >$25,000 range at a minimum. Comparing a gasoline rotary engine to a diesel is not a fair comparison. That being said, if the diesels were readily available for our application (we want to be airborne within 6 months) then we would have considered it. I must say when I met Chris, I was DEAD SET against auto conversions in aircraft. Chris prompted me to look at the rotary, I did my homework and can understand how the rotary, while not perfect, is a much better/more reliable source in my opinion than a horizontally opposed, air cooled, reciprocating aircraft engine.

 

There are a few folks out there with hundreds, even over 1000 hours on their rotary engines and are flying... Ed Anderson and his RV-6. Tracy Crook and his RV-4, building an RV-8 with a renesis). Dave Leonard and his Turbo RV-6. John Slade just started flying his Turbo Cozy Mark IV. I will say that most of the probs with flying rotary engine airplanes appear DIRECTLY related to using the stock automotive turbo in an aircraft application (OR.. to improper rebuild..even by alleged engine professionals). I would recommend a low pressure/high output/High A/R turbine/compressors. I am still working out the details on what aftermarket turbo to install on our (chris and I's engine) and I want to see how Dave Leonard and John Slade do with their latest turbo incarnations.

 

If you dont want to build your own, I would recommend Bruce Turretine as a source for a rebuilt, "complete" powerplant (rather than using a local engine guy). he is considered the "go to" guy in rotary aviation circles, and sells many of the parts needed to do a rebuild, as well as a fairly decent "how to" video.

 

Dave

[David Staten]

I did ask him about rotary reliability. He says they are reliable powerplants today and should have little problem running over 250K miles. Of course he is still using cars as a reference, I do not know how he would feel about them in airplanes.

 

What would be really interesting is to see just how much maintenance is actually performed and if someone can give service intervals on beasts.

250,000 miles at an average of 50 auto miles/hr comes out to 5000 hrs engine use.

100,000 miles at the same average comes out to 2000 hrs engine use

 

Typical aviation engine maintenance specifies oil change at every 50 hrs(2500 miles auto equiv at highway speeds).

 

100 hr inspections come out to 5000 auto miles equiv. This would be a good time to lube up everything, check compressions in the combustion chamber, check the coolant system. Check the belts and hoses. Inspect the plugs. Check bolt torque, look for cracks anywhere.. etc.. standard things that an aviation engine would be looked at.

 

If you dont hit 100 hrs in a year, then at LEAST do the "100 hr" annually. At 100 hrs a year, or even 200 hrs a year, you will have to take 5-10 years to hit "100,000 miles equivalent"