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  #1  
Old 11-25-2005, 12:38 AM
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Default Turbo experiments continue

I'm sorry to report that my hi-flow turbo from Turbonetics (Au) passed away quietly this morning.

Yesterday I reprogrammed the EC2 to give me a little more fuel at higher MAP. This helped a little, but then I aborted the take-off because the power level was still too low for my liking. Searching for the cause of the power loss today I did a runup with the cowl off and the intake filter removed. Rpm on full fine pitch was 4400. Adjusting timing a little either way made little difference. MAP 32 at 4400 was all I could get.

As I taxied back to the hangar there was quite a bit of blue smoke coming from the engine. The compressor wheel is still in place, but it has a lot of play and oil is leaking from the turbo internals.

I'll report on the post mortem when I have the results.

No. I'm not giving up on turbos. I see ceramic bearings and possibly a T04 in my future....
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Old 11-25-2005, 08:31 AM
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John, Have you given any thought to using a supercharger instead of turbo? When I was at Bruce Turrentine's shop last spring, he was very insistant about scraping any ideas I had of using a turbo for aviation purposes in a rotary because of high heat and back pressure. He said they are fine for intermittent automotive use, but not suitable for high rpm aviation use. His recommendation was a Vortec Supercharger system. I'm gonna wait and see how my Renesis performs N/A before I supercharge. Keep us posted of your findings on the cause of the turbo's demise.
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Old 11-25-2005, 10:41 AM
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Quote:
Originally Posted by David Clifford
turbos... fine for intermittent automotive use, but not suitable for high rpm aviation use. His recommendation was a Vortec Supercharger system.
That's exactly what I was thinking of using to normalize the Renesis.

Mike (back to shingling)
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Old 11-25-2005, 12:31 PM
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Dave, I really don't want to rework everything and install a supercharger. I'm sure that a suitable turbo solution can be found - I just havent found it yet.

The good news is that I did the Mazda hard copy output compression test this morning. It's like going to a cardiologist and getting an EKG. The tape shows that my engine is in perfect health. The Mazda guy said that even peaks around 60 or more would indicate that the engine is fine. All my peaks are above 90. His reaction was that that's perfect - did I just get the engine rebuilt?

So the question is - why did the turbo blow and what do I replace it with. The local Mazda guy says he thinks I've been running it too rich and overheated the bearings. He says there's a narrow band for safe operation 11.4 - 11.7. Too lean and you'll detonate, too high and you'll melt the turbo. Stay in the range and it'll run forever. This brings to mind Mike's comments of a few months ago - I need a wide band sensor so I can have a useful indication of what the mixture is. The current sensoer is way too sensitive to read. A touch of mixture adjustment to the left and it goes full lean. A touch to the right and it's off the scale rich. A wide band would sure make life a lot easier.
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Old 11-25-2005, 01:41 PM
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I think you've just made Mike's Friday...
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  #6  
Old 11-25-2005, 01:45 PM
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Longevity of the turbo is related to basically five things rotational speed, proper lubrication, proper air filtration, not operating in the surge zone and limiting maximum turbine inlet temperature. If you can accomplish all five, the turbo should outlast the engine.

It is critical with Wankels to avoid TITs in excess of 1600-1650F when using Inconel wheels and standard nickel/ iron turbine housings. They just won't last long above these temps.

Higher temp $$$ solutions are available. Ni-resist, 321 stainless or inconel turbine housings are available for some brands and MAR-M247 turbine wheels are available also extending the max TIT to about 1800-2000F.

Turbine rear bearing and C ring seal failures are usually caused by lubrication, overtemp and/or overspeed conditions.

As a general rule, people who don't understand turbos fear them, both in the dyno room and on the track. Turbos are far more reliable than superchargers when properly engineered in my view. How many diesels are fitted with superchargers today?
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Old 11-25-2005, 04:05 PM
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Quote:
Originally Posted by rv6ejguy
Turbos are far more reliable than superchargers when properly engineered in my view. How many diesels are fitted with superchargers today?
Yes, but were talking about its application on the rotary engine in John's case. I was wondering and you would be the one to know, would one of those more expensive ball bearing turbos that use engine coolant and oil for cooling/lubrication be a better choice for the rotary? The way Bruce explained it to me, along with showing me some convincing overheated parts from a turboed rotary, is that its a valveless engine,,,even though the backpressure from the turbo is slight, that causes higher exhaust port temps than a valved engine. Even though I don't intend to turbo my Renesis, I still had the rotors ceramic coated to lower my exhaust temps.
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Old 11-25-2005, 05:06 PM
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We're not really talking about an engine failure here, just the turbo failure at this point. Nobody really knows how long a 13B will last in this application. Certainly small turbine wheels and small A/R housings are not a good idea for engines operated at continuous high power and high rpm.

John's OE based turbo is unsuitable in my view for this application thus the failures.

John and I have discussed this at length now on the phone and I'm running some numbers here to match a proper Garrett turbo for the application.

Ball bearing turbos have not been well proven at this time in continuous high rpm running. They are wonderful for high boost, short duration applications like drag racing. In the future, they may well prove themselves to be superior to sleeve type bearings in all applications.

There are other factors here which deserve attention. Lubrication and EGTs are possible areas of concern with this installation.
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Old 11-25-2005, 05:33 PM
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I know this may be seen by some a a backward step, but have you considered a RayJay F40?
These are a nice big unit, with an external wategate and a good reliable sleeve bearing that I tried really really hard to kill before it ingested a small screw from who knows where and broke more than a few of the compressor blades. To it's credit it jammed the wheel and did not allow the small screw to get ingested into the engine. I then replaced it with a T04.
I do believe that the RayJay is used in aircraft and high other output applications simply because the sleeve bearing can withstand that sort of duty. The reason I went to a T04 rather tha rebuild the RayJay was I wanted a quicker spool response, something that really would not be of any great consequence with John's application.
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  #10  
Old 11-25-2005, 05:36 PM
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Porsche just announced as a big breakthrough the first VTG (variable turbine geometry) application in gasoline engines. VTGs are old news for diesel engines, they have been commonplace since the 90s. It's all a matter of exhaust gas temperatures. Diesel engines have the coolest EGTs, then come piston gas engines, then rotaries. I'm afraid John is fighting a very uphill battle and he'll have to find some cutting-edge turbocharger with very heat resistant blades, or maybe he could place the turbo farther from the engine, thereby allowing the exhaust gases to cool off a little. He'd have more turbo-lag, but that's hardly a problem in an aviation application, I admire his tenacity and will to overcome the problem, I'm sure he'll find a way.
For the Porsche story with a discussion of diesel/gas EGTs see this article:
http://www.germancarfans.com/news.cf...id/2051115.002
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Last edited by Kumaros : 11-25-2005 at 07:09 PM.
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  #11  
Old 11-25-2005, 08:14 PM
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Quote:
Originally Posted by mplafleur
That's exactly what I was thinking of using to normalize the Renesis.
Are you guys aware of all the TSBs, Service Bulletins, and campaigns on these engines before you put them in? If anyone wants them, I'll ask our warranty sheriff if I can let you all know. I know there is a problem with the RX8s renesis flooding and ending up in a no-start situation. Of couse, if you buy a renesis that has been manufactured after the bulletins are issued, it should have been corrected.

-Danny
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  #12  
Old 11-25-2005, 10:42 PM
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Quote:
Originally Posted by John Slade
I'm sorry to report that my hi-flow turbo from Turbonetics (Au) passed away quietly this morning.

Yesterday I reprogrammed the EC2 to give me a little more fuel at higher MAP. This helped a little, but then I aborted the take-off because the power level was still too low for my liking. Searching for the cause of the power loss today I did a runup with the cowl off and the intake filter removed. Rpm on full fine pitch was 4400. Adjusting timing a little either way made little difference. MAP 32 at 4400 was all I could get.

As I taxied back to the hangar there was quite a bit of blue smoke coming from the engine. The compressor wheel is still in place, but it has a lot of play and oil is leaking from the turbo internals.

I'll report on the post mortem when I have the results.

No. I'm not giving up on turbos. I see ceramic bearings and possibly a T04 in my future....
what would happen if you put in the T 6 ?
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Old 11-25-2005, 10:53 PM
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The Rajay F 40 would have a compressor far too small for this application and a turbine A/R ratio way too small without a gigantic wastegate. The relatively poor material of the turbine housing would not stand up to the Wankel's hot breath for long either and they are short on thrust bearing area.

I've seen many cracked B and F turbine housings in my time and many bearing thrust faces worn down to nothing on these units. When the latter happens, the 4 oiling grooves disappear, then there is no way to get oil to the turbine side thrust face, then the bearing and turbine wheel thrust face turn black and start to gall.

The Garretts are superior in almost every way, especially aerodynamically and from a metallurgy point of view.

As far as variable vane turbines go, Aerodyne and Garrett both had designs back in the '80s for gasoline auto applications. An excellent idea if it can be made reliable but of little use on aircraft where low end response in unimportant.

Since we don't know what parts were modified on John's hybrid turbo from Oz, it is difficult to know if an overspeed or harmonic is causing the bearing failure. I'm not keen on mix and match components from different brands applied by small shops without the engineering saavy to evaluate the impact of these mods. I've seen many hybrid, small shop "secret" creations with cropped turbines and compressors in revised housings frag bearings and offer questionable performance gains.

Sticking with the approved trims within one brand is a more likely way towards success. Being able to source a compressor map is essential for matching in aviation applications also.
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Old 11-25-2005, 11:01 PM
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Quote:
Originally Posted by Steve parkins
what would happen if you put in the T 6 ?
I feel the T61 compressor is a good match to the typical Wankel at low altitudes and full chat (250hp or so) however, all the T compressors have very narrow islands and surge at high altitudes would be a concern when throttled back in cruise above 15,000 feet or so.

The much wider compressor islands of the E compressors and higher peak adiabatic efficiencies make them more suitable IMHO.
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  #15  
Old 11-25-2005, 11:13 PM
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Ohh yes - had not thought of the EGt problem, as this turbo is only eight inches from the engine i bet you the turbo would be hotter. but, as the turbo is liquid cooled and oil flowing in the bearing, wouldn't that compensate for the extra heat and make it a non issue.

john - i stopped by mplafleur's today and we chatted about the A/F ratio, the mazda guy is all wet - with the standard ox sensor - you can't tell a A/F ratio other than from about 14.65 to 14.75. so his 11. whatever number numbers make no sense what so ever.

On the lights on your A/F ratio and not being able to keep them in the middle - that too makes sense - the only sensor you currently have is the narrow band that can only measure around the 14.7 mark and that is it. when ever you richen it past that point-BAM all the bars come alive and they would all be lit fro 14.688888888 down to 1 and on the lean side they would all be lit from 14.722222222222222222 to 30 to one.

Nathan - shame on you, i felt really bad for john, immediately pm'd him and then followed that up with a call .

John has listened to experts - just the wrong dam ones - the turbo guys from AU said they were and talked the talk - they are mfger's - he has been unlucky to have dealt with a few experts that were all wet.

On being able to turbo a rotary - bruce t says it cannot be done, i think because of heat going back into the combustion chamber from the hot pressurized gas in the exhaust - i think that it can be done and that the only problem will be premature wearing out of the engine because of this extra heat. BUT - i doubt if it will be a problem, i mean do you really care if you have to rebuild at 1200 hours rather than 1400 hours.(for example) that i think is the kind of wear we are talking about.

BUT, the proper turbo must be matched up to the application and the person that he is getting advice from now is an expert and will be really close to picking the proper one. I also think that he will give john some post turbo temp numbers and boost numbers that will allow him to properly track what is actually happening in that spinning machine
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