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  #1  
Old 05-14-2004, 10:17 PM
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Default Turbo = Hanger Queen

I have been told this by a very close friend, who was told this by a friend he respects. Because of this i have been on a quest to find out WHY?

We have had two turbo falures in the past week or three, one costing a turbo, one an engine, fortunatly a rotory and not a continental, far less to repair.

1 Oil flow - turbo must have oil or it is toast
2 Overboost - controlls have to be up to the job of NEVER allowing an overboost condition, even for a moment

I have been told by many experienced turbo pilots that controlling boost is no problem, just set it and well ...watch it.

One way or another my controlls will be up to it, Two pop off valves (diferent kinds), i hope, set at 32 im, 31.5 is my max and 32 will pop the lid one way or the other.

Now on oil flow to bearing, i think a sensor is needed there to insure proper flow.

After shut down pump to cool bearing for five or so minuites after shut down

electronic controll of waste gates interconnected with ECU, end of DAMN story.

As an aside, juan, have you tested your radiator cap for the boost preasure it will allow?
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  #2  
Old 05-14-2004, 11:43 PM
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Am I skipping over too much? Who had a turbo failure besides Juan?

I was told by Bruce that he recommends no turbo for the Renesis since the compression is already at 10:1 and it can't take much more with detonating. That was unless I was looking for altitude compensation.

For these lower elevations I think I'd prefer keeping it simple and safe. But for flying in Colorado and cruising above the bumpy layer it would be good to have.

5-minute cool down? I did this flying the turbo'd jump plane in Colorado. At touchdown I would hit a stop-watch and didn't shut down until 5 minutes had passed, never mind that I just spent 20 minutes coming down from altitude at a lower power setting.

Another form of turbo failure happened twice with this plane. FOD got into the turbo impeller and knocked off all the impeller blades. The FOD was a little magnet used to on a relief door on the side of the induction. Somehow it jiggled lose and was sucked in.
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  #3  
Old 05-15-2004, 03:58 AM
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I had all sorts of troubles with turbo's when I did my turbo motorcycle.
Cooling, Cooling, Cooling, and Cooling are going to be you greatest concerns.
Most cars have a whole bunch of room to get ducts, and space all about to cool their turbo's espescially with a rotary... those engine bays look HUGE with just the engine in there!
I know it's a little , but I'm going somewhere here...
Two things will haunt you with turbocharging....
both are temperature related. The first one affects the life of the Turbo more than the engine, and that is Oil cooling.
In a small environment, (cozy (snug ) cowling or a bike) The whole lot heats up very rapidly, and every little thing helped. I found that a small oil cooler in line with the turbo oil feed worked wonders. The return line, should be BIG as you want to get the HOT oil away from the bearing as soon as possible.
The next issue effecte the life of the engine more than the turbo. Detonation can kill an engine so fast it's not funny. It sounds like a kind of a rattle , espescially under load. The biggest culprits are heat and pressure. too much boost/compression in conjunction with a too low octane ratio will lead to detonation, The same applies to temperature. The theory is, that gas of a specific octane rating will detonate at a specific temperature, this temp can be produced by a combination if the temp of the incoming air/fuel mixture and the heat generated by the compression stroke.
Usually, the compression ratio is worked out that in normal oreating conditions, the temperatre of the compressed charge in the cylinder will be just below the flash point dictated by the octane rating. The higher the Octane rating, the higher the flash point, and the mixture can withstand a greater compression before ignition, and thus produce more power. This is why cars (and planes) designed to run on high octane fuels can experience detonation or "pinging" when run on lower octane fuels.
This is why you need to look at lower compresstion engines for forced induction, as the relative compression ratio can be markedly increased.
With this incrrese in pressure comes an increase in temperature, becuase when a gas is compressed, it heats up, and with turbo's you also get some heat carried over into the compressor from the turbine itself.
It is this reason that the use of intercoolers developed, to cool the incoming charge , this does two things, it allows more air/fuel to be introduced into the cylinder (as cold air is denser), and it reduces the risk of detonation due to extreme temperature.
On one of my motorcycles, I used an air/gas intercooler I built specifically because of my space requirements, and it worked extremely well (once I sorted the bugs out) It was simply a 12V car refrigeration system. I had a small radiator made up to fit in the induction tract before the butterfly, and another to sit out by the oil coolers. set it all up and re-gassed it, and viola! one super cooling intercooler! I had to fit a tacho switch to shut it down when the RPM dropped below 1500, otherwise the inlet would ice up, but other than that it worked better than I ever could have hoped!
The use of a boost control is also important in installation that can easily exceed the design limits of the engine. The two simplest and mostly used methods are poppet wastegate and blow by valves. Usually they are used in conjunction with each other. Typically, the blow by valve is installed after the compressor, with it's pressure line coming off from the first bend back from the butterfly valve (or directly off the inlet plenum in the case of multple valves) It's release setting should be only just above the maximum boost pressure for the engine. The exhaust is usually plumbed back in to the inlet before the compressor to prevent the engine from leaning out due to the difference between the MAP sensor and the airflow sensor. On installations where the mixture is wholly MAP controlled, then it can be vented to the atmosphere to give that cool "psssshhhh" noise the kids all love! The next is the exhaust wastegate valve. I prefer to use turbo's with externally mounted wastegates, cos they are easier to work on, but a lot of the smaller turbo's only come with built in ones now... Anyway, the exhaust wastegate is usually calibrated to a few PSI above the relief level of the blow by valve, and as such will act as a failsafe in the event of overboost. The take off for the pressure line is usually at about the same place as the blow by, but is sometimes place somewhat closer too the compressor.
The other option is to use an in cockpit variable boost controller similar to the ones sold in speed shops, something I never worrired about myself, because I felt it more a fancy gadget where a simple and effective method works just fine..

Ps... love the new icons!
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Old 05-15-2004, 08:52 AM
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We'll strangle-ed, I'm not really too crazy of going thru alot of hassel and putzing to have a turbo and your medicine is working on me this morning. The only reason I'd want a turbo is for altitude compensation and I just bet I could make do without it.

I am aware Mazda's had recalls earlier due to occasional engine fires too.

I may join the +3 club and screw the turbo club. In reality-land, I really don't want the hassels. From now on my visualizations will not include a turbo.
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  #5  
Old 05-15-2004, 10:17 AM
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Dont forget - one of the main reasons for using a turbo, even if you never use much boost, is that the turbo acts as a muffler. Loose the turbo and you need a muffler.

PS Who the hell's Juan?
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Old 05-15-2004, 10:21 AM
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Often I don't pay attention.

Juan, I assumed that was you.

Muffler vs turbo? I did ask Bruce about that. He went into detail about how the exhaust ports on a Renesis are in a different place now and it somehow has a positive effect on the amount of noise and heat in the exhaust. I had brain-lock at the moment and didn't capture it.

Oh wait, I think you meant a muffler as a good thing because you don't have to keep it lubricated and cooled and it's simpler and cheeper than a turbo too. I got you.

Last edited by tnt : 05-15-2004 at 11:12 AM.
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  #7  
Old 05-15-2004, 11:33 AM
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See, there you go. most, at least the verbal ones, agree. Turbo = hanger queen. And i did forget one mod that i am planning, a naca scoop in the top of the turtle deck for more cooling air.

I have also been advised that radiant heat will get you every time, it goes to areas that you just do not expect, soooooo, i will take heed of that advice also and make sure that noo part of the exhaust manifold to tail pipe can be seen.

I have a dream, and it will be done, tested, and double done.

heh heh heh thats why i bought the tsio and not an io

Juan, you are in southern florida and you don't know juan???

I will not ground run the engine to cool the turbo, ground running air cooled aircraft engines seriously decreases thier life, i would rather coke the turbo than the engine.

I am also considering an anti knock sensor, just need a ECU that can understand the signal. Knock sensors send out allot of chatter, just like this forum, and the ECU must be able to properly read the signal to take action.

I thought the detonated rotary was caused by overboost?
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  #8  
Old 05-15-2004, 12:41 PM
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I think, if memory serves me correctly, the detonated rotary on the RV-9 was overheating related, engine got too hot~incoming charge gets hotter faster, and detonates during compression, result, one dead rotor.
John's (present) problem (I think, I'll have to go read his thread again ) stems from overboost~too higher relative compression ratio & charge detonates during compression, result, one dead rotor.
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Old 05-15-2004, 05:50 PM
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Quote:
John's (present) problem (I think, I'll have to go read his thread again ) stems from overboost~too higher relative compression ratio & charge detonates during compression, result, one dead rotor.
I've lost track of this conversation altogether. Are you talking about me? If so, I don't have a "present" problem, and I certainly dont have a dead rotor.

Someone is getting confused. I think it's me.
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Old 05-15-2004, 07:57 PM
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Dont know if this is wise, but here goes.

Todd Bartrim blew a rotor. The reasons are complicated. His site.
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
I do not belive he has any info there about the engine problem.

Dust's further suggests there is a long history of problems with turbos, just like what happened to todd, such that they have earned the reputation of hanger queens.


Dust suggests some ideas to keep your turboed aircraft from becoming an hanger queen

Automatic Boots Control
Cool down oil pump.
A sensor to monitor oil flow

The problem Todd had is directly related to dust's point, which is an automajical device should control the boost. This would have saved todds engine.

An electric oil pump could pump oil to the turbo after shutdown to keep it cool, and lubricated, as it may not be stopped when the engine shuts down.

In this day and age of cheap data monitoring and logging a oil flow sensor just makes sense. This may have saved John a turbo.
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Old 05-15-2004, 08:54 PM
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It's been a long time but I believe the act of running that engine for 5 minutes before shutdown was called for by the aircraft operating manual. Last year after my son's chopter ride in Marathon Florida the pilot just sat there and ran the engine for 5 minutes after landing. I asked his buddy if he was letting the turbo cool, he said there's no turbo but it's to cool off the motor.

I don't think running just that little bit of oil thru the turbo lube channels is sufficient to cool that thing. It takes air-flow also.
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Old 05-15-2004, 09:23 PM
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Quote:
In this day and age of cheap data monitoring and logging a oil flow sensor just makes sense. This may have saved John a turbo.
I'm not sure this would be worth the trouble. The turbo is lubricated and cooled by engine oil and cooled by engine coolant. If I have oil pressure (which I watch like a hawk) then the turbo HAS to be getting oil....unless, of course, the feed line is crimped.

The feedline ain't gonna get crimped again. Lightening never strikes twice in the same place, unless you hold up a big metal pole in a thunderstorm.

I'd better off spending my time and money chasing something that hasnt happened yet.
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  #13  
Old 05-16-2004, 11:22 AM
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Default my 2 cents: complexity=hangar queen

A turbo installation can range from super-complex (High boosting refrigerating intercooler with dual Blow-Off Valves, in line oil cooler and sensors everywhere) to super simple (Altitude compensating, manual wastegate, basic intercooled)

The question, as you've put it ("Turbo or no turbo?") Isn't specific enough. For example Bruce said no turbo on a Renesis, because of the 10:1 compression. Now ask him about using just altitude compensating boost, Keeping the MAP Below 17 psia, I bet he changes his answer.

You only put sensors on only for failures you can't design out. John doesn't need more sensors, he's found and corrected the problem (Though I think he'd be better off using a hard-line until he gets closer to the turbo, but he's flyin' it so I defer to his judgement)

Rather than adding after-run pumps, simply work into the checklist to idle for X minutes or until the oil temp reaches Y, You can determine X and Y in on the ground tests.

I would not add complexity unless you have to.
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Old 05-16-2004, 12:30 PM
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Good point on complexity Aaron. I would only want a manually controlled waste gate with a separate lever, not connected to the throttle. Also could maybe have some supplemental idiot lights and bells and electrodes taped to my feet. I'm very concerned about heating under these fiberglass cowls.

As for post-shutdown when the turbo has been used, it would be as you said and as I did per the jumpclub pilot operations guide. Run the motor for 5 minutes after shutdown.

Bruce did not have an issue with running a turbo for altitude compensation. I mentioned I am on TDY to Alabama from Colorado. Flying at 8000-9000msl along the front range of Colorado is just what you normally do. To get over mountain passes you need at least 12k msl in many places, 14k would be better, especially in the summer. This can often be a challenge in NA (normally aspirated) mode.

Last edited by tnt : 05-16-2004 at 12:45 PM.
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  #15  
Old 05-16-2004, 12:44 PM
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There are two issues being confused here.

Dusts point is that air cooled aircraft engines do not take kindly to ground running. He has lots of evidence of that.

Slades Engine is a different thing entirely. Ground running will not harm his engine. Although it only has a use for cooling the turbo.

We have not yet reached a high level of refinement to the installs. I was thinking that until we build a history of what works and what doesn’t, sensor your critical and informative systems to get an early indication of issues.

Shutting down a hot turbo cost Chrysler and its customers a lot of money back in the day. One small sensor would have saves a lot of money. A turbo exit oil temp probe would tell you if you need to ground run, is there was a oil flow issue, if you had an exhaust issue, and a bunch of other things.
This might be useful for john, but more so for dust.
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