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  #1  
Old 04-18-2007, 09:28 AM
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Default But I just want to normalize!

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Originally Posted by rv6ejguy View Post
Most turbos are limited to a pressure ratio of between 2.8 to 3.6 to 1. At say 14,000 feet where air density is about half of sea level, your PR is about 2 to 1 to maintain 30 inches Ab and about 3 to 1 to maintain 45 inches.
when I talk to builders and prebuilders about turbos they usually come up with this statement "But I just want to normalize!"

This is what it takes to "just normalize", pressure ratios that make ground bound turbo people shudder with jubilation at the amount of power that would be made on their cars with such high pressure ratios.

Just normalizing on a plane is a BIG thing, not a "just" thing
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  #2  
Old 04-18-2007, 11:11 AM
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Yes, if you can get up high with a normalized Lyco or Conti, you can really move. Smaller engines like 13Bs or Subes might require a bit more manifold pressure to get the same hp so turbo overspeed is a possibility if you are going to 25,000 feet and trying to run 40 inches up there even with a modern Garrett.
Efficient intercooling is a must at these altitude even on normalized installations.

With factory turbos, high compressor discharge temps, high EGTs and really high N1 speeds will almost certainly lead to a very quick failure of the turbo. I think John has already demonstrated this.

Proper matching is essential at higher altitudes to avoid all kinds of possible problems.

Manual wastegates are just a lot of trouble in this day and age of electronic or even straight mechanical controllers.
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Old 04-18-2007, 12:54 PM
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ok, may I try and express my layman understanding of this:

a turbo is a big "fan" which is driven by exhaust gasses.
this fan sucks in air, compresses it, and stuffs it into the engine.

at ground level this means more air which can burn more fuel --> more power

normalizing: on ground the turbo is essentially more or less unused, but as altitude is gained the turbo needs to suck in enough air to make the engine think it is still on sea level.
So essentially, the higher you go, the "more" of the thinner air up there is needed to make the engine think its still on MSL.

ok, turbo's have their limits, i get that part too. so just as a number game:

engine on MSL (1013 mbar or 29.92 InHg):
needs 100 gal of air per minute, this can be accomplished in the standard "sucker" configuration without turbo, but works better with the turbo giving the engine the 29.92 mainfold pressure (ambient pressure, not plain sucker mode)

engine on 5000 (3/4 of MSL air pressure or 850 mbar):
still needs 100 gal of air per minute for 100% power, thus the turbo needs to accomplish a pressure ratio of 1,2
(please correct me if my math sucks, but 1013/850=1.19)

engine on 10000 (1/2 of MSL air pressure or 500 mbar):
still needs 100 gal of air per minute (actually, this never changes ...) for 100% power, thus the turbo needs to accomplish a pressure ratio of 2.0, meaning it needs to suck in twice the amount of air volume to have the engine receive MSL pressure

as pressure does not reduce linearly with altitude, the turbo REALLY needs to get going at, say 20000 ft MSL. ( I'm approximating around 4.5 to 5.0 pressure ratio ?)

calculating the 10.000 pressure ratio down to MSL again would mean a turbo that is capable of producing 60 InHg pressure at MSL. Boy, that's quite some power ...

going up to 20.000 pressure ratio (let's say 5.0) this means the turbo would need to produce around 150 (149.6 excactly) InHg at MSL. OH MY DEAR ...

ok, so as I see it, a normal turbo won't produce enough air for that. but, what about a twin turbo setup ? (not talking about space in the cowling and so on, just plane theoretics)
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Old 04-18-2007, 01:15 PM
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mmm - your math is off somewhere as the PR at 25000 isa about 3 to 1

twin turbo as in in line and not separate?

Yes the in line set up would work easily to produce 3 to 1 ratio, BUT, it be really tricky to set up. the first would feed the second compressed air, then the second would then further compress it.

If you give the second one too little air and give it too much power - kaboom overspinning, not a good thing

It is a balancing act that someone with big pockets could figure out with computations and lots of testing, not an easy or inexpensive task

If you are talking about twin turbos, one for a bank of cylinders, that would just make each one have to do the same thing on a smaller scale, but with the same P/R.

My point is, "just normalizing" is a big deal and not to be taken lightly, if you want to add power with a turbo at SL, then it all gets even more tricky because as you go up the P'R would correspondingly increase
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  #5  
Old 04-18-2007, 01:45 PM
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Normalizing at medium altitudes is pretty straightforward but not without potential problems of course. Success with any turbo system at 25,000 feet and above is a bit harder as are the physiological effects on the human occupants in non-pressurized aircraft. O2 problems up here can kill you pretty quickly and O2 consumption is pretty high up here even with the latest electronic regulators. This is generally just a PITA with full masks and built in mics.

I had great plans to be up at 18K a lot but never do. How many on this list routinely cruise at 25K? Interested to know.
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Old 04-18-2007, 01:48 PM
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Old 04-18-2007, 01:50 PM
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I have met two long drivers that have spent lots of time going cross country at 18,000
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Old 04-18-2007, 02:25 PM
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Quote:
if you want to add power with a turbo at SL, then it all gets even more tricky because as you go up the P'R would correspondingly increase
Quite right. But keep in mind that, from my experience, one of the most valuable benefits of having a turbo is increased power at SL. It reduces your take-off distance dramatically thus adding a safety factor especially at high DA and/or high gross for short or one-strip fields. The quicker you can achieve a safe (glide return) altitude the less risk of off-field landing. A balancing act is required between good power at SL and overspeed at altitude.
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Old 04-18-2007, 02:34 PM
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John's got a real point there
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Old 04-18-2007, 02:50 PM
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Yes, and a good point it is, but remember that the rotary, normally aspirated produces less HP than the standard lycoming at SL and the higher you attempt to hold that power after take off the faster the P/R sneakes up on you.

John knows this stuffffff well, this is just meant for all those who tell me "but i just want to normalize", so they understand it
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Old 04-18-2007, 02:58 PM
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there is one thin i do not understand. I get the pressure ratio thing, but actually it's all about the volume or air being moved.

at SL (back to my example) an engine might need 100 Gal of air per minute.

at 5000 that would mean 120 Gal of ambient air to compress it into 100 Gal of MSL air (layman talk here), giving you the ominous 1.2 Pressure Ratio.

at 10000 that would mean the turbo needs to suck in 200 Gal of ambient air and compress it into 100 Gal of MSL air, giving you the 2.0 ratio.

so, the bigger the turbo, the easier it will suck in the air right ? it's all about volume of air here.

so if i make this into a two turbo system, each turbo will only need to produce 60 Gal at 5000 and 100 Gal at 10.000, wrong ?
as two cylinders only need half the air as 4 would need. so I don't understand why you'd want to go inline turbo, instead of just one turbo for 2 cyls (on a 4cyl that is)

don't forget, just an example
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Old 04-18-2007, 02:59 PM
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I'm glad that that part of the project is so far off for me!
The turbo solution sounds great ........ as long as the dependability is not diminished. I will be installing a rotary in my build but the question is will it be Turbo Charged. I know it won't be Supercharged.

Like Dust....my objective would be to maintain SL performance while at altitude.

I will really have to crunch some numbers over this .
2 rotor engine:
291 Lbs / 190 HP (Naturally Aspirated Rotary)
328 Lbs / 230 HP (Turbocharged Rotary)

3rd rotor:
375 Lbs / 300 HP (Naturally Aspirated Rotary)
420 Lbs / 360 HP (Turbocharged Rotary)

When I look at the 300 HP Rotary vs. the 230 230 HP (Turbocharged Rotary) ... It's costing me another 47 LBS for 70 HP and no turbo to fail.
Is that killing an ant with a sledge hammer? I don't know.
Every pound counts so where do I draw the line?

It way out there on the horizon for me right now so I am real anxious to hear the progress made by those who are venturing into this area.
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Old 04-18-2007, 03:06 PM
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Quote:
Originally Posted by Leon View Post
so if i make this into a two turbo system, each turbo will only need to produce 60 Gal at 5000 and 100 Gal at 10.000, wrong ?
don't forget, just an example
You are doing this with 1/2 the power and the p/r still stays the same.

I am using 2 turbos to simplify the 1400F(on a piston engine) EGT piping to the turbo.
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Old 04-18-2007, 03:24 PM
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Quote:
You are doing this with 1/2 the power
so you mean to say that the exhaust power will not be sufficient to do this ?
never thought of that end acuatlly, cuz i always thought the wastegate releases alot of extra exhaust into the open anyhow, so why not use more ...
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Old 04-18-2007, 03:30 PM
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you, have not changed the P/R and the turbo you pick will influence how much of your turbo you will be able to use at which altitudes, i will be using all of mine at full power at 25000 feet, heh heh heh

if you are dumping both into a common manifold - the pressure in that manifold will still be the same as if you used one, each smaller turbo still has to pump it into the same P/R
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