OT Turbocharger Question
 

I need to boost the power output of an engine that will see no more than 2800 rpm.

I need the boost to come on at virtually idle (to prevent any visible "lag") and the engine will not see any speed over 2800 rpm. I will have the room for one turbo and the displacement will be around 360 ci. I am looking for somewhere around 5-8 lbs of boost.

I am considering going with a belt driven centrifugal, but I don't have a good drive source. I am looking for suggestions here.

Any thoughts?

Pete

Centrifugal, as far as I know, don't build boost at low rpms. What you need is a screw (Eaton) or Lysholm (Whipple) blower. They build boost much sooner.

Well, in such a narrow rpm range, i can gear the blower to think it's at a higher rpm than it really is. I'm not worried about that aspect, but I still need a viable drive setup if i go that route. I wouldn't even want to think about mounting a screw type blower.

Pete

Diesel motor? whats the CR?

forget the turbo. go with a blower

Use a belt driven turbocharger.

See http://www.studebakerclubs.com/21stCenturyTurbo/

Okay,

maybe this will help. It's not a diesel, it's a flat air cooled 4 cyl going on an airplane I am buiding.

I started building a Steen Skybolt a few months ago and I am now to the point where I need to finalize my plans for an engine (Oshkosh '06 or bust). The plans recommend an IO-540, but I think I want to do something a little different.

Originally I was planning a large 6 (anywhere from 470-550) and although I am a big Lycoming fan, they don't have the valve configuration I want. I want my exhaust port on the bottom and the intake port on the top. This however puts me firmly in the Continental camp. So be it.

I was looking at around 300-325 hp (not really a problem with a big 6 if you have the $$$$$$$$$), but after wrenching on GA motors for nearly 10 years I think (under the banner of "experimental") I can do better. EFI coupled with a distributorless ignition (with maybe a single mag as backup. Maybe) I think I can raise the efficency and reliability to a whole now level.

This got me thinking again, that if I can do this on a six, perhaps I can do the same on a four and save some weight. BUT 300hp from a NA 360 is wishful thinking at best (at 2800rpm at least), so, whats a guy to do? Turbo/blower.

Now, I can obviously mount a turbo with no problems, but I need a turbo that is sized to my needs (ie 5-8psi at 2800rpm) but even that should be a no brainer given the industry these days.

BUT, I was wondering if a centrifigual blower might more closely match my needs (instant boost, no lag, etc) *IF* I can figure out how to mount and drive it. I might be able to run an addiional pulley off the crank snout or I was wondering if I can run it off the accesory gear box, but that's a lot more work with a lot less room.

Oh and the factory compression ratio is around 8:1, so this shouldn't be a factor.

Thanks,

Pete

Hmm...I don't know where to start.

Aircraft engines have whole different set of specifications and reliability is a paramount. That's one of reasons we still see WWII technology in small aircraft engines. It's tried and true and few dare to change it.

Have you checked that such alteration of your engine is legal to begin with? I mean, you cannot just "park it on a hard shoulder" should that supercharger belt snap...

Even if you decide to do all this by yourself, I firmly believe supercharger is the worst option, and centrifugal supercharger is worst option in superchargers. Superchargers are inherently less reliable than turbochargers as they have many moving parts. They are also less efficient. Actually, only good thing with them is that they give instant boost but that's quite unimportant in your case as you will never slam your throttles so fast that it will make any big difference. Aircraft engines are usually operated in steady,continuous manner for longer time. Centrifugal superchargers have to spin almost as fast as turbochargers, which means complicated and power-eating gearboxes. They also have annoying side-effect of boost raising proportionally to revs. So for low-rev boost you either have to gear it high, and then waste excessive boost when higher up in rev-band, or gear it so max boost hits higher up.

As I said before, I believe you should be very careful with fiddling with aircraft engine yourself as your life actually depends on it.
If you really want to build some sort of supercharging device then I recomend turbocharger wholeheartedly. It has only one moving part, it is actually developed for aircraft use from beggining, it is more efficient than supercharger as it uses otherwise wasted heat stored in exhaust gases etc.

I don't know much about aircraft engines but as far as I remeber there are two main turbocharger designs on smaller single-engined airplanes:

1. Turbo-normalizer, that just keeps intake pressure at constant level, independently from height (which means that turbo is "making up" for thiner air and keeping output constant)

2. Turbocharged, where you actually see positive manifold pressure.

Once again, please be very carefull and do lot's of research with people who are familiar with your particular engine.

Here is a link to marvelous series of articles, written by John Deakin of AV-web.

http://www.avweb.com/news/columns/182102-1.html

He covers exactly the very thing you are planning to do.

You would want to build something like this:

http://www.avweb.com/newspics/pp31_tatturbo.jpg

There are many turbochargers that would work well with 360ci engine turning at 2000 RPM. From the top of my head, Garrett GT35 would work fine.

And no, I don't think you want boost from idle. Boost from idle would force you to use too small turbo, which also means high backpressure, EGT and compressor operating in non-efficient region while take-off.

Yes, I know that you have lot's of expirience with superchargers but I'm sure that turbocharger is better/cheaper/safer option in this case. With little luck, you'll be able to find a kit for your engine.

Regards.

Not knowing a lot about aircraft engines I do believe that both turbos and centrifugal superchargers have been used in the past. I think that only later engines were using turbos because it is a much more simple in design and fewer moving parts.

Don't piston driven aircraft engines use relatively long stroke engines because of the low rpm /high torque required?"

aha. since this was for an an aviation application, I initially wasn't sure why you were worried about lag. but since it's for an acro, it's obvious. in this case, I think supercharging would be the safer bet, as a turbo small enough to not have any noticeable lag would probably not have the power you need (unless you went with a twin-turbo setup)

reminds me of the time I worked on converting a Subaru SVX block for aviation conversion...

and oh yeah, Continental all the way! :p

Thanks for checking in Goran, it's been a while since we "chewed the fat".

Actually, the limits on general aviation have more to do with the fear of liability from the lawyers than any real "reliability" issues. Unfortunately as long as we have a litigation happy society over here, we won't see real change in commercial (piper/cessna/etc) aviation for quite some time. It doesn't however mean that it can't or shouldn't be done.

Fortunately, the FAA has an experimental classification which is very broad and allows for some very creative adaptations. This being a "homebuilt" and already certified under the experimental rules gives me a huge amount of latitude.

That being said, I spent quite a few years "picking up" wrecked airplanes to really understand and appreciate the concept of safety. (Being the Safety Chair and part of our NTSB "Go-Team" at the airline I fly for helps a little too) So, this will not be a duct tape and baleing wire effort by any stretch.

Now, for my needs.

This will not be a "cruise only" airplane. I am building this to +8/-6gs and intend to use it as such. I spend my workday cruising straight and level, so I want my off time to be spent vertical and inverted. I need a responsive engine that handles negative as well as positive g loads and will not complain with a lot of rapid throttle movements.

I don't really need boost at idle, but I can't have a lot of lag either. What is the normal rpm range of the current stock of turbos? I am only looking for a 2000 rpm window (1000-2800) and I am sure that virtually any turbo can offer that. But then again, I am full of "theory" and short on practical use.

I remember you were telling me before that these modern turbos are using engine coolant, so what do I use for an air-cooled motor to keep the bearings cool? Oil?

Are you guys running inter (or humor me here "after") coolers? Would you encourage or discourage the use in this application? I think I can plumb one and I might even be able to use the byproduct for cabin heat, but I don't know yet.

I know I am beating a dead horse with you here, so I apologize in advance BUT, I know a ton of guys using Paxton/Vortec etc and I haven't heard of one failure (other than belt related) but I won't harp too hard on this, this time because as I said before, I have no way to effectively drive the darn thing. I had however thought of what to do as a back up due to component failure and I was considering a pseudo-alternate air door if you will, downstream of the compressor so that if the compressor is lost, it would run purely naturally aspirated, but again these are very basic thoughts only.

Thanks for your input (and everyone else here) and for the link. I hadn't seen a 2 stage/2 speed supercharger since I flew a Convair 340 (R2800) years ago. I miss those old radials.

Pete

Yep, oil is used. Turbos can be configured/built to use either. Some modify coolant type turbos for use in oil cooled cars but it's a compromise.

Intercoolers are used, the colder the air the denser it is and the better. But at high altitudes I wonder.

Do you have to be FAA certified to wrench a plane?

Is your engine fuel injected?

"Do you have to be FAA certified to wrench a plane?"

Well, it depends on a lot of factors such as Certificated A/C or not (experimental) whether its a repair station or not and so on. I have an A&P and my skybolt is an experimental, so it's not necessary, but it gave me a lot of experience I never could have gotten without it.

As far as the intercooler thing. I will probably use one, but I actually haven't gotten that far in my planning to worry about it yet. On a car, I wouldn't build one without an after cooler.

I also plan on running a dry sump oil system (due to the whole inverted thing) so plumbing a turbo for cool oil won't be an issue.

Pete

I am planning on building an EFI system based either on a FAST or Electromotive TEC 3 system, but I haven't worked out the details yet.

Pete

With todays turbo technology, the manufacturer will be able to correctly size the compressor side as well as the turbine side to your engines bore/stroke and rpm range.

They should also be able to tell how much boost you'll need to produce the desired HP increase.

Here are some turbo calculators: http://www.turbofast.com.au/javacalc.html

Well you can consider the prop as big "torque converter" anyway, so I don't think properly sized turbo will introduce noticeable lag. You are using hand throttle and not hitting it with your feet so chances are you'll never feel turbo-lag anyway.

1000-2800 or 2000-5600 it doesn't matter. Engine is just a big airpump and turbo doesn't know how fast motor is spinning. It just cares about mass-flow. With other words, you want a turbo that can boost between 2000 and 5600 RPM on a car engine with volume of 180 cid ;)
There are lot's of turbochargers that will work in those conditions.

Most bigger turbochargers are only oil-cooled. Watercooled turbochargers are small units made for soccer-moms that run them hard and then instantly shut off the engine, cooking the bearings. If you let it idle 30 secs after full throttle (which you probably have to when landing) it'll be OK. so it's just one oil-hose doing both lubrication and cooling. You have to have some sort of dry-sump system though if you plan pulling G's or oil will seep trough the bearing-seals and cause lot's of smoke otherwise.

Yes. Intercooler is a good thing. It gives you more power, less heat produced in the heads and will also kepp shrapnel from entering the engine in unlikely event of turbine failure.

Ehh...if you want some serious power out of those things you are talking about 20-30HP transmitted trough a rubber belt in a vibrating enviroment that's seeing 5G of accelleration. It's your call but I wouldn't feel comfortable with that, even if I found the way to drive it. Those people running Paxton, are they using them on airplanes or cars? If belt snaps, there will be no "failure" on car per definition. Engine will stop and car will coast down. If belt snaps in your application you'll be "out of airspeed and ideas" pretty soon. SmileWavy
Air-door would work as long as it's situated before throttle-body (otherwise MAP will get confused) and EFI is used.

I had never seen one :) Too young.