Tom Smythe wrote:

Hi,

I know the supercharger is larger and draws horsepower from the engine
directly versus the smaller turbocharger and indirect horsepower draw
(backpressure). But, wouldn't the supercharger provide quicker response,
more even power increase with throttle changes (predictable power
changes versus the sudden turbo boost as the turbo gets into it's "sweet
spot"), and longer life (not exposed to the high exhaust temps)?

Again, I now the supercharger weighs more and is a bit more "complex" in
that it requires a drive mechanism off the engine. But, if a
supercharger fails, you revert to a NA engine (with appropriate gates to
prevent a close system - could be spring-loaded to allow opening should
MP fall below value "x" and the supercharger drive could be clutched to
prevent driveshaft lockup, as well). If a turbo fails, you've got
exhause issues to deal with that could be handled with a bypass of some
kind, but now you've got two paths of exhaust (two areas of high heat
under the cowl) to deal with instead of one that is already being snaked
around enough to get to the turbo. With the supercharger, you simply
dump the exhaust overboard via the quickest route possible (and
hopefully through a low backpressure muffler of some kind - spiral
perhaps?).

You are right in most of what you said.
However a properly sized and installed Turbo will not have any noticable lag,
especially in an aircraft. You will not be able to tell if you have a
supercharger installed as it will act just as if it was N/A, but of course a
little more power across the board.
The turbo if sized and installed correctly will also act pretty much the same
way.
I am speaking from my knowledge of recripocating engines and not from a rotary
experence base. However there are certain rules for the turbo that applies to
any installation.
If you get a kit, either for a turbo or a supercharger, most of the
installation problems should be worked out for you.  Either installation
requires proper sizing and setup.  If you are designing an installation for
yourself, you will have to work out all the detailes yourself.
As far as a failure is concerned the supercharger would most likely trash out
the belt system, and the turbo would not. A clutch of some kind might solve
that problem.

A turbo has some advantages, (so does a supercharger, there are two schools of
thought on this) such as using some of your wasted energy to add power to the
engine, quiten off the exhaust system,  is usually smaller and lighter, but
not always.  Cost wise it can be 6 of one and half a dozen of the other.
Chrysler produced a lot of 4 cylinder engines with a garrett turbo, and they
can be had from a junk (salvage ) yard for not much money.  They are easy and
inexpensive to rebuild.  We have several of these turbo's and none of them
have needed to be rebuilt.  They are also water cooled so the oil doesn't coke
in the bearing area on shut down like an aircooled.

A bearing seal/kit for one of these units runs around $75.00.
The bearings are aluminum and float.  The shaft spins so fast that the shaft
and bearings float centered in the oil film.
We like turbo's for all these reasons.

Royce

 
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