marc wiese wrote:

The primary control of a turbocharger is the wastegate valve position (I am
talking aircraft systems here). Although there are purely manual control
types (knob controls wastegate position), most use a spring loaded to open
position flapper type wastegate, with oil pressure supplied by the oil pump
positioning the flapper valve via a rod by varying the return oil pressure.
Oil pressure closes the valve for more boost. But some systems have an "
ground adjustable restrictor" in the bypass line in place of the wastegate
set for the critical altitude, which is non-adjustable in flight. The BOV
protects this type of system below that at full throttle!
There are many variations of oil pressure control, depending on how you
want to control the turbine (altitude type control, boosted type, etc.)

Most use a APC (absolute pressure controller) that varies oil pressure in
relation to the upper deck pressure in the intake manifold. It is usually
set to open at max of 1" above the max design mp. Some systems add a "ratio
controller" which limits the tc from boosting the upper deck pressure
higher than 2.2x the ambient-it is mounted in parallel with the APC-It
appears this is an overspeed device. OK? Then you can have a system with a
"rate of change controller" to limit the guess what to a rate of between 2
to 6.5" a second.  Sea level boosted type controls (turbo-normalized
aircraft) use a density controller and a differential pressure controller
(helps stop bootstrapping) to set the flow of oil to the wastegate.  Then
there are even more hybrid systems as well that take throttle position into
consideration (VAPC).

Most systems include a BOV or "pressure relief valve" in the intake
manifold for back up and protection. I would recommend one on any system,
set at the max psi you expect your engine to handle continuously. (Would
that be 65"hg like the P-51? Noooooo)

It seems that a ripe opportunity exists for an electronic controller for
these things in experimental aircraft......they are already on cars but use
vacuum and pressure to control the wategate position instead of oil. Would
be lighter and less clumsy with all the oil lines
Marc Wiese
(trying to adapt an aircraft system type control circuit to my 13BT-too
many parts)

 
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