SNIP:
   ...........I turbo normalize plus (make moderate gains in power at S/L
   through use
   of the turbo then 'normalize' that amount of power for benefit at
   altitude). I achieve that by use of the throttle.

   I have a fixed waste 'gate' (exhaust bypass really) because it was the
   easiest way for me to get a big wastegate. I believe an aircraft style
   wastegate is an excellent choice, but a LARGE automotive style can work
   equally well and is more available and less expensive.

   David Leonard

   Turbo Rotary RV-6 N4VY
   N4VY.RotaryRoster.net
   www.RotaryRoster.net
   leonardiniraq.blogspot.com

   David,
   Again I apologize for my ignorance, but can you explain exactly what you
   mean by "fixed wastegate"? If I understand the term "fixed
   wastegate", its basically a wastegate that is always open a little to
   allow a constant leak? That would also allow a constant percentage of
   the exhaust to flow into the turbine side of the turbo. If that is
   correct, Why use a "wastegate" at all? Why not just have a small
   port before the turbine that leaks exhaust around the turbo and back
   into the exhaust pipe? I guess a set up like that would require some
   sort of trial and error getting the % of exhaust bypass correct. Maybe
   some type of restrictor in the bypass port? But you would have much
   control of the turbo that way!! Is that why you use a "fixed
   wastegate"? So you can adjust the amount of bypass? How does that
   differ from the normal wastegate operation? I thought a wastegate
   cycled from open to closed based on its duty cycle. That's different
   from the fixed wastegate isn't it?? Damn I'm confused!!!!! Also what
   do you mean by, "then 'normalize' that amount of power for benefit at
   altitude). I achieve that by use of the throttle." I didn't follow
   that part at all.
   Don


   Hi Don,

   See if this helps. Your concept of the "fixed" w/g is correct...it's a
   small but calculated size pipe that starts ahead of the tubo and
   bypasses a calculated amount of exhaust gas around the turbo and into
   the exhaust pipe. It's only virtue is simplicity....it is never
   efficient low or high up but is an excellent choice to add boost with
   minimal complexity.

   "Turbo- normalizing" is a term coined by the aircraft industry to make
   turbo assisted engines have a meaning to the aircraft buyer. As Paul
   accurately stated you can't turbo boost an airplane engine (racing
   engines excepted)....it is already on the ragged edge of power output in
   the normally aspirated mode...but what you can do is make the turbo
   provide a *normal* sea level "atmosphere" for the engine to work with.
   In other words if an engine is designed to produce 300 HP wide open
   throttle (WOT) normally aspirated at sea level the turbo is requested to
   provide zero boost at sea level. But at 5000 feet where the normally
   aspirated engine has lost about 2.47 PSI in the intake manifold an
   subsequently is producing 275 HP at WOT the turbo is asked to supply
   2.47 PSI boost of compressed air into the manifold to restore the
   300 HP.

   A Wategate determines how much exhaust energy is to be used to compress
   air for induction and how much should be *wasted* or bypassed to the
   exhaust pipe. Adjustable w/g's are either manual or automatic. Manual,
   the pilot operates a lever connected to a "trap door" of sorts and
   monitors a manifold pressure gage. Upside: simple, efficient at all
   altitudes, inexpensive. Downside: Pilot error can leave a boosted engine
   boosted operating at low throttle (ie landing approach) and
   overboost---read shatter apex seals--when an immediate full throttle is
   applied (missed approach go around). Cure??? Interconnected levers has
   been successful. An automatic w/g requires no pilot input. It contains a
   device-some mechanical,some electronic- that monitor inlet manifold
   pressure and controls the w/g "door" accordingly.

   Somethings you may not have considered. Having a turbo is really only an
   asset if you travel above ~12,000 ft ASL then it becomes worth its
   weight and maintainence costs. You'll notice above that WOT is a buzz
   word. If you cruise at 8,000 ft ASL and you are happy with your cruise
   speed and you are BELOW WOT , a turbo will do nothing for you--the power
   you require to be happy is already there for you. But above ~12,000 ft
   ASL virtually all engines will benefit from some boost even if to simply
   "normalize" the intake manifold pressure. Be aware that above 12,000 ft
   ASL the pilot requires Oxygen. Also at your proposed 18,000 ft ASL
   cruise you will need to have a constant speed or controllable pitch prop
   to insure enough prop load to absorb your projected 350 HP at a prop RPM
   that remains subsonic at the prop tips. Now consider this: your
   automatic W/G is adjusting your manifold pressure to the engine load but
   at the same time your prop governor is trying to adjust the prop pitch
   to the power applied which in turn affects manifold pressure. If both
   these items self regulate then a "hunting" will occur between them. My
   current thinking to eliminate this interaction and maintain simplicity
   is to use the manual W/G and develop a fool-proof pilot control
   lever that allows throttle to go to WOT ,then bring up turbo boost. A
   lever similar to an outboard motor single lever control that lets you
   shift and by continuing the lever advance you would increase
   throttle. The rational is any boost will only be nessessary when WOT
   power is less than desired. And the manifold pressure gage will be the
   biggest, easiest to read gage I can find!

   Dave M



   Good points, all.

   I would just add that a turbo will also enhance climb performance
   past about 6000 ft. At this altitude, particulary on a hot day a
   normally aspirated engine will already be limited to under 75
   percent power.

   You can use my turbochart spreadsheet to see the numbers. At 6000
   feet and 95 degree temp on the ground (SL), you will have only 23
   inches of maximum MAP at 6000 feet.

   So while it is true that a turbo plane is really in its element at
   altitudes above 10,000 feet, it is also nice to have a strong climb
   on those hot humid days even if you are not going all that high.

   Above 10,000 feet there will be a huge difference in climb
   performance with the turbo. If you fly IFR, that climb performance
   could be very handy for climbing out of cloud, especially if there
   is chance of icing.

   Regards,

   Gordon.


The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2006 All world wide rights reserved.