Turbo controllers can be quite simple or very complex. I had them both.
Ultimately the only thing that controls the amount of turbo is the amount of
exhaust gasses that are shunted through the turbocharger rather than going out
of the exhaust pipe. the more sent to the turbocharger, the more boost. The
controls of this device (called a waste gate) is where the complexity and
possible danger comes in
The simple one is a system that I used in my twin comanche (turbo) where
the turbos were used to make up lost MP as the aircraft ascended. The technique
was to use full throttle until the MP started to decrease and then use two
additional throttles (vernier as opposed to the quadrant normal throttles) to
increase the MP.
The next in degrees ov coplexity is the fixed waste gate which was
used on the early piper senecas. (don't know if it is still being used for them.
In this the waste-gate which normally is variable, is fixed and a specific
amount of exhaust gas is fed through the turbo all the time. The MP is
controlled by one throttle.
The final system is one that I had on a turbo Viking and it was totally
automatic. The device (electrohydraulic) looked at the MP and other things and
automatically adjusted the wastegate to give the selected pressure. That was the
only thing that had to be reconfigured (in a new aircraft) from the start.
Which ever you choose, there are popoff valves available which limit t he
amount of pressure so not as to overboost the engine.
One thing of which to be aware is that when compressing air it heats up
significantly so although you are pumping more air into the cylinders
(trochoids) the air is less dense and much hotter. this decreases the
effectiveness of a straight turbocharger.
Many or most of the modern turbo charged aircraft use intercoolers
which reduce the temp of the inlet charge at the cost of complexity and
weight.
Over the past almost 50 years of flying-- if I flew in the mountains a lot,
I would have a turbo charger. since I am in the midwest, I chose the simpler and
more reliable route and am using a NA renesis.
Your indutional persuasion may vary.
Rich
In a message dated 10/8/2015 5:21:02 P.M. Central Daylight Time,
flyrotary@lancaironline.net writes:
Tom is
that a PP 3 rotor? If side port, is it ported in any way?
I am not denying all that you say. But 2 rotors are way more
readily available and my friend has one already, allegedly basically brand
new. We do need to do some tests on it, but if it is a good motor, I
think he will want to avoid trying to source a 3 rotor or build a PP out of
his 2 rotor. But he thinks he needs more power, hence the turbo
option.
Question about turbo control for you all. If your goal is very
modest boost at sea level, but normalizing at altitude, can you not just use a
boost controller and set a MAP as in manifold absolute pressure and stick to
that? Say you set it for 3 psi (roughly 18 psi absolute), that would be
very modest boost at sea level, but at altitude, the turbo would try to stick
to that - maybe it is 6 psi or whatever over atmospheric, but the same
absolute pressure. Is there any reason to feel you are stressing the
motor if you are sticking to reasonable boost like that?
— James
Whenever the topic comes up about adding a
turbo to a Rotary I go back to what was the reasoning I used when making the
decision to go Rotary in the first place.
My reasoning was to eliminate as much
mechanical complexity as I possibly could. If I added a turbo then the level
of complexity (and weight) went up.
I reasoned that if I needed (or just plain
wanted) additional power, I would just add another rotor. That actually
gives me more power that the turbo for where I need it most and the weight
comparison is negligible for the trade-off in power/complexity.
I believe that a 2 rotor (using Mistral
Engines as a benchmark) produces 190hp N/A (291 lbs) vs. 230hp Turbo (328
lb). The three rotor generates 300 hp @ 375 lb so yes, it’s it’s roughly +50
lbs but +70 hp as well without a significant increase in complexity.
I opted for the 3-rotor solution. Less things
to go wrong (which is important to me.)
T Mann