Turbo Charging - controls?

[Guest bfindlay]

I am interested in learning more about TC controls in the cockpit. If a plane is turbocharged, is there an additional power control, or just the usual suspects? I am guessing not - that the only thing you notice is increased manifold pressure, and you have to be careful about not exceeding an MP redline - overboosting.Any info on this, or intercoolers, or wastegates would be duly appreciated!

[CraigC 0]

Im not quite sure on this either, and am interested in finding out from someone who knows. Im pretty sure its your usual power, prop, mixture combo. I think the only thing different about the set up is the turbo chargers (which I think are just ultra high speed fans, but this Im definitely not sure about) which allow much better performance at higher altitudes. This is definitely something Ill learn this semester while completing my commercial.Craig

[Guest RiddlePilot]

Turbocharging simply allows the aicraft to produce the same amount of power at higher altitudes as it does at sea level. In a normally aspirated engine, there is a constant decrease in performance as altitude and, as a result, pressure decreases. The turbocharger takes normal exhaust and routes it through the compressor, which spins extremely fast (60,000-120,000 RPM). The compressed air then enters the cylinder for combustion. The mechanism that controls the amount of air that enters the turbocharger is called the wastegate. If it weren't for this, the engine would tear itself to shreads. At low altitudes, the wastegate is nearly all the way open. This is because the air is already dense enough for normal combustion. As you climb though, the wastegate gradually closes to force more and more air into the turbocharger for compression. At "critical altitude", the wastegate is fully closed, and the turbocharger can no longer maintain sea level pressure inside the manifold.Now, to answer your question. There are 4 types of wastegate controls. Fixed, Manual, Mechanical, and Automatic.Fixed: Used by Piper on the Arrow and Seneca II (it needed SOMETHING to help it out). The position of the wastegate is, well, fixed. At least some air will always pass by the turbocharger and go to waste. With this set-up, you will notice max manifold pressure at about 1/2 to 3/4 throttle on takeoff. Overboosting is a common mishap with a fixed wastegate.Manual: This requires an extra lever in the cockpit, and extra attention by the pilot. Normally, you would have the wastegate fully open, increase power for takeoff to the recommended MP. In the climb, you would increase the throttles to maintain climb MP, until the throttles are at the stop, then you would begin closing the wastegate to utilize the turbocharger.Mechanical: Very similar to the Manual, except they are tied into one lever. Usually, the first half of throttle travel is actually throttle, the second half being the wastegate control. Turbo Skylanes use this.Automatic: Its really complicated and I'll leave it to these two links to describehttp://www.kellyaerospace.com/articles/RAJAY.pdfhttp://142.26.194.131/systems1/Engines/Turbochargers.html

[CraigC 0]

That was a pretty good explanation, Travis. I actually got out the Jeppesen Instr/Comm manual to bust you for plagerism (since I thought maybe that is what they use at ERU), but no joy. :) I see that I have quite a bit to learn about turbocharging....all in due time. :)Craig

[Guest RiddlePilot]

Actually, its out of "Flying High Perfomance Singles and Twins" by John C Eckalbar (A VERY good book). Some of the more difficult parts to describe are word for word, but most of it my own. You can sure bet that our Commercial operations class teacher drilled this stuff into our head.

[Guest]

>Turbocharging simply allows the aicraft to produce the same >amount of power at higher altitudes as it does at sea level. This is a definition of a Turbo Normalized aircraft engine - one that is designed to produce its originally rated power to a much higher altitude.There is also another use of turbocharging in aviation - to increase the available power from a given egnine size, much as in car engines. So I think we should also say that "Turbocharging also allows the aircraft to produce a greater amount of power for any given altitude". This was more common in military aircraft, for whom power is more important than life cycle cost or maintenance schedules but it is also found in GA. ChasW

[Guest bfindlay]

Dude - thanks! So what is an intercooler?PS - especially thanks for the book recommendation - I will be checking it out pronto.

[Guest tinman]

Intercoolers are used to cool the air leaving the turbo before it enters the combustion chamber, due to the simple law of physics that with an increase in pressure, you also gain an increase in temperature. This helps keep CHT and EGT down, which if the charge were not cooled, could lead to a pre-ignition or detonation in the cylinders. :)