Cessna TC210M Turbo waste gate: how does it work?

[nico87]

Hello all,

This is my first post on PPRuNE.
I'm a PPL pilot and I would like to ask some information about the Cessna 210 Turbo handling.
Reading the documentation I've found over the Internet, I understood that the waste gate of the Continental TSIO-520 is completely automatic and it keeps the MAP constant while the aircraft is climbing. Is this true? To me, it looks strange that the pilot doesn't need to adjust the throttle to keep the MAP costant during climb/descent.
Unfortunately, I cannot check this by myself because there isn't a TC210 around the area I live in.

I report part of the documentation I've found about the TSIO-520 turbocharger's wastegate that keeps me thinking about a "constant MAP" behavior:

The variable pressure controller links the throttle to the wastegate actuator through a cam, spring and aneroid arrangement. When the throttle is opened, the cam on the controller rotates to compress the spring. This action closes a valve within the controller allowing oil pressure in the wastegate actuator to increase, which drives the wastegate toward the closed position.
This action causes more exhaust gas to flow through the turbine assembly, increasing its speed and resulting in more output of induction air from the compressor, since it is connected to the opposite end of the turbine shaft. Now. as the compressor output increases, manifold pressure increases. The aneroid unit on the controller senses compressor discharge pressure and its action opposes the force of the spring, that is, it tends to open the valve, believing oil pressure in the waste-gate actuator which allows the wastegate to move toward open.
In operation, the forces between the spring and the aneriod are balanced and the controller serves to maintain constant compressor discharge pressure as selected by the throttle and therefore main-tains a constant manifold pressure. When the throttle is reposi-tioned the cam, spring, aneriod and wastegate are displaced until the forces are again in balance for the new compressor discharge pressure.


Thanks to everyone who can shed light on this! :)

[flybymike]

I have no significant experience on a C210, but many years operating a TSIO520 on a C206 and C335.
The auto waste gate fully automates and maintains MAP by varying the waste gate setting based on throttle and atmospheric pressure (altitude) Thus MAP will be maintained right up to the "critical altitude" when the waste gate is fully closed and any further climb will result in loss of MAP. From memory this is typically around 18000ft.
The main thing to watch out for on these engines is not to over boost at low level ( typically on the take off run when turbine lag can catch you out)

[nico87]

Thank you Mike.
So, "automatic wastegate" means that the wastegate automatically adjusts to keep the MAP you set with the throttle but it doesn't prevent you to overboost the MAP itself by pushing too much throttle. Am I right?

[Big Pistons Forever]

No

The waste gate is designed so that at the full throttle position you will get max permitted MP in a steady state condition

What Mike is talking about is that during the takeoff roll rapidly advancing the throttle will mean the waste gate can't close fast enough so you will get a momentary over boost before the engine will correct itself and the MP will steady up at the max MP. This is particularly noticeable if the oil is not fully warm as the waste gate is operated by engine oil pressure.

[nico87]

Thank you!
I was thinking about this since few days ago, when I saw a video on Youtube. The pilot pulled back the prop to 2500RPM after takeoff but the MAP didn't rise. Usually the MAP would rise a little bit but in this case it was just the wastegate doing its job.

Another thing I noticed is that after passing 29/30'' of MAP, the FF rises abruptly. Is it because of the turbo boost?

[flybymike]

Suffice to say that the fuel flow on these engines is horrendous under virtually all circumstances....;)

[Big Pistons Forever]

Thank you!

Another thing I noticed is that after passing 29/30'' of MAP, the FF rises abruptly. Is it because of the turbo boost?

The fuel controller is set up to provide excess fuel flow at high power settings in order to help cool the cylinders. The jump in fuel flow you see is that extra fuel being added

This is why you should never do a reduced power takeoff in a turbocharged engine. Always use full power !

[nico87]

Thank you all! These information are really useful to shed light on my doubts.:ok: