Airborne_Again wrote:
What’s the advantage with a manually operated wastegate over a fixed wastegate? That you can save wear on the turbo when you don’t need an MP higher than ambient pressure?
Evolution was other way round: First there was the manually operated wastegate in GA airplanes, installation of turbos started there in the 60ies. Then presence of human error showed, that it’s not a good idea. Thereafter you had the fixed wastegate, which could not be operated terribly wrong but didn’t have the output power, until the automatic wastegate was invented.
If, however, a manually operated wastegate is used as intented you can save fuel and wear and in addition gain higher output power than the competitors. The fixed wastegate is fixed to some intermediate value, like 50% closed. The manually operated can be opened entirely, and closed completely, thus explaining that the Turbo Comanche should have takeoff power up to 20.000 feet (called Turbo Critical Altitude). Additionally I can run “oversquared” also at altitude, thus more economic.
But yes it is yet another item on the checklist.
Dimme wrote:
mighty mouse
As it’s a Piper you’ll need some Monterey Jack; for TB21 either Camembert or (for high altitude use) Comté.
Airborne_Again wrote:
What’s the advantage with a manually operated wastegate over a fixed wastegate?
Replacing potential mechanical failure by human failure?
Dimme wrote:
It releases the mighty mouse.
That is hilarious!
UdoR wrote:
@Malibuflyer I assume you mean the Turbo Comanche setup I’ve shown above? It is a manually operated wastegate for a turbonormalized engine.
What’s the advantage with a manually operated wastegate over a fixed wastegate? That you can save wear on the turbo when you don’t need an MP higher than ambient pressure?
Malibuflyer wrote:
What is the purpose of this lever?
Is there a limit for max continuous MAP that is lower than peak and therefore you can add some “extra power for climb”? Or is that more a method to save fuel?
@Malibuflyer I assume you mean the Turbo Comanche setup I’ve shown above? It is a manually operated wastegate for a turbonormalized engine. I can only increase to standard pressure 1013.25 hPa or 29.8"Hg, not more. Else you blow the engine. It’s as simple like that. And because it is so simple to blow the engine, there are only very few around. If you know what you’re doing you can run the engine far more efficient, but if not, well, there is an overblow valve, but you’ve won a complete overhaul.
Malibuflyer wrote:
What is the purpose of this lever?
It releases the mighty mouse.
Very interesting – never seen it before.
What is the purpose of this lever?
Is there a limit for max continuous MAP that is lower than peak and therefore you can add some “extra power for climb”? Or is that more a method to save fuel?
How do you operate it in practice?
I’ve seen Lake Amphibians with a turbo charger control. Uncommon, but there are some…
If the engine is a PT-6 turbine, that lever would be the stand by throttle, a fully manual control, in case the fuel control unit fails (which I have had happen). The standby throttle is more sensitive, and without some protections against exceedances, but will get you home. On Cessna Caravans, they are typically copper wire locked off, so pilots do not use in error, but I have used that control while doing engine set up in a Turbo Beaver, so got the hang of it then…
NinerEchoPapa wrote:
First time I’ve seen a turbocharger lever! Is that a Comanche?
And there aren’t many possibilities to see this type of setup. There have been 26 factory built Turbo Comanches with this lever-type adjustment of the wastegate. It really feels like a second throttle in climb. I don’t know, though, how many aircraft still fly around with this type of configuration, including maybe other types (but not, for example, the Twin Comanches, which use a knob-like adjustment of the wastegate)
Peter, sorry I couldn’t resist to add my “four lever foto” here, and your initial question had been answered before…
