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Two questions to all you experienced pilots or engineers.

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Two questions to all you experienced pilots or engineers.

Old 20th Jul 2014, 12:25
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Old 21st Jul 2014, 01:49
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would that also then provide a cooling effect across the turbine like in a piston aircraft and enriching the mixture?
Negatory I am afraid. Turbin's do not function like Piston Engines (which can only get so much air into themselves due to the valve timing). If ya put more fuel into a Turbin then the more fire you get, the hotter it runs, and the harder it drives the Turbin and the Compressor which is attached to the other end of the shaft. Hence more gas is produced which increases all the parameters, and these readings keep on climbing until you either become Temp, Torque, or RPM limited, whichever comes first, prior to some kind of melt down or other engine destruction if you keep over fuelling it for long enough.
Take care out there. BE
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Old 24th Jul 2014, 04:14
  #23 (permalink)  
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The whole point of the question is asking if you can get more out of the engine than just hitting the firewall with the power levers.
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Old 24th Jul 2014, 17:10
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The whole point of the question is asking if you can get more out of the engine than just hitting the firewall with the power levers.
And the answer to that question is Most Possibly YES!!

In normal operation the fuel control is scheduling the fuel into the fuel manifolds and nozzles such that the Gas Generator is maintaining a selected speed (Ng). Pushing the Power Lever all the way to the forward stop will tell the Fuel Control Constant Speed Governor to produce a sufficient flow of fuel to provide the Maximum Speed of the Gas Generator. (Any limiters you have on the engine will override this and stop the increase in fuel flow at the limit.)

This position may or may not be at the full open position of the metering valve as the maximum FUEL FLOW - (Not Ng) is determined internally by the "Most Open" position of the Fuel Metering Valve.

Using the Manual Override may push the Fuel Metering Valve all the way to the Maximum Fuel Flow position. (Most Open)

Providing you have sufficient Fuel Pump capacity, advancing the Manual Override may give you additional fuel flow to that already commanded by the Power Lever.

Say Bye Bye to the engine!!! It will by that point in time have:
Over Temped - Over Torqued - both the engine and the propeller - and Oversped at least the Gas Generator.

Solid Reliable Information available here!!


PT6 Info - FreeBee


Hope this helps.

So much mis-information out there from folks who really don't know this engine - but think they do!!

kingRB in post 6 had it first!!

Mx

Last edited by MX Trainer; 24th Jul 2014 at 17:19. Reason: Credit for previous poster.
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Old 25th Jul 2014, 03:29
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Thanks for that link MX, I had not seen a schematic of the override system before
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Old 25th Jul 2014, 04:57
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Using the Manual Override may push the Fuel Metering Valve all the way to the Maximum Fuel Flow position.
Then again, it *MAY* not.


One very good reason it may not is engine preservation. The EPL is there to get you to an airstrip should there be a failure of the FCU pneumatics at some time after takeoff. It is not there to give extra power for obstacle clearance.


It is very likely that the pilot's ability to rapidly destroy the engine has been limited - deliberately - by Cessna.


On the PC12, the EPL is called a MOR (manual override), and you cannot get anywhere near full power with it.
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Old 25th Jul 2014, 10:56
  #27 (permalink)  
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FGD~ I understand what its primary function is for. Basically anyone who flies the caravan does.
If it has provided a secondary effect that may be available to save the ass of a pilot who has got himself into serious bother, shouldn't that option be discussed?

The whole point of the discussion is to get to know the "172 on steroids" a little better.

Firewalling the lever may not be enough and you may end up dead, so why not give something else a try that could be the difference between life or death? If it doesn't work, well the end result could be the same as firewalling the lever anyway.
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Old 25th Jul 2014, 11:16
  #28 (permalink)  
 
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FCU and EPL lever

Personally I wouldn't risk it,id think you would get better performance making sure you were clean,torque maxed out(if i remember it can take 2400 for 20 seconds but been long time since flew one) prop fully forward and maybe chuck ignition on too.
I had FCU failure on the ground at startup once it just threw extra fuel in ,that just got spat into the exhaust and smoked everywhere.I would guess you have higher chance of compressor stall/flameout without FCU not to mention cooking blades and having them spat out too.
Where your flying now my best advice would be weigh everything yourself to make sure your never over weight(less surprises after takeoff) and always wait for good gap in weather before leaving.
Stay safe
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Old 26th Jul 2014, 02:20
  #29 (permalink)  
 
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lilflyboy262...2,


I understand perfectly what you're trying to do, and applaud and commend you for your curiosity.


This thread will have dramatically increased your knowledge of issues related to the EPL, but I don't believe it has answered your original question anywhere near authoritatively enough to warrant your usage of it in the given scenario.


Given that the readily available documentation on the aircraft (and engine) does not address this question, you would need to obtain positive, documentary evidence from both Cessna and PWC before committing your mind to that course of action. I would not automatically believe what any LAME has to say on the matter.


In the absence of such confirmation, I would just use the power lever, but without concern for exceeding torque, temperature or Ng.


Good luck with your flying in PNG!
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Old 29th Jul 2014, 13:40
  #30 (permalink)  
 
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OK here are the facts


The EPL will give you slightly more power and each engine is different it must via certification give at least 100% power


Its designed in the event of an FCU failure and its the pilot that controls the power now and not the FCU via fuel in


Next over temp the blades and you will have an expensive fireworks display out side with along a loss of power.


Next there is no un metered fuel sent to the nozzles in normal operations only metered fuel even with the use of the EPL


There are on ALL PT6s two different nozzles a primary usually around 4 and 10 secondary each engine has different specs.


The primary start the engine and at around the 22% mark after light off the second set is opened by the flow divider by increased fuel px and acceleration up to idle occurs.


Tq limiters are not on ALL engines.


Next the more fuel in the more heat is produced. Less fuel less heat. Less heat less power and so on.


Generally around 54 turbine blades in the ct wheel. these take the most heat and as such are the easiest to damage. damage these blades and it don't matter how much fuel you put in power will be lost.
in the 114A each blade produces around the 25 hp mark. That include HP to drive the compressor which a rule of thumb is around SHP plus SHP Ie 675 plus 675 to run the compressor ,


So in the event of you having to use the EPL be very careful you may do more damage to your self but watch your ITT temps when using it.


Cheers
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Old 29th Jul 2014, 13:47
  #31 (permalink)  
 
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extra point


Its very unlikely that you would have a gearbox failure from an over tq in what you have described. The engine would have to be removed etc after an incident that you have described but I cant make this point hard enough watch the ITT temps because once you damaged the blades power is dramatically reduced.


cheers
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