A few Caravan / PT6 questions...

[lilflyboy262...2]

Ok the first.

On the top of the panel, on the pilots side, there is a placard that shows 4 RPM and Torque limitations.
Now I know that (Torque x RPM) / 5252 = SHP
The engine is rated to 675 SHP.

The first total is at a reduced torque, but max RPM, and it = 674 SHP
The second total is at max torque, but a reduced RPM, and it = 675 SHP

The engine can run all day at a reduced torque, and max RPM or vice versa, so that has me thinking, since max RPM and max torque would give around 705 SHP, is the 675 SHP a engine limitation, or an airframe limitation?

Question number two.
Once the fuel goes through the flow divider. It passes around the engine to the 10 primary nozzles and the 4 secondary nozzles.
There is no pump or anything like that, the fuel just passes through the pipes to the nozzles.
How does it find its way equally to all of the nozzles....? Like how does the first nozzles not end up with more pressure, while the top ones end up with next to none?

I just figured since fuel is a liquid and its not compressible, once it reaches a certain pressure in the nozzle as it tries to force its way out of the nozzle hole, it takes the path of least resistance and moves on to the next one, and so on and so on.

But that seems way too basic, but looking at the engine, its just a ring around the outside and into the nozzles... can't see anything special.


Question number 3.

What indications would a blocked fuel nozzle give you?
I realize that this is highly unlikely as the fuel passes through a filter, a 75 micron mesh, and a 10 micron mesh.... BUT... If it happened... What would I likely see?
I'm guessing a reduced torque, higher ITT's than normal for the torque setting, and inability to produce full power.

Would this damage the burner can by having an area that is not burning?


Sorry if the english is a bit off. It's been a long day in class....

[werbil]

I can only answer the first question - Propeller Reduction Gearbox Limit.

[lilflyboy262...2]

Awesome thanks.
Never would have thought about that.

[aerobat77]

I can only answer the first question - Propeller Reduction Gearbox Limit.

i dont think so since the gearbox is approved to take the higher tq at lower propspeed.

its more a certification limit of the airframe with the option for keeping the rated power output at lower prop rpm ( eg cruise)

cheers !

[werbil]

It is an an engine limit - refer to the Pratt type certificate which can be found here: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/90c641493420043b8625752f006482e8/$FILE/E4EA_rev24.pdf.

If you want a fit a 900hp Honeywell engine to a van you can get a conversion here Texas Turbine Conversions - Supervan 900 - (http://www.texasturbines.com/ttcaravan/TTcaravan.htm)

[plane breeze]

The 675 SHP is an engine limitation and not the airframe

The Supervan 900 dilivers a downrated 900 SHP but the engine is thermo limited to 1150 and there is no major addtional inspections required with the conversions even thought the rate of climbis almost double and the the airspeed has been pushed to over 205 Just ask ATC at OR Tambo

[TOINFINITYANDBEYOND]

Is this college course homework? :) Fuel is delivered from the aircraft tanks via boost pumps to the FCU which decides on how the fuel will be distributed to the nozzles. Bad fuel nozzles will make a mess of you combustion chamber and poor performance. (wihtout typing everything from the type course notes)

[blackhand]

is the 675 SHP a engine limitation, or an airframe limitation?
Would have been decided at type design stage. An engine prop combination is chosen to deliver the power required. Consider that thrust horsepower isn't engine horsepower.
The STC from Texas Turbine changes the original Type Certificate and would have had to satisfy FAA about the changes.
Fuel flows from Boost pumps to EDFP to FCU to Flow Divider to fuel nozzles. The fuel pressure is developed by the engine driven fuel pump and the FCU, it isn't high pressure like a diesel engine.
Blocked fuel nozzles could give hung start and or low power.
Although have found partial blocked nozzles on servicing them without any defects recorded in flight log.
How does it find its way equally to all of the nozzles....? Like how does the first nozzles not end up with more pressure, while the top ones end up with next to none?Basic physics, "pressure is exerted equally and undiminished......".
Would this damage the burner can by having an area that is not burning?Damage to the can would be caused by "streaking" from partially blocked nozzle, don't know about damage from total blockage, but would think not.
Cheers
BH