camg
Member
Posts: 31 
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Post by camg on Jun 8, 2009 6:49:41 GMT -5
I would like to change the time it takes the prop to stop rotating when I shut down a turboprop engine. Is the spool-time something that is determined by a table or setting in the .air file, or is it hard coded in the .mdl file?
Cam
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Post by Tom Goodrick on Jun 8, 2009 19:30:34 GMT -5
No idea. Try adjusting the pitch after shutting down. Go to full feather.
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Post by flaminghotsauce on Jun 9, 2009 6:06:26 GMT -5
I downloaded an IA 58 Pucara off Simviation (the one that's 4.x mb in size) and it took a good while to spin down the props. You might try getting that and see what's inside.
Most stop way too soon in my opinion.
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n7rg
Member
Going Home to Alaska
Posts: 62
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Post by n7rg on Jun 10, 2009 0:18:43 GMT -5
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Post by Tom Goodrick on Jun 10, 2009 9:36:17 GMT -5
What Milton Shupe says is correct. he and I have talked a couple times. He generally pretty sharp. BUT!!!
The prop behavior determined by those parameters has much more important aspects during a flight than the mere control of spooling up or down during start-up or shut-down. I consider those phases of operations to be completely irrelevent compared to what the prop does when you change prop speed or engine speed during flight. Prop MOI relates to "frequency" in a sinusoidal variation of power. Tc is a time constant implying a decay but in repaeted iteration influences a periodic variation.
In many cases we have had problems with with propeller surging duirng the transition from climb to cruise, cruise to descent or during power adjustments on final. The latter condition is the most important for a turboprop. You fly final with a fair amount of power in a turboprop. Small adjustments are often needed to stay locked on the glideslope. You don't want any long-period oscillations in power. This is what can happen when you mess with these parameters.
Go ahead and try just to see what happens. But first, write down the initial settings for those values. If you are using my FD for the B200, I think I worked on those parameters to get flight power control behaving well.
This is a big problem with most flkight parameters. Tweak them to solve one problem and you will create other problems. A final setting is often a compromise over a range of phases of flight.
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Post by Tom Goodrick on Jun 10, 2009 10:00:26 GMT -5
OK. I did what I suggested to you at the top of this thread. Pulling back the prop levers shortens the spool-down time significantly.
With my handy digital stopwatch and using my FD for the B200, I measured spool-up time (to engine start) as 9.32 seconds. after the engines stbilized for some time at idle and the oil warmed up a bit, I shut down. Time from fuel shut-off to 0 rpm with hands in lap was 1:47.19 or about one and 3/4 minute. I repeated this but this time after shutting off the fuel I pulled the prop levers full back. The time was 0:32.31 to 0 rpm or just over 30 seconds.
It works!
This is the normal procedure. I forgot to use my Turboprop Power panel to see what the blade angle was. MY FD does not give a perfect feather angle but it is high enough to do the job.
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camg
Member
Posts: 31
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Post by camg on Jun 16, 2009 7:02:57 GMT -5
Yes--pulling the prop lever back shortens the spool-down. I was ready to start experimenting with prop MOI and the prop time constant, but I'll leave those alone.
I had checked the Mu-2, KA 350 and Caravan. They all took over 50 seconds to spool to a stop, which seemed too long. When I pulled the prop control to feather right after fuel cut-off, the prop stopped in 17-19 seconds. (Full disclosure: I did this in FS2002.)
Some day soon I'll go over to my local airport (KFCM) and try to catch an actual King Air shut-down. My guess is that an actual spool-down is 25-30 sec.
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Post by Tom Goodrick on Jun 16, 2009 9:17:57 GMT -5
Which airport you going to? I used to hang around Minneapolis airports in the late 1950's and early 1960's.
Look at a parked turboprop and see which way the props are set. They should all be turned toward the side, so the leading edge faces forward.
I think pulling the prop lever back (ie- "feathering" the props) is in the standard checklist. It keeps the wind from turning the props and hurting someone.
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