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Propeller Commuter Airliner Startup And Shutdown  
User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Posted (9 years 9 months 2 weeks 3 days 6 hours ago) and read 1780 times:

I want to know what goes on when those dashes and saabs start. Its like they turn the engine on, and have the propeller halfway going. Then its like the engine kicks in. And when they Shut down it revs up and then Suddenly shuts down with kind of a loud farting noise and the propeller will be halfway going again, then its like the pilos has control of how fast the prop is going without the engine or something. I have no clue. So can someone please explain what exactly is going on.

24 replies: All unread, jump to last
 
User currently offlineLinemechqx From United States of America, joined May 2004, 77 posts, RR: 0
Reply 1, posted (9 years 9 months 2 weeks 3 days 5 hours ago) and read 1725 times:

Well as far as dashes go, the engines are always started and shut down with the props in feather. A typical start procedure for a D-8 200 would be start in feather at flight idle power setting, then pushback, then selecting props to min which is followed by the prop speeding up, not really the engines, it just sounds like it. On shut down, the props are once again feathered but it happens much faster making a loud noise as the props suddenly change pitch. QX company policy calls for a minimum 30 secs at feather to cool the engine but sometimes pilots will feather #1 on taxi in to facilitate servicing of the a/c.
Thats a fairly short explanation hopefully it answers your questions.

Late
PC


User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 2, posted (9 years 9 months 2 weeks 3 days 5 hours ago) and read 1718 times:

so, when it seems like the propeller is going very slowly, its at idle and featherd, giving off that impresion that the engine isnt starte right? And when it seems like the engine is kicking in, its actually the prop speeding up. Thank you very much

User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 3, posted (9 years 9 months 2 weeks 3 days 4 hours ago) and read 1715 times:

As for as the Saab 340 starting procedures, it sounds like your describing a Residual Start. This is done when the engine temperature is above 200C. With the Fuel/Condition Lever and the IGNITION in the OFF position you engage the starter. This spools up the engine and sucks in nice cool air, dropping the ITT and will also very slowly turn the propeller only from the air passing through the engine and turning Free Turbine. You then quickly move the Condition lever to the START position. This introduces fuel into the burner can, and then quickly flick the IGNITION switch to the Normal position. Now you have fuel and a spark. Depending on how quickly you do this, sometimes a little extra fuel builds up in the can and you'll get a quick 'fart' as you described. Also, if you release the Starter switch too quickly, the engine may spool down a little before the rest of the start sequance is completed. Now, once the engine is up and stabilized at the Start position, its only turning at Ground Idle. This is when you turn on your DC GENS and Air Con PACS. When you then move the Condition Lever above the MIN gate, the engine will then spool up and turn much faster.


"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 4, posted (9 years 9 months 2 weeks 3 days 4 hours ago) and read 1704 times:

i only hear the big fart upon shutdown.

User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 5, posted (9 years 9 months 2 weeks 3 days 4 hours ago) and read 1698 times:

That is just the fuel being cut off.. It will sometimes 'pop' or 'fart'


"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 6, posted (9 years 9 months 2 weeks 3 days 3 hours ago) and read 1692 times:

ok. thank you. I have always wondered what was going on.

User currently offlineCylw From Canada, joined Apr 2000, 427 posts, RR: 0
Reply 7, posted (9 years 9 months 2 weeks 3 days 3 hours ago) and read 1682 times:

I think that "fart" sound you're refering to is when the props are feathered upon arrival at the gate.

User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 8, posted (9 years 9 months 2 weeks 3 days 2 hours ago) and read 1677 times:

no, ive got that covered. thats the chchchchchchchchch sound.

User currently offlineLimaFoxTango From Antigua and Barbuda, joined Jun 2004, 771 posts, RR: 1
Reply 9, posted (9 years 9 months 2 weeks 3 days ago) and read 1646 times:

Actually Cylw is correct. That infamous "farting" sound is made when the props are being feathered. After the props are feathered, then it makes that "chchchchchchchchc" sound. Also, when the engines are started, they are started with the props feathered. When they appear to "speed up", they are not actually speeding up, the props are simply being unfeathered.


You are said to be a good pilot when your take-off's equal your landings.
User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 10, posted (9 years 9 months 2 weeks 2 days 23 hours ago) and read 1635 times:

yes i know that, i got that covered. i thought cylw was talkig about when ther are taxiing to the gate, i know the fart noise is when they are feathered and shut down nearly at the same time.

Sooo, feathering slows down the props too right?


User currently offlineCylw From Canada, joined Apr 2000, 427 posts, RR: 0
Reply 11, posted (9 years 9 months 2 weeks 2 days 20 hours ago) and read 1608 times:

Feathering changes the blade angle of a propeller blade. If I can remember this right, a feathered prop has an almost 0 degree angle compared to the relative airflow. A feathed prop produces zero or very little thrust. A feathered prop also produces the least amount of drag. If you happen to have an engine failure, you're going to want to feather the prop on the failed side to reduce drag. Alot of turboprops have an autofeather system that automatically feathers when theres an engine failure.

Im sure others could explain it in more detail.


User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 12, posted (9 years 9 months 2 weeks 2 days 12 hours ago) and read 1545 times:

ooh, i see.
Feathering has less drag.


User currently offlineJjbiv From United States of America, joined Jan 2001, 1226 posts, RR: 5
Reply 13, posted (9 years 9 months 2 weeks 2 days 10 hours ago) and read 1523 times:

Is that what the autocoarsen system on the Saab does?

joe


User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 14, posted (9 years 9 months 2 weeks 2 days 9 hours ago) and read 1515 times:

not sure, i hope the experts get back in here though.

User currently offlineLiamksa From Australia, joined Oct 2001, 308 posts, RR: 0
Reply 15, posted (9 years 9 months 2 weeks 2 days ago) and read 1463 times:

A feathered prop has less drag in-flight (ie: with forward airspeed) but more drag on startup. When starting a feathered prop the blades are 'slapping' the air rather than 'slicing' through it - more drag (resistance). For this reason direct drive turboprops (which must swing the prop with the starter motor) have feathering locks (or the equivalent) which ensures the prop doesn't feather on shutdown to make startup easier.

Autofeather systems are AFAIK only used for takeoff, and feather the prop automatically when a certain condition is sensed.

As for all your noises - ?  Big grin


User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 16, posted (9 years 9 months 2 weeks 1 day 23 hours ago) and read 1452 times:

lol. well, its hard to see exactly whats going on from the outside, but you sure do hear different things on the good old turboprops.

User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 17, posted (9 years 9 months 2 weeks 1 day 18 hours ago) and read 1422 times:

Is that what the autocoarsen system on the Saab does?

Yes.



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineMYT332 From United Kingdom, joined Sep 2003, 9112 posts, RR: 71
Reply 18, posted (9 years 9 months 2 weeks 1 day 16 hours ago) and read 1408 times:

Oh man this thread is funny. You guys have mentioned farting seven times already. I'm sure theres a better word.

Ahhh  Laugh out loud



One Life, Live it.
User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 19, posted (9 years 9 months 2 weeks 1 day 12 hours ago) and read 1390 times:

lol, dont lie. U know thats what it sounds like.

User currently offlineFLY 8 From Austria, joined Dec 2000, 329 posts, RR: 0
Reply 20, posted (9 years 9 months 2 weeks 17 hours ago) and read 1333 times:

@ linemechqx!!

are you sure the power levers are at flight idle?? i pretty sure they must be in GROUND idle!!



yes i can handle that alone. - - -famous last words
User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 21, posted (9 years 9 months 2 weeks 14 hours ago) and read 1316 times:

im pretty sure the prop is just feathered. dont know which idle it is.

User currently offlineFLY 8 From Austria, joined Dec 2000, 329 posts, RR: 0
Reply 22, posted (9 years 9 months 2 weeks 13 hours ago) and read 1312 times:

sure the prop is feathered! on ground you actually never move the power levers out of ground idle unless you are about to take off.
when taxiing, you control the blade angle with the power levers wich is called beta mode. if you move the power levers over a detent position you go into reverse! that means you have 3 gates at the power levers wich are. reverse, ground idle, normal (wich is above the flight idle gate).

selecting gound idle during flight is prohibited.

for the condition levers we have following positions:

-fuel off - everybody knows what that means.
-feather- if you move the condition lever from fuel off to feather, the fuel shutoff valve opens.
-minimum- means propeller unfeathers but is at a very great angle. (you use that during cruise and app.)

and that you still have a very you long way to push those condition levers to max. (but there will be no more detent position, where you need to lift a little knob on the side of the condition levers)



yes i can handle that alone. - - -famous last words
User currently offlineKcrwflyer From United States of America, joined May 2004, 3763 posts, RR: 8
Reply 23, posted (9 years 9 months 2 weeks 12 hours ago) and read 1307 times:

interesting, didnt know that.

User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 24, posted (9 years 9 months 2 weeks 6 hours ago) and read 1292 times:

KCW-

I finally put your noise together was a running Saab 340. As has been said above, after the aircraft is started and up and running you move the Condition levers above the MIN gate up to the MAX gate. On the ground, this will only take the props out of feather and will have no control over the blade angle once over the MIN gate. Taxi speed and blade angle are now controlled by moving the POWER levers out of the START gate. After you have done all your checks and have returned to your parking spot, the whole sequence is reversed. You now pull the POWER levers back to the START gate. (Now, here comes your noise..) As you pull the Condition levers from MAX to just above the MIN detent nothing happens to the blade angle, 'UNTIL' you pull the Condition levers over the MIN gate. At this point the blade angle will go from Ground Fine ( l ) into Feather ( - ). If you do this quickly, the blade angle will change rapidly, causing the air around the prop to make your 'farting' sound. I was taught when bring the Condition levers over the MIN gate to slowly retard the levers until you see the slight spike in PGB oil pressure. This is the internal piston in the prop beginning to move. Once you have the spike, you stop moving the Condition lever until the prop slowly transitions into Feather. Either way works, neither way causes undo wears. I just think it shows much more care of the aircraft when you do it the way is was taught.
On the Saab you will also hear this noise after the crew has the aircraft up and running and they have do their pre departure checks. Part of the checks is the 'Autocoursen' test. When you do the test, prop blade angles will change quickly from Ground Fine to Feather and will make the same 'farting' sound.

[Edited 2004-07-15 22:25:57]

[Edited 2004-07-15 22:32:23]


"It's not the size of the dog in the fight, but the size of the fight in the dog"
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