Flyboy80 From United States, joined Jul 2001, 1641 posts, RR: 5 Posted (3 years 11 months 4 weeks 1 day 22 hours ago) and read 1494 times:
I went on a recent day trip..among the flights, I did a LAX-RNO-LAX on a QX Q400...anyways, something I've always wanted to ask...during taxi in the dash's I hear differen't sounds being generated...curious to if this is the pitch changing while they taxi, depending on the amount of thrust the cockpit wants? thanks for any info!
Musang From United Kingdom, joined Apr 2001, 432 posts, RR: 9 Reply 2, posted (3 years 11 months 4 weeks 1 day 16 hours ago) and read 1432 times:
Flybot hits the nail just about on the head. Blade pitch directly modified via the power levers to regulate thrust, in what's called the "beta" range. At high power, lever movement controls fuel flow to engine, prop SPEED is fixed (RPM lever) so prop accomodates power change by coarsening or fining the blade angle, taking a bigger or smaller bite out of the air.
It wouldn't be feathered on the ground except during the feathering checks, done once a day or once a sector according to the airline. Blade angle is then average 90 degrees to the direction of rotation, drag so high it slows the engine right down, which would be obvious to anyone who heard it.
SlamClick From United States, joined Nov 2003, 9996 posts, RR: 78 Reply 4, posted (3 years 11 months 4 weeks 1 day 8 hours ago) and read 1378 times:
Quoting Skydrol (Reply 1): Just have to add the comment...
Absolutely hate riding on the Dash-8 at all. At least in the passenger cabin. Did they HAVE to make those nacelles blot out the entire view? Horribly claustrophobic. The only DeHavilland of Canada product I didn't love.
Happiness is not seeing another trite Ste. Maarten photo all week long.
FLY2HMO From United States, joined Jan 2004, 3784 posts, RR: 4 Reply 5, posted (3 years 11 months 4 weeks 1 day 8 hours ago) and read 1376 times:
What you heard was the props going "flat". In my last flight in a DHC8, I was sitting in the window right next to the prop. I was constantly staring at it, watching how the pilot adjusted the pitch while taxiing, if he got too fast, he'd give it a few seconds of flat pitch, which I guess makes the whole prop act like a large speedbrake and you can really feel the whole plane slow down. It is when they do this when it gets much louder. When landing, reverse thrust looks totally different from "flat" pitch. When the engines are shut down, the props are feathered.
Here's the airplane flying handbook, go down to page 210 for more info:
Ralgha From United States, joined Nov 1999, 1614 posts, RR: 7 Reply 6, posted (3 years 11 months 4 weeks 1 day 7 hours ago) and read 1354 times:
The airplane flying handbook power quadrant illustrations aren't quite accurate for most turboprops, including the Dash-8. Most do not have a propeller control lever(s), only power and condition levers. King Airs are the only ones I can think of off hand that have a propeller lever.
Also, the visual difference between flat and reverse when taxiing is probably not very noticeable. During landing you saw full reverse, during taxi, full reverse is not used, though minimal reverse is not uncommon.
LimaFoxTango From Antigua And Barbuda, joined Jun 2004, 342 posts, RR: 1 Reply 7, posted (3 years 11 months 4 weeks 1 day 6 hours ago) and read 1339 times:
Quoting FLY2HMO (Reply 5): What you heard was the props going "flat"
This happens when the pilot's move the throttles aft to what is called "Discing". In this range, the props are flat against the airflow causing an increase in drag which slows the aircraft down. Futher aft of discing, is the reverse thrust. It is pretty interesting to note that most times, Dash 8 pilots rarely go into reverse thrust. Discing does a good enough of a job to slow the aircraft down pretty quickly.
Dufo From Slovenia, joined May 1999, 682 posts, RR: 6 Reply 8, posted (3 years 11 months 4 weeks 1 day 4 hours ago) and read 1291 times:
Quoting Ralgha (Reply 6): The airplane flying handbook power quadrant illustrations aren't quite accurate for most turboprops, including the Dash-8. Most do not have a propeller control lever(s), only power and condition levers. King Airs are the only ones I can think of off hand that have a propeller lever.
This depends on the engine type. PT6's have all three controls, while Single-shaft (Garrett, Allison too?) engines usually have two.
I seriously think I just creamed my pants without any influence from any outside variables.
Flyboy80 From United States, joined Jul 2001, 1641 posts, RR: 5 Reply 9, posted (3 years 11 months 4 weeks 1 day 3 hours ago) and read 1283 times:
Yeah I've flown a lot of turbo props..I absolutely love them... I noticed when we landed in RNO on the Q400, the pilots only had the props in reverse for literally a few seconds if, then flat, with some minor braking...and we used about 4k...pretty nice...well thanks guys, i was just curious to as where that sound was coming from, I was pretty sure it was caused by pitch, but I thought it may be something else! thanks!
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