detpilot

I've noticed a lot of saab operators seem to taxi with one engine feathered, yet running. Why is this? On our plane (PT6), it burns the same fuel at idle feather as it does at idle unfeathered (assuming no beta use, etc).

Is it just to prevent them from needing beta on that side to keep taxi speeds down, and in that case, does beta really burn that much fuel over an idling engine?

Or is the reason not to save fuel, but to increase bleed air for passenger comfort? In that case, would you go to flight idle or even higher, with the prop in feather? Thanks!

AmericanEagleFO

On the ATR the feathered prop saved a minute amount of fuel, but saved non the less.

minitour

Even 10 pounds/leg can add up.

10#/leg * 6 legs/day * 345 days/year (leaving 20 days of "down time" for mx) = 20,700# per plane.

If you have 10 planes, that's 200,000 # of gas or ~ 29,600 gallons.

At even $2.00/gallon, that's almost $60,000.

Not earth shattering, but hey....it adds up.

...and before someone wants to know what operator I got those numbers from, I didn't. I picked some. At random. I don't know (or care) how your operator operates xyz aircraft. I just picked a number for the discussion. M'kay?

-mini

crj700

On the Saab, you should have the engine in feather before opening the High Pressure bleeds for better cooling. One operator I flew for would allow the HP bleeds open with the props out of feather but you had to be very careful with the power lever or you would exceed the ITT limits.

atr42flyer

another reason is noise, i know on the dash some captains would keep the #1 in feather because the FA was sitting next to the door and well its loud. also if you just landed most turbine engines need a cool down period so to speak in feather. so why not just do it on the taxi in with one in feather and you can shut it down that much sooner. instead of parking at the gate and waiting for 30 sec to a minute to turn them both off.

trent890

For the Dash-8, I'd start them both up when making a right turn off of the gate. For a single engine taxi, after pushback there may not be enough space in front of the plane to get some forward momentum going before making a 90 degree right turn away from the dead engine, or enough space behind the plane to make a 270 degree left turn "the long way around" into the dead engine.

So I'd start them both up, use differential power, a free-castoring nosewheel, and a tap on the inside brake to turn off the gate. Once away from the gate and moving straight ahead, the hydraulic nosewheel steering comes on, and the left engine gets feathered for a normal taxi time in order to save some gas and reduce the noise. If the taxi time is going to be excessive, then #1 will be shut down after having at least 30 seconds in feather.

For the Dash 8-300, I would start them both up every single time, but #1 would usually stay in feather until getting close to takeoff. For the -300, it's real easy to exceed the maximum steering angle for the hydraulic nosewheel steering when trying to make tight turns during single engine taxi. I've seen too many guys exceed the steering limit, the hydraulic steering kicks off, and now there is no way to get the nosewheel straightened out unless you stop to take the time to now start the #1 engine and then use differential power to bring the nosewheel back into the steering limits.

So on the -300, I'd start them both up and leave #1 in feather. Whenever there was a time that I might exceed the maximum steering angle, I'd then just have to lift the #1 condition level out of feather and up to the idle detent in order to use differential power to straighten out the nosewheel at the completion of the turn. Once back on a relatively straight stretch of taxiway, I would put the #1 engine back into feather. Very rarely, almost never would I ever truly "single engine" taxi the -300. The #1 engine was always in feather.

detpilot

Thanks guys, that clears things up a bit. I guess I didn't consider how such a small amount of fuel could add up. Also, I didn't consider the F/A noise reason (we don't have those, lol).

However, I'm not following CRJ700's reasoning with ITT- unless your engines are cooled differently. For us, the engine depends on airflow going through the oil cooler to keep the oil temp down (not ITT), but it will heat up just as fast in feather as it would in beta, as both modes have little to no rearward airflow. We're supposed to use beta to come to a stop, then once stopped, come out of beta to allow some rearward airflow to keep the oil temps down.

How would feather keep the ITT down better than the combination of Alpha and Beta used for taxi?

Ewfflyer

Which ones? I do only fly PT6's, but I have never heard of any requiring a cool-down. Now on turbo-charged piston engines, absolutely, but never have heard of a cool-down prior shut-down.

I do know on the TPE331's you should run the prop through after shut-down to run some cool air through the system, plus rotating the shaft to keep it from warping, but that's about all I know of those specific engines.

detpilot

+1






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flyandive

We're talking about engines larger than a PT-6. The Q400 with PW-150s requires a 30 second cool down in feather before shutdown. I've seen most turboprop airliners do something similar. EMB-120, Dash 8 Classic, Saab 340, etc.