Dash-8 question

[Airmanship Police]

Probably simple answer but: Why is it that I see a lot of dash taxiing with #2 feathered?

[hangar3]

As far as I know, it's to save money on fuel. One turbine is enough to move the plane on the ground, and uses less fuel than two turbines would.

[Airmanship Police]

well it's feathered not shut down.. so it's still burning fuel.

[hangar3]

Whoops, sorry, misunderstood your question! :O

[Pilot Research]

Hangar3 has it right - taxiing with one engine in feather is primarily a fuel and cost saving measure. On the Dash 8-100 or -300 while taxiing, the feathered engine burns roughly 50% less fuel than the non-feathered prop. (I've never flown the Q400 so I can't speak for that aircraft). It does not matter which engine is feathered when taxiing. Leaving a gate area the pilot will unfeather whichever prop. is most needed for any turns. Unless the apron is ice/snow contaminated in which case both propellors would be unfeathered for the taxi for better maneuverability. Also, both propellors should be unfeathered when taxiing in freezing fog conditions to reduce the chance of ice accumulating on the blades.

Just as an aside, some operators prohibit their D8-100s or D8-300s from taxiing with an engine shutdown.

[FriendlyBear]

The reason that the pilots feather one engine during ground taxi is to save fuel. The specific fuel burn with an engine in feather is significantly less than if it was not feathered. Over time such procedures render a significant overall fuel savings.
This is true for both legacy Dash 8 aircraft (100/200/300 series) and the Q400.
I hope that clarifies your question.
Fly safe
Cheers
The Bear

Ps: normally the Captain selects the #1 engine to start/feather during taxi because the #1 engine will be the first engine shutdown upon reaching the park position and the #2 engine will then be feathered and allowed to stabilize (30 sec is normally good), then selected to fuel off position.

[Valhalla]

Just as an aside, some operators prohibit their D8-100s or D8-300s from taxiing with an engine shutdown.

Bombardier does not approve this procedure (for reasons only they know), which is why some operators choose not to do it. Rumor has it that this may soon change for all variants, including the Q400. So, in the future, you may see more operators taxi this way to save gas.

[davecessna]

I could imagine there could be small risks with running asymmetrical thrust on the ground, as Pilot Research mentioned. Not very insightful on my part, there ya go.

[Pilot Research]

Just as an aside, some operators prohibit their D8-100s or D8-300s from taxiing with an engine shutdown.

Bombardier does not approve this procedure (for reasons only they know), which is why some operators choose not to do it. Rumor has it that this may soon change for all variants, including the Q400. So, in the future, you may see more operators taxi this way to save gas.

OK good to know it seems to be a Bombardier only procedure because I was looking at my systems diagrams here and could not figure out a good reason why taxiing with an engine shutdown would be such a problem. You would of course, not have the engine driven hydraulic pump on the side with the shutdown engine powering the systems on that side. But the standby pump should still be able to power the hydraulic systems on the shutdown side because the standby pump operates on electrical power from the opposite engine (for redundancy).

[Rowdy]

They are at min-flow in feather are they not?

As such, less fuel burn, it's already lit, already turning the gen and any accessories. Seems like a good way to operate.

[capt.pilot]

Lets say for instance you were taxiing with #1 Shutdown and had an #2 AC Generator Failure, you lose the #1 SPU (Hydraulic Standby Pump), and there by lose all the #1 Systems.. Not so much of a problem for the Flaps, Inboard Spoilers, Lower Rudder Actuator, and the PTU, but what about the Antiskid / Brakes???? All you have left for Braking is the Emergency or Park Brake.

Not my idea of a good day, because you elected to shutdown one to save maybe 40 or 50 pounds of fuel. I am sure most operators would rather spend the 60$ on Fuel than the $600,000 on repairing their shiny new Q400.. But then what do I know, I am flying old 100's, maybe the insurance would pay for the upgrade to Q400's..

Just as an aside, some operators prohibit their D8-100s or D8-300s from taxiing with an engine shutdown.

Bombardier does not approve this procedure (for reasons only they know), which is why some operators choose not to do it. Rumor has it that this may soon change for all variants, including the Q400. So, in the future, you may see more operators taxi this way to save gas.

OK good to know it seems to be a Bombardier only procedure because I was looking at my systems diagrams here and could not figure out a good reason why taxiing with an engine shutdown would be such a problem. You would of course, not have the engine driven hydraulic pump on the side with the shutdown engine powering the systems on that side. But the standby pump should still be able to power the hydraulic systems on the shutdown side because the standby pump operates on electrical power from the opposite engine (for redundancy).

[Pilot Research]

That's very good advice. Aviation is full of attempts to save money that ended up costing many more times what could have been saved. Also, it's not usually a good idea to go against what is written in company/manufacturer procedures, lest ye finds yourself explaining to an accident investigator or lawyer why you thought your way of doing things was better than their way.

[CID]

Taxiing with number 1 feathered lets it cool down/stabilize for shut down by the time they arrive at the gate. Allows ground handlers to start the deplaning process faster. Pilots will start the cool down/stabilization of number 2 right after arriving at gate and shut it down a couple of minutes later.

[iflyforpie]

Does the PW100 need to cool down after regular taxiing? Pt6 drivers usually feather and cut it seems.

But yes, running with the prop feathered saves on fuel..... for the same reasons feathered propellers allow for faster and easier engine starts on free turbines.

[motox415]

The reason Bombardier does not recommend taxiing on one engine is due to past history of cracked nose gear sidewalls and cracked outer nose gear cylinders. Dowty attributes the cracked outer cylinders due to single engine taxi.

[AOW]

Does the PW100 need to cool down after regular taxiing? Pt6 drivers usually feather and cut it seems .

Yes, I understood it may have something to do with emptying the oil from the prop. In any case they must be run in feather for at least 30 seconds. (All 2nd+ hand info, somebody with 1st hand experience can probably explain it better)
Most PT6 installations shouldn't be run in feather for extended periods because of the reduced airflow , leading to poorer cooling.

[FL001]

The fuel flow on a Dash 8 PW123 does not change if the engine is feathered or not with the power lever at the FLT IDLE detent. What does change the fuel flow is bringing the feathered engines power lever back into the Beta Range. The EEC keeps the engine above 66% but you lose the bleed air from that engine. It saves between 100 - 130 pph on the respective engine. Not a lot unless you are holding for a long time on the ground at the edge of your fuel reserves.

Flt Idle Nh = 78%
Feathered Beta Nh = 66%

This can not be done if the engine EEC's are offline or in the manual position.

The AC Generators are run off the reduction gearbox so that is the only system you actually lose with the engine feathered.

AOW, the 30 second stabilization prior to shutdown is in the AFM and it is related to the oil in the prop hub after feather.

[justwork]

Lets say for instance you were taxiing with #1 Shutdown and had an #2 AC Generator Failure, you lose the #1 SPU (Hydraulic Standby Pump), and there by lose all the #1 Systems.. Not so much of a problem for the Flaps, Inboard Spoilers, Lower Rudder Actuator, and the PTU, but what about the Antiskid / Brakes???? All you have left for Braking is the Emergency or Park Brake.

Not my idea of a good day, because you elected to shutdown one to save maybe 40 or 50 pounds of fuel. I am sure most operators would rather spend the 60$ on Fuel than the $600,000 on repairing their shiny new Q400.. But then what do I know, I am flying old 100's, maybe the insurance would pay for the upgrade to Q400's..

It is my understanding that Q400 operators, if they choose, will be able to taxi on one engine very soon. Meaning there will be an AOM revision approving this. Not only will the operator still need to stay within the restrictions outlined in the AOM but being responsible they will also have to amend their SOP's and implement some sort of training to do this. You can't just say one day that you can do single engine taxi with no SOP revision and expect to save money, the bent metal will quickly negate years of savings. At some airports this will save significant amounts of fuel while at others it will save virtually none.

Now I have no knowledge oh how this will all go down but I would imagine that taxing with the #1 engine running and the #2 shut down is what will be standard. The #1 hydraulic system powers a PTU to drive the #2 hydraulics. This makes a lot more sense to me than running the #2 engine and having a standby pump powering your #1 hydraulics which is what your brakes are on.

Fuel is a huge cost, and this cost will continue to go up. If you can find a way to decrease your fuel consumption by a few % points, you're going to save millions.

[iflyforpie]

They should put traction motors on the wheel assemblies. They could use regenerative braking during rollout to charge a set of batteries, then use the batteries to drive to the terminal.

[YYZSaabGuy]

They should put traction motors on the wheel assemblies. They could use regenerative braking during rollout to charge a set of batteries, then use the batteries to drive to the terminal.

Like this? http://www.greentaxiing.com/overview.html

"Using the Auxiliary Power Unit (APU) generator to power motors on the main wheels, the electric green taxiing system allows aircraft to push back without a tug and then taxi without requiring the use of the main aircraft engines. One wheel on each main gear is equipped with an electric motor, reduction gearbox and clutch assembly to drive the aircraft, while unique power electronics and system controllers give pilots total control of the aircraft’s speed and direction during taxi operations."