Dash8: No need to unfeather

[19AB67 16]

 

Hi folks,

 

it seems that the Dash8s don't need unfeathered prop blades during shut down.

Do the pilots unfeather them before engine start, or can the starters stand unfeathered engines starts?

 

Thanx,

[scandinavian13 5,192]

Correct. Dash 8s are not geared turboprops like the J-41. The vast majority of commuter props aren't.

[NJ_Flyer 3]

The props are feathered before start. Once both are running we push the condition levers to MAX (Fine pitch). Before shut down, the props are feathered and 30 seconds later the engines are shut down. (20 seconds after selecting start/feather we turn off engine bleed air and then after 30, fuel off)

[19AB67 16]

The props are feathered before start.

 

Uhh, so the starters face the load of paddling a lot of air.

Why are they not unfeathered before start?

Again due to missing gear this is not necessary?

 

Thanx Kyle and Ryan.

[scandinavian13 5,192]

Again due to missing gear this is not necessary?

 

The short answer is yes.

 

The explanation below has been grossly oversimplified:

The only part that needs the starter is the "turbo" part. The "prop" part is not directly connected to the "turbo" part, so the feathered prop really doesn't affect the starter. Once the "turbo" part is started, the air drawn in begins to spin the "prop's" inner workings and the prop begins to spin.

 

Here's picture of a version of a free turbine turboprop (of which the Dash is similar):

 

You can see in the image that the parts marked "power turbines" (which drive the prop) are not directly connected to the other turbine components (which are started by the starter). Because of this, the drag from the prop is negligible during the start.

[19AB67 16]

Totally comprehensible now.

Thanx a lot, Kyle.

The J41 constraints make us act extremely cautiously...

[NJ_Flyer 3]

As has been stated. The PW100 series are a "free turbine" engine. Meaning the propeller gear box (Reduction Gear Box) is not connected to the HP turbine. It is spun only by the gas generated by the HP turbine. (same principle to a turbo in a car).

Not at all recommended you try this, but much like the PT6, you could hold on to the propeller during start and stop it from moving. However, the pressure will build up quickly to the point it will over power you and start spinning.

 

The props are feathered as the starter generator only has to spool up the compressor and turbine section. The Garret engine found in the J41 and Metros are a single shaft, meaning the starter generator has to spin the entire engine. So as you said, if feathered, the props would be hard to move and the Starter would struggle. By having the props fine, they slice through the air much easier and therefore the starter has a much easier job.

 

Hopefully this makes some sense...

[cosnowboarder_777 11]

I had a teacher in school that used to work on twin otters and said they would tie off the prop and run the engine on low idle after doing engine maintenance. The ATR actually uses a prop brake on one of the engines to run it like an APU (called hotel mode). Apparently though this was very unreliable and extremely noisy so I'm not sure if they still do it. on a lot of the pt-6s on planes like the king air, 1900, twin otter, etc, that have the seperate prop and mixture levers, even if you don't feather the prop during shutdown, the prop will still eventually feather as the oil drains out of the prop hub.

[Houghton11 12]

Hotel mode is still used all the time on the ATR's. There's simply no other option except ground power. I'm not familiar with any APU installation availible on the ATR.

 

PT6's don't have 'mixture' levers...they have condition levers :wink:. Depending on the variant of engine and installation, there may be a high/low idle setting, or simply on/off. Basically it's the fuel lever.

You are right about the prop though. Without oil pressure, the prop will simply feather. You can start the thing with the prop in the feather or fine position, although most use full fine for start. As oil pressure reaches the hub the props will begin to unfeather. Keeps the hot nasty swirling gases coming out of the front of the engine from making a mess.

[cosnowboarder_777 11]

Sorry Patrick I guess I had piston aircraft on the brain with the mixture levers lol. I'm not as familiar with the turboprops that have the condition and prop levers as one. My instructor got a job recently flying the q400 so I'm sure I will get to know a lot more about them.

[Houghton11 12]

Lol no worries.

 

To add to your confusion, the "Condition levers" on some PT6 aircraft (like the King Air) actually have no control over the prop governor at all! Unlike the Dash's "Condition Levers" which, like you said, fulfill both fuel and prop control duties. Can't make up their minds! :lol:

[NJ_Flyer 3]

Lol no worries.

 

To add to your confusion, the "Condition levers" on some PT6 aircraft (like the King Air) actually have no control over the prop governor at all! Unlike the Dash's "Condition Levers" which, like you said, fulfill both fuel and prop control duties. Can't make up their minds! :lol:

 

We only had the condition levers at MAX in the kingair if we needed full reverse on landing.

[Avi8tor1 1]

We only had the condition levers at MAX in the kingair if we needed full reverse on landing.

 

Or the air con running high on a hot day ;) Full reverse would increase the RPM/Torque regardless without the condition levers at max, no?

[Air France 19]

Is there a Dash-8 for FSX?

[NJ_Flyer 3]

Don't want to hijack this thread but the Kingair condition levers are fuel only. MAX is only needed for full reverse (hardy ever required). Or as you said, to help with the aircon system.