Feathering the prop at idle.....

[ILLINI]

I fly freight in a Cessna Caravan (PT6A-114) and was hoping someone could answer something for me.

Every once in a while one of our loaders will come running up to our planes after we've started up waving an envelope they forgot to put in back. I usually bring the fuel condition lever to low idle and bring the power back to idle and they hand me the letter through my window and i'll throw it in back. One of the other guys does the same thing, but also feathers the prop, which eliminates all of the prop wash. I've heard the Be1900 has a time limit for having the prop feathered while at idle on the ground. I've looked through the Caravan manual and can't find anything on this topic. Does anyone know if it is safe to do this, and if so, is there any sort of time limit like in the 1900? Thanks!

And yes, I will discuss this with our Dir of Ops and mechanic. I was just hoping to hear from some of you as well.

 

[ifly4food]

The feather limit on the B1900 is due to exhaust blowing on the window of row 4. Without propwash to cool the airflow, the exhaust blows directly on the window and will melt it quickly. I've seeen one melted.

 

[Cornelius]

Certain companies are approved to have the Be1900D have a prop feathered on the ground. Usually you can only have it feathered when the deicer is spraying you down. Other than that, Ifly4food is correct about the exhaust melting the windows if feathered.

 

[MTOP_set]

Our SD3-60s have a larger version of the PT6 (67R). I know in this airplane you need to be careful of engine temps, in particular the engine oil temp. Without the airflow the temps can rise quickly in feather and even in the beta range.

 

[~~~^~~~]

As a former Caravan pilot I do not remember any restriction on feathering the prop. Check the limitations section of the POH, or OPS Manual and if it isn't prohibited, feather away.

 

[Cardinal]

Not that I have, or intend to do such, but....

What about your average piston flat-six, aside from cooling issues will low-power full-feather or low-pitch hurt these powerplants? Just curious.

 

[Wiggums]

You don't want to put a piston engine into feather while it's running. The only time this should be done is on the ground, just for a second while you are running up the engine to be sure the engine would feather if needed. The problem is the tremendous load placed on the engine since the blade has to push rather un-aerodynamically through the air. The PT6 is a free turbine, the prop and the engine aren't connected, so when you put the engine into feather the prop spins slower, but doesn't load the engine.

Try starting a feathered piston engine. Better get some ground power for it.

 

[AeroDMB]

FedEx Policy on fuel slips

At Fedex, the policy in place is to stay as far away from the prop as possible. Besides, there's not much propwash from the Caravans at idle. We either throw them in the rear pod or in the aft cargo door.

FedEx Guy

 

[avbug]

If you don't want to put a piston engine into feather while it's running, you certainly won't be able to do it when it's not running, with the exception of the hamilton standard hydromatic prop.

In most cases, you need to be above a specific RPM, typically around 800-1,000 in order to feather, because spring-opposed centrifugal pins will prevent feathering below those speeds. Therefore, the engine must be running, and turning a certain RPM.

One doesn't run a piston engine with the prop feathered; in most cases this is an impossibility. This is true of most direct drive engines, piston, or otherwise. However, for starting many piston engines which have been feathered, the engine is started in the feather position and then run out of feather, or done so simultaneously (depending on the engine). In the case of air starts, the engine is typically windmilled by bringing it out of feather, and then it is started.

As for running a PT6 in feather, in most cases, you can do it all day long without any consideration for the engine. Someone mentioned temp issues in beta; this is different than running in feather. Other than an exhaust issue as identified for the BE1900, there are few idle feather limitations on the PT6 series of engines. I'ts not a big deal for a free turbine engine.

Remember that turbine engines don't require airflow for cooling purposes in the same way that pistons do. The airflow inside the engine is for cooling purposes, but at idle speeds, the engine isn't receiving any significant ram air recovery rise to make any difference at all, and in most all cases, it makes no difference. Airflow over the engine doesn't make any difference; only inside it. At idle, feathered or not, the internal airflow isn't appreciably altered. Reverse airflow such as a tailwind makes a far greater difference.

 

[OtterFO]

The twin otter has feather, beta, and reverse time limitations above a certain ambiant temperture. This is because sometime long ago someone melted an engine cowel. When I was flying the king air, the DO told me there was no limit. The BE-99 doesn't seem to have a time or temp limit, but there is an airspeed limit for reverse. Above 40 kts only....

Have I muddled this thread enough?