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Fail passive
5th Jul 2007, 13:47
Hi all

Could someone please verify this.

I was told that pulling the prop lever to feather while taxiing (of course am talking about a twin turbo-prop, say a PT6), the aircraft will actually slow down ie.not applying any brakes etc. Now I have always tried to taxi using beta if necessary to control aircraft speed on the tarmac, but have noticed that even after landing, a few pilots tend to feather the engines in order to slow it down...that is with the throttles already at idle.

Now...with the aircraft having forward speed (that is while taxiing), wouldnt feathering the props reduce drag and while in full fine be creating more drag???

In other words...wouldnt the pilot be just increasing the forward speed (if only slight) if he/she feathers the props after landing???!!

:ok:

411A
5th Jul 2007, 16:21
...wouldnt feathering the props reduce drag and while in full fine be creating more drag???

Generally not, with PT6 powered airplanes, in my experience.
Remember that even in fine pitch, the propeller still provides forward thrust.
However, the idea of feathering more than likely has to do with fuel consumption rather than anything else.
Using beta for taxying is generally a better idea and in addition, it provides a method whereby the engine is properly cooled (IE: stabilized temperatures) prior to complete shutdown.

zerozero
5th Jul 2007, 16:22
I would not recommend this practice for a couple of reasons:

1) As the prop moves through course pitch towards feather, there will be a "surge" of thrust as the AoA of the blades increase.

2) If this practice becomes habitual, then one day on a contaminated taxiway, the pilot will go to feather and as things never happen quite symmetrically on twins there could be the chance of a loss of directional control.

Personally I hate it when pilots try to reinvent the airplane and start making up their own little techniques. Just operate the plane the way it was designed and stop mucking around.

:8

werbil
6th Jul 2007, 04:32
The PT6 114A /3 blade Hartzell does produce less thrust in feather than at fine pitch ground idle at taxi speeds. I fly float planes, fine ground idle in nil wind will pull the aircraft through the water at around 6 knots. Feather ground idle will pull the aircraft through the water in the same conditions at around 2 knots. The surge in thrust as you feather is very noticeable on water - you have to plan for it.

I approach boats / moorings in feather in light winds and in beta in moderate winds and stronger. In light conditions a beta approach can blow the boat away from you, in moderate winds or above a feathered approach may not allow you to reach it.

As for cooling to stabilize temps for shutdown - it is the cooling air supplied by the compressor that cools and stabilizes the internal engine component temperatures - a PT6 gas generator can't tell if the prop is in feather or beta - increase the engine power though and watch the ITT rise. Do keep an eye on the oil temp. BTW feathering has no significant effect on fuel flow in a PT6 - they are a free turbine.

W

Fail passive
11th Jul 2007, 14:11
Thanks all...sorry for the late reply..being away for a while. I never noticed reduction in taxi speed with use of props from full fine to feather. However, a few new captains seem to want to feather the engine every chance they get...maybe to impress a few pax!!!! :ugh:

Gets abit irritating especially when all they seem to do is play around with prop pitch while taxiing. Only reason they give when questioned about the procedure is "it slows the aircraft down"!!!! Well...i for one dont see no change in taxi speed!! And then one comes up with "as soon as I feather the engine and apply brakes, the aircraft does slow down"!!! Well.. damn that...who would have ever thought applying brakes would slow an aircraft down!! Feel like throwing the SOPs book at their face!!!

ANyway...thanks again for your help. :ok:

highalti2d
22nd Jul 2007, 04:12
"As for cooling to stabilize temps for shutdown - it is the cooling air supplied by the compressor that cools and stabilizes the internal engine component temperatures - a PT6 gas generator can't tell if the prop is in feather or beta - increase the engine power though and watch the ITT rise. Do keep an eye on the oil temp. BTW feathering has no significant effect on fuel flow in a PT6 - they are a free turbine."

I agree the engine internals are cooled BUT depending on the aircraft type, you have to be careful where all of that hot exhaust is blasting on to(Caravans; would be the side of the airframe, king airs; nacelles etc.). I think that that was what the original cooling comment was directed at. My 2 pence.:cool:

Otherwise, I think it's pretty silly to invent your own procedures, as per previous comments. Is this in the 'Normal Procedures' section of the manual? Of course, floatplanes are the exception...

Fail passive
23rd Jul 2007, 12:21
Yeah, just the other day doing my base check, I asked a check and training captain his thoughts on this procedure..that is straight after landing, feather the engine to slow aircraft down instead of using beta.

His answer was that it does slow the aircraft down without causing much noise (that is the noise created with the use of Beta), plus beta causes no cooling whatsoever!!! and therefore thinks it ok to be used!!

Only place i have seen this procedure used...mind you I will stick to using beta while taxiing. Nothing in the SOPs about this procedure (that is feathering after landing)

con-pilot
23rd Jul 2007, 19:22
The only aircraft I ever used feathering to reduce speed on landing and taxing was an old straight King Air 90. The original 90 had no beta/reverse. The trick was to judge the speed where going into feather would decrease speed by reducing thrust as opposed increasing speed by reducing idle thrust drag too soon.

After some practice it became easy. You could feel the difference.

MrBernoulli
24th Jul 2007, 00:14
llrr,

No offence, but it is 'empennage'. :ok:

dash6
24th Jul 2007, 02:57
Werbil. Thanks for that. You are obviously having too much fun! Swap jobs?

( Boring Boeing)

Dream Land
24th Jul 2007, 05:29
Been a while since I operated the B200, -41 engines, correct me if I'm wrong, isn't there a temperature limitation associated with operation while feathered, never used this as a landing technique but occasionally dropped one or both into feather to slow the taxi speed, from what I recall that will shoot up the ITT, maybe it was on the -135 on the Cheyenne. :}