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Feather and 12" MP for zero thrust?

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Feather and 12" MP for zero thrust?

Old 23rd Sep 2012, 23:57
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Feather and 12" MP for zero thrust?

Can anyone explain this to me? At first glance it looks like for zero thrust they are recommending to run the engine at 12" MP and prop in feather!

What really happens?



Arrrgh, ok can't get image to work so:

SIMULATED ONE ENGINE INOPERATIVE for Baron B55, procedure is:

1. Propeller Lever - RETARD TO FEATHER DETENT
2. Throttle Lever - SET 12 in. Hg MANIFOLD PRESSURE

The procedure should be accomplished by alternating small reductions of propeller and then throttle until the desired setting has been reached.

What is the 'desired setting' in this situation? Without a fair amount of experience in flying with an engine actually feathered, how is one supposed to know when you're at zero thrust without just taking the POH's word for it. Does the prop actually feather? Hope not for the engine's sake.

Last edited by Lumps; 24th Sep 2012 at 00:07. Reason: trying to add an image
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Old 24th Sep 2012, 00:40
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Not sure about zero thrust setting in a baron; sure there are some instructors out there that would know! A good way to establish what zero thrust power setting is in your twin is to go through an inflight shut down, set the aircraft up to fly on one with other feathered then trim the machine out so you can hold S&L ( I know not always achievable in twins ) then once settled conduct an in flight restart and adjust the power setting on your recently feathered engine until the aircraft maintains your previously trimmed out attitude.

Worked well in light training twins anyway

Last edited by Blank; 24th Sep 2012 at 00:40. Reason: typo
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Old 24th Sep 2012, 00:49
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I think you need to read what it says and think about it.

Retard TO Feather Detent. TO the detent, not through it.

morno
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Old 24th Sep 2012, 01:32
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Yes, adjusting the pitch to the detent and setting the above MP does simulate a feathered propeller quite well. It will not feather as long as you don't go past the detent.

Make sure you restore the mixture to rich if you have used the mixture to simulate the engine failure, otherwise you will not achieve the small amount of thrust simulating the reduction in drag/feathered prop.

Closing the cowl flap on the 'failed' engine too in some situations may be appropriate, otherwise it will cool very very quickly!

If someone gives me a gob-full about simulating engine failures with the mixture, I really don't give a hoot about your opinion. Enough was discussed in a very lengthy thread about a year ago.
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Old 24th Sep 2012, 03:12
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What is the purpose of setting zero thrust?

If you consider that question you will realize that in order to simulate a situation where there is minimal drag i.e. feather, you will need to produce some thrust to offset the drag of the windmilling engine therefore you need to have some pitch but not full course (feather). From memory in a Chieftain we set full fine and about 17" of manifold pressure. I could be wrong, it has been a long time.
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Old 24th Sep 2012, 04:23
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Morno's got it.

Just me or does anyone else see a problem with encouraging someone who (correct me if I'm wrong) does not hold an instructor rating with ME approvals to experiment with intentional inflight shutdowns.

A little knowledge is dangerous. Think about it.

Nothing personal, Lumps, but do it with an authorised person if you feel the need to engage on this sort of activity. Otherwise, you may discover a whole new way to kill yourself.

Flying spike, wrong pitch setting.

Last edited by MakeItHappenCaptain; 24th Sep 2012 at 04:28.
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Old 24th Sep 2012, 05:27
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Pitch,

Yep, like I said, it has been a while (20 years). I fully concur with the remarks about being appropriately qualified and experienced to play with engine failures. It is totally different being the instigator and having to take over if it handled incorrectly.
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Old 24th Sep 2012, 07:34
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Thumbs up

Not encouraging experimentation! plus you would have to be pretty daft to take some PPRuNe information and just give it a go; particularly with twins and shutdowns...

Came across that technique flying with a CFI during my META a few years ago and used it in flight to established power setting for zero thrust simulation. Only time to "try" that sought of thing whilst under close guidance
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Old 24th Sep 2012, 08:19
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Spike, try full coarse and 17 inches
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Old 24th Sep 2012, 08:33
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Lumps

I think others have covered that if you are in feather you have zero thrust, not simulated zero thrust.

From my experience I think 12" is probably a fair bit less than zero thrust. I have operated a 55 extensively and I have feathered one several times and they had reasonable performance.

At low RPM, manifold pressure is not your primary indication of power, RPM is!

(Remember below about 1800 RPM the CSU is not governing so basically your prop is behaving like a fixed pitch prop and on the B55 it is in course pitch at lower RPMs as well!!! No matter where your propeller control lever is except for the feather detent.)

For training we used about 1,400 RPM and propeller control in full fine pitch... we came up with this after firstly checking with the manufacturer and then verifying performance with one actually feathered. I think 1400 RPM was slightly worse than zero thrust but served us well for training.

We also used about 1300 - 1400 RPM on Barons, 310s, Chieftains and 402s all verified after testing.

I came across this excellent Cessna explanation from the C303 POH, but it is also relevant to most IO and TSIO 520s, and I'll bet it is pretty close to the IO-470s in your B55

"Propeller Control - Full Forward
Throttle - Adjust for RPM as below;
2,500ft & 10C at VSSE (80KIAS)- 1,150 RPM and at VYSE (97KIAS) - 1,450 RPM
5,000ft & 5C at VSSE (80KIAS)- 1,250 RPM and at VYSE (97KIAS) - 1,550 RPM
7,500ft & 0C at VSSE (80KIAS)- 1,350 RPM and at VYSE (97KIAS) - 1,700 RPM
10,000ft & -5C at VSSE (80KIAS)- 1,450 RPM and atVYSE (97KIAS) - 1,800 RPM

Add 50 RPM for each 15C above standard and subtract 50 RPM for each 15C below standard"
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Old 24th Sep 2012, 08:48
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Flying spike, wrong pitch setting.
Spike, try full coarse and 17 inches
Wrong!

Beech, Cessna & Piper (models after about 1980) have all recommended full fine for "simulated" OEI operations.

After the simulated failure the mixture should be adjusted to rich and propeller lever full forward. If you need bring back the power on your "failed" engine in a hurry you only need to advance the throttles.

Last edited by hiwaytohell; 24th Sep 2012 at 08:49.
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Old 24th Sep 2012, 09:25
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Beech, Cessna & Piper (models after about 1980) have all recommended full fine for "simulated" OEI operations.
Are there references for that?
(Apparently, the Beech flight manual seems to directly contradict this recommendation and Mix up, Pitch up, Check Power/Power up never takes me THAT long...)

(Remember below about 1800 RPM the CSU is not governing so basically your prop is behaving like a fixed pitch prop and on the B55 it is in course pitch at lower RPMs as well!!! No matter where your propeller control lever is except for the feather detent.)
And slight amendment.....
The governing range covers around 1800 up to max rpm. Correct.
At low rpm, yes it is behaving as a fixed pitch, but because the prop is in a severe underspeed condition, the prop is on the fine pitch stops trying to increase rpm by reducing the propellor torque (ie. smaller bites of the air).

Last edited by MakeItHappenCaptain; 24th Sep 2012 at 11:06.
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Old 24th Sep 2012, 12:12
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Thanks Morno, tripped up by wording it seems. So just minimum rpm and 12" is what they're saying.

MakeItHappenCaptain - nothing personal taken, not about to go and try something in the air that I had questions about on the ground! You can't run a piston engine in feather hence my post.

I've only ever had the instructor set 12" regardless of the rpm of the 'failed' engine. technically not correct it seems - the Cessna 337 POH also has specific simulated feather RPMs for front or rear engine that is reached by pushing pitch to full fine the adjusting MP to get the specified RPM, also dependent on altitude and temperature. The aerodynamic / mechanical reasons for the variations front to rear go waaay over my head but if someone knows feel free to elucidate here.

Last edited by Lumps; 24th Sep 2012 at 12:21. Reason: repeated myself
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Old 24th Sep 2012, 12:35
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Simulated hundreds of OEI in B55's over many years and 12", full fine never failed me. Retard mixture til it ran smoothly, otherwise was horribly over rich. Temp generally held steady.

The real shutdown was the part I hated most. Cringing at the CHT needle dropping that rapidly was something I was glad to only have to do once per student.

I found minimal, if any difference in performance with one feathered compared to 12".

Careful doing EFATO. Have your hands right there, plenty of students tried to feather the live engine no matter how many times we briefed, touch drilled etc... And I'm with aimpoint: always the mixture to simulate the failure
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Old 24th Sep 2012, 12:44
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CAAP 5.23-2(0)
5.7 Setting zero thrust
5.7.1 Reports from Australia and overseas have repeatedly shown that fatal accidents have occurred following practice engine failures because instructors have failed to set zero thrust on a windmilling engine to simulate a feathered propeller. A windmilling propeller causes the largest component of drag on an aircraft that suffers an engine failure. If the propeller is not feathered following an actual failure, or in the case of a practice failure zero thrust is not set to simulate a feathered propeller, the aircraft’s climb performance cannot be guaranteed. In many cases it is likely that the aeroplane will only be able to maintain a descent. Therefore, any pilot giving multi-engine asymmetric training must know how to set zero thrust on the propeller aircraft type that they are flying.
5.7.2 The zero thrust setting depends on the engine type and aircraft’s airspeed, altitude and temperature. In a piston engine aircraft zero thrust is normally achieved by setting a manifold pressure that causes a specified RPM; and a turbine propeller engine by a torque and in some cases RPM for a particular airspeed. Unless stated otherwise in the flight manual, CASA recommends that VYSE be used for setting zero thrust. Remember that if zero thrust is set and the airspeed increases above VYSE, there will be a corresponding increase in propeller drag from the windmilling engine.
5.7.3 Before conducting asymmetric flight training it is important for an instructor to determine an accurate zero thrust power setting for the aircraft type being flown. If a zero thrust power setting is not specified in the aircraft’s flight manual, a method of doing this would be to climb to a minimum of 3000 ft AGL, feather a propeller, shutdown an engine, and find what power setting will allow the aircraft to fly, trimmed at VYSE. Restart the engine and adjust the RPM and manifold air pressure (MAP) combination on the restarted engine to re-establish the airspeed at VYSE, and return the aircraft to the previously trimmed state. This procedure may take some time and could involve manipulation of the engine controls to determine a reliable power setting. The RPM to indicated air speed (IAS) relationship could vary significantly between aircraft and engine types.
This online POH for a BE-55B with IO-470-L's (260hp) says 10"/FP, is zero thrust.

Last edited by Trent 972; 24th Sep 2012 at 12:53. Reason: fix link
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Old 24th Sep 2012, 15:13
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Careful doing EFATO. Have your hands right there, plenty of students tried to feather the live engine no matter how many times we briefed, touch drilled etc... And I'm with aimpoint: always the mixture to simulate the failure
Now that is what I call famous last words; or put another way practicing bleeding. Mind you I am somewhat biased as one of my very old friends was burnt to death practicing pulling the mixture. Fate caught up with him after he had been pulling mixtures for years.
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Old 24th Sep 2012, 21:56
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It was much easier in days gone by when you could set it by ear.

After the simulated failure and simulated shutdown:- Mixture back up to rich, MP up til you get the borderline of the whooshing sound as the prop starts to bite. Pitch position irrelevant due to power being below governing range, but full fine is the tidiest position and best for a rapid recovery.

Works all weights, all conditions and is as near as dammit to the book settings, without gumming up the neurons with numbers.

Pity you can't do it that way on these new fangled dangles. Life was much simpler back in those days. Those days when maps were paper and not glass, didn't stop working when you dropped them on the floor, and the batteries never went flat. Those days when full reporting was the norm, and we had ops control, and Flight Service to keep an eye on us. Those days when we graduated to bigger things, there was a hairy autothrottle and systems manager sitting behind (electrons not required, just beers later)

Recommended viewing "Children of the Magenta Line" Youtube.

Life was simpler, way back then.

M

Last edited by maui; 24th Sep 2012 at 21:58.
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Old 24th Sep 2012, 23:09
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And slight amendment.....
The governing range covers around 1800 up to max rpm. Correct.
At low rpm, yes it is behaving as a fixed pitch, but because the prop is in a severe underspeed condition, the prop is on the fine pitch stops trying to increase rpm by reducing the propellor torque (ie. smaller bites of the air).
This is true for constant speed propellers, however for full feathering systems not necessarily the case:

This is what the McCauley book says:

"Pitch is changed hydraulically in a single-acting system, using engine oil controlled by the propeller governor to change the pitch of the propeller blades. In constant-speed systems, the pitch is increased with oil pressure. In fullfeathering systems, the pitch is decreased with oil pressure."

On the full feathering McCauley props that were fitted to most Barons counterweights and strong springs try to force the props towards feather.

After a simulated engine failure (either mixture or throttles) the props are windmilling a fairly low RPM. I can't recall exactly but <1,200 RPM.

The full feathering props were designed in the event of an engine failure to go towards course pitch as it reduces drag.

Are there references for that?
I posted one already from a 303 POH I have here. I am sorry I did not keep copies of other POHs from my past.

Although 12" or thereabouts provides realistic simulation to teach OEI procedures, and I bet many instructors use this. It is based more on feel than on fact.

Because the propellers are acting like fixed pitch props at such low power, RPM & MP will vary markedly with speed and altitude

From first hand experience 12" in a Baron seems to be somewhat less than zero thrust.

IMHO 1,400 - 1,500 RPM at VYSE is a better starting point.
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Old 24th Sep 2012, 23:12
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@T28

I hate to harp on about semantics but full coarse = feather. So my memory wasn't that bad after all. Thanks for clearing that up. Once again, don't try this at home. I have heard of one or two thinking that they could demonstrate their superior ability by failing one on themselves only to highlight their stupidity.
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Old 24th Sep 2012, 23:25
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Spike what twaddle there is a very real difference between full coarse pitch and Zero effective pitch ( ~90degrees ) otherwise known as feather.

And a very real diffence in the pitch control selecting either,the detent or gate is there for a reason andthe engine is (must be ) shut down in feather, not so in full coarse pitch,in the early days of radials over oceans it was a common practice of the adventurous to extendrange using full coarse and careful throttle to avoid the potential overboost and engine destruction.
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