Zeru thrust settings

[Fokkerwokker]

Can anyone tell me what a realistic zero thrust setting for both the Cessna 340 and Cessna 402 might be?

Ta

FW

[hugh flung_dung]

I can't give you numbers but the way to find them is to feather an engine, trim in all axes, restart without changing the trim and adjust the MAP on the previously-feathered engine until the aircraft is in trim again.

For a wide range of light twins it seems to end up somewhere fairly close to 11".

HFD

[Tinstaafl]

The power setting required on the 'failed' engine will vary with speed & density alt. Usually the exercise mentioned above is done with the a/c trimmed for Vyse but there's nothing to stop you getting a number of power settings to cover various speeds.

11-ish inches seems common across a range of types. Check in the a/c manual. The manufacturer sometimes publishes a zero thrust power setting.

[john_tullamarine]

One caveat which often is overlooked.

During the landing flare, there may be significant asymmetric drag as the throttles are moved to the idle position with one feathered - the situation would be worse were we to be looking at a dual failure on the same side. The drag on the side with the operating engine(s) can provide a surprise if the endorsement training didn't consider the matter.

With the idle thrust operation, all move to the nominally same condition during the flare.

[Keygrip]

JT - a very good point, which I'd never considered (and can't remember from the one time that I have landed with a fully feathered).

I'd be curious to know how you approach the training for this in the average light twin. Just verbal warning or something physical?

[FlyingForFun]

How would the prop setting affect the zero thrust setting?

My aircraft's POH gives a zero thrust setting with the prop fully coarse (but not feathered), I think it's 8" off the top of my head. My employer prefers us to leave the prop fully fine (which seems sensible in case the student advances the wrong power lever on go-around, for example), with more like 12". Is there any reason (other than the one I've stated) why one setting should be preferred over the other?

As for JT's point, I've never considered that. I've always been taught - and taught my students - to close the throttle for both the live and the dead engine as they come into the flare, thus removing any asymmetry. But perhaps a more realistic asymmetric landing would involve leaving the throttle on the dead engine alone in the flare (or perhaps the instructor should reduce the power slightly to maintain a thrust setting which gives zero thrust at the lower speed of the flare)? Like Keygrip, I didn't notice any real asymmetry during the flare the one time I've done it for real - but it was my student who was handling the aircraft, not me.

FFF
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[hugh flung_dung]

FFF
With the MAP set to 8-12" the prop will be on the fine pitch stop, so the RPM lever won't do anything - leave it fine in case you need some power.

The zero thrust setting is specific to an IAS and configuration - that's why you reduce the MAP slightly as your stude slows down on the approach.
Also, don't forgrt to remind studes to centre the yaw trimmer as part of their asymmetric pre-landing checks.

(Edited to delete a load of tosh resulting from an inadvertant brain dsconnect)

HFD

[Fokkerwokker]

I can't give you numbers but the way to find them is to feather an engine, trim in all axes, restart without changing the trim and adjust the MAP on the previously-feathered engine until the aircraft is in trim again.
For a wide range of light twins it seems to end up somewhere fairly close to 11".
HFD

Ta fer dat HFD.

Was trying to find a 'ballpark' figure for training without going thru' that palaver!

I shut an engine down for real a few weeks ago and don't particularly wish to do it again unless I really have to!

Many thanks anyway.

All useful feedback/comments/tips welcomed!

[Centaurus]

The problem was only significant on four-engine types with both props feathered on one side. On the landing flare when the live engine throttles were closed (Viscount for example), the aircraft would yaw into the live engines because of the discing of the props and especially when they went into ground fine. It is a non-event in a light twin except it is a good thing to ensure both throttles are fully closed at the flare. In other words the throttle of the engine previously set slightly open to simulate zero thrust, should be fully closed at the flare.

[BigEndBob]

Have a look at page 3-17 in POH. Dated 1 November 1977.