Asymmetric Flight + Weathercocking

[ardypilot]

At school recently, we've been learning about asymmetric flight in twin engine aircraft, particually how to keep straight and level during a single engine failure.

I've been trying to recreate this scenario in FS in the Just Flight Seneca, cutting down one throttle to idle, then fully feathering the prop and pulling the mixture out until the blade stops moving which results in a yaw towards the dead engine.

In my CPL manual, it says, using only rudder, the aircraft will want to weathercock back towards the live engine, which you correct with opposite rudder resulting in a sideslip, creating a new relative airflow towards the aircraft towards the dead engine wing, which due to the wing dihedral will want to create more lift on that side and therefore will require counteracting with aileron towards the dead engine side.

So, the reason I'm making this post is to ask whether weathercocking into the wind is a dynamic which FS9 is capable of recreating, and if so, what realism settings/ general settings do I need to activate in order to successfully accomplish the above mentioned straight and level flight method? At the moment, flying into a slight headwind, only applying opposite yaw to counteract the thrust imbalance seems to have any effect- applying aileron, however slight, towards the dead wing just makes it want to roll.

Any help would be much appreciated. Being able to visulise what your're reading about in text books makes things much easier to understand!

Cheers.

[cowpatz]

QUOTE (Trolly @ May 2 2009, 09:57 AM) <{POST_SNAPBACK}>

In my CPL manual, it says, using only rudder, the aircraft will want to weathercock back towards the live engine, which you correct with opposite rudder resulting in a sideslip, creating a new relative airflow towards the aircraft towards the dead engine wing, which due to the wing dihedral will want to create more lift on that side and therefore will require counteracting with aileron towards the dead engine side.


Cheers.

lm not quite sure what you are getting at here Andrew. A failure of an engine will result in a yaw towards the dead engine. The yawing motion will also cause a roll in that direction as well (further effect of yaw). Applying rudder will stop the yaw. Some lighter aircraft suggest a slight (up to 5 degree bank towards the live engine to assist in directional control). This is because a slight sideslip is created whereby the relatiive airflow acts upon the vertical stablisers to create a yawing moment. Any change in speed will require a change in rudder input. Increasing speed increases the "weathercocking" effect and thereby the rudder can be reduced. As rudder is reduced the aileron can also be reduced. However it should never get to the point that aileron HAS to be applied towards the dead engine.
With an engine failure in a jet, aileron is applied to keep the wings level and rudder is applied to the downside of the control column to return it to a central position. In a swept wing jet the rudder is very powerful and it is imperative (especially on take off) that rudder is applied in the correct direction.
The procedure for an eng failure on takeoff in a jet is:
1. Keep straight rudder (just squeeze in a reasonable amount and HOLD...dont pedal it)
2. Maintain wings level. When the wings are level apply rudder to the downside of the control column to centralise it keeping the wings level.
3. Trim.

[HardCorePawn]

Not sure about the aileron use you have quoted Andrew, I have heard the phrase "Raise the Dead" used in relation to asymmetric flight in twins.

[redkiwi]

If you are using FS for training then i'd suggest getting a copy of X-plane

[cowpatz]

A lot depends on the aircraft modeling as to how well the aircraft handles asymmetric flight. I have found that the default Beech Baron is quite good. It is enough to give you a very good idea anyway.

QUOTE (HardCorePawn @ May 2 2009, 09:07 PM) <{POST_SNAPBACK}>

Not sure about the aileron use you have quoted Andrew, I have heard the phrase "Raise the Dead" used in relation to asymmetric flight in twins.

Correct but one does need to be a little careful with the application. At slow speeds, and to the detriment of using rudder, the down going aileron effectively increases angle of attack on the dead engine wing. This together with no prop wash and increased drag can increase the yawing/rolling motion (adverse yaw) leading to a spiral or spin.

[ardypilot]

QUOTE

lm not quite sure what you are getting at here Andrew. A failure of an engine will result in a yaw towards the dead engine. The yawing motion will also cause a roll in that direction as well (further effect of yaw). Applying rudder will stop the yaw. Some lighter aircraft suggest a slight (up to 5 degree bank towards the live engine to assist in directional control).[/quote]
Thanks for the reply Cowpatz- and sorry if my post was to vague in posing the question.

I'm aware of the connection between lateral and directional stability, and that initially there is a yaw towards the dead engine, and then that the weathercocking and slide sliping motions can follow if using roll and yaw- however, I understood that there are three different ways to correct the failed engine situation, by using rudder only (which initially causes the yaw towards the dead engine, but then weathercocks into the new RAF hitting the opposite side of the fuselage in the other direction which you then further correct with more rudder and trim), by using aileron only (slipping the aircraft as you mentioned and using the keel surfaces to maintain balance), or a combination of the two, with the 5 degree bank allowing for a small amount of slip.

I think I've posed the question to make what I was asking more complicated than it really is- let me try again:

Because I don't have enough actual flight experience to understand how much of a yawing effect occurs in a light twin failure example (we are using a Beech 76 Duchess), I'm trying to find out how much the yawing movement is relative to the weathercocking- ie, does the weathercocking turn have such a dramatic effect that it creates a noticeable large swing that you can feel whilst flying, and does FS model this? (not just in an engine failure, but anytime once airborne with more than 0 knots of wind set)- or do the initial yaw and WC'ing happen so fast that you never reconise it and I'm making a mountain out of a molehill?

I just cant understand why I have written in my notes that you'd want to apply aileron towards the dead wing- I am mistaken? I can't get it to make sense in FS or in my head!

Also, as a bit of a PS- Does anyone know of a way to control different engine throttles individually in FS2004? I'm using a joystick with one one throttle lever, and have to disable that axis and use my mouse to pull each throttle up or down in the VC which is rather distracting one short finals having whilst trying to remain centered and flicking the screen view around on the hat switch!

EDIT:

QUOTE

Increasing speed increases the "weathercocking" effect and thereby the rudder can be reduced. As rudder is reduced the aileron can also be reduced. However it should never get to the point that aileron HAS to be applied towards the dead engine.[/quote]
Just reread this, and this makes more sense- the situation our lecturer had been talking about was engine failure on take off, and I was trying it in the sim cruising along at about 130 knots, so I guess it would be much more noticeable at slower speeds- will give it a try later. Still confused about this opposite aileron business though...

Last edited by ardypilot on Tue Apr 28, 2009 6:03 pm, edited 1 time in total.

ardypilot

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[Alfashark]

As far as modeling the yaw towards the dead engine in FS9, the default Baron does a fair representation of this - nothing too troubling or overly difficult to handle.
If you have the WoP/A2A Heinkel He-219, this will certainly give you a good example of the strength and speed of the yaw effect when you pull the pin on one engine

As far as dealing with individual throttle inputs, I would simply flick the mags to "off" and then drag the mixture and prop controls to the cutoff and feather positions... you'll have to ignore the dead engines throttle moving when making power adjustments on the "live engine" but it wont be supplying any power at least.

[ZK-KAG]

Andrew I can say with pretty good authority that weathercocking in assymetric flight is all but non-existent. This is because the yaw (and roll if you let it) is so great from the live engine that the aircraft will not want to align itself with the normal airflow.

You also most definately do not want to apply aileron to the dead engine as the yaw from the live engine is so great that roll is always encountered in the direction of the dead engine (yaw's secondary effect is roll remember). The standard procedure for a dead engine in the Seneca is 2/3 degrees of angle of bank towards the live engine (which requires quite a bit of right aileron) and as much rudder as is needed to maintain half ball deflection towards the dead engine.

Hope this helps, if not get me on MSN

~KAG~

[cowpatz]

Yes weather cocking is virtually non-existent and only noticeable if you happen to close the tap on the live one
You dont really need a separate throttle control for handling practice. Just put a failure in the FS9 failures menu and give it a go with the one throttle. You could set up a macro with FSUIPC so that only one throttle moved when a certain key is pressed if you really want to. Make sure you have rudder trim keys selected so that you can easily trim out the rudder. It can be awkward trying to twist the grip and find an obscure key. I dont have pedals but have set up 2 switches on my CH throttle quadrant to have rudder trim......diff brakes down and rudder trim up. The Default Baron would be an excellent trainer for the Duchess....very similar.

[ardypilot]

Thanks for all the answers in cleaning up my confusion- I checked with my lecturer at school today, and he confirmed that you'd never usually apply aileron towards the dead wing, only theoretically in worst cast scenario. Not sure how I ended up writing it down on my paper

Will give the FS9 failures a go when I get my keyboard working, thanks again guys.

[FlyingKiwi]

Flight Simulator's modeling of engine-out characteristics isn't the best. IL-2 actually does a reasonably decent job - take something like the A-26 for a flight, shutdown an engine, keep your feet/hand of the rudder and see the results.

[happytraveller]

Just purchased the RealAir Beech Duke and from reading the manual, it sounds like it recreates the effects of engine failure well. Not tried it yet, but it is on the list of things to do. The Duke also allows easy control of either throttle by either left or right clicking the mouse.

If you get the chance to try out a light twin for real, then you will be very surprised at how much rudder is needed at low speeds, and what a strain this can put on your leg until you get it trimmed out. The saying was 'dead leg, dead engine', and you will quickly understand why!!!!

smooth landings!

[waka172rg]

QUOTE (happytraveller @ May 6 2009, 02:03 AM) <{POST_SNAPBACK}>

Just purchased the RealAir Beech Duke and from reading the manual, it sounds like it recreates the effects of engine failure well. Not tried it yet, but it is on the list of things to do. The Duke also allows easy control of either throttle by either left or right clicking the mouse.

If you get the chance to try out a light twin for real, then you will be very surprised at how much rudder is needed at low speeds, and what a strain this can put on your leg until you get it trimmed out. The saying was 'dead leg, dead engine', and you will quickly understand why!!!!

smooth landings!

Yeah sorry was supposed to reply here but its as real as it gets with this duke hope it will be like this with Seneca
good stuff Happytraveller
PS sound it perfect/great!

[FlyingKiwi]

QUOTE (happytraveller @ May 10 2009, 02:03 PM) <{POST_SNAPBACK}>

If you get the chance to try out a light twin for real, then you will be very surprised at how much rudder is needed at low speeds, and what a strain this can put on your leg until you get it trimmed out. The saying was 'dead leg, dead engine', and you will quickly understand why!!!!

My instructor once told me he didn't like the "dead leg, dead engine" saying because he felt that once you got out of the plane the leg that was doing all the work would be a "dead leg". He used to say "lazy leg, lazy engine" although to be honest I always just think of it as dead leg.