Featherable props or not ?

[Hueyman]

Hello, I've tried to voluntary kill an engine in flight and then set the prop to feather position but nothing happen, the prop continue Windmilling and the pitch is visually like it is in normal configuration.

I run the 1.1 version.

Thanks

[Goran_M]

Hello, I've tried to voluntary kill an engine in flight and then set the prop to feather position but nothing happen, the prop continue Windmilling and the pitch is visually like it is in normal configuration.

I run the 1.1 version.

Thanks

You cannot stall the engine in the Duchess by feathering the props in flight.  The Duchess has constant speed props and they can be used to actually start a stalled engine in certain circumstances (an example would be flooding the engine from the engine running too rich for the altitude).  

You can confirm that the props are feathering by having the throttle pushed full forward and watching the RPM drop as you feather the props.

If you want to deliberately kill an engine, pull the red mixture lever or levers all the way back or cut the fuel to the engine by turning the fuel supply off using the fuel control on the floor.

[Hueyman]

Hello

So,it's the 3D animation of the prop which not follow the plane maker prop pitch change ?

Cause they can be feathered : http://www.youtube.com/watch?v=gGfR9BpmRDs

And when I cut the mixture back with the extreme low pitch ( feather iF i understand well ), the prop continue windmilling.

[Goran_M]

Hello

So,it's the 3D animation of the prop which not follow the plane maker prop pitch change ?

Cause they can be feathered : http://www.youtube.com/watch?v=gGfR9BpmRDs

And when I cut the mixture back with the extreme low pitch ( feather iF i understand well ), the prop continue windmilling.

Apologies in advance because it seems there may be a language barrier here.  If I understand you correctly, you are thinking the props don't feather because they keep windmilling.  Everything was done to make the props feather correctly and to the correct feathering angle.  There are certain limitations, graphically, within x plane and this will affect the appearance of the prop.  To confirm you have fully feathered 1 prop, check the RPM gauge.  One of the needles will be much lower than the other one.  If you'll notice in the video, the pilot has the red mixture lever AS WELL AS the blue prop lever pulled all the way back.  If the mixture lever was pushed forward, enriching the fuel mixture, the engine would actually start.  It would still be a lower RPM than the other engine if it was still fully feathered, but it definitely would start if fuel was turned on.

I hope I have answered your question.

Please feel free to clarify if I haven't answered your question properly.

[Hueyman]

Hello, thanks for the explanation.

There is something  I got trouble with.

IF the part of the blade ( As a PPL student pilot, the pitch is given for a blade for a point that is located at 70 % of the blade lenght, from the blade root to the edge ).

So, if at this location ( 70% of the blade lenght ) , the pitch is 90 ° from the plane of rotation, with the twist of the blade, one part will have more pitch and the other less pitch. The aerodynamic forces that applying to it result that the blade will not turn in any direction, clockwise or counter clockwise , because each forces cancel the others, do you follow me ?

So, if the prop would be REALLY feathered, if the prop is stopped ( like the real one in the video , not the actual X-Plane version ) even with full mixture, the engine would NEVER start again, cause the initial mouvement can't be done only by windmilling, you'll have to press the starter a bit until the explosion is done.

This video of B-25 prove it, the pilot apply full mixture, then press the start a bit and imediately pushing pitch control all the way on so, the starter just help to do the initial mouvement of the prop and the flat pitch produce windmilling which help the prop to take RPM.

It depends on ACF, prop airfoil and relatice wind, for this example, both prop are Hamilton Standart, and on this DC-3,the prop start turning by itself only with windmilling when the pitch was changed :

And also on that Seminole, the pilot even don't pull back mixture, just reduce throttle then pull the prop control all the way down, then restart without starter, just push the prop control .

So, if the prop have really 90 ° when feathered, the RPM should be very low, if I cut the mixture off, the engine would stall and would NEVER start again if I apply mixture, it would start if I set a low pitch ( which is nearly impossible on a constant speed prop cause the governor need engine oil press to move ) so it would need a bit of starter.

I tried to set min pitch and feather pitch to 90 ° in Plane Maker, and the prop STOP ! but I had to select the " Manual Pitch Prop " instead of Constant Speed, so it's a problem with the governor parameters, it doesn't allow the pitch to go to 90°, maybe it stay at 70 or 60° ( about )

So, I hope to explained that as best as I can, I know my language is very poor but I'm french, and only 16 years old !

regards, Valentin.

[Goran_M]

I used to think the same as you when I was a student pilot. 

The blades of the propeller do not go to a full 90° perpendicular to the wind.  There is still an angle relative to the wind direction and because of this, the propeller does windmill.  Theoretically, if they even went to 89°, there is an angle there that the wind could take advantage of and start the propeller windmilling.  Even in the video you posted, the propeller started windmilling quite fast towards the end.  And also, because the Duchess has constant speed propellers, it is able to do a windmilling start as long as there is electrical current going to the magneto's and the mixture is set to rich.    However, it is recommended that the propellers are not feathered to perform a windmill start. 

The major factor in all of this is the Constant Speed propeller design.  It's operation is very different to that of manually adjustable propeller pitch or Fixed Pitch propellers.

That, along with the counter rotating engines and T-Tail design (which is out of the way of the engines slipstream) make the Duchess one of the safest twin engine GA aircraft in the world.

For a more detailed explanation of Constand Speed Porpeller Design, please see:

http://en.wikipedia.org/wiki/Constant_speed_propeller

Just to re-iterate, I am certified to fly the Beech Duchess aircraft and that, coupled with consulting with my old flight instructor who has about 2000 hours in the Duchess, feel confident that the way the x plane Duchess was designed and operates is 98-99% accurate. 

[Hueyman]

Ok that's more clear for me now ;-)

Do you know where I could finf liveries ? I see a beautiful blue one somewhere !

[Goran_M]

Ok that's more clear for me now ;-)

Do you know where I could finf liveries ? I see a beautiful blue one somewhere !

I think there are a few of them at x-plane.org in the download manager.  Just do a search for "Leading Edge Sim Duchess"

We don't have any plans to make more repaints at this time.  We may make more in the future.

[steven winslow]

I've done a few custom liveries for the Duchess.  Here's one I posted on the org:

http://forums.x-plane.org/index.php?app=downloads&showfile=13443

If you have a photo of a particular Duchess that you would like to have painted, I would be happy to do it for you.  Just drop me an e-mail with the photo at winslowphoto@yahoo.com and tell me the tail number you would like use.

[Hueyman]

Hello guys, thanks for the answer, just sent you a PM Steven.

[steven winslow]

James, I can't get PM's.  Please e-mail me at winslowphoto@yahoo.com

Thanks

[sd_flyer]

I used to think the same as you when I was a student pilot.

The blades of the propeller do not go to a full 90° perpendicular to the wind. There is still an angle relative to the wind direction and because of this, the propeller does windmill. Theoretically, if they even went to 89°, there is an angle there that the wind could take advantage of and start the propeller windmilling. Even in the video you posted, the propeller started windmilling quite fast towards the end. And also, because the Duchess has constant speed propellers, it is able to do a windmilling start as long as there is electrical current going to the magneto's and the mixture is set to rich. However, it is recommended that the propellers are not feathered to perform a windmill start.

The major factor in all of this is the Constant Speed propeller design. It's operation is very different to that of manually adjustable propeller pitch or Fixed Pitch propellers.

That, along with the counter rotating engines and T-Tail design (which is out of the way of the engines slipstream) make the Duchess one of the safest twin engine GA aircraft in the world.

For a more detailed explanation of Constand Speed Porpeller Design, please see:

http://en.wikipedia....speed_propeller

Just to re-iterate, I am certified to fly the Beech Duchess aircraft and that, coupled with consulting with my old flight instructor who has about 2000 hours in the Duchess, feel confident that the way the x plane Duchess was designed and operates is 98-99% accurate.

Sorry I didn't see that post earlier, so opened my own thread. Electcial current has nothing to do with Duchess propeller. Propeller feathring has to do with the prop governer. Prop governor uses mechanical linkage and oil pressure to control the prop.

If you move RPM leverage into feather position, the speeder spring via pistons adjust propeller pitch into the feather position. Propeller doesn't windmill in this position. In fact, the whole idea of feathering is to reduce drag from windmilling prop. In order to unfeather, RPM leveler must be moved to full forward position. Then nitrogen is used to pushe blades from feathered position to the acceptable AOA and they start windmilling. However, prop would not windmill below 100 IAS, so there must be some good airflow.

Here in states we don't certify people to fly Duchess with just give them multiengine rating. Multiengine rating give them ability to fly nearly any pistion twin engine which doesn't require a type rating. The most commonly used aircraft are Beech Duchess and Piper Seminole. During multiengine training usually applicant perform at leats one complete shut down and restart....Nedless to say they learn all systems including IO360 and prop gverner..

[Goran_M]

If you'll notice, when I mentioned the electric current, I was talking about an electric current going from the battery to the magnetos, which in turn sends a current to the spark plugs, which in turn is able to ignite the fuel in the combustion chamber. Without an electric current, the engine won't start. The magnetos send a spark (dependent on the piston position) at the correct timing and location of the piston inside the combustion chamber of the engine.

"it is able to do a windmilling start as long as there is electrical current going to the magneto's and the mixture is set to rich"

Edited December 16, 2011 by Goran_M

[sd_flyer]

If you'll notice, when I mentioned the electric current, I was talking about an electric current going from the battery to the magnetos, which in turn sends a current to the spark plugs, which in turn is able to ignite the fuel in the combustion chamber. Without an electric current, the engine won't start. The magnetos send a spark (dependent on the piston position) at the correct timing and location of the piston inside the combustion chamber of the engine.

"it is able to do a windmilling start as long as there is electrical current going to the magneto's and the mixture is set to rich"

I can cut the mixture and still have windmilling prop given that RPM level is not in feather position. As a mentioned before Dachess prop governer is independant from electrical current.

[Goran_M]

I can cut the mixture and still have windmilling prop given that RPM level is not in feather position. As a mentioned before Dachess prop governer is independant from electrical current.

I'm not really sure what you are trying to correct. I never said the feathering or the prop governor was dependent on the electric current. I said you need an electric current to cause spark plug ignition. The windmilling will start the engine if the mixture is set to rich, there is an electric current going to the spark plugs and the prop levers are pushed fully forward. Without an electric current, the spark plugs won't fire and the engine won't start.

[Hueyman]

Hey it's James Hetfield from Metallica !!

More seriously, the props on this wonderful LES Duchess doesn't VISUALLY move according to their pitch angle.

Try to tick the box corresponding to " prop pitch " in " input and output " menu of X-Plane during a flight, and move the prop RPM lever, you'll see the values are changing, but visually nothing.

You can check if the blade angle comes down to 81°, but they still windmill a lot.

My personnal clue :

I've modified that for any ACF I love in X-P.

In the B-17 G, the prop , when feathered, continued to windmill, because their angle is not good against the relative wind. If I remember well, I changed the default 89,0 ° value to 80,4 ° and the propeller never windmill again.

Didn't tried that yet in the Duchess but I'll.

Goran : I hope to see in the DC-3, a fully realistic feather and overall prop management, both in systems and visually ;-)

Good luck boys !!

[carthorse]

James, what i wonder about is x-plane. In a piston engine aircraft. YOu can sit on the ground and watch the prop blown about by the slightest breeze. It's as if it's a turbine engine. I don't think x-plane models piston engines correctly when it comes to compression stopping the prop...having said that, it might cause a lot of problems for developers when it comes to fully feathering...what do you think?

[Hueyman]

As a former MSFS user, I find that X-Plane has a pretty good engine compression/prop interaction, we really feel there are a crankshaft and pistons behind that, just try stop an engine in X-Plane and in FS to see the difference..

In FS, when you kill the engine, you have a pre recorded ammount of time that the prop will spin, by it's own inertia ( I'm in the case of a ground shutdown, no wind ), the prop will slow down, then promply STOP, like if it has hit the ground or something that stopped it instantly. Moreover, except very good adds on like accusims, we don't feel the compression at start, the engine RPM just go high with starter, like if the prop was totally free.

In X-Plane, if you set the good parameters in Plane Maker ( prop weight so Inertia, starter strenght etc.. you'll have a visually realistic startup, with props going slowly until the engine fires up ( like the XPFR B-17 G ). And it's the same for shutdown, we clearly see the prop slow quick just when the engine is in it compression cycle, then , when the piston is " released " you see that the prop turn a bit faster, all that until all stop.

Of course, a such good system have its drawbacks, the prop are almost always moving, even on the ground with all cold and dark, I think it's because all the maths which runs behind the scene, the prop is affected by everything, the wind, how the engine is now ( T°C, oil pressure etc.. )

It's like turbine helicopter in X-P, they never stop, even with rotorbrake, until you set a clutch in PM and disengaging the clutch, so they stop.

To come back to that feathering thing, the best test to set the good feather angle in PM is, set a free turbine in PM, so you have no more compression, the propeller is almost free and windmill very fast , like a wind turbine.

Then, fly the ACFT in straight forward flight, at cruise speed. Kill the desired engine ( if they are several ) and feather the prop. Watch how the prop is going, or she will slow down but continue to spin slowly, or they will slow down the turning in the opposite direction. Those both case mean that the angle is not the best feathering angle.

You have to tweak that angle until the PROP don't turn AT ALL, it could take time, it's something more precise that 0.0 degree.

On the B-17, I set 80.4 °, and it turned sometimes one compression right, but when I put 80,5 °, it turn left .. we would need a 0.00 degree precision , that is not possible in real ACFT..

So why the real one don't spin ( I mean piston )

Because the compression is too strong to allow it. Only on weak engine, the prop could turn 1 round sometimes.. but try to feather a big radial engine like the B-17 one and see if the prop turn by itself when it was stopped.. no.

For example, when the ground crew make those big Hamilton turning to " dégommer " the engine before start ( Don't know the english world, in cold weather, they turn the prop by hand to allow the oil to come into cylinder, before hitting the starter ) so it require several arms and hands, the torque quite consequent.