Bf110 slats

[F/JG300_Gruber]

Hi everybody,

 

 

I noticed that the two slats on the Bf110 are behaving quite differently from each other.

 

The left seems to show the same behaviour as on other planes of the game, but the one on the right wing seems to pop out very easily. On take off, the left one retracts itself pretty quickly but the right one stays extended during the initial climb to speeds up to 280km/h in straight line. And on moderatly soft turns, it also have a tendency to extend when it's not necessary, while you have to pull the stick quite harder to extend both of them.

 

I know that in real life, there was some problems of slats not always extending symetrically, but here it looks like it's either a bug or really overmodeled. Any thoughts ?

 

 

Grub'

[JG300_Olrik]

Maybe the non symetrical wash of the propellers ?

[F/JG300_Gruber]

I don't know, it must do something but on the 109s, both slats retracts very quickly above 210-220km/h.

The right one seems to be a little bit easier to extend, but nothing comparable to what you can see on the 110.

[Hoots]

Yeah similar, climbing out the right slat is always partially deployed. I guess there's some reason but can't help with what it would be. If the aoa on each wing was that different then I think there would be other issues.

[6./ZG26_Klaus_Mann]

It seems to me that the right wing has a tendency to drop. I guess without the slats the aircraft would just snap right. Apparently the Propwash causes the right wing to drop first. 

[Holtzauge]

Yes, if both engines turn the same way then one wing will experience a higher effective aoa than the other due to the propwash which will cause the slat to deploy earlier on that side. AFAIK only the P-38 had counter rotating props.

Edited January 5, 2016 by Holtzauge

[6./ZG26_Klaus_Mann]

Yes, if both engines turn the same way then one wing will experience a higher effective aoa than the other due to the propwash which will cause the slat to deploy earlier on that side. AFAIK only the P-38 had counter rotating props.

Counter Rotating Props are a luxury, since you require two seperate assembly lines and engines. You also have to store two different kinds of engines and props on base, and if one batch was destroyed you wouldn't be able to replace them quickly. Counter Rotating Props are a stupid idea for wartime. That's why no one else did it. 

I like to think that with American Aircraft germany would have lost the war of attrition in a heartbeat. 

[JtD]

The He177 also had counter rotating props.

[6./ZG26_Klaus_Mann]

The He177 also had counter rotating props.

And failed miserably.

[Crump]

Hi everybody,

 

 

I noticed that the two slats on the Bf110 are behaving quite differently from each other.

 

The left seems to show the same behaviour as on other planes of the game, but the one on the right wing seems to pop out very easily. On take off, the left one retracts itself pretty quickly but the right one stays extended during the initial climb to speeds up to 280km/h in straight line. And on moderatly soft turns, it also have a tendency to extend when it's not necessary, while you have to pull the stick quite harder to extend both of them.

 

I know that in real life, there was some problems of slats not always extending symetrically, but here it looks like it's either a bug or really overmodeled. Any thoughts ?

 

 

Grub'

 

As long as it is not effecting the control, it is realistic.

 

 

Yes, if both engines turn the same way then one wing will experience a higher effective aoa than the other due to the propwash which will cause the slat to deploy earlier on that side. AFAIK only the P-38 had counter rotating props.

 

Probably more useful to think of it in terms of the propwash energizing the boundary layer which increases the section Clmax since these are high aspect ratio designs.  Effective angle of attack is the 2D polar for the section.  

 

It is absolutely not an issue and represents most twin engine designs even today.

[Holtzauge]

Probably more useful to think of it in terms of the propwash energizing the boundary layer which increases the section Clmax since these are high aspect ratio designs.  Effective angle of attack is the 2D polar for the section.  

No, that’s not correct. My answer was in reply to the OP's question about the operation of the slat and this is connected to the resulting angle of attack which is affected by the propwash and not by the propwash “energizing” the boundary layer.

[Crump]

No, that’s not correct. My answer was in reply to the OP's question about the operation of the slat and this is connected to the resulting angle of attack which is affected by the propwash and not by the propwash “energizing” the boundary layer.

 

 

No it is correct.

 

In fact it is a fundamental characteristics of tractor propeller designs....

 

 

 

 

It is the cause of why you are seeing the slats deploy asymmetrically.   Since the slat operates as the wing requires, it has no other effect outside of the pilot looking out and seeing the asymmetrical deployment.

Edited January 7, 2016 by Crump

[6./ZG26_5tuka]

Out of curiosity, how does the second pic relate to what people referr to in this thread? It shows a F4U with a fixed triangle leading edge installed on only the right wing. That does not explain why an double engine airplane with retracting slats on both wings shows asymmetrical deployment.

Edited January 7, 2016 by Stab/JG26_5tuka

[Holtzauge]

No it is correct.

 

In fact it is a fundamental characteristics of tractor propeller designs....

 

 

 

 

It is the cause of why you are seeing the slats deploy asymmetrically.   Since the slat operates as the wing requires, it has no other effect outside of the pilot looking out and seeing the asymmetrical deployment.

You see this is where you get mixed up: You are confusing the effect the slipstream has on the wing lift which will results in a higher Clmax power on with the asymmetrical deployment of the slats which are two different things. Even a plane without slats will benefit from slipstream effects just like the picture you posted shows.

[Crump]

 

Out of curiosity, how does the second pic relate to what people referr to in this thread? It shows a F4U with a fixed triangle leading edge installed on only the right wing. That does not explain why an double engine airplane with retracting slats on both wings shows asymmetrical deployment.

 

I edited it.  I thought it was a tuft test report that have somewhere on my hard drive.

Edited January 7, 2016 by Crump

[Crump]

You see this is where you get mixed up: You are confusing the effect the slipstream has on the wing lift which will results in a higher Clmax power on with the asymmetrical deployment of the slats which are two different things. Even a plane without slats will benefit from slipstream effects just like the picture you posted shows.

 

 

Yes, if both engines turn the same way then one wing will experience a higher effective aoa than the other due to the propwash which will cause the slat to deploy earlier on that side. AFAIK only the P-38 had counter rotating props.

 

 

You will not admit a mistake will you even why I try to let you off the hook nicely???  The general effect of a propeller running is to reduce the angle of attack.  The reduction in angle of attack is not symetrical because of the spiral motion component of the slipstream.  Irrelevant...the general effect is a reduction in angle of attack.  NOT an increase....that is just wrong.  

 

Your explanation is misleading.  It causes one to think that the propellers have increased the angle of the attack of the wing.  That is wrong.

 

 

"Effective Angle of Attack" is a specific term refering to induced angle of attack effects.  This has absolutely NOTHING to do with Induced Angle of Attack.

 

Edited January 7, 2016 by Crump

[Holtzauge]

Crump, do us all a favor and go back and read what the OP asked and to what I replied. The question was why the slats open up earlier on one side than the other. Nothing in the picture you posted above contradicts what I said. Your post only goes to illustrate the point you don't understand the question let alone can provide a lucid answer.

[Crump]

The answer is very lucid. 

 

 

 

if both engines turn the same way then one wing will experience a higher effective aoa than the other due to the propwash

 

 

 Your explanation is wrong.  The propeller slipstream has not INCREASED the angle of attack.  

 

The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack.

 

The propeller slipstream has LOWERED the section angle of attack.  

 

The spiral component of that slipstream has placed the wing section at different LOWERED angles of attack.

[Holtzauge]

 Your explanation is wrong.  The propeller slipstream has not INCREASED the angle of attack.  

 

The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack.

 

The propeller slipstream has LOWERED the section angle of attack.  

 

The spiral component of that slipstream has placed the wing section at different LOWERED angles of attack.

Bingo! Now go back and read my first post which you initially disagreed with and you will see that the only difference is the straw man you have built claiming I have said the aoa is INCREASED when what I really said was "one wing will experience a higher effective aoa than the other" which you have now just reformulated as: "The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack."

[F/JG300_Gruber]

The question was why the slats open up earlier on one side than the other. 

 

Well, more precisely my question was why is there on the 110 almost 100 km/h difference between the retractation of the right and left slat whereas on the 109's it's only about 10km/h or so. 

I don't see why propwash on a twin engine might cause 10 time the effect than on a single engined aircraft. 

 

[Holtzauge]

Well, more precisely my question was why is there on the 110 almost 100 km/h difference between the retractation of the right and left slat whereas on the 109's it's only about 10km/h or so. 

I don't see why propwash on a twin engine might cause 10 time the effect than on a single engined aircraft. 

 

And that is a good question because it does sound fishy if the difference is that large. Would be good to get some IRL data on this. Probably it is a question of how the modeling is done in BoM. Maybe would be good to put a question to the devs about this and see if its a known issue and if they plan to do something about it?

Edited January 7, 2016 by Holtzauge

[Crump]

Bingo! Now go back and read my first post which you initially disagreed with and you will see that the only difference is the straw man you have built claiming I have said the aoa is INCREASED when what I really said was "one wing will experience a higher effective aoa than the other" which you have now just reformulated as: "The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack."

 

Nothing has been reformulated nor is there a straw man.  You even listed the P-38 as being immune to this effect.  The P-38 experienced the same effects.  The counter-rotation just eliminated the moments about the CG caused by asymmetrical section angles of attack due to the propeller slipstream energizing the boundary layer.

 

 

 

Probably more useful to think of it in terms of the propwash energizing the boundary layer which increases the section Clmax since these are high aspect ratio designs.  

 

 

Is exactly the same as:

 

 

 

The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack.   The propeller slipstream has LOWERED the section angle of attack.     The spiral component of that slipstream has placed the wing section at different LOWERED angles of attack.

Wow, this editor is way to sensitive.  Took an "ly" ending off because the spell checker added it.  List the whole post as being edited.

Edited January 7, 2016 by Crump

[Holtzauge]

Well Crumpp, you jumping into this thread to "explain" ended up as another Crumpp classic: In post #16 you are talking about letting me of the hook but I can only hope that the complete 180 you did by now saying "The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack." is simply a rather transparent attempt to let yourself off the hook because if you actually believe as you say above that your original post:

 

 

 

Crump, on 07 Jan 2016 - 02:11, said: Probably more useful to think of it in terms of the propwash energizing the boundary layer which increases the section Clmax since these are high aspect ratio designs.

 

Quote:  "Is exactly the same as:"

 

 

 

Crump, on 07 Jan 2016 - 20:13, said: The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack. The propeller slipstream has LOWERED the section angle of attack. The spiral component of that slipstream has placed the wing section at different L

 

Then you truly have my sympathy......

[Crump]

Try sticking to the facts.  If my explaination is so confusing and not correct....it should be very easy to provide a "lucid" answer to refute it.

[Crump]

 

 

Crump, on 07 Jan 2016 - 20:13, said: The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack. The propeller slipstream has LOWERED the section angle of attack. The spiral component of that slipstream has placed the wing section at different L

 

 

Let's not leave out important parts of the quote Holtzauge to try and turn it into something it is not.

 

Also, I will help you to understand what "energizing the boundary layer" means in Aeronautical Sciences.  It is just a fancy way of say the air goes faster or becomes more turbulent.

 

The correct explanation is the slats open asymmetrically because the wings are flying at different angles of attack.

 

The energy from the additional velocity of the propeller slipstream has LOWERED the section angle of attack. 

 

The spiral component of that slipstream has placed the wing section at different LOWERED angles of attack.

 

 

 

 

Crump, on 07 Jan 2016 - 02:11, said: Probably more useful to think of it in terms of the propwash energizing the boundary layer which increases the section Clmax since these are high aspect ratio designs.

 

 

 

 

Boundary layer control devices include leading edge slats, trailing and leading edge flaps for high lift applications as mentioned previously. With slats the higher pressure air from beneath the aerofoil section is sucked over the aerofoil upper surface, through the slot created by deploying the slat. This high velocity air re-energizes the stagnant boundary layer air moving the transition point further back increasing lift.

One fixed device that is used for boundary layer control is the vortex generator. These generators are literally small metal plates that are fixed obliquely to the upper

surface of the wing or other lift producing surface and effectively create a row of convergent ducts close to the surface. These accelerate the airflow and provide higher velocity air to re-energize the boundary layer.

 

 

   Keep arguing "Mr Engineer"!! 

[JtD]

This is unbearable. Can you please go open up your own forum? Thanks.