Bf109 K-4 pre-stall buffeting...

Btw the slats are supposed to deploy slightly assymmatrically in certain situations, as the inside wing goes slower than the outside one. However the slats already start to deploy well before the critical AoA, so in a tight turn they will both be fully out, regardless of a little slip.

 

No disturbance around any axis should be felt, and the stall should be mild.

 

Atm we have excessive flutter and wing rock during tight turns, which wasn't/isn't present on the real aircraft.

 

 

 

That may be part of the problem with the ingame aircraft and why it experiences wing rock, on the real aircraft slats start to deploy already at ~7 deg AoA, gradually extending until fully open around 11-12 deg AoA. Really the pilot should hardly notice or feel them deploy.

Or you pull too much compared to a real pilot, therefore causing more vivid response.

Or you pull too much compared to a real pilot, therefore causing more vivid response.

Pulling hard in the real plane and all you'll feel is a slight notch (or clunk) on the stick as the slats deploy, no disturbance to the aircraft's motion about any axis is seen or felt. Dave Southwood, Mark Hanna, Skip Holm & Klaus Plaza are all quite specific about this.

Also slats either deploy fully or not at all, aerodynamic forces being strong enough for split second deployment once preset AOA is reached.

This is incorrect, leading edge slats deploy/move purely in response to the forward movement of the center of pressure as AoA is increased towards the stalling AoA.

So for a given AoA, airspeed and G loading the centre of pressure will be at a certain MAC %. IF the center of pressure is not positioned far enough forward, there will not be enough aerodynamic forces to "suck" the slats out completely against the free stream air holding them in.

This is true for any aircraft with aerodynamic leading edge slats, including the F-86 and Lysander for example.

This is incorrect, leading edge slats deploy/move purely in response to the forward movement of the center of pressure as AoA is increased towards the stalling AoA.

 

So for a given AoA, airspeed and G loading the centre of pressure will be at a certain MAC %. IF the center of pressure is not positioned far enough forward, there will not be enough aerodynamic forces to "suck" the slats out completely against the free stream air holding them in.

 

This is true for any aircraft with aerodynamic leading edge slats, including the F-86 and Lysander for example.

Correct.

As mentioned on the real aircraft slats start to deploy already at ~7 deg AoA, gradually extending until fully open around 11-12 deg AoA.

In short the operation of the slats is smooth and should hardly be felt by the pilot, it most certainly wouldn't cause the instability around the axis of roll we see ingame atm. So that's at least one area where the FM can improve. Perhaps this will be corrected later.

Perhaps he means the ability to throw our sticks around like a mad man, compared to would you could really do in the real aircraft...

Well I don't really do that to begin with, esp. in turns, and I don't think most people do either :)

The problem atm is the wing rock & instability about the axis of roll that the ingame aircraft experiences once settled in a turn, a situation where no other stick movement than slight changes in how far back you pull the stick occur as you try to ride the Clmax.

The real aircraft experiences none of these problems, it remains completely stable until the point of the stall, which in itself is described as a very mild slow drop of the inside wing.

Anyway as I understand it the FM is WIP, so we might see this problem solved in the future.

This is incorrect, leading edge slats deploy/move purely in response to the forward movement of the center of pressure as AoA is increased towards the stalling AoA.

 

So for a given AoA, airspeed and G loading the centre of pressure will be at a certain MAC %. IF the center of pressure is not positioned far enough forward, there will not be enough aerodynamic forces to "suck" the slats out completely against the free stream air holding them in.

 

This is true for any aircraft with aerodynamic leading edge slats, including the F-86 and Lysander for example.

That completely makes sense. I just assumed the margin of equilibrium in the forces pushing them in and out is small. The german tests I know talked about aprupt deployment at an specific speed or angle of attack. But may I ask how G loading affects the deployment?

Hi,

i think, slats should also deploy by just moving the ailerons (roll axis).

Slats on the 109 are as long as the ailerons.

So when the right aileron (in a left roll control movement) moves down, the AoA at that part of the wing rises.

As AoA rises, slats should deploy.

On the left side AoA is reduced (getting negative), so no slats deployment.

Watch from 13:17 when the 109 trop flies in close formation.

[ame]https://www.youtube.com/watch?v=yeyRoyLxqXU[/ame]

You can see that slats are partly deployed by very little aileron movement when the pilot just compensates thermals and gusts.

greez mugen

That completely makes sense. I just assumed the margin of equilibrium in the forces pushing them in and out is small. The german tests I know talked about aprupt deployment at an specific speed or angle of attack. But may I ask how G loading affects the deployment?

G-load shouldn't really have any effect as the air pressure easily will keep the slats at the angle they should be. (you can push them in with your little finger when the aircraft is standing on the ground no problem) The slats themselves also barely weigh anything being made of aluminium and wood.

However keeping the mechanism clean (pivot or roller arm) as well as ensuring that the fit of the slat itself is precise is always important, otherwise you risk the slats sticking which can cause anything from a violent deployment to assymmetric deployment when you don't want it or in a worst case scenario a complete jam of one of the slats.

All of these same problems were experienced by Sabre units in Korea as it used the same slat design.

Hi,

 

i think, slats should also deploy by just moving the ailerons (roll axis).

Slats on the 109 are as long as the ailerons.

So when the right aileron (in a left roll control movement) moves down, the AoA at that part of the wing rises.

As AoA rises, slats should deploy.

On the left side AoA is reduced (getting negative), so no slats deployment.

 

Watch from 13:17 when the 109 trop flies in close formation.

 

https://www.youtube.com/watch?v=yeyRoyLxqXU

 

You can see that slats are partly deployed by very little aileron movement when the pilot just compensates thermals and gusts.

 

greez mugen

This is actually a great view showing what I was talking about before!

The extension of the slats there is not from the movement of the ailerons, but instead small changes in AoA as the aircraft moves around in the air. The lower wing has a slight increase in AoA, which moves the center of pressure forward slightly. Which sucks the slat out.

The pilot corrects the slight low wing with aileron, as the bank angle returns to straight and level, the slat retracts due to the lower AoA.

So the ailerons look like they are causing the slat deployment, but the use of ailerons is simply the corrective action of the pilot to bring wings level. But everything happens nearly instantly, so it is hard to tell what is the case and what is the effect.

Good video find though!

But may I ask how G loading affects the deployment?

Yeah as Hummingbird said, disregard what I said about G and deployment. I have a vague memory of there being an issue with G-Loading and slats but its probably just mush!!

The effect I was alluding to is the efficiency of the slats as G increases at high airspeed.

A couple of pictures I took during the Roskilde Airshow last summer where I also had the pleasure to talk to the chief mechanic about the aircraft:

I just tested ingame, slat deployment starts at 6.8° AOA and is completed at about 7.3° AOA.

As mentioned on the real aircraft slats start to deploy already at ~7 deg AoA, gradually extending until fully open around 11-12 deg AoA.

Where did you get the 11-12° AOA number from Hummingbird? It seems a bit high to me, since 4-5° delta AOA, as well as correlating center of pressure shift on the wing is quite a lot.

The forces pushing slats out and in must be just before/beyond equilibrium state and the gradual deployment being only due to non zero mass of the slat as well as slat rail friction. So correct me if I am wrong here but my sense of physics tells me, this margin just cannot be 4-5° AOA.

Very nice pictures by the way! Its red 7 isnt it?

Edit:

So I took a look at the document I mentioned earlier and measured the speed at which slats deploy ingame. At 230 km/h (6.8° AOA) the slats began to deploy. The document mentions optimal speed at which slat deployment should start to be 230-240 km/h (Kampfleistung). So at least the start of deployment seems to be set pretty much to historical standard.

wwiiaircraftperformance.org/me109/VB-109-10-E-42.pdf

Probably not, and I was exaggerating somewhat anyways, but its easy to probably pull harder (even slightly) than you might be able to or would in the real thing, and I think that was the point, the plane could respond unrealistic to our unrealistic flight controls.

Our sticks are too short and maybe our hands are too long or our fingers too thick . But with the same stick i can fly on the edge of the stall much more easily with the p51 and pull a tighter turn when all scientific evidence points to the contrary: laminar airfoil , no slats, weight vs hp .

I don't think anything will change but i can't say it's all fine when it's not.

I just tested ingame, slat deployment starts at 6.8° AOA and is completed at about 7.3° AOA.

Which is a flaw, no slats have that narrow a deployment range.

Where did you get the 11-12° AOA number from Hummingbird? It seems a bit high to me, since 4-5° dAOA is quite a lot as well as correlating center of pressure shift on the wing.

The forces pushing slats out and in must be just before/beyond equilibrium state and the gradual deployment being only due to non zero mass of the slat as well as slat rail friction. So correct me if I am wrong here but my sense of physics tells me, this margin just cannot be 4-5° AOA.

I'm currently writing from my laptop, but when I get home I'll find the document regarding the deployment angles.

The RAE also tested it on the Emil with similar results, the slats starting to deploy at 8 deg AoA (CL ~0.8 ) and were fully open at 11.5 deg AoA. (1 G power off config)

Very nice pictures by the way! Its red 7 isnt it?

Thanks, wish I had gotten some better lighting though.

Edit: Yes its red 7 :)

So you are saying right now you can out turn a 109 easily every time?

If i may .There are a few things i want to mention :

First of all because of the way stick forces are implemented there is a delay between my input and the 109 stick in game. i can post a video but this is obvious. It's like playing a game with lag the lower the speed the lesser the lag but it's still there.If i set up a pitch curve for the 109 the lag gets worse.But if i use a curve for the 51's pitch there's no lag.

Second if i fly with the 109 without ammo there is a difference in handling, turning .It's small but it's there and the weight displayed on the mission editor is modified by how much ammo you choose to load.

Now if i choose an empty mw50 tank the weight does not change in mission editor.The plane also doesn't feel different with an empty mw50 tank.

If i may .There are a few things i want to mention :

 

First of all because of the way stick forces are implemented there is a delay between my input and the 109 stick in game. i can post a video but this is obvious. It's like playing a game with lag the lower the speed the lesser the lag but it's still there.If i set up a pitch curve for the 109 the lag gets worse.But if i use a curve for the 51's pitch there's no lag.

 

Second if i fly with the 109 without ammo there is a difference in handling, turning .It's small but it's there and the weight displayed on the mission editor is modified by how much ammo you choose to load.

Now if i choose an empty mw50 tank the weight does not change in mission editor.The plane also doesn't feel different with an empty mw50 tank.

Otto,

in my case I do notice a difference when I empty the fuel tank, even if, strangely, there is no change in the GW figure in the mission editor.

It's a matter of ME and FM interaction. It was checked, as I wrote earlier, and now MW-50 tank is filled proportionally to the main tank. At least in the FM for now and we plan to do the same in ME.

 

Hope it will be in the release version soon.

Thx Yo-Yo,

and indeed the trim I now use is, depending on my load and fuel, is very plausible and in agreement with what Klaus described in his messages !

I believe we're close to final :thumbup: