Slats pop out and do not move out gradually as they should

It looks like the slats just pop out and don’t move out gradually as they should IRL: The slats on the Me109 either had a linkage system (early model) and later a rail system with rollers. Both were designed so that the resulting aerodynamic forces on the slats would pull them out gradually.

So if the aoa is gradually increased, the slats should move out only gradually starting at Cl=0.8 and aoa 12 degrees and then move out progressively as aoa increases to about 18 degrees (Cl=1.2) when they are out against the stops. Reference: Hoerner Fluid Dynamic Drag book page 6-9 figure 16 which in turn comes from German WW2 report by Petrikat, Slats in a water tunnel test, Ybk D Lufo 1940 p I-248.

Consequently, it would from a visual perspective be nice if this was modeled in the sim, i.e. that if you gradually increase load factor, the slats move out gradually as well.

However, one question that also springs to mind is how the slats are taken into account in the DCS AFM? If this has an impact on the flight model then the slat issue is more serious than a mere eye candy issue I think.

I believe Slat functionality is being looked at internally already.

OK,good! Do you have any info on if it's going to impact the AFM or is it eye candy only?

it's not eye candy, I was testing last night and the slats were giving behaviour expected of a slat equipped aircraft quite convincingly.

Found a nice in cockpit video of the recently restored Bf109-G 'Rote 7' of the Messerschmitt museum - slat deployment on right wing during landing approach can be seen very well from around 5:0.

MAC

P.S.: further great videos on same youtube channel, and on http://flugmuseum-messerschmitt.com/index.html

I have a Soviet report about 109G and the info about slats. It was written that right slat opens at 235 kph ( level flight is presumed for sure) and closes at 250. The left one at 225 and 260.

If we presume that the CL range is 1.5 (1.2/0.8) then the ratio of IAS must be close to 1.225 (sqr(1.5)).

Trying the pairs of IAS we have 1.06 and 1.15 that does not correspond to 1.225.

Ok, let's read Mr Southwood report about stalling 109 Black 6: "A 'clunk' was heard as the slats deployed as angle of attack was increased". I guess that 'clunk' the pilot can hear through the engine noise and a helmet must be very loud that means very fast slats deploying.

Anyway, I left the question to Erich Brunotte as he is the nearest 109's pilot... :) and I also can contact Buchon's pilot as well.

Well AFAIK the Me109 slats are a derivate of a design by the British company Handley-Page and the stated idea with this design is exactly the automation and that the flaps are deployed gradually which was also patented by the same company.

However, slats of this type that are not properly set and aligned can come out with a bang: As an example, if there is a gap on the slats trailing edge this will cause a suction force that keeps the slat closed until the leading edge suction forces overcome this and the slat deploys instantaneously with a bang. This could very well explain the Russian results that they deployed with a bang at a higher Cl than expected. In addition, that they open and close at different speeds is not strange since the slats in the figure I referred to in post #1 also show this type of hysteresis.

In addition, British RAE report RM2361 Me109 handling and performance evaluation, M B Morgan, states that the slats deployed at Cl=0.865 so this seems to be in line with the German numbers I posted before in post #1.

So I’m more inclined to go with the German numbers and explanation for how the slats should move as mentioned in post #1: If well maintained and properly aligned and trimmed, they should deploy gradually and not just snap out.

Anyway, would be great if you could get some info from former pilots on this.:thumbup: