Flight Design CTSL - Cruise Flap Setting (-12) no change in drag / airspeed

I’m doing some extensive flying on the CTSL with my trip from South Africa to Scotland. @TicTocRock and I have both noticed that the cruise flap setting (-12) has zero impact on the drag and airspeed.

If you set cruise power with 0 Flaps and then change to -12 Flaps there is a need to trim up to maintain level flight but the airspeed remains exactly the same (it should increase with less drag).

This issue was present before the World Update 3 Flaps lift Issue. Is anyone else experiencing this?

Since World Update 3, a flaps coefficient flaw was introduced which doubled the effect of that control surface. Have you modified the Aircraft Config file since then to mitigate the effect? The CTSL is in the Standard Package which means the file is accessible for edit and not encrypted.

Hi as mentioned above the issue was around before the world update 3, there is also no change after world update 3 with or without the config fix.

The challenges with world update 3 are with lift whereas the ctsl is very much with drag you can tell when you go to -12 that the lift reduces but drag and airspeed remain the same.

Maybe there is a tweak for drag in the config. Bit beyond my expertise though :slight_smile:

I see this under SU5. No significant difference between flaps 0 and flaps -12 except for the pitch.

The POH I found online claims the aircraft should accelerate “markedly” when engaging -12 flaps in level cruise due to decreased drag, and it does not. :slight_smile:

I have not altered the aircraft’s .cfg file.

Glad i’m not the only one that is facing this issue :slight_smile: Would be interested in a config tweak if anyone can find one :slight_smile:

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Looks like it may be fixable in flight_model.cfg. The FLAPS.0 section lists the flap positions like this:

flaps-position.0 = -12, -1, 0, 0, 0, 0, 0
flaps-position.1 = 0, -1, 0, 0, 0, 0, 0
flaps-position.2 = 15, -1, 0.5, 0, 0, 0, 0
flaps-position.3 = 30, -1, 0.75, 0, 0, 0, 0
flaps-position.4 = 35, -1, 1, 0, 0, 0, 0

According to docs at Flight Model Config Definition the first three values are degrees (self-evident), airspeed limit (I guess -1 means no limit), and drag coefficient.

Note that both -12 and 0 degree slots here list 0 for drag coefficient. I don’t know if a negative drag coefficient will work, but it’s worth trying!

I’m in the middle of a flight now, I’ll try it later. :smiley:

Think you might be onto something here! Let me know how it goes… we might end up with a supersonic CTSL :wink:

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No luck so far. :frowning:

Couple things I’ve tried:

  • setting a -0.4 value for drag in flaps-position.0 doesn’t seem to do anything (-0.4 being a linear extrapolation to -12 degrees from the 0.5 value for 15 degrees, which is probably wildly wrong but ought in theory to be visible at least)
  • setting a positive 0.4 value for drag in flaps-position.0 doesn’t seem to do anything
  • reducing the base drag_coef_zero_lift does increase speed, but I can’t compensate for it by adding drag on the 0-degree flaps flaps position?

From what I can read at Defining A Flight Model the given drag value is multiplied by the angle in radians, then the drag_scalar in the flaps section and finally the drag_coef_flaps from the aerodynamics section.

This means the drag from 0-degree flaps will always be zero, with no way to increase it at that angle.

And that given a positive value for the position’s drag and a negative angle, it should give a negative drag coefficient? But that’s not having the expected effect, which may indicate it’s being thrown away instead of being added to the total drag?

I can’t think of another way to compensate offhand. ;_;

Thanks for trying! :slight_smile: I guess it’s a fundamental limitation with the flight model and probably the reason why Asobo didn’t get it right in the first place :frowning:

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I never noticed this thread - we’ve had to struggle with negative flap settings in FSX and now MSFS for many years in gliders. Basically negative flap settings “don’t work” in MSFS currently - the drag goes UP for any +ve or -ve flap setting from zero due to the simplistic modelling of flaps as flat plates in the airstream independent from the main wing. In real aircraft, the negative flaps reduce the lift of the entire wing and so reduce the total induced drag.

Today Asobo (dev update) announced ‘negative flaps’ will be fixed in Update 10 although Seb Wloch called it a “sort of a spoiler-flap” which doesn’t sound promising.

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Confirmed fixed in SU11 beta; I get 5-8 knots boost at cruise now with the negative flap setting. :smiley: