Wind and Propwash / Jetwash....

jcomm · May 5, 2018 at 10:01 AM

How does AEFS2 FDM deal with x-wind situations regarding the deflected propwash from, for instance, an aircraft with it's prop ahead of the fuselage / wings taking off under x-wind ?

Is the propwash deflection due to stronger x-winds, specially during initial full power takeoff run taken into consideration, with the "wash cone" being deflected downwind and hitting mostly the downwind wing and fuselage / tail sides, as well as taking it's "central core" away from the tail surfaces and reducing their efficiency during the initial takeoff run ?

Jet-Pack (IPACS) · May 6, 2018 at 1:20 PM Official Post

Currently the propeller wash is not simulated as a cone or cylinder as far as I know. From my experience I think the wash is just a vector with direction and strength and some rotation/twist, the direction could be affected by sideslip or angle of attack but the effect on the aerowings is such that the vector is scaled by the prop wash factor of the wing and the twist or rotation is scaled with the prop wash rotation parameter. At least I think that is what is going on, I have not seen the code for this yet...

So assuming my understanding is correct:

- propeller creates a "wash" (direction, strength, twist) based on local angle of attack of the blade and the propeller's mass flow, diameter, etc,... Sideslip of the propeller is also taken into account for the thrust calculation and opposing airflow movement (that means it's affected by local wind and airspeed and takes crosswinds into account automatically)

=> prop wash depending on aircraft speed, wind speed, propeller parameters

- aerowings gets the wash of a certain propeller (only one per wing currently) and adds that onto its own airflow, wing has a factor which we can chose to represent how much the wash usually affects the surface (e.g. high for a cessna tail, low for its wings)

=> strength of the influence is a fixed parameter per wing (to account for position/configuration of wing and prop), direction of the wash is probably taken into account (windspeed and propeller wash probably just added as vectors), airflow affects entire aerowing equally (at least in the current implementation)

jcomm · May 7, 2018 at 10:55 AM

Jan,

thx for your answer.

Since that parameter / factor that associates an aerowing with the propwash is fixed, I guess it doesn't differ between upwind / downwind aerowings, so, it should be symmetrical during the takeoff run under x-wind ( ? )

Anyway, I see the propwash vector can itself be affected by the wind, which influences other flight dynamics aspects, and that's good to know.

Jet-Pack (IPACS) · May 7, 2018 at 1:15 PM Official Post

The factor on its own makes it symmetrical but the deflection of the propwash vector makes it asymmetrical... Plus you also have a sideslip for the wings anyway, so its not symmetric even without propwash. But the "how much of the wing is affected by propwash" is fixed, doesn't change due to sideslip or angle of attack yet.

jcomm · May 8, 2018 at 8:21 AM

Quote from Jet-Pack

The factor on its own makes it symmetrical but the deflection of the propwash vector makes it asymmetrical... Plus you also have a sideslip for the wings anyway, so its not symmetric even without propwash. But the "how much of the wing is affected by propwash" is fixed, doesn't change due to sideslip or angle of attack yet.

Well, here's a nice chance for further improvement of your FDM

It would also bring interesting effects for rotaries, now that they're coming along so nicely

Getting my mind prepared to hover in the R-22.....

HiFlyer · May 8, 2018 at 10:27 AM

Getting my mind prepared to crash repeatedly and curse a lot......