Loadout and roll rate question

[TobiasA]

vor einer Stunde schrieb Furiz:

 

are you even reading the post?

 

Mav on Sta 7 is at the exact oposite spot from Sta 3 where GBU-38 x2 are

when you drop 1 of GBU-38s you lose the weight so that station now holds 1052lbs while Mav holds 1082 lbs, so you tell me which side is heavier now?

 

First of all, I need to apologize since I mixed up the sides in my head. I'm sorry, you are right because the mav is on the right side, not the left one.

You are correct about the weights.

Mav: 794lbs
2x GBU: 1263lbs

Both without pylon, those are out on the equation. If you now drop a JDAM which should be 590lb, station 3 would hold 673 lb which is less, even without the TGP even though the inner bomb is dropped.
Adding a rough 90lb to the already heavier side would give 884 on the mav side and still 673 on the JDAM side so you would have to add about 200lbs of weight GIVEN SAME LEVER lengths. Roughly, but it doesn't really matter.

 

However, the solution to our question is the drag. The JDAM rack has a considerably higher drag, which will mean that the plane is slipping to the left. That slipping which is offsetting the tailfin to the right pushes the tailfin to the left, creating a roll to the left.

But: Only at higher speeds. Get below about 250kts, which will mean less drag difference, less slipping, less force on the tailfin and it will start rotating to the right because the weight wins, and not the tailfin. At higher speeds, the uneven drag will cause the tailfin to take up the force resulting from the left side being more draggy, which will lead to a rotation towards that side.

 

 

Edited July 5, 2021 by TobiasA

[Furiz]

That could be a good explanation,

but did you consider TGP drag as well? Cause I know the plane rolls to the right side when TGP is loaded, with even loadouts on the each wing, so TGP drag has some impact on the roll too.

[b0bl00i]

What's the conclusion? Is the roll rate correct or not?

 

[Furiz]

I guess we need ED to make a final statement ;D

[Machalot]

Can you observe the FPM and whether it's sideslipping?

[TobiasA]

Am 5.7.2021 um 22:29 schrieb Furiz:

That could be a good explanation,

but did you consider TGP drag as well? Cause I know the plane rolls to the right side when TGP is loaded, with even loadouts on the each wing, so TGP drag has some impact on the roll too.

 

It is basically the same "lever issue" in the other axis, I guess. At some point, the drag further out will win because the lever length does not change but the drag increases by a power of 2.
At least I think so.

 

Am 6.7.2021 um 17:05 schrieb Furiz:

I guess we need ED to make a final statement ;D

Probably. I'd appreciate if one of the FM guys would post here from time to time, because I am really interested in stuff like that.
And: I find it quite interesting that such details are modelled, hats off to the ED flight model team! While some coefficients might be a little off as of now, the simulation itself is impressive.

 

Am 6.7.2021 um 17:29 schrieb Machalot:

Can you observe the FPM and whether it's sideslipping?

No, I looked at the slip indicator. I think my mission has some wind in it, I didn't reset it and by default, there is some iirc.

[Frederf]

Best would be to have aero data for the ailerons and work backward through the FLCS laws to figure out what kind of stick input equals aileron which should counter the asymmetry in stores. We kinda already have that from the table which describes how many dots of aileron trim to give the airplane on takeoff given certain stores asymmetries.

[Machalot]

4 hours ago, Frederf said:

Best would be to have aero data for the ailerons and work backward through the FLCS laws to figure out what kind of stick input equals aileron which should counter the asymmetry in stores. We kinda already have that from the table which describes how many dots of aileron trim to give the airplane on takeoff given certain stores asymmetries.

I would be so thrilled if ED would release a public API for their aero models so we could query using home built tools to answer questions like this. 

[Furiz]

Well we have the weights, but we don't have the distance from pylon to the center line, if we had those its easy to calculate force on each wing.