Adverse Yaw | Slip | Aircraft list

[HomieFFM]

@CpMoustache

FWIW I just gave a quick test drive to the 172 with its 4.3 fuselage cx and, as predicted, it drops like a rock in a slip. I can get 2400 fpm clean and 3100 fpm dirty which is grossly exaggerated. For comparison, the real life Porter in inflight beta with full flap will descend at 4000 fpm. The 172s I’ve got hundreds of IRL hours in might hit 1500-1800 fpm with full flap in a slip but certainly nowhere near 3000+.

Ha. If you quickly add/remove rudder in the G1000 172 you can quickly lose/gain 20-30 knots of speed like a yoyo.

I tested it and I achieved - 5000 fpm in a nose dive, I was laughing so hard

So yes 4.0 is definitely a typo in the flightmodel.cfg Cessna and one time in the SDK documentation, it wouldn’t make any sense because it’s a drag coef.

However as the default number 0.4 seems way to low for most of the aircraft, after looking more into it.
I’m gonna quote a few very good comments from the bug report from @WartedSummer2 :

@WartedSummer2

If it is a drag coefficient as typically used, 4.0 is probably the typo. See Drag coefficient - Wikipedia

@WartedSummer2

That being said, I noticed something peculiar when checking out a document cited in the Wikipedia article. The SDK says 0.4 is the “about the perpendicular drag of a cylinder.” If they are using the typical drag coefficient, 0.4 is about equal to the drag coefficient of hemisphere and sphere, but not a cylinder.

The circular cylinder is more like between .75 and 1.2 (see Fluid-Dynamic Drag : Sighard F. Hoerner : Free Download, Borrow, and Streaming : Internet Archive page 3-16, figure 28). The drag coef. never goes below about .7, even for a cylinder with an aspect ratio of 1 (e.g. 1" span x 1" diameter). Logic would dictate the coefficient would get bigger the more squared the cylinder is, and lower the more elongated its cross-section in relation to the direction of airflow. So perhaps fuselage_lateral_cx should be sitting more in the range of like 0.7 to 1.3 rather than 0.2 to 0.8.

It almost makes you wonder if the folks writing the SDK saw the picture of the sphere and assumed it was a cylinder. A sphere has much less drag than a cylinder. Since I have little knowledge on the subject and no engineering background, it’s pretty much speculation on my part. But if there’s something to it, that would still be pretty significant for developers to know.

@WartedSummer2

Those cylinders are positioned axially (in line) with the airflow, but they did have perpendicular ones in the book that came from too linked above. Either way, 0.4 - 0.8 seems way too low.