View Full Version : Airwrench questions

October 11th, 2008, 05:35
So, here i am again, a new question:

System tab: Hydraulic System Scalar(FSX), what is that, someting with the brakes maybe but what do the scalar do??

Thanks Fredrik

October 11th, 2008, 07:35
From the FSX SDK:

hydraulic_system_scalar: The ratio of hydraulic system pressure to maximum brake hydraulic pressure.

For example: Airbus A321( hydraulic_system_scalar = 1 )

As general rule of thumb, if a parameter in AirWrench is followed by '(FSX)', it's an FSX feature documented in the FSX SDK. (Yeah, I know, that still doesn't mean anyone - including me - understands what it does or doesn't do without some experimentation)

October 11th, 2008, 10:06
haha ok thanks, well then i know where its from atleast

Shane Olguin
October 11th, 2008, 14:20
Some aircraft do not use the full system pressure for their brakes. For example, the KC-135 has a deboost valve that regulates the normal system pressure of 3000 PSI down to the normal operating pressure of the MLG brakes at 1200 PSI.

I would imagine that's what the scalar is for.

October 23rd, 2008, 02:16
I attached a drawing of my problem, nice huh?

The thing is that when i fly sideways, roll 90deg, the nose tilts down much more than i want it to. Is there a way to make it go straight?
When looking at footage from airshows the plane doesnt drop the nose at all.
Another thing is the roll: after a 360 roll the nose is also pointing down to much. maybe its the same solution for both problems.
Ive tried to read about the aerodynamic effects but english isnt my first language so i have troubles with the words= i dont get it...

Thanks Fredrik

October 23rd, 2008, 20:46
I gather that you are talking about knife edge flight. in a real aircraft, the fueslage supplies some degree of lift. A degree of angle of attack, establishing a verticle component of thrust is also important in maintaing a reasonably level flight regeim. To obtain this it is necessary to use a lot of rudder, especially as it will not usually have as much area as the elevator.

In Flight Sim, the definition of fueselage lifting charcteristics, especially with regards to lift and pitch moment when the aircraft is in knife edge flight, is somewhat nebulous.

All that said, it is possible to achieve a degree of knife edge flight. Required; good power loading; a CG not too far forward; a very effective rudder. Essentially you are relying mostly on a positive pitch achieved by the rotational moment caused by the rudder, and some verticle lift component of the thrust.

Sorry if that is not as helpful as it might be.


October 24th, 2008, 20:38
I agree with Tom that if you roll 90 deg and do nothing else, the nose will tend to drop. Rudder is required to keep the nose up.

If you roll 90 deg, the fuselage lifting charcteristics are determined by what you would call 'sideslip' charcteristics if the plane were flying level. So to improve the ability of a flight model to maintain a knife edge in FS, increase the sideforce due to yawing (sideslip) coefficient.

With AirWrench, if you set the Aircraft type to 'Aerobatic' on the Tuning tab, you will increase both the baseline rudder coefficient and the sideslip coefficient.

Shane Olguin
October 26th, 2008, 20:38
How much of an increase are we talking about Sparks? Most of the time that coefficient is decidedly negative. Are you talking about making it a positive value? How does that affect the sideforce drag when the plane is slipping in level flight?

October 27th, 2008, 23:21
One might be able to measure the drag increase vrs slip angle using a utility such as AFSD. I would try that right now, but it is almost midnight and I have a trip starting tomorrow.


Shane Olguin
October 29th, 2008, 17:34
Of course you could use AFSD to measure the amount of drag induced with a control deflection, but I was curious how much of a change from standard is required to reduce a plane's tendency to slice with extreme bank angles.

October 29th, 2008, 21:58
There are two primary sideforce coefficients, Cy_B and Cy_rudder. This post is about Cy_B (sideforce due to yaw)

Cy_B must be zero or negative. Positive values are unstable.

Sideforce is in the direction of the yaw, i.e. if the nose yaws to the left, the resulting sideforce pushes the aircraft to the left.

When there is no sideforce (Cy_B=0 and Cy_rudder=0) rudder input causes the aircraft to yaw (the nose points in a new direction), but the direction of travel with respect to the ground does not change. If held level, the aircraft skids sideways like a helicopter. When the rudder is released, the nose returns to the original heading.

With more appropriate Cy_B values, rudder input will again cause the aircraft to yaw; however, the direction of travel with respect to the ground will now change. When the rudder is released, the aircraft will not return to it's orignal heading. If the aircraft is held level, you get a boat turn.

Too much sideforce is not a good thing either. Excessive Cy_B values will make an airplane turn like an air boat.

November 26th, 2008, 07:47
Interesting point about the coefficients. Whay are so many of the FMs in CFS3 set to 'General Aviation' and not 'Aerobatic?' Resetting them might help a lot.

November 26th, 2008, 09:45
Back to the brake question... wonder why they have done this feature? Perhaps for some future more sophisticated hydraulic modeling? As the brake scalar is usually adjusted to achieve an appropriate degree of braking power, I cannot see the direct utility of this. It sometimes seems as if the wheel skid effect is overdone. Most larger aircraft have (and need) anti-skid braking, so has anyone found an anti-skid equipment feature yet? The joys of reverse engineering!

Cheers: T.

November 26th, 2008, 13:11
Back to the brake question... wonder why they have done this feature?

Systems simulation, i.e. ESP

November 26th, 2008, 20:33
Thanks for the info. I see the drift here, some applications beyond the general Flight Sim community are possible.

Cheers: T.