Asymetric Handling 1 x AIM9

[IvanK]

After firing one AIM9 there is a significant roll couple that I believe is overdone. I dont believe the F5E should instantly become the handful it is as soon as one AIM9 is fired. Searching through the various manuals confirms my suspicion.

 

The top refrence from the USN nATOPS for the F5N. The lower section from the USAF F5E Dash 1

 

Note the manuals say that the the Rudder and Aileron trim requirements are negligible. That certainly isn't the case aileron trim wise in the Belsimtek F5E

Edited August 1, 2016 by IvanK

[Svend_Dellepude]

I am having the same thought as you Ivan.

Unfortunately i think it is related to missile drag coefficient rather than the F-5 itself, but I hope i'm wrong.

[IvanK]

Could be as its prevalent on the Mir2000C as well.

The F5E becomes operationally limited from a handling point of view with just 1 x AIM9.

 

Something somewhere is wrong.

[Eddie]

The same tendencies seem apparent with an asymetric load of 1 AIM-9 and 1 AIS pod as well, so perhaps the missile itself being the issue makes sense indeed.

[Svend_Dellepude]

Or maybe missiles doesn't generate lift until launched but drag and weight still increases with AoA and G's when on wing.

[Ktulu2]

It should not be a drag issue : more drag on one side of the plane would induce a side-slip,not a roll, the weight of the missile is what seems to be causing the issue.

[Svend_Dellepude]

asymmetric drag will indeed cause a roll since you change the symmetri of the aircrafts wing sweep in relation to flight direction.

[Ktulu2]

Well, the only aerodynamic force an aim-9 brings in the vertical axis would be the minimal lift of the control surfaces, the drag of the missile will simply slow down the plane and induce a slide slip. Now, assuming the plane is flying at positive AoA, that supplementary lift should conteract the roll that the weight of the missile brings.

 

That is of course taking the missile and the wing as two separate entities, which only works up to some extent and probably won't work at transonic speeds (which is not problematic here). Not sure if this is what you were implying?

 

In anycase, my point was that if we have a roll, it should very mainly be caused by the weight of the missile, and not it's drag.

[Invisibull]

I'm seeing this effect as well.

[IvanK]

Either way the issue is a biggie that severely limits the F5E handling post missile launch. The fact that a similar issue exists with the Mirage2000C points to a fundamental FM type issue rather than a specific airframe type issue. Devs need to take a look at this. Both types can then benefit from the fix.

[Svend_Dellepude]

Well, the only aerodynamic force an aim-9 brings in the vertical axis would be the minimal lift of the control surfaces, the drag of the missile will simply slow down the plane and induce a slide slip. Now, assuming the plane is flying at positive AoA, that supplementary lift should conteract the roll that the weight of the missile brings.

 

That is of course taking the missile and the wing as two separate entities, which only works up to some extent and probably won't work at transonic speeds (which is not problematic here). Not sure if this is what you were implying?

 

In anycase, my point was that if we have a roll, it should very mainly be caused by the weight of the missile, and not it's drag.

 

No, I'm talking about the wings on the A/C that now meets the relative airflow with different angle of attack in yaw axis due to sideslip caused by the remaining missile.

This will make the wing opposite the missile create more lift than the wing with the missile which will result in a roll into the side with missile still onboard.

This rolling tendency can be more or less depending on some factors but its there and its very dynamic.

Of course missile weight is also a factor but, it's not the only one.

 

In this example the right wing will produce more lift than the left and therefor induce a left roll.

 

EDIT: Just to add: The aim-9 is less than 100kg so it's not a heavy missile, but then again, the F-5 is not a heavy aircraft.

Edited August 1, 2016 by Svend_Dellepude

[Azazel]

Obviously, I've noticed this as well. The behavior just seems very pronounced. I'm wondering if the flight computer CADC should be correcting for it or is that not real. Based on what the flight manual says about this particular type of asymmetric load I'm guessing that the aircraft's desire to roll is not as strong in real life. Perhaps the devs can ask a real world F-5E driver for us?

[Ktulu2]

The yaw AoA should not change the lift of a wing (assuming the wing is a pure plane, which isn't too far for a fighter symmetrical wing), as the area is the same and the speed of the air going over it is also the same. As for the Cl, I do not see why it would change as it is only affected by the ''real'' AoA and the AR. It will change things like the drag of the plane due to the fuselage being more exposed, which would only increase the yaw slip with a symmetrical fuselage.

 

 

The only thing I see is that the portion of the wing that is behind the fuselage, as seen from the airflow, will have a disrupted/stalled airflow going over it, reducing the lift. But assuming a reasonable yaw AoA (<5°) for stable flight, the impact should be quite small compared to the torque the missile's weight does.

 

The rest is just me having fun, just a very rough approximation to prove my point.

 

We know all the wing will be in disrupted airflow if the AoA is 90°, and none if the AoA is 0. We can infer that the area under disrupted airflow will be proportional to Sin(Yaw_AoA), so 5° would be pretty small. This doesn't take the shape of the wing into account, but assuming a rectangular wing that is at 90° from the fuselage , the area is equal to the triangle formed by both orthogonal projections of the fuselage over the wing at 90° from the airflow and in the direction of the airflow. Meaning the area, for an angle of attack in yaw under arctan(wing span/wing root), is equal to Root*cos(AoA) [height] * Root*sin(AoA) [base] /2=R²sin(AoA)cos(AoA)/2=R²0.04341

This approximation also works fairly well for the F-5, as it has rectangular triangular wings, so as long as we stay below the max angle, it's good.

 

Now, the area of the F-5 wing is 17.28m² and the wing span of one wing is 8.13/2=4.065m. Using an extenal model scaler, I could find that the tip root is 1.12m

So A=(B+b)h/2 So 17.28=(B+1.12)*4.065 B=3.13m

 

Area with disrupted airflow = 3.13²*0.04341=0.43m²

In comparison to one full wing : 0.43/(17.28/2)=5%

So one wing has 95% of the lift of the other. BUT this difference is a the beginning of the wing, so the torque generated by this difference will be even smaller.

Now I could get exact numbers for the torque of the lost lifting area by using an integral, but at this point I feel like I'm it's unlikely someone actually reads through this so I'll stop here as I think that I have shown that the torque generated by the lift difference will be MUCH smaller than what the missile brings.

Edited August 1, 2016 by Ktulu2

[Svend_Dellepude]

I think we not agree, but maybe we can keep it at that? :thumbup:

[Ktulu2]

Sure, as I said...time to waste lol

[acdelta57]

The yaw AoA should not change the lift of a wing (assuming the wing is a pure plane, which isn't too far for a fighter symmetrical wing), as the area is the same and the speed of the air going over it is also the same. As for the Cl, I do not see why it would change as it is only affected by the ''real'' AoA and the AR. It will change things like the drag of the plane due to the fuselage being more exposed, which would only increase the yaw slip with a symmetrical fuselage.

 

 

The only thing I see is that the portion of the wing that is behind the fuselage, as seen from the airflow, will have a disrupted/stalled airflow going over it, reducing the lift. But assuming a reasonable yaw AoA (<5°) for stable flight, the impact should be quite small compared to the torque the missile's weight does.

 

The rest is just me having fun, just a very rough approximation to prove my point.

 

We know all the wing will be in disrupted airflow if the AoA is 90°, and none if the AoA is 0. We can infer that the area under disrupted airflow will be proportional to Sin(Yaw_AoA), so 5° would be pretty small. This doesn't take the shape of the wing into account, but assuming a rectangular wing that is at 90° from the fuselage , the area is equal to the triangle formed by both orthogonal projections of the fuselage over the wing at 90° from the airflow and in the direction of the airflow. Meaning the area, for an angle of attack in yaw under arctan(wing span/wing root), is equal to Root*cos(AoA) [height] * Root*sin(AoA) [base] /2=R²sin(AoA)cos(AoA)/2=R²0.04341

This approximation also works fairly well for the F-5, as it has rectangular triangular wings, so as long as we stay below the max angle, it's good.

 

Now, the area of the F-5 wing is 17.28m² and the wing span of one wing is 8.13/2=4.065m. Using an extenal model scaler, I could find that the tip root is 1.12m

So A=(B+b)h/2 So 17.28=(B+1.12)*4.065 B=3.13m

 

Area with disrupted airflow = 3.13²*0.04341=0.43m²

In comparison to one full wing : 0.43/(17.28/2)=5%

So one wing has 95% of the lift of the other. BUT this difference is a the beginning of the wing, so the torque generated by this difference will be even smaller.

Now I could get exact numbers for the torque of the lost lifting area by using an integral, but at this point I feel like I'm it's unlikely someone actually reads through this so I'll stop here as I think that I have shown that the torque generated by the lift difference will be MUCH smaller than what the missile brings.

 

Lots of fancy words and numbers here but unfortunately you are incorrect (slightly) and technically you are both right.i really tried getting my head around your torque statements but you must understand that torque is reactionary. Not something generated by an objects weight. However in fluid dynamics possibly maybe it makes sense but my brain starts to hurt when thinking into it that deep. Years as an aerobatic instructor and many more in career aviation I prefer the KISS method "keep it simple stupid." And keep in mind I am here not to insult anyone's intelligence as it is very apparent you are well educated in this subject. While I will stay out of the yaw conversation I'll focus on roll. The aim9 creates drag. If you agree with that statement (as anyone should) the drag produced will decrease the the effectiveness of the wings lift (in the real aircraft very negligible as stated per manual and poorly modeled in DCS). That's what drag does inhibits lift. Not to mention increased induced drag from the missile design itself, this ever so slight increase in drag is unproportional to the opposite wing. So what does that wing do? Creates more lift than the one loaded with the aim9 causing it to roll or have a tendency to pickup. That fact can't be argued and wing shape/design/sweep/ won't change this as both wings are proportional when clean.*** BUT the majority of the disrupted flow WILL cause the aircraft to side slip, this is increasingly apparent on the wingtip rail as the distance between the missile and center of pressure(lift) and center of gravity are at its absolute greatest. Now throw a mk82 on the inboard pylon and a clean wing on the other side and you have a whole other ball game! So the only person wrong here is DCS! What a surprise lol anyway that's my two cents!

[Ktulu2]

I do not contest the missile drag has an effect, just that it is relatively small, but to really have a solid proof you need a double integral, which already makes it hard to explain and than you have to consider the flight characteristics (temp, pressure/altitude, new lift coefficient, etc). BTW, the point of the wing being less effective because of the missile is something I hadn't thought of, and that I do not (yet) have the tools to study. But seeing how little DCS does according to you all this seems pointes LOL (had fun anyway)

 

In any case, I want to be able to keep on fighting without jettisoning my second missile me too!!!