reported F-5E's AOA capability is too low.

[nairb121]

The F-5E in DCS, when clean, has an angle of attack at full aft stick of approximately 21° when gun ammunition is loaded, and approximately 25° when the guns are empty. Based on the public sources I've found, these are too low; capability should be approximately 30° (presumably with guns empty).

The paper here https://arc.aiaa.org/doi/10.2514/3.45660 concerns the departure characteristics of the F-5E and the means by which an impending departure could be detected and the pilot warned. This section (found at the top of the second page) states that pitch acceleration follows stick position up to about 30 degrees, at which point further pitch up is prevented by the aircraft's aerodynamic stability.

Fig. 7 also supports this - it shows time history of various flight parameters during an extended full-aft stick stall. The angle of attack can be seen as approximately 30 degrees for the majority of the time, further increasing to 40 degrees at the onset of post-stall gyration. (It should also be noted that the DCS F-5E shows little tendency toward PSG in this regime)

An additional source for the F-5E's AOA capabilities is this NASA report regarding the development of the "shark nose" used in the F-5E and F-5F. https://ntrs.nasa.gov/api/citations/19790001876/downloads/19790001876.pdf . This report mostly concerns the F-5F, but also includes some F-5E data. Figure 6 shows flight data for 1g power-off stalls for the F-5E - the charts are more difficult to read, but they do show similar AOA tendencies of 30 degrees at full aft stick, and up to 40 degrees upon departure.

I've attached a track in DCS attempting to replicate these tests by performing an extended wings-level 1g stall with guns unloaded. Upon full application of aft stick, the AOA remains between 25-26°, never approaching 30.

F-5 1g stall test.trk

Edit: I didn't realize the first document linked was incomplete; a full version is attached.

F-5E_Depature_Warning_System2.pdf

Edited April 2, 2024 by nairb121

[f-18hornet]

Reported.

[f-18hornet]

Hi @nairb121,

there may be confusion between true angle of attack and angle of attack units. The indicator in the cockpit shows units that are different from the real AoA. In your track, it can be seen that indicator shows values above 30 AoA. Are you checking the bottom information line where real AoA is shown?

[nairb121]

2 hours ago, f-18hornet said:

Hi @nairb121,

there may be confusion between true angle of attack and angle of attack units. The indicator in the cockpit shows units that are different from the real AoA. In your track, it can be seen that indicator shows values above 30 AoA. Are you checking the bottom information line where real AoA is shown?

Yes, the numbers referenced in my post are true AOA in degrees, as reported by the status bar. The NASA and Taylor/Skow documents are both also measuring true AOA.

[f-18hornet]

In the TO-1 manual in Flight characteristics section it is mentioned that stall occurs at 27-28 units AoA.

Quote

"yaw oscillations. For later aircraft, stall occurs at approximately 27 to 28 units AOA, and the dominant characteristic is wing rock.."

[=475FG= Dawger]

55 minutes ago, f-18hornet said:

In the TO-1 manual in Flight characteristics section it is mentioned that stall occurs at 27-28 units AoA.

Units not degrees. The OP has presented evidence for 30 of the latter. 

[nairb121]

On 5/18/2024 at 5:14 AM, f-18hornet said:

In the TO-1 manual in Flight characteristics section it is mentioned that stall occurs at 27-28 units AoA.

Yes, that is correct. I'm not disputing the stall AOA (in units) - the manual is very clear on that. The sources I've posted seem to indicate that the F-5 should be able to pull more beyond stall than we can currently, depending on CG position. The manual supports that the F-5 should have some degree of post-stall AOA capability (page 6-4): 

It's difficult to properly correlate units and degrees, since no source seems to use both, each using either one or the other. The only factor I've seen relating them is the stall AOA, which is stated in the Taylor/Skow report to be 23 degrees, and in the -1 manual to be 27-28 units - however, in DCS 27-28 units corresponds more closely to 20° AOA. See below, from my track attached in my original post.

null

Is it possible that the relation between true AOA (in degrees) and indicated AOA (in units) is slightly off in DCS, with the stall and maximum AOA being based on the incorrect indicated AOA and therefore falling short of the true values?

[nairb121]

I located an additional source for further clarification on maximum AOA for the F-5E:
https://apps.dtic.mil/sti/tr/pdf/ADA029071.pdf
Page 5-10 has this chart showing the AOA limits as a function of CG for tail deflections limited to 17° (as in the production F-5E) and 20°.

CG with full fuel and no ammunition is approximately 12.5% MAC, full fuel and ammo loaded is about 11%. Correction - I had read these values from the incorrect charts - for the clean E-3, guns empty CG is about 17.5%, and with guns loaded it's about 12%. This gives a AOA of up to about 30°, which closely matches the references above.

Edited August 20, 2024 by nairb121

[nairb121]

Checking back on this - is there any other information needed on this? With the FC2024 version of the F-5 using the same flight model, this is now an issue with two modules.

[Bucic]

Could we please have a confirmation of the current status of the issue?

[Bucic]

Any updates? That seems like quite a meaty case.

Edited October 25, 2024 by Bucic

[nairb121]

Yes, it would be nice to get an idea of where the team is on this.

[NineLine]

It's reported and planned to be fixed but I do not have a timeline for it, sorry. Thanks.