Northrop F-5E Technical Description

[nairb121]

@Curly I wanted to ask in a new topic to leave your aileron bug report relatively clean - in the Technical Description documents you have, is there any discussion of the relationship between true AOA in degrees and the displayed AOA units? I suspect there is a mismatch in our DCS F-5E, but have been unable to find much useful. See post here for previous discussion:

 

[BIGNEWY]

Ive sent Curly a PM, we would like to see this document if possible, as long as it is a public one of course. If anyone has this please DM me. 

thank you 

[Bucic]

Are you talking about

units vs AoA mismatch or 

units-AoA relation real vs units-AoA in-game

?

[nairb121]

2 hours ago, Bucic said:

Are you talking about

units vs AoA mismatch or 

units-AoA relation real vs units-AoA in-game

?

Both, really - I've been unable to find much to correlate the true AOA and indicated units, only scattered references to stall AOA - stated in one report to be 23°, and in the -1 to be 27-28 units - Notably, this does not seem to match DCS, which places 27.5 units AOA at about 20°. This doc seems promising though, I hope we can see it in full before too long.

[Bucic]

On 10/28/2025 at 2:52 PM, nairb121 said:

Both, really - I've been unable to find much to correlate the true AOA and indicated units, only scattered references to stall AOA - stated in one report to be 23°, and in the -1 to be 27-28 units - Notably, this does not seem to match DCS, which places 27.5 units AOA at about 20°. This doc seems promising though, I hope we can see it in full before too long.

Ok. So let me tell you this - neither correlation matters. You fly by the units. Not only F-5E real flight manual doesn't bother with a conversion table or tape. There used to be a thread on this citing FMs of even newer machines with the same caveat. I am aware of the subject, I'm allergic to arbitrary, vague units and I've never seen a single reference pointing to a conversion data set. Because it does not matter in real flying.

 

Hell, you can do a quick conversion yourself. Note down 5 pairs of units vs aoa (from the in-game info bar) and just dump it into excel. Insert a trend line with the option to reveal the equation. Done.

I'm guessing it's always linear, so you can draf t a quick conversion tape like this

Edited October 29 by Bucic

[nairb121]

1 hour ago, Bucic said:

Because it does not matter in real flying.

You're correct, knowing the "true AOA" is not relevant to typical piloting situations - all operational numbers are based on the gauge units. But the true AOA is relevant from a flight modeling standpoint, and as you know, there is fairly substantial evidence that the DCS F-5 has something amiss with its AOA modeling. I suspect that the root of this issue is an error in the correlation between indicated and true AOA - but I have no data apart from a single point, the stall AOA as mentioned above.

[Bucic]

On 10/29/2025 at 10:59 PM, nairb121 said:

You're correct, knowing the "true AOA" is not relevant to typical piloting situations - all operational numbers are based on the gauge units. But the true AOA is relevant from a flight modeling standpoint, and as you know, there is fairly substantial evidence that the DCS F-5 has something amiss with its AOA modeling. I suspect that the root of this issue is an error in the correlation between indicated and true AOA - but I have no data apart from a single point, the stall AOA as mentioned above.

For that there would have to have been ¿ a scenario where FM programmers had no data point for a specific flight condition available in plain AoA so they had to resort to AoA units gauge. Highly unlikely. 

It's also problematic from a bug reporting standpoint. It's just compounding variables.

There's a dedicated documented and acknowledged bug report on AoA capability inaccuracy. The error is significant, to the point any other discussion on AoA in higher numbers seems a waste of time until that modeling error is fixed.

[nairb121]

On 11/2/2025 at 2:31 AM, Bucic said:

For that there would have to have been ¿ a scenario where FM programmers had no data point for a specific flight condition available in plain AoA so they had to resort to AoA units gauge. Highly unlikely. 

I'm far from an expert, and I don't know what all their sources were, but It doesn't seem that unlikely to me. The flight model adheres closely to the -1 performance data, but there's nothing in there tying it to true AOA. It seems very possible that some assumptions had to be made in development.

On 11/2/2025 at 2:31 AM, Bucic said:

It's also problematic from a bug reporting standpoint. It's just compounding variables.

There's a dedicated documented and acknowledged bug report on AoA capability inaccuracy. The error is significant, to the point any other discussion on AoA in higher numbers seems a waste of time until that modeling error is fixed.

Indeed, that's my report. But it's important that it be fixed correctly. I'm fairly certain already that there is an AOA indication error, due to the mismatch in reported stall values from what we have in DCS. I think the AOA limit is just a symptom.

My theory/conjecture:

1. An incorrect assumption was made on the relation of the True AOA in degrees to the Indicated AOA in units. The flight model was based primarily on available performance data and descriptions in the -1 manual, which describe the aircraft handling purely using Indicated AOA.
2. Of particular note is the Stall AOA.
   1. The -1 manual states that stall occurs at 27-28 units (indicated) for our F-5E-3 - or 24 units in "older F-5E".
   2. The Taylor/Skow report linked in the AOA bug report, meanwhile, states that stall occurs at "approximately 23 deg angle of attack". The report does not precisely indicate which subvariant it concerns; however, based on the departure descriptions and the age of the data presented, an older variant seems much more likely.
   3. Testing in DCS shows that the AOA gauge indicates 27.5 units at a True AOA of only 20 degrees - this is wrong if Taylor/Skow is for F-5E-3 (unlikely), and very wrong if Taylor/Skow is for F-5E (which stalls earlier).
3. Two more data points: takeoff (with nose hike) and landing roll. The video quality leaves much to be desired, but these appear to indicate about 11 units and 6 units respectively. Landing roll should be at 0° AOA; takeoff nose hike adds 3°. I have not yet confirmed these in DCS. https://youtu.be/WPtpS2wf-0Y
4. Plotting these points gives a very rough idea of how "Indicated" and "True" AOA relate:
   
5. How this connects to max AOA: visually extrapolating (and correcting a little for the noticeable, but unsurprising, nonlinearity) places 30 units indicated close to 30° true AOA. This aligns closely in my view with language in the -1 which indicates various departure onsets in this AOA region, and a small ability to pitch beyond stall. Simply increasing pitch authority to fit the expected 30° AOA would result in the ability to pull 50% beyond stall - this is not consistent with the language in the manual or the expected behavior of this type of aircraft. It's my belief that the entire pitch axis behavior is scaled improperly, and not just the peak AOA, but also the lift and drag polars need to be reevaluated.
6. Another possibly related problem: the wing-snap issue. If the pitch rate is right, but the stall AOA is wrong - then you will reach max lift more quickly, the g-onset is too fast, and the wings are rapidly overloaded.
7. One more ongoing concern for me is the departure resistance - while our IHQ F-5E-3 should be much improved over the older F-5E, few if any of the departures detailed in the -1 for the E-3 are present in DCS. I'm not sure if this connects to the AOA issue at all, but I thought I'd mention it while we're on the subject.

Please let me know your thoughts - maybe I'm overthinking this, or have missed something critical, but that summarizes my thinking on this matter.

[Bucic]

@nairb121As usual, great work! I clearly needed a refresher on that bug report. But I was kind of correct - the Max AOA report should be the master report. I just forgot it also mentions the AoA units problem  

[Curly]

There are 2 distinct conversations going on in this thread, the conversion of AOA units to degrees, along with a discussion about AOA capabilities of the F-5E.  

First lets briefly touch on the conversion of AOA units to degrees in the F-5E. 

I have finished scanning the entire Northrop F-5E Technical Description manual and it is now posted on archive.org for free.  

https://archive.org/details/f-5-e-technical-description

This document does not contain a definitive algorithm for converting AOA units to degrees. 

However, utilizing the description of the Air Data Computer from the F-5E Technical Description, along with additional data from the 1986 version of the Skow and Taylor report “F-5E Departure Warning System Algorithm Development and Validation”, The Air Force AFFTC F-5 Spin Report, And better scan of the NASA Shark Nose Report.
it is possible to make a good approximation of the relationship between AOA units and degrees. 

Based on my evaluation of the source material, I would estimate that AOA units = AOA true in degrees * 1.1

The data and procedures used to determine this value will be provided below.  Following a brief discussion of stall and max AOA’s of the F-5E.

Briefly, the max AOA that is possible in the F-5E is dynamic and dependent on pitch rates, inertial coupling, and aircraft configuration.  

In the 1986 version of the Skow Departure Warning System paper.

https://arc.aiaa.org/doi/abs/10.2514/6.1986-2284

There is  a table of Maximum AOA’s, the pitch rates, and the pitch acceleration due to inertial coupling. The data was taken from F-5E flight tests and air combat training.  The aircraft were configured with the CG at 18.5 to 19.0 % of the Mean aerodynamic chord.

 

 

Examination of the max AOA’s obtained without inertial coupling, indicated that pitch rates greater than 30 degrees per second might be required to achieve AOA’s greater than 21 to 25 degrees.  

 

Lets now return to the issues of converting AOA units to degrees in the F-5E.
As stated previously my estimate for AOA conversion factor is.

AOA units = AOA true in degrees * 1.1

It is based on the description of the central air data computer, CADC, contained in the Northrop F-5E/F Technical Description.  One of the key functions of the CADC is to convert Indicated AOA to True AOA for the gunsight system.

<iframe src="https://archive.org/embed/f-5-e-technical-description" width="560" height="384" frameborder="0" webkitallowfullscreen="true" mozallowfullscreen="true" allowfullscreen></iframe>

https://archive.org/details/f-5-e-technical-description/page/4-111/mode/1up

 

The CADC provides True AOA  to gunsight from -4 to 29 degrees, thus True AOA is reported over a range of 33 degrees as,  4 + 29 = 33 

The system is accurate to +-1 degree over the range -2 to + 24 degrees. Therefore the system is accurate over a range of 26 degrees.

Indicated AOA is reported from 0 to 30 Units., a range of 30 units.

Let's put these values in a table to clarify.

 

	AOA Units	AOA True	AOA Accurate
max	30	29	24
min	0	-4	-2
Range	30	33	26

 

 

 

Lets begin by asking if we can even assume that the relationship between AOA units and degrees is even linear in a 1g stick aft stall. 

I managed to acquire a physical copy of the NASA Shark Nose report and  created a high quality scan of some of the flight test data. To my surprise the F-5F 1 g stall test data  actually does contain a record of AOA true in degrees and AOA units. 

 

 

 

The relationship between units and degrees does appear to be linear in these tests. Which means that converting AOA units to degrees may be as simple as dividing  either 33 / 30 or 26 /30.

The description of the CADC gives two ranges over which AOA true is computed for the gunsight. The range in which the system is accurate to +-1 degree, we’ll call the AOA Accurate and the larger range between 29 and -4 degrees, well call AOA True. Now must decide which calibration, Accurate or True is correct.  

To determine the correct AOA conversion factor, we will convert AOA data from the flight manuals and test with both calibrations, Accurate and True. Then pick the most reasonable fit.

 

	AOA Units	AOA true	AOA Accurate
max	30	29	24
min	0	-4	-2
Range	30	33	26
Deg to Units		1.1	0.866

 

 

The F-5E pilots manual states that the AOA for on speed for the landing approach is 15.8 units indicated
on the dial. Lets determine the Approach AOA in degrees  

 

	AOA Units	AOA true	AOA Accurate
max	30	29	24
min	0	-4	-2
Range	30	33	26
Deg to Units		1.1	0.866
Units to  Degs		1 /1.1	1 /0.8666
Approach AOA	15.8	14.36	18.23

 

AOA True predicts the approach AOA is 14.36 degrees.
AOA Accurate predicts the approach AOA is 18.23 degrees.  

Now let's look at some data from the F-5E flight manual. The flight manual notes that the stall AOA for the early F-5E’s is 24 units. Lets compute the stall AOA for the Early F-5E.

 

	AOA Units	AOA true	AOA Accurate
max	30	29	24
min	0	-4	-2
Range	30	33	26
Deg to Units		1.1	0.866
Units to  Degs		1 /1.1	1 /0.8666
Approach AOA	15.8	14.36	18.23
Early FM	24	21.8	27.69

 

AOA True predicts the stall AOA to be, 21.8 Degrees.
AOA Accurate predicts the stall AOA to be, 27.69  

Let's compare the computed stall AOA’s to stall AOA from some flight tests.

An extract from the Air Force’s F-5E/F Spin Report , gives the stall AOA as 21 to 25 degrees.

 

 

See Pages 146 and 147.

https://apps.dtic.mil/sti/pdfs/ADA319981.pdf

 

The conversion factor AOA True ( AOA units = AOA degrees * 1.1) seems to be more accurate. As it closely matches the results of the Air Force Flights.

 

	AOA Units	AOA true	AOA Accurate
max	30	29	24
min	0	-4	-2
Range	30	33	26
Deg to Units		1.1	0.866
Units to  Degs		1 /1.1	1 /0.8666
Approach AOA	15.8	14.36	18.23
Early FM	24	21.8	27.69
Air Force		21

 

 

In The 1986 version of Skow’s Departure Warning System report. The aerodynamic stall AOA is given as 23 degrees. He also notes that the F-5E becomes directionally stable at 22-28 degrees AOA, referring to this area as the departure window.  In tabular data,  the largest AOA achieved without pitch coupling was 33 degrees.

 

Skow is also the one of the authors of the report “Design of Technology for Departure Resistance of Fighter Aircraft” from the AGARD conference paper often cited here. He gives the Max 1 G trimmed AOA of an F-5E with missiles and a center fuel tanks as 24 degrees. 

 

 

It should be noted that the max trim AOA is not the same as the maximum or stall AOA. Max Trim AOA is the largest steady state AOA that can be with the flight controls.   

Let’s take all these data points along with the stall AOA from the Air Force report, put them into a table and convert from degrees to units.

 

	AOA Skow	AOA True	AOA Accurate
	Degrees	Units	Units
Stall	23	25.3	19.9
Departure	22	24.2	19.1
Trim AOA	24	26.4	20.8
Max AOA	33	36.3	28.6
Air Force Stall	21	23.1	18.2

 

 

We’ll conclude the analysis by returning to the pilots manual and examining the auto flap system on the F-5E3. 

The maneuvering flap schedule is based on indicated AOA. The position of flaps changes with indicated AOA and the air speed. Up to 330 KIAS the flap position changes at 13.6, 12, 10 and finally at 7.5 units of AOA. The aircraft Stalls at 27 to 28 units of AOA, buffet on begins at 15 to 17 Units of AOA. If the stick is held full to 30 AOA The Aircraft will drop a wing depart 

 

	AOA Units	AOA true deg	AOA Acc deg	Skow AOA Deg
Depart	30	27.3	34.6	22
Buffet	17	15.5	19.6
Stall	27	24.5	31.2	23
Stall	28	25.5	32.3
Flap Max	13.6	12.4	15.7
Flap Mid	12	10.9	13.8
Flap Mid 1	10.1	9.1	11.5
Flap Lo	7.5	6.8	8.7

 

I’ll probably make being making an export script and use most of this information later. 

 

 

[nairb121]

@Curly great stuff! Thank you very much for scanning and uploading the technical description, I'm looking forward to digging into it.

I'd missed that the F-5F 1g stall charts included a production unit scale - well spotted. I'd been focusing on the F-5E 1g stall data. It does look like the same is present on the F-5E post-stall gyration chart though (page 67), which might be useful as a point of comparison:

Plotting these the best I can, up to T=10 to avoid the regions where the meter is pegged at 30, gives a very similar slope to the 1.1 factor you proposed above:

If you have this page, I suspect you could get this much more accurate than I can. It would be interesting to see a comparison with data from DCS - I haven't measured this in particular, but I did find in previous testing that at nominal stall AOA, 27-28 units, DCS only reported an AOA of about 20°. Between all of this, I think we have substantial enough data to submit a bug report - I'll work toward that this weekend.

On the subject of trim AOA - the data in the "Design Technology for Departure Resistance of Fighter Aircraft" is an excellent source for the F-5E. The text is quite clear that data for figures 15, 16, and 20 (which you also posted) were obtained during 1g stall flight tests, so this is indeed indicating trim AOA:

This gives me a lot of confidence in the data for the early F-5E - but for the F-5E-3 in DCS, I haven't found much about the IHQ upgrade's effect on trim AOA or other aerodynamic factors. The -1 provides some qualitative descriptions of differences in handling, but not much else other than an increased stall AOA (which may or may not correlate to a higher trim AOA).