investigating Aileron Spring Stop / Aileron Limiter

[Curly]

Requested Change: Move the position of the spring stop to 80% of the aileron axis. 

Problem: On the DCS F-5E, the aileron limiter / the spring stop, is located at 50 % of the aileron axis. 
Placement of the Spring Stop here is inaccurate and makes the F-5 difficult to accurately control laterally.

 

To be clear, I am not calling for the removal of the spring stop, only that it moved to 80% of the joystick axis. 

While it is true that the spring stop limits the total aileron deflection by more than 50%, as is stated in the F-5E flight manual:

Examination of more detailed descriptions of the flight control contained in official Northrop documentation

Indicates that aileron deflection per control stick movement (the aileron gearing) is not linear and that the spring stop should be located at 80% of the roll stick travel. 

 

With the landing gear down: Stick Travel is  = +- 4.0 inches, and the max aileron angle is 35 degrees Up, 25 degrees Down. For a total Aileron Angle of 60 degrees 

When the landing gear is up, the aileron limiter / spring stop is active.
The Stick Travel is limited to: +- 3.2 inches. 
Thus the spring stop is located +- 3.2 inches from the center. +-3.2 being equivalent to 80% of the total Stick Travel (4 inches). As (3.2 / 4) = %80

At 80% stick travel; the aileron angle is limited to 18.5 degrees Up, 14 degrees down. The spring stop therefore limits total aileron angle by more than 50%. As (18.5+14) / (35 +25) = 54%

While the details of the  Northrop Technical Manual match the description of the Aileron Limiter from the  Pilots Manual, “Limits the Aileron travel to one half”.  Neither sources state that the flight controls are limited to 50%  / half travel when the landing gear is raised.  

Plotting the aileron angles and stick position from the Technical Description, and connecting these points by the appropriate slope. We constructed a diagram depicting the aileron angle as a function of the stick position, often called the aileron gearing ratio.  

This chart indicates that the aileron limiter in the landing gear up (aileron limited) config, cannot be located at  50% position of the total control stick travel (+-2 inches) like in DCS. 

As the location of the points which coincide with Landing Gear Down (aileron limited) Config, like  (3.2,18.5) are not located half way from the points which coincide with Gear Up Cofing, like (4.0, 35), along the slope of Gear Up Config.

 

It is likely that the aileron gearing ratio is not linear. Rather it is constructed of two distinct gradients. Connected at the location of the Spring Stop, +-3.2 inches from the center of the control stick. This point being = to 80% of the total control travel (4 inches)

 

 

Simply stated the Spring Stop has to be located  where max aileron is achieved in Gear Up Config. Which means that the Spring Stop can  only be located at +- 3.2 inches of stick travel, 80 % of the total stick  travel.

The aileron flight control system seems to be designed to provide linear response of the ailerons to control stick inputs up to the Spring Stop. The steep gradient beyond the Spring Stop would provide feedback to the pilot that the critical range of operation had been exceeded.  

 

As compared to the DCS 50 % the spring stop implementation  The Northrop implementation of the Spring Stop (At 80%, +--3.2 inches stick travel) would result in improved lateral control (roll rate / bank angle) of the DCS  F-5E.

 

Moving the spring stop from 50% to 80% of the stick travel range, increases the range of motion of the player's joystick by 30% in the roll axis. The result would be a 1.6 times increase in the  gearing ratio of the player's Joystick position to the F-5E’s aileron angle. Making the DCS much more precise and controllable about the roll axis. And may reduce inadvertent wing destruction caused by unintentionally high roll rates.  

 

Placing the spring stop at 80% of the stick travel, should be considered as it is realistic and would match the description in both the Pilot’s Manual and the Northrop Technical Description.  While  also improving the lateral flying qualities of the F-5E

 

The derived non linear /  multi / gradient aileron implementation also appears to be valid. Given the similar approach used by Northrop in the longitudinal flight  controls. 

Consider the implementation of the tri-gradient feel spring in the pitch axis.  Designed to linear relation between tail deflection and Load Factor (g’s).

 

 

Aileron Limiter Track F-5E Roll Coupling .trk

Edited October 18 by Curly
Format and Images

[Bucic]

Well done! You've put in so much work into this!

[nairb121]

Agreed, very good research and suggestion.

Have you measured stick vs. aileron deflection in DCS to determine whether any such curve or gradient is implemented?

Also, do you have a source for that document? Not that I am doubting its authenticity or applicability - I just want it for myself!

[Curly]

On 10/20/2025 at 7:58 AM, nairb121 said:

Agreed, very good research and suggestion.

Have you measured stick vs. aileron deflection in DCS to determine whether any such curve or gradient is implemented?

Also, do you have a source for that document? Not that I am doubting its authenticity or applicability - I just want it for myself!

Hey I'm happy to see this post getting some engagement. I was away on vacation last week and unable to respond. 

I have two physical copies of the Northrop Technical Description of the F-5E/F from different dates. I got the both from Ebay

Both reports have the same Northrop Report number NB 74-36, but with different revision dates. 

 

The cover to the report posted above is from 1975 version. 

   

I also have a copy the 1976 version of this manual.

It contains most of the same information as the 1975 version of the same document. 

 

The 1975 Version of the document is more interesting as it describes the Air To Air Refuling System:

 

 

Here's a video of the test pilot describing the flight testing of the Air to Air to refueling system and the problems they encountered.

 

The 1975 Version also describes the planned implementation of the Maverick Missile System:

 

The performance of the APQ-153 radar:

 

And the expected performance of the upgraded fire control which would become know as the APQ-159.

 

There's also a  few other  details and diagrams, such as the angle of operation of the throttles. That  home simpit buliders like @Bucic may find interesting.

 

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I'll post the table of Contents for the 1975 version below.  I'm happy to provide scans of sections of the manual upon request. After I upgrade my scanning setup, I'll post a complete scan of both documents.

 

In DCS I have measured the stick deflection Vs aileron angle using active pause and Photoshop. 

 

In DCS, At 50% stick Deflection, where the aileron spring stop is located: The aileron angle is equal to half of the maximum.  

Which indicates that the location of the spring stop (aileron limiter) and the gearing ratio of the aileron angle to control stick input in DCS is inaccurate.

  

 

The equivalent aileron gearing ratio of the DCS F-5E;  18.5 Degrees of aileron angle,  per 2 inches of stick movement (18.5/2). 

Is 1.6 times greater than the gearing ratio of the real F-5E: 18.5 Degrees of aileron angle per 2 inches of stick movement (18.5/3.2)

as (18.5/2) / (18.5 /3.2) = 1.6 

Thus, along the roll axis the DCS F-5E is much more sensitive to roll inputs than the Northrop documents indicate. 

 

Edited Saturday at 06:28 PM by Curly
Format and Images

[Curly]

In order to match the lateral (roll) handling qualities of the real F-5E.  I have created a custom joystick curve which transforms the aileron gearing ratio (aileron angle / control stick)  of the DCS F-5E  to match the real aircraft as closely as possible. The realistic / custom axis curve results in improved precision without reducing roll rate performance. 

I would recommend that this custom roll axis curve be implemented in the nonlinear joystick axis settings of the DCS F-5E, as it is historically accurate. 

The roll axis curve as implemented in DCS.

 

Was based on information from the Northrop Technical Description and from flight testing the DCS F-5E . Which has been previously presented.

 

 

Based upon this data we know that the Aileron Limiter  / Spring stop in DCS is located at 50 % joystick output. While in the real aircraft, the Spring Stop is located at 80 % of the Stick travel, 3.2 Inches)

Lets plot and compare the ratio of the aileron angle to stick deflection of the real aircraft and the DCS F-5E.  From 0 stick deflection to the Spring Stop.

The custom roll axis curve presented above will move the DCS Aileron Limiter / Spring Stop to 80% of the joystick travel and match the linear slope of the gearing ratio to the spring stop. 

 

 

 

This was achieved by multiplying the output of DCS joystick axis by 0.625 for the first 80 % of the joystick output. As 0.625 is  = (The F-5E Aileron Gearing Ratio (18.5  / 3.2) / The Gearing Ratio of the DCS F-5 (18.5 / 2)

The custom roll axis curve also closely matches the aileron gearing ratio when the control stick is pushed beyond the spring stop.

Let compare the aileron gearing ratio of the DCS F-5E and Northrop F-5E when the control stick is moved pasted the spring stop 

 

Note that the aileron gearing ratio of the DCS F-5E is the same across the entire range of control stick deflection. At 100 % stick input we could assume the max aileron angle of the DCS F-5E is about 37 Degrees trailing edge up. And at 90% Stick input the aileron angle is 33.3 degrees.

In the real aircraft the aileron gearing ratio increases when the control stick is moved past the spring stop. At 100% stick input (4 inches) the aileron angle is 35 degrees. And at 90 Stick input, the aileron angle is 26.75 degrees.  

To best match the real Aileron gearing with our custom DCS joystick Curve. We'll adjust the joystick output at 90 % to match the Northrop data. We need to reduce the output of the joystick axis from 33.33 to 26.75. We also need to keep in mind that the max aileron angle of the DCS F-5E is 37 degrees. 

In order to best fit the Real Curve we should Reduce the Stickout put by 72.3%, as 37*0.723 = 26.57

The purposed custom roll axis curves, depicted in blue below, results in a nearly identical aileron gearing ratio, when compared to the real aircraft

 

 

 

 

The improved aileron gearing ratio below the spring stop. improves the flying qualities of the DCS F-5E by making it less sensitive, which improves fine tracking and bank angle control. 

Comparing Northrop F-5E Roll Rate Flight Test from the Technical Description:

 

 To DCS F-5E roll rate tests conducted under the same conditions with custom axis curve implemented. 

Indicate similar roll rate performance.   

 

https://www.desmos.com/calculator/fd1tis4pnk

 

I've also attached my Joystick Config file with custom axis curve. I high recommend using a txt editor like notepadd ++ to implement this curve on other joysticks. As you can not use decimal places within the DCS custom curve tool.

 

 

 

 

 

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F-5E Warthog Stick With Curve_2.diff.lua

[BIGNEWY]

Hi Curly, thank you for the detailed post. 

I will ask the team however in DCS we are dealing with lots of different stick configurations, we have a direct relation between stick movement and the aileron deflection. 

Can you clarify why you think it should be 80% and not 50%? 

thank you 

[Curly]

52 minutes ago, BIGNEWY said:

Hi Curly, thank you for the detailed post. 

I will ask the team however in DCS we are dealing with lots of different stick configurations, we have a direct relation between stick movement and the aileron deflection. 

Can you clarify why you think it should be 80% and not 50%? 

thank you 

 

Sure,

First lets clarify what is exactly stated in the flight manual about the aileron limiter. 

 

The flight manual states that full Aileron travel is 35 Degrees Up 25 Degrees Down. 

The manual also states that the spring stop limits AILERON TRAVEL  to 1/2.

 

The Flight manual does not state that the control stick is limited to half of its travel when the spring stop is engaged.  

 

The description of the aileron flight controls from the Northrop F-5/E Technical Description proves that the aileron limiter is physically located at 80% of the control sticks travel.

 

 

This document contains the Stick Travel Limits, and the aileron travel limits.

When the Landing Gear is down: The aileron limiter is turned off.  And Full Aileron Travel is available, (35 up / 25 down), and Full Stick Travel to 4 inch is available.

 

 

When The Landing Gear is UP, The aileron limiter is on. Aileron Travel is Limited to 18.5 Up / 14 Down, Stick Travel is Limited to 3.2 Inches.

Thus when the Aileron limiter is active. The Stick travel is limited to 80% as  (3.2 / 4) = 0.8

And Aileron travel is limited to 50 %  as (18.5 / 35) = 0.52

Thus, the Aileron Limiter / Spring Stop is physically located at 80% of the sticks travel (3.2 inches) and limits aileron travel to 50%.  As described in the pilots manual.

 

If the stick is limited to 3.2 inches and the aileron 18.5 degrees, than limiter can only be located at 80% of the stick travel. 

 

 

 

 

 

 

 

 

 

[BIGNEWY]

Thank you, 

I have sent you a PM, but will reply here also, the flight model teams are currently busy with other work so it maybe some time before I get a detailed reply, but I will report it so the team can investigate once they have free time.