F-14A use of manual override for forward sweep observations

[captain_dalan]

Here's something i've been planning on doing for a long time, but i just didn't get the time. I ran some semi-casual tests of basic performance with the wings set in auto, and with them swept fully forward. I used a standard A-A loadout of 4x4, no external tanks, and 53873lbs gross weight. Standard atmosphere, 5000ft altitude. The tests aren't run in a precise enough manner for FM testing, on contrary, the goal was just to establish some base of comparison between the two regimes, and evaluate possible merits of using the emergency wing sweep lever in this manner.

The results are somewhat surprising, at least for me. While the ITR test showed rather expected outcome, and the overall g available per mach was increased across the tested range of airspeeds, the acceleration and STR tests were either strange or at the very least unexpected.

STR showed expected changes from mach 0.4 to 0.6, that is, the STR dropped as mach increased. Then between mach 0.7 and mach 0.8m it suddenly jumped quite a bit. Finally, the plane struggles to reach mach 0.9 in this configuration, so at least that didn't bake my noodle.

The acceleration tests was arguably even stranger, as it didn't seem to make any difference what the angle of the sweep was until the plane reached mach 0.8+. I would have expected the extra drag to start affecting the plane sooner, seeing how the wing sweep programmer starts moving the wings sooner. 

Any similar observations by you guys? What are your thoughts are interpretations? Should i run the same tests at higher altitude of 15000ft?

Cheers and hope you had a great weekend. Video bellow
 

 

[Spurts]

I would love to see the difference at say 36,000ft, but that is consistent with my low altitude testing as well.

[captain_dalan]

10 hours ago, Spurts said:

I would love to see the difference at say 36,000ft, but that is consistent with my low altitude testing as well.

Roger, 35-36000ft will be coming next! 

[RustBelt]

I mean they’re still 20+ degree swept wings full forward. Planes would regularly go supersonic with less. Just nowhere near as efficiently. And the Tomcat has some very powerful engines. Plenty of straight winged planes had no problem hitting transonic buffet in WW2 and cruising in the 0.6M territory at altitude. 
 

The sweep really starts to matter in the transonic range, where you are noticing the difference. So that does track. 

[captain_dalan]

9 hours ago, RustBelt said:

I mean they’re still 20+ degree swept wings full forward. Planes would regularly go supersonic with less. Just nowhere near as efficiently. And the Tomcat has some very powerful engines. Plenty of straight winged planes had no problem hitting transonic buffet in WW2 and cruising in the 0.6M territory at altitude. 
 

The sweep really starts to matter in the transonic range, where you are noticing the difference. So that does track. 

That may be true, however in this case, there either seems to be no difference at all until you hit mach 0.9, with linear acceleration, or the extra lift seems there and modelled but not the extra drag, like when sustaining g's between mach 0.6 and mach 0.8+. 

I'm not saying the F-14 (in this case the A) should break the sound barrier with the wings at 20 degrees (even though it actually can't in the sim with this configuration, as it hits a wall at mach 0.9), but the wings were truly optimized for excess power, then i would expect better acceleration with wings in auto. Both loaded (up to 0 excess power) and unloaded, like in a dash. Even if that difference is miniscule.

EDIT: and the even stranger thing is, that around mach 0.6 it really is so. The plane is slightly draggier. But at higher mach (0.7 and 0.8), it's actually less draggy. 

null

Edited September 17, 2024 by captain_dalan

[captain_dalan]

Addendum:

I seldom quote myself, but it would appear we have had a similar discussion back in 2021, and back then the things were much different, that is, the jet did sustain less with wings manually set at 20 degrees override. So something changed in the meanwhile?
 

 

[scommander2]

Well, I broke my wing sweep and CADC @ 27K with around 250 air speed.... lol...

[RustBelt]

8 hours ago, captain_dalan said:

Addendum:

I seldom quote myself, but it would appear we have had a similar discussion back in 2021, and back then the things were much different, that is, the jet did sustain less with wings manually set at 20 degrees override. So something changed in the meanwhile?
 

 

There is always the issue that anything in DCS is a constantly moving target with little to no documentation. Here and in the Phoenix conversation some hard truths about games have to be addressed. 
 

This is not BMS, nobody here except the Heatblur team has any access to the source code, or any insight into the constant and sometimes seemingly arbitrary changes to the game engine. And the Heatblur team seems to be bound under some implicit or explicit NDA’s meaning users are never going to know fully why anything. 
 

At best, the community can only create a living, regularly updated errata to compare against the real NAVAIR. And report oddities in the bug section. 
 

edit: what I would really like to see by some code boffin, is a mod package that can qualitatively probe DCS’s apparent reality, so the modeled environment itself can be applied to compensate the real world plane data. We have little actual insight on what the world is doing to compare to a specific chart. Is DCS even really modeling an ISA environment? And if not, how?

Edited September 17, 2024 by RustBelt

[captain_dalan]

EUREKA..... i think.... 
Take a look at the diagram below. If HB used the first chart, or at the very least their data matches it, then optimal L/D roughly coincides with the current performance. Granted, this is for 1g flight, but i took a look at the Cl and Cd per alpha charts i have, and indeed, at 10 degrees (true), the increase in lift for sweep of 22 degrees is still greater then the increase in drag, when compare to a 50 degrees sweep, which is where the wing sweep would be at mach 0.8, when following the CADC programming.  

But take a look at what the Cl/Cd chart indicates, at mach 0.8 the optimal ratio is at 35 degrees sweep. The current programming doesn't follow this curve. You know which programming does? The original one. Or at least it follows it more closely. Take a look at the 3rd image. The wings start going back way after mach 0.7. Which means, the original program, not only provided better Cl max, it provided better Cl/Cd, which for same amounts of thrust per mach, would also mean better excess power, at least up to 10 degrees alpha, or roughly best sustained alpha. What was the new programming good for then? If you ask me, one thing and one thing alone.... airframe longevity. You have less g's available all around, and less g's you can sustain up to mach 0.8, possibly even higher. If i have enough time next weekend, i might give the original scheduler full test, up to mach 1.2. 

This means we have been fed less then true information over the years? 

One mystery remains though, and that is the dip in performance (with the wings in manual 20 override) around mach 0.6. This shouldn't exist at all, not according to the Cl/Cd chart, nor the individual Cl and Cd curves per alpha. 

Images below:
 

[captain_dalan]

Results (STR, 5000ft, 4x4, half internal fuel) of data samples taken from the sim for the F-14A:
- first chart: current wing sweep program on auto and original wing sweep manually adjusted with the wing sweep lever
- second chart: same as the above, but mach 0.6 value projected to fallow the the same Cl/Cd values as the current wing sweep
- F-15C STR added for reference 

It would seem the F-14's flew with both hands behind their backs, as except for the transonic envelope (literally around mach 1), the original wing sweep program would have given a much higher performance, up to 8g's sustained in the above mentioned configuration. Makes you wonder how things would have turned out had the Navy got all the jets they ever wanted... 

EDIT: that mach 0.6 dip still sticks like sore thumb! 

EDIT: say want you will about Maverick, but may just have had some idea about what he did when you pulled that emergency lever! 


 
 

Edited September 19, 2024 by captain_dalan

[captain_dalan]

On 9/16/2024 at 12:41 PM, Spurts said:

I would love to see the difference at say 36,000ft, but that is consistent with my low altitude testing as well.

Got some flight time tonight, and here's the result. The numbers are much closer together this time around, seeing as how the g's available are lower, and the acceleration times make a bit more sense, though the sample is smaller, again due to the narrow band in which the wings move up here, only after mach 0.72 or 0.73 or so. I don't really know what to make of it. I tried setting the wings to 22 instead of 20 degrees, but as expected no real difference there. Am i missing something? Maybe in the wing sweep schedule and how i'm reading it?
 

 

[FWind]

2024/9/19 AM8点21分，captain_dalan说：

Results (STR, 5000ft, 4x4, half internal fuel) of data samples taken from the sim for the F-14A:
- first chart: current wing sweep program on auto and original wing sweep manually adjusted with the wing sweep lever
- second chart: same as the above, but mach 0.6 value projected to fallow the the same Cl/Cd values as the current wing sweep
- F-15C STR added for reference 

It would seem the F-14's flew with both hands behind their backs, as except for the transonic envelope (literally around mach 1), the original wing sweep program would have given a much higher performance, up to 8g's sustained in the above mentioned configuration. Makes you wonder how things would have turned out had the Navy got all the jets they ever wanted... 

EDIT: that mach 0.6 dip still sticks like sore thumb! 

EDIT: say want you will about Maverick, but may just have had some idea about what he did when you pulled that emergency lever! 


 
 

 

[captain_dalan]

11 hours ago, FWind said:

That was definitely informative and educational. So structural integrity was a major player from the very start. This would explain all the changes made and the fine balance they needed to maintain over airframe stress and airplane performance. Using the above charts, i ran i new test, this time comparing wings in auto, wings following the maximum lift to drag chart and wings fixed at fully forward position. 

The findings somewhat confirmed my previous  findings and some of the data in those charts. Using the max CL/CD settings does provide a non-insignificant increase in performance. However, something is not quite right with the forward most setting. Namely even though the charts suggest best performance around mach 0.6 with sweep angle of 20-22 degrees, in game, best performance is achieved at an angle of 25 degrees. Further more, while the wing sweep of 22 does seem to provide best performance around mach 0.7, as the charts suggest, the performance should sharply drop at that angle by mach 0.8. In game however, the performance is exceptionally better then at sweep angle of 33-45 degrees which should provide best performance. So it would seem, something is not quite right, with the way drag is modelled for this sweep angle and/or close to it.

This is the recording of my tests:

And these are some of the data points i took notes for:

 

15000ft
manual
0.6 - 22^ - 3.8
0.7 - 22^ - 5.0    
0.8 - 35^ - 5.4
0.9 - 54^ - 5.4
0.96 -68^ - 4.7
auto
0.6 - 25^ - 4.1 
0.7 - 32^ - 4.6
0.8 - 46^ - 4.9
0.9 - 60^ -  5.0
0.96 - 68^ - 4.6

20^ fixed:
0.6 - 3.7
0.7 - 5.1
0.8 - 5.8

Makes me wonder if some of this isn't an artifact of previous changes in the FM?
@IronMike does this constitute a bug? Should we file it as one? 

 

[draconus]

You need to ask @fat creason about that.

[captain_dalan]

On 9/22/2024 at 9:11 AM, draconus said:

You need to ask @fat creason about that.

Looks like nobody's at home. Who do we contact under such circumstances? And ED moderator maybe? 

[RustBelt]

Have you considered waiting more than a day? 

[captain_dalan]

5 hours ago, RustBelt said:

Have you considered waiting more than a day? 

You mean like 2 or 3? 

[r4y30n]

A moderator can't help you here.  Go ahead and file a bug and put all your data there.  If they agree then they'll move it to the backlog.

[RustBelt]

On 9/25/2024 at 1:45 AM, captain_dalan said:

You mean like 2 or 3? 

I’d think more like until the next weekend. Making pretend airplanes isn’t their only job. 

[draconus]

2 hours ago, RustBelt said:

Making pretend airplanes isn’t their only job. 

Not charity either.

[captain_dalan]

On 9/26/2024 at 4:07 AM, r4y30n said:

A moderator can't help you here.  Go ahead and file a bug and put all your data there.  If they agree then they'll move it to the backlog.

The thought crossed my mind, but i first wanted to consult the team, just in case it's a feature and not a bug, or maybe they are already aware of it, or even if maybe though aware, they don't consider it worth the changes. 

[r4y30n]

Sure but that's also part of the bug triage process.

[captain_dalan]

On 9/27/2024 at 5:12 AM, RustBelt said:

I’d think more like until the next weekend. Making pretend airplanes isn’t their only job. 

Well...it's dead Jim! 

[RustBelt]

Yep, that’s them politely informing you they’re busy. 

[captain_dalan]

8 hours ago, RustBelt said:

Yep, that’s them politely informing you they’re busy. 

Customer support 101! 
At least it's good to know what to expect in the future. Have a great weekend everyone