missing info F-5E Turn Performance and Drag Model

I have been a long-time lurker on the forms but hesitant to join under the advisement of some members of the DCS community. I am posting to report a bug with the F-5 flight model, primarily, in regards to sustained high AOA and instantaneous turn rates. To be brief, the DCS F-5 slows down too rapidly when maneuvering in high AOA pulls or when sustained high AOA maneuvering is required. At 350 to 400 knots the F-5 should be able to maintain a continuous ~4.3-4.8 Gs with a turn radius of ~5000 feet at 5000 feet MSL. (conditions would be 2 Aim 9P5, no wing or cl stores and full fuel at a weight of ~13,500 pounds). This was normal for the F-5E-3 pre Open Beta 2.5.4.28090, however at some point when the textures were broken it feels as if the drag coefficient has increased slightly and could be described as if the aircraft was flying through Jell-O. The Aim-9P5 has also been affected with tacviews from pre 28090 showing the missiles were able to hold their energy better. The difference between Pre 28090 and post 28090 is about a 5% performance decrease in acceleration, climb, level speed and turn performance of both the F-5E-3 and the Aim-9P5. While I don’t expect the DCS F-5 to match the real F-5, I do expect a finished module to remain constant in its performance.

See combat performance section FA8 with turn performance starting at page 410. http://www.avialogs.com/index.php/en/aircraft/usa/northrop/f-5tigerii/t-o-1f-5e-1-f-5e-flight-manual.html#download

+1 for fixing the F-5E FM

The data is available why break it ED?

+1. I hope this product has not been avandoned as it is, and the devs will continue improving it and fixing bugs and problems.

Pardon me, because what you say might well be correct, but, the document linked is for a CF-5A not the F-5E-3. Are the documents applicable to both?

Pardon me, because what you say might well be correct, but, the document linked is for a CF-5A not the F-5E-3. Are the documents applicable to both?

No, the F-5E-3 has LERX and automatic flaps so its turn performance will be different from a CF-5A. However, the E's performance charts in this manual at pages 466-469 (edit: link deleted to avoid breaking rule 1.16) show that the E, when carrying only two AIM-9s, should be able to sustain between ~4 and ~5.5ish G with a turn radius of ~3500 ft at the speeds and altitude cited by the OP.

No, the F-5E-3 has LERX and automatic flaps so its turn performance will be different from a CF-5A. However, the E's performance charts in this manual at pages 466-469 (LINK REMOVED) show that the E, when carrying only two AIM-9s, should be able to sustain between ~4 and ~5.5ish G with a turn radius of ~3500 ft at the speeds and altitude cited by the OP.

So the manual I linked to is the F-5E-1 which is the first production version of the F-5E, the document you posted has identical charts as it also is the F-5E-1 but also covers the F-5F-1 which for all intensive purposes is the same. The F-5E-1 charts should have the same performance for all aircraft versions and upgrades that do not include engine upgrades which are only found on 2 field upgrade versions of the F-5, the AT model and the Super Tigris.

In regards to your maneuver perimeters, I should have specified full mil power for mine and your are for full afterburner.

-1 is a reference to the manual not the aircraft - you can see the designations:

F-5E Starts at AF71-1417

F-5E-1 Starts at AF76-1526

F-5E-3 Starts at AF79-1681

Actually TLTeo suggest you delete that link very quickly.

Ah my bad. I thought the manual I linked was from 78.

-1 is a reference to the manual not the aircraft - you can see the designations:

 

F-5E Starts at AF71-1417

F-5E-1 Starts at AF76-1526

F-5E-3 Starts at AF79-1681

 

Actually TLTeo suggest you delete that link very quickly.

Ah my bad. I thought the manual I linked was from 78.

The manuals are identical across all factory production aircraft in terms of performance, what changes between the manuals are safety and procedural processes.

Regardless, even though the manuals are now public record as ALL factory versions of the F-5/CF-5 and T-38 are in civilian hands and have been through the FAA's experimental exhibition airworthiness process making the manual as public as the manual for a 737, Yak 52 or even the MiG 29 (as their is 2 flying in the us in civilian hands). I have edited my quote to remove the link to the 1990 reprint of the 1984 change #8 of the original 1977 F-5E-1 manual.

I'm aware but ED is very strict with that rule, so I'd rather be on the safe side.

Seconding this, flight model concerns take serious priority when it comes to bug fixes, in my opinion. 5% may not be enough to notice on maneuvers but it's still a significant factor.

Any nwes? Any words from developer?

+1!

+1

You seem to get punished a lot more in the F-5 than anything else when doing BFM. It's pretty frustrating especially when compared to the AI F-5 SFM. Only had 1 ride in the T-38 many moons ago, but I remember it regaining speed way faster than what's currently in game (acknowledging F-5 and T-38 are different airplanes).

As a little extra data point, a guy that flew multiple fighters and currently flys the T-38 recently did a video and he mentions in passing that the sim seems to have more drag than it should while flying the break. Take that FWIW.

How many of you guys are leaving the flaps in AUTO during BFM? I really struggled with BFM until I started making use of the thumb switch. Whenever I want smash, I just unload, thumb the flaps to UP, and I regain speed like a rocket. I also bleed less speed when pulling G with flaps UP. When I want to go slow and keep high alpha in scissors or to force an overshoot, I'll go AUTO.

How many of you guys are leaving the flaps in AUTO during BFM? I really struggled with BFM until I started making use of the thumb switch. Whenever I want smash, I just unload, thumb the flaps to UP, and I regain speed like a rocket. I also bleed less speed when pulling G with flaps UP. When I want to go slow and keep high alpha in scissors or to force an overshoot, I'll go AUTO.

Yeah, I'm always leaving it in AUTO. Thanks for the tip, I'll give it a go. :thumbup:

Whenever I want smash, I just unload, thumb the flaps to UP, and I regain speed like a rocket. I also bleed less speed when pulling G with flaps UP.

Since the flaps are AoA controlled, don't they automatically retract when unloading?

While speed might bleed a bit less with the flaps up in a steep turn, the turning circle will be noticable greater.

Some years ago(Agu 2016) my friend that is a active brazilian F-5EM pilot got in contact with Alexander Pidchenko, that time Alexander was looking for some info about the maximum angular velocity of the rotation limiter of the aileron and also for some RL pilots to test the BS Tiger FM. My friend did the tests right in front of me and passed all the info to this guy. I don't know if it was implemented in the sim.

I'll get more details about the AUTO flap switch with him soon and when I get the info I'll put it here for you guys.

****Edit****

Leave the flaps in AUTO position during all the stages of the flight including DFG. He told me now that the early models of the F-5(before 1978) have a mode for maneuvers and in theory the 78 models you can leave in AUTO mode all the time.

Hope it helps you guys a bit.

No telling how it is implemented in the game, but in reality, having the flaps automatically move to the best position for a given angle of attack should provide the best lift-drag ratio. So, if you lock your flaps up, you guarantee minimum drag at low to no AoA, but for any given lift coefficient that requires any significant AoA, the auto position should in theory be superior. Auto should give you no flaps at low to no AoA, so auto shouldn't adversely affect unloaded acceleration. If auto didn't improve performance, there would be no point to using that feature.

The reason to disable auto would be similar to why a stick can be superior to an auto transmission in car racing: if auto chooses to shift during a turn, it could cause you to lose control. Manual flaps guarantee stability, so the flaps won't move and mess up your aim or your landing approach if you are adjusting your AoA too much for auto to leave the flaps in their current position.

No idea on the physics of it, but that's just what I've noticed in DCS. Speed indicator seems to move faster when I thumb the flaps to UP.

Have you tested the aircraft vs the EM charts?

Has this been looked at with the new math/FM tweaks that were done for the A-10 II C? I recall they mentioned that they found some incorrect math for drag and high AoA/induced drag.

The F-5 is of similar vintage and might be using some of the same underlying "old" math.

It still seems that the FM is deficient.
I have a Tailchase training mission from “The Air Warfare Group” in which you can switch both your plane and the agressor to F-5E; I cannot keep up with the agressor at full burn while sticking to his tail like glue. He simply has more power or less drag.

I would echo the flaps  to up and also add, that you need to make sure that the throttle range button is mapped , if you actually reliably want to go into burner...

The sim has too much drag. You can see this in many flight conditions and not just turning. Try doing level acceleration, or flying climb profile (MIL or MAX). It can't match the published performance data.

The reason UP gives better turn performance is because it eliminates the drag induced by the slats when they extend. It maintains energy for longer improving the turn.

Slats are supposed to assist with lift, but the problem we have in the sim is we bleed speed so quickly any benefit gained is lost due to loss of speed.

I have no idea why, but too much drag is a chronic problem in any sim you care to name. It blows my mind why this is so wrong so often.