F-5E can pull 13+G?

[Pavlin_33]

Been doing a bit of dog fighting in a Fulcrum A against the Tiger and I was surprised that I could not keep up with it in a turn, only to review the TacView and see that it can pull 13.4G, without breaking a part!
Should it not be rated for a max of 7.3G? 13.4G is almost double that. Also shouldn't the onset of 13G in a span of 3seconds black out the driver?

[Sarowa]

I suspect this is a Tacview inaccuracy.

The DCS F-5's wings suffer catastrophic structural failure at 11g in the best of cases. Sometimes this occurs at a lower g if there's more payload on the aircraft (e.g. greater than half internal fuel, external fuel tanks, bombs, rockets, etc.).

7.3 g is the rated limit, but all(most?) aircraft have a design load factor of 150% applied to this number, where the structure meets or exceeds the capability to hold such a load without failure. At least in the F-5's case, DCS interprets this as the exact point catastrophic structural failure will occur.

Here's an example from the Cessna 172 Pilot's Operating Handbook (POH):

Edited January 8 by Sarowa

[nairb121]

The structural failure point is highly dependent on stores and fuel weight - clean and at 60% internal the wings fail at around 12g, and near fuel exhaustion it can get to around 14. Rapid G onset might cause it to fail earlier though.

(Also I think that's me in the screenshot, hi!)

Edited January 8 by nairb121

[Pavlin_33]

3 hours ago, Sarowa said:

I suspect this is a Tacview inaccuracy.
...

7.3 g is the rated limit, but all(most?) aircraft have a design load factor of 150% applied to this number, where the structure meets or exceeds the capability to hold such a load without failure. At least in the F-5's case, DCS interprets this as the exact point catastrophic structural failure will occur.

Well acording to the flight performance of that turn, 13+G seems about right.

IRL Flanker is rated as an 8G platform, and in DCS it desintegrates if you go over 12G for even a micro-second (150% limit), so there is definitely something off here in terms of consistency.

150% of 7.3G is 10.95G; compare that to 13G

1 hour ago, nairb121 said:

(Also I think that's me in the screenshot, hi!)

Edited January 8 by Pavlin_33

[nairb121]

From the manual, for no stores except wingtip - limits are 6.5g above 2200 lb internal fuel (about 45%, gross weight roughly 12,900 lb) and 7.33 g below 2200 lb internal.

Full gross weight is around 15,600 lb (all weights including full ammo).

6.5g at 15,600 lb = 101,400 lb "effective" weight supported by the wings;
7.33g at 12,900 lb = 94557 lb.

Taking 101,400 as the "rated maximum" weight, and using a 1.5 safety factor, that gives a failure force on the wings of 152,100 lb.

If I'm running on fumes and out of ammo (at empty weight of 10,308 lb), that means I can pull 14.8 g at the same wing strength.

(Full discosure - I was not aware before that g was limited to 6.5 above 2200 lb internal fuel.)

[=475FG= Dawger]

Its AI or game flight mode or something similar.

 

 

 

 

[nairb121]

16 minutes ago, =475FG= Dawger said:

Its AI or game flight mode or something similar.

It's neither, just a very hard (but, importantly, smooth and symmetrical) pull at very low weight. The tolerance of the wings is very sensitive to aircraft weight, and the aircraft was clean and, as this point, probably below 1000 lb fuel. Refer to my post above - given the ultimate strength implied by the prescribed g-limits at the maximum applicable weight, at very low weights the aircraft should be able to survive over 14g. 

[WTFCSon]

Were you using your own mission, mission packaged with the module or a DCS community made mission? Either way, any chance you can post .miz file or even a .trk file? Just curious if I can help reproduce.

[Pavlin_33]

39 minutes ago, WTFCSon said:

Were you using your own mission, mission packaged with the module or a DCS community made mission? Either way, any chance you can post .miz file or even a .trk file? Just curious if I can help reproduce.

It was from a mutliplayer dogfighting server, so no track I am affraid. I also don't own the F-5, so I can't make a track.

 

51 minutes ago, nairb121 said:

...given the ultimate strength implied by the prescribed g-limits at the maximum applicable weight, at very low weights the aircraft should be able to survive over 14g. 

I am not so sure about that statement, at least from the consistency point of view.

I am not aware if any other DCS module has these kind of margins when it comes to overstressing the frame.

[=475FG= Dawger]

1 hour ago, nairb121 said:

It's neither, just a very hard (but, importantly, smooth and symmetrical) pull at very low weight. The tolerance of the wings is very sensitive to aircraft weight, and the aircraft was clean and, as this point, probably below 1000 lb fuel. Refer to my post above - given the ultimate strength implied by the prescribed g-limits at the maximum applicable weight, at very low weights the aircraft should be able to survive over 14g. 

You math is off a bit. You should use the lower figure of 94,557 at low fuel weights, which gives you 13.7 Max G at your stated 10,308 lbs empty weight. Your maximum weight to be able to sustain 13.4G is 10,584 lbs.

Seems more like a Tacview glitch than anything else.

[VZ_342]

Seems easy enough to duplicate...10% fuel, no stores, low alt., max horizontal turn.

[nairb121]

1 hour ago, VZ_342 said:

Seems easy enough to duplicate...10% fuel, no stores, low alt., max horizontal turn.

My thoughts as well - I recorded a short track at 10% fuel and 50% ammo. First pull is to 13.1g, second is to 14.0. Third pull to structural failure - interestingly, this occurred at 13g - maybe I introduced some roll inadvertently.

F-5 14g.trk

[VZ_342]

That, or the over-G damage may be cumulative... 

[nairb121]

16 hours ago, VZ_342 said:

That, or the over-G damage may be cumulative... 

It's not impossible, but it would surprise me if this were the case on an older module like the F-5. Also, the original screenshot at the top was taken after several minutes of flying with high g-loads (though I don't know the exact numbers reached) - if that's why it broke at 13g after 2 hard pulls, then it probably would've broken far sooner in the original scenario.

[Pavlin_33]

All I'm saying is that F-5 has clearly higher tolerance than 150% (of max rated G), which I believe is the standard for DCS.

[nairb121]

3 hours ago, Pavlin_33 said:

All I'm saying is that F-5 has clearly higher tolerance than 150% (of max rated G), which I believe is the standard for DCS.

The thing is, the wings don't break because of a specific g-value - they break because they are carrying a force greater than the structure can withstand. The same g with a lighter jet is a lower force (F=ma), so a lighter aircraft can pull more g at the same wing stress. This is what the 1.5 design safety factor is applied to. This is also part of why a clean, light jet typically has higher allowable g-loads (like in my manual excerpt above) than a loaded, heavy one (the main other reason being store carriage limits).

If another aircraft in DCS always breaks at the same g regardless of weight - then that is a modeling inaccuracy on that aircraft and shouldn't reflect on the F-5.

[RedeyeStorm]

Shouldn’t the pilot blackout with that much G?

[nairb121]

2 hours ago, RedeyeStorm said:

Shouldn’t the pilot blackout with that much G?

A g-load that high can't be sustained for long, but the pilot should still last at least 2-3 seconds (and that's all this maneuver was).

There's an IRL case of an F-15(C I think) pulling 13-14g in an emergency dive recovery. IIRC they were able to RTB safely, but the plane's structure was permanently bent, so it was written off.

[=475FG= Dawger]

2 hours ago, nairb121 said:

A g-load that high can't be sustained for long, but the pilot should still last at least 2-3 seconds (and that's all this maneuver was).

There's an IRL case of an F-15(C I think) pulling 13-14g in an emergency dive recovery. IIRC they were able to RTB safely, but the plane's structure was permanently bent, so it was written off.

Which is what should happen to the F-5 when it exceeds it G limit instead of catastrophic failure. Other parts would fail long before the wing, in any case. 

[Pavlin_33]

11 hours ago, =475FG= Dawger said:

Which is what should happen to the F-5 when it exceeds it G limit instead of catastrophic failure. Other parts would fail long before the wing, in any case. 

Well, that should happen to any plane, but that's not how it works in DCS for other air frames.

[=475FG= Dawger]

12 hours ago, Pavlin_33 said:

Well, that should happen to any plane, but that's not how it works in DCS for other air frames.

Yes, it is quite possibly the most arcadish aspect of DCS. However, not all aircraft go straight to catastrophic wing failure. Some modules exhibit more realistic modeling. 
 

And some appear to suffer no ill effects whatsoever. 
 

Consistency is lacking. 

[GGTharos]

On 1/10/2024 at 2:55 PM, nairb121 said:

A g-load that high can't be sustained for long, but the pilot should still last at least 2-3 seconds (and that's all this maneuver was).

There's an IRL case of an F-15(C I think) pulling 13-14g in an emergency dive recovery. IIRC they were able to RTB safely, but the plane's structure was permanently bent, so it was written off.

12.5 for several seconds as recorded by internal sensors.

[zerO_crash]

On 1/8/2024 at 6:42 PM, Pavlin_33 said:

Well acording to the flight performance of that turn, 13+G seems about right.

IRL Flanker is rated as an 8G platform, and in DCS it desintegrates if you go over 12G for even a micro-second (150% limit), so there is definitely something off here in terms of consistency.

150% of 7.3G is 10.95G; compare that to 13G

 

Flanker is rated as a 9G+ platform, same as MiG-29, both in all of their iterations. DCS and IRL alike.

Edited January 19 by zerO_crash

[Pavlin_33]

19 hours ago, zerO_crash said:

Flanker is rated as a 9G+ platform, same as MiG-29, both in all of their iterations. DCS and IRL alike.

 

According to the manual, I have, it's 8G - not sure if it's because it's an export variant.

Edited January 20 by Pavlin_33

[zerO_crash]

Which manual are you refering to? (If you're unsure if it's legal, don't link it here, simply give me the name or version.).

 

From the Russian Su-27SK manual:

 

General PU (G-load) is 8G max below M=1.25. Above that, it's 6,5G max. There are more values to consider here, chief amongst - weight. However, for simplicity, it's what's stated above.

 

However, the manual states shortly thereafter that for short durations, PU (G-load) of 9G max, is permitted.

 

In other words, the manual makes a distinction between short overload bursts, and sustained. What's essential to keep in mind here, is that the sustained G-load restriction has nothing to do with steuctural design (Su-27 family of fighters is designed for 9G+), but rather extending the airframe life for as long as possible. Think of it as the soft limiter of US F-18, where non naval variants (Finnish for example), are rated at 9G. The briefly mentioned 8G sustained thus becomes merely a policy, not a technical/structural resteiction.

Edited January 20 by zerO_crash