Slow left roll after dogfight/pulling Gs

I've noticed that after dogfights or pulling heavy G's that the aircraft has a slow uncontrolled roll to the left. I have done numerous tests to rule out some kind of controller calibration issue. But when I start a flight without any heaving maneuvering, without any roll trim I can go hands off indefinitely and the bank will stay at 0. When the uncommanded roll is present I added massive deadzones to my stick and rudder and the roll is still there. Always to the left. It is not a asymmetrical load issue as during all my tests I only had external tanks and nothing else. I tested it on flights without touching trim to rule out some kind of inadvertent roll trim. I brought up the in game control display, and everything is zeroed out. So is this perhaps a feature of the module? That heavy G loading will "warp" the airframe or something? Anyone else getting this?

You most likely bent the jet (over G)

That’s what I assumed it was, it’s just odd that it’s only to the left. If it was overstressing the frame I would think it could happen on either side, depending on which direction I was pulling

That’s what I assumed it was, it’s just odd that it’s only to the left. If it was overstressing the frame I would think it could happen on either side, depending on which direction I was pulling

You most likely bent the jet (over G)

The airframe was tested to 13 G without bending, so I doubt that.

So unless you went nuts and pulled over that then it shouldn't be airframe related.

The airframe was tested to 13 G without bending, so I doubt that.

If that's the case, how come it's relatively easy to rip the Tomcat's wings off at ~10g or so? I've lost many a planes lately just because I pulled too hard and the wings did not agree with me...

If that's the case, how come it's relatively easy to rip the Tomcat's wings off at ~10g or so? I've lost many a planes lately just because I pulled too hard and the wings did not agree with me...

The airframe is one thing the wings are another. Part of the wings sweeping was to take the load off them and put it onto the fuselage that was stronger. The Cat was limited to 7.5G and some pilots took it to 9G at Topgun but were very careful as they were close to the limit over 7.5G.

Part of the problem with sims is you can just yank stick and pull 15g. In real life even 4-5 G is massive strain on the body let alone 7.5G or 9G. Then there is sustained G and instantaneous G. If you for a split second pull 12G you probably wont tear plane to pieces but if you hold it there then you are going to start straining and breaking things quickly.That being said no pilot is going to put up with anything over 9G for very long.

The airframe is one thing the wings are another. Part of the wings sweeping was to take the load off them and put it onto the fuselage that was stronger. The Cat was limited to 7.5G and some pilots took it to 9G at Topgun but were very careful as they were close to the limit over 7.5G.

 

Part of the problem with sims is you can just yank stick and pull 15g. In real life even 4-5 G is massive strain on the body let alone 7.5G or 9G. Then there is sustained G and instantaneous G. If you for a split second pull 12G you probably wont tear plane to pieces but if you hold it there then you are going to start straining and breaking things quickly.That being said no pilot is going to put up with anything over 9G for very long.

The pedant in me says: 'airframe' is defined as the aircraft minus engines (so that includes the wings).

"Part of the problem with sims is you can just yank stick and pull 15g. In real life even 4-5 G is massive strain on the body let alone 7.5G or 9G."

I remember seeing somewhere that USAF pilots are subjected to 9G sustained for a specific length of time in a centrifuge as part of their medical or yearly "checked that box" thing. I don't recall the length of time, but it wasn't long, and it looked absolutely brutal.

The Problem is airframe limit in this circumstance refers to when you damage the body beyond repair and the whole airframe is just scrap metal.

The fact that beyong 9-10 G the INS gyro disintegrates and you smash parts of the engine turbine against its housing leading to engine failure, leading to a couple other issues, still requires you to not exceed 7.5 G or you may or may not break important things. Still this can be repaired if you manage to bring the jet home, but I guess after 13 G the plane is barely scrap metal, if it doesn't disintegrate right away.

The pedant in me says: 'airframe' is defined as the aircraft minus engines (so that includes the wings).

That's also what I referred to as airframe

The airframe is one thing the wings are another. Part of the wings sweeping was to take the load off them and put it onto the fuselage that was stronger. The Cat was limited to 7.5G and some pilots took it to 9G at Topgun but were very careful as they were close to the limit over 7.5G.

 

Part of the problem with sims is you can just yank stick and pull 15g. In real life even 4-5 G is massive strain on the body let alone 7.5G or 9G. Then there is sustained G and instantaneous G. If you for a split second pull 12G you probably wont tear plane to pieces but if you hold it there then you are going to start straining and breaking things quickly.That being said no pilot is going to put up with anything over 9G for very long.

I'm aware of those differences.

What I was getting to is - the aircraft in the sim disintegrates at ~10g for a few seconds rather than 13 (and my pilot blacks out in the process). I'm not sure if that's correct or something related to e.g. the damage model, which in DCS is notoriously inaccurate.

So I was up last night for about an hour driving myself nuts trying to get to the bottom of this. Doing miles and miles of straight and level flight and carefully watching the VDI. I would take off from nellis with tanks only, climb up to 15,000 or so and test. I found some strange things.

There was one flight where I made sure to avoid any kind of high G load. The highest G from that flight was around 5. The idea of this flight was from the fact that this slow left roll is after extended AB usage in dogfighting. So I trimmed her out straight and level, and it held 0 bank indefinitely. Now, when I went full burner and got above around Mach 1.2 a slow left roll showed up. I decelerated below mach 1 and sill, the plane was rolling. The control indicator was showing neutral stick/rudder/roll trim indications. I even went into the controls menus and removed the pitch and roll axis. I added huge deadzones both in DCS and the joystick software. Nothing. And what’s interesting, is that after decelerating to below 250 or so and working the throttles through the full range, I was able to get the rolling to stop. Not with any consistency though, it would just kind of go away on its own.

I don’t think it’s anything speed related because I first noticed the problem after doing the instant action fight with the F-16 on NTTR, and I never got above Mach 1. The only consistent thing I can pin down is prolonged AB use. It’s very strange. I even managed to get a slow roll to the right last night, up until then it was always left. Not even sure what I did to get that. Again, this was on the flight where the most G I pulled was 5 or so.

Is anyone else seeing anything like this?

Ok, so i think i may have narrowed this down. Now the question, is this something only on my end?

I just did a flight, it lasted about 5 minutes. Clean aircraft, no tanks. Took off from nellis in MIL power, turned north and climbed to 15,000. Trimmed it out for level flight and bank stayed 0. I went to full AB and sure enough, right around mach 1.2 a uncommanded roll to the left began. I'm going to do some more testing and pinpoint if the issue is length of AB engagement or speed.

If anyone has the time, could they try replicating this? Just trim for level flight and go full AB and see if the plane begins to roll?

Likely not the frame, more the INS and related systems, stability augmentation comes to mind. Does the HUD look out of sync, as well?

Yes it does (and the VDI also) both of their pitch ladders got roll error, after pulling some SERIOUS G's.

After that landed the AC, repaired it, asked Jester to do an "INS go fine", but after a while when taxying, the VDI got the roll error again.

How do I get the HUD and VDI right ?

Yes it does (and the VDI also) both of their pitch ladders got roll error, after pulling some SERIOUS G's.

 

After that landed the AC, repaired it, asked Jester to do an "INS go fine", but after a while when taxying, the VDI got the roll error again.

 

How do I get the HUD and VDI right ?

Just a hunch, but when you land is your left slat extended and right one retracted? Been seeing that bug quite a bit.

As for G, its force isn't uniform throughout an airframe. It's a balanced system through force, some with the G, most against. Any surprise you can create shear forces well in excess of the limits. Keep it smooth.

To qoute Lunaticfringe on the matter of G limits:

With respects to the G limitation, the F-14's original sweep program was for CL max. The Navy didn't like the amount of flexing moment they witnessed in the wing, and had Grumman reprogram the system for Ps.

 

This gets into the G limitation for the reason that the test flight aircrews were told to treat it like a 13G airframe and fly it accordingly. Military aircraft are generally designed for stresses up to 1.5 times operational G limit (although there are exceptions: see F-16, having a substantially lower margin).

 

If 13G was the point Grumman was telling their pilots how to treat it- and you can be certain that the flight test aircraft were abused to make sure the state of the art construction/fabrication techniques used in the type, you're realistically looking at a design target of 8.5-9G.

 

As others have said elsewhere, it was the reality of the 70's economy that made the Navy begin worrying about long term purchases; some of this involved the nature of the flyaway price lockdown that Grumman offered to the Navy, which blew up in their face with the energy crisis. Had clearance not been given for the sale of the Tomcat to Iran, if memory serves, Grumman would have been forced to close its doors in 1977 because the prices were not permitted to change over the first few Blocks.

 

When you're up against that sort of situation, you're going to baby your favorite toys, because you may never get any more of them, and you're a long way away from being able to get a suitable replacement.

 

The flipside of this what was done to the machine in service. Hoser put 10+G on one avoiding Hawk Monroe, and did even worse at AIM/ACE. Muczynski put 10.2 on Fast Eagle 107, and there wasn't a single issue during the required inspection. A good pal of mine, former RIO, had his pilot put 9.5 on in a break turn during a FFARP setup, and nothing was found in the way of stress or damage- this was 1989 at this point, and was in an A from what would have been the 82/83 timeframe (if memory serves), and they'd all been pushed pretty good by this point during multiple excursions over the op limit.

 

Some of the electronics hated the stress that would be put on them, which caused many of the changes over the years in replacement versions of the boxes, but the machine itself was a beast. I know a lot of ex-crews, and I am hard pressed to find any of them who have recollection of overstress doing anything substantial

Yeah, but how do I get the HUD and VDI right ?

IRL this would ground the jet for definitely more than a day.

As I said, do not break it in the first place. ;)

Remember those are operational limits which were put in place to achieve absolute maximum longevity.

 

Had the deal gone as initially planned the operational limits would've been 8-8.5 G's as this was what the aircraft was designed for. It was however pretty soon discovered that the deal would be for less aircraft than assumed, and thus the limit was first reduced to 7.5 G's and then later 6.5 G's as even less aircraft were ordered.

Anyway, beyond 9-10 G the INS Gyro starts moving through the housing and if you go beyond that, the engines disintegrates, at least in DCS...

Well, if you try to keep it at 6-7 G you only sometimes pull more than 8G in the heat of battle or when trying to recover from an accidental dive.

Anyway, beyond 9-10 G the INS Gyro starts moving through the housing and if you go beyond that, the engines disintegrates, at least in DCS...

The engines & airframe should be able to handle over 12 G. But you're right about the electronics, which didn't really improve until the D version.

In either case, I think it's best to just keep G's below 9 as a general rule, esp. since maneuvering above that comes with no benefits.

The airframe was tested to 13 G without bending, so I doubt that.

 

So unless you went nuts and pulled over that then it shouldn't be airframe related.

14G's actually :v:

Well, if you try to keep it at 6-7 G you only sometimes pull more than 8G in the heat of battle or when trying to recover from an accidental dive.

Anyway, beyond 9-10 G the INS Gyro starts moving through the housing and if you go beyond that, the engines disintegrates, at least in DCS...

So that's probably the problem I'm having when the HUD and VDI get their ladders misaligned / inclined roll error, or complete malfunction - no doubts here, but:

- a repair seems to do nothing;

- is the "INS go now" command for Jester supposed to solve this ?

So that's probably the problem I'm having when the HUD and VDI get their ladders misaligned / inclined roll error, or complete malfunction - no doubts here, but:

 

- a repair seems to do nothing;

- is the "INS go now" command for Jester supposed to solve this ?

No that is the type of alignment, to have a precise INS alignment you need "fine", which takes 8 min.

Oh I see - I thought the "INS go now" was the most complete - back to manual I guess.

But you mention that, only for roll misalignment error, (and not for a complete malfunction where the VDI gets almost all black and the HUD loses its ladder and compass), right ?

What did you mean with the engines desintegrate ?

My engines only malfunctioned when I purposedly slammed them in the ground, (I'm still with the very first F-14 release...)

You need a new aircraft... my guess is normal repair does not fix this.

IRL this would ground the jet for definitely more than a day.

As I said, do not break it in the first place. ;)

Well it seems not.

After some experimenting, I've got more info:

- at the least once, the Jester command to "INS go now" placed the HUD and VDI correct again;

- either the roll error at the ladders, and the complete VDI blackout and HUD compass fail.

... but it can only align/corrrect/repair them, if you keep ground air supply and electric power on (during the all INS process), even after both of the engines are started ?

I though these 2 could be disconnected after both engines started.

Pic1 - VDI blackout and HUD compass fail.

Pic2 - roll error at the ladders