MiG-19 FM Dynamic stability comparison to MiG-15 and F-86

[HWasp]

I have tried to compare the dynamic stability of the modules above (the oscillations after a certain pitch control input).

!!Test was done and measured with time compression set to 1/16 (time slowed to 1/16)!!

My method was to trim the planes to 1G flight at around 250 - 260 kts, then full aft stick until AoA = 15 (infobar), then release stick to neutral and observe the oscillations

!!Test was done and measured with time compression set to 1/16 (time slowed to 1/16)!!

I've drawn a chart to show the resulting oscillations:

Edited April 24, 2022 by HWasp

[HWasp]

As you can see on the chart, all 3 planes make similiar oscillations in pitch, but the MiG-19's oscillations have much less amplitude, and return to the initial state extremely quick.

The MiG-19 does not have a pitch damper or anything similiar.

Is there any reason, why the 19 should have such high dynamic stability?

 

Please see tracks attached (Slow time to 1/16 or more to be able to see what is happening)

MiG-15Dyn1.trk MiG-19Dyn1.trk F86Dyn1.trk

[TLTeo]

16 minutes ago, HWasp said:

Is there any reason, why the 19 should have such high dynamic stability?

Higher wing loading perhaps? You could test that by comparing with the Mig-21 as well. If wing loading is the reason, then the Fishbed will be even more stable.

[HWasp]

1 hour ago, TLTeo said:

Higher wing loading perhaps? You could test that by comparing with the Mig-21 as well. If wing loading is the reason, then the Fishbed will be even more stable.

MiG-21 is much less stable.

I tested the F-5 with the Pitch Damper ON though :

[HWasp]

Overall I think the MiG-19 has the least amount of oscillations (at least regarding non FBW modules)

It returns to the original AoA twice as fast as the other modules, and that seems quite strange to me. 

[MiG21bisFishbedL]

It's been a while since I've read anything on the minutia of the Farmer series. I seem to recall that, due to bad PIO in testing, the MiG-19 did have some kind of mechanical or passive means of dampening inputs. It could be part of the ARU-2V FCS.

[HWasp]

1 minute ago, MiG21bisFishbedL said:

It's been a while since I've read anything on the minutia of the Farmer series. I seem to recall that, due to bad PIO in testing, the MiG-19 did have some kind of mechanical or passive means of dampening inputs. It could be part of the ARU-2V FCS.

ARU-2V does not dampen or stablize, it just changes the ratio between the stick input and elevator motion according to speed and altitude.

(Less elevator motion for a given stick input as speed increases simplified)

[TLTeo]

Yeah, the Mig-19 definitely did not have a pitch damper. Even most Mig-21s didn't have one, iirc it was introduced in the -bis. @myHelljumperthoughts?

[MiG21bisFishbedL]

4 hours ago, HWasp said:

ARU-2V does not dampen or stablize, it just changes the ratio between the stick input and elevator motion according to speed and altitude.

(Less elevator motion for a given stick input as speed increases simplified)

Okay, thanks for correcting me on that one, at least.

Still, could it be a side effect of it making those adjustments? Just throwing things at the wall.

[TLTeo]

I doubt it. The pitch gearing shouldn't change at all if you're at such low speeds, you should always get the full elevator authority in that regime.

[LowRider88]

Just some pre-research guessing from me, but perhaps the stability of the plane is with respect to the Center of lift vs the Center of weight, at your test speed, the size and number of fences and other lift devices, and also perhaps due to the span of the wings extending further back in the later aircraft.

The only way to know if the stability is correct is if it matches what ever info may be scrapped from the flight manuals.

[Koty]

Keep in mind the 19P has an extended nose with a radar in it compared to the original day-light fighter. This brought a notable change in stability.

[Aviator78]

On 4/24/2022 at 8:57 PM, HWasp said:

Is there any reason, why the 19 should have such high dynamic stability?

I'd approach the issue from the other end: Why do the other fighters show these insanely excessive pitch oscillations?

I know this comment will draw a lot of fire from the fans, but here goes nothing: Many DCS fighters show unrealistically excessive pitch oscillations. Old-school fighters were designed to be dynamically stable, and at a certain speed they just fly like on rails, not considering meteo effects.  Pitch oscillations like in DCS would create massive amounts of drag in real life flight.

From what I can tell from my flying background, the DCS MiG-19 is actually more realistic in that aspect than other modules.

[HWasp]

1 hour ago, Aviator78 said:

I'd approach the issue from the other end: Why do the other fighters show these insanely excessive pitch oscillations?

I know this comment will draw a lot of fire from the fans, but here goes nothing: Many DCS fighters show unrealistically excessive pitch oscillations. Old-school fighters were designed to be dynamically stable, and at a certain speed they just fly like on rails, not considering meteo effects.  Pitch oscillations like in DCS would create massive amounts of drag in real life flight.

From what I can tell from my flying background, the DCS MiG-19 is actually more realistic in that aspect than other modules.

 

I don't think other DCS modules have "insane" pitch oscillations at all. What aircraft did you fly, that would suggest otherwise? Also control inputs made during the tests were not exactly "normal operation".

For me, the other modules feel more realistic in this regard, compared to anything I've flown or seen flying. 

Do you think the MiG-15 or the F-86 have a problem with oscillations? For me they are totally controllable and very stable.

 

[Aviator78]

10 hours ago, HWasp said:

 

I don't think other DCS modules have "insane" pitch oscillations at all. What aircraft did you fly, that would suggest otherwise? Also control inputs made during the tests were not exactly "normal operation".

For me, the other modules feel more realistic in this regard, compared to anything I've flown or seen flying. 

Do you think the MiG-15 or the F-86 have a problem with oscillations? For me they are totally controllable and very stable.

 

You are right, I was thinking of MiG-21 and MiG-29 primarily, those are/were really bad in terms of pitch oscillations, haven't flown the 29 lately though, there might have been FM improvements in recent updates. The MiG-15 feels a little better in this area, it has other quirks though. 

I'm not saying the MiG-19 FM is perfect, but I like the 'stiffness' of the control input vs. reaction precision. It feels a lot more like an 8 tons fast jet that pretty much goes where you point it.

My impressions stem from F-4F and Tornado full-flight sim time and the usual single engine piston aircraft.

[HWasp]

1 hour ago, Aviator78 said:

You are right, I was thinking of MiG-21 and MiG-29 primarily, those are/were really bad in terms of pitch oscillations, haven't flown the 29 lately though, there might have been FM improvements in recent updates. The MiG-15 feels a little better in this area, it has other quirks though. 

I'm not saying the MiG-19 FM is perfect, but I like the 'stiffness' of the control input vs. reaction precision. It feels a lot more like an 8 tons fast jet that pretty much goes where you point it.

My impressions stem from F-4F and Tornado full-flight sim time and the usual single engine piston aircraft.

MiG-29 had issues with the stability augmentation system not being simulated correctly, as it turned out, now it is completely tame imo. (unless you take off before the warm-up of the system is done )

Both F-4 and Tornado have Stability Augmentation System, I don't think they are really good for a direct comparison to old MiGs. Sounds interesting though. Did you have the opportunity to test the extremes in those sims?

[Aviator78]

3 hours ago, HWasp said:

Did you have the opportunity to test the extremes in those sims?

No, I was just interested in flying some basic aerobatics and a few traffic patterns. Another guy without any flying experience very quickly put the F-4 into a flat spin though and crashed.

[Tiger-II]

I think people forget that older aircraft had it designed as part of the "DNA" to be relatively stable in the absence of pitch stability or FBW.

The reason modern jets are crammed with stability augmentation is because the aircraft are designed to be unstable by default, to such an extent a human could not actually fly them. Ergo, they are designed to be flown using FBW control systems, and as part of that, require stability augmentation as they want to depart controlled flight.

Older aircraft needed to be able to be flown by humans, so their stability is actually greater than that of modern aircraft. Where older aircraft have a problem is they can be departed from controlled flight more easily, but this does not mean they are not stable inside the normal flight envelope.

Edited August 7, 2022 by Tiger-II

[HWasp]

On 8/7/2022 at 8:16 AM, Tiger-II said:

I think people forget that older aircraft had it designed as part of the "DNA" to be relatively stable in the absence of pitch stability or FBW.

The reason modern jets are crammed with stability augmentation is because the aircraft are designed to be unstable by default, to such an extent a human could not actually fly them. Ergo, they are designed to be flown using FBW control systems, and as part of that, require stability augmentation as they want to depart controlled flight.

Older aircraft needed to be able to be flown by humans, so their stability is actually greater than that of modern aircraft. Where older aircraft have a problem is they can be departed from controlled flight more easily, but this does not mean they are not stable inside the normal flight envelope.

 

 

Sorry, but what are you talking about?

I have made a comparison to the MiG-15 and F-86. 

Where did you see modern FBW aircraft with relaxed stability mentioned here?

Excessive stability due to very far forward CG has a large performance penalty IRL, I'd be interested, what is the normal CG range for the 19P compared to 2 other modules mentioned.

 

Other than this, it is also interesting for me, that I am having better results flying and fighting in the 19 module with ARU-2V set to manual with maximum control deflections to stick input ratio (low speed mode) even at high speeds.

MiG-21s did suffer accidents due to pilot induced oscillations when their ARU-3V failed. This makes me wonder why the system is even installed in the MiG-19, if it is perfectly controllable without it even at highs speeds. (For me the MiG-19 is less sensitive in pitch with the ARU set to maximum control deflection to stick input ratio manually, than many other modules in normal config at high speeds) ((no curves!))

Edited August 22, 2022 by HWasp

[HWasp]

With ARU-2V set to manual mode and to maximum control deflection / stick input ratio (low speed mode), still around 40% of the max pitch input is needed to achieve 8 Gs over 1000 km/h.

I'm not claiming that this is wrong, but I certainly find it strange, that the aircraft is still this easy to control in this config. If the real aircraft was this tame and easy to fly in this configuration, it raises the question for me, why they implemented the ARU-2V at all? 

MiG_19ARU_Man.trk

Edited August 22, 2022 by HWasp

[Tiger-II]

I think you don't understand why the ARU-2V is present at all.

It has nothing to do with aircraft handling, and everything to do with control input vs. deflection, and artificial feel.

The ratio changes as the aircraft accelerates in order to reduce the relative deflection of the elevator vs. stick input, in order to give a fairly consistent control response throughout the speed range.

If that system didn't exist, then as the aircraft accelerates, the elevator would become more and more sensitive. That is not to say too sensitive that a pilot couldn't control the aircraft, but sensitive in that he would start experiencing larger control response than desired. It is this effect that could lead to overcontrol of the aircraft, or PIO in pitch, in certain situations.

The other problem is that with the larger control effectiveness at higher speeds, it would become possible to start overstressing parts of the aircraft inadvertently or during certain manneuvers, so to reduce these problems, they reduce the deflection of the elevator with speed.

As for the relevence of modern FBW designs vs. older aircraft, you need to read my post again then go and do some study. It's quite relevent to explaining older designs. If you're my age (40-something) then FBW aircraft would be the norm. Historically, aircraft were designed to be very stable and easy to fly in the absence of computer control, stability augmentation, and other aids (that is not to say such aircraft don't or didn't have bad behaviors, such as nasty, sudden, and sometimes violent stall/spin entry for example because they sure did).

There is this great misnomer that aircraft must be squirrely or hard to fly. That is absolute nonsense. People with less thans 10 hours flying experience were flying Spitfires in WW2. Whenever I hear someone tell me an aircraft is "hard to fly" I laugh them out the building. Maybe they are not so good at piloting them?

"The F-104 is hard to fly and will kill you instantly". Oh yeah???

Good old-fashioned stick and rudder skills are all that are required to fly anything. Knowledge doesn't mean much if you can't fly the aircraft.
 

 

Edited August 22, 2022 by Tiger-II

[HWasp]

1 hour ago, Tiger-II said:

I think you don't understand why the ARU-2V is present at all.

It has nothing to do with aircraft handling, and everything to do with control input vs. deflection, and artificial feel.

The ratio changes as the aircraft accelerates in order to reduce the relative deflection of the elevator vs. stick input, in order to give a fairly consistent control response throughout the speed range.

If that system didn't exist, then as the aircraft accelerates, the elevator would become more and more sensitive. That is not to say too sensitive that a pilot couldn't control the aircraft, but sensitive in that he would start experiencing larger control response than desired. It is this effect that could lead to overcontrol of the aircraft, or PIO in pitch, in certain situations.

The other problem is that with the larger control effectiveness at higher speeds, it would become possible to start overstressing parts of the aircraft inadvertently or during certain manneuvers, so to reduce these problems, they reduce the deflection of the elevator with speed.

As for the relevence of modern FBW designs vs. older aircraft, you need to read my post again then go and do some study. It's quite relevent to explaining older designs. If you're my age (40-something) then FBW aircraft would be the norm. Historically, aircraft were designed to be very stable and easy to fly in the absence of computer control, stability augmentation, and other aids (that is not to say such aircraft don't or didn't have bad behaviors, such as nasty, sudden, and sometimes violent stall/spin entry for example because they sure did).

There is this great misnomer that aircraft must be squirrely or hard to fly. That is absolute nonsense. People with less thans 10 hours flying experience were flying Spitfires in WW2. Whenever I hear someone tell me an aircraft is "hard to fly" I laugh them out the building. Maybe they are not so good at piloting them?

"The F-104 is hard to fly and will kill you instantly". Oh yeah???

Good old-fashioned stick and rudder skills are all that are required to fly anything. Knowledge doesn't mean much if you can't fly the aircraft.
 

 

 

 

Hey, thanks for the condescending reply, great way to start the usual sh.tshow

To be honest, the only jet I ever flew was the 737 (400 and 800) irl, and obviously my experience of the extremes is from the full flight simulator, so I'm not a 19 expert of course, but let me tell you, that the 737 being a f.... airliner is much more sensitive in pitch at high mach high altitude, and it is much more prone for oscillations in the low speed high aoa region (obviously I don't know what she does at 550 kts on the deck...). 

I am looking for a constructive debate, I don't claim that I know how the real MiG-19P flies, so let's try and keep this civil. 

I am comparing the MiG-19 module to the ED MiG-15 and F-86. For me those 2 behave much more natural and believable while also being completely stable and controllable.

Do you have either of those modules for comparison?

Edited August 22, 2022 by HWasp

[HWasp]

8 hours ago, HWasp said:

 

I am comparing the MiG-19 module to the ED MiG-15 and F-86. For me those 2 behave much more natural and believable while also being completely stable and controllable.

 

 

Just to be perfectly clear, this is regarding the subject of the topic only, not a general comparison. I am not claiming, that those 2 module's FMs are superior overall, this is just an opinion about this particular aspect of the fm. 

 

10 hours ago, Tiger-II said:

 

There is this great misnomer that aircraft must be squirrely or hard to fly. That is absolute nonsense. People with less thans 10 hours flying experience were flying Spitfires in WW2.

 

 

Also, again, to be very clear, this topic is NOT about it being difficult to fly or not, it is about the specific subject of dynamic stability, how the aircraft behaves after an abrupt control input compared to some other modules. (Are the F-86 or MiG-15 difficult to fly in DCS? No, not at all.)

BTW, a lot of these 10 hour Spitfire pilots died during training, so it might not be the best example. Although, of course it was not the "flying" but the take-off and landing, that got them mostly...

[HWasp]

Thank you for the FM improvements last patch! I have just tried it, and I think it is great, feels much more realistic.

Very nice to see, that problems are being adressed, looking forward to the MiG-23 and F-15!

Edited August 27, 2022 by HWasp

[Hummingbird]

Excited to hear about a change here, as the 19 felt way too stiff in pitch last I tested it. So really looking forward to trying her out again once I get back to flying