reverse ground effect

I'm just going to leave this video here, since I just got through flying the landing and creating the video from it. In the meantime, Yo-Yo has commented. In my experience, the -29 never feels like it suddenly gets pulled toward the ground. I'm not using any special equipment like stick extensions, etc. Just paying attention to the airspeed, altitude, tach reading, sink rate, in anticipation of the roundout point.

The TRK used to create this video is attached.

MiG-29S Landing Krymsk.trk

... But it clearly shows that the plane changes its trim IGE as the stick is fixed.

...

I wouldn't stress the FM-designers "defending his baby". I think this (his/their) programming has depth, and to be honest more and more I come to the conlusion that it is of a quality some of us might underestimate a bit (just my personal opinion right now). Let's not be offensive on the guys in this particular case. I have reasons for saying that, because I am currently not sure what caused the change in pitch angle (which can be seen when using F2 view, talking about my TRK).

For me two reasons are imagineable:

First:

Due to the inexact trim status (because it is nightmare to really find the right amount/setting for a nice and constant pitch angle), the aircraft was in a pitch-down just before the threshold ANYWAY (flying its phugoid).

This circumstance would by consequence decrease lift and increase the sinkrate, which by the way can be clearly seen on the VSI.

Second:

Due to the pitch down moment when using trailing edge flaps, I can imagine that this moment increases when ground is closing.

For both the same counts: As can be seen clearly, I did not counteract this pitch down tendency, because I aimed for not "disturbing" the happenings.

What I am a bit surprised is the fact that when entering the ground effect, the lift on the main wing should in my thinking increase, but which is not noticeable. I think this increase is "killed" by the stronger pitch angle decrease (which is about 3 degrees, which is a lot when talking about airflow). Long writing, short summary: Nice story, but anyway I will leave for the time beeing and start up my Viggen. :D

MiG-29 pilots are tought to pull the stick at flaring, and they just counteract the tendency of reducing G due to reducing AoA IGE. So, it's absolutely intuitive for them.

Exactly that. I remember when someone asked about the pronounced pitch down on the 767 when reducing thrust to idle during the flare and I honestly thought that this doesn't happen.

On my next flight I consciously observed my yoke movement during the flare and I was surprised that there was a pitch down moment and not exactly subtle.

It requires considerable force on the yoke to keep the nose from dropping, but once you get used to it you don't notice it.

Due to the pitch down moment when using trailing edge flaps, I can imagine that this moment increases when ground is closing.

Why should there be a pitch down moment from the flaps once they have stopped moving?

All right, after some serious testing today, here's a track with 21 traffic patterns/landings. Speeds, altitudes, power and pitch settings do vary, as I was experimenting back and forth what was going on here.

On my first landing I initially thought 'See, there it is, ground sucking effect', but after analysing the whole mission and the MiG-29s flight characteristics, I come to the conclusion that it's a combination of the "elevator loss of effectiveness in ground effect" AND a coincident power idle. My tests showed that the MiG is VERY susceptible to power changes, they induce significant pitch changes. If the elevator effect and the power-induced pitch change happen at the same time close to the ground, there is a rapid increase in sink-rate that cannot be countered quickly enough with stick aft movement, it literally happens in the fraction of a second.

That being said, my track shows three things. First, the pitch axis is way too sensitive in DCS. I'm using a TMW with 10cm extention and 90% saturation on the pitch axis plus a 20% curve. As long as you have the MiG trimmed right on speed on final and during the flare, everything is fine, but as soon as you are out of trim and give some elevator input, things become very whobbly, you get oscillations very easily. This became very apparent during touch and go and keeping the nose up at around 260km/h, pitch easily varies between 5-10° NU in a second. This of course also affects the flare and the let-down to the runway. If you are trimmed on the spot, things are great, not so if trim isn't spot on, as a nose up command can make you balloon nose up easily. Please compare my stick movement with the RL video of the MiG-29 landing posted here in this thread. If I had used inputs like this, I would have been all over the place. Using even more saturation or curves would make the MiG an airliner in a fight.

Second, ground effect seems to be too weak or almost non-existant, and that's quite odd with a lifting body like the MiG-29. Landings 3, 5, 6, 7, 8, 9, 11, 13, 14, 16, 17, 18, 19 and 21 all showed good speed, good NU pitch, yet sinkrates increased quite rapidly and touch down was harder than expected. In real life these would have been grease jobs. So my conclusion is that ground effect is way too weak and does not cushion a touchdown in the MiG-29. Speed was always between 280-310 km/h in a clean aircraft with fuel between 3000 - 1000kg, so don't tell me I was too slow and stalled out.

Another thing I noticed was that the mentioned elevator loss of effectiveness in ground effect doesn't apply if you come in with power and do not go to idle - see landing 20. In DCS this is probably due to the nose up effect of the power, but shouldn't the elevator effect still be there and require a stick aft movement to avoid the nose to pitch down nevertheless? Here it didn't (or the stick inputs were very minor, but had great effect -> see hypersensitive pitch)

Also, pitch and resulting sinkrates in ground effect (or the lack of) seem exaggerated. A minor change in pitch of 1-3° resulted in significant increase in sinkrate, which feels wrong compared to what I've experienced in real aircraft so far.

So, fine, there doesn't seem to be a negative ground effect, but no (significant) positive ground effect either, and there definitely is the need to look at pitch/stick behavior of the MiG-29. It is a PC simulation after all, and I figure 45cm extentions can not be mandatory to fly this module.

MiG-29_Landungen_003.trk

What is the exect number of the track you experienced this effect?

According to my notes I took you can see it in the first take-off, and especially during patterns/landings 13 and 14, but I think my track shows that in all patterns pitch control can get out of a pilot's comfort zone very easily. Just compare stick input and resulting pitch output, there are situations where my pitch movements were excessive, especially during turn to final and on final, even though I used very minor stick movements.

Two more tracks.

The first one shows oscillations when you don't trim. This seems logical, if you (have to) use curves, at some point your precise, smooth stick input becomes a broad, rapid input. That's what curves do. The other solution would be to decrease saturation, but then you wouldn't get full deflection. For the MiG-29 that would mean less than max. g at high speeds.

The second one shows the positive effects of trimming on pitch input, yet still you can see some uncommanded pitch-outs during turn to final and during flare.

And speaking of pitch, is it realistic that gear up/down induces these severe pitch changes?

And with regards to my second landing, a nice example of missing or too weak ground effect. Pitch was good, AOA was good, speed was good (310 km/h with a clean a/c, 3400kg fuel), flare was good, I should have been in ground effect, so why did I drop like a stone there? I know I put power to idle early, but I came in fast and had the right speed during flare... it shouldn't dump like a brick here. If this was in an F-104 or a MiG-21, ok, but this is a clean MiG-29!

MiG-29_no_trim_oscillations.trk

MiG-29__trim_just_small_oscillations_bad_landing.trk

Two more tracks.

And with regards to my second landing, a nice example of missing or too weak ground effect. Pitch was good, AOA was good, speed was good (310 km/h with a clean a/c, 3400kg fuel), flare was good, I should have been in ground effect, so why did I drop like a stone there? I know I put power to idle early, but I came in fast and had the right speed during flare... it shouldn't dump like a brick here. If this was in an F-104 or a MiG-21, ok, but this is a clean MiG-29!

At high AOA your thrust has a huge vertical lift component

At high AOA your thrust has a huge vertical lift component

Not at 10° NU and throttle almost at idle.

If that was true, all aircraft would have to be flown with power on all the way to the ground, which is not the case (except for aircraft with BLC like F-104 or MiG-21). Normally shortly before or during the flare you cut the power.

Not at 10° NU and throttle almost at idle.

 

If that was true, all aircraft would have to be flown with power on all the way to the ground, which is not the case (except for aircraft with BLC like F-104 or MiG-21). Normally shortly before or during the flare you cut the power.

Not in Fulcrum. Read again the manual as it specificaly warns about that. Do not cut the power before TD:

https://forums.eagle.ru/showpost.php?p=4462766&postcount=154

Also BLC doesn't prevent the airframe gliding capability - just that it's landing speed is higher without power.

btw: These two pages of manual exactly describe the DCS Mig-29 experience. I may agree it's much harder to handle than other DCS aircraft but whatever you come up with, it's there already described.

Not at 10° NU and throttle almost at idle.

 

If that was true, all aircraft would have to be flown with power on all the way to the ground, which is not the case (except for aircraft with BLC like F-104 or MiG-21). Normally shortly before or during the flare you cut the power.

Not in Fulcrum. Read again the manual as it specificaly warns about that. Do not cut the power before TD:

https://forums.eagle.ru/showpost.php?p=4462766&postcount=154

 

Also BLC doesn't prevent the airframe gliding capability - just that it's landing speed is higher without power.

 

btw: These two pages of manual exactly describe the DCS Mig-29 experience. I may agree it's much harder to handle than other DCS aircraft but whatever you come up with, it's there already described.

Yup, and on top of the loss of “lift” by cutting power it’s also important to note that the thrust line is very low and causes a pitch up coupling with power. So by decreasing the throttle above the the runway, it increases the pitch down tendency that’s the subject of this thread. I’m sure you can do it by cutting throttle if you have extra speed and anticipate with upward elevator, but no reason to make your job harder then it needs to be:)

About pitch control:

Two tracks of traffic patterns with Su-25 and Su-27. These modules are good examples of what I as a pilot would expect from an aircraft in terms of pitch management.

Please mind that I have never flown the DCS Su-27 in a pattern before, yet here I was easily able to do it based on all my other flying experience. The DCS MiG-29 is a pilot killer compared to these two. So can anyone explain why it has to be this way in the MiG-29?

Su-25_Landungen_001.trk

Su-27_Landungen_001.trk

It's all good... except that Su-25 and Su-27 are way different from MiG-29. Su-27, for example, has neutral stability and the taileron is controlled with ACS, though MiG-29 is naturally stable and has direct controlled taileron...

Yes, sure. As one of my IPs once said when transfering on a new type: "It's just another f***** plane man!" My point with the Su-25/Su-27 comparison was that there are certain general handling characteristics that a pilot can and must expect. Some general control authority is one of them. If a plane was as nervous as the DCS MiG-29, it wouldn't be very successful but outright dangerous. The tracks also show that I do not have POI with these planes.

Unfortunately, I can not replay your tracks in the current version - something is changed in the world - but, regarding your description, the oscillation is PIO, and I suspect that it is due to the joystick force loading. Using MSFF2 I just freeze it after touchdown, and the plane is stable at main wheels as a rock (see the video).

Which video do you mean? This one?

It clearly shows at 0:22 and 0:30 and especially around 0:35 how pitch control gets away from the pilot.

But let's assume it is my joystick that causes POI (which it clearly doesn't with many other DCS aircraft!). What settings can you recommend beyond buying a FFB or a 45cm extention? 10cm + 90% saturation + 20% curve + 5% dead zone don't seem to cut it... well, no, on most DCS aircraft they do... :noexpression:

Here is PIO on takeoff. TRK file by me.

Mig29 takeoff oscillation crash ACME_WIdgets.rar

I can not recommend any non-linearity for pitch. The only case I can use saturation is a formation flying in Spitfire or P-47 where the full stick travel is much more than necessary to enter a stall. But in this case the linearity is kept.

Otherwise all non-linear things obviously cause PIO.

That consequently means the DCS MiG-29 cannot be flown properly without a really large stick extension or a ffb stick. I don't think this is the right approach for a PC flight simulation, where there are certain hardware limitations for most users. And still the question remains why other DCS aircraft can be controlled very easily with normal PC flight simulation hardware, whereas the MiG-29 can't. I doubt that the real MiG-29 is so much harder to control compared to other real aircraft either. This is something you should reconsider.

FFB itself is nothing to improve joystick loading. .... For example, for MiG-29 you can trim the plane at 300 kph on final and then you will need only to pull it more or less during flaring.

Hey Yo-Yo!

Would you accept my (some others) wish for a setable/changable "trim rate per click" settting in the "special options" for the MiG-29?

Its a computer game, flown by peoply with short sticks, mostly having no practical experience in a real MiG-29, so .... come on man! :)

@Pilot Ike

To a certain extent, they're all ''just another airplane'', they all fly by the same basic principles. That doesn't mean they all have the same characteristics or that some of them don't have ''unusual'' characteristics.

As for ''oh they would never build something this way''. Yeah, they would, and they did, and they have dozens of times over the last 120 or so years they've been flying with some being outright dangerous and/or poorly designed, yet they still entered mainstream usage (F-104 anyone?).

In the MiG-29's case, it is clearly not a ''pilot killer'' and if its export history is amything to go by, it's very popular. And in virtually every case anyway it's just a case of training. A REAL pilot, particularly for combat aircraft, spends more than ten minutes skimming a manual before flying his plane. He's also thoroughly instructed on any quirks or ''need to knows'' ahead of time.

It's not a Cessna 172. It does not fly like it. Civil aircraft, whether GA or commercial, are designed explicitly for stability and ease of flight. Military aircraft are explicity designed for INSTABILITY to enhance maneuverability, and since they often have unique ''design challenges'' (detachable external stores, short takeoff runs, supersonic flight, supermaneuverability, EM signature reduction, etc etc etc) that GA aircraft do not have, they often end up with quirks that would make a GA aircraft unsuitable.

For military aircraft, barring trainers, stability/safety merely needs to be sufficient that the pilot and control systems can compensate for any deficiencies or quirks. Reverse ground effect is not even a deficiency, it's just a characteristic that a real pilot of said aircraft would know about well ahead of time and already know how to deal with it.

On 11/13/2020 at 9:35 PM, TOViper said:

 

Hey Yo-Yo!

 

Would you accept my (some others) wish for a setable/changable "trim rate per click" settting in the "special options" for the MiG-29?

Its a computer game, flown by peoply with short sticks, mostly having no practical experience in a real MiG-29, so .... come on man!

 

 

+1 

Trimm in the 29 currently feels like two drunk men that are fighting over a vodka bottle. I have no idea why the MiG wobbles so much in DCS. 

17 hours ago, Cmptohocah said:

+1 

Trimm in the 29 currently feels like two drunk men that are fighting over a vodka bottle. I have no idea why the MiG wobbles so much in DCS. 

All in Mig FM is totally off, flying this one is just frustration, it's like you said " feels like two drunk men that are fighting over a vodka bottle" :), su-25 FM is great.

It's sad that one of the best Fighter of it's time in RL, is just a nightmare to fly in this game