L-39 Flight Model

First let me say that the graphics and beauty of this aircraft is stunning inside and out, but I'm going to risk all of my reputation power on this comment (Oh wait, I have no reputation power)...but I'm going to say it any way, I'm a bit disappointed in the flight model/physics/dynamics. Its a bit too tight, like its on on rails for my liking. I prefer more of the illusion of floating, roll and movement with stick movement and direction changes. I wouldn't be too concerned, but this is the PFM, so I'm assuming no changes are forthcoming? Nevertheless this is an incredible aircraft that will see a lot of hours in the sky.

Do you have any real life experience to compare it to? And I ask that not in any way to be rude, just out of curiosity for the potential discussion :)

Hello. No experience, well 1hr in a 172, but that's not much help. This is purely subjective. I personally prefer a looser feel. For me, on my system, of the aircraft I own, the jets with the best feel/illusion of flight are the SU25, SU27, A10C, F-86 and the Mig21(before 1.5) not necessarily in that order. I have no knowledge of aircraft design, physics etc and Im sure that on paper, the build and design of this aircraft is modeled as close to the real thing as possible, but we cant experience the real thing, all of the stimuli of a real aircraft behind a monitor, so I like a plane that will create the best illusion of flight that we can possibly...even if on paper its not correct.

To each his own I guess, but personally I would prefer the FM to be as close to correct as possible? I seriously doubt an L-39 is going to feel "loose" compared to a single engine Cessna.

I have no experiance in an actual L-39 unfortunately. I do have close to 1000 in single and multi Pistons which really means nothing in judging a flight model of an aircraft I have only seen fly from the ground. The DCS L-39 is very stable which make sense being as its trainer, The stalls are pretty brutal though, I was trying some slow flight (around 160 kilometers p/h) holding level and I got to say it feels like balancing on a needle point at the brink of snap rolling inverted. I even tried an inverted spin and mucked up the recovery and recovered at around 50' down from around 10k, very believable inho even though I'm not sur the little turbine could stay running during a maneuver like this. In the end I find it convincing and fun to fly

Hello. No experience, well 1hr in a 172, but that's not much help. This is purely subjective. I personally prefer a looser feel. For me, on my system, of the aircraft I own, the jets with the best feel/illusion of flight are the SU25, SU27, A10C, F-86 and the Mig21(before 1.5) not necessarily in that order. I have no knowledge of aircraft design, physics etc and Im sure that on paper, the build and design of this aircraft is modeled as close to the real thing as possible, but we cant experience the real thing, all of the stimuli of a real aircraft behind a monitor, so I like a plane that will create the best illusion of flight that we can possibly...even if on paper its not correct.

So in other words you want the FM to be what you feel like it should be. This is not a rational position. The FM is what it is, some will like it, others will hate it. That doesn't matter. The plane should behave as close as possible to how the real plane behaves.

Not having a single hour on a real plane does not prevent to have several thousands hours on the simulator and feel something weird on a specific airframe. :music_whistling:

I actually feel something weird with the FM too - push/pull the stick max and you do cobras. :D

Not having a single hour on a real plane does not prevent to have several thousands hours on the simulator and feel something weird on a specific airframe. :music_whistling:

 

I actually feel something weird with the FM too - push/pull the stick max and you do cobras. :D

How many of those thousands of hours did you fly on a simulated L39 air-frame? Just because something 'feels' wrong doesn't necessarily make it wrong. In fact due to the small, straight wings and a small air-frame I would think that the aircraft could probably perform something very similar to a Cobra maneuver. It is after all an aircraft that is used in real world aerobatics flying and racing.

Hi,

The problem of people don't flying real aircraft is how they cannot set the flight control setting correctly in the sim.

I have never flew the L-39, but I have +4000h on propeller and jet liner.

I set the Y,X and Z axis as follow :

Deadzone : 5

Both saturation : 100

Curvature : 40

I cannot judge the flight model of the L-39, but I am pretty satisfied with those preleminary settings.

Read also the real flight manual available on this forum. The nose was bouncing slightly during an approach at 200 km/h until I discovered that the speed should be around 230 km/h. The aircraft is more stable like that.

Also, try to roll at the maximum at slow and high speed. You will notice a difference in flight path stability.

This aircraft has maybe not the best flight model, but as far as I know, it seems to be close to the real one.

Cheers,

Vincent

I am going to try a deadzone because it is very twitchy when trimmed out, I wonder if its hardware related IE some play on my pitch axis

I also think that the FM will undergo some tweaks before the beta turns into release :)

I cant disagree with that. If you are going to build a specific plane it only makes sense to build it accuratley in all aspects and I should probably learn to appreciate and be satisfied with how the model behaves knowing that it is accurate. I am just wondering if the devs take into account that a sim no matter how accurate it is, cant reproduce the physiological inputs and feel of real flight. So, should they...and maybe they do, take into account in the design, a need for a sense subtle movement in the aircraft at all speeds. Some of the mods do this better for me than others, but thats just me. For someone else it will be different. I am going to tinker with the axis settings as the other poster has mentioned.

FYI, as far as I know ED have at least one former L-39 pilot on staff (or near to it), and will definitely have access to quite a few more, and will also have access to a lot of data. It's going to be as good as they can make it.

Besides, it's a beta release.

Unfortunately in the Royal Canadian Air Force we don't fly the L-39. But I can tell you that this plane feels more realistic, and more similar to our Hawk trainer (CT-155) than the actual Hawk module itself.

All in all it's very difficult to simulate something so complex as a flight model properly on a desktop pc.

I have experience in 0-, 1-, 2- and 4- engined planes, recips, turboprop and jet. Been flying for just about 30 years now and stopped really counting my hours at 14k ( and that was a while back )

One of the most difficult things to model properly in a sim is the transfer of a real life feel and ease of use of systems and flightmodel to a program. Let me give a few examples..

When I program or use the FMS in my "office""my hands and fingers have it's own memory and inputs can be made instinctively and "on the fly". When I do that in a PMDG sim it takes up a a lot more of my resources, attention, and physically hands on then in real life. An A10 pilot will most likely have the same feeling when hitting all the buttons in the sim. It's soo much easier in the real plane.

Same goes for something like using the gear in the Mig 21. Doing it in the plane will be a matter of fact and won't require as much attention as hitting a few keys or trying to hit the right spots with the mouse while trying to keep your TIR stready.

When you talk about flight model there is again a very big discrepancy between sim and rl. Some planes have high control forces or a big difference between roll and pitch inputs. Different feel between high and low speed flight. And ofcourse the lack of physical feedback. A lot of sims model a high speed stall with one wing just dropping violently. Since there is a complete lack of feedback you ( Well me personally.. ;-) ) find yourself too quickly at the limits with a consequent departure of normal flight.. ;-).

Since there are a lot of different hardware setups, settings and curves it's very difficult to recreate the right "feel" for everyone. Personally I do have the feeling that the flight-model is acting a bit strange in some parts of the flight enveloppe but since I have no experience in the -39 or any other of the DCS planes I can't really comment on that right now. Since the release of the beta there will be a few more people flying it who do have -39 experience who can hopefully make some educated comments about the flight model.

On a personal note, I like where the FC3 planes are going. Proper performance of plane, systems and weapons. Using radar and other systems take the same amount of effort to use as irl. Giving an experience that is comparable to real life. By making the interface to make the systems do what you want them to do easier you counter the extra attention required to do so behind a screen with hotas and mouse.

I am exaggerating now >> Just think of yourself driving a stickshift.. in the car it's done without even thinking about it. If you model it on a pc you need to hit a key for the clutch, then shift , then ease the clutch back up. When you do that with a mouse you will have all your attention on just accomplishing that task. Easing that whole input procedure with a single up and down keystroke or keybinding makes sense to me. To me the FC3 planes are like that.

Like I said this is my personal take on how far complex systems should be modelled in the sim. If you want to mouseclick all over the pit to make it do what you want, go for it!

Best explanation i have read so far on ANY sim forum. I'm ex-Airforce myself and i hold a "civilian" licence as well. I'm trying to explain to wifey (who flies with me) why it's hard to hold a nice steady climb after take off on a sim because im busy clicking the mouse all over the place. I have a G940 and i did assign a lot of things on my hotas such as gears, flaps, speed brakes, like most people i'm sure. Having purchased a Track IR made a huge difference because you don't have to play with your thumb on a hat to look around the cockpit and outside and it gives a much more natural feel when you fly. Best example i can give is when i flew choppers. In real life: no problems, In DCS? i do ok but you wouldn't know i'm a real pilot cuz i'm missing that "feel" more so during take off and landing. One thing: it's great for IFR training! No vertigo! (a vivid incident back in the '80's comes to mind here...) Anyhow thanks for this great reply. Gonna have the wife read it!

Thank you for your kind words.

I've been thinking about this a lot. Been flying Sims since I got my zx spectrum. First flight lesson was in 1984 iirc. To me a flightsim should recreate the feel and ease of action, not necessarily all actual buttons, dials and other controls in minute detail. I do love it when the fm, performance, weapons and radar perform as they should though. In the DCS world I'm probably a minority, welcome to our small niche.

On a related note. I was surprised that the Albatros requires very little rudder input. I had to set the curve to 30 and I still have to only touch it very gently in turns. Unless I'm doing something crazy the ball is pretty much centered almost all the time. Did you guys notice ? What you think about that ? I'm no pilot so I'm just asking out of curiosity for other people's opinions.

On a related note. I was surprised that the Albatros requires very little rudder input. I had to set the curve to 30 and I still have to only touch it very gently in turns. Unless I'm doing something crazy the ball is pretty much centered almost all the time. Did you guys notice ? What you think about that ? I'm no pilot so I'm just asking out of curiosity for other people's opinions.

Yes, thats true for all controls.

As soon as i use more then 50% input, the aircraft is shaking horribly and doesnt react to steering input.

Why is that ? Is it possible to check if the control surfaces deflection with 100% stick and rudder input is the same like on the original plane ? :joystick:

Also the trim control is a bit too sensitive for my taste.

I cant really trim it exactly, one click up is too much, one click down is too much in the other direction.

Yes, thats true for all controls.

As soon as i use more then 50% input, the aircraft is shaking horribly and doesnt react to steering input.

Why is that ? Is it possible to check if the control surfaces deflection with 100% stick and rudder input is the same like on the original plane ? :joystick:

 

Also the trim control is a bit too sensitive for my taste.

I cant really trim it exactly, one click up is too much, one click down is too much in the other direction.

Yeah, it's not quite what I mean though. It's not a question about sensitivity but rather the fact the plane flies nicely coordinated pretty much by itself which surprised me. I expected that a lot more legwork would be required :)

PS: I based this expectation on absolutely no experience or expertise what so ever :lol: It's not a bug report or anything I was just curious to hear from someone more experienced/educated than me if the L39 flies really this nicely which I did not expect from an airplane without a fly-by-wire system. ;)

I have a question about the FM: when I push the stick to either side to start a turn, I noticed that the slip ball remains dead centered without me ever having to use the rudder pedals. Normally one has to use ailerons and rudder to make a coordinated turn, but no rudder needed in the L-39. Does it have some auto-rudder functionality mechanically built into it, or is it just so benevolent in its flight characteristics, or is it a bug in the FM?

I have a question about the FM: when I push the stick to either side to start a turn, I noticed that the slip ball remains dead centered without me ever having to use the rudder pedals. Normally one has to use ailerons and rudder to make a coordinated turn, but no rudder needed in the L-39. Does it have some auto-rudder functionality mechanically built into it, or is it just so benevolent in its flight characteristics, or is it a bug in the FM?

Yeah, that's exactly what I'm talking about. :)

So to test it a bit a set up a quick 8 minute test flight with quite intense weather (20 m/s gale strength crosswind). Note how the ball remains pretty much centered during the entire flight without any rudder input what so ever (only full during takeoff and landing). That doesn't seem right.

edit: bah, I removed the track cause it's pretty broken. In reality I spent 8 minutes in the air but when viewing the track the plane just ends up in a grass 15 seconds after start and does not move anywhere. Well I guess you will have to test it for yourself.

Yeah, that's exactly what I'm talking about. :)

So to test it a bit a set up a quick 8 minute test flight with quite intense weather (20 m/s gale strength crosswind). Note how the ball remains pretty much centered during the entire flight without any rudder input what so ever (only full during takeoff and landing). That doesn't seem right.

 

Runway closed you say? We will see about that! :pilotfly:

Sorry lanmancz, didn't see your earlier post about the magic rudder. But now that 2 have raised this question, hopefully some answers will be coming. I am curious to find out if this behavior is realistic.

Sorry lanmancz, didn't see your earlier post about the magic rudder. But now that 2 have raised this question, hopefully some answers will be coming. I am curious to find out if this behavior is realistic.

Yeah, well, I'm starting to think that it's probably a WIP thing. Subject to change. Meanwhile, hey we got L39C with FCS :lol::pilotfly:

All in all it's very difficult to simulate something so complex as a flight model properly on a desktop pc.

 

I have experience in 0-, 1-, 2- and 4- engined planes, recips, turboprop and jet. Been flying for just about 30 years now and stopped really counting my hours at 14k ( and that was a while back )

 

One of the most difficult things to model properly in a sim is the transfer of a real life feel and ease of use of systems and flightmodel to a program. Let me give a few examples..

When I program or use the FMS in my "office""my hands and fingers have it's own memory and inputs can be made instinctively and "on the fly". When I do that in a PMDG sim it takes up a a lot more of my resources, attention, and physically hands on then in real life. An A10 pilot will most likely have the same feeling when hitting all the buttons in the sim. It's soo much easier in the real plane.

Same goes for something like using the gear in the Mig 21. Doing it in the plane will be a matter of fact and won't require as much attention as hitting a few keys or trying to hit the right spots with the mouse while trying to keep your TIR stready.

When you talk about flight model there is again a very big discrepancy between sim and rl. Some planes have high control forces or a big difference between roll and pitch inputs. Different feel between high and low speed flight. And ofcourse the lack of physical feedback. A lot of sims model a high speed stall with one wing just dropping violently. Since there is a complete lack of feedback you ( Well me personally.. ;-) ) find yourself too quickly at the limits with a consequent departure of normal flight.. ;-).

 

Since there are a lot of different hardware setups, settings and curves it's very difficult to recreate the right "feel" for everyone. Personally I do have the feeling that the flight-model is acting a bit strange in some parts of the flight enveloppe but since I have no experience in the -39 or any other of the DCS planes I can't really comment on that right now. Since the release of the beta there will be a few more people flying it who do have -39 experience who can hopefully make some educated comments about the flight model.

 

On a personal note, I like where the FC3 planes are going. Proper performance of plane, systems and weapons. Using radar and other systems take the same amount of effort to use as irl. Giving an experience that is comparable to real life. By making the interface to make the systems do what you want them to do easier you counter the extra attention required to do so behind a screen with hotas and mouse.

I am exaggerating now >> Just think of yourself driving a stickshift.. in the car it's done without even thinking about it. If you model it on a pc you need to hit a key for the clutch, then shift , then ease the clutch back up. When you do that with a mouse you will have all your attention on just accomplishing that task. Easing that whole input procedure with a single up and down keystroke or keybinding makes sense to me. To me the FC3 planes are like that.

 

Like I said this is my personal take on how far complex systems should be modelled in the sim. If you want to mouseclick all over the pit to make it do what you want, go for it!

Great post.

Yeah, that's exactly what I'm talking about. :)

So to test it a bit a set up a quick 8 minute test flight with quite intense weather (20 m/s gale strength crosswind). Note how the ball remains pretty much centered during the entire flight without any rudder input what so ever (only full during takeoff and landing).

(steady) wind will have absolutely no effect on ball behaviour.

As for rudder requirements, I can't say if the L-39 is correct, but the theory of not needing much isn't necessarily wrong.

Differential ailerons can be used to reduce/eliminate adverse aileron roll when entering/exiting a turn. When in a turn, if an aircraft is very directionally stable but not very laterally stable, rudder may not necessarily be required either.