Flight Model & engine issues

[YoYo]

I collected all (I think) reported problems by users. To summarize the observed flight model and engine performance issues:

- the flaps give too small drag, in a smooth approach to landing with flaps at even 50 degrees (which is even too big) and the full IDLE engine, the plane is able to accelerate (how is possible?), at 50 degrees it should almost brake in the air and recive even stall in such a situation with the engine on IDLE position
- the engine descends from RPM too slowly and accelerates RPM too slowly, I have never been able to get ATA 1.0 also which is strange (full power Throttle and max propeller), so it brakes too slow in the air with flaps open too
- the rudder is too sensitive
- model with wind greater than 5kts behaves very unstable (espesially near the ground), as if it was made of paper (ultralight) and not a 1,3 ton machine, it is too sensitive to any gusts, it is not a natural behavior, shakes him terribly, pls use for test real weather (for example from Peenemunde airfield (Germany) EDCP)
- the model during straight flight rotates to the left all the time (do roll), airplanes are designed to be aerodynamically stable, a well-trimmed airplane flies straight even with wind (hands and legs off), it is impossible here, it rotates to the left all the time (even with no wind), as if the ailerons were deflected to the left (maybe center wasn't reseted?), 
- difficult to keep a straight take-off line if there is any wind present, wheel lock in MSFS helps but it doesn't work 100%, good example of taildragger is AH C140 for MSFS.

[YoYo]

revision:   have never been able to get ATA 1.0 also which is strange (full power Throttle and max propeller  

[YoYo]

Example of take off issue during crosswind.

Airfield EDCR, runway 07, wind direction 360 (sidewind), 12 kts , so near calm wind. Test containts tailwheel lock + full rudder to right, left, and free (+ no tailweel lock). This is a bit of a hardcore example, but it shows that regardless of the rudder angle, the model behaves in such a way that it turns to one side, sharply. This is a problem noticed by many and concerns the behavior of FM in the model along with the wind.

 

[Deleted Account]

Two questions for you:

Where are you collecting those user reported problems from and have you ever flown a BF108 in the real world?

I don't want to sound dismissive, but the BF108 handles very poorly in crosswind condition in the real world. Pilots told us, that unless the wind was on runway heading, they wouldnt fly the bird if the wind was stronger than 7 knots.

[tinyalien]

I can confirm the constant left roll tendency. Can't say anything about the real plane but that doesn't seem right.

[YoYo]

1 hour ago, gumbyger said:

Two questions for you:

Where are you collecting those user reported problems from and have you ever flown a BF108 in the real world?

I don't want to sound dismissive, but the BF108 handles very poorly in crosswind condition in the real world. Pilots told us, that unless the wind was on runway heading, they wouldnt fly the bird if the wind was stronger than 7 knots.

It all depends on the experience of the pilot :). Flying even in higher winds is possible, but it often requires a mix of even aileron deflection. I don't want to blame you 100% here because I also realize that MSFS itself still has a problem with this and the crosswind problem is not solved (especially visible to the taildragger, its a long story still), but the fact that some models handle it a bit better. Collected issues are from the official MSFS Forum as well as the SoH Forum from several users.

What I noticed too - center of gravity is fully back, it doesnt help. Changing it completely to the front (even to a negative value) is much better. Also in the weight we have marked passengers in the back 340lb, which are not visible :). All in all, they might not be needed there.

[YoYo]

Btw. What the pilots complained about, as with the Bf-109, was the short wheelbase of the landing gear. But this should cause the tilt to the wing immediately and the circle on the ground with such a wind. We have something else here.

[Deleted Account]

Heya again!

Firstly many thanks to all of you for such great engagement on the product over the weekend!

We have discussed the community comments regarding the FM and in particular the difficulties users are experiencing with the take-off roll. We have an number of pilots within our development and testing teams that have experience on tail draggers and light aircraft that have tested the FM extensively. We also discuss flight characteristics with pilots of the specific aircraft we are modelling where possible which we have been fortunate enough to do with BF108. Tailwheel aircraft are difficult to fly, which is why a number of aviation authorities require pilots to have specific endorsements on their licence to fly one.

      In this instance the requirement to use aileron and rudder, even in still wind conditions, is correct due to the fundamental aerodynamics of a tailwheel aircraft. Although there are many factors affecting the stability of the aircraft, especially with the use of CFD, we have highlighted the main points below.

•       Tailwheel aircraft are dynamically unstable due to a CofG behind the main landing gear. This means any inertia acting on the aircraft will drag the aircraft in the direction the CofG is trying to push the aircraft. The slightest crosswind or torque reaction from the engine will start an imbalance.

 

•      The factor which is affecting the turn/roll tendencies most significantly in this aircraft is gyroscopic procession. This effect is more pronounced in tail wheel aircraft as the tail leaves the ground. It is also at a critical point in the take-off roll where the aircraft is just reaching full control authority effectiveness, so raising the tail too early can be detrimental to directional control.

 

•       The aircraft crosswind is also significantly less than most modern GA aircraft. Another point to note with aircraft of this era was they were generally not limited to taking off on specific runway headings. Airfields of the time were generally large areas of open grass with approximate manoeuvring areas defined, this meant that pilots could take-off almost directly into wind.

We believe in providing the highest level of realism with regards to flight dynamics and have discussed if using alternative flight models available within the sim would be beneficially. For now, we have decided not to make any adjustments. Our reason for this is simple, one of the attractions to flying tail wheel aircraft in real life is the requirement to learn a new ‘style’ of flying, and we wish to keep that authenticity here. We are also one of a handful of developers using the sims excellent CFD model. This doesn’t mean that other models are wrong, but it is something we as sim pilots will need to adjust to if we want a realistic experience.

There are numerous articles and refences online to further explain the unique aerodynamic qualities of a tail wheel aircraft and how to fly them online. We think this video explains most of the tendencies particularly well: https://youtu.be/E3q2Swzi2q8

We do not want to negate any feedback and are testing all feedback / comments and will make changes where necessary, but hopefully this gives some more insight into our thinking / evidence behind our workings!

 

 

[YoYo]

Many of what you're saying is true, but keep in mind that MSFS is not a 100% realistic pilot training simulator (unlike P3D Professional, for example) so if the 100% real environment isn't what it should be, then that some functions and parameters on paper or in Excel do not exist here, because they do not work. The model is supposed to simulate a lot of real behavior on the simulator engine, which is not perfect either, so maybe some weird things just need to be hidden or tweaked. I also compare the flight model behavior to other great simulators like DCS and P3D and unfortunately MSFS still falls short for taildraggers. 

What users definitely need is to be able to fly it, and from what I read, some people have a problem with it. This applies mainly to take-off roll and unnatural rotation around the longitudinal axis during flight. Both things should be slightly tweaked. So that in an unnatural environment, which is a simulator, the plane behaved quite naturally. 😉

[YoYo]

Btw. I checked your flight_model.cfg, but why you dint use those values from MSFS SDK:

• ground_crosswind_effect_zero_speed
• ground_crosswind_effect_max_speed

Lack of this parameters can bring take off problems. Maybe its a good idea to match these values to the model?

[Deleted Account]

10 minutes ago, YoYo said:

Btw. I checked your flight_model.cfg, but why you dint use those values from MSFS SDK:

• ground_crosswind_effect_zero_speed
• ground_crosswind_effect_max_speed

Lack of this parameters can bring take off problems. Maybe its a good idea to match these values to the model?

We used those parameters during testing and they made zero differences with the CFD modelling.

Although the use of CFD allows us to simulate a realistic flight model we appreciate this doesn't appeal to everyone, however, this allows us to make use of the sims built-in assist options. To counteract some of the more unique tendencies of the aircraft we suggest enabling the following found in "Assistance Options>Piloting" turn Auto-Rudder, Assisted Landing and Assisted Takeoff ON.

[YoYo]

19 minutes ago, gumbyger said:

We used those parameters during testing and they made zero differences with the CFD modelling.

Ok, I'll try it too, those prameters are interesting too (make the tires stick to the ground more):

ground_high_speed_steeringwheel_static_friction_scalar and ground_high_speed_otherwheel_static_friction_scalar

https://docs.flightsimulator.com/flighting/html/Content_Configuration/SimObjects/Aircraft_SimO/flight_model_cfg.htm

Edited February 27, 2023 by YoYo

[YoYo]

Those parametres works, Im sure 100% 💪:

ground_crosswind_effect_zero_speed = 
ground_crosswind_effect_max_speed = 

I'm looking for a good setup.

Those not, maybe they are better work for aircraft with nosewheel.

ground_high_speed_steeringwheel_static_friction_scalar = 
ground_high_speed_otherwheel_static_friction_scalar = 

 

[YoYo]

After my testing, those settings looks very interestong for me in current MSFS 💪.

(in flight_model.cfg)

[FLIGHT_TUNING]
.....

ground_crosswind_effect_zero_speed = 45.57
ground_crosswind_effect_max_speed = 91.13

pls back with info. 

For take off:

Trim: +1
Flaps: 10
Lock tailweel: LShift+G (my MSFS)
position yourself against the wind as much as possible

This function works for sure, and it's worth adding that Asobo is aware of this problem, which is why it added it in SU10 to be used by developers, especially taildraggres. Try it.

[YoYo]

The first good opinion about those value: http://www.sim-outhouse.com/sohforums/showthread.php/129884-Inibuilds-Bf-108-Taifun-Released-2-24?p=1308067&viewfull=1#post1308067 

I moved the minimum forward speed a bit when the rudder starts working, which also after 2 days of my flying still gives a very nice and realistic result (you need still the rudder but the plane during take off run and landing is more stable). If you want, you can add it in the next build. 💪

Edited March 1, 2023 by YoYo

[No4124485]

What about the too little drag with fully extended flaps? With landing gear down and flaps fully down, the plane behaves like an efficient sail plane and it is very difficult to lose altitude without exeeding the flap speed limit, a light gust or thermal can catapult you into the air in this configuration. Maybe the gear drag could be increased to reflect some resistance?

[No4124485]

So I have made a test flight (version 1.0.1) to check the drag, my plane configuration was 170lb on pilot seat (rest of the payload empty) and all tanks at about 70% (reserve tank at 100%). I took the throttle fully back so it was in idle, when I reached 150km/h I watched for the plane to get slower. At a vertical speed of 0m/s (continually pulling the yoke back) it took me a whole minute to get the airspeed from 150km/h to 120km/h. Considering the idle spinning propeller adds a certain amount of drag on its own, even without flaps or gear, it should decelerate much faster, I don't know where the energy comes from. 

Even on final approach with landing configuration (gear down, flaps 30°), throttle at idle when I dipped the plane a bit down down, I was instantly at 150km/h again and when pulling the nose back up, it took a great amount of time to lose that speed again even with gear and flaps down. Adding flaps and gear has only a negligible effect on drag.

 

[Deleted Account]

The drag is at what we expect it to be. Even at idle thrust the engine will produce thrust. If you want to slow down, get to 185 KMH and then use flaps; that´s what our real world pilots advised.

[Ala13_Kokakolo]

I tried the new version today. With 7 knots crosswind (50 degrees so less than 7knots) the plane sinks left wing whatever I do. I know is a sensitive plane, but I do not believe this plane cannot take of with a sligtly crosswind breeze.  

[Ala13_Kokakolo]

 I added a section of the manual of one of the existing 108, the Nord 1002 Pingouin II.

[Ala13_Kokakolo]

11 hours ago, Ala13_Kokakolo said:

I tried the new version today. With 7 knots crosswind (50 degrees so less than 7knots) the plane sinks left wing whatever I do. I know is a sensitive plane, but I do not believe this plane cannot take of with a sligtly crosswind breeze.  

Forget what I said there. I was testing today in diferent crosswind speeds. I can take of with 90 degree wind (from the right) up to 10 knots 

[Ala13_Kokakolo]

11 hours ago, Ala13_Kokakolo said:

I tried the new version today. With 7 knots crosswind (50 degrees so less than 7knots) the plane sinks left wing whatever I do. I know is a sensitive plane, but I do not believe this plane cannot take of with a sligtly crosswind breeze.  

Forget what I said there. I was testing today in diferent crosswind speeds. I can take of with 90 degree wind up to 8 knots with a bit of aileron, ruder and break. 

[Ala13_Kokakolo]

I have tested 

ground_crosswind_effect_zero_speed = 45.57
ground_crosswind_effect_max_speed = 91.13

The plane behaves similarly to the original FM but the crosswind effects happen somehow more progressively with the plane speed rather than abruptly when reaching a given speed. I do not know which of both is more "real", tbh, but the more progressive one gives me more "warnings" to start counter it. Still is quite a challenge to take of with crosswinds up to 8knots, anything above that speed is impossible if you do not have a wide enough pist to change direction towards the wind.

[YoYo]

30 minutes ago, Ala13_Kokakolo said:

I have tested 

ground_crosswind_effect_zero_speed = 45.57
ground_crosswind_effect_max_speed = 91.13

The plane behaves similarly to the original FM but the crosswind effects happen somehow more progressively with the plane speed rather than abruptly when reaching a given speed. I do not know which of both is more "real", tbh, but the more progressive one gives me more "warnings" to start counter it. Still is quite a challenge to take of with crosswinds up to 8knots, anything above that speed is impossible if you do not have a wide enough pist to change direction towards the wind.

Exactly, that's the point of this post. You can react and it happens more gradually, not suddenly, like a huge gust from some hurricane that completely pushes the plane to the side 😉.

[YoYo]

On 3/4/2023 at 11:13 PM, gumbyger said:

The drag is at what we expect it to be. Even at idle thrust the engine will produce thrust. If you want to slow down, get to 185 KMH and then use flaps; that´s what our real world pilots advised.

Yes, drag of flaps is present on better level after the 1.0.1 update and landing behavior is much better. Thx for this.