Pitts / Fixed Wing Flight Model Review

  • I am a private pilot (and fairly avid VR flight simulator user) and have been taking real-life instruction in a Pitts S-2C (and have some time in a Pitts S-2A) out of KSDL. I have been using the AeroFly Pitts S-2B as a training aid to supplement real-world flying. Site picture is perfect in VR, control response, and speeds are pretty close but there are some gaps that exist that I have identified going back and forth between real plane and simulator. These probably apply to other planes as well but I am limiting discussion just to the Pitts because that is all I have been using in Aerofly.


    In the air:


    1. Adverse yaw is very understated in AeroFly especially at slow speeds. Real Pitts has a lot of it.
    2. P-factor doesn't seem to be modeled in Aerofly. During climb at 110mph in real Pitts, if you take your feet off rudder pedals, plane will yaw by ~5 degrees per second to the left requiring constant right rudder. In fact, in a left climbing turn, no left rudder is needed - you only need to reduce right rudder pressure to stay coordinated. In AeroFly you need no rudder input, and you still track perfectly straight. The converse of this is when pulling power (for example abeam the numbers on landing) in the real plane the nose will move to the right requiring momentary left rudder input due again to p-factor.
    3. The model will not forward slip. Anything more than a mild aileron input and there isn’t enough rudder authority to prevent the aircraft from simply turning. The real Pitts forward slips incredibly well.
    4. In flare, the Aerofly Pitts floats a bit long. Even with the two-blade prop it should decelerate a faster and touch down.


    On the Ground – Landing Roll and High-Speed Taxis:


    The real Pitts is very sensitive on the ground during rollout and is easy to overcontrol. To get students used to this, the instructor has you perform high speed taxis on the runway (with tail down) at about 30mph. Goal is to first track straight down centerline which is surprisingly hard the first few times. The plane is easy to overcontrol with rudder. So, a slight deviation will result in you putting too much rudder in (and/or leaving it in too long which is probably the bigger issue) giving you a slightly bigger deviation the other direction, and so on. By swerve 3 you are on your way to running off the runway. Anyway, you eventually get the feel of this. Then he will have you move left of centerline 10 feet and then right of centerline, etc. Until you can do it without getting into any swerves. This whole procedure is performed with the stick completely back. In Aerofly, with the stick completely back, it is as if the plane is on rails. It is perfectly stable and the tailwheel is basically locked to the ground. This isn’t accurate. I have found you can sort of recreate the real instability in Aerofly by keeping the stick 3/4 of the way forward of neutral and keeping the speed low. In Aerofly, this will sort of recreate the swerve tendency that exists in real life. However, when you start picking up any speed in Aerofly, the stability increases regardless of stick position (for example, when you are still moving fast on landing roll). In real life, this swerving tendency also exists at higher speeds especially when decelerating on rollout. (The plane is obviously easier to control on takeoff with full power pulling the nose forward giving the plane more stability.)


    On the Ground – Regular Taxi


    In a real tailwheel plane when doing s-turns for example, once you input rudder and get the turn started, the plane continues to travel through the arc even after you neutralize rudder. In Aerofly, the turn stops as soon as you neutralize rudder.


    On the Ground – Takeoff


    Real-plane – Smooth full power with stick initially fully back combined with very gentle rudder inputs to keep tracking straight. Requires some constant right rudder presumably due to p-factor of the plane sitting at a high angle of attack in three point attitude and engine torque putting more weight and friction on the left tire. About the point you get to full power, release back pressure on stick slowly. The stick will move forward on its own through about the midpoint between full aft and neutral which will require a gentle forward pressure to push through this. If you push too hard through this (which I have done), you get a very pronounced and startling swerve to the left due to gyroscopic precession of the tail coming up which you inevitably overcorrect for giving you a swerve to the right! Anyway, get the plane in slightly nose high attitude and then keep tracking straight until it flies off. (When first learning, there is a very strong urge to just lift the plane off too early. This is because once the wheels get light, they sort of start hopping and skipping across the runway giving you the urge to just get off the ground and into the safety of the air!). This is obviously wrong, but I had a lot of mental trouble with this.


    In Aerofly, from the start there is still too much stability in the takeoff roll. Also, in Aerofly if you push the nose forward too quickly it doesn’t show the exaggerated gyroscopic forces. In fact, a while ago Aerofly actually had the force going in the wrong direction. When you would push the tail up, the plane would yaw to the right. I had submitted a bug and it seems like it was sort of fixed. But either way, the stability on takeoff in the sim is too much and the gyro force is understated.



    Conclusion


    I am by no means an expert in the Pitts. I am a student learning. But I have had the unique perspective of going back and forth between the real airplane and the simulator and trying to closely document the differences. I saw there is a professional flight model for the new R-22 helicopter. I was hoping there might be a professional flight model for fixed wing aircraft and also hope that this post may be useful. I would be happy to provide any more input and perhaps can take some GoPro video of the next flight to demonstrate some of the things I have mentioned in this post. Aerofly is a really great sim and I would love for it to get to an even more advanced place.


    One final note, the most accurate tail wheel sim I have used so far is the DCS P-51 Mustang. I obviously have never flown a real Mustang but prior to getting my tailwheel endorsement, I practiced heavily in the DCS Mustang – takeoffs and landings (normal and crosswind), high speed taxis, and wheel landings. I flew in a Super Decathlon for my actual tailwheel endorsement and found it very easy and intuitive. To me that is proof that the DCS flight model is done very well. It is mainly a military sim though. If Aerofly could recreate that on the civilian side it would be fantastic. For reference, my hardware consists of Warthog flight stick and throttle with 10cm extender on the flight stick to match real plane dimensions better. I have slaw device rudder pedals which was an upgrade from MFG Crosswinds. All of the tailwheel stuff I mentioned requires good rudder pedals to get value out of a good flight model.

  • Thank you for your feedback on the Pitts flight model. This is the first feedback in a long time that I'm receiving from an actual pitts pilot (or soon to be) :)

    I find that student pilots often still have a better attention to detail. Each time I flew a new glider I immediately noticed a lot of things different to other gliders but after some time you just get used to them and it becomes normal.


    When I set up the Pitts flight model I wasn't too too happy with the result and I didn't have a real pilot to work with, like I had with the Extra. Our Extra 330 LX flight model is much better I think, it should also handle differently on the ground. In our pitts the spring for the tailwheel might be too high, this way probably done intentionally to help users takeoff and land this aircraft with all sorts of devices. Imagine taking off the real pitts but all you have is the aileron stick, no rudder. That's at least 50% if not 75% of our clients right there and they all want to takeoff and not crash every single time. (The reason why it currently takes off too easy may well be that it was intended to do so)


    My biggest issues with the setup were the lack of data, videos and feedback. When I find videos of the pitts they are usually filming an aerobatic show and I don't see any of the pilots controls. Also we don't have much data on the Pitts, e.g. I would like to know how heavy the prop actually is, how quickly the tail comes up, e.g. if you hold the brakes and go full power, at what elevator deflection does the tail start to lift up. But I also didn't have a value for where the center of gravity is located, forwards/aft as well as height above ground? Does anyone know what the wing mass is? How heavy is the upper wing or the lower wing(s)? Whats the empty weight for just the fuselage (wings detached, fuel empty)? That is the sort of data I need to create an authentic flight model....


    The nose going into the wrong direction when you push the nose... that would indicate a different propeller spin direction?

    The p-factor as such is not a physical thing. There are multiple reasons for the aircraft to turn left or right on takeoff and they often cancel each other and change with airspeed and rotation speed of the propeller. Effects that are modeled in aerofly include: propeller torque, propeller wash on tail including twist, propeller gyroscopic forces (procession), wheel friction based on normal force and a few more (I need to prepare for new years eve, I'll skip the rest)

  • Hi Jan,


    Thank you very much for the prompt reply and happy new years eve! I am surprised you didn't have more input on the Pitts as the main stuff is generally right. The 3d model is perfect, the roll rate and general feel of the plane in the air is really good. Speeds are pretty close -- in actual plane I fly 16" MP on downwind and that's about 115-120mph. Same in the sim. Just the yaw and ground handling that could be enhanced. I'll see if I can research any stats you mentioned. A convenient thing is the Pitts I am training in is owned by a family member so easier access. Granted much of the info would need to come from Aviat or Hartzell. Also the 3-bladed prop has more drag when power is removed than the two blade in the Aerofly Pitts.


    I tried the Extra and the ground handling is still overly stable (i.e., turns don't want to stay turning). Having said that, as you mentioned above, without good rudder pedals it would be very difficult to handle tailwheel aircraft on the ground which would be frustrating to a lot of users. So I assume a lot of the stability was built in on purpose for that reason. As such, any changes to that would probably have to fall under an optional professional flight model or something like that.

  • The "professional flight model" vs. "easy flight model" option is a myth. The flight model is always the same highly realistic and fine tuned one, we just activate an assistance when you don't select the profi mode. The assistance stabilizes the vehicle, just like some real world helicopters that actually have a flight controller. It does not alter the physics in the slightest, it still is the exact same flight model, there are no two versions, just assisted and non assisted. The option to switch flight models has been invented by users...


    Having said that, there won't be a different flight model for the pitts either. We can indeed turn up the assistance for the rudder on a taildragger. When the user doesn't have pedals we can turn on an assistance that helps to keep the pitts straight. Our goal is to always get the aircraft as realistic as possible and then bridge the gap with some other means for beginners. The R22 profi mode option is the perfect example for that.

  • The "professional flight model" vs. "easy flight model" option is a myth. The flight model is always the same...

    Interesting to learn: then why use the term "profi" mode - doesn't this exacerbate a misconception?


    If you stick with "profi" I suspect you will continue to have many confused users moving forward. I am pretty confident most logically would assume activating "profi" mode gives a different flight model, not an "assissted" one as you clearly explained. Why not call it "flight assist" or something more accurate to what it really is or at least have popup text appear when you hover over the "profi" option to explain what it actually does? (Especially true if other planes may get the same treatment in the future)


    Just my 2 cents

  • Hi Jan,

    The "professional flight model" vs. "easy flight model" option is a myth. The flight model is always the same highly realistic and fine tuned one, we just activate an assistance when you don't select the profi mode.


    Yes, that makes sense that they are the same flight model and thanks for clarifying that. I guess to restate, if there is a raw underlying flight model that drives planes like the Pitts, but stability assistance is built in to some planes by default to make them more stable, perhaps there could be a setting to turn off the assistance similar to the R22 Profi button. Just a thought and maybe something for the future.


    Thanks!

  • There is no raw underlying flight model like in other sims. In Aerofly each aircraft defines its own rigidbodies (mass distribution), wings, airfoils, propellers, etc. and the physical behavior is a result of all the components working together. Our simulation technically doesn't even know it is simulating an aircraft, it's simulating individual mechanical parts that work together like a machine and some of these parts happen to create aerodynamical lift. The beauty of this is that we are never limited by a fixed set of parameters that describe an average airplane. Instead we can use the same building blocks to create new aircraft like the helicopter. And there are code parts or modules that act on the aircraft from the outside, this is where we can artificially stabilize the R22 for example.


    We named it profi mode because it is meant to be used by professionals or those that know how to fly the helicopter. The checkbox could have been labeled assistance with the checkbox state being inverted, default checked on.

  • Hi Jan,


    Makes sense. I am not trying to question to validity of the modeling. I also understand that it is arbitrary what the "Profi" check box is called. I guess here is my main point:


    You had mentioned earlier that you add stability to some planes including tailwheel aircraft so they can be used by all users. In the R22 you add stability but then give the users a Profi checkbox to remove it. The R-22 is the only craft that has that checkbox. Do you foresee ever adding that to other aircraft?


    Thank you!

  • Making assist the default for the R-22 is the best choice, the number of posts from people who have not tried to investigate how to fly a helicopter is surprising. I wonder how ‘outside people’ get on if they do not check out forums or YouTube?


    Aero4428 is the Pitts so hard to do a wheeler (main wheels only and not bouncy) landing in real life?

    Jan is the Ju52/3m any closer?

  • Aero4428 is the Pitts so hard to do a wheeler (main wheels only and not bouncy) landing in real life?


    Hi Overloaded,


    I have not done a wheel landing in the plane and the instructor doesn't teach them. The general consensus is they aren't commonly done in the Pitts for a few reasons. First, the plane sits in three point at less than stall attitude. So, you don't really do full stall landings anyway and as such your touch down speed is already fairly high ~75-80mph. I believe it is the high touchdown speed more so than the short wheelbase that makes it difficult to control on the ground. A wheel landing would have the mains touching down at near 100mph which I believe would make everything that much more sensitive. Also, the Pitts from what I understand is naturally a very good crosswind plane (presumable from the high touchdown speed, short wings, and lower than normal 3 point attitude) so from what I am told there isn't a good "reason" to do them in the Pitts and those two points make it not that common to do. However, I have seen youtube videos of people doing them in Pitts so its obviously done.


    I did a lot of them in the real Super Decathlon and the behavior was very similar to doing them in the DCS Mustang. Was actually easier in the real plane for me which again is why is see so much value in simulation even for stick and rudder training.

  • We named it profi mode because it is meant to be used by professionals or those that know how to fly the helicopter. The checkbox could have been labeled assistance with the checkbox state being inverted, default checked on.

    In my opinion that would be a good thing to do.

    I assumed 'profi' is either some technical term I'm not familiar with, or an uncommon abbreviation of 'professional' or 'proficient'.

    It is otherwise meaningless to me, as a casual player.

    'assistance' (or some variation of it) is plain English and easy to understand.

    1. P-factor doesn't seem to be modeled in Aerofly. During climb at 110mph in real Pitts, if you take your feet off rudder pedals, plane will yaw by ~5 degrees per second to the left requiring constant right rudder. In fact, in a left climbing turn, no left rudder is needed - you only need to reduce right rudder pressure to stay coordinated. In AeroFly you need no rudder input, and you still track perfectly straight. The converse of this is when pulling power (for example abeam the numbers on landing) in the real plane the nose will move to the right requiring momentary left rudder input due again to p-factor.
    2. The model will not forward slip. Anything more than a mild aileron input and there isn’t enough rudder authority to prevent the aircraft from simply turning. The real Pitts forward slips incredibly well.

    Both points are definitely weak areas in FS2. If it's e.g. the 172 or the DR400, both don't need any rudder to be kept straight, even at stall speed and full power. Side slipping both isn't realistic either.

    Another weak point are the way too powerful ailerons in a stalled condition. E.g. in the Extra and the Pitts you should be able to steepen/flatten the spin attitude with aileron input.

    In FS2 opposite aileron will reverse the spin direction! (while maintaining full aft stick and full pro spin rudder).


    Nevertheless, the immersion is still unmatched and it's still the only sim I can really and always fully enjoy.

  • In my opinion that would be a good thing to do.

    I assumed 'profi' is either some technical term I'm not familiar with, or an uncommon abbreviation of 'professional' or 'proficient'.

    It is otherwise meaningless to me, as a casual player.

    'assistance' (or some variation of it) is plain English and easy to understand.

    Profi is the German abbreviation for professional.

  • In our pitts the spring for the tailwheel might be too high, this way probably done intentionally to help users takeoff and land this aircraft with all sorts of devices. Imagine taking off the real pitts but all you have is the aileron stick, no rudder.

    Just curious if the spring rate is something that's easy to adjust in the model? I suspect that a lot of the ground stability that doesn't match real life could be due to this. Not saying you should lower it for everyone, just curious if this is something that's easy to change if I figured out how to mess with the flight model?


    Thank you Jan!

  • Thanks Jet-Pack (IPACS). Now, if I make adjustments to this file, but then Aerofly makes enhancements to the Pitts in the future, will it overwrite the file and my adjustments? Or, will my adjustments "break" it from updating in the future? I guess neither would be ideal.


    Is there a way I can copy the whole Pitts folder into a new folder called "Pitts Experimental" and have the plane display? I tried this before but the copy of the plane never showed up in the main menu allowing me to fly it.

  • Thanks Jet-Pack (IPACS). Now, if I make adjustments to this file, but then Aerofly makes enhancements to the Pitts in the future, will it overwrite the file and my adjustments? Or, will my adjustments "break" it from updating in the future? I guess neither would be ideal.


    Is there a way I can copy the whole Pitts folder into a new folder called "Pitts Experimental" and have the plane display? I tried this before but the copy of the plane never showed up in the main menu allowing me to fly it.

    Yes, any update could reset any changes made to the default aircraft files.

    What you can do is move the entire pitts folder to your user documents directory. Steam doesn't know about that path and shouldn't touch it and your progress should be safe there. It might be that steam adds the default pitts back in and that you will have either two aircraft or some other strange issues until you "get rid" of the default folder again.


    For a more permanent solution check out how I made my cessna mod... https://www.aerofly-sim.de/download/download-aeroflyfs2

    basically copy the folder, rename it, rename the tmd, tmc and tmb files inside it and you should be good, too

  • Jet-Pack (IPACS) This is terrific. I actually got the ground handling to a pretty good spot by reducing the spring constant. Had a couple more questions if you have time.


    1. What is the best way to model propeller drag in the x-direction associated with the blades flattening out? If so, what's is a parameter that would increase this? In the real plane, when you reduce power and the blades flatten, there is a pretty rapid deceleration due to the drag of the flat blades hitting the air. I can sort of fake this by increasing Cdx of the fuselage but then that affects all other air speed and climb rate metrics (which are actually already pretty good). I really need to add drag that only occurs when the propeller blades flatten (go to negative AoA with respect to the air hitting them). The one setting I think is CdAlpha for the propeller blades. Any other ideas of how to best accomplish this?
    2. Is there a way to make any of the parameters in the tmd file a function of other parameters. For example, making a spring constant some function of forward velocity, etc?


    Thanks!

  • 1. There onces was a fake airbrake installed, that section is currently not being used but you could reactivate it for exactly this purpose.

    In my tmd file that block starts at line 422 (near "PropellerAirBrake"), if you just remove the double slashes // in front of the lines to enable that block you should have more drag when going to idle.


    We have not quite experimented enough to find out why our propellers are too slippery at idle. I think they are windmilling too efficiently.

    Maybe the engine itself needs more drag, maybe there are certain blade tip effects we are not accounting for yet, maybe the real engine actually cuts the fuel completely like in a car when going down hill... Maybe the stall on the negative angle of attack range is too soft and should cause more drag... as I said we have not fully tested everything and it is hard to verify the numbers. Any pilot would just say: the propeller acts more like an airbrake but we have to investigate and understand why and then also reproduced that in the simulation.


    2. No, constants are actual constants. What are you trying to do?