_____________________________ VERSION 3.1.0 UPGRADE NOTES Author: Andreas Zenner _____________________________ This is a documentation of the changes I made to vitos' beautiful model of the MiG-15 in order to improve its realism. Feel free to participate, point out any errors you may find in here and have fun flying it! Cheers Andreas Table of Contents _________________ 1 Sources 2 Tweak factors 3 Flight dynamics model .. 3.1 Lift ..... 3.1.1 change in lift due to ground_effect ..... 3.1.2 eta_L ..... 3.1.3 calculations/aero/coefficients/CL ..... 3.1.4 lift due to alpha and flags ..... 3.1.5 delta lift due to alpha and mach ..... 3.1.6 delta lift due to speedbrake ..... 3.1.7 delta lift due to elevator deflection .. 3.2 Drag ..... 3.2.1 change in drag due to ground effect ..... 3.2.2 drag due to alpha and flaps ..... 3.2.3 drag due to altitude ..... 3.2.4 Induced drag ..... 3.2.5 Drag due to mach and altitude ..... 3.2.6 Drag due to gear ..... 3.2.7 Drag due to fuel tanks .. 3.3 Side ..... 3.3.1 Side force due to beta .. 3.4 Roll ..... 3.4.1 Roll moment due to beta ..... 3.4.2 Roll moment due to yaw rate ..... 3.4.3 Roll moment due to difference in ground effect .. 3.5 Pitch ..... 3.5.1 Pitch moment due to alpha and elevator ..... 3.5.2 Pitch moment due to pitch rate / alpha rate ..... 3.5.3 Pitch moment due to gyro effect .. 3.6 Yaw ..... 3.6.1 Adverse yaw ..... 3.6.2 Yaw moment due to roll rate ..... 3.6.3 Yaw moment due to gyro effect 4 Aircraft systems .. 4.1 Control surfaces ..... 4.1.1 Elevator symmetry ..... 4.1.2 Elevator and rudder range at high speeds ..... 4.1.3 Aileron booster .. 4.2 Engine ..... 4.2.1 Engine idle thrust ..... 4.2.2 Engine respond time .. 4.3 Gear friction .. 4.4 Instruments ..... 4.4.1 Airspeed indicator ..... 4.4.2 Turn indicator ..... 4.4.3 Radiocompass 5 Simulation .. 5.1 Sound ..... 5.1.1 Engine rpm ..... 5.1.2 Wind noise ..... 5.1.3 Touch down noise ..... 5.1.4 Random sounds at startup ..... 5.1.5 Is the sound bug gone? ..... 5.1.6 clickfix in Nasal1.nas .. 5.2 Damage due to limit violation ..... 5.2.1 Maximum g-load ..... 5.2.2 Landing gear ..... 5.2.3 Maximum speed for gear and flaps ..... 5.2.4 Engine flame out .. 5.3 Appearance ..... 5.3.1 3D model ..... 5.3.2 Czech aerobatic livery .. 5.4 Replay .. 5.5 Chase view .. 5.6 Metar string .. 5.7 Menu -> MiG-15bis -> Configuration ..... 5.7.1 Rudder exponent ..... 5.7.2 External tanks, headsight, magnetic compass, flight stick ..... 5.7.3 Vertical speed at touchdown ..... 5.7.4 Standard atmoshere ..... 5.7.5 Throttle crack sound effect .. 5.8 Aircraft info 1 Sources ========= - [1] "Samolet MiG-15bis. Tekhicheskoe opisanie. Letnye kharakteristiki samoleta. (Kniga 1)". You can find it online, for example here: [http://airspot.ru/book/file/1108/MIG15bis.pdf]. This is what vitos referenced as well. - [2] "Aircraft UTI MiG-15, Description Book One, Flight Charakteristics", an english manual for the MiG-15 trainer version. Most parts of it are translated copies from [1]. Both aircraft are identical except the second pilot seat, less gun power, less tank volume and an older version of the engine (RD-45 instead of the VK-1). As I don't speak russian, this was very helpful. I bought it at a flight manual online shop. - [3] "Aerodynamik des Flugzeuges, zweiter Teil", written by Schlichting and Truckenbrodt (german). Some of the FDM calculations are based on empirical or theoretical formulas for flight performance estimations found in this book . - [4] "Dubbel - Taschenbuch für den Maschinenbau", a generic engineering handbook. 2 Tweak factors =============== In many cases the available data used to determine the flight dynamics isn't perfect, so for the fine tuning you need to (or: "might as well") rely on intuition. I inserted some properties called "/fdm/jsbsim/tweak_factors/..." at several locations in the fdm code, to make it easier to play around with some flight characteristics in real time while flying. The sound and the damage detection routines can also be altered by tweak factors. Feel free to experiment with them and make suggestions for different settings in the forum. 3 Flight dynamics model ======================= 3.1 Lift ~~~~~~~~ 3.1.1 change in lift due to ground_effect ----------------------------------------- The ground effect acts like an air cushion that gives extra lift to the airplane and reduces the induced drag (a win-win situation), as soon as your height is less than a couple of meters. Without it, the ground is like an optical illusion until you actually touch it. I simply took the ground effect from the c172p, this should do it for now because it's a basic aerodynamic effect that mainly depends on ground proximity. The effect is calculated independently for the left and the right wing, because in ground proximity it matters if one wing is closer to the ground than the other (see "roll moment due to difference in ground effect"). 3.1.2 eta_L ----------- For each wing, one can determine a center of lift, which is the location where a hypothetical net lift force would have to be attached to get the same flight characteristics. eta_L is the relative y-position of that point. eta_L = 0 means middle of the plane, eta_L = 1 is at the wingtips. This position depends on the flap setting, because in landing configuration more lift will be produced by the flaps at the inner half of the wings, so eta_L will decrease. This property is needed for the roll_moment_due_to_sideslip and the roll_moment_due_to_ground_effect. I tried two different approaches to estimate eta_L: First, one can look at [1] Fig.51/52, to find out how much the lift force changes at a given angle of attack if the flaps are extended. From there it can be estimated how much of the net lift force is contributed by the inner (flap-) part of the wings and the outer (no-flap-) part. The second method involved [1] Fig.68. Given the flap setting and the angle of attack, the equation to calculate roll-moment-due-to-sideslip can be used to determine eta_L. The 55 deg-result turned out to be unrealistic, which is no surprise, since Fig.68 was derived from a scale model in a wind tunnel. Eventually I chose a compromise which is close to result 1, leaning a bit towards result 2: Flaps | 1.method | 2.method | compromise ----------------------------------------------------- 0 deg 0.47 0.56 0.50 20 deg 0.43 - 0.42 55 deg 0.41 0.19 0.37 3.1.3 calculations/aero/coefficients/CL --------------------------------------- I renamed it from "liftalphaflapnorm" to "CL", because this is the main lift coefficient calculation table. CL depends on angle of attack (alpha) and flap position. I corrected some errors in the 55 deg column and added some values to increase accuracy in the maximum lift area. The average ground effect of both wings is multiplied by the ground effect tweak_factor and added to the lift coefficient. 3.1.4 lift due to alpha and flags --------------------------------- Removed redundancy by replacing the table with the normalized lift table mentioned above. 3.1.5 delta lift due to alpha and mach -------------------------------------- Corrected a mistake in the table setup. 3.1.6 delta lift due to speedbrake ---------------------------------- Disabled. Instead of wingflaps the MiG-15 uses spoilers mounted in the aft of the fuselage. They are most likely designed to cause no lift to avoid an extra pitching moment. I found no indication for speedbrake related lift in the documents. 3.1.7 delta lift due to elevator deflection ------------------------------------------- This section was commented out before, but the calculations seem OK, so I enabled it. 3.2 Drag ~~~~~~~~ 3.2.1 change in drag due to ground effect ----------------------------------------- This was also taken from the c172p. 3.2.2 drag due to alpha and flaps --------------------------------- - Changed the table so it depends on alpha instead on the lift coefficient according to Fig.51 and 52. This is neccessary to model the rapid increase of drag when approaching the maximum lift coefficient (stall), because one lift value might correspond to more than one drag values, making the function ambiguous. - Fig.51/52 shows the drag curves for M=0.2 only, but with several flap and gear configurations. Fig.55/56 shows drag due to mach number, but only for the clean aircraft configuration. So we need to combine Fig.51/52 and 55/56. For M=<0.6 the curves are nearly parallel, so as an approximation we can add a constant value to the curves from Fig.51/52, depending on the Mach number. This is done by subtracting 0.018 (and adding tweak_factor/drag_offset), to move the curve to Cx=0 and then again adding the offset for Mach. For Mach-numbers >0.6 the curves aren't parallel so there needs to be another factor to bend the curves to the right. The estimations I used here are quite rough, this is not very accurate and needs to be corrected in the future to get a realistic simulation of fuel consumption, maximum speed and range. Effect: During flight with very high angles of attack you will lose speed much quicker than before. 3.2.3 drag due to altitude -------------------------- 3.2.4 Induced drag ------------------ Disabled, because induced drag is already included in the figures [1] 51,52,55,56 and accounted for in the previous sections. 3.2.5 Drag due to mach and altitude ----------------------------------- Disabled, already covered by the sections above. 3.2.6 Drag due to gear ---------------------- Probably due to a deprecated property, the drag was always active, even with the gear retracted. I fixed that and applied a more accurate drag depending to CL according too Fig.51/52. 3.2.7 Drag due to fuel tanks ---------------------------- I changed this section to make the extra drag depend on the lift coefficient as seen in Fig.53. 3.3 Side ~~~~~~~~ 3.3.1 Side force due to beta ---------------------------- Turning the aircraft's nose to one side will move the airplane to the side where the nose is headed. A typical situation where this effect comes to show would be during landing, when you notice that you're not aligned with the centerline. Then you can use the rudder to shift the aircraft sideways laterally while keeping the wings level with the ailerons. (But don't do this with the MiG-15, abort the landing instead!). I corrected a factor-10-type-o here, so the effect is noticable now. 3.4 Roll ~~~~~~~~ 3.4.1 Roll moment due to beta ----------------------------- When applying the left rudder in horizontal flight so the aircraft's nose turns to the left, the MiG-15 will generally start to roll counterclockwise. This is mainly due to its swept wing, because the right wing now exposes a larger area to the airflow and produces more lift. But - if the roll continues to a 90 deg bank angle, and the wings aren't producing lift anymore, the effect will vanish. And during inverted horizontal flight, it will be even negative. This is because altough the right wing still produces more lift, the lift force now points the other way: Up, which is towards the wing's downside. So now the roll moment will turn the plane clockwise. The underlying reason is that roll-moment-due-to-beta depends on the lift coefficient. This effect is the cause for roll stability and is quite strong in swept wing aircraft. To reduce roll stability (and increase manoeuverability), the MiG-15 has a negative dihedral angle, also called an anhedral wing (the wings point downward). According to [3], chapter 7.5, the roll coefficient can be approximated by: Cl = ((A + B * eta_L) * CL + K ) * beta where: Cl roll coefficient (M_roll = q A s Cl) A 0.124 B 0.350 eta_L y-position of the center of lift (see section on eta_L) CL lift coefficient K -0.028, constant value due to dihedral angle beta sideslip angle [rad] The values of A and B depend on CL, they were calculated using the wing's shape and sweep angle. eta_L is the lever that transforms the delta lift to the roll moment. K represents the anhedral wing effect, it is negative, and does not depend on CL. This means that if the lift coefficient is sufficiently small (like when flying with low g-force), then both effects may cancel each other out or the negative effect may have the upper hand. So in these cases, pointing the nose to the left may cause a clockwise roll. At speeds higher than about 700..900km/h, depending on height and weight, this will even happen in level flight. A, B and K are adjustable as tweak factor properties. 3.4.2 Roll moment due to yaw rate --------------------------------- Following the estimation given in [3], p.111, I increased the aeromatic factor from 0.15 to 0.22. 3.4.3 Roll moment due to difference in ground effect ---------------------------------------------------- The closer a wing gets to the ground, the more its lift will be increased by ground effect. So if one wing is closer to the runway, it will produce more lift and cause a roll moment with the tendency to level the wings - it's a pleasant little effect. It depends on the center of lift position (eta_L), because that is the lever which turns the delta lift into a roll moment. 3.5 Pitch ~~~~~~~~~ 3.5.1 Pitch moment due to alpha and elevator -------------------------------------------- - Fixed the problem that when pushing the flight stick full forward, the elevator's effect was limited to a deflection of 5 deg instead of 16 deg. - Added more detail to the table and fixed a type-o. - Extended modelling range from -2 deg AOA to -14 deg AOA. 3.5.2 Pitch moment due to pitch rate / alpha rate ------------------------------------------------- I don't fully understand these two aeromatic sections. There can't be much of a difference between pitch rate and alpha rate - I suppose one is for the elevator influence and the other one for the (much weaker) main wing influence. According to my calculations using [3], the pitch_moment_due_to_pitch should be only a third of the aeromatic value. But then the aircraft pitches really fast, leading to annoyingly high g-forces (and a blacking out pilot or a breaking aircraft). So for the time being I left it as it is. There's a tweak factor in case you are curious how a smaller pitch damping feels. 3.5.3 Pitch moment due to gyro effect ------------------------------------- The rotating masses inside the engine cause a gyroscopic effect, depending on the engine speed. During a pitch up movement, the effect will produce a yaw moment to the left, and during a yaw left movement, it will produce a pitch down moment. Both moments combined increase stability of the aircraft's symmetry axis, because every movement in pitch or yaw direction leads to a counteracting moment. According to [4], the moment M given off by a gyroscope is (in 3D vectors): M = - omega_f x D D = omega_rot * J omega_f rotational speed forced upon the gyroscope [rad/s] D rotational impuls omega_rot spinning speed of the gyroscope [rad/s] J rotational inertia (3rd grade tensor) Expressing the vectors in the aircraft body frame (forward, right, down), we can reduce D to the engine rotation axis x, neglecting the y- and the z-axis. The engine rotates counterclockwise in flight direction, so omega_rot = -omega_engine. If the aircraft is forced into a yaw motion to the right with the rotational speed omega_f [in rad/s], the equation takes the form: 0 -omega_engine J_x M = - ( 0 ) x (( 0 ) * ( 0 )) omega_f 0 0 The result is: M_y = omega_f * omega_engine * J_x, a positive pitch moment (nose up). To estimate the value of J, I looked at drawings of the rotating shaft in a rolls royce nene engine (the VK-1 is based on a copy of the nene, see [http://www.avialogs.com/index.php/en/engines/united-kingdom/rolls-royce/nene/rolls-royce-nene-turbo-jet-aero-engines.html]). I made scale drawings and broke them down into many simple shaped slices to calculate the inertia of each slice ( dJ = r^2 dm ). The result is J=7.63(kg*m^2) The factor 0.0772 is needed for unit conversion (RPM/(rad/s))*(Nm/(lbf*ft)). 3.6 Yaw ~~~~~~~ 3.6.1 Adverse yaw ----------------- When the ailerons are applied to make the aircraft roll clockwise, the left aileron moves down to create more lift. As a side effect, it will also create more drag, leading to a yaw moment turning the nose to the left. To fly a clean turn without sideslip (or even the risk of entering a spin), the rudder is always used simultaneously with the ailerons. This is the reason why the Wrights invented the rudder in the first place. If you don't have a rudder input device, switch on auto-coordination. In [2], Fig.25 the aileron effectiveness is given as "change in angle of attack per 1 deg of aileron deflection" and has a value of about 0.16. From the change in AOA one can derive the change in lift and then the change in drag (that's what happens in the table). Then multiply this by the ratio of aileron area / wing area and by the lever distance between aileron and center line. 3.6.2 Yaw moment due to roll rate --------------------------------- Rolling an aircraft results in an increase of AOA on the wing going down and a decrease of AOA on the wing going up. Similar to the adverse yaw effect, this will lead to an asymmetrical drag distribution which causes a yaw moment, trying to turn the nose towards the downgoing wing. According to [3], p.106, for an elliptic wing, the yaw coefficient is: m_z = -0.053 * omega_x * b/2V * C_L 3.6.3 Yaw moment due to gyro effect ----------------------------------- Same as pitch moment due to gyro effect, except now the (nose up) pitch movement omega_f causes a yaw moment of: M_z = - omega_f * omega_engine * J_x, which is a negative yaw moment (trying to turn the nose to the left). 4 Aircraft systems ================== 4.1 Control surfaces ~~~~~~~~~~~~~~~~~~~~~ 4.1.1 Elevator symmetry ----------------------- According to [1], the MiG-15's elevator has a maximum deflection angle of 32 deg up and 16 deg down. That means if both the 'up' and the 'down' ranges are mapped to the full flight stick movement, then the elevator will move twice as fast in the upper range than in the lower. That's because while pulling the stick all the way back, the elevator travels 32 deg, but it will only travel 16 deg when the stick is pushed all the way forward. To obtain a continuous steering behaviour, the input needed to be clipped to the range [-1.0...0.5]. 4.1.2 Elevator and rudder range at high speeds ---------------------------------------------- The MiG-15 is a jet fighter without hydraulic steering assistance for the elevator and the rudder. So at high speeds, the pilot wouldn't be able to move the controls too quickly. One problem with flying a simulator without force feedback is that you can easily exceed g-forces or cause excessive sideslip angles when flying very fast. This wouldn't happen in reality because the pilot would have to overcome the hinge moment of the control surface. As an attempt to model this, this function can scale down the elevator and rudder deflection range at high speeds. So when flying really fast, the control surfaces will not move the whole way. I calculated the hinge moment for maximum deflection using [1], Fig.77 and [2], Fig.63, and scaled down the range of the elevator and the rudder depending on the maximum hinge moment. The function that governs the control range looks like this: ^ "fcs/[elevator|rudder]_scale_factor" | 1+--- | \ | \ | \ B+ ----- 0+--+---+----> M "fcs/[elevator|rudder]_maximum_hinge_moment" 100 A Up to a hinge moment of 100Nm the range is still 1.0 (100%) and then it starts decreasing to the range A at the hinge moment B, and stays like that. You can change this behaviour by editing the tweak_factors "[elevator|rudder]_range_at_high_speed_[A|B]". The default values are A=1000Nm (which is hardly ever reached) and B=0.3. To deactivate this feature, set B=1. 4.1.3 Aileron booster --------------------- This system is usually active and can be switched off in case of a malfunction, so I believe there are only two settings for this lever. 4.2 Engine ~~~~~~~~~~ 4.2.1 Engine idle thrust ------------------------ Idle thrust was too high, which lead to unrealistic low sink rates during approach. Made a cheap and dirty workaround by applying an external force calculated by a nasal script. At idle rpm the thrust is now reduced to 75kg. 4.2.2 Engine respond time ------------------------- I increased the 'bypass ratio' to make the engine acceleration slower. (Actually bypass ratio should be zero for the Klimov VK-1 engine, but in the jsbsim jet module it only serves as a time constant for acceleration). 4.3 Gear friction ~~~~~~~~~~~~~~~~~ According to [2], the aircraft should start moving at an engine speed of 8000...9000 rpm. I increased the gear friction (a lot) to get closer to that behaviour. 4.4 Instruments ~~~~~~~~~~~~~~~ 4.4.1 Airspeed indicator ------------------------ The wide pointer is the "indicated airspeed", which is of interest for most flight characteristics. The narrow pointer indicates "true airspeed". 4.4.2 Turn indicator -------------------- This instrument now indicates the turn (yaw) rate. "45" means one full circle takes 45 seconds to complete. 4.4.3 Radiocompass ------------------ Added a little mark to the frequency scale to make it easier to find a certain frequency. This mark doesn't exist it reality, because the accuracy of the scale is much lower than the mark would suggest. This feature should be dropped in future upgrades when tuning the receiver can be modelled more realisticly. 5 Simulation ============ 5.1 Sound ~~~~~~~~~ 5.1.1 Engine rpm ---------------- I wanted the sound to give a better impression of engine rpm, so I added two high-pitch frequencies representing the rpm. The volume can be adjusted via the "tweak_factors". 5.1.2 Wind noise ---------------- Watching some cockpit videos of the MiG-15, I noticed that the wind noise often is louder than the engine. I suppose for a real life pilot the sound is an important information regarding the airspeed. I think sound is one of those areas where realism isn't the main consideration, because in a simulation you might want to emphasize some effects to make up for the lack of certain sensory input like vibrations or g-force. So I made wind noise louder, proportional to the net drag force (but I'm still not quite happy with it yet). 5.1.3 Touch down noise ---------------------- Another important cue for sim pilots, so I turned it up. 5.1.4 Random sounds at startup ------------------------------ Introduced the property "calculations/init_volume" to get rid of them. 5.1.5 Is the sound bug gone? ---------------------------- First thing I did was a workaround for a FlightGear related bug that lead to a choppy engine sound. In the meanwhile the bug seems to have disappeared, so I reverted what I changed. The fix was to simply comment all the tags in MiG-15bis-sound.xml. Let me know if you hear choppy engine sound. 5.1.6 clickfix in Nasal1.nas ---------------------------- I must have messed something up by mistake which stopped the click sounds from working. This little nasal procedure got the switches clicking again. 5.2 Damage due to limit violation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In general, the aircraft is now less prone to breaking than before. The reason I changed this was not to just make it easier to fly, but because I believe it is more realistic this way. After all, the MiG-15 is famous for its rugged design. 5.2.1 Maximum g-load -------------------- The manual says "destructive load 12g", so I made this the limit where the aircraft breaks. I disabled breaking gear in flight due to sheer g-force. 5.2.2 Landing gear ------------------ The limits for breaking gear are now determined by their vertical velocity at touchdown and the aircraft's weight. The limits (for a weight of 4000kg) can be changed via the tweak_factors. There are three limits: Main gear, front gear, and 'front gear single', that's when the front wheel is the first to touch down. The gear takes longer to extend and retract, so now it's closer to what the source [2] says (about 8 seconds). 5.2.3 Maximum speed for gear and flaps -------------------------------------- I increased them because according to [2], p.33 the gear should be extended at a speed as high as 450km/h. I found no explicit data on the maximum speed for flap extension, so I set it to 500km/h for 20 deg and 380km/h for 55 deg flaps. 5.2.4 Engine flame out ---------------------- [1] , table 19 states that the maximum engine power may be applied for 5 minutes continously and even 10 minutes when flying higher than 10000m. So I changed the Nasal code to make the flame out occur much later- not sure when, because it depends on temperature. Actually I doubt that, in reality, exceeding the time limits would neccessarily cause a flame out, but I kept that behaviour for now. 5.3 Appearance ~~~~~~~~~~~~~~ 5.3.1 3D model -------------- I wanted to get rid of the seams that could be seen on the fuselage of the old model, so I merged some of the parts together. This messed up the uv-mappings, so I had to repaint the aircraft. Unfortunately, some level of detail was lost during that process, because the old texture contained structure patterns like rivets and little gaps. They were quite faint but nice and accurate. I didn't have the time yet to transpose them to the new textures, so I'll include the old 3D model and liveries in the file to preserve the information. 5.3.2 Czech aerobatic livery ---------------------------- The aerobatic livery was inspired by images I found here: [https://forum.warthunder.com/index.php?/topic/194985-kamufl%C3%A1%C5%BE-mig-15bis-6sbolp-slia%C4%8D-20-v%C3%BDro%C4%8D%C3%AD-snp-2981964/]. The page says that this livery was used during an air show at the Sliac airbase on August 29, 1964. I didn't investigate the accuracy of this information. 5.4 Replay ~~~~~~~~~~ Fixed the replay function by assigning it to the usual shortcut Ctrl-R, disabling the damage detecting routines when in replay mode and configuring the flight-recorder section in MiG-15bis-set.xml. 5.5 Chase view ~~~~~~~~~~~~~~ I inverted the up-down mouse-movement in 'chase view', 'chase view without yaw' and 'model view'. Now it follows the same logic as the left-right movement and actually makes sense. It had to be done, get used to it :) 5.6 Metar string ~~~~~~~~~~~~~~~~ Pressing Ctrl-M shows the current metar string. Good for checking the wind condition if there is now ATC around. 5.7 Menu -> MiG-15bis -> Configuration ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 5.7.1 Rudder exponent --------------------- I've made the experience that the MiG-15 is hard to control when using rudder pedals with a linear characteristic. The reason is that small rudder input can induce strong roll moments to the aircraft. It's much easier to handle with an exponent (aka 'power') set to at least 2. This has the same effect as the 'power' setting in Menu -> Help -> Joystick Configuration / Rudder. Attention: Both settings will multiply, so if you're already happy with the 'power' setting in joystick control, you should set this value to 1. 5.7.2 External tanks, headsight, magnetic compass, flight stick --------------------------------------------------------------- They can be attached or removed by checking the respective boxes. External tanks might be unneccessary for short missions. Headsight and compass aren't needed for aerobatic flights and hiding the stick makes it easier to observe the turn indicator. 5.7.3 Vertical speed at touchdown --------------------------------- Shows the vertical impact speed for each wheel, so you can evaluate the quality of your landing or find a suitable setting for the gear-breaking limits. 5.7.4 Standard atmoshere ------------------------ For testing and training purposes. Turns off all winds and sets temperature and pressure (depending on altitude) to the "1976 U.S. Standard Atmoshere", which is almost the same as the "International Standard Atmoshere (ISA)". 5.7.5 Throttle crack sound effect --------------------------------- At high g-forces the throttle handle occasionally makes a grinding noise (see documentation). You can turn off the noise with this checkbox. 5.8 Aircraft info ~~~~~~~~~~~~~~~~~ Pressing shows a window containing infomation about the aircraft's basic limitations and procedures as they are stated in the manuals (except max.flap speeds, which are guesses). Note that a limitation printed there is not neccessarily simulated in the model. ---------------------------------------------------------------------- Andreas Zenner , Leipzig, 31.12.2015