It might be that. There was a discussion on the FSDeveloper forums several years ago about the long-standing bug in FS9/FSX. An aerodynamicist there reverse-engineered the algorithm that was apparently being used in MSFS for IAS and determined that the term for compressability was likely being applied to the wrong side of the equation.
Apparently LM cannot fix the bug in P3D because some of the core aerodynamics calculations in Sim1.DLL come from original MSFS DLLs written in assembler for which LM was never given the source code when they purchased ESP.
This might be of a help, the EAS = TAS x square root of density ratio from the table below. TAS should be available on the ND on the Airbus and otherwise in the “HUD” in external view below the airspeed indicator. If we now calculate CAS from TAS not taking into account compressibility effect we should be able to check if the extra 20 kts is justified.
Pressure alt. 38000 ft
SAT -56C (ISA)
IAS 250 kts
TAS 447 kts
GS 447 kts
Mach .78
TAS = GS without any wind so TAS calculation is correct
Local speed of sound should be 38.94 * square root of 217 K = 573,62 kts
Mach number = TAS / LSS = 447 / 573,62 = 0.7793 Mach
Mach No. calculation is correct
EAS = TAS x square root of p/po = 447 x square root of 0.2710 = 232,6977 kts
CAS calculated from TAS without taking into account compressibility = 246,5 kts
Airspeed should be 13,8 kts overreading it is actually 17,3 kts overreading.
CAS = 3,5 kts off.
I found a website to calculate CAS / TAS / EAS based on pressure altitude and ISA delta. No idea how accurate it is but so far it confirms my calculations:
Yes, that is much closer than the last time I specifically checked in the A320. That was during the Alpha several weeks before release, and at the time I was getting 277 knots IAS at FL 360 / Mach 0.78 at ISA instead of the expected 258 for that Mach.
I did report it to Zendesk at the time, so it would seem that when it marked “solved” it truly was fixed.
I’ll try it again later, but based on your test it looks like it is pretty close now.
I only tried it at 38000 in ISA so there might be conditions in the flight envelope which deviate more? Would be interesting to see if the low speed / stall indication on the speed tape increases accurately with increasing EAS.
I guess not since everything on the speed tape on the A320 is complete garbage, as soon as you lift of VR is below stall speed according to the speed tape, at flap retraction F if you retract the flaps again the speed tape shows below stall (both cases without stall warning activation, so wrong speed tape indication). I had a situation where the green dot speed was ABOVE maximum flap extend speed for flaps 1. So can’t slow down any further, neither can you select flaps. Good job Asobo
I may have misread your last post, you were calculating the effect of compressibility rather than reporting on observed IAS?
If so, the air data computer in any transport category aircraft automatically compensates for any variations caused by compressibility, which are minor in any case until approaching Mach 1.0 Testing air data systems is one of the main responsibilities in my current job. As an example, at FL 390, at a speed of Mach 0.80, the IAS should be 248 knots. This is something that is tested on a regular basis.
Looking at the aircraft maintenance manual for the CRJ-200 right now, and the allowable IAS error at FL390 at Mach 0.80 is +/- 1 knot
IAS according FS2020 was exactly 250 kts where it should have read 246,5 kts so 3,5 kts difference. The 246,5 kts is calculated from TAS using pressure altitude and temperature. You can skip the whole EAS part, that only becomes relevant when checking if stall speeds etc. are accurately corrected for compressibility. I calculated everything from the TAS, so from TAS to CAS, TAS to EAS and TAS to Mach as I know that TAS is correct for sure (same as GS with nil wind)
The airspeed itself is not corrected for compresibility, at least Airbus and Boeing display CAS I’ve read and instead correct stall speeds etc. for compressibility and show the cues correctly on the tape. Learning something everyday, I fly the Embraer 190/195 myself, no idea what airspeed it displays it isn’t clearly written anywhere, not relevant for pilots to know I assume.
Ah, so I did not misunderstand. Yes if the actual IAS was 250 then the previous bug I saw in the Alpha has apparently been fixed. It may not be perfect, but a 3 knot difference is much better than 20 knots.
That is one problem with Zendesk. Sometimes “solved” really does mean solved - other times it means “we have read your report, and put it on our backlog”…
They did a pretty good job in this area I think, even the temperature becomes isothermal from 36000 ft up at -56C if you turn live weather off and hit zero ISA deviation, exactly like it should be in standard atmosphere.
Yep, the real aircraft really needs corrections during takeoff. The issue, as it was already said by others, is that here on the simulator we don’t have the body feedback of how the aircraft is behaving, and it makes us to “over-correct” the aircraft tendencies and it leads to higher and higher oscillations. Adjust your control’s sensitivities and it will probably help
P.S: Taildraggers are even more aggresive when it comes to torque on takeoff phase.
Flight (and ground) models of the 150 and 172 are a mixed bag. I have not tried the larger birds yet but I suspect they have similar issues.
-No inertia. You can taxi (or drive) the planes around at high speed with no risk of tipping.
-No bounce making landings too easy. Those two model stick to the ground on contact.
-No simulation of dynamic modes - longitudinal, lateral or spiral. Planes feel like they are always on rails (or auto pilot). The lack of spiral divergence is the biggest deal breaker for me.
You can trim a plane for level flight in windy conditions, walk away for mins, and the plane is still safely flying on its own in a level holding pattern. Modern FM is no better. Sorry, most planes would be spiraling down into the ground in no time. Makes VFR flight into IFR conditions a joke.
I don’t think the developer had anyone with a basic physics or piloting background working on this sim with reguards to flight or ground modeling.
What do you mean by “mixture increasing the RPM on a loaded prop”? I don’t know what conditions you are referring to but yes leaning the mixture could increase the engine’s power output and considering the C172 has a fixed pitch propeller this would mean an increase in RPM.
Why should a trimmed out stable high wing trainer like a 152 (or any other aircraft with the quite usual positive spiral stability) be “spiraling down into the ground in no time”?
Well they can work on their flight model a bit. It feels like its FSX. Some airplane mike the Extra and Pitts still suffer the rudder illness like back in the FSX days. Many things are not Simulated in this “Simulator” prop feathering is not visually and accurately Simulated neither are engine outs. If your engine dies it does not still run at 2400rpm until you land. The few airplanes I fly eg Baron, Bonanza and Cessna 172 are fairly close like 70% there. Don’t get me started on the basics its missing. This happens if you build a Sim on outdated technology like FSX.
I stalled the Cessna in an attempt to get the propeller stopped as I wanted to check if propeller drag is accurately simulated (comparing rate of descent between windmilling and stopped prop.), indeed even with zero speed the prop doesn’t stop, or stops and then starts windmilling as soon as airspeed picks up, I’m still not convinced propeller effects are accurately simulated, there isn’t any slipstream effect noriceable at all, seems to me deceleration of prop aircraft is somewhat slow and glide range too far, but this is subjective and hard to proof. Yes if the windmilling RPM would really be 70%, the drag would be enormous .
Cessna Caravan the propeller doesn’t feather for some reason.
I disagree regarding a spin developing after a wing drop, the chances there are reasonable. I have over 1000 hours in the C152 and a slightly lesser amount in the C172 over my aviation career, a lot of that doing aerobatics and spinning with students. They will both spin quite easily if you set power to about 1500RPM and at the stall pull back and apply full rudder.
The use of aileron in a stalled condition is simply because it will increase the angle of attack on the wing you are trying to pick up. Increasing the angle of attack on a stalled wing will reduce its lift (remember the angle of attak/lift curve). Drag plays a much smaller part.
I also disagree about your high speed stall comments. Stalling has no relation to speed, only angle of attack. The issue is that most (light) aircraft do not have an angle of attack indicator.
Your comments worry me about your understanding of the basics here. something to consider for yourself.
Not trying to flame, just to correct information here.
Actually you don’t need to raise the nose much in the A320, as the aircraft is almost in the landing attitude already. Only say up an additional 1-2 degrees is needed. I agree the ground effect is still a bit too strong (but much better than it was earlier on!)
However if you do float a little in the A320, it does quite literally drop out of the sky. BANG!
On the Jetstream and Kingair we had a little trick, if the FO was flaring down the whole runway again, just cycle the de-icing boots and its quickly over (don’t try this at home)…
None of the props feather in the Sim. I have about 10 tickets open for bugs and issues. Also, the engine is at about 2400rpm when it’s windmilling! They have a LONG way to go still. Nothing of the Flight “Simulator” is actually accurately Simulating any situation of an Airplane correctly
and a slightly lesser amount in the C172 over my aviation career, a lot of that doing aerobatics and spinning with students. They will both spin quite easily if you set power to about 1500RPM and at the stall pull back and apply full rudder.