Acceleration & AoA - Some Observations.

[QuiGon]

An interesting piece about the F-16N, the Navy Hot Rod: https://www.thedrive.com/the-war-zone/3383/what-it-was-like-flying-and-fighting-the-f-16n-viper-topguns-legendary-hotrod

 

It was by far the fastest (non-NASA?) variant of the F-16 that ever existed and capable to go supersonic without afterburner!

[Dee-Jay]

In cold weather I’ve experienced a strange bug with the F-16 a handful of times where the airspeed indication will go haywire, displaying that I’m accelerating to mach 2.20 when I’m clearly not going that fast. I haven’t been able to replicate it reliably but I think you might be running into it.

 

Mach number is in direct relation with temperature:

 

where

 

• a = speed of sound [m/s]
  
• T°C = atmospheric temperature in degrees Celsius (°C)
  

You can calculate it in game and check if it is correct or not if you have some doubts.

 

CAS/Mach/TAS/EAS Conversions : http://www.hochwarth.com/misc/AviationCalculator.html

...

Edited January 13, 2020 by Dee-Jay

[Deano87]

Mach number is in direct relation with temperature:

 

where

 

• a = speed of sound [m/s]
  
• T°C = atmospheric temperature in degrees Celsius (°C)
  

You can calculate it in game and check if it is correct or not if you have some doubts.

 

CAS/Mach/TAS/EAS Conversions : http://www.hochwarth.com/misc/AviationCalculator.html

...

 

 

I am aware of that Dee-Jay, the bug I’m referencing was such that the indicated mach went from 1.2 to 2.2 in the space of 1.5 mins with the jet in a steady state (CAS not changing) on a jet loaded with 2 x tanks + 6 Aim-120s. Tacview showed that I was still at 1.2m but the HUD showed mach 2.2. The trk is too long so I can’t upload it for bug reporting but I couldn’t replicate the issue reliably to make a short trk of it.

 

Is there anyway to determine outside air temp in the sim?

Edited January 13, 2020 by Deano87

[bkthunder]

Little heads-up: wind affects the FM.

https://forums.eagle.ru/forumdisplay.php?f=638

[HILOK]

Good point Hilok, but I actually calibrated the pitch ladders using a 3rd screenshot taken while both aircraft were climbing, the pitch ladders in the climb are much clearer and gave me excellent accurate reference for scale, from the horizon to 20 degrees. However due to both aircraft pitching up and down a lot during the flight I couldn’t actually get a climbing shot where we were both at a stable 1G, at the same Mach during the climb so I omitted it from the comparison and only used it as a calibration tool.

 

The pitch ladder has no relationship to AoA. AoA is the distance between the gun cross and the Velocity vector. I only used the pitch ladders to scale to the two images correctly so I could make the measurement. Beyond that the position of the pitch ladder doesn’t matter.

 

Looking at you pic, I’m not quite sure why you’ve measured between the gun cross and the negative 5 degree line on the pitch ladders? Notice on the top left image the horizon line is out of view, but you can also see from the two purple lines on your image that my pitch ladders are quite well matched in size, but are in different places, which doesn’t actually matter when calculating AoA as that’s independent of pitch angle. I used the pitch ladders to calibrate the size of the images but then ignored it after that, their exact relationship to the gun cross in regards to AoA is not really relevant as far as I can see. Can you explain what you mean?

 

you're right! actually i should have taken the waterline into consideration as well. i was assuming the gun cross over the waterline in my calculations, which is only roughly the case.

 

The pitch ladder has no relationship to AoA.

not sure what you mean, because the pitch ladder is the only reference you got to quantify the AOA, when using gun-cross & FPV over the HUD.

 

I actually calibrated the pitch ladders using a 3rd screenshot taken while both aircraft were climbing, the pitch ladders in the climb are much clearer and gave me excellent accurate reference for scale, from the horizon to 20 degrees.

ok, the point of my post was bringing this to your attention, so fair enough : )

[Basher54321]

An interesting piece about the F-16N

 

It was by far the fastest (non-NASA?) variant of the F-16 that ever existed and capable to go supersonic without afterburner!

 

 

 

Unlikely, all F-16s are limited by the inlet at altitude and below that more a case of thrust v drag. The N was a small mouth block 30 having less thrust than the bigmouth block 30 and block 40 to 60.

Even the A models could go over M1 in some conditions - the N was sold at rock bottom dollar yet replace a gun with ballast and voila super plane!

 

If instead talking about quickest then my money is still on the block 60 despite the weight - start your drag race at the same int fuel and even stick on empty CFTs - bet it would still eat that lot - get me the charts LOL :thumbup:

[Badlego]

I see, that in the lower two pictures you pull 1.1G in DCS while the RL plane flies stable 1G. It may not be much, but as soon as you pull G, you also increase AoA. That may affect your comparison.

Best Regards

[Deano87]

I see, that in the lower two pictures you pull 1.1G in DCS while the RL plane flies stable 1G. It may not be much, but as soon as you pull G, you also increase AoA. That may affect your comparison.

Best Regards

 

Good point, Dunno how I missed that! I blame being sick with the flu at the time lol.:thumbup:

 

Here is an updated version, I'll edit the original post as well.

 

[Deano87]

Hey All.

 

Seeing as BKThunder has discovered the same F-5 wind bug is present here with the F-16:

 

https://forums.eagle.ru/showthread.php?t=260650

 

I suggest any acceleration tests be performed with 0 wind as the results with wind will not be representative.

[mvsgas]

In cold weather I’ve experienced a strange bug with the F-16 a handful of times where the airspeed indication will go haywire, displaying that I’m accelerating to mach 2.20 when I’m clearly not going that fast.

On occasion with cold weather the DCS F-16 will act like the pitot tube is frozen. I seen this with the pitot heat on or off and it should not matter since in the RL aircraft pitot heat come on automatically with the aircraft in the air (Weight on Wheels, or wow) regardless of the switch position.

[Deano87]

On occasion with cold weather the DCS F-16 will act like the pitot tube is frozen. I seen this with the pitot heat on or off and it should not matter since in the RL aircraft pitot heat come on automatically with the aircraft in the air (Weight on Wheels, or wow) regardless of the switch position.

 

Interesting... Is this happening when you have your incredibly fast accelerations to M2 indicated?

[mvsgas]

I have not find the reason. It has happened on NTTR and Caucasus. From mach.88 to supersonic. One occasion, the speed went to zero and started jumping around on another it went to max then started to jump. All below 0°C.

[mvsgas]

Try this mission to test the icing, Caucasus Openbeta version 2.5.5.41371

Ice testing.miz

 

It happened once after flying all the way points, with pitot heat on since before take off. Came through the cloud layer and AMI went to zero, HUD still showed speed Calibrated. after a minute or so it worked fine. I landed, refueled but could not duplicated.

Edited January 13, 2020 by mvsgas

[Deano87]

Try this mission to test the icing, Caucasus Openbeta version 2.5.5.41371

[ATTACH]224960[/ATTACH]

 

It happened once after flying all the way points, with pitot heat on since before take off. Came through the cloud layer and AMI went to zero, HUD still showed speed Calibrated. after a minute or so it worked fine. I landed, refueled but could not duplicated.

 

Guess it took too long so you couldn't record a track?

 

Do you think icing was the reason you managed the "1:49 from mach .88 to 2.00", which is insanely fast (that is to say that it was displaying erroneous Mach readings). Or do you think it was the wind bug BK has noticed?

 

I'll give the mission a try on wednesday when I get a chance to play and hopefully record a track.

Edited January 13, 2020 by Deano87

[mvsgas]

The track was to big since I did a cold start, I think the wind was the reasons for the fast acceleration. The compounding problem is if the thing that tells us speed is not working properly, how can we test acceleration? So I think both of these are link. Also note how ground speed show zero in the HUD and is fine in the INS page.

Edited January 13, 2020 by mvsgas

[Deano87]

The track was to big since I did a cold start, I think the wind was the reasons for the fast acceleration. The compounding problem is if the thing that tells us speed is not working properly, how can we test acceleration? So I think both of these are link. Also note how ground speed show zero in the HUD and is fine in the INS page.

 

Very Good points... wonder if Tacview gives accurate speed readouts?

[Frederf]

Good gouge on the probe heat mechanization. Tacview doesn't understand wind so G/S is fine but CAS/TAS isn't.

 

You can kinda do some testing for AOA by looking at best range speeds which happen at LDmax AOA which should be ~6.8 degrees.

[dolfo]

Hey All.

 

 

 

...

 

My non-perfect flying aside, You can see that the DCS version keeps up pretty well until about Mach 1.35 at which point the IRL jet starts to pull away...

 

 

...

 

Cheers

D

 

Nice investigative initiative.

 

Not here to accuse or defend the Flight Model, but take a look at your video, starting at time 1:10.

 

You seem to pull a little harder than the reference video in the final part of the zoom, giving away a bit of energy. Also you pull to a pitch considerably higher than that of the reference video (look at the gun cross, not FPM). Coincidentally or not, that is when your speed starts to drop quicker than the reference.

 

Maybe try a few more times, taking extra care not to give away too much energy from pitch 5 to 10, and try and keep the gun cross closer to the 10 degree pitch line as in the video?

[Deano87]

Nice investigative initiative.

 

Not here to accuse or defend the Flight Model, but take a look at your video, starting at time 1:10.

 

You seem to pull a little harder than the reference video in the final part of the zoom, giving away a bit of energy. Also you pull to a pitch considerably higher than that of the reference video (look at the gun cross, not FPM). Coincidentally or not, that is when your speed starts to drop quicker than the reference.

 

Maybe try a few more times, taking extra care not to give away too much energy from pitch 5 to 10, and try and keep the gun cross closer to the 10 degree pitch line as in the video?

 

Good point! I’ll try again to be smoother.

 

I don’t think it will make much difference tbh as I never really loaded the aircraft up, but who knows.

 

Also I was ignoring the gun cross completely and just flying the FPM because the two aircraft are flying at different AoA. So if if I put the gun cross in the same place as his I will not be climbing at the same angle as he was, If that makes any sense. If I’m tying to fly the same profile I would have thought it would make more sense to match the FPMs so if he’s in a 5 degree climb, so am I. If I match gun cross positions instead of FPM I will not climb as high but I will dive more steeply. I think that would make the test less representative?

[The Falcon]

From the video we understand that you were slightly slower in accelerating and it was as if there was a wall starting from mach 1.85 onwards, I remain of the opinion that neither the AoA nor the G can make the difference. To tell the truth you were also a little out of the altitude compared to the original video. For me without knowing the external air temperature we can't go on.

Edited January 14, 2020 by The Falcon

[Deano87]

From the video we understand that you were slightly slower in accelerating and it was as if there was a wall starting from mach 1.85 onwards, I remain of the opinion that neither the AoA nor the g or things of this type can make the difference. To tell the truth you were also a little out of the altitude compared to the original video. For me without knowing the external air temperature we can't go on.

 

How can I find out external air temp from the sim? It was a standard day so 20C at sea level. No wind.

[The Falcon]

How can I find out external air temp from the sim? It was a standard day so 20C at sea level. No wind.

I really don't know, i'm waiting for the help of someone who knows. This external air temperature thing is just to test and confirm that there is a problem anyway.

[Deano87]

I mean if I adjust the temp so the CAS and Mach match at the same altitude as in the video then we should be good I suppose?

[Frederf]

Check at 30kft time in seconds to accelerate the basic airplane at 32klb GW:

200 0

300 33

400 54

500 76

600 97

700 127

Speeds are KIAS (so round gauge not HUD)

 

+-20C temperature from standard day is 8%/5% respectively for times until supersonic at which point the temperature effect grows up to about 40% nearer mach limit. Default DCS atmo is +5C from standard so figure 2% more time through M1.0. For ease of comparison setting DCS to 15 SLT removes that as a factor.

 

Graphing the above numbers with DCS performance will suggest if the performance is close or quite divergent.

[Deano87]

Check at 30kft time in seconds to accelerate the basic airplane at 32klb GW:

200 0

300 33

400 54

500 76

600 97

700 127

Speeds are KIAS (so round gauge not HUD)

 

+-20C temperature from standard day is 8%/5% respectively for times until supersonic at which point the temperature effect grows up to about 40% nearer mach limit. Default DCS atmo is +5C from standard so figure 2% more time through M1.0. For ease of comparison setting DCS to 15 SLT removes that as a factor.

 

Graphing the above numbers with DCS performance will suggest if the performance is close or quite divergent.

 

 

Sounds good. I’ll give it a go. Clean + no pylons, Correct?