How high/fast can you go in Viper - challenge

[jackmckay]

Here's some challenge: 

HiAlt:

High Speed:

now beat me  

Edited February 11, 2023 by jackmckay

[silverdevil]

nice! we need rules. how much fuel at start? how much fuel at end? how fast to 74k? should we be avoiding AA at that altitude?

[jackmckay]

22 hours ago, silverdevil said:

nice! we need rules. how much fuel at start? how much fuel at end? how fast to 74k? should we be avoiding AA at that altitude?

30% fuel, unlimited. just for fun. high jump, burn down.

[Redounet]

Edited February 13, 2023 by Redounet

[jackmckay]

On 2/13/2023 at 5:18 PM, Redounet said:

 

niiiceee. almost SR71 altitude level. angels 79.  who's going to space?

[Kamicosmos]

When I first got the F-16 last summer I wanted to hit Mach 2.0.  So here's a screen of that.  I think I had just done an air start, jettisoned stores and Punched It in level flight.  I did hit Mach 2.0. 

I do like the Challenge here though, so I'll give it a shot this weekend.  I think I'll try to 'Yeager' it: Do a ground take off to max altitude, and then come screaming back down for Max Speed.  I'll report back!

[skywalker22]

On 2/13/2023 at 5:18 PM, Redounet said:

 

Do you have the track, or tacview?

[d0ppler]

Almost 80K (79960 ft)

Screenshots in VR are absolutely horrible quality. Sorry for that.

 

But here's the trackfile:

F16_altitude.trk

And it includes a safe landing as well

Edited February 17, 2023 by d0ppler

[Exorcet]

Made an attempt out of Nellis, did a climb to 40000 ft, accelerated to almost M2 and then pulled up:

I've broken Mach 2 before, but I don't think I've ever tried to zoom climb. I feel like you can exceed 80,000 ft if you started from the right altitude.

[AndrewDCS2005]

Cool stuff!

Let's use the same units for consistent measurement and comparison - TAS for max speed, ASL for max altitude.

Here's my lazy attempt (Tacview track attached):

- TAS 607 m/s = 1359 mph; which was achieved as Mach 2.03 at 9920m

- ASL 28498 m = 93498 ft

 

f16-93.5kft.acmi

Edited February 18, 2023 by AndrewDCS2005

[AndrewDCS2005]

We can have all three goals set to be achieved in one flight in this challenge - max TAS, max ASL, shortest time to both max TAS and ASL  

Clean plane, 50% fuel, no chaff/flares, no gun ammo, start from runway hot.

Also weather conditions matter a lot so I created a mission for this with Caucasus map (which we all have), temperature 0 degrees Celsius, pressure 760mm Hg, no wind, no clouds, start at 10 Oct 2022 08:00 local time out of Kobuleti. See attachment.

max-altitude-flight.miz

Edited February 18, 2023 by AndrewDCS2005

[DukeAngus]

the airplanes HUD altimeter only goes to 80k so what I do is put the info bar at the bottom of the screen to know when I go past 80k

[Kamicosmos]

Excellent, Andrew!  I've downloaded that mission and will give it a few practice runs here in a bit.  I'll save my track, take screenshots, and probably record the whole thing as well.

 

Edit for update:

From take-off in the mission, I got to about 48,000. Hit Bingo fuel, realized I wasn't going to go much higher, so I shot back down to max the 'speedo' at 900kts. Like altitude, the HUD maxes at 900, so the external view actually showed me continuing above that threshold.  I was at about 910 when I lawn darted.   

Might have to make a second mission where we start at like 40K.  Then accelerate to near Max Speed, and perform the Zoom Climb to max altitude. May or May Not have the Fuel to do a Max Speed on the way down.

 

Another Edit:

Perhaps take a drop tank to get to cruise altitude and Mach 2.  Then drop the bag, and ZOOOOOM!   So many things to try!

Edited February 19, 2023 by Kamicosmos

[jackmckay]

Angles 93? That is insane. I do the same approach, go up to angles 25, level, max AB to max speed and then zoom up 40-60deg. it stalls up high but who cares. I wonder will anyone reach angels 100 (30km)? maxspeed is like a wall, cant go over 900 even in hard dive. PS: i cheated by setting unlimited fuel at 30%. that could go even on 5% but for relevant fair deal that should be like with bags and realistic fuel flow. keep it up. Yaeger stuff is always fun.

On 2/18/2023 at 4:34 PM, AndrewDCS2005 said:

We can have all three goals set to be achieved in one flight in this challenge - max TAS, max ASL, shortest time to both max TAS and ASL  

Clean plane, 50% fuel, no chaff/flares, no gun ammo, start from runway hot.

Also weather conditions matter a lot so I created a mission for this with Caucasus map (which we all have), temperature 0 degrees Celsius, pressure 760mm Hg, no wind, no clouds, start at 10 Oct 2022 08:00 local time out of Kobuleti. See attachment.

max-altitude-flight.miz 6.84 kB · 5 downloads

 

Ill grab that file and try.

[AndrewDCS2005]

After many tries the highest I can get in conditions specified above (0 degrees, 760mm Hg, no wind, no precipitation) is ASL 28756m = 94345ft 

ASL (aka True Altitude) is by definition more accurate than indicated altitude on the altimeter (which depends on pressure and temperature), and in this challenge I only refer to ASL.

I usually end up with ~500lbs fuel left at the peak which definitely plays a role - with lower total mass of the plane its kinetic energy is lower and it will not go as high, however the weight is also lower and gravitational force will have less effect so the plane can go higher. There's definitely some balance here, need to play with energy formulas to find out the sweet spot 

 

Max speed I can't get more than TAS 607 m/s = 1359mph maybe this is the limit due to aerodynamic drag and pushing beyond that requires modifications to the airframe

 

Side note - wonder why F-16C altimeter stops at 80kft, is this by design or a bug? Can someone from ED or real pilots clarify?

Edited February 22, 2023 by AndrewDCS2005

[Scott-S6]

On 2/22/2023 at 10:57 PM, AndrewDCS2005 said:

Side note - wonder why F-16C altimeter stops at 80kft, is this by design or a bug? Can someone from ED or real pilots clarify?

Consider the service ceiling of the viper, issues with engine failures over 80kft, effects of loss of cabin pressurization at that altitude (no provision for a pressure suit) and so on. There's little sense in having instrumentation that can measure well beyond operational range and 80kft is massively beyond operational range.

[razo+r]

On 2/22/2023 at 11:57 PM, AndrewDCS2005 said:

 

Side note - wonder why F-16C altimeter stops at 80kft, is this by design or a bug? Can someone from ED or real pilots clarify?

 

It doesn't go higher because ED decided that at that altitude it just stops working.

 

[AndrewDCS2005]

@razo+r thanks, this is interesting, and actually raises a question how well F-16C is modelled at altitudes above >50kft.

Putting pilot/human model aside (temp, oxygen, pressure, etc) I wonder if there are any modeling simplifications or limits which makes high-alt flight behavior different from what would be expected to happen in real world. How do we ask folks in ED team ?  @NineLine ?

[S]

19 hours ago, AndrewDCS2005 said:

@razo+r thanks, this is interesting, and actually raises a question how well F-16C is modelled at altitudes above >50kft.

Putting pilot/human model aside (temp, oxygen, pressure, etc) I wonder if there are any modeling simplifications or limits which makes high-alt flight behavior different from what would be expected to happen in real world. How do we ask folks in ED team ?  @NineLine ?

I would say there probably are a lot of simplifications. I base this on expected real-world performance of an aircraft with a T:W of greater than 1. Even in clean configuration, I can't gain speed in a vertical climb from takeoff. 

If you're interested in running this experiment yourself, the real-world thrust rating on the F-16 is 27,000 lb. Clean the plane up (remove pylons) and adjust fuel so you're under 27,000 lb takeoff weight (I set fuel so my ramp weight was 25,000 lb) and go for a 90-degree climb after takeoff. The plane stalls around 20,000 ft MSL and does not accelerate while going vertical. Compare that to videos online of 0-30,000 MSL F-16 unrestricted takeoffs.

Edit: Not exactly apples with apples, but I've done a lot of modding in MSFS to try to squeeze a little more realism out of their flight models (specifically the C172 which I fly IRL) and I've noticed that the physics tend to break down when you put thrust greater than weight (tried this when pushing the boundaries of the physics engine to figure out how the simulator really works). My best guess is that there's something that would require a very different handling of the drag simulation in flight simulators to truly handle thrust:weight ratios near and/or over 1:1 to keep from having 'unlimited speed'. That guess is based on my experience modding MSFS and also helping to develop the very arcade flight model for World of Warplanes. I don't know too much about the physics engine behind DCS yet as I'm pretty new to the simulator, so this is just a guess for now. I may have more data in the future, but I'm not promising anything. 

Edited February 25, 2023 by S

[AndrewDCS2005]

Well DCS F-16C according to DCS: F-16C Viper has F110-GE-129 engine which according to GE https://www.geaerospace.com/sites/default/files/datasheet-F110-GE-129.pdf is rated at 29000lb=129kN of thrust. I think this rating is at zero ASL, however this is a normal airbreathing turbofan and its thrust goes down with altitude. Not sure if there is any public data about the thrust/altitude of the engine to see how DCS modeled that. So the thrust:weight definitely goes below 1 at some alt and there can't be unlimited vertical climb - @S can you please share videos of F-16 doing vertical climbs to 30kft MSL? 

[Fulcrumkiller31]

On 2/25/2023 at 10:28 AM, S said:

I would say there probably are a lot of simplifications. I base this on expected real-world performance of an aircraft with a T:W of greater than 1. Even in clean configuration, I can't gain speed in a vertical climb from takeoff. 

If you're interested in running this experiment yourself, the real-world thrust rating on the F-16 is 27,000 lb. Clean the plane up (remove pylons) and adjust fuel so you're under 27,000 lb takeoff weight (I set fuel so my ramp weight was 25,000 lb) and go for a 90-degree climb after takeoff. The plane stalls around 20,000 ft MSL and does not accelerate while going vertical. Compare that to videos online of 0-30,000 MSL F-16 unrestricted takeoffs.

Edit: Not exactly apples with apples, but I've done a lot of modding in MSFS to try to squeeze a little more realism out of their flight models (specifically the C172 which I fly IRL) and I've noticed that the physics tend to break down when you put thrust greater than weight (tried this when pushing the boundaries of the physics engine to figure out how the simulator really works). My best guess is that there's something that would require a very different handling of the drag simulation in flight simulators to truly handle thrust:weight ratios near and/or over 1:1 to keep from having 'unlimited speed'. That guess is based on my experience modding MSFS and also helping to develop the very arcade flight model for World of Warplanes. I don't know too much about the physics engine behind DCS yet as I'm pretty new to the simulator, so this is just a guess for now. I may have more data in the future, but I'm not promising anything. 

 

You are forgetting about drag, even if the T/W was 1.1 at any altitude (it isnt) you would still need enough thrust to overcome airframe drag. So no matter what you will not accelerate at least above a certain altitude in any jet. Otherwise you would be a Falcon 9 Rocket!

[Nuggetz]

I have managed to get the F16 up to M2.05 a number of times and this week up to M2.06 (twice). Today I surprised myself and got a speed of M2.09.

[AndrewDCS2005]

@Nuggetz cool! Do you have the track/tacview to check what was the TAS at that point? Also curious what was the weather setup - temp and pressure?

[S]

19 hours ago, Fulcrumkiller31 said:

You are forgetting about drag, even if the T/W was 1.1 at any altitude (it isnt) you would still need enough thrust to overcome airframe drag. So no matter what you will not accelerate at least above a certain altitude in any jet. Otherwise you would be a Falcon 9 Rocket!

I didn't forget about it, I just didn't want to get into a discussion about drag specifics. That's why I said to compare it to unrestricted climb videos, because there are definitely some noticeable performance differences.

[Nuggetz]

@Nuggetz

1 hour ago, AndrewDCS2005 said:

@Nuggetz cool! Do you have the track/tacview to check what was the TAS at that point? Also curious what was the weather setup - temp and pressure?

I am not sure if I saved the file but I will check. I think the key to getting such high speed was using a porpoising technique to climb high 55k+, pitch down up to 15 degrees accelerate to M2 pitch up and repeat 3+ times. I generally find there is too much drag below 36,000 feet to maintain speed. As far as weather goes I did not select anything specific. If I don’t have the track file I will try and repeat and save at the next attempt. Regards

Edited February 27, 2023 by Nuggetz