Max ground speed 1494 kn?

[-Vindicator-]

I frequently get the F15 clean (i.e., without external tanks) to 1494 knots, ground speed, in level flight above or around 37K.  But sometimes I can get it to 1504 or 1505 knots and I once (I think) got it to 1514 or 1515 knots.  The problem is I can’t seem to reliably or predictably get speeds over 1494 knots.  Sometimes it seems I can descend to 37K or a little below that and get above 1494.  Sometimes it helps to bank.  Sometimes it’s better not to have full internals.

What is the maximum GROUND speed in level flight of a clean f15 and what precise PROCEDURE (altitude, pitch, ascent/descent, bank, fuel quantity, wind, changes in these, and/or anything else) do I use to attain it?   A video showing the procedure and speed attainment would be nice but is not necessary.  (I’m assuming a clean F15 reaches the best speed; if not, please let me know.)  Thanks!

[Cmptohocah]

9 hours ago, -Vindicator- said:

I frequently get the F15 clean (i.e., without external tanks) to 1494 knots, ground speed, in level flight above or around 37K.  But sometimes I can get it to 1504 or 1505 knots and I once (I think) got it to 1514 or 1515 knots.  The problem is I can’t seem to reliably or predictably get speeds over 1494 knots.  Sometimes it seems I can descend to 37K or a little below that and get above 1494.  Sometimes it helps to bank.  Sometimes it’s better not to have full internals.

What is the maximum GROUND speed in level flight of a clean f15 and what precise PROCEDURE (altitude, pitch, ascent/descent, bank, fuel quantity, wind, changes in these, and/or anything else) do I use to attain it?   A video showing the procedure and speed attainment would be nice but is not necessary.  (I’m assuming a clean F15 reaches the best speed; if not, please let me know.)  Thanks!

Ground Speed is the air speed of an aircraft plus/minus the wind speed, so technically speaking there is no maximum ground speed, well accept the speed of light that is .

At higher altitudes you want to use the Mach number and at lower altitudes you would use indicated air speed.

Real Eagle has a limit of 800knots indicated air speed and above Mach 2 point something - can't remember the exact value.

[-Vindicator-]

Thank you.  Everything you’ve said is well-known and I appreciate your answer.  However, technically speaking I have yet to get anywhere near around 186000 miles a second ground speed.   If anyone can get the F15 reliably above 1494 kn ground speed in level flight please let me know how.  That’s what I’m interested in; others may be interested in something else.  

[-Vindicator-]

P.S.: Again, thank you for taking the time to reply.  I was just thinking: maybe an issue is the terrain, or altitude of the terrain, that I’m flying over.  Or maybe ground speed above 1494 knots cannot be reliably sustained in level flight in the F15 in DCS; if it can’t, it would help if someone knowledgeable said that.  Or maybe no one knows; that’s cool too.

[Nahen]

In DCS, the speed of the F-15C is limited to a maximum of Mach 2.606 / 1494 knots. How high do you go to that speed - I tried at around 55,000 feet and like in this video at around 40,000, when you reach this speed and start descending more or less sharply - of course, all the time on afterburners - can't to cross that speed. This is the limit imposed in the DCS.

 

Edited July 3, 2022 by Nahen

[-Vindicator-]

Thank you Nahen and thanks for the video!  However, I’m focusing on GROUND speed and, if you’re referring to that, I’m sure I’ve exceeded 1494 kn sustained ground speed several times in level flight.  I’m sorry I don’t have a video of that.  Maybe I’ll hear from some who’s exceeded 1494 gs.  Again, thanks!

[Nahen]

The radar screen shows your "true" speed and your "ground speed". Note that the faster you fly, the two speeds differ less and less. And at some point they are the same. At speeds of> Mach 2, the ground speed may only depend on altitude. But at these speeds, and at altitude 40 - 60K feet, difference of 10,000 feet — about 3,000 meters — will not make much difference.

I'm just thinking...

[-Vindicator-]

I hear you, thanks!

[draconus]

Going after silly thing you probably found a bug. I tried to make a record but got only about 1507 diving a bit from max speed at 37k. So I tried to help myself with the 97kts of wind @33k which should add exactly that amount to the ground speed but it did not. It stayed at the limit of 1494.

[-Vindicator-]

Thanks Draconus.  The hud indicated you  reached 1507 knots ground speed?

[draconus]

14 minutes ago, -Vindicator- said:

The hud indicated you  reached 1507 knots ground speed?

No, the HUD shows CAS. Ground speed reading is on the radar screen marked with G.

[-Vindicator-]

Correct.  So just so I understand:  (1)  Your radar reflected 1507 knots ground speed? (2)   This appears to be a bug?  (3)  So even if gs exceeds 1494 knots as reflected on the radar, I’m in fact not exceeding 1494 gs?  Thanks!

Edited July 4, 2022 by -Vindicator-

[Ironhand]

19 hours ago, -Vindicator- said:

If anyone can get the F15 reliably above 1494 kn ground speed in level flight please let me know how.

Text deleted. Misread the problem. No answer here.

F-15C Speed Test 1.trk

Edited July 4, 2022 by Ironhand

[-Vindicator-]

Thank you!  I’m dying to see this but I won’t be able to access my computer until tomorrow.  Do you exceed 1494 knots ground speed?  I notice you mention “accelerating until you reach 1494.”  Thanks again!

[draconus]

7 hours ago, -Vindicator- said:

Correct.  So just so I understand:  (1)  Your radar reflected 1507 knots ground speed? (2)   This appears to be a bug?  (3)  So even if gs exceeds 1494 knots as reflected on the radar, I’m in fact not exceeding 1494 gs?  Thanks!

Now, you're being silly - why did you even started that research? You don't know what is ground speed or how to read it in the F-15C.

1. No, my radar is off so it does not send any signals. It just happens that on this same MFD called VSD there are two speeds shown: G - the ground speed and T - true air speed,

https://en.wikipedia.org/wiki/Ground_speed

2. A bug is that even when aircraft air speed limit is hit the wind should add to the ground speed, when applied in the mission in the same direction as the aircraft heading. But it apparently does not in DCS F-15C.

3. This question does not make sense as it is based on wrong assumptions and lack of topic understanding.

 

@Ironhand The task was to exceed the 1494 GS limit, not to reach it.

Edited July 4, 2022 by draconus

[Ironhand]

5 hours ago, draconus said:

The task was to exceed the 1494 GS limit, not to reach it.

Ahhh...damn. That's embarrassing. Obviously, I don't read so well, either, these days.

EDIT: So DCS isn’t factoring in wind speed as a part of the GS equation. Then the question becomes, in the TRK I had posted above, can I maintain Mach 2.5 in level flight at a sufficiently low altitude to raise the TAS above 1494?

The approach in the track is probably correct given internal fuel limitations. Perhaps dropping to 30,000 ft might work…if M2.5 can be maintained. If no one else bothers to try, I will but it won’t be today.

 

Edited July 4, 2022 by Ironhand

[-Vindicator-]

Thank you Draconus.  I try to be courteous and your responses frequently are, but I notice that sometimes in these forums some folks, perhaps insecure at times, confuse demonstrating expertise with demonstrating discourtesy.  I get the “manly military men insult” thing lol but I ain’t been drafted, DCS ain’t the military, and It should come as no surprise that people asking questions may err lolol.  Ironhand’s been around awhile but he inadvertently misunderstood my question; folks err and that’s life.  He also demonstrated humility.  This is not a DCS issue but a character issue.  I get it that people often unnecessarily argue with you in this forum, but don’t assume that’s always happening or assume a personal challenge when people pose a question; the question may simply reflect a mistake.

1.  For example, one possibility you did not expressly discuss is that when I said, “your radar reflected 1507 knots ground speed,” I simply meant “your radar SCREEN reflected 1507 knots ground speed.”  That’s what I meant lol.  I’ve been trying to figure out why people say max gs is 1494 kn when my radar screen sometimes reflects more than 1494 kn gs. So I will simply assume that your radar screen reflected 1507 knots ground speed and that this is a bug lol.

2.  For example, if you think your sentence beginning, “A bug is that even when aircraft air speed limit is hit the wind,” etc., is a model of clarity, I don’t what to say, but I tried to understand what you said and I think I know what you meant.  
 

3.  My question 3 meant to refer to radar “screen” and distinguish what the screen reflects or says the gs is in knots, versus what the gs really is.  Apparently the radar screen can say 1507 knots ground speed even though in fact I cannot exceed 1494 knots ground speed.

4.  Finally, please do not feel obligated to respond further; I’ve flown the F15 in DCS for years, I think I understand what you’ve written, and I will now monitor this topic, however long it continues, for any input by others only (although I think everything’s probably been covered).

12 hours ago, Ironhand said:

Text deleted. Misread the problem. No answer here.

F-15C Speed Test 1.trk 173.65 kB · 3 downloads

 

No problem.  Thank you Ironhand!  
P.S. to Ironhand:  It sounds like you’re suggesting this may not be a bug but related to altitude.  I mentioned earlier that I was wondering if that was what’s going on.  I’ll be away from my computer a few days, so If you try dropping to 30000 ft., etc., I’ll be very interested in what you find. 

Edited July 4, 2022 by -Vindicator-
Addition

[Nahen]

There is no chance of maintaining Mach 2.5 in level flight at an altitude of 30,000 feet.

[Ironhand]

23 hours ago, -Vindicator- said:

…P.S. to Ironhand:  It sounds like you’re suggesting this may not be a bug but related to altitude.  I mentioned earlier that I was wondering if that was what’s going on.  I’ll be away from my computer a few days, so If you try dropping to 30000 ft., etc., I’ll be very interested in what you find. 

 

You can get above 1494 (this number is both GS and TAS) but you have to follow a decent flight profile. You won’t get much above it because M 2.5 is as fast as I’ve seen this jet go in level flight. That said, I can hold 1503 at 35,000 (M2.5). At 42,000 ft, the number was 1494. I may have been able to get a bit faster at 35,000 ft or some lower altitude with a better profile but this is about as much time as I want to spend trying.

Edited July 5, 2022 by Ironhand

[-Vindicator-]

On 7/3/2022 at 7:09 PM, Ironhand said:

Text deleted. Misread the problem. No answer here.

F-15C Speed Test 1.trk 173.65 kB · 3 downloads

 

No problem.  Thank you Ironhand!  

 

1503?  Great!  That’s what I wanted to know.  Thanks Ironhand!

[Ironhand]

On 7/3/2022 at 2:25 PM, Nahen said:

…I tried at around 55,000 feet and like in this video at around 40,000, when you reach this speed and start descending more or less sharply - of course, all the time on afterburners - can't to cross that speed.

Watched your video and I might know why you didn’t see an increase. The closer you get to the upper limit, the slower the TAS/GS increases. You only allowed 30 seconds and, also, were in too steep a descent which created a few issues of its own. I’ve been using a -3* pitch (more or less but never greater than -5) during the decent from altitude once I’m at 1494.

During your descent CAS was noticeably increasing but some of that was due to altitude loss. Your TAS may have been increasing a bit (I couldn’t really tell because I’m viewing it on a small screen). But your GS probably wouldn’t have been increasing (and may have been actually decreasing) due to the steepness of your descent. It’d be interesting to see, if you made a more gradual descent whether or not the result would be different.

[-Vindicator-]

This is really interesting.  Believe it or not, as I mentioned I thought I got it once to 1513-1514 kn gs, but could never duplicate it.  Now maybe I know why.

[Ironhand]

1 hour ago, -Vindicator- said:

This is really interesting.  Believe it or not, as I mentioned I thought I got it once to 1513-1514 kn gs, but could never duplicate it.  Now maybe I know why.

You just need to fly a very precise profile in order to duplicate something like that, when pushing the limits. So it’ll probably take some experimentation to get all of the pieces right. It wouldn’t surprise me to see TAS numbers a bit higher than 1514. 1522-1523 might be worth aiming for…

Edited July 5, 2022 by Ironhand

[Nahen]

3 hours ago, Ironhand said:

Watched your video and I might know why you didn’t see an increase. The closer you get to the upper limit, the slower the TAS/GS increases. You only allowed 30 seconds and, also, were in too steep a descent which created a few issues of its own. I’ve been using a -3* pitch (more or less but never greater than -5) during the decent from altitude once I’m at 1494.

During your descent CAS was noticeably increasing but some of that was due to altitude loss. Your TAS may have been increasing a bit (I couldn’t really tell because I’m viewing it on a small screen). But your GS probably wouldn’t have been increasing (and may have been actually decreasing) due to the steepness of your descent. It’d be interesting to see, if you made a more gradual descent whether or not the result would be different.

I can assure you that I have been flying this module for several years - I ONLY FLY THIS MODULE, I risk saying that I know it like my own pocket. I am not interested in how faithful it is to the real F-15C. I know all its capabilities as a DCS module. Currently, it is impossible to exceed the speed of 2.606 Mach / 1494 knots in level flight. Just like in "diving", you will not exceed this speed either. No matter what angle you descend, whether the is 3 degrees or 45. You will maintain a speed of 2.606 Mach / 1494 knots until you reach the altitude at which simulated air resistance due to its increase in air density begins to slow down the plane.
You do not believe? Give it a try.

 

And one more thing - if you want to check something thoroughly, turn off the wind. Because only under such conditions does it make sense. if you set a strong wind and you fly "against the wind", perhaps the DCS physicist will add a few knots. But from experience - sometimes yes, sometimes not.

Edited July 5, 2022 by Nahen

[-Vindicator-]

Ok, thanks for your thoughts, Ironhand and Nahen.  You’ve got me thinking.  I’m not arguing with either of you but I do want to make sure I understand what each of you is saying.  Let’s leave aside what the F15c can do in real life.  And let’s assume for sake of discussion that the F15c in DCS cannot simulate exceeding 1494 knots ground speed and that a radar screen showing in excess of 1494 ground speed is wrong.  Nonetheless, Ironhand clearly implies to me that his radar screen (right or wrong) SAID (caps for emphasis, not yelling) that he did 1503 knots ground speed.  
 

So, if I may, my question to Ironhand is: did your radar screen SAY you reached 1503 knots ground speed?  And if Ironhand is saying that that’s what his radar screen SAID, my question to Nahen is: are you disputing that his screen SAID that?  Thanks!