DCS aircraft top speeds

[brettt777]

So, last night I was bored so I decided to go on a series of high speed runs. And to my dismay, I found that all the aircraft I tested underperformed. I took a number of high speed Mach two capable aircraft, stripped them down of all weapons, drop tanks and even pylons, loaded them with half a tank of fuel and set it for unlimited fuel cuz half a tank wouldn’t be enough for this flight, then climbed to about 36,000 feet and set the altitude hold with maximum thrust. I flew north across the Persian Gulf for about 150 miles. Clear skies, no winds to speak of. Here’s what I got:

F-14B, top speed M2.34…… I got up to M1.94

F-16C, top speed M2.05…… I got up to M1.93

F-15E, top speed M2.5+…… I got up to M1.93

FA-18C, top speed M1.8…… I got up to M1.72

I even tried the F-5E, top speed M1.6….. I got up to M0.95

Again, 36,000 feet, no stores at all, half fuel, and full afterburner for about 150 miles. Now, I worked in the aviation community for most of the last four decades both military and civilian so I know that to reach these speeds the conditions have to be absolutely perfect. Well I got them as close I could. And I mean, the F-15E Strike Eagle, arguably one of the fastest modern fighter jets, and I couldn’t even get Mach 2??? What’s up with that?

[razo+r]

I have gotten the F-5 over M1.0 without issues, and the F-16 once upon a time over M2.0. 

Or like the F-14 in the picture below, above M2.0 with the fuel tank pylons still on at ISA+5 degrees C 

So it seems like there is something wrong on your side.

What are the meteorological conditions in your test?

Can you confirm your throttle is properly calibrated and you actually get 100% thrust?

Edited July 8, 2023 by razo+r

[brettt777]

5 hours ago, razo+r said:

I have gotten the F-5 over M1.0 without issues, and the F-16 once upon a time over M2.0. 

Or like the F-14 in the picture below, above M2.0 with the fuel tank pylons still on at ISA+5 degrees C 

So it seems like there is something wrong on your side.

What are the meteorological conditions in your test?

Can you confirm your throttle is properly calibrated and you actually get 100% thrust?

 

Weather conditions couldn't be any better. Clear skies, no wind, 36,000 feet. As for the throttle..... I'll get back to you on that. I know AB was on but not 100% sure on the 100%. 

[razo+r]

5 hours ago, brettt777 said:

Weather conditions couldn't be any better. Clear skies, no wind, 36,000 feet. As for the throttle..... I'll get back to you on that. I know AB was on but not 100% sure on the 100%. 

Temperature and pressure? 

[Lace]

Go higher.  I've seen over M2 in the F-16C & F-15E.  Why did you pick FL360?  Arbitrary or was there reasoning?  What was the OAT?

Also, you shouldn't need unlimited fuel, perhaps in DCS that does something funny to the gross weight?  You will need to burn off that weight as you climb and accelerate, and probably run it down to nearly empty.  Remember, as you said, these speeds are the very edge of the envelope and require everything to be perfectly optimised to reach.  You will never see them in normal operations.

[saburo_cz]

12 hours ago, brettt777 said:

And I mean, the F-15E Strike Eagle, arguably one of the fastest modern fighter jets, and I couldn’t even get Mach 2?

Yes, but without CFTs. Plane is slower with them.

With them airspeed limit is 700 Knots CAS, somewhere around M2 at your altitude (800 without CFTs). It does not mean that you can not reach higher airpeed, i know.

 

I was able to reach 2.23M at 45k altitude, standard atmosphere and with clean plane.

Speed limit for 45k feet is even lower than 700 Knots CAS, i was quite out of envelope..

Edited July 9, 2023 by saburo_cz

[some1]

Planes can fly faster when they get lighter. Do not test top speed with 50% unlimited fuel.

[Lace]

Here's a quick test.  M2.1 for the Viper at FL450 ISA+0, M2.3 for the Mud Hen.  Clean jets, full internal fuel.

Tacview-20230709-093432-DCS-Vmax.zip.acmi

[Ala13_ManOWar]

What goes on is the absolute maximum speed happens at a certain FL and conditions, and even when it happens depending on your atmospheric settings it may change so you won't see the absolute speed in your anemometer, MACH counter might be because that only depends on temperature (so watch that), but not indicated airspeed.

So, I haven't tried those models and conditions you mention, but I've tried for fun with MiG-21 to see it's limits, not only you can reach that top speed but you can even overspeed and following manuals it's realistic and you shouldn't because at some overspeeding point there's a lost of control (like 2.1M is your limit but you could reach much more and over 2.2 could be fatal but the aircraft keeps accelerating, I've reached 2.15M). Same with F-104 which I've also tried but since that's a mod we can't be as certain it's absolutely accurate (pretty good for my taste though) and it's the same, you can even overspeed, you shouldn't. BUT, it was really hard to achieve those exact conditions in which that speed is reached. For starters any external loadout prevents you from reaching the top speed, any, so watch out that (even pylons just in case) and total weight. Besides, the top speed is reached at the altitude and conditions the manual and charts tells you, it's not arbitrary, and off those limits you won't see the top speed ever at the indicator. For the MiG-21 there're videos on YT showing the process, might those tell you something you didn't think about in the conditions for that speeding trial, may be there're also others for the models you mention.

The other fun trick to try is zooming with top or even overspeed and then pulling almost vertical attitude to see where the aircraft is able to get you in altitude (altitude records were done like that indeed), also plenty of YT videos on that. And yes, aircraft performances are a biatch and not that straightforward as one might think when seeing those absolute numbers on Wikipedia.

Edited July 10, 2023 by Ala13_ManOWar

[okopanja]

Caucasus, pick winter(air temperature matters) and repeat the tests.

Pretty sure you will get better results.

Edited July 10, 2023 by okopanja

[brettt777]

5 hours ago, okopanja said:

Caucasus, pick winter(air temperature matters) and repeat the tests.

Pretty sure you will get better results.

 

I'll give it a try. Interesting... I tried the M-2000C this morning at the same altitude and location. I got up to M2.23 and had to slow down because apparently I was overspeeding the airframe. Guess I gotta go higher for less IAS.