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Old 01-28-2018, 03:41 PM   #21
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Actually yes.

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Originally Posted by rudellj View Post
Does any of this matter once the F-18 comes out? Are any of us going to be flying the F-15 anymore? haha
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Old 01-28-2018, 03:50 PM   #22
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Originally Posted by Maverick Su-35S View Post
The F-15 can't accelerate straight up empty, for example?
... why this necropost?

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I read that very useful and interesting document about this guy who flew the F-15, F-16 and MIG-29, yet he says that the T/W ratio was less than 1/1 due to loadout and perhaps he didn't benefit from the 25000lbf engines that the DCS F-15 should have.
Missiles, fuel + 1 bag puts you at 50000lbs, thrust is 47000. That's before we account for the store drag.


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The real F-15C should be able to prove a T/(W+D), where D is drag force (it matters even at null lift AoA) above 1 even with full fuel empty weight while starting a vertical climb (90 degrees pitch) from sea level if he manages to remain with at least 300-400km/h after reaching 90 pitch. In this condition, the F-15C with 25000lgf engines should normally find an initial TAS (not IAS) increase up to 1.5..2km height before it starts to decelerate (TAS decrease). Under the mentioned conditions, our DCS F-15 has it's TAS drop quite quick instead of slightly increasing. I have the feeling (at least by the numbers) that our DCS F-15C has it's engine thrust lower than it should at low altitude. At high altitudes, it can reach Mach 2.5 so the thrust to drag ratio is relatively correct, even if the drag and thrust may not be correct/realistic, their ratio is as long as it reaches Mach 2.5.
Wrong technique. To get maximum thrust out of the engines (installed thrust is 80% of rated, typically) you need to get moving. If you want to accelerate straight up you need 500kts before you pull up. You'll accelerate for a short time, as you'll soon reach a density altitude where again you're not ramming enough air into the engines to maintain all this thrust.

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For some reason, in DCS, the F-15 has a lower T/W and also T/(W+D) than the Mirage 2000C from RAZBAM and also lower than the Harrier O.o from RAZBAM. Who hasn't inputted the right engine performance data, ED or RAZBAM? If you try a Mirage vs Eagle player vs player battle in DCS, the Mirage outaccelerates the F-15 in the vertical. I've done a test in which I had both planes with 50% fuel, started from 1000MSL and at 700km/h IAS I started a 3G climb until I reached 90 and held 90 pitch until the tailslide took place. The Eagle only reached 8400 meters, while the Mirage passed through 9000m. How come?
The F-15 is fine. It might be the other aircraft that need some adjustment OTOH the Harrier shouldn't have anywhere near the performance of an eagle at medium to high altitude, and neither should the mirage. Down low it's another story.

Also, the mirage is light. Very different airframe.
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Old 01-28-2018, 05:36 PM   #23
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If I remember correctly, the Harrier does hold the time-to-altitude record for 15,000ft.
The Mirage with old flight model had indeed superior supersonic acceleration compared to the F-15, but that was fixed with the new flight model.
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Old 01-28-2018, 07:33 PM   #24
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Quote:
Originally Posted by Maverick Su-35S View Post
The F-15 can't accelerate straight up empty, for example? I read that very useful and interesting document about this guy who flew the F-15, F-16 and MIG-29, yet he says that the T/W ratio was less than 1/1 due to loadout and perhaps he didn't benefit from the 25000lbf engines that the DCS F-15 should have. The real F-15C should be able to prove a T/(W+D), where D is drag force (it matters even at null lift AoA) above 1 even with full fuel empty weight while starting a vertical climb (90 degrees pitch) from sea level if he manages to remain with at least 300-400km/h after reaching 90 pitch. In this condition, the F-15C with 25000lgf engines should normally find an initial TAS (not IAS) increase up to 1.5..2km height before it starts to decelerate (TAS decrease). Under the mentioned conditions, our DCS F-15 has it's TAS drop quite quick instead of slightly increasing. I have the feeling (at least by the numbers) that our DCS F-15C has it's engine thrust lower than it should at low altitude. At high altitudes, it can reach Mach 2.5 so the thrust to drag ratio is relatively correct, even if the drag and thrust may not be correct/realistic, their ratio is as long as it reaches Mach 2.5.

For some reason, in DCS, the F-15 has a lower T/W and also T/(W+D) than the Mirage 2000C from RAZBAM and also lower than the Harrier O.o from RAZBAM. Who hasn't inputted the right engine performance data, ED or RAZBAM? If you try a Mirage vs Eagle player vs player battle in DCS, the Mirage outaccelerates the F-15 in the vertical. I've done a test in which I had both planes with 50% fuel, started from 1000MSL and at 700km/h IAS I started a 3G climb until I reached 90 and held 90 pitch until the tailslide took place. The Eagle only reached 8400 meters, while the Mirage passed through 9000m. How come?
I started typing a response and realized I typed nearly the same thing in this very thread....3 years ago

Quote:
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You can test it out in game with a clean jet and a few thousand pounds of fuel. Start out in level flight, around 2-3kft at 220 knots. Smoothly pull the stick aft. Around 180 knots increase thrust smoothly to MIL. Once you have the nose pointed straight up to 90 degrees, plug in full AB. Your airspeed will start increasing! So, briefly, you can accelerate in a vertical climb in DCS. Should you? How much energy will you come out with on top? You're in a state of decreasing energy and exiting the maneuver means you need to spend more energy pulling back down towards the horizon. Not a very efficient flight path.


When did you do this test vs the mirage? Before or after the Mirage FM update?

I’ve performed climb tests/levelacceleration before and after the flight model update using a constant .9~.95 Mach climb profile. As you know, maintaining a constant mach number through varying the pitch angle in a climb means the aircraft it constantly accelerating while climbing. in a In my testing the mirage no longer out climbs the Eagle to 40,000ft (12km). Also, the mirage no longer out accelerates the eagle in level flight at 40,000 ft.
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Old 01-29-2018, 01:51 PM   #25
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Originally Posted by SinusoidDelta View Post
When did you do this test vs the mirage? Before or after the Mirage FM update?
It seem's he used the AI FM of the Mirage as a data source if his test description in the Mirage forum is correct...

I also can't confirm that the Mirage out accelerates the Eagle at high alt.
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Old 01-29-2018, 07:13 PM   #26
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Are any of us going to be flying the F-15 anymore? haha
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Originally Posted by GGTharos View Post
Actually yes.
Me too. I just can't figure out if the current Eagle's popularity is driven by it's greatness or the simple fact that it's the only "easy" American fighter available.
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Old 02-02-2018, 03:10 PM   #27
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Quote:
Originally Posted by Elysian Angel View Post
If I remember correctly, the Harrier does hold the time-to-altitude record for 15,000ft.
The Mirage with old flight model had indeed superior supersonic acceleration compared to the F-15, but that was fixed with the new flight model.
It was fixed? Read again some more. It still beats the F-15 between some IAS airspeed ranges and at altitudes above 11000meters, besides that it outclimbs the F-15C in every way.

Check these threads latest news and get convinced:
https://forums.eagle.ru/showthread.php?t=197059
https://forums.eagle.ru/showthread.php?t=199528

The Mirage is still a WIP.
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Old 02-02-2018, 04:24 PM   #28
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Quote:
Originally Posted by Maverick Su-35S View Post
It was fixed? Read again some more. It still beats the F-15 between some IAS airspeed ranges and at altitudes above 11000meters, besides that it outclimbs the F-15C in every way.

Check these threads latest news and get convinced:
https://forums.eagle.ru/showthread.php?t=197059
https://forums.eagle.ru/showthread.php?t=199528

The Mirage is still a WIP.
As I asked you in the Mirage forum... The tracks please. Even your engineer collegues would agree that fancy graphs without supplemental raw Data are not worth the paper they are printed on.
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Old 02-02-2018, 05:34 PM   #29
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[QUOTE=GGTharos;3370193]...
Missiles, fuel + 1 bag puts you at 50000lbs, thrust is 47000. That's before we account for the store drag.

Quote:
Originally Posted by GGTharos View Post
...
Wrong technique. To get maximum thrust out of the engines (installed thrust is 80% of rated, typically) you need to get moving. If you want to accelerate straight up you need 500kts before you pull up. You'll accelerate for a short time, as you'll soon reach a density altitude where again you're not ramming enough air into the engines to maintain all this thrust.
Just 80% of 23500 (47000 / 2), which makes 18800lbs? Is that what you try to say? That in DCS, the F-15C has 18800lbf at FULL AB on each engine? At 500kts it's capable to have a T/(W+D) higher than 1? If it's KIAS, then I don't know if the engines (although indeed their thrust increases with dynamic pressure or IAS) would be capable anymore to generate a total thrust higher than the weight + drag in order to accelerate on X-axis at higher than 1G, if this is what you say!


Quote:
Originally Posted by GGTharos View Post
...
The F-15 is fine. It might be the other aircraft that need some adjustment OTOH the Harrier shouldn't have anywhere near the performance of an eagle at medium to high altitude, and neither should the mirage. Down low it's another story.

Also, the mirage is light. Very different airframe.
The Mirage is light, but it doesn't make any sense to beat the F-15 in horizontal acceleration and climbout (only between some IAS and altitude ranges after latest updates, but still not correct) giving their real T/W ratio. Even by neglecting the drag, the T/W ratio difference is colossal, so it doesn't matter if it's light if by performance isn't that capable. The lift force of the Mirage is also found to be exaggerated. It can't fly in reality as slow as it does now in the sim.

Regards!
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Old 02-02-2018, 05:39 PM   #30
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Originally Posted by rudellj View Post
Does any of this matter once the F-18 comes out? Are any of us going to be flying the F-15 anymore? haha
Some of us would rather NOT be drag queens, ya know...
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