SLLOOOWWW...and pitch problem

[Tiger-II]

Hi,

Flying a clean jet, having never taken it out of AB from takeoff, I could only achieve Mach 1.8 in a steep dive. Pretty sure she was faster than that?

Same problem with the Phantom as I see with the F-5 - will not go supersonic in level flight at sea level. Seems this is a DCS problem rather than a specific aircraft? F-4 should be able to accelerate faster than Mach 1.0 in level flight.

I didn't get to land...extended the flaps and suffered an immediate and hard pitch-over that was unrecoverable.

1000000000 / 10. Would die again.

Edited May 23, 2024 by Tiger-II

[CaptJodan]

What altitude (for the former)?  

I just got back from a speed flight, and was able to get up to mach 2.1 or so.  Took bags, which obviously did not get me up to that speed till I dropped them, but used them to get up to speed and altitude, then dropped and burned the rest of the way.  Did this on Kola.  

I've also reached about 1.2 at or around sea level.  

Anyway, can confirm she isn't slow, just takes a while to get there and less than 100% fuel.  

[Tiger-II]

I was kidding a little with "slow".   For attention.

I took her up clean to 45000 ft, then did a slowly descending acceleration. Seemed to take a moment to break Mach 1.0, then eventually made Mach 1.4 but it didn't seem to want to go much faster.

Tried a level accel at Vegas, and barely broke 600 kts after several minutes. Checked everything was retracted.

Performed zoom climb (AWESOME), then vertical dive from 50000 ft. Best I could get was Mach 1.8 before needing to pull up.

Controls checked and engines producing max thrust.

Edited May 23, 2024 by Tiger-II

[CaptJodan]

Maybe it's map dependent?  Vegas is relatively small (and hot?, though by default most maps start at the same temp).  Kola gave me a ton of run time from one airbase to another.  

I'd try a large map, cool air, bags to get you up there and get you started above mach 1, and then drop and try and maintain level flight or maybe just a bit of a dive ~45-35k feet.  All I can say is it held up for me (though had a heat warning on the master caution panel).

[Tiger-II]

1 minute ago, CaptJodan said:

(though had a heat warning on the master caution panel).

Hit the cooling air reset button by the caution panel after start.

I'll try a different map.

Edited May 23, 2024 by Tiger-II

[Victory205]

When you quote speeds, it’s meaningless without altitude and configuration.

With four sparrows in the missile wells I consistently saw Mach 2.03 at FL350 and 1.12 at sea level. That’s right on the Dash-One charted speeds.

“Operationally, the F-4E is a Mach 2 aircraft. In level flight, it’s fastest at 35,000, and can achieve the dash one charted speed of just over Mach 2. Unload in a dive, and if you sport an adequate moustache, you can hit 2.2 plus. You can have fun figuring out the profile for that for yourself.

At sea level, a low drag configuration tops out at 1.12-1.15 IMN. Adding external stores will reduce max Mach proportionately.”
 

 

[Mike_CK]

I’m guessing that you are diving down into thicker air and that is why. If you start at 45k feet and initiate a shallow dive that puts you at 20k feet by Mach 1.7, you ain’t going faster even if you go straight down

head up to about 40,000ft and light them off. Stay in level flight until you are about maxed out (guessing around Mach 2). THEN dive a little and see where you are around 36,000 feet or so. Once you start getting below 30,000-35,000 feet, the air just gets too thick for Mach 2 flight 

[r4y30n]

Diving at constant G (flying straight) isn’t really an effective way to accelerate. As Victory205 said, unloading will help you out and it’s not quite the same thing. Holding less than 1 G (parabolic flight) will temporarily reduce drag to get your speed up.

[HWasp]

Didn't have the chance to fly the F-4 yet, but in general for the era, it's best to start a shallow descent for the initial acceleration starting from the high 30-ies to reach Mach 1.4 in the low 30-ies or latest around 28k. Then a level segment to reach an optimum indicated speed for the type (if not already there), followed by a shallow climb, keeping the same indicated speed, until maximum Mach number is reached.

[Qcumber]

5 hours ago, Victory205 said:

Unload in a dive, and if you sport an adequate moustache, you can hit 2.2 plus.

Could this be the issue? The speed is relative to the growth and bushyness of your moustache. You need a mach 2.2 moustache. 

[Badger1-1]

6 hours ago, Tiger-II said:

I was kidding a little with "slow".   For attention.

I took her up clean to 45000 ft, then did a slowly descending acceleration. Seemed to take a moment to break Mach 1.0, then eventually made Mach 1.4 but it didn't seem to want to go much faster.

Tried a level accel at Vegas, and barely broke 600 kts after several minutes. Checked everything was retracted.

Performed zoom climb (AWESOME), then vertical dive from 50000 ft. Best I could get was Mach 1.8 before needing to pull up.

Controls checked and engines producing max thrust.

 

Mach is a function of Temperature and Speed, you wont get a high Mach just by diving down. In that case your IAS will rise but mach wont go above a certain value since Air is getting thicker and warmer.

 

High Mach-> High Alt and as a function lower IAS (thats why theres a coffin corner at high alts)

Edited May 23, 2024 by Badger1-1

[pii]

8 hours ago, Victory205 said:

and if you sport an adequate moustache, you can hit 2.2 plus.

Levels of power:

Mil

Afterburner

Moustache !!!

[Victory205]

Mach number is the ratio between your aircraft's actual speed and the local speed of sound, which is directly proportional to temperature. Temperature decreases proportionally with altitude, so the speed of sound at SL is 661 knots, reducing linearly to 573 KTAS at 36000 MSL, above which it remains constant. That’s true airspeed, not indicated.

The real world isn't that predictable of course, so the aircraft's Mach indicator uses pressure and temperature to calculate relative Mach number. It's a fairly complex calculation, because friction causes the local air temperature to rise at high airspeeds.  
  
You may have noticed that that jet aircraft performance charts show maximum attainable velocities at 36000 feet MSL. The reason is that FL360 is the location of the tropopause, where temperature stops decreasing with increasing altitude. The minimum temperature remains constant at -57ºC.  

This all assumes standard day conditions (definition), but as you know, the real world temperatures and height of the tropopause are quite different. So Mach meters are complex instruments that use local temperature, ram rise and dynamic pressure to calculate the Mach ratio that a pilot sees in the cockpit.
  
The practical matter is 36000 feet is where the speed of sound is lowest, and due to reduced air density, the ratio of thrust versus drag is optimal. When you unload and descend to denser, warmer air, even though thrust increases, you are also fighting both higher parasitic drag, and chasing an increasing Mach number ratio.

The figures that I posted for level flight (the exact number was 2.057 IMN at 35,000), were achieved with a completely level acceleration run. Flying an unloaded descent added .20 IMN (Indicated Mach Number) to the maximum speed. 

You can probably do better, post your results.

Think about your Max Mach profile, and what altitude you would want to end your acceleration descent.  

To add to the challenge, we could specify a requirement to take off from an airfield, fly the profile and land safely on an airfield.  Don't cheat by using "unlimited fuel", but configuration is your choice. This is where it gets interesting.

You could also test for max speed attainable at MIL power only.

As an aside, there is often shear turbulence at and within 4000 feet below the tropopause. Next time you have a bumpy cruise phase in an airliner, ask your pilot if they were fighting turbulence because we were too heavy to climb above "The Trope". 

Don't mention that you know me when you do it though. 

[stuart666]

6 hours ago, Qcumber said:

Could this be the issue? The speed is relative to the growth and bushyness of your moustache. You need a mach 2.2 moustache. 

Make sure that sucker is waxed like the RAF did, or you will lose speed in drag.

[Tiger-II]

A descending acceleration may not be an OPTIMUM profile in either time or distance, but it should still assist. I know there are optimum profiles for specific airframes, but given I can fly until I'm out of fuel, I'm not too worried, unless the F-4 specifically has a drag profile such that top speed is NOT attainable WITHOUT flying a specific profile. There are several aircraft with that characteristic.

I started at 45000 ft, just below Mach 1.0, and descended between 5 and 10 degrees nose-down towards 35000 ft.

Again, the aircraft was clean, and while I know I started with 12000 lbs fuel, I don't know what the fuel state was at the time, but given I had flown at max AB at low altitude for a good 5 minutes prior, it should have burned off a bit.

Call me a "slow learner", but while some people are already bombing stuff, I'm still learning procedures and cockpit layout, but I'll be sure to know where the fuel quantity indicator is this flight.

I'm going to try this again on a different map with standard atmosphere. Vegas should also be standard atmosphere, but it eliminates a possible variable/bug due to map elevation.

Edited May 23, 2024 by Tiger-II

[HWasp]

Ok, so without any profile, I just hit M1.0 at 36000 ft in 02:50 after brake release (clean, full, 20C), hit Mach 2+ at around 06:30 with a DUCT TEMP HIGH warning, pulled up to 30 degrees and, climbed over 76k ft, then back to below 40k with a 180 deg turn, hit M 1.8. At that point Jester reminded me to check the fuel state, so I came out of burner and ended up subsonic over 30k with 2300 lbs remaining and 50nm to go for the runway. By DCS safety standards, thats comfortable.

So, yeah, it is slow... compared to the MiG-29

[Tiger-II]

Took her up a couple of time this evening, and reached Mach 2.1 this time.   That's more like it!

Now to figure out why I have no display in the front cockpit.