Supersonic, Zoom Climbs - Possible?
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flip into TAS or use mach indicator in HUD. by default the airplane uses CAS, which is a fudged number to tell you how your plane will behave in turns based on airflow over control surfaces. at altitude the plane can be traveling 300~ CAS and actually be at mach 1.2 for instance, whereas near sea level you can hit 800 kn CAS at mach .8
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Right. Looking at the Mach meter, 1.4 seems to be around 800 knots at 30,000 feet. In any case, this table suggests about a 100 knots difference in the speed of sound between altitudes:
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Thank you Cik! That finally makes some sense, will try it.
EDIT: Yes, indeed. The HUD mach number is in the range of 1.88-2, while the airspeed indicator dial and HUD airspeed scale read 700-800 knots. Now, (just for curiosity sake), I am wondering how to set the airspeed scale to true airspeed.
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edit:
sorry, guess you hadnât read my last post. no hostility here ~
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Must have missed whatever you were planning as a response, but a big thank you for pointing out the use of CAS. Think that has been misleading me a long while now.
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NP bro
iâm only paying it forward. someone else wrote a 3 paragraph essay on how it worked when i was confused. for reference the switch is on the right side of the cockpit, where your knee would be. 3 position switch, defaulted to up (cas) middle position (TAS: true air speed) and bottom position (GN SPD: ground speed) as you climb, youâll notice your CAS decreases sharply, because of the much thinner air. your plane will handle like a whale, even at mach 1.2 because thereâs so little air to manipulate. youâll be going much faster though, and your engine will be sipping something like 4000~ fuel throughput to maintain speed. if you are going to travel a long distance, itâs almost always worth it to make the climb to angels 30.
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Many, many thanks! After flipping the appropriate toggle button on the HUD controls, true airspeed now reads 1200 knots, corresponding to Mach 2 in level flight, which the HUD also displays. Wow, to think something so simple was so confusing, this has been plaguing me for months!
Now to see if some of the climb/altitude behavior makes more sense with a usable airspeed indicator.
Thanks again, pushing back up to 1100 knots at 40,000 feet again, and very happy!
EDIT: Yes, indeed altitude behavior is much more comprehensible, with much more intuitive speed/altitude relationships. Managed to retain 1000 knots at 60,000 ft without embarking on a zoom climb, and the plane definitely launches upward better from its 50,000 ft service ceiling.
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In a nutshell, itâs very difficult to tell how âfastâ you are really flying. In relation to what? The ground? If you flew in the direction that the earth is spinning, and flew as fast as itâs spinning, would you be moving at all? These are all considerations that have to be understood before you can contemplate âspeedâ. CAS is important to understand how your aircraft will perform in a specific altitude regime but it wonât tell you how âfastâ you are actually going. Itâs important to understand these concepts before you can break the âsound barrierâ multiple times over
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Iâve gotten the BLK52 up to M1.95 or maybe M2.00 in level flight. Check your HFFM/HAF performance charts; the line goes across the 2.0 threshold under narrow conditions.
The maximum ceiling of temporary excursions above sustainable altitude is an interesting one. Energy charts express both height and speed in the same units. Specific power âPsâ is expressed in feet per second climb. So 100 fps Ps represents the ability to raise 1 kg of airframe 1m higher against gravity 9.8 m/s² in a certain time (higher Ps, lower time). It takes a certain power (energy per time) to increase the potential energy of the aircraft by moving it farther from the Earthâs center. Ps 100ft/s also represents a power which is able to accelerate the aircraft.
The minimum time to climb profiles are made under the assumption that if you maximize Ps, you maximize energy entered into the system. It doesnât care if you are using this power to go faster or higher. The idea is that Ps curves have ânegative curvatureâ and youâll reach a maximum value at some speed. If you pitch to maintain that speed you will go higher to avoid going faster and leaving the max Ps curve peak. Itâs assumed that adding speed and adding height are adding the same substance and that you are free to convert freely with 100% efficiency between the two with no delay. Of course in reality it isnât. Mach 10 at ground level doesnât translate with 100% efficiency to convert all of that speed to altitude instantly.
Energy charts can be âbumpyâ like humps on a camel. It is possible to exist in a steady state at do different height/Mach points on the graph just fine but for it to be impossible to exist on a point directly between those two zones. The transonic region has a higher drag than the sub or supersonic region usually. In some cases you have to take an interesting path to go âunder the dipâ in the graph. This is were diving to get into the faster regime comes from. Usually this âfollow the valley around the mountainâ path in the F-16 is near M0.9.
Back to the original question maximum altitude depends on two things:
1. Total energy
2. Converting as much speed energy to altitude energy as possibleBeing at maximum sustained altitude is a tall launching point for a zoom but your zoom potential here is zero. It is the sum of the altitude at each point on the sustainable chart plus the zoom potential that we wish to maximize. Then there is the zoom technique to consider. Too harsh and drag saps the energy so it wonât become altitude. Too gentle and gravity*time saps the energy. The ideal transient zoom profile maximizes the ratio of climb rate to energy loss. This is a difficult problem for my brain.
The FLCS is not a significant hindrance to pushing the envelope except perhaps at extreme AOA. These energy regimes generally are smooth and require minimal flight surface movement. Indirectly the FLCS is a benefit because the airplane can be designed without traditional draggy stability concepts.
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Many, many thanks! After flipping the appropriate toggle button on the HUD controls, true airspeed now reads 1200 knots, corresponding to Mach 2 in level flight, which the HUD also displays. Wow, to think something so simple was so confusing, this has been plaguing me for months!
Now to see if some of the climb/altitude behavior makes more sense with a usable airspeed indicator.
Thanks again, pushing back up to 1100 knots at 40,000 feet again, and very happy!
you are welcome. keep in mind though that CAS is a very useful mode, because it provides a metric on how your airplane will handle independent of altitude. if you are in a fight and ask yourself âcan i turn into this MIG-29 and get an advantage?â CAS will tell you how your aircraft will behave. corner airspeed will be at 400~ kn regardless of altitude. it just confuses people because itâs the default mode.
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Iâve gotten the BLK52 up to M1.95 or maybe M2.00 in level flight. Check your HFFM/HAF performance charts; the line goes across the 2.0 threshold under narrow conditions.
Yes, indeed, I am pushing similar performance now.
maximum ceiling of temporary excursions above sustainable altitude is an interesting oneâŚ
Being at maximum sustained altitude is a tall launching point for a zoom but your zoom potential here is zero. It is the sum of the altitude at each point on the sustainable chart plus the zoom potential that we wish to maximize. Then there is the zoom technique to consider. Too harsh and drag saps the energy so it wonât become altitude. Too gentle and gravity*time saps the energy. The ideal transient zoom profile maximizes the ratio of climb rate to energy loss. This is a difficult problem for my brain.
Exactly, and true airspeed seems to be a much better indicator as to how much energy is available.
The FLCS is not a significant hindrance to pushing the envelope except perhaps at extreme AOA. These energy regimes generally are smooth and require minimal flight surface movement. Indirectly the FLCS is a benefit because the airplane can be designed without traditional draggy stability concepts.
Thank you very much for confirming this.
EDIT: Yes, Cik, CAS is definitely useful for aerobatic/combat situations. Personally, I just feel like starting with zoom climbs and similar maneuvers to get some idea as to the energy/altitude tradeoffs involved with a (hopefully) more accurate flight sim than what I am used to.
EDIT2: Definitely, TAS is proving much easier to understand going into a zoom climb. Pushing 70,000 feet easily now, without needing to depart from controlled flight.
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Exactly, and true airspeed seems to be a much better indicator as to how much energy is available.
Absolutely not, CAS is there to remind you of how your aircraft will perform AT CURRENT ALTITUDE! Never forget that, as corner remains relatively the same with CAS! Go by TAS and you will die in a dogfight
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Also when gear is out you will automatically read CAS speed on HUD no matter what configuration youâve set up because of its importance regarding flight behavior.
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Right, right. CAS is useful. TAS is useful too though, as an indicator of what the plane is actually doing. Case in point, just pushed the Mig-25 flight model to Mach 3.05 (1798 knots) @ 55,770 ft. Meanwhile, CAS read out just 1801 knots.
Oh, and pulled off an 85,000 ft zoom climb from there. No doubt even greater altitude is feasible.
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Right, right. CAS is useful. TAS is useful too though, as an indicator of what the plane is actually doing. Case in point, just pushed the Mig-25 flight model to Mach 3.05 (1798 knots) @ 55,770 ft. Meanwhile, CAS read out just 1801 knots. âŚâŚ
Regardless of what your âdisplayedâ speed is set to (TAS, CAS, etc.), doesnât your mach readout tell you the correct mach number for whatever altitude youâre at? If so, what do you need TAS for?
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True, I can rely on the Mach number, but the greater precision TAS number does indicate gains and losses more precisely. Most important thing is just realizing that CAS is different from TAS.
Suspect that CAS becomes less relevant at supersonic speeds, assuming most airframes reduce flow to subsonic by the time it reaches the sensor.
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Altitude and TAS (or G/S, jury is out) determine energy state. The math is very straightforward to the point you can compare two airplanes at different speeds and altitudes to see who âwinsâ the energy game.
Example problem:
Airplane A is 400 KTAS, 20,000â
Airplane B is 500 KTAS
What altitude must Airplane B be at to have equal specific energy as airplane A?Solution:
Convert values for easy calculation
A: 205.8 m/s, 6,096 m
B: 257.2 m/s, ?,??? mEquations for Total, Kinematic, and Position Energies
Es = Ts + Us
Ts = T/m = 0.5*(v^2)
Us = U/m = 9.8*hEs[A] is 80,918 J/kg or expressed as a height 8257 m. For Es **to be equal the sum of its speed energy (33,075 J/kg) and its height energy. By subtraction the height energy must be 47,842 J/kg which is a height of 4,882m.
A: 205.8 m/s, 6,096 m
B: 257.2 m/s, 4,882 mConvert back to knots and feet.
A: 400 KTAS, 20,000â
B: 500 KTAS, 16,017â** -
Right, so I take it TAS is the number to watch closely while pulling zoom climbs and other speed/energy tradeoffs.
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Right, so I take it TAS is the number to watch closely while pulling zoom climbs and other speed/energy tradeoffs.
again, CAS is critical to understanding how your aircraft will perform AT CURRENT ALTITUDE! So take it like this, TAS is NOT the number to watch closely! Example: Watching TAS will not tell you when the aircraft will stall, whether zoom climb or at corner speed. MACH is your friend
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Right, I get that. CAS determines when the aircraft will stall, and in turn, the maximum angle of attack. Nonetheless, exact TAS (as opposed to the slightly more approximate Mach number) is helpful too.