Most probably it is right that Subsonic fuel efficiency is better than Supercruise, but it is better to confirm with SFC data for same jet, say F-22, at M 1.8 & M 0.8, IDK if it is avialbale to public.
The thing to note is - there is always some compromise & losses. What matters is objective. For SR-71, fuel consumption with repeated AA refuelling was worth for CIA/USAF bcoz Spy-Sats were not available. Today the case is opposite.
What is more important for USAF with F-22? F119 SFC is lowest 17 gm/KN/s, so they may not worry much about fuel if the VLO F-22 shoots down all its adversaries.
Mach 1.8 - 17 gm/KN/s - 100 % throttle - 116 KN+
Mach 0.9 - ?? gm/KN/s - ?? % throttle - ?? KN
And don't forget, to launch JDAM, SDB, etc, higher altitude & faster launch speed will increase range. f-22 will do it perhaps w/o revealing its IIRS but other jets will use Reheat revealing their IRS.
I think it's very clear at this point & we can safely conclude that subsonic efficiency is more than supersonic efficiency (SuCr/AB).
But now we should take the discussion of fuel/distance/speed efficiency a little further if we want to really come to a decisive conclusion on this topic.
In this discussion of speed/distance efficiency, we kept on stressing on two terms that are
supersonic &
subsonic.
When an aircraft travels slower than mach 1, it is said to fly at subsonic speeds. E.g, mach 0.6, mach 0.7, mach 0.8 etc.
When an aircraft exceeds mach 1, it is said to fly at supersonic speed. E.g mach 1.2, mach 1.3, mach 1.8 etc.
So one thing we are certain of is this: When aircraft "A" travels at supersonic Speed (
any mach value above mach 1, but below mach 5. Mach 5 & beyond is considered as hypersonic speed) and aircraft "B" travels at subsonic speed (
anything below mach 1 is considered as subsonic speed) then aircraft "A' is faster than "B", there is no doubt about it here at all.
So my point is, when using the term Supersonic & Subsonic, we are just comparing two speeds of an aircraft.
Point to be noted: In subsonic speed simulation that we may do in our discussion of any aircraft be it civilian or military, we can't go way too low, why? For e.g let's take the example of mach 0.01, is it subsonic speed? yes it is because its less than mach 1 but no fighter aircraft/civilian aircraft will travel at this speed simply because the aircraft will stall at this speed as there won't be enough lift generated by the wings.
So the range of speed that we will use for any mach value in subsonic regime for any plane would be like this.
A number line from X to Y. Where:
X=> Minimum speed the aircraft can travel, any lower and the aircraft will stall. All the numbers between A & B will be mach values.
Y=> Right before Mach 1. Right before Mach 1 is more apt for fighter aircraft because top speed of most civilian airliners cannot cross mach 1. Their top speed is right before Mach 1. One exception is Airbus A380 whose max speed is 1,185 km/h or roughly mach 1.2.
Now we should discuss this. This is what I had brought up in a previous post of mine.
In what kind of a configuration can the absolute maximum ferry range of an aircraft be achieved? This will finally answer the question of efficiency of supersonic vs subsonic. For this we will perform a HFT.
In our hypothetical flight test (HFT) we will use an F-16.
F-16 can travel at both subsonic as well as supersonic speed. As we will use an F-16 for the HFT, we won't need to do the same for other aircraft such as F/A-18, F-22, F-35, Rafale, Su-30, EF-2000, Tejas, Airbus, Boeing, etc because we will come to the same conclusion of Speed/fuel/distance efficiency because all of them are planes at the end of the day. Unless you want to gauge out the specific numbers (e.g, exact range, exact speed, exact drag characteristics etc) that will be a lot more difficult and take a lot of time to do so.
If someone gave me the chance to pilot an F-16 and asked me:
"
How would you pilot this aircraft so that you can cover the absolute maximum amount of range?"
Then I would go about the following>
An F-16 is a fighter aircraft, it can carry a variety of payloads ranging from weapons, fuel tanks to sensors.
Please note that the above chart may not be the most accurate, you can find other charts on the internet, mine is rather more generic.
In aerodynamics, any aircraft which carries a lot of payload will be very heavy itself. Heavier the aircraft, more the lift will be required, and to generate more lift, we will need more thrust. When you add more missiles, pods & other external attachments on the aircraft's pylons then not only are you increasing the overall weight of your aircraft, you are also increasing the overall drag. The case would have been different if the F-16 had internal bays to store missiles, bombs internally to deal with the issue of drag but it doesn't. Irrespective of internal carriage, weight will still be added while drag can be taken out of the equation.
The F-16 I will pilot should have no payload like sensor pods weapons, only fuel & drop tanks. I am trying to cut down on as much drag as I possibly can. Yes I will be considering CFTs in the HFT, they will increase drag but not as much as adding AMRAAMs, Sidewinders, Pythons, Rocket pods, ARMs like HARMs etc.
Let's name our F-16 that will use for the HFT as F-16
HFTF. Where HFTAF stands for
Hypothetical Flight Test Frame.
Before that I will use three F-16s, lets mark them as F-16 #1, F-16#2, & F-16#3. All three will have the M61A1 Vulcan 6-barrel rotary cannon in them. None will use CFT, and will fly solely on internal fuel.
F-16#1 will carry 6 AIM-120 AMRAAM + targetting pods (any kind, F-16 can carry more than one type).
F-16#2 will carry 4 AIM-9 Sidewinder.
F-16#3 will carry just two AGM-88 HARM.
So which will have the maximum range? It's very simple, it would be F-16#3. Just two AGM-88 on F-16#3 will give less drag & weight than what 6 AIM-120 +Targetting Pod & AIM-9 will give on F-16#1 & F-16#2. More drag & weight for same speed need to be compensated with higher thrust which in result consumes more fuel & at a faster rate.
Now coming to F-16 HFTF.
When piloting the F-16, I will remove out the
M61A1 Vulcan 6-barrel rotary cannon to reduce weight, I won't be needing the cannon during this test at all, unless I am going to use it in combat & this HFT won't involve combat at all.
I won't be carrying anything on the pylons with the exception of CFTs which I will ditch/eject as soon as they run out. Because they have no more use to me, rather they impose unnecessary drag and weight on my aircraft which is counterproductive in aerodynamics.
Now let's take a brief look at T/W ratio. Correct me if I am wrong but the T/W ratio of any aircraft improves with time because while the fuel does get depleted, the weight goes down too because the fuel is being used up (fuel weight is also accounted for in T/W) and when the T/W ratio improves, the engine has to generate less thrust to push less weight and when less thrust is used, the rate of depletion of fuel goes down and you can use more fuel over the course of your flight which automatically translates into more range.
And I will fly the F-16 at the minimum speed needed for it to achieve lift. I think you will understand why I am doing this, because fuel consumption increases greatly with speed.
If I used the same F-16 HFTF and travelled at Mach 1 till I ran out of fuel, the range I will cover will still be less than what I would cover if I flew the F-16 HFTF at Mach 0.8 till I ran out of fuel.
I think you will understand why I would choose to fly the F-16 at the absolute minimum speed till I run out of fuel, there is no question of me flying any slower because I will immediately stall and crash.
I think we can finally conclude that not just efficiency of subsonic is better than Supersonic but rather the efficiency of slower speed is better than faster speed!
But I am sure that you will find more satisfactory answers in flight manuals. Flight manual of aircraft like F-16, F-18, F-4, MiG-21, MiG-23 etc are available but not the flight manuals of aircraft like Su-57, J-20, F-22 or F-35. But like I said, using just one aircraft as an example can help us gauge the same conclusion of other planes unless you want to get the specific numbers which is a lot more difficult and involves a lot of calculations.
Feel free to correct me if I may have made a mistake anywhere, this is the best I could come up with after thinking about it for a few days. I am happy to learn from my mistakes.
You mentioned the example of F-22 and SR-71 when speaking of fuel efficiency in terms of distance & economics. Both SR-71 & F-22 are military aircraft. Yes there are always compromises to be made. You will have to compromise between things. You cannot have everything at once.
Now we will have to make the comparison between military and civilian jetliners based on priority when it comes to cost to efficiency.
For military, cost is not a priority but for civilian airlines, cost is a priority. Civillian airlines want to make profit from passengers, and I think the word
profit itself answers on whether the fact that efficiency decreases at higher speed is more important to military or civilian airlines.
Ok, why sorry, apologize?
Sir, I have this habit of apologizing too much to others even when I may not have done anything to offend anyone. Not a lot of people in real-life interact with me, and whenever I get the chance to get into a conversation, I get in but at the same time I stay at their mercy & agree with most of their points even if I may have a differing opinion, in short=> I am desperate to have company of any sorts. Hopefully I will be less of the apologetic kind with time.
Did i say something on DFI? Feel free to take screenshots of my DFI posts, but use it constructively.
We have to see what exactly we said earlier in what context, etc. Our knowledge & understanding improves with time.
You didn't say anything on DFI & neither am I talking about you at all. I was talking about someone else, not you or me. He is a very knowledgeable engineer and he can contribute a lot to our discussion, at my request he has joined the site. I assure you that you will enjoy his presence here because of his tech oriented discussions. I learnt a lot about radars, aircraft, missiles, warships, aerodynamics, turbofan engines etc from him since I first started speaking to him in 2021/22.
In my limited knowledge from Discovery Channel documentaries since 1990s, Lifting body fuselage are of 2 types - air pushes the front belly of fuselage up; & parts of the fuselage longitudinal cross section like LERX are like that of a wing, creating a low pressure on top. I think MiG-29, Su-27/3X have this kind of LERX.
Interesting but nowadays I don't watch discovery channel, Discovery science, or any other documentary channels. I mostly depend on my mobile phone for searching about anything such as quora, Reddit, X, YouTube, or forums like this one. And I am sure that in today's modern digital age where almost everyone has access to a smartphone will use that to get any information on a certain topic rather than sit in front of a TV & watch hour long documentaries.
"SUPER-FLANKER", good to see you here. Nice strategy to stay passive.
Nice to see you here too, you are the same Bhartiya Sainik from erstwhile DFI, By the way my actual name is "Neil" but you can call me whatever you feel like, "Super Flanker" or "Neil". It's up to you. This is most likely going to be my permanent username on DFB. And my strategy of staying passive need not necessarily mean that I don't actively participate in any given discussion, rather I try and understand what is going in the discussion, and add points that may help all the participants to reach a definitive answer.
- I discuss what I can & not what I cannot.
- I comprehend what I can & ignore what I cannot.
- I don't ignore what I can understand & ignore what I cannot/don't understand.
This is the way I participate in any forum discussion.
I am sure 2 people who don't like advanced maths can discuss well
In the past you said you weren't a fan of PCM during your schooling/college years. In my case, I like mathematics & physics a lot more than chemistry. I dislike chemistry the most out of P,C,M especially OC (Oraganic Chemistry) which goes above my head whenever I try to understand it. I find maths & physics more interesting. That said, I have never hated any subject completely at all, I have always liked/enjoyed some aspects of a subject while disliking other aspects of the subject.
On a side note, I think we have written a lot of posts about Jet-engines, I do not think that these posts should be on the AMCA Thread at all.
@Bhartiya Sainik @scholar of war
Will resume the discussion after the posts are moved to the other thread. Thank you.