So, I'm getting pretty jelous of people with maxed out aircraft or sporting B2 bombers. Why? Because it takes forever for me to build up enough credits! The darn bombers are like exotic cars and upgrading anyhting past 7 is just hell on the savings. Is there a way to get credits faster without buying tons of fuel and spending $$? I play twice a day with my gift fuel, and it seems like i'll never save up a million, or even think of getting close to 3mil for the b2.
I do use mercenary contracts when I play more than my usual, but it still is a long stretch to hit the mil mark.
If you don't intend too use money, then it will be a painfully long path towards anything, the only way I can recommend of gaining more money is by saving up stocked fuel and burning them all at once using forced sortie and merc contract. That is the only way thay doesn't involve any spending of money that I know of, since I don't have that problem, it will still be very long too do though.
I agree with EtherealSeraph, you should save up on Stock Fuel for Forced Sorties and/or Mercenary Contracts.
Also, you shouldn't spent too much credits on upgrades, parts, or aircraft you probably would not use often/ever. It will not make sense to just spend money on upgrading a MiG-21bis, where it could be better saved up for the more expensive ones, such as the FB-22 or the T-50 PAK FA.
You're talking about having a highly boosted F-15E in the other thread. So, may I assume that you're okay with your fighter and performance in online missions? If that's the case, how far are you in the research tree? Unlock the important Parts like Roll+, Pitch+, and Homing+ if you haven't. These are for you so you can hit aerial enemy more easily. The point here is that you want to have a good performance in missions which would reward you a lot of credits.
If you want though, you can stop researching. You can get credit reimbursement from every online mission as long as you're not researching anything. That's also a big additional load of cash you can get. By completing 1 mission, you can get reward of completing 2. I've done this once when I've unlocked all Parts in the tree and it returned a richly rewarding result.
Also, aside from the advices given above me, my personal advice is that you should cap your aircraft level. Stop at certain level. I did it at level 7 max; that's where all special weapons are unlocked. Anything beyond that level is just too expensive for too little boost IMO. You're better off unlocking Parts that I've mentioned and sharpening and relying on your skills. If you already have an aircraft past level 7, stop it at its level. As for bombers though, with appropriate Parts you can get MVP even at level 1. So, don't level up bombers whatsoever. Actually, that goes without saying. Seeing the upgrade cost alone is enough of a deterrence.
Having nothing being researched is good for compensation credits. S ranks can net ~20k per sortie (performance and win/loss dependent) with no research going on, can easily make 100k a day using supplied alone.
Well, if it means anything, I have been playing sporatically since the launch last May and haven't spent any money at all on the game. I only fly three or six sorites on any given weekday when I do play, and I save any stocked fuel and extra contracts that I earn for weekends featuring forced sorties and increased frequency of special raid missions. Grinding away at it that way, I have earned just shy of 20,000,000 total credits thus far, allowing me to upgrade two special planes all the way to Lv.10 and four different special wepaons to Lv.5. I have maybe half of the whole tree unlocked. It takes time and patience, but by saving your fuel and spending it wisely during events, you can be competitive with even the largest whales out there.
I was obsessed with buying all the parts and planes, also getting them to at least lvl 5 so that if I liked the plane or a special challenge came up I could get it to lvl 7. The F-15E I worked towards immediately buying the game only because that was my job in the AF, mechanic on them and it's a great all-round aircraft.
I have pretty much given up leveling anything else until I get a couple of my special jets to 10, but I would love to go back and level the mig-21 to 15 just so I can rock it and school some high tier aircraft, lol.
My own preference though, is to upgrade special weapons for whatever aircraft you love. They signifigantly help out. My 4AGM at 5 is a godsend, and leveling my SFFS to 5 makes it litterally 5 times more effective because reload speed is insane and power goes up drastically. That's what I'll be saving my credits for first from now on.