How can I make my air force more effective?

I'm playing the Long War mod for XCOM: Enemy Within and I'm nearing the end of month two. It's never been easy to shoot anything down... it usually takes 3-4 interceptors just to take down a small scout. Now that the game is progressing, it's getting even harder, and even rotating through 7 different interceptors I'm running into problems where they're all out for repairs when new UFOs hit. This is even considering the fact that I let the larger ones through without engaging!

I feel like I need to focus my research on some improvements that will improve the effectiveness of my interceptors. I've seen the tech tree for Long War but honestly that thing is so huge and lacking in description that I'm having a hard time making heads or tails of what path I need to head down to become more effective as quickly as possible.

What short term and longer term plans can I make so that my air force stays effective?

I'm current mid way through a play of a long war game and thought I'd offer a few bits of advice I've determined from experience and researching within the wiki for my own knowledge.

First of all, gaining an upper hand in aerial combat is going to take a long time. The mod intentionally makes the air game a constant lose battle. As always, if you rush to these improvements first you'll likely suffer in the tactical game, so a careful balance is required.

There's a few ways to improve your effectiveness in dealing with UFOs:

Pick your Fights

Don't try and shoot down large, or even medium, sized craft until you've improved your air force. A lot. You really just have to let them go at the start.

Even the small UFOs will require multiple stock interceptors to shoot it down, so don't go into a fight unless you're happy to have damaged interceptors for a while.

Scare them Away

You don't always need to shoot down a UFO to (possibly) prevent it from completing it's objectives, sometimes just damaging it is enough. This allows you to still deflect some missions at the cost of less down time for your interceptors.

For example, a UFO that's hunting satellites will have a reduced chance of success if damaged, and will fail if it's health has dropped below 50%.

UFO Analysis

Once you have completed a tactical mission against a type of UFO - either after shooting it down or because it has landed - you will have the option of performing a UFO Analysis research on that type of craft. Completing this reasearch will give a damage bonus to all inteceptor attacks (with all weapons) against that type of UFO in the future.

Weapons

As you research better weapons you can construct equivalents to be mounted on to your interceptors. The path through weapon research if fairly obvious so I won't repeat it here.

Also, in the early game when you're still using the default weapons do note that the armour piercing Stingray Missiles work best against the armoured Fighter small craft, while the Avalanche Missiles work best against the Scout small craft - so it can be worth swapping the default weapons around a bit.

Modules

As with the vanilla game, you can use Tracking, Aim and Dodge modules during combat to temporarily increase combat time, interceptor accuracy and interceptor change of dodging shots.

All of these require the Aircraft Boosters foundry project to have been completed - this is available after completing the Alien Materials research, which is available immediately.

Tracking (Aircraft Booster) requires no additional research.
Aim (Uplink Targeting) requires the Floater Autopsy research.
Dodge (Defense Matrix) requires the Cyberdisc Autopsy research.

Upgrades

There are several Foundry projects available that provide perminant upgrades to all interceptors - more health, better accuracy, dodging, etc - that can be used to improve your chances in the air.

Many of these are unlocked by the Advanced Aerospace Concepts research project, which will requires Experimental Warfare, Alien Weaponry and Alien Materials to start. The Seeker Autopsy and Alien Propulsion projects also unlock other upgrades.

There's too much information to repeat here, so go have a look at the UFOpaedia's Foundary (Long War) page and scroll down to Aerospace Improvements for a full breakdown.

I replace damaged interceptors with the fresh ones from other continents. Surprisingly, even heavily damaged craft can be transferred, and it seems that repairs continue during the transfer.

In order to win the air war you need to pick your battles. I personally have found in the beginning of the game to read the tags associated with the boogie. Those being NOE(Nape of the Earth), low, and high. Its only really worthwhile to attack targets low or those scanning for satellites. My luck with high targets is abysmal, and usually blow up on impact with the earth. NOE means that the target will almost always land or start a mission saving the need for air engagement. That understanding saves people from a lot of deployments.

It is also critical to know your enemy. If you see a large vessel move out of the way, odds are it is going to land or is going to start a mission with far less troops to deal with even if you somehow took it out with avalanche/stingray missiles.

Finally it is most critical to know the deployment of the aircraft. The best time to pull out an aircraft is within the first 2 hits. Keeps the repair time down to about a week at max. However at the beginning of the game it is probably best to keep sending aircraft aggressively. This gives you and the ufo a +15% chance to hit, which is probably going to hit you far more than you hit it regardless. Until better weaponry and foundry upgrades from Advanced Aerospace Concepts which are really expensive in cash and materials you probably don't have even then.

It should be noted that this is a method of attack for the early months of the game, while the same principles apply through-out, there is a greater need for supplies as well as a change of attack patterns. Those larger ships stop ignoring you, and start bum rushing you. Truly a sad day when you have to deal with a battleship and entourage headed directly at you. This starts happening when you get to the point of the firestorm however, don't fret just yet.

In short? Pick your battles, because like long war recovery, it isn't a kind mistress.