Close Air Support

Most airforces are in the process of replacing their ageing fleet. Modern air superiority fighters like the Rafale, Typhoon and Grippen can be used as bombers. It is foreseen to use them as ground attack weapons, because novel targeting pods and high precision bombs allow attacking targets on the ground.

However, I don't believe that these aircraft are suited for the close air support.

Close air support (CAS) is defined as air action by fixed or rotary winged aircraft against hostile targets that are close to friendly forces.

The requirements for fulfilling the role of close air support are:

Integration with ground operations:

The main purpose of close air support is to support ground troups in a battle against an enemy force. Consequently, the attack aircraft must coordinate its attacks precisely with the friendly ground troops. The chances of mistakenly hitting a friend are quite high in this mission. The situation on the ground may change rapidly. Therefore, the ground troops and aircraft must both positively identify the position of an enemy position, before the attack aircraft attacks. 

Precision Attack:

The ground attacks carried out by the aircraft must be very precise, because the proximity of the ground troops with the enemy increases the chance of hurting friendly troops.

Availability: 

The need and possibility of administering a successfull ground attack can change rapidly in the course of a battle. Consequently, the attack aircraft must react fast to the changes on the ground and be ever present in case it is needed.

Protection: 

The aircraft must be protected against enemy fire. The enemy ground forces are going to attempt to shoot down the aircraft using anti-aircraft guns as well as surface to air missiles.

These requirements dictate the capabilities of the aircraft.

Loiter time: 

In order to be readily available the aircraft must be able to loiter above the battle field for an extended period of time. This improves the availabilty of the aircraft to the ground forces.

Slow and Low: 

The capability of flighing slow and low both facilitates the reconnaissance of enemy forces and the presision attack.

Agility:

Speed and agility offers protection against enemy fire. Fast turn rates are necessary in order to avoid hits from surface to air missiles.

Protective Armour:

Again, this is desireable in order to sustain hits from enemy guns.

The integration with ground troops demands that the aircraft must have a high speed data link and radio communication with ground forces. Furthermore, a suite of sensors such as radar, optical and infrared sensors as well as high precision bombs and missiles. However, these weapons can be integrated into any possible aircraft. No special aircraft is needed in order to meet these requirements. 

These requirements are in parts mutually exclusive. For example, protective armor adds weight to the aircraft, which in turn reduces the speed and agility. Aircraft, which can travel slow and low usually are not very agile. High loiter time requires high fuel efficiency and lots of fuel, which adds to the weight of the aircraft.

Slow and low, how important is this? The improvements in sensor technology and precision guided missiles and bombs have mitigated the advantages of aircraft capable of hovering above the ground. The advantages of low speed in reconnaissance and precision attacks are less obiouvs than in the past. On the other hand, the advances of small and protable surface to air missiles has mitigated the advantages of highly protective armor, because no armor can withstand the explosion from such a missile. Consequently, both protective armor and low speed capabilities have become less significant. A specialized aircraft for close air support must relie on its agility in order to evade enemy fire.

The resulting priorities for such an aircraft should be:

1 Loiter time:

2. Agility

3. Protection

4. Slow and Low

Let's compare how military aircraft fulfill these requirements:

Ground Attack Aircraft?

1. A-10 Thunderbolt II Warthog;

2. Panavia Tornado

3. AV-8B Harrier II

Attack Helicopters?

1. AH-64D Apache Longbow
2. Eurocopter Tiger

Attack Drones?

The main contenders are the Apache longbow and the legendary A-10 warthog. They are specifically designed for the close air support mission. The other aircraft were merely included because their specific abilities and as a comparison.

So how do they compare?

1. Loiter time: 

We don't know the exact time that the apache or warthog can loiter over the battle field. This certainly depends on the distance the aircraft can be parked from the battle field. In this regard, the helicopters and harrier jump jet have a clear advantage. The warthog can lift of from short and rugged runways.

a) Required airfields:

1. Apache + Tiger

2. Harrier II

3. Warthog

4. Tornado

The range of the aircraft does indicate the time it can loiter above the airfield.

b) Range:

1. Tornado = 1,390 km

2. Warthog = 1.030 km
3. Tiger = 800 km

4. Harrier II = 556 km

5. Apache = 407 km

Overall, the winner in this category is the tiger, because it combines vertical take off capabilities with a fairly long range. The warthog is second, because it can take off from short runways and has an extended operating range. 

1. Tiger

2. Warthog

3. Harrier + Apache + Tornado

2. Agile enough to evade SAMs

1. Tornado (1,482 km/h)
2. Harrier (1,083 km/h)
3. Warthog (706 km/h)
4. Tiger (290 km/h) + Apache (265 km/h)

The tornado is the fastest of these aircraft with the highest turn rates. The warthog and harrier are sufficiently fast and can turn fast at low speeds. The Tiger and Apache are very slow and can hardly turn compared to the fixed wing aircraft. In this field, the fixed wing aircraft outperform the helicopters by a large margin. The ability to turn fast in order to evade enemy missiles gives them a clear edge. 

3. Protection against enemy guns

In this regard, both the Apache and the Warthog are extremely capable. They were built to withstand enemy fire.  The tiger is a close second. Tornado and harrier are virtually unprotected against gun fire.

1. Warthog + Apache

2. Tiger

3. Tornado + Harrier II

4. Slow and Low

1. Apache + Tiger

2. Harrier 

3. Warthog

4. Tornado

In this category, the helicopters clearly outperform the fixed wing aircraft. The harrier can fly slowly using the vectored thurst and the warthog is decent in this field due to its wing design. The tornado uses swept wings in order to fly slowly but cannot compete with the other aircraft in this field.

Overall the warthog is the best aircraft for close air support. Why? Because it performs well in all of the key performance areas. The Apache and Tiger are both on second place; the tiger's range is superior but the apaches protection is better. However, both helicopter's performance in terms of turn rates and speed, i.e. agility is very bad compared to the fixed wing aircraft. In terms of slow and low flying they perform best.

Due to improved precision bombs and missiles, flying slowly has become less important for precision attacks and reconnaissance. Since this feature has become less significant, the future of close air support are fixed wing aircraft, not helicopters.

The Harrier is interesting, because it's technology shows that a fixed wing aircraft can be made to fly very slowly. The tornado also implements a technology, namely the variable swept wings, that is interesting. The wings are swept back for high speed and swept forward for low speed. 

Overall performance:

1. A-10 Thunderbolt II Warthog;

2. AH-64D Apache Longbow + Eurocopter Tiger

3. AV-8B Harrier II + Panavia Tornado

The future of close air support aircraft are fixed wing aircraft and not helicopters. The A-10 Thunderbolt is king of the hill. A future thunderbolt should have the speed and agility of the tornado and the low speed performance of the harrier. How could this be achieved?

The A-10 has superior maneuverability at low speeds and altitude because of its large wing area, high wing aspect ratio. These design choices should remain. However, the top speed of the aircraft is limited due to the high drag of the wings. But top speed is not all that important. A close air support aircraft is not expected to fly supersonically. But, high turn rates are of prime importance in order to evade surface to air missiles.

In order to reduce the drag, a swept wing, in particular delta wings, are usually used. However, the swept wing reduces the ability to fly slowly and loiter above the battel field. The Tornado uses variable sept wings in order to perform well in high-speed and low-speed flight. The harrier jump jet uses thrust vectoring in order to improve the low speed capabilities of the aircraft. Both solutions are expensive.

The best solution without regard to the cost would be to build a harrier jump jet with variably swept wings. However, the price of this solution would be exceedingly high. In my opinion it would suffice to variably deflect the thrust from the jet engine exhaust at the tail of the airplane in order to improve the low speed performance of the airplane. This technology is used in the F-22 as well as Russian designs like the Mig 29. The aircraft should have fixed wings, which are less swept than those of dedicated fighter jets. Such an aircraft wouldn't have the low speed performance of a harrier or helicopter, but it would be on par with the A-10. The swept wing configuration would improve the speed and agility of the aircraft. Thrust vectoring would not only enable low speed performance but would also improve the maneuverability at low speed. The resulting airplane would have the low speed performance of the A-10, but would be far more agile and fast. Since low speed is no longer a top priority, this aircraft would offer a far better overall performance than current designs.

Finally, the A-10 is built around a huge 30 mm gattling gun for firing armor piercing rounds. At the time of its design this weapon seemed to be ideal for destroying tanks and other armored vehicles on the ground. However, the rational for this gun no longer exists because heat seaking hellfire missiles are more capable for this job.  The missiles have the additional advantage that they can be fired from a greater distance and the airplane turned away immediately after firing. The heavy gun should be dropped from the plane.

A-10 design:

The warthog has quite an unusual placement of the jet engine above the wings, which does not lend itself to the implementation of thrust vectoring. Preferably, the jet exhaust should be placed at the back such that the jet exhaust can be directed into any desired direction. The wings should be swept back in order to reduce the drag of the airplane. Thrust vectoring should be employed to improve the maneuverability and turn rates.