This recently published 360-degree video shows four F/A-18 Hornets performing impressive maneuvers what appears to be only a few inches apart.
Considering the risk of impact I find it hard to believe that a very slight contact would lead to immediate disaster.
Is this true? Assuming no damage is caused to the aircraft, how much impact can be handled (somewhat) safely?
@Lnafziger is correct that absolutely ZERO contact between aircraft flying in formation is acceptable, with Aerial Refueling (AR) being the sole exception to this -- but in that case the AR equipment is designed to allow for what's going on.
The problem with contact IS the significant risk of damage to the aircraft involved, so the assumption in "assuming no damage is caused, how much impact..." is outside of typical experience. IF you could assure no damage, then all sorts of things might be possible, but even pretty stoutly built fighter jets still aren't "bumper cars" and shouldn't be treated as such. Even if a collision didn't cause an immediate structural failure, the risk of damage to the internal structure of the wing/tail/whatever would be enough that the aircraft would have to be taken apart & xray'd (or another non-destructive inspection method) to ensure that there wasn't damage that would later result in structural failure.
The one exception to all of this that I can recall was a technique that the RAF used in WW II to defeat the V-1 "buzz bomb" cruise missiles. While the Spitfires could shoot them down, the small size of the missile meant that you had to get so close that you were probably flying through a cloud of debris right after you killed it (i.e. the warhead would detonate and the shrapnel might bring down the Spitfire as well). They discovered that the gyroscopes in the V-1 guidance (i.e. the primitive autopilot) would tumble if they were inverted, so some pilots would fly formation with the V-1 then intentionally make contact with its wing with their own, flipping the buzz bomb onto its back. At this point, the autopilot lost its bearings and the V-1 went down into (presumably!) empty countryside, crashing far from its London target.
Other than this, formation flight is carefully planned out so as to minimize all risk of contact between the aircraft. Even in the (very cool!) video of the Blue Angels, you can see that there is always space between the wingtips -- more space for the more dynamic maneuvers, with the least space during a fairly brief and reasonably stable pass. Remember, these pilots are extremely good & highly experienced in this sort of formation flying, and while there IS oscillation in pitch & roll, the formation is designed so that this can safely go on. There just isn't much risk there of a force that would move one aircraft directly to the left or right of its position. Turbulence might produce a rolling or pitching motion that could LEAD TO a collision, but the pilots have enough control authority to correct these sorts of forces.
That's why they're able to do what they do, safely.
Fly Navy!
During formation flying, no contact is acceptable. At the speeds of demonstration, any contact will be dangerous.
During formation flying, the pilots take every precaution to prevent accidental contact, including preventing accidental movement of control stick. According to Commander Shaun "Linus" Swartz of Blue Angels,
The Blues attach a 40 lb spring to the stick in the jet. This spring applies 40lb of nose down stick pressure, so to fly straight and level each pilot is essentially doing a 40lb curl. The purpose of this is it takes out the slop in the stick (imagine driving down the street in your 1965 Ford F-100 and the wheel moves +/- a couple inches left or right without the truck actually moving, same thing happens in a jet, and you can't have that flying a few feet apart).
As an example of what will happen if there is contact during formation fling, consider the crash of two Il-38s in 2002. During the ceremonial fly past, the wings of the two two aircraft brushed against each other, resulting in the death of all flight crew and another 3 on ground.
During formation flying, even flying into the aircraft wake can be dangerous- like the XB-70 Valkyrie crash. Note that in both these examples, the aircrafts were flying in same direction.
In summary, no contact is permitted in formation flying and pilots take every precaution against that.
