old aircraft vs new aircraft

[Jaepheth]

Ok, I tried posting this in testing hoping for a quick answer, but no one responded, so I guess I'll try here.

My question is, if an old aircraft like a B-29 were flying around, could a supersonic aircraft knock it out of the sky by simply flying past it? If so, how fast and how close would it have to fly? What would the damage be and could it still be landed or would pilot and crew have to bail out?

[Batman]

There's a reason nobody responded to it, you know.

[Broomstick]

Well, it's an interesting question on one level, but I think there are some presumptions going on here that make a one-line definitive answer difficult or impossible.

There is an enormous range of aircraft out there, both WWII and modern era. Size also counts. Bullets, for example, are supersonic but merely whizzing by an aircraft won't "knock it out of the sky" or cause major damage because not enough force is imparted by its wake to cause damage. On the other hand, passage of even a sub-sonic jet near a small airplane such as I fly has caused the smaller airplane to tumble out of control or crash or cause major damage.

You also have to define "close". A kilometer of separation between aircraft is often considered "close" or even a "near miss". So you need to define that term.

I would guess that some WWII era airplanes that were very large could survive a realatively close encounter with with, say, a modern fighter going around Mach 1, maybe a little above, although you'd certainly notice it. A WWII era cloth-covered airplane vs. something going well over Mach 1 is going to suffer disaster.

So - be specific. Which aircraft, how close, how fast is each going, and is it convergence or overtaking that's going on?

[Jaepheth]

ok, a B-29 is flying at 10,000 ft @ 360 mph, when an F-22 flying at 11,000 ft going mach 2 passes directly over it at a right angle.

[Big Phil]

That B-29 is bigger than the F-22. I doubt even a Mach 2 shockwave would affect it too much...

[Nephtys]

An XB-70 could probably do it.. with it's engine vortex. It caused a chaser fighter to crash, didn't it?

[Spoonist]

Flying close to one side giving extra lift to one wing only would definately shake things up but it would be an easy correction for the pilot to make to stabilize it again.

[Admiral Valdemar]

An XB-70 could probably do it.. with it's engine vortex. It caused a chaser fighter to crash, didn't it?

The chase got too close to one tailfin and clipped it, which took that plane out of action (F-5, IIRC) and caused the Valkyrie to plummet as the supersonic airflow got disturbed by the aerodynamic anomaly.

The SLAM from Project Pluto would be another candidate. A freight locomotive sized nuclear armed and powered autonomous missile flying at Mach 3+ would produce significant shockwaves (to the point that NOE flight by the missile would be a weapon in itself).

I also recall a video of a US carrier where a helo was landing and a fast mover flew by, just close enough to cause a disturbance in the rotorwash and cause the helo to fall out of the sky.

[Pu-239]

(F-5, IIRC)

F-104

[Admiral Valdemar]

In that case, the F-5 and F-4 were piloted by sane people. It doesn't help that the Starfighter sucks for a lot of reasons, aside from speed.

[Sea Skimmer]

In that case, the F-5 and F-4 were piloted by sane people. It doesn't help that the Starfighter sucks for a lot of reasons, aside from speed.

Its an excellent aircraft for its intended role as a point defence interceptor. Then the Europeans got the great idea to use it as a low level fighter bomber with insufficently trained crews and the rest is history.

[Admiral Valdemar]

I always liked reading about the sorties some F-104 jockeys went on in the Far East, where they'd zoom off to meet the MiGs who simply held back until fuel ran out, and the Starfighters zoomed back home after a tiny engagement time. Little wings and a greedy engine made for short interception missions. The T-tail was a bitch too. The Luftwaffe didn't help the reputation though, as you say.

Still, I forget how the incident with the prototype XB-70 transpired. I'll have to find my air power magazine that went on about it. Needless to say, that bomber flying by at full speed would ruin your day (or at least your hearing, given it was the loudest plane you could fly).

[Broomstick]

ok, a B-29 is flying at 10,000 ft @ 360 mph, when an F-22 flying at 11,000 ft going mach 2 passes directly over it at a right angle.

You have 1,000 foot vertical separation.... hmmm.... Well, that's adequate separation for a couple hundred miles per hour speed differential, although with a 200 mph speed differential the smaller, lower airplane will get rocked a bit by the wake.

It's quite possible that, given the right angle flight path intersection and the speed of the lower, slower airplane, the sub-sonic plane may actually get far enough away from the super-sonic airplane quickly enough that it escapes the worst of the shockwave. I'd expect you'd notice the passage of the faster airplane, you'd get shook up and rocked around a bit, but probably survive without damage. That's a guess, not a rigourous analysis.

More hazardous might be if the two airplanes were traveling in the same direction, the faster one overtaking the slower one, because the slower plane would be in the wake/shock path for a longer period of time and take more of a direct hit. Put the smaller airplane above the faster one and you'll likely have less hazard, as the wake vortices descend under gravity and thus you'd have only the upward aspect of the sonic boom to deal with.

[FedRebel]

An XB-70 could probably do it.. with it's engine vortex. It caused a chaser fighter to crash, didn't it?

The chase got too close to one tailfin and clipped it, which took that plane out of action (F-5, IIRC) and caused the Valkyrie to plummet as the supersonic airflow got disturbed by the aerodynamic anomaly.

I remeber reading that F-5 got too close to the vortex created by the XB's aerodynamics and was sucked into one of the wings.

Hypotheically if that was the case, then the XB would bring down the B-29, but the planes would have to be close enough together that the Enola Gay would take the mach 3 capable prototype with it.

[victorhadin]

I somehow doubt it, though like everyone else here I have no numerical evidence to point at that. The main hazard of the boom would be its fairly concentrated nature (the overall energy release as the F15 flies past the B29 would likely be small) and the prospect that it might shake loose certain sensitive bits 'n' bobs, but a B29 is decidedly lacking in sensitive bits 'n' bobs and decidedly over-supplied with structural integrity that it needn't have, this being designed in an era before aeroelasticity was well understood.

Or to put it another way, let's fudge some numbers and make some brutally inaccurate calculations:

Mach 2 at 10'000ft is about 330m/s, ish. We can assume that the Mach cone will be at sin^-1(1/M)=30 degrees, and assuming the B29 is stationary (it isn't, but it makes this easier) and that the F15 flies perpendicular to it along the centreline, the shock will reach the B29 foreplane and tailplane in 1/20th of a second after the F15 is directly overhead (assuming negligible vertical separation: Obviously untrue, but whatever). By ths point the F15 will be, of course, 33m further away.

At maximum thrust, an F15's engines can put out about 200kN (let's make the massive assumption that is is doing so now), which is 10kJ over the period that this shock is travelling over the B29. Let us say half of that 10kJ goes into resisting wave drag, i.e 5kJ... and of this, only a small fraction will actually go into the 'boom'.

So to summarise: Will it 'knock the B29 out of the sky'? Not a chance in hell. The shock passage might disrupt some sensitive equipment on the aircraft, and make the crew deaf, perhaps, but that's about it. It would certainly be loud.

[Batman]

I realize Mach numbers drop as altitude goes up but for Mach 2 to be slower than Mach 1 at a measly 3,000 meters seems rather farfetched.

[Sea Skimmer]

I realize Mach numbers drop as altitude goes up but for Mach 2 to be slower than Mach 1 at a measly 3,000 meters seems rather farfetched.

Yeah, its is. The difference in the speed of sound between 0 feet and 40,000 feet is about a 100mph decease. Interestingly though in the stratosphere the speed of sound actually rises again, before falling off again in the mesosphere until you go so high sound can no longer be transmitted.

[Wicked Pilot]

A B-29 could knock out an F-22 simply by flying in front of it. Of course you'd need some serious SA problems to lead into that type of situation.