Effect of Shockwwaves on aircraft in flight
 

Hi all,

I am finalising a degree in geosciences and have my final year dissertation - the effect of shock waves on aircraft in flight, so I am trying to locate (publicly accessible) data on the effect of atmospheric shock waves on aircraft in flight (in particular, commercial aircraft operating at cruising altitude - fl370 or thereabouts).

The source of the shock wave is to be "airbursts / bolides of non terrestrial origin" (Think Chelyabinsk / Tunguska). The likely magnitude is going to be in the 10 to 50kt range. These shock waves are very different to sonic booms so data on those is not being helpful. Unfortunately, military data on shock waves from atmospheric atomic weapons tests is scant (obviously) and tends to refer to surface effects rather than the effect on aircraft in flight.

If anyone has any links to academic papers or books/datasheets which they feel may be of help, I would really appreciate some links as I am struggling to find information to take the project forward.

To keep the thread "clean", feel free to contact me direct at: [email protected].

Thanks in advance

Dave

What a fascinating question.

I've working in various corners of aviation research for a quarter century, and studied hypersonic aircraft design as one of the minor topics when I was an undergraduate. Yet, I can't honest recall ever seeing anything on this topic. Quite a lot on internal interference where an aircraft is affected by its own shockwave, but not on external shock sources.


Now, having said that I've just done a search of a couple of databases not readily accessible from outside aeronautics. I've found one quite informative paper from 1961 which looks into the impact on other aircraft of supersonic shockwaves. If you want to PM or email me an email address, I'd be glad to send it to you - it's from a restricted database, but not actually classified (nor interesting seems to have been even in 1961). It has a grand total of five references, but all of them seem relevant and that might get you down the right rabbit hole.

Have a look on here also - this is a database generally extremely good for pre 1960 aeronautics research.

MAGiC NACA Archive


Now a few other thoughts. I recall Bill Sherlock, who was one of the microlight pilots flying overhead photo-chase on the Thrust SSC talking about the impact on his aircraft (from memory "I thought that something had failed in the wing" were his words). He wrote about that in a few places - possibly "Microlight Flying" magazine?

I'd also have a look at the accounts by pilots who flew nuclear bombers. One man written about quite a lot is Leonard Cheshire (yes, the man who developed charity homes) - he was in the chase aircraft at Nagasaki and there may be things he or other people have written about what they observed and experienced. Aviation historians tend to be prolific, and wading through some appropriate biographies and autobiographies could yield some direct observations from the American, British and French nuclear tests. It won't be hard scientific data, but is likely to be informative and citable nonetheless.

I'd love to see how your research develops - this is a really fascinating research question.

G

I don't understand an airburst that makes a Shock wave that travels at 10-50kts? But lots of military crew have experience traveling through local shock waves from air bursts. It's not the shock but the shrapnel that you worry about.

I initially thought the same thing, i am now wondering if the OP means KiloTonnes perhaps?

"airbursts / bolides of non terrestrial origin" - That would seem to be meteors or other non terrestrial event. I will bet you however the non-classified 1961 paper dealt with shock waves from nuclear explosions. The question being for aircraft designers, how can the B-52, B-58, F-105 and the British Vulcan escape a low or even high level blast. How far do the blast / shock waves from the weapon travel and what are the anticipated safe operational envelope for deploying various nuclear weapons from an aircraft.

Any suggestions for further useful dissertations in "geosciences" (???)

The effect of Tunguska style events on laundry cleanliness?

The effect of super novae on Terminal Control procedures.

The effect of an aircraft flying through turbulence on laundry? (that's air pockets to a laundry worker)

Flippineck! Talk about degrees awarded for underwater basket-weaving.

Are there really no useful things left to investigate?

That's how I read it.

G

No, it actually dealt with shock waves from supersonic transports and the safety effect on other aircraft.

Not spot on - but the only think I could find in a quick literature review.

G

Hi all,

thanks for taking the time to look and comment

Yes - kt meant KiloTonnes - the range I quoted may be a bit on the low side though (upto 500kiloTonnes may be more appropriate)

No, we are not looking at laundry cleanliness, although I guess the dry cleaning bill afterwards would be significant (and that of the seats) - another paper there I feel ;-)

Yes, we are talking about meteors/small comets

Shrapnel - yes, point taken, but I am not looking to take an aircraft out, rather the opposite, looking to see if the aircrew can do anything to mitigate the effect of an external event. Initial first reading seems to suggest turning towards the event until the shockwave has passed causes less damage to the airframe. Now we need to consider residual dust and the effect on the engines - has this been sorted out since the 2010 Eyjafjallajökull volcano events?

Shockwaves from supersonic transports may be relevant, especially for the phase where the object is travelling at high speed in the atmosphere prior to disruption

Although I am not looking at the specifics of the design of aircraft intended to deliver nuclear weapons (and survive the nuclear blast), the description of how the shockwave interacts with the airframe and how the aircraft behaves as the shockwave passes would be useful. I am minded of research on Alaskan crab fishing boats where it was found that the least favourable option in a storm was to run with the wind/sea, and the most favourable option was to turn into the storm.

Thanks again

Dave
[email protected]

drichard, what do you mean by "residual dust and the effect on the engines"? If the aircraft is close enough to be affected by the dust, I'd imagine the shockwave would reduce the airframe to smithereens. Or are you talking about the longer-lasting effect (day? weeks? months?) of a comet impact on air travel?

Interesting topic.
Looking at sea storms may lead you into interesting irrelevancies! At sea in a storm there are many options depending on the type of vessel, the wind conditions, the sea conditions and where you are. If you can't hide from it before it gets to you, the safest option may be to run with the storm (if you've got enough sea-room), or to sail into it, or to heave-to, or to lie under "bare poles", etc. And a sea storm lasts a long time, hours or days, whereas I think you're looking at a sudden event that you may see coming, but that doesn't last long when it comes.

NiclasB : My thoughts were running along the lines of the disruption of the object leaves dust residue. This is likely to be silicates - similar to volcanic dust. If the aircraft were to fly through this cloud, would a hazardous condition exist or has the research and technology since 2010 advanced such that it is not anticipated to be a problem.

OldLurker: Running from the storm increases the likelihood of a capsize - even more so than taking the waves side-on. If the absence of shelter, taking a "nose in" approach to the prevailing seas/winds is the safest option.

Yes, I am looking at a single event where the aircrew have the opportunity to react - I just want to ensure that the reaction is the correct one. As the shockwave is a compressive wave there is a hazard from pressure changes. That, with movement of the air, taking it "on the tail" leads to a sudden drop (in milli-seconds, of 100's m/sec) in airspeed (not ground speed) - how would an aircraft respond? Also, the air behind the blast wave is likely to be turbulent and flow non-laminar.

drichard: I'm no expert, but I've read wise words by those who are experts and have been out there in anything up to a hurricane/typhoon. In a medium or large ship with the usual high bow, butting straight into the wind and sea (if they're coming from the same direction) is often the right choice; in a sailing vessel, especially a small yacht, it can be different. You're right that running from a storm increases the likelihood of a capsize: it's a dangerous option, not to be undertaken by the inexperienced: the vessel needs constant skilled handling, which is very tiring: but all the same it can be done and may be the best option in certain conditions.

What everyone who knows seems to agree on is that there's no knee-jerk "safest option" in all cases under all conditons – a competent captain and crew will choose to do what suits their vessel under the prevailing conditions at the time, which is the general principle that's relevant to this thread.

The technique used for the Hiroshima and Nagasaki drops was to turn immediately after the drop, to be flying directly away from the detonation point at the moment of detonation.

However I think this was simply to maximise range from the blast rather than any particular advantage of presenting the rear of the aircraft. After all, continuing straight would also mean the detonation was directly behind, but obviously at a much shorter distance.

I'm not sure I understand....

Flying at a constant speed at the point of delivery, surely it is far easier to simply continue to fly in the same direction as that does not waste any time in turning around? Did they turn round so that they were on the 'right' side of the explosion so they could find a safe place to land?

At the point of drop the device is travelling at the same speed and in the same direction.

Obviously it is falling vertically but the lateral separation will increase only gradually while the device's forward speed decays with drag.

The turn puts distance between aircraft and device much more quickly.

About 55 years ago, during a university course on fluid dynamics, the lecturer mentioned in passing a paper by William Penney published about ten years earlier in the Journal of the London Mathematical Association. The subject was water waves induced by high energy events, and Penney was leader of the development on the British atomic and hydrogen bombs. The paper, which I did not follow up on, was assumed to be a sanitized version of research into potential effects of atmosperic nuclear explosions. Although principally concerned with free-surface effects, the techniques employed in the paper may be of interest to the OP.

Residual dust (taking the easier one first) - volcanic ash is primarily silicates (rock, formerly molten). The specks of dust can be abrasive, sand-blasting windscreens and paint, and causing some internal engine abrasions. But their largest and most dangerous impact is that they melt again at turbine engine temperatures and thus collect in the engine as a gooey molten mass, clogging the internal airflow pathways. That is what shuts down the engines if one flies through such a cloud.

If your bolide is primarily ice or nickel-iron, the ice will evaporate in the blast and become mostly a non-issue (although, if the water vapor thus formed refreezes in the atmosphere, see the effect of high-altitude (10-15km) ice crystals on airspeed probes, Air France 447 among others). The nickel-iron will be much denser than the silicates, and precipitate to the ground fairly quickly (although how quickly is worth researching). It is the rocky percentage (if any) of the bolide that will pose the biggest threat in terms of dust or ash to aircraft.

As to aerodynamic effects of the shock or pressure waves: The two aircraft that dropped the Hiroshima and Nagasaki bombs were both tail-on to the blasts (lateral distance ~18km plus slant range), blasts ~16 and ~21 Kt. Noticeable shocks, but no airframe damage. Bockscar from Nagasaki lost its radios, but that may not have been due to blast.

Aircraft are obviously designed to face, and operate, into the prevailing "wind" or slipstream of flight. Their flight controls (rudder, elevator, ailerons, spoilers/spreedbrakes, flaps (at least simple flaps, not so sure about complex types) are hinged along the front, and free floating at the back. Thus they are susceptible to (to use the sailing metaphor) a "jibe" - or being slammed rapidly from one extreme to the other, by a wind or shock wave from the rear, and damaged or even ripped off.

One example - elevator cable separation in an Air Moorea Twin Otter, which was suspected, but never proved, to have been weakened by blast on the locked elevator from the jetwash of nearby large taxiing aircraft, while parked at an airport.

But obviously the distance involved in the WW2 bombings attenuated the blast to the extent that this did not happen to them.

Therefore, the intuitive idea that turning to face the blast source is a good one - up to a point. Aircraft are designed to withstand a much larger shock or wind from the nose than from the tail.

Aircraft toughness or tolerance to the forces in forward motion are generally described as the Vne, which is the speed (Indicated Air Speed on the gauge - minus a large safety factor) at which the dynamic pressure of the airflow may fold the wings or tailplane backwards. At high altitudes, a Mach operating limit is imposed, but that has less to do with strength (one may be well below Vne) and more to do with the creation of localized continuous shockwaves in places where funneling of the air around parts may cause the local airspeed to approach Mach 1, which can cause control problems. Not directly applicable to the passage of an instantaneous shockwave, although also worth exploring.

Aircraft "toughness" in the up/down direction (a blast above or below) is generally described in G forces. How many G can cause a wing or tail to fail, up or down. Generally, the absolute limit for commercial aircraft will be in the middle-high single digits (the rated limit much lower to incorporate a safety margin), with the positive limit being higher (since the wings are supposed to lift the plane) than the negative limit. Military jets may have +G limits reaching into double digits.