Submarine Aircraft Detection

[Coochycool]

I wonder if any former/present MRA boys on here might care to comment on the following.

Helping the next door neighbour's boy with his maths homework, the following question was posed:-

A submarine at a depth of 150 feet detected an aircraft flying at a height of 30,000 feet. What is the difference in height between the two?

So simple was the answer of 30,150 feet, we suspected a trick question.

But moreover, I was left wondering at the premise of the question. I am aware that subs have acoustic capability, but can subs actually detect aircraft at such altitude from such depth?

Bearing in mind that this is a public forum :cool:, anyone care to enlighten me on rough parameters?

I do recall once receiving nothing but a funny look upon querying a P-3 flyer on the range of his MAD boom :uhoh:

Cheers

Cooch

[QTRZulu]

Coochy,

To answer both your questions in simple terms;

1 - Yes
2 - No, but a quick Google search will give you the physics/maths for this

As for the Q posed to the P3 guy - you probably confused him hence the odd look ;)

[Buster Hyman]

The only Submarine Aircraft I know of is Skydiver. (Or Sky 1)

[barnstormer1968]

Surely the answer is that the question doesn't contain enough info to provide an accurate answer.

[Basil]

Height is not really the correct altimetric term but the answer would be 30,150 feet.
Re detection, a towed phased array radar is used which uses the surface of the sea as an aerial. The devil is in designing the algorythm to use the correct basic frequency for the temperature and sea state. The PRF must not be a harmonic of the basic or lesser wave patterns or the surface returns swamp the air return.

[barnstormer1968]

Basil, how did you arrive at that answer?

How tall was the submarine in your equation ;)

[Fonsini]

I'm sure that the answer is the simple one of 30,150 feet.

But I would say that height does not have a negative component, when we dig a mine we don't say that it has a height of -600 feet, we switch to depth as with submarines. Therefore the true difference in height is 30,000 feet.

[Wander00]

This has all the attributes of the old junior school maths question involving fence panels and posts................

[barnstormer1968]

Wander.
Here's one for you, it's roughly the same as one my kids had when at school.

How many 1.25 metre long lengths of wood would be required to make a pentagon shaped frame with five equal 1 metre sides.
Trying to explain to the teacher that the answer was six and not five was interesting :)

[Wander00]

I can believe it - but marked "wrong" if not the answer on the crib

[Pontius Navigator]

Brainstormer, ok, I'll bite. You might get away with 4 even. Then again was the one metre side internal or external.

My difficulty, aged 9, was explaining to the teacher that the sum of the internal angles of a triangle were not necessarily 180 degrees. While I won the argument she then changed the rules.

[barnstormer1968]

Pontious, thanks for the bite but I've had to put myself in detention for EXTREME thickness :)
I should have said that the answer was 5 and not 4 as the teacher had wanted.
I have no excuse for getting those numbers wrong, sorry, I must have had a bit of a brain freeze moment.
The teacher just added the total length of sides of the pentagon frame and so thought 5 metres of wood would be enough, but of course that doesn't mean that 4 x 1.25 metre lengths would do the job.

In regards to rules being changed, that's just school life :)
Pupils are first taught that the boiling point of water is 100 degrees C, then once they get a bit older they are then shown how it can boil at a wide range of temperatures :)

[Pontius Navigator]

BS, the last was a physics project I tried to set up. It was to boil water in a pressure cooker with various weights on the valve. Perfectly safe of course as H&S had yet to be invented. Sadly I could not mainly a seal with the thermocouple leads.

My next effort was to make some selective weed killer. At the last moment the master who had offered his lawn was advised not to. I had to make do with a school lawn. Unfortunately the recipe did mention dilution.

Finally one pupil demonstrated the effect of boiling sulphuric acid.

Happy days.

[langleybaston]

the sum of the internal angles of a triangle were not necessarily 180 degrees.

Please educate us.

[Pontius Navigator]

Spherical trig, do I need to go on?

What is the angle between lines of longitude and latitude at the equator?

[langleybaston]

Thank you.

Cheat!

[barnstormer1968]

Pontious
How about a fairly safe but educational water boiling experiment.

Materials are a bottle of wine or just a wine bottle.
Thermometer
Wine saver vacuum pump.

Pour boiling water from a kettle into a wine bottle, fill about half way.
Allow to cool for a few minutes then use the wine saver to create a partial vacuum thus allowing the water to boil again at a lower temp. Repeat over and over until the water boils around 65c

At this stage you can either say 'this is how hot water boils at the summit of Mount Everest. :)

[Pontius Navigator]

BS, the first problem is the bottle shattering as you add the boiling water :)

The second is not knowing the vacuum pressure.

The alternative was to place a bottle of carbonated drink in a freezer which was demonstrably liquid at -18, remove the cap, the pressure instantly reduces and the contents freezes.

More pleasurable was to do this with a lager in St Vincent while sheltering from a tropical downpour. Physics without fun is boring.

Mind you, attacking a submarine at 150 feet is fun - blind darts.

[PDR1]

Spherical trig, do I need to go on?

What is the angle between lines of longitude and latitude at the equator?
Well to be picky - a triangle is a 2-dimensional shape so wrapping it onto a 3-dimensional form makes it no longer a triangle. Internal angles adding up to 180deg is indeed a characteristic of all triangles!

PDR

[Pontius Navigator]

PDR,no, using the world, take a plane from the poles along a circle of longitude. The angle between the axis from the centre of the earth to the pole and a line of longitude at the pole is 90. The angle between the axis and a radial to the equator is also 90 which gives 3 internal angles summing to 270.

The issue is not that it is 3-dimensional, it clearly isn't, but that Euclidean geometry, where the internal angles of a triangle sum to 180, is based on straight lines.

[barnstormer1968]

Pontious
I'm yet to see a wine bottle shatter, and I've done this demo yearly for over 25 years :)
The vaccum isn't the important thing, it's the temp that counts. The same goes for the pressure cooker demo, as its hard to accurately gauge pressure whereas the temp is much easier.

[Pontius Navigator]

BS, I am not sure but I presumed the pressure cooker provided 1.33, 1.67 and 2 atm pressure based on the valve weights.

Regarding shattering wine bottles that was TIC and based on the differential expansion of glass from boiling water. Just a little play on the lack of H&S in those days.

The sulphuric acid instance was very real. His blazer and shirt instantly dissolved as he ripped them off. He was very lucky as I don't remember his getting as much as one drop on him. No gloves, no goggles, no face mask in those days.

[Bigbux]

I'm sure that the answer is the simple one of 30,150 feet.

But I would say that height does not have a negative component, when we dig a mine we don't say that it has a height of -600 feet, we switch to depth as with submarines. Therefore the true difference in height is 30,000 feet.
Is it HMS Astute and is the tide out?

[Coochycool]

Well we have been having fun, haven't we?

I do however have to sadly point out that almost no-one on here has bothered to address the task they were assigned, tut-tut.

Go stand in the corner Barnstormer.

And Ponsy Nav, I expect 100 lines to be on my desk by Tuesday morning, "I must not attempt to blow up the Science Lab".

And don't give me any feeble excuses about jeopardising your MoD Pension.

A gold star does however go to Basil, go to the top of the class Basil! :D

Teacher :8

[Glaaar]

I wonder if any former/present MRA boys on here might care to comment on the following.

Helping the next door neighbour's boy with his maths homework, the following question was posed:-

A submarine at a depth of 150 feet detected an aircraft flying at a height of 30,000 feet. What is the difference in height between the two?

So simple was the answer of 30,150 feet, we suspected a trick question.

But moreover, I was left wondering at the premise of the question. I am aware that subs have acoustic capability, but can subs actually detect aircraft at such altitude from such depth?

Bearing in mind that this is a public forum :cool:, anyone care to enlighten me on rough parameters?

I do recall once receiving nothing but a funny look upon querying a P-3 flyer on the range of his MAD boom :uhoh:

Cheers

Cooch


UWB Impulse SAR, mounted on an aircraft as small as a Cessna 172, can look through several hundred feet of ice and sometimes rock to find voids where there might be a P-38 or a cache` of chemicals decidedly more nasty to your health than Sulfuric Acid. It is most commonly used in FOPEN to track tanks and people.

I would not be at all surprised if modern 'periscope wake tracking' ISAR modes did not incorporate a bit of this capability as there is a suprising amount of garbage on the ocean surface, especially in the inshore littorals. None of which is 350-370ft long.

Could a similar system be made to work from beneath the waves, going the other way? You certainly would have your choice in terms of parabolic antenna area as wavelengths to operate with as the entire bow of the submarine is a 20-30ft wide dielectric fiberglass dome. The problem would be knowing the Doppler variances and range gated PRF scales likely to be occupied by a high flying ASW platform like the P-8 without losing water penetrability on the returns.

IR is another option. Da used to work for an oil company and they were using LWIR geosurvey stuff way back in the 1970s. Once, looking at an ocean map, they spotted a pair of wakes and 'doing the math' (which see: Teacher's Pet and Spherical Trig) they figured the tracks were around 800-900ft down and moving in excess of 30 knots. Parallel to each other about 20nm apart.

Not whales.

This definitely works the other way 'round too, given a buoy could mount a camera and IRST (ADADS is small enough to be manpacked) package.

The biggest problem with submarines being the emission source of anything of course is that they are sluggish and huge, to say that they turn like a truck is rather an insult to Mack. You skulk or you die.

Since dragging a tail really doesn't do much, other than increase your silent speed noise threshold, the key would seem to be to employ air dropped atmospheric sensor buoys (faster, wider, network setup) and long-line acoustic transducer networks, together with munitions carrying (missiles in box) CAPTAM mines. Leaving the SSN to play spider-in-her-web games.

Now your apertures can float which, by itself, would radically change the LOS horizon nature of submarine warfare from 1-2 CZs out to perhaps several hundred nm distant from the operational area, using point to point laser or directional microwave (possibly bent through a satellite) which would be LPI relayed back down to perhaps 1-5 master nodes which could then talk to the sub via a digital Gertrude or bluelight lidar at minimal hull risk, well outside the combat area. Even if they intercept the up and down link, nobody would know /precisely/ where the sub was.

This would indeed (IRST as much as radar) let you see an airliner at FL300 without exposing the 2 billion dollar hull to push up a mast, near the surface.

Taking the majority of sensorization and particularly heavy AShM and LAMs off the sub would, in turn, let you reduce the size of the sub to perhaps half it's present state, taking manning ratio down to say 50 or so (three shifts of CIC crews and a galley service) while employing a much smaller RTG/battery stack in a sealed motor room instead of a noisy, dangerous, steam kettle while retaining only defensive weapons with things like SCav interceptor torpedoes or possibly even 'gun' turrets to kill inbound shots. You would still likely have to escort or barrier the sub with a small 'school' of UUV, roughly the size of an ASDS. But since these robots would be cheap, they could use active sonar in sprint-drift packs to cover very large volumes of protected seaspace, kamikaziing threat subs, much farther out.

Nobody has ever sunk a sub with a DF-21D but playing stalking games with an 8,000 ton hole in the water is stupid...

[msbbarratt]

Sound in the atmosphere doesn't couple well into the ocean. That just means that you can't hear things in the sky very well whilst under water. But if it's a loud enough aircraft, it will be detectable. I've no idea how loud it'd have to be though.

It's the same physics behind the reason an ultrasound scan needs a gel between the scanner probe and the missus' belly. Without it the sound energy coming from the probe would have to travel in part through the air (unless the operator presses really hard). The gel ensures that there's a good impedance match between the probe and the belly. Same for the physio's ultrasound massager. Apparently those used to break quite easily if switched on without being gelled up and in contact with skin. The impedance mismatch reflects a lot of power back into the probe, and it cooks itself and no one's the wiser...

[Pontius Navigator]

Glaar, 3,000 feet is nothing :)

[PingDit]

Something like a P3 will leave a visible mark on the acoustics suite of a submarine. It's very much dependent on things like ambient noise in the sea, sea state, type of acoustic processor or towed array and acoustics operator experience. A typical detection range for such things may be around 1nm radius and up to as much as 10,000 feet. A jet aircraft however will not usually be detectable on the submarines acoustic suite but could be audibly detected by the operator at similar ranges.

[PDR1]

PDR,no, using the world, take a plane from the poles along a circle of longitude. The angle between the axis from the centre of the earth to the pole and a line of longitude at the pole is 90. The angle between the axis and a radial to the equator is also 90 which gives 3 internal angles summing to 270.

The issue is not that it is 3-dimensional, it clearly isn't, but that Euclidean geometry, where the internal angles of a triangle sum to 180, is based on straight lines.

Oh I see - I'd assumed you were claiming the sides were straight because they were straight lines along the surface of the earth.

The *full* definition of a triangle is a plane (2-dimensional) shape comprised of three straight lines which meet at three corners. It is a subset of the group called "polygons" which have the same definition with the exception that the words "a finite number of at least three" are substitutes for the word "three". Something cannot be a polygon if it has curved sides because it cannot be fully described by just the ordered co-ordinates of its corners.

With this definition the sum of the internal angles of a triangle will always be 180 degrees and from this is can be shown that the sum of the internal angles of any polygon of n sides will always be 180x(n-2).

Applying 2-dimensional triangle properties to 3-dimensional shapes with curved sides is about as meaningful as defining the stalling speed of the surfaces of a trimmed airship.

PDR

[Pontius Navigator]

PDR, the point was the teacher did not know the definition and could not explain the difference. 'Twas my father, a far more experienced navigator thani ever was that spun me that one.

[barnstormer1968]

Coochycool
As you are handing out good stars you must think you know the answer. :)
Before we progress can you answer a very simple question:
Let's say the sub in question was 31 feet tall. If it was at a depth of 150 feet below the waters surface as per the question (and for simplicity we'll assume the sub was in blue water) how far from the waters surface is top of the submarine?

[PDR1]

Depth in a submarine is measured from the lowest point of the keel, because it's actually quite important to know if they are seeming at a depth where the keel would be lower than the rocks ahead on a chart!

PDR

[barnstormer1968]

PDR1
That's why I posted above :)
It's also why coochycool has handed out one gold star too many :)

[glad rag]

BS, I am not sure but I presumed the pressure cooker provided 1.33, 1.67 and 2 atm pressure based on the valve weights.

Regarding shattering wine bottles that was TIC and based on the differential expansion of glass from boiling water. Just a little play on the lack of H&S in those days.

The sulphuric acid instance was very real. His blazer and shirt instantly dissolved as he ripped them off. He was very lucky as I don't remember his getting as much as one drop on him. No gloves, no goggles, no face mask in those days.

We made nylon with a couple of Bunsen burners, flasks etc.

And it worked! drawing a line of nylon out of the mix! Stuff with acids etc, it was great fun.

[Coochycool]

Barnstormer

Your impertinence is based on the unsubstantiated assumption that the sub is in straight and level trim.

See me after class

For me the fun stuff was demonstrating sublimation with Potassium Dichromate, you made your own little volcano!

And who could forget the film of Potassium being introduced to water (too violent to try for real we were advised), it blew the not insubstantial glass turine in 2!

Flooding Q in readiness

Cooch

[langleybaston]

Home made mortar.

Take one banger .... the most powerful available to a schoolboy. Take one empty baked bean or golden syrup tin. Drill hole in tin near the open end, insert banger [fuse outside], tamp with clay or putty.

Make small earth mound ridge at right angles to target. Place bomb angled towards target.

Place additional bombs at varying angles to give a spread.

Light fuses.

Unwise to await fall of shot if the target greenhouse was hit.

[Pontius Navigator]

6LB, how primitive. What was wrong with carbon, sulphur and potassium nitrate. Mix any quantity required and pack the container including a suitable length of Jetex ignitor cord. Place as required, light fuse and retire nonchalantly to a safe distance, say a 100 yards, where "it wasn't me Sir," had a slight chance of being believed.

[andytug]

Our chemistry teacher did sodium in acid...... Sodium in oil in test tube, pour acid on top verrrry carefully, hold at arms length, then drop into a bin.

Then evacuate the chemistry lab due to clouds of choking white smoke.........

Also let us all do sodium in water, but seal conical flask with bung of cotton wool in case sodium jumps out. Slight flaw, sodium fizzes around a while producing hydrogen, so at the end there is a 'pop'... and 30 balls of flaming cotton wool fly across the lab, chaos ensues as the box of cotton wool sets afire and has to be quickly doused in the sink, etc. Health and safety..... er, what?

[The Oberon]

"Boris" Holt showed us the principles behind the mess cannon, large tin with a hole in the bottom to accept the Bunsen tube, and a small hole in the lid. Turn on gas, light the gas at the small hole and then withdraw the Bunsen tube. He also told us about the potassium, carbon and sulphur mix but no demo, we had to find out for ourselves, and we did.

[Pontius Navigator]

TO, one of our Rotarians is an explosives engineer. In his job talk he brought some black powder. He lit it and it fizzled.

Then he got a second batch. I can't remember the ignition process or the tamper but it blew a foil dish 6 feet. Impressive in the dining room.

Earlier, at Waddo we had an IED demo, litre of petrol, thunderflash and tin hat. That made 50 feet and blew the rim off.

[triskele]

Ah! Jetex fuse...I heard banned by the cabinet early Op Banner. But those electric ignited solid fuel rocket motors are the bees geniculates. (I might have that last bit not truly right)

[langleybaston]

To be fair, our primitive trench mortars were conceived and fired at age 8 or so.

Also the banger dropped down the bicycle seat tube, or inserted in the handlebars, of the unsuspecting.

Did the earth move?

It certainly shook up any untested descendicles!

[barnstormer1968]

Barnstormer

Your impertinence is based on the unsubstantiated assumption that the sub is in straight and level trim.

See me after class

For me the fun stuff was demonstrating sublimation with Potassium Dichromate, you made your own little volcano!

And who could forget the film of Potassium being introduced to water (too violent to try for real we were advised), it blew the not insubstantial glass turine in 2!

Flooding Q in readiness

Cooch

How do you come to that conclusion?
I've asked how tall the sub was as the bottom (or lowest part) is the depth not the top, that would be very same no matter what angle the sub was at or even if it was upside down. I'd measure the depth from the lowest part of the sub in the water for the obvious reason posted by another poster. Either way your gold star was for an incorrect
answer :) :)

As for things being in straight and level trim, you are further reducing the ability to reach an answer as the question didn't state the type of aircraft or its angle or attack or roll state.............bearing in mind different aircraft have their sensors in different locations. :)

Ok, it's after class now. What you you think is the correct answer based on the info given in the question and your subsequent addition of an unknown variation?

[ORAC]

The only Submarine Aircraft I know of is Skydiver. (Or Sky 1)

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[Wander00]

I recall Maurice Venn, former RAF pilot, CCF officer and part-time geography teacher enliven a CCF Inspection "platoon assault" demo with a home produced mortar constructed of a piece of pipe at an angle to the ground, light thunderflash, inert in tube followed by second thunderflash. cue large bang. Second thunderflash sails across school field and almost ignites wooden changing room at the swimming pool. Great fun.

[pasta]

bearing in mind different aircraft have their sensors in different locations.
That's not relevant though, because the aircraft is being sensed, rather than doing the sensing, so its sensors don't come into it.

If I recall correctly, the altitude of the aircraft would be with respect to Mean Sea Level, whereas depths in nautical charts are relative to Mean High Water Springs. You would therefore have to subtract half the tidal range (at Spring tide) from your calculation.

I was blessed with a very wise Chemistry teacher, who recognised that some of us would inevitably want to play with explosives whether we were allowed to or not, and set up an after school club to enable us to do it in a slightly more controlled environment...

[Pontius Navigator]

Pasta, as my school was within sight of Windscale that was a given, and often entertained by the guns destined for HMS Tiger.

[The Oberon]

To be fair, our primitive trench mortars were conceived and fired at age 8 or so.

Also the banger dropped down the bicycle seat tube, or inserted in the handlebars, of the unsuspecting.

Did the earth move?

It certainly shook up any untested descendicles!
Langley, a bit none PC but as a 10 year old, who cares. When smoking was allowed in cinemas a group of small boys could be seen emptying bangers into the cinema ashtrays and leaving it for some unsuspecting smoker to stub his ciggy out. So somebody told me.

[MoateAir]

If I recall correctly, the altitude of the aircraft would be with respect to Mean Sea Level, whereas depths in nautical charts are relative to Mean High Water Springs. You would therefore have to subtract half the tidal range (at Spring tide) from your calculation.

Would QFE / QNH / FL also be a factor in this equation now?

[albatross]

We all know of "Standard Atmosphere"..temp, pressure, lapse rate.
Just curious but is there a "Standard Sea" .. Surface temp, thermocline, water clarity, salinity, ect?

[KenV]

If I recall correctly, the altitude of the aircraft would be with respect to Mean Sea Level, whereas depths in nautical charts are relative to Mean High Water Springs. You would therefore have to subtract half the tidal range (at Spring tide) from your calculation.Also keep in mind that a submarine's depth is measured at the keel. There's a lot of submarine above the keel. At what point on the submarine does one begin the measurement between the submarine and the aircraft?

[albatross]

Well unless there are more variables given than those posed in the original question.
Height would be assumed to be above the surface and the first part of the submarine encountered is 150 feet below that surface.

Depth of ocean or state of tide matter not.
Are we not overthinking this?
Interesting discussion but we have wasted the entire exam period and haven't answered this simple question. LOL Looks like a "time trap" to me.
Now if the question gave variables such as Submarine keel to top of sail distance, Indicated altitude of the aircraft, air temp ect and the "students" had been taught how to compute and were expected to be deal with these variables..we would be off to the races.

[DaveyBoy]

Pasta: it's heights of things above water (eg bridges, cables) that are referenced to 'high water' datums such as Mean High Water Springs or Highest Astronomical Tide on a nautical chart. Depths are referenced to 'low water' datums such as Mean Lower Low Water (MLLW) or Lowest Astronomical Tide. <gets coat>

[Wander00]

NAROBS - you have lost me there (but then I left in 1962) - but over the front door is a window that is a memorial to John Boothman, winner outright of the Schneider Trophy in 1931

[Basil]

That (http://thelawwestofealingbroadway.********.co.uk/2011/07/little-off-topic-philosphy.html) also refers to: "PLANK IS GOD"
I wonder if they meant 'Planck'?
Or were they referring to fixed wing pilots? :E

p.s. replace the ******** with b*l*o*g*s*p*o*t (no asterisks)

[Wander00]

Narobs - were the honours boards still up in the hall when you were there? If so you will have seen my name as a Cranwell entrant in 1962/5, the Sixth Form year from which we sent one each to Sandhurst, Dartmouth and Cranwell. Two of those still turn up for the annual year group reunion lunch. Dad was an Old Gayt too.