Turbojet powered cruise missiles

[kool kitty89]

Moved from the other discussion given how far off topic it went, perhaps worth moving the discussion on chemical/nuclear weapons here too? (at least as far as their ability to be deployed on cruise missles)

The tendency for V2s to bury themselves before detonating might have made them more effective as chemical weapons systems than conventional, or at least have a lesser detriment to effectiveness. Potential for the earth/debris to muffle the explosion and cause the dispersion of gas to be more focused at low level and remain concentrated around populated areas more, that and potentially contaminating groundwater.

One alternative to V1s might have been turbojet powered cruise missiles, something that may have been further benefited by the relatively low cost of materials and man-hours per engine for (and limited service life) of the Jumo 004B, or perhaps an even simpler specialized low-life engine that used even more mild steel in place of stainless alloys. (I do wonder how long a plain mild steel turbine might hold up when used in a similar air-cooled configuration, especially with zero concern for throttle changes further increasing wear)

More costly than a V1 to be sure, but perhaps a great deal less costly than the V2, and faster than the V1, heavier payload, and potentially longer range, plus fewer hurdles with vibration to work though. (with the pulse jet's fuel pressure regulation issues at altitude avoided, pushing heights more around 10,000 ft cruising around 500 MPH would make it both hard for AA to hit and impossible for fighters to intercept)

Even if using standard 004B engines, it should have been more practical, reliable, and less costly to manufacture/operate than the jet powered mistel developments on the drawing board, and probably could have been adapted/executed sooner had it actually been developed as part of the V1 program. (500 mph cruise missiles carrying more than a cookie's worth of high explosives at 500 MPH may have even been more cost effective in terms of damage operational use than the actual V1 -plus, just slow/low enough to still waste resources TRYING to intercept them ... head-on/side long passes at top speed might have had limited success, enough to be a major distraction as well as a strategic weapon)


I should probably bring it up in one of the Jet engine threads too (or start a cruise missile thread), but the un-cooled radial turbine that allowed relatively consistent operation on Heinkel/Ohain's early engines may have been well suited to short-life disposable engines made with most/all hot components of plain steel. (aside from the bearings, Ohain's HeS 3 and 6 were nearly entirely mild and stainless sheet steel and aluminum, including the compressor and diffuser -using rolled or forged aluminum blades fastened to a steel hub for the impeller, less aerodynamically efficient but faster/simpler to construct than the machined impellers used in most superchargers -also easier for Heinkel's airframe manufacturing facilities to construct in the late 1930s prior to any access to engine manufacturing facilities)
Such disposable engines may have been aided somewhat by specific fuels being used. Methanol in particular has a lower flame temperature and may have made for a somewhat lower turbine/exhaust temp and lesser wear and easier to start Heinkel's early, hydrogen-warmup dependent vaporization dependent combustion systems on -soot tending to clog the injectors if gasoline/kerosene was introduced too soon, or especially at start-up. (but also less than half the energy density of kerosene, reducing range or payload ... but also the cheapest synthetic fuel to manufacture AND its corrosive issues -especially with aluminum- being totally moot in a disposable machine -blending with ethanol, acetone, ether, among others could improve things somewhat, some vaporizing easier than others -ethanol the worst of those, diethyl ether better than methanol, dimethyl ether would be useful too but it's a gas unless under modest pressure or dissolved in other fuels)

In fact, methanol is one of the easiest fuels to get pulse jet engines to reliably function on, and may have even accelerated V1 development somewhat and eased starting compared to the acetylene+gasoline/kerosene start-up procedure. (diethyl ether would probably work even better, dimethyl more so and almost as cheap to produce as methanol but would need pressure containment somewhat similar to butane, or disolved/blended with other fuels -methanol included, though given the pressure feed system on the V1, omitting the fuel pump and using pressurized liquified fuel directly might have been useful and no special start-up fuel needed -could work in a turbojet just as well, and even simplify start-up)

So, on top of that, use of easier to burn (yet still cheap to synthesize) fuels might have accelerated pulse jet and turbojet development and improved some of the reliability problems Heinkel was having early on, particularly those relating to unstable combustion and hot spots (enough to make the early test designs only work on hydrogen and still plaguing the HeS-8 for most if not all of its development period -in fact the problems with the HeS 8 seemed worse than those experienced when the previous HeS 3/6 program wound down). And while the HeS 3 and 6 were bulky, they were still relatively light and compact enough to be decent for high-speed configurations, and narrower than Whittle's designs. (perhaps better embedded in the body/tail of a missile than piggyback -the HeS 8 was much narrower but more troublesome, perhaps less so as a 'throw away' engine)

Aside from that, development of specifically designed, inexpensive, short-life engines may have bypassed the issues with usefully long service lives/TBO times and turbine wear issues, though developments focusing on even cheaper engines using less or no stainless steel in the hot section (something Heinkel's early designs used heavily) would have needed a bit of work. (with the superior wear characteristics of radial turbines, an uncooled steel bladed configuration may have been usable, and the disadvantage of sheer size/weight of costly stainless steel would be mitigated -in fact, you could increase the thickness of plain steel turbine in this case, compromising spool-up time, and adding to weight slightly, but being fairly unimportant for such a throw-away engine)


I should note that the HeS 3 of 1939 only produced slightly more than half the thrust of the 004B (about 990~1100 lbf) so the payload increases over the pulse jet powered V1 wouldn't be as great. (perhaps closer to a 50% gain plus improved range due to altitude and much better fuel consumption -even the crappy 1.6 lb/lbf/hr of Ohain's early engines was more than 2x as good as the Argus pulse jets)


Finally, mild steel is very easy to weld, so the quality/consistency advantages seen in the cromadur vs tinadur blades would have been relevant in spite of the low creep strength and oxidation issues. (this applies to a hypothetical mild steel turbine on the 004 as well) In fact, given there's zero nickel or other typically creep improving metals in cromadur, it may not hold up that much better under heat+stress than plain low carbon mild steel, with oxidation and related erosion being the main problem. (unimportant for an engine only intended to run for a couple hours at most -possibly unworkable if attempted on a combat aircraft though, aside from maybe a point interceptor that had engines/turbines replaced after each mission -I highly doubt even 10 hour service TBO would be reliable with such engines, Jumo worse than Heinkel given the cooling air might oxidize the turbine blades from within, plus the stresses are much higher than on the radial blades)

 

[GregP]

V2's weren't powered by turbojets nor were they cruise missiles. The V2 was rocket powered and was a ballistic missile.

The V1's pulsetjet was very cheap compared with any jet engine and the aiming device was going to be the same. Why spend more for a 1-way weapon than you have to? And since the jet-powered one would be a bit faster with the same aiming device, the circle of error would be even bigger than it was, making them even less accurate.

I can't see what was wrong with the V1 as used other than needing a more accurate aiming system which it never got. Without that, airframe performance improvement would be largely a waste of effort if you hit even fewer of your targets than with the pulsejet version.

One thing they might have tried would be radio homing. By using German agents in the UK and setting up small transmitters that could be turned on some minutes before the V1 was expected overhead so it could home in on the expendable transmitter. I have no idea if they ever tried it, but it seems like maybe that would at least allow taking out some high-value targets ... assuming the small transmitters could be placed and the agents make an escape before being blasted themselves. Wouldn't work too often but it would keep the radio direction finders busy for a few minutes. It would have worked better with directional antennas ... at least until the British caught on and started looking at the UK from the direction of an incoming missile.

If they had tried that in concert with a jet-powered V1 ... maybe. But I still can't see what was wrong with what they really did versus the cost of doing it.

 

[Milosh]

How accurate/inaccurate was the V1?

 

[Shortround6]

It had trouble hitting greater London, over 600 sq miles. Plenty did hit but a fair number did not. Makes the British night bombers (before radar) look like precision bombing.

 

[Milosh]

Didn't the Brits have something to do with the V1s not hitting greater London?

 

[GrauGeist]

The Germans were relying on impact data from their spies to give them feedback in order to adjust their targeting. However, all of the German spies stationed in England had been converted to double agents and were giving false impact reports.

And if anyone's ever curious about how many bombs fell on London, see this article and interactive map: The astonishing interactive map that show EVERY bomb dropped on London during the Blitz | Daily Mail Online

As far as accuracy, 5,091 V1 and V2 managed to find London and it's boroughs well enough.

 

[GregP]

Overall, about 25% of the V-1's hit their target. So 15,000+ did NOT manage to hit London and its boroughs well enough. A good thing since that's a lot of warheads that could have done even MORE damage. Edit: This number can't be right as they didn't launch that many. I'll get back to it. but a LOT missed.

That is not very accurate, but does do some level of damage at 2,000 pounds per V-1. It's a decent-sized bomb any way you cook it.

Had they been going any faster, even MORE would have missed because of the added speed but the same timing accuracy.

 

[stona]

Overall, about 25% of the V-1's hit their target.

That figure is surely not including those destroyed by British defences. This is a map published showing the V-1s destroyed over Essex and its coast. It matches the official maps well, but has the grid and grid references removed for clarity as it was published in a local history book.

As the V-1 offensive really got underway on June 15th 1944, 244 V1's were launched from 55 sites. 73 hit Greater London and 71 hit areas outside of London. 100 V1's failed to get across the Channel. That does give an initial success rate of a little better than 25%, on a target the size of Greater London and before the British reacted with increased and coordinated defences.
To get an idea of the scatter gun effect of a V-1 attack, this map shows where the V-1s launched at Manchester fell on 24th December 1944. Only 1 of the 31 recorded actually landed in Greater Manchester.

Those unfamiliar with English geography should understand that the V-1s fell across at least five counties and that the backbone of Northern England, the Pennine Hills, runs down the country between Lancashire (Manchester) and Yorkshire (Leeds). It is a very lightly inhabited area, largely composed of moorland. Most of the V-1s fell across this area. Here's a picture, taken in 1993, of one of the impact craters on Midhope Moor which lies between Manchester and Sheffield.

It is just possible that a few sheep may have been inconvenienced by this particular V-1, as all the others that fell across the moors, but the British war economy certainly wasn't. On the same night the RAF sent 338 aircraft to bomb the airfields at Lohausen (Dusseldorf) and Mulheim (Essen) which certainly did inconvenience German efforts to fly supplies from the Ruhr to the Ardennes.

Cheers

Steve

 

[rochie]

Going from memory, I think the total V-1's launched against England was just under 9000, killing around 6000 and wounding 3 times as many people

 

[rochie]

This is sourced from the people's war Great Britain 1939-1945
A total of 9,251 V-1s were fired at targets in Britain, with the vast majority aimed at London; 2,515 reached the city, killing 6,184 civilians and injuring 17,981. Croydon to the south, on the flight path of the V1s suffered severely taking 142 hits.

 

[tomo pauk]

Wonder whether the V-1 would've made sense as an anti-radiation missile?

 

[rochie]

And for the V-2.
1,115 V-2s were fired at the United Kingdom. The vast majority of them were aimed at London, though about 40 targeted (and missed) Norwich. They killed an estimated 2,754 people in London with another 6,523 injured. A further 2,917 service personnel were killed as a result of the V weapon campaign. Since the V-2 was supersonic and could not be heard (and was rarely seen) as it approached the target, its psychological effect "suffered in comparison to the V-1

 

[stona]

London was the principal target.

Targets in the North were attacked using air launched V-1s which rather obviously reduced the numbers that could be launched.

The Southampton-Portsmouth area was attacked with a few (22 seems most likely) ramp launched V-1s but Von Runstedt soon received a signal ordering the cessation of such launches which were seen as a diversion from the attack on London. Later Von Kluge did allow air launched V-1s to be used against the ports. They were also used against London which was a frivolous waste of the flexibility of this version of the V-1.

In the end the V-1s managed to deliver about 2,500 warheads to London over roughly a five month period. Call it 2,500 tonnes of explosives at a rate of about 500 tons per month. This is somewhat less than the tonnage of high explosive and incendiary ordnance dropped on Dresden on the night of 13/14 February '45 (2,660 tons).
During the same five month period as the V-1 offensive against London the RAF alone was dropping around 70,000 tons per month on targets in Germany and occupied Europe.
Because the war was nearly won and because of the civilian casualties there is a tendency, most noticeably in Britain, to get the impact of the brief V-1 campaign out of proportion. I understand why the citizens of London, and Antwerp for that matter, might do this, but historians have no excuse.

Cheers

Steve

 

[kool kitty89]

The V1's pulsetjet was very cheap compared with any jet rngine and the aiming device was going to be teh same. Why sped more for a 1-way weapon than you have to? And since the jet-powered one would be a bit faster with the same aiming device, the circle of error would be even bigger than it was, making them even less accurate.

I can't see what was wrong with the V1 as used other than needing a more accurate aiming system which it never got. Without that, airframe performance improvement would be largely a waste of effort if you hit even fewer of your targets than with the pulsejet version.

Wouldn't a somewhat larger missile allow for more options for practical guidance devices?

I also omitted the issue of turbojets having superior altitude performance on top of fuel consumption, though I'd assume increases in altitude would increase the target errors as well. (or I suppose it depends more on altitude, particularly where the most problematic wind/weather conditions tend to be)

One thing they might have tried would be radio honing. By using German agents in the UK and setting up small transmitters that could be turned on some minutes before the V1 was expected overhead so it could home in on the expendable transmitter. I have no idea if they ever tried it, but it seems like maybe that would at least allow taking out some high-value targets ... assuming the small transmitters could be palced and the agents make an escape before being blasted themselves. Wouldn't wrok too often but it would keep the radio direction finders bust for a few minutes. It would have worked better with directional antennas ... at least until the British caught on and started looking at the UK from the direction of an incoming missile.

Wouldn't using pathfinder aircraft to drop beacons/transponders make more sense? (similar to the flares dropped by mosquitos)

Granted, then you get into jamming and decoy signal countermeasures being developed.

If they had tried that in concert with a jet-powered V1 ... maybe. But I still can't see what was wrong with what they really did versus the cost of doing it.

It may have actually been faster to get a turbojet based missile operational. Pulse jets are extremely simple in operation, but making them useful and reliable is another matter (as it was, the German engines omitted a few extremely -mechanically- simple features that would vastly have improved performance -a simple 1-way valve for fuel injection control, and a thrust augmentor duct -combined, they could have nearly halved the specific fuel consumption while increasing thrust). The bigger issue though, was the vibration issues that created structural failure problems as well as some problems with the instrumentation.

Heinkel had simple, functional, flight worthy turbojets in 1939, not only that but the radial based turbine arrangement scales /down/ a lot more easily than axial turbines, so smaller engines than the HeS 3 or HeS 6 would have been possible. (significant if they did want to attempt turbojet powered missiles of approximately the same size as the existing V1)
Though making a somewhat larger design would probably be more advantageous.

And, of course, there's the fuel consumption and altitude performance advantages, plus turbojet exhaust is far less visible (though burning methanol or ether would make a far less visible flame than the V1's kerosene/gasoline) and with less noise. (though thrust augmentors tend to dampen both the flame and sound to some extent, those were never implimented by the Germans)

Another thought might be the possibility of a largely wooden construction missile (more than just the wings) with the engine buried in the fuselage reducing radar detection. (I don't think that would be practical with a pulse jet due to the vibration problems, but a turbojet has a lot more flexibility there)



I'm not saying it would be better in all respects than the V1, or that it would merit canceling pulse jet development entirely, but more that there were unique merits. (and on grounds of cost, may at least have still been far less expensive than the V2)

The Germans were relying on impact data from their spies to give them feedback in order to adjust their targeting. However, all of the German spies stationed in England had been converted to double agents and were giving false impact reports.

Wouldn't recon flights be a better measure of success, or even chase planes? Only jets would be able to actually keep up, but aside from that, you could still have prop based recon flights over the target area. (or launched ahead, with the missiles catching up on the target area around the same time as the recon craft)

You couldn't have recon flights following low, obviously, so weather/cloud conditions would determine ability to document the immediate effects on targets.

 

[rochie]

Found this on Wiki.
A certain number of the V-1s fired had been fitted with radio transmitters, which had clearly demonstrated a tendency for the V-1 to fall short. Oberst Max Wachtel, commander of Flak Regiment 155(W), which was responsible for the V-1 offensive, compared the data gathered by the transmitters with the reports obtained through the double agents. He concluded, when faced with the discrepancy between the two sets of data, that there must be a fault with the radio transmitters, as he had been assured that the agents were completely reliable. It was later calculated that if Wachtel had disregarded the agents' reports and relied on the radio data, he would have made the correct adjustments to the V-1's guidance, and casualties might have increased by 50% or more

 

[stona]

The V-1 had a substantial error on all axis. It wasn't just a matter of falling long or short. A typical map for the impacts on any one attack, discounting those that fell more than 40 miles from the target, generally takes the shape of an ellipse, typically about 30-40 miles long and about 10 miles wide at the widest point. Considering the V-1s had usually flown less than 200 miles from launch this is not impressive. Obviously bringing the centre of the ellipse directly over the target might increase the number of impacts on the intended target, but I'd love to see some proper data for the notion that casualties could have increased by 50%. It is NOT the same as bringing the centre of bombing from a reasonably concentrated air raid back (or more likely forward) to the aiming point.

Range did have an effect on accuracy. I have one map showing V-1 impacts after the French bases were lost to the Germans. The V-1s fell over an area extending from 50 miles north to 40 miles south of London and back to the east coast both north and south of the Thames estuary (there is no way to accurately work out how many fell into the sea). Few fell much to the west of London which means that as they were approaching from a more or less easterly direction they tended to fall short rather than fly long. It's still a huge area in which covers Hertfordshire, Essex, Surrey, Kent and East Sussex as well as Greater London itself.

Cheers

Steve

 

[Shortround6]

It kind of depends on the definition of 'accuracy' or what the standard is. The V-1 as used was useful for targeting a very large city AND it's close suburbs. It wasn't much good for anything smaller.

For some perspective greater London is about 609 sq miles, New York City is 469 sq miles. Against New York the V-1 would have been in position of one missile hitting Staten Island and the next one off the launcher hitting the Bronx or worse.

It killed and wounded people and caused property damage and a great deal of resources to be tied up countering it but those are different than accuracy.

 

[stona]

It kind of depends on the definition of 'accuracy' or what the standard is. The V-1 as used was useful for targeting a very large city AND it's close suburbs. It wasn't much good for anything smaller.

As illustrated by the Southampton-Portsmouth attacks. Of the 42 V-1s that actually fell on land between 10th and 15th July none impacted within the extensive docks area.

Some damage and casualties were caused. On the night of 14th/15th July the worst incident caused fifteen deaths and ninety eight wounded when a V-1 came down in Newcomen Road, Portsmouth. This one was close to the docks, but nowhere near close enough to do any damage to the naval installations.

Cheers

Steve

 

[Shortround6]

That rather illustrates the problem with attacking a coastal city because the if the center of the ellipse is the docks in the center of the ellipse then roughly 1/2 of the fired missiles will fall into the sea to begin with. To get 42 missiles to fall on land how many were fired?

 

[pbehn]

There are some areas in London that are densely populated but even today in greater London there a lot of open spaces.