Turbojet powered cruise missiles

[Koopernic]

Stona, Milosh,

FuG 101a had the two ranges with the lower one very useful for blind landing, the FuG 101 had only the coarse one.

The FuG 101 and its mechanical FM techniques was used as a basis of a proximity fuse for bombs called MARABU. The allies expected this and had developed techniques they thought would pre detonate it.

Basically a rapidly rotating motor was used to alter the frequency of a transmitter. By mixing the transmitted frequency (transmitted on say the left wing) with the received from a ground reflection (say on the right one) the phase difference indicated altitude.

I rather suspect MARABU would be a lot cheaper than FuG 101a and perhaps if only say +/-30m accuracy was required a cheaper device or a device working on different principles might do. German electronics engineers were very busy with anti jamming measures and developing a new generation of microwave radar at this time.

The accuracy of Barometric instruments would I think be adequate to go down to 100ft. I believe altimeters work reasonably well to 20ft and might be relied upon so long as one had good topographic maps.

 

[stona]

The motor speed was voltage sensitive and the PSUs were not consistent. The motor had to be calibrated to the PSU which was easy to do in a manned aircraft, trickier for a missile.

The separation of the transmitting and receiving antennae wouldn't be a problem. It had to be 1.4 -2.0 metres.

Cheers

Steve

 

[Koopernic]

I keep seeing these figures and am wondering where they come from...

See post #53 in this thread. Speed improvements were achieved at development facilities around Jan/Feb 1945. Germany was soon split in two.

The long range Fi 103 "F-1" version which had less warhead, was lighter due to a wooden nose was also faster.

 

[tyrodtom]

Barometric altimeters are set to the atmospheric pressure of where the aircraft takes off.

150 miles away it's usually going to be different. No problem for piloted aircraft because no pilot is going to expect 20 foot accuracy from a altimeter, or need it. He's got eyes.

Not so with a missile depending on a altimeter set to atmospheric pressure where the missile took off.

 

[Shortround6]

I think we are confusing radar altimeters with terrain following radar. Not at all the same thing. The first simply tells the pilot or auto pilot how high above the ground he/it is. The second measures the height of the ground in front of the aircraft and takes appropriate action to prevent contact from occuring. I would note that even anti-shipping missiles in the 60s could be adjusted for different sea states to prevent rogue waves from contacting missile. Rougher sea state called for higher altitude.
Sorry but landing a plane at around 200 kph is a whole different thing than flying cross-country at 600kph at even 10 meters.

 

[pbehn]

If it were possible to control the altitude to a low level why not a low powered prop driven version launched at night?

 

[Shortround6]

And since it would have much better range you could make it drop a bomb and return home for re-use.

Wait a minute, that sounds like the Miles Hoop-la.

 

[Koopernic]

And since it would have much better range you could make it drop a bomb and return home for re-use.

Wait a minute, that sounds like the Miles Hoop-la.

I believe the Fi 103 can trace its roots to a fly back piston powered aircraft, It was fairly small, more like a light aircraft. There are sketches of it about, I can't find any of it or the Hoop-la. It's obviously a far more complicated to return a vehicle then land it. Most early drones resorted to the idea of deploying a parachute than attempt fully automatic blind landing. Automatic blind landing had been achieved in Germany in 1940 but even then the pilot still had to cut the engines when the FuG101a told him he was a 2-3 meters of the ground and of course had set up the aircraft in the landing beam, set the autopilot to work of that beam and the right descent rate. It sounds attractive and it sounds possible with WW2 technology but there are so many little factors involved.

If it was possible for the Oboe radar blind bombing system to send course corrections as audio signals to a pilots headphones its not much harder to convert those audio tones into suitable electrical signals that can trim in adjustments to an auto pilot. I think the problem is that one would need mechanisms for each phase of flight: take-off, cruise, bombing, return cruise, approach, landing plus something to stitch it together. Possible in 1940 but expensive and not reliable.

If it were possible to control the altitude to a low level why not a low powered prop driven version launched at night?

It might have done well, the pulse jet generated a huge flame that Mosquito pilots found easy to see from many miles away.

I think we are confusing radar altimeters with terrain following radar. Not at all the same thing. The first simply tells the pilot or auto pilot how high above the ground he/it is. The second measures the height of the ground in front of the aircraft and takes appropriate action to prevent contact from occuring. I would note that even anti-shipping missiles in the 60s could be adjusted for different sea states to prevent rogue waves from contacting missile. Rougher sea state called for higher altitude.
Sorry but landing a plane at around 200 kph is a whole different thing than flying cross-country at 600kph at even 10 meters.

A radar altimeter does help to get down somewhat lower as one doesn't need to worry about navigating and consulting topographic maps simultaneously quite as much. Obviously one uses a different standard of 'low' for Essex versus say St Moritz.

I believe the terrain avoidance radar on the F-111 could conduct a 3G pull-up if it perceived terra firma ahead. This would pin the crew into their seats, essentially disabling them. It reacted not only off those funny little hills that jut out of the flat landscape in parts of Vietnam but sometimes a strong rain squall. Some kind of terrain avoidance radar was likely possible in WW2 but it certainly wouldn't have been priority.

 

[nuuumannn]

I suspect some of you might be over thinking this.

I would think one would have to just rely on launching many V1 from as many locations as rapidly as possible.

That was pretty much the gist of the V 1 campaign as it was. The Fi 103 was designed to be as simple as possible for rapid production in large numbers. The V 2 was more complex and far more devastating, although again, not precisely accurate to the degree that could be done with, say, dive bombing, but more so than the V 1 and far more difficult to counter once it had been launched.

 

[kool kitty89]

The man hour numbers are just that. You could factor that at a normal labor rate of consider the free "slave labor" that was available. You have to consider the cost of material, but regardless the sources at Wiki are showing that a complete V-1 airframe is nearly half the cost of a Jumo engine alone. Throw in the rudimentary guidance systems of the day and I see no way you could get "more bang for the buck" with what was available at the time. The V-1 was cost effective and IMO if introduced earlier in the war "would have" been more of a game changer than an earlier deployment of the Me 262.

I was suggesting possible compromises to get the best bag for the buck of a hypothetical throw-away turbojet design and the possibility of going slightly larger than the existing V1 to better justify the added engine assembly costs.

But then, the material costs might be more significant anyway (both in terms of using a smaller engine and a similarly sized V-1 airframe/payload). That and I was assuming larger engines of similarly simple design would be more cost effective (ie scaling down would be cheaper, but have diminishing returns in terms of cost to performance).

In any case, a slightly scaled down derivative of the HeS 3 of 1938/39 with similar cruise thrust (and higher static thrust) to the As 014 would have the advantages of being available sooner, avoiding development problems tied to vibration, and would consume less than half the fuel. (enough to make up for the heavier engine, if not more so)

Switching over to Pulse Jet power later on could certainly make sense if that proved more economical on the whole, but if a small, centrifugal compressor radial turbine jet engine could have been the earliest workable powerplant for a V1 style cruise missile, than that timing advantage alone may have made it worthwhile. (particularly if said jet technology was suitable for mass production only for very short-life engines)



The other question remains whether that would have been more cost effective than engineering similar engines into manned aircraft, and for that matter, raises the question of whether short-life turbojet designs would have been better suited to some of the attempted low-cost pulse jet powered fighters and attack aircraft. (given the valve life of the 014, a 'throw away' turbojet might have been attractive ... or a turbojet with a mostly throw-away hot section -or even just the turbine- intended to be totally replaced with frequent overhauls would have been fairly attractive, plus you'd save dramatically on fuel use)


There's a lot that could have been done with Ohain's early turbojets if you look beyond Heinkel's tunnel vision for fighter aircraft. (particularly ones intended to directly displace the Bf 109) Though ironically, Heinkel spread a bunch of resources between multiple follow-on designs from Ohain (derivatives of the HeS 8 ), Muller/Wagner's team, and several ducted fan designs based around Hirth's air cooled inline engines, yet the HeS 3 and 6 were abandoned.

For that matter, using Heinkel's jets as JATO boosters might have been useful as well. (and again, unlike the As 014, didn't have the serious vibration and noise issues -in fact, the LACK of vibration was Ohain's original inspiration for developing jet engines, intending to bring the elegance of glider-smooth flight to powered aircraft)

 

[cherry blossom]

Not really on the thread topic except for where it diverged to take about altimeters etc but since many V1s were shot down by AA guns, it is not obvious that increasing the V1's speed will have a dramatic effect although it will obviously help. The success of British guns was probably considered very unlikely by the Luftwaffe as they did not know about the proximity fused shells.

However, assuming that they realised what was happening, I have been considering what could they have done to reduce loses from AA. Would it have been possible for a V1 to fly a zigzag course by incorporating a timer and shifting the course from 30 degrees east of the true course to 30 degrees west of true every perhaps 20 seconds (ideally each bomb would have its own time set perhaps between 15 and 30 seconds)? Obviously that will cost some range. Naively reducing it only by a factor of 0.866 but actually much worse because speed will be lost during the turns. They could get some range back by adding a second timer to start the zigzag only as the V1 approached the British Coast. There will also be some loss of accuracy, which was bad enough when the bombs flew straight. Including the radio signalling system should reveal both the accuracy and, by comparison with bombs flying straight, whether zigzagging is worthwhile. It also seems that such V1s should be launch at night as the zigzag would allow British fighters to catch up if the pilots could judge what the V1 was doing.

 

[tomo pauk]

The V1s were also engaged by 40mm cannons, even by 20mm Oerlikons Polstens? Add another 100 mph to the V1, as it was done in 1945 (yes, historically too late) and you have all but cancelled those light AA guns from the V1's threat list.

 

[tyrodtom]

The V1 had only elevators and rudder for control surfaces, no ailerons. Only slow, gradual, course corrections were possible.
That's why tipping the V1 brought them down. You only had to tilt the aircraft beyond the ability of the 2 axis control to recover, and it went out of control.

Zig-zaging , unless very gentile , would be beyond what a 2 axis could do.

 

[Koopernic]

According to Wikipedia by March 1944 Fi 103 V1s were produced in 350 hours (including 120 for the autopilot).

Figures from Anthony Kay's "German Gas Turbine and jet engine development 1933-1945" for the BMW 109-003A-2 taking 600 man-hours out of a planned 500. These are actual German figures and conform with the production engineers Dr Fattners estimates of 500 man-hours per engine.

The Porche 109-005 of course had to produce about 50% less thrust and was required to have a total life of only 2 hours as opposed to a MTBO of 25 hours for the 003A2 (probably refurbished 4 times if no combat damage)

It's therefore not conceivable that the Porche 109-005 or simply 005 could be 50% x 50% less cost ie 25% as much (say 150 man hours) than the man rated BMW 003A2.

Noteworthy is that this doesn't include the cost of raw materials it such as sheet stock. Material is not expensive if steel but can be used but unless it includes nickel and chromium due to the high cost of mining and refining it. If the turbine inlet temperatures are kept below 650C the turbine can be made a 2 hours throwaway item of pure steal, this is what was planed for some of the German jet engines. Your turbojet is inefficient and big but its still better than a pulse jet.

If we assume the V1 cost 230 hours (excluding autopilot) and that 25% of this cost was the pulse jet (57.5 hours) then substituting the turbojet only adds 90 hours cost.

Out V1 now costs not 350 hours but 440 hours total and has both more accuracy and range. If we assume the electronics for guidance system (Ewald 2 also known as Ewald-Sauerkirsche added the same as the autopilot again (120 hours) we end up with a long range turbojet powered guided V1 for 560 hours compared to 350 hours for the short range unguided versions.

Some things are known of the 109-005. It used a geared compressor to optimise both the compressor and gas turbine. Though this sounds fancy (geared compressors are absolute state of the art Pratt and Whitney tech) this is a small gearbox that could be cast and machined in one piece. It would considerably reduce project risk as matching the compressor to the turbine is simplified by adjusting the gear ratio. It was also intended to shed ice.

The BMW disposable turbojet was of a conventional design.

So yes a guided turbojet powered V1 was probably only 50% more expensive as a shorter ranged unguided one and even if it were twice the price it would be 'affordable'. If you say its twice as expensive I say its still cost effective.

Interestingly the Germans experimented with the idea of semi disposable aircraft that were pulse jet powered. The deposable 109-005 gave these projects, such as the Me 328 a new life.

The Ewald 2 guidance system worked by receiving a single pulse from the V1 missile whose differences in arrival times in 3 fixed ground stations allowed a position to be calculated. Now consider that Three carrier aircraft launch a missile each. At a certain point one of the missiles emits its location pulse which are received by all three aircraft and then instantly relayed to three ground stations. There is now enough information from the differences in arrival time to locate not only the position of each of three aircraft but the missile.

Hence air launched turbojet powered guided V1 allow for considerable potential in long range and reasonably accurate guidance.

The reason I know it works is because the US built the Loon and that means an independent set of highly competent military officers and engineers analysed it.



Figures from Anthony Kay's "German Gas Turbine and jet engine development 1933-1945" for the BMW 109-003A-2 taking 600 man-hours out of a planned 500.
German Production Costs

This is much less than a piston engine.

Breakdown is:

Machining 220
Sheet Metal Work 160
Starter Governor 60
Miscellaneous 100
Assembly 60

There are further breakdowns with the 66 turbine rotor blades requiring only 10 hours.

Of course this doesn't cover the cost of refining and transporting metals and raw materials.

The time taken for the Jumo 004 was 700 manhours. (But remember cost drop as production is refined.

In both engines there was very little nickel, chromium or manganese. At most 6kg of each with nickel virtually eliminated to 200 grams in some versions. Nickel was in very short supply.

The website Vorwort lists the manhours required for a BMW 801 as

"Durch eine Optimierung der Fertigung wurden die Preise für die Motoren immer weiter gesenkt. Der Preis einer BMW 801 Motoranlage lag 1940 bei 80700 RM und Ende 1942 nur noch bei 45000 RM. Davon entfielen 35600 RM auf den Motor und der Rest auf das Kommandogerät (3000 RM) und die Verkleidung des Motors (6400 RM). Die Anzahl der Fertigungsstunden betrug Ende 1942 etwa 16000 Stunden pro Motor."

Or in English

"The prices for the engines were continuously lowered by an optimization of manufacturing. The price of a BMW 801 engine was in 1940 80,700 RM and at the end of of 1942 only 45,000 RM. Of this 35,600 RM were allotted to the engine and the remainder to the control unit (3,000 RM) and the lining of the engine (6,400 RM). The number of manufacturing hours amounted to at the end of 1942 about 16,000 hours per engine."

I would assume that a V12 engine like the DB603 would be about the same.

 

[stona]

Adding more sophisticated control surfaces, just like adding more sophisticated flight instruments like radar altimeters, is a waste of time, money and resources. If the Germans had wanted to create a more sophisticated weapon system they would have needed a different platform for it and most obviously a better guidance system. The only thing the V-1 had going for it was it's cheapness, take that away and there's not much left.
Cheers
Steve

 

[Koopernic]

Adding more sophisticated control surfaces, just like adding more sophisticated flight instruments like radar altimeters, is a waste of time, money and resources. If the Germans had wanted to create a more sophisticated weapon system they would have needed a different platform for it and most obviously a better guidance system. The only thing the V-1 had going for it was it's cheapness, take that away and there's not much left.
Cheers
Steve

That would be partially true but adding a bit of electronics and a substituting a turbojet doesn't increase the cost very much.

Adding turbojets and even optionally adding electronic guidance combined probably only adds 50% at most 90% to the cost of the V1, so its not going to take away its cheapness.

It will double the range and increase accuracy by about a factor of 8. The expectation of accuracy for Ewald Sauerkirsch guidance was around 2km, depending on where the mid course update was done it could be much better.

Vacuum tubes are only little pieces of glass and steel. The electrodes that penetrate the glass are made of copper clad iron filaments which have the same thermal coefficient of expansion of glass and platinum. The Germans started making the heating filaments out of titanium (a material they had) as tungsten became scarce but I suppose they could have used even carbon filament's to heat the cathodes.

The alternative is to just throw more V1's into the air and accept that only 20% are going to hit built up areas. The problem with this is that even if you have man hours to throw at a problem its no good if you don't have steal, there being only so much wood that could be used.

The "over the radar horizon" guidance system I postulated based on the Ewald system requires no new electronics on the missile, the computation is done in the ground stations and they relay aircraft equipment is also simple and not thrown away.

The radar horizon of a V1 at 1000m is about 140km so if this is the chosen cruising altitude that is where the midcourse update would be. Of course the V1 could fly higher, the ground stations could be atop 100m towers (which adds quite a bit) or the ground stations might even be relay aircraft. There are no fancy Adcock direction finding antenna, just timing signals.

One would think that unguided V1's would I expect be used as seductive decoys to hide the guided ones which would be targeted towards high value areas.

 

[FLYBOYJ]

I was suggesting possible compromises to get the best bag for the buck of a hypothetical throw-away turbojet design and the possibility of going slightly larger than the existing V1 to better justify the added engine assembly costs.

But then, the material costs might be more significant anyway (both in terms of using a smaller engine and a similarly sized V-1 airframe/payload). That and I was assuming larger engines of similarly simple design would be more cost effective (ie scaling down would be cheaper, but have diminishing returns in terms of cost to performance).

Full size turbine engines of the day barely worked, you think a 'scaled down version' was worth it?

In any case, a slightly scaled down derivative of the HeS 3 of 1938/39 with similar cruise thrust (and higher static thrust) to the As 014 would have the advantages of being available sooner, avoiding development problems tied to vibration, and would consume less than half the fuel. (enough to make up for the heavier engine, if not more so)

Wishful thinking, again full size engies were barely functional.

Switching over to Pulse Jet power later on could certainly make sense if that proved more economical on the whole, but if a small, centrifugal compressor radial turbine jet engine could have been the earliest workable powerplant for a V1 style cruise missile, than that timing advantage alone may have made it worthwhile. (particularly if said jet technology was suitable for mass production only for very short-life engines)

Again you're assuming that a small, RELIABLE and cost effective turbine engine could be produced to make the increase in performance and cost worth wild, I just don't see it based on the technology and resources available at the time. The Pulse Jet was the perfect engineering solution.

The other question remains whether that would have been more cost effective than engineering similar engines into manned aircraft, and for that matter, raises the question of whether short-life turbojet designs would have been better suited to some of the attempted low-cost pulse jet powered fighters and attack aircraft. (given the valve life of the 014, a 'throw away' turbojet might have been attractive ... or a turbojet with a mostly throw-away hot section -or even just the turbine- intended to be totally replaced with frequent overhauls would have been fairly attractive, plus you'd save dramatically on fuel use)

How much thrust you think a smaller engine would have produced? In reality the first jet fighters were underpowered when you consider their weight.

 

[GrauGeist]

See post #53 in this thread. Speed improvements were achieved at development facilities around Jan/Feb 1945. Germany was soon split in two.

The long range Fi 103 "F-1" version which had less warhead, was lighter due to a wooden nose was also faster.

I had assumed we were discussing units actually used in combat, not prototypes and test specimens.

Otherwise, we can stray into all sorts of 1946 projects that included As014 and As044 engines...

 

[FLYBOYJ]

I had assumed we were discussing units actually used in combat, not prototypes and test specimens.

Otherwise, we can stray into all sorts of 1946 projects that included As014 and As044 engines...

 

[pbehn]

surely a turbo jet that only has to run at one setting for an hour is cheaper than those fitted to a 262?