Ruhrstahl X-4: Difference between revisions

{{short description|WWII guided missile developed by Nazi Germany}}

The '''Ruhrstahl Ru 344 X-4''' or '''Ruhrstahl-Kramer RK 344'''<ref>[http://www.nevingtonwarmuseum.com/kramer-rk-344.html Nevington War Museum - Kramer Rk 344]</ref> was a [[Wire-guided missile|wire-guided]] [[air-to-air missile]] designed by Germany during [[World War II]]. The X-4 did not see operational service and thus was not proven in combat but inspired considerable post-war work around the world, and was the basis for the development of several ground-launched [[anti-tank]] missiles.{{cn|date=May 2023}}

[[File:X-4 UdvarHazy.jpg|thumb|A Ruhrstahl X-4 on display at the [[Udvar-Hazy Center]].]]

During 1943, the [[Royal Air Force|RAF]]'s [[RAF Bomber Command|Bomber Command]] and the US Air Force mounted a series of heavy raids against Germany. Despite heavy bomber losses, these prompted ''[[Luftwaffe]]'' research into considerably more powerful anti-bomber weaponry in order to reduce the cost in lost [[fighter aircraft]] and aircrew. A massive development effort resulted in a number of heavy-calibre [[autocannon]] designs, [[air-to-air rocket]]s, [[Surface-to-air missile|SAM]]s, and the X-4.

Work on the X-4 began in June 1943, by Dr [[Max Kramer]] at {{ill|Ruhrstahl AG|de|3=Ruhrstahl}}. The idea was to build a missile with enough range to allow it to be fired from outside the range of the bombers' guns (what is now called a [[standoff missile|stand-off]] weapon). The bombers' defensive guns had a maximum effective range of about {{cvt|1000|m}}. The missile was to be guided with enough accuracy to guarantee a "kill". The X-4 met these specifications and more. Its BMW 109-448 rocket motor accelerated the missile to over {{cvt|1150|km/h}} and kept the X-4 at this speed during its "cruise", between {{cvt|1.5 and 4|km|1}}.

The rocket burned a [[hypergolic]] mixture of [[S-Stoff]] ([[nitric acid]] with 5% [[ferric chloride|iron(III) chloride]]) and [[R-Stoff]] (an organic amine-mixture of 50% [[dimethylaminobenzene]] and 50% [[triethylamine]] called [[Tonka (fuel)|Tonka 250]]) as propellant, delivering {{convert|140|kg|lb|abbr=on}} thrust initially, declining to {{convert|30|kg|lb|abbr=on}} over the 17-second burn.<ref>Fitzsimons, Bernard, general editor. ''The Encyclopedia of 20th Century Weapons and Warfare'' (London: Phoebus Publishing Company, 1978), Volume 24, p.2602-3, "X-4, Ruhrstahl".</ref> As there was no room for a fuel pump, the fuels were forced into the motor by pistons inside long tubes, the tubes being coiled (similar to a [[coil spring]]) to fit inside the airframe. S-Stoff was so [[corrosion|corrosive]], it dissolved all base metals and was extremely difficult and dangerous to handle. The Germans planned to replace the motor with a [[solid fuel]] design as soon as possible.

The missile was spin-stabilized at about 60 rpm,<ref>Christopher, John. ''The Race for Hitler's X-Planes'' (The Mill, Gloucestershire: History Press, 2013), p.132.</ref> or one rotation a second, so any asymmetrical thrust from the engine or inaccuracies in the control surfaces would be evened out. Signals to operate control surfaces on the tail were sent via two wires (a method chosen to avoid radio jamming),<ref>Christopher, p.132.</ref> which unwound from [[bobbin]]s housed within long, bullet-shaped fairings, themselves mounted either on the roots of an opposing pair of the larger mid-body fins (there were four, swept 45°),<ref>Christopher, p.132.</ref> or on one pair of those same fins' opposing tips; these contained a total of about {{convert|5.5|km|smi nmi|abbr=on}} of wire.<ref>Christopher, p.132.</ref> The wires were controlled by a [[joystick]] in the cockpit.<ref>Christopher, p.132.</ref> A [[gyroscope]] kept track of "up" so control inputs from the pilot's joystick in the launch aircraft could be translated into [[Yaw angle|yaw]] and [[Pitch (flight)|pitch]] as the missile spun. Flares attached to two of the midsection wings were used to keep the missile visible through the smoke of its motor.

The warhead consisted of a {{convert|20|kg|abbr=on}} fragmentation device that had a lethal radius of about {{convert|8|m|abbr=on}}. It was thought that the guidance system would allow the pilot to get the missile into this range in terms of pitch and yaw. But with the ranges the missile could operate at, it would be almost impossible to judge range to the target bomber anywhere near this accuracy. For this reason the missile mounted a [[proximity fuze]] known asa ''Kranich'' ([[Crane (bird)|Crane]]), using an acoustical system tuned to the 200&nbsp;Hz sound of [[Wright R-1820|the B-17's engines]] in cruise,<ref>Fitzsimons, p.2603, "X-4, Ruhrstahl".</ref> activated by the [[Doppler shift]] as the missile approached.<ref>Christopher, p.133.</ref> The trigger range was {{convert|7|m|ft|spell=in}}.<ref>Fitzsimons, p.2603, "X-4, Ruhrstahl".</ref>

The first flight test occurred on August 11, 1944, using a [[Focke-Wulf Fw 190]] for the launch platform.<ref name="Ford">{{cite book|last1=Ford|first1=Roger|title=Germany's Secret Weapons of World War II|date=2013|publisher=Amber Books|location=London, United Kingdom|isbn=9781909160569|pages=224}}</ref> Subsequent tests used the [[Junkers Ju 88]] and [[Messerschmitt Me 262]], although they were not launched from the latter. The X-4 had originally been intended for use by single-seat fighters (including the Me 262 and possibly the [[Dornier Do 335]]),<ref>Christopher, p.133.</ref> but the problems in guiding both the missile and the aircraft at the same time proved unworkable. Instead, the X-4 was re-directed to multi-seat aircraft like the Ju 88, while the unguided [[R4M rocket]] was to be used in single-seaters.

After the war, French engineers tried to develop a domestic version of the X-4, the [[SS.10|Nord SS.10]]. 200 units were manufactured between 1947 and 1950. However, the program was disbanded due to the dangerous pre-flight refueling involved (the hypergolic nitric acid and Tonka combination was highly explosive).

* Length: {{convert|2|m|ft|abbr=on}}<ref name=":1">{{Cite book |last=Fitzsimons |first=Bernard |url=https://www.worldcat.org/oclc/4515654 |title=The Illustrated encyclopedia of 20th century weapons and warfare |publisher=Colombia House |year=1977 |isbn=0-8393-6175-0 |volume=24 |location=New York |pages=2602–3 |language=en |chapter="X-4, Ruhrstahl |oclc=4515654}}</ref>

* Wingspan: {{convert|74|cm|in|abbr=on}}<ref name=":1" />

* Launch weight: {{convert|60|kg|lb|abbr=on}}<ref name=":1" />

* Speed: {{convert|880|km/h|mph|abbr=on}}<ref>Fitzsimons, p.2603, "X-4, Ruhrstahl"; Christopher, p.133, says {{convert|620|mph|m/s|abbr=on}}.</ref>

* Warhead: {{convert|20|kg|lb|abbr=on}} fragmentation<ref>Christopher, p.133. </ref>

* Weight: {{convert|10|kg|lb|abbr=on}}<ref name=":0">{{Cite book |last=Fitzsimons |first=Bernard |title=The Illustrated Encyclopedia of 20th Century Weapons & Warfare |publisher=Colombia House |year=1977 |isbn=0-8393-6175-0 |location=New York |pages=2603 |language=en}}</ref><!-- [20] doesn't specify whether this weight refers to launch weight or system weight or if there is a distinction. -->

* Speed: {{convert|100|m/s|mph kn km/h|abbr=on}}<ref name=":0" />

**Penetration: over {{convert|200|mm|in|abbr=on}} at 30°<ref name=":0" />

* Range: {{convert|1000|m|yd|abbr=on}}<ref name=":0" />

* Date deployed: never<ref name=":0" />

* [https://archive.today/20110805100057/http://www.rafmuseum.org/cosford/collections/missiles/missile_info.cfm?missile_id=25 Ruhrstahl Kramer X4 - Royal Air Force Museum, Cosford (UK)]

* [http://www.lonesentry.com/ordnance/x-4-aircraft-launched-antiaircraft-rocket.html X4: Aircraft Launched Antiaircraft Rocket] {{Webarchive|url=https://web.archive.org/web/20180502213626/http://www.lonesentry.com/ordnance/x-4-aircraft-launched-antiaircraft-rocket.html |date=2018-05-02 }}

{{RLM aircraft designations}}

[[Category:Air-to-air missiles of Germany]]

[[Category:Wire-guided missiles]]