The Problem of German Rocket Configurations in WWII

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hippo2004

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From the A4 through the A9/A10, German rocket projects in the Second World War generally seem to exhibit a bulged center, tapered ends configuration, with the effect becoming even more pronounced in the A9/A10. Rather than adopting the later, cleaner cylindrical fuselage, these designs retained a fuller mid-body and more strongly converging fore and aft sections. Wouldn’t this have increased drag and reduced usable internal volume? Why did German wartime designers not shift toward a slimmer cylindrical layout?
 
I have no concrete answer for your question but especially for the A4 they were testing the configuration during hundreds of wind tunnel hours to guarantee a stabil flight during the whole speed range. It seems that the chosen configuration worked.
 
Why would it increase the drag? If they have the same radius, an aerodynamicaly optimized ogive like body design will be more aerodynamically efficient than a flat cylinder body. Cyclinder body is not optimum for drag reduction, it is used due to its ease of design and manufacturing and larger internal volume as you have said. If a cyclinder was more aerodynamically efficient then we would use nose cyclinders in front of rockets and not ogival nose cones.
 
Perhaps the Germans were expressing their well-known trait of 'Over-Engineering', yet again, yet again ??
 
Basil said:
Not sure where the myth comes from. Especially during the later periods of the war most german items were engineered and produced in a very efficient way.
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And that remains the case to this day. After all, this small country is the fourth-largest exporter. That wouldn’t be the case if everything were unnecessarily complicated and expensive.
 
You have misunderstood my point. I agree with the design logic of an ogival nose cone; what I am discussing is the rocket body itself. If a load-bearing propellant tank structure had been adopted, the maximum diameter could have been reduced directly, and the internal volume could have been used more efficiently. By comparison, the ogival body design of the A9/A10 increased both diameter and drag.
MarineEngineer said:
Why would it increase the drag? If they have the same radius, an aerodynamicaly optimized ogive like body design will be more aerodynamically efficient than a flat cylinder body. Cyclinder body is not optimum for drag reduction, it is used due to its ease of design and manufacturing and larger internal volume as you have said. If a cyclinder was more aerodynamically efficient then we would use nose cyclinders in front of rockets and not ogival nose cones.
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On a different but related note, the Germans failed to develop and produce any solid rocket fuels beyond diglycol, a nitrocellulose-based propellant that had been around since before WW 1. This put a severe limit on what they could design and produce in a solid-fuel rocket. Worse, when used in multiple boosters, it made for a very difficult to solve issue of asymmetric thrust that could drive a rocket using those into an out-of-control gyration that ended with the rocket's failure.
 
hippo2004 said:
You have misunderstood my point. I agree with the design logic of an ogival nose cone; what I am discussing is the rocket body itself. If a load-bearing propellant tank structure had been adopted, the maximum diameter could have been reduced directly, and the internal volume could have been used more efficiently. By comparison, the ogival body design of the A9/A10 increased both diameter and drag.
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Ok thanks for opening that up. The Germans already had a really hard time making V-2 rockets work reliably while using a separate structural load-bearing body and mildly pressurised propellant tanks. I seriously doubt they could make a fuel tank that was both a load-bearing structure for the rocket and a mildly pressurised tank that could work reliably for the A9/A10. By the later stages of the war German metallurgy was really struggling because they couldn't access metals they needed. Perhaps they made these design compromises to keep the system manufacturable?
 
MarineEngineer said:
Ok thanks for opening that up. The Germans already had a really hard time making V-2 rockets work reliably while using a separate structural load-bearing body and mildly pressurised propellant tanks. I seriously doubt they could make a fuel tank that was both a load-bearing structure for the rocket and a mildly pressurised tank that could work reliably for the A9/A10. By the later stages of the war German metallurgy was really struggling because they couldn't access metals they needed. Perhaps they made these design compromises to keep the system manufacturable?
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They probably could have. The Wasserfall SAM was a smaller version of the A-4 in terms of the body of the rocket itself. On it, the tanks formed the integral skin of the missile to give more room for fuel. I don't see, in particular, why the A-4 couldn't have had that done as well. Another thing the Germans failed to do was use a detachable warhead on the A-4. That would have allowed the whole missile to be built to lower load tolerances since it wouldn't have to survive reentry. A lighter missile means better range for the same fuel and thrust along with saving "strategic" materials in its construction.

I suspect, but don't know for sure, that the leading reason those things didn't happen was that the war situation was deteriorating so rapidly that the engineers and such on the A-4 program simply didn't have the time and resources to put into making those changes and even if they had, testing wasn't possible, and the factories weren't going to be able to implement them any time soon.
 
This and it was a new technology with no experiences. The first generation of Western and Eastern missiles did not have detachable warheads either. It was a long learning process.
 
xena said:
This and it was a new technology with no experiences. The first generation of Western and Eastern missiles did not have detachable warheads either. It was a long learning process.
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Not true. The first US ballistic missile--completely designed and built with US technology--was MX 774 HIROC in late 1945 - early 46. It was specified in the original planning that it have a detachable warhead. It was recognized that this would allow for a lighter missile giving more payload and range for any given amount of thrust.
 
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xena said:
And that remains the case to this day. After all, this small country is the fourth-largest exporter. That wouldn’t be the case if everything were unnecessarily complicated and expensive.
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Plus, the "unnecessarily complicated and expensive" part of the market is already cornered by the Swiss.
Ha!
 
MarineEngineer said:
Why would it increase the drag? If they have the same radius, an aerodynamicaly optimized ogive like body design will be more aerodynamically efficient than a flat cylinder body. Cyclinder body is not optimum for drag reduction, it is used due to its ease of design and manufacturing and larger internal volume as you have said. If a cyclinder was more aerodynamically efficient then we would use nose cyclinders in front of rockets and not ogival nose cones.
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A pure cylindrical structure would have also been more prone to buckling. the outer skin of the A4 was just sheet metsl if I got it right. Todays rocket first stages have their skins made out of milled, rolled and welded aluminiumplates, This solution woulf have been by far more expensive.
 
Nicknick said:
A pure cylindrical structure would have also been more prone to buckling. the outer skin of the A4 was just sheet metsl if I got it right. Todays rocket first stages have their skins made out of milled, rolled and welded aluminiumplates, This solution woulf have been by far more expensive.
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The A4 was built like a conventional airframe for an aircraft would have been. That is ribs and stringers with a stressed skin all riveted or tack welded together. I believe most of it was steel rather than aluminum to save on using scarce aluminum.
 
Actually, aluminium was never extremly scare in Germany during WW2 because of the downed enemy planes and lower than expected production of new aircrafts.
 
As stated in previous posts, the tapered nose and tail shape is more aerodynamically efficient compared to a "Straight sided cylinder and Nose Cone" design. At the time of the design of the first A4/V2 reduced scale prototype (the A3 around 1936) the best understood shape that was known to be efficient at supersonic speeds was the high velocity bullet or shell, with the characteristic ogive nose and truncated ogile tail. There was a huge amount of ballistic testing data available for this shape, at a time when supersonic wind tunnel data was very scarce. Complex curves are harder to manufacture however, so it was a trade off of reduced risk and higher aerodynamic performance against manufacturing cost. Is this an example of over or under engineering ? Not sure. To me its an example of good engineering in that it reduced development time and risk while not introducing unacceptible levels of manufacturing complexity.

The choice of stringer and rib construction, with separate internal tanks was another technically conservative decision. Experience in aircraft construction meant it was fairly well understood. Not so much for monocoque construction. Wasserfall was a mix of monocoque and rib and stringer construction. But it was a smaller, later missile with pressurised fuel delivery (rather than turbo pumps) so required stronger more rigid tanks, more suitable for acting as a monocoque. The monocoque section required new welding techniques to be developed, caused some problems with wing attachment, impossible to fix tank leaks, and made for a more delicate missile. A4's were launched with holes punched in them through mishandling during transit. Because the outer skin wasnt the tank skin, they were still flyable.

With hindsight going for stringer-and-rib for A4 and partial monoque for Wasserfall look like very reasonable design choices. None of these choices seem to be "problems" (the title of the post) but fairly sensible compromises given the state of the art at the time and the need to get systems operational when they could be of some use. As one wag quipped "the war won't wait for Prof. von Braun".

The greater availabity of wind tunnel data and the operation experience gained with the A4/V2 made it clear that the less optimised cylindrical body shape was an acceptible aerodynamic compromise, while being a lot easier to manufacture. So when von Braun and his team designed the Redstone for a new customer, it had a much simpler profile. This continued right up until they put a man on the moon with the Saturn 5.
 

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