Comments by "Keit Hammleter" (@keithammleter3824) on "The Kamikaze Nazi Rocket Plane - Lippisch P13" video.

@bradywomack9751 : Bearing mind this was supposed to be a one-time-use ramjet (disposable) I don't see why a coal engine couldn't be made to work. A friend of mine, on discovering that local sawmills had huge piles of sawdust that they couldn't give away and just burnt, decided to make a sawdust fuel turbine engine. He set it up in his backyard with the exhaust pointing straight up. He got it working (inefficiently), but combustion within the engine was nowhere near complete, and huge flames came out the exhaust. The neighbors seeing the flames phoned the fire brigade, who were not amused, and stopped the work. If one can make a sawdust engine work, one could certainly make a coal dust engine work, since coal, unlike sawdust, has less ash and negligible water content.
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@dannydaw59 : Yes. The energy density of lithium ion batteries is 0.3 MJ/Kg and lithium ion powered toy planes do fly. Lithum polymer batters can be as good as 0.9 MJ/Kg and have made all sorts of battery UAV planes practical and manned battery planes are being investigated. But batteries pale in comparison to coal, which gives 33 MJ/Kg - not as good as gasoline at 45 MJ/Kg but still vastly better than any battery, even after losses in converting to mechanical energy - about 90% for electric motors and about 47% for aircraft gasoline engines and around 55% for ramjets at the likely speed. Weight for weight we can expect a range around 60% of what you would get with gasoline engines.
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@josega6338 : The pulse jet engines, as devised by the Germans for the V-1, were not self-starting - they required launching from a powerful catapult. It would make the thing too complex and costly anyway. The idea was to have a dirt cheap disposable / one-time use machine that could be used by crews with minimal training.
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@colinpowell4788 : The V-2 was not a ramjet craft, and not a flying bomb. It was a ballistic missile powered by a rocket engine using alcohol (with water to reduce peak combustion temperature to manageble levels) and oxygen stored in onboard tanks. A ramjet would be useless in a V-2 as it flew far too high to get sufficient atmospheric oxygen, and also useless because the V-2 accelerated from rest on the launch pad under its's own power, which a ramjet cannot do.
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@williamzk9083 : Presumably you meant Walter Kaaden, who had nothing to do with V-1's or V-2's and barely out of college in WW2. He did his thing on 2-stroke piston engines in 1961, long after World War 2 had ended. I would be surprised if Suzuki used any industrial espionage of German innovation in their 2-stroke engines, as they developed their Posi-drive engines in the 1960's, which were disk valved, forced lubricated, used straight gasoline, and were unique. Perhaps you have come across a Facebook myth.
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@Trollwatch : Interesting. Wood flour could be air-injected as was Diesel's original idea, but would not be a clean fuel. The ash would cause severe wear. I take it that it wasn't based on burning wood in an air-starved external combustor, thereby producing carbon monoxide, which burns cleanly and effectively in a spark-ignition engine? This method is unsuitable for aircraft as the wood combustor was very large - typically the size of a large fridge when supplying a car engine. This method was not unusual in sawmills in the 1920's., and widely used to run cars on wood in Australia during World War 2. Gasoline was tightly rationed and effectively not available for non-work related use. Car owners either bolted the combustor on the back or towed it on a trailer. A trailer was preferable as it gave a longer range and the combustors were often home made and sometimes exploded.
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@williamzk9083 : It didn't actually work at zero speed. Actually, iwhen the fuel was ignited, pulsing would usually start with a lowish fuel flow without any forward movement of the V-1. But it was not proper pulsing and the thrust was minimal, well under that required for the V-1 to fly (well below the thrust required to achieve aerodynamic stall speed). On launch, V-1's were accelerated to over 300 km/hr by a catapult device, essentially a piston in a very long cylinder driven by a huge volume of steam created by reacting hydrogen peroxide with sodium permanganate. At nearly 300 km/hr the pulse jet began to work properly and produced full thrust, continuing the flight. You can watch a German training film on how a V-1 launch works at https://www.youtube.com/watch?v=YJ-dAFQ6Jzo. The catapult system was quite elaborate. The link you provided is not valid.
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@williamzk9083 : A water/coal slurry will not work in a diesel engine, as atomisation is critical to ignition and burst combustion, which must occur with a few degrees (10 or 15 at most) of top dead centre, or efficiency will be low. For the same reason, particle size would need to be well under 0.1 mm or the engine may not even fire. Remember - combustion is two processes - pyrolysis followed by oxidation. Oxidation cannot occur until pyrolysis has started - in a diesel engine this must be fast, so requiring particle surface area to be large compared to diameter. It should be fine in a turbine though - since combustion is continuous and can occur in as much volume as needed. The L13a (not L13) was meant to be simple and cheap, so pellet by pellet dispensing is no good. It was essentially a pre-loaded fuel cartridge system
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@williamzk9083 : I'll rely on the original German training films and manuals. They say that the engine cannot accelerate a V-1 from rest and make it fly. They ought to know. If the engine was good at zero speed as you claim, why on earth did they need the expensive catapult running on a very dangerous but dramatically effective propellant? Incidentally, in the metric system, jet engine thrust is measured in newtons. Thrust is a force, not a mass. The V-1 engine had maximum output of 3.53 kN at 750 km/hr, equivalent to 360 kgf. However, V-1's had a speed regulator that throttled the engine so as to run the craft at 550 to 600 km/hr air speed. It so happens that the speed achieved by the catapult was 320 km/hr. Did you mis-read your reference?
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@williamzk9083 : I told you - the link you provided is invalid. Provide a working link to a valid webpage and I may then be able to view it. Kaaden worked as some kind of assistant to the designer of the Hs-293 glide bomb, and later was flight engineer during testing the Hs-293. The Hs-293 was a radio controlled glider bomb, not a missile. Kaaden never had anything to do with missiles, and certainly had nothing to do with the V-1. It's no good you, without any backup, just repeating your implausible and unlikely claim that Suzuki copied or used industrial espionage to design their engines. What is your source? I note that Suzuki was by no means the only 2-stroke motor cycle manufacturer to use rotary disc valves in the 1960's. E.g., Kawasaki's 2-stroke was also disc valved. Same with Bridgestone. But Suzuki's motorcycle engine was unique in its lubrication system. It was also high revving with (by 2-stroke standards) a wide power band. It was unlike a tuned racing engine that really only functioned well within a narrow rev range - it was designed to compete with the Honda 4-strokes. Kaaden didn't invent rotary disc valves - Daniel Zimmerman did. Nor was Kaaden the first to think of or understand resonant exhaust tuning - an Erich Rolfe did that for m/c 2-strokes, 10 years before Kaaden worked on it. So, basically, rotary disc valves and exhaust tuning was just something the Kaaden and lots of others were working on in the 1960's - refining it, not devising it. You claim is implausible.
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@bradywomack9751 : I agree with you, although what the Germans were trying to do was significantly eased by intending it for a one-time use for a very short flight time. All the early workers in jets had their biggest difficulties with combustion temperatures too high for the available engine construction materials, causing rapid failure, or using ways of keeping teemperature so low efficiency was so low as to be useless. This problem does not occur to anywhere near the same degree in a piston engine because combustion is not continuous - it only occurs within a few degrees of top dead centre every second crank turn. The other 700-odd degrees of crank turn are available for heat to flow out of the cylinder head walls etc. If the P13a engine came apart from heat after 15-20 minutes it would not have mattered - its' job was done. Solving the heat problem in jets for Britain was Rolls-Royce's brilliant innovation, having an inner and outer combustion chamber with holes in the inner where the air goes in. This meant the inner chamber could be made of an alloy that withstands heat but needs no mechanical strength, while the outer chamber needs an alloy with strength to withstand combustion pressure, but is not subjected to heat. I think this thread was on the question "Could a coal fueled jet engine have worked?" The answer is clearly yes. On the question "Could it have been useful for normal aviation?" I very much doubt it. There is one very good reason why nobody has made a coal powered rocket engine - in most applications of rockets (as distinct from applications of jets), the weight of fuel at launch is the limiting factor. The energy content per unit mass of coal is much less than other fuels such as kerosene, hydrogen, etc. Coal could work but not very well.
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@Thinkle911 : I think you have overlooked a couple of things:- 1. The P13a engine design called for the coal to be in the form of small granules. How small is small? Unfortunately I don't know. 2. The design separated the locations of pyrolysis and combustion. The coal granules were to be heated in an air-starved "basket" thus producing carbon monoxide. Additional air was to be downstream mixed with the carbon monoxide and burnt. By separating pyrolysis and combustion in this way, the pyrolysis part does not require much air and can be a "slow" process in a large volume. This is essentially the same idea that enabled people to run cars on wood during World War 2. According to Wikipedia, a preliminary design was built and tested, and found to work but not very well. A better pyrolyser design involving a rotating basket was proposed as a result. However, no reference is given, so the Wiki author might be wrong.
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@Thinkle911 The wood burning gas generators used for cars were roughly about the size of a kitchen fridge. But there was no need to think of ways to make them small. One of the reasons for the size was so the driver didn't have to stop extra times just to stoke it with more wood. The energy density by volume of wood depends on the wood but for hard woods it is usually about 0.5 to 0.75 of the energy density of coal. So it seems feasible that a gas generator fueled by coal could be half the size or less, perhaps quite a bit smaller. The power output of a car engine running on carbon monoxide was reduced to about 70% of that with gasoline. Overall, I still think a coal fueled airplane for a short flight is doable, but it wouldn't be very good. I think you are right in believing it a gigantic waste of material. Only for if you are desperate, which in the later part of the War the Germans certainly were. They would have needed to get the thing good and hot before a flight. This could take sufficiently long such that the Allies could have defeated it by randomising their bomb run directions and times. The various sorts of Messerschmitts could be scrambled in a few minutes, as could Spitfires etc.
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@josega6338 : A model constructed in 1993 has no relevance to what the V-1 engine could do. It indicates self-take-off is possible in a light aircraft with 2 engines, but it wasn't in the case of the V-1 fully loaded with explosive (~2 tonnes total mass), even though the V-1 flew pretty fast for its' day. The video does clearly show that engine operation at zero airspeed is problematic - he had a lot of trouble getting the engines to pulse, although this could have been due to some fault in his set-up or design. The main purpose of the V-1 catapult was to accelerate the V-1 to a speed at which the pulse jet engine could operate properly and develop enough thrust to take over and continue the flight. That's what the original German training materials state. A secondary but still important function of the catapult/ramp was to point the V-1 towards the target (London), as the onboard flight control (compass and autopilot) was designed for a simple straight line flight. According to the German documentation, the stall speed of the loaded V-1 was 240 km/hr. The catapult accelerated it to 320 km/hr, considerably above the stall speed but sufficient for the engine to be certain to develop enough power to maintain the speed and accelerate as fuel mass was consumed. All types of jet engines, including pulse jets, essentially produce a thrust that increases with aircraft airspeed, as with increased airspeed, a given mass of air is forced in in less time, permitting a greater fuel flow for stochiometric operation. (In practice, modern jets may be restricted at high speed by the engine management computer in order to stay withing design stress limits at high speed but retain good take-off performance.) But with pulse jets there is an additional problem - at low speeds the pressure and flow conditions are not right for proper resonance, and while it may pulse, it won't pulse properly. You can watch a German training film on how a V-1 launch works at https://www.youtube.com/watch?v=YJ-dAFQ6Jzo. The catapult system was quite elaborate.
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@josega6338 : Actually, I'm none too good at following spoken German either, despite German parentage - not enough practice. But I can read German ok. You've got an extra f in stuffung. Aircraft carrier catapults are primarily for getting enough airspeed to be above stall in a short distance, and the relatively heavy weight of typical fighter planes (eg Crusader 15 tonnes take off mass) or observation planes requires an impressive catapult, even with propellers, which work just as good at zero airspeed. But the V-1 catapult was designed to impart a much greater speed to 2-tonnes of V-1 + fuel + warhead to get the pulse jet engine up to flying thrust, well above stall as I described.
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@josega6338 : You have ignored the point I made (true, repeatedly) - yes, the engine RUNS at zero airspeed, but it doesn't generate enough thrust for flight at zero airspeed. It has to be accelerated to near 320 km/hr before it can develop enough thrust to sustain flight. Unlike a normal airplane, a V-1 could not take off on its' own. It could not accelerate from a standing start to a speed sufficient for take-off, no matter what sort of runway was provided. or how long it might be.
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@josega6338 : I told you - how a modern day light weight model, probably 50 kg or so, with 2 engines of unknown design performs has absolutely nothing to do with how a wartime single engine that had to shift 2 tonnes performs. The original German training materials for the V-1 state that the aircraft has to be accelerated WELL OVER the stall speed in order for the engine to take over - they should know. Modern fighter jets can reach Mach 2 routine. By your reasoning that means any jet fighter can reach Mach 2, including the wartime Me-262 (which could barely reach Mach 0.8).
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@josega6338 : You claimed in your last post that the Me-328 model contradicts me. It does nothing of the kind, so I responded explaining why. You are being silly now. You can go imagine a MiG-25 with an engine from the Enterprise NX-01 if you like. Should get a speed of Warp 10, whatever that may mean. A pulse jet is the last choice you would want for a take-off engine. I told you, go back and read it again - jets of all kinds inherently produce thrust that increases with airspeed, so they are relatively weak at take-off, unlike propellors driven by piston engines or turbines. In addition to that basic weakness of all jets, pulse jets have an additional problem - as they are a resonant system (tuned for cruise airspeed), the pressure and flow conditions at zero airspeed are not as designed, and thrust is even weaker still - in fact they can be difficult to start, tending to blow flame instead of pulsing. A rough analogy is a racing bike 2-stroke engine - they are also a tuned i.e., resonant system and at RPM lower than intended produce little power and run audibly very rough, erratically misfiring.
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