>> 3. You could try "my" 'Pistonless Piston Pump. I invented this as a >> rocket propellant pump some years ago and only subsequently found >> out >> that Lockheed Martin had patented the idea about 4 years before >> that. >> A version of this was independently invented by and being developed >> in >> secret by Flometrics (see it at >> http://www.flometrics.com/rockets/rocket_pump/rocketpump.htm) when >> I >> caused them some consternation by publishing my design. > I can't quite see why it's that complicated - why not just meter the > Very High Pressure into the top of the > main tank and force it out that way? What does the oscillating flow > achieve, apart from a pulsed output? To answer several people's questions including the above. 1. Pressure fed rockets are still very much in use. In fact there is a very good case for using pump fed systems only for first stages and not necessarily even then. Google "Robert Truax" [[ the great, admiral etc :-) ]] - a very very clued up gent from the golden age of US rocketry (50s-60s) and still going. FWIW he designed Evil Knevel's Snake River canyon steam rocket and many of the rocket powered drag cars of the 60's and 70s. 2. THE hardest thing to design in a turbo-pump fed rocket system is the turbo-pump. They are works of immensely arcane black magic. A rocket system is really almost just a support system for its turbopump :-). And this applies to the Spec Shuttle as well. Next comes the eg topping cycle engines that the TPs feed. Eliminating the TP if possible is a grweat gain. 3. As is explained on the Flometrics site, for a range of rocket configurations and sizes (not all) the PPP (Pistonless Piston Pump)(my name - they just say pistionless pump) is superior in performance and mass and more to a TP system. ALL aspects of the system must be considered. 4. Pressurising the main tank works fine EXCEPT that to attain the required pressures the tank must be far far far too heavy due to the need to resist the pressures involved. Most main tabnks are pressurised to a few psi and the TP takes it from there. Also, in a fully pressurised tank system at very high pressures the mass of pressurant gas is amazingly high. Google on "tridyne" to see one way of attempting to address this issue - the pressurant gas is 'burnt" to increases its temperature and pressure. It works BUT stand clear, don't try this at home, YMMV, boo..... If you pressurise your main tabnk to say 2000m psi not only is it heavy BUT all the gas is there at the end of the burn and your final mass may be more than doubles. As mass ratio (Mfull/Mempty is an ultra critical parameter in orbital ocketry this is very bad. Only lowish pressure systems can afford to do it this way. The PPP has all the advantages of the pressurised tank system and few of the disadvantages. What the PPP does is allow you to have a very small tank which is pressurised to full pressure and then emptied. It is then refilled from the main tabnk at low pressure while one or more companions are emptied at high pressure. A great bonus is that after each emptying of the pump chamber the pressurant gas can be thrown away and does not have to be taken along for the whole ride. This is an immnse advantage over pressurised tank rockets. Compared to the TP the PPP is lighter in many (not all) cases when all system masses are considered. It is also *MUCH* easier to build. Almost anyone who wanted to could build a reasonable PPP with low tech tooling. A decent TP requires myultiple advanced degrees in the black arts and typically millions of dollars. Or 100's of millions for the very best. > Are you referring to Thomas Savery's pump? In which case it was > 1698! :-) That's the one. The pressure stroke, which they don't dwell on greatly there, is essentially a PPP at work. My ideas are different enough to be different but based on the same broad principles. I didn't know about Savery's pump when I thought of the PPP. I was AFAIR looking at a Lawrence Livermore labs rocket piston pump when it occurred to me that the pistons were an unnecessary appendage :-). The PPP is so trivially obvious that once people understand it it feels that they have known about the principle forever :-). It's only when you go into it in detail that it becomes obvious just how good it can be compared to existing alternatives. ____________________ > Why is this good ? Here is the Savery engine: > > http://www.egr.msu.edu/~lira/supp/steam/savery.htm > With any high speed pump the speed will be limited mostly by the low > pressure ducting and suction therein, I think. A rocket certainly > needs > high speed liquid pumping (besides the pressure). Filling is not the major issue. You only need to be able to fill a chamber in the same time it takes to empty it. This is an easy task in most cases. A much lower power filling pump could be used but in rockets modest tank pressurisation or even justv the "head" induced by acceleration are enough to do the job. For simple low pressure plastic versions gravity feed alone can suffice. The output pressure can be designed to be whatever is required, quite independent of the low pressure aspects. > And why is such a > design 'lighter' than a turbopump ? A 20hp turbo (automotive, built > of > common materials and not aerospace stuff) is smaller than a six-pack > of > beer and weighs under 4 kgs. How can a gas piston pump compete with > it ? Flometrics provide some worked examples I believe. The relevant mass is the total system mass BUT a PPP itself is a relatively trivial device - 2 (typically) pump chambers plus some non return valves plus one multiport controlled valve per pump chamber. I suspect that in the example you give a PPP could be of much the same size and mass. The big difference in the automotive example is that the gas feed to the turbine in the automotive example would not be suitable for driving a PPP of arbitraily great pressure output but it is capable of driving a turbine which dricves a "pump" of whatever characteristics are reqyuired so in that application a turbo has advantages. In rocketry the characteristics of the energy (drive gas) source can be tailored to the application. > Afaik gas pressurized fuel feed for rockets was abandoned since the > 1950's. No ? No. See above. Still very much in use and even more potentially applicable than currently employed. One problem with orbital rocketry is that the big budgets have locked in certain very expensive assumptions and design paradigms which are not necessarily the best ones now and may never have been. There is vast debate on this in the rocketry community but various up and coming systems use quite different design approaches to those of the main stream past. RM RM -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist