tag:blogger.com,1999:blog-66929581667616709042024-02-08T06:25:55.603-06:00Universal Transport SystemsProviding the technology to move humanity into the space age.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.comBlogger22125tag:blogger.com,1999:blog-6692958166761670904.post-11063113760837982782012-06-04T11:17:00.000-05:002012-06-04T11:18:51.358-05:00Mission: Small Business $250K grantFor those that want to help out by clicking on links, we have registered for the Mission: Small Business $250K grant competition. You'll need a facebook login to vote, but presumably you already have one...
<br><br>
You can get instructions from our home page:
<br><br>
<a href="http://www.universaltransportsystems.com">www.universaltransportsystems.com</a>
<br><br>
But basically you go to the site <a href="http://www.missionsmallbusiness.com">www.missionsmallbusiness.com</a>, log in using facebook, search for "Universal Transport Systems" in the search box, and then press "vote".
<br><br>
For every person that does that, Chase and Livingsocial add $5 to the pot. Small companies that get over 250 votes will be eligible to get a $250K grant!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-7995030085625160682012-06-04T11:11:00.001-05:002012-06-04T11:18:42.663-05:00Status updatesThis last Saturday we spent the day firing the new test engines. I was expecting a lot of trouble, as this particular engineering challenge sounds pretty bad on paper. We needed a seal that could hold high pressure, hot gasses in the chamber but still move freely.
<br><br>
But then it worked perfectly, first time. We re-ran the tests, and it worked perfectly again! Since things were moving so well, we decided to move on to the next tests early. This next test is to stop the engine's burn before the next propellant segment ignites.
<br><br>
We didn't have enough time to do anything fancy, so we just threw something together (involving cut out cardboard!). Amazingly enough, it actually almost worked - the engine was almost shut down before it re-lit. A simple amazing result, considering how quickly we put the test together.
<br><br>
We are progressing very rapidly, and should have more interesting things to share soon!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-68421286205987338412011-01-20T22:44:00.002-06:002011-01-20T23:00:46.663-06:00Google Lunar X PrizeFor a short while, I was on a team competing for the Google Lunar X Prize. Unfortunately circumstances conspired against us, but I'd like to share some of my thoughts on the difficulties involved in the prize.<br /><br />The basics of the prize are that your team designs a lunar rover that can drive around on the moon and take video. Very possible - but you only win if your vehicle actually gets to the moon. The prize is about the rover - it doesn't matter how you get to the moon. Most teams were planning on tagging along on either a NASA or Russian flight.<br /><br />To me, the primary issue is that the activity that a team undertakes to attempt to win the prize is a tiny percentage of the project effort, and the team controls almost none of the failure risk. Most of the challenge in driving a rover on the moon is in getting to the moon, not the rover! Getting to the moon costs billions in development for the transit vehicles - even the incremental costs are in the hundreds of millions.<br /><br />It just seems a little suboptimal to have a prize that awards a team for getting a government space program to select your rover as additional payload on a government mission, rather than anything that an average team has any control over.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-23941726128667138392010-07-14T15:32:00.001-05:002010-07-14T15:34:23.194-05:00Poll results - How much would you spend to visit space?Here is how readers have responded to "How much would you spend to visit space?"<br /><br />33% Six month's pay<br />66% Only if I won the lotteryDavidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-3308096202619570482010-07-14T15:28:00.002-05:002010-07-14T15:31:10.488-05:00Nano-Satellite Launch ChallengeThis is the most exciting news I've seen out of NASA in quite a while! This is right in line with what we have been planning.<br /><br />Details:<br /><br />Objective: to place a small satellite into Earth orbit, twice in one week.<br /><br />PRIZE PURSE: $2 Million<br /><br />Satellite mass - at least 1 kg <br />Satellite dimensions - at least 10 cm cube <br /><br />Must complete at least one Earth orbit. Task must be accomplished twice in one week.<br /><br />Purpose: To stimulate innovations in launch technology and to encourage creation of commercial nano-sat delivery services.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com1tag:blogger.com,1999:blog-6692958166761670904.post-17320300015786925242010-03-02T09:19:00.004-06:002010-03-02T11:15:26.446-06:00Moon Ice Water RocketNASA recently announced the discovery of vast amounts of water ice on the moon. If you are a lunar geologist, it is extremely exciting news - but most people don't see a way to take advantage of it in the short term. Cracking ice into rocket fuel is just too hard, and will take too much infrastructure.<br /><br />But there is another way to use the ice - a simple water rocket! <br /><br />From the moon's surface to lunar orbit takes an impulse of about 2 km/s. Going all the way back to the Earth takes about 3 km/s. Really good water rockets can get about 1000 m/s exhaust velocity, or an Isp of 100 seconds or so. Using the rocket equation:<br /><br />delta-v=(exhaust velocity)*ln(mass ratio)<br /><br />The required mass ratios are 7.5 to lunar orbit, or 20 to Earth return. That means that for every pound lifted off the moon, you would need 7.5-20 pounds of water melted from the ice. Gathering this is a lot more manageable than setting up a chemical plant on the moon! It could be as simple as smashing the ice using heated tools, and dumping it into a slightly heated hopper.<br /><br />The engine is really just a water pump. There are many pump designs that can pump dirty water, so there is no need to even filter the "mined" ice. The pump's power is related to the flow rate and pressure required. For example, a 200 atmosphere pump that lifts 1 ton would need to pump 0.01 cubic meters of water a second. This would require only 200 kilowatts of power, while typical rocket engines generate megawatts or even gigawatts!<br /><br />You can almost certainly do better than that, though. If you start with a normal rocket engine, and inject water near the throat you can get higher Isp at much lower pressures. Just using 5-10% normal rocket propellant in your mass flow provides enough energy to completely vaporize the water, greatly increasing Isp. <br /><br />Each pound landed on the moon takes over 50 pounds of propellant to get it there. It costs about $10,000 or so per pound delivered to lunar orbit. So not having to bring your return propellant with you is a big deal!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-76910818700271709502009-12-03T08:36:00.002-06:002009-12-03T08:41:50.712-06:00Quick UpdateJust a quick update, since we haven't said anything for a while...<br /><br />We have been working on the business side of things for a bit: hiring people, seeking additional funding, that sort of thing. We have also simplified the engine design dramatically while keeping all the good features - hopefully we will be able to discuss that soon as well. We're hoping to have some engine tests in the coming months, making flames and shock diamonds!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-64513571240031097732009-07-24T16:30:00.001-05:002009-07-24T16:31:42.998-05:00More discussion on Selenian BoondocksThere is another good discussion going on at <A href='http://selenianboondocks.com/2009/07/ribbon-ii/trackback/'>Selenian Boondocks</a>.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-90832719583378982482009-07-16T14:20:00.003-05:002009-07-16T14:47:40.841-05:00Ribbon propellant discussionThere is a discussion of a few ribbon propellant usage options at <a href='http://selenianboondocks.com/2009/07/fakir-or-ribbon-propellant-alternate/'>Selenian Boondocks</a> that may be of interest.<br /><br />I've been meaning to say more about a few points raised by our contest entrants, but have not really had the time... so I will quickly touch a few points here. Both entrants discussed many good points about the properties of ribbon propellant systems that I will be skipping over.<br /><br />Mr. Blake raised some good points about the difficulty of sealing the propellant feed system. This is definitely something that has to be addressed in your injector design. He slightly overstates the problem, however, when he says that any leakage is completely wasted. By aiming the leaks backwards, you can still get a significant proportion of the impulse even of the leaked gases. (Of course, good seals are even better.)<br /><br />Mr. Cate's first concern is about throttling. He correctly states that deep throttling of liquid rockets takes some effort. Solids operate through a very different mechanism, however. Solid rockets can typically be throttled very easily, by customizing the burn profile. This is really a solved problem for solids, and we get to keep most of the advantages solids have in this regard.<br /><br />Mr. Cate also took issue with the expectation of lift from the ribbon. To be fair, we were never really looking at using the lift generated by the ribbon for many up the reasons he states, but he does overstate the issue somewhat when he postulates that a ribbon provides no lift. In fact, it is relatively straightforward to experimentally prove this. Just get a thin ribbon, and dangle it in front of a fan. Instead of hanging down, it stretches out, blown by the wind. The key is that it is mostly still in a line - so the lift is manifestly spread out over the length of the ribbon. Ribbons produce lift in the same way that the Chines of the SR-71 do, by generating vortices.<br /><br />I have previously addressed the drag issues in this blog, so I will skip over them here. Flutter is something that will be addressed - at this point, all I can really say is that it is a fairly well understood aerodynamic issue.<br /><br />I have also addressed the injector pump mass and power earlier. The injector power and mass are actually lower than a comparable liquid rocket.<br /><br />More to come later!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-57743168246636260442009-07-07T21:07:00.004-05:002009-07-07T21:15:18.112-05:00Contest results and updatesCongratulations to Joshua Blake and Henry Cate, the winners of Universal Transport Systems first contest! You can see there entry on <a href='http://www.universaltransportsystems.com/content/Contests.htm'>our main web site</a>. Joshua's hardware category entry was especially impressive! We will be starting another contest soon, keep checking back. If you have an idea for a contest, reply to this post with it... maybe we will use it!<br /><br />We have also been working on our initial engine version. The current version is working in simulations, and we are building the hardware for the first cold flow tests. Once that is working we will have a lot more to say - please stay tuned!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-18745023874211044852009-06-14T16:39:00.002-05:002009-06-14T16:45:08.533-05:00Last day for contest entrantsTomorrow, June 15, is the last day to register for the <a href='http://www.universaltransportsystems.com/content/Contests.htm'>current contests</a>! Prizes will be awarded July 1, so there are about two weeks to finish up your projects. Remember to send in / publicly post your project results for judging.<br /><br />Good luck!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-40974524615615471732009-05-22T16:49:00.006-05:002009-05-24T22:19:01.254-05:00Rocket Propellant InjectionHere are some tables with calculations for propane and oxygen. I think if you are going to do something like this, propane is what you want to use. It has a huge liquid range, and so can be subcooled very deeply. Oxygen is the most likely oxidizer - but note that it is far less useful, because of it's narrower liquid range. <br /><br />Perhaps the best option would be propane and hydrogen peroxide - though peroxide has it's own issues, and a peroxide injector could be quite dangerous!<br /><br />Anyway, the key to good injection is subcooling! (Well, don't superheat the steam too far either - you want it to exit the nozzle just above boiling.)<br /><br /><style type="text/css">.nobrtable br { display: none }</style><br /><div class="nobrtable"><br /><table border=1><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Substance</B></TD><br /> <TD ALIGN=LEFT>Propane</TD><br /> <TD ALIGN=LEFT>Propane</TD><br /> <TD ALIGN=LEFT>Propane</TD><br /> <TD ALIGN=LEFT>Propane</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Gas Heat Capacity</B></TD><br /> <TD ALIGN=RIGHT SDVAL="1.66908563134978" SDNUM="1033;">1.67</TD><br /> <TD ALIGN=RIGHT SDVAL="1.66908563134978" SDNUM="1033;">1.67</TD><br /> <TD ALIGN=RIGHT SDVAL="1.66908563134978" SDNUM="1033;">1.67</TD><br /> <TD ALIGN=RIGHT SDVAL="1.66908563134978" SDNUM="1033;">1.67</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Liquid Heat Capacity</B></TD><br /> <TD ALIGN=RIGHT SDVAL="2.230587808418" SDNUM="1033;">2.23</TD><br /> <TD ALIGN=RIGHT SDVAL="2.230587808418" SDNUM="1033;">2.23</TD><br /> <TD ALIGN=RIGHT SDVAL="2.230587808418" SDNUM="1033;">2.23</TD><br /> <TD ALIGN=RIGHT SDVAL="2.230587808418" SDNUM="1033;">2.23</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=28 ALIGN=LEFT><B>Latent heat of evaporation</B></TD><br /> <TD ALIGN=RIGHT SDVAL="425" SDNUM="1033;">425</TD><br /> <TD ALIGN=RIGHT SDVAL="425" SDNUM="1033;">425</TD><br /> <TD ALIGN=RIGHT SDVAL="425" SDNUM="1033;">425</TD><br /> <TD ALIGN=RIGHT SDVAL="425" SDNUM="1033;">425</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Boiling point (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="-42.1" SDNUM="1033;">-42.1</TD><br /> <TD ALIGN=RIGHT SDVAL="-42.1" SDNUM="1033;">-42.1</TD><br /> <TD ALIGN=RIGHT SDVAL="-42.1" SDNUM="1033;">-42.1</TD><br /> <TD ALIGN=RIGHT SDVAL="-42.1" SDNUM="1033;">-42.1</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B><BR></B></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Gas Velocity (m/s)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="300" SDNUM="1033;">300</TD><br /> <TD ALIGN=RIGHT SDVAL="300" SDNUM="1033;">300</TD><br /> <TD ALIGN=RIGHT SDVAL="300" SDNUM="1033;">300</TD><br /> <TD ALIGN=RIGHT SDVAL="600" SDNUM="1033;">600</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Gas Temperature (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="0" SDNUM="1033;">0</TD><br /> <TD ALIGN=RIGHT SDVAL="0" SDNUM="1033;">0</TD><br /> <TD ALIGN=RIGHT SDVAL="0" SDNUM="1033;">0</TD><br /> <TD ALIGN=RIGHT SDVAL="0" SDNUM="1033;">0</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B><BR></B></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Liquid Temperature (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="-180" SDNUM="1033;">-180</TD><br /> <TD ALIGN=RIGHT SDVAL="-180" SDNUM="1033;">-180</TD><br /> <TD ALIGN=RIGHT SDVAL="-180" SDNUM="1033;">-180</TD><br /> <TD ALIGN=RIGHT SDVAL="-180" SDNUM="1033;">-180</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Liquid Density (kg/m3)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="582" SDNUM="1033;">582</TD><br /> <TD ALIGN=RIGHT SDVAL="582" SDNUM="1033;">582</TD><br /> <TD ALIGN=RIGHT SDVAL="582" SDNUM="1033;">582</TD><br /> <TD ALIGN=RIGHT SDVAL="582" SDNUM="1033;">582</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Mass Mixture Ratio</B></TD><br /> <TD ALIGN=RIGHT SDVAL="0.9" SDNUM="1033;">0.9</TD><br /> <TD ALIGN=RIGHT SDVAL="0.8" SDNUM="1033;">0.8</TD><br /> <TD ALIGN=RIGHT SDVAL="0.55" SDNUM="1033;">0.55</TD><br /> <TD ALIGN=RIGHT SDVAL="0.55" SDNUM="1033;">0.55</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B><BR></B></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Mixed velocity (m/s)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="30" SDNUM="1033;">30</TD><br /> <TD ALIGN=RIGHT SDVAL="60" SDNUM="1033;">60</TD><br /> <TD ALIGN=RIGHT SDVAL="135" SDNUM="1033;">135</TD><br /> <TD ALIGN=RIGHT SDVAL="270" SDNUM="1033;">270</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Mixed temperature (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="-146.226852379016" SDNUM="1033;">-146.23</TD><br /> <TD ALIGN=RIGHT SDVAL="-116.894404229362" SDNUM="1033;">-116.89</TD><br /> <TD ALIGN=RIGHT SDVAL="-62.9913440422936" SDNUM="1033;">-62.99</TD><br /> <TD ALIGN=RIGHT SDVAL="-62.9913440422936" SDNUM="1033;">-62.99</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=15 ALIGN=LEFT><B>Stopped Pressure (Atm)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="2.59306930693069" SDNUM="1033;">2.59</TD><br /> <TD ALIGN=RIGHT SDVAL="10.3722772277228" SDNUM="1033;">10.37</TD><br /> <TD ALIGN=RIGHT SDVAL="52.5096534653465" SDNUM="1033;">52.51</TD><br /> <TD ALIGN=RIGHT SDVAL="210.038613861386" SDNUM="1033;">210.04</TD><br /> </TR><br /></table><br /></div><br /><style type="text/css">.nobrtable br { display: none }</style><br /><div class="nobrtable"><br /><table border=1><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Substance</B></TD><br /> <TD ALIGN=LEFT>Oxygen</TD><br /> <TD ALIGN=LEFT>Oxygen</TD><br /> <TD ALIGN=LEFT>Oxygen</TD><br /> <TD ALIGN=LEFT>Oxygen</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Gas Heat Capacity</B></TD><br /> <TD ALIGN=RIGHT SDVAL="1.8375" SDNUM="1033;">1.84</TD><br /> <TD ALIGN=RIGHT SDVAL="1.8375" SDNUM="1033;">1.84</TD><br /> <TD ALIGN=RIGHT SDVAL="1.8375" SDNUM="1033;">1.84</TD><br /> <TD ALIGN=RIGHT SDVAL="1.8375" SDNUM="1033;">1.84</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Liquid Heat Capacity</B></TD><br /> <TD ALIGN=RIGHT SDVAL="2" SDNUM="1033;">2</TD><br /> <TD ALIGN=RIGHT SDVAL="2" SDNUM="1033;">2</TD><br /> <TD ALIGN=RIGHT SDVAL="2" SDNUM="1033;">2</TD><br /> <TD ALIGN=RIGHT SDVAL="2" SDNUM="1033;">2</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=28 ALIGN=LEFT><B>Latent heat of evaporation</B></TD><br /> <TD ALIGN=RIGHT SDVAL="426.25" SDNUM="1033;">426.25</TD><br /> <TD ALIGN=RIGHT SDVAL="426.25" SDNUM="1033;">426.25</TD><br /> <TD ALIGN=RIGHT SDVAL="426.25" SDNUM="1033;">426.25</TD><br /> <TD ALIGN=RIGHT SDVAL="426.25" SDNUM="1033;">426.25</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Boiling point (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="-182.95" SDNUM="1033;">-182.95</TD><br /> <TD ALIGN=RIGHT SDVAL="-182.95" SDNUM="1033;">-182.95</TD><br /> <TD ALIGN=RIGHT SDVAL="-182.95" SDNUM="1033;">-182.95</TD><br /> <TD ALIGN=RIGHT SDVAL="-182.95" SDNUM="1033;">-182.95</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B><BR></B></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Gas Velocity (m/s)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="300" SDNUM="1033;">300</TD><br /> <TD ALIGN=RIGHT SDVAL="300" SDNUM="1033;">300</TD><br /> <TD ALIGN=RIGHT SDVAL="600" SDNUM="1033;">600</TD><br /> <TD ALIGN=RIGHT SDVAL="1200" SDNUM="1033;">1200</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Gas Temperature (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="-150" SDNUM="1033;">-150</TD><br /> <TD ALIGN=RIGHT SDVAL="-180" SDNUM="1033;">-180</TD><br /> <TD ALIGN=RIGHT SDVAL="-180" SDNUM="1033;">-180</TD><br /> <TD ALIGN=RIGHT SDVAL="-180" SDNUM="1033;">-180</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B><BR></B></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Liquid Temperature (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="-215" SDNUM="1033;">-215</TD><br /> <TD ALIGN=RIGHT SDVAL="-215" SDNUM="1033;">-215</TD><br /> <TD ALIGN=RIGHT SDVAL="-215" SDNUM="1033;">-215</TD><br /> <TD ALIGN=RIGHT SDVAL="-215" SDNUM="1033;">-215</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Liquid Density (kg/m3)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="1140" SDNUM="1033;">1140</TD><br /> <TD ALIGN=RIGHT SDVAL="1140" SDNUM="1033;">1140</TD><br /> <TD ALIGN=RIGHT SDVAL="1140" SDNUM="1033;">1140</TD><br /> <TD ALIGN=RIGHT SDVAL="1140" SDNUM="1033;">1140</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Mass Mixture Ratio</B></TD><br /> <TD ALIGN=RIGHT SDVAL="0.9" SDNUM="1033;">0.9</TD><br /> <TD ALIGN=RIGHT SDVAL="0.85" SDNUM="1033;">0.85</TD><br /> <TD ALIGN=RIGHT SDVAL="0.85" SDNUM="1033;">0.85</TD><br /> <TD ALIGN=RIGHT SDVAL="0.85" SDNUM="1033;">0.85</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B><BR></B></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> <TD ALIGN=LEFT><BR></TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Mixed velocity (m/s)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="30" SDNUM="1033;">30</TD><br /> <TD ALIGN=RIGHT SDVAL="45" SDNUM="1033;">45</TD><br /> <TD ALIGN=RIGHT SDVAL="90" SDNUM="1033;">90</TD><br /> <TD ALIGN=RIGHT SDVAL="180" SDNUM="1033;">180</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=14 ALIGN=LEFT><B>Mixed temperature (C )</B></TD><br /> <TD ALIGN=RIGHT SDVAL="-189.889196875" SDNUM="1033;">-189.89</TD><br /> <TD ALIGN=RIGHT SDVAL="-182.67" SDNUM="1033;">-182.67</TD><br /> <TD ALIGN=RIGHT SDVAL="-182.67" SDNUM="1033;">-182.67</TD><br /> <TD ALIGN=RIGHT SDVAL="-182.67" SDNUM="1033;">-182.67</TD><br /> </TR><br /> <TR><br /> <TD HEIGHT=15 ALIGN=LEFT><B>Stopped Pressure (Atm)</B></TD><br /> <TD ALIGN=RIGHT SDVAL="5.07920792079208" SDNUM="1033;">5.08</TD><br /> <TD ALIGN=RIGHT SDVAL="11.4282178217822" SDNUM="1033;">11.43</TD><br /> <TD ALIGN=RIGHT SDVAL="45.7128712871287" SDNUM="1033;">45.71</TD><br /> <TD ALIGN=RIGHT SDVAL="182.851485148515" SDNUM="1033;">182.85</TD><br /> </TR><br /></table><br /></div>Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-48233536178004023052009-05-22T15:57:00.004-05:002009-05-22T17:01:27.153-05:00Steam InjectorsI was thinking this morning about posting on the topic of steam injectors, and their applicability to rocket engines – and then the conversation on Arocket turned to steam injectors. With that confirmation in hand, here are some thoughts/calculations. (Note that Universal Transport Systems is not currently planning on using systems like this.)<br /><br /><span style="font-weight:bold;">What is a steam injector?<br /></span><br />Simply put, a steam injector takes steam, accelerates it through a nozzle, mixes the steam with water, and finally decelerates the steam/water mixture. Let's follow that through some example calculations:<br /><br />1) Acceleration through a nozzle: about 3 atmosphere superheated steam is accelerated through a nozzle to the speed of sound (call it 300 m/s), dropping to 1 atmosphere. The steam cools somewhat to (let's say) 110 C. Note that if you slowed the steam back down at this point, you would end up just short of where you started in temperature and pressure.<br /><br />2) Mix with water: The steam is mixed with water (let's say 90% by mass) at 20 C. Water has twice the heat capacity of steam, so each degree change of the steam changes the mixture temperature by 0.2 degrees. In addition, condensing the steam takes 500 times the energy of raising the water one degree. So the mixture ends up as all water, at about 80 C. The velocity of the mixture must conserve momentum, so it ends up at 30 m/s. But while the mixture is 90% slower than the steam, it is 1000 times denser!<br /><br />3) Decelerate the mixture: as you decelerate the mixture, the pressure goes up. Because you have made the steam denser, the pressure goes up higher than the original 3 atmospheres! So you have taken used steam to take water to a higher pressure than the original steam.<br /><br />According the the Bernoulli equation, the velocity squared divided by two plus the pressure divided by the density does not change. This "pump" works as long as the effect on final pressure caused by the change in density is larger than the effect of the slowing of the mixture. From the example above, here is the calculation of pressure gained from slowing the warm water from 15 m/s to a stop:<br /><br />30^2/2 + P1/1000 = P2/1000<br />P2=P1+450000<br /><br /><span style="font-weight:bold;">So the pressure goes up by more than 4 atmospheres!</span><br /><br />Note that the effect depends on the water increasing in temperature but not increasing in volume. This is where I believe most past efforts to apply this to rocketry have failed – the liquid to be used really needs to be sub-cooled. I'll follow this post up with an application of this to some of my favorite propellants!<br /><br />Here is a table of some illustrative options:<br /><style type="text/css">.nobrtable br { display: none }</style><br /><div class="nobrtable"><br /><table border=1><br /><tr><td>Substance</td><td>water</td><td>water</td><td>water</td><td>water</td></tr><br /><tr><td>Gas Heat Capacity</td><td>2</td><td>2</td><td>2</td><td>2</td></tr><br /><tr><td>Liquid Heat Capacity</td><td>4.19</td><td>4.19</td><td>4.19</td><td>4.19</td></tr><br /><tr><td>Latent heat of evaporation</td><td>2270</td><td>2270</td><td>2270</td><td>2270</td></tr><br /><tr><td>Boiling point (C )</td><td>100</td><td>100</td><td>100</td><td>100</td></tr><br /> <br /><tr><td>Gas Velocity (m/s)</td><td>300</td><td>300</td><td>600</td><td>1500</td></tr><br /><tr><td>Gas Temperature (C )</td><td>110</td><td>110</td><td>110</td><td>110</td></tr><br /> <br /><tr><td>Liquid Temperature (C )</td><td>20</td><td>20</td><td>20</td><td>20</td></tr><br /><tr><td>Liquid Density (kg/m3)</td><td>1000</td><td>1000</td><td>1000</td><td>1000</td></tr><br /><tr><td>Mass Mixture Ratio</td><td>0.9</td><td>0.86</td><td>0.86</td><td>0.86</td></tr><br /> <br /><tr><td>Mixed velocity (m/s)</td><td>30</td><td>42</td><td>84</td><td>210</td></tr><br /><tr><td>Mixed temperature (C )</td><td>77.22</td><td>97.05</td><td>97.05</td><td>97.05</td></tr><br /><tr><td>Stopped Pressure (Atm)</td><td>4.46</td><td>8.73</td><td>34.93</td><td>218.32</td></tr><br /></table><br /></div>Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-24052832335953643142009-05-16T07:59:00.002-05:002009-05-16T08:09:41.654-05:00So why not air breathing?In the last post we showed that if you could raise engine Isp by 20% you could double the vehicle mass and still come out ahead. Since that is the case, why don't all aircraft use air breathing which have much higher Isp?<br /><br />The first issue is that even if you don't go to space you want to get above the thick atmosphere as quickly as possible. The atmosphere's drag keeps you from going as fast as you want. That means you can't really use air breathing engines for most of the flight - just at the start and end. So even a high Isp air-breathing engine may not raise the average Isp by 20%.<br /><br />The other issue is the air-breathing engine tend to have pretty bad thrust to weight ratios. Since you want to get above the atmosphere as quickly as possible, you want to go pretty much straight up. That means your vehicle must have a thrust to weight ratio of at least one, and start from a standstill. Really good air-breathing engines that can do that only have a thrust to weight ratio of about 10:1. So your engine weighs 10% of your GLOW!<br /><br />Unfortunately, that means that most air-breathing rocket assist engines do not work out.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-14377716465694619492009-05-04T15:17:00.002-05:002009-05-04T15:40:11.234-05:00When is higher Isp a good idea?OK, so you have come up with a magic thing-a-ma-bob. It makes rockets way better, improving Isp (the amount of thrust a rocket produces per pound of propellant). But does it improve rocket performance, considering that you have to now carry a thing-a-ma-bob all the way up?<br /><br />Your magic device increases the final mass, so the critical equation is:<br /><br />delta-v = 9.8 * Isp1 * ln (StartMass/FinalMass)<br /><br />compared to<br /><br />delta-v = 9.8 * Isp2 * ln ([StartMass+ThingMass]/[FinalMass+ThingMass])<br /><br />If you look at this in a spreadsheet, you find some interesting results.<br /><br />For 9,000 m/s rocket aircraft, starting from a 250 Isp:<br />If your device increases Isp 10%, it can weigh half your vehicle's mass and still come out ahead.<br />If your device increases Isp 20%, it can almost double vehicle mass and still come out ahead.<br />If your device increases Isp 40%, it can almost triple vehicle mass and still come out ahead.<br /><br />On the other hand, if you start from an Isp of 350:<br />If your device increases Isp 10%, it can weigh a third of your vehicle's mass and still come out ahead.<br />If your device increases Isp 20%, it can weigh half your vehicle's mass and still come out ahead.<br />If your device increases Isp 40%, it can weigh one and a half times your vehicle's mass and still come out ahead.<br /><br />In other words, starting from a lower Isp makes fun optimizations like air breathing ascent/descent stages more tempting...Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-68711660640078556172009-05-04T15:01:00.001-05:002009-05-04T15:02:56.544-05:00Final Poll ResultsHow important is sub-$10,000 orbital space access to you?<br /><br />Very Important: 75%<br />Important: 0%<br />Not really important: 8%<br />Unimportant: 16%Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-41013420785066319632009-04-28T12:34:00.002-05:002009-04-28T12:39:10.464-05:00Contest Registration Opens!You can now register for Universal Transport Systems' contest online at:<br /><br /><a href="http://www.universaltransportsystems.com/content/Contest_Registration.htm">www.universaltransportsystems.com/content/Contest_Registration.htm</a><br /><br />If we get a good response from this, we will be doing many more of these. Note that prizes will be awarded July 1, and registration ends June 15. Register today!<br /><br /><span style="font-style:italic;">Universal Transport Systems, LLC ("UTS") is sponsoring a contest soliciting your inventions and ideas to advance ribbon propellant rocket engine technology. There are 2 contest sections with 2 prizes awarded in each section. In the hardware section, the first prize is $3,500 with a $1,500 second prize. In the non-hardware section, a $750 first prize and $250 second prize will be awarded. Entrants will be judged on the best demonstration of solid ribbon propellant rocket engines, including innovation, creativity, implementation and design.</span>Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-83269756796984618662009-04-28T12:19:00.002-05:002009-04-28T12:26:15.720-05:00Ribbon Propellant Engine Injector PowerA ribbon propellant rocket plane has different pump/injector power requirements compared to a typical liquid engine. A 100% efficient liquid engine's pumping power requirement comes from the equation:<br /><br />Power=volume per second * pressure<br /><br />So for example, the Space Shuttle pumps 1.1 cubic meters of oxygen per second to 30 MPa (about 300 atmospheres). This requires 33 MW of power. It also pumps 3 cubic meters of hydrogen per second to 45 MPa (about 450 atmospheres). This requires an additional 135 MW of power. The overall power delivered by a rocket engine is given by the equation:<br /><br />Power=force * velocity<br /><br />The Space Shuttle's engine produces 2 MN of thrust at 4.5 km/s. This makes a total engine power of 9 GW - so the pump takes about 2% of the total engine power.<br /><br />Note that the liquid engine has to pump the propellants to a much higher pressure than the chamber pressure (about 200 atmospheres, 20 MPa). This is because of injector and line losses in the feed system. So about half the power requirements of the pump system are due to these losses.<br /><br />On the other hand the ribbon propellant feed system uses a rack and pinion like feed mechanism, where the ribbon is fed into the engine between drive gears. This is an extremely efficient feed mechanism, with very low power requirements. In addition, solid propellant rockets neatly bypass the injection problem - there is no need to have a large injector pressure drop for chamber stability. A further advantage solids have is higher density. Typical solid propellants are many times denser than liquid propellants. <br /><br />Assembling all this, injecting a ribbon propellant into an equivalent thrust engine at 200 atmospheres chamber pressure takes 10 MW. (This assumes a 1.5 g/cc propellant density, 270s Isp, and 2 MN of thrust. This leads to a volume flow rate of 0.5 cubic meters per second.) This can be compared to the engine power of 5 GW (This is lower than the SSME because solid propellants have a lower Isp). So the pumping power requirement is only 0.2% of the engine's power.<br /><br />All is not perfect with ribbon propellant, however. The engine does need to lift the propellant before it is injected. The power required for this can be calculated using the formula:<br /><br />P=force * velocity<br /><br />The force required is easy to estimate - assuming that most of the mass is in the ribbon (which is valid during peak power requirements), the force on the ribbon is equal to the engine thrust (2 MN for this example). The velocity is similarly easy to calculate: It is the length of the ribbon divided by the Isp, times the current acceleration in Gs. So for a 1 G acceleration (as planned for the time of max power requirements), a 1 km ribbon feeds in at 4 meters per second or so. This yields a power requirement of 8 MW, bringing the total pumping/injector power required to about 0.4% of the total engine power.<br /><br />The power required to lift the ribbon approximately doubles the power requirements of our notional "similar to SSME" engine - but note that the total pumping power required is still only 1/8 the power of the liquid propellant rocket engine. This is primarily due to the more efficient injection and higher density.<br /><br />All this said, this is nowhere near the engine we are designing. But the overall message remains - pumping requirements for ribbon propellant rocket vehicles are much lower than more typical liquid propellant rocket vehicles.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com3tag:blogger.com,1999:blog-6692958166761670904.post-37106272919646869722009-04-24T15:29:00.004-05:002009-04-24T17:16:41.274-05:00Figures of meritDo you sometimes lay awake at night, wondering how a solid ribbon rocket vehicle stacks up against typical rockets using various figures of merit? Me too! Let's look at a few of the common ones:<span style="font-weight: bold;"><br /><br />Payload:GLOW</span><span style="font-family:monospace;"><br /><br /></span>A common figure of merit among rocket vehicles is the ratio of payload to gros lift off weight. While the utility of the figure of merit is debateable (GLOW has little relation to actual costs), it is common enough to merit investigation. Current vehicles with a 9,000 m/s delta-v capability are about 1% payload. For example, the space shuttle is 1.2% payload at takeoff. The Ariane 5 is 2.06%. Both of these vehicles have multiple stages, and use liquid hydrogen as a fuel. <span style="font-family:monospace;"><br /><br /></span>The solid ribbon rocket design, if used as a powerplant for a disposable vehicle like the Ariane, would consist of just the engine, propellant, and payload. The engine masses less than 1% of the gross lift off mass. Since the rocket equation specifies that 97% of the mass is used applying 9,000 m/s delta-v, more than 2% of GLOW is payload. This is equivalent to the Ariane 5, though relatively uninteresting to me. I'm not really that excited about disposable rockets...<span style="font-family:monospace;"><br /><br /></span>The Space Shuttle is much closer to a rocket airplane - it has wings, landing gear, etc. A rocket aircraft built around the solid ribbon rocket engine like we are building is expected to be one third engine, one third airplane, and one third payload. This gives a Payload:GLOW of 1% - very respectable for a small rocket plane!<span style="font-weight: bold;"><br /><br />Payload:Dry Mass</span><span style="font-family:monospace;"><br /><br /></span>The dry mass is the amount of vehicle left over after you have gotten where you were going. It is perhaps the most important figure of merit in my opinion, because dry mass is expensive. When you build a rocket aircraft, you are building the dry mass. <span style="font-family:monospace;"><br /><br /></span>The Space Shuttle has a payload to dry mass ratio of 23.2%. A solid ribbon rocket vehicle would have a 33% ratio. So for a given payload, it would be 40% lighter dry!<span style="font-weight: bold;"><br /><br />Minimality</span><span style="font-family:monospace;"><br /><br /></span>An ideal rocket should be payload, engine, and propellant - and ideally, the engine should weigh nothing! The ribbon rocket comes very close to this ideal - the ribbon is 97% of the mass at takeoff. Although the engine weighs quite a bit, it is slightly smaller than the payload. This is fairly unusual as most rocket vehicles have engines much heavier than the payload, not to mention the proppelant tanks! When you add in the fact that the solid ribbon rocket plane has a much lower dry mass, it is the clear winner in a minimality contest.<span style="font-weight: bold;"><br /><br />Isp</span><span style="font-family:monospace;"><br /><br /></span>Well, Isp as normally formulated is mainly a function of the propellants used. It is the amount of time the propellant can provide enough force to lift itself. For example, solid propellants typically have an Isp of about 300 seconds. That means 1 lb of solid propellant can provide 1 lb of thrust for 300 seconds. Liquids in general have higher Isp (350-450 seconds). Since solid propellants have marginal Isp (and this is our blog, so we have to win!) we will cheat :)<span style="font-family:monospace;"><br /><br /></span>Thinking about the Space Shuttle vehicle as a system the "propellant" includes not just the oxidizer and fuel - most of the rocket is also useless mass (from a payload perspective). Looking at it this way, the system as a whole has an "effective Isp" that can be calculated by using the rocket equation. Just plug in the delta-v provided (about 9,000 m/s), the starting mass (the GLOW), and the end mass (payload). A simple calculation later you have the "effective Isp" of about 200 seconds.<span style="font-family:monospace;"><br /><br /></span>Performing the same calculation on the solid ribbon rocket aircraft, and you also get 200 seconds. So our "effective Isp" is just as high as the Space Shuttle! <span style="font-family:monospace;"><br /><br /></span>Do you have a favorite figure of merit that I have left out? Let me know in the comments.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-30974997038908360192009-04-18T10:34:00.002-05:002009-04-18T11:42:27.734-05:00Rockets and the Altitude ConundrumA rocket powered vehicle, like any aircraft, needs maximum thrust at takeoff. No matter if you have wings or just a pillar of fire, that's where you need the most bang for your engine kilogram. With turbojets and propellers that happily coincides with maximum engine thrust - because those engine types use the air to their advantage. Unfortunately, rocket engines lose some of their thrust in the normal atmosphere.<br /><br />A rocket engine's efficiency is related to the ratio of chamber pressure inside the engine to the air pressure outside the engine. This means that on takeoff (deep within the atmosphere) a rocket engine is less efficient. Some of the engine's power is used up just getting the air out of the way, as it were. This can be compensated for somewhat by increasing the engine's internal pressure, but that makes the engine much heavier (not to mention more difficult to actually build).<br /><br />As the rocket vehicle climbs out of the atmosphere, the engine produces more thrust. A simple equation gives you a rocket's thrust:<br /><br />Thrust = ThroatArea * (ChamberPressure*ThrustCoefficient + ExpansionRatio*[NozzleExitPressure-AtmosphericPressure])<br /><br />Notice that the thrust is decreased by the term "ThroatArea * ExpansionRatio * AtmosphericPressure". This can result in on the order of 10% less thrust at ground level than at high altitude in low pressure engines. So when you need the highest thrust, a rocket engine provides 10% less thrust than normal!<br /><br />Under these conditions, a rocket aircraft using ribbon propellant has an advantage. Because the propellant ribbon is supported by ground equipment during liftoff, maximum thrust is not required at lift off, but rather when the ribbon is fully deployed. By the time the ribbon is fully deployed, the aircraft is already at 5,000 feet or so. At this altitude, air pressure is about 15% less than at ground level. <br /><br />It is not a huge effect (your engine can be made 1-2% lighter), but it is another advantage of using ribbon propellants.Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0tag:blogger.com,1999:blog-6692958166761670904.post-50854799024976406862009-04-04T11:54:00.002-05:002009-04-04T12:18:40.172-05:00High delta-V rocket aircraftWell, we presented at Space Access... off we go!<br /><br />The basic premise of our presentation was about mass ratios, and how making high mass ratios easier to achieve is perhaps more important that achieving a high Isp (or engine efficiency). The basic measure of a rocket craft system is the amount of delta-v (velocity change) provided to a set payload. So for discussion, let's compare options for a 9,000 m/s delta-v rocket vehicle.<br /><br />NASA tends to focus on liquid hydrogen/liquid oxygen. Given liquid hydrogen's outstanding performance, only 87% of the rocket's take off mass has to be propellant. This leaves 13% of the mass to be rocket. Using somewhat standard numbers for other masses as a percentage of take of mass:<br /><br /> 1% Engine<br /> 10% Tank<br /> 1.5% Heat Shield<br /> 3% Landing Gear<br /><br />These add up to 15.5% - so you have to trim some mass through clever engineering. This can be done, but finding almost 20% of mass to cut will be difficult - and even at that point, the payload will be a tiny fraction of the vehicle.<br /><br />A lot of NewSpace companies focus on denser fuels, such as liquid hydrogen/RP1 (essentially kerosene). The combination has lower performance, so 93% of the rocket's take off mass has to be propellant. This leaves 7% of the mass to be rocket. Using somewhat standard numbers for other masses as a percentage of take of mass:<br /><br /> 1% Engine<br /> 2% Tank<br /> 1.5% Heat Shield<br /> 3% Landing Gear<br /><br />Notice that the tank is now much lighter. These add up to 7.5% - so you still have to trim some mass through clever engineering. Finding 7% of mass to cut will be easier than the liquid hydrogen case - but still a challenge, and the payload will be a small fraction of the vehicle.<br /><br />Our design uses solid rocket propellant, but completely eliminates the tank. Solid rocket propellant has even lower performance, so 97% of the rocket's take off mass has to be propellant. This leaves 3% of the mass to be rocket. Using our design numbers for other masses as a percentage of take of mass:<br /><br /> 0.5% Engine<br /> 0% Tank<br /> 0.5% Heat Shield<br /> 0.1% Landing Gear<br /><br />The tanks are now gone, and everything else is much lighter. The engine can be lighter because the maximum thrust requirement has dropped. Takeoff has the highest thrust requirements, and during takeoff most of the propellant mass is supported by ground equipment. The heat shield is much lighter because much of a standard heat shield's mass is spent protecting the tanks, and there are no tanks. The landing gear is also sized by the takeoff load, and during takeoff the ground equipment supports the propellant.<br /><br />These masses add up to 1.1% - so you have a 63% margin. You can use this as payload, or simply increase the sturdiness of your vehicle. Either way, you can now build a vehicle that masses less than the payload it carries!Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com2tag:blogger.com,1999:blog-6692958166761670904.post-8517231307703517612009-01-16T15:12:00.003-06:002009-01-16T15:17:25.114-06:00Technology - introOur revolutionary solid fuel technology enables much smaller high performance rocket aircraft - making them safer, simpler, and less expensive. At least that's what we think...<br /><br />What do you think?Davidhttp://www.blogger.com/profile/03631369308165105200noreply@blogger.com0