Ramjet Primer

[tap_sa]

Glenn Olson has written a nice piece of ramjet information; Ramjet Primer.<br /><br />I found especially this very promising news:<br /><br /><i>"There are no physical limits to the minimum weight of a ramjet other than design and materials. The 1950's Marquardt RJ43-MA-7 had a <b>thrust/weight (T/W) ratio of about 40.</b> With today's engineering and materials that could probably be brought up to <b>150-200</b> without too much effort. Such T/W ratios would make ramjet powered vehicles excellent accelerators."</i><br /><br />I had no idea ramjet T/Ws are that high.

 

[drwayne]

Thank you! I *love* this kind of site!<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[drwayne]

You know, I have never thought about jet engines in terms of ISP - that's strange - I just realized that.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[tap_sa]

You know TSFC, the jet and propeller engine version for measuring Isp? If I read the equation right then conversion goes like 1/TSFC*3600s = Isp in seconds. <br /><br />edit: Found the ramjet link from http://www.rlvnews.com/. It's a great source for articles like this.

 

[propforce]

That's correct. Just don't include the mass flow of oxidizer (in this case - air) in the Isp and SFC equation <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

Wow, thanks for the info... That answered a question I had asked on another thread.

 

[spacefire]

Is anybody familiar with the Regulus Ramjet-powered missile? What are the specs on that?<br />I saw one at a museum yesterday and I'm curious to know more about it. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[barrykirk]

Thrust to Weight ratio of a Merlin Engine is 96<br /><br />Thrust to Weight ratio of a SSME is 73.3<br /><br />RamJet possibly 150 to 200!!!<br /><br />And it has a much higher ISP than a rocket.<br /><br />I had mentioned in another thread about the possibility of using a jet engine as a stage zero to help get a rocket off the ground. Well this certainly helps, except that it doesn't work at low velocity.<br /><br />Several solutions.<br /><br />1) Horizontal takeoff with one of several methods to get to ramjet speeds.<br /><br />a) Catapult.<br />b) Conventional Jet.<br /><br />2) Small Solid Booster for the first 30 seconds of flight to get up to speed.<br /><br />That would be weird. Rockets to Jets and back to rockets!

 

[propforce]

<font color="yellow"><i>RamJet possibly 150 to 200!!! </i></font><br /><br />Where are you getting this number?<br /><br />I'd like to ask an insensitive question here: how many of you have had actual design/ performance analysis experience with a scramjet?<br /><br />If not, why are you spewing these 'wet dream' on the internet? Have you even seen or touch a scramjet in your life? Are we all fustrated design engineer here?<br /><br />Do you even have engineering training at all?<br /><br />Sorry if I offend anyone with these comments, I just don't know how to make out some of the comments you guys come up with, not knowing your background, etc. <br /><br /> <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

First of all, the numbers are from article linked in my original post which is about plain ramjets, no supersonic combustion.<br /><br />I for one havent seen, touched nor done thoral performance analysis on ramjet. I just found the article interesting and thought perhaps others might find it interesting too.<br /><br />If you have seen, touched and analysed ramjets perhaps you could tell us if any of the article's numbers and facts are wrong, and if so, why.<br /><br />Also if you can point to some other article/books etc that are cover ramjet basic well then please, enlighten us.

 

[vulture2]

Both rocket and airbreathing engine performance is often measured in pounds of thrust per pound of fuel burned per second. The difference is that the weight of the oxydizer is counted for rockets but not for airbreathing engines. This makes airbreathing engines appear to have higher performance. But the downside is that ramjets are this efficient only over a very limited range of speed and altitude. For space launch the vehicle is under constant acceleration, so their practicality is uncertain.

 

[JonClarke]

<i>That would be weird. Rockets to Jets and back to rockets</i><br /><br />A great many cruise missiles and SAMs designed over the years used booster accelerated ramjets. Navajo, BORMAC, Talos, Bloodhound, Seaslug, Seadart, and the soviet SA-4 and SA-6 (NATO designation). Simple and effective.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>First of all, the numbers are from article linked in my original post which is about plain ramjets, no supersonic combustion. <br /><br />I for one havent seen, touched nor done thoral performance analysis on ramjet. I just found the article interesting and thought perhaps others might find it interesting too. <br /><br />If you have seen, touched and analysed ramjets perhaps you could tell us if any of the article's numbers and facts are wrong, and if so, why. <br /><br />Also if you can point to some other article/books etc that are cover ramjet basic well then please, enlighten us. <p><hr /></p></p></blockquote><br /><br />I am glad that Vulture2 resurrected this thread so I can respond to Tap_Sa.<br /><br />First, I apologize to Tap_Sa for reacting the way I did on my post. Second, I re-read the link provided to make sure I did not miss anything, where I verified that the author simply put the statement out there that "...With today's engineering and materials that could probably be brought up to 150-200 without too much effort. Such T/W ratios would make ramjet powered vehicles excellent accelerators....", which leads me to my Third point.<br /><br />Just because someone put up a website and put some statement on it does not make that it credible.<br /><br /><br /><font color="yellow">If you have seen, touched and analysed ramjets perhaps you could tell us if any of the article's numbers and facts are wrong, and if so, why. <br /></font><br /><br />Yes I have and I do think the claimed T/W of 150 ~ 200 is unsubstantiated. Let me explain why. You basically get thrust from 2 major variables, mass flow you eject out and/or the (chamber) pressure you can attain prior to ejecting the mass out. That's pretty basic and anyone who doesn't understand that should consult on Sutton's book "Rocket Propulsion Element". To simply eject more mass out (in creating thrust) without increasing chamber pressure, you'll simply have to m <div class="Discussion_UserSignature"> </div>

 

[owenander]

"At 40,000 ft the air density is about 1/4 that of sea level and therefore the thrust would also be about 1/4, given otherwise similar flight conditions. At 80,000 ft the air density is about 3.6% that of sea level with an equivelant reduction in thrust."<br /><br />Air density went up at 80,000 feet? Must be reading it wrong.

 

[qso1]

I read it this way:<br /><br />At 40,000 feet, air density is 1/4 sea level or 25%.<br /><br />At 80,000 feet, air density is 3.6% sea level or well below 25%. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>