Sunday, July 21, 2024

Biden Withdraws!

Today (Sunday 7-21-2024) there was the sudden (but not unexpected) announcement that Joe Biden is withdrawing from the 2024 election race,  instead endorsing Kamala Harris as his preferred successor.  And we are seeing the usual BS from the GOP opposition,  up to and including a ridiculous demand from the Speaker of the House that President Biden immediately resign from office,  on the “theory” that if he cannot run for another term,  he cannot continue to serve. 

These are not any sort of “loyal opposition”,  they are people who demonstrably prioritize party advantage far above the good of the country,  in what I consider to be violation of their oaths of office.  And that oath-breaking needs to be criminalized!

I disagree with the obsessive coverage of Biden’s rapidly-advancing infirmities by the mainstream media!  They have been influencing most democrat voters and the big donors,  by convincing them Biden is unfit,  through sheer repetition (a propaganda thing used by the Bolsheviks in Russia,  the Fascists in Italy,  and the Nazis in Germany).  That is NOT the job of the American “fourth estate”!

I will say that the internet,  which is totally unpoliced for truth,  is actually far worse about lying than the mainstream media (with the long-known exception of Fox “News”). Your on-line echo chambers are lying to you,  very egregiously,  for nothing but profit!

We have had presidents with physical infirmities before,  most notably Franklin Roosevelt,  who actually died from his,  not very long after being re-elected for his fourth term.  It is the mental infirmities that we really need to worry about,  and we have seen that before,  too,  most notably with Ronald Reagan slowly succumbing to dementia in his second term,  and also with Woodrow Wilson’s sudden stroke.

I see no need for Biden to do anything but faithfully serve out his term.  If he becomes unable to serve before Jan. 20,  2025,  there is the 25th amendment and a very capable Vice President Kamala Harris to step in and take power,  in a now well-defined and legal manner. 

As for Kamala Harris becoming the new Democratic nominee for the 2024 election,  I have no problem with that at all!  She is very capable,  well-versed in what has been going on,  and at age 59,  she is young enough to serve well for many years to come.  I think the Democratic Party would be utter fools not to nominate her almost immediately by some sort of acclamation.

To make Harris more credible to more American voters than former President Trump,  I think she should come up with a VP pick very soon;  possibly Michigan Governor Whitmer,  or any of a handful of others.  I also think she should retain Biden,  and former President Obama,  as some sort of special advisers,  outside the usual appointed or elected roles.  Age and infirmities would not matter in that kind of special role. 

More importantly,  she has to make the case that former President Trump is also too old to serve another term,  besides him being a threat to our democracy! 

He also stumbled during the June debate,  just not as obviously as President Biden stumbled.  This has been ignored by the mainstream media in their obsessive coverage of Biden’s stumbles,  but the evidence is there for all to see,  if they but look!  Where he lost his train of thought and repeated what he said seconds before,  indicates the mental infirmity stumbles as different from the other numerous deliberate acts of not answering a single question put to him,  even repeatedly.

As for the threat to democracy that former President Trump poses,  there is the Jan. 6 insurrection,  which he did nothing about for hours,  and then ineffectually,  when he finally did act.  Plus,  there are the remarks about “dictator on day one”,  and the “Project 2025” blueprint for imposing a dictatorship in the US,  which he falsely denies having anything to do with.  Plus his predilection to leave or disable NATO (also a matter of public record),  at a time when we are in a proxy war with Russia,  with Ukraine as our proxy.  That predilection is tantamount to treason in a time of war!

And then there is the chronic lying.  It is a matter of the public record that nearly every claim ever made by former President Trump was a lie,  even before his election in 2016!  If nearly everything said is false,  then how can a citizen track what the administration has really done?  Biden and Harris demonstrably do not suffer from that fault!

If Vice President Harris does indeed become our next President,  I strongly recommend to her that she award the Presidential Medal of Freedom to Joe Biden as soon as possible!  This would be for his exemplary service to the country over his entire long career in public service,  and the many good things he did for the country as its President.



Wednesday, July 17, 2024

Requests for Rocket Engine Estimator Spreadsheet

I have seen multiple requests for my rocket engine performance estimator spreadsheet.  These requests are usually comments left on the “Rocket Engine Calculations” article posted here on “exrocketman” 1 October 2022.  That spreadsheet was “liqrockets.xls”,  and the recommended worksheet in it was “allin1des”. 

I have since reworked that spreadsheet analysis in a new Excel file named “liquid rockets.xlsx”,  with the worksheet “r noz alt”,  which includes the propellant data library worksheet from the older file,  plus an isentropic compressible flow worksheet for finding expansion Mach number and pressure ratio for a given expansion area ratio.   

This newer spreadsheet is the one I now recommend.  It comes as an Excel file,  plus a user manual as a pdf document,  and a png file into which you paste a data block generated by the spreadsheet,  for data reporting purposes.

There are 3 ways you can obtain this set of 3 files:  (1) contact me by email and I can email them to you,  (2) you can go the New Mars forums at newmars.com/forums/,  and go to the Meta New Mars section,  and to the thread titled “GW Johnson postings and @exrocketman1 youtube videos”,  with the links in post #298 of that thread,  or (3) try to use the direct link below.  These are free downloads.  You need to download the Excel spreadsheet file to make it work.  It has multiple worksheets.

Direct link to engine performance spreadsheet:

https://www.dropbox.com/scl/fi/mcmgvky9p1xukj6m6nmqo/20240330-liquid-rockets.xlsx?rlkey=zypo0wegrzzhtudesw1fiqvjk&dl=0

Direct link to user manual for spreadsheet:

https://www.dropbox.com/scl/fi/z01cwbeqesk8fnhy83o0n/20240330-User-manual-liquid-rockets.pdf?rlkey=xuoyzafq4og2tyiev3hnhpi33&dl=0

Direct link to the data reporting form:

https://www.dropbox.com/scl/fi/9scws7nh485qs9xaqfwi3/20240330-engine-sizing-report.png?rlkey=pynvmgdkohwb0gixlvrnwb7fi&dl=0

This is what that data reporting form looks like:


This is a png file created in the old 2-D Windows “Paint” utility.  You cut out the example data block,  and paste in the one you created with the spreadsheet.  Then adjust the headings above the engine sketch to match what you need.

I do recommend that you visit the New Mars forums and take a look around.  You should consider joining the forums and participating.  If you would like to join,  send an email request to newmarsmember@gmail.com

 

PS -- I verified the links,  they work.
 

Monday, July 15, 2024

Texas Heat

 This one is presented as a funny,  without comment.  Enjoy.



Saturday, July 6, 2024

Obsessive Coverage Obscures the Risks to Weigh

This article is a warning to the news networks to do your jobs properly!  The continuation of our democracy,  and perhaps world peace,  are at stake.  Obsessing only over the latest gaffe,  instead of reporting all the facts drives up ratings,  but it also distorts public perceptions and opinions!  This is an unstable feedback,  that has already gotten out of control,  with the reporting of the June presidential debate.

Assessing Cognitive Difficulties

Everybody is focused on Joe Biden’s fitness to serve another term,  after his debacle in the June debate.  Transient or not,  his physical and mental infirmity was obvious.  The coverage of this is so all-consuming,  that it is actually driving opinions about this issueto the exclusion of other facts.

Nobody seemed to notice Donald Trump’s own mental infirmity,  which (so far) is much less obvious than Biden’s,  but still there for all to seeif they but look!  The obsessive coverage of Biden’s problem completely ignores this!  And that is both wrong and irresponsible!

Trump never answered a single questioneven when the questions were repeatedly put to him,  instead always repeating the same debunked lies that he has spouted for some years now.  Dangerous lies,  too:  one has already sparked an attempted insurrection!  

Part of this question avoidance might be deliberate,  but part is not.  Failure to deal with an unexpected question can be a definite sign of cognitive decline!  Trump even lost his train of thought a few times (just like Biden),  but recovered more quickly than Biden,  simply repeating what he had already said seconds previously.  That fast repeat is actually how you can tell the cognitive stumbles from the deliberate question avoidance!

Who Would Take Over if Unable to Serve

Biden has a credible backup in VP Kamala Harris,  should he become incapable of serving while in office,  a fairly likely possibility at his age and in his condition. 

Trump does not have such a credible backupand at his very-similar agethe very same risk of becoming unable to serve also applies!

We do not yet know who the Trump VP pick might be,  but all the purported candidates would be new to the job,  and they all spout the same dangerous and debunked lies that Trump spouts,  being selected for utter loyalty,  not ability.  I see no good choices there for the country! [Update 7-17-2024:  it is Sen. J. D. Vance of Ohio,  quite the far-right extremist on most issues,  and a former "never-Trumper" who is now a fierce loyalist,  spouting the same lies as Trump.]

Behavior that Poses Threats

And then there is the behavioral history:  it is on the public record that Trump threatened to renege on our obligation to defend our NATO allies.  He clearly would prefer that we were not part of NATO,  and has said publicly that he would give Putin everything he wants in Ukraine and elsewhere in eastern Europe. That is a serious threat to world peace,  and to the other democracies.

It is also on the public record that Trump also tried multiple means,  both legal and illegal,  to overturn his 2020 election loss.  This included using his debunked lies about the 2020 election over multiple months (not just the “ellipse speech”,  although that was the final trigger),  to finally incite an insurrection at the Capitol,  on Jan. 6,  2021.  That was his last remaining possibility of staying in power past the end of his term.  He so very clearly did not want to leave office, and that was,  and is,  a very serious threat to our democracy!

And he chronically lies,  about everything.  The fact checking makes that chronic lying a matter of public record.  That makes it very much harder to understand what the executive branch is really doing,  or not doing,  when nothing that is said can be trusted!

Joe Biden poses none of those threats!  And yet I never see that reported!

My Criticism of the Obsessive Coverage

So,  I ask all the news media,  where is the reporting of this overall picture?  I don’t see it!  I just see obsessive coverage of the latest flap or gaffe,  with no overall context.  This is irresponsible! 

The obsessive coverage of Biden’s debate problems is just sensationalism,  to the point of actually driving viewer beliefs,  and the response of pandering politicians to it.  That way lies high ratings,  yes,  but also the destruction of our democracy,  for lack of a responsible “fourth estate”!

Consequences of Irresponsible Reporting

Without the whole picture,  no voter can properly weigh the risks!  So,  the bulk of them don’t.  

And that is how we ended up with the chaotic disaster that was Trump’s term in office.  Complete with vilification and persecution of refugee immigrants,  to the point of separating children from their families,  that resembled nothing so much as what happened entering the Nazi death camps!  And sucking-up to the worlds’ worst despots,  in public!  Plus threatening to renege on our NATO obligations!  Not to mention that nearly every claim he ever made was a lie.  And still is.

Concluding Remarks

So,  I am asking you to change your ways,  and report all the facts,  and also report on how they fit in the big picture.  That is what all Americans desperately need,  so we can weigh the risks,  and vote wisely.  We once had news reporting that actually did this,  several decades ago.  We need it again!

A Visual Example of Weighing Risks This November

This is what weighing the risks, which requires all the data,  actually looks like,  for the election coming this November.  Considering the similarity of the two candidates’ ages,  and how fast physical and mental condition can deteriorate with advancing age,  both parties are offering the wrong choices!  One candidate is deteriorating a bit sooner than the other,  but such deterioration is inevitable,  for both of them,  before the next term will be over. 

But,  given those choices,  one candidate brings huge risks,  while the other does not.  This kind of overall picture thing is exactly what you news media should be showing to the American public in your opinion pieces.  It is your civic duty!



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Update 7-9-2024:  My wife found this cartoon on her Facebook feed.  It came from a good friend who posted it there,  for which I thank him.  I do not know the ultimate source,  being unable to make out the signature on it. 

It illustrates quite well my point about there being obsessive coverage of Biden's infirmity,  to the exclusion of  any coverage of  the dangerous problems Trump brings,  that include the beginnings of his cognitive infirmity,  also visible (but ignored) in the June debate.  ("MSM" on the figure in the cartoon is the "mainstream media".)

That unbalanced,  and therefore irresponsible,  obsessive coverage is actually now fueling the calls from other Democrats for Biden to step aside,  thus influencing the election,  and also thus doing some of the Trump campaign's job for them!  Pandering politicians respond to this crap as the next bandwagon to jump upon,  and so apparently do some big donors.  


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Update 7-14-2024:  It took an assassination attempt upon Donald Trump to turn off the obsessive media coverage of Biden's infirmities-with-age,  in favor of obsessive coverage of the Trump assassination attempt.  I find that a sad example of the very thing I am complaining about:  obsessive coverage of details that utterly ignores context (the "big picture").  

I have never made any secret that I oppose Trump and everything he stands for.  But assassination is not the way to stop him!  It would seem that Biden agrees with me on that,  based on his public statements. 

I would rather see the various judges stop giving Trump "get out of jail free" cards,  and get on with the various criminal trials properly.  Those have been delayed far too long,  and should have taken place before the election.  

What would have come out in court would have had a very definite utility toward weighing the risks of Trump presidency against the risks of a Biden presidency,  for making a wiser choice in the November election.  We have been denied that,  by those delays!

I see some judges that ought to be impeached for those "get out of jail free" cards they have been handing out to Trump.  Justice should be the same for all,  and we ordinary citizens certainly do not get those "get out of jail free" cards.

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Update to Risk Balance,  with Harris Replacing Biden                                               7-22-2024

Harris poses little or no risks from age and infirmities.  At age 59,  she is young enough to serve vigorously for many years yet (while Trump cannot).  The rest of her risks are about the same as with Biden,  excepting the choice of VP.  Anybody she chooses will be as new to the job as Trump’s pick Vance,  posing about the same risk.  The revised risk balance still says the same thing:



Tuesday, July 2, 2024

Recent Heat Protection Items: 3 of 3

I was recently an invited speaker at a recent American Carbon Society meeting held at North Carolina State University in March 2024.  The meeting topic was thermal management,  and it mostly (but not entirely) dealt with carbon-based materials.  Dr. Cheryl Xu of the school’s Department of Mechanical and Aerospace Engineering ran across me and invited me to attend.  The meeting was managed by Dr. Xu and by Dr. Weiming Lu of the American Carbon Society,  a senior employee of Collins Aerospace. 

I submitted 3 presentations in both slide set and submittable paper format,  which were all accepted.  Only one could be presented live,  the other two would be poster presentations.  In point of fact,  all three were made into posters.   Being about the oldest person present,  I felt quite obsolete among specialized experts used to dealing with complex software.  But,  apparently because of my having turned an awful lot of heat protection materials into char during my defense career,  they seemed glad to have me there. 

The “live” one was “Early Ballpark Analysis:  Entry”,  which took entry as the specific example for a generalizable concept screening process that makes true brainstorming feasible in terms of time and budget.  Plus,  being able to get ballpark estimates without software makes possible the recognition of garbage-in,  garbage-out problems when using software.  Those were my messages.  They seemed well-received.

My other two presentations were “Old Ceramic Composite”,  an update on a paper I gave previously at a Mars Society convention a few years ago,  and “Ramjet Ablative Liners”,  about some experimental combustor insulations I tested years ago as part of a very productive ramjet direct-connect test series.   

I have already posted a sort of trip report on the conference,  the entry screening paper,  and the ramjet ablatives paper,  on this site.  They are just below as “Presenter at Workshop” 23 April 2024,  “Entry Concept Screening” 3 May 2024,  and “Ramjet Ablative Liners” 1 June 2024. 

What follows is the text of the submittable paper for “Old Ceramic Composite”.  A related article here on this site is “The ‘Warm Brick’ Ramjet Device”,  posted 2 November 2021.

-----------------------    

Old Ceramic Composite           GW Johnson        12-31-2023

Abstract

At one job many decades ago,  the author had need of an insulating liner for an airbreathing combustor,  which could be fired many times without needing refurbishment.  Inspired by NASA’s Shuttle tile,  he tried low-density ceramics,  and was successful on his second attempt with a fabric-reinforced ceramic composite. 

That effort long ago was done on company R&D funding,  with a low budget.  There was no money for real materials development and characterization activities,  it had to be made from commercially-available products,  and not the most expensive ones at that.  What worked was a commercial ceramic pipe insulation paste,  reinforced with a commercially-available ceramic fire curtain cloth used in aircraft engine nacelles. 

Many years after that effort,  the author realized that this material had potential as a refractory entry heat shield material.  He identified some ways and means to use it for that purpose.

Background

The author was doing feasibility testing for a towed aircraft infrared decoy concept back in 1984.  This thing used a fuel-fired, ram-fed airbreathing combustor as a hot gas source for creating the infrared signature.  It was intended mostly for high subsonic to transonic flight,  at low altitudes.  That corresponds to the ground attack and ground support scenarios.

The author needed a cheap combustor insulator that could support multiple burns without any refurbishment,  and the then-available ablatives were not “it”.  Inspired by NASA’s low-density and consequently low thermal conductivity shuttle tile,  he decided to try low-density ceramics himself.  This was low-budget company R&D,  though.  He could only use ordinary commercial materials,  and certainly not the most expensive ones. 

Experimental Material

The author selected a moldable pipe insulation paste from Cotronics Corporation called 360M,  which was a water-based slurry of alumino-silicate flakes and fibers,  cured by drying out.  Handbook data indicated far lower density and hot thermal conductivity than most dense ceramics. 

It was quite porous and he did not want hot combustion gas entering those pores,  so he needed a surface sealant.  He used as a “paint” a ceramic adhesive from Cotronics,  designated 901,  for that sealing function.  It,  too,  was water-based,  cured by drying.  Both were recommended as max 100 C oven cures,  although the author cured them at 103 C “just to make sure”.  Both of these materials are still available from Cotronics today,  although you generally have to ask them about the 360M paste,  it is considered obsolete.

The author’s liners were retained inside the combustor shell,  but not bonded to it.  See Figure 1.  The first example worked fine,  until the fuels testing reached the point of determining rich and lean combustor blow-out limits.  Rich blowout is marked by very strong instabilities,  showing up as harsh pressure oscillations.  Those cracked the fragile insulator all the way through,  and the combustor promptly spit the whole unit out in pieces,  starting a grass fire that had to be stomped out. 

Figure 1 – Basic Data About the Two Experimental Liner Materials

Taking a cue from his experiences building fiberglass canoes and kayaks with his father,  the author decided to try fabric reinforcement for his low density ceramic liner as the means to withstand the nasty oscillating pressure loads.  As it turned out,  3M Corporation offered as a commercial product a ceramic fire curtain cloth for aircraft engine nacelles.  This cloth was going to be used anyway,  as the heated source of infrared signature from the decoy. 

A that time,  3M offered Nextel 312 alumino-silicate fibers as yarns woven into cloth.  If memory serves,  the cloth designation,  specifically chosen for its high air permeability,  was AF-14.  Since then,  more ceramic materials have become available from 3M for a variety of purposes.  But Nextel 312 is still available in the AF-14 cloth from 3M today. 

The author molded the ceramic composite liner as alternating layers of 360M paste and wraps of the cloth,  again cured at 103 C,  just like the plain liner.  This one was very successful,  resisting many rich blow-out instability events,  several dozen test burns of varying lengths,  and accumulating several hours of burn time,  all without any refurbishment at all.   When it proved successful,  he just used it;  he never characterized it for any of its properties.  There was no money for that.

About The Old Decoy Testing

See Figure 2.  It shows the test combustor rig hardware,  Figure 3 below shows the test facility used for this work.  The combustor shell has the dimensions of 2-inch iron pipe,  about 1.5 inch diameter as insulated,  and about 3 inches long,  inside.  Ahead of it is a duct piece where fuel-air mixing takes place,  and ahead of that is an inlet piece where air capture and diffusion,  and fuel injection,  take place. 

The author and his team used an automotive spark plug and an aftermarket automotive high-energy ignition set to achieve fuel-air ignition,  mounted in the recirculation zone just downstream of the step area change that was our flameholder.  They successfully tested with hydrogen,  propane,  aviation gasoline,  commercial jet fuel,  and technical grade ethanol as the fuels. 

Figure 2 – The Decoy Test Article

Figure 3 – Improvised Free Jet Test Facility

The test facility comprised a PVC pipe stilling chamber with a wooden convergent-only nozzle block that created a jet of high-speed air,  up to about Mach 0.9.  It was powered by what in 1984 was the largest-capacity rental air compressor trailer,  anywhere in Texas.  The temperature of the air stream was measured as 190 F in the exiting jet. 

The test article was mounted on a heavy steel stand made of plate and pipe.  This was positioned about a stilling chamber diameter downstream of the air nozzle block’s exit,  immersed in the exiting jet.  That’s basically a “poor man’s free jet test facility” for ramjets.  Fuel control was by the sight,  sound,  and smell,  as sensed by the author,  standing a few feet away in the hot jet blast behind the test article. 

As a minimum,  it took the author and a technician to operate the facility and run tests.  Sometimes the team included a second technician,  and up to two junior engineers as assistants.

Simple Molding Tools,  Near-Pristine Used Liner

See Figure 4 for an image of the molding tool set that the author used constructing the combustor liner and nozzle pieces as ceramic composites.  The molding plug mandrels are wooden items he made using his drill press to spin them,  in lieu of a lathe. (As previously mentioned,   this was low-budget company R&D stuff.)  The finish on the mandrel plugs is just a coat of varnish.  The combustor shell was its own liner outer mold shell.  He had a separate outer shell for molding the nozzle blocks. 

Figure 4 – Very Simple Molding Tools

In Figure 5 is a view of the combustor liner after all the testing was done.  Note the near-pristine appearance of the ceramic composite.  The nozzle was similarly near-pristine.  The surface temperatures approached the 3250 F melt point of the material,  as evidenced by some very localized surface-flowing downstream,  most of that in the nozzle block throat,  where heat transfer film coefficients are highest. 

This material normally has an ultimate max service temperature of about 2350 F,  limited by shrinkage cracks upon cooldown.  There are some such cracks visible,  but they do not go all the way through thanks to the fabric layers,  and there was very little in the way of fluid shear forces to “pick” at these cracks,  since the internal flow velocities were so low.    

Figure 5 – Liner Condition After Testing Concluded

Attempted Material Characterizations,  Decades Later

Many years later,  the author analyzed the combustor performance for typical test conditions,  and then used these to help set up a cylindrical steady-state heat balance model of the insulated combustor.  This hardware was immersed in 190 F air as its external coolant,  turbulently flowing by at high subsonic speeds.  On the inside,  full-rich flame temperatures dropped across the internal boundary layer to very near the meltpoint of the ceramic,  at its internal surface. 

After an hour-long burn at the indicated conditions,  one can presume that heat transfer is steady-state.  Back in 1984,  the author licked his thumb and touched it to the shell,  to find that it would just barely boil spit,  meaning it was near 215-220 F in thermal equilibrium.  The shell itself was 300-series stainless steel,  with a high thermal conductivity,  and thus very nearly isothermal,  as the numbers indicated.  

Not knowing what the actual hot thermal conductivity of the ceramic composite was,  the author ran his thermal analysis repeatedly in a spreadsheet,  across a large range of possible thermal conductivity values.  The one that “fit” the observations of “near-melt” and “boil-spit” the best (and this is crude, of course),  was 0.02 BTU/hr-ft-F,  which is in metric 0.035 W/m-C.  See Figure 6 below for all the data,  and Figure 7 below,  for the temperature distribution plot obtained at the “best” thermal conductivity value.  

That hot thermal conductivity is actually lower than the hot thermal conductivity reported in the Cotronics handbook for the 360M paste alone!  Because low thermal conductivity correlates with low density (or high void volume fraction),  this implies the density of the author’s composite was lower than the handbook density,  as well.  He honestly does not know what that finished density really was,  but it subjectively felt like it was somewhere near that of industrial-grade styrofoam.

Figure 6 – Simple Cylindrical Steady State Heat Balance,  Parametric On Liner Thermal Conductivity

Figure 7 – Temperature Distribution for “Best-Fit” Thermal Conductivity

While the heat balance analysis was actually done in US customary units,  I converted the temperature distribution to metric for Figure 7.  The thermal gradient indicated for the evidently low thermal conductivity liner is quite remarkable!  It’s in the vicinity of 270-275 C per mm of thickness,  or in US units 12,000-13,000 F per inch!  And that effect is a very real result!  The hot gas temperature and outer shell temperature are known well enough to support that assertion.

Possible Explanation for Low Thermal Conductivity and Density

The apparent low thermal conductivity and density,  estimated years afterward for this ceramic composite,  are well below the Cotronics handbook values for their cured 360M material.  See Figure 8 below.  There are only two differences here between the normal use of that paste as trowel-on pipe insulation,  and what the author did with it:  (1) he cured his liner at a higher-than-recommended temperature by about 3 C,  and (2) there is a cloth of some inherent porosity embedded within it. 

Cotronics recommends at most 100 C for the cure temperature that drives the water out by evaporation.  The paste is aluminosilicate solids slurried in water,  with something in the water that enables the solids to adhere together,  once the water is gone. 

The elevation where the author did this work is about 500 feet above mean sea level,  so the normal boiling point of water there is very slightly below the sea level value of 100 C.  He cured at 103 C,  so the slurry water in his layup actually flashed into steam,  at least partly.  He suspects that the steam “wormholing” its way out of the layup,  acted to increase its void fraction,  thereby lowering both finished density and the resulting thermal conductivity. 

Only the water in the slurry could penetrate into the pores of the fabric,  and into the pores between the fibers in its yarns.  The solid flakes and fibers could not do that,  and yet being similar materials,  the cure chemistry did allow them to bond with that fabric.  But the large inherent porosity in that fabric would necessarily add to the void fraction in the finished article.  That would also act to lower density and thermal conductivity of the finished product. 

At least,  that is the author’s hypothesis.  There is no proof,  other than “it worked”.  

Figure 8 – Rough Estimates of Material Properties Made Decades Afterward

 

Adaptations for Use as an Entry Heat Shield

To use this stuff as an entry heat shield material,  three things must be addressed:  (1) achieving high thermal emissivity to make re-radiation cooling more effective,  (2) the risk of shrinkage cracks in a high fluid shear environment,  and (3) mounting on a exterior surface.

The two plots in Figures 9 and 10 show calculated results for a black surface of high emissivity in Figure 9,  and in Figure 10 for the stock white surface of low emissivity.  In making the plots,  “high” thermal emissivity was assumed to be 0.80,  and “low” as 0.20.  The plot ordinates are equilibrium surface temperature such that re-radiation to Earth temperatures exactly balances stagnation heating,  versus how much stagnation heat flux as the abscissa.  Also shown are the max surface temperature limits imposed by the onset of cracking and melting.  

Figure 9 – Calculated Steady-State Heat Balance For High Emissivity

Figure 10 – Calculated Steady-State Heat Balance For Low Emissivity

The switch to a high emissivity black surface would seem to be easy enough to address.  The author called Cotronics and asked if significant carbon black could be added to their 901 adhesive.  Their answer was that a fair amount actually could be added,  and they could do it.  So,  you just seal the surface pores of your layup with a black “paint” instead of a white “paint”.   Nothing exotic. 

To address the risk of high fluid shear forces tearing at shrinkage crack lips,  one simply operates at conditions below the shrinkage crack limit,  in turn well below melting.  That makes stagnation zone service for Earth entries at around 25 W/sq.cm very marginal,  but it would have application to Mars entries either from low orbit or directly off the interplanetary trajectory there. This does presume very blunt shapes with very large effective “nose radii”.  Stagnation convective heating flux is modeled per H. Julian Allen’s 1953-vintage warhead entry analysis:  Qconv/A =  K(density/nose radius)0.5(velocity)3.

NASA‘s shuttle tile was bonded directly to the structural substrate (metal airframe surface) with an RTV adhesive.  That bondline is a single point failure mode,  however!  The same could be done with my ceramic composite,  but there is another possibility arising from the fabric reinforcement that is embedded within it! 

If made in panels upon a metal substrate panel as depicted in Figure 11,  it can be bonded with RTV to that substrate,  but the free edges of the reinforcing fabric can also be folded around the edges of that substrate,  and clamped in place on its backside.  That provides the redundant retention that NASA’s tiles never had!

Figure 11 – Achieving Redundant Retention

All this requires in the way of vehicle design change is putting the airframe’s metal skin panels onto the airframe framing as already-insulated substrate panels,  instead of installed bare-metal panels to be insulated afterwards.  That does require fasteners instead of welding or rivets,  to facilitate removing individual panels for repairs.

Development Status

The author’s ceramic composite from 1984 is basically decades obsolete,  and never received any materials development effort,  rendering it technologically immature.  Others have since gone far beyond where the author ever got.  But the concept of a ceramic cloth reinforcement embedded in a ceramic matrix still has very good promise today!  The greatest of these promises is the possibility of redundant retention.  But his notion of a ceramic matrix composite has already been used. 

Figure 12 shows what NASA developed from its Shuttle tile technology,  that is currently flying on the USAF X-37B.  This serves even in its stagnation zones,  where the older shuttle tile was inadequate.  NASA calls this “Tufroc”.  It features a ceramic composite cap of higher density,  strength,  and temperature resistance,  atop a low-density ceramic substrate,  in turn applied as a tile.   


Figure 12 – NASA “Tufroc” 2-Piece Ceramic Tile as Used On USAF X-37B

The cap piece is a reinforced composite,  similar to the author’s concept:  a carbon fiber preform reinforcing a ceramic matrix.  The substrate piece is a low-density ceramic that is a strength improvement upon the older shuttle tile material.  It is not a composite,  although it could be.  The two pieces are mechanically linked,  but the substrate is still just bonded with an RTV adhesive to the metal airframe substrate.

This material will handle Earth low orbit entries in stagnation zones,  it is much more resistant to impact and erosion damage,  and it does not suffer from surface shrinkage cracking.  However,  the bond to the substrate is still a possible single point failure!  

If the substrate piece were at least partly a fabric-reinforced composite,  then it could possibly incorporate the author’s clamped-fabric idea for redundant retention.

None of these NASA materials are ordinary commercial products.  They are special-made,  and available only in smaller sizes. The author’s stuff is made of fairly-inexpensive ordinary commercial materials,  and it could be made in rather large panels.  Nobody is doing that,  just yet.

Conclusions

The author’s material is very promising,  but totally undeveloped.  It “just worked” as a combustor liner.,  and it was made of ordinary commercially-available materials.

There are other more recent materials of good promise,  that are mature and flying.

Adding the author’s clamped reinforcing fabric concept to those newer materials might well solve the redundant retention problem. 

About the author:

The author had a 20 year career in aerospace defense doing new product development design,  analysis,  test,  and evaluation, entering the workforce in the slide rule days with a master’s degree in aerospace engineering.  Transition to the then-expensive pocket calculators was underway,  but desktop computers were still years in the future.  That career was mostly (but not entirely) in rocket and ramjet missile propulsion.  It ended with a plant shutdown and layoff in 1994,  just when the industry was shrinking drastically.  The author then had a second 20 year career that was mostly in teaching (at all levels from high school to university),  plus some civil engineering and aviation work.  He earned a doctorate in general engineering late in life,   to support that second career.  He is now retired. 

 


Friday, June 28, 2024

Thoughts on the Presidential Debate

On the format of the debate –

I thought having microphones off except during the allotted time to speak was the right thing to do!  That got rid of the constant interruptions seen in the last ones.  The missing element was fact-checking,  which should have been happening essentially real-time!  This is actually the bigger risk to democracy,  as it is impossible for anyone to make good decisions,  based on bad information.

Evaluation of the fitness of the candidates –

I saw a person with both physical and cognitive difficulties in 81-year-old Joe Biden,  as did all who watched the debate.  But,  I also saw cognitive difficulties in 77-year-old Donald Trump,  which many seemed to have missed as they watched,  simply because they were not as glaringly apparent.  I saw fewer physical difficulties with Trump,  but at his weight and with his bad lifestyle preferences,  I foresee failing physical health coming very soon,  likely a heart attack,  stroke,  or diabetes.

The risk of cognitive problems in the job of President is obvious,  and need not be further pursued here. 

The risk of physical health difficulties is not so obvious,  although this has already come up in prior Presidencies over the last 2 centuries.  The main risk lies in the suitability and readiness of the Vice President to take over the duties of President.  This is compounded by the nature of the job,  which at least from Franklin Roosevelt forward,  visibly ages all who serve.

Observed cognitive deficits –

With Joe Biden,  it was obvious,  and compounded by evident physical frailty.  He completely lost his train of thought while answering one question,  and never recovered it,  an event ended by the timing-out of his time to speak.  I saw 3 or 4 other such stumbles,  losing his train of thought in the middle of speaking,  but he was able to recover it,  and continue speaking.  These were noted as “rambling answers” by other observers.  I know what they really were,  I have seen such before!

With Donald Trump,  it was not quite so obvious,  but it was there for all to see:  he never actually answered any of the questions put to him!  Instead,  he invariably jumped repeatedly into the same debunked lies he tells at his political campaign rallies.  I actually saw him stumble and repeat himself,  while telling these well-practiced lies,  about 3 or 4 times.  The exaggerated nature of the lies themselves were alarming enough,  but not actually answering any of the questions is even more alarming,  as it indicates rather low cognition of the unexpected!  That is very dangerous to the country,  in the job of President!

Truthfulness –

Biden wins hands-down in this category!  Virtually everything Donald Trump said was an exaggerated,  egregious,  and long-debunked political lie!  While the conventional wisdom says politicians lie anytime their lips are moving,  there is actually a wide spectrum of how serious the deception is,  and thus how dangerous it is.  With Trump,  the deception is extreme,  and therefore extremely dangerous.  With Biden,  it is not.

Vice Presidential choices –

With Joe Biden,  there is Kamala Harris,  who is still young enough physically and mentally to serve well.  She is knowledgeable about what is going on,  and could step in and come up to speed almost immediately,  something very important in a time of war,  or impending war.  She,  like Biden,  does not pose a threat of extremely deceptive lies. 

With Donald Trump,  we do not yet know who his Vice Presidential pick will be.  Those purported to be on his “short list” are all “Trump wannabees”,  spouting the same extreme,  dangerous,  and long-debunked lies that Trump does.  I do not see a choice here that is not just as dangerous a threat to democracy as Trump is,  with those lies. 

Legal issues –

Trump has these “in spades”.  Biden does not,  despite years of trying by the “Trump wannabees” in Congress.  Depending upon future jury verdicts,  they could preclude Trump actually serving effectively,  independent of any health risks.  Further,  the President is supposed to be a role model.  The felony conviction,  with more looming,  precludes that role for Donald Trump.

Conclusions –

Neither of these men is actually mentally fit to serve another term as president,  especially in a time of regional wars that threatens general war.  And both men present risks of failing physical health,  simply due to advanced age.  The 25th Amendment and the line of succession is supposed to take care of that risk,  although it perhaps cannot be done quickly enough in an emergency,  unless the President actually quickly dies.

The second scheduled debate (in August,  I think it is) [actually,  September 10th] absolutely must have real-time fact-checking in its format,  and continue the dead mike practice!  Such fact-checking is utterly essential to identify good information for the voters to make informed decisions.  Lies of the type Trump repeatedly tells,  are very dangerous to our democracy.  They cause insurrections,  as we have already seen.

Neither party has any business running candidates for President as flawed as these two men.  Polls say about 70% of Americans agree with me on that.  But since they are the apparent candidates,  physical and mental health risks are not the worst issue here,  telling the truth is,  because lies are so dangerous! 

On that truthfulness basis alone,  I recommend you vote for Biden/Harris,  and against the many other Trump “wannabees” down-ballot. 



Update 7-2-2024:  To summarize,  what we are required to trade off here is the rather strong likelihood of infirmity leading to inability to function,  in Joe Biden,  if selected for another term as President,  versus the strong likelihood of severe damage to,  or even the loss of,  our democracy with another term for Donald Trump,  plus the fair-to-middling likelihood of at least some infirmity trending toward inability,  affecting Trump during another term.

Joe Biden has a good,  credible backup in his VP,  Kamala Harris,  who could assume the duties and come up to speed almost immediately.  There is no risk to democracy with either her or Biden.  Donald Trump’s potential VP choices pose the same threat to democracy that he does,  since they all publicly promote the same lies that demonstrably provoked one insurrection already.  None of those VP choices would be immediately ready to assume the duties of President,  should Donald Trump’s cognitive or physical issues quickly worsen to the point of inability to function.

And then there is demonstrated behavior histories of the two candidates to consider.  Trump did everything he could,  legal or not,  to overturn his election loss in 2020,  up to and including using his lies about that election (over months) to incite an insurrection at the Capitol,  Jan. 6,  2021.  He also threatened to renege on our NATO obligation to defend our allies,  and clearly wanted us out of that alliance,  instead giving Putin everything he wants.  Biden has none of those rather egregious faults.

Weigh the risks for yourself:

Significant likelihood of inability with Biden,  but with a good replacement in Harris;  versus severe damage to,  or loss of,  our democracy with Trump,  plus no credible VP backup for Trump if inability should happen. 

The choice is quite clear:  Biden.



Saturday, June 1, 2024

Ramjet Ablative Liners

In March 2024 I was an invited speaker at an American Carbon Society meeting held at North Carolina State University in Raleigh,  North Carolina.  I brought 3 presentations to that meeting,  only one of which could presented live.  The other two were converted on site to poster presentations,  so that all three were gen in one form or another.

My report on the meeting is given in the posting on this site dated 23 April 2024 and titled “Presenter at Workshop”.  The live presentation and associated text document was about using old-time by-hand analyses for initial concept screening,  to enable a real brainstorming process,  without the expense of creating an actual design and multiple computer models,  for each and every concept.  The example for this was by-hand calculations of re-entry dynamics and conditions.  That presentation is also documented on this site as the posting dated 3 May 2024 and titled “Entry Concept Screening”

The other two presentations,  converted to poster presentations,  existed as potentially-live presentations and text documents when I went to NCSU.  One had to do with ablative ramjet insulations that I tested in actual ramjet direct connect tests a few decades ago.  The other was an update to a previous presentation and posting regarding a low density ceramic composite burner liner that I tested a few decades ago.  That earlier posting was dated 18 March 2013 and titled “Low-Density Non-Ablative Ceramic Heat Shields”.

To quickly find any posting here on this site,  all you need is its posting date and its titleUse the blog archive tool on the left side of this pageClick first on the year,  then on the month,  then on the title if need be (if more than one posting was made that month).

To see an enlarged figure in any given posting,  click on the figure.  There is an “X-out” button top right,  that takes you right back to the article.

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Presented here is the text document of the ramjet liner presentation,  based on those tests long ago. 

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Ramjet Ablative Liners               GW Johnson        12-24-2023

Abstract

For several years,  the author worked on the Hercules-McGregor plant’s “Airbreathing IR & D” project,  where “IR&D” means “Independent Research and Development”,  and is reimbursed by the government.  The focus of that project was a fuel-rich solid-propellant gas generator-fed ramjet,  which included an integral booster housed within its combustor.  

During 1989-1992,  a series of ramjet tests were performed in the McGregor direct-connect test facility,  that addressed 3 objectives.  First,  the combustion performance of multiple experimental fuel propellants was evaluated.  Second,  a fuel rate control approach with no moving parts was evaluated.  Third,  multiple possible alternate combustor ablative insulation materials were evaluated,  as possible alternates for Dow Corning’s DC 93-104 silicone ablative,  which is the subject here.

Presented here are the heat protection results from that testing series.  Included are a unique way of extending the time that heat protection can be obtained,  and the means by which chemically incompatible materials can be bonded together. 

About the author:

The author had a 20 year career in aerospace defense doing new product development design,  analysis,  test,  and evaluation, entering the workforce in the slide rule days with a master’s degree in aerospace engineering.  Transition to the then-expensive pocket calculators was underway,  but desktop computers were still years in the future.  That career was mostly (but not entirely) in rocket and ramjet missile propulsion.  It ended with a plant shutdown and layoff in 1994,  just when the industry was shrinking drastically.  The author then had a second 20 year career that was mostly in teaching (at all levels from high school to university),  plus some civil engineering and aviation work.  He earned a doctorate in general engineering late in life,   to support that second career.  He is now retired. 

Background:

Figure 1 illustrates how drastically-different the conditions are in a ramjet,  versus those in a solid rocket.  It was already known that the types of insulation that work in rockets simply could not cope with the heavy fluid shear “scrubbing” and very long burn times in the ramjet. 

The materials commonly used in rocket cases are randomly-oriented fibers reinforcing some type of rubber.  In the old days,  asbestos fibers were used,  replaced in recent years with things like Kevlar fibers.  One common rubber was EPDM (ethylene propylene diene monomer),  easily compatible with cast composite propellant binder systems.  These are shown in Figure 2,  along with the candidates being considered for ramjet testing. 

These materials were usually B-staged as partially-cured sheets,  so that a layered wrap upon a mandrel could be inserted into a primed case,  that mandrel inflated to exert pressure against the case wall,  and then heat-cured to vulcanize the rubber.  This was very cost-effective processing,  but the materials were inadequate for ramjet application. 

Figure 1 – Rocket Vs. Ramjet Conditions

Figure 2 – Candidate Materials

Replacing the randomly-oriented fibers with layers of fully-woven cloth was the approach that was hoped to be adequate,  while preserving the preferred cost-effective processing.  We already knew about Dow Corning’s silicone material with the higher pyrolysis temperatures,  so we switched to their poly dimethyl silicone (PDMS) polymer,  and attempted carbon and silica fabric reinforcements. 

Dow Corning’s DC 93-104 ablative is PDMS polymer loaded with 3 solids.  Two are silica and silicon carbide granulates,  the third is carbon fibers in random lengths. This is a very “thick” (viscous) material that can be troweled,  or pressure-cast around installation tooling. 

We had significant experience with it in the ASALM-PTV program,  where we insulated with DC 93-104 and then cast integral boosters,  into 20-inch OD combustors,  for ramjet propulsion designed by the Marquardt Company.  We applied this same experience to our 7-inch OD ramjet engine.

We also identified a Japanese more-or-less equivalent to DC 93-104:  Type 0 Shin Etsu. It processes identically to DC 93-104.  We also tested it.

About the Ramjet Testing:

Over several years,  we also obtained a lot of experience and hardware for a 7-inch OD ramjet engine being considered for an advanced propulsion replacement for the AIM-120 AMRAAM missile.  This used the same DC 93-104 liner that ASALM used.  Figure 3 shows the geometry and dimensions of the ramjet engine,  and typical test conditions.  There is even an approximate thermal analysis plot of the temperature distributions expected from the flame.  There are drops across the thermal boundary layer,  across the char,  across the virgin,  and finally a tiny one at the case.  

Figure 3 – Typical 7” Test Conditions

Note that the thermal conductivity of the char is about factor 3 times that of the virgin material,  leading to the strong temperature gradient slope change at the pyrolysis zone.  Despite this,  the char is still more of an insulator than any sort of thermal conductor.  That is an important result!

Such tests in full flight-weight 7” hardware usually burn 30-60 seconds,  but sometimes can run longer,  which is challenging even for DC 93-104.  That problem was solved on ASALM,  and that same solution was used for the AMRAAM engine.  The IR&D tests being shorter-burn tests,  we did not need to use that solution in these IR&D tests.  There is more information about that solution below. 

Figure 4 shows a color-highlighted table of some 8 tests conducted for 3 different reasons:  (1) to test experimental fuels,  (2) to test an experimental fuel control technique (unchoked-throat self-throttling),  and (3) to test and compare experimental and “stock baseline” combustor insulations.  

Figure 4 – 7” OD Test Results

 

Of these,  the first test was an unintended no-burn using the PDMS-carbon cloth insulation,  leaving it intact.  It was re-used “as-is” in the second test (blue),  a short-burn run with a “clean” fuel. 

The third test was another “clean” fuel short-burn test) with the PDMS-silica fabric insulator (green.  It was in such good condition,  we re-used “as-is” in the fourth test (also green),  another short-burn test of a highly-metallized fuel. 

The 5th test was a long-burn test of a low-boron fuel,  using DC 93-104 as the case insulation (orange). 

The 6th test was another low-boron fuel test,  this one a short burn,  using the Shin Etsu “clone” of the Dow Corning material (yellow).  The 7th test was a longer-burn test of an older baseline fuel with the unchoked “throttle”,  and a re-used Shin Etsu insulator (again yellow) from test 6. 

The 8th test (no color) did not give us any useful data,  it being almost-a-no-burn,  with a very disappointing highly-experimental fuel,  on another DC 93-104 insulator,  not a re-used one.

Specific Test Results:  PDMS/Carbon Fabric

Figure 5 shows our hybrid flight-weight combustor/heavyweight lab motor hardware,  as mounted on the thrust stand in the Hercules-McGregor direct-connect test facility.  This is a hybrid,  using a flight-weight combustor with a heavyweight lab motor as the fuel-rich solid propellant gas generator,  in a gas generator-fed ramjet.  (ASALM was a liquid fuel ramjet).  IR&D stuff is never “pretty”,  and this one certainly is ugly-looking.  Figure 6 shows the post-burn appearance of the insulator.  It was mostly used-up after only an 11 second burn.   That was very disappointing,  as we usually got over a minute out of DC 93-104,  even without the very-long-burn solution.

Figure 5 – Hybrid Test Hardware:  Flight-weight Combustor and Heavyweight Lab Motor Gas Generator

Figure 6 – Results From One PDMS/C Fabric Test

 

Specific Test Results:  PDMS/Silica Fabric

Figure 7 shows the white textured appearance of the as-built PDMS/Silica fabric insulator.  Figure 8 shows the  post-burn appearance after two short-burn tests,  one after the other,  on the same combustor insulation.  The first was a 10-second short burn repeat “clean” fuel test.  The second was a 15 second short burn of a very-highly metallized boron-titanium fuel.  Total accumulated burn for the two tests was only 25 seconds.  There was not enough liner left to risk a third re-use.  Again,  that was disappointing. 

Figure 7 – Pre-Test Appearance of the PDMS/Silica Fabric Insulator

Figure 8 – Post Test Appearance of the PDMS/Silica Fabric

 

 

Most of the 7-inch IR&D tests looked like what is shown in Figure 9 for the boron-titanium test.  The fuel is 28% metallized boron-titanium.  The gas generator throat is choked.  The liner is the PDMS/Silica cloth being reused “as is” from the previous test.  The sparklers are not from the fuel,  they are coming from the liner as it erodes.  Otherwise,  the clean plume is quite amazing for such a highly-metallized fuel.  Incidentally,  this was the very first time anyone ever burned high-percentage boron efficiently,  in a ramjet engine!

Figure 9 – Typical 7” Test Appearance:  BTi/PDMS-SiO2

 

 

Specific Test Results:  DC 93-104

Figure 10 and Figure 11 are post-test,  just two different views.  This was a long-burn test of a low-boron fuel,  rate-controlled by the unchoked throat.  Note the typical “mud crack” cracking pattern,  which is what we usually see with DC 93-104 liners.  With that kind of cracking,  it is abundantly clear that the char layer is very strongly held by the virgin material beneath.  That would be the effect of the randomly-oriented carbon fibers connecting the char layer to the virgin.   There was enough left after this 40 second test to possibly have risked a short-burn reuse,  but we did not do that. 

Figure 10 – DC 93-104 Post-Test Appearance, one view from rear

Figure 11 – DC 93-104 Post-Test Appearance, another view from the front

 

 

Specific Test Results:  Type 0 Shin Etsu

Figure 12 and Figure 13 show two post-burn views of this insulator.  The first one is after a 15-second short burn with a low-boron fuel,  unchoked.  The second one is after a 42-second long-burn unchoked-throttle test with an old baseline fuel,  in which the same Shin Etsu liner was reused “as-is”.  Total accumulated burn was 57 seconds,  about what we usually get from DC 93-104.  

Figure 12 – Type 0 Shin Etsu Post-Test Appearance,  after low-boron short burn

Figure 13 – Type 0 Shin Etsu Test Appearance,  after re-use in a long-burn unchoked throttle test

 

There was some instability in the 42-second burn,  resulting from a flow-control aero-grid failure in one of the 2 inlets.  Despite this flow asymmetry,  the burn was “good” and the liner survived the pressure pulsations. 

What we saw with Type 0 Shin Etsu was poorer char-retention strength atop the virgin material,  but with a “slicker-looking” and apparently-harder char layer.  It would generally shed most of the chunks of char layer after the actual burn,  during air rundown,  not during the burn itself!  This was seen as a “puff” of black in the air-only plume after the flame went out. 

The Extended-Burn and Chemical-Compatibility Solutions:

These liners (and the one in ASALM) were only about 0.20 inches thick.  In the 7-inch hardware,  we would get about a minute’s burn with DC 93-104 before the charring reached the case wall,  releasing the char layer to break up into chunks and fly downstream.  Only the Type 0 Shin Etsu matched that duration performance.  Both are thick pressure-castables. 

To get a longer protection duration,  one has to mechanically retain the char,  after the virgin material bonded to the case wall has been fully pyrolyzed away.  The means to do this is illustrated in Figure 14,  and was developed at Hercules-McGregor on the 20-inch ASALM program,  working together with Marquardt.   If you take thin strips of stainless steel about 0.1 inch wide,  kink them on a 1 inch spacing to extend up about halfway through the liner,  and spot-weld them to the case spaced about an inch or so apart,  this will retain the char layer in-place,  long after the virgin has charred through.  The kink tips are buried deep enough inside the char so as not to overheat.  

Figure 14 – Details Matter:  Long-Burn and Propellant Compatibility Solutions

 

This worked for up-to-15-minute burns in ASALM!  It was adopted for the 7” AMRAAM engine as well,  on the contract programs.  We think it might help address char chunk loss with the Shin Etsu,  as well.

The other issue with PDMS silicone is chemical incompatibility with composite propellant binders,  very important if integral boosters must be packaged within the combustor!  This problem was also solved on ASALM.  One has to chemically isolate the materials with an inert separator sheet,  yet still retain good adhesion to both the ramjet liner and to the propellant.  This was achieved with thin Teflon film (essentially a large size “Saran Wrap”),  acid etched on both sides to provide cleaned surfaces with rough texture. 

This separator is bladdered onto a liner surface primed with DC 1200 from Dow Corning,  and cured in place.  Then the exposed inside surface can be primed appropriately for the propellant binder system,  before propellant is cast and cured.  The bonds are strong,  yet the chemical isolation is absolute.

Conclusions:

DC 93-104 is the best by far,  compared to bladderable fabric-reinforced rubbers

               For burns > ~ 1 minute,  must use the kinked strip retention system

               Kinked strip retention system tested in 20” diameter for burns up to 15 minutes

 

Type 0 Shin Etsu is almost as good as DC 93-104

               Char-virgin strength is weaker

               Sheds char chunks during air rundown

               Retention strips might ease these troubles

As the conclusions indicate,  the greater pressure-cast processing and separator-sheet preparation efforts are worth the better protection afforded by DC 93-104,  especially with the post-char-through protection afforded by use of the kinked retention strips.  The kinked retention strip detail is not something Dow Corning thought of,  but it makes their product perform very much longer! 

The strips would likely enhance the performance of the Japanese material,  as well.  It is not an exact clone of the Dow Corning material,  with the apparent weaker char layer retention,  but we believe the strips might help correct that,  based on these IR&D test results.

References:

#1. Dow Corning Product Information Sheet “Dow Corning 93-104 Ablative Material” ,  available as a pdf file from their website.

#2.  MSDS (Material Safety Data Sheet) for DC 93-104 kits,  MSDS number 000001189166,  issued 2 April 2015,  last revised 6 April 2015,  available from Dow Corning as a pdf file.

#3. US Patent 3,623,904 “Elastomeric Composition Containing Silicon Carbide for Use as an Ablative Coating”,  issued to James A. Ramseyer and assigned to Dow Corning Corporation,  30 November 1971.

#4. Cheryl L. Resch,  “Ablation Models of Thermal Protection Materials”,  published in the Johns Hopkins APL Technical Digest,  Volume 13,  Number 3,  dated 1992.