Okay, the company’s recommendation based on cubic feet is absurd… you have to also take into account the number of occupants (600 BTU per person) and about 3.4 BTU per watt of electrical equipment in service inside the enclosure.
So we pretty quickly upgraded from the CR-2550 unit to the CR-5000ACH (being the largest that they have) late summer last year. They gave us a goodwill discount towards the new purchase but there was no trade-up or trade-in program so we resold the CR-2550 (which surprisingly retained its value pretty well).
As we got into autumn months where the evening temperatures were below 60 and the daytime temperatures were above 70 we noticed that the AUTO mode behavior was significantly different from the CR-2550 unit. The AUTO mode on the CR-5000ACH is essentially worthless.
Our first summer show (June 28 and 29) where we were taking rides all day we noticed that the avionics bay temperature crept up from 72 to 100 over the course of the day both days. The front seat in the cabin was comfortable but the back seat was starting to get toasty. Standing in back was miserable. It was clear that we needed another unit.
An additional CR-5000ACH (or so we thought) was ordered last week. However, when it arrived the unit was bigger and substantially heavier (20%) than the old unit. Amazing to me is that the model numbers are absolutely identical. None of the bolt holes or the drain line up.
I will say so far I like some of the changes made to the “2015” CR-5000ACH unit. But why does the heat mode draw so much more power with no increase in BTU (almost 20% more amperage)? We will certainly be examining if the AUTO mode was corrected in this new model (contrary to statements made by their customer service and the manual). However, there was some damage discovered on arrival which I have already reached out to the company about.
This article from earlier this week revealed something that I had no clue was possible – that the abundance of CO2 in the Cytherean atmosphere could actually be used as an oxidizer!
Combustion is the process of chain-reaction oxidation. Most combustion (for example, with organic materials) takes oxygen from the air and uses it to oxidize carbon atoms, producing CO2 (and H2O in organic compounds). However, with the correct substrate, it is possible to “burn” carbon dioxide by using it as the source of oxygen for oxidation (this reduces the carbon, and black carbon residue is a product of the combustion) through a process called decomposition.
This is frequently done in chemistry demonstrations where magnesium is ignited and surrounded with dry ice (solid state CO2). This produces Magnesium Oxide (MgO) and carbon (C). MgO has slightly less free energy than CO2, making the reaction exothermic (and hence combustion possible), but it has a very high activation energy, mostly involved in the dissociation of CO2. Burning magnesium is quite hot and provides the necessary activation energy and will “burn” the CO2 if there is no O2 available (this is done by piling the dry ice on top of the burning magnesium, or a similar method).
So now the question becomes which fuel to use? Magnesium isn’t the only fuel that will decompose CO2 (and liquids are simpler to use for propulsion than powders):
- B2H6 Diborane cryo liquid at -165C
- B5H9 Pentaborane liquid at room temperature -46C to 60C
- SiH4 Silane or Silicon Hydride cryo liquid at -113C
- LiBH4 Lithium Borohydride solid at room temperature melts at 268C, ignite at 180C!
- Al(BH4)3 Aluminium Borohydride liquid at room temperature -64C to 44C
- H2 Hydrogen cryo liquid hydrogen -253C WTF that sounds expensive
- Mg Magnesium solid melts at 650C, auto-ignition at 473C?! WTF that won’t work
- NH3 Ammonia cryo liquid at -34C
- N2H4 Hydrazine liquid at room temperature 2C to 114C
- C2H2 Acetylene cryo liquid at -84C (not included in original research but found from a second source)
Chemicals that are higher density are more efficient to store, but need to result in a high specific impulse with CO2 as the oxidizer. Not sure where to get those numbers as well as mixing ratio. Are any of these hypergolic? Or do we definitely need an ignition source now?
An environmental CAS message that I see all too often – this past weekend operating at the Maker Faire the avionics bay got up to almost 100°F and we actually had a part fail (possibly due to the temperature). The pilot seat stayed cool since the air was blowing directly on them but the gunner’s station was getting a little uncomfortable.
Last week I added a circulating fan for the avionics bay. Over lunch today I ordered a second AC unit. I am also working on upgrading the flexible ducts to an insulated, lighter colored solution like the image below.