lr64
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Once rails were fastened inside, you could cut away some of the tube.
Space Needle planning and build thread
- Thread starter Adrian A
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A 12-foot Sono-Tube might be a little clumsy to carry to the away pads and it would definitely be heavier than Adrian's little beauty
OTOH, I would love to see a workable design for a tube launcher with sabots
-- kjh
I'm making a dedicated thread for the tower over in the ground support forum.
https://www.rocketryforum.com/threads/38mm-space-shot-tower.188859/
https://www.rocketryforum.com/threads/38mm-space-shot-tower.188859/
My plans for this rocket have evolved a little. Assuming I can get my sustainer over 30,000 feet and ignite it, the biggest challenge is going to be aeroheating. If the sustainer is as light weight as it can be, then the sims predict Mach 7. I’ve been learning more about aeroheating, and I’m pretty sure that even with 450F epoxy, aluminum leading edges, etc, I can’t make a sustainer that would survive that, even at 40,000-50,000 feet.
So the new strategy is to keep the first two stages as light as possible, and make the sustainer as heavy as it needs to be to keep the top speed in the survivable range.
So the new strategy is to keep the first two stages as light as possible, and make the sustainer as heavy as it needs to be to keep the top speed in the survivable range.
Adrian,
Are we back to the tungsten-epoxy nosecone, or do you have something else in mind?
Are we back to the tungsten-epoxy nosecone, or do you have something else in mind?
Like this?A 12-foot Sono-Tube might be a little clumsy to carry to the away pads and it would definitely be heavier than Adrian's little beauty
OTOH, I would love to see a workable design for a tube launcher with sabots
-- kjh
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I did some analysis based on NACA aeroheating papers, mostly from this one:
https://ntrs.nasa.gov/citations/19930084365
It is based on a thin-skinned magnesium rocket that they flew in the mid 1950s:
They measured the wall temperature throughout the flight, at several different locations along the body.
The adiabatic wall temperature is effectively what the apparent air temperature is that is flowing over the rocket surface at the supersonic speed of the rocket. The skin temperature lags behind the adiabatic wall temperature because of the heat capacity of the skin. The data at several stations along the rocket at different points along the flight, with different speeds ant altitudes, all nicely correlates with the model:
So if you calculate the Reynold's number and the Prandtl number, you can use that equation to get the Nusselt number, which is a non-dimensional form of a heat transfer coefficient that you can convert into units of your choice.
Note that this is for the airflow along the length of the rocket in this experiment, and does not include extra heating from leading edge shockwave pressure. There are other experiments and equations for that, but I'm focused on the parallel plate flow because it tells you what most of the rocket will experience, including the body tube and most of the fin. No use worrying about leading edge treatments if the heat is already too much for the rest.
There are also equations for the air stagnation temperature that depend on the static temperature, and the Mach number, which also varies with altitude and speed. I put this all together into a spreadsheet where you can paste in your RASAero export and it will use the altitude and Mach number from the sim results to tell you the apparent air temperature and the flat plat heat transfer coefficient. From there it models the heat capacity of a fin, and estimates the fin temperature and heat flux throughout the flight.
I have included this Excel workbook in this post.
I was hoping that this analysis would tell me that as long as the sustainer was high enough, I didn't have to worry much about aeroheating, even if the Mach number got really high. Sadly, this is not the case.
Igniting a sustainer at high altitude is great for reducing drag. That's how I'm getting such eye-popping simulation results with such a small rocket. At 40,000 feet above the black rock desert, the drag is only 26% of what it is at 3000 feet AGL, and it drops quickly from there. At 100,000 feet the drag and the density are down to 1.4%. The reduction in density also helps reduce the heat transfer coefficient. It takes longer to heat up a fin at higher altitude. Unfortunately, the end temperature for Mach 5 is above Aluminum's 90% strength loss temperature (~400C) whether your rocket is going Mach 5 at 1000 feet or 60,000 feet:
The equilibrium temperature goes up fast with Mach number. Another way to look at this is to see how much faster you could go at high altitude than low altitude for the same temperature. 400 C equilibrium temperature will buy you the capability for steady state Mach 3.5 flight at 50,000 feet vs. Mach 3 at 10,000 feet ASL
High altitude gives you a much lower convective coefficient, which means that it will take longer for your fin to heat up, but give it enough time at a high Mach number and and it will get to nearly the same temperature no matter the altitude.
Heating up slower does definitely help, though. If I take my 3-stage rocket and add enough sustainer mass to drop the max speed down to Mach 6, here's my estimate the resulting temperature of an aluminum fin, 5 cm behind the leading edge:
700C is a lot better than 1250 C, but it still hot enough to melt aluminum.
https://ntrs.nasa.gov/citations/19930084365
It is based on a thin-skinned magnesium rocket that they flew in the mid 1950s:
They measured the wall temperature throughout the flight, at several different locations along the body.
The adiabatic wall temperature is effectively what the apparent air temperature is that is flowing over the rocket surface at the supersonic speed of the rocket. The skin temperature lags behind the adiabatic wall temperature because of the heat capacity of the skin. The data at several stations along the rocket at different points along the flight, with different speeds ant altitudes, all nicely correlates with the model:
So if you calculate the Reynold's number and the Prandtl number, you can use that equation to get the Nusselt number, which is a non-dimensional form of a heat transfer coefficient that you can convert into units of your choice.
Note that this is for the airflow along the length of the rocket in this experiment, and does not include extra heating from leading edge shockwave pressure. There are other experiments and equations for that, but I'm focused on the parallel plate flow because it tells you what most of the rocket will experience, including the body tube and most of the fin. No use worrying about leading edge treatments if the heat is already too much for the rest.
There are also equations for the air stagnation temperature that depend on the static temperature, and the Mach number, which also varies with altitude and speed. I put this all together into a spreadsheet where you can paste in your RASAero export and it will use the altitude and Mach number from the sim results to tell you the apparent air temperature and the flat plat heat transfer coefficient. From there it models the heat capacity of a fin, and estimates the fin temperature and heat flux throughout the flight.
I have included this Excel workbook in this post.
I was hoping that this analysis would tell me that as long as the sustainer was high enough, I didn't have to worry much about aeroheating, even if the Mach number got really high. Sadly, this is not the case.
Igniting a sustainer at high altitude is great for reducing drag. That's how I'm getting such eye-popping simulation results with such a small rocket. At 40,000 feet above the black rock desert, the drag is only 26% of what it is at 3000 feet AGL, and it drops quickly from there. At 100,000 feet the drag and the density are down to 1.4%. The reduction in density also helps reduce the heat transfer coefficient. It takes longer to heat up a fin at higher altitude. Unfortunately, the end temperature for Mach 5 is above Aluminum's 90% strength loss temperature (~400C) whether your rocket is going Mach 5 at 1000 feet or 60,000 feet:
The equilibrium temperature goes up fast with Mach number. Another way to look at this is to see how much faster you could go at high altitude than low altitude for the same temperature. 400 C equilibrium temperature will buy you the capability for steady state Mach 3.5 flight at 50,000 feet vs. Mach 3 at 10,000 feet ASL
High altitude gives you a much lower convective coefficient, which means that it will take longer for your fin to heat up, but give it enough time at a high Mach number and and it will get to nearly the same temperature no matter the altitude.
Heating up slower does definitely help, though. If I take my 3-stage rocket and add enough sustainer mass to drop the max speed down to Mach 6, here's my estimate the resulting temperature of an aluminum fin, 5 cm behind the leading edge:
700C is a lot better than 1250 C, but it still hot enough to melt aluminum.
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I'm probably missing something here. What speeds/altitudes are you staging at? Getting a ~Mach 5-6 speed boost off of a K motor breaks my mindsim, but I also don't do much in high altitude or high performance so its calibration is probably off.
Why not cover the nose in phenolic? With an aluminum core? The phenolic will keep the aluminum at a temperature it can survive.
Start at the top of the thread.
Phenolic composite could be part of the answer, since we know from nozzles that it has good strength and ablative properties. The nosecone (which needs to be RF transparent, so no aluminum core), the motor case/body tube, and the fins are all somewhat different problems.
I want to be able to re-use this rocket after a lower-speed test flight, but I'm o.k. with the sustainer being single use for the space shot.
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With respect, I did do that. I see the altitude/time plot in #1, but it's awfully hard to pull velocity data off of that, plus there's been quite a bit of design development since then. There's discussion of max speeds in #8, but not staging speeds. #8 also has an explicit mention that you haven't optimized staging times. There's further discussion of max speed in #34, but it appears to be repeating the info in #8.
Sorry
With the minimum plausible mass and diameter, smooth paint, and perfect biconvex fins, here's the Mach number plot:
The little upward motion in the Mach number after upper stage burnout is likely due to the air getting colder again in the mesosphere. The velocity is going down the whole time after burnout.
Here's a closeup of the staging times and speeds:
The sustainer ignition altitude in this sim is just under 40,000 feet and burnout is just over 50,000 feet.
Sorry for making a bad assumption.
With the minimum plausible mass and diameter, smooth paint, and perfect biconvex fins, here's the Mach number plot:
The little upward motion in the Mach number after upper stage burnout is likely due to the air getting colder again in the mesosphere. The velocity is going down the whole time after burnout.
Here's a closeup of the staging times and speeds:
The sustainer ignition altitude in this sim is just under 40,000 feet and burnout is just over 50,000 feet.
I see, a phenolic nose will probably work the body can't be getting that hot so CF will work there ( it appears you can make it work to 1500C if you get special stuff, dragon plate can do 250C) the fins are going to be hardest a ablative will mess with the air flow to much I'd think, they'll just have to tank it a CFC plate with a tungsten edge might work.
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No worries.
That confirms that my mindsim was just broken.
I would have guessed that sustainer plus second stage would be ~twice the weight of the sustainer alone, so the sustainer would have ~twice the delta V as the second stage, but clearly I was wrong. You obviously can't really let it slow down any more at staging, and it probably wouldn't do that much good if you did. On the other hand, if you're hitting 500K feet on a perfect day, you have some room to lose some altitude to a heavier/draggier sustainer!
What can make it counterintuitive is that the effect of mass is non-linear, and the closer you get to having zero mass after burnout, the closer you get to having infinite velocity.No worries.
That confirms that my mindsim was just broken.
https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/ideal-rocket-equation/
The second stage has the full sustainer above it, so it's never going to have a very high mass fraction during its burn. But not so for the sustainer. An easier and more conventional way to do this space shot would be to have a much larger booster and a somewhat larger 2nd stage, and smaller sustainer so that the peak velocity would be more like M3, M3, M3.5 rather than M1, M2, M6. I have started to look at using 54mm booster and maybe 54mm second stage, but I should also look at just making the sustainer smaller.
That would be nice. Steel melts at less than 1500C.
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Looking forward to what comes next!
https://www.graphitestore.com/Carbo...R7z3lCT84pJYa-wRLUZy04ZqsZnY8hYCxFlSIbv0ahpgO they only have plate no tube but it would make for good fins, insanely expensive but it might be possible to make something similar or get lab rejects or something like that.
Wow, that material would ac
Wow, that material looks like it would actually work for fins.
If so, price isn't too bad. Those sheets are huge. The 3mm stuff is only about 1.6x the price of 1/8" quasi-isotropic Dragonplate (which itself is roughly double the cheap CF plates I've bought from Ali Express).
Edit to add: strength looks pretty low to what I see quoted for CF plate. I guess a thick enough plate would work for fins. Also possible I'm not reading correctly.
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Just keep it so it doesn’t have the fibers pointing into the plasma stream so that they don’t peal apart and shred the fins.
Another problem is that the EBay may get hot enough to melt solder so you may need to insulate it.
Wrapping the leading edges of the fins with titanium could help with that. But there's still the problem of the nosecone and the body tube. For the body tube, maybe some spray-on ablative coating could help. Adding a high-temperature (steel or titanium) stinger to the nose can reduce the heating by keeping the shock wave away from the nosecone surface.
This is going to sound crazy but,
What about a balsa core? It will be relatively cool under a medium thickness phenolic layer and in the absence of oxygen there will be no fire if it gets too hot it’ll turn into carbon and become an insulator itself! And it’d be strong enough and super light as well as RF transparent.
@Adrian A --
After studying your build threads here on TRF as well as a Rocketry Planet reprint posted here on TRF, one take-away for me was your Tungsten Powder nose weights.
If "Space Needle" needs nose weight, I wonder if one could come up with a Tungsten Stinger to balance the rocket AND to take the heat ?
I recently made a trip with the girls to "Mr Jenson's fishin' store" down in Austin to inspect his Tungsten, bullet-shaped fishing weights.
They wont work for me in my nose cone, but I wonder if they could be machined and threaded and fastened to a threaded, blunted tip of an Aluminum Nose Cone with some sort of insulator between the Tungsten and the Aluminum to minimize heat-transfer from Tungsten -to- Aluminum -to- Fiberglass ...
Anyhow, you said "stinger" and you reminded me of my recent adventures with Tungsten nose weights ...
HTH
-- kjh
After studying your build threads here on TRF as well as a Rocketry Planet reprint posted here on TRF, one take-away for me was your Tungsten Powder nose weights.
If "Space Needle" needs nose weight, I wonder if one could come up with a Tungsten Stinger to balance the rocket AND to take the heat ?
I recently made a trip with the girls to "Mr Jenson's fishin' store" down in Austin to inspect his Tungsten, bullet-shaped fishing weights.
They wont work for me in my nose cone, but I wonder if they could be machined and threaded and fastened to a threaded, blunted tip of an Aluminum Nose Cone with some sort of insulator between the Tungsten and the Aluminum to minimize heat-transfer from Tungsten -to- Aluminum -to- Fiberglass ...
Anyhow, you said "stinger" and you reminded me of my recent adventures with Tungsten nose weights ...
HTH
-- kjh
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