Going for 100,000 Feet

Mach 2 is quite mild. I would not expect much aeroheating during a typical rocket flight.

Check out https://www.aerospaceweb.org/design/scripts/atmosphere/ With is calculator you can figure out the amount of heat that might be transferred to the structure at altitude.

At Mach 2 the air flow behind the shock is ~200C (~400F) at sea level. While the air is hot, the density is low compared to a solid structure. The heat transfer is proportional to the delta T, the density of the air, and the heat transfer coefficient, and the thermal conductivity and heat capacity of the underlying structure. As we said before the heating is directly proportional to the air density which drops quickly as you increase altitude, and as the cube of the Mach Number. If you look at the calculator, you will see the term equivalent Mach number. At sea level, the equivalent Mach number is the actual Mach number. As the altitude increases, the Equivalent Mach number decreases, and on a comparative basis, the ratio of the heating at altitude is reduced the ratio for the Equivalent Mach Number divided by the actual Mach number squared. Just play with the calculator. Look at the recovery temperature as a function of altitude at Mach 2. At sea level it's 428 F, but at 7.5 miles it's only 208 F. That's at bit much for aluminum continuously at sea level but fine at 7.5 miles. At Mach 3, it's 890 F at sea level but a much lower 555 F at 7.5 miles. Way too hot for aluminum but fine for titanium or stainless steel. If you push Mach 4, it gets to hot for almost all metals. 1536 F at sea level and still 1041 F at 7.5 miles. Heat capacity in a well designed rocket can handle the transient heating but nothing made of metal is going to that that temperature at sea level, so you need ceramics.

When you go fast in the atmosphere, you really have to do a transient calculation that includes heat transfer, thermal conductivity and heat capacity to determine if a structure will survive and for how long.

Current RASAero II sim has the booster hitting Mach 1.84 at 4,100' then we have separation. Sustainer coasts upward for 18 seconds. At 27,500' the sustainer ignites. Sustainer breaks Mach 2 at 34,500'. Sustainer reaches max speed of Mach 2.80 at 44,000'. Sustainer then coasts upward for another 31 seconds and achieves apogee at 123,700'. This assumes a launch from Black Rock, which according to Google Earth is 3,981' above sea level.

Open Rocket's simulation actually projects altitude at Black Rock to be 109,000', but with OR you can also plug in temperature and barometric pressure. I assumed it was going to be a 90+ degree day. My initial sense was that 110,000' was probably where it would settle out.

All that being said, heat is still a concern, but there are configurations where it would get a lot hotter.

Above 10K feet (plus the 3900 from Black Rock) I would not be worried about speeds around M3.

Have you considered expanding and lengthening the inter-stage so you can put a boat tail on the sustainer for base drag reduction during the coast phase? It would ejected upon sustainer ignition so you could use a boat tail smaller than the aft end of the motor. I played around a bit with RASAero and Open Rocket today, and they generally agreed that a 141k (RAS) or 142k (OR) was possible by using a longer coast and a drag-reducing boat tail. This is leaving the RASAero nozzle diameter at zero, though it indicated higher when using any reasonable nozzle exit diameter. I can share my methods and files in more detail with you if you'd like.

Firefox said:

Have you considered expanding and lengthening the inter-stage so you can put a boat tail on the sustainer for base drag reduction during the coast phase? It would ejected upon sustainer ignition so you could use a boat tail smaller than the aft end of the motor. I played around a bit with RASAero and Open Rocket today, and they generally agreed that a 141k (RAS) or 142k (OR) was possible by using a longer coast and a drag-reducing boat tail. This is leaving the RASAero nozzle diameter at zero, though it indicated higher when using any reasonable nozzle exit diameter. I can share my methods and files in more detail with you if you'd like.

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Makes sense... But I would think it would be more complicated to go this route and probably more expensive/labor intensive to build the transition. Might as well just stuff a bigger motor in the sustainer or booster at that point...

Firefox said:

Have you considered expanding and lengthening the inter-stage so you can put a boat tail on the sustainer for base drag reduction during the coast phase? It would ejected upon sustainer ignition so you could use a boat tail smaller than the aft end of the motor. I played around a bit with RASAero and Open Rocket today, and they generally agreed that a 141k (RAS) or 142k (OR) was possible by using a longer coast and a drag-reducing boat tail. This is leaving the RASAero nozzle diameter at zero, though it indicated higher when using any reasonable nozzle exit diameter. I can share my methods and files in more detail with you if you'd like.

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I'd love to see them. I am looking at using CTI motors and they have a tapered aft closure that could accomplish roughly the same thing. Seems a little simpler and would hold down on the weight issues as well as eliminate the need to track a third small component in recovery.

Both RASAero and Open Rocket take some fiddling to get them to simulate boat tail sustainer stages, which I've done in both cases. First, to maintain a good stability margin with the boat tail, I've lengthened the tip chord and span of the sustainer's fins a bit. Also note that I'm using a double-wedge profile on all fins in RASAero, in case you weren't.

With Open Rocket, there's no way to hide the boat tail inside the interstage, so it's hanging out in the wind. Considering the drag increase is minimal for the sake of simulation and the first stage is dropped a few seconds into flight, this is a reasonable approximation of the boost-coast-ignition aspect of the flight. I've adjusted the coast phase times for the two most promising flights, M1590-L265 and M2045-L945. Because the stage comprising the boat tail interrupts a ignition after burnout routine, they use ignition at T+ a set time after launch. The OR and RAS simulations have slightly different staging delays to optimize altitude in their respective sims; OR delays are a second or two shorter.

RAS Aero II doesn't like boat tails at all on anything but the sustainer, so I had to be a bit more clever here. There are two simulation files, one with a boat tail on the sustainer and a regular Mi with just the stretched interstage. The boat-tailed sustainer was used to determine velocity and altitude at S2 ignition. Then using those numbers, I added a slightly more powerful first stage motor to the modified Mi and adjusted the first stage weight to match the velocity and altitude at second stage ignition, except this time with no boat tail.

With the L265 motored upper stage, the sims agree pretty well, OR is about 2.5% lower than RAS. However, with the L945 upper stage, OR is 21% lower than RAS. If I had to guess, this difference is in the way OR handles the sustainer going M3 for several seconds.

I've attached the OR and RASAero files to this post. TRF doesn't like CDX1 files, so they're in the zipped folder.

View attachment 100K Project - Mi with Boattail.ork

View attachment Mi.zip

Very interesting. I would think that the boattail is going to get pretty hot, though, and the metals allowed for something like that will readily transfer heat to the airframe, softening the epoxy and ultimately causing the boat tail to come loose.

If I use Cesaroni motors, I can use the Pro 54 Tapered Aft Closure and achieve at least some semblance of a boattail with something designed for the heat. It probably would not get all of the same performance, but I would have a much lower risk of failure from heat or the higher speed.

I may need to turn 1/16" off the forward end of the closure so it will fit into the transition to the booster, but that should not have an adverse impact on the retainer since it is the threads that are most important in retaining the nozzle. Of course the other option would be to fabricate a section of airframe that slips around the outside of the sustainer airframe, which would not be that difficult to do.

I don't think I'm following your thinking, why would the boat tail get hot? The idea is for it to drop off at sustainer ignition so it benefits the rocket during the coast between booster burnout and sustainer ignition. You could build it from the same material as the rest of the airframe as far as I can tell.

Just reread this. Some questions:
Is it acceptable to eject the boat tail without a recovery system?
Can the boat tail be constructed of some sort of flammable material so that it can incinerate at ignition of the sustainer?
Would an essentially pressure-fitted boat tail be prone to drag separation?

Hypothetically, since it is not subject to near as much heat, it could be made from paper or phenolic and closed completely shut, essentially transforming the sustainer into a boosted dart until the second stage fires. Motor ignition could either burn through the boat tail (which would be nearly instantaneous), incinerating it or blow it off. Either way, a paper product would be biodegradable at the worst, or nothing but ashes at the best, and it should not cause damage if it hit something on the ground.

Another benefit is that it would contain a small amount of air that should be richer in O2 than what would normally be at that altitude. That could help with sustainer ignition.

Having it burn is a very bad idea, a risk of starting a fire on the ground.
A small Nomex/Kevlar chute can be put in the tailcone loosely and it will be tossed out by the tumbling.

M

MClark said:

Having it burn is a very bad idea, a risk of starting a fire on the ground.
A small Nomex/Kevlar chute can be put in the tailcone loosely and it will be tossed out by the tumbling.

M

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Just from my opinion, he's probably going to be launching this at Black Rock. If you can MANAGE to start a fire on black rock desert I'd be impressed.

MClark said:

Having it burn is a very bad idea, a risk of starting a fire on the ground.
A small Nomex/Kevlar chute can be put in the tailcone loosely and it will be tossed out by the tumbling.

M

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When this ignites, it will be 25,000 feet in the air. Not sure how long it takes for something like that to fall, but I am pretty sure the fire would be out by then.

EeebeeE said:

When this ignites, it will be 25,000 feet in the air. Not sure how long it takes for something like that to fall, but I am pretty sure the fire would be out by then.

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That's if the flight is nominal. If not, you don't want something combustible falling to the ground when you're also trying to keep track of other pieces. However, a biodegradable tail fairing might be doable.

Steve Shannon said:

That's if the flight is nominal. If not, you don't want something combustible falling to the ground when you're also trying to keep track of other pieces. However, a biodegradable tail fairing might be doable.

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Hmmmmm, A biodegradable tail fairing that can withstand high temperatures that's affordable. That's an interesting concept. The combustible one is even more interesting. Have it withstand high temps and then have it burn when thou'st wants it to. Kurt :wink:

ksaves2 said:

Hmmmmm, A biodegradable tail fairing that can withstand high temperatures that's affordable. That's an interesting concept. The combustible one is even more interesting. Have it withstand high temps and then have it burn when thou'st wants it to. Kurt :wink:

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As I understand the concept, it blows off when the sustainer motor ignites so motor heat is not an issue. There is no real "leading edge" to this component so it should therefore not be subject to much heat during the coast phase. Hypothetically it could be made out of paper, whose kindling point is 451 degrees F. The leading edges and the nose cone tip may get a lot hotter than that, but until the motor ignites, the aft end shouldn't.

Steve Shannon said:

That's if the flight is nominal. If not, you don't want something combustible falling to the ground when you're also trying to keep track of other pieces. However, a biodegradable tail fairing might be doable.

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We're talking about a paper tailcone that is 54mm in diameter and about 3-4" long. If there is a CATO at the pad, I'm pretty sure that there is going to be far more concern about extinguishing a lot of AP and a lot less concern about a smoldering cardboard section that is about the size of an ice cream cone that can be stamped out with a decent sized boot.

All that being said, this creates a lot more complexities in the design and the build. How do you keep the tail cone on at separation, when the rocket speed is about Mach 1.8? How does it stay on when the rocket approaches Mach 3? If I want to pursue a record, do I have to recover this thing which has no tracker, no chute, and in the desert would be the proverbial needle in the haystack? As I mentioned a couple times, the tapered CTI motor closure does narrow the diameter of the aft end. Not as much as a boat tail, but it does to a certain extent.

Sorry but I am thick sometimes and lost track. Why does the tailcone have to come off during this flight?

If its light and not structural how about making it out of paper as described and soaking it in a solution of boric acid like with recovery wadding to make it self extinguish if it starts to burn? Then let it flutter harmlessly to the ground.

Should be no more hazardous then motors spitting liners like EX motors seem to do on occasion and no gets in arms over that practice.

jderimig said:

Sorry but I am thick sometimes and lost track. Why does the tailcone have to come off during this flight?

If its light and not structural how about making it out of paper as described and soaking it in a solution of boric acid like with recovery wadding to make it self extinguish if it starts to burn? Then let it flutter harmlessly to the ground.

Should be no more hazardous then motors spitting liners like EX motors seem to do on occasion and no gets in arms over that practice.

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John, that's very good. That's what I would suggest.
The earlier idea to have it completely burn before landing would have (in my mind anyway) required the tailcone material to be able to burn at high altitude, to easily light when exposed to the sustainer's ignition, and to not extinguish when exposed to high air velocity. That's not just paper, but more akin to flash paper.

Working now on the first part of this effort which is to finish the design and build "Do." This will be a 29mm rocket 2-stage rocket with a PML Urethane conical nose cone (I cannot find anyone who sells a 29mm FG nose cone any more). It will have a FG airframe with G10 fins. I will fabricate an outer sleeve that will be glued to the transition and will hold the booster.

The sleeve will be two (maybe three) wraps of 6 oz. fiberglass, I will wrap an airframe with plastic as a mold, then tightly wrap the glass and epoxy mix (thinking of using RocketPoxy cut with alcohol) with plastic. I should be able to get a decent finish this way that can be further smoothed with more Rocketpoxy. I will taper the edges of the sleeve as much as I can, but this should be no more than 1/32" thick when it is done. The aft end of it will be glued to the transition.

The sustainer will be single deploy at apogee... Either a streamer or a very small chute. Making it dual deploy adds considerable weight (and in this case an extra ounce is "considerable"), and takes up a lot of additional room that is needed for the tracker, battery, and altimeter. Matbe if I am lucky I can take an old MD80 480i camera that I have and have it look out the altimeter vent hole. The guts of that including its battery is only about 0.25 oz.

The nose cone is solid urethane. This seems to be the strongest thing out there in this size and is designed for high speed high altitude flights of small rockets. It will need to be drilled and have a 1/4"-20 stainless rod inserted into the center. Primary reason is that the design needs nose weight, but the secondary reason is that it can also function as the tracker antenna. The sled I will use will have a bolt built in, and the tracker antenna wire will be soldered to it. I insert the sled through the payload bay and tighten the nose cone stainless rod to the sled bolt.

I'm thinking that a G10 or other FG sled will be strong enough to hold the payload bay together. The coupler is then bolted to the sled, using the threaded end of the eyebolt to also hold it in place. One bulkhead at the aft end of the coupler is all that is needed so the payload bay becomes about 29mm in diameter by approx. 6" long.

As I mentioned earlier, the electronics for the big rocket will be MARSA flight computers. For this and the next size up-, however, MARSA electronics will not fit, so I am thinking about using a Raven 3, which is accelerometer based, and also has the capability of igniting the sustainer. It is tiny and will fit inside with a Beeline tracker and a battery.

I will use an MT4 in the booster to separate the booster and sustainer at booster burnout. The booster motor will deploy its chute about 9 seconds later.

Finsim suggests that if the fins are attached with Rocketpoxy (Stated shear strength is 14,300 PIS, but people who have conducted their own experiments suggest it is more like 6,000, which is the number I used), the rocket should be good to about Mach 2.6. This will only top out at Mach 2.0 or so, so I should be in good shape.

Motor configuration is a CTI H255 to a CTI H255. Total NS is 632...99% of an I, so it should establish a TRA complex I record. There currently is none that I can see. Open Rockets sims to about 17,500'. RASAeroII sims to about 20,700'. I'm thinking it will be somewhere in between those two numbers.

This is its current look. 46" long, a little less than 2.5 lbs. loaded. Sustainer is 1.4 lbs. Thrust/weight ratio at launch is 23:1 and at sustainer ignition is a little over 40:1. If all goes well I will do a shakedown flight with some mid power motors this fall, then next spring I'll fly it at a major event somewhere at full strength.

I have a 29mm conical FG nose that was given to me, I'd be willing to give it to you.

patelldp said:

I have a 29mm conical FG nose that was given to me, I'd be willing to give it to you.

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That would be very nice of you.

I like the idea of the urethane NC. It's ablative without delaminating.

jderimig said:

Sorry but I am thick sometimes and lost track. Why does the tailcone have to come off during this flight?

If its light and not structural how about making it out of paper as described and soaking it in a solution of boric acid like with recovery wadding to make it self extinguish if it starts to burn? Then let it flutter harmlessly to the ground.

Should be no more hazardous then motors spitting liners like EX motors seem to do on occasion and no gets in arms over that practice.

Click to expand...

My thought was the opposite, John. Spray the inside of the tailcone with a spray adhesive. Sprinkle BP into it until there is a fine layer coating the entire interior. When the motor ignites, the tailcone would go off essentially like flashpaper. It wouldn't entirely vaporize, but the remaining pieces would fall harmlessly to the ground. Either way could work, and this one is a little more dangerous, although this would not lead to an explosion, but rather a flash of light since the BP isn't confined.

Steve Shannon said:

I like the idea of the urethane NC. It's ablative without delaminating.

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It will probably be subject to up to 500 degrees of heat even with this flight. Do you think it would survive?

I think any tail fairing, in order to have sufficient effect on airflow at transonic velocity will have to have some structural strength.
I don't think an internal coating of BP will have the effect you wish. Soaking the material with an oxidizer might. The BP coating would be easy and interesting to test though. I'd like to see it anyway.

EeebeeE said:

My thought was the opposite, John. Spray the inside of the tailcone with a spray adhesive. Sprinkle BP into it until there is a fine layer coating the entire interior. When the motor ignites, the tailcone would go off essentially like flashpaper. It wouldn't entirely vaporize, but the remaining pieces would fall harmlessly to the ground. Either way could work, and this one is a little more dangerous, although this would not lead to an explosion, but rather a flash of light since the BP isn't confined.

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Cool, instead of spray adhesive, make a paint of NC lacquer with meal powder (mortar and pestle BP) and paint the inside.

Papier-mâché with rosin paper and sodium silicate as the binder. Super light, cheap, sandable/finishable, disposable, biodegradable and not very flammable.
Get your sodium silicate at auto-parts store. Often disguised as a sealant for radiators. Aka - waterglass.

jderimig said:

Cool, instead of spray adhesive, make a paint of NC lacquer with meal powder (mortar and pestle BP) and paint the inside.

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That would work. the lacquer is flammable as well.

Igotnothing said:

Papier-mâché with rosin paper and sodium silicate as the binder. Super light, cheap, sandable/finishable, disposable, biodegradable and not very flammable.
Get your sodium silicate at auto-parts store. Often disguised as a sealant for radiators. Aka - waterglass.

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That could work, but I was thinking just use a section of 54mm BT. Cut 6 wedges to a point, and then taper in to make the cone. They can be glued together with carpenter's glue.

The one challenge I see with this is that adding a tailcone will reduce stability during coast because the tailcone extends the airframe. Stability will return once the cone is blown off. Will this cause an issue? If it does and the sustainer fins need to be larger, will the increased fin size negate most of the benefits of the tailcone?