RCS aerospike nozzles

[Charles_McG]

This is a good point and it might be why previous studies to investigate the axi-symmetric aerospike for commercial HPR were inconclusive. A way around this statistical variation would be to do a minimum number of trials, perhaps, 6 trials for example. At $36 a pop for the AT aerospike would be expensive, but it could be done.

You’d have to do some trials to see the actual variability before you can set the real number of tests. There’s a Power of the Test formula that relates the size difference you are trying to find - and what certainty, the standard deviation (perhaps standard error, I’ve forgotten) and the number of replicates.

 

[aerostadt]

I can think of another benefit for aerospike nozzles. Perhaps, this is a stretch, because I don't know how badly the Aerotech aerospike gets beat up during a firing. In general in conventional convergent/divergent nozzles the highest erosion is at the throat. This means that the area ratio actually decreases during the burn and consequently the performance also decreases. However, for an aerospike nozzle it is not obvious that the performance decreases, because the area ratio no longer has any meaning, because the expansion is external. A larger throat may mean that a longer spike is needed and I don't know the role that the spike plays in this situation.

 

[Cameron Anderson]

But not in practice with this particular version. The limitations are just too onerous to possibly make up for any improvement in efficiency.


Tony

Maybe, maybe not. Let's fly it an see.

 

[aerostadt]

I bought the Aerotech aerospike nozzle yesterday. It will be interesting to see what it looks like. I am looking forward to hearing the results of the Aerotech J1000ST motor.

 

[Banzai88]

Anyone fire off one of these things yet?

Does it look like this?

 

[aerostadt]

Anyone fire off one of these things yet?

Does it look like this?

That is really cool !! Up close you can see that the flow pattern is very different than a conventional convergent/divergent nozzle, but from far away I don't think anyone could tell the difference in the plume. Aerotech was talking about trying there aerospike nozzle with their own special J1000, but I never heard anything about their results.

 

[prfesser]

I can think of another benefit for aerospike nozzles. Perhaps, this is a stretch, because I don't know how badly the Aerotech aerospike gets beat up during a firing. In general in conventional convergent/divergent nozzles the highest erosion is at the throat. This means that the area ratio actually decreases during the burn and consequently the performance also decreases. However, for an aerospike nozzle it is not obvious that the performance decreases, because the area ratio no longer has any meaning, because the expansion is external. A larger throat may mean that a longer spike is needed and I don't know the role that the spike plays in this situation.

Although the aerospike does not have a conventional throat, it has three narrow arcs through which the hot gases pass. The area ratio does have meaning for an aerospike; Kn = (area of burning propellant) / (area of the arcs). I think these arcs would erode just as a nozzle throat does...though how much they erode is a question that needs an answer. Anyway, that erosion would cause area ratio and chamber pressure to decrease during the burn (unless a rather progressive grain shape is used) which would decrease thrust.

Perhaps thrust would not decrease as much as with a conventional nozzle, as nozzle expansion is no longer a factor (maybe?). As you said, it depends on how badly the aerospike is beat up by exhaust gases. The exit cone of a conventional phenolic nozzle isn't greatly eroded by the expanding gases, so maybe the performance of the cone would not be impaired significantly.

Best -- Terry

 

[Banzai88]

Although the aerospike does not have a conventional throat, it has three narrow arcs through which the hot gases pass. The area ratio does have meaning for an aerospike; Kn = (area of burning propellant) / (area of the arcs). I think these arcs would erode just as a nozzle throat does...though how much they erode is a question that needs an answer. Anyway, that erosion would cause area ratio and chamber pressure to decrease during the burn (unless a rather progressive grain shape is used) which would decrease thrust.

Perhaps thrust would not decrease as much as with a conventional nozzle, as nozzle expansion is no longer a factor (maybe?). As you said, it depends on how badly the aerospike is beat up by exhaust gases. The exit cone of a conventional phenolic nozzle isn't greatly eroded by the expanding gases, so maybe the performance of the cone would not be impaired significantly.

Best -- Terry

But would any of that matter enough to make any significant difference or impact at the scale of motors that we're using?

At what point is size or power or application does this become an advantage?

 

[prfesser]

But would any of that matter enough to make any significant difference or impact at the scale of motors that we're using?

I very much doubt it.

At what point is size or power or application does this become an advantage?

At a guess, significantly larger than the largest amateur solid motor made so far. At some point the exit cone of a conventional nozzle is heavier than an aerospike, though I don't know what that point is. Where an aerospike makes a difference is in a high-altitude (decreasing atmosphere) flight that is under power most of the time. At high altitudes and low air pressure, the aerospike should become more efficient due to lack of over- or under-expansion.

All just my opinion.
Terry

 

[aerostadt]

One of the nice things about the video in Post#35 is that it shows the exhaust diamonds in the plume downstream of the aerospike. This means that the flow is supersonic and working the way it should. Consequently the flow along the spike is exerting high pressure on the cone. I am thinking that this is not an aluminized propellant and therefore the flow is quite visible. Actually, there is a situation in large professional solid rocket motors (longer burn-times) where aluminized propellants can produce extra erosion in the divergent nozzle section. The small smoke-like aluminum oxide particles follow the gas flow well, after the throat and do not impinge on the divergent nozzle surface. However, the larger aluminum oxide particles have more inertia and impinge on the nozzle surface like a sand blaster. The impingement angle can clearly be seen post-fire.

 

[Rob702Martinez]

How are these held/put together?

 

[AlphaHybrids]

This is an aerospike that I developed and tested a lot in a hybrid.

https://alphahybrids.blogspot.com/2008/08/for-those-about-to-rock.html
Edward

 

[Cameron Anderson]

I have two AT K1100T's in going to fly next year the same day in the same airframe...one with the aerospike, one without. I figure that would be a good comparison of performance.

 

[Walter Longburn]

I have two AT K1100T's in going to fly next year the same day in the same airframe...one with the aerospike, one without. I figure that would be a good comparison of performance.

I suppose you remember this post?

We have tried K550W and K1100T 54/1706 reloads with the Aerospike. Both were extremely hard on the nozzle.

Nevertheless I still look forward to hearing the results.

 

[AlphaHybrids]

I have barely noticed any difference on the test stand between a convergent/divergent nozzle and an aerospike. They were similar and if I didn't know each thrust curve/pressure curve was, I wouldn't know which was which. I did 10 of each as a comparison in 2007. These hybrids had no metals and did not experience erosion on the nozzles.

Edward

 

[Cameron Anderson]

I suppose you remember this post?
Nevertheless I still look forward to hearing the results.

I pointedly asked Aerotech which reloads they recommended and they were suspiciously silent. I think they only tested those two reloads and lack any real data to offer an opinion. They said don't use hot loads and don't use long-butning loads...how long is long? Two seconds, 4?
I went with the K1100 because while it was hard on the nozzle, it at least survived the firing.

 

[RGClark]

In regards to the heating issue with the aerospike, could they be made of ceramics which can withstand higher temperatures?
Another possibility would be to use tungsten which has the highest melting point for metals.

But there is another approach to accomplishing the same thing as the aerospike. The aerospike is a form of altitude compensation, which means the nozzle area ratio increases as the altitude increases and air density decreases.

But we can also do this by making the nozzle opening get larger as the altitude increases. You would use an ablative nozzle that burned off gradually from the inside during the burn.

An advantage here is the burning nozzle material could contribute to the thrust. In fact it could even be made of the same material as the propellant, though it would then need an outer casing just like the motor.

But there are disadvantages. One is that since the nozzle is burning off it would have to be quite a bit thicker than a usual nozzle in order to have a large opening by the end of the burn, which means it would be quite a bit heavier. This might subtract from any benefit you would get from the altitude compensation because of the heavier weight.
Another disadvantage of the large nozzle is that on launch from the ground this would produce large air drag, which again might detract from any benefit of the altitude compensation.

Bob Clark

 

[RGClark]

I have barely noticed any difference on the test stand between a convergent/divergent nozzle and an aerospike. They were similar and if I didn't know each thrust curve/pressure curve was, I wouldn't know which was which. I did 10 of each as a comparison in 2007. These hybrids had no metals and did not experience erosion on the nozzles.

Edward

You probably wouldn’t notice much difference on the ground. The advantage of the aerospike is its high altitude, low air density performance.

There is a way of simulating high altitude, near vacuum performance on the ground used by space agencies and aerospace companies:

https://www.techbriefs.com/component/content/article/tb/tech-exchange/nasa-tech-needs/5522
But I don’t know if this can be done cheaply by amateur experimenters.

Bob Clark

 

[FredA]

Easy to see --- set the ambient pressure in Burnsim and run a few sims....
Not until you get above 10k MSL will see any noticeable effect.

For example - for a randomly chosen 4G75 motor:
Sea Level = 14.7 PSI = 1.96"
4k MSL= 12.7PSI = 2.06"
10k MSL= 10PSI = 2.23"
27k MSL = 5PSI = 2.84"

All of this will probably be lost in the +/- 10% variation of hobby motor performance.

I optimize my motors for the 10k MSL number.
I launch at ~4k MSL so 10k is just 6k off the pad and is mid-burn on most flights.
DO NOT USE the 14.7PSI default as your expansion will always be wrong.

 

[RGClark]

Thanks for that. Can BurnSim calculate it for very high altitudes ca. 100k? According to that NASA Stennis article the air pressure is about 0.16 psi., easy to remember because it’s about 1/100th sea level pressure(the relation between altitude and air density is not linear.)

Bob Clark

 

[FredA]

Continuing on - with the same motor:
At 1PSI - Burnsim indicates 5.12"
At 0.16PSI Burnsim indicates 10.27"

 

[FredA]

Clearly an Aerospike should payoff at high altitudes.
Note that the above expansions are for a 4G75 big L motor.
Achieving 5 inches of expansion is not possible on a 3-inch motor.....

Trying one on a sustainer might be beneficial, but I would only be interested if it could also survive a long burning motor suitable for a sustainer.

 

[RGClark]

Yes. That is the key advantage of the aerospike. You would not need the nozzle to actually be that wide. The aerospike accomplishes it by its unique shape.

Bob Clark

 

[Jacob Ritzke]

Not to reactivate an old thread, but I flew my aerospike today. Flew perfectly.

 

[aerostadt]

Somewhere (maybe it was on the TRF AeroTech thread) AeroTech said that they are releasing a reload J615ST-20A RMS to be used for their aerospike nozzle and the 54/852 case. So far, I have not been able to find this reload on the Wildman Rocketry or Apogee motor list. I suspect that the demand for this reload will not be very high. Also, the 2022 flying year has not started, yet. Perhaps, I will check with my local club motor vendor in the Spring.

 

[jimzcatz]

Not to reactivate an old thread, but I flew my aerospike today. Used a 54/426 case with an I229T motor kit. Flew perfectly.

That is not a certified load. to date there is only one certified Aerospike load, the J615. It is my understanding that one cannot just replace the nozzle in a standard load with an aerospike and use it a a non-research/NAR launch.

 

[Jacob Ritzke]

Somewhere (maybe it was on the TRF AeroTech thread) AeroTech said that they are releasing a reload J615ST-20A RMS to be used for their aerospike nozzle and the 54/852 case. So far, I have not been able to find this reload on the Wildman Rocketry or Apogee motor list. I suspect that the demand for this reload will not be very high. Also, the 2022 flying year has not started, yet. Perhaps, I will check with my local club motor vendor in the Spring.

I too heard about this certification, but I haven't really seen much else about it online.

 

[tfish]

Not to reactivate an old thread, but I flew my aerospike today. Flew perfectly.

Somewhere (maybe it was on the TRF AeroTech thread) AeroTech said that they are releasing a reload J615ST-20A RMS to be used for their aerospike nozzle and the 54/852 case. So far, I have not been able to find this reload on the Wildman Rocketry or Apogee motor list. I suspect that the demand for this reload will not be very high. Also, the 2022 flying year has not started, yet. Perhaps, I will check with my local club motor vendor in the Spring.

https://www.rocketryforum.com/threads/new-motors-certified-oct-16-2021.168936/

Tony

 

[FredA]

Interesting Burn #2 - any notion of the cause for the 30% jump in thrust -- way outside the +/-10% of nominal.

 

[AeroTech]

Somewhere (maybe it was on the TRF AeroTech thread) AeroTech said that they are releasing a reload J615ST-20A RMS to be used for their aerospike nozzle and the 54/852 case. So far, I have not been able to find this reload on the Wildman Rocketry or Apogee motor list. I suspect that the demand for this reload will not be very high. Also, the 2022 flying year has not started, yet. Perhaps, I will check with my local club motor vendor in the Spring.

This is going to be a 2022 release.