RCS aerospike nozzles

[Cameron Anderson]

I just got notification that my aerospike nozzles shipped. I know it's more of a cool factor than anything truly performance enhancing, but I think when used as sustainer nozzles, aerospikes could result in increased performance at altitude on long burn motors. Anyone else order them, and if so, what motor are you planning on using them with?

My first planned flight is an MD 54 to 54 two-stage...L935 to L1090 with the aerospike.

 

[AeroTech]

They are best used with cooler burning propellants with short burn times. The aerospike nozzle is affected by heat more than a traditional nozzle.

 

[Cameron Anderson]

They are best used with cooler burning propellants with short burn times. The aerospike nozzle is affected by heat more than a traditional nozzle.

Great to know, thanks.
Specifically for the 54mm 2800 and 1706 cases, what reloads would you recommend for use with the aerospike?

 

[WillMarchant]

I’d completely forgotten about it until I got the email yesterday...

 

[troj]

Mine showed up in the mail today!

For those wondering what this is, it's a new nozzle that Aerotech helped fund via an Indiegogo Crowdfunding campaign. The nozzles shipped to backers over the past few days and are now available on the RCS website. Note that no motors are currently certified with these, so using them makes your motor a research motor.

 

[Cameron Anderson]

They are best used with cooler burning propellants with short burn times. The aerospike nozzle is affected by heat more than a traditional nozzle.

Got my aerospikes today...there inserts labeled 3, 4, and 5. I assume 3 is for a 0.422 nozzle, 4 is 0.555 nozzle, and 5 is for 0.625 nozzle, can you confirm?

Also, they look amazing!

 

[FredA]

I guess I don't see the point, especially since they are NOT suitable for long burn motors.
If you burntime is short, the pressure span is small, so what's the point beyond the novelty?

 

[Cameron Anderson]

It is just novelty at this point. Even if I light a motor at 20,000 MSL moving at mach 1.50, a 2 second burn wouldn't experience enough pressure change to make an aerospike beneficial. But it's a first step towards more reliable aerospikes that could handle long-burn motors where the benefit is more pronounced.

 

[dhbarr]

I bought in because I want to fly an Aerospike, and this is by far the cheapest way to do so.

Only weeks after I ordered did I realize that I was probably someday going to marry one to my AT hybrid.

 

[aerostadt]

I might add that I not sure that an axi-symmetric aerospike flow will benefit like an aerospike 2-D planar flow, which was proposed for the Venture Star and the X-33. I know of one analyst who looked at axi-symmetric CFD runs for a possible air-launched aerospike tactical motor years ago and results were not conclusive. To date I know of no tactical missile that uses the axi-symmetric nozzle.

 

[ksaves2]

It’s the cool factor man, the kewl factor!!!! $36.00 for a single use nozzle. Ummm, ok.
Kurt

 

[Tim51]

Curious - do they make any visible difference to the flame or plume?

 

[aerostadt]

Curious - do they make any visible difference to the flame or plume?

The flow pattern will definitely be different, because the outside flow (or plume) expands to ambient with no surface to constrain it.

I tend to think that the axi-symmetric aerospike nozzle is not going to perform as well as a 2D planar nozzle. Look at the forward projected area that the nozzle has to offer. The coefficient of thrust (performance of the supersonic portion of the nozzle) depends on both the forward projected area and the pressure distribution. Putting the issue of the pressure distribution aside, let's just talk about projected area. Just eye-balling the projected area of an axi-symmetric nozzle shows the area to be wanting, because it is based on the "inner" radius of a circle of an annular throat. The projected area of conventional divergent supersonic nozzle is based on the outside radius, which is naturally larger.

 

[aerostadt]

This could really lay the grounds for a very interesting science project. Fire and measure the thrust for the aerospike motor. Then measure the thrust for an equivalent convergent/divergent nozzle motor that has the same throat area and compare the performance. On a theoretical basis 1-D compressible flow will give a fairly accurate prediction for a conventional convergent/divergent nozzle. Not so, for an axi-symmetric aerospike nozzle, because the flow is 3D. This means that a more complicated analysis like CFD is required.

 

[aerostadt]

I looked at an Aerotech ad for the aerospike nozzle and I must admit the "cool" factor is dfinitely there. Also, there are cross-sectional drawings on the TRF Open Aerotech thread. Just eye-balling things it looks like the design has a fairly large forward projected area for the center aerospike. This accomplishment might be at the cost of having a smaller gap for the annular throat, which will have more area for skin friction. Of course, the spike is truncated. There are several ways to handle the throat. Aerotech has decided to use an annular throat. Other designs use separate "circular" jets aimed at the spike, The X-33 did this. I have also seen a proposed tactical missile with finite circular jets aimed at the spike.

https://www.rocketmotorparts.com/54mm_Aerospike_Nozzle/p1577809_20383178.aspx
A simple but more qualitative way of comparing the performance of the aerospike to a conventional divergent/convergent nozzle would be to take two different motors with the same chamber pressure time-history and the same throat area and comparing the measured altitude. I think this has been done in the HPR community more than 10 years ago. Some rough information was even reported in Aviation Week. I also think a private HPR company looked at comparable altitudes. I think results were inconclusive.

 

[dhbarr]

In a sense, the medusa is a plug-cluster aerospike. Actually it could be converted fairly easily with a graphite spike....

 

[aerostadt]

In a sense, the medusa is a plug-cluster aerospike. Actually it could be converted fairly easily with a graphite spike....

I think of the medusa nozzle simply as a bunch of convergent/divergent nozzles each with its own throat and no external expansion after the divergent section. It is nothing like an aerospike.

However, yes, if you had a ring of a finite number of circular throats (with little or no divergent section) slightly aimed at the central inner spike.

 

[AeroTech]

We have tried K550W and K1100T 54/1706 reloads with the Aerospike. Both were extremely hard on the nozzle. This is why we recommend short burn or cooler burning propellants. I would not recommend putting one in a 2800 motor unless you were using Black Max or similar.

Great to know, thanks.
Specifically for the 54mm 2800 and 1706 cases, what reloads would you recommend for use with the aerospike?

 

[aerostadt]

We have tried K550W and K1100T 54/1706 reloads with the Aerospike. Both were extremely hard on the nozzle. This is why we recommend short burn or cooler burning propellants. I would not recommend putting one in a 2800 motor unless you were using Black Max or similar.

The 54/1706 case is fairly long compared to what I have. I have a 54/852 and a 54/1280 case.

 

[AeroTech]

Here’s something we’re going to try with Super Thunder:

 

[FredA]

This could really lay the grounds for a very interesting science project. Fire and measure the thrust for the aerospike motor. Then measure the thrust for an equivalent convergent/divergent nozzle motor that has the same throat area and compare the performance.

I suspect motor-to-motor inconsistencies will swamp your data.

 

[manixFan]

"Experimenters should consider the use of short burn and cooler burning propellant configurations at pressures no greater than 500 PSI"

So pretty much the opposite of enhanced performance.


Tony

 

[Banzai88]

I suspect motor-to-motor inconsistencies will swamp your data.

"Experimenters should consider the use of short burn and cooler burning propellant configurations at pressures no greater than 500 PSI"

So pretty much the opposite of enhanced performance.


Tony

Then it would seem like we're looking at a 'difference' without much of an impact.....except maybe a higher cost due to the different nozzle. Other than that, likely, as in most things commercial, the cheapest solution will prevail on it's own.

Anyone fired off one of these things yet, or has this all been an elaborate thought experiment with a cool souvenir?
Is there any difference in how the flame looks? Video?

 

[5x7]

Here’s something we’re going to try with Super Thunder:
View attachment 432743

I love the core on that, you could get lost in it.

 

[AeroTech]

They are K2050ST grains, they need a big core.

I love the core on that, you could get lost in it.

 

[KenRico]

Here’s something we’re going to try with Super Thunder:
View attachment 432743

Goody ! I have a 54/852 and this looks even more fun than my other favorite (secret!) J180T .

Right now my Favorite propellants are: Propellant X , Super Thunder, Metalstorm, Mojave Green & Dark Matter ..and Non-Hazmat required reloads

 

[aerostadt]

I suspect motor-to-motor inconsistencies will swamp your data.

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.

 

[Theory]

aerospike or not, i REALLY dig the idea of a J1000 in the 54/852 case!!!!

 

[aerostadt]

I just got notification that my aerospike nozzles shipped. I know it's more of a cool factor than anything truly performance enhancing, but I think when used as sustainer nozzles, aerospikes could result in increased performance at altitude on long burn motors. Anyone else order them, and if so, what motor are you planning on using them with?

My first planned flight is an MD 54 to 54 two-stage...L935 to L1090 with the aerospike.

There is actually merit in Cameron's first post in this thread. In principle an aerospike nozzle could be better for an upper stage at altitude, where the ambient air pressure is lower, even if the motor is not long burning. This is aside from the other practical considerations of using a lower performance, lower burning temperature, less erosive propellant that have already been mentioned. The reason is that the standard AT convergent/divergent nozzles has an area-ratio that is designed for near sea-level performance. There will be an increase in thrust at higher altitude for that standard nozzle, because of the increase in pressure-thrust, but the increase in momentum thrust will not be there, because the area-ratio is not optimized for the higher altitude. In principle the aero-spike nozzle is optimized for momentum-thrust at all altitudes, because the external plume adjusts to any back-pressure.

 

[manixFan]

There is actually merit in Cameron's first post in this thread. In principle an aerospike nozzle could be better for an upper stage at altitude, where the ambient air pressure is lower, even if the motor is not long burning. This is aside from the other practical considerations of using a lower performance, lower burning temperature, less erosive propellant that have already been mentioned. The reason is that the standard AT convergent/divergent nozzles has an area-ratio that is designed for near sea-level performance. There will be an increase in thrust at higher altitude for that standard nozzle, because of the increase in pressure-thrust, but the increase in momentum thrust will not be there, because the area-ratio is not optimized for the higher altitude. In principle the aero-spike nozzle is optimized for momentum-thrust at all altitudes, because the external plume adjusts to any back-pressure.

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


Tony