# [Tech] DART Aerospike - Repost; Additional Info

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Gentlemen:

Repost and Additional Info on the DART Aerospike.

For Background a Repost:

For those who had not seen this previously, here is some information on the NASA-Dryden DART aerospike solid rocket flown at the Pecos County Spaceport in Texas. I was a co-principal investigator on this project.

Photos of the aerospike and the rocket can be found at:

You can also go to the medium or large jpeg photo sections and zoom in and check out the aerospike in detail.

The DART aerospike rocket is documented in a tech article authored by Scott Bartel and myself published in the August 2004 issue of High Power Rocketry Magazine (Vol. 35, No. 5). The tech article has lots of photos and complete documentation on the aerospike rocket. It's available as a back issue from High Power Rocketry.

The aerospike was built by Cesaroni Technology Incorporated (CTI). The aerospike retrofits onto a CTI O5100 motor case in place of the conventional conical nozzle.

Aerospike uninstalled performance is measured by taking the thrust coefficient of the aerospike and dividing it by the ideal thrust coefficient with ideal expansion (thus no divergence losses, throat losses, or under- or over- expansion losses). CF/CFideal is plotted versus the chamber pressure divided by the atmospheric pressure (Pc/Pa). Below is an example plot from a post some time ago on sci.space.policy by Kevin Ryan.

1.0 .----.----.----.----.----.----.----.----.----.----. | + T +T T + +/ +/ +/ +/ T +/ | T + / : + / | / 0.9 | / : / Area Ratio = 75:1 Nozzle | / nozzle length = 25% equivalent Efficiency | / conical : / 0.8 | / / Bell Nozzle | / + Aerospike (predicted) : / T Aerospike (test data) | / | 0.7 :----.--/-.----.----.----.----.----.----.----.----. | | | | | | | | 10 100 200 400 800 2000 4000 10000

Pressure Ratio: Pc/Pa

Where Nozzle Efficiency is CF/CFideal. Note that if the lines don't line-up in the plot above, check here for a possibly better version of the plot:

Sea Level Pc/Pa values for chamber pressures of 400 psia to 1,500 psia vary from 27 to 102. Near vacuum Pc/Pa values are in the 1,000 to

10,000 range. Note that the plot above has a log scale for Pc/Pa going out to Pc/Pa = 10,000.

Historical Rocketdyne annular (toroidal) aerospike performance data, and other aerospike performance data similar to the plot above typically show a delivered CF/CF ideal = 0.90 - 0.92 at operating conditions of Pc/Pa = 20 - 80.

How well did the centered Prandtl-Meyer all-external expansion DART aerospike perform? The DART aerospike delivered the following uninstalled performance in static test:

CF/CFideal = 0.97 at Pc/Pa = 25.5

Remember, all of the above is uninstalled performance, i.e., a uniform pressure field around the aerospike (Pa), with zero velocity (static conditions). Flow around the rocket in flight creates an initial flowfield in front of the aerospike which makes the installed performance different from the uninstalled performance; measurement of which was one of the key technical objectives of the DART aerospike rocket flights.

More on the inflight-measured installed performance in future posts, although I will mention that we did see a dip in installed performance at transonic Mach numbers, which had been predicted in many prior studies and expected from CFD predictions, but which many have wondered whether it would actually occur in flight.

Will the DART aerospike design hold the high level of CF/CFideal uninstalled performance (97% of ideal efficiency) all the way out to vacuum conditions (Pc/Pa = 1,000 - 10,000)? We had plans to do a hot fire test using a complete motor in a ground test facility at a simulated 100,000 ft altitude (Pc/Pa = 2,360), but it turned out that our "free" test was going to use up half our budget, so we had to drop the test.

Chuck Rogers snipped-for-privacy@aol.com

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A historical expert replied One small quibble: using the original 1960s terminology, this is a spike nozzle, not an aerospike nozzle. Aerospike was originally short for "aerodynamic spike" -- what you get when you truncate the spike and add some secondary flow into the middle to substitute for the lost length.

That said, the term *has* been applied more loosely in recent times... and regardless of details of terminology, it's great to see someone actually flight-test *any* sort of unconventional nozzle.

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nozzle, not an aerospike nozzle. Aerospike was originally short for "aerodynamic spike" -- what you get when you truncate the spike and add

some secondary flow into the middle to substitute for the lost length.

actually flight-test *any* sort of unconventional nozzle.

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The term "aerospike" in recent times has been more loosely applied to any spike-based altitude compensating nozzle, with or without spike truncation or base bleed. The Cal State Long Beach spike was essentially a full spike (small truncation at the end), with no base bleed, and it's been referred to in all accounts including AIAA and SAE magazines as an "aerospike".

Photo of Cal State Long Beach aerospike:

Technical Committee Highlights (see photo caption first page, on the second page see University Activities):

Often the term "aerospike" is defined by starting with a full spike, truncating the spike, and then making the truncated spike act like a full spike by adding "aero" effects via adding base bleed.

There's just one problem with this definition; you don't need base bleed to make a truncated spike perform like a full spike.

As part of the DART aerospike program we ran CFD for the 100% full spike, and 25% and 50% truncated spikes (25% and 50% by length of the full spike). We had excellent predicted performance, and excellent predicted altitude compensation, all with no base bleed. I also have some old historical Rocketdyne data which shows very little performance loss for a 25% truncated annular (toroidal) aerospike nozzle with no base bleed compared to 0.5% and 2.7% base bleed. The 0% base bleed,

0.5% base bleed, and 2.7% base bleed data are all very close, and many of the data points lay right on top of each other on the CF/CFideal versus Pc/Pa data plot.

Based on the CFD runs and the historical Rocketdyne data a truncated aerospike works fine without base bleed. Hence the problem in tying the definition of an aerospike to the presence of base bleed.

A 25% and 50% truncated spike altitude compensates by plume expansion and external "aero" effects. So does a 100% full spike. With base bleed not really needed, when does a 25% or 50% "truncated spike" become an "aerospike", or conversely, why shouldn't a full spike be called a "100% (non-truncated) aerospike"?

As I've stated, tying the definition of an "aerospike" to base bleed has problems, because you can skip the base bleed and still get good performance.

Technical definitions do change with time compared to the definitions in the 1960's. It will be interesting to see where this all goes.

Based on the above, I think it was certainly proper for the DART team to call the DART nozzle an "aerospike".

Chuck Rogers snipped-for-privacy@aol.com

Jerry Irv> >

length.

times...

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That's what *I* said... earlier in this very forum. :-)

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Mike:

I checked out some photos of your aerospike on your website. It's an older photo, but it is described as a true aerospike design with truncated tip and base bleed.

it also appears that the spike tip has very little truncation.

How much was your spike truncated (as a percentage of a full-length [100%] spike)?

With very little truncation of the spike tip, it appears to me that there would be no need for base bleed, even if it was effective (which as I posted earlier I don't think it is). The spike surface flow is almost done being turned to parallel to the freestream flow. Any base pressure effects over such a small area would be neglible. If the base bleed jet plumes out beyond the spike base area to try to get some aerodynamic effect, you're just going to get shocks at the end of the spike. This loss might be small because the base area is small, but again I just don't see any benefit.

A good test to perform would be a static test with your current truncated spike tip with base bleed, and then a full spike tip with no base bleed. You could compare the two thrust levels and see if the base bleed is having any effect.

Are you measuring chamber pressure in your ground tests? As I discussed in my Nozzle Thrust Coefficient tech article in the October

2004 and November 2004 issues of High Power Rocketry Magazine, you really need to measure chamber pressure (and make corrections to the measured chamber pressure) to accurately determine the nozzle thrust coefficient, and really figure out what's going on relative to nozzle performance. Although in the article I did discuss some techniques for using thrust stand static thrust data, versus making chamber pressure measurements, to track whether design changes are increasing or decreasing nozzle performance, or in this case to compare small truncation with base bleed to no truncation with no base bleed.

Chuck Rogers snipped-for-privacy@aol.com

B> >>One small quibble: using the original 1960s terminology, this is a > spike

length.

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in the 1960's. It will be interesting to see where this all goes.

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I was not following the discussion all that carefully, but the whole points eems to be that "aerospike advocates" like the cool name and do not want to give it up just because they have varied from the literal definition.

Why not rename it to [specific variant] [general term]?

That way nobody can complain about a definition to a term you coined!

Now three people have "thanked" me for posting this. This is rmr. Positive feedback MUST be evidence it was bad judgement to post :)

Jerry

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jerry, you lying sack! How could three people thank you for you posting the above, when they could not have possibly read you post, prior to you sending it?

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You are actually stupid, aren't you?

"" On Fri, 04 Mar 2005 05:17:34 -0800, Jerry Irvine

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So, how did three people read your post, prior to you posting it?

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Resolved.

You are actually stupid.

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As was posted:

Rather than the "literal" definition, people are actually referring to what would be best put as "the 1960's" definition.

As I stated, technical definitions do change with time.

As I posted, according to the AIAA Liquid Propulsion Technical Committee the Cal State Long Beach nozzle was an aerospike (AIAA Aerospace America Magazine, 2004 Liquid Propulsion Highlights);

Additionally, according to the AIAA Hybrid Propulsion Technical Committee the EAC hybrid nozzle was an aerospike (AIAA Aerospace America Magazine, 2004 Hybrid Propulsion Highlights); (I don't have a quick web link for this one)

The Cal State Long Beach aerospike had a small truncation, no base bleed.

The EAC hybrid aerospike had virtually no truncation, no base bleed.

So no "marketing", no "it sounds cool".

These were year-end report submittals by the AIAA Liquid Propulsion Technical Committee and the AIAA Hybrid Propulsion Technical Committee. And published in 2004, not the 1960's.

So I'd submit that it's pretty clear that in 2004 the AIAA Liquid Propulsion and Hybrid Propulsion Technical Committees consider a centerbody spike nozzle with little or no truncation, with no base bleed, to be an aerospike. I could probably find some SAE material which also lists these nozzles as aerospikes.

So the AIAA Technical Committees have spoken. These nozzles are aerospikes.

Chuck Rogers snipped-for-privacy@aol.com

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BATF has spoken. They were wrong.

TRA has spoken. SU motor manufacturing requires a LEMP. They were wrong.

You have spoken. All AT 18mm reloads are certified. You were "wrong".

Question authority. They seem imperfect.

I noted you snipped my suggestion. To simply coin more specific terms to address the obvious debate.

It worked for me: MRT

It worked for Mike Nelson: HPR magazine

It worked for Gary Rosenfield: Restricted Access.

:)

Jerry

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And this has what to do with [Tech] or aerospikes?

The best specific term is aerospike, because the "spike" "aero"-dynamically altitude compensates, whether it's a full or truncated spike. The nozzle outer wall is not a physical surface, it's an aerodynamic (plume) boundary.

Apparently relative to the current (2004) definition of an aerospike the two largest aerospace engineering organizations agree.

Chuck Rogers snipped-for-privacy@aol.com

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It defines you as a liar. I keep wondering what your professional colleagues would do if they knew your history of lying about such things?

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

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No I think he was talking about the people half way up his @&&..(:-)

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This isn't a [TECH] thread, however my suggestion to coin terms specific to a particular variant of Aerospike is directly on-topic. Anytime language can be made to conform to technical differences, communication is enhanced.

Any time regs can conform to industry practice, the "public is served".

Cool.

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Shhhhhh.

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In jerry's case, there's no distinguishable difference between his head and his ass.

They're both full of the same smelly crap.

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