Hybrids 2024

[G_T]

Hell yeah. I'll check out the vids. Are micro hybrids any simpler? Or just more convenient because size?

I'm in the US unfortunately I'm a member of MDRA, and they have a large club so there is bound to be someone flying hybrids. I've only see solid rockets there though... I'll have to check if there are any club rules or restrictions to be safe.

If you are going to be at the upcoming big Potter launch, look me up. I'll be bringing THRP-1 to fly.

Gerald

 

[sjsyracuse]

For the most part this seems to be the case. For something like paraffin you usually have the opposite problem as Paraffin's ideal O/F ratio with nitrous for example is like 9:1, but it regresses extremely quickly. For Oxygen, the regression rates are usually faster than with N2O so it somewhat offsets the lower required O/F ratio.

Thanks, Drew. It seemed to me that the Regression Rate of, well, pretty much anything, had to be greater with GO2 than with N20, Oxidizer pressures and flow rates, and Tchamber, being equal. (I think that I got that right!?!?)

The following is from the paper than cfb_rolley found, referenced, and sent earlier::



The numbers, 2.0, 2.7, 4.3, etc. relate the distance in mm from the Gaseous Oxidizer Source to the POM Surface being combusted - tested for Regression Rate. I can look up the Pressure; the Oxidizer Flow Rate (velocity, here) was 90 cm/sec. But, the important thing here - and the reason I wanted to show you this - is that in GO2, the POM Regression Rate at 2.0 mm is 2.25 times the POM Regression Rate in N2O.

I guess that it's no surprise that it's greater; and perhaps it's no real surprise that it more than 2x greater.

 

[G_T]

Just keep in mind that GOX, O2 etc have more critical regression rates than monopropellants such as N2O and H2O2. You can be off by quite a bit with these latter two and still get decent behavior and performance. For the former you want to be pretty close.

CO2 is an example of an oxidizer with very narrow O:F ratio requirements (with appropriate heavily metalized fuel). That makes it a possible but impractical oxidizer. Performance is pretty poor anyway so nobody has bothered with it that I'm aware of. But it is the safest oxidizer I know of. I admit to being tempted to make one someday for the novelty factor. Performance should be closer to black powder motor performance.

N2O doesn't need any fuel you just have to get it lit and prevent it from consuming the combustion chamber. On the other end of the scale, optimal O:F can be as low as 3:1 with at least one fuel, without even adding any oxidizer to the fuel. Since most any fuel is denser than N2O unless you really chill it, it is worth considering fuels requiring low O:F as a way of increasing the overall effective, call it system density impulse - How much total impulse you can get out of your motor divided by total weight including the fuel and oxidizer.

Too bad all the other nitrous oxides have significant issues.

Low O:F ratio fuels and higher density fuels allow for a more compact motor for the same total impulse, thereby shaving hardware mass. So does chilling the nitrous, if you can still get it lit.

Gerald

 

[cfb_rolley]

Sorry to change topics because this has been a killer read recently, but I’ve encountered a bit of a problem.

My club is looking in to purchasing ground support equipment for flying Contrail hybrids but a problem we’ve encountered is what flyers are going to use for ignition? We can’t get pyrodex pellets in Australia, and for the other option of using a piece of AP propellant, I have a couple of aerotech D15 24mm reload that I could use for that, and there is no replacement source for these small reloads now, only 29mm and up and the cost and wait time is nuts.

Soooo, any other ideas of what could be used instead of the pellets?

 

[OzHybrid]

Sorry to change topics because this has been a killer read recently, but I’ve encountered a bit of a problem.

My club is looking in to purchasing ground support equipment for flying Contrail hybrids but a problem we’ve encountered is what flyers are going to use for ignition? We can’t get pyrodex pellets in Australia, and for the other option of using a piece of AP propellant, I have a couple of aerotech D15 24mm reload that I could use for that, and there is no replacement source for these small reloads now, only 29mm and up and the cost and wait time is nuts.

Soooo, any other ideas of what could be used instead of the pellets?

I'll PM you with a working epoxy formula.

 

[OzHybrid]

Preheater grain mould. Create your own size preheater grain and cast a standard epoxy-based preheater formula grain into it.
Change the sizes to suit yourself....

 

[cfb_rolley]

Rad, thank you. Still hoping I can find something off the shelf though to make it easier for club members to get in to hybrids. I get the impression that since it’s a big investment, the club would be apprehensive about buying the equipment without knowing that some people will commit to it. I’ve paused my own equipment purchases for now just in case they go ahead with it, but if not I’ll just keep going and bring my own along.

 

[OzHybrid]

Rad, thank you. Still hoping I can find something off the shelf though to make it easier for club members to get in to hybrids. I get the impression that since it’s a big investment, the club would be apprehensive about buying the equipment without knowing that some people will commit to it. I’ve paused my own equipment purchases for now just in case they go ahead with it, but if not I’ll just keep going and bring my own along.

Is this QRS?
In the US, you'd use a slice of White Lightning from an appropriately sized reload, and I've done that in the past. I've also done cast preheaters grains and they work just the same. These days you'd have to sell your first born to buy a reload in OZ.
The Rattworks M900 uses a slice of WhiteLightning 54mm reload. If you could buy one, it would take 6 months to get here.
To make it takes 5 mins max. plus curing time. The moulds make it super easy.

 

[cfb_rolley]

Is this QRS?
In the US, you'd use a slice of White Lightning from an appropriately sized reload, and I've done that in the past. I've also done cast preheaters grains and they work just the same. These days you'd have to sell your first born to buy a reload in OZ.
The Rattworks M900 uses a slice of WhiteLightning 54mm reload. If you could buy one, it would take 6 months to get here.
To make it takes 5 mins max. plus curing time. The moulds make it super easy.

Yeah it’s QRS. I’m happy to make a stack of preheaters myself it’s just that I’m just not certain if a licence would be required for that under QLD laws or if making our own preheaters would be a dealbreaker for the club, can’t imagine it would be if it’s allowed though.

 

[OzHybrid]

Yeah it’s QRS. I’m happy to make a stack of preheaters myself it’s just that I’m just not certain if a licence would be required for that under QLD laws or if making our own preheaters would be a dealbreaker for the club, can’t imagine it would be if it’s allowed though.

Mixing chemicals and burning them is not technically prohibited unless you make an explosive. Proving that what you're making is not an explosive is another matter. The formula I gave you is not shock sensitive and burns slowly, but consistently for preheating the plastic grain and melting through the fill line. it's an igniter formula, not explosive. It's no more dangerous than a box of matches. In fact you could cut the heads off a box of RedHeads and fill the mould. Problem solved. Throw a little bit of steel wool in as a bonus booster.

 

[Aeva]

If you are going to be at the upcoming big Potter launch, look me up. I'll be bringing THRP-1 to fly.

Gerald

Haven’t been there yet, but will do!!

 

[cfb_rolley]

it's an igniter formula, not explosive.

Ahhhh I see! That does make sense now, I know there’s a provision for that which makes it fine to make igniters under our laws. might make a few real small discs and see if they work in the micro for that too.

 

[OzHybrid]

Ahhhh I see! That does make sense now, I know there’s a provision for that which makes it fine to make igniters under our laws. might make a few real small discs and see if they work in the micro for that too.

 

[OzHybrid]

Yep. Works as that and can be easily machined.

 

[hybridfreak]

Had a great day testing my motors yesterday, forgot an SD card reader so I only have a very basic "screenshot" right now...

That's the 54mm with 205mm / 8" printed ABS grain. 450g / 1lb of nitrous burned a tad too much ABS for an average O/F of 4,9, producing 1050Ns at an ISP of 195. Pretty good for the first iteration, more to come

I'll post more data and video once I get home!

 

[sjsyracuse]

Just keep in mind that GOX, O2 etc have more critical regression rates than monopropellants such as N2O and H2O2. You can be off by quite a bit with these latter two and still get decent behavior and performance. For the former you want to be pretty close.

Thanks!! I think that this is an important point. I do remember reading that, with N2O and certain simple polymers (PE, HDPE, PP, PS, PC, PMMA - if I recall) the relationship b/w O/F Ratio and Isp is a fairly smooth curve; no sharp rises or fall offs; some decent (forgiving) plateaus.

With Oxygen, however, these curves are, well, less forgiving; the plateaus, where they exist, are, well, not as wide re O/F. I'll see if I can find the graph I'm seeing in my mind and describing so poorly, here!!!

 

[sjsyracuse]

CO2 is an example of an oxidizer with very narrow O:F ratio requirements (with appropriate heavily metalized fuel). That makes it a possible but impractical oxidizer. Performance is pretty poor anyway so nobody has bothered with it that I'm aware of. But it is the safest oxidizer I know of. I admit to being tempted to make one someday for the novelty factor. Performance should be closer to black powder motor performance.

Your thought is to catalytically, or thermally, decompose the CO2, to get the 'free' O2 for use, in the chamber, I presume, as an Oxydizer?

If I recall, CO2 decomposes - disassociates, actually - into CO + O; or perhaps it's CO + O2. And that's thermally. I don't know about catalysis!

If this worked, one benefit is that CO is a super light MW, stable species to exhaust!! That, and H2O, of course.

I know that I had to read this twice to 'get it,' conceptually.

 

[sjsyracuse]

That's the 54mm with 205mm / 8" printed ABS grain. 450g / 1lb of nitrous burned a tad too much ABS for an average O/F of 4,9, producing 1050Ns at an ISP of 195. Pretty good for the first iteration, more to come

I'll post more data and video once I get home!

Nice Shot!!! Thank You for sharing!!!!

This is N2O + ABS, with an O/F of 4.9, Yes!?

May I ask the Pchamber and the ~ Tchamber - if you know or can estimate these!?!?

 

[rocket_troy]

Your thought is to catalytically, or thermally, decompose the CO2, to get the 'free' O2 for use, in the chamber, I presume, as an Oxydizer?

If I recall, CO2 decomposes - disassociates, actually - into CO + O; or perhaps it's CO + O2. And that's thermally. I don't know about catalysis!

If this worked, one benefit is that CO is a super light MW, stable species to exhaust!! That, and H2O, of course.

I know that I had to read this twice to 'get it,' conceptually.

CO2 can't be catalytically decomposed to my understanding. It's a product of combustion like H2O. Both can be used as oxidizers, but it requires lots of energy to decompose and you need a fuel with very low electronegativity to get a nett energy liberation from combustion. Mg has been proposed as a fuel for CO2 for Mars based systems, but performance isn't great. Lots of condensed phase products and what gases there are, are heavy.

TP

 

[sjsyracuse]

Thanks!! I think that this is an important point. I do remember reading that, with N2O and certain simple polymers (PE, HDPE, PP, PS, PC, PMMA - if I recall) the relationship b/w O/F Ratio and Isp is a fairly smooth curve; no sharp rises or fall offs; some decent (forgiving) plateaus.

With Oxygen, however, these curves are, well, less forgiving; the plateaus, where they exist, are, well, not as wide re O/F. I'll see if I can find the graph I'm seeing in my mind and describing so poorly, here!!!

Well, I found the reference (the figure) and pretty seriously butchered it in my 'memory'!!!!

This is from Newlands: The Science and Design of the Hybrid Rocket Engine. Pg. 27.


In this case, the 'plastic' is HDPE. HTP is, I believe, High Test Peroxide (H2O2); I can't find the % H2O2 anywhere......

It is the plateau-like shape of the N2O / HDPE Isp vs O/F Ratio that Newlands' 'likes.'

I'm sure that quite a few of you have this book, but, with this figure, he says:

This means that unlike other oxidizers, a graph of Isp vs O/F Ratio doesn't have a sharp peak at best (stoichiometric) mix that drops off sharply on either side of the peak as LOX does. The graph shown here for N2O/HDPE exhausting to vacuum is the flattest compared to the others, decreasing by less than 5% of the optimum Isp over a range of 5:1 - 10:1 O/F.

 

[sjsyracuse]

CO2 can't be catalytically decomposed to my understanding. It's a product of combustion like H2O. Both can be used as oxidizers, but it requires lots of energy to decompose and you need a fuel with very low electronegativity to get a nett energy liberation from combustion. Mg has been proposed as a fuel for CO2 for Mars based systems, but performance isn't great. Lots of condensed phase products and what gases there are, are heavy.

TP

Yea.... Thanks! As I read this, 'it all comes back to me.'!!!

Thanks for the note re Mg + CO2 for Mars! Very cool!!

 

[hybridfreak]

As promised some video

And two thrust curves (all in Newtons):


As you can see in the graphs and the video, after ignition it's running quite lean before the plastic really starts to burn. Then things go a bit to rich just to lean out again towards the end. At least that's what I gather from the fact, that the smaller tank test ran at ~4,5 OF and the bigger one at ~5 (both averaging over the entire burn). This tells me I can make some gains by tweaking ignition and grain geometry. But that's for later, for now I'll make it fly next

 

[cfb_rolley]

Holy smokes, you’ve got yourself a pretty stout motor there! Congrats on the success!

 

[hybridfreak]

Holy smokes, you’ve got yourself a pretty stout motor there! Congrats on the success!

Thanks I hope I can finish the rocket for it to fly it in three weeks at our club's launch event!
And I want to thank everyone who's also building (hybrid) motors and not keeping their secrets but sharing their knowledge. It's amazing how much information is out there and what you can do with it if you pick the right bits of it for your project.

 

[sjsyracuse]

For your ABS - N2O system, two questions:

You're working in the O/F 4.5 - 5.o range, Yes?

May I ask the Pchamber and the ~ Tchamber - if you know or can estimate these? Or your target/design Pchamber?

Oh! And the Total ABS Mass consumed/combusted!!!

(I want to test ABS - GOX, but I find your NOX work both very cool, and very, very Inspiring!!!!!

Dankeschon!!

 

[hybridfreak]

For your ABS - N2O system, two questions:

You're working in the O/F 4.5 - 5.o range, Yes?

May I ask the Pchamber and the ~ Tchamber - if you know or can estimate these? Or your target/design Pchamber?

Oh! And the Total ABS Mass consumed/combusted!!!

(I want to test ABS - GOX, but I find your NOX work both very cool, and very, very Inspiring!!!!!

Dankeschon!!

Guess I'm right at the sweet spot then



(Source: Nytrox as “Drop-in” Replacement for Gaseous Oxygen in SmallSat Hybrid Propulsion Systems )

I designed for 27,5 bar / 400 psi chamber pressure but didn't measure it, thrust only. Temperatures were a bit low ( around 10°C / 50F instead of the 24C / 75F I used in the calculations) and it did burn a tad longer so I guess it all came very close to the calculations!
It burned 76g with 340g of nitrous and 94g with 450g of nitrous IIRC but I can look up those numbers.

Make sure to post some pics of your work here, bitte!

 

[sjsyracuse]

This is SWEET!! And, the amazing thing - well, it's not 'amazing,' is that I read this paper perhaps 2 days ago!!

Dankeschon for the graphs and the information/data!

By 'temperatures,' I was thinking about Chamber Temperature; with your ~ 10 C, are you referring to your N2O - correct me if I'm wrong!! - delivery Temperature??

If, empirically, you 'came very close to the calculations,' well, congratulations are in order!! And - and - you've survived to tell the tale!!!

I will certainly post some photos, and some data, as I continue to work! Thanks for the invitation! Sometimes, I find, the simple fact of the genuine interest and curiosity of another human is Tremendously Encouraging!!! Danke!!!

May I ask what your ABS Cross-Section and/or Port(s) Design looked like?

Yesterday, I tested some solid Polypropylene with GO2, in a single port vs multi-port configuration. Flowed 100% O2 at 10 L/ min. All controlled.
Single port was simply a single 9/32' hole in a 1.75" diameter 6 cm long solid PP Rod.
Multi-port was 5 ~ 1/8 ports in the an identical 1.75" diameter 6 cm long solid PP Rod.
The total open area (total open area of all ports combined) in the latter case = the cross-sectional area of the 9/32" single port.

Burned both under identical conditions, circumstances, environments, etc. for exactly 60 seconds. These are end-burning, in that the GO2 is injected at the base, and the combusting surfaces / surface area is at the very opposite end.

Calculations show that the available surface area for GO2 + PP combustion is identical, and the O2 flow rate is identical.

The Mf (fuel mass) consumed in the multi-port end burning sample was 26% greater than the Mf consumed in the single port end burning sample.