Hybrids 2020

[DRAGON64]

A recent post on a facebook page run by Contrail Rockets LLC has highlighted a new 72" long by 98mm N15000 that has an improved injection system, and a 42-star fuel grain!!! (See the images posted below)

Had I not been following Contrail Rockets on facebook, I might not have found this info/images, and this new thread would not have resurrected the topic of hybrid rocketry... yet here we are!

Previous Threads:

Hybrids 2015
Hybrids 2016
Hybrids 2017
Hybrids 2018
Hybrids 2019

Why another year in hybrids? Especially with interest nearly non-existent? Because 2020 marks the 11th anniversary of the NAR & TRA winning the lawsuit against the ATF, where-by removing APCP from the explosives list. This is the proverbial line in the sand, marking the time which we begin to see the decline of hobby based hybrids. Why you say? Because, of the 4 or 5 manufacturers that supplied our hobby, there is one left. One who still believes, and is trying to support us, and provide new hybrids for the small market. I am referring to Contrail Rockets.

Recently I was browsing YouTube for the latest hybrid videos that had come out in 2018... contrary to the traffic here on this forum for the topic, hybrids, specifically research hybrids, are alive and well. Small research companies and universities are still building, testing and flying the latest in hybrid technology. I have watched videos on rockets flown on paraffin and HTPB fuels, acrylic, PVC and even coffee. Most interesting are the 3D printed fuels. Watching these videos late last night, I ran across my own video of a paraffin test I was a part of... so yeah, lets give this topic another year to discuss.

It would seem that hybrids are thriving in the research world, rather than the commercial hobby industry. So, if you are indeed researching hybrids and or tri-brids, please post up the research in the proper research forum. But be sure to share your videos and flights here in the Hybrids forum. So, without further ado:

Another flying season gone-by, and a new one is just ramping up... what are your goals for flying hybrids during the 2020 flying season? Anything and everything hybrid related is welcome!

* Motors
* Vehicles
* Ground Support (GSE)
* Research motors discussion (within the limits of a non-research forum)
* Electronics
*Altimeters; Vent sensors; GPS etc etc
* Commercial/Professional advancement hybrid discussion
* College development (i.e. TUDelft etc etc)
* Events/Launch coverage
* New flyer questions

 

[Speaknoevil]

Wow-nice!

Do you have a link to the Facebook page? (Since I'm not in FB, I have a hard time searching on the site.)

 

[DRAGON64]

Here is a link to their page:

https://www.facebook.com/ContrailRocketsLLC/

 

[Yukon@K-9 Rocket Tech]

AMAZING! That injector assembly though, looks awesome! Like mini Aerospikes!

 

[Voyager1]

Last year I had some really nice flights with my Contrail 38mm 36” hybrid motor in the sustainer section of a Double Shot, flown as a single stage.

This year I will be using a Contrail 54mm 28” hybrid motor installed in the booster of the Double Shot, but still as a single stage flight.

Later in the year when I have finished building my MC Frenzy XL 4”, I will be launching it with a Contrail 75mm hybrid with a 1400cc N2O tank and 8” grain.

I’m also rebuilding my hybrid launch controller so it can remotely monitor tank pressures and masses, and flight tank venting.

So, for me 2020 will be mostly hybrid launches. I can’t understand why more people aren’t interested in hybrids.

However, all this talk of launching might turn to porridge if this COVID-19 situation gets any worse. I suppose I could just spend the rest of the year drooling over pictures of the new Contrail N15000 motor.

 

[AlphaHybrids]

Things have mostly been on pause with hybrid motors for me. Working more with liquid motors lately. Not that hybrids aren't cool, but man, once you design and test a liquid hybrids seem to fade away.

Edward

 

[G_T]

Have GSE now, but no tank of nitrous. So no testing/flying yet. I would like to perform another static test or a flight test of THRP-1. Perhaps I'll try something in the fall.

If interested in the project, you can find a VERY detailed thread with lots of design info and pictures in the research section. I recommend reading through it for anyone who wants to design their own hybrid.

Picture is from unsuccessful static test. Preheater ignition shot enough flame to burn through one of the lines prematurely, causing massive nitrous dump through at least one of the injectors before preheater was really lit. Once preheater was lit the motor pressurized and burned fine. The motor progressed from cold flow (little thrust) to hot monopropellant mode flow (which generates a fair bit of thrust) to hybrid operation (which generates full thrust). But the motor only had one second of liquid nitrous left at the point where the burn became stable in hybrid mode. Picture is what the end of the liquid burn looked like. 5' motor, 5' flame. Loud and very smooth.

The biggest difference between this hybrid and standard nitrous hybrids is using a pressure relief valve to chill and densify the nitrous in the flight tank. Anyway everything worked perfectly except for being too energetic igniting the preheater and having a preheater which wasn't energetic enough. That's the science and engineering part of rocket science! Design as best you can, then push the button... Among all the numbers I ran doing the design, I neglected to run the numbers on what the preheater really had to do for this sort of motor. Sigh... Inadvertent bias on my part from dealing nearly exclusively with solids before this motor. Solids are simpler to light.

Too bad the videos are huge. I can't post them.

Funny thing about hybrids like this one. 5 minutes later I was on the tower by the motor. The tank was cold. The combustion chamber was definitely warm but not hot like a solid motor would have been. The wax component of the fuel provided a liquid film coating of the nozzle which kept it's temperature much cooler than would have been the case for a solid motor. And the remains of the fuel provides good insulation for the combustion chamber itself. You know the slag you remove from the nozzle of a typical solid propellant motor? In this case, you have a thin film of wax left on the absolutely pristine nozzle. Looks like it never had been burned, just waxed!

AFTER this motor works, then I might think more seriously about tribrids and liquids. They definitely interest me.

Gerald

 

[Funkworks]

[...] of the 4 or 5 manufacturers that supplied our hobby, there is one left. [...]

Is Hypertek still breathing?

 

[DRAGON64]

I cannot say for sure that Cessaroni has stopped production, but a little looking around nets little to no stock of HyperTEK product. The HyperTEK website is still showing 2002 as the latest build, and 2004 as the last posted update. I would suggest you call or email Star Rocketry and ask what they have or can get, as they were the premier HyperTEK dealer in years gone-by: https://www.starrocketry.com/

 

[DRAGON64]

If the price of AP continues its trend of soaring price increases, I would think that hybrids could look a lot more enticing again... as a hybrid enthusiast, one could hope.

 

[DRAGON64]

Okay, some info on the unique injector pictured above; those are turbine injectors. I emailed Mr. Sanders about this new design, and he sent me a cool video of how a single injector might work when high pressure air is applied to it. The injectors are called High Performance Turbine Vortex (HPTV). I do not have permission to upload the video here on the forum, but if you email Contrail at [email protected], and Mr Sanders about the HPTV, he will send you the video.

 

[Funkworks]

I wouldn't mind getting into hybrid rocketry, but I can't even find a single hybrid-ready kit. And I just don't feel like spending endless amounts of time designing and looking for parts and then paying to have stuff delivered from who knows how many different places.

 

[DRAGON64]

PML and LOC both made hybrid ready kits in the past, and I believe PML for certain still shows them as production kits. In all honesty, buying a "long" rocket kit is usually best, as most hybrid motor systems, no few and far between, utilized long motor components. Case in point, I am talking with Contrail Rockets about a 98mm motor, currently only offered in a 60" length. So at a minimum, the vehicle booster should be 60" in length... The MadCow Blue Iguana comes to mind. Buying a kit and modifying to fit is not out of the question either. To that, I will say, you would have to work a lot harder to modify any kind of military style rocket to fly on a hybrid, as making tubes longer really detracts from the scaleness of the build. There is a build thread on here where a forum member modified the internals of a V2 rocket to take on a 76mm Contrail Rockets hybrid, without lengthening the rocket... but motor extended all the way into the nosecone. Recovery design really comes into play at this point.

Here is video of the flight of that V2:

Here is a video of the member testing the ejection charge system of the rockets, and you can plainly see the motor is mounted all the way into the cone:

I believe the forum members name is Legranddudu and he has not checked in since March of 2018...

The point is, you can make a hybrid motor fit most any design, but finding a long rocket is best...

 

[Funkworks]

That's really cool. I prefer scale kits in general, but with a first hybrid, I would just care about getting something to work regardless of looks. I would either need clear written guidance for a build, or find someone locally who's been there.

 

[Voyager1]

I wouldn't mind getting into hybrid rocketry, but I can't even find a single hybrid-ready kit. And I just don't feel like spending endless amounts of time designing and looking for parts and then paying to have stuff delivered from who knows how many different places.

It’s actually very easy to modify an existing kit to accept a hybrid motor. If the kit’s booster section is not quite long enough, it only requires a simple extension with centering ring and coupler to accommodate the extra length of the motor tube. I have used this technique on several kit rockets including a PML Gamma and RW Double Shot sustainer to accept 38 mm Contrail motors; MadCow Frenzy XL 4” to accept a Contrail 75 mm motor; and a Double Shot booster to accept a 54 mm Contrail motor. In each case you just need to have the extension long enough to allow for the vent tube to exit the booster forward of the top of the motor case - except for the 75 mm which vents out the aft end.

 

[Funkworks]

So would a same rocket be able to accept either one of a contrail motor, a hypertek motor or a solid APCP?

How do hybrid motors from different manufacturers differ?

 

[Voyager1]

The short answer to that is yes! However, I can only give that assurance for the Rattworks 29mm I80 and I90 motors; the Contrail 38mm, 54mm and 75mm motors. I have no experience or knowledge of any of the other hybrid brands such as HyperTek. The motor mount tubes for the hybrids I have are the same diameter as for APCP motor cases, so you can still use normal solid motors in these rockets and with the same motor retainers. Others might be different.

The motors I have and have used from Rattworks and Contrail have standard motor case widths, but different lengths. The other main differences (but not that different) are in the floating injector body; the forward closure vent; and the retention methods. The Rattworks forward and aft closures were screwed on; the Contrail motors uses c-clips for closure retention and aft tube stop. The Rattworks 29mm had its forward closure vent out the side; the Contrail 38 mm and 54 mm vents are out the top of the forward closures, while the 75 mm motor vents back out the aft end.

 

[Voyager1]

I meant to add this pic as an example of a modified kit model. This is the sustainer section of a RW Double Shot with a removable extension (darker green section in mid airframe) for a Contrail 38mm 36" hybrid motor. This sustainer was built with a standard 38mm motor mount. The extension is just a 400mm length of 54mm F/G airframe with a coupler and centering ring for the forward end on the 36" motor case. It is secured by four plastic rivets through the coupler at the aft end. The extension houses the forward end of the motor case and a drogue chute. This is a redundant dual deployment configuration with two Altus Metrum Easy Mini altimeters in an avbay between the extension and the upper main chute section. There is also a Featherweight tracker in the nosecone.

The extension of the rocket airframe does make them overstable (cals of 6 - 9, or more), but this has never been an issue because the off-the-rail velocity has always been high enough (>25 m/s) to minimise any wind cocking, if any.

This particular flight was on a Contrail 38mm 36" motor with a J246 reload up to about 5,000'.



I also use this same rocket without the extension for standard 38mm APCP motors.

 

[mikec]

It’s actually very easy to modify an existing kit to accept a hybrid motor.

Agreed. Some designs are usable with any extensions. For example, a stock Wildman Darkstar 3 could accept a Contrail 54mm 28-inch or 36-inch hybrid as is, all you need to do is drill a hole for the vent line.

 

[ericm541]

Last year I bought some old hybrid equipment, figured it would be fun to do something different and learn about hybrids. Most of it is outdated, skyripper,rattworks and the GSE, tanks had some nitrous in them but are well past the inspection date and so far one failed on inspection. I bought some contrail 38MM set and an older version of contrails launch controller off TRF. I've had one successful flight last year with an H277.

I'd like to make the GSE safer though, the fill solenoid and purge solenoid work good however, the lines are plastic connected by barrel style fittings and pneumatic quick connects. So are brass fitting fine to use and is there a better alternative to the plastic lines? How far should the tank be from the pad?

 

[Voyager1]

Most of my fittings are brass and all my fill lines are nylon. I have never had any issues with any of them or the the quick connects. The main fill lines from the tank are about 5’ long, so the distance from the fill tank is typically about 4’ away. I usually keep the fill tank to the side and behind the launch stand, away from the exhaust blast.

 

[AlphaHybrids]

I made a 1010 assembly that uses 1/8" pipe fittings to position a fitting right under the rocket to connect to the nylon fill tube of a U/C motor. I have a braided stainless line that connects to that. Keeps things from whipping around after if burns through.

 

[strud]

I've been putting more work into my 4" modular hybrid motor, focusing on injector optimization and getting it into the air this year.

Ignition pic from recent static test

After reading quite a lot of papers about N2O injection and the benefits of swirl, I made up an injector assembly implementing as much swirl as I could get given the existing geometry I had in the motor design.

The injectors are made from M5 x 16mm brass bolts and are drilled to the orifice diameter needed. Those in the photo above are 1.6mm, but from initial testing it looks like to achieve the motor tune I'm after initially (1350N) they will need to come down to 1.2mm

The water flow test pics make it easier to visualise what is going on

Initial static test was only partially successful, with motor blowing out not long after the pyrovalve fully burned through.

A bit of analysis led me to the conclusion that I had used far too low a discharge coefficient for these injector inserts (0.6) and that a more realistic value of 0.8 should be used.
Adding to that, the swirling oxidiser flow changes the flux distribution such that more oxidiser is near the fuel surface and less travelling down the middle of the port. The result is for the same overall flow, a higher flux is achieved at the surface and hence more likely to cause a flameout/blowout.

Video summary of test stand and first test here: 1st test with new injector

I have the drill bits to make the new injector inserts now so once that it done I'll get another set of tests done (drilling these small long aspect ratio holes in brass is non-trivial....)

This motor will be flown half filled in the HPV4PoC vehicle hopefully in the middle of this year.....

Here it is partially built. Fins, avionics and some motor plumbing bits still to go.

First flight will need to be limited to <15kft.

Future versions of the motor with longer tank and optimized air-frame should see this getting to pretty significant altitudes and velocities, but the PoC flight(s) need to be done first before I get too excited.

 

[AlphaHybrids]

Awesome 4" motor - do you have a comparison on the performance increase due to the swirl injector?

Edward

 

[strud]

Hi Edward,

I do not have numbers myself yet (from testing) but there are many research papers stating combustion efficiency improvements of 10%, mostly due to less oxidizer being pushed down the core of the port and the centrifugal action causing more intimate interaction/mixing in combustion ie near the fuel surface. The full 10% improvement requires a post CC to be achieved.

Another area of improvement is in combustion stability with the centrifugal flow of the oxidizer has a stabilizing effect on combustion.

Very useful references:
"Experimental Study of the Swirling Oxidizer Flow in HTPB/N2O Hybrid Rocket Motor" by Heydari et al
"Swirl Injection Effects on Hybrid Rocket Motors" by Gomes et al
"Performance comparison of oxidizer injectors in a 1-kN paraffin-fueled hybrid rocket motor" by M. Bouziane et al

Other important improvements I have made in this design is in the injectors themselves. The key improvements here were:
- Chamfered entry (very important to have predictable discharge coefficient)
- Aspect ratio of 10 (also important to have reliable performance)

very useful reference : 'Mass Flow Rate and Isolation Characteristics of Injectors for Use with Self-Pressurising Oxidizers in Hybrid Rockets' by Waxman et al

Most if not all of the above papers are available online without payment.

 

[AlphaHybrids]

That is inline with what I have seen. I've been testing hybrids for 15+ years, and found that trying to upgrade the injectors has been an adventure in diminishing returns. Somehow performance increase is inverse to the amount of time it takes to machine the injector.

I'll preface this by saying that I do not use U/C valved hybrids, all are actuated by a valve. I use two types currently, Showerhead and pintle.
Showerhead, typical orifice size is 0.040" (1.016mm) Arrange so that the stream hits the midpoint on the fuel web of the grain and doesn't go down the core. I also use inserts similar to you - but brass set screws. Most of my fuel grains are some sort of finocyl arrangement.

The other style is a pintle. Liquid flows on the outside of the pintle, and I have a tap for gasesous nitrous above the liquid line that flows on the inside and spreads out the flow into a cone. These sound hard to manufacture, but it is three pieces. There is a brass tee, the pintle screws into the bottom of the elbow, the liquid line screws into the side of the tee, and the gas tap is the top of the tee. This whole assembly screws into the forward closure.

Both of them I have tested ISP values up to 205s, but can consistently reach 195-200s. But, as people know, ISP is really meaningless with hybrids because half of it is the fuel. These are with polymer based fuels with metal and wax in them. All motors have a pre and post combustion chamber, minimum 1 diameter.

For the amount of work, the pintle gives me great performance, and saves me having to drill out lots of small orifices. Also, it allows me to change the configuration of a motor just by machining a new pintle, a single part, instead of adjusting a drill pattern.

Edward

 

[strud]

Thanks Edward, very useful.

Can you quantify how much improvement you see using a post CC? Do you have issues with heat flow in post CC for long burns (I assume you don't have any fuel in this section)

 

[AlphaHybrids]

I have never done a test without a pre and post combustion chamber, so I don't have data to compare to.

The longest burn motor I have tested is an N1000, 17 second burn. I used PVC pipe for the liner and fuel chamber. In this motor, the liner in the post combustion chamber only had about "0.050 that had ablated from the surface. By the time the combustion products had reach it, there wasn't much free oxygen left based on how much liner was left.

Edward

 

[Not Quite Nominal]

Hi Edward,

I do not have numbers myself yet (from testing) but there are many research papers stating combustion efficiency improvements of 10%, mostly due to less oxidizer being pushed down the core of the port and the centrifugal action causing more intimate interaction/mixing in combustion ie near the fuel surface. The full 10% improvement requires a post CC to be achieved.

Another area of improvement is in combustion stability with the centrifugal flow of the oxidizer has a stabilizing effect on combustion.

(Disclaimer: never built a hybrid)

If you are trying to get more mixing in the chamber, would it make sense to have impinging swirl injectors? Increase the tilt on every other nozzle so that the oxidizer stream impinges on the next one and you may get more oxidizer dispersion and perhaps better mixing.

 

[AlphaHybrids]

Disclaimer: Static tested over 2000 hybrids, from H to O sized.

Definitely, you can have impinging injectors. One great thing about nitrous oxide is that it atomizes very, very easily because it flashes from liquid to gas in the chamber. I never saw that like-like impinging injectors were substantially better than the the two I described, other than making machining more difficult.

Edward