Need Hybrid help

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Max Thrust

Jan 17, 2004
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I'm looking to hook up with hybrid-experienced rocketeers to learn and discuss various hybrids. Experience with non-Hypertek is especially welcome and experience with EX hybrids even more so.

For Hybrids, go to . Doug has a lot of hybrid info, and he also created the site ...which is apparently down at the moment.

If you can't find what you want to know there, ask specific questions, one of us geniuses might know:)

I personally fly RATT's, so I have some knowledge. Just ask:)
Thanks... but been there a while ago. I'm looking for an experienced hybrid person who I can learn from and discuss hybrid engines... particularly non-Hypertek engines and EX type hybrid's.


TRA #9881
I can share some knowledge, I know the basic technology and designs. PM me with some questions and I will do what I can.
Well, the RATT motors are actually among the most attractive to me. While I find the Hypertek's quite elegant from an engineering perspective, I like the per-flight cost of the RATT motors better. I'm also quite taken with the Trybrid concept. I'm looking for specific feedback on the RATT motors and ground support systems.

Secondly, I'm an engineer by training and I'm thinking of working on very large (relatively speaking) hybrids - in the O through R or S range and I'm looking to talk to anyone working in that field - either amateur or professional.

Hi there Max,

Whike I know you mentioned the Rattworks motors specifically, there are two other companies also making high thrust hybrid motors. Personally, I know very little about hybrids so farand will learn more soon as I have both Rattworks and West Coast Hybrids motors on the way. Marcus Leech at Propulsion Polymers knows a lot. (To say the least) I saw his M level hybrid launch in Spetember and it really rocked. It is also able to be launched in an "N" configuration. Scott Harris of West Coast Hybrids is also making some larger motors too and has a TON of information. Both of these guys are very approachable and have designed great products.

WCH can be found at:

and PP can be found at:

My photo in the background of the PP website by the way. ;)

I'm sure these guys will answer your questions.

Len Bryan
I've played with a few Tribrids (Dave is beta testing at our launches here at Lucerne). Neat motors. I've also flown several RATTs and helped out with a lot more. Living in the same county as Dave Griffith really helps :)

Jeff Jakob would also be one to talk to regarding really big hybrids. He's a nice guy and flew a Q hybrid motor 100% successfully at BALLS last year. His website is at

What are some of your questions? I'd be happy to try and answer them :)
man that is a big hybrid, so much much.
Now we're starting to talk about where my ambitions are headed... I see P, Q, R and even bigger hybrids in my future... I want to experiment on LOX hybrids or tribrids... I want to break 100,000' or more with a hybrid...

Mainly though, I want to get into a conversation with someone moving in that direction already with some experience designing hybrid engines and rockets intended for large hybrids.

I can picture myself and a few others i know certainly will be going down that road in the semi-near future as well.

One very good program you might want to check out is the Hybrid Design Program at That will help you get started.

A good way to get your feet wet would be to buy a Ratt K240, and try some different propellant types, etc. Or if you really want to start at the beginner level, you could always pick up a Micro Hybrid from Rene Caldera to do some backyard experimentation

I apparently have the use of a couple Hypertek's - I/J, K and an M from one of my new buddies and he's got serious experience with the Hypertek's but none with other hybrids. They are seriously elegant from an engineering standpoint but what kills me is the per-flight cost is nearly that of standard composite solids and the ground support is a huge expense.

The RATT and similar motors look pretty cool, have lower group support costs and much lower reload costs but I don't like the fixed capacity of the motor as far as nitrous capacity is concerned. I'd like to see something with a separate nitrous tank in various sizes. The ability to experiment with different propellant grains is a really nice plus with this system though.

I love the design of the Aerotech, but I haven't run into anyone who has actually used one or owns one and with Aerotech bankrupt who knows what's going to happen with that. While I've heard Animal Motor Works has put in the high bid on Aerotech, I don't know if they got the deal from the bankruptcy trustee or if they'd continue manufacturing a motor competitive to their own large composite solids.

Also, with the Aerotech, the standard compressed cellulose propellant grain isn't the direction I want to go. Some of the plastics used in the RATT and similar motors have literally 0 pollution due to the plastics breaking down into CO2 and water. Cellulose does have substantially more toxic byproducts. HAS anyone experimented with making polystyrene or polyurethane fuel grains for the Aerotech hybrid? I already own a Dr Rocket 38mm motor and all the casings for that size and it would be mighty convenient and cheaper for me to use those for smaller motors.

Finally, for now, is anyone out there currently making hybrids larger than M - even at the experimental stage. While I know Burt Rutan has commissioned a very large hybrid for his spaceplane project, what is the amateur and hobby rocketry community doing in this direction? Has anyone built an N, O, or P motor that is even being considered for certification?

By the way, I am going to be contacting the Propulsion Polymers guy and any other serious researchers I hear about through here. With the whole LEUP situation and my deep seated desire for privacy from the government, hybrids are the only way to go for large motors. I will never invite a BATFE agent to my house to inspect my magazine or go through whatever investigation they feel they need to do. Feels an awful lot like registering rocket motors just like they want everyone to register guns.

Hybrids are the way around this LEUP crap and even better, hybrids can be made to emit far less pollution than any composite solid motor.

Also, anyone experimenting with LOX hybrids out there?

Max (Warren)
While a number of large hybrid engines have been made in the N, O, and P classes, none have ever been made for certification. A P motor wouldn't ever be cert'd since it is beyond the certified limits of HPR. But that shouldn't stop you from making one:D

One area of interest i have had is the reverse hybrid, with solid oxidizer and liquid fuel. While it may not have any real advantages, i like a challenge, just for my own knowledge and the fun of experimentation.:cool: Another facet of hybrids i would like to explore is a FAST hybrid, and i am talking Kosdon fast! Using large injector orfices and metallized fuels.

you might want to check out the RRS site <> they have some very impressive liquids and hybrids that they have built, many of them using LOX. Also, if you can find out a way to contact him, you might try Rick Loehr <never sure if I spell that last name right:rolleyes:>, he builds some VERY large LOX hybrids, after having done large solids for years. He still builds the massive composite engines fro Ky's spaceshots though

There's been a ton of professional work done with big hybrids.

Safety and convenience are the big motiovators for large professional hybrids. A hybrid theoretically should be able to generate the specific impulse of a liquid motor, with the convenience of a solid motor while at the same time have unparelled safety since the motor can be shut down simply by stopping the oxidizer flow. If the structure should fail, the chance of an explosion due to fuel oxidizer mixing in a liquid is eliminated since the fuel is a solid.

The latest trend in big hybrids is to use a parafin wax as the fuel (essentially solid RP-1), the theoretical specific impulse is virtually the same as LOX/RP-1 or NOS/RP-1.

Try a google search on "hybrid rocket motors"

NASA Marshal has fired a 24" hybrid.

Check out Scaled Composites Spaceshipone and the hybrid competition between Environmental Aeroscience Corporation (eAc), and SpaceDev.

The most serious problem with large hybrids is the uniform distribution of the oxidizer throughout the central core of the solid fuel. Unless the distribution is uniform, the specific impulse suffers and is more similiar to that of a solid vs that of a liquid. The oxidizer injector design is the major stumbling block with big hybrids.

Nitrous is not cryogenic so it offer handling advantages over LOX with a 10% reduction of specific impulse. A 70/30 PE/LOX hybrid has an Isp ~ 295 seconds vs a 90/10 PE/NOS hybrid with and Isp ~265 seconds. (PE is polyethylene which is thermoydamically equivalent to wax.)

Inverse hybrids have also been investigated, but they offer no advantages, and have several disadvantages over the conventional hybrid design. The packaged volume of an inverse hybrid is greater than a conventional hybrid since fuels have a lower density than oxidizers, and an inverse hybrid is not easily shut down since the hot oxidizer will continue to pyrolize and generate oxygen which could fuel a casing burnthrough after fuel flow is stopped.

Bob Krech
Great reply Bob. This is the kind of info I'm looking for. Are there any non-professionals working with hybrids in the O and larger range?

As a side question, why is it that high power rocketry is limited to O class motors on the high end with EX motors seeming to top out at Q class. Is there some specific regulations that say something to the effect that unless you're a professional or work for a defense contractor or the federal government, you can't play with toys bigger than that?

Max (Warren)
There is nothing to keep you from making a Q sized and up hybrid or whatnot. It is just not that often that someone builds a motor larger than that. If you do go and build a Q hybrid or larger and you want to fly it at BALLS you would have to notify the Tripoli BOD several months beforehand for approval. Usually no t a problem. If it uses LOX instead of NOS, then you would also have to mention that.

Build away!:D

The regulations as to the upper impulse limits on rocket motors are very extensive, confusing and nonuniform from state to state.

Both NAR and Tripoli basically follow NFPA 1127 for certified High Power flyiers which sets the maximum single engine limit to 40960 NS (O) and a total rocket impulse limit of 81920 NS (P). (Additionaly I believe that motor burn time is restricted to 15 seconds by some regulation I can't quote.)

NAR does not have EX but Tripoli does. They list EX records for P (81920 NS) and Q (161340 NS) so I don't have a clue what regulation or restriction they are under here. (I think that they may actually extent to low R at 200,000 NS but don't quote me on that limit.)

Amateur rockets are restricted to 200,000 pound-seconds or less (890,000 N-S, 15 second burn times, and ballistic coefficients less than 12 psi. I know there are exceptions to the standard amateur rules for Tripoli HP as listed on the AST website that permit burn times to 60 seconds. It's possible that NAR HP also has this exception. (It is not normally an issue with the exception of hybrids and a few other long burn motors in multistage rockets.)

Interestingly the California Regulations appear to limit single experimental motors to 10240 NS (M) and total rocket impulse to 20480 NS (N) and Storage of Fireworks in California.doc

There are a bunch of other regulations. Dave Schultz has a pretty good referenced list of regulations.

Bob Krech
I've been looking around at the FAA site and commercial space regulations that you pointed me at and all I can find is that amateur rocketry is capped at 200,000ns and a max 15 second burn. What happens if you makes something with a 30 second burn? or a 200 second burn? I can't seem to find those figures actually in any regulation, just in a "definition" of amateur rocketry. Obviously, fueling an engine that size is beyond mighty expensive... BUT, if you've got the ceiling in the waver - such as at BALLS, why not? Would Tripoli give permission for something in the R class for instance?

I've read those RRS guys have broken 250,000' with one of their LOX/RP1 creations... not that I'm looking in the direction of liquid fuel as they did...

I'm just being a bit blue-sky at the moment here... trying to find out what the limits are and why.
Just as an aside, I should say I'm a serious BAR. Was a rocketry nut back in my childhood and early teens until I discovered girls, electric guitars and beer. Saw 15 minutes of the Discovery rocket challenge show last November and have been ramping up rapidly with all my engineering background to get serious in a way I never imagined I could.

I'm already starting to play with EX even though I'm still waiting to get my Level 1 cert (that bird is built, a PML Cirrus Dart that will fly on an I284 sometime in the next couple weeks.) I've got some APCP on order as well as aluminum powder and PBAN polymer. I'm planning on making grains for my AMW case and possibly for my Dr. Rocket 38mm motor set.

I'm 3/4 thru my Level 2 bird and that's just waiting on my Level 1 and an AMW K570 or K950 reload since I've got an AMW 54/1750 motor. Also, I on the edge of ordering a RATT K350 Tribrid. I already have a number of Hypertek motors available to me if I want to pay for the reloads.

Max (Warren)
The aRocket list is a good place for you to get information.

General information about the mailing list is at:

There are a lot of amateur rocketeers who post there. Some of the pioneers of hybrid rocketry post messages on the list too. It's a very good amateur resource. This list is in the form of a listserve rather than a forum like this. I believe there are archives but I have not looked for them in a long time.

Len Bryan
I'm just getting into hybrids both commercial and EX ones, alone with the other guys in A few things is what are some good books to read up on this subject? i know of Rocket propulsion elements by Sutton is there any other books? like maybe a bit less technical/theory based like a hybrid version of ECP (hmm i hope someone knows what i am meaning) or any good web sites on the subject

To be honest, I think you have a lot to learn before you get to building your own hybrids. You also talk about wanting to build and fly P, Q, R class motors but complain about the cost of Hypertek support equipment. If you want to play in this area of rocketry you are going to have to throw budget out the window. Getting a rocket back from 50,000+ ft is no trivial task. Getting a rocket to 50,000+ ft is no trivial task. You should read and understand Sutton's book if you want to build hybrids of that size and class. You will find a LOT more help with making your own APCP motors than you will hybrids. There are only a hand full of people who actively make their own hybrids. The people who have done it have put thousands of hours of work into learning what goes into a hybrid. Solid fuel is much easier to learn because of the amount of help that is available. If you are serious about it you will need to join the RRS and spend your vacation time on site with them. You will need to get to know them face to face. People who work on this edge of the hobby do not spend a lot of time in these forums for the most part. First, get your L1 done as it will be a challenge just to find that rocket after you fly it on a I284. Fly it a few times before you worry about L2. You need to read Terry's book before you do anything with APCP production. Learn it backwards and forwards. It is a great book. Come to Balls and fly. You might even be able to speak with Jeff Jacob at Balls. He has built R class hybrids and knows his stuff. Don't expect these people to give you a design class on how to make these things. You will need to make the right friends before you will get serious help in this area. You can do it but you need to realize that a Q motor is at least 5 years out for you. You don't just buy a tube and build a Q motor. Master high power rocketry first. Get your L1, L2 and L3 but don't try to do them all in one year. There is a lot to be learned along the way. Go to as many launches as possible and make friends. You will learn a lot from the people in this hobby. Lots of great people to know. The RRS will be where you will end up when you get serious about huge hybrid motors. If Jeff brings his rocket to Balls again this year you will get an idea of what you are talking about. His creations are truely stunning.
Best of luck on your journey.