The Saga of the "Versa Rocket"

[broken flyer]

Hello everyone
I'm new to the forums here, just joined actually, but I've been following Flite Test for quite some time and I've been designing, scratch building, and flying model aircraft for most of my life and I thought you all might be interested in seeing what I have been working on over the past year. Granted the base air frame is a Versa Wing with the payload bay addition, so this may not fall under the "mad scratch built" category for some of you(I have seen some amazing builds on here), the power system for this plane which turned it into the versa rocket has been a little on the mad side though. Now as well as being an airplane guy I am a bit of a space nut and anyone who knows me knows that it is my dream to work in the private space industry and I've been working towards this goal in whatever capacity I've been able to since high school so when I started getting into rocket engine design a little over a year ago it was a logical leap for me. This story begins during a cold Minnesota winter in 2015 when I began experimenting with DIY amateur rocket engines and found moderate success with my third engine design of a PVC sugar rocket.



As I figured out the chemistry and the mechanics of rocket propulsion more I began to push the boundaries a bit and as is so often the case with rocket science the learning curve is pretty steep and I had my fair share of catastrophic failures.



Eventually though I got it dialed in and began flying what was essentially an overgrown bottle rocket to test the engines in flight.

All the while though in the back of my head I kept thinking that as cheap as these home built DIY engines were, they were inconsistent performance wise and still more expensive than the propellant itself that was inside them. I wanted a fully reusable rocket engine that I could just keep refilling again and again so that I could fly rocket powered model airplanes with it frequently and not have it be prohibitively expensive. So as I refined my understanding of solid propellant rocket engine design, I began the design for what would become the XR58 rocket engine...



I designed this new engine to be 3D printed out of stainless steel, but I realized right away that it was going to expensive and heavy so before I spent any money on a full blown prototype I went back to my DIY engine building experience and built what I would call an analog of the design to validate the sizing and general operating principal, the XR58E for expendable. This engine worked beautifully, it worked exactly as intended, no unpredictable behavior and it had an almost linear thrust profile which was exactly what I wanted knowing that I would be using this to fly a rocket plane at some point.

With renewed confidence I decided to get an engine printed, but I still wasn't ready to spend the money to do one out of steel and I was wary of how much it would weigh, so I did a variation of the design that I believed would work with 3D printed ceramic instead. The 3D printed ceramic engine had an excellent surface finish(since was glazed after being printed), was heat resistant to over 3,000 degrees Fahrenheit, was lighter, and was approximately 10% of the cost to produce the initial design out of stainless so despite knowing beforehand how brittle ceramic alone could be I decided to try it anyway. Unfortunately it just crumbled essentially when ignited(well cracked actually), but you get the idea. Not a good material for making a rocket engine out of(by itself anyway, larger solid propellant engines have used ceramic inserts in the throat of the nozzle). At the time the only 3D printing service that offered ceramic was located in Europe and if I recall correctly I believe this first 3D printed engine of mine was printed in Germany.



Finally admitting to myself that ceramic alone wasn't going to cut it, I broke down and dished out the money to do the first prototype out of 3D printed stainless steel.



Now with an engine that could handle the pressure and the heat(for the most part, I did have an issue with nozzle erosion initially), I began testing and I fired that engine 5 or 6 times over the course of a couple of weekends and proved to myself that it was possible to do a fully reusable engine this way. This engine was heavy though and because I had opted for a longer burn duration and lower thrust, the power to weight ratio on that first engine was not good enough to fly anything really.

It was around this time that the internet began to take notice. 3DPrint Article on the XR58 Engine

The prototype engine was heavy though as aforementioned and I was not happy with the quality of the product. The design at the time lent itself to the nozzle twisting during the manufacturing process and there was an unacceptable amount of nozzle erosion for the desired lifespan of the engine, so I went back to the drawing board, taking my design and iterating to a new design that would have the same performance, be significantly cheaper, lighter, more versatile/adjustable, and durable. Behold the second version or the "production"version of the XR58 Engine. While I was still having some quality issues with the prints I received(and still am, though I'm working on this with the supplier), the performance of this engine was perfect, I couldn't have asked for it to work any better or be more consistent, especially given the inconsistent nature of the propellant(more on this further down). I did experience a number of failures with this engine during testing when I was trying to get more thrust out of the engine than it was designed to do, but in the baseline configuration as designed, it performed flawlessly on the test stand.

Finally I had something I could put on an airplane... However, now I needed an airframe and it was surprisingly hard to find an airframe suitable for a rocket engine and a relatively heavy one(the trade off for making it out of steel so it'll last rather than cardboard or plastic like most disposable model rocket engines). Having designed and built quite a few models before I instantly started getting grandiose ideas of all the cool models I could build and fly with this engine(a profile model of a Me163 is currently at the top of my list when I get to that point), but I needed something quick that I knew would fly to try it on so I could eliminate a variable or two and in stepped my friend and co-worker(we both work at Cirrus Aircraft full time in the manufacturing engineering department for SF50 product development) and he offered up his old tried and true Versa Wing for the task as he was an avid Flite Test follower as well and has a small fleet of their designs. Thus was born the "Versa Rocket".





We have "flown" the Versa Rocket a couple times now and attempted to fly it many times, but it's been rough. Lacking a purpose built launch rail and the combination of the Versa Wing being slightly too large/heavy for the XR58 engine we haven't had the best luck getting it off the pad(it's veered off sideways a couple times because it wasn't placed perfectly center and has gotten hung up on the ground a few times).





The most successful flight we had ended in a tip stall/snap roll that put the wing into the ground after a few seconds of air time(the XR58 actually has a 7 second burn duration in the baseline configuration so it should be really awesome on a purpose built airframe) and the least successful flights ended in destruction...



We have suffered two explosions during all of these flight attempts, both due to irregularities/anomalies in the fuel(cracks, air pockets, voids, etc), but I am confident this can be avoiding in the future by closely inspecting everything after fueling and potentially be alleviated altogether in the future with more thermally stable propellant mixes.

Anyway, I have lots more pictures and video of both partial success and failures that I have yet to upload so keep an eye out for those soon! With any luck when we get another wing built(planning on using a modified mini arrow for the next attempts) and the time to work on this stuff some more there should be rocket flights galore and lots of great video!

What do you guys think? Anything I missed that you'd like to know? Things you'd like to see pictures of or videos? I'll try to oblige you if I have them. Or just project ideas for reusable RC rocket gliders in the future? I know I've got a few I can hardly wait to build once we get some solid(no pun intended) rocket flight experience under our belts

 

[broken flyer]

Some video of a partially successful flight.

Enjoy!

 

[broken flyer]

Reserved for Updates

 

[broken flyer]

Reserved for Updates

 

[CrossedUpChris]

This is really cool. There is was thinking my rocket boosted viggen was going to steal the rocket plane lime light. Mines just got a c2 plug motor built into the back though.

That reusable rocket motor looks the business. Have you measured the thrust it produces in the standard configuration?

Perhaps you could try mounting it on a something that could fly under its own electrical power, then use the rocket as a boost, just to get a feel for how it works in the air.

 

[SnowRocker88]

Why 3D printed though? I would imagine a weldment for the "chamber" and a machined billet for the "nozzle" would be just as cheap, or maybe even less expensive, than a 3d laser sintered part.

This is an awesome project though! Super cool stuff you're doing here!

 

[OttoPilot]

If you don't mind...who did you have print the components for you?

You mention a flat thrust profile; are you using a circular core in your grain or did you go with a 'star' (finocyl)?

 

[area66]

Sorry, but this design will never work. In a rocket engine you have to control the pressure, the grains as to be design in a way that no more surface is exposed or else the propellant will burn faster , the motor will over pressure and kaboom. If the grains get more surface we use nozzle that will enlarge with the erosion of the particles projected outside the motor with the combustion ( the metal part in the grains)

Now if you don't know what is a grain, well......


I know you are in Europe, but your sugar motor attach to a rod ( like Chinese firework) is completely illegal in US and Canada , a rocket need a recovery system. So folks don't try it; it will only bring more control to the hobby and we don't need it. Beside using PVC is very risky, if the motor explode and you have chaps pieces enter in the body, they don't show on the X-ray. At Tripoli we do experimental launch with home-made motor, but sugar one and especially PVC one are ban.

They are a forum to discuss motor building and formula, but you need to Certified High Power and also be a US citizen.

I get burn third degree on my left hand at 17 making rocket motor , and recentle the Chemist of Cesaroni a rocket motor company get burn at 75% of his body and after few months still in stable but critical conditions, the guy have a factory well equip and a Phd, so if you think you are smarter, well good luck


http://www.yorkregion.com/news-stor...-burned-in-stouffville-rocket-fuel-explosion/

 

[broken flyer]

Sorry, but this design will never work. In a rocket engine you have to control the pressure, the grains as to be design in a way that no more surface is exposed or else the propellant will burn faster , the motor will over pressure and kaboom. If the grains get more surface we use nozzle that will enlarge with the erosion of the particles projected outside the motor with the combustion ( the metal part in the grains)

Now if you don't know what is a grain, well......


I know you are in Europe, but your sugar motor attach to a rod ( like Chinese firework) is completely illegal in US and Canada , a rocket need a recovery system. So folks don't try it; it will only bring more control to the hobby and we don't need it. Beside using PVC is very risky, if the motor explode and you have chaps pieces enter in the body, they don't show on the X-ray. At Tripoli we do experimental launch with home-made motor, but sugar one and especially PVC one are ban.

They are a forum to discuss motor building and formula, but you need to Certified High Power and also be a US citizen.

I get burn third degree on my left hand at 17 making rocket motor , and recentle the Chemist of Cesaroni a rocket motor company get burn at 75% of his body and after few months still in stable but critical conditions, the guy have a factory well equip and a Phd, so if you think you are smarter, well good luck


http://www.yorkregion.com/news-stor...-burned-in-stouffville-rocket-fuel-explosion/

I am not in Europe(not sure where you got that from) and the design most certainly does work, did you not watch any of the videos or look at the pictures? And this engine is legal in the US and so was the PVC motors I was doing before. This is a Class I engine, so you do not need to be high power certified for this engine, and the grain configuration is what is commonly known as an end burner grain, but I like to refer to it as being coreless and with an end burning grain you have constant surface area for the duration of the burn. The bottle rocket setup I did was a test I did(on private land from a safe distance) almost a year ago and is not what I am doing at all by building rocket powered RC planes, the plane would be the recovery system in that scenario and I know the rocketry organizations have provisions for flying rocket gliders as does the AMA and this is in compliance with their policy.

Rockets are inherently dangerous, there is a lot of energy stored in them and they can be explosive depending on what fuel & oxidizer you're using(sugar and potassium nitrate does not detonate/isn't classified as an explosive though you can cause the pressure vessel to rupture if there is too much pressure) and command respect and when people don't take the adequate safety precautions people get hurt, but that is the case with many things in this world. Lithium batteries are very dangerous as well(though not really in the same way that rockets are, just using this as an example), but we don't not use them because of that, we just use them carefully.

I might also add that there is no metal in the grain... The only solid propellant grains that I can think of that have "metal" in them are APCP which use aluminum commonly as the fuel portion of the propellant.

 

[broken flyer]

If you don't mind...who did you have print the components for you?

You mention a flat thrust profile; are you using a circular core in your grain or did you go with a 'star' (finocyl)?

I don't mind at all, the process used isn't DMLS(direct metal laser sintering), but is called "binder jetting" which can be read about here. The parts have been coming from Shapeways, but Shapeways has ExOne produce all of their steel parts as far as I understand.

It does have a pretty flat thrust profile because this is an end burner grain design so there is a constant amount of surface area throughout the whole burn. A star core in your grain will give you a relatively flat thrust profile as well, but I wanted a longer burn that was lower thrust for use on RC planes so that's why I went this route. I am hoping to do a version of the engine though that uses a larger throat nozzle and a core through the center for a high thrust/short burn duration so it could actually be used with model rockets rather than just airplanes, but I haven't had time to work on that yet.

 

[broken flyer]

Why 3D printed though? I would imagine a weldment for the "chamber" and a machined billet for the "nozzle" would be just as cheap, or maybe even less expensive, than a 3d laser sintered part.

This is an awesome project though! Super cool stuff you're doing here!

The labor is the problem, the material cost is way cheaper if you just machine it. I wanted to machine it initially, but CNC shops seem to charge about $100 an hour so between set up and the time it takes to machine stainless, it was cheaper to 3D print it, and 3D printing allowed me to make the body of the engine one piece whereas it would have had to have been multiple pieces and welded had it been machined just like you asked about. That and I can have these produced as I need them rather that needing to get them made in quantity to keep the price down, but in the future I would really like to be able to get some tooling set up and do a bulk run so they could be cheaper.

 

[broken flyer]

Thanks for the positive feedback and good questions guys

 

[wilsonb]

Are you casting the grain directly into the steel body?

 

[broken flyer]

Are you casting the grain directly into the steel body?

Yes, the propellant gets cast directly into the steel casing and so far I have had no issues with it separating/burning on the sides or anything like that. I pour the propellant in, let it cool, bolt the top on with a bit of clay between the retaining ring on the top as a seal, run the engine, let it cool, wash it out with water, and repeat.

 

[SnowRocker88]

The labor is the problem, the material cost is way cheaper if you just machine it. I wanted to machine it initially, but CNC shops seem to charge about $100 an hour so between set up and the time it takes to machine stainless, it was cheaper to 3D print it, and 3D printing allowed me to make the body of the engine one piece whereas it would have had to have been multiple pieces and welded had it been machined just like you asked about. That and I can have these produced as I need them rather that needing to get them made in quantity to keep the price down, but in the future I would really like to be able to get some tooling set up and do a bulk run so they could be cheaper.

If you could use standard SS Pipe sizes, maybe Sch10, you could buy commercial items and weld up the kettle pretty easily I think. Or have it setup to be welded fairly easily. I work as a Mechanical Designer for an engineering firm. We have our own fab shop and I'm pretty heavily involved on that side of things. If you want some ideas or pointers, I'd be glad to bounce some ideas off of you. For the nozzle, I'm pretty sure machining from billet or 3d printing would be the only routes you have. I wonder if you could ceramic or tdc coat the nozzle for longer life.

 

[area66]

Well you can make them and use them at home but , unless you own a BATF permit, you can't transport or sell those motors. And no rocket association will accept you launch them, and I'm pretty sure AMA will not like them too. If you purchase an Estes, Aerotech, CTI and other the motor casing is design to have lateral resistance to explosion, so it's the ends that will give away in case of over pressure, giving more protection as a rocket is launch vertically. At the end of the day your motor will never been certified and you will never be able to sell them.

Of course I look at the video and what I see is a poor rocket motor with barely no trust. Your design is simply too fat and not long enough. Sugar motor are poor man solution, they are not reliable and to repeatable as you experience your self, way less trust than AP motors too. If you want to build motor why not use AP instead ? so you will be able to use them at Tripoli experimental launch. seem a more smart choice and with more future. I start to build rocket motor in 1974. So if I tell you your design will not work, I know what I'm talking about.

 

[broken flyer]

If you could use standard SS Pipe sizes, maybe Sch10, you could buy commercial items and weld up the kettle pretty easily I think. Or have it setup to be welded fairly easily. I work as a Mechanical Designer for an engineering firm. We have our own fab shop and I'm pretty heavily involved on that side of things. If you want some ideas or pointers, I'd be glad to bounce some ideas off of you. For the nozzle, I'm pretty sure machining from billet or 3d printing would be the only routes you have. I wonder if you could ceramic or tdc coat the nozzle for longer life.

I have a very similar job to yours actually. I'm an Engineering CAD Technician/Designer at Cirrus Aircraft full time and I work in the manufacturing group in the engineering department designer production tooling (things like molds for composite parts and jigs and that sort of thing) for our SF50 jet. We fab a lot of our own stuff too and I agree that it wouldn't be too hard to do it that way/make it cheaper that way if I could do them in quantity/had a shop at my disposal but paying another shop to do it gets expensive fast. I was thinking of sort of a hybrid approach if I ever go to bigger motors, taking a welded pressure vessel using off the shelf hardware and then 3D printing the nozzle portion of it. There is this really cool process I heard about through work where you take and machine the shape you want to produce into a piece of billet, essentially like an injection mold, and then inject a charged gas that has nickel in it and the nickel deposits on the surface and then you just open it up and walla you have your hollow part. I think that would be pretty darn cool and it would make for very cheap parts but getting tooled up to do that would be expensive. Another thing I've considered is having them stamped out of sheet metal in halves and having them welded then like some performance mufflers for cars are done, but again, high initial expense to get set up to do that. I'm not sure about coating the inside of the nozzle, I'm sure there's a way, but I haven't found a simple/affordable way to do that.

 

[broken flyer]

Well you can make them and use them at home but , unless you own a BATF permit, you can't transport or sell those motors. And no rocket association will accept you launch them, and I'm pretty sure AMA will not like them too. If you purchase an Estes, Aerotech, CTI and other the motor casing is design to have lateral resistance to explosion, so it's the ends that will give away in case of over pressure, giving more protection as a rocket is launch vertically. At the end of the day your motor will never been certified and you will never be able to sell them.

Of course I look at the video and what I see is a poor rocket motor with barely no trust. Your design is simply too fat and not long enough. Sugar motor are poor man solution, they are not reliable and to repeatable as you experience your self, way less trust than AP motors too. If you want to build motor why not use AP instead ? so you will be able to use them at Tripoli experimental launch. seem a more smart choice and with more future. I start to build rocket motor in 1974. So if I tell you your design will not work, I know what I'm talking about.

I appreciate your in-site and experience, but I am not sure that directly applies to my motor, my design, or my process. As an end burner grain the motor needs to be that wide to have sufficient surface area to burn and it is the length it is because of the propellant volume I am restricted to since I am trying to avoid needing to tell the FAA every time I launch one of these and as it is intended for RC aircraft the way it is set up right now it is better to have a lower thrust burn that is longer, as I have with this design. It is comparable to a large Estes motor in terms of impulse because it's an KNO3 based propellant just as black powder is and the reason I am using an KNO3 based propellant rather than an AP propellant is because even though it is lower performance it is an order of magnitude cheaper, it burns cooler, and isn't burdened by regulation like AP, Ammonium Perchlorate for those who don't know which is classified as an explosive depending on where you are and how finely it's ground. My goal isn't to build the highest performance motor out there and never was, I am simply trying to make a fully reusable motor that will allow people to fly rockets/rocket powered model aircraft more often for less money. Ideally I would like to find an KNO3 based composite propellant to use in this engine since that will be much more repeatable and have less issues with cracking and such, but I haven't gotten to that yet.

I might also argue that KNO3 is safer since it will not auto ignite by itself as it lacks any hydrocarbons whereas AP will since it has four hydrogen atoms. I can also sell and ship these legally because there is no propellant in them when they're empty, without propellant these motors are little more than a chunk of steel, and that also avoids the hazard fees you have to pay for shipping AP around. And as a safety feature that I have tested, my motor design also fails at the end of the motor because either the screws or the flange fails before the pressure vessel does. I'm acutely aware of the dangers involved and would encourage everyone to take every safety precaution possible when using rocket motors(or anything flammable for that matter) in any capacity. This is not a traditional model rocket engine and it really can't be judged as one.

For you this may seem like everything is wrong, but for my purposes this is exactly what the doctor ordered and that is why I designed it the way it is.

 

[broken flyer]

Had a quick moment tonight and uploaded the video of the most "successful" flight we've had so far from a couple different angles. Hopefully I'll get some time to upload some of the failures as well if you guys want to see them.

Enjoy!

 

[broken flyer]

This is really cool. There is was thinking my rocket boosted viggen was going to steal the rocket plane lime light. Mines just got a c2 plug motor built into the back though.

That reusable rocket motor looks the business. Have you measured the thrust it produces in the standard configuration?

Perhaps you could try mounting it on a something that could fly under its own electrical power, then use the rocket as a boost, just to get a feel for how it works in the air.

I looked at your thread just a bit ago and a rocket boosted Viggen is pretty cool too! Reminds me a bit of the Saunders-Roe SR.53 I think it was called?

It does about a pound and a half of thrust for 7 seconds in the standard configuration, so it falls into the F size motor category. I've always wanted to do an RC rocket glider, but I just couldn't quite justify the 30 something dollars a piece that a big model rocket motor goes for and the hazmat fee you get charged if you order them online, so that was sort of what drove me to do this. This costs me about $1.13 every time I fire it if I get the propellant ingredients locally, but it could be operated even cheaper if someone wanted to buy propellant in bulk. Granted my engine does have a slightly steeper initial cost that a $30 disposable one.

It would probably be fun to put this on something that had an electric motor as well so you could keep flying after the rocket is done, but what I really need to do is get a plane built that's a bit lighter/smaller than the Versa Wing and is better set up for this. The mount on the Versa Rocket was a bit make shift and this was all done in a hurry so the launch system wasn't very good. I think with a smaller/lighter airframe where the motor is definitely on perfectly straight and is launched from a rail with guides, that'll work a lot better than the attempts we've made so far to fly this thing. Though it would be nice to know how the plane flies/test fly it without the rocket launch portion first so maybe something with two power systems would be the way to go from that perspective.