M3R (the Mach 3 Rocket): an Embry-Riddle Aeronautical University Project

[bandman444]

M3R is an extreme project with an extreme team of students from Embry-Riddle Aeronautical University in Prescott, Arizona, trying to learn what is possible from an engineering design and with limited university resources.

Let me introduce the team:

Chad Reinart (chadr77) - Team Lead
William Carpenter (RedMaxFlyer)
Daniel Dyck (Daniel777BD)
Cameron Kurtz
Julie Levitt
Bryce Chanes (Bandman444)

We can't start what is going to be a mega post without thanking the many individuals and groups that have supported us:

Embry-Riddle's Undergraduate Research Institute - Funding
Dr. Matt Pavlina - Project Advisor
Dr. Michael Fabian - Propulsion Advisor
Mr. Michael Brady - Director of Campus Safety
Mr. John Jerome - Campus Fire Safety Director
Scott Korsmier - motor design questions
Tripoli Phoenix - Launch site and FAA liaisons
The Eagle Space Flight Team - Lab-use and equipment
Eagle Aerospace - Lab-use and equipment





Now for the build thread!



Starting with the fin can fabrication.


Thanks to various aerospace donors, our campus has two freezers full of prepreg material. Carbon, fiberglass, bidirectional, unidirectional, just resin, it's all expired, but pretty much all still usable.

For those who are not familiar with preimpregnated cloth, it's the same cloth you would use for your regular layup, except the epoxy is already mixed in, but not cured. It remains uncured at cold temperatures (hence the freezer). When heated to specified temperature, at a specified rate, for a specified time, it flows and cures. This is done in a vacuum bagged setup so the fibers don't move around and the flowing epoxy can be well distributed during the cure.

To start the fin can we made a cylindrical tube of two wraps of carbon.

We started by taking a 98mm Trucore motor case as the mandrel and wrapping it in exactly one layer of release film held together by a long strip of kapton tape. The release film was held onto the mandrel by a strip of tape on the top and bottom. It is important to note that the release film was longer than the carbon part we intended to make and the tape was never covered either, this was to help facilitate easy removal after curing.



One of the great benefits of using prepreg is how easy it is to cut very precisely. This will be more apparent when we start doing the fin layers, but even getting a perfect rectangle was much easier than with dry cloth. I liken it to cutting thin leather. Pliable, yet stiff when cold. It grows to being slightly tacky as it warms up, another trait that will be important for the fin stock fabrication later on.



While a regular vacuum bag could have worked for this this lay up, we wanted to prevent the chance of wrinkles and also Chad had some heat shrink release tape that he purchased just for this kind of part. Starting below the part, I acted as a human lathe, rotating the part on a dowel while chad tried to lay down as consistent of a wrap as possible. This took some practice, but by half way down the tube Chad was laying down a nice wrap. Again, after wrapping past the part, a piece of kapton tape held it so our beautiful wrapping job wouldn't come off.

Because our on campus curing oven is only run during school hours, we had to put our oven-ready tube in the freezer till the next day.



In morning we get to put the tube in the oven. (A pretty big oven for such a small part, I know, but...that's what we have)



After the 5 hour baking process with a max temperature of 350F we were able to remove our cured tube. Removal of the heat shrink tape was painless but left a spiral of extra epoxy that squeezed out during the cure.



Chad enjoyed getting his photo taken while pulling the heat shrink tape.



Prior to sanding, the tube weighed only 73 grams and 0.021” thick. Which worked out to around 5 grams per inch.



A little bit of wet sanding removed those spirals and now we are ready to move onto the next step.



Fin preparation



For this extreme project we were pulling out on all the stops on having a beautiful and intentional airfoil. To do this we need to pick an airfoil, the NACA 64008, then represent that airfoil as a series of layers for us to cut. You could think about it a little like 3D printing, we started with a flat and thin carbon sheet, then added 6 progressively larger pieces that would form the foundation of the airfoil. To create the template shapes, we used a program called 123D to slice our 3D CATIA models.

To cut these pieces out, we made paper templates then used those to make aluminum templates which we would trace with a knife to get our pieces. Again we used the prepreg carbon as its tackiness would aide in the aligning process.

As I mentioned above, there are 6 unique shapes to cut out, and each fin gets two sets, that's 48 piece we needed to cut out, so we got to work!
We cooled down a steel sheet to cut on so that we could work with the carbon for as long as possible without it getting warm.



We cut out our airfoil plan on thin steel sheet scraps. Since we needed to make a lot of them, 8 of each carbon shape, the metal guides would be a lot more friendly than paper forms.

 

[bandman444]

The beginnings of 56 little pieces of carbon.



Most of the pieces look to be cut out.



We cut the largest pieces last. In retrospect, we should have done these first so that any scrap could be used for little pieces.



We needed a way to keep track of how many pieces we needed, so 3 people cutting and a tallier!



Phew, once those were all cut, four blanks were cut from high modulus 1mm carbon sheet that I was donated by a rocketeers scrap pile from work.



Once the layers were carefully aligned on each side of the stock, a layer of peelply was applied before the breather and vacuum bag. The assembly, along with the nipple for the vacuum hose, was placed in the freezer overnight to keep the prepreg cold till we could run the oven the next morning.



The next morning the bag is vacuumed and placed in the oven with some other composite parts for other unrelated projects.



After the curing cycle the bag and breather are removed and we find that the peelply has absorbed some excess epoxy.



A close up of the fins with the peelply still on.



This wasn't the end of the fins, we would need 5 more layers to complete the airfoil we intended, but those would come as "tip-to-tip" layers later on.

Next we cut alignment templates from posterboard so that we can tack on the fins. We used regular 5 minute epoxy on the tops and bottom to get them on there.



Daniel stands next to the first time the fins are near the 6 grain motor case. He’s very excited.

 

[bandman444]

I helped add the rocketpoxy fillets to the fincan. Note that the 1 grain case is used here to minimize the chance for inducing warping.



After peeling the masking tape and a small amount of touch up the can is ready for the final tip-to-tip layers.



Now we can turn our focus to the final layup for this project, and it would be the trickiest one yet. Because of our choice of prepreg again, we were constrained to vacuum bag the entire layup, versus what we were used to by doing unbagged wet layups. I had prior experience with doing one tip-to-tip section with a vacuum before, but time constraints having to do with cycling the oven led to us needing to do all four together at the same time.

We mocked up a simpler and less wasteful bagging setup below with masking tape and pre-used bags. This failed miserably and we went with the method you will see later.



We haven’t yet talked about the design of the tip-to-tip pieces, and that is because it took us a long time to come up with a design we liked. I had the idea of “airfoil-ing” the body tube by not running the root-to-root segments perpendicular to the root, but by sweeping them sinusoidally so that it would end up thickest where we wanted it, but gave us the smallest lip possible on the airflow during the flight.

Below is what the 4 tip-to-tip segments would look like and this shows them like a contour map.



We then cut them out on pieces of foam board, thinking that with only 4 of each to cut we didn’t need the metal forms…



We were wrong and used metal forms anyway.

Note: For this layup we switched to brand new, purchased prepreg carbon. We ran out of material we thought would cure properly and we needed one yard. We found some room temperature stable prepreg and with some money left in our grant, we could afford the $200 pre yard cost to ship it to us. I will never do this again, while it cured properly, the gaps in the fabric and cut fibers were unacceptable for the price we paid…of well…learning, that is what this project is about.

We had very little material left that we wanted to use, so we mocked up every individual piece to make sure it would fit. We aren’t cutting on the black lines, that were just guides for general orientation and spacing.



Four of every part is cut, and we are ready to begin the layup.



Step one: Vacuum bag tape around the top and bottom of the fin can.



Step 2: Apply the carbon from smallest layer to biggest layer.



Cover with peeply

 

[bandman444]

Next add the breather. And hold it in place with a little tape and do that 4 times.



Next we carefully positioned the bag material and minimized wrinkles. We first adhered it the vacuum tape we put on earlier to help it settle in one position.



We didn’t forget that we needed an attachment for the vacuum.



Lastly we used more vacuum tape to seal the leading and trailing edges.



Rinse and repeat for all four joints and we are ready to rocket and roll!



Tested the vacuum that night to make sure we didn’t have any leaks. And now for the freezer to sit over night to wait till we can run the oven, NOT! Room temp prepreg meant it was good to hang out all night without a freezer.



*drum roll*



Tah Dah!



Now we got to have fun adding epoxy and sanding it off to fill the pin holes.



Mid way through the sanding process.

 

[bandman444]

What you won’t see till the end is that we added jet black rocketpoxy on the leading edges for delamination protection, and also the VHT Clear coat we added as a clear coat and “thermal protection”. (Quotes for my dubiousness of its actual benefit here)

Now onto the rest of the rocket!

…which there isn’t much of…

The body tube is a 98mm FWFG coupler tube cut to 6 inches. Chad is seen below cutting the tube on a vertical band saw with the fence at the right distance to give him a tiny bit larger cut. Then the tube was sanded flat and to the right length.



Since a coupler tube made the airframe, we needed to make a couplers coupler that would join the nosecone and body tube pieces. We happened to have a 3.5” OD piece of aluminum to use as a mandrel. We decided to use a long piece of bidirectional prepreg fiberglass. It was extremely easy to cut and roll the tube before applying the heat shrink tape, like we did at the beginning. We calculated the number of layers needed to create the thickness we needed based on the average thickness of a layup using the same material. 6 layers were needed, and we knew we would have a tank of a part. I’m ok with a little extra strength on my coupler.



Next we needed a nosecone for our rocket, and unfortunately they don’t make nosecones that have an OD that matches the OD of standard coupler tube. To make one ourselves would have been a lot of work, so we took a 98mm 5:1 Von Karmen FWFG nosecone and cut off the bottom of it so that the OD matched the outside of the coupler.
That completes all the external geometry and begins us talking about the inside.
Due to their size and familiarity, two Altus Metrum Easy Minis were chosen for primary and backup deployment. For tracking, a 70cm GPS and 900MHz beacon from Big Red Bee were used. Our school just got some BRB900s and we wanted to give them a try at some high altitude.


The below component connects the red fiberglass body tube to the top of the forward closure. This mount is aluminum and was made on campus by our campus machinists.



Next is the 3D printed av-bay. Printed from ABS, each compartment would hold a EasyMini or 9V battery. On the outside are the ports for the screw switches which lined up with holes drilled in the airframe.



Each altimeter was premounted onto a sled that allowed us to easily connect all of the charges, switch and battery prior to loading into the holder.



The av-bay has a sealing lid that helps channel outside air from the switch holes to the altimeters while simultaneously preventing ejection charge gasses from damaging the altimeters.



Four long bolts mount it to the aluminum adapter.



In the nosecone we mounted both GPS units on either side of a short piece of all thread which connects the nosecone tip to a 3 inch bulkplate.



After that the space in between was used for parachute packing.
We used a pink 72 inch topflight parachute as the main and a Rocketman Kevlar drogue. The main was retrained using two redundant cable cutters.




That about covers the build thread portion of this project, and in fact. The rocket has already flown. A busy last semester for me has led to me not getting this posted till about two weeks after the flight.




On April 23rd, M3R flew with the Tripoli Phoenix crew at the Eagle Eye launch site near Aguila, AZ.

Prep started early and had her in the tower around 10 am and flew at 10:37am.

 

[bandman444]

The experimental N3600 roared to life and pushed M3R to over 36,000ft!


image051 - Copy by bandman444, on Flickr


[YOUTUBE]n2i7XjKGjbs[/YOUTUBE]


Due to only using barometric altimeters our maximum velocity was harder to pin down. We modified a couple parameters in RASAero till the same apogee was reached, and we can guess that we reached about Mach 2.5 (The raw EasyMini Data is attached)

Recovery was slightly less than desirable with the main seeming to come out at apogee, probably due to the ziptie not being tight enough around the parachute bundle. With the fast upper level winds they pushed us farther from the launch site than we'd have liked, but we managed to receive packets from the 70cm GPS till about 400 AGL and through the whole flight. The 900Mhz Regained lock around 25,000ft and remained till about 1,000ft AGL. Recovery required a fair amount of off-roading through BLM land along the designated jeep trails. From that we were able to get around 3/4s of a mile away and walked the rest. Poor GPSs made the search longer than we hoped as the VX-8DR didn’t have the GPS module ad the Garmin we brought was from the late 90’s. My personal VX-8GR with the GPS built in would have been much more helpful here had I not loaned it to another rocketry group at camp. Oh well… We managed to find it and haul it back in the 90F+ heat.



All-in-all this project managed to be extraordinarily successful and we can’t help but be proud of the work we did. We are hoping to refly this guy on a Blue N perhaps at XPRS in Black Rock this year. We want to add a camera on board and we want to really hit the Mach 3 that we advertised.

Thank you all for reading through this thread.

image053 by bandman444, on Flickr

Pictured: Bryce Chanes, Daniel Dyck, Chad Reinart, and Cameron Kurtz. Not Pictured: Julie Levitt
Myself and the other members are subscribed to this post so do not hesitate to ask us questions and offer your criticisms.

If there are questions about the build process that appears missing I will update the above posts with that info as well as reply below.

 

[rstaff3]

Cool stuff, thanks for sharing!

 

[ksaves2]

You're right. The -GR would have been a better rig. It actually has the ability to send the APRS waypoints to any laptop APRS tracking program. Or you could have
connected a round port Garmin 60Cs or CsX mapping GPS to the -GR and had a map-in-hand.
Your handheld 7 element Yagi on 70cm is the best to grab the packets especially if a 100mW Beeline GPS was used.
A laptop APRS program would have given the reassurance of developing a trend/drift line you can see immediately. Nonetheless, any flight you can get an intact rocket
recovered is an excellent flight! Congratulations! Kurt Savegnago

 

[TRFfan]

Nice!!

 

[dhbarr]

Very cool.

 

[OverTheTop]

Great effort everyone!

 

[T-Rex]

Awesome job!

 

[Viperfixr]

Subscribed! My dream job after USAF retirement is teaching at ERAU Prescot while doing school rocketry projects like this.

 

[bandman444]

Subscribed! My dream job after USAF retirement is teaching at ERAU Prescot while doing school rocketry projects like this.

That is awesome! You will fit right in. I just graduated in their Aerospace Engineering program and there a couple great clubs and organizations for amateur rocketry, we even have a NAR chapter associated with the school club.

 

[bandman444]

You're right. The -GR would have been a better rig. It actually has the ability to send the APRS waypoints to any laptop APRS tracking program. Or you could have
connected a round port Garmin 60Cs or CsX mapping GPS to the -GR and had a map-in-hand.
Your handheld 7 element Yagi on 70cm is the best to grab the packets especially if a 100mW Beeline GPS was used.
A laptop APRS program would have given the reassurance of developing a trend/drift line you can see immediately. Nonetheless, any flight you can get an intact rocket
recovered is an excellent flight! Congratulations! Kurt Savegnago

Understood! Trust me, we learned pretty quickly that it wasn't the best situation.

I brought my -GR with me, but I left it with another team who needed to track their vehicle so I couldn't use its built in GPS features. But nonetheless a recovered rocket, is a recovered rocket.

 

[THarrison]

Nice build and flight -- That fincan layup looks great!

 

[Zebedee]

Very nice thread and flight - What was the condition of the fin can post flight - particularly the leading edges?

 

[grouch]

Very cool guys. Thanks for taking the time to post the project. They lay ups look awesome!

 

[bandman444]

Sorry it took a little while to get these post flight fincan photos.

A couple shots of the trailing edge. Broke down to the cloth, likely on landing.



Again, landing.



All the leading edges look good.



Except this one... A small piece of epoxy missing from the leading edge.



Overall though, a great return. I really like how well the sinusoidal tip-to-tip looks in between the fins.