Double Shuttle has double cato

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aerostadt

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Last Saturday my scratch-built Double Shuttle had a double cato. The Double Shuttle consists of twin rocket gliders with a 24 mm motor in each half. They are joined together by a friction fit and separate when the ejection charge is ignited. On Saturday I had two E12-4's in the model and the temperature around launch time was about 18 Deg.F. I reported the cato's in a NAR mess report and I sent an email to Estes describing the event. Later Estes asked me for photo's, which I sent. Estes is going to send me a new pack of motors and a kit of my choice. I think that the model may be repairable and I have started rebuilding. I do not plan on using E-motors at these cold temperatures again.

In the attached photos you can see the Double Shuttle on the pad. On ignition there was a loud pop and one cato did more damage than the other. The wings separated from one glider, but the other glider went to about 20 feet high. The other glider looked alright in the snow, but when I picked it up the wing had separated from the tube on one side and had damage.



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Aksrockets

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It was a bad day for ALL bp motors. I think we had 4 catos out of 8 or so motors. Those arn't good percentages!
I'm glad that it can be rebuilt, that cato was pretty nasty (but interesting).

Alex
 

Green Jello

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It was a bad day for ALL bp motors. I think we had 4 catos out of 8 or so motors. Those arn't good percentages!
I'm glad that it can be rebuilt, that cato was pretty nasty (but interesting).

Alex
Low temperature?
 

aerostadt

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The propellant grain of black powder motors have a tendency to crack or fracture at low temperatures. The flame front then propagates into these cracks and the burning surface area increases too fast and the motor has a catastrophic failure. My two E-motors blew out the clay nozzle, but the case did not split. I have a pdf file describing low temperature effects. This attachments is based on a science fair project that I did in 1965 using 18 mm motors. I maintained in that study that the temperature difference during firing caused the cracking and there was a test to check to see if there was a critical ambient temperature. I must admit that my populations size of only about 2 or 3 motors was very small. This topic has been visited many times since then and many researchers have found that temperature cycling can be a contributor, too. On Saturday I tried to keep the motors warm up until the time they were fired.

View attachment ambient temp effect on model rocket perfomance.pdf
 
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Verna

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Love your shuttles.

E's are notorius for catos in colder weather. Personally I wouldn't use an E if it were below 50*, I'm sure someone will take issue with that but every one I've ever seen cato was below 50*.

Verna
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chadrog

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The E12's I've seen thus far don't seem to care what the temp is, maybe it's geography. Spring, summer, fall ,winter, seems nearly every one that comes to Wisconsin blows up!
 

aerostadt

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The E12's I've seen thus far don't seem to care what the temp is, maybe it's geography. Spring, summer, fall ,winter, seems nearly every one that comes to Wisconsin blows up!
The two E12's I used last summer worked and the two pair before that worked alright.

BTW I found the catalog listing for the thrust stand that I used for the ambient temperature study years ago. It is on page 25 of the RDC catalog shown below. It is just amazing that ninfinger website has all this old information.

http://www.ninfinger.org/rockets/catalogs/rdc66/66rdc.pdf
 

aerostadt

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Repair work has started. I cut the excess epoxy fillets on the body tube sides with the Dremel cutting wheel and the remaining epoxy was ground down with a Dremel sanding drum. For repair work those Dremel tools really earn their keep. One glider was more damaged than the other, but both had enough damage that I needed to cut off the aft end of the motor tube. I have enough 24 mm tube parts in my inventory that I will not need to order anything. I made sure to salvage the E-motor clips. I found that these things are kinda of expensive and take time to order. As shown in the attached photo the motor tube ahead of the forward coupling port was severely heat affected. I think that it is basically strong enough, but as an added precaution I slipped a new 24 mm tube inside of it. I did this by cutting a short section of 24 mm tube lengthwise and notching it a small amount as to not block the forward coupling tube. I then coated it with epoxy and slipped into the old tube. A dry fit for the short 24 mm tube is shown in the photos.

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aerostadt

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I am taking new 24 mm tube and inserting them into the old tubing. First, I attached E-motor engine hooks to the rear of the tubes using drywall tape to somewhat hold the epoxy in place as shown in the photos. This is a trick that I learned from the Vatsaas Brothers website years ago (whatever happened to those good guys!). The drywall wall tape tends to lift somewhat as the epoxy cures, but I was able to tape it down with masking tape (not shown in the photos).

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I decided to couple the 24 mm tubing with some old spacer (yellow) tubes that I had left over from old LPR kits. It is not as strong as regular couplers, but it is looser and slides easily into place. In fact, on one of the tubes it slid too easily and I had to wait for the epoxy to cure before sliding it into the other tube. Since, the spacer tubes are very thin-walled I coated them with epoxy both inside and out. This step calls for gloves (not latex) on both hands. I will need to cut and build the rear coupling ports into these new 24 mm tubes.

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aerostadt

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I got some work done on the two rear ports, one in each glider. This consists of first making a 24 mm diameter paper template and putting it on the motor tube and tracing a pattern to cut. Of course, the cut holes must line up with the rear holes in the corresponding wings. As shown in the first photo I also cut the small 24 mm mating tubes that will fit perpendicular to the motor tubes.

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These mating tubes fit well into the motor tubes as shown in the photo below. Also, shown is the needed new wood plug with a central hole drilled. The plug is cut from a 3/4" diameter hard wood dowel. It is a little small for the 24 mm mating tube, but I can wrap masking tape around it until I get a good fit. I tacked each perpendicular mating tube into the motor tube with gap-filling CA to hold them in place for the next step.

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I cut two small pieces of fiberglass for each mating tube and securely bonded the mating tubes to the motor tubes with epoxy.

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aerostadt

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I have epoxied the new vent port plug into place as shown. Also, I found some weak heat-affected old tubing and put fiberglass and epoxy at the same time.

The wing of glider no.1 had the worst damage. I cleaned it with baby wipes and then lightly sanded it. I re-papered the bad spots with business stationery and Elmer's white glue. Most of the patched spots will be under the fuselage shell when it is epoxied back on. This Eaton 24-pound (25% cotton) business stationery is terrific stuff for papering balsa wings. I don't know if it is still available. I bought it about 20 years ago for resumes. Now that I am retired I have found a much better use for it.

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aerostadt

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I'm continuing to wrestle with the refurbishment of the Double Shuttle. First I tacked down the fuselage shell on the glider with less damage with Titebond Wood (yellow) glue and placed a dictionary on top. Once this dries I can come back and put on an epoxy fillet. The next glider was in worse shape and so I tacked it into place on its corresponding wing with gap filler CA. I did a test fit with the two gliders and found some resistance between the rear vent port plug and vent tube. I little bit of grinding with the Dremel tool on the rear vent port tube solved this problem. I decided that I needed a better bond between the fuselage and the wing of the glider that was in worse condition and that it would be best to glue while it was in the final configuration. So, I found some empty space on a nearby shelf and piled on the books again and bonded this glider with a relatively large amount of wood (yellow) glue. Right now the model does not look as good as new, but the hardest parts of reconstruction are over.

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aerostadt

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I received the free Estes replacements today and with no shipping costs to me. I got three E12-4's and a kit of my choice, the Shuttle Xpress. Thank you, Estes!

I put an epoxy fillet on the Double Shuttle wing fillets. I should have done one Shuttle at a time, because the epoxy started to cure before I was done. Consequently, I had to file the lumps as well as I could with a rat-tail file and then with the Dremel (another good use for the Dremel). Since things are still rough I applied some Bondo.

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aerostadt

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Shown are the masked double shuttles ready for painting and the re-painted shuttles. With a few touch ups and re-fitting of the vent port plugs the model should be ready to fly again.
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Spooks

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I will NEVER use Estes E motors again...

I had a CATO from E12's, one...rebuilt and flew today on a F26!
 

Madison Alum

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The repairs came out looking really great. If I understand correctly, the vent tube plugs on one glider nest in the vent tubes on the other one and the ejection charge pops them apart? Cool idea!
 

aerostadt

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The repairs came out looking really great. If I understand correctly, the vent tube plugs on one glider nest in the vent tubes on the other one and the ejection charge pops them apart? Cool idea!
Madison Alum,
Yes, that is correct. In practice the fit has got to be pretty good and I have found that making a good fit with just enough friction is difficult to control. I was working on the fit yesterday and I took the rocket to our club launch today, but I felt that the connection is not ready, yet. I need to look at the model so more. I do wonder if the model was designed a little bit differently, it might be better, but that is too late now.
Bob
 

aerostadt

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I put some tracing paper around the aft plug/vent hole to see if that connection was good.
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After inspection I decided that this plug and vent hole was the problem for preventing a good fit. I decided to cut a green motor block in half and glue it to the aft plug on the aft side. The type of parts are shown in the photo below. The photo is fuzzy. I then put some epoxy with micro-balloons on the aft side with the glued in-place motor block and then later filed it down a small amount. The motor block is shown already sanded down.
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I then tested a fiber 24 mm coupler on the vent port plug and it fit well.
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I came to realize that the fiber coupler would not fit in the vent port without grinding down the port down with my dremel tool especially on one side. Remember that the vent port was thin 24 mm tubing with epoxy/glass on the outside. I actually had to grind down the vent port until a small hole appeared in the side. Even though there is a hole in the side a dry fit showed that the fiber coupler would now fit nicely into the hole.
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I proceeded to put the fiber coupler around the aft plug with a thin layer of epoxy on the coupler outside. The epoxy must be thin enough so that when the two shuttle gliders are fitted together the fiber coupler will stay bonded to the vent port of the other glider after curing. This worked and the fit is good. The photo below shows the fiber coupler glued in place.

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aerostadt

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Here are some videos of the Double Shuttle from last summer at Hellfire-17. The Double Shuttle requires two BP E-motors. A pair of D12's will not be enough to get good altitude. The first video shows what happens when the fit between the two gliders is not snug enough. All Double Shuttle launches are out by the far-away pads.

http://youtu.be/qdxBdG4Awvw

This second video shows the Double Shuttle launch when the fit between the two gliders is snug enough.

http://U9TeK_-ClHo

I had some difficulty splicing the Double Shuttle launches out of all the UROC activities, so the videos overlap into some of the other activities.
 
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philip

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Really nice second launch aerostadt. Are you going to develop that any further eg RC?
 

Saluki

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This is a nice looking rocket/glider. Are there any plans available for it?
 

aerostadt

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Really nice second launch aerostadt. Are you going to develop that any further eg RC?
Thanks for your interest. I do not have any plans to use R/C for this model. My objective is to repeat the last successful flight.

This is a nice looking rocket/glider. Are there any plans available for it?
I do not have any plans, but I do have a RocSim file. The Rocsim file is here: View attachment Double Shuttle 1b.rkt
If you have RocSim, you could get information, dimensions, etc. from there. The main airframe is 3" diameter LOC tubing cut in half. The balsa nose cone is BMS custom-made for the 4x Orbital Transport glider, but I didn't like the shape, so I used it for the Double Shuttle instead. The nose cone was hollowed out and cut in half. I'm sure there are other nose cone alternatives out there. The LOC tube was cut in half lengthwise. The wings are made from 1/8" thick balsa with papering (24 pound stationery & Elmer's white glue) on both sides. In some ways the concept reminds me of the old Cox Shuttle America (~1972-73 timeframe) in that the glider wings provide the fin stabilization on the way up.
 
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aerostadt

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I re-built the Double Shuttle again and flew it successfully last Saturday. This time on two E9-4's. The lot number was 06 28 11. I am thinking that the model doesn't go as high as on two E12's, but it might be my imagination or the model has gained some extra weight after two re-builds, not counting the first original build. The E12 has about the same total impulse as the E9 although the thrust to weight ratio is better with E12's.

As always I want to thank Mark at Sticker Shock for all his decal support. The model flew well separated as it should with both gliders circling down and landing intact.

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aerostadt

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This time I went with a design change that probably works better. Previously the two glider halves were coupled with 2 wood plugs protruding into vent ports. These wood plugs were replaced with 3 modified stage couplers. This time I cut a new center panel out of the wing to put in a 24 mm tube containing the motor mount arrangement and vent ports.

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Of course, bulkheads for mounting the long 24 mm tube were made as usual.

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The wood plugs used in the previous two versions of the model are now replaced with 24 mm stiff fiber couplers bought from Semroc. Since the couplers were not quite long enough the couplers themselves were coupled together to make a longer coupler.

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aerostadt

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The final configuration now has 3 connecting vent ports. When the 2 gliders are mated together there is a tendency that either the nose will be perfectly flush or the aft end will be perfectly flush. I decided to keep the nose flush in order to minimize the tendency for the 2 gliders to separate prematurely. I put a little bit of double-sided scotch tape on the forward end, but I don't know if this really helps very much. The gap at the aft end was only about 1/8". The wing surface is very large and the model has been flown 3 times, so there is probably some warpage in the wings keeping them from being perfectly flush. In any case this latest flight was good.

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aerostadt

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I got another good flight of the Double Shuttle at Hellfire-19. I used a cluster of two E124's. The lot number is A 06 22 12, which worked fine. The mating fit seems to change over time. This time I did not use double sided scotch tape, but just put a small amount of masking tape on each of the vent tubes. Both E12's fired, but the Double Shuttle arced over a little too early. I have not checked the elevons in awhile and the duct tape holding the elevons to the paper clips had come loose. I am thinking that the two pairs of elevons on each side of the model may not have been symmetrical with their counter-part on the other side, which then caused the model to arc over early. The twin gliders did separate successfully. This was my only launch at HF-19 that landed completely unscathed.

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