Double Shuttle has double cato

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Thought you might find this article on balsa fillers and strength/weight useful: https://rocketn00b.blogspot.com/2018/05/balsa-grain-fillers-and-added-weight.html

It seems to agree with you that a glue coating adds a lot of strength (though a paper and glue combo also tends to add a lot of weight). Interestingly making a white glue and water slurry with talc as filler (and no papering) appears to really strengthen balsa with less of a weight penalty. Having said that, in your situation I'd prefer strength over weight too because of the strain from the motors.

Rktman, There is a lot of detailed information there. I think I would agree with you that strength is pretty important for my application.

Frank, I did use iron-on monokote years ago on the Estes AstroBlaster and Dr. John Kallend's LadyHawk years ago. The finished product looked very good, but I spent a lot of time working on the monokote. I am so far happy with the balsa white-glue coated label paper.
 
It is easy to cut the wing material with a scroll saw. I took my electric ironing tool for applying monokote and tried it on the wing that had label paper with white glue and tried to get rid of the wrinkles. I think it helped a little bit. Elmer's white glue has vinyl in it, so applying a hot iron tends to melt the vinyl slightly. I found that it was best to take the sock off the iron and move the iron slowly while pressing down.
 

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I had Boyce Aerospace make new 3D printed plastic T-sections for the Double. The fit of the parts is excellent. Shown is a photo for the vent tubes dry fit of the two shuttle halves along with some close-up photo's of the T-section 3D printed parts.
 

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I glued the T-sections into the vent tubes for both half-shells. I coated the tubes before gluing with a sodium silicate solution except where the tubes were glued. I had some concentric tubing left over from a previous project that slid nicely over the tubes making the tubes double-walled. A dry fit with the wings looks good. Boyce Aerospace met the specified height of the protruding T-section just right so that it is flush with the wing surface.
 

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I glued the T-sections into the vent tubes for both half-shells. I coated the tubes before gluing with a sodium silicate solution except where the tubes were glued. I had some concentric tubing left over from a previous project that slid nicely over the tubes making the tubes double-walled. A dry fit with the wings looks good. Boyce Aerospace met the specified height of the protruding T-section just right so that it is flush with the wing surface.


IMPRESSIVE! Precise, clean craftsmanship too.
 
So do these interlock somehow and then the ejection charge blows them apart reliably via the vent holes?

Frank, that's right. It looks great, when it works. I am hoping here to improve the design and construction to increase the reliability. Another factor on the reliability is the cluster of two E12-4's, but I am partial to that motor. Perhaps, I could cluster a pair of 24 mm composite motors, but my frame of mind is not there, yet.
 
The last T-section went in very good. The tolerances of the 3D printed parts are very good. The T-sections are essentially flush with the glider's undersides. I wanted to show the Boyce Aerospace nose cone halves before gluing them in place. Again, the tolerances are very good and consequently the fit is very good. The printed nose cones are a little bit heavier than balsa. I find that a comparable hollowed finished (balsa filled and finished) balsa nose cone is about 1.87 ounces, whereas the plastic printed (unfinished) nose cone is 2.56 ounces. It is getting harder to find the balsa nose cones, so I'm going with the printed nose cones. Holding the printed nose cones to the light shows that they have some kind of standard 4-sided internal fill. The plastic nose cones appear to be very strong and gluing them in place will make the model even stronger.
 

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The short vent tubes are roughly 24 mm diameter. The white tube shown is a thin wall tube from Balsa Machine Services and I think the thick brown tube that fits inside is from e-rockets. At first I had trouble getting the vent tubes from one rocket glider to align and fit in the mating glider, but then I sanded the T-sections on one side very slightly with a Dremel tool. After several dry-fits I used Testor's plastic cement on the front and back tubes and then later I glued in the middle tube. For the final assembly I need to fit the two gliders together, so that all 3 vent tubes mate simultaneously. With a little bit of practice this works pretty good. The final clearances and tolerances are very good.
 

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The new Double Shuttle with 3D printed parts flew at the UROC launch on Saturday. It flew with a cluster of two E12-4's using e-matches from Blackjack. I tamped the e-matches in place with a tiny amount of tissue paper with a tiny screw driver and put masking tape on top for good measure. Doing this I was able to prep fast and the ematches seemed to hold in place well. I had the wrong mindset thinking that this Double Shuttle was the same as previous versions even though the nose cones were heavier and so I did not use any pre-set "up" elevons. I think now that this was a critical error. In any case one glider came straight down and had considerable damage. Fortunately the other glider worked enough to sustain no damage.

 

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Sorry to hear one twin didn't make it. Did the one that survived have some up flap? Just wondering why one glided while the other came in ballistic. (At least you had a 50% success rate).
 
Sorry about the crash. Maybe time to put some RC gear in the remaining Shuttle?

Actually, in a way I have already done something like that. I have a red glider, which is slightly larger than the Double Shuttle glider and has R/C. It has flown twice as a parasite glider on the 4xOT successfully. In fact I have a new 4xOT blue glider that is approaching completion, which has R/C along with in-flight ignition for a model rocket motor.

My current plan is to rebuild the damaged Double Shuttle glider. I am going to look into finding a lighter nose cone. Also, I want to do a hand-toss test glide of the remaining good glider with higher preset up-elevons.
 

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I hand tossed the one good glider with a higher pre-set up-elevon and that seemed to help. Since I have a spare nose cone and I need to re-build the damaged glider anyways, I decided to cut off the bottom plate and the rear-end of the old nose cone with my dremel tool and see how things go. While I was doing this I removed some of the mirco-fill of the 3D printed nose cone. However, the micro-fill is so light, this step is probably not necessary. While I was doing this, the nose cone broke. I glued the pieces together with CA and later put epoxy on top of that fix. The nose cone weight went from 2.568 oz to 0.73 oz, which is a 1.838 oz reduction. Overall, I am thinking that this re-build will work. It is definitely worth a try.
 

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I hand tossed the one good glider with a higher pre-set up-elevon and that seemed to help. Since I have a spare nose cone and I need to re-build the damaged glider anyways, I decided to cut off the bottom plate and the rear-end of the old nose cone with my dremel tool and see how things go. While I was doing this I removed some of the mirco-fill of the 3D printed nose cone. However, the micro-fill is so light, this step is probably not necessary. While I was doing this, the nose cone broke. I glued the pieces together with CA and later put epoxy on top of that fix. The nose cone weight went from 2.568 oz to 0.73 oz, which is a 1.838 oz reduction. Overall, I am thinking that this re-build will work. It is definitely worth a try.

That's quite a reduction in weight for a glider. Looks promising, I'm with you on a rebuild.
 
Are you maintaining the same Center of Gravity location? (For boost and glide?)

Crawf,
In all honesty I have not paid much attention to CG and CP in designing and building this model. Perhaps, I can appeal to using mindsim as I think Daddyisabar would do. Early on I did build a RocSim model to check for stability during ascent. Such a sim model is easy to setup with the two gliders together. I believe RocSim measures the CG and the CP from the nose. On that basis with two E12-4's the prediction is CG=15.74" and the CP=21.56" giving a margin of 1.88. From experience the Double Shuttle flies straight up with no problem. I just checked the undamaged glider for CG, which was easy because it has the launch lugs. So I just put a wooden dowel through the lugs and suspended the model with a string. I don't have a burnt-out E12 (they are too stinky to keep in the house), so I put in a burnt-out AT single use 24 mm motor. I got a CG=16", which is essentially the same thing as before with motors loaded. I am not sure how accurate that is,because I would have expected the CG to have shifted more forward with a burnt-out motor.
 
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Really good answer. ;)

I build kits most of the time, so I am targeting recommended guidelines. But when developing a model, so much of the analysis is simply based on observations of performance.
 
I tried the Double Shuttle last Saturday. Both E12-4's fired successfully with Blackjack e-matches. However, the gliders failed to separate and there was a hard landing. Amazingly, damage to the gliders is small and the gliders are easily repairable. I still have two E12-4's left, so another try is warranted.

 

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Ouch! Did the ejection charges not go off? I don't think I heard them.

Rktman,
I didn't hear the ejection charges, either. I went back and looked at my original copy of the 05/05/2019 launch. It looks like ignition is at about 5 or 6 seconds into the video and apogee is at about 11 or 12 seconds. So, remembering that an E12-4 burns for about 2 seconds and then the delay is about 4 seconds, there should have been enough time for the ejection charge to go off near or after apogee. It looks like the white smoke on boost stops after about 2 seconds, so I am thinking that was burn-out. Both motors were burnt-out and the Double Shuttle would not get that high without both motors. At the crash scene the gliders would actually apart, but very close to each other. When I think back about past Double Shuttle flights, this has happened several times before. I don't think that BP ejection charges fail very often, if ever, if the thrust producing part of the burn is alright. I now tend to think that the ejection charges fired (the inside vent tubes look like they had a lot soot), but the gliders did not separate. Perhaps, the gliders were too tight together or there is some gas leakage somewhere.
 
I revisited the Double Shuttle today with a backyard ejection test. I am suspicious of the E12-4 performance. Not only with regard to the Cato's, but also with regard to the reliability of the delay charge and the ejection charge. On post No. 113 of this thread the Double Shuttle did not separate and hit the ground head on. Remarkably, there was no significant damage. Before today's test I inspected the ejection tubes as well as I could with a flashlight and could see no damage or possible leaks. So, I ordered some 24 mm couplers from "erockets" and cut them to size to fit in the Double Shuttle. I plugged one end with a cut-off rubber stopper and put a small diameter copper tube through the stopper. Then I filled the remainder of the tube with epoxy. I can then thread an e-match through the copper tube. I put a wood plug in the other simulated motor and proceeded to use about 0.3 gram of 4f powder for the first test. The first test was successful and the two halves of the shuttle separated fine. I now plan to build a 2-motor cluster with 24 mm composite motors. If that works, I will use composite motors instead of the E12's.
 
Bob, what about an F-24? That's almost what the two D-12 cluster might get you, and much lighter than two motors?

Or you could do an E-18 or F12 if you want to tone the boost down
 
Bob, what about an F-24? That's almost what the two D-12 cluster might get you, and much lighter than two motors?

Or you could do an E-18 or F12 if you want to tone the boost down
Frank, the current model is built for 2 motors. One motor in each glider half. The thought had occurred to me some time ago to somehow make the gliders powered by just one motor in a new design. That would increase reliability, but I have stayed with this design. OK, I think I see what you are saying. I could just put in one F-motor and plug the other motor location. I would be concerned that the thrust would be off-center a little bit, but perhaps I could compensate for that. I will keep this in mind.
 
Frank, the current model is built for 2 motors. One motor in each glider half. The thought had occurred to me some time ago to somehow make the gliders powered by just one motor in a new design. That would increase reliability, but I have stayed with this design. OK, I think I see what you are saying. I could just put in one F-motor and plug the other motor location. I would be concerned that the thrust would be off-center a little bit, but perhaps I could compensate for that. I will keep this in mind.
Well, I thought about this some more and decided to use a cluster of two F24-4's. I loaded the motors several months ago and I think that I drilled down the time delay on one motor by a few seconds. I was concerned, because I have never ignited two 24 mm motors before. I used the Aerotech FirstFire Jr.'s. One of the FirstFires wouldn't fit through the nozzle, so I just simply took another one out of the box. The fit was snug enough, so didn't use any thermalite. I had a good flight at LDRS-39. I now have no plans to go back to E12's.
 

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I got some great lift-off pictures from Jim Wilkerson/Tahoma Photography.
 

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