Flight of the Sandman

[DynaSoar]

I've been working on a design for a few months now where the airframe itself is a cluster of minimum diameter tubes, rather than a larger tube with a cluster of motor tubes inside. The theory being that with 1/3 less frontal cross section (the major source of drag) it'd out perform the cluster-inside-airframe design.

When building the first of the three, I asked Sandman to carve me out a special transition, which I further carved into a smooth transition from three tubes to one. I chose to name it after him. The three birds are in the attached picture; the Sandman is the one on the left. It's essentially three 30" long 24mm (BT50) tubes filleted along their length, with the fins glued into the joints (giving them double the contact area and so less likely to sheer).

I finally got a chance to test the design. For the shake down flight I decided to keep things low power. I built three 18 to 24 mm motor adapters, loaded them up with C6-5s, and packed it for flight. Locked and loaded, it weighed 9 ounces.

Continued on next message because I can't figure out how to put two pictures in one messsage.

 

[DynaSoar]

To keep the weight low I used the three-tube nose cone I carved, rather than the original 3-to-1 transition. The attached pic is the nose cone on the Sandman booster. One tube carried the shock cord, the other two had a 12" chute each attached to the nose via three screw eyes. Launch rod was 1/8". I used a 4 foot rod due to the length and the fact I was afraid it'd start off slow on just C's.

T minus zero, and the thing screamed off the rod, straight up. The delay started and the smoke continued straight up. With such a small cross section from directly below it was nearly invisible. It was STILL going straight up when the ejection charges went off. Best as I can figure is that it was so over-stable (the solid nose being 1/3 of the weight) that it fought arcing over. When the charge did go off, it went sideways so fast that it probably still had siginifcant forward speed. It may have still been going on on C6-7s. It's hard to estimate from directly below, but I wouldn't be afraid to guess a thousand feet.

There was a mishap, in that one of the motor adapters hadn't gotten locked under the 24mm motor retainer hook, and ejected. I didn't realize this is what happened until I happened to find it while chasing down a later launch. What I saw was the body go horizontal, the nose seperated, and it started to come down without chutes. Due to loss of pressure, the chutes didn't get pushed out of the tubes.

But as it happened, without that adapter and with the fuel burnt, it was now under 8 ounces (measured after I got home), and the configuration was just perfect to make it come down horizontal. The nose and the body fell at the same rate, a few feet of shock cord apart, absolutely horizontal, and all but floating down. It landed that way too, so slow that there was no damage to the 1/16" balsa fins. Given the problems and the result, it was truly a charmed flight.

It might have been different with the heavier E engines it was built for. But then, had I launched it on E's, all by myself like I was, I might have never seen it again. When the time comes for that, I'm going to have someone launch it while I'm way off the side where I can see the profile, because I expect it to go big big plenty much way high. And I'll probably use one chute to slow it, and a nice shiny mylar streamer so I can see it. I'll definitely make sure I can safely recover these birds before I start adding the payload sections (see first pic) for an altimeter. Then I'll be able to prove it's a good design. But from the first test, I'd say it's a pretty sure thing already.

And then, on to 29mm. Since I can pack over 1,000 n/s (three Ellis I69's = 1,107 n/s) into three 29mm tubes, with a frontal area of only 22 cm^2 (89% of that of a BT70 at 2.2" diameter) and still keep the whole thing below 3.3 pounds loaded and ready to launch, I think I can really do some damage to the atmosphere.

Congratulation Sandman, it's a healthy new sky puncher.

 

[sandman]

WOW!

I got a rocket named after me...just 'cause I made a part...COOL!

Cool rocket too!

Get some flight pics if you can.

sandman

 

[radiO]

Super RAD!

 

[rstaff3]

I always figgured it would take an 'M' to boost the sandman...guess I was wrong!

DynaSoar, cool rocket, man. Can you post slightly larger pics?

 

[DynaSoar]

Originally posted by rstaff3
I always figgured it would take an 'M' to boost the sandman...guess I was wrong!

DynaSoar, cool rocket, man. Can you post slightly larger pics?

I had to cut down the pics I had because I only had one of those disposable cameras, and the jpegs they make for me at the drug store come out to 150 or 200 kb each, way to big to post here. Something like that. My wife actually did the graphics stuff. 25 years of doing computer stuff and I still can't get a handle on doing anything having to do with graphics.

I'll see about getting some better pics, and some flight pics, at the next CATO launch. Foks there have much better equipment and capability than I do. Or if the launch Saturday gets rained out, I'll get together with someone to help me fly it on another day. It's hard to take pictures and not lose it flying by yourself. I really need to get some pics because I want to submit it to the Descon contest. Deadline is 8/31.

Oh, and something I left out, but just got done berating someone with elsewhere: all wood glue, paper and balsa. No mid/high power materials, just good building techniques. With the booster stage, and 6 E9's, it'll push over H power. I'm waging war on overbuilding.

 

[lalligood]

Originally posted by rstaff3
Can you post slightly larger pics?

I think what rstaff3 meant was could you crop the default image to show just the nose cone/transition instead of resizing the total image? Please. Looks way too cool even with what little detail that can be made out!

 

[DynaSoar]

Originally posted by lalligood
I think what rstaff3 meant was could you crop the default image to show just the nose cone/transition instead of resizing the total image? Please. Looks way too cool even with what little detail that can be made out!

I'll ask the boss. I have the same problem with computer graphics and with cars: if I mess with them I can only make them worse.

 

[rstaff3]

Originally posted by lalligood
I think what rstaff3 meant was could you crop the default image to show just the nose cone/transition instead of resizing the total image? Please. Looks way too cool even with what little detail that can be made out!

Yup, that's what I meant

 

[DynaSoar]

I've got some replacement pictures taken but not processed yet. They'll be up soon.

Sadly, today I forgot to take the camera with me. I sent the Sandman up under full power for the first time, three E9s, and with the payload section. Recovery was shock cord in one tube, streamer in the second, 10" nylon chute in the third.

There was some significant wind, so I was launching into it about 10 degrees. I sent up a couple sensitive to wind (Big Bertha) and fairly insensitive (Lil' 'Tinker, an altidude bird from plans in Model Rocket News in the 60's) I had by angles down. Still, so as not to lose it in case the wind high up was stronger, I packed several ounces of gravel into the payload section, bringing it up to the edge of 16 ounces loaded.

Liftoff was slow at first, all three flames clearly visible bright orange. Off the rod, there was no tipping and it gained speed and alitude fast. Trajectory looked fairly ballistic, not as much effect of wind as the Bertha showed.

Coast followed ballstic trajectory. Apogee was only about 1000 feet, but about 300 feet upwind. Ejection was about 2 seconds past apogee (probably the extra weight).

Separation. Streamer. No chute. Body and payload came into sight orbiting each other horizontally and falling slow enough that landing in the hay field wouldn't be a problem. Still no chute. No chute, no drift. The rocket settled down gently and horizontally beyond the trees and well into the Rocket Eating Swamp. I tried to retrieve the Omloidinator from that swamp. I didn't get 10 yards into it. This was at least 30.

Alas, farewell. Good flight, adequate recovery (would have survived easily), no retrieval.

BUT. This is but the first of three. The lugs were poorly balanced, the clustered body tube fillets were excessive, and the aft end of the tubes had suffered crimping due to trying to fit apparently humidity swollen E engines into it. The other two are step wise improvements in construction and design. Now that the design is proven, the others can carry on.

Now will they be the end. Next to come, upscale to 29mm. But until that time, there's plenty of flying left in the family.

"Ahm just gittin' started!"

Blue side up.