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  #1  
Old 10-08-2012, 07:00 PM
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Default Large Midget? Is that like Jumbo Shrimp?

A Large Midget -- now there's a concept. Kind of like "jumbo shrimp."

In this and the following posts are some photos of two of my Midgets, all dressed up in their Sunday best. The smaller of the two (red) is my K-40 clone, replacing the original one that I only got to fly once back in 1970. The other one (blue) is my 168% Upscaled Midget. The clone has not been flown yet, but the upscale made several flights while still in primer. It uses standard 18mm motors; in fact, that was one of the reasons that I built it. I wanted to recreate my old Midget, but in a size that used a larger variety of readily-available motors and that would be easier to visually track in flight. I have launched it on B6/B6 and C6/C6 combinations and I have also launched the sustainer alone. It was actually the first one of the pair that I built.

Semroc has recently released a Retro-Repro version of the Astron Midget. These two were built with Semroc parts but both predate the release of that kit by several years.


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  #2  
Old 10-08-2012, 07:13 PM
A Fish Named Wallyum A Fish Named Wallyum is offline
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Cool! What size are the tubes on the upscale? Why haven't you done a review on it yet? What kind of height did you get on the flights? I like the idea of a bird like that for B6-4 Field.
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  #3  
Old 10-08-2012, 07:39 PM
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Astron Midget clone. This one is the most recent of the three Midgets that I have built, and is the only one that hasn't been flown yet. With Estes now making A10-0T booster motors again that will change. Like the original Midget, it has 18mm diameter Series III motor mounts. (Similar to standard motors, but 1" shorter.) Due to the tube lengths, especially the booster's, it cannot accommodate standard 18mm motors. But that's not a problem, because one can reproduce the equivalent of a long OOP Series III (shorty) motor by inserting a modern-day Mini T motor into a casing from a spent standard motor that has been cut down to the correct length (1.75").

The Midget used "conventional" staging, with the booster and sustainer motors being taped together in line. For this one I intend to tape together the 18mm adapters after I have inserted the motors in them.


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Old 10-08-2012, 08:04 PM
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For the upscale I used ST-16 for the sustainer and LT-115 for the booster body tubes. The fins are papered balsa and the sustainer boattail is cardstock, like the original.

On a B6-0/B6-4 combination it reaches something like 400 feet. On a C6-0/C6-5 combo it goes around twice as high or higher. I haven't launched with an A8-0 in the booster yet, nor have I simmed it to see if that would even be feasible. In contrast to the original and Mini-Brute Midgets, this one uses gap-staging with venting out the aft end of the booster. Another difference: the motors in both stages have old-style (C-shaped) motor clips. Since it uses gap-staging, neither clip interferes with clean staging. You can actually see jets of smoke shoot out of tail end of the booster when it stages, followed a fraction of a second later by a loud "pop" as the two sections separate. This is especially easy to see with the B motor combination.

One other thing: with the large fin area, it is rather prone to weathercocking. My theory is that this represents a rare, but foreseeable, pitfall with upscaling. The original Astron Midget needed all of that fin area for stability. Both my old one in 1970 and my Mini-Brute clone flew absolutely straight up. But on rare occasions when you upscale a design of a small rocket, the correctly-scaled fins can end up being a little bit larger than needed for that size of rocket on the motors that it uses. This seems to be the case here. At least that's my theory, anyway.

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Old 10-08-2012, 08:44 PM
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Quote:
Originally Posted by Mark II
I haven't launched with an A8-0 in the booster yet, nor have I simmed it to see if that would even be feasible.


It will work.....and stage below treetop level. Kody's Aerobee Hi is much larger than the upscale Midget and it stages around 15-20 ft. Give it a shot on a calm day.
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Old 10-08-2012, 08:58 PM
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Quote:
Originally Posted by tbzep
It will work.....and stage below treetop level. Kody's Aerobee Hi is much larger than the upscale Midget and it stages around 15-20 ft. Give it a shot on a calm day.
The B6-0 doesn't stage much higher than that! But I'm intrigued by the idea (definitely on a calm day).
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Old 10-08-2012, 09:42 PM
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Quote:
Originally Posted by Mark II
One other thing: with the large fin area, it is rather prone to weathercocking. My theory is that this represents a rare, but foreseeable, pitfall with upscaling. The original Astron Midget needed all of that fin area for stability. Both my old one in 1970 and my Mini-Brute clone flew absolutely straight up. But on rare occasions when you upscale a design of a small rocket, the correctly-scaled fins can end up being a little bit larger than needed for that size of rocket on the motors that it uses. This seems to be the case here. At least that's my theory, anyway.
Beautiful work, Mark. Outstanding!

While I agree, in theory, as exemplified by the Reynolds number concept, that as the scale goes up, the fins become more effective. But I'd say, in your ST-16 (BT-60) case, with the C6 booster, you just don't have enough air speed to satisfactorily counter the weathercocking effects of any cross wind.

Regardless, those shore are purty rockets

Doug

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Old 10-08-2012, 09:50 PM
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Interesting that you mentioned a low staging altitude, Tim. My old Astron Midget, had the strangest flight profile in its only launch in 1970.

Of course I don't remember the motors that I used in it that day, because I never logged anything back then, and any physical remains from that era in my rocketry career are long gone. But after looking through the old Estes catalogs, I think that I used a 1/2A6-0S in the booster and a 1/2A6-4S in the sustainer. I remember that I didn't want it to be underpowered but I also didn't want the little guy to go totally out of sight either. It was the first mulltistage rocket that I ever launched. (My second-ever multistage flight was some years later, with my Mini-Brute Midget in 2006.) I got it as a free kit right when it came out in 1969. We were in the process of relocating though, so I didn't get to launch it until after we had moved to Western New York the next year.

My father caught me as I tried to slip out of the house with my Electro Launch and my Midget, but instead of forbidding me to launch it he decided to accompany me "in case you get arrested." It was the only rocket launch of mine that he ever witnessed. I set up my pad and my rocket in a very large overgrown field just past the end of our block. My father kept urging me to hurry up before anyone saw us.

When I pressed the launch button my Midget shot up to about treetop level, and then did something that I have never seen before or since. It stopped and started backsliding straight back down, with the motor still firing! I heard my father yell "Oh oh!" as it dropped several feet, while still pointing straight up all the way! Then with a loud "Pop!" it staged. The whole thing probably took just a fraction of a second, but to me everything seemed to be happening in slow motion, so it seemed like it lasted perhaps five seconds.

Not being used to multistaged flights (I had never seen one before), I watched the booster tumble down and checked where it landed. As a result I missed the sustainer's flight. My father saw it, but lost sight of it. Neither he nor I had any idea where it went. I heard the pop of the ejection charge and anxiously scanned the sky for it but didn't see it. After about a minute or two I decided that enough time had passed for it to land, so I decided to start looking through the tall grass for any sign of a parachute or wadding.

I was just turning around to head further down the "goat path" that we were on when my father shouted, "Look!" I turned around to look in the direction that he was pointing and about 100 yards away and about 50 feet up, there it was. My Midget sustainer was floating gently down on its fully deployed parachute. Neither it nor the booster had received any damage. I quickly gathered everything up and we didn't waste any time walking back out of the field and back home.
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Old 10-08-2012, 09:58 PM
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Quote:
Originally Posted by Mark II
I was just turning around to head further down the "goat path" that we were on when my father shouted, "Look!" I turned around to look in the direction that he was pointing and about 100 yards away and about 50 feet up, there it was. My Midget sustainer was floating gently down on its fully deployed parachute. Neither it nor the booster had received any damage. I quickly gathered everything up and we didn't waste any time walking back out of the field and back home.



Too bad that did not get him hooked on the hobby...


Bill
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Old 10-08-2012, 10:00 PM
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Quote:
Originally Posted by Mark II
The other one (blue) is my 168% Upscaled Midget.



I just love that upscale ratio. Big enough to be impressive; not so big as to be too big. And plenty of commercial tubes of the right size.


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