Saturday, June 22, 2019

Oeuf and Ool

As I mentioned in my previous post, I have started designing and building my rockets for this year's Geezer TARC. The first of these, Oeuf (french for "egg"), is an Alpha-like model based on the Centuri ST-18 body tube (minimum diameter for a regulation TARC egg). It's powered by up to 4 18mm motors, though OpenRocket is saying two D motors will be sufficient, provided I don't exceed the design weight. If I do,  I can always put A, B, or C motors in the other two tubes - Oeuf ain't nothing if not flexible. Right now, she's waiting for her first primer coat to dry.

OpenRocket visualization of Oeuf during dual motor thrust (Click to enlarge).
I have just started work on the second design, called "Ool" after the name for food in one of my favorite movies, "Caveman." Ool is a 3 finned BT-55 to BT-70 rocket, propelled by a single 24 mm motor. She's designed light, a tad over 200 grams without motor, and will sport the Apogee conformal rail guides - a first for one of my rockets. OpenRocket is projecting that a single E12 will provide more than enough juice to make 800 feet; thrust-to-weight is an acceptable 4.7:1, close enough to the magic 5:1. Motor mount is assembled, body tube spirals have been filled, and the balsa fins have been cut and skinned. I originally had smaller fins, but they struck me as too small, even though the sim was telling me the static stability margin was 1.5 without the egg and altimeter. So I upscaled them by 125%, which appeased my rocket instincts and improved the stability margin up to 2.1 without the payloads.

Visualization of Ool under E12 power (Click to enlarge).
Yeah, I know Open Rocket said it was stable, but I have seen too many TARC rockets that were rated as stable by the sim go very squirrelly after leaving the rail. Not going to happen with one of my birds.

I hope to have the fins on Ool tomorrow and to apply primer sometime during the upcoming week. Depends on if we can get a break in the recent bout of stormy weather.

6 comments:

  1. Good lord, my friends and I paid full price to see Caveman. We figured anything with Ringo in it had to be a masterpiece. I was a Breaking Away fan, so I knew who Dennis Quaid was, but no one else did. Good for a few laughs, but I can't honestly say I've seen it since 1981.

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  2. We have a lot of college teams do cert flights with us, and they often have such tiny fins. A lot of them come off the pad and wiggle or cone to an iffy or worse flight.

    Ool looks good to me! I'm sure you could get away with smaller fins, but I like what you have there.

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    1. Are you going to name one of your future builds "Zug-Zug" ?

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    2. Very likely! There’s probably going to be a “Macha” as well.

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