V2: The laws of physics were suspended yesterday (swing test)

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Blast it Tom!

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So back to the subject, I started reading Barrowman's thesis today and he's right. We don't fly our rockets sideways!
 

bschultz32

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"any discussion on TRF involving calculations will devolve into reminiscing about our slide rules!" - that does it, I can't resist:
My first engineering-career boss had a beautiful high-end slide rule mounted on an oak plaque on the wall over the door in his office. It had a brass plate that wryly alluded to its being obsolete, "Sliderulus Obsoletus" or something like that. I thought it was a quaint nod to the "old days" by an engineer who graduated in the 50's. One day, I came into his office unannounced and surprised him using it at his desk! I was stunned; I assumed it was permanently bolted to the plaque, but in fact it merely rested there, and was easily taken off if you reached up for it. He smiled sheepishly and said "Okay, you got me, yes, I do indeed occasionally use my old slide rule to crunch a few numbers, just for fun." Then he challenged me to use it for his next calculation. I was taught to use a slide rule in junior high school (about 1969 or so), so with some fumbling I was able to produce a credible result. Today, in 2021? Forget it, too much water under the bridge, I'd have no idea how to do it. But that's okay, time rolls on . . . .
Bob Schultz
 

Blast it Tom!

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"any discussion on TRF involving calculations will devolve into reminiscing about our slide rules!" - that does it, I can't resist:
My first engineering-career boss had a beautiful high-end slide rule mounted on an oak plaque on the wall over the door in his office. It had a brass plate that wryly alluded to its being obsolete, "Sliderulus Obsoletus" or something like that. I thought it was a quaint nod to the "old days" by an engineer who graduated in the 50's. One day, I came into his office unannounced and surprised him using it at his desk! I was stunned; I assumed it was permanently bolted to the plaque, but in fact it merely rested there, and was easily taken off if you reached up for it. He smiled sheepishly and said "Okay, you got me, yes, I do indeed occasionally use my old slide rule to crunch a few numbers, just for fun." Then he challenged me to use it for his next calculation. I was taught to use a slide rule in junior high school (about 1969 or so), so with some fumbling I was able to produce a credible result. Today, in 2021? Forget it, too much water under the bridge, I'd have no idea how to do it. But that's okay, time rolls on . . . .
Bob Schultz
I can still do multiplication, division, and of course the square/cube roots are do-able but a little more arcane. Trig isn't too bad either... but all those log-log scales and what-not, criminee, I can't remember if I ever DID know how to use them!

It sure takes me back; especially when I read Barrowman's thesis and NARAM reports from 1966-67, and just this morning, my MIT Press "Topics in Advanced Model Rocketry" (1973), which I understand was the original basis for Rocksim and OR. It's really great to be able to understand it all now!
 

Chas.alpha1

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Holy smokes, you put motors in those pods? YOW! o_O

I don't have enough field for that kind of altitude, but I'll bet that's something to see!

No reason to have pods if ya ain't gonna load 'em! Had to make a special 10" 5 clip whip for it. On this iteration, I set the engine blocks 3/4" lower to alter the CG/CP. Still have about 4 oz. nose weight to keep it stable... Next time I will make the pods 3/4" longer!
 

Lord Alveric

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I used slide rules in grade school in the 1970s... I think I was the only kid to do so. For me, they were basically a "poor man's calculator" at the time, since I could not afford a calculator.

Later on, calculators dropped significantly in price -- but by then I had a job with an ever growing income. No longer a kid. :D
 

Blast it Tom!

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I used slide rules in grade school in the 1970s... I think I was the only kid to do so. For me, they were basically a "poor man's calculator" at the time, since I could not afford a calculator.

Later on, calculators dropped significantly in price -- but by then I had a job with an ever growing income. No longer a kid. :D
Well, friend, you're a little younger than me... but yes, the price certainly WAS a factor as calculators came on the scene. I learned them in high school and in 1973, when I started college, only a few calculators were on the hips of engineering students. The rest of us had our "swords" dangling from our belts! Usually a "fancy" HP calculator was thought of as a sign that you're well-to-do, but I can imagine a kid working an after-school job to save up for his, especially if he came from a hardscrabble background (as I did).

Welcome aboard!
 

Lord Alveric

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Well, friend, you're a little younger than me... but yes, the price certainly WAS a factor as calculators came on the scene. I learned them in high school and in 1973, when I started college, only a few calculators were on the hips of engineering students. The rest of us had our "swords" dangling from our belts! Usually a "fancy" HP calculator was thought of as a sign that you're well-to-do, but I can imagine a kid working an after-school job to save up for his, especially if he came from a hardscrabble background (as I did).

Welcome aboard!
Little younger? Yeah, I will be 60 this year. :)
 

brockrwood

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All the more reason to crack the books on the real stability criteria! Yeah, my spreadsheet is basically a motorized cardboard test. But that's the first time I've heard that the string test puts it rearward. Are you saying the fact that it "passed" the string test is not necessarily proof that it will not become a skywriter?
Is the string long enough to do a reliable string test? I think I remember the old Estes technical manual saying you need a good, long string. “A good long string.” How is that for scientific precision? ;-)
 

Blast it Tom!

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“A good long string.”
Or as my boss used to say, "How many zeros behind the decimal point there, sport?" :D

Yes, I had it out about 10' from me and going fast enough to hear wind (I know, I know - how many zeros after THAT????). I could not get it to fly backwards no matter how I tried, it would just flip back to nose first. Tried varying the string position a little fore and aft of the balance point - not too far, it's surprisingly sensitive - and it goes nose into the wind almost immediately. Barrowman says the actual CP is aft of the lateral centroid of the projected area. I'm reading up on it now, fascinating stuff!
 

brockrwood

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Or as my boss used to say, "How many zeros behind the decimal point there, sport?" :D

Yes, I had it out about 10' from me and going fast enough to hear wind (I know, I know - how many zeros after THAT????). I could not get it to fly backwards no matter how I tried, it would just flip back to nose first. Tried varying the string position a little fore and aft of the balance point - not too far, it's surprisingly sensitive - and it goes nose into the wind almost immediately. Barrowman says the actual CP is aft of the lateral centroid of the projected area. I'm reading up on it now, fascinating stuff!
So the string has to be just about dead on the CG for the test to work?
 

Blast it Tom!

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So the string has to be just about dead on the CG for the test to work?
Well, that's the idea, that you are supported at the CG and you are checking how the moment of the total of the aerodynamic forces acts because the string has only the slightest (i.e negligible) resistance to being twisted, so essentially simulating free flight conditions. If you move off the CG the rocket quickly starts to hang nose up or nose down, but even in those conditions I couldn't get it to fly backwards.
 

brockrwood

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Me as well. I started college in 1973. Should've graduated in 1977, but managed to put it off until 1987... The boss I mentioned above gave us all 6" plastic ones as well. He said, "In case the power goes out!"

I thing that any discussion on TRF involving calculations will devolve into reminiscing about our slide rules!
In defense of slide rules (and log tables and trig tables), learning math the old fashioned way (and learning it by doing model rocketry) shows you the relationships between different values that a calculator doesn’t show you. Those relationships are more important to the understanding of the math than the precise value you arrive at. If a kid takes a tangent of an angle and the calculator spits out a number, what has he/she really learned? If a kid measures the angle of a model rocket at apogee (using a protractor, a drinking straw, a piece of string, and an eraser) and then looks up the tangent in a trig table, he/she intuitively sees that there is a relationship between the size of the angle and the ratio of the length of the base line and the length of the opposite side of the triangle. You can scan the tangent table and see the ratio change as the angle changes.
 
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jrap330

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I used slide rules in grade school in the 1970s... I think I was the only kid to do so. For me, they were basically a "poor man's calculator" at the time, since I could not afford a calculator.

Later on, calculators dropped significantly in price -- but by then I had a job with an ever growing income. No longer a kid. :D
I went to Brooklyn Technical HS. In fall 1975, the first weeks of Electrical Eng course was learning the slide rule. In Spring Semester (1976) the school allowed calculators. Learning the slide rule did make you understand the math better, since you could not afford a mistake in your equations...after all that "sliding": around.
 
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