Issue with reading scale drawings

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El Phantasmo

Well-Known Member
Mar 2, 2010
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I'm having trouble interpreting this scale drawing, and others for that matter. Some of it is pretty easy to read and/or figure out but some things confuse me.

I'm going to make my own Falcon GAR-1. If the measurement at the bottom of the tail cone (86.50") represents the total length, then where is the 8.658" measurement at the top of the nosecone derived from? What does STA stand for?

Another thing, the Smithsonian's web site has different measurements. They say it's 76 13/16" long. If someone can explain what's going on, it'd appreciate it.

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STA numbers are STAtion values. They usually start at the nose or base of the rocket.
The numbers identify stations; points of change, interest, or parts along the body relative to station 0.000, the reference.

When creating almost anything, the design team needs a reference or datum line from which to measure. In most cases it is completely theoretical and does not necessarily match up to anything or any part of the missile/aircraft/ship. It's just there on the computer so all members of the design team can dimension their part drawings from a single common reference point.

When selecting this reference, some far-thinking project engineer will often say "Let's set this reference point way out in front, so when we build the advanced version (more product sales, more $$$$$) with the new super-seeker, the design will still fit within our measurement system." So they pick a point in space, the most forward extent of the version they are currently working on ends up at Statn 8.whatever, and if you want the total overall length you subtract the nose statn from the tail statn.

Someday you might see an advanced version with a bigger motor, or a new IR homing head, or an improved warhead. It may be longer (they usually are) but as a small measure of mathematical "tidiness" all the station labels will still have positive values.

Did any of that make sense or did I only confuse you worse?

Edit: As to different measurements, this can easily happen. A company like Hughes may get the credit for "building" the missile but they probably only really manufacture the seeker (the hard part, usually the expensive part, certainly the most glamorous part). They subcontract (buy) the other parts. Another company makes the warhead, the motor, maybe the fin control unit. Over the years, after switching a few vendors from time to time, the parts can become slightly different. Or maybe Hughes themselves make a few minor model improvements that change the external shape slightly. Anyway, it's basically still the same missile/product....but it can be slightly different.

Example: Spend some time making a close study of the radome shape of the Phoenix missile. You will see a range of shapes, starting with what appears to be almost an ogive, phasing into later shapes with a more conical forward shape to the radome. Is it still a Phoenix? (Sure!)
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Some prominent point on the rocket is used as the point of reference (usually the tip of the nose or the aft end of the airframe, but not always), and relevant measurements are expressed as distances away from this point (Station 0). Also, when you look at plans or schematics, pay attention to the units of measurement (English or metric) that are used.

All rounds of a particular missile do not necessarily share the same precise dimensions; there are variations. Designs are quite often changed (updated) over the course of the missile's lifetime, and these will, of course, affect the dimensions. Some changes are major enough to produce a new model number or military designation (see, for example, the two models of the Army Honest John). Others constitute minor tweaks in the design from one production run to the next. Not large enough to necessitate any big change in the missile's launch and support equipment, but just large enough to drive scale modelers crazy. ;)

Thanks to all of you so much. That pretty much clears up everything that confused me.
Sometimes the “Zero” point for the Station Number is nowhere near the tip or the base.

See this link for one of the Little Joe-II’s:

STA 0.0 is sorta in the middle, the Little Joe-II parts below it, and the Apollo parts (with increasing negative numbers) above it.

If you want your mind to get a bit more twisted, there’s the Space Shuttle. It has three different coordinate systems. “O” stands for Orbiter, “T” stands for Tank, and “B” stands for Booster (SRB). And those are preceded by the axis being represented, along the X, Y, or Z axes. See this early working drawing which I left in a lot of the coordinates:

The orbiter’s own X axis Station zero point is ahead of the orbiter’s nose. The orbiter itself does not begin until XO 235.

- George Gassaway
In aircraft construction drawings there are FS (fuselage station), WS (wing station), and WL (water line).

FS is basically length. In the drawing referenced the nose cone tip is at STA 8.658 and the aft end of the rocket is at STA 86.500. The total length of the rocket is then 77.842.

WS are basically width measurements usually from a center line. WS 36.75 is 36 and 3/4 inches from the center (usually but not always). These are indicated by left and right as well.

WL are a measurement of height. In my experience there are often negative water lines more often that the others but all three can be expressed in negative numbers depending on where zero is.

I worked at Lockheed over thirty years ago and am going by memory so this may all be hogwash. Just so you know. :)
JoeG is correct, this is indeed one way of designating measurements. To add to the confusion, some companies also use "Wing Station" measurements along the swept wing leading edge. I have seen one that used "Wing Station" measurements taken on the wing 25% chord line. (Talk about a PITA to calculate!)

I am most familiar with Buttock Line as the lateral measurement, where each BL station is parallel to the vehicle longitudinal centerline. (This is sometimes shortened to Butt Line.) This term goes back to the olden days of shipbuilding. (Kinda brings to mind the story of why railroad tracks are set to the same width as Roman chariot wheels.)

If any of this is confusing you can always revert to the simple system of X, Y, Z.