## [space-modelers] Re: Shuttle Thrust Structure comparison

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• ... Rockets of the World . He does provide most dimensional data, including the measurement for the width of the beaver tail flap (the Monogram shuttle is
Message 1 of 9 , Jul 1, 2001
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>>> Secondly, I do indeed have a copy of Peter Alway's fantastic
"Rockets of the World". He does provide most dimensional data,
including the measurement for the width of the beaver tail flap (the
Monogram shuttle is closest here, the Revell being too narrow).
However, no measurement is provided for the width of the tail higher
up, where the OMS pods are. This is where the difficulty lies.
Imagine you are looking at the orbiter squarely in the tail, at the
SSMEs and the rear of the OMS pods. Alway's plans show the tail
section
(roughly) as a square with a triangle on top where the OMS pods are
mounted.(Which is how Monogram depicts its orbiter.) Other plans,
including those widely available official schematics from Rockwell
(see Marshall Kaplan "Space Shuttle: America's Wings to the Future",
Second Edition, pp190-193) have what can be descibed as "a triangle,
cut off at the top, with a smaller triangle on top".(Forgive my
clumsy
descriptions, geometry is not my strong point.)This is how Revell has
chosen to depict its model.<<<<

Alway's drawing does show a slight taper, it might look square but if you put
a straight edge on it and extent the straightedge to the top view of the
orbiter you can see it. But it is a bit understated.

>>> I think the reason for this difference in plans is that, when
looking at the orbiter from the rear, wheels down, the thrust
structure is not perpendicular to the ground, but the top is angled
away from the viewer, giving a distorted measurement because it is
further away. When looking at the orbiter in plan view, the top of
the thrust structure is hidden by the OMS pods in all plans that I have
seen.>>

The end views are supposed to be axial dead-on end views. If a drawing is
supposed to show an end view as seen wheels down on the ground, the drawing
typically should indicate that in some manner. Such as an end view showing
the wheels down with horizontal lines at the bottoms of the tires to show the
ground plane.

As for the thrust structure being "hidden" by the OMS pods, not really. The
thrust structure has that style of cross-section from just behind the aft
payload bay door bulkhead rearwards. None of the thrust structure extends up
inside the OMS pods, each upper side has a flat surface with an access
opening, that the OMS pod is bolted onto. In Dennis R. JenkinsÂ’ book "Space
Shuttle - history of the Space Transportation System", second edition, there
is a photo on page 214 which shows the vertical tail being mated to the aft
compartment without the OMS pods in place. If you have some other edition
then that photo is probably in there but likely on another page.

If you do not have Jenkins' book, you really ought to.

If you do not have the book, I'll just say that the way the Monogram 1/72
orbiter kit, and various other kits, show a flat surface that the OMS pods
are glued onto, is pretty much just like the real aft compartment cross
section. Except for the lack of the bolt attach hard points and access hole.

BTW - A 1/72 drawing I made of the shuttle, specifically for STS-47, is at:
http://www.spacemodeling.org/gcg/shuttle_1_72.gif

- George Gassaway
• Adrian, Sorry this took so long. I finally found my Datagraph 5 and Alway and decided to try and answer your question. I use the following convention: Xo/Yo
Message 2 of 9 , Dec 13, 2001
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Sorry this took so long. I finally found my Datagraph 5 and Alway

I use the following convention: Xo/Yo is the X/Y-axis of the Orbiter
and Zt is the Z-axis of the External Tank. (The Orbiter's center line
is at Zt 400)

From Alway, the thrust section is 216 in wide at Xo 1306.9 and 264 in
wide at Xo 1528.3. I did a little scaling from Datagraph 5 and
figured the station where the bottom of the thrust structure meets
the bottom of the Shuttle is at Zt 273.75 (shame on me for two
decimal place accuracy from a scaled Datagraph). I took the angle of
the 2 SSME section (lower) to be tilted forward 10 degrees from
vertical (based on engine cant at 0 gimbal), up to Zt 420 resulting
in Xo 1502.5 and Yo 129.2 (or 258.4 in wide). From there the Single
SSME section (top) is angled 16 deg from the vertical (engine cant
angle again).

The top front of the thrust structure is at Xo 1306.9 and Zt 501.

****** You are now entering the Ed Zone ******

This is where some assumptions come in.

Ed Assumption 1 - The OAMS pod mounts are on planes angled 45
degrees. This makes the top front at Xo 1306.9, 54 in wide.
Ed Assumption 2 - The top rear of the thrust structure is angled 10
degrees up from the front.

Based on the above, the top rear is at Xo 1471.1, Zt 529.1, and Yo
16.5 (33 in wide).

In flat pattern, both lower and upper parts are trapezoids (triangles
with the tops cut off)

The lower section bottom: 264 in, top 258.4 in, height 148.5 in.

The upper section bottom: 258.4 in, top 33 in, height 113.5 in.

If you have better info than my assumptions let me know and I'll redo
the calculations.

Ed
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