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tech / rec.crafts.metalworking / Re: Apollo Splash Down Module

SubjectAuthor
* OT: Apollo Splash Down ModuleBob La Londe
+* Re: OT: Apollo Splash Down ModuleJoe Gwinn
|`- Re: Apollo Splash Down ModuleJim Wilkins
`- Re: OT: Apollo Splash Down ModuleJim Wilkins

1
OT: Apollo Splash Down Module

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From: non...@none.com99 (Bob La Londe)
Newsgroups: rec.crafts.metalworking
Subject: OT: Apollo Splash Down Module
Date: Mon, 8 May 2023 14:25:41 -0700
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 by: Bob La Londe - Mon, 8 May 2023 21:25 UTC

OT: Apollo Splash Down Module

There might be some metalworking in here, but that is not the question.
This is more of an aerodynamic question.

Would the splash down module self correct in free fall r did it "have to
be" oriented properly. I don't mean if it had massive out of control
inertial spin/tumble, but rather if it just happened to be out of
correct orientation when it started to hit significant atmospheric drag.

Long gone are the days when I could ask my grandfather a dumb question
like this and he could show off by asking the eggheads over at Lewis
before responding.

Anything I read on this topic is long forgotten. I've haven't been a
space nerd in a long time.

--
Bob La Londe
CNC Molds N Stuff

--
This email has been checked for viruses by AVG antivirus software.
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Re: OT: Apollo Splash Down Module

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From: joegw...@comcast.net (Joe Gwinn)
Newsgroups: rec.crafts.metalworking
Subject: Re: OT: Apollo Splash Down Module
Date: Mon, 08 May 2023 18:28:09 -0400
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 by: Joe Gwinn - Mon, 8 May 2023 22:28 UTC

On Mon, 8 May 2023 14:25:41 -0700, Bob La Londe <none@none.com99>
wrote:

>OT: Apollo Splash Down Module
>
>There might be some metalworking in here, but that is not the question.
>This is more of an aerodynamic question.
>
>Would the splash down module self correct in free fall r did it "have to
>be" oriented properly. I don't mean if it had massive out of control
>inertial spin/tumble, but rather if it just happened to be out of
>correct orientation when it started to hit significant atmospheric drag.

It is designed to orient itself correctly solely from aerodynamic
forces. Which is actually easy to do, and far more reliable than any
active controller could ever be.

Civilian aircraft are also designed to be aerodynamically stable, so
they won't do anything dramatic if the pilot lets go of the controls.

Modern fighter aircraft are designed to be aerodynamically unstable,
rendered stable by a fast-acting control system, the reason being to
improve maneuverability, which is useful in dogfights, and
outmaneuvering anti-aircraft missiles.

With an unstable aircraft, if the control computer is out for more
than something like a tenth of a second, control cannot be recovered,
and the wings are likely to soon tear off. A very bad day.

Joe Gwinn

>Long gone are the days when I could ask my grandfather a dumb question
>like this and he could show off by asking the eggheads over at Lewis
>before responding.
>
>Anything I read on this topic is long forgotten. I've haven't been a
>space nerd in a long time.
>
>--
>Bob La Londe
>CNC Molds N Stuff

Re: OT: Apollo Splash Down Module

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From: muratla...@gmail.com (Jim Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: OT: Apollo Splash Down Module
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 by: Jim Wilkins - Tue, 9 May 2023 00:51 UTC

"Bob La Londe" wrote in message news:u3bpcl$3vrok$1@dont-email.me...

OT: Apollo Splash Down Module

There might be some metalworking in here, but that is not the question.
This is more of an aerodynamic question.

Would the splash down module self correct in free fall r did it "have to
be" oriented properly. I don't mean if it had massive out of control
inertial spin/tumble, but rather if it just happened to be out of
correct orientation when it started to hit significant atmospheric drag.

Long gone are the days when I could ask my grandfather a dumb question
like this and he could show off by asking the eggheads over at Lewis
before responding.

Anything I read on this topic is long forgotten. I've haven't been a
space nerd in a long time.

Bob La Londe

--------------------------------

https://ntrs.nasa.gov/api/citations/19670010564/downloads/19670010564.pdf
"The Apollo command module is designed with an offset center of gravity to
provide a trimmed entry angle of attack (with the heat shield forward)."

In contrast Columbia lost its necessary active stability after the punctured
wing's hydraulic lines burned through. It apparently entered a flat spin,
the damaged wing came off, followed by the payload bay doors which exposed
the aluminum structure to burn through at the joint between the payload bay
and the crew cabin. The freed front end tumbled until its tile-protected
outer shell was blown off by shock wave pressure entering at its rear, then
the exposed aluminum cabin burned up in about 10-15 seconds. Based on stored
mission shoulder patches found early in the debris track they think the
pressurized cabin shifted and was punctured in the storage compartment
holding the patches by part of the outer shell frame, and since the crew
hadn't lowered their face shields (intentionally?) to pressurize their suits
they likely passed out very rapidly in the near vacuum before it burned.

If they had survived down to SR-71 flight conditions they could have bailed
out and parachuted down, but not at Mach 18.

I knew an excellent NASA source at Mitre until he retired. He explained in
detail how the Apollo 11 flight control computer he helped design became
overburdened by routines they kept adding to it and unforeseen flight
conditions, until the loop watchdog timer briefly lit its fault light at the
end of each cycle before being reset. The programmers hadn't thought to
extend the hardware timeout, and by then he was on another project.

I built a lab demo of a proposed DS5 laser comm crosslink for TDRSS, partly
in my basement, otherwise my space program involvement was on ground
terminals for Milstar.
https://en.wikipedia.org/wiki/Milstar

It's an upgrade to an early, encrypted predecessor of of Starlink. The US
military has had a global secure communications network similar to wired and
wireless Internet since the 1960's (with Teletypes and card readers), and I
maintained it in the early 70's.

Re: Apollo Splash Down Module

<u3cah4$58g7$1@dont-email.me>

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From: muratla...@gmail.com (Jim Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Apollo Splash Down Module
Date: Mon, 8 May 2023 22:17:02 -0400
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 by: Jim Wilkins - Tue, 9 May 2023 02:17 UTC

"Joe Gwinn" wrote in message
news:8dti5ihibpcl93nl7ph2cbt6ksq4j0khrc@4ax.com...

Civilian aircraft are also designed to be aerodynamically stable, so
they won't do anything dramatic if the pilot lets go of the controls.

Modern fighter aircraft are designed to be aerodynamically unstable,
rendered stable by a fast-acting control system, the reason being to
improve maneuverability, which is useful in dogfights, and
outmaneuvering anti-aircraft missiles.

With an unstable aircraft, if the control computer is out for more
than something like a tenth of a second, control cannot be recovered,
and the wings are likely to soon tear off. A very bad day.

Joe Gwinn
----------------------

AF447, the French airliner that fell into the South Atlantic, had a brief
problem with pitot icing in a thunderstorm that told the autopilot the plane
was flying too slowly, somehow resulting in a sharp pull-up that zoomed the
plane up into a real stall. Afterwards the plane fell in a flat stall that
confused the flight crew who saw normal RPMs which should mean normal power
from the engines although they weren't taking in enough air to produce much
thrust.

It seems no one tests the stability of $200 million airliners (without
ejection seats) in stall conditions, they rely on simulations and didn't
actually know what would happen. The plane stayed relatively level in pitch
but rolled considerably and was difficult though not impossible to correct,
as it did have a little forward airspeed. The stall warning was disabled
below flight speed to avoid being set off by ground wind. When the pilot
nosed down as he should have to gain forward airspeed the stall warning
became enabled and sounded, thoroughly confusing them. The fell to their
deaths in a perfectly good airplane that was doing something they didn't
understand.

My hang gliding instructor had a model aircraft, and a borrowed homebrew
analog computer that modeled the flight equations for it, that was stable
only in certain sizes (he said). It was merely a 14" long straight wing with
a dowel extending from the center of the leading edge. At the flying hill he
showed me that it would glide back and forth in the updraft, recovering
nicely from upsets by turbulence. At home he released it to follow a phugoid
oscillation, with the computer output needle following its changing angle of
attack.

I've been wondering if I would ever find a good excuse to write "phugoid" in
a posting. Thanks.

https://en.wikipedia.org/wiki/Inverted_pendulum

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