Carrier Aircraft Catapault Hold-Back Bar / Mechanism ?

[Robert11]

Hello:

Retired Engineer.

Have always been interested in carrier catapaults.

I have tried to find a good, relatively technical, description on the web
with some diagrams or pix of the aircraft hold-back mechanism that's used
immediately prior to launch that restrains the plane.

Doubt that they still use breakable (frangible) type of bolts, but perhaps ?
Do they ?

Anyone know of any good sources to learn more about how this is actually
done, and what
these mechanisms look like ?

Thanks,
B.

[frOg]

"Robert11" > wrote in message
. ..
> Hello:
>
> Retired Engineer.
>
> Have always been interested in carrier catapaults.
>
> I have tried to find a good, relatively technical, description on the web
> with some diagrams or pix of the aircraft hold-back mechanism that's used
> immediately prior to launch that restrains the plane.
>
> Doubt that they still use breakable (frangible) type of bolts, but perhaps
?
> Do they ?

The 'breakable' holdback certainly is still in use today. It's not a bolt,
but looks more like a 'double mushroom' where the center has been machined
down to certain specs. It is designed to separate at a predetermined stress
point.

[Yofuri]

Robert11 wrote:
> Hello:
>
> Retired Engineer.
>
> Have always been interested in carrier catapaults.
>
> I have tried to find a good, relatively technical, description on the web
> with some diagrams or pix of the aircraft hold-back mechanism that's used
> immediately prior to launch that restrains the plane.
>
> Doubt that they still use breakable (frangible) type of bolts, but perhaps ?
> Do they ?
>
> Anyone know of any good sources to learn more about how this is actually
> done, and what
> these mechanisms look like ?
>
> Thanks,
> B.
>
>
The tension bar contains a breakable link that looks like a piece of
2-1'2" diameter steel shafting about 3" long was chucked in a lathe and
parted in the middle except for the last 1/2" to 3/4". They are
color-coded by aircraft type.

http://www.tpub.com/content/aviation/14014/css/14014_86.htm

(figure 4-16)

http://www.tpub.com/content/aviation/14018/css/14018_27.htm

Rick

[Gordon]

> > Doubt that they still use breakable (frangible) type of bolts, but perhaps ?
> > Do they ?
> >
> > Anyone know of any good sources to learn more about how this is actually
> > done, and what
> > these mechanisms look like ?
> >

I have one in front of me, from my first S-3 launch. My half (other
half stays in the shuttle until the deck crew discards it) looks like
half of a palm-sized purple yo-yo. Each a/c type used a different
color as each a/c had a slightly different holdback fitting.

v/r
Gordon

[frOg]

"Gordon" > wrote in message
ps.com...
>
>
> > > Doubt that they still use breakable (frangible) type of bolts, but
perhaps ?
> > > Do they ?
> > >
> > > Anyone know of any good sources to learn more about how this is
actually
> > > done, and what
> > > these mechanisms look like ?
> > >
>
> I have one in front of me, from my first S-3 launch. My half (other
> half stays in the shuttle until the deck crew discards it) looks like
> half of a palm-sized purple yo-yo. Each a/c type used a different
> color as each a/c had a slightly different holdback fitting.

Agreed. And they are NOT interchangeable deliberately so Sailors don't screw
up and put the wrong one in.

If the wrong holdback fitting *could* be installed (with the associated
incorrect release pressure), the results could be disastrous. The cat could
either release without enough steam pressure to get the aircraft fully
airborne or the 'live cat' could just sit there without enough pressure to
break the holdback (instead of actually launching the aircraft) until the
steam pressure is bled off (aborting the cat shot).

[Gordon]

> > I have one in front of me, from my first S-3 launch. My half (other
> > half stays in the shuttle until the deck crew discards it) looks like
> > half of a palm-sized purple yo-yo. Each a/c type used a different
> > color as each a/c had a slightly different holdback fitting.
>
> Agreed. And they are NOT interchangeable deliberately so Sailors don't screw
> up and put the wrong one in.
>
> If the wrong holdback fitting *could* be installed (with the associated
> incorrect release pressure), the results could be disastrous. The cat could
> either release without enough steam pressure to get the aircraft fully
> airborne or the 'live cat' could just sit there without enough pressure to
> break the holdback (instead of actually launching the aircraft) until the
> steam pressure is bled off (aborting the cat shot).

What?! Are you suggesting squids occasionally eff-up? :)

ok, ok, I'll agree - if we CAN screw something up, at some point, some
kid will. I watched an A-3 take off once, followed by an A-7...
Problem? The cat was not reset and the Corsair was tossed off the boat
"with alacrity", causing noticible damage (belly pan detached during
the blistering fast takeoff run among other problems). Whenever
someone makes a device idiot proof, along come better idiots!

v/r
Gordon

[Robert11]

Hi,

Thanks for info.

a. What happens to the piece of the breakable link that is part of the bar
that stays with the plane ?
Does it go flying with the plane to be removed later, or... ?

b. Any info on the newer, I think, types of hold-back mechanism that do not
utilize the breakable bar, but apparently use some type of captivated
spring/cam mechanism as part of the bar (permanently) ?

Thanks again,
Bob

----------------------------------
"Robert11" > wrote in message
. ..
> Hello:
>
> Retired Engineer.
>
> Have always been interested in carrier catapaults.
>
> I have tried to find a good, relatively technical, description on the web
> with some diagrams or pix of the aircraft hold-back mechanism that's used
> immediately prior to launch that restrains the plane.
>
> Doubt that they still use breakable (frangible) type of bolts, but perhaps
> ?
> Do they ?
>
> Anyone know of any good sources to learn more about how this is actually
> done, and what
> these mechanisms look like ?
>
> Thanks,
> B.
>

[frOg]

"Robert11" > wrote in message
. ..
> Hi,
>
> Thanks for info.
>
> a. What happens to the piece of the breakable link that is part of the
bar
> that stays with the plane ?
> Does it go flying with the plane to be removed later, or... ?

Yes, and it is later removed by the Plane Captain as part of the "Turn
Around Inspection" after landing.



> b. Any info on the newer, I think, types of hold-back mechanism that do
not
> utilize the breakable bar, but apparently use some type of captivated
> spring/cam mechanism as part of the bar (permanently) ?

Not part of the Steam Catapult system. The holdback may change with the next
generation of launch systems.

[Jason H]

"Robert11" > wrote in message
. ..
> Hi,

> b. Any info on the newer, I think, types of hold-back mechanism that do
> not utilize the breakable bar, but apparently use some type of captivated
> spring/cam mechanism as part of the bar (permanently) ?
>
> Thanks again,
> Bob

Yes, they're called RRHAs (Repeatable Releasable Holdback Assembly). They're
a one-piece bar that fits into the back of the (A/C's) strut and on the
strut there are two metal plates that sandwich the holdback bar. In order to
launch, the bar must have enough force applied to it for it to slide past
the metal plates/springs. It's basically like some cabinet doors that have
the little pokey thing that have to slide inbetween two springs in order to
open... they come in different shapes and sizes for different airplanes so
they don't get one with the wrong-sized "fist". Since nothing breaks during
launch, they can be reused. They just have to be inspected every once in a
while to make sure there's no stresses inside the bar that might make it
break, and also to make sure the fist hasn't worn down too much.

Jason