Rivets vs Welding

I've not fully studied aircraft construction techniques so forgive me if the
answer to this is obvious. I've noted that most(if not all) aircraft made
with aluminium airframes seem to be riveted rather than welded. I'm not
sure about aircraft with composite or fibreglass skins so I won't be
dogmatic on that point, but anyway.

Is there a reason why aircraft would be riveted rather than welded together,
particularly on the airframe, not the skin? I would have imagined that
welding would produce a stronger join, although it may be harder or
impossible to disassemble if needed. Thanks,

David

Richard Riley wrote:

That said, "friction stir welding" is the newest thing in airframe
construction. It works below the melting temperature of the metal,
and leaves good properties behind.

How does this work?


Matt

How does this work?

http://en.wikipedia.org/wiki/Friction-stir_welding

Thanks,

David

David Findlay wrote:
How does this work?


http://en.wikipedia.org/wiki/Friction-stir_welding

Thanks,

David

I found similar descriptions at The Welding Institute where the
technique was invented. However, I don't see any applications other
than for butt joints. I can see this being used for joining aircraft
skins, but I don't see how it can replace rivets for joining the skin to
internal support structures such as ribs and fuselage formers. Anyone
know if this is possible with this technique?


Matt

So you'd have to weld the airplane together, then heat treat the
entire thing.

Thanks, was pretty sure the must have been a reason, but not having looked
into it I didn't know.

That said, "friction stir welding" is the newest thing in airframe
construction. It works below the melting temperature of the metal,
and leaves good properties behind.

I take it that this would be beyond the average home builder as yet though.

In terms of construction time and difficulty, how would composite compare to
aluminium riveted construction? Thanks,

David

David Findlay wrote:

snip

Is there a reason why aircraft would be riveted rather than welded
together, particularly on the airframe, not the skin? I would have
imagined that welding would produce a stronger join, although it may be
harder or impossible to disassemble if needed. Thanks,

One key point is QC.

With the rivets a Al batch of a known alloy is turned into a bazillion
rivets by a machine. A small number of these rivets are tested to confirm
the batch of rivets is up to spec.

Using well understood and documented techniques a joint is designed for the
required stresses with x rows of rivets at y spacing etc. The joint is then
riveted.

QC on the joint itself merely requires visual examination, no fancy ND
techniques etc.

Routine inspection in service likewise is done by visual inspection.

--

regards

jc

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"Matt Whiting" wrote in message ...

I found similar descriptions at The Welding Institute where the technique was invented. However, I don't see any
applications other than for butt joints. I can see this being used for joining aircraft skins, but I don't see how it
can replace rivets for joining the skin to internal support structures such as ribs and fuselage formers. Anyone know
if this is possible with this technique?


Matt

So their overall costs are going to be a few percent below, say, the
Cessna Citation Mustang.

Competitively speaking, Cessna is in pretty good shape. They're very
good at reducing the amount of labor in building an airplane. They
have a large product line, experienced workers and plenty of capitol.
They have long experience getting airplanes certified, that shouldn't
be a problem. So if their cost on the Mustang is slightly higher,
they're in good shape to price it with or below the Eclipse to
preserve market share. If it's a price war between Cessna and
Eclipse, which company can hold out longer? And if you were a
corporate aviation buyer deciding between the two - and they were
priced the same - would you buy a plane from a company that had no
track record, or one that was very, very well established?

Eclipse is dead, they just won't admit it yet.


Yes that's why even with the new engines there price is still about 1/3 the
price of the cessna, and they have over 2000 firm orders! Don't count them
out yet. Oh yeah their plane IS flying!
John

Richard Riley wrote:

On Sun, 02 Jan 2005 01:33:54 GMT, UltraJohn
wrote:

:
: So their overall costs are going to be a few percent below, say, the
: Cessna Citation Mustang.
:
: Competitively speaking, Cessna is in pretty good shape. They're very
: good at reducing the amount of labor in building an airplane. They
: have a large product line, experienced workers and plenty of capitol.
: They have long experience getting airplanes certified, that shouldn't
: be a problem. So if their cost on the Mustang is slightly higher,
: they're in good shape to price it with or below the Eclipse to
: preserve market share. If it's a price war between Cessna and
: Eclipse, which company can hold out longer? And if you were a
: corporate aviation buyer deciding between the two - and they were
: priced the same - would you buy a plane from a company that had no
: track record, or one that was very, very well established?
:
: Eclipse is dead, they just won't admit it yet.
:
:
:Yes that's why even with the new engines there price is still about 1/3 the
rice of the cessna, and they have over 2000 firm orders! Don't count them
ut yet. Oh yeah their plane IS flying!
:John

Yes, their list is $1.175m. Do you believe that they are making any
money at that price? I mean, it just about covers the cost of the
engines and avionics.

The orders are cancelable if they can't meet their price. They wont.
Or Cessna will dramatically lower theirs. Cessna got about 350 orders
in the first week after announcing.

And you can bet your bottom dollar that Cessna will make money on the
Mustang.


Matt

On Sat, 01 Jan 2005 17:36:39 +1100, jc wrote:

David Findlay wrote:

snip

Is there a reason why aircraft would be riveted rather than welded
together, particularly on the airframe, not the skin? I would have
imagined that welding would produce a stronger join, although it may be
harder or impossible to disassemble if needed. Thanks,

One key point is QC.

With the rivets a Al batch of a known alloy is turned into a bazillion
rivets by a machine. A small number of these rivets are tested to confirm
the batch of rivets is up to spec.

Using well understood and documented techniques a joint is designed for the
required stresses with x rows of rivets at y spacing etc. The joint is then
riveted.

QC on the joint itself merely requires visual examination, no fancy ND
techniques etc.

Routine inspection in service likewise is done by visual inspection.

and in service a stuffed rivet can be merely drilled out and replaced.
a cracked weld would probably result in expensive repair, or the
resorting to rivetted in place patches.

rivets may not be the best in an ideal world but they are practical
and result in almost infinitely repairable aircraft.

david something that bears consideration is that over the full life of
an aircraft every component will come to need repair as it wears out.
so every component needs to be got at, removed, replaced or repaired
and put back into service. rivets may be tedious but allow this to
occur. welded components may lead to an entire airframe sitting on the
tarmac or in a hangar while repairs to cracks are thought through and
attempted.

australia's macchi jet trainers have cast ring beams in the fuselage
to which the wings attach. cracks in these saw lots of downtime while
repairs were contemplated and eventually led to the scrapping of the
aircraft. ...which isnt good for repeat business.

Stealth Pilot
Australia.