airplane construction

Bill Watson wrote:

The more you know the more you can do.

Nothing like assembling a sailplane, loading it full of water and
bombing down a ridge at red-line for a few hours.

Then you just pull the wings and tail back off and trailer it home.

the size of those pins/bolts that hold the wings on should attract the
attention of any pilot not used to rigging sailpanes :-)

wrote:
Robert M. Gary wrote:
Mike wrote:
Robert M. Gary wrote:
I'm guessing that's why there's wing struts How many bolts secure the
wings to the fuselage?
On the Cessna I don't remember how many "wing nuts" there were holding
the wing on, I just remember the very small area in which the wing
attaches to the body. There must be insane amounts of stress on that
small area of metal.

On the Mooney, there is but one single wing. The spar runs right under
the seats. No one has problems with wings coming off but the Mooney
design makes me more comfortable.

-Robert

The 172 has a 7/16" bolt on the front spar attach, and a 3/8" at
the rear, IIRC without going downstairs and looking it up. Both are in
double shear. The bolt is stronger than the aluminum fittings, and the
fittings are much stronger than they look or need to be. The airplane
is rated for 3.8g positive, with 150% design limits beyond that, and I
can't remember the last time I heard of a 172 shedding a wing unless
the pilot tried to fly through a thunderstorm, in which case he'd have
died anyway. The stabilizer is weaker than the wing in many light
aircraft.
The struts are connected with 1/2" bolts in double shear.

The Mooney's one-piece wing spar is made of many smaller
pieces, all held together with tiny rivets. No stronger than the 172, I
bet. The Mooney's POH should give a g rating for the airframe.

Which reminds me: a friend recently told me of an accident in
the Southeastern US where a new Commercial pilot flew a Monney into a
thunderboomer at night. They found the wreckage scattered far and wide,
and the Mooney engineers that examined the bits and pieces estimated
that the aircraft experienced an upward acceleration of between 20 and
23 Gs. The passenger, complete with seat, went through the bottom of
the airplane and was found some distance behind the rest of the mess.
Even if the airplane had held together the occupants would have been
incapacitated or killed by the damage wrought by the acceleration.

Dan


Thanks for the insight, Dan. I never knew that about the C172 (or should
I say high-wing?). Definitely learned a few more things today.


--
Mike

Understand that bolts used in aircraft construction are not
"hardware store" items. The steel and the tolerances for
aircraft grade fasteners are better than hardware store
Grade 8 bolts. Beech uses bolts in tension to hold the wing
on the Bonanza, Baron and King Air models. When there is a
crash, the bolts are rarely broken. But if the bolts are
not properly installed and maintained, corrosion can weaken
the bolts causing them to break.

Cessna uses a bolt installed in shear through fittings like
you fingers meshed. This is called "double shear" and as
long as the bolt is a snug fit in the hole the bolt can hold
more load than the airplane is designed to experience.
But a bolt in tension is stronger than a bolt in shear.


"george" wrote in message
ups.com...
|
| Bill Watson wrote:
|
| The more you know the more you can do.
|
| Nothing like assembling a sailplane, loading it full of
water and
| bombing down a ridge at red-line for a few hours.
|
| Then you just pull the wings and tail back off and
trailer it home.
|
| the size of those pins/bolts that hold the wings on
should attract the
| attention of any pilot not used to rigging sailpanes :-)
|

Jim Macklin wrote:
Understand that bolts used in aircraft construction are not
"hardware store" items. The steel and the tolerances for
aircraft grade fasteners are better than hardware store
Grade 8 bolts. Beech uses bolts in tension to hold the wing
on the Bonanza, Baron and King Air models. When there is a
crash, the bolts are rarely broken. But if the bolts are
not properly installed and maintained, corrosion can weaken
the bolts causing them to break.

Cessna uses a bolt installed in shear through fittings like
you fingers meshed. This is called "double shear" and as
long as the bolt is a snug fit in the hole the bolt can hold
more load than the airplane is designed to experience.
But a bolt in tension is stronger than a bolt in shear.


The hardware-store Grade 2 bolts (no marks on the head) is
around 55 to 60 ksi, really dangerous stuff on anything other than your
kid's push kart. Grade 5 (three radial marks on the head) are 120ksi,
same as an AN bolt. The Grade 8 (five radial marks) is 150ksi, better
than the AN bolt.
But the AN bolt is made of 2330 nickel steel, making it more
corrosion-resistant and more ductile, which means it will stretch more
before it breaks. The part will appear loose before it comes off. The
AN bolt's tolerances are a bit better and the thread length is just
what's needed, not the great length of thread on the industrial bolt
that ends up inside the joint where it doesn't support the shear loads
well. And the thread fit is far better on the AN bolt.
Shear strength for steel is typically 70% of tensile.

Someone asked about the Cardinal's (177) wing attach. It's been a
long time, but I think it was something like 1/2" bolts in sextuple
shear, spaced about 7 inches apart. The spar fittings were cast
aluminum.

Dan

Jim Macklin wrote:

Understand that bolts used in aircraft construction are not
"hardware store" items. The steel and the tolerances for
aircraft grade fasteners are better than hardware store
Grade 8 bolts. Beech uses bolts in tension to hold the wing
on the Bonanza, Baron and King Air models. When there is a
crash, the bolts are rarely broken. But if the bolts are
not properly installed and maintained, corrosion can weaken
the bolts causing them to break.

Cessna uses a bolt installed in shear through fittings like
you fingers meshed. This is called "double shear" and as
long as the bolt is a snug fit in the hole the bolt can hold
more load than the airplane is designed to experience.
But a bolt in tension is stronger than a bolt in shear.

I'd have to pull out my AISC manual to be sure, but I believe that a
bolt in double shear has more capacity than in tension. If you are
comparing single shear to tension, then I agree with you.

Matt

I'd have to pull out my AISC manual to be sure, but I believe that a bolt in double shear has more capacity than in tension. If you are comparing single shear to tension, then I agree with you.

What is "double shear" and "single shear"?

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

wrote:
Robert M. Gary wrote:
Last summer, Texas/Louisiana neighborhood, I think. The
details were in the story, not the time and place.

I'd like to see the actual report on that. I did a search from 1980-now
for fatals in any Mooney that includes the word "thunderstorm" and only
came up with 3, but none mention the pilot having left the aircraft.
This is what I found.
http://www.ntsb.gov/ntsb/brief2.asp?...FA032& akey=1

http://www.ntsb.gov/ntsb/brief2.asp?...FA116& akey=1

http://www.ntsb.gov/ntsb/brief.asp?e...14X36345&key=1

The only Mooney fatal I could find in the SE last summer was this one
http://www.ntsb.gov/ntsb/brief.asp?e...31X01061&key=1

Perhaps that's the one?? The report is only preliminary but doesn't
mention whether the pilot was with the aircraft or not.

-Robert

Jose wrote:

I'd have to pull out my AISC manual to be sure, but I believe that a
bolt in double shear has more capacity than in tension. If you are
comparing single shear to tension, then I agree with you.


What is "double shear" and "single shear"?

It refers to the number of planes in shear. Think of the rivet in a
scissors. There is one shear plane where the two halves of the scissors
meet and are held together by the pin/rivet.

Now think of a sandwich of three pieces of metal held together with a
bolt or pin or rivet. There are now two planes that are in shear and
thus you have twice as much shear resistance of the outer two pieces of
metal are pulled one direction and the middle piece is pulled another
direction.


Matt

"Jim Macklin" wrote in message
...
...
Cessna uses a bolt installed in shear through fittings like
you fingers meshed. This is called "double shear" and as
long as the bolt is a snug fit in the hole the bolt can hold
more load than the airplane is designed to experience.
But a bolt in tension is stronger than a bolt in shear.



But you don't want to be standing under the wing if someone jerks the stut
off.

Boink!!!

;-)
--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

Without the strut, which is in tension during normal flight
and compression when at less than zero G, the wing would
just flap up and down.

The close fit of the bolts in shear is required so that
loads are transferred evenly to the structure.The torque on
the shear bolts is minimal and the nut just serves to keep
the bolt from falling off/out.
A bolt in tension is torqued so that the bolt is loaded into
the elastic range and the tight bolt is stretched very
slightly and then, as long as the bolt stays tight, it does
not accumulate stress until the loads exceed the elastic
limit.



"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com
wrote in message
...
|
| "Jim Macklin" wrote
in message
| ...
| ...
| Cessna uses a bolt installed in shear through fittings
like
| you fingers meshed. This is called "double shear" and
as
| long as the bolt is a snug fit in the hole the bolt can
hold
| more load than the airplane is designed to experience.
| But a bolt in tension is stronger than a bolt in shear.
|
|
|
| But you don't want to be standing under the wing if
someone jerks the stut
| off.
|
| Boink!!!
|
| ;-)
| --
| Geoff
| The Sea Hawk at Wow Way d0t Com
| remove spaces and make the obvious substitutions to reply
by mail
| When immigration is outlawed, only outlaws will immigrate.
|
|