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dean.psiropoulos(at)veriz
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 Posted: Sun Jul 01, 2007 9:47 pm Post subject: Nutplates vs Stop Nuts |
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I was assembling my baffles for final installation today. I am mounting the
oil cooler on the pilot's side aft baffle and thought I'd be real smart and
use nutplates riveted to the baffle material instead of metal or nylok
stopnuts at the other ends of the bolts that hold the cooler on. But
looking at the nutplates as I was installing them it hit me that there is no
where near the amount of metal surrounding the threads of the bolt with a
nutplate that there is with a standard nut.
Since the engine does a lot of shaking and a cooler full of oil is not
exactly light in weight, was the nutplate idea a bad idea (I wanted to have
that many less nuts and washers in the assembly and liked the idea of just
having to install the bolts). Any mechanical engineers out there savvy with
the strength differences of the two fasteners and what do you think? Never
heard anyone bring this up on the list before so I'm probably being my usual
paranoid self, but thought I'd ask anyway. On a side note, did some
transition training with Mike Seager in Portland last week and had a ball.
Mike's a great (and patient) mentor and I really enjoyed it (even if I did
have a heck of a time getting used to taxiing and steering with the brakes
and getting the landing flare just right). Thanks.
Dean Psiropoulos
VR-6A N197DM
Inspection around the corner.
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Vanremog(at)aol.com
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| Posted: Sun Jul 01, 2007 10:19 pm Post subject: Nutplates vs Stop Nuts |
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In a message dated 7/1/2007 10:48:53 P.M. Pacific Daylight Time, dean.psiropoulos(at)verizon.net writes:
| Quote: | I am mounting the
oil cooler on the pilot's side aft baffle and thought I'd be real smart and
use nutplates riveted to the baffle material instead of metal or nylok
stopnuts at the other ends of the bolts that hold the cooler on. But
looking at the nutplates as I was installing them it hit me that there is no
where near the amount of metal surrounding the threads of the bolt with a
nutplate that there is with a standard nut. |
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Dean-
Standard nutplates riveted to sheet metal are really meant for light fastenings and not for structural attachments as you indicated. Now, there are nutplates that are designed to carry more of a shear load and those are the countersunk variety (as used on the fuel tank attachments, where you also dimple the skins into them).
That said, sheet metal (baffle aluminum) can't carry much of a load either, even if you use a standard bolt and nut. I would recommend installing at least a 1/8" thick (3/16" is what I used) doubler riveted to the sheet metal over the whole general area where you intend to make the oil cooler attachment in order to spread the load and stiffen the part, use long standard bolts to go thru both the front and rear oil cooler flanges and attach using all metal locknuts. Use all six mounting points and make sleeves/spacers to go in between the oil cooler flanges out of steel tubing. This is not a place to wimp out with a light duty attachment. As Jerry Lee said, there's "a whole lot a shakin' goin' on".
GV (RV-6A N1GV O-360-A1A, C/S, Flying 859hrs, Silicon Valley, CA)
See what's free at AOL.com.
[quote][b]
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jim jewell
Joined: 09 Jan 2006
Posts: 82
Location: Kelowna B.C. Canada
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| Posted: Sun Jul 01, 2007 11:34 pm Post subject: Nutplates vs Stop Nuts |
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Hi Dean,
I am not an engineer so I will avoid the comparative structural strengths of
nutplates verses Nylok fasteners etc.
My oil cooler is mounted in the position that you intend to use. I used
floating nutplates similar in strength to what you describe.
Based on others descriptions of successes and failures you should consider
adding some strength to the baffles in the area around the oil cooler
mounting position.
I have seen pieces of aluminium angle being used as braces running from one
of the engine case half bolts back to the oil cooler to add stiffness to
that corner of the baffles.
I chose to add doublers to the baffle parts in that general area. They show
up in the first attached photo.
I used all six bolts for the added strength to hold the oil cooler in place.
I have low hours on my 6-A to date but I doubt that the nutplates will be a
failure point in the foreseeable future. I will be watching for cracks in
the baffles but I don't expect to see any very soon.
Since the attached pictures where taken I added a filler piece to the top of
the baffles so that the baffle seal material runs straight across the top of
the rear baffle with out the usual joggle just above the oil cooler, (much
neater and easier). This addition also added a little more rigidity to the
area.
I will wait to see one of the engineer types supply the strength data you
request.
Keep building, it's not far now,
Jim in Kelowna, RV6-A C-GIIG 30 hr. since first flight
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pitts_pilot(at)bellsouth.
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| Posted: Mon Jul 02, 2007 5:02 am Post subject: Nutplates vs Stop Nuts |
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I'm no structural engineer, but I think the nutplates would be as strong
as a nut provided the amount of threads are there. The nut/nutplate is
in tension, with all the tension in the threads. Wouldn't make any
difference if the nut were as big around as a soda can, the same amount
of tension would strip out the same number of threads made of the same
material. Having said that, my experience is that nutplates are made of
stronger steel than the standard AN nuts we're using. Also, remember
that a nylok nut MAY have fewer metal threads than a standard nut!
Firm, strong mounting is a necessity ..... not only do you have the
weight of the oil cooler filled with oil, you also have some rather
large hoses attached.
Linn
do not archive
DEAN PSIROPOULOS wrote:
| Quote: |
I was assembling my baffles for final installation today. I am mounting the
oil cooler on the pilot's side aft baffle and thought I'd be real smart and
use nutplates riveted to the baffle material instead of metal or nylok
stopnuts at the other ends of the bolts that hold the cooler on.
snip
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| Quote: |
Dean Psiropoulos
VR-6A N197DM
Inspection around the corner.
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