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Steve Geard
Joined: 09 Dec 2013
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wlannon(at)shaw.ca
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 Posted: Tue Feb 14, 2017 8:10 pm Post subject: YAK55m wing bolt replacement |
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Hi Steve;
I have no specific information to offer you on the Yak 55 wing attachment,
only a few general observations:
The wing attach straps are not castings. These are high strength steel
forgings, probably a Russian equivalent of AMS 4340 (or similar) and heat
treated to a minimum UTS (ultimate tensile strength) of not less than
170,000 psi.
The factory manual may allow the use of an oversize bolt (factory supplied)
with rework of the fittings possibly by precision grinding rather than
reaming.
The maximum increase in hole dia. will likely be in the order of 0.25 - 0.5
mm (0.010 - 0.020 in.) A typical maximum clearance between the bolt and
wing fitting would be in the order of 0.05 mm (0.002 in).
If you know a good professional engineer have him do some measurements and
calculate the lower attachment load at your normal (positive) max. "G" load.
He will probably give you a number around 30 ton.
Fly safe;
Walt
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heaysr(at)telus.net
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| Posted: Tue Feb 14, 2017 10:15 pm Post subject: YAK55m wing bolt replacement |
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Hi Steve,
I'm told that the main spar wing and fuselage fittings are titanium.
Those fittings take on an oval shape with long term aerobatic loadings while
the bolt remains perfectly circular at its original diameter.
The fix is to ream the fittings and install over- sized bolts to match.
Reaming titanium is not an easy matter and doing it while keeping the holes
aligned so as not to change the rig is an added challenge. I was told you
need a 17 flute reamer.
There are two ways of getting oversized bolts. One is to build up the
existing bolts and grind them back to the oversize diameter needed. The
other is to order oversized bolts from the Yak 55 factory in Eastern Russia.
As of two years ago Vladimir Yestremi had the equipment and contacts to do
the whole job. I'm not sure if Vladimir is still in that business.
Jill and Carl at M14P also have knowledge of the process. Jill - are you
there - can you please comment?
I did some calcs a couple of years ago as attached. Walt's 30 tons (imperial
tons?) is pretty close to the 28 T (metric tons) I calculated.
I'm not an aircraft engineer and don't stand behind the calcs. But they
certainly convinced me to be very wary of having the right bolt strength.
They are high end bolts that are required.
Hopefully Vladimir reads this and can correct me if needed.
Regards
Royden
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jandhbialek(at)hotmail.co
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| Posted: Tue Feb 14, 2017 11:04 pm Post subject: YAK55m wing bolt replacement |
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Usually forward spar is 80 percent and rear spar is 20 percent. There are load cases where one wing takes more load than the other when combining rolling loads with "under G" pitch rate loads. Regardless, important to know what the max gross we're trying to figure this out for. based on max gross and worst case maneuvering load we can begin to sneak up on the number the bolt should be good for.
Jason Bialek
yak55m KAWO
[quote] On Feb 14, 2017, at 9:15 PM, "Walter Lannon" <wlannon(at)shaw.ca> wrote:
Hi Steve;
I have no specific information to offer you on the Yak 55 wing attachment, only a few general observations:
The wing attach straps are not castings. These are high strength steel forgings, probably a Russian equivalent of AMS 4340 (or similar) and heat treated to a minimum UTS (ultimate tensile strength) of not less than 170,000 psi.
The factory manual may allow the use of an oversize bolt (factory supplied) with rework of the fittings possibly by precision grinding rather than reaming.
The maximum increase in hole dia. will likely be in the order of 0.25 - 0.5 mm (0.010 - 0.020 in.) A typical maximum clearance between the bolt and wing fitting would be in the order of 0.05 mm (0.002 in).
If you know a good professional engineer have him do some measurements and calculate the lower attachment load at your normal (positive) max. "G" load.
He will probably give you a number around 30 ton.
Fly safe;
Walt
--
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Steve Geard
Joined: 09 Dec 2013
Posts: 36
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wlannon(at)shaw.ca
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| Posted: Wed Feb 15, 2017 11:30 am Post subject: YAK55m wing bolt replacement |
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Hi Royden;
Wow! Trying to work all that out would give me a massive headache; well
done, mine was just a wild ass guess.
Would not be surprised if the spar is titanium but would not expect the wing
attach fittings to be, though I do not know and understand Russia has been a
leader in Ti technology for many years.
The bolt of course is the least critical factor in this type of joint. It
is loaded is double shear and, in this, is able to exceed the UTS of the
attaching straps which are loaded in pure tension. Industry standard for
the bolt repair/oversize is grind, hard chrome plate, stress relief and
grind to size.
As you noted these are high quality aerospace standard bolts.
If, as I suspect, the straps are high strength steel in excess of 170 Kips
(could be as high as 200!) the chances of successful line reaming are slim
to none. Well, maybe with a 17 flute reamer??
The tensile load on the straps is concentrated in two distinct areas: 1.
Shear out - compensated for at manufacture by increasing the material
between the hole and the strap end. 2. The combined area at upper and
lower (90 deg.) hole extremities; the amount of material remaining here
will determine the max. hole dia. which will be in the structural repair
manual.
Cheers
Walt
ps. I don't even know if Ti is ferrous! I would think not. If not check
with a magnet.
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