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Hi-loks, recommended sources

Shear

All shear apps. so titanium, steel, 7075, lots of
options can be used. Replacing AD6s in the spar. Being ?out of order? will make bucking (more) difficult. I can provide part numbers (several would work)
 
KLX Aerospace

I work in the heavy aircraft overhaul business, and we currently use KLX Aerospace for most of our fastener procurement. My RV-4 is built with Titanium Hiloks in almost every location that an AN bolt of permanent installation was called out. I also used Titanium bolts in the other 99% of the locations, as well as Titanium reduced head screws for every panel, fairing ect. having been in the industry for 38 years, I have been able to get these items easily. I probably only saved a few pounds, but I am a huge fan of Hiloks and even took some to OSH years ago to talk with Van himself about his thoughts. For most folks, understanding a proper transition fit, precise hole reaming, pricing and the other associated installation quirks, Hiloks are less appealing.
 
A few years back a friend of mine who worked at an airline facility that was shut down gave me a half-full 5 gallon bucket of titanium NAS bolts of various lengths. Took me a while to sort thru them all but needless to say I have a lot of titanium bolts in my rocket.
 
Thanks

Please keep the suggestions coming. Hi-loks are a great product. They were used on the Space Shuttle Heat Shields (and other places) in my early engineering days. Many times they were utilized without their dedicated collar but with standard MS locking nuts as a "one sided" fastener. Also used where low their profile heads provided an advantage. Replaced some huck bolts in certain certified aircraft with them many years ago but I can't remember where they were bought.

I will try gen-aircraft-hardware and KLX aerospace. Not a fan of skygeek.com. I think they are purchase/resale type of operation. Ordered some "in stock" firewall sealant from them then given a three week ship date after I'd paid. They still charged a "restock" fee so they will never make another dime from me (thread drift, sorry). As mentioned, please keep the suggestions coming.

Scott F
 
eBay is another source of surplus hardware. I'm on the hunt now for a set of oversized Ti Hi-Loks for the wing center section in my Rocket. You may not get them all at once, but they don't go bad with age.
 
FWIW, while the Ti 6-4 bolts are stronger and lighter, the nice feature of AN bolts is their ductility and much greater elongation to failure. for the limited number of bolts on an RV I don't believe the weight savings of Ti offset the durability of a AN bolt.
 
Yes and No

@Steve Melton. Thanks for your reply. Respectfully, I believe you're both right and wrong here. All rivets should be in shear application. Likewise, titanium should never be used in tension. When using something other than a rivet that swells to fill the hole in the stack, the structural integrity of the joint/assembly is assured by the diametrical close tolerance(s). The properties of ductility don't really come into play. Supporting evidence =

- the same fastener in shear application is typically torqued to ~45% of same in tension application (you can win some bar bets with that one).

- No Hi-lok pin material has inferior structural qualities to 2117 even after stain hardening.

They're also a great application for places for where a rivet gun can't go, as well.

I've been fortunate to work and know some very smart people. There's also a bunch here on VAF that will call BS on me where needed. Thanks for your reply.
 
Wait until you see what they cost. Titanium is total overkill, the only time I used them was on the XB47 prototype project when contracting at Northrop. When I was forced to replace the huck bolts some idiot removed from a Mooney spar I used hi loks with Mooney engineering approval. eBay is your best bet and I prefer to use jap nuts on them. All Douglas aircraft used jap nuts instead of the hi lok collars, they are acceptable and won't snap off early like a hl70 can.
Like I said new they're about $5 each.
I see no need for them on a RV.
 
And you better be dead on with your reamer when I was a inspector at voight if you could get a .001 feeler gaug to touch the hand under the head it was rejected. At Northrop inspector would have to buy off every hole for size before when even installed one. They are not for the inexperienced. That job required 25 years metal experience to even be considered.on flush hi locs the limitations were never above flush and .002 below flush.
Every hole was drilled using a drill bushing. XB-47 was all titanium with a carbon skin.
 
My reason for using Titanium

As I mentioned in my earlier post, the Titanium only saved me a couple pounds AT BEST, but as used in virtually every commercial airliner construction for the last 20 years, the aluminum coated titanium Hiloks and bolts have superior corrosion resistance..my main reason for going with titanium. Because they are relatively hard to find a vendor or even understand the trade name designations, its much easier to build with and resource "AN" hardware. Some of us have spent years of our life working with these, and they are "normal" in our world.There are cross reference documents available, and engineering data that can enlighten one about the shear/tension KSI ratings,compatibility and all the stuff to make substituting for AN and MS equivalents structurally correct. For me, I have spent many years making my living as a structures specialist and engineer on heavy jets battling stress and corrosion, so it is second nature.
 
Hi-Loks are very expensive fasteners and have specific collars. They come in titanium, steel and high strength and high temperature nickle alloys. They are again not cheap. If you have the part number you can google it and distributors will come up.

For 6Al-4V Titanium (Alloy Steel) standard Dia. part numbers are
HL 10 (HL18) Protruding Shear
HL 11 (HL19) 100º Reduced Flush Shear
HL 12 (HL20) Protruding Tension
HL 13 (HL21) Flush MS24694 Tension

The part number is for example protruding tension head titanium HL13()()-() 1st () are letters after fastener code is coating, second () diameter in 32nd and thrid () in 16th.
HL13VU6-12 bare no lube, 3/16" dia and 3/4" grip. The charts and specs are on line.

You can have tension on hi-loks if they have tension heads and tension collars...

Why? Steel AN hardware is fine, and the weight savings will be small in a small airplane. A jet that has 100,000's of fasteners, Ti Hi-Loks saves weight. Did I say this stuff is expensive for low volume purchases... 25 years ago Boeing had a surplus store in Kent Washington. They use to have barrels of Hi-loks for penny's on the pound. It is what they swept off the factory floor or mixed up surplus... They stopped selling the fasteners, because people were buying it and selling on the open market as approved hardware. You can't do that. All parts for commercial transports need records, including fasteners. Too bad. I have a box of some Ti bolts and hi-loks. Be aware there are China made bootleg Hi-Loks on the market, with bogus quality.
 
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Expensive in small quantities, yes. But I used to do financial proposals for my company and I know what they cost when you buy them by the truckload, and in most cases a Ti Hi-Lok is less expensive to the company than you or me buying the equivalent AN bolt from Spruce.

And BTW, those center section bolts are big and heavy as a set. A set of Ti Hi Loks there will save you well over a pound. Saving weight on an airplane is never a bad idea if the structure is not compromised.
 
This discussion has been joined by several people who have hands on knowledge of the Hi-Lok fastener system through their employment in ?big airplane? companies. I too have decades of ?big airplane? employment and like them, have buckets of surplus Ti fasteners. I also agree with them wholeheartedly that proper hole prep is paramount to a properly engineered shear connection. In an interference fit such as used in the center section bolts, an out of round or oversized hole will destroy the strength of that connection, no matter what material the fastener is made of.

In short, a perfectly round, reamed to correct interference fit hole is required whether you are using an exotic Ti Hi-Lok or an AN bolt from Spruce. The precision of the hole is the key to strength (assuming the pin meets minimum engineering specifications).

That said, I take exception to the cautions in this thread that seem to imply the Hi-Lok pin is somehow less tolerant of perfection than an AN bolt. It is true that Hi-Loks are a specialty fastener and the ?big airplane? companies like mine require training on their installation, but that is true of almost EVERY critical operation found on the shop floor. The Hi Lok system is in many cases a direct replacement for a traditional permanent bolted connection, and it?s not a difficult process to learn. Here?s what the company?s website has to say:

The HI-LOK? Fastening System:
? is basically a threaded fastener which combines the best features of a rivet and a bolt. It consists of two parts, a threaded pin and a collar
? is rapidly and quietly installed by one person from one side using standard power tools or hand tools with less worker fatigue than with either regular rivets or bolts.
? easily adapts itself to large scale production in a variety of pin and collar material combinations for high strength and high temperature performance.

A bolt and nut system is heavier than the HI-LOK? Fastening System. Minimum weight results from elimination of the wrenching surfaces on a bolt and nut system. Wrenching clearances are minimized and great weight savings result from the design of more compact structural joints.

Bolt and nut systems require calibrated torque wrenches and torque inspection. The HI-LOK? Fastening System eliminates these concerns.



So, the bottom line as I see it: When it comes to hole prep for a critical shear connection, ?Perfection? is the standard we should strive for; regardless of the fastener system we are using. If any of our more experienced shop personnel have a reason why a Hi-Lok pin is more intolerant of a properly prepared hole than an AN bolt, I?d sure like to hear it. I?m always ready to learn something new.

As for ?worth it? regarding the cost vs. weight savings, that?s for the individual to decide. As has been discussed, these can be acquired for a huge range of pricing from ?free? to ?eye watering?. And even if you have to pay full price, spending $500 bucks to save a pound on your center section bolts is far better money spent than an exotic, multicolor paint job (IMHO).
 
I wouldn't substitute a fastener to use something that is even further away from aluminum on the galvanic corrosion chart...
 
I wouldn't substitute a fastener to use something that is even further away from aluminum on the galvanic corrosion chart...

the Galvanic table shows that steel and aluminum are reasonably compatible, but if titanium and aluminum contact, the aluminum will be the anode and corrode.
 
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Al/Ti interface

To throw another technical aspect in the mix..The Titanium Hiloks most often used are aluminum coated from production which is identified in the part number code (K on Boeing hardware), and gives the fastener protection from the Ti being in direct contact to the Al structure. It is way better than what happens when alloy steel rusts in an aluminum structure.
 
The Confession

I should have probably started with this instead of jumping right to the Hi-Lok topic. I'm making F1/F4 wings from a partially completed RV-4 set. Being "out of order" in assembly (bottom skins on), makes it more difficult. A couple of the holes where AD6s were removed are less than perfect. My brain jumped straight to Hi-Lok option. May be able to draw the rivets all but one of the locations. Others have stated Vans approved (without a paper trail) installation of AN4 bolts in these locations. Any related advice/stories/suggestions are appreciated. Thanks again
 
Hi-Loks for RV-4 spar attach?

A good friend was flying his newly purchased RV-4 Fastback from Wyoming to Alberta when he lost his canopy at Cut Bank, MT. We drove down from Alberta with my trailer and removed the wings to haul it home. When I removed the NAS bolts at the center spar attach point, I could not get a socket on many of the bolt heads? It turned out that that bolts were hammered so hard when installed that the heads were smashed in. I have not examined the holes in the spars yet,but can't imagine them being very nice? Slightly oversize Hi-Loks with properly reamed holes might be a good fix??

Phil
 
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