Seatbelt Attach layup oops

[Cozy1200]

Just about the time I think I'm doing some good layups....

 

I got a nasty bubble in a bad place. I've got an airbubble in the outside seatbelt layup. I'm suspecting it was my technique. I laid up all 7 ply bid on plastic, then cut to size, then transferred to the place in one piece. Very much like I do most small layups and bid tapes. I think the problem was it was too many layup to do at once. I think the individual plies weren't able to conform to the shape. It definitely wasn't there last night, so I'm happened later during cure. The pics show that it's about a 1 to 1 1/2 inch bubble. Anyplace else I'd just inject the bubble as per plans.

 

But seatbelt attachment is so important that I'd like to get some outside advice. Do I inject it or sand it off and repair?

 

Sanding would likely require taking all 7 plies off and starting over. Doable, but tedious.

[Phil Kriley]

If you have a Fein tool, it would not be that hard to "shave" off the layup and redo. That's what I would do.

[Kent Ashton]

I'd leave it alone or maybe drill two tiny holes--one at each end--and inject some epoxy. I've done the same sort of thing but sometimes I use a piece of foam over the layup (with saran between), weighted with a brick, to force the layers to conform.

 

Never heard of anyone saying their seatbelts tore out in a crash--'course, those folks might be taking the dirt nap. :-(

 

BTW, I sanded a depression in my outside foam & longerons in order to avoid counterboring the outside skin to recess the bolt head and added a couple of layers to the outside, too. I suppose you could also beef the area up with a small.032 plate on the outside, recessed.

 

Just don't hit anything solid.

[argoldman]

Just about the time I think I'm doing some good layups....

 

I got a nasty bubble in a bad place. I've got an airbubble in the outside seatbelt layup. I'm suspecting it was my technique. I laid up all 7 ply bid on plastic, then cut to size, then transferred to the place in one piece. Very much like I do most small layups and bid tapes. I think the problem was it was too many layup to do at once. I think the individual plies weren't able to conform to the shape. It definitely wasn't there last night, so I'm happened later during cure. The pics show that it's about a 1 to 1 1/2 inch bubble. Anyplace else I'd just inject the bubble as per plans.

 

But seatbelt attachment is so important that I'd like to get some outside advice. Do I inject it or sand it off and repair?

 

Sanding would likely require taking all 7 plies off and starting over. Doable, but tedious.

 

Bummer of a birthmark, Hal (for those far-side fans)

 

The picture is a little fuzzy, but it looks like the bubble is right in the middle where the attachment angle sits.

 

Did you use any heat while curing or adding the layup to the substructure??

 

Sometimes with large layups you can trap air which before cure finds its way together and gives bubbles. Or heat may create it.

 

If it were me, I would sand the bubble off till the top is smooth, sand the entire lay-up with 40grit, fill the defect with flox and lay another 7 ply layer over the old, now scuffed layup.

 

Alternately, you could go 1" or so beyond the defect and put a patch on, but the strength of this layup is critical (when needed) so spend the extra glass and weight.

 

This layup is sandwiched between the structure just below it, be it wood, or aluminum if kit aerocanard, and transmits the load through the plys to the fuselage. You will have two holes (mounting for the bracket) already in it, so one would think that if you just fill the defect (smoothing it out so that the bracket fits flush) would substantially reduce its strength since a major part of the glass strands will have little but cosmetic function. Perhaps Marc or other glass expert can shed more light on this, (or shoot me down)

 

For some reason, I am now thinking of Larson's "Boneless chicken Ranch.

[Steve Innova]

Re-do. I'm not convinced the designed seatbelt attach points meet aviation standards for safety anway -- certainly wouldn't want to compromise there.

[steve]

i think the bolt gets its strength from the rear (underside) and not so much from the front, but if it fails it all fails. id grind it down till gone or peel the hole thing off and redo. pliers some times can grip-and-rip

[TMann]

I switched to Phonelic for all of these types of hardpoints. Much cleaner application.

I got the Idea after looking at the Berkut drawings.

[Kent Ashton]

I can't believe you guys are saying to redo that. It won't gain him a thing. Just a waste of time. And cutting the bubble and patching over it? That'd just make it weaker. Jeez, leave it alone.

[Jack Morrison]

I agree with Kent. I had two true tests of the strength of the plans seat belt construction. First was when I was doing the testing of the supercharging system on my E Racer in 2000. Was on a extended downwind for rw33 and on my turn to final, 1/2 mile out at 400 ft the engine quit. would not restart and I did a gear up landing in a bean field about 1/8 mile short of rw33. The groung was soft from two days of rain and when the AC was at 2ft, the right dug into the raising terrain and exploded(blew of the right wing ) flew 300 feet behind the AC. It felt like I hit a solid rock. Point being, the seat belt anchors were not compromized in any way. Second, When I had the inflight fire incident last year, I put the AC on the runway hard and fast, 200 mph, colapsed the left main grae and slid down the runway 1500 ft, still did not compromize the seat belt anchors. That is until the fire consumed the AC. My opinion, move on, that little air bubble will make no difference in the safety of the seatbelt system.

 

Jack

E Racer Extreme

[rickh]

I got a nasty bubble in a bad place.

Now that we *all* know you're building a defective plane...

 

The seat belt brackets are held in by two relatively small washer-head AN screws, bearing on a piece of pine, and some flox... Me thinks you could even stair-step those reinforcing plys with no ill effects. Shoulder harness attach points are 'nother story in my book.

 

Disclaimer: I'm not an engineer, but did sleep in a Holiday Inn Express dumpster last week.

 

Rick

[argoldman]

Idonnknow,

 

If the seatbelts are held by the pine, or the aluminum in the Aerocanard kit or the phenolic, then why the heck put 7 layers of glass over them extending to the fuselage. Common guys, the wood has little strength in shear (especially perpendicular to the grain. The purpose of the wood, aluminum, phenolic is to try to resist crushing and to fill the concave space between the bottom of the fusealge and the flat part of the seat belt bracket and to give a flat area for the bolt heads or nuts to sit on. In the aerocanard the aluminum is tapped. How much strength do you think that the underlying foam in the center consoles (MK IV builders) gives to stop the seat belt from shearing its attachment off. It is the layers of glass on top which like the side layups distribute the load---NOT THE DIRECTUNDERLYING STRUCTURE. The overlying glass distributes the load in an acceptable manner.

 

Now if the bolts extended through the fuselage and bolted on the outside (using a filler block to give a perpendicular surface of appropriate size), that would be a different story in that the load would be distributed to the outside skin. That's an airplane of a different color and is not what we are dealing with here.

 

In an accident, although the wood/glass epoxy bond would hold somewhat the wood would split at the bolt heads were it not for the sandwich that I mentioned before. It is the top (inside) piece of bread that is the saver. It's similar to a hat section. One (I) wonder(s) if were it not for the difficulty in manufacture (the plans are written so that almost anybody with a modicum of skill can produce an aircraftoid product) if a hat section of glass, with the same dimensions, bonded to the fuselage in the same way, without the wood, phenolic etc as the filler, would yield the same strength results.(although the filler does stop it from parallelagramming and failing in that mode)

 

Having, had my gizzard saved by seatbelt attachments (aluminum squares, drilled tapped and bonded to the top of the dragonfly wing, by appropriate layers of fiberglass), I don't think that I would try that (especially since my attachments in my aerocanard are finished)

 

 

There is essentially no difference between the lower seat belt attachment and the seatback belt attachment. It is merely a matter of where and how you distribute the load caused by the tension of the belt (it is not explosive as the belts stretch in an accident.

 

Phenolic is great stuff to work with, aluminum is used in the Aerocanard kit, but don't count on the junction between either of those or wood, and the underlying glass to hold a belt on.

 

If you do think that that is where the strength lies, why don't you just bond 4 pieces of wood, aluminum, or phenolic to your firewall, counterbore, from the inside, till you hit the wood, or whatever and bolt your engine to that. (tongue extracted from cheek)

[Steve Innova]

I can't believe you guys are saying to redo that. It won't gain him a thing. Just a waste of time. And cutting the bubble and patching over it? That'd just make it weaker. Jeez, leave it alone.

This arguement comes up every few weeks. There seems to be line of reasoning in this hobby, that states to the effect of: No need to verify information with testing, just follow the plans. As long as you don't crash, the safety equipment isn't neccessary. Ok.

[Steve Innova]

Shoulder harness attach points are 'nother story in my book.

The shoulder harness attach points are structually deficient, IMHO, and directly contributed to the loss of two lives in a crash.

 

I intend to test these to failure, and demonstrate their deficient design.

[TMann]

The shoulder harness attach points are structually deficient, IMHO, and directly contributed to the loss of two lives in a crash.

The shoulder harness caused a plane to crash?

 

Sounds to me like the blame belongs a bit further upstream don't you think?

I'd like the link to that NTSB report.

[Steve Innova]

The shoulder harness caused a plane to crash?

 

Sounds to me like the blame belongs a bit further upstream don't you think?

I'd like the link to that NTSB report.

Perhaps a more gramatically correct statement would have been: In a Cozy MkIV crash, the shoulder harnesses failed, contributing to the deaths of the pilot and front seat passenger. The two rear seat passengers survived.

 

The crash wasn't caused by the shoulder harness, it was caused by striking a wire on approach.

[TMann]

The crash wasn't caused by the shoulder harness, it was caused by striking a wire on approach.

I see ....... so falling below the glide path was the first link in the chain?

[Steve Innova]

I see ....... so falling below the glide path was the first link in the chain?

This arguement is common and tired in experimental aviation. It can be summarized as:

 

"If you don't make any mistakes, you won't crash, and you won't need any safety equipment. Therefore the only worthwhile investment in safety is in improvements that reduce the likelyhood of a crash."

It's not surprising to hear this arguement, as pilots are some of the more self confident (arrogant?) individuals, most of whome, upon reading an accident report, are quick to point out how they would never have let those circumstances happen to them in the first place, by virtue of their superior decision-making and pilotting skills. Sure, whatever.

 

If that's your position, I'll wish you luck, not that you'll ever need it, of course... I, for one, happen to believe that most light aircraft accidents (which happen, even to the best pilots, BTW), are in fact survivable. A 2 lb investment in an improved shoulder harness attachment seems like a small price to pay.

[Kent Ashton]

This arguement comes up every few weeks. There seems to be line of reasoning in this hobby, that states to the effect of: No need to verify information with testing, just follow the plans. As long as you don't crash, the safety equipment isn't neccessary. Ok.

How you gonna test your seat belts? Pig carcass or hire the homeless?

[Steve Innova]

The static tests detailed in the FARs.

[Kent Ashton]

The static tests detailed in the FARs.

OK, so you're just testing the restraint system for normal loads plus a fudge factor. How do you plan to do that? :

 

"Sec. 23.785 Seats, berths, litters, safety belts, and shoulder harnesses.

. . .

(a) Each seat/restraint system and the supporting structure must be

designed to support occupants weighing at least 215 pounds when

subjected to the maximum load factors corresponding to the specified

flight and ground load conditions, as defined in the approved operating

envelope of the airplane. In addition, these loads must be multiplied by

a factor of 1.33 in determining the strength of all fittings and the

attachment of--"

[TMann]

I plan on doing my flight tests with a parachute but now I'm having second thoughts.

I have a lot of jumps that I have made with a sport rig (2 chutes) but how should I test an emergency chute?

Does anyone know where I could rent a pig?

Then comes the problem of getting it out of the plane.

[argoldman]

The shoulder harness caused a plane to crash?

 

Sounds to me like the blame belongs a bit further upstream don't you think?

I'd like the link to that NTSB report.

 

Any idea of the failure mode of the seatbelt failure. Did the brackets pull the mountings out of the seatback brace or did the seatback brace separate from the fuselage?

[Marc Zeitlin]

The shoulder harness attach points are structually deficient, IMHO, and directly contributed to the loss of two lives in a crash.

I am assuming that you're referring to Dr. Larson's crash on New Year's Day, 1995. The writeup in the COZY newsletter can be viewed at:

 

http://www.cozybuilders.org/newsletters/news_49.html#accidents

 

and the NTSB report at:

 

http://www.ntsb.gov/ntsb/GenPDF.asp?id=MIA95FA053&rpt=fa

 

Neither of these makes any mention of seat belt or shoulder harness failure - the report from Mike Pinnock indicates that the plane was demolished from the front seatback forward, leading me to believe that at least in this case, it wouldn't have mattered how well anyone was restrained. If you have different input, I'd be interested in hearing it.

 

This arguement is common and tired in experimental aviation...It's not surprising to hear this arguement, as pilots are some of the more self confident (arrogant?) individuals, most of whome, upon reading an accident report, are quick to point out how they would never have let those circumstances happen to them in the first place, by virtue of their superior decision-making and pilotting skills. Sure, whatever.

Now, with this set of statements and thought process, I will agree 100%.

 

A week and a half ago, I gave a presentation at Scaled that covered my trip east last summer - one that I obviously survived. But I had three EI failures on that trip and flew 35 hours with about a gallon of adrenaline in my bloodstream while I stared at the engine monitor. I haven't touched the plane nor flown as PIC since I got back on 8/4/2008. In retrospect, I can count 13 stupid decisions I made on that trip, any one of which could have led to an emergency off-field landing. Three of them were with family in the plane. I've put together a slide presentation that will eventually get to the web.

 

I will say, with no humility whatsoever, that I am an extremely intelligent person - I've proved that through school and work experience and the responsibilities that I've earned. But the basic idea is EXACTLY as Steve states - folks read NTSB reports and think "I'm no idiot - I'll never do <that stupid thing>". But smart people DO do stupid things, and I applaud him for attempting to ensure that his aircraft meets at least SOME of the safety regulations that have been determined by history to be reasonable. The analysis of Paul Conner's SQ2000 crash:

 

http://www.cozybuilders.org/N2992_Accident_Eval/

 

clearly indicates that the seat/seatbelt system in the plane was completely inadequate, and had it BEEN adequate, Paul might have survived. Making the statement that merely avoiding the accident is all that's required is demonstrably false - car crashes have become far less dangerous over the past 40 years, even as the mileage driven has risen tremendously, and it's almost ALL due to better design and testing of crash survivability. Applying just a little of that to airplanes, especially homebuilt airplanes, can only be a good thing.

 

At any rate, I will be very interested in Steve's test results.

 

All that said, probably injecting the bubble that Drew has with epoxy would be a good enough fix, given the structural needs of the area - it would at least be as good as the "correct" layup would be, however good that is.

[Steve Innova]

Any idea of the failure mode of the seatbelt failure. Did the brackets pull the mountings out of the seatback brace or did the seatback brace separate from the fuselage?

I am assuming that you're referring to Dr. Larson's crash on New Year's Day, 1995. The writeup in the COZY newsletter can be viewed at:

http://www.cozybuilders.org/newsletters/news_49.html#accidents

and the NTSB report at:

http://www.ntsb.gov/ntsb/GenPDF.asp?id=MIA95FA053&rpt=fa

Neither of these makes any mention of seat belt or shoulder harness failure - the report from Mike Pinnock indicates that the plane was demolished from the front seatback forward, leading me to believe that at least in this case, it wouldn't have mattered how well anyone was restrained. If you have different input, I'd be interested in hearing it.

 

As Marc mentioned, I'm refering to the fatal 1995 crash of Dr. Larson's Cozy MkIV. My info is coming from a message posted to the Cozy Builders email list by "TEllis (titled: Re: COZY: Seatbelt prices too high), describing the complete failure of the forward seat-belt and shoulder harness attach points in this crash.

 

"Both the pilot and front seat passenger were thrown thru the instrument panel and died. There were two teenage boys (as I recall) in the back seats and they survived with little injury.

 

The fact is that there was no problem with the front seat belts themselves. The sholder attachments pulled out, both outside belt attachments pulled out and the whole center heat duct seat belt attachment unit separated from the fuselage. From the front of the strakes forward, the whole fuselage disintegrated so it is extremely improbable that the front seat passengers could have had a chance in any event, but the rear seat belts and their attachments held and saved the rear passengers. Which is a miracle in itself."

Of course, this accident may have been entirely unsurvivable, but it is worth noting that the rear seat belts held, and both the rear passengers survived. One thing that's certain though -- survivable crashes become very unsurvivable if the human body is not adequately restrained inside the vehicle.

 

I recall providing first aid to a guy ejected from his vehicle in frontal crash w/roll-over. The car was destroyed, but everyone else survived with minor injuries, except for that guy who hadn't worn his seat belt.

[Steve Innova]

I plan on doing my flight tests with a parachute but now I'm having second thoughts.

I have a lot of jumps that I have made with a sport rig (2 chutes) but how should I test an emergency chute?

Does anyone know where I could rent a pig?

Then comes the problem of getting it out of the plane.

I think the difference is that you didn't build the parachute yourself. Or maybe you did... in which case I would test it first.