Date: Thu, 10 Sep 1998 08:21 -0500 (CDT) From: Michael Pollock Subject: Re: COZY: Loud Pop??? Nat and Cozy Builders, When I said our airplane, I was speaking of our Velocity that we are flying. I am in a group of 4 people who built this Velocity and I hold the repairman cert. We did hard-shell the canard per recommendation as listed below. We followed the plans exactly except for the hard shelling of the canard. We thought that since the recommendation from Alan Shaw showed up in the newsletter, it was an acceptable method to lighten the weight of the canard. He said he used the procedure and it did lighten the weight. I guess one should only stick to the plans and do ONLY what is spelled out in the plans. The problem we have experienced in localized in only one area that is already repaired, but it could happen to others who have done what we have done. I WILL NOT be doing any hard-shelling on my Cozy MKIV, and will recommend against it for the reason listed below. Sorry for the confusion. michael.pollock@mci.com Flying Velocity N173DT Building Cozy MKIV #643 Date: Wed, 09 Sep 1998 09:11 -0500 (CDT) From: "Nat Puffer" To: "Michael Pollock" Subject: Re: COZY: Loud Pop??? Michael, I think you told all the Cozy builders that this airplane was one of the flyers/builders of our airplane. Would you tell them that it was a Velocity? And it used hard shelling? Otherwise you are leaving them with a mystery---was it a Cozy? Did the builder follow the plans? Was hard shelling involved? I think you owe it to Cozy builders to tell them what you told me. Nat ---------- > From: Michael Pollock > To: Nat Puffer > Subject: Re: COZY: Loud Pop??? > Date: Wednesday, September 09, 1998 8:00 AM > > Nat, > > This is our Velocity that the problem showed up on, and the canard > was hard-shelled per recommendation of Alan Shaw, before he started the > wing business 'Dynamic Wing Corp.'. His recommendation came to me > via the Velocity Newsletter some 4.5 years ago when he was working > with Velocity. Since that time, it has come to my attention that hard-shelling > is not recommended due to the nature of the bond caused by the hard-shelling. > It is highly possible that we got a small bubble between the hard-shelling > and skin of the canard during the glass layup process. When the airplane > was flown to a much higher density altitude, it is possible that the > bubble forced a larger space between the hard-shelled surface and the > glass skin. We used alcohol to clean the glass surface between filler > and glass. Also, the only pin-holes drilled were in the winglet cavity > and under the canard outboard above the counter-weight. Now that we > have remembered "dummy us" that we used closed-cell foam for the canard > and wings, we will have to fill the couple of holes drilled. > > > > Date: Thu, 03 Sep 1998 14:57 -0500 (CDT) > From: "Nat Puffer" > To: "Michael Pollock" , > "Cozy_Builders" > Subject: Re: COZY: Loud Pop??? > > Michael, > We have been monitoring the Canard Pusher for over 20 years now and have > never heard of anything like this before, with possibly one exception. If > you use too much solvent in preparing fiberglass for finishing, on the > wings and canard, it can weep into pinholes and dissolve enough styrafoam > underneath to cause delamination, which will eventually show up as a > bubble. That could have been the cause, or it could have been due to "hard > shelling", which isn't as strong a bond as a wet layup over foam as > recommended in the plans. Drilling pin holes through the surface of > airfoils is NOT RECOMMENDED. If fiberglassing and finishing is done > correctly, there should be no air between the foam and fiberglass which > could result in a later delamination. Remember, this is closed cell foam, > and the open cells on the surface are supposed to be filled with micro > before glassing, in which case there would be no "air" below an air-tight > surface. Was this a Cozy? If so, whose? It would be most helpful to > determine the cause, because it should not have happened. > Regards, > Nat > > ---------- > > From: Michael Pollock > > To: Cozy_Builders > > Subject: COZY: Loud Pop??? > > Date: Thursday, September 03, 1998 12:00 PM > > > > I just thought I would pass this information along to builders and > > fliers. One of the builders/fliers of our airplane heard a loud pop > > while flying around 13,500 feet in route back to Texas from Oshkosh. > > When the builder/flier returned to Texas, it was noticed, some time > > later, that the canard had obtained a bubble on the left top, just > > forward of the spar. It has been determined that the bubble formed > > due to the pressure differential at that altitude and the canard was > > air tight. The delamination was repaired by injecting epoxy into the > > bubble and placing weights over the problem surface area. No > delamination > > occurred over the spare area, only over the forward surface over the > > foam. To eliminate any future problems, we drilled very small holes > > into all surfaces that we think could be air tight. I have heard of > > this problem on a Glassair, but did not think that we had airtight > > construction. Date: Thu, 10 Sep 1998 23:46:15 +0200 From: Rego and Noleen Burger Subject: COZY: Loud Pop??? Thanks to Michael Pollock for the details of an effect of hardshelling. I'm "sure" some are grunting "I told you so". RSA builders beware. I have even had parts delam rather too easy from just using more than normal micro in my slurry mixes to try and save weight....not worth it on wings and canard or any high stress area for that matter.... I feel "hardshelling" where the prep filler has cured for longer than 12hrs is a suspect practise. Maybe It's time I did some sample testing with figures again! -- Rego Burger CZ4#139 South Africa Web:http://home.intekom.com/glen/rnb.htm Work e-mail, mailto:burgerr@telkom.co.za Date: Thu, 10 Sep 1998 15:50:31 -0700 Subject: Re: COZY: Loud Pop??? From: alwick@juno.com (ok How) I didn't hardshell my construction. I don't think the evidence provided should lead one to assume that hardshelling doesn't work. Blaming hardshelling sounds much more reasonable than the pressure change theory I heard previous, but it's still just a theory. After all the glass construction I've done, I suspect there are many ways I could compromise adhesion to foam. It's possible that the area was a little lean. Or perhaps something else. I'd say that if you are going to try hardshelling, make 6 samples using strips of foam to do a comparison between the two methods. Then place lead weights on samples til they break. Something like that. I agree with Rego, don't assume one way or the other. -al wick 84% comp. Cozy MkIV sn 389 with stock Subaru 2.5 engine. Computerized cockpit. Done building components, now installing rudders. Expect completion date 4-30-99. On Thu, 10 Sep 1998 23:46:15 +0200 Rego and Noleen Burger writes: >Thanks to Michael Pollock for the details of an effect of >hardshelling. >I'm "sure" some are grunting "I told you so". >RSA builders beware. I have even had parts delam rather too easy from >just using more than normal micro in my slurry mixes to try and save >weight....not worth it on wings and canard or any high stress area for >that matter.... I feel "hardshelling" where the prep filler has cured >for longer than 12hrs is a suspect practise. >Maybe It's time I did some sample testing with figures again! _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866] From: Jim Hocut Subject: COZY: Hard Shell (was Loud Pop) Date: Fri, 18 Sep 1998 15:13:31 -0400 I forwarded the relevant posts to a Velocity builder friend of mine, who forwarded them to the Velocity newsletter, who forwarded them to Alan Shaw, whose response follows: Note: I got a copy of the Velocity newsletter that had the article about hard shelling. The procedure was a little different that what has been discussed here, in that instead of painting pure epoxy over the hard-shell they advocated using a micro slurry between the hard shell and glass cloth. That is what Alan is referring to when he says that problems show up when dry micro is used instead of slurry. Jim Hocut jhocut@mindspring.com Velocity wing construction is very different than Easy's here because the Spar is pre molded. It is difficult to fit and fill the area between the spar and foam blocks by hand without leaving pockets of air hidden. The air left in this area expands, leaks to the skin and causes problems. In the molds we have the advantages of pressure and vacuum to minimize the air that gets trapped in the wing but some always remains. We have worked out a procedure for molding the spar at the same time as the wing....that saves a lot of time and money too, but change is hard to impose on a 14 year old procedure. Hard shelling was done for two reasons. One because the Safety-Poxy used on Velocities has some styrene that eats into the foam and adds resin weight. The other is that the micro balloon surface could be sanded true and glassed clean and straight. The problem was when dry micro instead of runny slurry was used and the lay-ups were squeegeed too dry. Even without hard shelling dry micro slurring and lean laminations cause the same problems. Any delams bigger than 6" in any direction probably should be slurried across the area with the aid of an Air Vacuum Pump from Harbor Freight Tools 1-800-423-2567 item # 03952-4CXH $9.99+S&H. Alan