cjensen said:
Somebody else want to count?
. The 'secret' to good bonding is lot$ of $pecial tooling! Matched metal molds and fixtures to hold bonded surfaces together do a great job, but are a bit hard on the budget if you're only building one airframe. It also helps to have an autoclave (BIG pressurized oven) for curing.
Putting on my canopy skirts is what is currently causing me some trouble. I think I have found a solution - using super magnets. They are quite powerful. Once I get back from OSH I'll give it a go. I can really see how bonding any kind of compound curve can be very challenging.
gmcjetpilot said:As a former structures engineer in the aerospace industry I can tell you bonding is process dependant. What does that mean? It means if everything is perfect, controlled with complete quality control, you can get great strength, but metal bonding is intolerant to any deviations in the process: Temp, pressure, coverage, flow, mixture and surface prep.........Bonding also involves some kind of inspection and testing to assure strength in primary structure, which is impossible to do with just your bare eyeball. (Primary structure is anything that could ruin your day, in a big way, if it failed.) Delamination is hard to detect.............. However real non-destructive testing requires eddy current or ultra sound and control samples. The operator of the equipment needs a high level of skill and experience. This is not avaiable to the average builder or it real expensive.
I agree , you are right Pro Seal is not structural, but was told by a BD-4 builder they used it for that purpose to an extent. I go back to my original idea and opinion, don't rely on any bond, rivet it.BJohnson said:
chuck said:
gmcjetpilot said:I agree , you are right Pro Seal is not structural, but was told by a BD-4 builder they used it for that purpose to an extent. I go back to my original idea and opinion, don't rely on any bond, rivet it.
Boeing does not give credit to pro-seal (BMS-5-95) for strength even though test show increased strength of mechanical fastened joints with it. Boeing does give credit for improvement to joint fatigue life. It does develop a fair amount of shear strength. I agree Hysol or other bonds are more structural.
Thanks for pointing this out B, and I did not know about the Loctite trick. So for the record, don't use pro seal for structural bonds. However for wire bundle stand-offs for wire tie supports I use pro-seal to bond them to metal. Works well and last a long time.
Cheers George
Gil I did not say it has NO structural application. As I said Boeing uses it in many joints and not just for sealing the fuel tank. It does help. But in the aerospace world, it's not considered a high strength adhisive but a "fay surface sealant". It is an epoxy and it does stick like crazy, with good shear strength. However as you point out not great tension or peel strength, but shear strength is a good thing. My guess is the repair on Grumman bonded structure is not for strength but to stop the de-lam from spreading, keep corrosion out (which proseal does very well) and keep it from flopping around. I also am guessing if the % area of the de-lam is too large you are SOL and in for a bigger repair. As an engineer who delt with the FAA I am sure the structures engineers proved that the "residual" strength was good enough even if the repair was not effective. I have never heard of a Grumman coming un-glued in flight. However with aging airframes it will be more an issue. Thus the one advantage of mechanical fasteners. Easy to repair, drill out, splice, patch, doublers, more rivets, etc.... No question of what the load path is.az_gila said:
You sound like a structures engineerDGlaeser said:
with "load path". You are right, bonding (whether proseal or another adhesive) can help. The cracking of the rudder/elevator stiffeners at the trailing edge was when they used thinner skins and the builder layed out and drilled the hole pattern (pre pre-punch). Often the aft end rivet in the rudder and elevator stiffeners where way too far from the stiffener end. The skin flexed around the last stiffener rivet and cracked. With the pre-punch kits, Van controls the rivet space and stiffener edge distance on the last rivet. I bonded the last inch of my RV-7 rudder and elevator stiffeners with pro-seal, just at the trailing edge. This makes the stiffener effective to the bitter end and keeps the skin from flexing around the end rivet. As far as a load path between the rudder / elevator stiffeners to the spar at the leading edge (LE), not neccessary. The skin is thick enough not to "cripple" in compression. There is little flex in this area. From thousands of RV's flying and who knows how many flight hours, the forward rivet line on the stiffeners is not a problem, (TE) kind of. Build it per plans. You may want to consider using a thin bond sparingly here and there with pro-seal.
gmcjetpilot said:You sound like a structures engineer
