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GrummanDude
Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA
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 Posted: Sat Oct 03, 2009 10:20 am Post subject: Horizontal Braces, EDM 830, Wheel alignment |
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Just in case I haven't said this before:
A couple of years ago, maybe 3 years now, I asked one of the structural engineers (DER) working on the structural certification portion of my cowling abut the horizontal braces. He works at a company which repairs the P-3s used for fire fighting here in California. At the time, I had a 77 Tiger torn apart with its braces out. We looked at and talked about the whole thing off-and-on for a couple of weeks.
Based on a finite element analysis and some good old fashioned engineering, he said the braces I proposed would be about 100% to 150% stronger than what was currently being used as a field repair. He chose a metal-to-metal bonding adhesive, Hysol 9330.3, that could be done in the field IF the surface of the fuselage could be properly prepared.
As it happens, there is a metal finishing company on the airport property here in Auburn that the DER also uses. A couple of weeks ago, I talked to the DERs contact at the metal finishers and asked if it were possible to build bulkheads in the area where the braces would be bonded and just do everything in place. His response, "We do that all the time in the field."
Well, 2 funerals later, the metal finisher was available to do the work . . . as soon as he got caught up.
Yesterday, after resealing the plastic bulkheads twice so they would hold water for 2 hours (of course it takes 24 hours for the RTV to cure), they alodined the inside of the fuselage where the braces are to be bonded. He told me, since he didn't have a heated drier for the alodine, that it's best to let it air dry for a couple of days. It sure looks good. When I do the project plane, I plan to do the entire aft section. We're working out the details to either take the fuselage to the shop or build a tank big enough to dunk the aft section.
The next step is to get everything fitted and match drilled. Then, take everything apart and do the bonding. I have a call into the DER overseeing this process. As soon as he's available, we'll do the bonding.
The specs for the Hysol says the maximum cure strength is after 1 hour at 180 degrees or 7 days at 77 degrees. Being the skeptic, I'll wait the 7 days before final assembly. It's getting cooler in Auburn so I'll build a tent around the aft section and keep the heat up. The tough part is going to be making sure the thickness is around 10 to 20 mils. That's where maximum strength is. I have a couple of ideas.
Today, after I do the paperwork for a JPI EDM 830 installation on a 2005 Tiger, I'm going to take the plastic bulkheads out and clean off the RTV. I'll possibly fit the braces today if I can find help to muscle the horizontal in place.
The EDM 830: What a sweet engine analyzer. If you aren't familiar with it, Google it.
I mentioned I have a customer with tires that wore quickly. I used a laser to find the angles in the wheels. In 23 feet, the wheels show about 0.4 degrees of toe-out. Some of that could be the accuracy of the alignment fixture I made. I think it's dead on, but, who knows. At any rate, it's straight for all practical purposes. They looked like new when the owner picked up the plane last year. This year, the tires appeared to be nearly flat. I asked the owner and he told me the follows the book recommendations for tire pressure. I think that's the problem. Still, like the owner who burned through a set of brake linings in 70 hours, it all pays the same to me. Note: I've been running 32-35 mains and 30 nose for 25 years without any problems.
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Gary
AuCountry Aviation
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| Posted: Sun Oct 04, 2009 6:11 pm Post subject: Horizontal Braces, EDM 830, Wheel alignment |
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I think your "Fireside Chats are great!
David
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