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G’day Brainstrust,
I am building the shelf and crystal holder to install the RCA radio power supply into the L-5 using drawings 76-72033, 76-72043 and 76-72018. As you would guess the aircraft bears little measurements resemblence to the drawings, that said I have cut to fit.
Today’s enquiry is in regards to the Stiffener and Bracket materials specs for the shelf: are they made from laminated wood or metal?
The all come with part numbers but no materials specs. While we can do both, I suspect the stiffeners are wood and brackets are metal but the drawings don’t say.
Anyone have any suggestions?
Hilly
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The angles and stiffeners (S-806-x) are bent plywood, the same as the rib attachment angles in the wings and empennage. The best method to fabricate them is to pre-bend individual layers of veneer and then laminate them together using a cold-molding process. That is the only effective way to reliably get radiused, 90-degree bends.
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Geoff: When you get to the crystal holder, you will need to decide if you are going to drill for stateside crystals or for those used overseas. Overseas, they switched to the FT-243 style crystals, which are much smaller than the AVA-10 or AVA-53 housings. The AVA’s are also much heavier than the FT-243’s. I’ve got almost a complete set of AVA’s for my airplane, to fill the holder and they weigh about a half pound each. The FT’s are much easier to find and probably weigh about 2 ounces each.
From what I’ve been able to find, the aircraft left the factory with the AVA series crystals, but they were removed and FT-243’s were used once the aircraft got overseas.
If you want to just have fillers for the AVA-10/53’s, I can give you most of the dimensions, other than a couple of radii, and you could 3d print a set and drill for your own banana plugs.
Craig
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G’day Graig & Jim,
Many thanks for your info Jim, exactly what we thought but didn’t know. We are currently in the throws of steam bending (see below) & laminating the rib brackets for our “sh1ttee wing” so that makes life really easy. We will make a couple more.
Thats good information too Craig, I will pass that onto the team and confirm what we are going to do for the crystals. we had simply planned to drill to the same hole dimensions as the radio. I only have access to one crystal atm and it’s with the radio tech in Melbourne, so I will follow that up. At half a pound per crystal makes it a very heavy load for such a light structure. The radio will prob never get used in anger so a pastiche may the way forward. Sage advice Craig, thank you.
Our steamer with former template:
Also taken the decision that we cannot make it to the US this year, too many priorities and too few resources. I think the world is all in the same boat by the sounds of it.
As they call in HHH: On! On!
Hilly
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Hilly: The AVT-112 takes both the AVA-10/53 crystals and the FT-243’s via an odd socket. If you choose to go with the FT’s they are readily available down there and inexpensive…..about 5$Aus each. You want to look for ones with the Bakelite cases, as I don’t think the ones with the metal face plates came about until after the war.
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Many thanks Craig, been a while but progress has been made.
The steam bending has gone well and the shelf with stiffners and brackets has now been built. Just the crystal holder and cover to be cut and added and job done. Have radio tech following up on your recommended crystals, so they won’t be far away as well I guess.
For the holder (76-72012) itself, it looks pretty simple to make and fit, but I cannot locate any drawings for it so not sure of dimensions and material specs. Is it ply wood, metal or phenolic material and are you aware of the dimensions? If not and as nothing else seems to fit a drawing, we will probably just “eye ball” it anyway. I mean, how hard can it be, right??
Hilly
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Hilly: 76-72018 should be the canvas cover for the holder. It shows to be part of the 76-72043 installation. From that drawing, it’s applicable to all the observer models from 76-627 and up. The holder is micarta and a little wider than the crystal, sized to hold 10 crystals, and around 1/2″ thick. I don’t have mine here at the house, but can go over to the warehouse this weekend and get some good measurements for you.
The earlier shelf got superseded by the 72043, probably for ease in manufacturing, as the original one was molded plywood.
Craig
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The one I got from Duncan, copied off an original one from a B model, was drilled for the AVA-10 or AVA-53 crystals, which are much larger than the FT-243’s. As the AVA crystals were removed form aircraft going overseas, and replaced in theater with Ft-243’s, they don’t fit due to using different hold spacing and pin diameter.
Speculation here, but I would believe as there were 80 or 90 individual crystals to a complete FT-243 set, that the pilots only pulled the primary two or three crystals for the day and kept them in a shirt pocket.
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G’day Craig, can I ask a favour please mate?
Do you have any photos of your crystal holder mounted to power supply shelf?
I reacon I know how its all mounted up but the drawings (including the dia in the IPC) are not clear. I plan to use four countersunk screws from the holder throught the mounting brackets on the shelf.
I can’t believe how such a simple operation is so easily sent down the rabbit hole. I am sure a couple of photos will clear it up and allow me to sign it off.
If you have some photos, please use my email: grhilly@ozemail.com.au
Hilly
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Geoff: I’ve got a B model so mine mounts differently. I took a quick run thru the IPB and depending on the s/n. In the case of your aircraft, if I remembered the correct s/n, I think you need to look at the 72033 and 72043 drawings for the mounting tabs, as the crystal holder will be at a right angle, hanging below the power supply deck. Mounting screws will be S422-8-12’s, which if I remember correctly, are button head, fully threaded machine screws and not countersunk.
Somewhere amongst all the paperwork and files around here, I have a conversion list from Stinson numbers to standard AN/MS numbers. I just got out of the hospital yesterday, after a week’s stay, and my office here at the house looks like a bomb went off in it. I’ll watch for it, but it may be a week or more before I find it.
Craig
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G’day Craig,
Many thankls for your kind assistance and I do hope you are safe and well. I hope you have been discharged well from your hospital stay. As an observation; for my working life, my office has been an example of what an office should look like but I think at my stage of life it is now allowed to look like….. Beirut!!
I didn’t realise you had an L-5B, your shelf looks metal in the IPC diagram and of course, no drawing in the AirCorps library.
I have been using both drawings you refer to. You may note that while 72043 refers to shelf 72033 and shows the original shelf design which differs from 72033 drawing. The phenolic block supports the ply (underthe shelf) that has been bent down. Figure 63 of the IPC shows the same self. The instruction on 72033 drawing is to dril 4 x holes to match the crystal holder in drawing 72012 which of course does not exist (at least in the AirCorps library).
Many thanks for you guidance and kind assistance Craig. Might have to John Wayne this one!! (shoot from the hip)
Stay safe and well mate.
Hilly
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