Wood Bottom former around bungees

[TimHicks]

The picture below is looking aft from underneath the bottom of the fuselage.
From a right below the cabin.

Look at the leftmost corner of this wooden part (where the leading edge of the bottom fabric attaches).
It doesn't seem to fair very nicely into anything.
I assume that the fabric is just gonna go sharply up to the longeron?
Or am I missing something?

[Robert Lees]

Re: Wood Bottom former around bungees

Aft of that end should be a wood former along the longeron. This tends to blend the fabric transition.

This former is curved to fit the longeron. I'll try to find a picture.

Rob

[Edit...does this picture explain it Tim? Bear in mind my fuselage was upside down when I took the pic. The former is then wrapped with fabric tape (I used 2" tape) around the longeron to secure it. I have several other photos if needed.]

[2nd Edit: Ignore the "One Piece" comment in the second photo...Heavens knows what that means after 10 years! Plus in the 2nd photo there are some small pices of timber missing.]

[3rd Edit: the last photo shows the blended fabric...you can seee how important this wood fairing is.]

Rob

[TimHicks]

Re: Wood Bottom former around bungees

Thanks Robert.
That is very clear. I have something similar on the top longerons.
But there was nothing down there when I uncovered the airplane. I guess that I'll have to make new ones.
Can you estimate how long are the wooden pieces that sit along the longerons?
Is there any easy way to cut that cove in wood?
I'll check to see if I can buy a router bit that size.

You can see that the old fabric pulled the corner of the wood back awkwardly.
I had to remake the wood because it was so warped.

[Robert Lees]

Re: Wood Bottom former around bungees

The router bit diameter is the same as the OD of the tube...so it's either 3/4 or 7/8, since they're the sizes of router bits I bought for the job (I replaced ALL my fuselage wood trim pieces). I bought my router bits from Trend, which looking at the packaging, might be an American company.

Both are Radius cutters: 3/4" is their p/no C056; 7/8" is their p/no C057 (both with 1/4 shank for a standard domestic router).

I purchased my raw timber about 1" thick, and did the routing first using my home-made table router (DIY router installed upside-down in a piece of MDF that I clamp to a Workmate). Then finally trimmed the outside profile using a belt sander, varnish & so on.

The length...well, I recall that they taper to zero before the next aft fuselage station, if that makes sense, so a bit longer than the ones on the top longerons to which you refer.

Hope that helps...keep up with questions if more info required.


Rob

[Robert Lees]

Re: Wood Bottom former around bungees

Hmmm..

When you DO get the timber resolved, be careful when fabricking the belly around the fuselage belly where the gear goes. When you lift off, the undercarriage tucks up nice & neat into the belly, so make sure that the fabric in the triangular aperture allows that to happen.

[Pearson]

Re: Wood Bottom former around bungees

Is there any easy way to cut that cove in wood?
I'll check to see if I can buy a router bit that size.

Yes there is an easy way to cut that cove. Just use your table saw and cut a v shaped groove instead of a curve. Also on one of my fuselages there is a small tab welded to the fuselage where this former goes. A screw goes through a hole in the tab to hold the former so the tightening of the fabric doesn't pull it to the inside. The tab is on the inward side of the former about 2 - 3 inches from the large end. The tubes the formers mount on are 7/8" diameter. My old former is about 1 & 1/8" tall at the thick end and 2 feet long. Below are a couple of pictures of one of my old formers.

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Re: Wood Bottom former around bungees

My T craft has a poor attemt of a sheet metal fairing, what does the metal fairing look like and does it use wood on the tubing?

Jerry Lane

[Pearson]

Re: Wood Bottom former around bungees

Jerry,

Not sure which fairing you are referring to. The bungee covers are metal and the area forward of the bungees is often metal.

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Re: Wood Bottom former around bungees

The areas behind the gear is metal on my T craft, it is cut out for the bungess to go through and has two metal stringers going toward the tail. Another project in the area has similar metal work with only one stringer. The part number is 2245-1

[Pearson]

Re: Wood Bottom former around bungees

OK Jerry, I am with you now. I have seen that part made out of sheet aluminum before, but most of them are wood and fabric. I don't know if metal was ever used by the factory or not. Of the ones I have seen made of aluminum, they still had the wooden fairing pieces shown in my post above. The ones I have seen looked like they were not original. If you don't care for the aluminum part, I don't see any reason you couldn't go back to the more common wood version. It is very easy to build, strong, and light. Maybe someone else on the forum will chime in here soon with some other ideas.

[Dick Smith]

Re: Wood Bottom former around bungees

QUOTE=Pearson;79679]Yes there is an easy way to cut that cove. Just use your table saw and cut a v shaped groove instead of a curve. Also on one of my fuselages there is a small tab welded to the fuselage where this former goes. A screw goes through a hole in the tab to hold the former so the tightening of the fabric doesn't pull it to the inside. The tab is on the inward side of the former about 2 - 3 inches from the large end. The tubes the formers mount on are 7/8" diameter. My old former is about 1 & 1/8" tall at the thick end and 2 feet long. Below are a couple of pictures of one of my old formers.[/QUOTE]
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Regarding the fabrication of the "cupped" fairing strips referred to in this thread: I made replacements using a table saw set up so as to allow the workpiece to "be pushed at an angle" into the spinning saw blade...slightly sideways so to speak...with the blade only about a 1/16 of an inch above the surface of the table. If you look at a tablesaw blade from the front, you see a thin rectangle...if you look at it from the side, you see part of a perfect circle...anywhere in between the two viewpoints you see some portion of an arc, depending on how high you have the blade raised. If you have the sawblade at just the right height and look at it from the right angle...it will match the shape and size of the "cup" shape you need. If you clamp a guide next to the saw blade at just the right location and push the workpiece along the guide, with the sawblade just barely, barely above the table...it will cut a tiny, but perfect arc. You need to use a pushstick and make tiny increases in the height of the sawblade, before each pass, until you have the desired height. Hope the pictures help. Be careful...it will work. Take your time and try some practice on scrap. Before long you will have the angle and blade height dialed in. It's sort of a "poorboy" moulding cutter. There is one point where the blade angle and height match the shape of the "cup"...once you find that sweet spot, you clamp the guide strip and lower the blade... just start nibbling a little bit more off on each pass until you've got what you want. I was amazed by the perfect fit obtained using this simple trick. I made a two by four fit a piece of 1 3/4 inch pipe just for fun. Dick

[Hank Jarrett]

Re: Wood Bottom former around bungees

This is an old joiners trick. Works great and if you want a PERFECT fit you just wrap sandpaper around the tube and slide the wood over it.

A BIG WARNING here. Be VERY careful as you do this and make the cove cut FIRST and in VERY SMALL cuts (bigger piece of wood is easier to control). The blade will try to kick the wood out and throw it across the room. Cut too deep or push too fast with a small piece and you will make holes in the shop wall sheet-rock (or YOU!).

A feather board and a piece to restrain the wood and keep it straight on the other side and on top wouldn't hurt.

This technique works, and works well, but the first time you see a 2x2 driven into a concrete block after a saw throws it, you get more safety conscious! NEVER stand in line with the wood or blade and ALWAYS use a push stick.

Hank

[Dick Smith]

Re: Wood Bottom former around bungees

Hank, thanks for adding emphasis to the importance of taking very small cuts when using the aforementioned method. I made the comment late last night and then laid in bed worrying about someone not doing things properly, safety-wise. If someone chooses to try this method, consider cutting the desired cove into a larger piece of wood and then cutting the individual pieces that are needed.
When I did my "coved and faired" pieces, I didn't have ready access to "aircraft" spruce, so I took my chainsaw mill out into the woods and slabbed off some straight-grained Alaska Black Spruce from a standing, dead tree. Used my table saw to rough out some "lumber" and used the method described above. Worked just fine. Dick

[Hank Jarrett]

Re: Wood Bottom former around bungees

When some people say they did it ALL, they mean they did EVERYTHING! I mean....I make a lot of my parts and do all my own work, but I don't grow the trees for the wood and mill it custom!

It is a LOT safer to take a larger piece of wood and cut the half round grooves first, then slice off the smaller sections with the grooves and shape the outside of the part AFTER the groove is in the wood. It is all about assuming the saw is going to try to do the absolutely WORST thing with the piece of wood. I will NEVER forget the sight of that piece of wood stuck in a concrete block wall. If anyone were sanding behind the saw pushing the wood when it happened, they would be dead! Angle cuts like we are talking about may NOT kick straight back. Sometimes they kick UP.

Hank

[TimHicks]

Re: Wood Bottom former around bungees

I ended up using a 3/4" diameter full-round router bit on a homemade router table to make the coves. I made two passes, stepping over 1/8" between passes.
Then I used a curved chisel to take out the ridge in the middle.
Once I made the new longeron pieces, I found that the other wood didn't fit up to the new wood. So I remade everything.
The longeron pieces are clear poplar and the other pieces are clear pine.
It's not perfect. But it's plenty better than what I had before (nothing) and plenty good enough for me (and my IA).