Rumva

ive actually used the giant pixie sticks ( kids candy like flavored sugar) and cut the ends off - worked great for me and large enough to handle the connectors

RAMFlyer

My Feedback: (65)

I usually use heat shrink tubing of a diameter large enough for the connector. Fits through a ROUND or OVAL hole and can easily be worked through the wing if you forgot to cut holes until after the wing was framed up (guess how I know!!! [sm=tongue_smile.gif]) Don't worry, it doesn't get hot enough at the field to make it shrink. (Tested in a black airplane in the Texas summer sun...)

scratchonly

Good idea; Where do you get it in long lengths?

RAMFlyer

My Feedback: (65)

I buy mine in 4 foot lengths at Midwest Surplus Electronics in Fairborn, OH. They have an internet store: http://www.midwestsurplus.net/ I would think that any decent electronics store that caters to the hobbiest would sell heat shrink in the longer lengths. Unfortunately those type shops are going the way of the good hobby shop...[]

Newc

On a long run - say an 80" wingspan - wouldn't you expect the heat shrink tubing to collapse and make threading the servo lead difficult? Any lengths of this material other than the 5" normally sold at hardware stores seems to not be very rigid, and even these short lengths are creased flat when you get them.

dyrbr_d

Newc you state under all conditions a circle is stronger, I really really doubt your material engineering background.

not to bring back the oval or circle debate, but you can't compare steel to balsa wood. Just because an indy car has a hole drilled in a piece of sheet metal then dimple died and they are engineered. You can't reverse engineer and tell yourself that it is the strongest. A sheet of balsa wood has a stronger axis and a weaker axis more like a sheet of uni-directional fiberglass than a sheet of steel. The grain of the wood must be taken into effect. So the orientation of the oval must be factored in vertical (normally the grain runs horizontal) or horizontal with the grain of the balsa.

Every material engineer I know would know that steel isn't balsa wood, wood has a grain structure that is unlike steel. I would like to know what background you have in materials engineering like you state, I don't claim to be a doctor just because I took an anatomy class. I don't claim to be a lawyer because I took a law class. And I don't claim to be a materials engineer because I have taken a half dozen different materials engineering classes. I know a rocket scientist, do I get to tell people I have a background in rocket science because we have talked about space travel and aerodynamic principles? You were given very specific diagrams by allanflowers and you disregard them because they don't take everything into account. He was working on the first order problems trying to simplify it.

foodstick

A friend of mine used to swear by the plastic tubes used for the giant pixie stick sugar candy! However he says you can't buy them locally anymore...no idea if they are available in other areas.

Newc

BS in Mechanical Engineering with specialties in Manufacturing and Materials Engineering. Then there was the 40+ years in industry including race car engineering.

camdyson

Oooh, this is hotting up!.........................[8D]

By the way, since when was the vertical compression strength of ribs worth worrying about (on our models)? Hands up all those who have had a wing fold where the break was span-wise!

Geeze. For the record, take the plugs off, use smaller holes/tubes, then put the plugs back on.

Cam

allanflowers

Another good reason to avoid "absolutes" like '...the circle is ALWAYS stronger...'
Any guess as to what and where the stresses will fall on a typical rib is quite speculative of course. Whether the wing is sheeted or not, has strong spars or not, takes landing loads (and how), etc. - all will make a difference. So there is no such thing as a typical rib. One would have to look at the whole airplane and its performance envelope to know where the stresses on its ribs would concentrate.
[quote]ORIGINAL: dyrbr_d

>>>>The grain of the wood must be taken into effect. <<<<

cyclops2

Maybe this disagreement has no basis or use in my solid blue foam flying surfaces.

Cut a deep slot the length of the wing. Glue in a spar. I leave a space on the bottom of the spar slot to run all wires and lines for whatever. Cover it with covering.

Their are no absolutes in anything. Someone comes along and proves otherwise.

It is called, PROGRESS.

kdc

The discusion about round versus oval holes is very interesting and worthwhile. However this is a case where making a sample and testing to destruction could settle the argument for model aircraft wings and inform us ordinary aeromodellers.
How about it you professional engineers! Put your theoretical ideas to the test.

Charlie P.

Something that occurs to me is that I can use a simple tool (compass saw, sharpened pipe, etc.) to form a round hole, but oval or elipse I would have to free hand. That means more "run-outs" with the razor knife and damaged wood integrity instead of smooth, even cuts. For lazer or press cut this doesn't matter, but with those they are what they are so I assume not part of this question.

goodinmw

Aloha,
I've found that plastic tubing used in aquariums (undergravel filter risers) is very good for servo lead runs in wings and through fuselages, as well as past landing gear openings. It comes in various sizes, typical 36in lengths are usually more than enough and it is cheap by hobby standards. Being really slick you can easily push the leads through- I've pushed as many a 4 servo leads through a 9/16th dia tube- and for those wishing to match an elliptical shape- the plastic is deformable.[8D]

RAMFlyer

My Feedback: (65)

Newc--Sorry it took so long to get back to you but needed some pictures and had to wait until my present project got to that point. Admittedly thes pictures are of a shorter run than the long one you mentioned but you can see the heat shrink tubes don't collapse on a 14" plus run and I have used then on a 96" wingspan (about a 40" run on the heat shrink).

pdmarsh

My approach on a recent project might be more work than necessary, but I didn't plan ahead, and was concerned about being able to thread a weighted string through holes in the ribs if I ever had to do that later on. Also, I couldn't find tubing flexible enough to slip through the ribs at this stage in the build. I ended up making square tubes out of balsa. I made three-sided tubes first, then cut them to length to fit between each rib. I glued them in place so that the top edges of each open tube were flush with the outer rib edge. Then I cut out the small area of each rib between the tubes. This was actually done on the lower side of the wing, so the bottom wing sheeting became the bottom side of the tubes. It worked great and wasn't really all that much trouble. I used thin CA, and it all came together quickly.

Paul

pc55bomber

Just use "McDonalds" straws joined together with a touch of zap. The thick ones.
Thats about the only decent thing to come out of a McDonalds store....
Oh, nearly forgot the plastic spoons, cut down they really make excellent air scoops.
You guys have the worlds biggest supplier.
And there freeeeeeeeeee.

MILDBILL-RCU

My Feedback: (6)

I dont want to debate "hole vs oval" issue, but for 20-something years I have cut holes through all the involved ribs with a sharpen'd piece of 5/8" brass tubing. Then when the wing is built, I install clear plastic sheeting that is made for school kids book report covers, or paper protectors. Its clear, lite weight, forms to just about any shape, & i just connect 2 or more together for longer wingspans. A drop of glue holds them in place nicely. Even works well in foam wings, if the groove is cut first. The inside is very smooth, providing a trouble free installation of servo wires, air tubes, or anything else. just my 2 cents worth.

Stickbuilder

For the paper tube wireway, visit your local grocery's butcher shop, and offer to buy some butcher paper. He will probably give you 10 feet of the stuff, and you cut it to the desired length, make 3 wraps around a 1.4" dowell, insert it through the holes in the ribs, and release the paper. It will expand to the size of the hole, and you can douch it in a couple of places with C/A to keep it located. If your holes are bigger than that, increase the number of wraps to make a larger diameter tube.

Bill, AMA 4720
WACO Brotherhood #1

jadec241

My Feedback: (29)

Another way to run the wire thru the wing is to get a piece of pull chain like you get from a lamp. The little balls roll easy & you can tape the lead to the end. then you can pull it thru easily. I have used this method on 1/4 scale planes with 80 to 110 in. wingspan.