What is I-Beam & its technology?

Dear stunter;
Would you mind explane for me "What is the I-Beam technique?"
and what differance between D-tube & C-tube ?
Thanks you so much
Bijan

This was discussed at the following thread:

http://www.clstunt.com/htdocs/dcforum/DCForumID1/1570.html

There is also good information at this website:

http://wooleycobra.homestead.com/index.html

Envision a Spar that has a cross section like a capital "I".

Now stack a bunch of rib profiles 1/4 of an inch high on the top and bottom of the I beam spar. The I beam provides the strength in bending and the profiles provide the airfoil shape.

Here is a calculator to help you figure out how strong your I beam structural member will be:

http://www.dynasoftinc.com/Sec-Prop-1.htm

There are a couple of illustrations of typical C-Tube and D-Tube wings in this article, from my BBP series, posted on the PAMPA web site: http://www.zianet.com/pampaeditor/bbp6.htm

L.

A classic "I" beam plane would be the Ares or the Cobra. The main spar is a 1/4" beam capped top and bottom with a 1/8" by 1/4" balsa strip, making the main spar look like a capital "I" when looking at it from the tip. A "C" type wing is one that has a top and bottom spar, no main spar, and the leading edge sheeting goes from the leading edge spar to the two center spars. If the wing is looked at from the tip, the front would look like a "C". The "D" type is like the wing in the Nobler. The main spar is a vertical web, with the sheeting from the leading edge to the web. This would look like a "D" if looking at it from the tip.

This has gotten me curious - which of the 3 designs
has the greatest torsional rigidity (flexes the least)?

Good question. I'd think that the planked LE and vertical sheet of the D-tube would be inherently stiffer, but.. Much of the strength comes from the covering, in strong tension. Properly built and covered, they are all adequately strong. Right?

L.

>This has gotten me curious -
>which of the 3 designs
>
>has the greatest torsional rigidity (flexes
>the least)?

Everything else equal, of these 3, the D-tube is by far the most rigid and the I-Beam the least.

> Properly
>built and covered, they are
>all adequately strong. Right?

Here's a good example of the "dangerous" question, answering of which alienates someone.

LAST EDITED ON May-21-02 AT 09:56 PM (CST)

I now recall reading (I can't remember where) that the I-beam
is quite flexible before covering, and derives much
of its final stiffness from silkspan and dope covering;
it is not a good choice for plastic heat-shrink films
like monokote or ultracote.

A question on I-beam airfoils, if I may.

From what I have read, most of the leading PA flyers use a thicker section percentage at the tip than at the wing root and some move the high point forward as well.

I cannot see how trimming the rib strips from the back does anything but move the high point back and possibly thin the tip section percentage.

Is my understanding of the geometry off? How much does it matter?

LAST EDITED ON May-21-02 AT 06:13 PM (CST)

About 1960, an article was published in AM Annual with templates for a logrithmic curve system, where the airfoil would remain the same, regardless of where you chopped the TE. It always seemed like a pretty cool idea. The "strip ribs" on an I-beam suffers in torsion and in bending, compared to D-box and C-box wings. The problem is that the spar flanges are not close enough to the surface of the wing. Spreading that distance does considerable to increasing the strength for the same amount of material. My own experience, (mostly F1A Gliders, where a 5/16" thick wing with 5.75" main chord and about 90" span, has to take at least 20 lbs of load) leads me to favor the "C box" wing with vertical grained spar webs, tapering those spars and reducing the thickness and density of the webs toward the tips. Essentially, the same spars would work in a typical stunter, but you only have 5/16" inches to put the spars in. Light tips count for a lot, especially in turbulent air. Finally, a stiff wing is a wing that is consistent under load...it will make a glider tow straight at high speed, and make a stunter be more predictable and efficient in high load portions of flight, as well as allow the controls to work properly, with a straight hingeline instead of a bowed one. When you see an "I Beamer" fly, you can see the wing bending. That's not good, IMHO. Steve

The strength and rigidity in twist and bend of an I-beam comes from the covering material. That is why traditional covering materials with butyrate dope are so essential to the proper function of an I-beam. The covering is in tension from the shrinking of the butyrate dope and that makes the wing very stiff in tension. The I-beam itself lends very little to the overall stiffness of the wing. Furthermore, I reinforce the spar caps with carbon fiber tape to add even more strength and rigidity. Get a copy of Billy Werwage's videotape on the construction of I-beam ships that is put out by Bob Hunt.

The three I-beamers (Argus, Atom and Cobra) I have built so far show this tension characteristic quite well and I enjoy flying them immensely. And I do not have a problem with twist or bending.

If you have not received or read the newest issue
of Model Aviation yet, there is an article by
Bill Werwage on the 1959 ARES in which he discusses
I-beam wing construction. He also recommends
getting the video.

Hi Bijon,

Your question regarding "I-Beam" description has been well covered in previous answers. This wing construction has been credited to Bob Dailey, formerly of the Detroit area, and also called Dailey wing (natch) as well as Detroiter and Strathmoor wing construction(after the member's club). If you check out Fred Carnes' excellent articles in Flying Models magazine a few years ago you will find much info. This wing is both hated or loved by many who have used it and dates back to the late forties and early fifties. It worked very well in the stunters as well as combat planes of the era as it provided a light, strong, and easy way to build a tapered wing. The original airplanes were covered with "Jap" tissue of the era and the stunters had twenty to thirty coats of brushed nitrate and butyrate dope. The profile combat planes (Ringmaster size)saw perhaps ten coats of clear over the colored tissue. The strength was in the covering and the planes were built to fly, not crash, which resulted in a bag full of broken parts (Hi Tom McLain!!).

Ed, which issue are you refering too? I have the June 02 issue and there is nothing by Bill W. in it nor anything on I beamers.

July issue, P. 44. Just got it, yesterday.

>The strength was in the
>covering and the planes were
>built to fly, not crash,
>which resulted in a bag
>full of broken parts (Hi
>Tom McLain!!).

Guilty as charged. My engine on my Atom died during the inverted part of a Reverse Wingover and I tried to climb inverted and then Split-S to landing. My wife was heard to exclaim "Why did you do that!""" A bag of bones is all I got for my stupidity. I salvaged what was left and built another Atom, sadder but wiser.

Amazing, I get Stunt News within 24 hours of it being mailed and Model Aviation takes a week. Chompin at the bit for that article. I am building an Ares (ready for paint) and a Cobra. Love them "I" beamers.