Leadout Rake

Adjustable lead outs aside, designs like Wooley's Argus and Cobra seem to have an excessive amount of leadout rake where the front leadout is postioned well behing the I-beam spar. Is there a particular reason for this that isn't obvious? It has to contribute to a sloppy flying aircraft, yet both aircraft made it to the worlds. By comparison, Werwage's Juno has what I'd decsribe as neutral leadout rake. Also, the inboard spar of Wooley's designs has a rather lengthy slot to accomodate the leadout which passes through it. This effectively weakens the spar and makes it spongy in compression.

>Adjustable lead outs aside, designs like
>Wooley's Argus and Cobra seem
>to have an excessive amount
>of leadout rake where the
>front leadout is postioned well
>behing the I-beam spar. Is
>there a particular reason for
>this that isn't obvious? It
>has to contribute to a
>sloppy flying aircraft, yet both
>aircraft made it to the
>worlds.

Your point about leadout rake on the classic era I-beam ships is well taken. That is why these ships when built today have adjustable leadouts and tip weight boxes. Therefore, worrying about the original rake is moot. Put in modern flight controls and the other adustable features of the modern ships and let your mind be trouble free.

By comparison, Werwage's Juno
>has what I'd decsribe as
>neutral leadout rake. Also, the
>inboard spar of Wooley's designs
>has a rather lengthy slot
>to accomodate the leadout which
>passes through it. This effectively
>weakens the spar and makes
>it spongy in compression.
>
>Eggbert

The long slot does not weaken the I-beam at all. The web that the slot is cut in is not the load bearing part of the I-beam, that partially belongs to the 1/8 inch I-beam spar caps that run from center section to tip on the top and bottom of the spar. Additionally, much more of the strength of an I-beam comes from the covering of the wing. 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. 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.

The originals of these planes were much lighter than modern folks tend to build. I I remember right, the original Argus was something like 34 or 36 ounces. It would need more leadout rake than we are used to seeing. I expect too that back then they didn't have to fly quite the caliber of flight you see in the top ranks these days.

You are correct. The Argus construction article mentions one model (the orig?)at 39oz with a Fox 29 for power. It also mentions a second bird built at a mere 34 oz (must have used helium for glue). Wooley further states that a 41 to 43 oz model will fly quite well. But he also says light weight is the secret to good stuntability.

Actually, I built 2 Argi back in the 60s. Although I have no idea what they weighed, both models flew better than I was capable of flying and I could do the entire pattern with them even with the severe line rake. It did take a delicate touch as I recall to prevent wallowing in the corners.

Although TM doesn't think the spar is weakened to any critical degree, I do think the slot does make it more felxible which could have a detrimental effect on performance. Looking at Werwages article on the Juno, he uses vertical strips to stabilize the strip ribs which I do think is a good idea in general for I beamers.