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Building Tips and technical articles. => Building techniques => Topic started by: Motorman on January 02, 2020, 05:59:02 PM
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Is it a profile?
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I have never reinforced a foam wing center joint as you did. What you have might work well enough but I have no experience with that particular method to prove anything, one way or the other. I have always used glass cloth and epoxy since that was the recommended practice when I started using foam wings years ago.
Does the wing have the spar reinforcement installed in each panel? This would be of lite ply or similar material, about 10 inches long, and glued into a slot that is cut into the forward foam spar. This lite ply spar would be full depth so that the sheeting will attach to it. This will help if you have any doubts about the polyspan and dope holding up.
With your project being a full fuselage, this might also help to some degree. Others with experience with both profile and full fuselage foam wing models might have more to add about this.
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Bob,
Can you expand on your comment about where the "actual breaking force" is?
Dave
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Bob,
Can you expand on your comment about where the "actual breaking force" is?
Dave
I have seen a few foam wing failures and none failed at the center joint. On one model with a full fuselage, the wing broke at the fuselage-wing joint. Another full fuselage model with a foam wing failed at the wing landing gear location. The builder of this model said he experienced a rough landing in the past and felt that there was hidden damage that finally led to the wing failing.
On a profile, would things be different? I would expect the fuselage of a full bodied model to contribute more strength to the wing center section than a profile. However, with a full fuselage, you have a sudden change in section right at the root. How much of a stress riser is created because of this?
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Sheeted foam core wing. I made 3 circles with polyspan and doped them on. Did this before I got the CF tissue I have now and wondering if it would be worth the trouble to strip this off and replace it with the CF. I think I learned this circle thing from Bill Mazoni so it might be ok, The rest of the wing is getting covered with Microlite film so no strength there. Do you think it will hold?
You don't need reinforcement beyond covering the entire wing, tip to tip, with silkspan or graphite veil. All the failures encountered (and the nutty schemes for reinforcement that Windy, et. al came up with) were because they built the airplane, then covered it only up to the fuselage sides, creating a stress concentration there, where all the force is applied. Cover the wing before installing it, not an issue.
They were also the first of us to discover that having lots of effective power (compared to what came before) greatly increases the cornering loads. The ST60 was the first widely-used engine that would routinely destroy the construction methods at the time. At first everyone thought it was the vibration, but it's much more that you can maintain speed in the corners more effectively, and thus increase the structural loads. Folding a wing on a stunt plane was rare to nearly unheard-of before the mid-80's, ST60 started it, and then piped engines raised the failure rate to a remarkable degree.
Brett