Smoking Ace Update

We are still alive. Just working on some other projects at the moment.

The Smoking Aces are still under construction. After flying the planes for hours on simulators and finally the real thing, we realized that you can't cheat physics. It makes for some interesting behaviors in short-coupled tail designs. What is kind of cool is that deeply-swept wings actually set the maximum angle of attack for the aircraft. We surmise that it is due to over-wing airflow. As the aircraft pitches, the airflow over the wing obscures the clean flow over the tail and finally completely blocks the flow.

Not so much block, but the distance between the tail and the wing is shorter than the mean turbulence. So the dirty air is not laminar enough to make a well-circulating flow around the tail. As the tail loses laminar flow and finally gets only turbulent flow it loses lift and finally stalls. This reduces the effectiveness of the tail and the plane rotates back to balance the tail input. This seems reasonable enough an explanation to the pitch wobbles, that are only partially-tamed by gyro input.

The first time we saw this behavior, it was exciting. Our pilot certainly thought so.

There is even a slight regression in our projects. Not so much as a negative thing, but more an artistic reawakening. I have to finish working up some drawings so we can discuss some design requirement changes. Building the Smoking Aces, we discovered that what we thought was a lot of space, was not. We also found out that 1000 in*lbs is a tough thing to take out in such a small space. Considering each wing applies this, we found some strange deflections in the air frame when the wings support large flight loads. These were certainly not unexpected, but we did not realize that our load paths were not as well controlled as we though.

Looking back through some old documentation, I found some of our original "Fat Man" designs. What we learned with the "Fat Man" was that fuselage depth or in its case root thickness was our friend. If you have healthy wing roots, there is a lot more space to manage payloads. More so, there is a trade off with larger thickness designs. The trade-off that is important is that often their curvatures do not change much.

When you build metallic structures, you see the need for structural caps. Without them, it is hard to fix skin to the structure without some heroic measures for the most part. Next time I will talk about some of the things that did not work for us.

Big Baby Developments... Daddy's Building a Brand New Plane

I am not ready to reveal the Big Baby just yet. It is going pretty well, symmetric and no smeared blood or anything. No blood this late in a project is a big relief.

The airframe for the next version will be a bit different. This time, I was careful to build the skin by wetting and pinning the skin to as closely as possible match the model curvature. Besides the 10s of pins that were used, the technique was pretty effective. 

Use masking tape along the down side of the board so that there is a basic joint between the pieces. Then just use a wet sponge to wet the downside of each of the planks. Lay the plank onto the surface of the model to be copied. Work from one end and pin along the edge every inch or so about a 1/10th of an inch from the edge each time. Do this for one inch rows along the plank. Depending on the curvature being copied you may need more pins or to pin in specific directions to keep the balsa layer in contact with the curve.

After the part has dried, overnight or after a few hours, adjust the pins to fit the planks as closely as possible to the curve. The planks may have to be rewetted to relax them into place. Then use a foam-safe (in my case) glue in the joints. The tape will be removed before you install internal structure. Once it is dried and the seams are glued. You will want to remove the pins and the part from the form. I cut simple cross-sections to support the structure. Then used CA glue to glue the seams and to bond the internal structure to the skin.