The construction technique for aluminum aircraft fuselages is known as semi-monocoque. A monocoque structure takes the entire load through the shell of the structure. In airframes, the skin is very thin and so frames and longerons are joined to the inside to provide additional rigidity while the skin still takes a lot of the load. If you haven’t ever seen the cross section of an aircraft structure, you may be surprised to see just how thin the skin panels actually are. They are perfectly up to the task of pressurization and bending loads so no need to panic.
An outcome of this design approach is that the panels between the frames and longerons can experience some load directions that induce a measure of buckling. Nothing that is beyond their elastic limits but something that can be apparent if the light comes from the right angle. The lower side of the rear fuselage of the Boeing 757 is an area that is susceptible to this in certain flight conditions. I saw a number of them recently – both -200 and -300 models – and they both were showing visible distortion of the panels. The sun angle meant that the shadowing of these areas was apparent.
The 757 is by no means the only aircraft to experience this phenomenon. The B-52 Superfortresss is a jet that shows this effect on plenty of occasions. I have heard people comment on it being a function of the age of the airframes but it is more of a result of the design of the basic structure than anything else. Certainly nothing to be immediately concerned about.
I have previously mentioned that I am more interested in getting to events that are slightly more individual than the bigger airshows these days. That also includes when I am trying to get material for the magazine together. One such event was the WACO Reunion in Mount Vernon OH. This was being covered for a piece that I was writing for Global Aviation Resource and will appear in an upcoming edition of the magazine. Consequently, I am not going to preempt the magazine piece here.
Instead, this is more about the time I had while I was there rather than a description of the event and the organization. I had been in contact with Andy Heins, president of the national WACO Club earlier in the year to make sure I could cover the event. Andy told me what I needed to do to be there and then made himself available to tell me all about what was going on. The event is a gathering of club members and their aircraft and is a very social event. There is no flying display. However, the members like to fly their aircraft and that is what they do. The middle of the day is quite quiet but early in the morning and later in the day when the weather is a lot more calm is the time when people get in their planes and fly.
Fortunately, that also included me getting to fly too. My first trip of the day was in a Citabria with Tim Ponds. This was to get some aerial shots of the aircraft parked to illustrate the article. Time was very accommodating and we got some video footage as well as stills of the site. While we were up, Steve Thomas was flying his WACO and we arranged an impromptu shoot. Normally I am not inclined to shoot air to air without a prior brief. However, we kept it simple and straight and level and I was able to grab some good shots. We also flew past the airfield and got a couple of shots with the aircraft parked in the background.
Then I got my first flight in a WACO when Susan Theodorelos took me up in her beautiful model RNF. This is an open cockpit model with the pilot in the rear seat and a two seat space up front for the passengers. I was on my own in this case so had some space to move. A couple of other aircraft joined up for some formations and I was able to grab some shots of them at the same time. Vibration was not too bad but keeping myself isolated from the airframe was tricky so getting good shots was a bit tricky. However, I got some I was pleased with.
One technique thing I learned from these flights was focus activation. I normally focus with the rear button on the camera rather than the shutter button. This is fine in almost all circumstances. However, when you are trying to shoot backwards at an odd angle, this is a lot harder to do and the shutter button becomes the best solution. Swapping the configuration in flight (I hadn’t expected to shoot another aircraft when we first took off) wasn’t practical so some odd contortions were necessary. Now I have added this config setting to my quick menu so I can make the change quickly if the situation should arise again.
Everyone at the flyin was very friendly. Aviation never fails to amaze me with the way in which you can show up somewhere for the first time with nothing but a shared interest and be welcomed so quickly by people you have never met before. The WACO people were a perfect example of this and I can’t thank them enough for their hospitality. I hope to be back again for future reunions. In the mean time, here is a little video that I got while there. Enjoy and don’t forget to buy the magazine when it comes out at www.globalaviationresource.com!
The construction technique for aluminum aircraft fuselages is known as semi-monocoque. A monocoque structure takes the entire load through the shell of the structure. In airframes, the skin is very thin and so frames and longerons are joined to the inside to provide additional rigidity while the skin still takes a lot of the load. If you haven’t ever seen the cross section of an aircraft structure, you may be surprised to see just how thin the skin panels actually are. They are perfectly up to the task of pressurization and bending loads so no need to panic.
An outcome of this design approach is that the panels between the frames and longerons can experience some load directions that induce a measure of buckling. Nothing that is beyond their elastic limits but something that can be apparent if the light comes from the right angle. The lower side of the rear fuselage of the Boeing 757 is an area that is susceptible to this in certain flight conditions. I saw a number of them recently – both -200 and -300 models – and they both were showing visible distortion of the panels. The sun angle meant that the shadowing of these areas was apparent.
The 757 is by no means the only aircraft to experience this phenomenon. The B-52 Superfortresss is a jet that shows this effect on plenty of occasions. I have heard people comment on it being a function of the age of the airframes but it is more of a result of the design of the basic structure than anything else. Certainly nothing to be immediately concerned about.
