So these brackets on the
outside of the fuselage were for the door props which allowed the door to be 'wedged' open a few inches for
probably a dual purpose, as Ric mentioned.
1. To allow for instrument sightings
2. To allow the 'skyhook' to be deployed without Fred having to hold it for 30 minutes or so
This is the skyhook Charles Lindenbergh used for the same experiments for the department of Agriculture. Can't say for sure yet if it is the same as the one AE and FN had on board but, it was for the same department and, the same person in charge of the experiments, Dr. F. Meier of the United States Department of Agriculture.
The red arrow points to the 'handle' which Fred would have to hold and, the blue arrow points to the tube which the aluminium collection cylinders were attached to.
http://www.nasm.si.edu/collections/artifact.cfm?id=A20030071000However, AE states that they had brackets fitted to the Electra at Miami which negated the need for Fred to hold the skyhook for 30 minutes or so in the slipstream while collecting the pollen/spores.
We devised a mechanical refinement for our sky hook. Noonan was too busy to hold it extended through either the cockpit window or the door of the fuselage, had either arrangement been practical. So, at Miami, we had brackets fitted to the side of the ship just behind the fuselage door. when this door was open a couple of inches, which was easily done, the device was clamped in these brackets, and the cylinder manually opened. Then for a period of thirty minutes of so nature took its course. subsequently the cylinder was closed, sealed and the place and time of it exposure recorded.
Which leads me to the conclusion that the brackets/clamps that AE refers to were fitted to the
inside of the fuselage and, fred would then attach a new cylinder to the skyhook, place it into the brackets/clamps on the
inside of the fuselage then open the door, fit the door props into the brackets visible on the outside of the fuselage slide the skyhook out into the slipstream and clamp it into position and, away we go for 30 minutes or so.
If all this sounds about right then, I need to look inside the fuselage for the
skyhook brackets/clamps, which, should be somewhere near the door as AE states