Lunch Update

Made a lot of progress over the weekend determining the surface area, surface normal, hinge axis, etc. for the flight control surfaces. This robust system will allow us to make any number of discreet channel controls in any configuration!

However, we are running into problems with the movie model again… we already identified that the engines were above the CG (which won’t work once we get to space) but now apparently the lower portion of the X-tail is as well!


1-26-2015 1-23-15 PM

Wind Tunnel

Sorry I haven’t been posting lately, I have had my head down working on the flight dynamics for a week.

At first I thought the tail design for the Dropship was a V-tail and an inverted Pelikan.


That would have worked with the existing wind tunnel algorithms from Rise but unfortunately what we are looking at is more like the X-tail concept which is a whole bag of worms with 4 discreet channels that can result in pitch, roll, yaw, and spoiler motions.


So I am rewriting the wind tunnel piece by piece, taking it to the next level in every respect. For example we used to only count the vertical stabilizer and rudder sections in the weather-vane algorithm. Now I have it computing the clean (gear up) and dirty (gear extended) profile drag and weighted arms for both Z (for yaw) and Y (for roll) tendency!


Pressure Sensor

Pretty slick!  I originally had a pressure switch that would be open below 60 PSI and closed above 60 PSI for monitoring the pneumatic system using a digital input.  That is for our fault tree compliance with ASTM guidelines (shut the motion down if we are below that threshold).

At some point I installed a backup electric compressor which is controlled by the computer.  If the pressure was below 60 PSI the compressor would turn on – but when do we shut it off?  It is a dumb pump with no switch of its own. The computer was instructed to only allow duty cycles of 10 minutes so it would basically run for 10 minutes then shut off and be above 60 PSI.

A solution was a different pressure switch – one that opened on pressure fall below 50 PSI but didn’t close the switch until it got to 90 PSI. Seemed like the perfect solution! However, for ASTM compliance we may comply with 60 PSI but not know until we got to 90 PSI.  There had to be a better way!


This guy has a 0.5 V to 4.5 V linear signal voltage representing 0 PSI to 200 PSI respectively. Instead of using a digital input, I put it on one of my available analog inputs and viola!  I have a pretty accurate measurement throughout the range of pressures at any time for about $25!