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Flight Test Log 13

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Summary
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This was the first powered flight of the 16 % subscale SVC. We're
experimenting with a twin pusher configuration, for the following reasons:

   o  To get the propeller out of the field of view of the Drop
      Vehicle camera.

   o  To reduce wear-and-tear on the powerplant. A nose-mounted
      powerplant tends to get beat up in crashes and hard
      landings.

   o  Safety issue -- when working in the avionics bay, the
      ground crew's arms tend to wander into the arc of the
      nose-mounted propeller. This makes IARC judges nervous,
      since electric motors can theoretically start without
      warning. Nervous judges are a bad thing.

Also, elevon servos were omitted. The vehicle was controlled by throttle
only, including differential throttle.

Results -- although the airplane needed more power, and steering was
ineffective due to lack of elevon control, the airplane otherwise flew OK.

The powerplants seemed to be resistant to crash damage compared to a tractor
configuration, but it's uncertain whether this was due to scaling effects
as opposed to the redesign.

Regarding the steering issues -- it's possible that attaching the Drop
Vehicle would fix the problem. The change would add a significant amount
of vertical surface area above the center of mass of the combined vehicle,
which would increase rolling moment due to sideslip angle.

This issue applies only to the small scale UAV. We have no plans to remove
elevon controls from larger versions of the UAV.

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   Test_ID:  43
      Date:  2006/03/30 (Thu)
      Time:  06:50
      Wind:  Calm
   Vehicle:  SVC
     Scale:  16 %
      Mass:  30 g
  Location:  Globe

First powered flight, first flight with twin pusher configuration.

To save time, increase simplicity and reduce weight, servos were omitted and
the elevons were taped in place. Control was with throttle only. The intent
was to control steering with differential throttle, altitude with total
throttle.

Several short flights were made. Steering was not very effective, possibly
because of wing anhedral, plus the vehicle was a bit underpowered. Otherwise
the vehicle was stable and flew OK.

Several hard landings were made -- no appreciable damage to motors or
propellers.

The powerplant and control system were cannibalized from an Aero Ace
biplane. The biplane mass was 19 g vs. 30 g for the SVC, which may explain
the SVC's lack of power. Note that the Aero Ace uses counterrotating
propellers.




One disadvantage to this configuration is that the motors add weight
significantly aft of the center of mass of the vehicle. We are optimistic
this problem can be offset in the full scale vehicles by moving the flight
batteries to the nose.

Note that this is a significant advantage of electric power compared to fuel
burning engines, in that the energy source has constant mass, and can be
used to adjust the center of mass of the vehicle as a whole. By contrast,
it's much less practical to use fuel tanks in the same way, since fuel mass
varies during flight.

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Last updated 2006/4/7 FLM