We conducted another flight test over the weekend and it did not go well, but we did learn a lot from it.
The airplane was stable when under power, as it had been in previous flights. It even flew relatively well in a very stalled scenario. (It is not necessarily visible from the video, but it was very stalled throughout even the beginning of the flight.) Our problems resulted from pilot error/misinterpretation as well as from a poor configuration of the airplane prior to the flight.
Prior to take off we noticed that the rear wing of the airplane was slightly pitched down with respect to the fuselage and that the canard was slightly pitched up when the joystick was neutral. We decided that it was not extremely important for both canard and main wing to be parallel with the fuselage for flight, which we still believe is true, (I will discuss this separately) but we did not comprehend the full impact and consequences of this configuration until too late.
We had not realized that this configuration would mean that "normal" fuselage attitude during climb would actually put the canard and main wing at high angles of attack. As a result of this we took off in a stall and maintained a stall throughout without comprehending what had happened and why the airplane wasn't performing as it had in our previous flights. With the fuselage in an appropriate climb attitude it was not immediately apparent what the problem was.
The airplane was stable when under power, as it had been in previous flights. It even flew relatively well in a very stalled scenario. (It is not necessarily visible from the video, but it was very stalled throughout even the beginning of the flight.) Our problems resulted from pilot error/misinterpretation as well as from a poor configuration of the airplane prior to the flight.
Prior to take off we noticed that the rear wing of the airplane was slightly pitched down with respect to the fuselage and that the canard was slightly pitched up when the joystick was neutral. We decided that it was not extremely important for both canard and main wing to be parallel with the fuselage for flight, which we still believe is true, (I will discuss this separately) but we did not comprehend the full impact and consequences of this configuration until too late.
We had not realized that this configuration would mean that "normal" fuselage attitude during climb would actually put the canard and main wing at high angles of attack. As a result of this we took off in a stall and maintained a stall throughout without comprehending what had happened and why the airplane wasn't performing as it had in our previous flights. With the fuselage in an appropriate climb attitude it was not immediately apparent what the problem was.
Flight Analysis
The airplane took off well from a hand launch in zero wind conditions. It began to climb, but as it climbed it became apparent that it was mushing through the air rather than establishing a proper climb. The pilot then controlled down slightly, but it was not enough and the airplane continued to mush through the air. As the airplane came to a complete stall it slid right and entered a sort of flat spin. It recovered from this and began to gather speed ending the stall, but at this point we decided to autorotate in an effort to gather what we could from a failing test.
Unfortunately, prior to the flight we had decided on an autorotation sequence that was improper and could never have worked given our greater understanding of the problem at hand. This sequence was:
The problem with this scenario is that as soon as we killed the power we lost yaw stability and the airplane went into a bit of a flat spin. As you may recall the airplane has no vertical stabilizer. It is therefore very unstable in yaw, and cannot be maintained in coordinated, controlled flight without thrust vectoring. The ability to use thrust vectoring is lost if the motor is turned off. Thus our flight plan was doomed to fail because we had planned to cut power before entering the autorotation. The airplane was already out of control before the autorotation sequence was initiated control was never regained.
The damage to the aircraft was not as serious as it may look on video. The part of the fuselage made of aluminum bent and I will need to machine a new one. Other than that, the airplane is in good condition for future flight tests and we will be conducting these as soon as possible.
The airplane took off well from a hand launch in zero wind conditions. It began to climb, but as it climbed it became apparent that it was mushing through the air rather than establishing a proper climb. The pilot then controlled down slightly, but it was not enough and the airplane continued to mush through the air. As the airplane came to a complete stall it slid right and entered a sort of flat spin. It recovered from this and began to gather speed ending the stall, but at this point we decided to autorotate in an effort to gather what we could from a failing test.
Unfortunately, prior to the flight we had decided on an autorotation sequence that was improper and could never have worked given our greater understanding of the problem at hand. This sequence was:
- Kill engine
- Change remote control to high rate setting (this allows the pilot to rotate the wings over large angles for autorotation rather than the low angle limits used during conventional flight).
- Begin wing rotation (~80 degrees)
- Approach ground and increase angle to ~100 degrees so as to generate sufficient lift to arrest descent.
The problem with this scenario is that as soon as we killed the power we lost yaw stability and the airplane went into a bit of a flat spin. As you may recall the airplane has no vertical stabilizer. It is therefore very unstable in yaw, and cannot be maintained in coordinated, controlled flight without thrust vectoring. The ability to use thrust vectoring is lost if the motor is turned off. Thus our flight plan was doomed to fail because we had planned to cut power before entering the autorotation. The airplane was already out of control before the autorotation sequence was initiated control was never regained.
The damage to the aircraft was not as serious as it may look on video. The part of the fuselage made of aluminum bent and I will need to machine a new one. Other than that, the airplane is in good condition for future flight tests and we will be conducting these as soon as possible.
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