Month: July 2014

An RS352 and a Big Open Space

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As the picture shows, the weather today was rather interesting, but the rain held off and it turned into another unbearably hot day. This is my usual aircraft, the profile EPP RS352 [robot birds link] from RC Factory. It will be two years old in October, but I’m still experimenting with it. It’s much better than some of the other profile 3D aircraft I’ve flown, as it flies more like a real aircraft should, rather than feeling like it’s just following the motor around the sky. It has a definite presence in the air, is capable of more manoeuvres than I can fly and, most importantly, I can fly it when the weather is horrible and keep putting in practice hours.

Today’s aim was to nail the snap roll. For an aircraft with ailerons which are 50% or the chord, it’s roll rate is quite tame compared to some of the aircraft I fly. That’s with turning the expo down from the recommended amount and increasing the throw. I’ve been experimenting with moving the C of G back a bit to try and improve the snap, which isn’t as crisp as it should be. The stability is already neutral, which is how I generally like to set up an aircraft, so the margin for movement is quite small.

For anyone wanting to check where the balance point is, the procedure for trimming is as follows:

  1. Gain a lot of height, but so that you can still see the aircraft.
  2. The aircraft should be trimmed to fly straight and level at this point.
  3. Turn the motor off and enter a steep dive somewhere between 45 degrees and vertical.
  4. Centre the controls and watch how the pitch of the aircraft changes.

If the aircraft pulls out of the dive abruptly, then the centre of gravity is too far forward (nose heavy). If the dive steepens and the aircraft tucks in, then the centre of gravity is too far back (tail heavy). If the aircraft continues in a straight line along the path you set, then it has neutral stability. The amount of down elevator required to maintain inverted flight is another test for correct balance.

My snap roll is getting better, but it still needs a lot of practice before combining it with the loop to make an avalanche. It’s really critical to get the timing of left rudder (100%), left aileron (75%), up elevator (60%) right and to enter the manoeuvre with the right amount of speed. I’ve tried varying the amounts of control deflection on each surface to see what works best and you can get some really interesting effects ranging from barrel roll to true snap. I think I need to apply some degree of control harmonisation in order to get this right and do a bit more programming of the radio. At this stage I don’t want to experiment with the flick button on the radio as I would always prefer to fly the manoeuvres myself.

Just when I thought I was going to be on my own all morning, somebody turns up with a hex copter. He had never flown before, never flown helicopters or multirotors and this was its maiden flight. To his credit, it all worked perfectly and just flew. Now that’s impressive for such a complex aircraft.

Wing Thing Two

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Test flight of wing thing two (red wings in photo). The steel ruler is a standard 12 inch one.

Although this has flown before, it was in the glider form with the black fuselage. I created a second fuselage with an electric motor for launching. The wing thing two is a smaller version of the original wing (blue and white wings above), but with reduced sweep.

Test flight one with the CG on the forward limit of the range used as a glider resulted in a loop from hand launch over my head into the ground. Power off early wasn’t possible as it went vertical immediately. Power off 5/8 way round the loop, but elevator not responsive to pull out and it hit the ground directly on the spinner cone. The impact caused minimal damage, so moved CG forward and attempted second launch.

There is significant torque when released, plus 50% power used resulted in left roll into long grass. On the third attempt, we have flight. Severe nose down despite moving trim all the way back and flew whole flight on 50% elevator. Throttle 50 to 70%, glide angle compromised by brake not programmed and prop windmilling in harmony with airspeed. Aileron response is too sensitive, but manageable. This aircraft is certainly agile and could turn tightly in a thermal if I wasn’t frightened of the spin I remember from the glider version. ESC cut at this point, around 3 to 4 minutes which is very early. Still have control, so rearm and power back. Tripped again and third time in quick succession while lining up to land. Approach speed too quick, caught left wing on grass and flipped it around. Post flight, ESC is hot, so switched prop from 9×5 carbon to Graupner 8×4.5.

The next flight lasted longer and I elected to land before the ESC cut this time. Launch showed the torque effect and the whole flight needed gentle applications of the throttle. There was a noticeable rocking laterally, but this could be atmospheric. The aircraft is responding to thermals. At one point while in a steep left turn I caught the spin, so the characteristic is there in a tight low speed turn power off. Landing again was too fast with no flare due to unresponsive elevator at low speed. This time it caught the grass straight and level and flipped straight over. All in all a successful first day.

Need to do some performance tests on the power train and some balance calculations before the next test.