Vertical Take Off

It was really hot and sunny this week. The only thing that let it down was a really devious wind. Devious because, one minute it was really strong, then it was gone, then it was from the other direction. This week’s flying session was really good though.

First off, I bumped into a really nice couple with an Inspire drone. They weren’t sure if they were in the right place because the board still has no rules on it. He had done all his homework, though, and knew exactly how far he had to keep away from people and that he couldn’t just fly it anywhere. I’m fine with that.

I then had a flight with the RS352 using a new LiPo, which makes it go like a rocket. The flick rolls were also something else, but more on that later. Then I had a flight with somebody else’s HobbyZone Champ, where I did actually persuade him to fly it for a bit. It was really too breezy for it, but these UMX lightweights (~30g) handle the wind better than you would think. After that I had another RS352 flight, but, noting how the trim seemed to have changed, I tried a balance test in the air. I gained lots of height, turned the motor off and pointed it at the ground. It immediately tried to tuck itself under, so I must have been flying it with the balance right back at the neutral point, or a bit behind, so that it was verging on unstable. Well, that explains the flick rolls. I made some pitch trim changes until I was happy flying it, as you could see the pilot induced oscillations. What I can’t understand is that I did a ground balance check and it all seemed fine. The new LiPos weigh 100g, the old ones 102g and the very old ones (now retired) 108g. I can’t see that making a huge difference and I do move the balance around depending on conditions anyway. The result of the pitch trim is that it’s now much closer with the flaps down or up, where flap up before resulted in a big nose down pitching moment. I always flew with the flaps down anyway, so it was trimmed to fly slower with the extra wing camber, which worked better. The point now is that I’ve been practising harriers, which this aircraft just does not want to do. It’s been impossible trying to get it to settle into a stable 45 degree nose up forward flight mode, but now, with the camber flaps retracted (zero flap), it seems easier. Maybe the answer is reflex, so I’ll have to do a bit more investigation?

I had another two flights with the RS352 using the older LiPos, but it was getting windy by this point and I didn’t want to push the aircraft too hard. In fact, the wind had damaged it, although this happened on the ground. I lost the tail skid when the wind blew the aircraft around 90 degrees in the yaw axis while it was sitting on its wheels. This ripped the tail skid out, but I managed to find it, so it’s an easy repair. I also had another flight with the Champ, giving its owner some more air time, before almost crashing it on landing when the wind whipped up just at the wrong moment in the wrong direction. I touched the ground at about 45 degrees off forwards, which resulted in it flipping over, but with almost no speed and no damage.

At this point we also had the Zeno and Heron (which really flew well in the conditions), a small, green Edge 540, which I haven’t seen since last year, and the Nieuport from last week was replaced by a new Ripmax Transition VTOL aircraft. The first flight of this was interesting to say the least. It launches vertically off the ground like a quadcopter, with all four motors on their wing pods pointing upwards. Closer inspection revealed that it has two positive pitch props and two negative pitch in diagonals just like a quadcopter. For control, it also has an elevator (elevon?) on each half of the rear wing. The motor pods can also be rotated forwards to transition to forward flight.

This wasn’t its maiden flight, but the take off was a non-event. It just lifted up, drifted across the field in VTOL mode, but a minute or two into the flight, I saw the right rear prop come off. At this point, I thought it would immediately flip over and crash, as I would expect with a quadcopter, but it continued to fly upright, drifted and yawed around its central axis and crashed fairly lightly in some grass. That’s very impressive control from the flight controller, because we know the pilot didn’t do anything. He hadn’t seen the prop fly off. What followed next was a hunt for the prop, as two of us spotted its position when it landed, but then followed the aircraft down and lost the exact spot. Nevertheless, we found it lying in the grass after a bit of a hunt.

Back at the pits and some investigation showed that the tilt rotor mechanism was damaged, but not badly. There’s a single servo inside the fuselage with some really thin piano wire (2mm or 3mm? push rod type), which drives the mechanism. The servo had come away from its mount, so the motor pods were free to move. This is where we had a bit of an accident and got really lucky. Being a computer flight controller, it doesn’t work like a regular fixed wing aircraft, but more like a quadcopter, which you would normally arm or unarm. He clicked the throttle trim switch, something happened and the aircraft flew off on its own. It crashed a little way downwind, but managed to miss all of us standing around it. The moral of this is never to trust a computerised control system. The arming sequence on a quadcopter is there for a reason. Here, we have what looks like a fixed wing aircraft, but with four props all pointing upwards in our direction. It needs to be treated like a quadcopter and assumed to be live whenever the LiPo is connected. OK, that’s the same as a fixed wing aircraft, but the aircraft has the prop at the front and pointing forwards, which you will be pointing away from people when you connect i.e. nothing in the disk of the propeller and nothing forward of the propeller. The computer control system of the VTOL aircraft is an unknown quantity here, so always assume it is live.

Anyway, it wasn’t badly damaged when it was recovered, but it was discovered that the nose wheel had gone missing. This is where there was a difference of opinion, as the pilot thought it was still present after the first crash, while somebody else remarked that he noticed that it was sitting very low to the floor when we were examining it in the pits after the first crash. So, the pilot went to the second crash site to look, while we went to the first. We won that round of the Easter egg hunt too, as it was just sitting there in the grass at the site of the first crash. He’s got all the bits and it looks like a simple fix, so I’m hoping to see it flying again fairly soon, as it looked really stable in the air and rather interesting to watch.

I had to go at that point, but there were some kids walking over with a drone, a glider and a jet model, so it was still very busy. We also saw somebody flying a big glider over on the other field, which was a bit worrying, and a guy on a big skateboard with another drone.

Sorry there are no pictures this week, but it was a lovely day and I just flew stuff all morning.

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