Month: April 2017

A Very Windy Bank Holiday

It’s the May bank holiday this weekend, but the weather’s not co-operating. Today started out very windy and just got worse as the weather front got steadily closer. Needless to say, there’s no flying this week, so I’ve been fixing up the indoor micro quadcopter that I 3D printed last week.

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It’s a “whoop” or “Inductrix” style quad with four enclosed rotors intended for indoor FPV flying. This one has space for the F3 Evo controller that I bought a while ago, so it should be a lot more interesting to fly than the modified HubSan ones.

When I say, “fixing up”, I still haven’t managed to get a successful print of this design yet. This one was from a LeapFrog HS, but the printer isn’t extruding the PLA very reliably. This shows up really badly in the supports, and you can see where it’s not printed properly in the photo. The top in the photo is the bottom when printing, so that’s the bit which sits on the plate. The guard rings aren’t too bad, but the thin stator vanes don’t come out at all well.

This is the best print I’ve had so far, and it looks like it can be modified to work, so I’ll just have to see how it goes.

Just to finish on the topic of the weather, I saw this really strange effect this morning:

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It looks like the con trail from an aircraft is casting a shadow onto the cloud. It took a while for me to get the camera, but to start with, the shadow and the white con trail were very close together, gradually diverging as the wind separated them.

Two Flying Wings

We had two flying wings in the air at the same time this week, which is fairly unusual. If a certain Zeno wasn’t on holiday then we might have got three. I was on the bike this week, so, in addition to my own design flying wing which fits in my backpack, the second wing was the HorizonĀ Opterra. With a 2 metre span it looked huge.

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That’s my wing transit system. The wing is in the Head rucksack, while my Futaba Field Force 8 is in the camera bag on the handlebars.

This is the scene part way through construction, when I’m starting to think about how the Multiplex Zeno just clips together and how cold it is when the sun goes in.

You can just see the box for the Opterra in the background as we’re both building our wings. The Opterra looks really well designed internally and reminds me of a full size aircraft’s cargo bay when its top is removed.

At this point I had already flown somebody else’s Horizon UMX Carbon Cub, which had a huge amount of down trim dialled in straight from the launch. It was probably a good thing that the owner gave it to me to test as he was going to fly it himself if I hadn’t arrived on the bike at that point. All I can think is that, on the previous flight, somebody had tried to trim it to fly with the flaps (yes, it’s only 90g and it has ailerons, rudder, elevator and flaps). These were assigned to a switch on the top left, so, after gaining some height, I flipped the switch. This caused a big nose up moment, which resulted in a partial stall and wing over. I’m thinking that maybe, somebody trimmed this out by mixing the elevator/flap compensation, but didn’t do it correctly and applied it to the main flight mode? The elevator trim was right up the top to start out, but I finished with it just about neutral. It made things interesting for a while, but not as interesting as my initial launch with my wing.

We all watched the first flight of the Opterra after that, but, once it’s in the air, it flies beautifully. Mind you, it does have a fairly advanced computer stabilisation system. My wing only has two micro servos connected to a FrSky D4R, so the stabilisation system is in my brain. The Opterra is just huge when it’s doing low passes.

So then we come to my first flight of the day with my flying wing. I did at least two complete 360 degree left elevon rolls straight out of my hand before managing to hit the ground flat with power off. It was really very impressive, but quite a high adrenaline launch technique. I wish I had some sort of data logger so that I could play back what I actually did with the sticks because I’m on automatic at that point. In your mind you go through, “oh, it’s rolling left… a lot… and my hand isn’t on the stick as it’s just hurled the thing forwards so I can’t catch it in time… power’s taking it up and away from the ground, but that was a complete 360 roll… but now I’ve grabbed the stick”. I think I modulated the power to keep it going up (i.e. power down when the nose goes down as the roll is more like a snap roll and the nose is making a cone shape), then caught the roll with full right, but hit the ground as there was no forward momentum, it pancaked, but upright and flat and with the power off.

The only damage seemed to be a slightly bent motor shaft where it hit the grass at a downward angle. I wanted to know what went wrong, so, after checking that everything was really all right and moving the spinner cone forward, I launched again. This time I put in a lot of right aileron trim in preparation, but ended up taking it all out. I didn’t think it was flying quite right, but maybe I was just being super-sensitive because of the first flight, plus it was a bit blustery and this aircraft never did fly in a straight line? I don’t know, but I had a fairly decent flight, even if the landing wasn’t my best. This aircraft catches you out as the ground comes up much sooner than you expect. You have to get into the ground effect, stop it getting sucked into the ground with a lot of elevator, and don’t bleed the speed off too soon.

On the second flight with the wing, it occurred to me what might have gone wrong with the previous flight. I’m using the new LiPos which I flew in my RS352 two weeks ago. In that aircraft, I remarked that the power difference between these new LiPos and the one year old ones was frightening. They have loads more power. Now, I’d just put one of these into the wing, so I probably had a lot more power and the roll was a combination of torque effect and bad launching. The second flight went without incident and I was able to fly around with the Opterra for a bit before making an absolutely perfect landing. This was the best I’ve ever done with this wing.

The analysis of the LiPos when I got home was interesting, as both LiPos were still 70% full, meaning I got two 11 minute flights out of 30% of the capacity.

Finally, we also had a father and son, each with small drones, and a little 8 week old flyer who said he would come over with a Mavic next week, or at least his dad did.

And, here’s an update on the Atom. The blades are finished, but need a bit of balancing, so it’s almost there. The silver and metallic blue look really good together with the white.

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Easter Sunday 2017

It’s Easter Sunday today, but the weather seems to be following the same pattern as yesterday. It’s bright and sunny, but with a strong north wind. I decided to stay at home this week and it looks like a good decision as the wind has steadily increased throughout the morning. This isn’t like it was in the old days when I remember getting in four consecutive days of flying over the Easter weekend. One time, I remember, I brought a different model every day and somebody remarked on the fact that I had flown an F16, a Vampire, a CAP231, a flying wing and a glider. It used to be that I always ended up flying my new models at Easter, so, this year, I had in my mind adding an AutoGyro to that list.

I’ve spent all morning covering the blades with white profilm. However, the more observant amongst you might notice that I’ve only got as far as finishing one of the three blades. This solarfilming is taking a lot longer than I remember. Either I’m really out of practice or the blades are just an awkward shape to cover? Trying to keep the square edge on the bottom of the leading edge is causing me problems. Normally with an aerofoil you can overlap bottom to top on the leading edge and there’s a nice gentle curve that you can smooth the film down on to. With this being square on an autogyro (according to the instructions, the blades won’t start to spin without this edge, but then I’m no expert on autogyros), it makes the covering harder. Not much harder really, I just always take a while to get going with covering jobs. Once I’ve got back into the groove, then I get a lot faster. I’m hoping to be done by this evening, then I’ve got three more days of holiday to finish the rest of the aircraft.

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.

Spring is Here!

It’s bright and sunny. There’s not much wind. It’s almost perfect weather for flying and I managed six flights with my RS352 and two with a UMX Taylorcraft.

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We’ve also got a new board to mark the flying site, but it’s not got anything written on it yet. Apparently, it was put up last week, but I wasn’t around then.

Anyway, my first fixed wing flying since February was with somebody else’s Ares Taylorcraft. This is a lovely little model, rather like the Champ, and I really like the dark red colour scheme. There was a bit of wind and it’s so light that the rudder doesn’t seem powerful enough at times. You hold full rudder for ages and nothing happens, then suddenly it bites and you have to back off. Most of the time, though, you could push it around the sky with ease. My second landing going with the wind as the ESC had cut was almost perfect, running along the ground on the wheels for quite a distance until it got stopped by a clump of grass.

In between the two Taylorcraft flights, I tried out the first of my new Hyperion G5 SV LiPos. The power available was frightening compared to the 1 year old EX G3 LiPos that I’ve been using. It’s going to be interesting to see how these last, as my original 3 year old CX G3 LiPos are holding up better than the newer ones, which have puffed up terribly. The very old ones will now be retired, followed soon by the 1 year old ones I suspect. Just charging the new cells back up now, I’ve only taken 450mAh out of the 1300mAh pack, so I was being very conservative with the first flights.

I got 2 flights with the RS352 with the brand new cells, then the 2 old cells and finally the 2 very old cells. These were basically trimming flights, as this was my first opportunity to fly in calm conditions since I changed all the servos over at Christmas. The only thing to note was that on the final two flights with the very old cells, the balance was completely off, with the model wanting to dive into the ground. This is weird as I’ve flown with all the old cells interchangeably and not had this problem before. I’ll have to do a balance check later just to try and work out what was happening.

In addition to me and the Taylorcraft, we had a Multiplex foam Extra 300S, a Nieuport biplane, a whole host of foam FPV aircraft (including some really dinky twin boom ones) and a drone. Then finally, an HLG flyer who we’ve seen regularly over the years.

I just love biplanes, so I tried to get a shot of it in flight, but this was the best I could manage. It’s right in the middle of the frame if you look closely at the big cloud.

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Finally, it looks like the skylarks are back again. I saw one of the little critters hovering and you could hear them all around singing to each other.

OK, so with no more drone masterclasses to run, I’m now free to finish off my Autogyro. I tend to test fly all my new models around Easter, so that’s a good deadline to aim for.