John Olsen 1

The wings on a biplane will interact to some degree, depending on the interplane gap and the stagger. That could easily mean that they do not take equal shares of the lift, unless the relative angles are adjusted. I seem to recall that one of the WWI German types had structural problems partly related to the top wing taking a greater share of the load than it should have. That does tend to imply that the structure was a bit marginal anyway. Porpoising sounds more like the longitudinal stability is marginal or inadequate. A lot of the early stuff had quite short moment arms at the tail...one of the Fokker types was extended by one fuselage bay during trials to improve things. The Northrop type flying wings are liable to fly along with a gentle undulating motion due to the marginal longitudinal stability. When a plane pitches up, increasing the angle of attack, the centre of pressure (lift) of the main wing moves forward. (For most normal airfoils) For best stability, the tailplane will normally be generating downforce, and as the plane pitches up, that downforce will reduce. The result of that should be that the overall centre of pressure movements cancel, keeping the centre of pressure behind the centre of gravity. If the centre of pressure manages to get in front of the CoG you have an unstable situation while if they coincide you have neutral stability. It used to be thought that making plane maneuverable required it to be unstable or nearly so. Hence the marginal stability of things like the Sopwith Camel. Actually that does not have to be the case. A plane can be built to be acceptably stable while still having large control surfaces and responding quickly to them. John

The "A" curve that is usually used to weight noise measurements is supposed to take into account the sensitivity of the human ear to noise at various frequencies. However, I wonder if it only takes into account the perceived loudness and not the unpleasantness of the noise. Noise measurements are fraught with all sorts of problems and are not always very repeatable. One gotcha with our situation is that we take noise measurements fairly close to the model, while the people who are likely to object tend to be much further away. If the particular noise is one that carries well over a distance, it will sound worse to the complainer than one that does not carry as well, even though they were both at the same level in a noise test close to the model. There are of course a few tricks to minimise the reading from a given model. For instance, make sure it is over grass, long if possible, rather than concrete or tarmac. Keep it as high as possible to reduce the sound reflected off the ground, eg on a starting table rather than on the ground. Electric pushers can create a lot of noise, especially when the prop is quite close to the trailing edge. This causes a sort of siren effect, eg the air off the top of the wing is hitting the prop at a different speed to the air off the bottom. You can duplicate this effect by blowing a jet of compressed air into a prop at one point. We've had one complainer who has claimed that we were overflying her house. This seemed odd, because her house is far enough away for a model to be nearly out of sight. It has taken us a while to realise that the problem is not actually us. We are quite close to a full size general aviation aerodrome, and she happens to be dead in line with the runway. They can and will overfly her house frequently, and it is unlikely that complaining about them will do her any good. John

Lots of homebuilt aircraft have VW engines. I am not sure if they tap the head for another plug and have dual ignition or not. But anyway, a great project. I've seen a rotary engine running that a local guy, now deceased, built many years back. It would be a similar size to this. John

Not to worry guys, there are more under way here in NZ. I think if you want one you would just have to front up to Avspecs with some money and some original parts and join the queue. I have met a couple of the guys who work on them. One flies control line, and builds his own engines, the latest being a V12 supercharged two stroke. The other is building a Pietenpol Air Camper (full size) and is putting a flash steam power plant in it. He has also built a steam motorcycle as a test bed. John

Well, we have a portaloo at our field. Now if I could only persuade the rest of the members to close the lid so the stink goes up the vent.... John

Going by my experience with fixing cars, the engine will be easier to fix than the rest of the plane. Engines are easy...sure you would have to make the parts for one like this, but in these days of CNC mills and lathes that is not the problem it once was. Some rotaries did have ordinary poppet valves in the cylinder heads, unlike the Rhone-Gnome monosoupape setup. One of the German ones even had a proper throttling carburettor. John

I only trust the meter to confirm that I have in fact picked the right battery, eg one that has been charged, not one that I used. So I expect to see either over 95% or under 50%. The flight time is short enough without starting with a partly charged battery. John

Les Batkin, that would be the one. One of the boats had a feed problem so he came off the water early, bur we had rides in the other two, upstream under the bridge and nearly as far as the island up that way. I've never been on the water there before, makes me want to get my own steam launch on the water. Did you know there is a guy in Tuakau building a steam aeroplane, a full size one? I think with the close wing spacing on a tripe, the down going aileron creates enough extra drag on that side to overcome any extra lift. John

I was down your direction on Saturday, with some mates and three steam launches. We had a get together at the Les Batley reserve, which I think is downriver from you a bit. Have you got differential on the ailerons? Might help to make them more effective if you do. Of course triplanes are very good at blanketing their own tail surfaces. John

Well, you could argue that the ESC fires are off topic, since the actual poll is for LiPo fires. However, since the two are quite closely associated and since it does appear that it may be more likely for an actual fire in a model to be an ESC fire, I think it is still pretty relevant. An ESC fire is of course only going to happen while it is attached to the battery, and my own experience is that they are not too hard to extinguish once you have disconnected the battery, I guess provided the fire has not got a good grip on the airframe. For my own setup, the plan is to reduce the load on the ESC to give it a bit more headroom..that particular plane is rather generously overpowered, being a 40 size Stik with a 60 equivalent electric plant. (Heaps of fun, great vertical performance!) So I can reduce the prop size in the meantime to give some more headroom. This will reduce the chance of a propstrike on takeoff, which may have been the initiating factor. Maybe later I will get a bigger ESC, but the only spare I have is the same size. I will also mount the ESC with something a bit fireproof between it and the fuselage. I am thinking that just for fun I might just varnish the slightly charred areas to protect them, and put on some transfer letters on the wing saying something like "FireStik", or maybe "Fireball". Perhaps "Phoenix" would be appropriate! John

That thing at the front is for catching insects. I know because I have a similar one on the front of a plane, and while the engine was running on the ground I once saw a large blowfly fly into it. However, no recognisable parts of a blowfly were observed to emerge behind it. Therefore I deduce that the blowfly got eaten. John

I wonder if anyone knows anything about an interesting problem we encountered recently. We had a couple of young blokes flying a foamy power glider. The older of the two was pretty good, the younger was just learning and they were passing the transmitter over when he got into trouble. I suggested trying a buddy box, so we had a go at buddying up my DX8 with their DX6. It worked, with mine as the slave, except that all the controls were reversed when the slave was in control. Reversing on the slave made no difference, and of course reversing on the master was no good since that would have reversed the controls for the master as well. So is there some reason why a DX8 can't be a slave to a DX6? Or am I missing something? John

Dick, I certainly agree that 250 Amps would be on the low side....I just multiplied the capacity of the battery by the claimed permissable discharge rate, which gives a figure in that ballpark. So very probably the battery could deliver a lot more, especially when fully charged, as of course it was at the beginning of the flight. For a plane like the Stik involved here, putting the ESC on the outside has a lot going for it. This one was the sort that has a little heatsink with fins, not covered with heatshrink tube. But having found that I have a spare ESC of the same type, I think I might reduce the prop size to reduce the current and give a bit more margin. That will also make a propstrike on takeoff less likely. John

I had my second fire today but it was not the LiPo, it was the ESC again. Same type of ESC as last time, and in the same type of plane,but different circumstances. This time it was on takeoff. It would have been just about at takeoff speed when all turned to custard. It is kind of hard to be sure about the order things failed in, but the prop was broken, and the firewall was ripped out of the front of the stick. (Great Planes 40 size stik with electric setup fitted.) It is or was a tricycle undercarriage. So either the prop blade touched and broke and the imbalance took out the firewall, the resulting loads on the motor causing excess current through the ESC, which then fireballed, or else maybe the nosewheel caught on an obstruction, ripped out the firewall, and thus lead to the prop breaking and the motor overloading. Either way, I think the ESC burning up was a secondary effect. It did take a bit of putting out, although the fact that the hatch had popped off after the firewall pulled out at least meant I could get at the battery connector. The ESC was on the outside of the plane in the airstream, so I wasn't having to reach too near the fire to unplug things, and once I had the battery unplugged the flames blew out OK from blowing on it. But had I taken much longer to get there, the wing and fuselage would probably have gone up quite well. Although it is hard to be sure, since in unplugging the battery the ESC end came away from the board...the solder joint had melted, So maybe things would have died down, although it was not looking like it. At its peak, while the plane was coasting to a halt, it looked like a fireball about six inches in diameter on the side of the plane. That ESC had about a 20% margin available, maybe I will go for more with the replacement, although I suspect that it might not be possible to prevent some sort of adverse effects from things going wrong in this way. The 5000mAh 6S lipo is probably capable of well over 250A. Anyway the Lipo itself seems fine. The plane will need some sanding and recovering plus some epoxy on the firewall. So if my own limited sample is anything to go by, the ESC is a bigger fire risk than the Lipo. John

I get the same as you. It will be a typo. The equations will have been typeset from a rough handwritten copy by someone who doesn't do maths. Then the author has failed to notice the mistake, a very easy thing to do. John

Even an arrow needs fletchings in both planes in order to be stable. It is not the centre of the area (either side for yaw or plan for the pitch plane) that matters, it is the centre of pressure. One point about this is that the centre of pressure will usually move forward as the angle of attack increases. If the centre of pressure is behind the centre of gravity, the object will be stable in that plane. If the centre of pressure is ahead of the COG, then it will not be stable. (the centres of pressure for pitch and yaw need not coincide, but both should be behind the CoG.) There is usually some side area ahead of and around the CoG, so therefore it is generally necessary to provide some side area behind to move the centre of pressure far enough back to give yaw stability. By providing a decent moment arm, eg the rear fuselage, the amount of area that needs to be added is reduced. John

I've written a couple off by damaging them, but they did not catch fire. It was just that I felt it unwise to continue using a banana shaped lipo, and in the other case, a lipo that was now about 3/4 inch shorter than it had started out. That was despite there having been a block of foam in front as a shock absorber. I have had an ESC catch fire, that was quite spectacular. But it had an excuse, it had been reused from one of the earlier crashes. It had done a few flights after the crash too, but I guess there must have been a crack in the board or something like that. Luckily it went on the ground while I was doing a check with the Wattmeter, so it was easy to pull the leads off. John

Phil, your theory is all very well as far as it goes, but what about the situation where I have been flying with two packs. (one at a time.) The first flight was cut short for some reason, the second went a bit longer. So now I have the two packs with one at say 3.9 Volts per cell and the other at 4.1. What happens when I parallel them up for charging? I notice that my charger says that the resistance of each cell is of the order of milliohm or so, so a difference of 0.2 Volts could drive a current of the order of 100 Amps between the cells. So although my charger is supposed to be able to parallel charge I have never actually tried to do it. It might be different if I was using two packs in series, eg 2 4S to make an 8S. Then they would have seen the same discharge, so should be at the same level for charging in parallel. I would still probably make up device to allow them to be paralleled with some resistance first, eg parallel them with maybe a 1 Ohm resistor between each balance point, and leave them like that for a minute or two before paralleling them on the charger without the extra resistance. I'm actually using one of the big Fat boy chargers from HK. This allows me to charge my biggest cells (6S 5000mAh) in about half an hour, depending on how hoonish I have been during the flight. That is actually plenty fast enough as usually there is a bit of chatting with the guys between flights, and I have two batteries for that plane. So by the time I have talked to the guys and done a flight on a battery, the other will be pretty well ready to use. John

Well, I converted a Saito 62FS and I find it runs fine. The carb is I guess not ideal, which makes getting the mixture right a bit critical, but having found settings that work, I don't need to adjust them. It does take a bit of a warm up after starting from cold. Until it is properly warm it will not accept full throttle. The Saito is probably harder to convert than your OS. I added a shim under the cylinder to reduce the compression. The other thing that makes the Saito harder to do is that there are webs on the front bearing housing so you can't just make a round mounting for the spark sensor. However since I have a milling machine it was no problem to mill out pockets to clear the webs. Apart from getting really good fuel economy, the engine can idle much slower than it would as a glow, and the pickup from idle is very reliable. After all, it always gets a good spark, instead of relying on a glow plug that might have cooled off. I did at first have problems with the fuel pressure connection from the muffler. The tygon tube doesn't stand heat as well as silicon, but of course silicon is not recommended for petrol. The muffler is probably running hotter with petrol. So I made a little finned extension piece that screws into the muffler with a nipple for the tube on the other end. This keeps the tygon cool so no problem now. I don't know how the power would compare, the plane only needs about 1/3 throttle to fly around perfectly well so full power is rarely used. There is a picture of the engine in my album. John

I'm not familiar with the BARCS league requirements, but usually with model gliders the aim is to achieve maximum duration from a given starting height. For this purpose a canard is not ideal, since maximum duration will be achieved when the main wing is trimmed to be flying at the maximum lift coefficient. This will usually be at the angle of attack just below stall. You can't trim a canard main wing to that point, since the foreplane would normally already be stalled. With a conventional layout, you can trim so that the main wing is just short of stalling, and often the design is given a long tail moment so that a small tailplane can be used. This maximises the area available for the main wing. For a power model, especially if it has radio control, none of this should matter very much, apart from not wanting a sudden viscous stall, specially when landing. I'm not sure what the best way to avoid that would be. Full size gliders would only use that type of trim when trying to maximise the rate of climb in lift.When they are trying to go somewhere, they would trim for the best lift drag ratio, which will generally be at a lower angle and a faster speed. The rate of sink would be higher, but the distance covered over the ground would also be higher, so they would get further from a given height, hopefully as far as the next lift. Slope soarers are of course a completely different proposition. John

Dihedral is mostly involved with lateral stability. If the plane banks one way, the dihedral will cause the lower wing to create more lift, tending to restore the plane to level. It does get involved in turning if you have rudder only control. The rudder will cause the plane to yaw, the dihedral will then cause one wing to lift and the other to drop, and you now have a nice banked turn. On the two planes I have with no ailerons, eg just rudder, elevator, and throttle, this works very well. I have the rudder set up on the aileron stick and it is much the same as flying with ailerons, eg you put the bank on then add a little elevator to bring it around the turn. So if you don't have ailerons, then not having enough dihedral will cause difficulty with turning. Some of the shockies have built in side area to enable them to do a rudder only turn. But the dihedral you have looks to me like it should be enough to enable you to control it OK with rudder only. For all practical purposes, the flat centre with angled tips will behave the same as if it was one big panel from the centre to the tip. John John

Regarding the stall...when the foreplane stalls the resulting drop in lift is supposed to drop the nose down, thus preventing the mainplane from stalling. But this depends on the lift from the foreplane reducing enough when it stalls. Depending on the characteristics of the foreplane, the drag will rise and the lift will reduce, but if the reduction in lift is insufficient to move the centre of pressure back far enough, the main plane may go into a full stall too. Bear in mind that as the angle of attack increases, the centre of pressure will normally be moving aft. So to get stability, we have to somehow compensate for that. The conventional layout does that by having the tailplane....as the angle of attack of the mainplane increases, any downforce from the tailplane reduces...or if it is a lifting tailpane, the lift increases. Either way the deviation from a straight path tends to be reduced. So anyway, I don't think it is quite true to say that a canard won't stall, it is just that the foreplane should stall first, and the effect of this needs to be enough that the angle of attack is not able to be increased any more...this means that the foreplane needs to be big enough to make a real difference. John

Hi Phil, Well, there is a lot of balsa and hardwood in there still that goes back to the original. The fuselage structure is all original, apart from added bits to attach the radio gear. I did have to redo a lot of the glue joints as the original pva was starting to let go. The wing ribs are all original apart from a few near the tip of the wing that originally hit the ground first. I did take a little off the ribs so that I could sheet the leading edge. The spars and the leading edge itself were replaced because the ones on the damaged side were a bit past it. I took the opportunity to replace the spars with New Zealand Kauri, a wonderful light straight grained timber that used to be favoured by the Royal Navy for spars too. The trailing edge and tips were OK. Most of that work was done about 25 years ago, when I was also building a sailing dinghy. It was quite convenient to have a project that could use left over mixes of epoxy glue. At that stage, I still had the tailplane and fin, they went missing a bit later on. Still, I would have had to chop them about a bit to add elevators and rudder. It spent some time in storage while we had a couple of years in Germany after that work. I still have the original engine, but it is now over 60 years old and I think has earned an honourable retirement. I also have the original wheels, but don't seem to have the wire undercarriage so I made that, and fitted some bigger wheels since they were more in keeping than the originals...modeling stuff was quite hard to get here in NZ in the sixties. The covering had all been stripped off after the crash in the sixties. Had I found out about Solartex in time it might have been covered with that, as being more in keeping with the original look...the glossy look is not really quite right for a vintage design. I flew it again the weekend before last, on a day where the breeze built up a little during the afternoon. While I would not try to fly it in a strong wind, it does cope quite well with a reasonable breeze, so will not have to be a calm weather only flyer. That is just as well, since calm weather is pretty rare around here. There was another vintage style plane flying too, so it was quite nice. The other was a modern electric replica, I don't recall the name, but it looked good. I haven't heard of Triggers broom, but I presume it is a bit like Captain Cooks axe. The story goes that someone asked the Maori guy about his axe, and was told that it had been given to the family by Captain Cook. Since then it had only had five new handles and three new heads. Of course I haven't seen the magazine with the letter yet, I just got the March one a week or so back. They take a while to get out this far. John

Provided the truck can reach the desired takeoff speed in a suitable distance, speed should not be a problem. But what occurs to me is that the plane is sitting on the trailer at a fixed angle of attack. If that angle is too low then it will not generate enough lift to fly. OTOH if the angle is too high then the wing will be stalled. Normally as you reach flying speed you can adjust the angle of attack using the elevators, eg a tricycle U/C type will rotate, a taildragger type will have lifted the tail at a lower speed and will put it down slightly to lift off, and a floatplane, will be up on the step and thus able to change the angle of attack to lift off. Sitting on a trailer makes that a bit difficult, so you would want the angle to be about right. I think the camera man is a bit brave too, if the plane lifts enough to come forward a bit and then stalls he would be mincemeat. John

It will make the biggest difference on a plane that would be too twitchy to fly without it. I have the little Mig and I think that would be very difficult to fly without the AS3X. But if the plane is already quite stable, it will not make much difference. It might help with the smoothness for aerobatics, and I can see some potential arguments coming up in the competitive area. I have played with it on some other planes and unless they really need it you may as well leave it out. It will not prevent things like tip stalls on takeoff if you yank it off the ground too quick. There is a thread here somewhere from a guy who found that a gyro on the rudder was a help in keeping the takeoff straight on a tail dragger. John