John Olsen 1

It is a mulching cutter, actually three small cutters, so you don't have to worry about clippings. Seems to work fine. Of course you can mow the lawn more often too, since you don't have the normal hassle, so there is less taken off each time. Another good feature is that it is very quiet, so you can set it going in the evening. John

Well, it would not be a practical solution for the original problem, but I can't resist telling you guys about my new lawn mower. It is a robot. You lay a wire around the edge of the lawn, staked down with pegs. That connects up to a charging unit which sends a signal down the wire. The mower starts at the charging unit, and can be programmed to start at any time and day you want. It will first follow the wire around and do the edge, then it does either a random or a zigzag pattern in the middle. It has bumpers so if it hits a tree it just stops and reverses. When the battery gets low or if it starts raining, it heads back to the charging station. All very clever. It would be great for a flying field, except that you would want to be there, someone would be sure to steal it even though it will not work unless you know the pin code. I'm putting it inside when it is not working and staying nearby rather than leaving it totally unattended. Of course that means that all sorts of other litttle garden jobs get noticed and done, so the place is looking better than it has for years. **LINK** John

The next development will be that it knows how far away the ground is and proactively avoids it. Although I suppose that would prevent landing! I suppose it would also need to know where all the local trees were for best results. I think I recognise the flying field in the video from Phoenix. John

So what would you rather have, Harvards painted in Zero markings or no movie at all? Assuming you want actual Zeros to be used, it is going to be a bit of a problem to source them since Mitsubishi stopped production about 68 years back. So unless you want all flying sequences to be CGI or models, you are going to have to accept a bit of "Hollywood magic". Now if you want a movie with some interesting old planes in it, try "Flying down to Rio", the first movie to feature Ginger Rogers and Fred Astaire together. There is quite an assortment of old American planes in that. The planes are the real thing too, although the wingwalking stunts were acheived by the special effects man. Well, some of the planes would never have got off the ground with that many chorus girls on the wing. Any resemblance between newspaper reports and whatever actually happened is purely coincidental. John

Hi Gerrit, Have you done anything with shaft drives? I'm toying with the idea of one for the rear engine of an ESM Dornier 335. This has been done by a German kit manufacturer for a larger model of the same aircraft so it is possible. I'm looking for information on things like shaft couplings suitable for this sort of service but most of the outfits here are only used to industrial stuff, eg higher powers but much lower speeds. The shaft itself would need to be about 800 mm long, the engine would be a 120 four stroke. John

Have a look at what the West system people have to say about it: **LINK** It seems that you would be best to find an epoxy that is formulated for the purpose with the viscosity you want rather than thinning it yourself. I've used lots of the West system stuff on a boat that I am building, over 100 litres of it. John

I wasn't suggesting the nuclear for a model, it would not scale well!! But it is an example of an attempt at a steam powered aircraft. Full size locomotives are actually doing well to get 7% efficiency. Model ones, as tested at IMLEC every year, get between 1% and 2% at best. Steam from a simple boiler will actually emerge at a higher temperature than 100C, depending on hte pressure. It will still be saturated steam. Superheating would be worthwhile, and it is one of the merits of the flash boiler that it tends to accomplish this, the disadvantage being that there is not much control over the amount of superheat. In a model, the superheat, at any degree, would not add much to the hazardous nature of the enterprise, the main hazard would be the high intensity fire needed to provide the heat. Incidently if you compare the kW ratings for quite moderate sized propane torches to what is available from batteries, you will see why batteries are not a serious option for providing the energy. As far as boilers go, most places have regulations about what is allowed in various sizes. I am in NZ so the regulations here may be different to yours, but I think you will find that the Model Engineering Societies are able to inspect shell boilers that run at up to 100psi, and with a capacity limit that is probably around 1 cubic foot or so. (Here it is 25 litres for a copper boiler and 50 for a steel one. ) A boiler for a model plane would be well below the capacity limits, but you might well want a lot higher pressure. This is the attraction of the flash boiler, since mostly they have not been subject to the same sort of regulation as shell boilers. This is because the tube never contains much water, and the main explosion hazard from a boiler depends mostly on the quantity of water it contains. We should not forget that in fact the first aircraft to fly under its own power was steam powered, see: **LINK** John

Well, I beleive there are still CO2 powered models about, they use what is in effect a steam angine, but powered from the Sparklets syphon type of thing, eg a little bottle full of CO2 compressed to within an inch of its life. A similar concept used to use a lightweight air cylinder pumped up with air. There are ways of generating steam for a short time without fire. Fireless locomotives used to come in two types. One just filled the boiler with hot water and steam from a stationary boiler every so often. After that, you can draw off steam, and the hot water will flash into more steam. The pressure will gradually drop, so after a while you have to go back and recharge from the fixed boiler. The other principle is similar, but the boiler also contains a container full of a suitable salt, I think potash was used. This is dehydrated by heat before starting, eg turned into the anhydrous form. Then during operation, some of the exhaust steam is allowed into the potash container. The potash absorbs the water, releasing the latent heat of chrystallisation, which makes more steam in the surrounding water part. I don't know if either of these can be made light enough for a plane, but it would eliminate the need for a fire on board. Some of the big rockets have turbo pumps driven by steam, or rather a mixture of steam and oxygen, generated by passing pure hydrogen peroxide through a catalysing screen. This is not something that should be attempted at home, and you are not likely to be able to source pure hydrogen peroxide anyway. (Some rockets use a smaller rocket firing into a gas turbine instead.) The nuclear plane was not a joke, they had it under serious consideration and spent millions on the project. I think however they started to realise that it would be as big a hazard to your own population as the enemy, eg if it crashed on your territory you would have a rather big cleanup job on your hands. Of course the same applies for the enemy if they shoot it down.... John

The main loads that the bolts have to resist are actually the vibration forces from the motor, rather than the G loads due to the motor mass. So it is more important to have some sort of anti vibration on the nut than to worry too much about the absolute strength. For example, a little Loctite on the nuts, or else a nyloc type of nut. John

Efficiency is not everything. The Stirling cycle can be quite efficient, but the engine usually ends up quite bulky and hence heavy for the power. Currently the most efficient thermal plants are combined cycle plants, but again these are large scale plants and weight is not a consideration. The Rankine cycle is in fact the steam cycle, and these end up heavy due to the need for heat exchangers, eg the boiler, the condenser, and if you want good efficiency, various reheaters and economisers. So you can get pretty good efficiency, but not in something that will fly. On the other hand if you will accept lower efficiency you can get enough power to fly. So the practical cycles for planes tend to be ones that are maybe not the most thermally efficient, but rather ones that can be built light enough to fly, while also having high enough efficiency that the fuel supply for a reasonable range can be carried. Note that Diesels are more fuel efficient than petrol engines, but are heavier. That has meant that they have not found much favour as aero engines, although the Germans had some success with them. The extra weight becomes worthwhile for longer range flight, where the weight of the engine is offset by the reduced weight of fuel. The Besler plane used the Doble steam car plant, probably modified a bit. This is a flash steam plant as I mentioned above, eg no heavy shell boiler, instead it uses a single long length of tube heated by a powerful burner. Water is pumped in one end, and steam emerges from the other. You control the amount of steam by varying the pump, and control the burner to avoid melting down the tube. Much lighter than a conventional boiler but needs a clever control system, especially if throttling is important. The plant can be built to a comparable weight to an IC engine, but tends to take up more space and is less fuel efficient. (When I say comparable, it would be heavier, but not by as much as you would expect. ) So as you can see the Besler plane flew, but nobody bothered to put it into mass production. Similarly a model with the same sort of plant could fly, and quite well too, but would hardly be worth the extra complexity. The Americans did quite a lot of work on a nuclear powered aircraft, although not to the point of actually flying a working plane...they did fly a test reactor in a conventional plane. This would have used a steam cycle, using turbines, and one of the downsides would have been that with the minimal shielding that could be carried, the airframe would have been radioactive after flight. The only shielding would have been a bulkhead to protect the cockpit. John

Never mind the fly to build ratio, what about the time at the field compared to the time in the air? Our last session, that is my son and I on Mothers Day, we were at the field for about four hours. I did four flights, with the timer set on eight minutes. So that would be 8 minutes out of each 60 actually flying. Mind you, my son shares my transmitter with me, so I can't fly while he is. He did three flights, probably of much the same duration. So what did we do the rest of the time? Some of it would be preparation, some would be letting nerves settle after flights with the sun in a bad place, most of it would be just chatting with the guys. John

It can be and has been done, but by the direct burning of fuel route, not by the battery route. There was one back in the sixties that went quite well, it was a big free flight power kind of model and used a shell type of boiler which I suspect would not have passed inspection at any model engineering society due to being ultra light in construction. The power would have been marginal. You can get a better power to weight ratio with steam by using a flash tube boiler. We have a hydroplane on display in our model engineering club that acheived about 70mph back in the fifties, there wasa time there when steam plant had higher records than internal combustion. However, if you think pulse jets are antisocial, you should see a small high power flash plant running...not quite as noisy, but very user unfriendly, since the blowlamp is running at around 500 pounds to the square inch, and the steam is about twice that, and is entering the engine hot enough to blister paint. Lubrication becomes a problem under those sort of conditions, and the whole setup is really a disaster just waiting to happen. I suppose not too bad on a racing hydroplane in a pond, where the inevitable fire cannot spread very far, but not so good up in the air. Still, I had an ESC catch fire the other day, luckily on the ground under test. It didn't go out until I pulled the battery. John

Posted by Ted on 16/05/2013 02:42:38: Steve Now thats not the right attitude for Your body does not run on IC but electrickery! Ted Not so, those little mitochondria are busy oxidising sugars with oxygen from your blood, which is why you breath out CO2. The electrical stuff is only the control system. John

Hobbyking are currently selling a bat plane, which is a batman logo shaped plane, eg a round disk with scalloping at the front and back. Contol is by elevons and throttle only, no rudder, although there is a vertical fin and fusealage. All made from foam, and flies very well. My son has one. I get the impression that you could make a rectangular shape with elevons on the back and a motor on the front, and after some experiment with the CoG it should fly Ok. John

This illustrates exactly why some help can be useful. It is not uncommon for controls to need reversing, which is usually pretty easy these days since most transmitters either have a switch or a menu choice to reverse each control. However, not only does the direction need to be right, the amount of travel available needs to be right too or at least within a reasonable range, to make it possible to control the aircraft. Usually there will be a recommended set of throws provided. Then there is the question of trim, which can make the difference between a demon and a pussycat as far as the behaviour of the model is concerned. So even if you are going to learn on your own, it would be quite a good idea to have someone check out the aircraft first. I did a certain amount of my learning with a cheap foamy on a nearby park, but only after some time on the buddy box and a simulator, and only with aircraft that had been checked out by the club instructor. Note also that even with help, more than one aircraft was involved, although most of them are reparable! John

The more complex control system with V tails would apply more with full size, where you have to combine the fore and aft movement of the stick with the movement from the rudder pedals to create the correct movement for each surface. While this still has to be done for a model, it is most likely to be done with mixing in the TX these days. John

My most spectacular crash was actually a solder joint failing inside the heatshrink, it was where the small wire to the SBEC was soldered onto the large wire, so I guess that was assembly/wiring, but most of my "incidents" have been due to being relatively new to radio control. "Good judgement comes through experience and experience comes through bad judgement". John

Well, having gone through the learning process over the last couple of years...I find some of you guys a bit unbeleivable. I would just about bet that I could have got a model into the ground faster than you could get the transmitter off me, get your thumbs on the sticks, and save it. I found the buddy process really helpful, and I think it probably saved the club trainer several times. I suspect the process of grabbing the Tx off the learner would be much more unsettling for the learner than just saying "I have her". I wonder how often the changeover is fumbled? If the simplest technology was the best, we would still be using stone axes. John

Could it be that the motor needs the timing adjusted on the ESC? This is not something I have ever had to do, the defaults have always worked for me, but if you check out most ESC instructions there is usually provision to adjust the timing. John

This will be the same as the one in my EDF Mig15. You don't need a bind plug as such, you turn the receiver on first when you want to bind, eg by connecting the battery. The led in the receiver will flash, shoing it is in bind mode. Then you turn on the TX and put it in bind mode. After it is bound OK, you do the ususal procedure of always powering up the TX first. John

Hey Dean, Are you using a four stroke plug? Running inverted the plug is more prone to get too cold and wet when idling. If the plug itself is not the problem, maybe you need to consider an onboard glow driver to help keep it hot enough when idling. These usually hook up to the throttle channel and can be set to light up the plug below a given throttle setting...usually about 25% or so. There is also a more sophisticated type that senses the plug temperature. The downside of either type is that you do need an extra battery to provide the juice, although since it is not running all the time it does not need to be as big as you might think. John

That is a thought...I have the ASP 160 myself, so far it has only had a couple of runs on the bench, but it starts and runs nicely. They sound good too. John

There is usually a catch 22, they won't accept any responsibility for anything you pack yourself. You are actually best with anything like models to pack and transport it yourself. They are also hopeless with machine tools and workshop stuff, anything out of the very ordinary. Last time we moved there was a solemn promise that everything that was packed and left the house would be labelled. Yeah right...they ran out of time, rushed out at the last with about six boxes unlabelled, which they promptly lost for weeks. I will never use Crown again. They also folded a diamond saw about 10 inches diameter in half to fit it into the box. John

There are multiple types of losses that occur in a switch mode device like an ESC, and the amount of loss in each one will vary with the throttle setting. However the one that is likley to put the greatest stress on things is the simple I^2R loss, eg due to the current flowing and the on resistance of the devices. This will predominate at high currents, naturally enough, especially since it is proportional to the square of the current. So the main thing is not to exceed the maximum current, and in fact to allow a little headroom just in case. How much to allow is of course a matter of opinion and how much you trust the makers not to be overoptimistic in their ratings. I did just have an ESC fail quite spectacularly, it went pop and caught fire, continuing to burn until I got the battery connection off. It was on test with a Wattmeter, and went just as I reached full throttle but I had not actually managed to see the reading. I don't know why it went, it had been running fine with a larger prop, and the identical replacement is running well within ratings. Still, the one that went had been in a crash about half a dozen flights before, maybe something got cracked! John

With some of the digital servos you can connect them to you PC via a suitable interface and then reverse them from the PC. They remember the state you have set them in. You can also change the travel, centering, speed, and deadband, and of course it makes a handy servo tester, since while it is conected up you can test movement in either direction. The setup I have is for Hyperion, I think there are others with equivalent features. This is one reason why digital servos may be preferable for some applications...you can tailor the servo behaviour to match what is needed. John