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Member postings for John Olsen 1

Here is a list of all the postings John Olsen 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: Hobby King Global Warehouse.
29/07/2014 11:32:25

I have used Hobbyking a bit, and the delivery time will vary depending who the carrier is. I haven't had any lately, but my club friends who have tell me that Malaysia post outfit is not a good one for speed. I'm told they have also used Fiji post, who are even worse. Better if it travels with Singapore post or fedex. Of course I am in the opposite direction, NZ rather than the UK but the distance is much the same. (Actually the UK is closer to Hong Kong than New Zealand is, beleive it or not.)

It can take a long time between the Hobbyking "we have shipped" email, and the item actually appearing on the tracking. Sometimes the tracking will effectively be saying "we know about the item but don't have it yet" for about a week. One theory is that HK have put the item in a container at their end, but the carrier does not pick it up until it is full. Another theory involves a bullock cart and a man in a straw hat making his way through the paddy fields.

In the sixties I once had an order from the UK arrive in eight days. That was from start to arrival, and the order went there by airmail post since I didn't have Internet in those days. So less than four days in transit each way, and the shipper can't have wasted much time dealing with the order.


Thread: Mystery Plane Over London
28/07/2014 00:08:13

If these planes were over my city (Auckland NZ) I would assume they were using infrared cameras to look for marijuana plots, but I guess that is unlikely in central London. I gather that weed stands out in infrared compared to other crops. If it is being grown indoors then the lights need a lot of power so the building tends to stand out, unless of course there is a deep basement.

I don't think it is very likely that they are monitoring cell phones, there are much easier ways to do that. You need the cooperation of the cell phone company, but a government agency would have that or be able to get it. The company that I used to work for did have a strict policy that they would not do any tracing for anyone without a warrant, but that would be easy enough for the police or any three letter agency to get if they wanted it. Quite common to need to try to track the movements of a phone for someone who has gone missing for instance. Obviously these sort of powers can be abused, and not just by the authorities. Back in the day there was a Post Office telephone exchange worker who managed to get himself sacked for tapping the phone of his ex-wife.

I wonder if what they are actually doing is taking air quality measurements? Or maybe monitoring traffic? (Makes me think of Jane in the "Coupling" TV series.) It will be something for which flying is worth the cost, since as we all know it is not a cheap thing to do, especially over a place like London.


Thread: Biggles' Mess (the renamed cafe!)
25/07/2014 10:35:34

We have the Skippers Canyon road in New Zealand, but I think that Kishtwar Kailash one looks worse. The one in Bolivia is also pretty scary.


Thread: Prop pitch question
21/07/2014 02:15:39

I used to wonder why the competition rubber jobs used folding props instead of just windmilling with a ratchet like the simple ones did. You would think a freely windmilling prop with little friction on the shaft should not produce a lot of drag. However, even when freely windmilling, the airfoil section of the prop is moving through the air so will have form drag and skin friction. Because it is following the helix angle of the airscrew, it is moving through the air at a relative speed that is higher than that of the plane. Where the helix angle is 45 degrees the airspeed relative to the prop will be 1.4 times the plane speed, so the drag will be doubled. As the helix angle gets less, out towards the tips, the relative airspeed will be even the 30 degrees point the speed will be close to double, so the drag will be quadrupled. Any friction in the shaft will make things worse, by putting a negative angle of attack on the airscrew and thus increasing the drag, although it will reduce the airspeed a little by slowing the prop down. (The airspeed at any point on the prop is the vector sum of the components due to forward velocity and rotation.)

So is it better to lock the prop in place? Full size practice is to feather the blades so that (apart from the twist) they are edge on to the airflow. This will give the least drag, and also means the airflow is not trying to turn over the engine, possibly doing even more damage if it is a bit broken. Model practice with rubber models has always been to fold the prop away completely, or else to use a simple ratchet to allow the prop to freewheel. If the prop is locked, the blades will be stalled and I suspect will provide a fair bit of drag, probably more than the free wheeling case. Otherwise why did we bother with the ratchet...if you leave it out the rubber motor will eventually halt the prop.


Thread: vintage RTP flying
21/07/2014 01:45:35

The Variac would go between the mains and the DC power unit. By varying the position of the knob you will be able to get any output Voltage you want from 0 to the maximum. For example if you are on the 18V setting on the DC supply and set the Variac to about 66 you should get about 12 Volts out. You can adjust this to get the maximum permitted Voltage or current at the actual motor, which will overcome the line losses. It might be good idea to get someone knowledgable to check out the Variac and the power supply if they have not been used for some time, and especially to check the connections if you are not au fait with this sort of thing. A Variac is not an isolating transformer, so the output side is just as dangerous as the mains. The DC side of the power supply will be isolated from the mains, but bear in mind that it is quite old and may not have been stored in ideal conditions. I wonder if a more modern supply might be a good investment?


Thread: Saito FA56 Spraybar wanted ( SAI65122A )
20/07/2014 12:09:01

My experience with getting Saito parts is that the main USA dealer is Horizon hobby. When you order spares from them they have a nice little habit of telling you to order through your local dealer. If I do that my local dealer will order from the local importer, who will order from Horizon hobby, and something over six months later I might receive the part, assuming they did not go out of production in the meantime. So last time I needed a Saito spare, a spraybar and needle valve for a 90 four stroke, I did a web search and got it through Mcgregor. Now, I might be wrong about this, but the actual deal went through Hobbyplastic, so as far as I know, Mcgregor and Hobbyplastic are the same thing, or at least are working together. Anyway, I was able to obtain my spare part within a week or so, so chalk up a satisfied customer.

One thing that does annoy me is that among the specs for their engines, nobody specifies the diameter and pitch of the exhaust thread connections. Enquiring minds would like to know! In my case, I want to fit a pair of flexipipes to an ASP 160 twin. So far as I can tell, nothing else has the same thread, but it would be nice to know for sure. I can turn up an adaptor, but I do need to know the specs.


Thread: Prop pitch question
20/07/2014 11:48:00

If the prop is drawing in less air then the angle of attack will be increased. In the limiting case, if the prop was not drawing in any air then the angle of attack would be the same as the geometrical helix angle at that radius, but then the air would have to go somewhere when the blade comes past wouldn't it. Generally creating turbulence is going to absorb more energy than a smooth flow, which is why we usually try to avoid it. The drag of an airfoil is not going to reduce with an increase of angle of attack, it is going to increase until it reaches the maximum at 90 degrees angle of attack, eg effectively a flat plate.


20/07/2014 00:50:21

This all seems very odd, and I would point out that if the higher pitch prop is stalled it will actually take more torque to turn it, which should be reflected in more current. When an airfoil stalls the lift (thrust) reduces but the drag increases. Even if it is not stalled, it will be operating at a higher angle of attack, and hence will have higher drag.


Thread: Can I attempt fixing a LiPo ?
20/07/2014 00:28:38

Strangely enough I seem to recall an article about how to do this sort of thing in the magazine within the last couple of years. I have done it myself to reconnect balance leads that had broken off. The major issue is not whether you can solder well, although naturally you need to be able to do a reasonable job. The really important thing is organising the work in such a way that an accidental short cannot occur while you are doing the job, and also while you are removing the plastic covering. After all, to remove the covering you will probably use metal tools which are also quite capable of shorting the cells. Once the working area is exposed you then need to arrange things so that only one terminal is accessable, and this can be done by using materials like plasticine or mastic to cover the connections you are not working on. On completion, the plastic covering needs to be restored with more heat shrink tube.

However, from the description of the damage, it may not even be necessary to open up the covering. The black balance connection will be the negative one. Rather than opening up the casing to get at the internal connections, that could be connected to the main negative lead outside the casing. (This assumes that this type of battery has the two large connections for the main power, and a set of smaller ones for the balance connection.) Then the other leads can be joined using the stubs. Care is still needed since if you short any of the stubs, you are still shorting one or more cells, and the balance wires are small enough to fuse with that sort of treatment. So you only strip the insulation back off one at a time, you thread on a tiny piece of heatshrink, solder the join and then protect it with the heatshrink. Repeat for the others. Make sure you get the leads connected correctly, eg to the same one they were connected to before. This is very important...if they are all different colours it just means matching them, but some I have seen have just one black and the rest all the same colour. If that is the case you need to know how to get them in the correct order, which will need a Voltmeter.

Note that even if the battery was nominally flat, there is still a considerable amount of power stored in them. It is not as dangerous as working on live mains circuits, which sometimes has to be done, but still needs a similar level of precautions.


Thread: August 2014 issue hits the doormat.
16/07/2014 22:30:39

Here in the land of the long white cloud the June issue has just arrived. So I finally get to see the picture of me with my Powerhouse in the letters section.


Thread: Biplane wing incidence
15/07/2014 00:58:01

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 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.


Thread: Four Strokes Only Please
11/07/2014 12:40:30

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.


Thread: You have to see this !
05/07/2014 08:57:04

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.


Thread: Mosquito return to flight.
01/07/2014 23:47:08

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.


Thread: At the end of the day
01/07/2014 23:29:37

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....


Thread: Old Warden Sopwith Triplane Accident
01/07/2014 23:25:28

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.


Thread: not to be trusted , battery meter
18/06/2014 23:57:17

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.


Thread: Tripe
09/06/2014 10:04:52

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.


09/06/2014 07:27:25

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.


Thread: Trouble with Li-Pos?
09/06/2014 00:07:42

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!


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