Peter Beeney

Colin, With respect, I’m tending to think your post is maybe a bit of a bit of a wind up or perhaps you are firmly convinced about this. If so, I wonder exactly how many £k’s you are firmly convinced? I’ve now found and watched WF’s vid about the model on the treadmill, and as he says, it does at least start to show the principles of what happens. And again with much respect but I’m not at all convinced about the wheels going faster or slower, either. I’m not sure that’s possible. “ Illogical, Jim!” All the time the wheels are in contact with a surface they only ever turn at a speed appropriate to the relative movements between the vehicle attached to the wheels and the surface they are bearing on. Just to keep the kettle boiling.. PB Edited By Peter Beeney on 15/10/2016 14:35:56

Dave, With the greatest respect I think that’s exactly what I am saying, but I’m afraid I tend to be a bit basic. ‘As long as the train’s speed always matches the car’s speed the car will stay where it is”. And anyway, I’d hazard a guess and say that a geostationary satellite would have to be travelling in the SAME direction as the earth’s rotation to be able to stay at a fixed point above it; I’m a bit suspicious that our car may actually be going in the OPPOSITE direction to the train. Parking our car back at the Royal Oak, (the driver’s not been drinking by the way!), (but if he stepped out of the car he might think he had been), the wheels are turning at at rate that carries the car forward at 50 mph. The road surface continues to carry the whole lump backwards at 50 mph. If we could now just instantly remove the engine’s drive and replace it with a prop that’s generating enough force to maintain the critical 50 mph forward the wheels will still turn at a rate that carries the car forward at 50 mph. The road surface still continues to carry the whole lump backwards at 50 mph. What exactly has changed? I’m afraid I’m unable to get any further on this one. But I do really really really do have some difficulty in getting my head around the sort of statement that say that because it’s an aeroplane with a different form of propulsion whatever the ground beneath does it makes no difference the the plane taking off. The reason being is that at all times I’ve always considered that it’s wheel have been firmly on the ground. If a plane is standing stationary on a stationary belt and it starts moving backwards the plane goes with it. I’m sure everyone agrees with that. If the plane now wants to go forward relative to an observer at the side it will have to go faster than the speed of the belt because it’s constantly being carried backwards. The forward speed is always whatever minus the rearward speed of the belt because the wheels are in constant contact with the belt. However, in the unique situation that the belt speeds up or slows down to match the speed of the plane it’s always going to remain in one position relative to the observer. It’s airspeed will be zero. That’s my take on it. Perhaps we should open a book… I’d certainly try and rustle up a few £k’s that says that a runner running at 5 mph on a treadmill with the belt moving at 5 mph in the opposite direction will appear to be stationary to an independent observer standing on still ground on one side. And I’ve never even seen a treadmill in the flesh… … I really do need to get out a bit more… PB Edited By Peter Beeney on 15/10/2016 11:56:30

Let’s try looking at this from yet another angle. A train is fairly long, is on a straight piece of track and has a road laid on the top. An open topped car is on the road, engine stopped and handbrake on, facing toward the back of the train. The train is travelling down the track at 50 mph. The car is therefore being carried backwards at 50 with it and the driver can feel the effect of the wind so created on the back of his neck. Starting the engine he accelerates up to 50 (indicated on his speedo) where he finds he now equals the trains speed going in the opposite direction and he’s come to rest opposite an oak tree on the side of the track which he can gaze at in comfortable no wind conditions because he’s now stationary relative to all his surroundings other than the train even though his speedo is showing 50; he’s stationary because the road is passing under his wheels in the other direction also at 50 which cancels out his forward speed. Then he thinks he might go and have a look further down the train so he starts to accelerate further. But the train driver, who is a bit of a devious dandy, has craftily connected the car’s throttle pedal to the train’s throttle; so now the train also accelerates in the other direction at the same pace. Now our despondent car driver is forced sit and look at the oak tree until all it’s little oak apples fall off. As long as the trains speed always matches the car’s speed the car will stay where it is. Let’s remove the car’s prop shaft and attach the microlight’s the engine and prop. What now can/will happen that’s different? Not a lot, in my humble opinion. All the time the car’s wheels remain in contact with the road’s surface it will respond in exactly the same way as the car with the driven wheels. Although if we now use an Air Speed Indicator to measure the speed when the car is moving backward relative to the train at the same speed, 50, it would indicate zero. I’m sure you could substitute anything in here now, on a mix ‘ n’ match basis. Even a large conveyor belt for the train; with an infinitely variable speed capability and unlimited input power. Then perch a yumbo yet on top. (With apologies to Reg Varney). Or indeed reverse right back down to the runner on the humble treadmill. One or other of his feet are always in some contact with the belt, if that’s moving backwards at say 5 mph and he’s running forward at the same 5 mph then he’s back to constantly studying oak apples again…. ……All a bit frustrating, really, I would think. Perhaps in a slightly more practical sort of way we could miniaturise all these components and call the treadmill a rolling road or even a railway. At least it’s not quite so James Bondesque… and I’m still convinced that the general principles remain the same anyway, whether great or small. Hopefully this is not too controversial… and can easily be shot down… PB

Great stuff! So perhaps there is now an answer in here somewhere to explain why what I think I’m seeing is in fact not actually what I’m seeing… Now I’m totally convinced that if I’m in my car and coasting down a shallow incline at a steady 30 mph under the force of gravity and the road then suddenly starts to to move toward me at a steady 30 mph the car would come to a standstill; although the wheels will still be turning. Then I drive on a flat road with the engine driving the wheels at 30 mph and in the same situation I again become stationary in exactly the same way. Strap a microlight engine on the back with a prop capable of pushing the car forward at at the same steady 30 mph and again the same rolling road will bring my forward progress to an end. Therefore I also have an overwhelming suspicion that the the motive force, whatever it might be, makes not an iota of difference; and by the same token if the backwards moving road speeded up to 40 mph I would go backwards at 10 mph; slow down to 20 and I go forward at 10 mph. Change vehicles downward to say a lightweight bubble car or upward to a juggernaut - no difference. At least to the visible actions. The main unseen change must be to the power required by the rolling road to maintain it’s drive against the weight of the different vehicles. Now substitute light aircraft for car on the same road. Light aircraft will also come to a standstill if progressing at a steady 30 mph with the wheels on the road. If the throttle is now opened fully to take off but it’s also arranged that the rolling road will accelerate at precisely the same speed as the plane but in the opposite direction of course, what will happen. My answer would be that the plane still remains stationary, right up point where the power input to the road equals the thrust exerted by the propeller. Well, at least it’s a little bit different, anyway… PB Edited By Peter Beeney on 14/10/2016 19:47:39

Just to satisfy myself I’ve done a little experiment. A plank of wood with one end raised just enough such that a cylindrical tube of sealant will roll slowly down. This happened in exactly the same way 5 times out of 5. Then I placed another plank on top and the tube still rolled down in the same way. Now I can pull the top plank backwards as the tube rolls down and I found that with some practise I can briefly match the speed of the backward pull, (I quickly run out of plank), to the forward rolling action of the tube. The tube’s rolling action appears to speed up when this happens; but crucially although it’s still revolving it physically stays in the same place relative to me as an observer and the ground underneath; and frankly had this not been so I think thunderstruck would not have even come close to describing my reaction. I’m guessing here, but I think what is happening is the as the tube rolls forward the rearward moving plank carries the tube backwards. At some point these actions are exactly opposite and equal. The two power sources, the watts expended by the force of gravity and the watts expended by the muscles in my arm, precisely balancing each other out. The next stage might be to try something similar with a model and a moving surface. With the throttle set so it slowly moves forward might be sufficient; standing/running slowly on a fairly large surface that I can move in a fairly straightforward way; and again if the result is anything other than that above I will be flabbergasted!! If this does prove to be so then as far as I’m concerned this can be scaled in which ever direction you choose; speed, size, weight, etc., the basic principles will remain the same. Keeping to the terms of the question, ‘The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction’, this implies that the speed can instantly be changed to suit and unlimited power can be applied at the same time, in short it’s just a guaranteed mirror image of the actions the plane. Now I’ve forgotten about the wheel speeds, plane speeds and other details, they may all be just a red herring. I’m looking at it as two equal and opposite power sources acting on an inert object. When this happens they just cancel out, whatever magnitude they may be, and the object still remains inert. Not sure if this is anyone’s rule, law or principle, but if not I’ll call it Pete’s Law, rule No 1! Maybe the (disguised) question might be ‘Can the plane actually move? In the rolling sealant caper I’m convinced that if I were able to drop the tube onto the plank when it was moving backward at the right speed it would remain in that spot and not move forward, although it would have to start to revolve. Considering the 747 on the belt, standard take off procedure. The plane starts to move forward, imperceptibly at first but the belt sensor instantly reacts to this and moves the plane back to where it was at the same speed. So now is it the case that as soon as the plane goes forward a small distance it gets moved back the same small distance? The timing and reaction for this stuff would I’m sure be a doddle for modern electronics, but I’m not quite sure about the belt drive motor. But I reckon the question assumes instantaneous reactions here, too. I’ve now convinced myself that the only way the the plane is going to take off is to blow the question wide open and overcome the ability of the belt to move the plane back, allowing it to move forward and eventually gain speed. All round a gigantic task and will probably only ever considered hypothetically. Time for a spot of flying… PB Edited By Peter Beeney on 14/10/2016 13:55:43

Cliff, With the greatest respect but perhaps you might care to read the original question again. ‘The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction’ . You have a fixed speed belt, the question is indubitably using an infinitely variable type. I think you’d find that if you tried to push your wheels forward and the belt’s speed increased to match that forward motion exactly it would be very difficult, if not impossible, to move the axle along the belt. Just my silly opinion, really… PB

It seems to me there is not very much trickery about the question, is it not a case of just considering the drive medium, flexible or solid? If the brakes were full on and the engines run up to full power the plane wouldn’t move, the braking force exceeding that of the engines but all the ‘motion slip’, being taken up in moving the air, or ‘flexible drive medium’, through the engines rather than moving the plane forwards. If the brakes were then slightly released the plane starts to move forward and instantly pushes against a pressure switch which applies enough power to start the belt moving backwards sufficiently fast enough to match the force moving the plane forward; the whole mass of the plane is now being moved backward at exactly the same speed as the wheels are taking it forward; nett result: the pane remains stationary. The brakes are released further and the same thing happens until the power applied to the belt ultimately equals that applied by the full power of the engines. Two forces acting in opposition just moving vast quantities of air. The power required to drive the belt backwards has to be in excess of 4 jet engine thrusts in parallel. It is after all effectively holding the dead weight of the plane against the engines. If the drive medium were solid, i.e. an externally driven winch rope pulling the plane forward against the pressure switch the rearwards moving belt would again prevent the plane moving forward and if the belt drive power exceeded the winch motor power unless there were some form of slipping clutch the winch motor would not be able to move and thus stall. Or something else would break! If the wheels were being driven by a solid prop shaft from the engines the plane would still not move, two power sources again acting in opposition, but with the ‘ flexible slip’ now being the relatively increased movement between the belt and the wheels; the power requirements very considerable again. I would hazard a guess after all this and say that because the plane is never going to move forward it’s never going to take off. Maybe the real question should be is what happens to the wheels in amongst all of this? The force required to overcome the natural inertia of the wheels must increase on some sort of exponential curve and in the end they simply refuse to turn any faster. I suspect they will then cry ‘enough is enough’. In practise it might be difficult to try this, but with enough determination it might be possible to scale it down sufficiently to try it. I certainly won’t be doing it though… I agree with entirely with John F, if you consider anything other than the question exactly as stated then it does become meaningless and any answer might cover any situation. Rehashing the question slightly, let’s say we have an object, on wheels, standing stationary on a road with a casual observer to one side. Then the object is moved forward with any means of propulsion, the observer sees this at say 10 mph. Then the road moves in a rearward direction at the same 10 mph. What does the observer see then? It surely cannot be the same 10 mph forward, I think it would be zero mph forward, the two motions are now balancing each other out. The forward motion is zero but the power is translated into increased motion between the wheels and the road. If the forward motion were created by means of a winch the coefficient of friction might play a part and the wheels simply dragged across the surface; but if the mass downward of the object and the power applied to the rolling road were more than sufficient I think the winch would eventually be stalled again. I’ll stick with this one until I change my mind… PB

I’d have also thought no, simply by the fact that if the engines were not running but the belt was going backwards the plane would move backwards. If the engines then were then started and the thrust resulting in the wheels turning forward to exactly match the belt under all conditions the plane would simply stand still. Thus to me it’s quite difficult to see how it could take off. How far does a person on a running machine actually move forward? All the forward movement is transformed into rearward movement, resulting in the runner staying in one place. PB Edit. Pipped at the post, Harry…  Great minds and all that! Edited By Peter Beeney on 12/10/2016 22:45:41

Kim, With respect and for what it’s worth, I try to separate the watts into the ESC from the watts actually turning the propeller, in my opinion at least they can sometimes be two different things; and again, as said before, I tend to use the tacho in the first instance, as far as I’m concerned it’s a bit essential. As an example I can quote a really well worn Riot which runs on 4 cells. The standard model runs on 3 cells using a supplied 12 x 6 black plastic prop. I lobbed in a 4S and experimented with smaller props, it now runs on a 9 x 6 APC i/c prop. The increased performance instantly rendered the ele and rudder control snakes useless, they started giving way under pressure so I moved the servos to the rear and used short heavy duty pushrods. Even then the ele plastic servo gears still didn’t appreciate the overtime rates and decided to pack it all in so I changed to a 17g BlueBird metal geared worker bee and this did the trick. Although I’ve just recently had to repair this too, I noticed the top half of the case had cracked right down where the drive shaft protrudes through. I’m quite happy to accept all this stuff, however, because I do consider that my flying style does get a bit eccentric at times, to say the very least! The motor is a 850kV, on 16.8 volts that’s theoretically around 14.280 rpm, and when I first checked it was very close to the 850 figure; I use a 12V car batt as a testing power source, very stable and doesn’t sag at all under load. I always do that first for a reliable benchmark. The 9 x 6 yields 12,000 static on the lipo, that’s an implied speed of 68 mph, which I should think from visual observation is somewhere near the mark. In a flat out power dive, with the prop fully unloaded, it may be somewhat faster, even. Checking the current flow to be about around 32 amps and guessing the voltage to be around 14 I make that about 450 watts so I consider that’s not bad, but to it’s advantage the Riot is quite a relatively light model. As it happens, remarkably the smaller aileron servos have been faultless through all of this. 12k is about 84% of 14k and I wouldn’t want to reduce the revs any further because I believe that the current flow would rise but the performance would fall; i.e. the watts output at the prop shaft are becoming less, but the watts input into the ESC are rising…. With regard to the 16 x 10 prop, this immediately seems to be too big just by Mk 1 eyeball standards. Roughly equating the rated electric motor’s 1440 watts to an i/c engine, around 1.8 HP, such as an OS 90 Surpass ll perhaps, at a complete guess the prop size would be around 14 x 7 to 15 x 6 at around 9k rpm, say. So I’m not sure the electric motor would ever turn a 16 x 10 successfully. Tachometer here. Good luck. PB

This picture perhaps shows rather better the moment the fin starts breaking away and leaning over to the left, which I guess can only be caused by the back end moving to the right? PB

Leaving aside the safety implications of this incident for a moment, I started tinkering around with the video and I managed to grab these screen shots. They are a bit hazy, probably due in part to my ineptitude, but they are simply just as taken. Interestingly, (to me), that as the model rolled to the right and the pilot used left hand top rudder to hold the nose up, I’d have thought that the weight would have been forcing the fin to the right; but it would seem from the photos that might not quite be the case and in fact the fin actually broke off, and in the event apparently quite violently, to the left. So was was there something else going on as well, such as maybe a side slip which was actually having a stronger and overriding effect? Once the fin had gone I suspect that the resultant violent pitch up at the nose may have caused the cockpit coaming and canopy to depart, this then started the chain reaction which as BEB rightly said, very rapidly sealed it’s fate! I too guess it all happened sequentially, but because our human perception is relatively quite slow it seems to be instantaneous. However, at the end of the day it seems that catastrophic structural failure was indeed the reason for the breakup; but I’m sure that by now the flying team will have carefully analysed the video frame by frame and drawn their own conclusions. Let’s hope the next one may be built to a better specification, as I’m sure it will. PB

Doug, With the greatest respect, but if you leave the motor standing for any length of time you really need to periodically charge the battery or disconnect it; these days I think there is always some small permanent discharge going on, even if it is only a flashing led. Over time the battery will eventually go completely flat. The positive plate in a lead acid cell consists of lead dioxide and the negative plate is made of lead. During discharge the negative plate turns to lead sulphate. If this is not changed back by recharging fairly quickly it start to harden which will only get worse over time. The harder it gets, the more difficult it is to recharge. They can be recovered though, I’ve seen some pretty desperate cases successfully brought back from the brink in the past. Leave your car battery on charge until it reads at least 14 volts. The car’s alternator charge level will be around 14.2 - 14.4 volts. You can leave a lead acid permanently floating across a charge voltage of 2.3 volts/cell, that’s 13.8 volts for the car battery. This keeps it in tip top condition without overcharging it. I rarely give up on anything until it becomes obvious that it’s not worth pursuing further… Good Luck! PB Edit - If you remove the battery for storage make sure it’s really fully charged first. Then it will stand quite a while. If it’s discharged, perhaps by only a small amount, it’s most likely to carry on self discharging, which then rather defeats the object of the exercise.    Edited By Peter Beeney on 20/09/2016 22:01:27

Simon, Apologies again, but now I think I’m getting your drift. Certainly in the case you quote the 20 amp motor should be fine. The current will be dictated by the applied voltage, in your case with 3 cells 12.6V fully charged down toward 9 volts when getting flat, and the size of the prop you fit. A bigger prop, both in diameter and pitch will increase the current flow; but not always the required performance. You said, ‘I figured as long as the amps aren't LOWER then it's OK as the motor will only draw what it needs?’. If I think what you might possibly mean is ‘I figured as long as the motor rating isn’t LOWER then it's OK as the motor will only draw what it needs?’ then that’s exactly so. An even larger motor would still run ok, but it might soon be a case of overkill, in size, weight and cost. In general terms, if you keep the maximum current flow of your power train below the maximum current rating of the motor you should be ok. I suspect that in the past some problems have arisen because the manufacturer might get a bit optimistic with his power output figures, plus the fact that that some modellers have also gone a bit over the top with their expectations of performance. I’ve never consulted any of the webcalc type info. charts and it has been said by others that although it may be a good starting point the theoretical figures don’t always meet the practical experience right in the middle and some adjustments may/will be needed; I’d go along with that every time. Be prepared to play around with it until you get the result you want. Makes it easier for the second time. Happy Landings… PB

Frank, yes, indeed, I only came up with that motor because it’s possibly one candidate as a direct replacement for the 480 brushed lump in the hobbyzone super cub. There are a couple of alternatives, an 850 kV version which has a max current of 28 amps but no time limit on it. Interestingly on 3 cells it gives a thrust figure of 1140 grams at 19.5A on a 11 x 4.7 prop. The 1320 kV flavoured can, max current 28A again, gives a thrust of 1310 grams at 25.2 amps on a 9 x 5 prop. The 1020 doesn’t have any similar data though, just 10 x 7 ~ 12 x 6 prop sizes. !0 x 7 on three cells at a guess. But it does state specifically ‘Suitable for sport and scale airplanes weighing 20 to 30 ounces’. So for general sport flying with a hobbyzone super cub I think I might like to place this as a strong contender. With the greatest respect, I must admit I didn’t really understand Simon’s OP and even after a second scan I’m afraid I’m still rather unsure. But I tend to tinker about with this stuff a bit sideways anyway, for instance I might check the motor current with a contact thermometer, as in if it’s getting too hot the current is too high; and if the max current is given as xx amps and there is no qualifying time limit then I’d consider that is most likely going to mean xx amps rated for an indefinite time; or to re-phrase perhaps, max amps are constant amps. Maybe the trusty thermometer might come into play here again, too, t’would soon prove the issue. But I’m not going there much anyway, as I’m always looking to reduce the amps if possible; I’ve never been a great believer in ‘the more amps the better’. But still maintaining or bettering the same performance, of course. As I’ve said before, I get the tacho out most frequently*!?; nowadays; this gives me the best clues… but that’s just me. Lots of ways to get confused on this electrickerty topic… PB

Simon, You may care to check out this for size, actually this motor does come with a few different kV rating so you may be able to fine tune if you wish. This result was the result of a quick Google and a spot of substitution, took all of five minutes. I’d absolutely agree with PatMc too, as far as starting from scratch is concerned. Very straightforward, the result of a lot of practical experience, I reckon. Why not make up a few hypothetical model examples and then find suitable power trains? Checking out some of the advertised planes and comparing which various items, batteries, ESCs and motors etc., are used might be a starting point. Good Luck! PB Edited By Peter Beeney on 15/09/2016 15:25:19

Kim, I’m sure it's quite in order to use any prop you choose, but it might be a plan to stay within the specifications……as per your OP. Actually, there would appear to be something of a little anomaly in there, too, why the significant discrepancy when using the recommended size propeller? I think that warrants a second coat of looking at; although a 16 x 10 does seem to me to be a trifle on the tall side anyway for that motor anyway, it would definitely not be my choice to start with. The max watts at 1440 equates to around 1.9 BHP, roughly the same as a 60 i/c engine. The engine develops this power, at the crankshaft, on a 11 x 7 or 12 x 6 prop at maybe 12000rpm plus. It really does seem to be asking a bit much for an electric motor to do the same on a 16 x 10… I’ve always thought that prop efficiency is generally fairly linear across the range, but it does improve as they get bigger up toward full size, I believe, and dropping off very rapidly as they get very small. Certainly, though, if any inefficiency results in a greater current flow the duration may suffer. You may well be right regarding the prop power and speed, but in my view the correlation between the power output at the prop shaft and the wattmeter measuring the battery output is not always that straightforward; so it may be difficult to gauge. To reduce the speed the ESC reduces the voltage, therefore if half throttle equates to half revs on your ESC, which is highly likely, then that’s half voltage, equivalent to a 3S pack. As it so happens, here the power output would be reduced by a factor of four, if, say, on 6S the current flow was 50 amps and the voltage 20 volts then 50 x 20 = 1000 watts. At half speed the current flow would be 25 amps and the voltage 10 volts, 25 x 10 = 250 watts, thus the power is reduced to one quarter. I’ve never owned a wattmeter; in the past I used a clamp meter and a contact thermometer plus a tachometer, but nowadays I seem to getaway ok with just using the tacho. I can estimate from the difference in revs how a particular model is going to perform on any one particular prop, and as I’m invariably going for the fastest turning prop anyway it soon becomes a one prop choice; and if using the same set up on a different model I’d know which prop to use from experience. As always, just my view… PB

Yes, very sorry about that Max, it just seemed rather obvious to me at the time that a larger prop would naturally be an increased load. I think that perhaps what I was trying to say, too, was that a bigger prop, or a heavier load, was not always necessarily the best way to go. Perhaps another way of phrasing it would be to say that the current flow is exactly proportional to the revs per minute; if the rpm’s are reduced by increasing the load the current flow will rise by the exact same proportional amount. I did mention the prop unloading in the air as well, but I guess that unless you have a telemetry function this is going to be a bit of an unknown quantity; also there could be some prop slip to take into account as well, although this might rather affect the model’s airspeed. My post was overall just a general guesstimate anyway; no more than my own view and might not always be that accurate; but as Steve says, ‘.....the theory often doesn't work out in practise.’ I also referred briefly to the flying characteristics of the model, but coupled to that possibly the pilot may also want the model to fly in a certain manner or style too. So if the motor was excessively loaded to enable it to fly very slowly say, then some duration of flight time might have to be sacrificed. PB

Kim. With the greatest respect of of course, and I’m only trying to be a little helpful here, but I think your possible tiny flaw @20:28:03 is in your statement: ‘but common sense would suggest that the speed will creep up a bit, therefore increasing the power consumed,’. I have to say that I think that if the prop speeds up the current flow will reduce, but the power output, at the motor drive shaft, will stay the same. But because the current flow has reduced the power supply from the battery will decrease by the same amount. It’s all to do with how the motor functions. The short explanation is that the power output from the battery is not always the same as the power output at the prop drive shaft. I reckon Steve has the best solution, poke and hope until you get the right result. Playing with Max’s nicely succinct figures for a moment, the 14 x 10 prop will result in a speed of 74mph. The 16 x 8 = 55mph and the 17x 8 equals 54mph. So between the first and second two props we appear to have something like a 26% decrease in speed for a 25% increase in power consumption. I’m not quite sure this is what we really want. This is all up in the air fag packet stuff, so to speak, the motor will unload in the air and reduce the current flow further for a start, but this is mostly the gist of it. We are operating permanent magnet motors and the torque, current flow and revs are all inexorably linked together, when one changes they all change. If we change the applied voltage or the load value this will also change the running conditions. It also now becomes clear from the figures that as the revs decrease the current flow goes up. Also it depends to some extent on the flying characteristics of the model, but I’d expect the Wot4 to be fairly agile, thus it would require a good forward speed. I think I’d start with the 14 x 10 and then maybe try a 13 x 10; it’s possible that the increased prop speed may give you around the same sort of urge but with a slightly increased flying time per battery. Or, in other words, the motor is operating more efficiently. Hope this is of some use… PB

Having just caught up with this thread, I think the Skyleader transmitter was configured so that when the battery switch was off the two 4 cell packs were connected together in parallel and when it was switched on they were wired in series. I never knew the confirmed reason for this but I always strongly suspected it was simply for charging purposes. The standard Skyleader charger was a dual purpose unit, with both a mains and a 12V input; and when this was connected to a car battery the input voltage was exactly that,12 volts with maybe plus a few ticks, but probably not very much more than 12.5 volts generally. This is not high enough to properly charge an 8 cell nickel pack, particularly as the circuit included diodes etc. which will only reduce the voltage still further; so the transmitter packs were always charged in parallel. I’d reckon that at least a 15 volt supply would be more useful, and even better still, perhaps, 20V. Not that easy to come by on the flying field, though. If the corrosion is fairly extensive I think I would feel the need to examine the PCBs etc. very carefully indeed. In my experience this stuff goes just about everywhere over time. I once checked out a second hand model that had been hanging up in a model shop for maybe a year or so, that one was easy, most of the metal in the circuit had disappeared. Also, almost accidentally, once upon a time I discovered that even when a piece of wire is completely detached if the corrosion has started it will just carry on destroying itself. And remarkably quickly, indeed. Phil Ramsey was, as I remember it anyway, also a member of the Skyleader team back in day, too. And from memory again, although now a bit dim, the RF meter only every read max or off, usually not a lot in between. So I’m not sure if that was really ever very much use, anyway. Only intended to be just casual info. really… PB

bees, Just chipping in here, and with great respect, think you may well be right about about the damaged soldering iron tip, if as I suspect it’s a conventional copper/iron plated variety then it’s perhaps not a very good idea to take a piece of sandpaper to it! The considered way to clean it is by wiping it on a piece of damp sponge from time to time and then re-tinning, but I often just use a piece of paper towel, if the tip does become very corroded then the only answer is probably a new one… I also have a pot of extra flux handy as well, I’ve used Powerflow for a lifetime and so far I’ve never had any grief from this; and sometimes this can make all the difference between a good joint and an excellent one! I’ve used a small blowtorch for many years on jobs such as piano wire undercarriage legs, this is a relic from work, that’s way back in the dim and distant now, a Primus bottle hired from builders merchants for plumbers. Travis Perkins will still change the bottles ok; and it’s possible to obtain a variety of nozzles to fit the spout. This really does make short work of this type of heavier soldering, indeed caution sometimes needs to be exercised not to overheat, so maybe it might be worth investing in one of the butane gas torches now available, although I’ve not much idea of the prices. Hope this is of some use… PB

Re. the fuel attacking the brass tubes within the fuel tank, it’s actually the methanol that is the culprit. This has been featured on the forum before. It happened to me many years ago and at the time I didn’t fully understand the reasons because I’d done a fair bit of of control line previously with all it’s associated homemade tin plate type tanks and brass tubes, that was always ok, but it soon occurred to me that the fuel is different; I was was playing with diesels then and their fuel is a mixture of oil, paraffin and ether, with a sprinkling of amyl nitrite or some such other exotic substance to taste. When I started to look into it I gathered the big users of methanol, such as dragsters etc., always replaced any brass components in the fuel system with items made from other materials first, usually stainless steel or similar, for this very reason. It was also difficult not to suspect that it had to be the methanol causing this anyway because I’ve always only ever used straight fuel, other than for some four stokes… I replaced mine with copper tube and this has never been been affected by the fuel, but I have read that in theory at least, methanol can occasionally cause copper and aluminium some grief, too. In my case the tube inside the tank had swollen up and split open, and it was a new model, from memory it happened over weeks/months rather than years. So, by and large, I would avoid using brass tube, (or what passes for brass tube these days), in any fuel tanks using methanol… PB