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Jeffrey Cottrell 2

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Jeffrey Cottrell 2 last won the day on February 16 2022

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  1. Hi Guys Masher Can't seem to find this post on the forum. can you confirm date? Brian If this is right, can you confirm if it was from the Colin Usher plan on Outerzone? Thanks jeff
  2. Hi Guys, thanks for your thoughts Andy Planning on using a spare OS40FP, so it won't be underpowered. If it turns out to be marginal I do have alternatives up to an Irvine 53. That should scare the horses. Also, I won't be using the build structure as per plan. Seems over engineered to me so there's plenty of scope for weight reduction. We'll see. Pat Double checked the decalage both on the plan and on the screen, and they both still show some negative. Bit of a puzzle, but doesn't really matter since I will be changing it all anyway. If you look at the bottom right hand of page 2 of the plan, you will see it titled 'Killer Watt' which is in fact the clone of an AcroWot, not the Wot4. Also if you read the text on Outerzone, you will see numerous issues, especially with the rib outlines. I am assuming the note on washout only refers to the tapered wing, certainly can't see any purpose on a parallel chord wing. Page 1 is usable, but I have pretty much discarded page 2. When I start the build I will be incorporating 1 deg of positive, the reason being if that proves not to be necessary it will be easy to remove it. Meanwhile, although it will not be a quick build, I will be keeping a running total of costs, to see how it compares with a commercial kit. Should be an interesting comparison. Cheers Jeff
  3. Hi Brian. Thanks again for your help, much appreciated. I did the same check as you, putting a ruler across the plan on the screen. Bit difficult to tell on that small scale, but I did find the same down angle on the wing as on the plan. However, no matter, since I will be re-doing that section anyway. I think we are both heading towards the same conclusion, from different directions. Decision has been made to switch to a fully symmetrical section, probably by using the curve of the lower surface on the top as well. Not sure that qualifies as a recognised section, but it works on the TLAR principal. Only thing I would change is this. I see your point about setting it up zero-zero to start, but I would be inclined to have a small amount of positive, say a degree or so, at the start, on the basis that it would be easier to remove if necessary. Other than that, we are on the same page. Will let you know how it works out. Jeff
  4. Hi Brian Been re-reading your post. Lots of useful info, thanks for that, but it does leave me in a little bit of a quandary as to how to proceed. First of all, although I have decided to dispense with page 2 altogether and go my own way, I do notice that the rib shape as shown on that page is almost identical to the outline as shown on the fuz side view on page 1. Also the rib outline as shown is very similar the that on my Limbo Dancer. This has flown very well for some years now, but its flight envelope is different to that I would hope or a Wot4 lookalike. Rough measure says this is at 1/2 degree positive, which would indicate that a semi-symmetrical aerofoil does in fact still produce lift even at very low values of decalage. However it might also mean that this set up would produce a flight envelope very similar to the LD, which is not what I want. So, how to progress: First of all, go with the plan as is. That is with the semi-symmetrical aerofoil at its set negative decalage. Caveman has downloaded the same plan and his shows the decalage as zero-zero. I believe this might be due to a difference in printer characteristics, but certainly seems a better option to my amateur eye. So, second go with the section as shown but reduce decalage to zero-zero as above. Not sure this will give the the flight style I want. Third. switch to a symmetrical aerofoil. The plan states NACA 63018. I have had a look at this one on the computer, but it looks similar to the upper surface of the plan section, albeit with the max thickness a little further back. but also a distinct curve to the rear edges, unlike the flat rear on the plan section. This would make construction more difficult, though not impossible, but I wonder if it would be worth it given the whole plot is experimental anyway. Rough measure from the screen gives 18% thickness Note being symmetrical this would need a positive decalage to produce lift. Fourth, use a symmetrical aerofoill, but of my own design (ahem). Again this would need a positive decalage, possibly about 1 - 1.5 degree, but wouldn't be an issue at this stage. I produced an aerofoil using the lower section of the plan one duplicated for the top. Sort of TLAR system, but doesn't need too much modification of the fuz outline, and gives a 16% thickness, which looks about right. So, I guess my question would be 'where can I get a four sided coin' to make the decision. Anyway, your thoughts? Jeff
  5. Hi Guys, thanks J D 8 Quite right, the correct term would be decalage. My bad. Not sure what the designer was trying to achieve, but I've found so many issues with the plan I prefer to go my own way. Caveman Could be due to different printers producing different results, but since I will be working from my plans, will keep your diagram for info only. RottenRow Poorly drawn hardly describes it. If you look at the bottom right corner of page 2, it says 'Killer Watt' which is the clone version of the AcroWot not the Wot4. As such neither the span or the wing chord match with the fuselage on page 1. Also, as you say, 63018 is a symmetrical section, but the section shown on the plan definitely is not. All in all, page 2 is useless. I am using the wing section taken from the fuz side view on page 1, and designing my own structure.That is definitely semi-symmetrical so I wonder where the chord line should be, if not where I have it. All in all, confusion relgns. Jeff
  6. Hi Guys, quick question. Just about to start a build of a Watt Four (Wot4 clone) from the Colin Usher plan on Outerzone. As downloaded, the plan does have a number of discrepancies, most of which are described in the accompanying text. However I have come across a very basic oddity which I would like to resolve before cutting wood. So: Given this is a high wing sports model, I would expect the wing to be at a slight positive incidence compared with the tailplane. The wing incidence on my plan is in fact negative. Being a semi-symmetrical aerofoil, I have drawn a line from le centre to te centre and treated this a chord line for incidence purposes. On the plan, the tailplane is level with the fuz top, so using this line as a reference, the wing chord at the le is some 3mm lower than the te, i.e.negative incidence. First things first, am I measuring this correctly? Obviously easily corrected before I start, not so much half way through the build ! Could use some advice, thanks Jeff
  7. Hi Guys Apologies, I haven't posted for a while. Believe it or not, I've been thinking. When I first questioned the tank height I was measuring it from the carb to the centre line of the tank. The diagram Jon posted shows the carb level with the top of the tank, when full. Logical, I suppose, but in this case makes things even worse. So, I've come to the conclusion that this motor and model do not go together. Much appreciate all the ideas you guys have come up with, especially the chicken hopper tank and the carb tube extension, but I freely admit I have neither the expertise or the facilities to make these work. Couple of other things influenced the decision. First of all, although I did run the engine in the model, it never seemed very happy. Not surprised considering the tank issue. However, pulled the motor and run it on my test stand, and it ran so much better. Not familiar with 4 strokes, but 9,800 rpm on a 13 x 6 sounded pretty good. I mount my stand on a Workmate and the motor was trying to tow this across the field, so thrust is not a problem. Also, in my kit mountain I have a Dave Smith Models Smart Move. Perfect size for the ASP, and being a kit I can choose my own tank location. Sounds ideal, and means the motor won't go to waste. Win win. Meanwhile what to do with the current model. 53 mounted sidewinder is very much an option, but a root through my box of junk (er, useful spares) revealed an electric motor, esc and battery just made for the job. Decision made. Thanks again for all your help Jeff
  8. Hi Guys leccyflyer Thanks for that, good advice, but I would suggest probably only for parallel chord or slight taper. Think the steep taper on mine has more effect than you might think. My root chord is 340mm, so 28% would be 98mm. Even the manual, which generally errs on the safe side, suggests 105mm as start point. Going even further forward seems like a step back. Anyway, starting to get a clear idea of what I have to do. Thanks to everyone who contributed Jeff
  9. Hi Matty Good point, well taken. Thanks for explaining. Obvious really, when someone else points it out. Jeff
  10. Hi Guys, thanks Paul Not quite clear what you are suggesting here. What does 'work out the surface' mean? If you're suggesting 25% of the root chord, this comes out to 85mm. Maybe ok for straight wings but these are very sharply tapered, see photo. Even the manual suggests 105mm and this is probably conservative. Mike This is the one I use. Found it very handy over the years, but concerned that is has no provision for wings that have a sharp taper on the trailing edge. Can't be sure whether this is significant or not, but looking at the wing planform, that's a recipe for tip stall if I get it wrong. Matty That's the same as the one Mike suggested, albeit with a more complex interface. Can you point out where the provision is for TE taper? Thanks anyway for your thoughts, most welcome Jeff
  11. Hi Guys Do you have a favourite way to calculate c/g of a model? Reason I ask is I have bought a second hand model with sharply tapered wings on both LE and TE. I do have a program which will calculate c/g, but it seems to take little account of the TE taper when filing in the dimensions. I did manage to find part of the manual for the model, which shows a c/g position of 105mm from root LE. The model does have some marks on it which look like c/g position, but they are some 135mm back, quite a difference. So, I need to calculate a c/g position for myself. How would you do it? Thanks Jeff
  12. Hi Nigel Good thought, thanks, but I don't know how much it will help. The tank floor is only some 10mm above the u/c mounting plate, and also the captive nuts sit on top of the plate so it would need some sponge packing below the tank to prevent the nuts chafing on it. In all, I figure I could only lower it about 5mm, which wouldn't be much use. Haven't done much with the motor, apart from give it a good clean. Will be putting it on the test bench soon, give it a good wringing out. Have to decide on the way forward with the model first. Jeff
  13. Hi Guys Jon Thanks for your interest. Unfortunately, can't show the engine install. Last time out I had a mishap (not engine related) but broke the engine mount into several pieces. Have done a lash up with an old mount I had, but I had the cowl front as a guide, so I think it's pretty close. The outside view can be deceptive. Above the moulded section is a piece of 1/4 ply which the u/c bolts to, and then the tank floor is a framework some 10mm above that. The red line on the fuz is the tank floor. I have a 10oz one, some 50mm deep, so even without any foam padding under the tank, the centre line is some 25mm above the red line. With the tank full that puts the fuel level at some 45mm above carb centre. Clue for me was on one occasion, trying to start it, I got a jet of pure fuel upwards out of the carb. Sure indication something's wrong. Nigel That is interesting. Would have thought an 80 4stroke would be more powerful that a 53. Did find a sales picture here which suggests a 54 4 stroke. That would have been underpowered. Wonder if they meant 54 2 stroke. Either way, should be good if I decide to fit my Irvine instead. Thanks for that Appreciate all your help Jeff
  14. Hi Guys Hope you don't mind me joining the party, but I noticed a couple of posts which might help with an issue I have. I have started a thread here but long story short I have bought a second hand model with an ASP80 mounted inverted in it. The engine position is determined by the moulded cowl, and the tank position by the bottom of the g/f fuz. Trouble is, as installed the centre of the tank is some 25-30mm ABOVE the c/l of the carb, not helpful. Can't raise the engine enough without half the crankcase being above the fuz top, and can't lower the tank except by cutting away the lower fuz floor which would compromise the strength and also the u/c mount which bolts to it. Wondering whether a chicken hopper tank might be a solution. Your thoughts? Jeff
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