Alan Jarvis Posted November 6, 2014 Share Posted November 6, 2014 Martin It appears so, they are 55mm O/D. I had to make the holes in the fuse bigger. Due to the fact there was no stock in the Hobbyking UK warehouse I ordered them from the EU warehouse and was surprised when they came with a "DrMadThrust" label although they have the 5 blade fan. Have been debating how to finish the model but have bought the Easycoat suggested by Tony N and paint it. I was hoping to find a covering in Nato grey. With so many people building warbirds I am surprised I couldn't find any of any make. It would also have been handy to find the green colour covering and then just paint the grey on. Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted November 6, 2014 Share Posted November 6, 2014 Posted by PeterF on 02/11/2014 09:25:19: Techincally 4 x 50mm fans = 100mm fan because it is the area (diameter sqaured) that is important not the diameter. Additionally, 50mm fans tend to have a relatively larger motor sat in the middle than a 100mm fan, hence more area is obscured and the free flow area of the fan is even less on a proportionate basis. Odd - I always thought that the area of a circle was π r2 Quote Link to comment Share on other sites More sharing options...
Alan Jarvis Posted November 6, 2014 Share Posted November 6, 2014 Here are some readings: I thought I had a power 'Y' lead but can't find it so I put the Watt Meter on each side in turn using a cheap Hobbyking 3s 2200 35c. Starboard side which runs the two centre fans. 256.3 watts 22.79 amps Port side which runs the two outer fans. 250.7 watts 22.29 amps TOTAL 507 watts 45.8 amps. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted November 6, 2014 Share Posted November 6, 2014 Peter F. is correct. A 100mm dia. fan has an area of 7855 sq.mm which is exactly the same as 4x 50mm dia. ones if you work it out. Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted November 6, 2014 Share Posted November 6, 2014 Oh I'm not arguing the area - just the formula stated (diameter squared instead of π r2) Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 6, 2014 Share Posted November 6, 2014 Hi Daithi, caught me out at first as well. It doesn't compromise the principle of Pi r2, it's the basic rule that if you double the size of something the area increases by the square and the volume by the cube. Square shape or circle, the rule stays the same. Made me scratch my head at first though. Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted November 6, 2014 Share Posted November 6, 2014 As I said, I'm not arguing the fact that 4 50 mm circles are the same area as one 100 mm one - it's the actual area calculation that's wrong. Using π r2 50 mm fan = 1963 square mm Using diamater 2 50 mm fan = 2500 square mm Quote Link to comment Share on other sites More sharing options...
PeterF Posted November 6, 2014 Share Posted November 6, 2014 The area of a circle is also calculated from the formula A = 1/4 π d2 because r = d/2 so r2= 1/4 d2 QED Diameter squared is the important factor as is equally radius squared, I could as easily have stated that. Radius and diameter are linear dimensions, the important factor is square dimensions, when comparing things relatively you do not need to both which it being radius or diameter or even with the pi. PeterF Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted November 6, 2014 Share Posted November 6, 2014 All I'm saying is that d2 is NOT the same as π r2. Quote Link to comment Share on other sites More sharing options...
PeterF Posted November 6, 2014 Share Posted November 6, 2014 Posted by Daithi O Buitigh on 06/11/2014 21:40:59: All I'm saying is that d2 is NOT the same as π r2. Of course it is not, but I never said it was, the issue was someone said 4 x 50mm fans was the same as 200mm fan. I said no it was diameter squared basis, 4 x 50 x 50 = 4 x 2,500 = 10,000 = 100 x 100 So 4 x 50mm fans has the same area as a 100mm fan, you do not need to worry about pick or the 1/4 factor as they appear on both sides of the equation, basic maths. Edited By PeterF on 06/11/2014 21:54:13 Edited By PeterF on 06/11/2014 21:54:49 Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted November 6, 2014 Share Posted November 6, 2014 "...it is the area (diameter sqaured) that is important not the diameter..." Quote Link to comment Share on other sites More sharing options...
PeterF Posted November 7, 2014 Share Posted November 7, 2014 I see, you have taken the statement literally, it does not mean that the equation for area of a circle is diameter squared but that the area is just a function of diameter and if you are doing a comparison of different circular objects on an area basis you only need work of the square of a characteristic linear dimension, you do not have to calculate the actual area as I showed above. Quote Link to comment Share on other sites More sharing options...
Alan Jarvis Posted November 11, 2014 Share Posted November 11, 2014 Just been looking for decals for the Vulcan and the ones suggested from Pyramid Models are over £30 inc postage. They may well be top of the range and good quality but there is no way I can justify spending that amount of money. They are not exactly complex or even many of them. Anyone have any ideas for doing them cheaper. Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted November 11, 2014 Share Posted November 11, 2014 http://www.modelmarkings.com/ maybe able to do something for you? And I have a set from Pyramid on my Viggen, that have already started to peel she's not even been flown yet! Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted November 11, 2014 Share Posted November 11, 2014 I think I'll stick with an ink compass, masking tape and a fine brush (and Letraset) Quote Link to comment Share on other sites More sharing options...
Alan Jarvis Posted November 12, 2014 Share Posted November 12, 2014 Reply from model markings: [email protected] If you just want the 4 roundels and RAF Fin Flash that will be £4.99 plus £1.50 postage. Sounds good. Quote Link to comment Share on other sites More sharing options...
Glenn Philbrick Posted November 14, 2014 Share Posted November 14, 2014 Spent a very interesting evening in the shed last night trying to make the thrust tubes. I used the template that Craig very kindly had worked out only to find that my tubes were too narrow, on measuring my fans I discovered they were 55mm, no wonder I had to relieve some of the wood from the holes into which they will fit. If anybody else has these fans the measurements are 19mm at wide end and 16 mm at the narrow end. I have used encapsulating film and thought the the tubes are quite flimsy so as a trial I put some through the encapsulater to see if heating them would stiffen it up, what I had not taken into account at this time is of course the heat sensitive adhesive, yes the film went round the rollers so I had a nice mess to sort out. That then got me thinking so some experiments with my covering iron and it is quite easy to join the tubes using this so there is no need to mess about with tape on a broom handle just iron the join together. I found some 40mm plastic drain pipe and this helps a lot in trying to make these bits. Quote Link to comment Share on other sites More sharing options...
Craig Carr Posted November 14, 2014 Share Posted November 14, 2014 Posted by Glenn Philbrick on 14/11/2014 11:16:40: Spent a very interesting evening in the shed last night trying to make the thrust tubes. I used the template that Craig very kindly had worked out only to find that my tubes were too narrow, on measuring my fans I discovered they were 55mm, no wonder I had to relieve some of the wood from the holes into which they will fit. If anybody else has these fans the measurements are 19mm at wide end and 16 mm at the narrow end. I have used encapsulating film and thought the the tubes are quite flimsy so as a trial I put some through the encapsulater to see if heating them would stiffen it up, what I had not taken into account at this time is of course the heat sensitive adhesive, yes the film went round the rollers so I had a nice mess to sort out. That then got me thinking so some experiments with my covering iron and it is quite easy to join the tubes using this so there is no need to mess about with tape on a broom handle just iron the join together. I found some 40mm plastic drain pipe and this helps a lot in trying to make these bits. Hello Glenn, That's exactly how I did it in the end. Bet you found you have to have the covering iron at just the right temperature and not leave it in one place for too long or the tube "crumples" and loses its shape. Also like you a broom shank was too narrow so I too used some 40mm plastic waste pipe which is just about the right curvature to stop the film distorting. If you eyeball up the tube you can see where the laminating adhesive has stuck. "Belts and braces" I also stuck a half inch wide length of "cross weave" tape along the join. Ive also brought the 40mm waste pipe back into action to slide through the tube to stop it distorting as I drilled a round hole through the cross weave tape for the motor wires. I think a round hole is better than just cutting open a square in the tube as a square hole is more likely to fracture /split at the corners Quote Link to comment Share on other sites More sharing options...
Glenn Philbrick Posted November 14, 2014 Share Posted November 14, 2014 Hello Craig. This is really spooky. I have also used cross weave tape to reinforce the tubes as you can see from the pics I have attached. You have also answered the nest question which was how to configure the holes to get the wiring through. I am waiting now for my speed controller to turn up from Hobby King, they are out of stock of the 25A. I also fancy putting lights on mine but not retracts as I think it would take too much battery energy to get it off our grass strip. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted November 14, 2014 Share Posted November 14, 2014 Wow, those tubes look great, much better than my effort. Just got the servo bearers fitted and am working on the retract and servo surrounds prior to sheeting the wing undersides. The wings will then be glued to the fus. and a thrust check done. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted November 16, 2014 Share Posted November 16, 2014 Got a problem now. The first pic shows the model as it stands with no fin, control surfaces, underbelly cowl or covering etc. The weight is 67oz! 4lb 3oz. The stated AUW is 3.5lbs. I have carefully selected the materials as usual so is 3.5 correct inc. batts? Also, I have done static thrust tests and the results, either on its wheels or suspended on the balance are only 29oz of pull. The motors draw 54A between them so there is no problem with those. Remember that the fan bodies have been shimmed to improve efficiency. What sort of weight is everyone else achieving? Quote Link to comment Share on other sites More sharing options...
Glenn Philbrick Posted November 17, 2014 Share Posted November 17, 2014 Hi Martin. I am nowhere near to being at the same stage as you are. It does sound as if something is amiss as you have come out a lot heavier than suggested. I only hope you do find more thrust as at this power to weight ratio I doubt it will get off the ground. I am certainly not building mine with retracts and will look to save weight as much as possible throughout the build. I have tried my fans on the bench as was quite impressed with the amount of air they shifted. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted November 17, 2014 Share Posted November 17, 2014 Hi Glen, I am wondering if the quoted weight is for the pusher version. This would seem more likely. There is nothing extra on mine which could account for it otherwise. The very much reduced thrust with the motors installed as opposed to that obtained individually is worrying. Even with the intake ducts and short efflux tubes fitted I cannot see a huge difference being made. I used the same digital balance to measure both. Perhaps Tony could come in here and enlighten me? Quote Link to comment Share on other sites More sharing options...
Martin Rowe 1 Posted November 17, 2014 Share Posted November 17, 2014 I have to say, I am not surprised. on mine I have a cone for a thrust tube, this is not good for a turbine. I also wonder how much area the air intake is compared to two fans. Did you do your thrust test with the tubes in place? You could try smoothing the edges out on the inlet and see if that helps. Edited By Martin Rowe 1 on 17/11/2014 20:27:19 Quote Link to comment Share on other sites More sharing options...
Tony Bennett Posted November 17, 2014 Share Posted November 17, 2014 there looks to be lots of ply in there that is just pushing the weight up. lovely looking aircraft though, nicely built. Quote Link to comment Share on other sites More sharing options...
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