ken anderson. Posted March 17, 2020 Share Posted March 17, 2020 nice model Raymond,well done.. ken anderson...ne..1...admiration dept. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 17, 2020 Share Posted March 17, 2020 Looks great. Just starting mine. Where did you get those pilots from? Quote Link to comment Share on other sites More sharing options...
Raymond Richards Posted March 18, 2020 Share Posted March 18, 2020 Hi Martin, got them from **LINK** 1/15th scale, they will make them for you if you drop them a mail and let them know what you want. I went for unpainted , but they will paint them for you too Good luck Ray Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 18, 2020 Share Posted March 18, 2020 Thanks for that, I shall take a look. Quote Link to comment Share on other sites More sharing options...
Dickw Posted March 18, 2020 Share Posted March 18, 2020 I also got mine from Real Model Pilots at 1/12 scale for my Gnat, but went for the painted version. They did a really nice job of painting - most impressed. Dick Quote Link to comment Share on other sites More sharing options...
Steve Jones 2 Posted March 18, 2020 Share Posted March 18, 2020 Yep - I went for the unpainted ones which did not take to much to colour up.. will use them again.. Great Model Ray, Good luck with the Maiden... Steve Edited By Steve Jones 2 on 18/03/2020 12:35:05 Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 18, 2020 Share Posted March 18, 2020 Which ones exactly did you go for please? Quote Link to comment Share on other sites More sharing options...
Raymond Richards Posted March 18, 2020 Share Posted March 18, 2020 Hi Martin, I just e-mailed them and mentioned the TN Provost and the scale of 1/15th and they did the rest. They are familiar with the pilots for this aeroplane. Hope this helps Ray Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 18, 2020 Share Posted March 18, 2020 OK. Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted March 18, 2020 Share Posted March 18, 2020 Martin, “4107 1/15 unpainted bust. “ is how it was invoiced. 4107 is the item number on their website. Tim Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 26, 2020 Share Posted March 26, 2020 Just had a look. Pilots are OK but no way am I paying £5.30 for shipping a few grams. Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted March 27, 2020 Share Posted March 27, 2020 Thought I’d use the home time to see if I can get my gnat sorted. I bought a 3S FMS fan and a replacement 4S fan to try. I thought I’d test thrust before installing them so made up a rig and thrust tube as per the drawings. the 3 S fan gave 540g thrust with the thrust tube and 620g without it, unfortunately it decided to shed its blades whilst at pretty much full speed, quite an interesting experience i then put the 4S fan onto the rig and measured 750g with the thrust tube and 880g without it, does anyone know why having no thrust tube increases thrust, I thought the whole point of a thrust tube was to accelerate the air and create more thrust ? Any one any ideas ? now got to try and perform surgery on the gnat and swap the fans over, it looking forward to that. It it’s the only way I’m going to see if I just have a low power fan in the plane at the moment, best thrust on a 4S with the original fan in the plane is ~470 g Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 27, 2020 Share Posted March 27, 2020 Years ago I tried to make model by P.E. Norman, son of Marcus the DF guru, and contacted him about it. Evidently the intake/efflux ratio is critical and he sent me their experimental data which of course I do not have now. I never did sum up the courage to run my home made 5" fan on a K&B pylon 40 motor. There is a YT video on here somewhere of a guy experimenting with efflux dia. v EDF dia. It would seem from that that Tony`s are the best compromise, in fact the efflux could not be any larger on the models and still keep them near scale. I have read that these are ballistic anyway, so why fit a 4s? You will reduce flight times and need to take a change of underwear. Interesting that yours shed its blades. You were not running a 3s on 4s were you? All of the ones I have were tested by just holding in my hand. All OK until the latest for my JP which burned my fingers. I must have distorted the case a bit because I could see where the blades had touched. Other than a scuff mark it seems fine now. Not that there is any rush with flying banned but I have been waiting ages for the mouldings and some tissue covering, no doubt due to the shortage of staff/couriers at the moment. Can get no further until these arrive. Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted March 27, 2020 Share Posted March 27, 2020 Hi Martin, yes it was definitely only a 3 S I was using and I’d successfully spun it up to full speed about a dozen times before it failed. I went 4S as I saw quite a few people having issues with the provost, seems mainly solved in the end by losing weight and adding extra cheat holes so thought 4 S would be fine and I could always limit the throttle travel if it’s crazy fast. I did see some of the articles on edf dia Vs eflux dia, not that I fully understand them all but it just seemed really strange that thrust increased by so much without a thrust tube, as if the tube was actually constricting airflow with maybe back pressure impacting the fan. Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted March 27, 2020 Share Posted March 27, 2020 Barry, it is now many years since I finished in the aircraft industry and jet propulsion in particular. So with the huge caveat that there is a huge scale effect involved which generally makes small scale less efficient.... First thing is that thrust is made up of change in momentum of the air flow and the difference in static pressure at exit multiplied by the exit area ( there is also a drag associated with intake flow but I will ignore that). If you push air down a convergent tube it will increase the speed and reduce the static pressure. There is an optimum balance to be had between the increased momentum and loss in static pressure. So one thing early to note is that engines generally have jet pipes and nozzles. The jet pipe is really just a means of getting from the engine to the nozzle. The longer it is the less efficient it is. What we really have in our small scale gnat is just a long jet pipe . I have never undertaken measurements at this scale so I am just guessing that the jet pipe gives more losses than any marginal increase in momentum. I guess the thing to remember is that all the input energy is in the fan , after that you simply exchange one form of energy for another. If it is an inefficient exchange you will loose out. Just ramblings of an old engineer . At this scale You really need measurements to find the sweet spot. Tim Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 27, 2020 Share Posted March 27, 2020 Don`t know if you have looked at my Gnat but in the pics you will see a small restrictor added at the outlet. This was to give it a more jet like sound but you can actually hear the fan speed up as well. I have not tried to take any thrust measurements with or without this. Try sticking your finger up the back end and you will see what I mean. Quote Link to comment Share on other sites More sharing options...
Jack Petrie Posted March 27, 2020 Share Posted March 27, 2020 I am currently building the Jet Provost and have a question about the build; when you cut the bottom sheeting to fit the wing, how do you fit the flat sheet back up the bottom of the dihedral wing, is it scraps of wood glued in to fit the shape after the top of the wing is glued to the fuselage? thanks! Jack Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 27, 2020 Share Posted March 27, 2020 The build pics seem to show that piece left on when cutting the fus sides but it would not be practical. I am going to glue on the wing, add the scraps to fill in and only then sheet the bottom in one piece. Quote Link to comment Share on other sites More sharing options...
Geoff Gardiner Posted March 28, 2020 Share Posted March 28, 2020 I glued the bottom sheeting to the wing and then filled in the gaps after: Quote Link to comment Share on other sites More sharing options...
Jack Petrie Posted March 28, 2020 Share Posted March 28, 2020 Okay thanks so I effectively glue down the sheeting at the trailing edge best I can and then fill in the gaps at the leading edge with strips of balsa? Quote Link to comment Share on other sites More sharing options...
Geoff Gardiner Posted March 28, 2020 Share Posted March 28, 2020 Yep, that's what I did. Seems to have worked OK. Make sure the edges are secure - the middle is cut out for the cheat hole: Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted March 31, 2020 Share Posted March 31, 2020 Finished the surgery on the gnat, I swapped the blades from one of the 4S fans to the 3S unit and installed that into the gnat. Getting 520g thrust and 50g lighter with using a 3S battery so hoping that when we are able to get out it’ll fly at last. In the meantime I’ve starting building the phantom Quote Link to comment Share on other sites More sharing options...
Lucas Hofman Posted March 31, 2020 Share Posted March 31, 2020 Anybody used tape hinges instead of fuzzy one's? The stabilers/elevators/ailerons are thin, and it is then easier to bevel one side and fix them with tape. Any opinions on whether this is good or not? Lucas Quote Link to comment Share on other sites More sharing options...
Trevor Crook Posted March 31, 2020 Share Posted March 31, 2020 I used film hinges on my Provost. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted March 31, 2020 Share Posted March 31, 2020 Mine is now nearly ready for spraying but have not yet made the launching handle. Is this really needed? Quote Link to comment Share on other sites More sharing options...
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