Dave Hopkin
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Everything posted by Dave Hopkin
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Posted by John Lee on 13/03/2018 19:42:20: Posted by Dave Hopkin on 13/03/2018 18:32:46: As a kid I used Nylon and Dope, is there any fabric on sale that heat shrinks that's not aimed at the modelling market, is there a specfic "breed" of polyester that will shrink under an iron?? As Don says there is Lightweight Ceconite, 66inch wide £6.26 a yard. Link Well ordered 3m of the Ultralight Ceconite - hefty postage charges so we will see.....
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Posted by Don Fry on 13/03/2018 18:39:36: Dave, economise on eating, buy the Oratex. You know it makes sense. The airframe is worth it. Care to explain that one to SWMBO? I'll have the ambulance and blood transfusion people on standby Edited By Dave Hopkin on 13/03/2018 18:46:47
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......But sooner or later the stocks of Tex will be sold and there will be no more, Oratex is available but costly What alternative fabrics are there to use As a kid I used Nylon and Dope, is there any fabric on sale that heat shrinks that's not aimed at the modelling market, is there a specfic "breed" of polyester that will shrink under an iron??
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Balsa & Ply Alternative to Max Thrust Riot
Dave Hopkin replied to Kim Taylor's topic in Trainer kits
Segull E-Pioneer perhaps? -
Rule of thumb - motor weight v power capability
Dave Hopkin replied to Geoff S's topic in General Electric Flight Chat
Posted by Gary Manuel on 11/03/2018 23:09:30: Posted by Dave Hopkin on 11/03/2018 22:00:13: Posted by Geoff Sleath on 11/03/2018 21:56:24: Power is proportional to the voltage squared (and current squared for that matter). I am not quite sure Mr Ohm actually said that, P = I x V Geoff is quite right, and I'm sure that Mr Ohm would agree that for a given resistance: P = I^2 R P = V^2 / R Easily obtained from Ohms law. V = I x R I = V / R P = I x V = I x (I x R) = I^2 R P = I x V = (V / R) x V = V^2 / R QE As I said V^2 is not a valid calculation as it ignores the "Divide by R" as you showed above particularly so as we are dealing with AC motors where Inductive Resistance is not a static value but changes with loading For a given Voltage the current will change dramatically as I increase the loading (ie the prop) and electrical power will increase -
Rule of thumb - motor weight v power capability
Dave Hopkin replied to Geoff S's topic in General Electric Flight Chat
Posted by Geoff Sleath on 11/03/2018 21:56:24: Power is proportional to the voltage squared (and current squared for that matter). I am not quite sure Mr Ohm actually said that, P = I x V -
Another option for Electric is the Gangster Lite by Mick Reeves laser cut kit - its the classic IC Gangster redesigned for Electric Scroll down about 2/3rds the way down the page https://www.mickreevesmodels.co.uk/~mickreev/other/p5kits.htm Edited By Dave Hopkin on 11/03/2018 08:31:42
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Yes... another ESC question!
Dave Hopkin replied to brokenenglish's topic in ESCs (Speed Controllers)
Posted by brokenenglish on 05/03/2018 21:07:19: and a very wise gentleman "Ollie P" wrote "If you're not sure of what you're doing, remove the prop first!!!". Personally I tend to think "the more you think you know what you are doing the more reason to remove the prop before tinkering" -
So if you want to see a grown man reduced to a so totally a seething rage by the misuse of English... When my 20 year old daughter shrugs and says "whatever" in THAT tone of voice #fumingoldfart Edited By Dave Hopkin on 02/03/2018 20:57:26
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And now for something completely different
Dave Hopkin replied to Biggles' Elder Brother - Moderator's topic in Helicopters
And here was me thinking you would be completing Mrs BEB's boat you started eons ago -
Building Jim Newberrys Puddleduck
Dave Hopkin replied to Dwain Dibley.'s topic in Build Blogs and Kit Reviews
Posted by Geoff Sleath on 02/03/2018 16:38:50: Funnily enough I've been looking at one of those XT60 surface mount units just about an hour ago and can't decide how it's supposed to work. Do you just glue the connector in? Because there doesn't seem to be any positive mechanical fixing and a fair bit of force is needed both to connect and disconnect XT60s. Good idea to fit the plug to a motor connection, Dave. I'll have a think about that because one of the advantages will be that you aren't going to be flexing the connection every time you replace the main battery. I've never bothered with an arming plug before because all the conversions I've done before have easy and quick access to the battery through a top hatch. I'm intending to fit one to the Moth as the battery hatch is less accessible than on my other conversions as it's on the bottom. (I'm just making a hatch). Geoff I prefer to use bullets as an arming plug - on this model the motor, esc and battery slide out through the cowl in one lump, so the arming plug had to be in a small hatch on the underside where the motor tray retaining bolts fit. -
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Building Jim Newberrys Puddleduck
Dave Hopkin replied to Dwain Dibley.'s topic in Build Blogs and Kit Reviews
a softer option for an arming plug is to put the plug on one of the motor wires, so if it attempts to start it will only judder and not run, the benefits of this is you can test all the other control surfaces with a disabled motor -
Ronseal Diamond Hard Floor Varnish is what this one was pained with
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A pedants joke.... Knock Knock Who's There No! Whom is there
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I hurl abuse at the telly when I hear people responding to a question starting with the word "So...."
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Posted by Old Geezer on 26/02/2018 15:53:17: Regarding Johnnie Foreigner - Quote Unquote on R4Extra this morning - attributed to a now deceased member of the Royal Family just back from a Royal Tour: ( I paraphrase ) "Abroad is absolutely awful, and full of nobody but bloody foreigners" Sounds suspiciously like a "Phil the Greek-ism" that one....... mind you for a Greek Matelot he married well...
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In terms of T'Interweb "Store" is the accepted term for an on-line shopping portal (as in Appstore) so I would suggest it is appropriate and since this thread is entitled "pedantic" then I feel justified in pointing out the origin of the word is old french.... Middle English: shortening of Old French estore (noun), estorer (verb), from Latin instaurare ‘renew’; compare with restore.
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The Vintage Aviator is a replica aircraft manufacturer that has created many WW1 aircraft to exacting standards as I am sure many of you already know, I recently contacted them asking for some specific details and they sent me a link to the photo collection of their official photographer James Fahey There are some fabulously detailed photos of all sorts of mouth watering subjects here.... **LINK** The Vintage Aviators web site is here **LINK** If you are into WW1 string bags its well worth a look!!!!
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The intention was not to scare you, but without details of the plane its an impossible question to answer and rather than just ignore you I was trying to illustrate the variables if the plane is 800g then you will be looking for around 150Watts To get 150 Watts from a 3S lipo then you will be pulling around 12 Amps max - so say 6 Amps average So your 1000Mah lipo will give you around 5 minutes flying time - give or take So its a reasonable set up so far What motor and prop have you ordered?
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There are many factors that affect "which battery" There is the question of size and weight - the bigger the battery the bigger and heavier it gets - obviously in any model there is a physical limit to the dimensions of the battery, there is also the question of weight - the Lipo is one of the heaviest things in the model so it will have a dramatic effect on balance - in most models the battery needs to go as far in front of the desired CoG as possible to avoid having to add (dead) weight to balance it - most people if they need more weight up front use a bigger capacity battery rather than lead Secondly there are the electrical questions? Duration of your flight and the ability of the battery to supply the current demanded by the motor/prop combo To estimate duration we need to know the current drain - that can be established roughly by taking a reading of the amperage at half throttle - divide the battery capacity by the current drain and yo have a rough estimate of duration of flight - the bigger the capacity the long the flight The current draw by the motor will vary with the prop you fit, a small one will use less current but provide less thrust, a larger one will give more thrust but use more current So where do you start???? We have a 3S 1500 Battery - you have ordered the motor, esc and prop - so when those arrive the best thing is to set up a test bed - fix the motor to a lump of wood (not balsa) and shove it in a vice- connect up the radio and bing in the ESC and test the motor WITHOUT the prop, you will need a WATT METER to check the current draw is below the ESC Rating with the motor running- now fix the prop and again read the current - it will have jumped up a LOT.... make sure that at full throttle there is still at least 15% headroom between max current drawn by the motor and the ESC rating As a rough (very) guide to power you will need (ish) at least 100 Watts per Lb of model for a typical training/sports model If you motor/prop/battery combo gives at least that - then great, if not one of them has to be changed
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Without vanishing down a rabbit hole of aerodynamic theory For practical design look at aircraft that fly they all have different design objective like heavy lift, STOL, pure speed, endurance, aerobatics etc etc - so that I would suggest would be a starting point "what sort of aircraft do you want?" Once you answer that question then look at full sized aircraft with the same design objective (that worked!) and look at what makes them successful in that role - use that as a starting point The decide how big you want your model think about things like storage, transporting it, power its liable to need - roughly similar models can give you a guide as to possible weights and power requirements So by now you have some rough parameters that will limit your design
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At the risk of going off-topic... I saw an advert for the new leaf and it said it only ha ONE pedal how the hell does that work.............. emergency braking????
