Pete D

1.  Island Hobbies   2.  Hobby King .com   3.  Century B25 Mitchell   4.  Horizon Hobbies

Thanks John, I will certainly take note of the metal gearing etc. you mention.   I think fom looking one of the Servo ads, that quoted torque, that I can probably over engineer the servos without too much size or weight penalty.  The problem in this respect is that normal shop ads do not quote a torque figure.   I sscrewed up one of the above figures,  the Rudder B figure of 12.43 N cm should read 1.4 N cm.  God knows where that came from and He ain't telling.   Anyway I will be checking the figures again to make sure and probable do some experiments hanging out of the car window or something but the figures so far seem to suggest we grossly overengineer most of the time with consequent weight penalties.

Using John's Electric Flight in Colerado servo calculator I managed to get the following for 2 speeds: A 50 MPH and B 60 MPH using a control throw of 20 deg from neutral. I think I will need to do some more calculations for a range of throws and speeds once I've figured what would be reasonable.   Rudder    A   1.4 oz-in,  1 N cm each,    for both  on one servo   2.7 oz-in, 1.9 N cm.                   B   2 oz-in,  12.43 N cm.                                                 3.8 oz-in,  2.75 N cm.   Elevator    A   3.8 oz-in,  2.7 N cm for one half,  full  7.5 oz-in, 5.4 N cm.                    B   5.4 oz-in, 3.9 N cm.                               10.7 oz-in, 7.7 N cm.   Aileron      A    2.3 oz-in, 1.7 N cm  using a seperate servo on each.                    B   3.3 oz-in,  2.4 N cm.   These figures would be the minimum and I should probably look for a safety margin of +30 to 50 %.   My physics is a bit rusty but I think 1 Newton is 1 Kg/cm/sec so I presume that the N cm figure would equate with the normal servo ratings of grammes or Kg at 1 cm on the output arm.   I will now go and look at the ads. in the mag. to see what is in the range so far. I would like to use the thinnest ones possible at the back to bury them in the tailplane if possible.  The wing is quite deep so not so much of a problem there.   The Aileron would be a mass balanced slotted Friese type to be scale accurate, I don't know if that alters the parameters.  Rudder and elevator would also be balanced.   I told you it was over ambitious.

Advice to Simon B.  (is that Jersey Simon?)                                                                 DUCK!

By the way for the number crunchers I have worked out the control areas as:   Rudder (each) 79 cm sq.  12.25" sq.  total 24.5" sq.  poss. 2 servos.   Elevator (each half) 187 cm sq.  29" sq.  total  582 sq.   Aileron  (each)  179 cm sq.    

I am curious to see what I get from John Gibbs' web site   http://atlas.csd.net/~cgadd//eflight/calcs_servo.htm   but am not sure of the speed component.  I tend to think of models as flying fast or slow in scale not absolute terms so what speed  in MPH would Simon Chaddock's Mossie do for example?   I would guess at 40 - 50 MPH but is that reasonable?

I am now waiting for some bright spark to sue his Local Authority for removing so many of life's risks that as a child he did not learn about risk avoidance or management.    The result being that he was unable to see or avoid a risk that, as children,  we would have learned to all about.     I wonder!!    Remember the school Authority that banned running in the playground because of the risk of falling?  Or the one that banned conkers?  I am so happy that the school that my granddaughter starts next term has recently held a conker bashing event, it was a great success and whenever we pass the school at playtime we can see the kids running and jumping about.  Needless to say it is a happy place which also manages to achieve good academic standards as well.

We could buy all the ingredients for proper black powder from the local chemist.  Powdered charcoal, saltpetre and sulphur as I recall.  We made up some great bangers and fired them with the element from one of those 6 volt gas r4ing lighters.  A couple of long wires then slam them across a 12 volt car battery's terminals.  Good stuff as I recall.  Also at cosford we got some tubing, closed off one end and broke up the ends of Swan Vesta matches.  Stick a small ball bearing down and heat up the end with a lighter.  Managed to put a hole into the billet dustbin and got 7 days jankers. those were the days.

Talking of H&S a true story:-   The son of a friend of my wife was serving with the RAF in Afganistan.  As in my day most groundcrew did turns of aircraft marshalling.  Said H&S Goon was insensed that he was not wearing a high visibility jacket or tabard so that the Pilot could see him.  At this point the Very bright RAF lad handed him the bats and told him to go forth and marshal himsel adding, "The snipers are just over there." As you say one size does not fit all except perhaps jobsworth hats.

Actually a Do 17z or 215.  I got some brilliant 1/20 drawings and a stack of factory photographs from Dornierwerke in Friedrichshavn together with an old Flight Magazine Cutaway from 1942 strangely reprinted in Dutch plus a load of other info. I have also aquired a  Classic Airframes 1/48 plastic kit to give surface and cockpit detail information so there will be no excuse for any inaccuracy.  There is so much glazing that interior detail will be a problem and I will need to find 1/10 mannikins (or make them) for the crew who will be visible in their entirety.I know Dragon make some brilliant ones but they are in 1/6 scale which would have meant a model of 3 metres.  Too much to think about. I first experimented with a 1/64 balsa/tissue stressed skin during Cosford days in 1956 when I skinned a KK Spitfire kit this way.  I intended to fit a 1cc diesel instead of the KK rubber power but was unable to afford one on the then RAF pay (or lack of it). All the hard work was lost with other posessions when I was posted to Swinderby and baggage went missing so I took up gliding instead, until I got grounded for doing aerobatics under 200 feet.  I had the CFI in the back seat and did 2 elevator turns instead of a gentle sideslip on finals.  Ah! the madness of youth, I have no illusions about the scale of the project I did say this was an overambitious project and I meant it but if you don't aim high and being retired!! 

Thank you all for your input, particularly John.  I have tried the link again and got in but as it's late will try adding figures tomorrow. The model will (I hope) be 1/10 scale electric with a wingspan of 1.8 Metres, about 70". I hope to use a pair of scale profile 3 blade Vario props of about 13.9" diameter.  I believe the pitch can vary from 4" to 16" and run at 8500 RPM max. so I will eventually be looking for an appropriate power train when I've saved a few more pennies after New Year.  I believe the Vario props give a very good thrust.   So far I've only got as far as drawing the tail feathers in detail but have the rest in outline.  Like Andy I believe that most models are grossly over engineered in the sense of using much too thick timber.  I have been experimenting with a dummy run of fin and rudder using 1/16" balsa for ribs and covered with 1/32 sheet with lightweight tissue pasted oover.  I was surprised just how strong the build was I believe it was stronger than !/4 sheet equivalent at least across grain.  The whole lot was extreemly light, but have now junked that one and have re designed with less ribs but not yet built a test piece.

By the way the proposed model is a twin WWII bomber type hopefully in scale.  Control surfaces would seem to be fairly large but have not measured them yet.

Thanks for the tip John but I tried the sites suggested in my search engine but it couldn't seem to find them.  Any other suggestions? Pete.D.

Having come back to the hobby after over half a century I am keen to progress from rtf/artf to own designs.  It was easy in my control line days as all you had was an elevator  which only needed a handle, lines, bellcrank and control horn.  All the necessary power to move said elevator being provided by the Mk 1 wrist. Now I am trying to draw up an over ambitious project I have come up against the problem of what servos to use. Is there a formula or useful rule of thumb that gives an appropriate value of servo output in grammes for a given control area in square centimetres. There seem to be so many types on the market from micro to standard or even larger.  Most though seem to give an output value in grammes or kilogrammes.  Is this at the outside edge of the output arm or say the mid point? Also would rudder, elevator, flaps or ailerons require a different power input for the same given area? So come on you experts help an old wrinkley to move at least one step nearer to own design heaven.   Pete D.

By the way any ex Cosford Brats out there?  We certainly got up to some brilliant pranks there.  Perhaps that's a subject for another memory lane thread.   P.D.

Another thing I can remember is building bikes from bits on the scrap dump.  We used to make them like the trial bikes that older wealthier brothers of friends used for scrambling Complete with cow horn handlebars and terrible brakes.  We then went up a steep hill so we could get up a good speed coming down,  across a small lane ( no dpoubt without looking for traffic) and into a friends farmyard where we had set up an old door with one end propped up on potato boxes. We then had competitions to see who could jump them the furthest, Evil Knevil style. Came off a few times and went home scraped, bloody but happy to be told in no uncertain times to go & get cleaned up and a right bolloking or worse for torn trousers etc.  IT WAS FUN though and this thread has brought back some fantastic memories.  I just hope my Grandson grows up having just as much fun and learns about risk and its consequences.  The odd thrashing was worth it though, wasn't it? Talking of school I remember our maths teacher, Brother Thomas, a de La Salle type who used to throw the blackboard eraser with stunning force and accuracy and we had to dodge the ricochets from the victim.  He would also cane us across the nuckles with the edge if his ruler.  I'm sure I should now sue the order for the odd twinge of arthritis I now get in my left hand.  He was careful to make sure he did not to stop us writing by hitting the wrong one.   Ho Hum! Pete D.

Sorry for the delay.  The schmeisser was not mine but a friend who got into severe trouble using it.  I grew up in Jersey.  My family did not get there until Jan'48 but most of the kids I went to school with and who lived near to home had lived through the German occupation.  Obviously I did not but there was still a lot of military hardware lying about when I arrived in the Island and boys being boys we played with it.   Pete D.

I certainly agree with the the above.  As a kid after playing with my control line in a public park we would go and play with the water cooled German machine gun a mate had in his barn.  I suppose it was a good thing that the 2 boxes of ammo he had were dummy practice rounds.   We used to go into the tunnels and one day brought out a kit to change the barrel of a flak gun plus five rounds in a clip which we proceeded to throw at the wall.  How we survived with all the detrius of the occupation around us I do not know but we did and learned about risk especially the mate who got twelve strokes of the birch for shooting crows with his schmeisser.   They confiscated it into the bargain.  Sadly a couple of kids did get killed in one of the tunnels supposedly opening a canister of poison gas but they should have known better, presumably they did not see or understand the skull and crossbone signs.  The other kids around at the time certainly took note.   I certainly liked to go down the steep hill on my go cart but I did have a Wermacht tin hat as a crash helmet and only seemed to get scratches stings and a few bruises for my trouble.  I am waiting for some bright spark to sue his local authority or school for not allowing him to learn about risk by being too health and safety consious.  It'll have to come.   Happy christmas and a good new year to all and long live rthose memories.   Peye D.

I wonder if Futaba or ripmax directors are vaware of this thread?    I would like to see some responces from them, to at least justify their pricing policy against as their US prices.  Perhaps the mag. could draw it to their attention or would that risk loss of much needed advertising revanue?   I would hate to see Futaba go the way of British Leyland or Burroughs computers.   COME ON RESPOND.

Having recently rejoined the hobby after many years I bought Futaba to fit in with the club instructor's buddy system but I have to say I am shocked at Rx prices.  As a pensioner this may severely limit bfutire purchasses and once solo may result in cutting loses bu flogging the Futaba gear. Ripoffmax note and learn, before you loose many more customers.

Excellent article,  I must confess I havn't used a crimp tool much since working at 103 MU in Cyprus in the late 60's but I seem to remember soldering as well as crimping where ever possible. Another thought from Air Wireless fitter training, I seem to remember that another advantage of twisted wires was their tendency to self noise cancellation.  external noise induced into the cable would tend to be in the same polarity and amplitude in close proximity wires so that the noise would self cancel at the terminals.  I seem to remember that this was quite common on things like microphone and headphone lines where as transmission lines tended to both lines being balanced about a common earth. Anyway at least two good reasons for twists in your wire.

I think I've already posted this somewhare but can't find it so I'll try again here.   I can't quite get round the comments on 3 blade props losing efficiency due to disturbed air from the preceeding blade.   Yes when the A/C is stationery or moving very slowly but if you take a 6" pitch as an example when at speed the theory suggests that by the time a blade passes in front of the earlier position of it's predesessor, in a perfect world, it should be 2" further forward and surely in clean air.  A 3 blader's tips when in forward motion describe a triple helix through the air.  With larger pitches this clearance would be greater so for a 9" pitch the clearance would in theory be 3".  All the turbulance should surely have been driven back towards the tail or if not, the prop should at least be moving in front of it. When the A/C is stationery prop blade interferance would perhaps be significant and therefore efficiancy at it's lowest so that acceleration from a standing start would be poorer.   When testing props are any tests carried out with forward movement of the test rig?  It would probably need a long one and be thertefore impractible but surely it must be accepted that efficience would inprove greatly with forward model speed. I can understand that a 2 blade prop would be more efficient due to the increased diameter needed to absorb the same motive power but surely this is all.   Sorry if I'm being a bit thick but please do comment.   Pete Davis.

Could Tony Nijhuis please tell us where to get those lovely looking scale props he used on the Sunderland photo shoot, or does any one else have any advice?  Looking for a reasonable looking 14" job but without Graubner's thich centre.   Also in last month design your own how is the engine/motor size to wing area ratio affected with multis?  Do you halve the size if using a twin setup or do you have to go a bit bigger to overcome efficiency problems?

Being a Wombles fan, how about Auringy's G-JOEY a bright yellow Trilander with big eyes.  Good fun as well as a serious build.  Would be a great one for the C.I.flyers.

Glad to be of service, I think mine's just hit the mat. Pete.