Ed Kershaw

Oh, apologies, Jonathan - your post appeared whilst I was writing mine.  Nice hover too!

For me, the point is that, a)  it looks fun - and I accept that this is purely a personal and subjective viewpoint, but also b) it requires an advanced level of control over the model that I would like to aquire.   I usually attempt this no lower than about 50 feet and it seems to work, after a fashion, for about 5 or 10 seconds then I either end up just climbing out of it as I apply increased power in an attempt to hold the nose up, or, like Palmerama, falling out, usually on its back.   Any tips on how to get it going, Brian?  You seem to be holding a nice hover in your photo (either that or you're one millisecond away from an unfortunate end to a nice tail-slide )

Hi All, Is prop hanging really possible?  One sees video of people prop hanging models about 5 feet off the ground, holding it stationary right in front of them.  In one video I saw, the rudder of this Pitts was thrashing from side to side like the proverbial door in the wind.  Does this need to be gyro assisted, or something?

When you're learning to fly, either rc or full size, the one thing you want to practice over and over again and be able to do really well every time is land.  Perhaps that sounds a bit boring, but later on when you've got a nice scale model, a really good approach, flare and landing not only looks and feels great, but can occasionally get you a round of applause too!   I think your Toucan does not have landing gear (?) but you can still practice "go arounds" - i.e. a nice square circuit at a constant height, keeping the model exactly where you want it, a controlled approach, descending at the rate and speed you want, with a prospective touch down point exactly where you want it, then at, say, 10 feet, open the tap and go around and do it again.   I suppose the point is that accurate flying takes practice.  Anyone can yank the sticks around and make their model career around the sky, but not that many people can put their model exactly where they want it, when they want.  And that's worth practising.

And further to Glyn's comment, my understanding is that insurance is only valid if you comply with the relevant section(s) of the ANO where it applies to model flying.  Indeed, you can be criminally prosecuted if you do not - see BMFA handbook which can be downloaded as a pdf.   In the case of a small model (less than 7kg) this seems to be limited to taking all reasonable precautions to ensure that the flight can be carried out safely.  Basically, I understand this means that you must satisfy yourself that your activities do not pose an unreasonable risk to other people or property (that includes animals too).   As far as size is concerned, I fly out of a field 70m x 70m and some of my models are 90 and 120 size.  But that field is also surrounded on three sides by fields too and much of my actual flying is carried out over those surrounding fields.  If your field is surrounded by houses or public areas, i.e. if you could not safely land (either in a controlled or uncontrolled manner) outside that field, I would think that it is too small.

This receiver thing is interesting.  Schulze alphas are often highly recommended, but I lost a nice plan built scale model due to one locking up in flight.  I then  replicated this phenomenon time and again on the ground by subjecting it to electronic ESC interference and have never used it since.  I tried all sorts - expensive Futaba Dual cons, Single cons, Jeti Rex, Webra etc etc.  I have found the only really stable 35meg receiver, when mixed with higher power EF gear, is the Multiplex IPD synth DS. Now, however, like Clive, happily converted to bullet proof 2.4gig.

I use 2x2100 3s Maxpoly in parallel - end to end - 4200 total.  My Spit's a few years old now, but from memory I think there was a small mod to the battery bay to make them fit.  I think there was a cross member at the front that had to be moved forward. Motor is an Axi 2826/10 with a 14x7 prop and a Jeti 40A ESC pulling 42A static.  It goes like stink and I get well over 10 mins of mostly full throttle.  I think a 2170 would be a bit limited if you're pulling high 30s amps. One thing - the ply motor mounting plate pulled out in flight.  I've heard this happens to others too.  You might consider reinforcing it with an epoxy fillet at the joints.  Oh, also the elevator joiner broke a couple of years ago during a full power dive.  It made a loud vibrating noise, not surprisingly.  It's now reinforced with piano wire and has been fine since. I've got one of the new kits too (as a spare) unbuilt.  The build quality of the new ones seems to be much better than on my old one. Ed

A few months ago I wrote an article comparing Scorpions and Axis for torque, output and efficiency using a dynamometer.  It was published on this site and may well still be here somewhere - but I can't seem find it.   My main conclusions were that Scorpions were superior in output to Axis, and at least equivalent in efficiency.  The overall build standard is, however, not as good as Axi.   I have a lot of Scorpions now, including a special wind 200kv version of the 4035 size that's going in my GP Super Stearman - max output 2.5kW (3.4bhp).  Not bad out of a 430g motor.  You do get a lot of bang for your buck with Scorpions, although this has been hit recently by the worsening exchange rate.   Ed

Hi Guys, Putting together an electric conversion of the GP Super Stearman, I want to use some good quality, slop free ball links for the control surfaces (i.e. not by radio-active, slec, etc). Does anybody know where one can buy these from in the UK?  Or am I going to have to mail order from the states?  SMC advertise Dubro, but apparently no stock now for some time. It seems like it's becomming increasingly difficult to buy good quality accessories in the UK.  Many thanks in advance for any replies.  Ed

Hi Marty, Thank you for the generous comments.  Quite unfounded, though.  Like most of us, I just like playing with this gear. I think what you're suggesting is that ECSs have different efficiencies.  Well, I've never tested for that - but I will - it's simple enough to do.  I've got some big and small Jeti and Scorpion ESCs (90A, 77A, 55A and 40A).  Regarding your experience with the Castle and the Tower ESCs, I guess one possibility is that the timings were different.  Hard timing can really push the current up compared to soft.  Actually, that's another problem - I don't think I can match the Axi timings with the Scorpions because Axis are just hard and soft, whereas the Scorpions time to a figure (5 degrees;15 degrees etc).  But I'll have a go in the next few days and let you know what happens. Ed

Hi Martin, If you want to reduce the torque effect on a model with low aspect ratio wings, you can, as you quite rightly point out, exchange torque for motor speed and maintain your power output.  This is something I hadn't really considered before because I don't fly "jet" shaped models, but could be a real issue if you do. Fortunately, I don't think you really need a dyno to measure the torque - you can calculate it.  And if you know what torque you're looking for, you can tune your system without leaving the comfort of your favourite chair (and PC).  Having asserted that, I'm sure someone will now  shoot me down in flames immediately.  But here goes, never the less. Since most brushless motors seem to operate at about 75% efficiency upwards, and motor shaft power = torque (in Nm) x speed (in radians/second), if you know your input power (volts x amps) and you know your output power (input power x efficiency), then, by measuring your motor speed, you can make a pretty good stab at your torque figure, accurate to probably not much more than +/- 5%, which should be good enough for most of us. As I think I wrote in my article, the dyno was really built to compare different motors - to see if there was a significant difference between top end and cheapies.  The thing that surpised me most about it was how accurate and repeatable the results seemed to be.  Ed

Apologies for being pedantic, but, whilst Shaun is largely correct, some twins do have contra rotating props, the P-38 being one of them (Piper Seminole and Seneca being others).  I don't know about any others. Ed

Hey - that looks like ONE FUN MODEL!

Derek, I agree with Birdy about the balance.  0.1V isn't really close enough.  If you had a 3 cell pack and charged it to 12.6V, theoretically all three cells would be at 4.2V, i.e. perfect charge condition.  But if you started the charge with 2 cells 0.1V below the third, then the third cell could eventually reach 4.4V, i.e. in a dangerous and possibly unstable condition. I'm not sure what Birdy means about high currents when they're connected up, unless that refers to connecting 2 packs in parallel.  If they're not pretty well identically charged, you can get high currents passing from one to the other, which is not good. Ed

Hi Jon, I get my bearings from here http://www.smbbearings.com/Framesets/Miniature_Metric_Frame.htm You need the shielded type - it keeps the dust out.  You have to take out the old ones, measure them, then order replacements.  From memory, they're pretty low cost. Regarding the E clip - I have to say, although I agree with what Andy says, it does look a bit minimal.  You could get a replacement shaft from Micron radio control (a Scorpion shaft) that comes with a grub screwed collar to hold it on.  They're only a couple of quid.  That looks like a 5mm shaft - they come in various lengths and have flats ground in to accept the grub screw.  You probably need a new shaft anyway. Ed

Jon, To be fair to the motor, if you've, er, "landed it firmly" nose first it probably could do with a new set of bearings ,at least, and probably a new shaft.  It's probably the bearings that are squealing and, if the shaft's slightly bent (you may not be able to notice this) it will force the bearing out of true as it runs. In my experience, any prop strike can damage the bearings.  Shock loads cause them to brinnell.  Bearings are quite small on electric motors.  I just keep a few new ones handy. What make is the motor?  Axi motors have a small circlip to hold the shaft in place, but this is backed up by a grub-screwed collar when it is rear mounted (i.e. for when prop load is transmitted through the circlip).  I've never known one fail, though. Ed

Micron seem to do them.  I think they're in the Devon or thereabouts. http://www.micronradiocontrol.co.uk/prop-apc.print.html Ed

Hi Alan, I use an Axi 2826/10 with a 40A Jeti bec esc and a 13x6.5 apc prop in mine.  I use 3300 3s 20C lipos or sometimes 2 x 2100 3s lipos in parallel.  Performance is excellent - fast with big loops ; power dives are superb - and it provides a good 10min plus flight on full chat, but can be extended well over 20mins with judicious use of throttle. I think it is more usual to use a 2820/10 or 12 and I expect this would give pretty good performance too.  The 2820 series is 30g lighter than the 2826. For a cheaper option, a Scorpion 3020-12, 14 or 16 would also do very well. The silver is a bit odd one the ground, but I think it looks great in the air.  In the air I think it makes a very convincing Spitfire. BTW, my Axi pulled the front off the motor mount after the first few flights, so reinforcing the glued joint with some cyano or epoxy might be a good idea. Ed

Erfolg, 1.  Efficiency is not constant over the rev range.  After reaching a maximum at a fairly low load, it then drops off with further increasing load.  It does, however, increase with cell count although I don't know why (back emf due to higher rpm, maybe).  As I said in a previous reply above, it is quite interesting to experiment with Scorpion Calc - it can be downloaded here http://www.scorpionsystem.com/downloads/  as it shows what happens when you change the motor parameters.  BTW, I have nothing to do with Scorpion motors, I just happen to have some and have found Scorpion Calc a useful tool for learning how motors behave under different conditions.  Scorpion calc is based on calculations, though, not measurements. 2.  I have only measured Axi and Scorpion motors so far.  There does not seem to be much to choose between the two regarding efficiency. 3.  I think that the efficiency curve shape between outrunners and inrunners is roughly the same.  Compare those on Scorpion Calc with those on Mega motors website here http://www.megamotor.cz/new/images/ac_motor_22_30_3_graph.jpg  They seem similar. Allan, Many thanks for the comments.  I am inclined to agree with you regarding the absolute accuracy of the measuring equipment.  But, as you say, it still results in a  useful tool for comparing motors and ancilliaries. I'd be interested to hear how you get on if you do build a dyno - how you decide to configure it and what results you get, etc. Ed

Hi Tim, It's well worth the read because I recall Pete Nicholson did various set-ups before he arrived at his final version, and his battery box was very innovative.  Also, it's got his email address in it - and he's very helpful with queries. Hope it goes well. Ed

Hi Tim, Pete Nicholson did one very successfully in the November 2004 issue of Q&EFI.  I can't find my copy right now, but there's always back issues.  Also, I found this page on it from Banbury model club. http://www.banburymodelflyingclub.co.uk/electric100.htm Hope it helps.  Ed

John, These are lovely engines and rather rare.  Unless you're determined to do it yourself, I'd just pop it in a box and send it to John Haytree.  It'll come back like new.  Just tell him it's brand new and you don't want it test run (unless you do, that is). Ed

Oooooh!  I've got just the motor for that little baby!

Simply gorgeous, Mike!  Your first picture could have been taken on any late 1930s airfield. I've got the Gordon Whitehead plan - but not the courage to have a go. And the cockpit details are just superb - very realistic and evocative.  It makes you just want to strap yourself in and shout "CONTACT!" as some "erk" swings the prop for you. Seconded re the wooden prop.  Mag switches would just add the final touch to the cockpit coamings (sp?) too.  They're so prominent on a Tiger. Congratulations. Ed

I totally concur with Tim and Bruce. I think what it also shows is how interesting a hobby aeromodelling can be for a range of people with such diverse interests and aptititudes.  With all the gear we have available there is so much to find out and exeperiment with (for the engineering/techy types).  But also, for those with less interest in that aspect and more wish to go and fly aeroplanes, go out and fly.  That's what it's all about. The main reason I built my dyno (really and honestly) was that I got a bee in my bonnet about it, and, with me, when that happens it won't go away until I've done something.  I don't really think the actual results I got are much of a surprise to anyone.  It just confirms, more or less, what we are already told by the manufacturers.  The only surprising thing to me was that it worked at all.  It's not often that something so simple is so effective.  Like Tim's fan units, I just wanted to COMPARE motors.