Martin Harris - Moderator
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Posts posted by Martin Harris - Moderator
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No chance of using 2 servos? If it had snakes installed before it might be that it was designed for a separate one for each half.Otherwise, another possibility might be if you can arrange one horn on top of an elevator and one below - assuming equal geometry you could use a double arm on the servo.
....or if you're really lucky you MIGHT be able to use adjacent holes on the servo arm and compensate by using different position holes on the control surface horns to give similar movements.
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Personally, given those choices, I'd go with the SC40.
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What do you want it to do? i.e. is it scale, sport, 3D, pylon racer etc. etc.
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I have the other Seagull 300S see here which I was fortunate enough to win from this very forum in a monthly draw last year (cheers, David/Graham!). As I had the choice of an old ASP61 or a Super Tigre 91 looking for homes, I naturally opted for the 91 and have not been disappointed!With the battery mounted at the rear wing former, there was no problem with C of G and it performs unlimited vertical manoeuvres on an APC 13 x 7. The recently discovered potential for knife edge spins never fails to amuse...
The only build problems were the tank which wouldn't fit due to misalignment of the hole in the forward former (which wasn't a major problem as it needed opening out a little in order to fit a slightly larger SLEC tank as I felt the original was a bit small for the 91) and having to epoxy the clevises onto the elevator/rudder pushrods at the servo end to avoid having threaded fixings at both ends which I don't consider to be good practice. As the pushrods were pre-fitted and accurately sized to length I couldn't put my usual Z bends in.
I also replaced the screw fixings for the canopy/access hatch with sprung catches after a few weeks as they were rather fiddly and could have potentially been lost in flight.
Other than the above, it's a very competent model with excellent flight characteristics and it's become the first model into the car ever since its first flight last summer - even the spats have survived the winter intact!Edited By Martin Harris on 16/04/2009 10:34:15
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My solution on my Hurricane sounds like it's very much along Timbo's lines:
The U blocks are threaded and I use socket headed screws from the outside:
...sorry about the state of the doors with their redundant holes but they've been well used and have been the subject of several different types of legs, culminating in the home made oleos now fitted. The top screw is simply threaded into the top of the leg - I can't answer for your Unitract legs but I designed mine with plenty of depth for threading into.It will be interesting to see how similar (or different) Timbo's method is!You could use countersunk screws to keep things more flush...Edited By Martin Harris on 16/04/2009 01:39:44
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Shaun,4 plugs seems a bit excessive! Are you using a power panel or a glowstick?
I've seen several panel glow drivers fail and apply the 12V supply direct to the plug with expensive resuts. It's usually on the 3rd plug that the penny drops!Edited By Martin Harris on 12/04/2009 21:43:24
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I don't remember where I set mine but the critical thing with autogyros is to make sure they hang nose down when supported at the rotor hub(s).
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A few drops of meths thins epoxy - also weakens it if done to excess but it's fine for fuelproofing...
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"A nice weekend's weather and I've got a cod"Wasn't a Giant Cod by any chance?
Edited By Martin Harris on 05/04/2009 21:28:44
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Engine Doctor,Unless Futaba have changed the design since I bought my 9C, I think you'll find that there is no diode in the charging circuit. There certainly isn't one in mine.
From the (US) manual on the Futaba site:Note that the 9C super transmitter system has electronic protection from overcharging and reverse polarity via a poli-switch. It does NOT have a diode in the charge circuit and may be discharged/peak charged with the battery in the transmitter.
...and in case anyone was wondering, PolySwitch devices are polymeric positive temperature coefficient (PPTC) devices, which are used to help protect against harmful overcurrent surges and overtemperature faults. Like traditional fuses, these devices limit the flow of dangerously high current during fault conditions. However, the PolySwitch device resets after the fault is cleared and power to the circuit is removed -
The most effective fuel-proofer I've used (but not the best finish although very acceptable for my 1/12 scale combat models) is Skincrylic water based varnish - which I assume is similar to Poly-C) which is fully fuel proof the next day (maybe even sooner?) It leaves a semi-gloss finish, reminiscent of a lot of restored full size warbirds and can be sprayed after thinning with a little water - although nasty feedback about spraying pondsealer, for example, would make sensible precautions worthwhile as there's no advice given about spraying it.
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Certainly more suitable for running in than the 14 x 7
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Not unusual on a ringed engine - allows copious lubrication. You may need to keep the glow battery connected to keep it running.I'd use a much smaller prop for initial running in. Keep the pitch down. A 13x 5 or 12 x 6 maybe? Even a 12.25 x 3.75 funfly prop...depends what you have to hand. The engine should pull a 14 x 7 if you're using it on a scale model but won't give the best performance.
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Thanks gents, I think I may have clarified a few points in my head with your assistance.Could you confirm that I'm correct in thinking (in simple terms) that if you have a resonant length (or thereabouts) of aerial wire, it makes very little (if any) difference if, say, you had a 40 degree bend half way along its length (the resonance being due to the physical length of the wire) and possibly a slight improvement end on.
The apparent length in this case (measured in a straight line from rx to aerial tip) will only have an effect on the maximum amount of RF energy captured (when at 90 degrees to the tx aerial) and no effect on resonance?
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When absolutely synchronised there is no beat. You hear the beat when the two engines are almost, but not quite, synchronised.
An old friend of mine used to signal his arrival to his girlfriend in Italy when flying a King Air on a regular newspaper/DHL run by knocking the propellers slightly out of synch to produce a beat when flying over the town on approach - apparently it was effective enough at around 07.00 for her to ring the local taxi driver to go to the airport to pick him up!
The full size technique (or at least 25 years ago it used to be) is to match the engines on the revcounters and then tune out the beat by ear. There is an instrument on most twins that senses the difference with a rotating indicator which you can set to be still when the engines are perfectly in synch but my friend used to rely more on synchronising by ear.
Mind you, it does sound good when a twin is beating!
Edited By Martin Harris on 29/03/2009 21:38:54
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"Lipo's don't overflow!"Just try putting in too much electrickery and watch them overflow!
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Brian,Sorry if I'm being a bit slow but at what point do the folds start to be significant?Am I right in thinking that once you have coils or folds lying parallel, inductance effects start to become meaningful?In the bottom case, will resonance be more or less acheived due to the electrical length being the same as the straight aerial with only slight inductance effects or is it the fact that you have 4 short aerials which interract against each other?If so, as the angles straighten, perhaps it's the case that the overall length starts to resemble the tuned length and the opposing sections have proportionately less adverse effects? At that point is it the fact that the electrons can start whizzing up and down at the speed of light without too much hindrance - the time and speed equating to the wavelength?
Hopefully the ramblings above might make some sense and perhaps you could help me understand the mysteries of aerial theory!Edited By Martin Harris on 25/03/2009 20:26:59
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In case of confusion the line:Its curious that nobody has tried FPV in your club when you have made it so easy.was the first line of Mark's reply - I just noticed that I pasted it into the copy of the original post incorrectly.
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...and this was my reply:Ouch Mark! Something seems to have rattled your cage!
I think we've taken a reasonable approach "on the basis of no actual experience or knowledge of the activity" If that's "blind prejudice" then I hold my hands up. If you re-read your quote from my post you'll note that I did stress that it might be overkill with a clear inference that this policy is not set in stone once some experience is gained.
You're absolutely spot on that an EasyStar isn't the most hazardous model in the world but who's to say we won't have our first interested person equipping a 35% CAP with FPV?
We're also guilty as charged over insisting on checks when the 2.4GHz GUID issue emerged and offerering timely advice on the brownout issue. We insisted on following the BMFA black peg guideline until more experience prompted debate at committee and a vote at the AGM to stop using them. Yes, the committee takes a lead until experience leads to questioning the initial precautions and informed debate can be entered into.
As to why no-one has tried FPV I'm doubtful that any reluctance to take it up would be influenced by our specifying a limited (but readily available) number of experienced helpers to satisfy the requirement to abide by the position promulgated by the BMFA giving the view (whether correct or not) that a safety pilot is a legal and insurance requirement.
I certainly haven't heard of any dissenting voices. Personally, I'd love to give it a go but at this time I don't really want to invest several hundred pounds to indulge in what might be a gimmick. Some friends at another club weren't particularly enthused over their own experience but if anyone at our club was experimenting, I for one would go out of my way to assist.. And I doubt that I'd be alone.
It is a sad fact that as a responsible club, we do have to be aware of the "modern Health and Safety mad, totally risk free UK" - not a mindset that I think encourages making balanced and considered judgements and may well be actually counter-productive in the long run, but that's a whole different debate.
You may not find this at all odd, but our club has a reputation locally for enforcing rules and discipline and that would seem to prove your case. However, it was like that when I joined and has remained that way BUT it is one of the friendliest bunch of blokes I've ever known, touch wood has no "political" issues, an approachable committee, sensible rules that are reviewed regularly and openly and very importantly due in no little part to observing our rules, good (touch wood very firmly again) relations with the neighbours.
We do seem to be wandering off topic with these posts - perhaps you might think of starting a new thread if the above hasn't put your mind at rest...Edited By Martin Harris on 25/03/2009 00:11:49
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Mark Chiocca posted the following starting with a quote from my previous post. Unfortunately, IE doesn't seem to display anything posted since (no problem with Firefox) so I've reposted it in this new thread:In our club, although no-one has tried it yet, we''ve decided that for the time being, only recognised instructors will be able to act as safety pilots as they are used to taking control at appropriate moments and will not be overawed by senior pilots. This may be overkill but we feel it''s a sensible precaution until more experience is gained.Its curious that nobody has tried FPV in your club when you have made it so easy.
Did you introduce the same safety measures when members started swapping to 2.4GHz radio gear? (We all know that there were lots of issues.) Did you have a similar scheme when folks swapped from gas to electric? From Nicad/Nimh to Lipo? And jets do you let folks fly them unaided?!?! In the modern Health and Safety mad, totally risk free UK it is obviously entirely reasonable to introduce the requirements you have. In fact I think an alarm bell should also be rung and the fire brigade put on stand-by. (Maybe a special warning flag should also be hoisted for the benefit of those members who are hard of hearing?)
But have you considered the alternative: that a model crashes. Where I used to fly I saw at least one crash every time I went to the club field. And then lets imagine that God Forbid - it is an FPV model that crashes! So more than likely an EasyStar weighing less than half a kilo, flying at 15mph and made from impact absorbing foam. Would this really be the worst thing that has ever happened at your club field?
If I was to join your club, and fly FPV, I now need to get my packed work schedule and the fickle weather schedule to coincide with an Instructors availability so what chance a quick squirt after lunch on Tuesday? Nah I'll fly on my own in my pal's field thanks.
You have (entirely reasonably and totally sensibly) effectively outlawed my interest on the basis of no actual experience or knowledge of the activity. In fact, just blind prejudice.
Edited By Martin Harris on 25/03/2009 00:15:34
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Flytilbroke,I hope you don't think I'm implying any criticism of the previous answers - I was hoping for replies from some of these knowledgeable previous contributors on a closely related but slightly different question. I think you'll see I was actually describing most of the named people in my request!
Edited By Martin Harris on 24/03/2009 22:03:07
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Thanks Brian - no CV necessary but I didn't want a stream of people telling me not to roll up/shorten the aerial instead of those who understood the question!I've lost count of the number of times I've heard that you "shouldn't bend the aerial, it won't be a resonant length any more" and similar quotes. I've always felt that the electrical length of the aerial is the critical factor rather than the distance (due to its routing) in a straight line from end to end. I think you've agreed with this if I'm not mistaken?
...But I'm not sure why your zig zag example needs the extra length - is there some inductance to take into account? I don't think electrons take much notice of slowing down for corners - or do they? They do have (a little) mass I suppose...My understanding was that the practical length is reduced by a factor from the theoretical length to take some other factors into account which might explain the shorter than theoretical distance you mentioned.
As I've said, I have little RF knowledge so please don't take my questions as any argument with your information - I'm just trying to understand the subject a little further.
Edited By Martin Harris on 24/03/2009 21:49:15
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I use 10% nitro (15% synthetic 2% castor) from Southern Modelcraft in a wide variety of 2 stroke and 4 stroke engines without problems.A lot of people tell me I should use this fuel and that fuel in different engines but I'm usually too busy flying to take much notice.
There might be a case for different fuels (high nitro) in YS and Cox's for example or low oil content in very large 2 strokes but not for the average engine.
Edited By Martin Harris on 24/03/2009 21:23:58
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