Sussex Pete

Thanks to all for your input which helped me think clearly about the problem and its limitations. And to find the bug in my alarm code that was triggering warnings way too soon! Doh! But back to the question, Am I receiving good data at the rx?, I have now learned where and when the answer is no and written new alarms for Link Quality low and critical to flag it up. There's a log tests and results here: Important Firmware Update - ACCESS 2.1.x - Page 31 - RC Groups (p. 31 post #460 ff). In parcticular, I have adopted voice alarms for my Archer rx, at these values: Link Quality Low: VFR Low 75% (can be reached sometimes near the 35dB "floor" zone of the RSSI data) or RF Signal Low 34db (i.e. once step below a 35dB floor and 1dB below the FrSky advised limit) Link Quality Critical VFR Critical 65% (reached into the weak zone but some way from link loss) or RF Signal Critical 30dB (before any sudden decline in VFR and 2dB below the FrSky advised limit) with a half-second allowance for dips while circling. My feeling is these will give me comfortable warnings to fly closer. I plan to set the alarm levels for each rx installation separately but expect the numbers to be similar.

Thanks Mike. I do understand antenna radiation patterns - a physics PhD doesn't wear off too quickly! 🙂 I generally hang my tx from a neck strap and fly facing the model with the tx antenna to one side parallel with the top of the tx so the radiated "donut" is maximal directly in front of me with the donut, rather than the antenna, pointing at the aircraft. But it's your point about VFR that lit a bulb in my head and suggests a paradigm shift: never mind the tx shouting about the RF signal level, the only question should be, am I receiving good data at the rx? In other words ignore RSSI, a value calculated in the rx and hence subject to all sorts of rx hardware assumptions and variabiltity, and concentrate instead on VFR, which is not a calculation but a simple counter of valid data received. And lo! And behold! My VFR remained excellent throughout! In the air and on the ground, the logged VFR stayed between 92% and 100% all day. In the flight above with my max altitude and max downwind, VFR stayed at 96% or above and mostly nailed at 100%. I was receiving good to excellent data despite the RSSI warnings. So does this sound like a plan? Ignore FrSky's generic "suggested" levels of 35dB and 32dB and use ground tests to determine an empirical, rx-specific RSSI at which VFR falls. Then set the RSSI alarms to a few dB above that. A bit more effort in setting up each model in exchange for a more reliable set of warnings? In fact I already have a LS/SF combo reporting high lost frame rates which wasn't triggered at all all day. Perhaps I should have heard that silence over the apparently misleading alarms!

FrSky expect 1km range in clear air on 100mW output and colleagues who fly F5J get much better range than I am. The rx is sending telemetry back at the same power (but lower frame rate). The tx doesn't record telemetry signal level but I don't see any loss of telemetry data - much as I have not seen a big dip in valid frames getting to the rx. Though I'm not sure of those last points actually tell me anything except I haven't quite gone out of range! :)

I see your thinking. Any pair of lines defines a plane but you're right that the current arrangement puts the antenna plane parallel to the wing and the CF in it (and indeed the CF boom). That was pretty much my first thought too once I saw the log plots. But other people (on FB) tell me they have the same arrangement of antennae and no RSSI problems, pointing fingers at a duff rx (or at least one duff antenna). This will need some testing to sort. This week I hope as the next round is weekend after next! 🙂

Thanks Steve very useful! Not very new I bought them a while ago with projects in mind. I will check with Richard if I don't get this sorted easily

Yes. And the rx has the latest firmware too

Thanks Denis you confirmed my suspicion: my wing is shadowing both rx antennae as I circle. Below is a plot of altitude and RSSI from a flight in yesterday's FxRES contest in Shrewsbury (where I topped just over 1000 feet 😇). The regular dips in RSSI pretty much coincide with my cirling. The steady decline in mean RSSI as altitude increases looks fine but the dips are HUGE - from 56db to 35 db, effectively a 7-fold reduction in received power and almost 3-fold reduction in range (if I have done my sums right). At 56db the rx is well within range but at 35db it's getting short - as well as annoying hearing repeated verbal warnings from the tx! The good news is that the valid frame rate only dipped from 100% to 97% in those moments of a few log intervals (0.2sec). Both my antennae exit the fuselage ahead of the wing at 90deg to each other. They are also well away from the metal pushrods which testing showed also significantly affected signal. However, in a thermal turn, the banked wing with a CF LE and spar can easily cross the line of sight from tx to rx. I committed the sins of testing the installation with the wing off and conducting pre-flight range checks with the aircraft facing me - both showed good range of course. I don't have a place to put a satellite rx - it's a pod-and-CF boom fuselage with nowhere (obvious at least) to put it. But I am going to rethink the antenna positions to try to ensure there's always one un-shadowed.

Hi Mike-- Can I ask where you found schematics? I just had my first TX Antenna Fault on power-up of an 18-month old Taranis X9D+ 2019 running OTX 2.3.11 and ACCESS. After talking to Richard at T9 (thanks!) I watched the RAS values on the Radio Hardware menu (Relative Antenna Status - was SWR, see user manual p.19, no Rx or telemetry required). I understand from the user manual RAS>51 is a fault to I'm guessing that's what happened. Untouched, RAS varied between 0 and 6. As I moved the antenna by hand, I got it up into the 30s in some holds/positions but it reverted to near zero when I moved my hand away. This essentially shows the impact of external factors on the antenna impedance at 2.4GHz. When I got the fault report last weekend, the tx was on damp grass and I was moving the antenna at the same time. Since then, I have been unable to reproduce the warning. So my guess is the combination of damp and hand momentarily took RAS over 51, but in normal operation, RAS<10 is fine (as Richard suggested). I took the back off the tx and checked the original factory-fitted antenna. Photos below. It looks like the glue blob is supporting the coax. I cannot actually see all of the solder joints but they look well aligned. The nearby SMDs look fine. I have to say Allan's before picture made be wonder if his antenna had been (poorly) repaired in the past. The antenna itself (probably - it's glued in) looks like a standard short FrSky coax antenna stuck into the plastic tube. The coax probably has the last 30.7mm of outer shield stripped back to make a quarter-wave monopole - just like antennae on receivers (and of course, both ends of a telemetry system are really transceivers so you'd expect some symmetry!). When you rotate the plastic tube containing the antenna, the coax is inevitably flexed so it's vital that glue and solder carries that load. That all checked out ok from my standpoint so I'm back to flying after adding "Check and test RAS<10" to my pre-flight procedures. Unfortunately, RAS is not a value accessible to logical switches to write your own warnings with a special function. Maybe we should put that in a a GITHUB request? Thanks to all the other contributors to this thread! Cheers --Pete

Hi-- Can anyone from the magazine - or indeed anyone! - tell me the name of the nice angular headline font used for article titles in the magazine? Just finishing a build from magazine plans (RES-Eagle, March 2018 edition) and I would like to add some decals in the same font. Thanks if you can help! --Pete Edited By Sussex Pete on 04/06/2020 10:00:45

Posted by buster prop on 12/02/2020 10:28:21: George Stringwell’s book about thermal soaring ... Thanks for the lead on that, BP, I didn't know the book before but Amazon just delivered a used copy. Very informative from a first scan through, I think my evening reading is sorted for a while! 8-)

Thanks PatMc - all good knowledge! I've found a nice adjustable tow hook from Hyperflight, maybe a tad too large (metalwork weight 16g) but fits the fuselage and is nicer than I could make myself Edited By Sussex Pete on 17/02/2020 11:51:21

Posted by Andy Stephenson on 16/02/2020 18:05:05: Posted by Sussex Pete on 16/02/2020 13:54:30:... - The whiskers are connected to the on-off switch (recommended in the Wildthing instructions). ... Does this mean you actually connected the whisker antennas to the on-off switch??? I'm intrigued to say the least. A. Don's right, just a piece of fishing line tied to the on-off switch in the middle of the fuselage. I had a Spektrum AR410 rx installed which does not have external antennae.  And hot-glue is great for quick assembly! Edited By Sussex Pete on 17/02/2020 11:26:57 Edited By Sussex Pete on 17/02/2020 11:29:08

Posted by CARPERFECT on 16/02/2020 08:42:45: I know the horse has bolted but, always set fail safe to Zero throttle(yes i know it does not have one ) and off set the rudder, That way it can not get too far away if there is a problem. Or does Spektrum not have fail safe on all channels ?. Only ever used Futaba and they have it on all channels The later Spektrum receivers (eg the AR410 in the lost plane) do have failsafe on all channels though they default to "hold position" unless you follow a slightly different binding procedure. I know it failsafed in this instance as I was in a hard banking turn when it lost contact and leveled itself out.

Posted by trebor on 16/02/2020 11:47:35: Pete, how did you go about making a nice job of your registration number sticker ? Thank you for the compliment! I used: MS Word to put the letters together. Ink-jet print on waterslide transfer paper (from Amazon). About 6 coats thin of spray matt artists varnish to seal. Slide transfer onto the wing and dab down with paper towel. Cover with clear Fablon (from Hobbycraft). Done! Only use the Fablon on plastic covering - usually I just dope over the top on tissue or nylon. I tried gloss varnish but it doesn't take dope so well.

To answer a few questions from earlier posts (thanks for the interest and recommendations!), - I am happy to say nobody got hurt! - The whiskers are connected to the on-off switch (recommended in the Wildthing instructions). BTW, the onboard battery was recently charged, and I've been running my Tx for 12 hours testing and not drained the Tx battery yet. - I did indeed put GBR197508 on it, in 25mm high letters, to be competition-compliant. Same on all my planes!  (Doesn't everyone want to go fly at the Nationals? - If I wasn't waiting for my CAA registration this month, the plane would have had the same, full, contact details all my other planes have (except they are on labels under dope, not removable as the CAA suggests!). Sod's Law... - The plane was trimmed to circle on failsafe. And it did. Beautifully. And climbing in very strong slope lift! Perhaps I should have reset the failsafe with a load of up-elevator too to stall it in like a D/T. Anyway, testing at home with several receivers (both Spektrum and Orange) points at the Spektrum DXe transmitter at fault. It's still generating radio frequency but the range is down to less than 50 metres. It is very clear the Spektrum Rx's deal with drop-outs, and with reconnection, better than Orange, but neither can overcome a 50m-range Tx! I did take the back off to see if there was anything obvious or overheating (I have a good IR thermometer but nothing was hot). The 2mm co-axial connector between the R/F board and the external antenna seemed loose, so I tweaked the female connector on the cable with a pin. No difference (but boy is that a tiny connector!) So, decision time: this is the second and, I now think, last Spektrum Tx I will own. The first (and the only reason I have Spektrum at all) was a DX5 that came with a (amazingly cheap at £140) RTF Supercub when I got back into the sport in 2016. That failed in a few months - same symptoms but luckily no lost aircraft and Hobbyzone replaced it under warranty in September 2016 with the DXe that has just failed. Before that, my last radio was a Futaba 6ch 27MHz set bought new for £400(!) about 1970, preceded by MacGregor single-channel in the '60s. I never had any radio problems with any of those (not even interference) even on my home-built 6ch Rx (with Real Transistors!). So, given that I've just lost (or, hopefully, only mislaid!) £150 worth of kit, radio and servos, I don't think "cheap" is going to be on my list of attributes for a new set. Next decision: Futaba, or Multiplex? Edited By Sussex Pete on 16/02/2020 13:55:55 Edited By Sussex Pete on 16/02/2020 13:57:09

Yesterday (14 Feb 2020) radio failure showed just how well trimmed my SAS Wildthing was on failsafe settings when it flew away from Wilmington Long Man bowl (East Sussex) in 37mph winds about 10 minutes into an otherwise nice slope soaring session. After searching the back of the hill for an hour a walker told me she'd seen someone local carrying it away from near Folkington Wood about half a mile downwind. Sadly I must confess I was waiting for my CAA number before doing a proper return address label. A big mistake: Sod's Law (aka Murphy's Law at the worst possible time!) applies as it always has. I have put the word out locally (door-to-door!) and on local social media but if anyone hears anything let me know please - I will reward its return. Perhaps my BMFA registration number GBR197508, will turn up in a Google search. My mobile is 07952 910184. I don't know the cause of the loss on contact yet. The elevons clearly went to neutral and the onboard Voltsaver battery alarm did not sound so I believe the battery was ok. I don't know if the receiver (Spektrum AR410) logged any losses as I don't have it. I am setting up a test of my Spektrum DXe transmitter, which itself was a warranty replacement for an earlier purchase whose RF board failed (without loss of a plane). Just glad it wasn't my Middle Phase in the air at the time - it would not bounce like a Wildthing.   Edited By Sussex Pete on 15/02/2020 12:25:01 Edited By Sussex Pete on 15/02/2020 12:26:18

Posted by buster prop on 12/02/2020 10:28:21: ...I will make sure my glider is trimmed by hand launches first before risking the bungee, don’t want three months work converted to matchwood in seconds! Meant to add I think you're dead right to be cautious! Bungee energy can be quite excting, and once you've launched, you're committed to using it! But that's why the carbon spars. The reported flutter problem, because the wing centre of mass is behind the stiff main spar, is scarier for me. I have yet to add stiffening gussets but I wonder if Ton could add a third 4mm CF member between the main spar and the l.e. but offset up a bit, to add a little mass forward and increase the torsional stiffness? I thought about drilling the ribs myself but didnt think I could be accurate enough on pre-cut ribs. I will also be building up speed carefully on bungee tests to avoid shaking the wing to pieces as well avoiding as folding it

BP, the 30deg-ahead-of-Cog rule of thumb was what I was taught as a kid. And it generally works too for most any model glider, FF or RC, although probably not very efficiently. However! What really matters is where exactly the centre of mass is, usually somewhere in the middle of the fuselage, not the point directly above the CoG (or below for a low-winger) where we hold the wing to check angle of attack when "balanced". So you have to be careful where that 30-deg line starts... Simons' book discusses the pitching torque the towline applies and the need for down-elevator (and consequent speed increase) needed to compensate. He also discusses stability on tow (generlly, worse than on glide) but not efficiency and only says a too-far forward hook with respect to CoG can lead to weaving on tow but down elevator again fixes it by reducing the wing angle of attack. PatMc, can I ask how you were towing? Running, pulleys, bungee or winch? The change of direction of pull during launch, the total energy that can be transmitted to the model and the rate of energy transfer (i.e. power) differ for and during each method, so any 'optimum' hook position for one will likely not be optimal for other methods or in other conditions. For bungee/Hi-start (however it's spelled!) I see the big issue as total energy available in the stretched line (in still air, wind changes everything!). So getting most of that energy into speed (and hence lift and hence height) and not wasting it dragging the glider towards the ground seems to me to be the right aim. I would expect a rearward hook to cause more nose-up pitching torque than a forward hook, needing more down elevator. Too far forward will need up elevator to get any climb. But _any_ elevator increases drag, wasting energy. I don't know where the compromises lie, but my guess is (a) somewhere in between and (b) it won't matter too much except in high-level competition in still air. So, after all that, and in order to get on with finishing this kit (and actually flying it in this year's BARCS postal comp!), I'm going to just follow Ton's advice and put the hook about 63mm behind the l/e, secure enough to hold 8kg, double the F3-RES bungee limit. 8-)

I'm ahead of you on cup hooks 8-). But the SLEC Large Tow Hook Hook **LINK** works fine on my 100" 3lb Kloudrider even off an S100 competition winch! Tough as old boots but too wide for F3-RES rules. As for CG and hooks, I might write later on all the fallacies one can trip on. Full-size practice for winch or aerotow puts the "hook" at the front way way ahead of CG... Suffice to say it matters nuch less than in free flight.