Here is a list of all the postings Gordon Whitehead 1 has made in our forums. Click on a thread name to jump to the thread.
|Thread: Vampire EDF|
That's a super project to resurrect John. What are the specs? It looks as if it might be for a 90mm fan, so a really nice size.
|Thread: Insanity seems to be setting in|
Thanks for the link Doug. I've emailed it to our daughters so that they can show it to our grandchildren.
|Thread: Individual cell voltage of LiPo flight battery.|
As a matter of interest, now that all cell voltages in a pack can be readily measured and logged, how much excess voltage depression compared with the rest of the cells in a pack makes a cell qualify as failed enough to make the pack unusable? Or do all the cells generally degrade at the same rate with a small random spread in full power terminal voltage so that whilst one cell will hit the warning voltage first, the others are pretty close anyway so that they can all be considered as failing together?
Is there any noticeable correlation between excess voltage drop at full power, say 12C for a 5000 pack, and capacity loss?
Hi Bob and Peter, those Frsky lipo sensors look the biz and the price is right too. If I had Frsky I wouldn't hold back from using that system.
I've found my Fusion lipo checker to tally well enough with what my charger and telemetry tell me so am satisfied with its readings.
As regards re-adjusting the warning level every flight, that's not practical and I'm only looking for long-term deterioration of capacity, not a change from flight to flight. In any case, with the Spekky system the warning level automatically suits the lipo requirement of the model selected on the Tx via the Modelmatch feature, be it 3S, 6S or whatever. Hacker recommends replacing a lipo when it has lost 20% of its capacity, which can be easily detected via a post-flight residual capacity check following a standard amount of energy extracted. I can't be bothered with hours of charge-discharge checks to achieve the same thing.
In case anyone was interested enough to read and be confused by my earlier post the vibe and tone warnings only apply to the old Gen 1 Dx18 which doesn't have voice alerts but does show that such a basic system can be useful, and with nothing else available at the time I used it on every flight. The DX9 has voice alerts of course, so that's what I use now.
In closing, thanks for highlighting the MLVSS and FLVSS sensors, which I'd never heard of before.
Thanks for all your comments guys.
@ Peter: my Lemon Rx is the LM0052 which came with a separate Lemon energy sensor. This Rx outputs altimeter and vario telemetry besides drive battery current, volts and mAh. I haven't got around to putting it in a plane yet and as it's 6 months since I last looked at it I dug it out and connected it to a 4-cell nimh, and bound it to my DX9 Black Edition to check out what the displays were. In essence the built-in telemetry outputs just the same info as my Spektrum TM1000 telemetry modules, so as long as your DX6 has just the same telemetry features as my DX9 and Gen 1 DX18, then you can measure mAh used and instantaneous drive battery voltage. You can set a low drive battery voltage warning for when it falls to your chosen minimum value. I use vibe for the mAh consumed warning as that's no distraction for pilots standing nearby. I use tone for the low voltage warning as I normally don't fly to that limit, and the occasional beep at full throttle would be an indication of battery ageing.
I accept Bob Cotsford's reasoning, but a cell going duff can be spotted by the voltage warning sounding unexpectedly at full throttle as the battery pack ages and loses capacity. Checking the pack after flight with a lipo checker should give an indication of which cell was the worst of the pack.
For instance, if the warning was set at 3.3V/cell ie 9.9V total in Steve's graph, the warning would sound on the 3 or 4 times he hit full throttle. If 3V/cell ie 9V was chosen, the warning would only sound when the pack had aged a fair bit causing a much lower full throttle voltage at max current draw, and tell you that it was about time to consider buying replacement packs.
When I was using the lipodimatics, the throttle would pulse when an individual cell dropped to my pre-set 3V on full throttle, and stop pulsing when I throttled back a bit to reduce current and let the voltage recover as seen in Steve's graph. Initially, when the packs were new, the pulsing never occurred. However, when they were a couple of years old and had puffed, the pulsing could occur as I firewalled the throttle for take-off, because of the instantaneous higher current as the prop was accelerated, but stop pulsing as I throttled down, and only re-occur at full throttle later in the flight with the pack becoming depleted. Incidentally, one thing I didn't mention in my earlier post was that the lipodimatic had an led which would pulse a repeating set of pulses to allow a post-flight check on which cell had fallen to the 3V/cell setting, the number of pulses in the set indicating which cell was guilty, eg 3 pulses repeating was the 3rd cell from the negative lead, ie the middle cell in a 5-cell pack.
When I began using telemetry to check pack voltage, similar indications happened, ie new batts, no warning on firewalling the throttle, but old puffed batts would lose enough instantaneous voltage to indicate one or more cells going low, though not which ones as the Spekky and Lemon telemetry only check total pack voltage.
Regarding the efficacy of measuring mAh used, if a flyer aims to leave 20% charge remaining in a pack after each flight, and sets the telemetry warning for when 80% has been consumed, then if the pack has lost 10% of its capacity, an after-flight check with the usual lipo checker will show only 10% remaining, which should give pause for thought. Naturally, having realised that there is some lost capacity, the energy sensor warning can be set to a value which will guarantee 20% remaining. eg if a 5000mAh pack has lost 10% capacity, the telemetry should be set to sound when 3500mAh has been consumed - or maybe a bit less to allow for a go-around.
Well that's how I use my Spekky telemetry, which won't suit everyone.
Reading the references quickly, it looks to me as if the Unilog is a data logger intended for post-flight evaluation of the measurements. Unless it can report in real time and sound a warning when Peter's 3.3V threshold has been reached, it seems to me to be of doubtful utility unless you are a data collecting enthusiast. Does the Frsky system announce when an individual cell has breached a chosen lower limit?
For several years in the days before telemetry I used a couple of Schulze Lipodimatic battery monitors on a couple of models. These were connected between the throttle channel and esc, and monitored all individual cell voltages via the drive battery balance connector. A desired minimum cell voltage (eg Peter's 3.3V) could be set into the device, and when this was breached temporarily, the device would pulse the throttle channel as a warning. Throttling down a tad stopped the pulsing as current reduced and voltage rose again. However, if the low voltage setting was breached permanently, the esc's full throttle setting would be permanently reduced to about 80% and the pilot had better land before the motor shut down fully with a flat battery. These weren't cheap but did the job, and were useful on high power 10S-12S edfs in which one could flatten and ruin a drive battery very quickly if careless with the throttle stick. Been there, did that in my pre-Lipodimatic days.
If the Unilog could send an audible warning to the Tx via telemetry to announce the same critical events in real time it could be a useful accessory in cases where the feature wasn't built-in to one's radio system.
These days I use my Spektrum telemetry energy sensors (I also have a Lemon Rx+energy sensor as yet unused in a model but bench checked satisfactorily) to warn me when a selected value of mAh has been used during a flight, at which point I land the model. I fly 5000mAh lipos, and generally set the alarm to sound when 2100mAh has gone through the motor, normally after about 7-10 minutes depending on the model. This is just the way I do it, as it leaves the batts with around 50% storage charge saving time at home. I only charge the batts to 95% too, hoping that this will make the batts last longer, and that's why I set the "50% remaining" warning to sound at 2100mAh and not 2500mAh.
Because the warning always sounds when the same amount of battery capacity has been consumed, I don't bother timing flights any more. An advantage of using the energy sensor in this way means that by checking residual charge after landing I can ascertain when the battery is beginning to lose capacity. In fact.the first time I tried this system was when I had some not-very-old HK lipos which unknown to me had lost some 20% of their capacity. This meant that the residual capacity was only around 25-30% instead of the 50% I was aiming for, and I spent quite some time cursing what looked like inaccuracies in both the lipo checker and energy sensor, until I realised that it was the batteries that had lost capacity. The realisation also explained why my previous flights, which I had always timed until that point, always ended up with less residual capacity than there should have been.
|Thread: 6 Turning 4 Burning|
SR71 said he has flue. In which case, would a chimney sweep be able to help?
|Thread: If I fit floats to my Senior Telemaster will I need a more powerful engine?|
If you're going to fly sometimes with floats and at other times with the land u/c, you need to take steps to ensure that the model's CG is always correct for the configuration in use without having to add or remove balance weight during the changeover. If you forget to make the balancing weight adjustment, you might end up with enough of a rearward CG to lose the model in an unintentional low-level spin.
I speak from experience with my one and only floatplane conversion of a model which usually flew as a landplane.
It's likely that the extra lift from that portion of the floats in front of the propeller will require weight added in their noses to move the model's balance point a tad further forward in floatplane configuration as compared with landplane configuration. So you should set up the model's CG for its landplane configuration first. Then, having established where the CG should be for the model as a floatplane, add weight to the floats permanently so that when converting from landplane to floatplane, the CG will be automatically correct the instant the floats are secured in place. I didn't get around to adding permanent balance weights so that through a moment's inattention when adding the floats before (its final) flight which my Dad was going to video, I forgot to add weight to the model's nose, with the eventual unfortunate consequence mentioned above.
Your flaps should come in handy for taking off from a smooth unruffled water surface. Never having seen mention of this, on the first flights of the model I eventually lost, I scooted the model around to create ripples per the conventional advice for aiding unsticking. Eventually, I discovered that lowering the model's flaperons, which I had always used previously for take-offs in landplane configuration, negated the need for ripples, so I lowered the flaperons for all future take-offs.
|Thread: Best DV11 plan|
My own Fokker DVII is a lovely flier. The plans, and building instructions together with extensive flying notes are also available on Outerzone. The model is compact enough to be stored and transported fully assembled.
Edited By Gordon Whitehead 1 on 09/01/2020 17:28:30
|Thread: BMFA News Dec 2019|
Well said Ken. Three 3 more from me too
Edited By Gordon Whitehead 1 on 07/12/2019 19:11:29
|Thread: Catapult Build for Ducted Fan Models|
If I understand correctly, you stake the bungee elastic down at both ends at right angles to the line of flight, and then fasten the cord linking it to the plane at the centre of the elastic. This then has the effect of preventing the bungee elastic being deviated by the wind. During launch, which doesn't take long of course, the model on the end of the linking cord will be pushed a bit sideways by a side wind, but far less than if the cord was in line with the whole length of the stretched elastic.
We fly on a narrow field bounded by trees, often with cross-winds, and if that idea works well it's worth bearing in mind for future reference. The only possible downside seems to be that there are two bungee stakes to try to miss on landing
BTW, I think I also saw another thread about the Miles Student in your avatar. I can't remember if it was ducted fan or pusher, or which forum it was in, but I do enjoy reading design and build threads. After partaking in this thread I'm beginning to feel like having another go at a li'l EDF, having had much joy from the little ones several years ago. Must finish my current bipe project first, though.
Re the H-K bungee setup, there's a video here which shows how to set it up and avoid some possible pitfalls. The ends of the ramp are designed to not snag the wing undersides, so I stand corrected there. Whether the distance between the ramp rails is compatible with the distance between the nacelles on a 52in span Canberra is something to consider, and could be cured by changing the lengths of the cross-tubes. The safety pin mod is worthy of note, as are the comments regarding tailplane clearance, and ensuring the bungee pin is well pushed down. Personally I'd use a screw picket/dog stake for that job.
Hope this helps
Hi Steve, thanks for your video which explains the foot release very well. It's a very clever design and looks to me to be more foolproof against accidental launches than the pin-through-a hole style of the H-K foot pedal.
I love your Sipa Minijet, which I believe you featured in a recent build thread. It brings back a memory of my Dad taking me to an air display at Yeadon Airport in the mid 1950's. The display included a handicap air race which had everything from piston bipes to a couple of jets, one of which was the Minijet, the other being the Miles Sparrowjet. I can't remember which was the faster jet, but a vision of the little egg-shaped Sipa flashing along at near to nought feet is still imprinted on my mind. One of the bipes was a Blackburn B-2 and there must have been a Tiggie or two as well. Leo Valentin, the "Bird Man" was there but his launch plane had engine trouble so he never got off the ground.
Hi Steve, your ramp is very impressive in its apparent simplicity. Do the rails pivot up with as the foot release is pressed? What is the bungee material, and how long is it and how much do you stretch it?
A safety note for Roy's benefit which I intended to mention before is that a very secure bungee stake is essential. It's not been unknown for the stake to come out of the ground when the bungee is stretched and come flying back to hit the operator.
The Hobbyking kit doesn't appear to include any means of linking the bungee to the foot pedal and model, and there's no instruction booklet in the pics. Plus I can't see how the pipe joiners won't carve chunks from the wing undersides as the model exits the end of the ramp. A length of pipe insulation on the rails would prevent this risk to damaging the model.
Another note about the bungee stake. It's worthwhile marking it with some sort of flag. We'd carry the bungee etc to the flying site in a supermarket bag, and fix that to the stake to blow in the wind. This highlights where the stake is in the ground so that at the end of a flight you don't crash the model into it on landing.
Edited By Gordon Whitehead 1 on 12/11/2019 09:30:11
Edited By Gordon Whitehead 1 on 12/11/2019 09:36:56
Not so my Frightnin' seen here
That has to be the most relaxing-to-fly supersonic fighter ever, Ray
Another variation on the Bobsleigh ramp was that of his club-mate Terry, who used a pasting board that not only conveniently folded for storage, but also had a carrying handle. Owing to Terry's seniority we called this one "Gramp's ramp" !
The next pic shows solarfilm base of slipper.
Next pics shows recesses in packaging foam to accommodate bungee ring and fuselage hook.
I used this ramp for many years. We called this one "Gordon's Grasshopper". If the grass is long, the stake cord passes over an A-frame. The frame is just two laths of wood linked by one screw as a pivot, and the cord passes over the vee at the apex.
Launch sequence follows. Note wing supports for Lightning, and also the way the nose dips at end of ramp as model pivots on tank - cured by later use of slipper.
Model seen on ground is Ron Laden's scratch-built Eurofighter Typhoon. Ron shot the launch and flying pics during one of our many enjoyable EDF flying sessions using this ramp set-up.
Edited By Gordon Whitehead 1 on 11/11/2019 14:43:36
The ramp is a 1/4in thick exterior plywood board with folding legs and which is sized to fit on the floor of the car boot with the rear seats folded forwards. The legs fold so that the ramp takes up minimal space when laid in the back of the car. The point of using a board is that planes on which the tail is lower than the wing such as the Lightning, TSR-2 etc risk catching the tail on the framework of a pipe ramp. This eventuality cannot occur with a board.
When set up for launch, note how the rear legs elevate the back of the ramp so that the release cord follows the same slope as the ramp.
The ramp slopes at no more than 10 degrees.
I measure bungee tension with a spring balance, and use 4x model weight, ie a 3lb model has 12lb bungee tension.
The Hunter pics show wing tip supports from pipe lagging and the Lightning needs taller supports which peg into the edges of the board seen in later pics.
The Lightning needs the slipper seen in the pics. Without the slipper the belly tank pivots the nose down when the plane reaches the end of the ramp. The slipper is made from foam plastic with a solarfilmed liteply base. It only flies about 3ft from the end of the ramp during launch.
If I’d fitted the ventral strakes to the Hawk, that would have needed the slipper too.
Here’s my bungee launcher based on a design by Bob Partington which we dubbed the "Bob Sleigh". The pics show the components of the bungee cord and ramp. These days I prefer the pin in tube method over the ring and hook, having broken a bungee hook previously.
Pic below shows pin-in-tube launch connector in Westwings Hunter.
The foot release uses a yacht cam cleat. The sideways foot movement does take a bit of getting used to, but there’s no ring. There’s a risk that elasticity in the stretched foot release cord can flip the ring forwards and wrap the cord round the tailplane during launch. The plate is secured by two tent pegs, and the third tent peg acts as a safety catch, only being removed just before launch. The cleat is secured to the plate by two 5mm screws into T-nuts.
Next pic shows cam on point of releasing cord as trigger is moved sideways with my foot.
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