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About Markdun

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  • Birthday 11/10/1955

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  1. Bruce, I've read a bit about the extremes some of the RV guys go to to get an extra knot or 2 by reducing cowl inlet and outlet. Anyway a common thread is that the outlet, or more precisely just before the outlet, is very important. Stuff like gascolators, airboxes battery and even engine mount tubing can reduce the air flow and in particular affect port and starboard sides differently. It would seem to me that as the inlet pressures are the same it has to be the outlets. I note your EGTs are very close for a Jab. I'm still getting a spread from 640C to 700C. I don't see CHTs up around 150 except on 30+C days with two people in the plane and after a long slow climb out, mostly they are between 120 and 130.
  2. Mark, I do not think it is as simple as many have replied. No matter what you use, the key question is whether it will fail under what load, the number of cycles for failure, & its mass. I'm sure the 10mm 304 1×19 stainless wire with 12.6mm 316 stainless turnbuckles which keep my yacht's mast upright with a breaking strain of around 30kN would work with your rudder cables, but it would be tad heavy. Stainless steel does work harden more than the steel alloy use in AN fittings. Stainless fittings with thread are also more likely to gall. Further, stainless fittings immersed in seawater can also corrode leaving them looking good, but very weak. Nevertheless, many aircraft have wire cables of stainless, some have galvanised (same for yachts, though increasingly yachts have plastic such as dyneema replacing wire rigging. My 11m yacht has 5mm dyneema braid for the rudder circuit & it has loads easily 10 times of what you would get in a light aircraft ). Both my aircraft have stainless cables and a mixture of AN turnbuckles and stainless ones. My scratch built Cygnet has stainless turnbuckles on the rudder circuit (20 years, 1000 hours). Each one has a safe working load of 5kN. The ailerons and elevator circuit has AN cadmium plated steel turnbuckles. All cables are terminated on a thimble with Nicopress sleeves. My Corby Starlet (40 years 300 hours), previously VH registered, also has stainless cables. Turnbuckles are all AN steel ones (no turnbuckles on the rudder circuit). However the cables are all terminated by swaged stainless fittings and were supplied by a certified aircraft cable supplier. Having built several aircraft (successfully) my advice would be to stick with what the aircraft designer specifies. If you want to change it, discuss with the designer. And remember the rule for assessing whether to add something or make it stronger than the designer specified. Hold it in your hand & throw it up in the air. If it stays up, it should be added. if it falls down it was never meant to fly and should be discarded. Cheers, Mark
  3. I agree with all the previous comments to the effect that the quoted claim 'seven times more likely' is most likely hogwash. In any research, raw results, like these, may be nothing more than a random chance event. There are statistical techniques, robust ones, to test whether the results are 'significant', and usually they are not significant unless the probability that the results are merely random chance is less than 5%...the so-called 95% confidence. Why haven't the ATSB used them? Either they haven't engaged a statistician, or they have and they are too embarrassed to publish the outcome. There are lots of dishonest studies, particularly where there are commercial or other vested interests. For example, I have seen low quality studies with very small sample sizes that found no 'significant difference' between the control and the variable which are then used to justify a 'no effect' finding and then used to undermine the credibility of studies with very large samples. There are some good books on this detailing the tactics activities of Big Tobacco and Big Pharma.
  4. Markdun


  5. Nev, my apologies if you took what I said applied to you. It was actually a reference to my age. When my kids were 6 or 7 they used to think that dinosaurs were around when their grandfather was young. Now, my grandkids think the same about me. My point was that the tension between those that rely on more recent technolgy and those that rely on older methods is not new. When i was sailing in the '80s using a sextant a 'fix' was within a 5nm radius or there abouts...you adjusted your navigation accordingly....i didn't try a night passage through a gap in a reef of only 1 to 2 cables wide. ..I hove to 10nm away & waited for daybreak (to be woken by a French navy patrol boat). Others with transit satellite nav & radar went straight through (& didn't have the experience of receiving a rousing cheer & waves from the french sailors when I stumbled naked into the cockpit to investigate the noise of the patrol boat). I would sail straight through now too with GPS. I think you are wrong on GPS unreliability now. ADSB relies on GPS, as do lots of other things. If the GPS system goes down, then there are far bigger problems than a guy in a light aircraft. And even if it did, as an RAa pilot you just have to find a reasonable paddock to land. I rely on GPS for my nav in aircraft, on the sea and bushwalking. I still carry paper maps and an orienteering compass but have not had to use them for ages except to teach others or to re-assure myself that things are tickety-boo. I have two aircraft; both with an MGL Xtreme EFIS/EMS as the main instrument and with a 'steam' ASI 'back-up'. I would be happy to replace the stream ASI for a secondary electronic ASI/ALT but the value is not there to justify it. There are some inflexibilities in the MGL Xtreme, but overall they are fantastic. Cheers, Mark
  6. Ahh, Skip, its called the 'astronaut syndrome'. Back in the mid 1980's, pre-GPS & only a few dinosaurs left, quite a few sailing boat owners sucuumbed to this syndrome, with their chart table/nav desk surrounded by dials, lights and switches and transit satellite navigation, probably with a clip-board and check lists. When I was in Nukalofa I think there was only 4 of us out of 30 cruising sailors that only had a compass, log & sextant (& charts) for navigation. Much discussion then that modern sailors wouldn't know how to use a sextant if the transit satellite receiver failed etc. Seems not much has changed regarding attitudes...but tech certainly has. ....i met a guy at 1770 a couple of years ago on a very fast 50' sailing cat who had sailed from Hawaii via lots of islands with just an ipad with downloaded charts for navigation.
  7. I'm also with Skippy. ..my primary navigation instrument is the right eyeball mounted just below my forehead. After 60++ years of service with just one replacement lens I think that is pretty good. (The left eyeball, being only good for things less than 1m away without the monocle, is reserved for the instrument panel). I'm not that keen on voice alerts and warnings...one of the joys of flying is that my wife doesn't like flying and stays on the ground. ..would seem silly to have an artifical replacement that would detract from the serenity. I was taught that if I ever landed 'wheels up' in a sailplane that once the aircraft stopped, to immediately jump out and pace the distance of the landing roll....vis 'I did it intentionally to see how quickly it would pull up'. We did always fly off lawn though.
  8. I've got a real nice electric vario in my Cygnet. I do miss the lovely beep beep beep of the audio it made in a glider. I can't hear it now over the noise produced by the iron thermal (or my 'too much engine noise hearing').
  9. How many of us have lost rc gliders? Like Bruce I lost one, but about 20 years ago. Hooked it up to the bungee, let it go. ...ooops, forgot to turn the power on in the glider. ..not to worry it will just come off and land nearby.....wrong! It came off the bungee in a nice right turn straight into a thermal. I lost sight of it as it disappeared into the base of cumulus about 2500' above. No lithium batteries though, just nicads. For those wanting a 'soft start', how about a mechanical decompression lever....works ok on hand start diesels? Or compressed air, shotgun cartridge...that would be cool. I'm now getting worried about fire from my lithium batteries; i think I'll mount them in a stainless insulated box with a quick release pin attached to a servo & temp sensor so if the tempersture exceeds, say 120C, it automatically drops out of the aircraft. And if it looks like a difficult outlanding, I could manually pull the pin to jettison the battery before 'landing'. Thinking of avoiding battery started fires on crashing, how many people have a battery fuse mounted on the battery box or positive battery terminal as motor vehicles do? I also wonder how many lead acid batteries explode from the explosive mix of H2 and O2 generated when they are charging? Or structural and corrossion damage aircraft caused by the weight and acid electrolyte? I've see at least one 24 xxxx registered aircraft with cracking on the firewall from the lead acid battery mount....it was quite difficult to rectify.
  10. Mike, the stator windings melted. We removed the stator completely before another flight because we couldn't exclude a short circuit developing in the melted stator windings which could lead to more smoke & hot stuff dripping on the carbie. At 2900rpm the alternator can obviously deliver a current that exceeds the capacity of the stator windings. The starting of our diesel firefighting pump with a very tiny lipo battery also starts off slowly and as Old Koreelah said, then it cranks it with some violence. No landing lights on my planes, and my LED strobes are hardly likely to warm up the battery.
  11. Bruce, be careful with the human voltage regulator. My comment about a destroyed Jab stator comes from experience on a delivery where the Jab/Kubota regulator failed and the voltage started to creep up towards 17V (this is with a lead acid battery on my side of the firewall just near my toes). The aircraft had a nifty switch in the cockpit (Alt) that open circuited the charging wire from the regulator. So I did what you do; as soon as the voltage reached 14, I switched it off. But I also switched it back on when the voltage dropped to 12.5V (it had a big panel with old instruments)...big mistake. ...blue smoke etc at 7500' and drops of molten copper dripping on the carb (we discovered that on the ground). Skippy, the slow start is only from an early black Jabiru starter motor which is a bit underpowered. I think its just that the lithium battery doesn't deliver the current until it warms up a bit...the same as a lead acid battery...but to warm those batteries up I understand you roast them in a camp fire for 15 minutes -- well that's what I saw on the TV series Bush Mechanics. The other thing is that lithium batteries' voltage doesn't drop away as you extract energy like a lead acid battery. I'm not that fussed about it as starters are pretty robust. ..i once drove about 250m in 3rd gear in a Mazda on the starter motor across a floodway on the Nullabor when the distributor got wet. And I've seen a few times people endlessly cranking a Jabiru refusing to start (because the rpm was enough for the ignition system to fire)...This would be far tougher on the starter motor compared to the few seconds it takes to get my motor going.
  12. I assume you have installed a sliding track from a front car seat for your wing attachment so you can easily adjust your CoG. I wish I thought of that when i installed a lighter Jab engine to replace a VW, requiring moving the engine forward 50mm, new engine cowls, and then 1kg of lead in the tail because 50mm forward was too much!
  13. I just splice in an automotive blade fuse holder on one of the two wires that go from the engine's alternator to the voltage regulator, and put in a 15A fuse. These fuses are designed for vibration. I don't use the glass tube type fuses in an aircraft as the unsupported fuse wire inside the glass tube can fatigue break from vibration. The Powermate website probably has a diagram of the details.
  14. I think the big practical issue is the charging of the Lithium batteries. If you forget to turn off your master switch and find you've a flat aeroplane battery you can't just 'jump' start from your car as you will exceed the charge rate for the lithium battery (depending on the battery management system in the lithium battery). Or if you hand start, or manage to get a start from a nearly flat lithium battery, the standard Jabiru voltage regulator will also not regulate the charge current and this could see the battery's charge rate exceeded, or the Jabiru's stator destroyed (if you have no fuse in the AC side), or both. The Jabiru/Kubota voltage regulator might also have a too high upper voltage .... one of mine was at 14.4V which was a bit over the 14.0V recommended for the lithium battery. I've installed the Powermate regulator -- it regulates the charge current to a max of 8 Amps and my voltage never goes above 13.9V now. The big difference I've found in use is that on a cold morning when you press the 'start' button the starter rotates the engine to the first compression and really struggles to move it through TDC, this occurs on the second compression too, but then the battery seems to finally wake up and gets the message that it is required to deliver lots of Amperes and voila, the engine spins like crazy & starts. And it does deliver lots of Amps....I had to increase my battery fuse from 100A to 125A.
  15. Modifications to the air intake on the side of the cowl (& its position) made a big difference to EGT spread on my Bing carbed 2200. So I concur with Hyundai. I ended up settling on a port mid height (ie. widest part of cowl just under the join) about 75mm forward of the firewall. I also have a small deflector on the forward side of the hole that extends outward about 1 cm. After lots of experimentation this seemed to give the best results at cruise & WOT throttle settings. Although I have to throttle back at WOT (rpm ~ 3100 FF 23lph) to avoid exceeding 700C egt on my rear cylinders (particularly #4) at the cost of about 50rpm, & at cruise (15lph) my #4 runs at around 640 to 650C when the others are around 710-720C. No data on manifold pressure unfortunately. Why the inlet matters I don't know as I would have thought the air filter and the little rubber flap on the air filter box would remove any significant pressure effect on the carb. Carb inlet vanes made bugger all difference, except when a 'vane' obstructed one of the pressure sensing ports of the Bing. My limited experience on a Rotec carbed 2200 with a J&H filter attached directly to the inlet drawing warm cowl air with no carb heat 'a la' many Rotax 912s is totally different. EGTs are evenly spread irrespective of carb rotation. Carb temp has never been less than 30C even on a 5C OAT day, and has seen 50C+. I do worry about vapour problems as there is no float bowl in this setup.
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