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Thruster Bob

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  1. Hi Kyle, I've been out of touch a bit. I didn't think Malta had enough flat space to have airstrips? Re struts, We don't have a factory as such anymore over here, I think Thruster Australia may be still be operating out of Evans Head?. TOSG has pretty much faded away now, otherwise the guys at Watts Bridge would have helped you out. Are the machined ends of the struts OK? If so then you just need to replace the aluminium tube , it will probably be an inch size. Any aircraft engineer could replace the tube. Although it needs to be anodised , so thats an extra cost. Cheers, BobT
  2. Holbrook: The trampoline of airports! Odd you should mention Holbrook, I'd only done wheelers during training and was pretty hopeless at them , but I normally use three pointers all the time. Then went to a fly-in at Holbrook, thought I'd do a wheeler, and did two huge bounces to the accolades of hundreds of onlookers!!! So embarrassing! Pud has a good point re tail wheels (and damage to them), after landing a three pointer, I'd pick up the tail pretty much straight away and do a tail up taxi all the way back (except with tail-winds) until I was ready to park. I think of the tail wheel as a handbrake, use it only when needed. It would be nice to be able to do a wheeler, and then gradually transition to a tail-high taxi, I've done this with Keith's thruster (with the stiff springs) , but mine has the big soft springs. The other point is , it's my suspicion that most Thruster three-pointers actually happen with the tail wheel about six inches to a foot off the ground when the mains contact, then the tail contacts a fraction of a second later (The angle of incidence suggests it has to happen this way too), you'd need to do a beach landing and use a tape measure to be sure. Yet another thing, you need to keep the wings level with your feet during a three-pointer, my suspicion is those pilots who have trouble flying at high angle of attack where the controls get all mixed up, non-linear and crossed over will have difficulty doing anything but a wheeler. Cheers, BobT
  3. Hi Pud , Looked at them on the weekend, My ends are good, there's a few spots of pitting corrosion (must be pinholes in the clear coating?) Cheers, BobT
  4. More on Strut Attachment & info on intergranular corrosion Hi Pud. I'm speculating the parts are made from 2024 alloy. (Based on your observations and mine of the powdery white corrosion) It's usually known as "machining grade". It has abysmal corrosion performance, even sitting on the metal rack in the shed it gets covered in a white frost. Given the operating conditions, a 606x alloy would have been a much better choice for this part (or even marine grade 5052 alloy). I think the original designers were led astray by the appeal of the higher UTS (60,000psi) of the 2024 vs ~40,000 & 30,000 psi for the other grades. --------------- Ok My machinery handbook says 2024 is prone to intergranular corrosion, so I google it up Intergranular corrosion - Wikipedia, the free encyclopedia and in Paragraph 5 it says aluminium alloys with copper (=2024) are subject to exfoliation corrosion, resulting in leafing or lifting effect , which pretty much describes the photos in the AD. A few more similar links: Intergranular corrosion Different Types of Corrosion: Intergranular Corrosion - Causes and Prevention Different Types of Corrosion: Exfoliation or Layer Corrosion - Causes and Prevention http://canteach.candu.org/library/20053207.pdf Metal Improvement | Exfoliation Corrosion (the above suggests cadmium plated fasteners may be implicated) Exfoliation Corrosion - JAMWiki and a tutorial on aluminium grades: Argentum Solutions Inc. - Sterling Guidance on Corrosion and Materials Degradation -------------------------------- Interestingly enough Austenitic stainless steel is subject intergranular corrosion after welding. This goes part of the way to explaining the failures on the other half of the wing attachment, where the TIG welded parts have the end of the weld (= stress raiser) near the high stress bend. Perhaps the whole thruster wing attachment method might be a good example of "how not to design something" for an engineering class. Cheers, BobT
  5. Hmm , Looks like the same part on the T500. I'll check it out next time. Looks like the fault is due to material defect in the aluminium alloy bar used to make the parts. (some kind of inclusion. like a "cold shut" ). "Cold Shut 2 (1) A discontinuity that appears on the surface of cast metal as a result of two streams of liquid meeting and failing to unite. (2) A portion of the surface of a forging that is separated, in part, from the main body of metal by oxide. " I wouldn't think this kind of defect would exist in extruded material though?. Thruster UK needs to trace back through their QC records to identify the batch and supplier of the alloy. Then ensure all the parts made from this batch are recalled and destroyed. The parts in the photo look like they are anodized, so I'm guessing that the acid used during the anodizing process leached into the edge of the defect, so in conjunction with atmospheric moisture this acid would slowly work its way through the length of the defect. Creating a small electrochemical cell between the oxide of the inclusion and the parent metal. Hopefully all the Aussie thrusters won't suffer from this as their parts would be made from a completely different batch made a decade earlier in a completely different factory. BTW (a long time ago) after I cleaned the surface white powder off my wing attachments, I polished them and sprayed them with clear lacquer. The offer of a 15% discount on replacements is a bit cheeky , the parts would have been defective "as supplied" by the manufacturer, and "unfit for purpose" and should be replaced free of charge. Seems the UK laws on trade practices are softer than in Australia. Cheers , Bob T
  6. Hi all, My vote is for three wheelers, It's what I've always done in my Thruster. I can do them on dirt, grass, sand, bitumen in upto 20kts headwind and 15kts sidewind. My worst landings have been my attempts at wheelers! I have the long, soft springs and some say this makes it more prone to bouncing/ballooning. Its helpful to have a quick hand on the throttle, as you will sometimes benefit from a little extra power, especially with Pax and full fuel. To do a dead-stick three-pointer can be quite tricky, as you need to arrange to have the right combination of vertical and horizontal speed (i.e. you need to be fairly fast, if you just waffle in you won't have energy to arrest your descent, and risk ploughing through a compression stall just before you hit the ground) Cheers , Bob T
  7. Thruster Bob

    trailering

    Hi Rocket Driver. I'm someone who has built their own trailer. It tows backwards, the basic frame is like a boat trailer (Mine is registered as a boat trailer, It's 180kg empty) , and the thruster wheels sit on pads behind the mudguards. The wings mount beside the fuselage (with skins still on) they are bolted to the trailer frame using the existing brackets on the wing spars. You need to take the elevators off, and put them in the vehicle. You should ideally take the propellor off , or a low hanging tree will do the job for you. The only problem with my trailer is the bottom of the fuselage scrapes on a trailer cross member when unloading. The trailer has done several thousand kilometres, the only mishap was a lost mudguard courtesy of a kangaroo. I've attached a pdf of the original drawings (these are like 15yrs old now!) If that's of some help. The trailer and airplane are currently in the shed if you need some photos. It takes about two hours to dissassemble/reassemble if you have three skilled people doing it. About half a day if it just yourself and your wife. Cheers, BobT thruster trailer.pdf thruster trailer.pdf thruster trailer.pdf
  8. Trailering : Best way to get your new plane home Oops, Thanks Tony for pointing out my omission. One of the most obvious reasons for trailering it is on aircraft acquisition. Having a new pilot fly an unfamiliar (and most likely dodgy) aircraft long distance is a recipe for disaster. You should assume if you buy an aircraft from anyone but Tony, that it almost certainly has one or two minor irregularities, which can be hazardous in all but the most competent pilots hands. Most aircraft accidents are not caused by a single factor, but a combination of individual factors, each of which is manageable individually. An unfamiliar aircraft in an unfamiliar location already has two factors stacked up, toss in some equipment failures, a bit of illness, failing light, low cloud, fuel, a missing map... suddenly all the holes line up on your pieces of swiss cheese. The moral here, as is Tony's war story is always to have a backup, other options, a spare, redundancy, an alternative, plan B, an alternate strip, he was lucky enough to have a spare pilot! I bought my aircraft as a complete aircraft, but with "some assembly required" from the Thruster "Factory", I modified an 8x5 trailer to pick it up. I hadn't finished my license by this stage. But the reason I built the trailer was to take the Thruster up to my family in Mackay over Christmas. I actually passed my license and passenger endorsement about 2 weeks before the first trip to Mackay, I didn't have a X-country endorsement at that stage anyway. So I based myself just north of Mackay and flew around for a couple of weeks from there just honing my "aviating" skills. You really need to build up a lot of experience before undertaking any kind of epic adventure. A year later I went up again by trailer, and with considerably more experience under my belt, this time we went as far as Hamilton Island (including a 5 mile overwater leg) This time we were mixing it with 767's into Proserpine, and the really windy Whitsunday strip, and finally flying into the Control Zone on Hamilton, with an interesting landing and takeoff on a 3km bitumen strip in 15 gusting 20kts, with some really interesting orographic wind flows. (On takeoff we were at 2000' before the end of the runway). So in summary, I had some 6000km of trailer miles, before I went on my epic adventure (7000km Red Nose round trip) and even then I did it in company. (But I think I'm crossing over to the other topic!) As far as trailer balance goes I think mine is about 5% on the towbar, and a bit more with full jerrycans, RTA recommend around 10%, and I'd agree with that. It's easy enough to push it around with a jockey wheel (But always remember to completely remove the jockey wheel and carry it in the boot!). My previous experience with towing trailers is that having a low c.g. and wide track yields good stability, and that's what I built into the trailer. Soft springs tend to destabilise the trailer. Standard leaf springs with rear shackles add stability, novel suspension types should generally be avoided. Cheers, bobT
  9. Trailer with assembled wings Hi Guys, I scratchbuilt a trailer to carry my Thruster, and it carried the wings fully assembled. Each wing bolts to an approx 4ft square rectangular frame of 1" RHS, using the standard wing attachment points. Each of these rectangular frames is pivoted where it attaches to the trailer, so the wing can go from horizontal for attachment to aircraft, to just past vertical for stowage on the trailer. The horizontal position has the wings at the same height as the aircraft so in theory one can just wheel up the fuselage and attach a wing,( in practice it is nearly impossible). In the stowed position there are shaped wooden blocks with padding to support the wing ends. I added a small jib which could swing out and support the weight of the wing during assembly, but it never worked properly and I removed it later. The wings are stowed leading edge down, bottom face to the outside. The fuselage is towed tail first, with the rudder and tailplane attached, and the rudder locked with padded clamps. The towball is 200mm horizontally in front of the back of the rudder, the trailer main frame is two 50mm RHS at 1800mm apart, and the rest of the skeletal frame is 25mm RHS and triangulated everywhere (i.e. a space frame) as a result the entire frame is rigid, so there is no twisting or bending which would cause rubbing of the wings, the Thruster is securely bolted to the frame at the tops of the springs, so everything is one big stiff structure. The propellor boss overhangs the trailing ends of the wings by ~ 200mm The lights and number plate are mounted on a duckboard, which attaches to the wing ends at the rear, so technically there is no overhang. It was registered in NSW as a "boat trailer" in about 1994, they had no issue except wanting longer mudflaps. The springs were really long and soft automotive leaf springs. It's nearly 8'wide (2250mm), with a hollow axle. It could be made narrower, but I have the wide wheelbase (2200mm) Thruster anyway. I screwed tarpaulin studs (like they use on utes) to the frame, and fitted a shaped tarpaulin front end. You can't tow it with a tarpaulin over the whole thing as it flaps a lot. I've never had issues with crosswind towing or speed wobbles upto 110km/hr. I've used it to drag the Thruster upto Mackay from Newcastle on two occasions, so that's 6,400 kilometers total on long trips, plus several local trips. Only issues were (a) bent mudguard due kangaroo (b) cracked welding around mudguard- added braces © fuel consumption (d) finding big enough parking spaces (e) nowhere to put the elevator, propellor, toolboxes and other paraphenalia Given the extra effort required in handling the assembled wings, and the careful choreography to get the fuselage onto the trailer I don't think there is much benefit compared to racking the wings on the "universal trailer" (I still have to remove ~ 10 battens anyway to accommodate the cockpit width). If you were to make a sufficiently large fully enclosed trailer, then you could carry the wings fully assembled. But the trailer would be the size of a large caravan, this may be a viable option where you are using the trailer instead of a hangar for storage. The wings & fuselage would fit together better (i.e. narrower trailer) if the wings are carried leading edge up, but it would be difficult to support the weight on the flap edge, and the prospect of damaging the flaps through handling is always an issue. From my experience the only reasons you would use a trailer are (a) as a cheaper alternative to hangarage (b) to recover a damaged aircraft. In my opinion, for long distance travel the best approach is with two aircraft and one large ground vehicle, and do it as a two family holiday. Cheers, BobT
  10. its all greek to me! Ah.. a common mistake translating the ancient Greek text to English : ο βρυχηθμός του θριάμβου του. has been mistranslated from το κουδούνισμα του θριάμβου του it should have read "The rattle of his Triumph could be heard through the streets of Jeruselem" Now we're talking legendry British workmanship!
  11. Yea therily It also mentions something about anointing with oil , so they were definately Trumpys!
  12. another Mustang I was hanging out for Beaver, but I'm another Mustang! You are a P-51 MUSTANG. You enjoy classic things. You like the beauty of old machinery, and the way that it awed the world. You love adventure, and you like being top dawg. You are powerful, and you are determined. You see qualities in things that most people do not. So buckle your seat belt and tear up the skies, it's your turn to have some fun!! BobT
  13. Thruster flight to Cape York for red nose day Hi Guys, In 1995 I did a fund raising trip to Cape York for Red Nose day (in my little blue Thruster with a red nose painted on). I should scan in the photos and upload them. We started in Newcastle and flew to Boonah to join up with the other 5 ultralights. We officially started the flight from Amberley AFB , then we went up to Cooktown inland then onto Weipa, then just two aircraft went up to the tip. ( I planned on going to the tip of Cape York, but lost an exhaust spring, and punctured a tyre on departure from Coen, so stopped at Weipa for a pit stop). We came back along the coast, and intended to drop in at Watts Bridge on the way back, but got socked in at Noosa (we had some marginal VFR on the coastal segments). Some very long days in there! I fitted a C172 bladder tank into the wing, for a total fuel capacity of 90litres, or 4 hrs + reserve. I've flown longer safaris in C172 and C182's but the Thruster trip was the most fun. Lots of fun times, plus we raised $20,000+ for a worthy cause. Cheers BobT
  14. Thruster Bob

    wheel base

    Mine measures 2200mm (no wings, on trailer) Hi Fly, Just ran down the shed and measured mine, it's a T500 (25-0294) . I have the long floppy springs. Wheelbase outer edge to outer edge of tyre is 2200mm, when on the trailer , this is with 6" wide tyres (Kenda 15x600-6) on aluminium rims . (I think I got my wheels from Airborne here in Newcastle, they are fairly standard aircraft tyres). The measurement would be slightly wider sitting on the ground, with wings attached, and fuel in the tank, (after pushing the aircraft forward a bit), probably close to your 2300mm then. I'm guessing we have the same springs. I originally welded some squares of angle onto a 5x8 tandem trailer to pick up the aircraft when first purchased. Then I built a custom trailer to carry it. Went to take the Thruster home a couple of years ago (after Cooranbong airport closed:crying:), and forgotten I had put wheel pants on ! Had to take them off before getting it onto the trailer again aargh !!! Originally my springs had sagged, and I took them to Dumbrells springworks, and they annealed them, re-bent them, and hardened them. As Tony says, there's nothing special about the springs, and the springmakers can make you a custom set to suit your preferences (and to a better standard than most of the Thruster OEM springs.) The axle bolts used by the "factory":clown: can be dodgy too, and the hole in the spring they attach through can be malformed, you may need to file the faces flat and deburr the edges of the hole (need to anneal the springs first). Check where the springs bolt onto the rectangular through beam too, if this connection is not rigid (ie the springs rock back and forth) then you may get fatigue failure on these bolts. Cheers, BobT PS I've uploaded some pictures, so you can see if yours looks the same front on, just click on "Thruster Bob" on the left side, select "view profile" and click on "album" , I've also uploaded a picture to the Thruster section of the gallery.
  15. Hi Phil. Since my last notes, I found my Californian Powers Systems catalogue, several hundred page gold mine of info about Rotax engines. And lo and behold Mike Stratman has scanned his excellent articles onto a web page. http://www.800-airwolf.com/articles.htm Page two of this part shows the different needle shapes http://www.800-airwolf.com/pdffiles/ARTICLES/part11.pdf Page two of part10 shows the expected mixture vs rpm http://www.800-airwolf.com/pdffiles/ARTICLES/part10.pdf He also makes a throwaway comment about exhaust systems being responsible for the "not holding a midrange rpm syndrome". Exhaust system tuning was to be one of the things I would have suggested to you also, but presumably the exhaust system hasn't changed, and a leak at the ball joint is normally noticable. I had an exhaust spring fall off during climbout once, and it was a real struggle to clear the terrain at reduced full power, (but power was reasonable at 75% throttle where the tuning is less critical)! Mikes part12 talks about CHT and EGT which was your original post anyway. Did you get a chance to look at the weblink I posted earlier at matronics.com , the guys there had similar problems with EGT and RPM hunting, and found switching to smaller needle solved their problems. I'm thinking a needle with a steeper slope will help you out (15K2?) certainly a new needle has a steeper slope than a worn one so there's a first choice I'm a bit surprised you still have high EGT's on the ground, the expectation is that max rpm will be lower, and EGT will be lower when on the ground. Here's a summary list of High EGT causes: (a) New Needle most obvious - yet to be tried (b) Low fuel level - fixed that © Main jet- tried a 10% bigger one maybe try a 170? (d) Your altitude is lower or its colder than before (e) Exhaust system detuned (f) Air leak on inlet side, check rubber carby mount (g) your aircraft is much slipperier than before, check your ailerons: do they both point up? (h) your propeller pitch is finer than before. (i) you are much lighter than the original owner (j) Different (thicker) two stroke oil, or higher oil:fuel mix BobT
  16. Ah this might be interesting: http://www.matronics.com/archive/archive-get.cgi?Kolb-Archive.digest.vol-dc look particularly in the area where the posting date changes from 11sep to 12sep. two interesting tips (a) use a shim under circlip (b) use a thinner needle see also http://www.thirdshift.com/jack/firefly/firefly58.html cheers, bobt
  17. Hi Phil. Ah having your own strip, what a luxury. My thruster is on a trailer in the shed as I am "between hangars" at the moment. So it's a couple of years since I've poked around with the engines. Ground tethered tests have their own problems, e.g. (a) great difficulty in untying the rope afterwards (b) getting a ring vortex around the propeller, particularly if you have a tailwind. It's not representative of real flight, but can be useful indicating if your engine is under-performing, (compared to earlier ground runs, but if you haven't got a history of earlier ground runs it's difficult to tell). Positioning of EGT probes is apparently important (but I have no direct experience), I have two EGT probes at the recommended position, and a switch to look at either one. (The 582 has two carbs , I think the 447 has only one?) As regards the floats , check this page http://www.ultralightnews.com/enginemaintenance/bingcarbtuning.htm (the page before the one in your first post) and http://www.ultralightnews.ca/bing/bingservice.html This will give you a quick indication of the actual level. When you have the bowl off, the floats stay in the bowl . There is a little brass wishbone shaped bracket the floats push on. If you push this up gently you should feel when the fuel valve just seats, (if some one else pumps the fuel, it will stop dribbling at this point), at this point the little arms should be parallel to the carby base. There is a little tang (pushes on the bottom of the fuel valve) that can be bent to change fuel level. Aha the second web page I pointed to says it can be done on a bench by turning carbies upside down! That's a much cleaner method!. Note that wear in carby parts invariably richens the mixture, perhaps a previous owner just changed circlip position and put in a smaller jet to compensate for wear? Its starting to look a lot that way. The heirarchy should look like this: (a) Get the fuel level to the correct value (don't tweak it to change mixture) (b) Select the main jet according to full throttle mixture © Select a needle to control midrange mixture (d) Adjust the circlip to suit altitude and temperature. The Bings are extremely reliable carbies (if you don't neglect them). Though you should expect to replace the needles every 200Hrs, and fuel valve, floats,(maybe float pin, maybe jets) every 400hrs. Also just check whether you have the ancient needle with three rings? And whether you have a tiny o-ring on top of the cir-clip (without the O-ring, the needle rattles a lot more and wears out quicker) aha see here http://www.ultralightnews.ca/bing/needleclipupdate.html (they reckon on 150hrs for the needles). I've never really been a big fan of reading spark-plugs or tea-leaves. With two strokes the type of oil and mix ratio affects plug colour, and whether you are burning unleaded (automotive) or high-lead (aircraft) fuel. Cheers, BobT PS It's winter now , expect to use a richer mixture, try the bottom groove, if it runs smooth over the entire range then all's good
  18. Tried new needles??? Hi Newairly. Two points (a) The right jet is the one that gives you the correct EGT, even if it's different to one in the Bing table! Because of the way two strokes work, the amount of air/fuel that gets sucked in depends on a lot of things , notably resonances in the exhaust system, and whether you have the correct prop. (b) Has anyone told you about the needles yet? There is a little circlip on them, you move it up a notch to go richer, down for leaner. You may need to change needle position from summer to winter or if operating at high altitude. Different needles have different tapers, and the taper varies along the length. From your symptoms though it sounds like you have a needle that is worn in midrange , making the mixture richer in midrange than usual, which gives the appearance of being lean at full throttle, pull the needle out, have a look at it, the worn area is usually visible. So you should replace the needles, always good to keep a spare set in the your kit on the airplane! (you do have a kit? under your seat, with a rag, spare plugs, plug spanner, philips/slotted screwdriver , spare cable ties, a bit of safety wire, spare safety pins) Normally the mixture is supposed to get richer at full throttle, i.e the EGT should go down at full throttle. The worst case EGT is usually on descent, particularly a forced descent at part throttle. If I have my needles setup for cruising, then I find I need to pull the chokes on in a rapid descent (It's a 582, but the same thing will apply). Note it's not a 2 stroke thing, CHT and EGT are only vaguely related, the situation on descent being a classic one, the EGT measures the temperature of the combustion gases, (and hence the temperature of the piston) irrespective of the volume of gas. On the other hand the CHT measures the heat transferred from combustion which is proportional to combustion temperature times gas volume, this heat is then removed by cooling air flowing past. So on descent you are windmilling, so the engine sucks in more air than the carby expects (as there is no exhaust back pressure) , so the mixture goes lean, and the piston gets really hot (it's not melting yet, but the crystal structure resembles a slush puppy) , but because the throttle is retarded, the volume of combustion gas is small but extremely hot, so heat flow into the cylinder is modest, but cooling airflow is high, so the CHT is quite low, in fact you can have the situation where the piston expands so much in the cold cylinder it seizes up. Which is why in real airplanes, they have engine cowls , that can be closed to keep the heads nice and toasty warm, and a mixture control that is always set to rich for descent. It's why real pilots make throttle adjustments slowly, watch the temperatures, and use cowls and mixture controls as required. This is why we have downwind checks, as the engine setting needs to be different during the final approach (setup to give maximum power if a go-around is required) than what it was earlier during descent (setup to preserve the engine). As I hinted at earlier, having an incorrect propeller / gearbox or incorrect exhaust can do odd things with EGT, check with other Tyro owners to see what they use. Although if I had money to bet, I'd go for the worn needles! While you are poking around in the carby, check the float level, the float should be just horizontal when the petrol starts to come out, (use a bucket under the carby, push floats up with your finger,and have an assistant work the priming pump) now take the floats off (without losing the fiddly bits) put them in some water or fuel , they should float high like corks, if they are half submerged - buy new floats! Now look inside the carby bowl, it should all be the same grey colour, if it is white near the bottom, then the aircraft has been left standing in the weather, with water left sitting in the bottom of the bowl, if this is the case then be alert for corrosion damage in the rest of the fuel system and the carby, bits of white powder play havoc with the jets. You may want to check your ignition too, I think the 447 has points? If so then check the advance angle and gap. (It's faintly possible an earlier owner ran it on high octane fuel, and advanced the ignition, but Rotax's can't handle the higher EGT) Cheers, BobT PS , I didn't actually answer your question yet; yes the CHT will drop at any particular throttle setting when EGT is lowered, but not by much ,100 of EGT = 25 of CHT maybe).
  19. Stress Corrosion Cracking ??? Hi Guys, I've had another look at the photos, the bottom one caught my eye, as it appears to be badly corroded. It is possible that water has got inside the tubing, and been retained in the gap between the short insert, and the part of the tube that cracked. In that case you have ideal conditions for stress corrosion cracking, this normally requires some existing stress in the metal part, but post-weld stress that has not been stress relieved would be sufficient. In this scenario the crack would have initiated on the inside of the welded tube. The 4th photo also show a forked crack. Stress corrosion cracking can usually be distinguished as the edges of the stress corrosion crack are jagged (like a lightning bolt) and will sometimes fork, weld cracks are straight, generally longitudinal but fuzzy edged fatigue cracks are generally fairly straight and shiny, although fatigue can finish the job that other modes start. It should be noted that in "real" aircraft, "tube oil" is run through the inside of the CrMo sections after manufacture (it's basically fish oil), to minimise internal corrosion. Cheers, BobT
  20. CrMo welding methods and cracks Hi All. Hats off to Robin for averting tragedy, I've practised attempting to land with simulated control failure. But this just involved letting go of the joystick, and just using throttle and rudder, this is very difficult, however it's not possible to flare properly, so the best you can hope for is to get ~6feet off the ground at low airspeed and go for the controlled crash. As for the actual cracked section I have four points to raise: (a) Has someone, who knows what to look for, looked at the cracked section? Fatigue cracks are usually shiny (or with clam shaped ripples), and extend usually around 80% of the section, with the last 20% or so being a matt grey colour where the material ripped. On the other hand shrinkage cracks from the original welding will be matt and brown from rusting. Welding defects such as undercut will crack along the edge of the weld. (b) The insert section looks to be too short? is it meant to be longer?, it would act as a doubler if longer. The short length as shown can only act as a stress raiser. Tony may some other examples to measure to see if the problem is a one-off manufacturing defect.The presence of this internal piece would act as a "chill" during welding, which is undesirable. © Chrome-Moly has a tendency for what is called "hot shortness" Essentially this results in shrinkage cracks, usually within the weld or just on the weld edge, particularly a problem when the metal is not preheated and/or a thin section is welded to a thick section or you are welding two short stiff sections at two ends (i.e. a tube passes through a tube and is welded at both sides), or current is too high with weld traverse speed too fast. It should also be noted that oxy-acetylene welding is much less critical. With TIG it requires some considerable experience to minimise thermal gradients. We had a particular issue at work trying to weld a CrMo bracket to a stiff piece of CrMo tube, it was welded at two places, the first weld was OK, but the second weld would invariably unzip, in the end we just brazed it. (Brazing of CrMo is the preferred method for bicycle frames anyhow) (cc) Mil-std-2219 requires preheating for welding of 4135 and 4140 CrMo (these are 0.35% and 0.4% carbon, the CrMo normally used is 4130 at 0.3%) and for Argon (or He) gas. Postheating for stress relieving and normalisation is also recommended. It is possible by poor welding technique to raise the carbon content in the weld bead e.g. carburising flame, oily steel, using CO2 weld gas. (d) Some kind of safety wire could be used to ensure the front of the tailplane wouldn't separate even if cracked. Heck even a cable around the boom would keep it together. I've had two case of weld cracking in my T500 (TTIS ~800hrs now) , one was on the vertical fin where one of the thin diagonal braces broke off. The second case was in the CrMo axle tube, this had ~1/2" OD x 3/8" ID bushes for the spring securing bolts. The bushes were welded at the top and bottom of the axle RHS section, all four bushes were at least partially cracked. I had them re-welded by an aircraft welder for good measure, although the axle assembly is perfectly functional even with cracked bushes. There are probably T500's out there with cracked bushes now, you just can't see the cracks until you pull the CrMo insert out. Cheers, BobT
  21. Yep I like the idea of a "sticky" post with approved modifications, (possibly as a table?) potential buyers can skim through this to see what kind of lemon they are buying. You need to indicate for which model number each modification applies to, there are probably many T600 "approved" parts that obviously won't work on a T300. Make some mention about the wing bracket AD as well. What about some of the variations that have come straight out of the factory, are these classed as approved because they came from the factory or what? Post should also have links to relevant TOSG website pages and RA-AUST pages. On a similar topic, what about fuel tanks, I have the rectangular type, rather than the beer barrel. The visual fuel gauge works brilliantly, but it is more difficult to refuel; are there any other fuel tank variants out there?. Cheers, BobT
  22. A big thumbs up from me !! Hi Tony and Ian. A big thumbs up from me here!:thumb_up: :thumb_up: :thumb_up: :thumb_up: :thumb_up: And some applause to . Certainly since I've discovered It , this is my number 1 Thruster site. (well, a toss-up between this and the TOSG website!) It's important to be able to discuss issues on a professional level with fellow aviators. I'm quite happy to use this forum as a Thruster/TOSG mailbox , (although I do mail Tony directly on occasion). And my 2c worth: having some RA-AUST people using this forum could only be beneficial to everyone. I'm in complete agreement with your aims, motivations and methods. Anyone who thinks Ian is on an ego trip should try maintaining a website for a while! Keep up the good work guys! BobT
  23. Hi Paul. Its good when it flies straight, gives you a chance to read the map :smiley4:. You might also want to (get to 4000'AGL first!) check to see if your power-on-stall response has changed. I haven't flown for a bit, so Tony will probably correct me here!. I think before your aircraft would have always dropped the right wing first. Now it should just hang there and sway from side to side (you are, of course, using your feet to keep the wings level at this stage). Don't push it too hard as you can drop into a tail slide/spin. It's useful knowing how your aircraft behaves in these conditions, so you can veer the correct side around a tree/windmill/powerline whilst climbing out.:ah_oh: Remember the golden rule for spin recovery "push on the top pedal" (this is the pedal that is closest to the pilot, you will feel it pushing against your foot). --------------------------- When I changed my mount brackets, I also changed to urethane bushes, thinking they would last longer. I flew just one circuit, then swapped back to the soft rubber bushes, as the urethane bushes were transmitting a lot more vibration back into the airframe. Cheers, BobT
  24. Hi Beau , As Tony says it's pretty simple. There are only two sensible options, the one that makes the engine pull you to the left is the one you want. I made mine from scratch, by copying another guys. Makes a difference to rudder trim!. While you are there, check the Chrome-Moly engine bracket for cracks around the welds, corrosion, and broken rivets. Also check the aluminium struts (that pass through the pod) at each end and at the pod pass-through point for wear. Check the rubber bushes too, and note that a well balanced, tracking propellor minimises wear and tear. Cheers, BobT
  25. Ahh Glide-slope , that's whats missing from mine!, where did you find yours?
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