Head in the clouds

'Glitches' like that (as we thought they were) were quite frequent in the '90s. It wasn't unusual for the GPS to suddenly drop out or to spend a while giving you false position information (on one occasion I apparently drove my boat, at night, straight over the top of a large island off the Kimberley coast ...). Since portable GPS was relatively new at that stage, and there were many fewer satellites than now, particularly ones visible in the southern hemisphere reasonably high above the horizon, we tended to assume they were all just drop-outs from losing contact with sufficient satellites for even a 2D fix, let alone a 3D one. Later we learned that the position error ones were probably due to US military operations, and they were quite entitled - they own the satellites, after all. Which is why GPS was never permitted to be the primary means of nav for aviation. The drop-outs were a different matter and were due to loss of signal from either obstruction when satellites were low on the horizon or poor antenna issues in the early portable GPS units and even some of the fixed antennas on the aircraft. We had one wily fella who always had trouble with nav, he was forever getting lost and regardless of the high cost of them then, he was delighted when personal GPS became available because only a few of the smaller aircraft were fitted with them. All of a sudden his nav woes were solved ... until he experienced his first drop-out and got lost again. He then had a 'bright idea' and promptly went out and bought a second GPS unit (twin engines never fail at the same time do they?). You can imagine his upset when both units always dropped out at precisely the same time. I think the reason we started to see much less of the position error thing as time went on, might have been a change in US military technology. It would seem that as they started to use laser-guided weapons more, the occasions of GPS position error reduced. I know US military do still use GPS extensively for ground troop and vehicle movement and positioning, but I think they also have a much cleverer means of changing the coordinates of some satellites but it not affecting everyone, probably just those who they'd like to confuse and disrupt at any given time. Additionally a very slight coordinate change can be quite enough to protect their own troops from anything incoming and GPS guided, while the overall system still being accurate enough for the average citizen to continue using for non-critical nav.

Yes, I expect you're right. My experience of it was in a large twin-engined helicopter and we were two pilots and a flight engineer and the other pilot was flying so I had plenty of time to experiment. After we got down it would have been quite a sight for any bystander to watch us virtually ripping the huge (40kg ish) battery out of its box in the chin and running to deposit it in a ditch so it wouldn't set fire to the helicopter.

I havent read all of this thread so apologies if I'm out of line but has anyone mentioned the obvious yet? As FH said if it's an oil fire a running engine will continue to supply it with oil, likewise a fuel pump for a petrol fire. The main thing to do, to stop any fire is to stop whatever is fuelling it. Switch off the engine if it's an oil fire, fuel cutoff for a petrol fire. Electrical/battery things generally cause loads of pungent and toxic smoke way before there's any flame so keeping a functioning engine is a huge benefit for getting on the ground safely and quickly. With toxic smoke in the cabin I agree completely with flying yawed with cabin vents/windows open - and if you have time to think about it, it works best if the venting side ports are more open than the pressure side, which from the point of view of being able to reach them, may well mean directing the airflow towards the pilot but, from experience, get the airflow right and the smoke forms a tight stream straight out the vent, leaving the cabin clear.

Not exactly, but it was the start of the second Gulf War ... '02, '03 I think, or was it earlier? I was flying that area from '99 to '03.

Don't they just ... I was flying a Jetranger full of pax in a remote area in Arnhemland and we'd relied on GPS for so long, and they'd got to the stage where they didn't drop out very often at all, that 'some of us' had got a bit lazy with our procedural nav. One moment I was about thirty miles inland in a rugged rocky area, the next moment my GPS had me about thirty miles offshore, and so it stayed for twenty minutes or so. Needlesstosay I got into some pretty frantic chartwork because up there fuel was always a primary consideration. I became a lot more diligent about 'proper' nav following that. I found out later that the USA had decided to argue with Iraq again and so they changed the GPS coordinates for a short while to prevent the other side using the system against them while they conducted some precision bombing.

Alright I shouldn't have said first 'half' - I was referring specifically to Bruce's figure for an AN4 bolt in single shear and the multiplication of that in double shear and for two struts, and if his assessment of the strut attach position and angle were correct then his numbers looked pretty close to the mark. I couldn't verify it absolutely because I'm not privy to the actual strut angle, but based on online images it looks like about 55°. And the strut attach point looks somewhere close to the 45% half span which is quite close in compared to many designs, and obviously increases the load on the strut and reduces it on the fuselage spar attach points (I guess the % half span position might vary on the long-wing and short-wing versions), then allowing for say 10% tip loss, the strut might well be carrying most of the vertical wing load. As you said, the strut doesn't 'generally' carry the full vertical wing load but then struts are often attached closer to the 60% half-span position. If that were the case, and with the same allowance for tip loss, then the strut would carry more like 2/3 of the total load and the fuselage attach points about 1/3.

It's the law!

Hey Bruce, I'd agree, spot on with the first half but when we get into composites there are too many variables within the manufacturing and ageing (UV, moisture, conductivity where CF is involved, and most of all, mould that gives off gases and breaks down the resin/fibre bond and/or matrix, environment that supports the development of osmosis, internal heat build-up in tropical climates causing degradation and much more), that it becomes necessary for composite manufacturers to over-build their products when new to ensure they will be serviceable at an age when they might reasonably expect to still be so. Given that composites supposedly don't fatigue in the traditional sense, some customers might expect their Jabiru (or similar) to still be 'perfect' when 50yrs old. But I ask you - would a Jab kept in a hangar in inland SA for 50yrs be the same as a Jab kept in the open, coastal, in north Qld for 50yrs? Some may say 50yrs is asking a bit much, but hey, some Jabs are 30yrs old and more already and I don't see any of those owners respectfully wanting to drop their plane off at the local tip just quite yet. Plenty of Sander Veenstra's aly/semi composite monocoque SV series planes still survive and are flying despite the aly components (spars etc) being subject to fatigue considerations - which he took well into account. It was his proudest statement that his planes would still be eminently serviceable in 50yrs if kept in hangars or trailers when not in use. As far as pranging a wing into the ground - well you have to compare apples with apples instead of oranges ... my point being that if you take any aly rod of equal ultimate strength to a glassfibre rod and poke a tree with it, the aly rod will bend and remain bent, but the glass rod will deflect and spring back to shape. Under load in the air the two of them behave very differently also. The glass wing will give you a far more gentle ride in rough air by flexing the wing (more so with cantilever wings like gliders - did you ever see Ingo at race starts with wingtips near vertical?) but the stiff aly wing will get you out of trouble much more quickly if you need to pull up sharply for some reason, much like a monohull or cat in sailing, the mono spills wind by heeling, the cat not so much, so it responds much more quickly.

Interesting - I had no idea that was the basis for choosing the 544kg weight. (45²/40²) x 430kg = (2025/1600) x 430kg = 1.2656 x 430kg = 544kg. Simples! But as you say the structural calcs are/would be another matter. Being composite structure, Jabiru tended to do most of their proving by load testing rather than rely purely on calcs though, some of their jigs and rigs are very impressive. I was at the very first load test they ever performed, at Caloundra in the Skyfox hangar around 1988/89 where they sandbagged the wings, amazing how high the sandbags were stacked and how much the deflections were. They had to stop at about +4.5g IIRC, the wings were still hanging on OK but the cabin roof structure and the jig were starting to fail due to the massive weight they had to support. It was enough to get them through that stage of the certification which was via BCAR S I think.

Theoretically it keeps the landing crash speed lower ...

Sorry if you felt my comments were getting personal, I didn't intend that, nor to offend you or anyone else. We do get a lot of 'unfounded opinion' on this forum which is frustrating when the documentation is there for all to consult and get the facts right instead of adopting a position which one feels 'should be the case'. Thank you for the reference though I am well versed in the current Tech Manual including Section 6, the MARAP process etc, as well as the previous versions of the Tech Manual. Just to be sure we're not talking at cross-purposes, 95.10 and 101.28/101.18 aircraft, and their owners were treated differently from each other in the past. Going back to TM Issue 2 (1996) and TM Issue 3 (2007) 95.10 owners could design and implement modifications and repairs at will if they were the owner and had 4 TM(2) paragraphs worth of knowledge in the Design (accurate knowledge of the forces involved, strength of materials, manufacturing processes), Manufacture and Installation (Good planning, workmanship, correct tools) Operation (fully tested and documented) Advice (contract qualified, experienced assistance where required). However, I was referring to the 25, 55 and most specifically 28 reg. series, where you have NOT, historically, been able to modify at will. At least as far back as 1996 modifications have had to be approved by a person holding a CASA Instrument of Appointment under CAR 35. See image - The 19 and the E24 registrations seem to be a can of worms in the TM(3) and I concede I have probably missed the point there. Section 3.5.3 does discuss where modifications have been made to kit or factory-built aircraft, though it doesn't discuss by whom, so I imagine anyone might have done so, including a subsequent owner, as you mentioned. However - although that subsequent owner might have conducted the modification 'at will' they still needed to be issued with an Experimental or Special Certificate of Airworthiness by an 'Approved Person'. That's all very well, and I think we all know those Certificates were being handed out quite freely at one time which resulted in a big mess for some people later on ... BUT (from para 3.a) that Special Certificate of Airworthiness "stops having effect if the aircraft is modified outside of the approval given by the manufacturer ..." (in which case see Section 7.5.4) which then makes it an E24 reg (private ops only) provided it still meets the LSA category regulations. Many of the kit/homebuilts wouldn't have met LSA category in the first place, so where would that leave them?

Your self admitted "point of view with little experience" is exactly what we don't need! There's no difference between scratch-built and kit-built. Your statement - "Until recently RAA saw no difference between builders and subsequent owners. Both can modify." - Rubbish. Nothing has changed in that respect since I joined AUF in 1983! The builder can modify at will until it's registered, years ago they could change it after registration. Subsequent owners with an L1 (or L2, L3 or L4) cannot design ANY modifications, it's expressly prohibited, they can only repair and/or replace - as I said, it's in the Tech Manual ... I guess you don't have even an L1? You'd know if you did ... Please get your facts together before you continue with your unsubstantiated nonsense. This forum is intended to be about promulgating valid information, not your kind of "I would have thought" and " A point of view with little experience" ...

No, you can't change the MTOW retrospectively, but you could have made it whatever you wished, up to the CAO max (at the time you registered it). jetjr ... with respect, it's no good saying "I would have thought ...", what you need to do is consult the appropriate documents which were the RAA Tech Manual Versions 2-4. I can let you have a copy of 3 if you like and 4 is available online. The reason you, as a builder, can just claim whatever CAO weight you like and can provide whatever justification you like for the data package, (or provide none!) is that the whole point of our experimental class is that no-one else in RAA claims to be, or indeed is, qualified to analyse any calculations you might provide, should you choose to do provide them ... so, as I said, in our RAA kit/owner design/builder category, you are the designer and certifier, it's in the Tech Manual ...

Yes, it's different for RAAus kit builds. In that case the builder becomes the designer and can modify the kit any way he sees fit and doesn't have to justify any of those changes when he declares it 'airworthy' at the end of the build. So he/she could specify any new weight they wish, which is a bit of a concern when a lot of the kits are already pushing their design envelope. Many of them started out as 450kg designs which have been beefed up a bit, sometimes with a belt-and-braces approach, to bring them up to the newer 540kg and 600kg categories. In some cases those earlier designs might have originally been +6, -3g designs that are working nearer to +4, -2g already (at 600kg). So someone just declaring a new weight of, say, 750kg and not severely limiting the Vne and Va, might be risking losing their wings on a turbulent day ... I'm concerned even more for the unsuspecting second owner who comes along a few years down the track.

Google Dynafocal mount ... the mounting bolts all point in towards a focused point so you can't move the engine back or forth until you remove the bolts and rubbers individually because the bolts' longitudinal axes are not in line of draw.

I think the bed mount is superior in many ways. Though they're rather more susceptible to transmitting vibration to the airframe through the rubbers because the rubbers are often oriented so that the attach bolt is vertical i.e. the engine is sitting on the rubber instead of suspended off the side of it, and if you orient the rubbers with the bolt horizontal coming in from each side, then one side's rubbers tend to fight the other side's. That's where the dynafocal mount concept comes into its own, but they're even more difficult to fabricate because they're only geometrically 'right' when the bolts are tightened so they tend to be mechanically 'locked' when you're trying to assemble or disassemble them - or to fabricate them unless you have a jig. An even better mount than the bed mount is on the Foxbat where it's effectively a three point attachment and to get at the difficult bits at the back of the engine (flywheel, magnetos, water pump etc), all you do is disconnect the top mount from the gearbox and the engine hinges down. I wished I'd seen that one early in the design process of DooMaw, I would have adopted it.

By the sound of what the dairy farmer said - that he was circling around low level "like a spray plane" and all seemed okay other than that, and then a big puff of smoke (big enough for him to think someone was burning off) perhaps he might have hit powerlines. I think the final burnt out result looks more like the fuel eventually caught alight, rather than a battery thermal runaway. I had one of those with a helicopter and the fire was quite intense but localised.

?? it was issued in August 2016, two years ago ... from the RAAus website (the bold is theirs, not mine) - Version 4 of the Technical Manual has been completed and commenced operation on Monday 1 August 2016. The manual is a complete rewrite that has taken a little over 2.5 years to complete. Here's a link for those who prefer the easier path - RAA Tech Manual Vn4

Yes, gold it is ... gather all the information you can before you get to the engine mounting process Marty. In fact if you can buy a mount, at any price and even if you have to modify it, I'd recommend that, I found the build of the engine mount to be the most difficult and most frustrating part of my entire DooMaw project, so far. There's just so very little space to play with, even fitting the ring mount itself to the engine is quite a tricky job and requires a fair bit of disassembly at the back of the engine, I also had to buy and fit new water inlet/outlets to the waterpump, available from Floods. Also - it would seem logical enough to just prop the engine where you want it and tack the mount together, but by the time you have the ring-mount on the engine it's so buried behind 'stuff' that it's hard to get anywhere near it to weld anything, not that you'd want to in case you harm parts of the engine ... not saying it's impossible but it's tricky. In the end I was able to get a 3D CAD model of the 912 from a fella in Russia (I can get his permission to share it with you if you can make use of it) and that provided me with the positions of the mounting holes on the engine (they're also provided in the 912 installation manual in x,y,z format) then I built a crude adjustable threadbar jig to hold the ring-mount in place. I'd made up aly facsimiles of the rubber mounts to bolt the receivers to the ring-mount (so I could weld without melting rubber), and had modelled the whole mount in CAD and pre-cut and coped the tubes - it's on Page 12 of the DooMaw thread if it helps. Here is a link to the Vibration mounts, this is where I bought mine, they're generally known as Universal Mounts. I bought three sets in different durometer rubbers so I can try harder or softer ones and see which produce the best damping at cruise revs. Note that these ones have a 9.9mm hole in the inner sleeve, to suit 3/8 bolts, whereas IBob said his are 5/16, so you need to check your ringmount to see what size the holes are, my ring-mount has holes about 10.5mm so I could use 10mm or 3/8 bolts. Regarding the receiver for the rubber mounts, it's like a piece of tube with a washer welded inside it, although it's not welded, they're machined from a piece of solid. You can see them in the last three photos in this post. If you need a better resolution picture send me your email address by PM. Hope it helps. EDIT - if you order anything from Vibration Mounts they tend to send by USPS expedited which costs about US$70 so talk with them about cheaper ways if you're not in a hurry and/or let us know you're ordering and others may want to buy stuff too and share the cost. If you want any kind of rubber mounts for your exhaust, instrument panel, ute toolboxes etc, they have everything you can dream of.

Excellent, first class work Marty!

I guess they probably vary between manufacturers because the information that came with mine is quite different. I have a Shorai Powersports 18AH LiFePO4 battery which weighs just under 1kg with 270CCA (compared with the 8.5kg lead/acid it replaced which had 220CCA). The general advice that came with it is that their Lithium Iron batteries can be charged quite fast from any state (i.e. from either flat, or half, or nearly fully charged) and the maximum rate of charge should not exceed, in Amps, the Amp Hour rating of the battery up to 30A. Batteries with higher than 30AH rating should be charged at maximum 30A. So since mine is 18AH, apparently it is happy to be charged at 18A from any state of charge. I spoke with the distributor about the actual condition in the aircraft, since the output of the 912ULS charge circuit is 20A, and he said to just keep some load on the circuit other than just the battery being charged. Since that's not always easy I have a ceramic wirewound resistor which can be switched in and out of circuit. It can get a bit warm but not enough to cause any damage to anything. I also have electric anti-ice carby heating so that can be switched on at any time too because since it heats the carbies rather than the air, it does not cause an engine power reduction. It has variable temperature settings so it can pull up to 12A at full power. Mine cost $250, BTW, you can see their range and info at the Shorai site. And they send them to you by airmail because they're not considered to be dangerous goods because they CANNOT catch fire. You can send them back for testing cell-balancing etc, also by air satchel and they return them the same way next day (apparently - I've not had to do that).

Hi Charles, Welcome to the forum. I love the SuperSTOL, and am building an own-design STOL (see my avatar), which I hope will have similar characteristics. And I'm also CPL(H) - so you and I have a lot in common! Regards, Alan

Pitot error ...

One of the best ads I ever saw was a fella selling his 911 Porsche. It said - My lovely Porsche got me a gorgeous girlfriend, Now my girlfriend is my wife, My wife doesn't want it to get me a girlfriend, So the car has to go ... :-(

Interesting ... It reinforces the major car manufacturers' decision to change their method of product promotion. Some of you may recall that Ford, Holden, Toyota and the like used to produce very expensive big glossy multi-page brochures each time they released a new model. Then suddenly that all stopped. I was told that it was because the manufacturers had conducted market research among people who had just purchased a new vehicle and they found that the vast majority only looked at the various brochures quite some while after they'd already made their purchase, using them to confirm that they had in fact made the right decision, rather than to assist with making the decision in the first place. So as far as the manufacturer was concerned the brochure was a waste of money.