aro
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Everything posted by aro
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Expanded airspace access for sports and rec pilots
aro replied to skippydiesel's topic in AUS/NZ General Discussion
If you look at a chart you can see it's not true. Lack of access to CTA forces you lower over tiger country. There's plenty of routes where through CTA and higher altitude would be safer. Suggesting the opposite is rubbish. But the problem in Australia is that you're likely to get "Clearance not available" even if you have the qualifications. -
Do you really think they flew this flight without an adequate briefing?? 100+ knots, 200 feet, at night near a busy airport? Military flying can be dangerous by necessity and people are killed in accidents occasionally. But it shouldn't be putting civilian traffic at risk. There's no justification for a route at 200' below landing civilian traffic.
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This accident really has to be blamed on whoever decided that helicopters flying at 200' below aircraft at 300' on approach to land was OK. The second factor was whoever decided that visual separation at night between aircraft in that situation was OK. With those factors in play it was just a matter of time and luck before this accident happened.
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There are a couple of videos on Youtube demonstrating how they work. Seems reasonably convincing. Arguably not as good as dynamic balancing, but it looks like the material should redistribute to reduce rotational vibration whatever the cause - maybe even blade pitch and tracking etc. They will always start out of balance due to gravity, until the vibration distributes the balance material. They will not do anything for power pulses through the gearbox, so won't allow lower idle RPM on a Rotax.
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CASA explains the rules (Please explain).
aro replied to Garfly's topic in AUS/NZ General Discussion
If you're referring to the common double-click acknowledgement, that conflicts with the standard. Communication using speechless radio transmissions: - 1 transmission - affirm, or acknowledge - 2 transmissions - negative - 3 transmissions - say again - 4 transmissions - request for assistance from ATC - 5 transmissions - additional emergency 1 long transmission - abandoning the aircraft Have you ever used any of these? The only example I could find was an ATC describing trying to use them in a comms failure, but the pilot was using 2 clicks for affirmative. Confusion resulted. Maybe we do need to educate on their use. Or maybe they are outdated and should be abandoned. -
CASA explains the rules (Please explain).
aro replied to Garfly's topic in AUS/NZ General Discussion
Have you read it? It's a terrible document. It reads like it was written by someone who hasn't done much/any VFR flying. Press and hold the PTT as long as possible as a signal you're abandoning the aircraft??? Really? Am I ever going to use that information? -
Yes, but you're answer only makes sense if you already know that the datum is just an arbitrary point chosen for convenience. Given that the original question was about how the datum is derived, it didn't necessarily help. I was trying to write a more complete answer.
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The datum is just a point chosen for convenience as the origin of all the other measurements. The datum doesn't have any aerodynamic significance. The datum could even be e.g. a point in front of the aircraft. The advantage of that is that the arm values for e.g. engine oil or a change of propeller are positive values and it simplifies the calculations.
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According to Wikipedia, mogas is "a slang for common gasoline (for cars, motorcycles, lawnmowers ...) used by aviators to distinguish it from avgas". According to BP, "Mogas is otherwise known as motor gasoline, is used by ground vehicles, while Avgas is specifically developed for aircraft use" Neither indicate it is a specific fuel different to what is available in Australia. Unless you can point to an example that shows Mogas actually exists as a specific fuel, I'm inclined to believe BP rather than just your say-so.
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Is there a product sold as Mogas anywhere? I've always heard it used in relation to aviation, i.e. it basically means not-avgas. In the USA they have gas/gasoline for cars and avgas for aircraft by I'm not aware of actual "Mogas".
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Yes. As I said:
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Here's a definition of suction: "the act or process of exerting a force upon a solid, liquid, or gaseous body by reason of reduced air pressure over part of its surface" I think it's fair to say we are exerting a force on a solid body (the wing) by reason of reduced air pressure over it's surface. https://www.merriam-webster.com/dictionary/suction
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What's not involved?
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You didn't give your definition of suction. Everything is just higher or lower pressure, but it's often a useful mental model to describe something as suction. If you want to say it's not suction, provide the definition you're using. Here is an example of suction from the Bernoulli effect: Pretty much every explanation of wing lift using the Bernoulli effect gets it wrong, so it's not very useful in that case. It just muddies the water usually.
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A pretty accurate summary, except that the Avgas octane measurement is more similar to MON, so maybe 110-115 RON equivalent? https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/avgas-facts-future.html
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Duplicate
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What's your definition of sucking? I would say it's a force generated by reduced air pressure...
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Bernoulli is a bit of a red herring. It is generally used incorrectly trying to explain lift. A flat plate at an angle of attack produces lift. At subsonic speeds there is a pressure wave ahead of and below the plate that changes the flow of air ahead of the plate. If you see the stream lines (e.g. smoke trail) you can see the air flows around the plate in a similar way to a conventional airfoil. The airfoil is just a way to improve the airflow, to make something that works better than a flat plate. If we make the leading edge more curved, we can get a smoother flow for less drag and keep the flow attached at a higher angle of attack. If we adjust the curve on top, we can change where the centre of pressure occurs, and how it moves at different angles of attack. If we change the curve on the bottom, we can reduce the drag at high speed... and many other factors. If you look at the airfoils used on the very early aircraft, they are often very similar shape to the air flow you get around a flat plate. The very start of refining the airflow around the wing...
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Posting details from the Stewart Systems manual is hardly trolling. All the information I posted is in investigation report someone else posted earlier. I didn't know anything about this before reading that, but it's scathing. Wing lift is what is trying to separate the fabric from the frame. Air pressure acts on the fabric, which transfers the lift force to the ribs and structure. You can see the fabric bulging between ribs, or even the aluminiun skins on some metal aircraft. Let's run some numbers... If the aircraft G limit is 4G, it must be able to handle 6G without failure. So for a 544 MTOW the wings need to handle over 3000kg lift force. That's 1500kg per wing. If the top surface produces 2/3 of the lift that's 1000kg force. Lets say the fabric covers 40% of the wing area, that's 400kg force trying to suck the fabric off the structure. To picture it, imagine turning the wing upside down, removing the bottom skin and stacking 400kg of sandbags on the inside surface of the fabric. That's what it has to be able to handle. Is a 35mm (or 50mm) glued joint enough? Personally, I prefer the standard method - wrapping and overlapping the fabric around the leading and trailing edges.
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You linked to the Stewart Systems page, it has the documentation on how to do it. From that document: "Fabric is attached to cap strips in many ways: rib lacing, screws with fabric washers, rivets and wire clips. All of these methods require the use of reinforcing tape under the attaching device. Do not rely on cement to hold fabric to cap strips." It is very common for wings to have e.g. the leading edge covered in wood or metal. The fabric goes over the plywood - not just as a patch over the open areas. You used the Stewart Systems products, but not the Stewart System if you didn't follow the instructions for using it. "Cemented overlap seams at wing leading edge shall be a minimum of 3”. This seam shall them be covered with a minimum of 4” wide finish tape, centered on outer edge of overlap seam... The trailing edge shall be glued with a minimum of a 2” glued seam. This seam shall be covered with a 3” or wider finish tape." You are describing zero overlap. If you didn't have the required overlap, you didn't have the strength designed into the system, and didn't meet the airworthiness standards it was designed to provide.
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I used Polyfiber, which is glued and heat shrunk. I had a read of the Stewart System and it is a pretty similar process. The Stewart System does require rib stitching (there are various methods e.g rivets, screws - not only thread.) Neither system seems to have a specification for a fabric edge joined to the structure. The fabric-fabric join is the strong joint, and they have specifications for the overlap required at the leading edge etc. The theory is that the fabric envelopes the whole wing, and the load is carried by the fabric joints. The fabric to structure joint is not a strong joint and needs reinforcement e.g. stitching. That's not to say you couldn't find an adhesive that gave you a good fabric to structure join. But I don't think the usual adhesives in these systems qualify, and it wouldn't be a standard practice.
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All I said was it didn't seem to meet commonly accepted standards. Can you point to a commonly accepted fabric covering standard that allows a 50mm bond area, with the edge into the slipstream? I have covered an aircraft so I have some knowledge of the usual practices, but I'm prepared to be educated. The usual processes generally have a large margin to allow for error, this type of failure is not expected.
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Very interesting. The fabric attachment doesn't sound like it meets the commonly accepted standards. Also interesting that they think the 10 year life limit is too long, since the failure occurred after 10 years 6 months.
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Interesting, replacing the covering is a pretty major job! What covering system do they use that has a lifetime of only 10 years? from the SB, it looks like maybe it doesn't use traditional rib stitching. That's one thing someone might choose to do if amateur building - use a covering system with a proven long life on wooden aircraft. Then presumably you would be expected to follow the maintenance requirements for that system, rather than the Atec instructions.
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They are standards used for assessing your skill during a test, not legislated requirements. And assuming the runway is wide enough, if you have a good e.g. safety related reason for taxying off the centerline of the runway you're unlikely to be failed for it. It's more about your plan, and whether you can control the aircraft to execute the plan.
