Bruce Tuncks
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Everything posted by Bruce Tuncks
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Stalls are more scary than spins.
Bruce Tuncks replied to APenNameAndThatA's topic in Student Pilot & Further Learning
You are braver than me Apen. Well by Jabiru has a notice about "no aerobatics, including deliberate spins." I don't need the notice. -
Well so far old K you are doing the right thing.... keep it up by telling them all loudly and clearly. At least they will have to steal your money honestly then.
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The "rough airspeed" figure is a regulation which, if lowered by 5 knots, would enable a lot more weight to be carried by the same structure. This was the tactic used to enable top motors to be carried on gliders. The rough airspeed is where the wing stalls when hitting an upgust. The stresses caused by this are in proportion to V^2, so a 5 knot reduction will lower the stresses a lot. Or enable more weight to be carried at the same stress levels. Stall speed is different, as has been said, this always increases with weight, well for the same lift coefficient it does. As I said earlier, the upgust is 40 knots by regulation. Now there are limits to how low you can make a rough airspeed. It is possible for an unusual attitude to allow inadvertent overspeeding. So there is a formula the designers need to apply.
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Yep, if you look up the accident reports, you will find that "loss of control" is the most common fatal event. The most common reported event is "near miss" .
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My Jabiru 230 POH says the airframe is stressed for 700kg but it is limited to 600 kg by regulations. My understanding is that without the rule of 50 kg more , float planes would be effectively excluded from RAAus Your aerodynamics are correct apename, but regulations are imposed on top. For example, if we were to turn back the clock and lower the max permitted stall speed from 45 to 40 knots, then a lot of safety stuff ( like extra fuel ) would be thrown out but the crashes would have less energy. Personally, I doubt that overall safety would be improved, and the crash statistics support this.
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There is a lot of that sort of mistake around these days. The spelling checker lets it through because "apart" is a proper word. The next generation of spelling checker might check the grammar too and decide the word was wrong... I hope.
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Went to Nhill yesterday so not going to serpentine today.
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Space, can you move the fuel tank back like the Jabiru has it? Even a smaller tank behind you would help
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Foxcon Project
Bruce Tuncks replied to Peasant_Pilot's topic in Aircraft Building and Design Discussion
Great job, please watch the weights. On my SK jabiru kit, I was fanatic about weight savings. In the end, it came out at the exact weight it was rated to be. It's just too easy to make things heavy. -
yep, the kinetic energy is also related to v^2, so I agree that the damage would be related to this figure.
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Pretty poor siting of the fuel load huh, if the burning off can transform a safe situation into a dangerous one. It sure was not a Jabiru.
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Oops its 45 knots, which makes the argument even stronger.
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RossK, you are quite right about the stall speeds. Years ago, we were limited by a requirement for a 40 knot stall speed. This meant that the Jabiru SK was limited to a weight of 430kg kg, which was not really possible to achieve with fuel and 2 people . This was magically fixed by increasing the allowable stall speed to 42 knots. Since the lift equation has a v^2 term, the allowable weight increase was quite a lot. Right now, the weight increase achieved by the RAAus is not worth much without a ( small ) increase in the stall speed allowed.
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Turbs, I think it is a bit lazy to say that the calculations are too hard for us. Gosh, in high school we would have loved for a WB calculation in the year 12 exams... it would have been the easiest question by far.
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There was a farmer in South Australia who put his tractor toolbox in his 2.2 jabiru. He put it BEHIND the fuel tank, and crashed on the take-off run... the plane over-rotated and stalled before leaving the ground. Apparently he climbed out unhurt, a sadder but wiser man. But, here's some figures which you can easily check out with google... My current J230 has a "max take-off weight =600kg" according to the pilot's manual. This is not much as the airframe weight =360kg and it can carry 90kg of fuel. This only leaves 150kg for 2 people. If the people add up to 200kg then you can only carry 40kg of fuel. If you google up " Jabiru J230 max take-off weight " the first report is a kitplanes review which states "to meet LSA regulations, J230 and J250 have a normal max gross of 1320 pounds, but if constructed as an amateur-built, can go to the J400 series maximum of 1540 pounds" So it seemed reasonable for me to see just what these figures meant. Why are these figures what they are? Well the answer lies in flight envelopes and definitions of just what "rough air" and "smooth air" mean. In the meantime, I sincerely agree with those who say that the official figures be adhered to , lest you go to jail etc.
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Of course it gives you safe flights... My question is whether or not a 5 knot reduction in the speed would give you flights just as safe, and indeed what that all means.
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I'd just love it if you were to go a little closer to the bone than by saying " the manufacturer's WD envelope gives you safe flights."
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I don't want to be a maverick because you guys are sort of right. You certainly have the powers that be on your side. I just would like if we looked beyond the regulations sometimes to see the real figures. Here's an interesting thing... have you ever seen a plane "hovering " tail down and prop up, like a helicopter? I have watched 3m radio control models do this for real and I have seen a full-size plane do it on video. Now the models, I know for sure, had a VERY rearmost c of g , way aft of what would be legal in a big plane. This was a difficult and unstable flight mode. I would never try it in my Jabiru. Not that the Jabiru has thrust greater than the weight.
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E-Props ...who has first hand experience with these
Bruce Tuncks replied to eightyknots's topic in Engines and Props
Skippy, I swapped my frp catch-jar on the Jabiru SK for an aluminium beer-can and saved a few hundred grams. I found the can while walking the dog, so it didn't cost much. -
yep Space, the Jabiru has fuel slightly behind the c of g. I think this is a common thing. On the subject of max tow, the regulations assume that you will, at maximum weight, fly at maximum allowable speed into a sharp-edged upgust of 40 knots. In 40 years of looking for strong upgusts in a glider, I never found a climb better than 15 knots. Mind you, I did stay away from thunderstorms. Wow that 15 knot thermal had the altimeter visibly winding up. I think I stayed in it for about 5 minutes to gain 7,500 ft. This was up near Quorn, about 300km north of Adelaide, and it was 40 degrees on the ground and a pleasant ten degrees at 10,000 ft. If you slow the allowable rough-air speed down say by 5 knots, you can vastly increase the mtow , but they have a formula which stops you doing too much of this. But one guy I knew sold Top motors for gliders and he used a reduction in rough airspeed to make them legal.
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And Space, I think we should all be more relaxed about the possibility of going to jail. I was prepared to go to jail because I ordered my kids to ride their bikes on the footpaths instead of the roads. My idea is that jail is like a cruise ship except that the stewards are not nice to you, but the fellow inmates might be more interesting.
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I got that wrong... they usually had boxes of lettuce but this one day they had boxes of cucumbers which of course are much heavier.
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But i have to say that Russia is losing the propaganda war..even with me
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Methusela, I really appreciate your showing us that there are 2 sides to every story. Please don't go.
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I reckon maintenance provides the hardest puzzles of all and the saving thing is that there is no real pressure timewise ( like problems in the air ) and you can seek advice. There are several places to ask for advice, this site being one. Yes you will get some jokes made at your expense but there are guys on here who really know good stuff. It's the reason why I come here.
