n5296s
2nd Feb 2016, 15:51
(cue Godwin's Law as applied to stall speed / angle of attack)
Very interesting flight in the Marchetti 260 at the weekend. A few months ago I was doing pattern work in it and my instructor was very clear about the importance of speed on climb-out - always true of course but he explained that if you do inadvertently stall this aircraft at low altitude, you will likely die.
Well, my plane is in yet another extended annual (its excuse this year is an engine overhaul), so we decided to go and explore this a bit more. Very interesting. It has a very thin wing, for a small piston aircraft, with relatively sharp leading edges. In consequence (as explained to me) the C/L curve has a very flat top compared to say a Cessna. Which means that the stall is far from being an "all at once" thing (not that it ever is).
In 1G flight, you can start to feel aerodynamic discomfort at around 95 knots. Keep pulling, and at about 82 you get real buffetting. At 80, the nose drops. Gently push the stick forward and fly out of it like any other aircraft.
So far, so normal, apart from the wide gap between first indications and actual stall.
BUT... now keep pulling past the nose drop, until the stick is full back. With a bit of footwork you can keep the wings more or less level. But now try to recover. Stick forward, accelerate to 85 knots, pull ever so slightly, and you get a secondary stall. In fact it won't begin to fly normally again until you get past 95.
What is happening, so it seems, is that once the airflow gets fully detached, the turbulence stops it reattaching until the AoA is significantly below the "critical AoA".
Hence the danger - if you get into a full-blown stall below 1000 feet, without knowing what is happening, you'll likely secondary stall your way into the ground. Of course even if you were half asleep, hopefully the stall warning horn (which goes off at around 87) would wake you up enough to stop this happening.
Just mentioning stall speed on this forum is sure to have people jumping down your throat. What I find interesting is that in this case, AoA is actually not a whole lot better. (We did explore a bit accelerated stalls at 2G/60 degrees, but not in as much detail).
I'm told that the T-38, with an extremely thin, highly loaded, wing (my instructor has over 2000 hours instructing in them) is a lot more exciting than this. Sadly, we don't have one to hand.
(I probably don't need to add, but will, "don't do this without an experienced instructor", etc - not many low-time PPLs will have access to a Marchetti to go try it, though Rich would certainly welcome anyone at Attitude Aviation if they did want to).
Very interesting flight in the Marchetti 260 at the weekend. A few months ago I was doing pattern work in it and my instructor was very clear about the importance of speed on climb-out - always true of course but he explained that if you do inadvertently stall this aircraft at low altitude, you will likely die.
Well, my plane is in yet another extended annual (its excuse this year is an engine overhaul), so we decided to go and explore this a bit more. Very interesting. It has a very thin wing, for a small piston aircraft, with relatively sharp leading edges. In consequence (as explained to me) the C/L curve has a very flat top compared to say a Cessna. Which means that the stall is far from being an "all at once" thing (not that it ever is).
In 1G flight, you can start to feel aerodynamic discomfort at around 95 knots. Keep pulling, and at about 82 you get real buffetting. At 80, the nose drops. Gently push the stick forward and fly out of it like any other aircraft.
So far, so normal, apart from the wide gap between first indications and actual stall.
BUT... now keep pulling past the nose drop, until the stick is full back. With a bit of footwork you can keep the wings more or less level. But now try to recover. Stick forward, accelerate to 85 knots, pull ever so slightly, and you get a secondary stall. In fact it won't begin to fly normally again until you get past 95.
What is happening, so it seems, is that once the airflow gets fully detached, the turbulence stops it reattaching until the AoA is significantly below the "critical AoA".
Hence the danger - if you get into a full-blown stall below 1000 feet, without knowing what is happening, you'll likely secondary stall your way into the ground. Of course even if you were half asleep, hopefully the stall warning horn (which goes off at around 87) would wake you up enough to stop this happening.
Just mentioning stall speed on this forum is sure to have people jumping down your throat. What I find interesting is that in this case, AoA is actually not a whole lot better. (We did explore a bit accelerated stalls at 2G/60 degrees, but not in as much detail).
I'm told that the T-38, with an extremely thin, highly loaded, wing (my instructor has over 2000 hours instructing in them) is a lot more exciting than this. Sadly, we don't have one to hand.
(I probably don't need to add, but will, "don't do this without an experienced instructor", etc - not many low-time PPLs will have access to a Marchetti to go try it, though Rich would certainly welcome anyone at Attitude Aviation if they did want to).