Ted wrote:
I am not saying your wrong, because various effects might cancel out, but the stall warning indicators of this type do not measure directly the angle of attack, they rely on the position of the stagnation point, so I think there is more to it. Of course you would expect that the VGs have been thoroughly tested, in each installation, and the supplier has the answer.
Yes but the measurement of the stagnation point is a proxy for angle of attack. A VG just allows airflow to remain attached at a higher AoA.
Peter wrote:
It seems intuitively correct, but – if true – it would mean that the stall warner on every plane on which the flap setting is not taken into account would be usable only at one flap setting, which is clearly not the case since the vast majority of piston planes have just a microswitch with a piece of metal attached to it, with no flap position input.
Well the stall warner comes on at a margin above stall. If you have a big enough margin than it will come on for a clean stall as well I suppose.
The reason I ask is that the Vr has been reduced by ten knots, which is very valuable for Accelerate-Stop, but if I rotate at the Vr I get a stall warning.
I think there is a little bit more to it
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930083830.pdf
Doesn’t help Timothy though, or maybe it does.
Great article – local copy.
1952… shows how little changes.
Here are a few papers about Vortex Generators by Professor Rogers:
Professor Rogers Technical Flying
Go to Flight Test articles.
On the basis of my experience with two Cessna Skylarks and a Maule MX-7-180, the answer to your question is yes, if you want to take advantage of the MicroAero VGs to take off and land at lower airspeed (i.e. shorter), you may have to get used to the sound of your stall horn (or perhaps adjust it). I didn’t adjust mine, so in still conditions it serves as an audible approach speed indicator.
Otherwise, you can just fly exactly as you do now, but with a greater margin against departure from controlled flight and with a slightly greater tendency to “float” after you flare for landing – in which case all you have to do is to adjust your aiming point perhaps another 10-15 m short of the threshold.
Jacko wrote:
Otherwise, you can just fly exactly as you do now
This is the difference between locating the aircraft 15 or 60 mins from the owner’s home. I have to get that balanced field length down, and 77kts, as opposed to 87, is the way to go. I have to take advantage of the VGs, but would prefer not to hear the stall warner.
Timothy wrote:
I have to take advantage of the VGs, but would prefer not to hear the stall warner.
How does your stall warner operate? Is it adjustable or a fixed mechanical type?
Very interesting thread.
Thimothy, I’ve never flown a twin so forgive my question if it doesn’t make sense: I understand that on most twins there’s a speed (blue line) below which the airplane won’t be flyable if it looses its critical engine. Is that speed lowered by the VGs, or with a VR lower by 10kts, is there an increase in the period of time you spend in that vulnerable zone?
There are a few posts assuming that what happens behind the wing can’t affect what happens in the front. I don’t believe that’s correct. I have haven’t had to deal with Navier-Stokes equations for a long time, somewhat thankfully, but I’m still fairly confident that in a fluid (like air) things don’t work that way. The whole flow of air over and under the wing is a system which must be looked at in its entirety.
understand that on most twins there’s a speed (blue line) below which the airplane won’t be flyable if it looses its critical engine.
Not quite. The critical speed is the red line. You never get airborne slower than that. Blue line is about performance following an engine failure.
Rotate is invariably between the two.
