Stall Question

[TDTURBO]

It was windy a few days back and I was trying to fly my 182rg backwards, I got it down to 5mph on the GPS and was told by a freind of mine to drop the gear. I don't see how this would decrease stall speed. Can anyone explain?

 

[ShawnC]

It won't, it adds more drag (and catch more wind) which would decrease your ground speed, which is what the GPS measures.

 

[TDTURBO]

I know it would increase drag, hence slowing it down causing a stall. My question is this, if you are flying flaps down at the edge of a stall and your ground speed is 5mph, will dropping the gear enable me to fly at a lower ground speed? I don't think so. The problem isn't that I have enough drag, it's at minimum flying speed already. I think the reason why Vso includes gear is because you usually need it to land, not because it decreases stall speed. Am I wrong?

 

[LAXSaabdude]

It won't, it adds more drag (and catch more wind) which would decrease your ground speed, which is what the GPS measures.

Wroooooonnnng!

If you simply want to decrease your speed, you could pull the power back without dropping the gear. The question is how does dropping the gear change the stall speed.

The added drag causes the aircraft to fly at a lower speed for the same angle of attack. Thus, since stall AOA is a fixed value, if you are right at stall AOA already, and you drop the gear, (flaps, as well), you can knock off a few more knots without going past stall AOA.

LAXSaabdude.

 

[bart]

Also, with the gear down, you will have to have a higher power setting to hold the same speed, which will result in increased accelerated slipstream over the wings, increasing lift and therefore allowing a slower airspeed.

 

[TDTURBO]

Thanks LAX, that makes sense, young grasshopper understands now!

 

[skeezer]

The added drag causes the aircraft to fly at a lower speed for the same angle of attack. Thus, since stall AOA is a fixed value, if you are right at stall AOA already, and you drop the gear, (flaps, as well), you can knock off a few more knots without going past stall AOA.

I would have to disagree. If you are flying very near stall and you drop the gear without adding power to overcome the drag, you will stall if you try to hold altitude.

To make it more clear...if you are flying at a fixed AOA and reduce your speed you will NOT be able to hold your altitude. Simple physics. With the same AOA and less speed the lift produced will be less, thus you sink.

Dropping the gear will NOT help you fly slower, just slow you down quicker.

Peace!

Skeezer

 

[A Squared]

Dropping the gear will NOT help you fly slower, just slow you down quicker.


Skeezer

No lowering the gear does lower stall speed slightly on some airplanes in some configurations. In the operating manual for the airplane I fly, the zero thrust stalling speed with 20 degrees flaps is about a knot lower with the gear down than with it up.

I can't explain why this is, as I don't understand it myself. All I can say is htat the gear alters the airflow around hte airfoil in some manner.

I'm skeptical that TD Turbo would get 5 knots less though.

 

[avbug]

The airspeed difference may be an indication issue, rather than an actual airspeed change.

If at maximum power and maximum angle of attack, increasing drag by lowering the gear will of necessit result in either a descent, or a stall if one attempts to maintain altitude.

 

[Eagleflip]

Hmm..dropping the gear can conceiveably move the CG and/or center of lift a little as well, which may well account for the difference in stall speed. But I'm reaching here...

Most likely, though, it is an indication problem. Dropping the gear would lower the stall speed only due to pitot-static errors inherent in the system due to the changed airflow around the fuselage.

In other words, dropping the gear does nothing aerodynamically to lower one's stall speed. Once the gear is down, the aircraft must fly with either a greater power setting (hence more or less the same AOA) or the increased drag from the gear causes the aircraft to slow, increasing the AOA to maintain level flight.

Assuming you are flying at the same airspeed, A Squared, I would surmise that despite the extra drag, the decrease in stall speed is due to an pitot-static calibration issue.

 

[Eagleflip]

Bug beats me to the punch! Again!

 

[Super 80]

Well we could test this sometime, but in the old equilibrium equation, increasing drag means to keep the equation which was balanced (steady state level flight) you'll have to add power to sustain the airspeed/pitch combination that is producing the lift you need to counteract God's g. I can't remember any AOA chart that was affected by the gear on an airplane.

Now if you could get some high pressure bleed air off the 13th stage of a jet engine routed through to a boundary layer control strip on the leading edge of that 182 (boy, I bet that avgas would love something around 500 degrees on the leading edge of the wing) or slats, or some other high lift device, you could shift the AOA curve further out thereby decreasing your Vso.

However, if you can't increase your lift because you're at your max AOA the only way I can see to lower the overall amount of lift you need and thereby lowering the airspeed component needed to keep the airplane aloft in level flight is to lower the amount that God's g is acting against you: throw the passenger out.

Just kidding.

 

[A Squared]

I had considered that it was just an indication difference. I thought that I recalled reading somewhere that landing gear could have a real affect on stalling speed, not just on the indicated speed. I can't at the moment, back this up with anything, so I'll shut up. If I come across that info I'll post it.

 

[Mickey]

It changes the CG.