Stall speed and gross weight

azpilot

azpilot

Line Up and Wait
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azpilot
I learned to fly in a Cessna 150, and then a 172. I'm a bigger guy and my instructor in the 172 was a little bit heavy as well. Consequently, most of my flights in the those two airplanes were conducted within 100 lbs or so of max gross.

Recently I've started flying a 182S. It's great. Lots of power. Climbs like a dream. But, I've never really flown it anywhere close to max gross weight. I would say I've typically been about 350 lbs under max gross. Well, this weekend, I took my dad, and two of my boys on an overnight trip to a remote strip out here in AZ. We were fairly close to the max landing weight at take off, which is 2950 lbs. Max take off weight is 3100 lbs.

I was really surprised at the difference in performance. Shortly after lifting off the runway, the stall horn even chirped at me. That got my attention REAL fast. I just pushed the nose down a bit and we were fine on the climb out. But it really caught me off guard. I flew the takeoff just like I had always done before, but I was carrying another 460 lbs compared to when I fly solo.

For me, the lesson learned here was to remember that a stall occurs at a specific AOA, not a specific airspeed. As weight goes up, the AOA has to increase for a given airspeed, so there is less margin to that critical AOA than I was accustomed to. I knew all of that before the flight, but I'd never really experienced it. I think it's also important for us all to know and understand how the airplanes we fly might behave differently at different gross weights.
 
mscard88 said:
You're the cat with the peeing neighbor right? o_O
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TANGENT!!!! ya... that's me. When we got back today it smelled so bad. It had been baking in the AZ sun all day. But the good news was that after a couple hours of flying at the higher weight, I'd figured out the different behavior and made sure not to stall and kill my family on short final. ;)
 
azpilot said:
TANGENT!!!! ya... that's me. When we got back today it smelled so bad. It had been baking in the AZ sun all day. But the good news was that after a couple hours of flying at the higher weight, I'd figured out the different behavior and made sure not to stall and kill my family on short final. ;)
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Now THAT is max gross...
 
Does AOA increase with weight? My AOA indicator disagrees.


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That was my point, the airspeed at which I arrive at the critical AOA changes, the critical AOA is always the same regardless of weight or air temp/ external influences.


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WannFly said:
That was my point, the airspeed at which I arrive at the critical AOA changes, the critical AOA is always the same regardless of weight or air temp/ external influences.


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Your post #10 didn't say critical angle of attack.
 
Speed doesn't cause stalls, the AOA does. As Ralph points out, the heavier you are, the more lift you need. You can get it by flying faster or increasing the AOA. You increase the AOA too much, you stall.
 
GRG55 said:
Your post #10 didn't say critical angle of attack.
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Critical or not, the AOA is same. U can fly a specific AOA during climb out or landing. Weight has nothing to do with AOA. Once u find the AOA it stays the same no matter how much weight You put on the plane or remove.

The airspeed at which You arrive close to the critical AOA or any level close to the stall horn will change with weight and other stuff

My comment was based on the original post where there is a statement about AOA increasing with weight.


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WannFly said:
...Weight has nothing to do with AOA...

...My comment was based on the original post where there is a statement about AOA increasing with weight.


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At a given airspeed you need a higher angle of attack to lift a greater weight.
 
Yes if u use airspeed to measure AOA, which is not correct, same thing about stall speed. Stalling a wing is about the AOA, but we are all taught about maintain this airspeed for not stalling and then we finish that sentence saying plane will stall at any airspeed.

Your AOA doesn’t increase with weight, ur airspeed to maintain the given lift changes. There is a difference


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WannFly said:
Yes if u use airspeed to measure AOA, which is not correct, same thing about stall speed. Stalling a wing is about the AOA, but we are all taught about maintain this airspeed for not stalling and then we finish that sentence saying plane will stall at any airspeed.

Your AOA doesn’t increase with weight, ur airspeed to maintain the given lift changes. There is a difference


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Unless the OP edited his original post you are agreeing with him, not correcting him.
 
Tarheelpilot said:
Unless the OP edited his original post you are agreeing with him, not correcting him.
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Lol. Yes I guess I am. I read it as the AOA changes with weight, clearly that’s not what OP posted.

I will go back to the closet now and hang my head


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@azpilot Temps are also creeping up... if you've been flying it in cooler temps, performance will drop off quickly as spring and summer come on. But you know that.

It's also worth looking at the stall speed table in section 5 of your POH -- once you get to the 182S model and above, they started showing the changes in stall speed by most forward and most aft center of gravity (my old 182P manual doesn't have it)... and you were probably a lot further aft then when you run around by yourself or with you and a big instructor up front.

Just for fun, while you're in Section 5, flip a couple pages forward and look at the Airspeed Calibration table and note some oddities Cessna documented in later 182s... Flaps 20 always indicates lower than Flaps UP or Flaps FULL. Many people don't notice that one. Not a huge change, but the slower you're flying the greater the calibration error.

Cessna nicely gives newer model owners the stall speeds in the stall speed table in both KCAS and KIAS, but there's a note below the table that KIAS speeds are estimates. Covering their legal hineys there a bit.
 
WannFly said:
Critical or not, the AOA is same. U can fly a specific AOA during climb out or landing. Weight has nothing to do with AOA. Once u find the AOA it stays the same no matter how much weight You put on the plane or remove.

The airspeed at which You arrive close to the critical AOA or any level close to the stall horn will change with weight and other stuff

My comment was based on the original post where there is a statement about AOA increasing with weight.


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The AOA needed to maintain altitude at a given airspeed increases with weight.
 
Even a 100 lbs over gross raises your stall "speed" only slightly, like around 1 knot or so. I used to fly a 172 with an AOA, and really fell in love with that thing. . .
 
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