182S Flap settings

Paveslave53

Paveslave53

Pre-takeoff checklist
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Dec 15, 2019
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Paveslave53
I’m curious as to why the flap settings on the 182 at 20 degrees have a stall speed of 29KIAS at 0 degree bank and full flaps is 35 KIAS at 3100 lbs ? Now the CAS is 50 knots at 20 and 49 at full. I recently finished 208EX training at flight safety and decided to start flying the 182 instead of the 172 I have been flying. They are the only 3 aircraft I have ever put time in besides an Extra 200. I guess I have never flown an aircraft with a lower stall speed with less flaps? Do full flaps create more disruption in airflow causing a higher stall speed? I’m not a wing engineer nor designer. It just seems odd to me. I know in my 172 I cant do a go around with 40 degrees of flaps(say they are stuck) when its really heavy,nor do I ever use that setting but I know that’s part of the reason they limit 172 models with gross weight increase to 30 degrees of flaps is for go around issues.
 
That definitely does not sound right... These are the numbers in your POH?
 
Yea here is a picture of my POH
 

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Paveslave53 said:
Yea here is a picture of my POH
Click to expand...
Idk, but you'll never be close to your most rearward CG. I knew the stall speed from 20-40 was about the same. Todd Peterson did a video on flap settings. I use 40 as a speed brake or to increase descent rate, like he says.
 
I understand the Aft GC is difficult to get to and I will more than likely never ever get to it at max its just an interesting figure. I guess I can go stall it and find out the real world difference between 20 and full.
 
ktup-flyer said:
Idk, but you'll never be close to your most rearward CG. I knew the stall speed from 20-40 was about the same. Todd Peterson did a video on flap settings. I use 40 as a speed brake or to increase descent rate, like he says.
Click to expand...

I also do the same thing with the flaps set to 40 if I’m to high or whatever. I very very very rarely use 40 on the 172.
 
As dmspilot said, It's the difference between KIAS and KCAS. In each case in your POH table, Calibrated stall speed is lower with more flaps, as one would expect. The full flaps position must really tweak the airflow to your pitot tube and/or static ports, making the error factor in Indicated airspeed dramatically different.
 
A lot of airplanes will show very low airspeeds at the stall break. It's the high angle of attack that results in the airflow not striking the pitot port head-on. So the indicated speed will be lower than the calibrated speed, the calibrated having been adjusted for that error. I have seen the airspeed indicator in my old Auster go a bit negative just before the stall break. As the angle steepens, the pitot begins to generate some suction. It doesn't need to be anywhere close to 90 degrees to the port to do that.

Look at the upwash near the leading edge. With the pitot head located in that, you can expect significant error.

main-qimg-2f4100fd39da3614441765da482aa4e4
 
Makes sense .... part of the reason AOA indicators are so great. They don’t care about pressure/ram air changes.
 
Paveslave53 said:
Makes sense .... part of the reason AOA indicators are so great. They don’t care about pressure/ram air changes.
Click to expand...

There’s actually another thread on that...

And they do. Especially depending on where they’re mounted. :)
 
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