Cessna's recommendation on flaps

kaiser said:
Really? I did touch and gos with a CFI in a DA40 and on one go we (it was him but I’m PIC, so “we”) commanded flaps up. I felt like the takeoff roll was double! Took ages to get off the ground.

In general regarding flaps on take off, I heard of an unofficial study* where you trade shorter take off ground roll for something like 100-150 fewer fpm.

*Bunch of guys took a 182 and measured performance in various configs
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Well, when your personal minimums are 10,000 foot runways, it's hard to notice that extra hundred yards or so! But seriously, I couldn't really tell the difference. I'm sure it was longer, but again, most of my takeoffs resemble a fully loaded AN 225 deployment.
 
I've always been told flaps help you get off the ground sooner. But, they will hurt you if you're trying to clear the trees. Soft field is the only time I've ever used flaps on take off.

And, on 172s, any more than about 20 degrees of flaps, and you'd better be damn slow before you try to round out, or you'll float way past where you wanted to touch down. I recently got back into 172s after flying an airplane with full span ailerons and no flaps. Flaps are a hassle!
 
bflynn said:
The airplane is 45 minutes away, but thanks to some idiot on American last week, I’m quarantining right now. it will be a while before I could go take a picture. However, I have a very clear memory of no flaps on takeoff and only 20 degrees for landings.
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Tons of POHs available online.
 
wilkersk said:
I've always been told flaps help you get off the ground sooner. But, they will hurt you if you're trying to clear the trees. Soft field is the only time I've ever used flaps on take off.
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The P/Q/R/S POH says you've been told wrong. Those say 10deg flaps will help not hurt you clear the trees. See post #15 and #21.
 
Don’t know about an S model, but my son in law had an M that he didn’t fly. He asked me to fly it whenever I wanted, just to keep it from deteriorating. In that airplane I found the flaps to almost always be unnecessary, but I did almost no short field operation. An SP being what it is, as a 172 goes, will hang on the prop. Even less need for flaps.

I know, I know,… landing with flaps is less stress on the gear, yada, yada, but folks, we’re still talking about a 172, not a G5 or even something small with a laminar flow wing.

To me, when it comes to flap use, a 172 is in the same category as my 140 which is: “Don’t need no stinking flaps!”

Don’t take the above opinion too literally. I use flaps when I need to.
 
wilkersk said:
I've always been told flaps help you get off the ground sooner. But, they will hurt you if you're trying to clear the trees.
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asicer said:
The P/Q/R/S POH says you've been told wrong. Those say 10deg flaps will help not hurt you clear the trees.
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Generally speaking, more flaps = shallower climb, but with low, close-in obstacles, just getting off the ground sooner makes the difference.

Trees at the end of a short runway? Flaps.

tall buildings a couple miles away? No flaps.
 
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Sac Arrow said:
I don't get the point of using flaps on takeoff other than a short or sort field, short of an airliner. The DA40 I had some hours in had one notch of flaps as standard on takeoff. The CFI that checked me out thought it was pointless. I thought it was pointless. I did it both ways. It didn't seem to make any difference on takeoff performance either way, except that the flaps hurt climb performance.
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Night time ops in the Comanche. 18 degrees of flaps gives me an elevator ride up, rather than staring into a black hole with the nose pointing at Cygnus. I started doing that after the Comanche incident in the Phoenix area headed back to Vegas.
 
asicer said:
The P/Q/R/S POH says you've been told wrong. Those say 10deg flaps will help not hurt you clear the trees. See post #15 and #21.
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But the earlier versions of the 172, it says the opposite. Saying "do it this way in a 172" isn't necessarily going to be correct depending on the model.
 
EdFred said:
But the earlier versions of the 172, it says the opposite. Saying "do it this way in a 172" isn't necessarily going to be correct depending on the model.
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Leave it to Cessna to say "Everyone's wrong!" (or "Everyone's right!", depending on your disposition).
 
Most of the 172 I have flown the takeoff checklist has a 0 to 10° range for takeoff.. since the flap lever is virtually infinitely variable I've experimented with all sorts of little adjustments and found just a touch of flaps to work quite well.. maybe a third of the way to 10°, so about 3°?
 
asicer said:
The P/Q/R/S POH says you've been told wrong. Those say 10deg flaps will help not hurt you clear the trees. See post #15 and #21.
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52182900135_6886a42ce2_z.jpg

52182667994_ec1b656d79_w.jpg
 
wilkersk said:
1975 Cessna 172 poh
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The 1975 is an M model.

The specification for Flaps at 10° for a short-field takeoff started midway through the N-model. At some point Cessna realized the additional thrust from the more powerful engine outweighed the extra drag.
 
The Cessna 150 l model has the same info in the poh as the 172.
 
POH (2004 revision) for 172S reads “ any flap setting desired” with caveat that “full flaps should be avoided” for steep slips.
D32797E5-E195-4DBE-BF74-073ED20D96EE.png A55B0823-FB6E-4D0B-84FB-B1D859E87466.png BA5490B2-8416-4C69-AD6A-4F197F29EC0B.png
 
dmspilot said:
Seems to be specific to the NAV III model. It does fly a bit different, owing to the higher empty weight and a different weight distribution than the conventional model.
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Oh by the way, the R172K (aka the "XP") also has the 10deg flap recommendation in the abbreviated section. The amplified section is almost the same as the P/Q/R/S, except the obstacle clearance distance is only reduced 5% and the speeds are different. Also, maximum takeoff flaps is 15deg instead of 10deg. 15deg is recommended for soft field while short field stays the same (10deg).
 
For the typical single-engine piston airplane, use of flaps may shorten the ground roll but will always decrease climb performance. The pilot must decide which is more valuable; a decreased ground roll or increased climb performance. The change in language over time in the POH/AFM for the "same" airplane hasn't changed this simple trade-off.
 
Ryan F. said:
For the typical single-engine piston airplane, use of flaps may shorten the ground roll but will always decrease climb performance. The pilot must decide which is more valuable; a decreased ground roll or increased climb performance. The change in language over time in the POH/AFM for the "same" airplane hasn't changed this simple trade-off.
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The climb performance we're talking about is the distance measured from the start of the takeoff point to fifty feet AGL. Flaps do not "always" worsen this performance, or we wouldn't be having this discussion. Cessna did not start recommending flaps for short field takeoff with an obstacle starting with the N model because they suddenly wanted to show worse performance numbers in their marketing materials. :rolleyes:
 
dmspilot said:
The climb performance we're talking about is the distance measured from the start of the takeoff point to fifty feet AGL. Flaps do not "always" worsen this performance, or we wouldn't be having this discussion. Cessna did not start recommending flaps for short field takeoff with an obstacle starting with the N model because they suddenly wanted to show worse performance numbers in their marketing materials. :rolleyes:
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I stand by my statement, which I worded carefully and remains accurate.
 
Ryan F. said:
I stand by my statement, which I worded carefully and remains accurate.
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Your statement is ambiguous, can be misinterpreted, and is not germane to the discussion on takeoff and obstacle climb performance.
 
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RyanB said:
Full flaps at 10 miles out is the best procedure in the 172.
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Huh??? I’m putting flaps 1 (slats only) in the Airbus 10-15 miles out… at a speed more than triple of your flaps 3.

Full flaps at 10 miles in a 172…
Ludicrously stupid.
 
Kritchlow said:
Huh??? I’m putting flaps 1 (slats only) in the Airbus 10-15 miles out… at a speed more than triple of your flaps 3.

Full flaps at 10 miles in a 172…
Ludicrously stupid.
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Well ... maybe he's flying the airliner approach and pattern! :p
 
Ryan F. said:
I stand by my statement, which I worded carefully and remains accurate.
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I think what he’s saying is one is shorter, one is longer. You need to tally up the two to see which is better for the individual circumstance.

It’s not “which is more valuable, ground roll or climb”… it’s the sun of the two.
 
MauleSkinner said:
I thought it was very clear and germane.
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You already understand the topic, or at least I'll assume that you do. So of course it is clear to you. Those who don't understand the topic will not learn anything from his post and may draw incorrect conclusions from it. Therefore it is a waste.
 
dmspilot said:
You already understand the topic, or at least I'll assume that you do. So of course it is clear to you. Those who don't understand the topic will not learn anything from his post and may draw incorrect conclusions from it. Therefore it is a waste.
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True. He shouldn’t have used the term “typical single engine piston airplane”. One could possibly not realize that it applies to all airplanes.

but since the discussion here is specific to the 172, I can accept it as relevant.
 
MauleSkinner said:
True. He shouldn’t have used the term “typical single engine piston airplane”. One could possibly not realize that it applies to all airplanes.

but since the discussion here is specific to the 172, I can accept it as relevant.
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Not what I'm referring to.

The thread is about takeoff performance, not steady-state climb performance.
 
dmspilot said:
The thread is about takeoff performance, not steady-state climb performance.
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The thread is about whether or not to use flaps for takeoff. Seems like ham stringing your ability to takeoff because you don’t understand what flaps do to the takeoff is relevant.
 
MauleSkinner said:
The thread is about whether or not to use flaps for takeoff. Seems like ham stringing your ability to takeoff because you don’t understand what flaps do to the takeoff is relevant.
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Maybe I was incorrect, and that you don't understand the topic after all.
 
MauleSkinner said:
Ok…what is the topic?
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Why do some aircraft specify flaps to clear an obstacle after takeoff? Why would they recommend something that, as you put it, would "ham string" your ability to takeoff?
 
dmspilot said:
Why do some aircraft specify flaps to clear an obstacle after takeoff? Why would they recommend something that, as you put it, would "ham string" your ability to takeoff?
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They specify flaps to, as you put it, optimize the distance to 50 feet. They make that recommendation because a 25-foot obstacle or a 100-ft obstacle (or anything other than zero or 50) aren’t part of the certification standard, so ultimately the pilot has to decide whether flaps are advantageous or not. The answer will probably be different for other obstacle heights, and if you blindly follow the manufacturer’s recommendation, you may hamstring yourself ability to takeoff.
 
MauleSkinner said:
They specify flaps to, as you put it, optimize the distance to 50 feet. They make that recommendation because a 25-foot obstacle or a 100-ft obstacle (or anything other than zero or 50) aren’t part of the certification requirements, so ultimately the pilot has to decide whether flaps are advantageous or not. The answer will probably be different for other obstacle heights, and if you blindly follow the manufacturer’s recommendation, you may hamstring yourself ability to takeoff.
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If flaps "always decrease the climb performance" (Ryan F) why would they be specify flaps be used to clear any height of obstacle?
 
dmspilot said:
If flaps "always decrease the climb performance" (Ryan F) why would they be specify flaps be used to clear any height of obstacle?
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Because if you start the climb soon enough, you can clear 50 feet sooner, even at a lower climb angle. But your climb angle IS decreased when you add flaps.

And if pilots don’t understand that, I’d say they’re more ill-informed than they would be by misunderstanding anything in Ryan’s post.
 
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