Performance Take Off's

[TwinOtterFan]

Good day all,

I was wondering if someone had a simple chart that illustrated the settings, speeds, and basic procedure for short field take off with and without obstacle and soft field takeoff with and without obstacle.

[David MacRay]

Short field? Balls to the wall, adjust mixture for maximum rpm, release the brakes. Without any obstacles zip along in ground effect until you’re givin’ ‘er then climb out like a saturn V on an angle.

[TwinOtterFan]

I meant more something like this, I was curious about the flap settings in particular. My old instructor had me always at flaps 10 for short or soft, but according to the POH on a short field takeoff with no obstacle no flaps seems like the better choice.

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[Squaretail]

Just do as the POH says. I will assume some of your confusion arises since Cessna flipped back and forth on what they thought was better depending on what year it was. If you are doing the flight test the real objective is the examiner wants to know that you know where to find said bit of information in the POH and the wrong answer to that question is “that’s the way my instructor showed me”.

If the school’s checklist deviates from the POH for that particular aircraft - as schools are want to do if they have general checklists for planes as opposed to specific ones - use the POH. And not the generic ground school POH you might have, but the one for that specific airplane. Or it’s certified copy of the original, as schools are allowed to carry instead of actual ones.

[David MacRay]

Darn it. I forgot the disclaimer.

Not a real dog or flight instructor, any and all advice is intended for entertainment purposes only, etc.

I am fairly confident the use of flaps will depend on what plane you’re flying. There are a some that you really don’t want to use any flaps for take off.

I believe there are some that use flaps for every take off.

[Colonel]

A horrible simplification is that for a little airplane, up to 20 degrees of flaps increases lift at the cost of extra drag. Beyind 20 degrees of flap, mostly what you get is more drag and not much more lift. Look at the stall speed chart for flap vs stall speed.

So if you have an airplane with oddles of power - my 210hp Maule comes to mind - it should be no surprise that 15 degrees of flap is used for a normal takeoff. A 182 will be similar. They have the extra thrust to overcome the drag if 10 or 20 flap and enjoy the benefit of the extra lift.

If you’re flying something terribly underpowered you probably don’t want to use any flap unless you’re doing something really strange. You simply don’t have the thrust to overcome the additional drag of flaps for takeoff.

That’s why I hate electric flaps. Gimme a Johnson bar any day. You want to pop it into the air on a stupidly rough or soft surface, start the takeoff nose high with no flap then use the Johnson bar to pop you into ground effect.

[Colonel]

It’s interesting to compare the POH procedures of the vanilla 172 and the 172 XP which is much more powerful.

Sure enough, Cessna says to use 10 flap for a short field takeoff for the XP.

[Colonel]

The very best Top Gun instructors used flap on the F-14 during ACM even though it was forbidden because of the extra lift at slow speed because they had two afterburners.

Watch Snort’s speech at the Smithsonian. He defeated an F-15 because he knew how to cheat. He said he was put on this earth to abuse the system (navy).

He knew the F-14 was a 13G airplane!

[TwinOtterFan]

Just do as the POH says. I will assume some of your confusion arises since Cessna flipped back and forth on what they thought was better depending on what year it was.

THIS^^

I found my old POH and compared it to the one I have now and now I understand the difference, I do not understand why there is one, just that there is and I can follow and perform the procedure.

[Squaretail]

, I do not understand why there is one

Mostly an exercise from Cessna’s marketing department, which was always striving to show the airplane in the best possible light. The best take off performance of the 172 line remains the earliest model, by virtue of the fact it’s the lightest. As the line developed it got fatter and fatter, so by the end of the first run before the bad ol’ eighties of GA, they really had to work to prove to buyers that the new 172 was as good as their old one, with more stuff.

The most obvious example of the Cessna math being constantly and rigorously re-engineered is the difference between the N and P models, where with identical airframes, the latter can magically carry a hundred more pounds by restricting the flaps to thirty degrees. Notably there is no O model (or I model) because Cessna thought that would be too confusing for pilots. To give you an idea of how engineers feel about pilots.