Is it normal practice to use 25 degrees of flaps when taking off at max weight in a PA-28-181?

Question

I recently started renting a plane (PA-28-181) from a new flight school and had to get checked out before I had the "OK" to rent.

I had brought 2 family members with me during my checkout because...

1. They wanted to experience a small plane for the first time
2. My intentions with the plane were to have the option to fly with a full load of passengers (which I couldn't do in the planes I was used to flying) so I wanted to experience what flying at max gross weight was like.

During the checkout, while in the runup area going through my checklist, the instructor encouraged me to go back through my checklist. Eventually after hearing this suggestion multiple times and not understanding what he was hinting to, he came out and said "You need to set your flaps to 2 notches because we're at max weight".

I hadn't heard this before and I'm not seeing a ton of discussions about this type of thing online. His point was, the flaps would increase lift since we're heavy - that makes sense to me... But they also increase drag.

Note: this was not a short-field takeoff. 5,503ft paved runway, although it was hot (90+ degrees fahrenheit).

So, this leaves me with 3 questions:

1. Is this correct? When you're on the "heavy" end of the spectrum, should you be deploying flaps?
2. If so, what would be the proper flap setting at max gross weight?
3. Since, in this case, the point wasn't to clear an obstacle, would you simply climb out at Vy instead of Vx?

Answer 1

The PA-28-181 POH I have read says to set first stage of flap (10 degrees) for a normal takeoff, and 2 stages (25 degrees) for a short or soft field takeoff. I've flown PA-28s quite a bit and I've never heard any suggestion of using 25 degrees for a normal takeoff. At maximum weight on a hot day at sea level 5,503ft should be plenty at 10 degrees, even if you are at 4000 ft pressure altitude it should still be sufficient, so I see no reason to set 25 degrees.

Setting 25 degrees for takeoff increases lift at the cost of drag, and risk as you are closer to performance limits. An engine failure on takeoff with 25 degrees of flap will give you less time to get the nose down, and stall characteristics are harsher with more flap.

If the runway was shorter I would see 25 degrees as good advice. There are plenty of light aircraft pilots who don't do performance calculations before they fly, drilling 25 degrees of flap when heavy into them may just save their bacon on a hot day on a short airfield.

Answer 2

I should preface this answer with 2 prudent points

1. My first flight of a PA-28 (Im unsure the exact model) was a week ago.
2. I have roughly 250 hrs on Cessna 150/152/172

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The answer to all of these sort of questions pretty much always comes down to "What does the POH for this specific aircraft say?". That is the authoritative source of information on operating the aircraft. Another useful source of information on the safe operation of any aircraft is to ask, and seek instruction, from a competent flight instructor who is familiar with an aircraft.

So, there is a fairly good chance that the instructor doing your check ride just knew the aircraft performance well, the airfield well, and the prevailing conditions well and was advising you based on their experience. There is no substitute for experience!

That said, it's easy enough to find a reproduction of a PA28-181 POH online - you should of course consult the actual POH of the aircraft you are flying but the general handling procedures are usually the same.

The POH linked mentions for standard take off

The [trim] tab set just aft of neutral with the exact setting depending on the loading of the aircraft. Allow the aircraft to accelerate to 48 to 53 KIAS depending on the weight of the aircraft and ease back on the control to rotate to climb attitude.

It goes on to mention a different procedure for short or softfield take off, or a takeoff with obstacle clearance

The flaps should be lowered to 25^o (second notch) [...]

So, no mention of flaps for a normal take off even at or near maximum weight. Take from that what you will - but personally I would still be listening to the instructor!

Answer 3

I'd like to add to Jamiec's excellent answer. The attached POH shows that the take-off distance with 25 degrees at maximum gross weight is a few hundred feet less than 0 degrees of flaps. While the current runway may have been of sufficient length for a take-off with 0 degrees of flap, the instructor performing an insurance checkout for the FBO may have wanted to instill the importance of the 2nd notch of flaps for when the pilot rents the airplane on his own and flys out of shorter runways with a full load of passengers.

Apparently for an Piper Cherokee Archer II the increase in drag of 25 degrees of flaps is more than offset by the increased lift allowing the aircraft to lift off sooner.