Flap trap

Aye Effaar

Aye Effaar

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JC
CFI in training here (busy working up lesson plans). A friend of mine is a DPE and we’ve been having a discussion about the type of flaps on a 172.

According to the Skyhawk 172 S POH, the flaps are a single-slot design (page 7-13). I believe they are therefore Slotted flaps.

My DPE friend maintains that the flaps are on a track, and travel rearward during extension and therefore are Fowler flaps.

Peter Garrison from Flying magazine had this to say (https://www.flyingmag.com/travels-mr-fowler/):

A true Fowler flap does not simply rotate about an external hinge; it always slides or rolls on tracks or is carried by some sort of complicated parallelogram linkage, and its hallmark, during deployment, is an initial period of moving more or less straight aft with little change of incidence.​

The Garrison quote is good, but obviously it's basically his opinion. Ideally, I'm looking for something "authoritative" to sway my friend, or (ack!) prove him right.
 
So basically a single slotted fowler flaps.
Sometime you can both be right
 
Garrison is correct. A Fowler flap moves significantly aft, increasing the wing area, before moving down at the end of its travel. A C-172 flap moves aft, too, but not nearly as much and it starts moving down from the beginning, so it's not a true Fowler flap.

The original Fowler patent was for a "variable area wing".
 
It’s a Fowler Flap, but barely because the travel on the track is short. The FAA’s description perfectly matches Cessna flap design and aerodynamic characteristics.

Fowler flaps are a type of slotted flap. This flap design not only changes the camber of the wing, it also increases the wing area. Instead of rotating down on a hinge, it slides backwards on tracks. In the first portion of its extension, it increases the drag very little, but increases the lift a great deal as it increases both the area and camber. Pilots should be aware that flap extension may cause a nose-up or down pitching moment, depending on the type of aircraft, which the pilot will need to compensate for, usually with a trim adjustment. As the extension continues, the flap deflects downward. During the last portion of its travel, the flap increases the drag with little additional increase in lift.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/08_phak_ch6.pdf
 
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I've seen them called "semi-Fowler" flaps; Cessna's marketing mavens called them "Para-Lift" flaps. But former Cessna aerodynamicist and test pilot Bill Thompson told the story this way:

The 1952 C-170B featured new slotted flaps that could offer extra lift for take-off and far more lift and drag for landing. We referred to the design as the NACA "2h" configuration, since the wind tunnel performance curves had been presented as Figure 2h in the NACA report.​
 
from the CFI Bible aka the Airplane Flying Handbook.

"The Fowler flap deflects down and aft to increase the wing area. This flap can be multi-slotted making it the most complex of the trailing-edge systems. This system does, however, give the maximum lift coefficient. Drag characteristics at small deflections are much like the slotted flap. Fowler flaps are most commonly used on larger airplanes because of their structural complexity and difficulty in sealing the slots."

Operative words "can be multi-slotted" with implies they don't have to be.

Brian
CFIIG/ASEL
 
brcase said:
from the CFI Bible aka the Airplane Flying Handbook.

"The Fowler flap deflects down and aft to increase the wing area. This flap can be multi-slotted making it the most complex of the trailing-edge systems. This system does, however, give the maximum lift coefficient. Drag characteristics at small deflections are much like the slotted flap. Fowler flaps are most commonly used on larger airplanes because of their structural complexity and difficulty in sealing the slots."

Operative words "can be multi-slotted" with implies they don't have to be.

Brian
CFIIG/ASEL
Click to expand...

The Boeing 727 had multi-slotted fowler flaps, which is one of the reasons it made a good short field machine for its size and day.61032544_10156063875880951_8749787944702705664_n.jpg
 
Probably more important to be able to teach what Fowler Flaps are and how to fly them vs other types of flaps.
 
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