Vortex generators and flap gap seals for a C 172

[kiloindiapapa]

I am looking for opnions on the vortex generators and flap gap seals. Heard that the VGs will improve low speed handling. I like the safety aspect of them, but are they worth it. Also the flap gap seals from Knots 2U. Did some reading on opinions and it seems that the flap gap seals may actually make landing speeds faster. found this information also ....There is an old Cessna report on the design philosophy of the semi-cantalever wing. In it they talk about the different types of flaps and the reason Cessna used the slotted flaps over split or plain flaps.

The slotted flap achieves maximum lift at 40 degrees of deflection while the split or plain flaps achieve maximum lift at 60 - 70 degrees of deflection.

It says that at 20 degrees deflection for take-off the slotted flap produces section lift forces that are 30% greater than the split flap and 55% greater than the plain flap. At full flap deflection the slotted flap produces lift forces that are 22% greater than the split flap and 31% greater than the plain flap.

It also says that for equal lift the slotted flap creates approximately 30% less drag than the split or plain type of flap. And that the slotted flap produces approximately 10% shorter take-off and landing distances than equivelent plain flaps. Slotted flpas have the unique advantage of creating high lift with relatively low drag for take-off flap settings.

By installing flap gap seals, one is changing the airflow over the slotted flap and altering the lift/drag characteristics.


Any opinions and experiences?...

[GoinNowhereFast]

From my understanding, putting flap gap seals on a normal slotted flap would basically turn it into a plain flap. The airflow clean from the bottom of the wing to the top of the flap is the reason slotted flaps are a superior aerodynamic design.

[Tail hook]

I think you will find that flap gap seals will (for all intents and purposes) increase both stall speed and cruise speed. VGs increase aileron authority at low speed but may also increase full flap stall speed on a single engine Cessna.
If you regularly expect and need max performance from your 172 you will find that a stock airplane will land shorter than it will launch. The benefits of the VGs may help you fly earlier at the 10/20 flap settings.
Personally I am not good enough nor do I try hard enough to take advantage of any benefit offered by VGs on single engine Cessnas except for C-188. Guys that fly floats may feel different.

[kiloindiapapa]

I think I am confusing myself. My cessna 172 has the fowler flaps, but Cessna calls them a slotted flap. In actual fact they are not slotted because they are a solid flap. Does this sound right?

Anyhow, with the cessna 172 flap (that is not slotted ) do I still need to worry about the flap gap seals increasing my stall speed?

[Adam Oke]

I flew a C172, 145hp 6 cylinder Continental, tail wheel conversion with VG's + oversized tires. I think it was built in 1947, but you can't quote me on that. I flew it both before and after VG's were installed and it made a very noticeable difference with respect to low speed handling and a reduced stall speed. Short field landings were spectacular, but the take off run and climb out still had poor performance. I can't recall if it made the take-off run better or worse, but I do remember being able to slow it right down and land extremely short. It made the stall characteristics very docile, and the plane really did not want to stall.

Top end lost at least 5-7knots, but that being said the oversized tires were installed along with the VG's. I would assume VG's take off a few knots in the cruise though.

[RatherBeFlying]

Gliders use gap seals to reduce drag.

You may get some cruise improvement by sealing the flap at 0 degrees, but that will come at the cost of reducing Lift Coefficient when the flap is extended.

C-172 flaps need the gap to increase Lift Coefficient. Closing that gap will reduce the effectiveness of the flaps unless the gap seal recedes when the flap is deployed.

[kiloindiapapa]

Gliders use gap seals to reduce drag.

You may get some cruise improvement by sealing the flap at 0 degrees, but that will come at the cost of reducing Lift Coefficient when the flap is extended.

C-172 flaps need the gap to increase Lift Coefficient. Closing that gap will reduce the effectiveness of the flaps unless the gap seal recedes when the flap is deployed.

Thanks, Rather Be Flying. your last sentence is what I have been told. I do not want to reduce the effectiveness of the flaps. Another 4 miles cruise will only take me another 16 miles with full tanks. Thats not enough of a gain for me to warrant the flap gap seals. I also heard that if you do not do the aleron seals at the same time then the aleron becomes mushy.

[iflyforpie]

Gap seals are for top end speed. The 172 has a ton of flap though and most people won't notice the difference in performance. The 206 I fly has gap seals and it makes little difference either way...

VGs are the best bang for the buck for low speed performance IMHO. Anybody can install them, they don't require any sheet metal work or additional airframe modification, they are relatively cheap (compared to even a basic STOL kit), and I've heard testimonial after testimonial praising these things.


The difference between a Fowler and Slotted flap is how they extend. A Fowler flap increases wing area when extending while a Slotted flap doesn't. Typically a Fowler flap will have a track and roller system (Cessna 172, Piper Navajo, Boeing 747) while a Slotted flap will be hinged (Piper Cherokee).

Unfortunately, different manufacturer's will call their flap systems different things. The flaps on the 172 were originally called 'Paralift' flaps.

Bottom line is, whether Slotted or Fowler: Air going through the gap will decrease cruise speed, but maintain lift at low speeds.