The International Cessna^® 170 Association

Does anyone have any information/pictures/etc on flap gap seals for the 170B? If not 170B how about C172. Thanks. Richard Baan 386-466-5674 bushmechanic@windstream.net

Without:


With:


You know, slotted flaps only do their job well if they have air-flow OVER them when deployed. The gap seals diminish that. If you don't want slotted flaps, a 170-A would be ideal. IMO

The Knots 2 U website has the following imaginative depiction:


I would suggest that the only time anything NEAR to that depiction occurs is at the near-moment of a full-stall with flaps retracted.... exactly when you'd WANT the wing-ROOT to stall before the wing TIPS....which is what that depiction suggests will occur. At cruise the relative wind blows right past the flap nose and continues aft.
If you want to see what cruise changes will likely occur to YOUR airplane.... get a roll of duct tape and tape up that gap and go fly. Make certain your weight and the density altitude is the same in both tests. If you can see the difference, I'll pay for the duct tape.
(Notice that their depiction does not accurately depict the actual shape of the flap-nose. I consider this misleading advertising. They show a huge "cup" to appear to "catch" the air. In actual fact, the flaps have a rounded nose and they seal up against the upper wing-skin when retracted, thereby blocking the air-transfer from below-to-above the wing that they wish to imply by their drawing. Their drawing is more descriptive of the ailerons than the flaps, but even that is not completely accurate because with an aileron deflected downward....the lower skin of the aileron ascends to fill the aileron-gap and reduces the airflow. With the aileron UP... it behaves as a "Frieze"-type aileron which helps to lower the wing (which is what an UP aileron is intended to do) and it also helps relieve air-pressures which assists in maintaining a light aileron "feel"...AND helps relieve adverse yaw!
In ordinary cruise, the relative wind continues on by the aileron, and neither of these depictions is accurate, in my opinion. Besides, their flap gap seal looks almost exactly like the aileron-to-wing gap in normal cruise. See their own photos above? There's no more gap in cruise in the ailerons than in their own flap gaps..... but wait! They don't sell aileron gap seals do they? So why are they deliberately drawing ailerons when they're trying to sell flap gap seals? MIsleading, in my opinion.) Again, slap some duct tape across the top of the ailerons and see what gap seals will do to your cruise speeds.
Oh, yes, I failed to mention that I once did a little free-lance instructing at a flying club that had two 172's only a year apart (64/65) the newer one had flap gap and wheel fairings. The 64 had neither. There was absolutely no discernable difference between the two, and they were frequently flown in formation by a couple of the clubmembers who remarked the same.
Your results may differ, and that's certainly no scientific test, but....

And seeing as how parasitic drag increases in proportion to the square of velocity, a 200KTAS airframe will experience 4 times the parasitic drag of the same airframe at 100KTAS.

To put it another way, if you put flap gap seals on a 100KTAS aircraft, it will benefit you 1/4 as much as if you put them on a 200KTAS aircraft.

Folks can spend upwards of $10K on fairings, cowlings, and seals on their Mooneys and end up with a net of about 5 KTAS. You'll probably get a better return on investment if you just keep your plane clean and waxed. And rigged properly.

Anyway, Horton also sells gap seals. http://www.hortonstolcraft.com/index.htm

I have the results from of a bit of empirical testing with flap gap seals.

When I first bought my 53-B in McCall Idaho it came with some "extra" uninstalled parts.
The fuselage had been rebuilt from the rear door post forward with ALL new parts.
The Horton leading edge cuff, stall fences, and aileron seals. The Horton flap gap seals were still in a box.

This plane had been converted to the Bush version of the 180hp and constant speed prop etc.
I got to fly it in the Idaho backcountry for two years before I actually bought it. I never had any problems getting it to come down when needed for some of the relatively short strips that are there.

I put twenty some additional STCs into getting it even "better" for Idaho. In the process of "improving" on the short field performance I came to the point where I had to decide to install those available flap gap seals or not. I asked the previous owner if there was a reason why he did not install them. He said. "Aw, they told me that those things were just dangerous here in Idaho." Hm?!?

I asked my mechanic at that time, Vern Miller, what he thought of them. He had some on his 180. Vern told me that he liked them on his 180, but that I should get an all new kit from Knots-2-U. He stated that the reason is you can take off the Knots-2-U seals if and when you need to. The Horton's are riveted on. Yeah you could drill em out.

So, I installed a set of Knots-2-U flap gap seals. No disernable problems in and around civilized airports.
Went back to Idaho the following summer and could no longer get the damned thing to come down out out of the sky. We were unable to get much more than five hundred feet per minute decent rate. Not Good!, especially in an area that often requires STEEP approaches.

Frustration led to the empirical test. I simply unscrewed 57 screws, threw the damned seals in a hangar, and tried again. This time I could easily get well over a nine hundred feet per minute decent rate. Problem solved.

Since I am still on good speaking terms with the old fahrt I bought the plane from, I went and told him of my "discovery." He said, " I told you not to put those danged things on, they will onlyest get ya kilt round here.

Seems that he was able to get the majority of the fuselage rebuilt while at some airborne type express maintenance shop somewhere in Ohio. One of their chief mechanics allegedly talked to one of the key designers, who warned him about the problem when you need to make short steep approaches.

Since my plane is set up for low and slow, mountain and canyon flying, I have not been concerned about cruise performance and can not speak to any improvement in that area.

Hope it helps.

I put them on 3225A about 25 years ago and as I recall, the speed differences were negligable. I installed them because I thought they looked nice.....They were kinda all the rage back then... one of the members and I think it was Gerald Brosher (God rest is soul) installed them with RTV so he could just try them out and if he didn't like them, just peel off.

Sounds like the guy who was trying to get his horizontal stabilizer adjusted for level flight and was about to test fly it wih the stabilizer fastened on with cleco fasteners.

blueldr wrote:Sounds like the guy who was trying to get his horizontal stabilizer adjusted for level flight and was about to test fly it wih the stabilizer fastened on with cleco fasteners.

Aha! Poor-man's Vortex-Generators!

Don't do it! If I could take mine off without leaving all those rivet holes to look at, I would. I learned to fly Dad's 170 which had them on. Back then I knew no different. I was only told how they ruined the flaps. How his stock 170 in a power off dive would jet past his friends 170 with a 180 conv. (heavier) also at idle. Also he talked about the extreme forces the gap seals placed on the flaps, the evidence being how hard it was to pull on the flap handle above 65 MPH. We have always made a conscious effort not to fly above 85 MPH with full flaps because of the altered forces created by the seals.
It wasn't until I bought my own 170 (same year 1955) that wasn't blemished with flap gap seals, that I appreciated the stock design of the Cessna "barn doors". I had more fun with that plane doing steep apc's. and being able to pull the flap handle at any speed below 100 mph as if it were power assisted.
The only benefit from the flap gab seals I can speak of, is the appearance.
Now that I have inherited Dad's 170 and a new paint job draws closer, my imagination is always working on a clean way to get rid of the seals (the dream being 175 wings).
Performance wise, the bottom end blows, and if the top end has anything to gain it's the pilots wishful thinking.

tweiss,

If you're really wanting to remove those flap gap seals without unriviting them from the wing, contact me and I tell you how I've removed them.

You mentioned about wishing for C-175 wings. I've got a pair of those for sale too.

Dick Lemmon