View Full Version : Flap Gap Seals
12-19-2002, 12:30 AM
I have gap seals on my flaps on my -18 with standard wings and flaps. Can anyone give me a comparison with and without these?
12-19-2002, 07:54 AM
For sure Murph.........the ones with flap gap seals have a narrow length of aluminum attached between the wing trailing edge and the flap.
Do you have a 337 for these? My guess is they would be more for speed, but I'm not an engineer.
12-19-2002, 09:45 AM
If it's for speed, I don't think it's working.
Dave, sometimes you just crack me up.
12-19-2002, 10:04 AM
Actually Murph...........I believe that the seals were put on to "hold" more air and make the flaps more effective instead of the air spilling out between the wing and flap. Anybody? Is this right?
12-19-2002, 10:40 AM
Most gap seals are for drag reduction and smoothing of flight surfaces, so I know their purpose. My question is, do these on a cub help anything? Slow flight? Speed? or just another waste of time and money. They fly fine, but I only fly my cub, so don't have anything to compare with.
12-19-2002, 11:15 AM
Are we talking about the stock ones on top or the strips underneath that completely close off the entire airflow? If it's the ones on the bottom, I have heard from someone who should know that they increase the stall speed and are a waste of time.
I would expect the flap gap seals to kill the slot function, decrease your CLmax, and increase your landing speed. They might increase the cruise, but I doubt if it would be all that much.
12-19-2002, 12:47 PM
I always hesitate to jump in on these discussions of aerodynamics. I thought I knew a couple of things, but then Jerry Burr or Jim C. comes along and I have to learn it all over again.
Flap gap FLOW is a GOOD thing, and helps in the production of low-speed lift.
Flap gap seals CANNOT be considered a help in the flight regimes (slow) that we love our Cubs for. If they're designed to SEAL the gap, gap flow will be eliminated, NO?
Yet, I haven't seen Murph's seals, so what do I know?
There you go, Jerry. I have set up a target. Shoot that sucker full of holes.
Jerry, did you get that new false-spar wing in the air yet?
I've kindof stopped building 'til I hear how the thing performs.
Will you be flight testing it without the slat, as well?
Sorry, guys. Off topic, but maybe we can all learn something we thought we knew.
12-19-2002, 02:46 PM
You have done a better job of asking the questions that I failed to convey.
First, do all -18s have the flap gap seals? If not, are they an enhancement or a detriment to slow flight? Many of us have retired from trying to go fast and now instead do everything possible to go slow. It seems to me that without the gap seals, you have more of a slotted wing and more STOL capability. But I'm just an old dirty-tailed duster pilot. What do I know?
By the way, I appreciated your article in Northern Pilot.
Thanks for the help!
12-19-2002, 07:42 PM
Hi Dave. Not Yet. Hi Murph. This is a tricky question. I would suggest you leave the stock ones on. They will help control airflow over the flap and create lift up to just past half flaps. From that point on the flaps are brakes and not major lifting devices. The seals will create better brakes than without them. Along with the 4" extension. The full flaps (brakes) allow you to carry more power and pull more air over the wing and create more lift and allow you to fly slower. The small slot created by the seal makes turbulence on the flap (at full flaps )which makes more lift than sealing them completely and having dead air over the flap. At that point it is tricky, and again depends on how you are pushing the envelope. :-? Jerry.
Jerry's right. As an aside, in a phone conversaton with the LoPrestis about Cherokee flap gap seals, they mentioned that in their experience, flap gap seals hurt stall performance in some Cherokees, helped others, and had no effect on some. They were of the opinion that in Cherokees, individual differences swamped the slot effect. I've not put flap gap seals on my Cherokee, but suspect tuning the slot might help STOL performance on the ragwing Pipers, and maybe the Cherokee too.
12-20-2002, 12:54 PM
T.J.'s experience is what I have been trying to point out in other posts. Not all changes are (noticeable). I have tested the gap seals and know they work. I didn't say how much. Some mods only contribute a small ammount individually. Put two or three together and it makes a difference. Some mods work together better than others, and produce quicker results. People laugh at me for using an ounce scale to weigh things. If I can loose 5 ounces a few times, I have shed a whole pound. The same can be said of mods. If performance is what you want, then it's ALL THE LITTLE THINGS that will get you there. Like T.J., I have also given thumbs down to the fabric seals. Jerry.
01-01-2003, 04:30 PM
You mention the 4" extentions on the flaps. Are these just fabricated on the inboard of the flaps back to the fuselage. Is this a kit or what? Are ribs required? Are they worthwhile since I'm in the re-cover mode?
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