qmdv wrote:I am almost 70 years old so I no longer have time to do stuff that offers questionable results

tim

Growing older is not for sissies, right?

Cary

hotrod180 wrote:
FWIW I've pretty much decided to remove the gap seals. Don't want to waste any of the good flying weather we've been enjoying around here, so it'll be happening during our next rainy spell.

Hotrod - you could have your own episode of Mythbusters! Take some data points BEFORE removing the gap seals and then repeat AFTER. Slow flight, cruise, etc.

It may not help you but you could be a hero to all of the Skywagon drivers out there by settling the age-old debate with modern evidence.

The C150 I flew before and after suffered during the stall. Before it was a nice clean predictable break, after it was best described as a violent wing drop to the point of wanting to go on its back and enter the spin. Nothing else was changed. I was a student but my instructor certainly was not. He actually liked it for training purposes but was sure to teach spin recovery from then on.

I went up the other day and did some approach stalls. Easing into it, power off / flaps 40, I got buffeting at 45 IAS & it let go at about 43. Not a clean break, sort of mushed into a break & as soon as the nose dropped it was flying again. I could probably get a sharper more definable break if I horsed back on the yoke, but I figure what I did was comparable to what you're actually trying to approach for landing on the edge of a stall.

Since now we're talking stall behavior, with my P172D set up as described, with the droopy tips before the flap gap seals were installed, the stall behavior was actually pretty standard 172, power off or power on, regardless of flap position. The roll control near the stall was much better--those droopy tips help quite a bit there.

After the flap gap seals were installed, the stall behavior power off changed to the extent that instead of a definable stall, it's more of a mush, not even a phugoid stall, again regardless of flap position. The nose gently drops a little, but that's about it. Power on, it's gentle but more definitely a stall break.

The other noticeable aspect is that my airplane has a better glide ratio than a stock 172. Whether that's contributed to by the droopy tips or the flap gap seals or both, I don't know, because I hadn't tried gliding for any distance until after the flap gap seals were installed. When my engine threw the rod and I landed in a field soon after I bought the airplane, I was at such a low AGL altitude that the glide wasn't very far anyway, so I really had no idea how it glided--I just did what had to be done to get on the ground safely.

Cary

I bet they do improve glide ratio by making it cleaner. That's where they have a tendency to float in ground effect.

High pressure air under the wing gushing up ahead of the flap (or aileron) LE creates a geyser of air which disrupts the clean flow over the flaps (or ailerons). Gap seals seal that gap & keeps everything pretty smooth.

Still can't wrap my head around an Oregonian drinking Coors Light! What the heck, Terry?

I went out flying yesterday in the beautiful weather and took some pictures of my flaps in different positions. Hopefully this will help. Or not. Sorry about the muddy plane.

Flaps up. Pretty clear here how the wing is cleaned up for cruise and flaps-up climb:



10 degrees. This is the smallest gap you'll get with any flaps.



40 degrees. This is what I, and I presume most here normally land with. Plenty of gap here, and I don't have any issues with floating. Also, the stall behavior is as nice as any plane I've flown. Hard to argue that somehow these are now just barn door flaps.



I can buy that if you're landing with 10 or 20 degrees of flaps that it'll be more slippery, but that's not what you'd do if you needed to land short anyway. On the other hand, that same drag reduction may help when taking off with partial flaps.

Again, I'm not trying to say that these things are an awesome mod. They came on my plane. Just adding some perspective after 9 years of ownership.

Looking forward to your A/B testing results!

Oregon180 wrote:Still can't wrap my head around an Oregonian drinking Coors Light! What the heck, Terry?

I went out flying yesterday in the beautiful weather and took some pictures of my flaps in different positions. Hopefully this will help. Or not. Sorry about the muddy plane.

Flaps up. Pretty clear here how the wing is cleaned up for cruise and flaps-up climb:



10 degrees. This is the smallest gap you'll get with any flaps.



40 degrees. This is what I, and I presume most here normally land with. Plenty of gap here, and I don't have any issues with floating. Also, the stall behavior is as nice as any plane I've flown. Hard to argue that somehow these are now just barn door flaps.



I can buy that if you're landing with 10 or 20 degrees of flaps that it'll be more slippery, but that's not what you'd do if you needed to land short anyway. On the other hand, that same drag reduction may help when taking off with partial flaps.

Again, I'm not trying to say that these things are an awesome mod. They came on my plane. Just adding some perspective after 9 years of ownership.

Looking forward to your A/B testing results!

Lol, I like our local beers, but 2 or 3 of them kick my but!
I've watched you land your airplane and you have it figured out, as to how you keep it from floating with those damn FGS, I'll have to grab another coors light and ponder.

wagonflyer wrote: Hotrod - you could have your own episode of Mythbusters! Take some data points BEFORE removing the gap seals and then repeat AFTER. Slow flight, cruise, etc.
It may not help you but you could be a hero to all of the Skywagon drivers out there by settling the age-old debate with modern evidence.

While I wouldn't mind being a hero for a change, instead of a goat, I wouldn't wanna screw up anyone's firmly-held opinions with anything like scientific data points!

Oregon180, whose flap-gap seals are installed on your airplane? How many mounting brackets besides the ones on the flap tracks? I think there's only a couple mfr's of these, Horton & Knots-2-U. I'm assuming mine are Horton's but for all I know they're home-made, considering that there's nothing to them -- just a flat piece of alum with one hemmed edge. Anyone with a shear & an eight foot brake could bang out a pretty nice set, no problem.

Hey Hotrod. I went back and looked in the logs. Mine are B&M flap gap seals. They were installed in 1976 (!) along with the aileron gap seals, so they've been on there a while!
I don't think B&M still sells this STC. It might have been sold to Horton or someone else.

wagonflyer wrote: Hotrod - you could have your own episode of Mythbusters! Take some data points BEFORE removing the gap seals and then repeat AFTER. Slow flight, cruise, etc.........

Well, I took the plunge and removed the flap gap seals today. In case you didn't know, cherry max rivets are a PITA to remove. Grind down the head a ways, punch the steel stem out, then drill them out. And they do like to spin.

About the only data point I took before removal was approach stalls, it let go at about 43 IAS with flaps 40. And cruise at 21" / 2300 seems to be in the neighborhood of 140 IAS, with the indicator seemingly about 5 mph optimistic.

I'm more interested in how it'll behave & feel when landing, which is probably pretty hard to quantify anyway. It's more of a seat of the pants kind of thing. I didn't get a chance to fly it today, but maybe tomorrow. I'll post when I have something to report.

hotrod180 wrote:

wagonflyer wrote: Hotrod - you could have your own episode of Mythbusters! Take some data points BEFORE removing the gap seals and then repeat AFTER. Slow flight, cruise, etc.........

Well, I took the plunge and removed the flap gap seals today. In case you didn't know, cherry max rivets are a PITA to remove. Grind down the head a ways, punch the steel stem out, then drill them out. And they do like to spin.

About the only data point I took before removal was approach stalls, it let go at about 43 IAS with flaps 40. And cruise at 21" / 2300 seems to be in the neighborhood of 140 IAS, with the indicator seemingly about 5 mph optimistic.

I'm more interested in how it'll behave & feel when landing, which is probably pretty hard to quantify anyway. It's more of a seat of the pants kind of thing. I didn't get a chance to fly it today, but maybe tomorrow. I'll post when I have something to report.

To be sientific you have to put them back on in 12 months and report back.

Tim

Hotrod 180

Hope you noticed what your max RATE OF DESCENT was with the seals installed.

The biggest improvement you should see is an increase in the achievable rate of descent which can be a life saver if you committed beyond the "abort point" and are high on short final to a no go around strip.

In my 180hp C-170 the flap gap seals limited me to a max of 400 ft per min. This was a plane that was comfortably controllable at 40 mph indicated, with 40 flaps and 1200 rpm.. Prior to putting them on I could easily get up to 700 ft per min. After taking them off the plane was again able to get up the old 700 ft pr min.

Of course the 170 also had the ability to "nose over" to 1400 ft per min with full lock left slip. Kinda scary the first time. Feels like you are pointed straight down to slightly inverted, but easily becomes just another tool in the bag.

Keep track of your numbers.

Trim.

I'm assuming you mean full flap /power off / approach speed, as opposed to a push-her-over dive. I have to admit that I never noticed a problem with achieving an acceptable descent rate with the gap seals in place. But haven't yet run into a situation where I was too high to make the landing on a short, no-go-round strip.

I flew yesterday and it appears that removing the gap seals didn't hurt my cruise speed. 21" / 2300 still seems to get me the usual 138-140 IAS. Little breezy yesterday so hard to tell if the airplane's manners have changed while in landing mode, and I didn't get a chance to do any approach stalls, so nothing to report on either of those. Hoping for a good dead calm day this week to get a handle on both of those.

hotrod180 wrote:I'm assuming you mean full flap /power off / approach speed, as opposed to a push-her-over dive. I have to admit that I never noticed a problem with achieving an acceptable descent rate with the gap seals in place. But haven't yet run into a situation where I was too high to make the landing on a short, no-go-round strip.

I flew yesterday and it appears that removing the gap seals didn't hurt my cruise speed. 21" / 2300 still seems to get me the usual 138-140 IAS. Little breezy yesterday so hard to tell if the airplane's manners have changed while in landing mode, and I didn't get a chance to do any approach stalls, so nothing to report on either of those. Hoping for a good dead calm day this week to get a handle on both of those.

On pins and needles waiting for more test results. I have a sharp drill bit teady

Tim

Flew some more today. Nice calm day so went up and did some approach stalls. Same drill as before: flaps 40, power off, ease into it. And the same result: it lets go about at 43 IAS. Seems like maybe it buffets more and/or earlier. Also shot some landings, didn't notice much difference in the low speed handling either.
I'd like to say I saw a big improvement, but overall I'd have to agree with whoever it was that said he wouldn't spend the money to put them on, but wouldn't spend the time to take them off either. But I'm glad I removed them, a least now I know. Who knows, maybe there is a difference but I'm just too ham-handed to feel it.

I recently brought up my flap gap seals with one of the aero performance engineers I work with; specifically regarding slow speed affects. He dug up the chart below. Basically math says:

stall speed: ~1-2% increase with gap seals or about 0.5-1.0 kts
lift force with 40 degrees of flaps: reduced by ~2% at a given airspeed for the overall wing

Overall you'll probably land 10-20ft longer and t/o might be 20-30ft longer. Guesstimate. Read page 21/36 in the pdf below. It has a good discussion on the effect the shape of the air passage (gap) has on the effective flap lift coefficient.




https://ntrs.nasa.gov/archive/nasa/casi ... 092003.pdf

Thank you HotRod180 for the test notes. Thank you BazzLow for the PDF!

hotrod180 wrote:Well, I took the plunge and removed the flap gap seals today...

Strong work! Never liked the gap seals for the kind of flying we are interested in here. And thx for reporting your findings.