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Olibuilt 's New Cub project

Been using Herc for years now, good stuff!

I like the lightening holes in the gussets of the fuselage sides, never seen gussets there before! Sure can't hurt.
 
Been using Herc for years now, good stuff!

I like the lightening holes in the gussets of the fuselage sides, never seen gussets there before! Sure can't hurt.

I forgot to comment on the Herculiner because I was taken by the flying. I've used it on drift boat bottoms. It is good stuff.
 
Courier Guy and RV Bottomly.........!Herculiner on drift boat bottom? wow. I am impressed.

aluminum, fiberglass, or glassed-wood boat hull?

any special prep?

how does it fail/scrape? does it come off locally at scrape or big sheets/chips?

have a skiff project I was planning on West System barrier coating in epoxy, but maybe there is a better way.
 
Courier Guy and RV Bottomly.........!Herculiner on drift boat bottom? wow. I am impressed.

aluminum, fiberglass, or glassed-wood boat hull?

any special prep?

how does it fail/scrape? does it come off locally at scrape or big sheets/chips?

have a skiff project I was planning on West System barrier coating in epoxy, but maybe there is a better way.

Plywood bottom epoxy-fiberglass coated. It was an old 'scrap wood dory' I built from scrap wood 20 years ago. The bottom rotted out so I cut it out and put a new marine ply bottom on it and sealed it up with epoxy fiberglass. After a few years of gouges in it from sharp rocks, I tried Herculiner as a coating. It stuck with no particular prep.

It's heavy, and not quite as streamlined, but it slid over rocks pretty well. No failure point except gouges in the material. It does not seem like it would ever come off.

The boat met its end because of a different problem. It got stove in by a log while tied to a bulkhead in a storm.
 
I should add a reply to your last sentence. I do not recommend it as a better way than epoxy and fiberglass for most boats. It is heavy. For most skiffs a single layer of fiberglass ought to be enough. If you are dragging it around, two layers would be better. Some have tried carbon fiber with mixed results. Others have added graphite powder as a filler in their epoxy. I think the verdict is out on that, too.
 
I've never used it on boats, only on my Airstreaks. It wears off, but I've never had it come off in large pieces. I get about 75 to 125 hours out of a coat (actually 2 or 3 thin coats, between letting it setup, better then goobering it on super thick all at once) using the (I believe) qt size can, about 30 bucks. I take that back, I had my rocker panels on my Dodge pickup looking pretty shabby from road rash, and darned if the stuff didn't stick like glue there also. No prep other then soap and water wash.
 
Something happened yesterday. For the first time in my Super Cub flying experience, I'm convinced I could land where I won't be able to takeoff. A weird feeling.

 
Always looking to improve the airplane.

Those wings were built with "aileron coves" shaped ribs all the way. The wings have a concave shape just in front of the flaps. Now that I see all those slot and slat mods, I think it could be improve.


So I added an inch to my flap hangers. I now have a little more room to fabricate some flap gap seal, thing that never went on those wings...



Flap gap seal questions:

- Main purpose of those seal is to close the gap for cruise speed OR redirect the air in the slot between the flap and the wing ???
- What size slot should I be looking for when full flaps ??

Thanks
Hoping for help.





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not a direct answer, but i use a scotch brite pad as my filler/gap setter when installing gap seals..... with flaps partially down, so i can drill bottom holes and install screws
 
Always looking to improve the airplane.

Flap gap seal questions:

- Main purpose of those seal is to close the gap for cruise speed OR redirect the air in the slot between the flap and the wing ??? Both
- What size slot should I be looking for when full flaps ?? 1/2"
Start by extending the top surface of the wing to where it almost touches the top of the flap. That will be between the 3" & 3-1/4" location on your tape measure.

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The angle from the lower surface of the wing up into the flap cove area looks to be a fairly sharp 90 degree bend. This wants to have a large radius in the 1-2" range to minimize turbulence. Then it wants to slope back in a lazy S shape clearing the leading edge of the flap and following the flap up until it meets the extension which you placed on the top surface at 3-1/4".


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I made mine from balsa wood gluing it on and covering it with fabric. It was shaped by placing sandpaper on the flap using the flap as a sanding block running it back and forth until there was clearance for the entire length. When the flaps are up there is a strip of tephlon attached to the underside of this seal used as a rubbing strip for the entire length of the flap.
Piper uses soft aluminum bent at a sharp angle where it almost touches the flap. This is screwed to the top trailing edge of the wing and the flap cove.

When the flaps are down this will give you a slot gap of about 1/2" at the top of the flap. When the flaps are moving down and back this gap will open.

The purpose of the gap seal is to prevent up flow of the air when the flaps are up improving lift in cruise. It also serves the same function as the leading edge slats when the flaps are down by accelerating the higher pressure air from below the wing and redirecting it over the top of the flap thus improving the boundary layer flow over the flap reducing the speed that the flaps stall, improving lift at lower speeds and smoothing the airflow over the tail. This reduces or eliminates tail shaking.
 
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What about a "lazy Z" ?
It leaves about 1/2 inch gap at full flaps
 

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What about a "lazy Z" ?
It leaves about 1/2 inch gap at full flaps
It would be better if that bend was not there. Make it a smooth curved section instead. The abrupt change in cross section disturbs the smooth air flow. If you have a long piece of 4" or 6" plastic pipe, use that to bend the shape. Then bend your tight bend afterwards.

It will work as you have done it but will be better if it is curved. Curved = smooth. Abrupt angle = turbulence.
 
Done with a curved prototype.


Before I go into mass production, is a 3/8 inch gap at full 65 degrees flaps enough ??




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Looking at the side view of your curved section, it would perform the best if the closest gap is at the very aft end of the filler and it opens fairly consistently from there forwards. This will induce the maximum flow energy at partial flaps as in your upper photo as well as offering a high energy at the maximum extension.
 
After you perfect your flap fairing try installing end plates on the flaps for added lift.
 

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Looking at the side view of your curved section, it would perform the best if the closest gap is at the very aft end of the filler and it opens fairly consistently from there forwards. This will induce the maximum flow energy at partial flaps as in your upper photo as well as offering a high energy at the maximum extension.

If I understand good, you are telling to add another + or - 1/2 inch in horizontal lenght.

I'v tried, but then there is no more gap. The fairing touches the flaps, even full flap down.
 
If I understand good, you are telling to add another + or - 1/2 inch in horizontal lenght.

I'v tried, but then there is no more gap. The fairing touches the flaps, even full flap down.

You do not want to open the outlet from where it is, you want the cross section from that closest point to open evenly going forwards. The goal is that as air moves from the lower surface it is accelerated into the highest energy stream till it goes out of the gap onto the upper surface of the flap.
This will draw air aft from the upper wing surface delaying or reducing flow separation as much as possible.
Looking at the two pictures, the full down position will only see small improvement. The partial flap will see the greatest gain since it has a fair amount of distance for the airflow to gain energy.
 
Done with a curved prototype.

Before I go into mass production, is a 3/8 inch gap at full 65 degrees flaps enough ??
That should work Oli.
65 degrees is a lot, your airplane will almost hover when you are done.
When you finish, tape some yarn to the trailing edge of the flap and notice how it trails with the full 65 degrees of flaps. If it streams back at a fairly steady almost straight line you have cracked the code. It will likely twirl around in the prop wash area.

Charlie, he moved his hinge point aft an inch which is giving him that extra distance forward.
 
After you perfect your flap fairing try installing end plates on the flaps for added lift.
Gary, I tried that on my 185 by installing a plate on the outboard end of one flap. It made no difference whatsoever. I did a series of stalls with each flap position expecting that the extra lift from the plate would cause the other wing to stall first. NOPE....Nothing.
 
That should work Oli.
65 degrees is a lot, your airplane will almost hover when you are done.

Charlie, he moved his hinge point aft an inch which is giving him that extra distance forward.

The trick as you are already addressing is to prevent the flap from stalling at high angles, I think you are going at it right.
 
Gary, I tried that on my 185 by installing a plate on the outboard end of one flap. It made no difference whatsoever. I did a series of stalls with each flap position expecting that the extra lift from the plate would cause the other wing to stall first. NOPE....Nothing.

Cessnas? Who knows and there's no warranty. The Citabria and Cub I had liked it and rolled away from the spill plated flap but again it's all an experiment.

Gary
 
Almost done. Thanks again!!

I really hope to notice an improvement in slow flight.

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Oli

From what I have been able to gather from others research, the gap, slot or nozzle (different terms in different researches) created by the flap should be about 1.5% - 1.75% of chord.......... but that would probly depend on how much air you had available from the entry area........... The engineer types in here could be more accurate I'm sure .......... And the aft edge of the piece you are adding should align about the center of the radius of the leading edge of your flap. It would be better to have a radiused entry from the false spar area aft of the rear spar to get more and smoother air into the "gap"......... maybe address that if you ever had to go into the wing. More air from below may be needed to keep flaps from a stall at 65 degrees. I believe CharlieN would be correct that you would have the most gain at a partial flap setting. More air and double slots for 65 degrees? I have mine designed for double slots and 55 degrees but will be end of year or so before I will be able to do any testing. Good luck with your testing and let us know how it goes........ really like your airplane!
 
...More air and double slots for 65 degrees? I have mine designed for double slots and 55 degrees but will be end of year or so before I will be able to do any testing.
The slot that Oli has is about the same as the one on my Cub. My long flaps are single slotted stock Cub airfoil, deflect to 56 degrees and are very efficient which was noted through tuft testing. So, I'm optimistic that Oli's 65 degrees being only 9 degrees more may also work well.
 
Might be that I don’t know what I don’t know, which is probably the case. But would the trade-off for the amount of lift You might get by allowing the air to go through the pressurized slot opening to gain increments of lift that the flap may produce, be more than made up for it if you close the slot and deflect it ALL downward as ground effect vehicles do. Seems to me the only time the flaps are at full deflection is close to ground affect anyhow.
Remember reading when some of the back country Cubs had a problem with blow back and not being able to get full deflection, and when the problem was resolved and they were able to get them to fully deploy it made a tremendous difference in the performance and the ability to get much slower approach speeds.
 
Might be that I don’t know what I don’t know, which is probably the case. But would the trade-off for the amount of lift You might get by allowing the air to go through the pressurized slot opening to gain increments of lift that the flap may produce, be more than made up for it if you close the slot and deflect it ALL downward as ground effect vehicles do. Seems to me the only time the flaps are at full deflection is close to ground affect anyhow.
Remember reading when some of the back country Cubs had a problem with blow back and not being able to get full deflection, and when the problem was resolved and they were able to get them to fully deploy it made a tremendous difference in the performance and the ability to get much slower approach speeds.

That high-pressure, high-energy air from under the wing is directed through the slot. The slot accelerates that air as it joins the boundary layer on the flap, which re-energizes that boundary layer and delays the boundary layer's separation (stall).

Short version - stealing some of the air from under the wing can help the flap resist stall longer.
 
The slot that Oli has is about the same as the one on my Cub. My long flaps are single slotted stock Cub airfoil, deflect to 56 degrees and are very efficient which was noted through tuft testing. So, I'm optimistic that Oli's 65 degrees being only 9 degrees more may also work well.

sky

Is your false spar at the flap as in Piper drawing 11670? That is what I was referring to by "more air". ................. more air from the high pressure side to get accelerated thru the slot. Oli's appears to have the "square edge" at the moment that might hinder flow.
 
sky

Is your false spar at the flap as in Piper drawing 11670? That is what I was referring to by "more air". ................. more air from the high pressure side to get accelerated thru the slot. Oli's appears to have the "square edge" at the moment that might hinder flow.
Yes mine is as per Piper's. We addressed Oli's square edge at the beginning of this discussion. Also he moved his flaps 1" further back from the wing so that his new fairing shape should take care of that issue which was also addressed. He has not yet shown a picture of that lower section of how he bent his fairing to compensate for that tight radius which was also a concern of mine. Even if he doesn't change that radius, just bringing the fairing down low and sloping back at an angle should help though not as much as the large radius as you have noted.
 
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