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Experimental Cubs & Extreme Stol Devices, Flaps,slats,sl

Thanks SpainCub for that graphic.

Are you guys thinking about the detrimental effect of all that stabilizer being dragged through the air at high AOA?

.....thus the recommendation to try a very large elevator and very small stab.

....ps......procceed carefully.

Also, the Keller Stabilizer with it 's ribbed-convex lower surface is a simple solution. A "quickie" test could be taped onto the bottom of a a stock stab so one could experience it without building new stabs.

PS. Finding a wing airfoil and flap arrangement that has LESS PITCHING MOMENT with the flaps deployed than our present Cub airfoil with slat and Keller flap would be another solution. I am sure there is one out there with a better cruise drag profile as well.
 
I went back and looked over the Keller Flap string from 2011 when he was working out the kinks. Looks like he came up with a fine product proven on a number of Cubs.

After studying the graphic Spaincub posted, the benefit in slotted flaps is certainly there but so is complexity and probably some measure of weight as well.

Back to slats....what if we used slats on the front of the wing, oversized Fowler type flaps and the lower convex shape on a larger horz stab to counter some of the high pitch issues associated with the slats? Not trying to take business away from Mr. Keller but don't you gain some degree of the benefits of the slotted flaps by using larger Fowler flaps? I chose the Riblett wing instead of the cub wing because of cruise speed gains (BTW, I still have the Carlson cub spars for sale).

Dave...maybe that's what you are saying in your "PS" in your most recent post.
 
The pitching I referred to is a nose-down pitching moment associated with the flaps, not the slats.

This is why Keller sought a solution in the convex lower surface of the Keller-stabs......and found it to work.
 
Dave wonder if Wayne's extending the chord on the flaps and ailerons would be a good mod for slow speed work?
 
Dave Calkins said:
The pitching I referred to is a nose-down pitching moment associated with the flaps, not the slats.

This is why Keller sought a solution in the convex lower surface of the Keller-stabs......and found it to work.
Click to expand...

Unless I'm understanding things wrong which is possible, I thought we agreed earlier that the slats cause nose drop when the power is reduced. And I thought Keller used the convex lower surface to get rid of the "stick shake" and the side benefit was to push down the tail providing a direct benefit to nose heavy aircraft. Flaps do cause pitch change and that is the benefit of the slotted flap...I think.
 
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Well Dave, I wish that could be an easy solution but consider the following:


The flap has it CG and deploying it changes the CP, pressure under the flap and the drag it induces, all creating the downward pitch...




CP_angle_of_attack.gif


That is hard to beat.

Now getting back to Slats, one of the issues I see is that the gains on the slats come at a higher AoA and that is creating other issues like tail stalls... this is also hard to beat as the gain in Cl from a Slat comes at the need of greater AoA... You see, you need greater AoA to harness the benefits of the slats:



Else, at the same AoA you have the same Cl as deploying your laps, and as you pool the stick back, you notice greater Cl but also the following:



You take away airflow to the tail!!!!




 
My words are typed in bold below

lowrider said:
unless i'm understanding things wrong which is possible, i thought we agreed earlier that the slats cause nose drop when the power is reduced. Slats do not cause 'nose drop', it is simply the way things are....for any airplane when power is reduced.

And i thought keller used the convex lower surface to get rid of the "stick shake" and the side benefit was to push down the tail providing a direct benefit to nose heavy aircraft. The stick shake is caused by (...we think...) the early stage of stall of the elevators and stabs.......when the keller flaps are deployed at the top of the white arc.......where they cause a significant nose down pitch. This nose-down pitch is less at lower speeds.

Flaps do cause pitch change and that is the benefit of the slotted flap...i think. Is it a benefit?
Click to expand...
 
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SpainCub..........some airfoil sections pitch less with flap deployment than others......There is no question. THE question is which airfoil does what I want it to do on a Cub?

Also, are we arguing flaps versus slats? I did not think we were.

I do not argue that slats become useful at high AOA, but are not necessary at low AOA

Also, I do not think that slat use is causing "tail stalls" as you said. But......pitching moment caused by the double-slotted flaps does require a strong tail downforce.

And lastly........................you really ought to get a flight in a slatted Cub!
 
I'm not confused yet so keep going. I did think Lil-cub was getting exaggerated nose drop with power off compared his plane before the slats so I read that to mean the slats are causing more pitch change than without them. I'm aware that pulling power causes the nose to drop in any airplane until it is re-trimmed.

My one question left is will an increase in flap cord cause the same pitch change as a longer flap as long as they both have the same area?

I'll sit back and listen and learn now.
 
1.Okay, so a Mackey-slatted Cub will hold on at an AOA of nearly 50 degrees..........thus, if you have the nose way the heck up there and reduce power it has a long way down to go..............you could use the term "exaggerated nose drop" if you want to.

2.increased flap chord versus "longer" flap. Compared to a stock length and chord flap........I have flown many increased span flaps, but I have only flown an increased chord flap that was also increased span.........Both will cause a nose down pitch when deployed versus a stock flap which will initially pitch nose up with deployment.
 
Sorry Dave, I did not mean to come across the issue of comparing Slats vs Non Slats, I think I made my point earlier about what I thought about slats, and I do like them.
The point I was making was regarding the discussion on how to get the tail flying if you where at a high AoA, if you are at that 30º plus, you are cutting airflow to the tail, period.

BTW, at 50ª AoA, what is the load distribution of the Spars? What is the design maximum (that is, including safety factor) and what happens to that load when you stall a wing?
From my calculations a design envelop of the current cub wing is -10º +30º AoA as the CP moves the spar loading between front and rear, at 80% and 60% respectively.

I am accepting all offers to get me on a Slated cub ASAP! :D
 
Interesting point about load distribution. Would a riveted aluminum spar/rib/skin better distribute the load than a fabric covered wing at high AoA?
 
Thanks for the clarification SpainCub. A slatted Cub at 50 degrees AOA is really just a flying stunt. There is no reason to do that. It takes a bunch of power, and if the airplane is loaded to gross, may not achieve that as a steady state.

Also, "...30 degrees AOA cutting airflow to the tail...".......and I suppose we want more elevator authority????????? check out this video and say if the a/c at near 30 degrees AOA is lacking pitch authority...... http://www.youtube.com/watch?v=4EDbUn0_2rg


Lowrider, I will keep to myself my thinking on perfect flap length, but the finest hotrod exp Cub I have flown has extended chord and span flaps.
 
Hey Dave, why not think out loud and share with us some thought on your flap idea? It´s not fun to keep things to yourself you know, you can go blind! :D
Yes, I have seen Ed´s landing many time, but strong laminar flow (headwind) and just about any plane an a good pilot (very good in this case) and they can get away with some amazing feet. In this case, the airflow is coming from nature, and you still keep pitch authority... take the wind out and all bets are off.
Where is the Kazoom? I have not seen in any of the STOL competition, I thought it was a sure winner...

Lowrider, I believe the design you are using... it has 100% load on the main spar (does it have one or two spar, your wing?)... it only has a single strut if my mind is not mistaken, correct?... regardless of how the wing is build, but probably this way if build is what allows for this (it´s all in the design). I like the idea of an all metal wing, and yes the weight is evenly distributed over 1 spar... or 100% of the load over the main spar, if there is a second spar, is it attached to the fuse? Anything that specific, I can only say for sure around the Cub wing, since this what I have been doing calculations for.
 
Dave,

I'm thinking half span aileron and flap. Question is does any extra cord really buy anything lift wise or does it just place extra stress on the hinges?

Spain,

All aluminum with two wing spars both attached to the fuselage and single strut off the main spar to the rear main gear perch.
 
SpainCub, everyone present estimated the wind in that video to be 12 to 14 MPH. The point is that at the angle of attack achieved in that video was with very little elevator deflection visible and the trim was not set at the extreme. I estimate the deck angle at near 30 degrees.

I want to do a full span flap and use spoilers for roll control. I have done a test by using a slatted droop-aileron Cub and causing roll by deploying only the outboard spoiler and was able to get it to bank while at minimum controllable with nose very high and power. I think it could work, but am looking at the problem of elevator authority and "pitching" with full-span flaps. It has been done, FYI....but not on a slatted/Kellerflapped SuperCub.
 
Won't the spoiler cause airflow disruption over the flap behind the spoiler reducing effectiveness.... or is it so small that it won't be a problem? It seems at MCA the spoiler would need to be pretty big to get the wings to deflect.
 
Lowrider said:
Won't the spoiler cause airflow disruption over the flap behind the spoiler reducing effectiveness.... or is it so small that it won't be a problem? It seems at MCA the spoiler would need to be pretty big to get the wings to deflect.
Click to expand...

Lowrider, The spoiler would be outboard ahead of the aileron (or where the aileron would be). The Mitsubishi MU-2 uses spoilers and does not have ailerons. The Helio Courier uses short span, large chord ailerons with spoilers (interceptors) ahead of the aileron. The further outboard the spoiler is located the more effective it would be. If you have watched the spoilers operating on an airliner, they are inboard for use at high speed, low wing bending moments. A Cub would want them outboard for effectiveness at low speed.
 
That makes sense and I was thinking of spoilers on gliders I guess.

Next question, wouldn't a full span flap add significant load to the wing outboard of the strut attach point and require wing redesign which would be heavy?
 
I like the idea of full flap and spoilers... sounds like an interesting design. Now I also understand your questions about airfoils....
BTW, I never commented on the amount of air, I was referring to the video in the sense that a good laminar headwind just ads to what the triple prop is blowing and the tail, also it does reduce some of the induced turbulence from the high AoA.


I was considering also a slated flap could be a good design on a cub. It would gibe you higher Cl than a regular flap, and at the same AoA would be higher than a Slatted wing...
I am still waiting to see if I can ever run some CFD on this design and see where the Cl vs Drag, and how CP moves through AoA envelop. I would also like to see how the Riblett behaves compared to the 34-B Airfoil in a 3D wing model, normal, Slat, Slot, and slated flaps. I thought about the change in cord, but I have not come up with any real benefit to the flight characteristics of a cub, maybe I am missing something? (I know about wing loading and Cl and shorter TO roll, but what else?)
 
Hello, throwing this back to a more basic level- I have a 33' square wingtip, 58" flapped EAB Wag cub. The flaps have gap seals on the LOWER surfaces. When full flap, at a normal approach of say 50 MPH, I will occasionally get a stick pulse with full flaps. Do I add the Dakota Cub type flap seals- Part # DC12795?

If I add the seals I assume I lose the slot effect putting high pressure air from the bottom of the wing through the slot in the flaps, giving them more flow than they would otherwise receive- that will make the flaps less effective in adding total lift- but would probably remove the stick pulse, as is cited in other posts.

My converse thought is why not put VGs on the flaps themselves and try and harness that slotted energy even more- by NOT adding upper surface flap seals?

I was going to add vortex generators, but with standard gear and 8 inch wheels, I can't really slow down the landing speed with more nose up at touchdown.

Has anyone added VGs to just the lower surface of the stab ahead of the elevator to dampen flap-induced stick pulses on a cub without flap seals?

The plane is well rigged and a joy to fly slow clean, 1/2 or full flap. I wanted to fly it 50 hours before adding VGs- though they may help w/ departure prevention, I would have to be flying well outside my comfort zone to wind up with a problem. I have a 14# prop, it has very little P-factor, and only 125HP on the engine to begin. From my Pitts flying, when you put a composite 3 blade on a plane w/ 260 HP vs. a 2 blade aluminum prop, the drop in P-factor allows a huge gain in avoiding unintended departures.

Thoughts?
 
moosepileit said:
Hello, throwing this back to a more basic level- I have a 33' square wingtip, 58" flapped EAB Wag cub. The flaps have gap seals on the LOWER surfaces. When full flap, at a normal approach of say 50 MPH, I will occasionally get a stick pulse with full flaps. Do I add the Dakota Cub type flap seals- Part # DC12795?
Thoughts?
Click to expand...

Loose the lower flap gap seals. They are blocking the flow of air through the flap slot thereby reducing the effectiveness of the flaps. The flap gap seals should be on the top surface to smooth the flow over the "down flaps" and to reduce the tail pulsing when down. The top seals also "clean/smooth" up the air leaving the wing when the flaps are up.
 
Skywagon8,

Thank you for taking my post one step deeper in ideas! I'll get a picture to post- The seals on the bottom are narrow enough that they don't appear to really cut the flow of extended flaps, but are easily removed to check.

Do you like the Dakota part number item I listed or is there a better source?

It seems like the upper surface gap seals are the cure to tail shakes.

I couldn't pull the OSH price of $595 (normally $695, full kit with templates) for Micro Aerodynamics- what's the favorite VG of the EAB Cub crowd?
 
moosepileit,
Since you are experimental, make your own. You could use thin aluminum or do as I did. I went to the local hobby shop, bought some balsa wood which I shaped for the purpose. The balsa was glued to the fabric with Stewarts glue. The balsa was sanded to fit, using the flap as a sanding block. Then the whole fairing was covered with fabric and finished with the rest of the wing. Simple and inexpensive.

I have not tried VGs.
 
And on the horz stab too please. I'm wondering what extra force the airfoil on the bottom of the stab will exert and if it is significant, would VG's on the top help keeping the elevator effective at a relatively high AoA?
 
My flaps are actually 69", longest Dakota sells are 67", probably why the previous restorer went with short bottom seals. The balsa idea sounds like a good one, with the removal of the narrow bottom seal. What thickness was the balsa? The aluminum stock seal's shape makes a lot of sense, I could see buying the 67" stock ones and butting them to the fuselage end as it's tail shake I'm aiming to reduce, while boosting the airflow to the top/back of the flaps. Once that is sorted, there would not be the room for VGs that there is now without top gap seals on the flaps- without the seals you could put VGs at the wing spacing at what would appear to be a pretty optimum spot. If I had 30 of them lying around, it would be a decent test to remove the bottom seals and add VGs, but that would be off into the untested- not guessing I woke up with a new, "good" idea, will probably go to the aluminum stock seals- if anyone has a a few inches of them lying around, I'd take them off your hands to make up the difference of 67-69"x2.
 
Moosepilot, VG's on the top of the flap leading edges have proved no performance gains in my testing. Jerry Burr confirmed this. If you don't listen to me, that is fine. DO DO listen to what Jerry Burr says. :)

I flew/tested a round-tip stock Cub without flap gap seals for a bit. I wish I had taken some numbers. The results/difference with seals and without seals are not worth remembering, as I recall :).

Let us know if they stop your tail from shaking. Also, let us know the performance of Piper gap seals versus your existing lower gap seals.

Lowrider.....very cool to see a photo of your airplane on gear outside the shop!!!..VG's under the stab at the elevator hinge line, like MicroAerodynamics places theirs, works very well to augment elevator authority. They are aiding flow attachment where the air is bending around the lower surface of the stab/elevator break when "up" elevator is commanded. Putting VG's on top of the stabs seems like not worth doing for pitch authority at high AOA.
 
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