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Olibuilt 's New Cub project

Had the time to do a little flight test today. It still fly, that is the good thing.. Hahah ...

First impressions may be wrong:

-less tail shake a 45mph, with 45 flaps
-less sink rate at 45mph with 45 flaps

Did only one landing. Will report feedback when I have the chance to test it more.




Pics bellow are at 65 flaps:

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The wings I am slowly building are similar to yours Oli. Thanks for your testing and posting. I don't fully understand everything that is going on here, but I know how to copy something that remedies something bad. Tail shake sounds bad. Pacers and Tri-Pacers appear to have the same cove as what you and I have. Do they/did they have a tail shake without the gap seals? Sounded like Christian from SuperCub project had the same deal. Lurking, Learning...

Thanks,

Jim
 
. I don't fully understand everything that is going on here, but I know how to copy something that remedies something bad. Tail shake sounds bad.. Lurking, Learning...

Thanks,

Jim
Jim, Think about this. Drag comes from behind where something is holding the plane back. In this picture those arrows which are turned around facing the airflow are drag. The idea is to reduce the amount of the drag which is done by making a suitable shape which minimizes the reverse flow. That flat trailing edge which Oli has on his wing is a large drag generator. Drag = Turbulence. Turbulence creates Drag. The part which he made in this discussion serves to reduce this reverse flow as well as directing the flow in an efficient manner over the flap. Once the air flows efficiently over the flap, it will not be turned into as much turbulence/reverse flow which in turn would start shaking the tail.

Pressure-drag20160808-15208-94nvii.jpg
300px-1915ca_abger_fluegel_%28cropped_and_mirrored%29.jpg

The swirling circular white lines to the upper right of the airfoil in the second picture is drag. Those white lines which are close together have a higher pressure than those which are further apart. If you are good at meteorology compare this to the isobars on the pressure gradient map. The whole idea is to minimize this swirling effect. Notice the far right swirling, that is causing the tail shake. What Oli has done will guide the air flow over the flap in order to reduce the amount of this swirling.
Placing a slat on the wing leading edge reduces these swirling circular white lines. What Oli is doing converts the wing into a slat for the flap.

Hope this helps.
 
When you take these off to paint them, try to iron out those two small bends in the lower forward part of the piece turning them into a smooth radius. This will make the part more aerodynamically efficient. It will make a small improvement, though likely so small that you will not see it.

Another thought.
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Those gaps in the flaps are allowing air to spill through rendering that small section of flap behind them unusable. If you could make a fairing which wraps around the hinge and up into that opening area blocking air flow, this could block some of the turbulence which is generated by the air flowing through the opening. Also, because you moved the flaps back 1" perhaps the opening doesn't need to be as large and you could make a small cover plate for the top of the flap which would also smooth the air flow.

Both ideas are just thoughts and may or may not make a noticeable difference. Small details can sometimes have big results. I can give examples.
 
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.

No argument here Tom on what makes slotted flaps work, Same aerodynamics at play as my Slats. My point was , Is the miniscule lift gained by slotting it [not considering the tail buffet help], outweighed by the Benefit of smoothly directing it all down. Seems there's one of the planes that sets records at Valdez that is setup more as a "ground effect vehicle" without the slots. Once you get close to landing {which is what most are concerned with} It would seem to make more sense to use the GEV's setups,and play off ground effect, Than something trying to maximize lift away from the ground. Not trying to talk nobody outta their slotted flaps, Or rewrite the aerodynamic rules. Just seems to me If the slowest touch down speed is what were after, As well as a good nose down approach, Might be worth considering a different way of looking at it. They's a reason we tape our control surface gaps closed, I know its slightly "apples and oranges" to the flaps but, It Makes them more efficient at deflection By not allowing any air to escape.
Would be a simple experiment for giggles, for someone with a set to tape the slots closed and shoot a few approaches.
 
My point was , Is the miniscule lift gained by slotting it [not considering the tail buffet help], outweighed by the Benefit of smoothly directing it all down. Seems there's one of the planes that sets records at Valdez that is setup more as a "ground effect vehicle" without the slots. Once you get close to landing {which is what most are concerned with} It would seem to make more sense to use the GEV's setups,and play off ground effect, Than something trying to maximize lift away from the ground. Not trying to talk nobody outta their slotted flaps, Or rewrite the aerodynamic rules. Just seems to me If the slowest touch down speed is what were after, As well as a good nose down approach, Might be worth considering a different way of looking at it. They's a reason we tape our control surface gaps closed, I know its slightly "apples and oranges" to the flaps but, It Makes them more efficient at deflection By not allowing any air to escape.
Would be a simple experiment for giggles, for someone with a set to tape the slots closed and shoot a few approaches.
Let me try to explain it as I understand what you are saying. You are suggesting that the slot be closed. This will give you what is called a hinged flap. Oli's goes down 65 degrees which exceeds the angle of attack at which most all airfoils stall. This means that the flap would be producing mostly drag with minimal lift.
A slotted flap of the same size and deflection has the advantage of the higher pressure air below the wing causing an accelerated flow over the top of the flap thus "blowing" down the turbulent air on the top of the flap. This creates lift as well as the drag from the deflected flap.
SO, if the hinged flap is producing little or no lift that means that the wing has to carry more weight per square foot of area.
The slotted flap will still be producing lift. Thus more wing area producing lift means less weight per square foot. Less weight per square foot means lower stall speeds, slower landing speeds and shorter landing distances.

Your observations at Valdez only demonstrates that the pilot with the hinged flap was a better pilot than the one with the slotted flaps on that particular day.
 
No argument here Tom on what makes slotted flaps work, Same aerodynamics at play as my Slats. My point was , Is the miniscule lift gained by slotting it [not considering the tail buffet help], outweighed by the Benefit of smoothly directing it all down. Seems there's one of the planes that sets records at Valdez that is setup more as a "ground effect vehicle" without the slots. Once you get close to landing {which is what most are concerned with} It would seem to make more sense to use the GEV's setups,and play off ground effect, Than something trying to maximize lift away from the ground. Not trying to talk nobody outta their slotted flaps, Or rewrite the aerodynamic rules. Just seems to me If the slowest touch down speed is what were after, As well as a good nose down approach, Might be worth considering a different way of looking at it. They's a reason we tape our control surface gaps closed, I know its slightly "apples and oranges" to the flaps but, It Makes them more efficient at deflection By not allowing any air to escape.
Would be a simple experiment for giggles, for someone with a set to tape the slots closed and shoot a few approaches.

A lot of the "directing air down" happens after the airfoil. It needs to be in a non-stalled configuration in order to direct the air downward and create lift to keep the vehicle from falling. Once the airfoil stalls, it just leaves an ugly series of vortices above it and no effective deflection on the flow underneath and behind the airfoil.

Once the wing stalls, it is unable to effectively direct air downwards and we don't create lift. Keeping the boundary layer attached delays the stall, allowing for slower flying speeds. Adding the slot will help delay the stall on Oli's flaps.

Nose-down attitudes associated with flaps have more to do with the wing's effective camber change when the flaps are deployed. Because of the change in camber, the wing's AoA will change when the flaps go down. This requires a more nose down attitude of the airplane to keep from climbing when flying at the same airspeed as before the flaps were deployed. It's more of a geometry problem than one involving slots/slats.
 
I think Flyrite is on to something. Couldn't tell you where I saw it, but somewhere there is thread where Frank Knapp talked of the process where he sealed off the slots on lil cub. He said the slot made a wing drop, sealing the slots fixed the problem.
Not an aeronautical engineer, but I think there is a velocity threshold at which a slot helps.
 
STOL contests wins are more dependent on getting a lucky gust of wind on takeoff and steady wind on landing than anything else. Having said that I know Frank does a lot of testing and I do respect his opinion. He did trade out his Keller flaps, BUT, his cub is a single mission plane. Not your basic daily flyer.
DENNY
 
On my PA-18A I attached small metal covers/seals fitted to the curve on top of the flaps over the hinge and pushrod locations. Seemed to help and would slowly roll away from the sealed flap when they were deflected.

Tuft testing on other controls like ailerons can show disturbed flow downstream from any openings like noted in #514 as shown here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930083935.pdf

One enigma though is we tend to slot flaps and seal ailerons. That may be simply due to the cove design in front of each. Citabrias are like that for their ailerons and partially sealed flaps. Unless it flows well to help then a seal simply reduces any loss of pressure air from below or above and makes the control more effective (like the aileron).

Crossinds STOL used to seal the flaps and ailerons on Cubs with fabric and still may. I'm sure there was a reason Cal and Gordon Mandell did that. I flew one with the flaps sealed then with them removed. I don't recall a marked change but it was the '80's.

An older summary of high lift techniques by Cornish and Tanner is available here: https://www.jstor.org/stable/44565002?seq=1#page_scan_tab_contents For example they examined the flap slot and nearby boundary layer flow then sealed the flaps on a Cessna L-19 to restore elevator authority. The flaps and horizontal stabilizer were end plated.

Gary
 
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One enigma though is we tend to slot flaps and seal ailerons. That may be simply due to the cove design in front of each. Citabrias are like that for their ailerons and partially sealed flaps. Unless it flows well to help then a seal simply reduces any loss of pressure air from below or above and makes the control more effective (like the aileron).
Gary
Gary, I learned to fly in a 7AC and do like the entire series of models, however their controls are sloppy at low speeds. The current manufacturer has an optional spade which is supposed to correct the aileron's sloppiness. It is only a band aid. The airplane does pass all certification requirements, however...........................

We can discuss this in depth if you wish but let's do it on another thread than Oli's.
 
Had the time to do a little flight test today. It still fly, that is the good thing.. Hahah ...

First impressions may be wrong:

-less tail shake a 45mph, with 45 flaps
-less sink rate at 45mph with 45 flaps

Did only one landing. Will report feedback when I have the chance to test it more.
Oli, How is this working out for you? Can you give us a report on how well the improvements worked or did not, please?
 
45* flaps at 45mph? Why?

Total flap deflection is an interesting topic. When I started building my plane we wanted 70*. That was problematic and as it turns out, unnecessary. These days it’s 50*. I don’t know where BCSC is with the Rev 3 flap but initially they were targeting 30*.
 
My TCOW 110" long and otherwise stock Piper flaps go to 56 degrees. There is no tail shake and only minor pitch up nearing max deflection.
 
Oli, How is this working out for you? Can you give us a report on how well the improvements worked or did not, please?

I realize I cannot say those gap seals makes a big difference. No extensive test were done...
Don't forget it is also the first BushWheels season with the 3"x3" extended elevators too..
And my skills are always improving

The thing is I've changed the way I handle the plane:
-I now only use flaps at 45*, instead of 65*. The plane appear to be able to fly slower at 45*
-I now feel comfortable at around 30mph IAS (smooth air)
-I'm now confident on my skills to handle water assisted landing.


I know that when you think you are in total control, it can bite. But I really feel I can handle that plane...



 
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Airplane is going strong, I really love it.
86" Catto prop pulls very hard, but I sometime wich a little more cruise speed....

A short video of my latest flying:



Hope you like
 
New suspension fairings. Hoping for supersonic speed, nothing less...

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Fairing the long shock struts could get tricky, probably why you haven't, yet?!I think I have the only faired cabane I've seen on Cub style gear, beside the shock struts and A frames, all with trailing edge taper, not just covered. If it's round, I want to fair it, don't care about speed so much but it helps climb and range also.
 
New suspension fairings. Hoping for supersonic speed, nothing less...
If you look at a stock PA-18 with the metal speed fairings over the shock cords after landing, you will see that they are not in line with the center line of the plane. They reflect the twisting of the airflow from the propeller rotation. While yours may appear to have streamlined the airflow, any advantage may actually be counteracted by the corkscrew flow from the prop.
Did you notice any difference in your speed? Aerodynamics is sometimes quite complicated and at other times a very small thing can make a big difference.
 
Did only a small flight yesterday, but it looks like about 4mph speed gain.

I will try to tape small aluminum angles to the trailing edge of the shock struts.
 
Had an issue with one of my Slick magneto last fall. Sparkplugs were also due to replace. So I've decided to go with two PMags for simplicity. I've very pleased with them so far, after about 20hrs of flying time. Starting is so easy engine cold or hot, and running smoother on idle. CHT went up a little, but maybe due to may cowling rework:

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Relocation of the EarthX battery firewall forward and,
I've also rooted the new engine breather direct into one of the exhaust. Filled with sand, the 5/8 tube was easy to bend with a standard conduit bender (thanks to this forum :) )



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New cowling hole for timing purposes... hahaha! :

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Cabin heat and carb heat were also rework for less weight and simplicity, thanks to Vetterman Exhaust carb heat box.












Cub is running better then ever!!! Very pleased.
 

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Oli -- You still hand propping with the Pmags?


No! I've installed a starter a few years ago, a little after building the new suspension. Shock strut is in the way when trying to reach the throttle from outside. But thanks for reminding me I should practice with the PMags.

Ring gear support was also lightened:

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Cabin heat and carb heat were rework for less weight and simplicity, but not more cabin heat....:

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be sure and clean that crankcase vent at each oil change if it does like the Carbon Cubs. It will coke up and block off.
 
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