Experimental Cubs & Extreme Stol Devices, Flaps,slats,sl
- Thread starter Wayne Mackey
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Little_Cub
MEMBER
Palmer, Alaska
I believe our problem is caused by the combination of weight loss, operating slightly behind the curve and s_l_o_w. The tail functions well to a point but if you try to slow down too far or loose power the nose will drop thru because the elevator no longer holds the tail down (the view changes rapidly).
Agreed if we hang it on the prop at an extreme AOA there is plenty air moving and you can almost stop.. it's fun, I personally like it flatter.
Dave Calkins
Registered User
Anchorage, Alaska
I dunno if anyone's done any of the Riblett wings.
I always mention Wayne Mackey's slats because Wayne has spent the time and tinkering to come up with a "compression ratio" (location and opening size) that work well on the Cub wing. Other slats (Helio, Storch, Zenair) use a different compression ratio and do not take full advantage of what is available.
This is Wayne's art.
SpainCub
Registered User
Hi, I have flown in both an original F. Storch and a clone made in CZ, on an engine off the original airplane you trim it all the way back and it "parachutes" down at 500 fpm and close to 50 km/h somewhere between 27-32 mph, the ultralight version does it a little faster, 600 fpm and almost full trim back and full flaps... 70 km/h otherwise you need lots of nose down to get energy on the plane... no flap then pull hard, hit the flaps and it is almost at a standstill when you hit the ground.... Now I never made it to the ground on the float down approach, I do remember that you still had aileron authority but I keep it very straight just in case (sorry, either did not want to ruin a friends plane or did not have the B/&%s to do it, take your pick either way 
)
One area of concern is the change in aerodynamic load and the movement of the Aerodynamic Center do to change in AoA and therefore moving the Center of Pressure and shifting the weight distribution (calculating for T) between the F. Spar and the R. Spar... These high lift devices tend to do that... not a major issue flying light, but when heavy, you could be getting close to design maximum depending on your AoA....
)One area of concern is the change in aerodynamic load and the movement of the Aerodynamic Center do to change in AoA and therefore moving the Center of Pressure and shifting the weight distribution (calculating for T) between the F. Spar and the R. Spar... These high lift devices tend to do that... not a major issue flying light, but when heavy, you could be getting close to design maximum depending on your AoA....
Thanks much for the reply, I have been giving the slat some serious consideration, I thought at first about making my own slats but not being a aeronautical engineer I thought its good to know what you don!t know. However I am still enamored about bolting a set on my exp 205 cub.
mike mcs repair
Registered User
chugiak AK
more thinking out loud.....
- so If you had this inflight incidence changeable easily(twist stays constant), I was worried how to keep it in sync/same on each wing... But then It dawned on me, maybe thats NOT what you would want, maybe you would want some differential control of each wing's incidence(maybe not whole possible incidence travel)using the stick(side to side), and then would this allow you to do away with the ailerons(and all associated parts and weight(flaps too??)) or make them smaller/lighter????
- would you need flaps if whole wing could greatly change incidence so easily?(now redundant system??) or maybe full length flaps?(if no Ailerons)
- if it would work, think of all the small parts(weight) it would eliminate, or at least help offset the weight penalty for the incidence changing system....
- how "strong" does this adjuster need to be?? the current weakest link is the spar attach fitting on wing is where that bolt goes through, thats where they always break... it never breaks the -5 bolt, maybe gives it a bow once in a while after you rip wing off in a wreck, but thats not a normal load.....
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Mike,
Are you thinking a jack screw like the horizontal stabilizer uses? Maybe you would do away with flaps but it seems a little complicated to make the wings move so you don't need ailerons....but what do I know. A never stall wing...that would be cool and pretty useful too!!
Are you thinking a jack screw like the horizontal stabilizer uses? Maybe you would do away with flaps but it seems a little complicated to make the wings move so you don't need ailerons....but what do I know. A never stall wing...that would be cool and pretty useful too!!
mike mcs repair
Registered User
chugiak AK
not sure yet.... started rethinking couple days ago, then that thought hit me today...
think more like moving wing attach fitings on spar(same effect like dave did on 12 using extra fixed holes in attach bracket on spar) but pivoting on one bolt on each end(spar & fuselage attach point)(or pivoting off a disc/arm if you need to change the math)... actuated by???? maybe have that also pivot wing fore and aft to keep twist constant/not flex wing... or maybe similar at strut attach..... all those bolts in spar & strut attach brackets are redundant leftovers from wood spar design days....
if closed hydraulic actuating system it would be super simple to do the aileron like control, have an additional hydraulic master cylinder with outlets on both ends, with ram hooked to stick... move piston one way fluid goes out one side and in other, move opposite, opposite actions....
EDIT:.... this would be WAY simple on a single strut wing like a Cessna...... but do the adjustable on rear spar....
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What would maybe work is a hydraulic cylinder inside the front stut, although you would have the problem of the jury struts. You could set it up with another cylinder on the front spar/fuselage attach, and either have both the strut and spar hydraulics work at the same time or have the strut work to twist the wing for roll and the spar attach work as the flaps. It maybe hairbrained, but it is fun to think about.
mike mcs repair
Registered User
chugiak AK
you don't want to twist wing... that just rips the screws out of leading edge....
all 3 points (strut attach, wing attach, jury) could all be on a cable/lever system? to keep them in sync.... ???
all 3 points (strut attach, wing attach, jury) could all be on a cable/lever system? to keep them in sync.... ???
SpainCub
Registered User
Mike, thinking out loud.... A counter lever wing with a high profile might do the trick, this way you could move the centered pressure of the wing and have a single spar, single attach point to a rotating attach mount. This way you could have a high and low adjustable AoA brace to limit AoA and let aerodynamics adjust AoA within those limits.... Could be a fun project for an RC test ah and you found then make the wings foldable 8)
I'll take the discussion offline with you if you'd like...
Getting back to cub-world, for me the priority would be a high lift device that would have less impact on cruising speed, slats take a lot of top speed from what I have seen thus far, unless you are talking low aspect ratio or symmetric airfoils, and slats are like those on the airliners, with complex moving parts.... a hig camber airfoil with slats or slots could also be another approach to keep cruising speed... Not sure if you get the performance for STOL though.
As for keeping the tail fying... I believe what has been said is quite accurate aside from moving the tail configuration from the cub. Question, is it not one of the reasons that the tail stops flying the "shielding effect" of the high AoA?
ah and you found then make the wings foldable 8) I'll take the discussion offline with you if you'd like...
Getting back to cub-world, for me the priority would be a high lift device that would have less impact on cruising speed, slats take a lot of top speed from what I have seen thus far, unless you are talking low aspect ratio or symmetric airfoils, and slats are like those on the airliners, with complex moving parts.... a hig camber airfoil with slats or slots could also be another approach to keep cruising speed... Not sure if you get the performance for STOL though.
As for keeping the tail fying... I believe what has been said is quite accurate aside from moving the tail configuration from the cub. Question, is it not one of the reasons that the tail stops flying the "shielding effect" of the high AoA?
Rob
MEMBER
AZ06
LC,
Why not a slotted tail? Slats back there could easily get fouled, but positioned (angled) correctly slots seem like they might help keep the air attached to the tail in 'mush mode' no? Currently VGs on the tail are optimized to aid the elevator. I am thinking of slotting the horizontal on my exp to aid the horizontal. VGs can take care of the elevator... I think with these uber wings we have run up against the limits of the slab sided symmetrical horizontals...
Take care, Rob
Why not a slotted tail? Slats back there could easily get fouled, but positioned (angled) correctly slots seem like they might help keep the air attached to the tail in 'mush mode' no? Currently VGs on the tail are optimized to aid the elevator. I am thinking of slotting the horizontal on my exp to aid the horizontal. VGs can take care of the elevator... I think with these uber wings we have run up against the limits of the slab sided symmetrical horizontals...
Take care, Rob
Dave Calkins
Registered User
Anchorage, Alaska
Rob, until we have made huge elevators and small stabilizers, we will not have hit the limit of slab-sided tails.
That said, a curved lower surface to our stabs and elevators would be better than flat ones.
That said, a curved lower surface to our stabs and elevators would be better than flat ones.
KInda like the Zenith inverted stab....flat on top and airfoil on the bottom?
skywagon8a
MEMBER
SE Mass MA6
Rob, The original 150 hp Cessna Cardinal had a problem with the tail stalling on landing, which caused the nose gear to hit rather hard. The solution was to install a slat/slot on the leading edge of the stabilator, "up side down", which increased the down lift at low speeds.
Sky/Dave,
Any idea to what degree the curved lower horz stab would have on compensating for a heavy(ish) engine and forward of CG weight? I would much rather use that than a slot...easier and less complicated to build, I believe, and a better option than adding lead to the tail. I don't think Zenith has all the answers but they do seem to put together things that work...albeit at a cost of cruise speed.
Any idea to what degree the curved lower horz stab would have on compensating for a heavy(ish) engine and forward of CG weight? I would much rather use that than a slot...easier and less complicated to build, I believe, and a better option than adding lead to the tail. I don't think Zenith has all the answers but they do seem to put together things that work...albeit at a cost of cruise speed.
skywagon8a
MEMBER
SE Mass MA6
Lowrider,
You would need to know and understand the aerodynamics and characteristics of the of the new horizontal tail surfaces. If you do not understand this for your proposal, I would prefer either to add the weight to bring the CG in line or perhaps lengthen the fuselage a bit to accomplish the same purpose. For example, what if you chose an airfoil shape which had an abrupt stall at an inopportune time?? Pitch forward?? This could be rather touchy if not done correctly. The added weight moves the CG. The altered tail surfaces changes the flight characteristics. It all depends on how involved you wish to get.
This "The Denali Scout also comes standard with an airfoil tail (optional for the standard Scout). The 20% increase in stabilizer area and airfoil cross-section provides strong control with lightened stick force." is from http://www.amerchampionaircraft.com/NewSite2013/NewAircraft/ScoutDenali/ScoutDenali.html
You would need to know and understand the aerodynamics and characteristics of the of the new horizontal tail surfaces. If you do not understand this for your proposal, I would prefer either to add the weight to bring the CG in line or perhaps lengthen the fuselage a bit to accomplish the same purpose. For example, what if you chose an airfoil shape which had an abrupt stall at an inopportune time?? Pitch forward?? This could be rather touchy if not done correctly. The added weight moves the CG. The altered tail surfaces changes the flight characteristics. It all depends on how involved you wish to get.
This "The Denali Scout also comes standard with an airfoil tail (optional for the standard Scout). The 20% increase in stabilizer area and airfoil cross-section provides strong control with lightened stick force." is from http://www.amerchampionaircraft.com/NewSite2013/NewAircraft/ScoutDenali/ScoutDenali.html
SpainCub
Registered User
You can calculate the downforce of the H. Tab, you need the sq area of the surface and the camber airfoil used on the surface... look into wing loading calculations and it´s basically the same. Also, note that the Friesen Storch resolved some some of this by extending the tail to remove the shielding effect the wing had on the tail surface at high AoA on a 3 point landing. You can really pull the stick back on these things with low power and it basically hangs on with minor air flow but eventually the tail stalls and you are nose down once more...
I guess I should have said "in theory"...I am using an airfoil horz. and vert. stab that I added 2" to and larger balanced surfaces that are complete so I'm not interested in changing anything now. I'm still fascinated with the wing slats...wish there was more details available on their construction and design. Even the Storch plans are pretty vague.
Rob
MEMBER
AZ06
Yes, very familiar, same with that flying brick the F4 Phantom :lol: which is what got me thinking about it.
i believe doing this is superior to just making the slab biggie... It works on the wing up front, any idea why it wouldn't work on the wing out back?
SpainCub
Registered User
Looking at some wing theory material, you are essentially extending the original airfoil... Slats are the leading edge of that airfoil, so once you figure out the gap and AoA where you will be modifying the airfoil, you just have to build to maintain that shape. critical part would be attach points on the wings and the intern "ribs" in the slats to maintain the shape. I believe that hardest part is really keeping the shape once you finished.
To recap, the way I would go about it, take one of your wing ribs, now project that airfoil shape to extend beyond your current rib, find the AoA for best use and project that to the leading edge of the original rib, (some where in my notes I have 10-20% angle for the alpha but I did not take down the source, so no references for you now) so, assuming you get dual leading edges like ( ( your are creating an angle stating at the bottom of the leading edge like so ( > ( "well sort off" the trick is figuring our what % you are adding to the airfoil to get your shape.
To recap, the way I would go about it, take one of your wing ribs, now project that airfoil shape to extend beyond your current rib, find the AoA for best use and project that to the leading edge of the original rib, (some where in my notes I have 10-20% angle for the alpha but I did not take down the source, so no references for you now) so, assuming you get dual leading edges like ( ( your are creating an angle stating at the bottom of the leading edge like so ( > ( "well sort off" the trick is figuring our what % you are adding to the airfoil to get your shape.
skywagon8a
MEMBER
SE Mass MA6
The stabilizer, being basically fixed (except for the small angle changes for trimming), would not likely have the angle of attack that the slot would require to be functional. It is the elevator which looses authority at max deflection. I toyed with the idea of a slat below the hinge line but decided that it could be a grass catcher and drag producer. Think of a curved piece of aluminum attached to the elevator below the hinge. With the elevator down the slot would be closed. With the elevator up it would be open and deflecting air around the hinge line to straighten the flow over the bottom of the elevator. Thus reducing the low speed turbulence/stall speed of the elevator.
Rob
MEMBER
AZ06
Thanks, the little light bulb just clicked, and this makes sense. Not a stability problem, an authority one. IIRC, Cessna did it to keep the tail from stalling and dropping the nose gear into the ground. This seems similar to the little cubs issue. Steel is cheap and I am a slow learner, probably build a set anyways
SpainCub
Registered User
You can always get more Cl toe more slats you add...
The favorable effects of a slotted flap on C[SUB]l[SUB]max[/SUB][/SUB] was known early in the development on high lift systems. That a 2-slotted flap is better than a single-slotted flap and that a triple-slotted flap achieved even higher C[SUB]l[/SUB]'s suggests that one might try more slots. Handley Page did this in the 1920's. Tests showed a C[SUB]l[SUB]max[/SUB][/SUB] of almost 4.0 for a 6-slotted airfoil.
Figure 7. Results for a multi-element section from 1921.
The favorable effects of a slotted flap on C[SUB]l[SUB]max[/SUB][/SUB] was known early in the development on high lift systems. That a 2-slotted flap is better than a single-slotted flap and that a triple-slotted flap achieved even higher C[SUB]l[/SUB]'s suggests that one might try more slots. Handley Page did this in the 1920's. Tests showed a C[SUB]l[SUB]max[/SUB][/SUB] of almost 4.0 for a 6-slotted airfoil.
Figure 7. Results for a multi-element section from 1921.
