Leading Edge Cuff

[Jerry Burr]

Stuff

Hi Aurele. I think that you have the angles down pat. I use deck angle to represent visibility out the front window in flight also. This is hard to explain without writing a book. I will try to be brief, and Jim will probably correct me or fill in the blanks. To answer an earlier question about AOA/CL, the way I see it is that the airfoil used in TN 2228 started with a geometrical AOA of minus 2. The airfoil then produced a CL of 1.37 at 14.45 AOA. Stock. With the cuff it produced CL 1.65 at 18.25 AOA. This is compared to a Clark Y with CL 1.4 at 24.5 AOA. That was starting with a minus 5. The Clark Y being the handiest data for me to grab and close to the USA 35B characteristics. The test in 2228 did not change the length of chord of the section. I quote from page 6 concerning the cuff. (some improvement in stalling characteristics was obtained, as indicated by the slight rounding near the lift curve peaks. This rounding is a result of separation of flow which occurred initially near the trailing edge of these airfoils. The complete stall of the airfoil, however, was probably the result of failure of the separated flow near the leading edge to reattatch) I agree with that statement. Which is the main reason that Micro VG?s work so well on the front upper camber of Charlie?s cuff.
To answer your question on AOA/stall. Let me put it this way. If two identical Cubs are flying side by side same weight/power setting/deck angle and wing with the exception of a cuff. The cuffed wing will stall at a lower TAS. If for no other earthly reason than that it has more square feet of wing and more wing camber than the other cub.
That answered the Cub with the cuff can with power, also stall at a higher AOA than the non cuffed Cub. The result also being a lower stalling speed, at the cost of increased deck angle. The last paragraph can also be said of slats, slots, flaps, droop ails.
I can hear Crash thumping the keyboard already. I?m out of here. Jerry.

 

[A BELLAND]

cuff

Thanks Jerry
I like to read this stuff and one day i would like to build a set of wings.
The J-5 with the 135 is nose heavy when light and hard to get to break.It has a stock wing and i think i am in the low 40 m.p.h. range.I am going to try VGs as a first mod when the weather warms up.I will continue to do a couple of stalls every time i fly till the VGs go on so should be able to know what diff they make.I have to remember to start looking at the GPS to see M.P.H. when it starts to mush and keep track of my speeds.

Thanks again,Aurele

 

[JimC]

I don't recall ever having occasion to correct Jerry on anything (Jerry impresses me). And besides that, I"m fumble-tounged.

Earlier, when I described the 63(1)-012, the 3 is the description of the camberline and the design lift coefficient is 0 for that airfoil. Oops. wish I'd uv said more so I could correct that too. Another example of the laminar 6 series wings is the 65(2)-415 used on the Cherokee, where the first 5 describes the camberline, the 2 means the drag bucket extends 0.2 either side of the design lift coefficient, the design lift coefficient is 0.4, and the maximum thickness is 15%.

As an aside Jerry, have you looked at Mike Selig's website at the University of Illinois for the data on the US35B? It may also be in Abbot & Doenhoff (spelling??), though I haven't looked to be sure.

The only thing that I might differ with in what you said, " The result also being a lower stalling speed, at the cost of increased deck angle. The last paragraph can also be said of ........, flaps, droop ails" is that flaps can stall at a greater CL, but still at a reduced deck angle, dependent upon the particular airfoil and flap configuration. What you said about that isn't wrong, but may not be all-inclusive.

In response to another poster, yes, the aoa (angle of attack) is the angle at which the chordline meets the free stream airflow. But it does not take into account the additional induced aoa increment which can be substantial and which varies spanwise.

JimC

 

[Dave Calkins]

So my wife just bought a Cherokee.

What must I do to it to make it fly like a Cub?

Are VG's worth doing?

Seriously!!

I'm thinking of the 1958 PA-18 scheme with the swoops on the fuselage.

Will that paint scheme help? It's all in your hands Jerry and Jim.

DAVE

 

[sj]

Dave,

They make a taildragger conversion for the Cherokees, you will definitely want that:

http://www.popularaviation.com/PhotoGallery/1989.JPG

I have flown a 140 with droop tips and it was pretty cool, HOWEVER, the droop tips are about 4.6 inches off the ground, so I think rough field stuff is OUT unless you can put stilts and bushwheels on it or something, or again, maybe the TD converision....

sj

 

[Jerry Burr]

Pipers

Hi David. Sorry, I've only worked with Cubs. :-? Jerry.

 

[Ursa Major]

So my wife just bought a Cherokee.

What must I do to it to make it fly like a Cub? DAVE

Dave,

Did you buy Dave V's Cherokee? Now there's a STOL project! I'd start with the bushwheels and float fittings.

 

[Steve Pierce]

That is Steve's latest project of Steve's Gascolator fame. It is a real deal going through certification. 8)

 

[S2D]

So my wife just bought a Cherokee.
What must I do to it to make it fly like a Cub?
DAVE

Start removing everything behind the firewall that doesn't resemble a Super Cub, Insert everything behind the firewall that looks like a Super Cub.

 

[T.J.]

Alright! Someone is gonna make a STOL Cherokee. They won't have a problem finding repair parts, there's one off the end of every strip on the Alaskan Peninsula.

 

[Dave Calkins]

Jerry, I was half joking on the VG's, but the discussion of VG's on the PA-28's 65(2)-415 section would be interesting.

Steve, I don't believe you on that TD conversion. When I'm done with this post I'll go and look at that link anyway.

Ursa, yep.

Steve P., I'm sure Steve's will be a honey, if Steve of "Steve's a/c" is doing it, assuming his gascolator is any indication of his skills and workmanship.

Actually, I've seen a floated Cherokee. It's probably great.

Also, In Western Alaska the Cherokee 6 is used quite a bit and does plenty of beach work.....on 8.50's of course.

I've been off airport on sand in one with 8.50's and it was fine.

Ours has 8.00x 6's and a 60 inch pitch prop. It does like...125 MPH....... It'll stay with a belly-podded 206 with Gar-Aero's..........

.....and it eats mountain goats for breakfast.

But man is it a confidence-building lander. Talk about land-o-matic!.......so I heard from some drunk dental hygenist..............

I've not flown one since my very first 3 real airplane landings when I was a kid. Can you say wheelbarrow? How about "good pitch authority"?

S2D, Should I leave the stabilator on it, though?

TJ, is the EXP Cub gonna have a stabilator to go with the slats. I've got an extra available if that one aint at the end of your strip.

DAVE

 

[JimC]

Dave, both cruise and stall can be improved on the PA-28 140,150,160, & 180 by addition of a single pair of vg's on the strakes. Indicated stall speed will be reduced by about 4 mph and cruise will increase by about the same amount. Very location sensitive. The 200 & 235 do not pick up the cruise increase. See Art Matson's website on his modified PA28-140 (Juliet). Art's stuff works, and he doesn't blow smoke. Also, look at his short-field takeoff photos. I've been in the plane during that process, and it is indeed impressive for a Cherokee. My own modified PA28-150 isn't running vg's at the moment, but with a 62" pitch prop, I do top out at 162 mph down low (lightly loaded, with just me and about 36 gallons of gas), and I cruise at about 155 mph at 8000' DA (similar loading). The 65(2)-415 wing responds well to cuffing. Though the cuffed wing does lose about 4 mph in cruise, the indicated stall speed will drop about 8 mph. I have a friend with a modified PA32-260 (both STOL and speed mods), who is cruising at about 165 mph at alttitude with moderate loads (two people, baggage, and about 60 gallons of fuel). The Cherokees aren't all that bad really, and they are so easy to fly that it ought to be against the law. Only downside, on wet, winter grass they are very prone to build grass up in the wheel fairings and intermittantly lock one of the wheels up. Stay off the brakes, and use the prop and rudder for directional control when landing on slick, muddy areas.

I strongly discourage droop tips on the Cherokees, for several reasons, but do like Horners.

All the best,
JimC

 

[tempdoug]

vgs on the tail strakes, would it double my effectivness if i put a vg on each side of my vgs? hmmm, im trying to figure out how to move that little guy with the bubbling eyes over here. doug

 

[Jerry Burr]

Why Not?

Hi Jim C. I think I have finally figured out why it is easier to make a cuffed wing go faster the faster you go. This is only true on a relatively flat wing however. The positive AOA created by the angle of incidence is cancelled by the negative AOA created by the lowered leading edge of the cuff. So the AOA of the wing is the same as the longitudinal axis of the fuselage. We know that the 35B has to see minus 2.5 deg AOA to achieve zero lift. So if the smart level reading on the longeron at cruise is reading minus 1.5 deg, that means that we have crossed from the dark side of Positive AOA lift induced Drag to the light side of Negative AOA lift induced Thrust. No wonder they go so fast. Jerry

 

[Steve's Aircraft (Steve)]

Steve, I don't believe you on that TD conversion. When I'm done with this post I'll go and look at that link anyway.

Steve P., I'm sure Steve's will be a honey, if Steve of "Steve's a/c" is doing it, assuming his gascolator is any indication of his skills and workmanship.

DAVE

Dave,

The taildragging cherokee is the real deal. The internal brackets are being cut right now to mount in our "drop test" fuselage. We are using a one piece gear leg mounted to the bottom of the fuselage. We have the gear built by Grove and a spacer plate already made. Will be using a 'stinger' type tail wheel. Plans are to make it a multiple STC covering the pre 1973 PA28-180 thru PA28-140. On a side note, the Stinger tail wheel we are working on for this conversion will incorporate a SCOTT 3200 fork with a new top that we machine. We have been thinking of using the same system to put a stinger on Cub's. Any interest??

Steve

 

[Tim]

Jerry & JimC
You guys amaze me with your knowledge. I have been here almost from the beginning and have learned much from both of you. Your last couple of posts are way over my head, I even had my wife read them and she didn't know what you were talking about, and she knows everything! Thanks

Tim

 

[Dave Calkins]

Great stuff you guys.

Also, Steve of "steve's a/c", You make a very nice gascolator, but I don't believe you about the TD-28.

Also, Jim C. must think me a total fool to believe he's ever seen 165 in his 28.

Two things are for sure, though. Jerry is hard to refute and Tim definitely hit the nail on the head. :roll:

DAVE

 

[Jerry Burr]

Wink Wink

Hi Tim. Hey I hope you caught the wink on my last post. I have to have some fun. Jerry.

 

[Dave Calkins]

Hi Jerry. Have you read TJ's post about his EXP?? (Making a right one out of a left one"; It has a decent description of his configuration, though he doesn't mention any aft-extended leading-edge wrap, or not)

How would it do with a full-flying stabilator? Any guesses on his weight?

Thanks. DAVE

 

[Tim]

Jerry, you're the man

 

[JimC]

Miscellaneous topics

Jerry is indeed the man.

And Jerry, you're right about the aoa vector. The beasties that I usually work on make regular use of this with wing rotation about the pitch axis during both the down and upstroke, and also make use of the effective variation in the vector due to the varying induced aoa.

>>Doug wrote, " would it double my effectivness if i put a vg on each side of my vgs?"<<

Not necessarily (and probably not). By way of loose example, on tests of drag mods due to shark skinning surfaces, making alternate rows identical but for a constant offset in spacing increases drag by about 11%. The same patterning but with random row offsetting reduces drag by about the same amount. Qualitatively variable results could also be expected with vg's..

David, you're quite right (and you're certainly NOT a fool) -- my Cherokee (a PA28-150 with a high compression STC) has never seen 165 mph. It will true about 162 in level flight at full power at low altitude and true about 155 at approximately 75% power at altitude (about 8000' DA and full throttle). I've made Vne (171 mph) one time while wide open in ground effect, but that don't count because of the ground effect. It was the friend's modified PA32-260 that is seeing 164 - 165 mph in cruise. By comparison, Art Matson's modifiect PA28-140 has occasionally topped 170 in level flight without benefit of ground effect, but his usual top speed is closer to 165 -166 mph. Art is roughly about 4 - 6 mph faster than me in cruise. I'm not an evangelist about convincing folks, but if you own a Cherokee up through a 180, it would be worth your while to try some of Art's mods (I run a few of his myself).

All the best,
JimC

 

[Dave Calkins]

I just took a peak at http://www.pipermods.com ......a Cherokee mod sight, apparently.

This opens a whole new world.

Apparently there is another way to get the job done than just a Cub.

...at a cheap price, with 4 seats, with a LOT of room in an "extended" baggage.

Go check out http://www.cherokee.org

Anyway, thanks for taking the time to discuss the meek PA-28!

DAVE

 

[JimC]

Dave, several years ago I flew co-pilot with Art in his Juliet (a highly modified Cherokee 140) in the Denver-Oshkosh airrace that then served as the inaugural for the EAA convention at Oshkosh. The race was a standing start - flying finish from Jeffco to Appleton tower, with the finish line being 500 feet agl over the tower. We did a non-stop flight 903 statute miles as the crow flies (we really did a bit more, as our route took us about 90 miles south of the straight line, in an effort to minimise headwinds. We averaged 130 mph airspeed and 127 mph groundspeed on 42.9 gallons of gas in 7 hours, 12 minutes and 5 seconds (if I remember correctly -- and note that the elapsed time included the takeoff roll at Jeffco). When we reached Appleton (about 10 miles north of Oshkosh, we had just over an hour of fuel remaining (6.1 gallons, and our average fuel burn during the flight was about 5.95 gallons per hour). During the final hour of the flight, the winds had shiifted as we crossed a front and were favorable, so toward the end we were seeing a groundspeed of about 181 mph at an altitude of about 13,200 feet. We could have gone about another 180 miles, for a no-reserve range of 1088 miles, which ain't bad for a Cherokee 140 with standard tanks and an average 3 mph headwind. These are timed results in a sanctioned EAA sponsored airrace, not something conjured up out by aid of smoke and mirrors.

Juliet is quite a performer for a Cherokee, and any Cherokee is capable of achieving similar results with appropriate mods..

All the best,
some sever JimC

 

[Dave Calkins]

Thanks Jim.

Anybody want to buy a couple of Cubs, cheap? I'll use the money to fund one of these fast -28's......just joking.

I was previously also joking with that the cherokee.org link. I just now clicked it for fun and whoooaaaa...it worked.

A guy could get into trouble joking around with stuff he doesn't understand!

So Jim, would a full-flying stabilator on a slatted cub be worth trying?

Jerry probably has some insight on it also.

Helio Courier's have 'em.

What would the advantage be in the high-alpha regime (high Angle of attack...i.e. slow-flight with a slat).

Any disadvantages besides maybe increased weight to support the structure.

 

[Jerry Burr]

Tail feathers

Hi David. Talk to Wayne Mackey. He was going to use that exact setup on his (Cub) type airplane. He has lately changed his mind. Talk to him. Jerry.

 

[Steve Pierce]

What about hinging the wing to the fuselage? It would probably be heavy but you wouldn't be staring at the sky when you are really slow.

 

[Dave Calkins]

Jerry, I talked to Wayne about it a bit. Sounded like his idea was a tiny stub-stab with large elevators hinged off of it. Funny how people can come up with similar ideas yet be completely geographically seperated.

Well of course, Steve, I've been thinking about that hinged wing also. But.....it introduces tons of complexity.

That's where these aerodynamicists come in. They need to come up with a wing for us that will make lots of lift at a zero deck angle, then also provide Cherokee-like (te-hee-hee :lol: ) top-end.

It would be much easier and sensible to have MUCHO camber changing (Fowler flaps on the trailing edge and slats on the leading edge, ala: every jet airplane you can think of) rather than changing the wing incidence.

Still, on a fully-cantilevered wing like the helio (or 210, or 177) the incidence chang-o-matic would be doable.

..you go first, I'm right behind you.

 

[JimC]

Several thoughts.

I don't much care for the idea of a stabilator on a cub, since they don't change the camber all that much as they are deflected (and those that do (such as the Cherokee), tend to change it at the trailing edge as a trim device. It can be hard to get a good tail download capability with a stabilator. What a cub really needs is the capabiltiy to create a substantial tail download at slow speeds and relatively low drag at moderate speeds. The best way to get that is to retain conventional elevators so that the camber can be modified by deflection, increase the tail aspect ratio, keep the planform elliptical, go to a symmetrical airfoil section, and place vg's on the lower surface, while keeping in mind the induced flow off the wings when the flaps are deployed. It might be a good idea to increase the trim range. I would defer to Jerry and Wayne on this subject, as it applies to cubs.

The pitch-hinged wing has been done and flown many years ago. It works, but is heavy and has some problems.

The Cherokee 65(2)-415 wing is actually quite a good, low drag section with good low speed characteristics and docile stall, but there are better low speed sections available. From memory, zero lift aoa for that section is roughly about a negative 3.5 or 4.0 degrees.

By comparison, the Selig S1223 or S123rtl have a zero lift aoa of about a negative 10 or 11 degrees and consequently generate a zero aoa CL of about 0.8 to 0.9 depending upon aspect ratio (they fly with a zero deck angle when moderately slow; a very negative deck angle at high speed). Max unflapped CL is about 2.1 or 2.2, flapped is better. However, they are draggy and the rear spar is really a bit thin for a cub, so one might wish to modify the section somewhat if used for a cub.

JimC

 

[Dave Calkins]

Jim, are these Selig sections working well at Cub-like Chord-Length Reynold's Numbers?

 

[JimC]

Dave, they do -- but they are draggy, and the rear spar would be very thin, top to bottom. Also, they load the rear spar and rear lift strut rather heavily. A compromise, like most everything to do with airplanes.
JimC