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smith1943
07-28-2005, 05:28 PM
I have built a set of D and E wings. After completing them, I measured the angle of incidence as 0 degrees. All of the discussion I have read on setting up a supercub call for 2 degrees. The mounts on the D and E spars are not adjustable and the mount points on the fuselage are adjustable only with great difficulty i.e. cutting and welding. It would require about an inch of change down at the rear or up at the front to get 2 degrees. I have been told not to worry about it as long as both wings are the same. What do you all think?

Cimarron
07-28-2005, 06:32 PM
It will cause the tail to fly lower and change the athority on the elevators and stabilizers. Will still fly but who knows how well. :drinking:

fobjob
07-28-2005, 06:39 PM
My cub had a blow-over history and undocumented repair when I purchased it. The wing angle was zero degrees. (Yes, I had the 2.5 degree twist)The lack of pitching moment caused the trim to be way out. Namely, it needed quite a bit of down trim at all times indicated by down elevator visible even at forward CG loadings. This resulted in a total lack of a stall.(sarcasm) It would spin instantly! The dang thing was a flying deathtrap, in my opinion. I bought vortex generators to try to save my life while I figured out what the heck was wrong with it. Later, I pranged it good on Mile Hi, (not because of the trim) and the top deck was replaced. Now the angle is two degrees(should be 1.843) and I'm slightly nose heavy as a result. Short of welding, you might try deflecting the flaps and ailerons down.....
p.s. The Micro VG's reduced my spin recovery from seven turns to 1/3 turn....

Bugs66
07-28-2005, 07:06 PM
Which surface did you level the fuselage with before you measured the angle.? Was the level a Smart level?

Crash
07-29-2005, 10:31 AM
I would not "free hand" weld on a new top deck. You really need to put everything in a "known" good PA-18 jig before welding it in place. Strings and Smart levels will not always get you to the same place and welding always changes things a little. Crash

Crash
07-29-2005, 10:34 AM
I have built a set of D and E wings. After completing them, I measured the angle of incidence as 0 degrees. All of the discussion I have read on setting up a supercub call for 2 degrees. The mounts on the D and E spars are not adjustable and the mount points on the fuselage are adjustable only with great difficulty i.e. cutting and welding. It would require about an inch of change down at the rear or up at the front to get 2 degrees. I have been told not to worry about it as long as both wings are the same. What do you all think?

They should have 1 degree (3/8") of twist (washout) setting on a set of "leveled" saw horses. This is the standard starting place if they are going on a PA-18 fuselage. Crash

Dano Bardwell
07-29-2005, 12:23 PM
crash what do you suppose would be the effect of one inch of wash on the saw horses?

StewartB
07-29-2005, 01:10 PM
They should have 1 degree (3/8") of twist (washout) setting on a set of "leveled" saw horses. This is the standard starting place if they are going on a PA-18 fuselage. Crash

I'm no authority, but this doesn't sound right. Are you sure?

SB

Dano Bardwell
07-29-2005, 01:42 PM
SB yep thats what the good book says, my question still stands!

StewartB
07-29-2005, 01:46 PM
I thought the washout was 2.5* on sawhorses, which equates to about 1* on a leveled airplane. As I said....not an authority.

SB

cubunltd
07-29-2005, 03:00 PM
SB,
The 2 1/2* is measured along the rear spar which equates to .75 - 1* at the outboard rib (or 3/8").

John

StewartB
07-29-2005, 03:06 PM
John,

On sawhorses or on the leveled airplane?

If the butt rib is level on a sawhorse, the difference at the rear spar on the outboard aileron rib is considerably more than 3/8....isn't it?

SB

smith1943
07-29-2005, 07:52 PM
I guess I will modify the mount plates on the spar to get 2 degrees. I measured the angle relative to the top longeron. I built the fuselage without using a jig. As far as I can tell it measures ok against the dimensions shown on the Northland drawings i.e. within an eighth of an inch (ok, three sixteenths in a few places). The D and E wings are supposed to be built without washout. That's how I built them. Now I am a little nervous. I'lll let you know if they kill me.

Dave

Dan2+2
07-29-2005, 08:30 PM
I have a set of D&E wings too built with zero washout . I specifically asked Earnie about it and he was adamant about not needing it. My sportsman 2+2 is built for these wings per the plans from wagaero with the rear spar fitting 1 7/8 in closer to the datum line than the front spar fitting. Or in other words the rear is 1 7/8 lower than the front. That is where the wing incidence is established. That fuselage spec. is unchanged whether it is cub wings or ribblet wings like mine. Or maybe I'm really confused. Anyway is your fuselage spar fittings and top deck equal distance from the datum line front and rear? If they are then the rear stabilizor needs to allow for it.

Bugs66
07-29-2005, 11:06 PM
From what I understand, you can still add washout to your wings with the strut rigging as per the L-21 manual. You should be able to do this whether you did the 3/8" block thingy or not. The 3/8" block on the end is to help alleviate potential oil canning of your LE sheet.

Crash
07-29-2005, 11:23 PM
From what I understand, you can still add washout to your wings with the strut rigging as per the L-21 manual. You should be able to do this whether you did the 3/8" block thingy or not. The 3/8" block on the end is to help alleviate potential oil canning of your LE sheet.

BINGO! And you can't force the washout into the wing if you've extended the leading edges. The extended leading edges lock the wing into shape like a Cessna wing. Crash

smith1943
07-30-2005, 02:13 AM
Dan:

Have you flown this wing? Ernie was adamant that washout was unnesessary but I haven't heard him say that 0 degree angle of incidence is correct. When I built the wings according to his instructions and measured how they will mount on the fuselage it comes out to 0 degrees. But I may have made a building error. After reading the post from fobjob I am doubtful.

180Marty
07-30-2005, 07:43 AM
I don't know if this will help anybody but just looked at a copy of an original PA 12 blueprint. The front spar fitting is 25 and 5/8 inchs above the horizontal reference line and the rear is 1 and 1/2 in lower.
Marty

StewartB
07-30-2005, 10:33 AM
http://sparky.supercub.org/photopost/data/500/medium/PA12_Cessna_on_a_sandbar_018.jpg

We set the washout and dihedral on the plane, and applied leading edge metal with the wings in place.

SB

cubdrvr
07-30-2005, 03:30 PM
OK guys..........maybe a dumb question here but.........given the weight and characteristics of a cub does it really need any dyhedral? And washout is built in to stall the wing from inboard to outboard......right?....so that only comes into play at low airspeeds....right?......so if you increase the inboard wing camber at low airspeeds by adding a notch of flap wouldn't that accomplish the same thing ( or better ) than washout? And wouldn't the wing provide more lift with zero dyhedral?
My SWAG is that you would have a better flying cub without either washout or dyhedral.
Anybody?

ground loop
07-30-2005, 04:07 PM
Years ago I had a famous cub shop rig my wings. They had the angle of incidence correct but no washout. It was absolutey awful to do stalls with and the ailerons were super mushy on landings. Crosswinds were a handful. I never figured it out. I thought it was just a bad cub. I went up with Tom Warliegh and he had me get the washout fixed immediately.
It was amazing how quick he figured it out.
You want the wing tip to stall last, hence the design of the BLR kit staggering the VG's. The BLR kit made X-wind landings awhole lot more fun. When doing the challenging stuff, I think one of the cubs shortcomings is having less aileron than I want. That is why I think the slotted standard wing is not a good idea and think that some VG's on the area beyond the slot on the extended slotted wing might be a good idea.

Dan2+2
07-31-2005, 11:51 AM
I have not flown yet. The plane is on hold til cooler weather. My shop is not air conditioned. I should be ready to cover this winter.

Crash
07-31-2005, 12:30 PM
I thought the washout was 2.5* on sawhorses, which equates to about 1* on a leveled airplane. As I said....not an authority.

SB

SB you have a PA-12, a PA-12 or PA-14 wing has about 1 3/8" twist in it when it is on leveled saw horses or 2.5 degrees from root rib to outboard full aileron bay rib when on the airplane. A PA-18 wing has 3/8". Ask Atlee Dodge why he builds different tanks for the PA-12 and PA-18. His PA-12 tanks have more twist in them to accomadate the additional twist of the PA-12 wing. Are you flying the 12 yet? Crash

Jerry Burr
07-31-2005, 02:30 PM
Hi Groundloop. Are you suggesting that when the famous shop rigged your wings that the wing tips were stalling before the rest of the wing, and that is what made them mushy? And by the way how is it possible to adjust the angle of incidence on the airplane while rigging the wings? :-? Jerry.

ground loop
07-31-2005, 02:56 PM
Jerry,
Thanks for entering the discussion, it could sure use your expertise to explain my experience. I never said the shop adjusted my angle of incidence, I just said that it was correct. I am not sure what everyone includes in their definition of 'Rigging", so there is the possibility of me using the word inappropriately.
As for the rest of the post "When they rigged it with no washout , the wing tips stalled first." I was saying that I thought this was very bad. Please explain my folly so that I may learn! :)

StewartB
07-31-2005, 03:22 PM
I thought the washout was 2.5* on sawhorses, which equates to about 1* on a leveled airplane. As I said....not an authority.

SB

SB you have a PA-12, a PA-12 or PA-14 wing has about 1 3/8" twist in it when it is on leveled saw horses or 2.5 degrees from root rib to outboard full aileron bay rib when on the airplane. A PA-18 wing has 3/8". Ask Atlee Dodge why he builds different tanks for the PA-12 and PA-18. His PA-12 tanks have more twist in them to accomadate the additional twist of the PA-12 wing. Are you flying the 12 yet?
Crash

I'm not particularly interested in arguing whether washout is a good thing or not, but I am interested in what the correct washout is. I agree that Atlee's 12 tanks are specific to 12's, but I'm not certain why. I've heard that 18's have less washout than 12's, and I've also heard the washout is exactly the same. That's why I asked about the 3/8" block, which would make perfect sense IF the 2.5* twist is correct and the block was being used on a leveled airplane.

Here's a pasted clip from another thread. I don't know what Mark was quoting, but I've got a couple of mechanic friends that agree with him.

AkPA/18
Supercub.org Supporter I



Joined: 08 Feb 2003
Posts: 258
Location: Big Lake Ak
Posted: 10 Feb 2005 23:53 Post subject:

--------------------------------------------------------------------------------

Crash---here you go.

Quote:
This is OK for a PA-12 or 14 but is not the way I would do it on a PA-18. Level the plane according to the directions and adjust for the wash out on the outside aileron bay rib. An 18 wing does not have the same twist in it as a PA-12, measuring from the butt rib to the aileron bay rib. Crash


e. The correct wing washout of the Piper
PA-18 model series and PA-19 airplanes is
2 1/2 degrees, the same as that of the Piper
PA-12, PA-12S, and PA-14 airplanes. The
PA-18 model series and PA-19 airplanes,
however, have a wing angle of incidence of
+1.843 degrees at the wing root (inboard end;
i.e., the centerlines of the wing butt hinge
bolts), while the PA-12, PA-12S, and PA-14
airplanes have a wing root angle of incidence
of -0.060 degree. The negative angle of
incidence at which the outboard aileron ribs of
PA-18 model series and PA-19 airplanes must
be set in order to produce 2 1/2 degrees of
washout is therefore much smaller than the
negative angle of incidence at which the
outboard aileron ribs of PA-12, PA-12S, and
PA-14 airplanes must be set in order to
produce that same 2 1/2 degrees of washout.
_________________
http://thrustline.com/

Takeoffs are optional--Landings are mandatory

SB

Flapman
07-31-2005, 03:54 PM
When Piper built Super Cubs at Vero Beach they specified that the wing washout would be set up on two leveled sawhorses. One under the # 1 rib and the other under the # 15 rib. A block of wood would then be placed under the # 15 rib flange just beneath the rear spar. This block of wood measured 1 and 3/8 inches.
As an aside, this washout was put in the wing BEFORE the drag wires are tensioned. If the wires are tensioned while the wing is flat, they will be out of tension spec and out of square when the washout is added.
Regards,
Flapman

StewartB
07-31-2005, 06:51 PM
Thanks, Flapman.

So in summary, before an argument breaks out on the topic of wing rigging and zero washout, it's clear that even some knowledgable Cub guys don't agree what the "standard" configuration of a Cub wing is, or at least how to get there.

SB

Jerry Burr
07-31-2005, 09:07 PM
Hi groundloop. OK I will lighten up a bit. I went back and checked our test data and the stall always started at the juncture of the flap and aileron, (With the flaps extended) on a flat or twisted wing. If you have no flaps or they are not extended then I may be out to lunch.
Boy's there is something that I don't understand. If 3/8 inch twist (washout) is the goal for the finished product on the completely rigged airplane, then why put the leading edges and flying wires in with 1 and 3/8 inch twist. And then twist, crank, pry or whatever to get them back to 3/8 inch twist when rigged on the airplane? I have used 3/8 inch on the sawhorses and will continue to do so until someone can give me a logical and sane reason not to do so. The picture posted by SB looks like it is going to be a bear to work on that way, but the theory is correct. It will have 3/8 inch twist when finished assuming that it is rigged by measuring the difference between the butt and aileron rib. The incidence has nothing to do with rigging. That's taken care of in the building stage. If the wing mount brackets are not correct then it was built wrong, not rigged wrong. I just rechecked Service Bulletin #1. Dated 2-15-46. For the E2,J2,J3 airplanes. It was a 3/8 inch block on top of a level to get correct washout and still is. :) Jerry.

Steve Pierce
07-31-2005, 09:23 PM
I always use a 3/8" block too Jerry. 1 3/8" on the Short Wing Pipers.

StewartB
07-31-2005, 09:37 PM
So, is the service bulletin specific whether the 3/8" block was used on sawhorses or a leveled airplane? It's kind of common knowledge that to duplicate the AOI of an 18 on a 12, one should lower the rear spar attach points by 1". If I rotate the wing 1" on my 12, and the initial washout was 1 3/8", what size block would yield a level meaurement on rib 15 of a leveled airplane? No matter, obviously the wings will fly either way.

By the way, it wasn't a bear to work on at all. There's no clutter 6' off the ground, and stuff I dropped announced itself on the floor.

I still want to know who's correct, per the factory standards. There should be consensus on this point. No confusion. No different than mag timing or bolt torque.

SB

T.J.
07-31-2005, 09:49 PM
delete

StewartB
07-31-2005, 09:59 PM
If Mr. Piper said so, post it, please. Let's achieve that consensus. Show us the goods.

SB

cubdrvr
08-01-2005, 06:59 AM
I'd still like some comments on my above post. Disregarding stall characteristics or stability wouldn't you have a more efficient flying cub with zero dyhedral and no washout? I would guess that a notch of flap may do the same as washout??

T.J.
08-01-2005, 11:19 AM
I believe the 3/8" washout is in Piper Service Memo No. 19.

StewartB
08-01-2005, 11:29 AM
Thanks, TJ,
You can see the service instructions here on page 13.

http://66.102.7.104/search?q=cache:Ua4h4KM0pxEJ:av-info.faa.gov/data/alerts/1997_08.pdf+piper+service+memo+19&hl=en

A 3/8" block is specified for determining washout on a leveled airplane. Further, in paragraph E the washout for a PA-18 is specified as 2.5*, which equals 1 3/8" on level sawhorses.

SB

fobjob
08-01-2005, 11:29 AM
The dihedral is there to add to yaw axis stability and to meet the requirement that you can lift a wing by applying rudder. The twist or washout is there to not only prevent sudden stalls, but to prevent tip stalls, which are aggravated by the lossy round tips....the price for that is paid by increased profile drag of the wing.

Jerry Burr
08-01-2005, 12:01 PM
Hi TJ. I'm surprised by your comments unless you are a AI. The bottom line here folks is that a flat cub wing is just as trustworthy in a stall as a twisted one. And creates more lift to boot. Everyone used to do it, that was why the AirStreak approval required a washout check to be approved. The problem is insurance and the rules. It will invalidate your insurance and if you are involved in a taxi accident or anything your insurance will be no good. And most of all no AI wants a customer to drag their Cub in and want the twist taken out. Makes for a bad relationship and leaves the AI hanging out to dry if there is a problem. Sometimes they can be accidently rigged slightly off in the twist department. Kind of like mag timing or the exhaust baffles on a race car going through tec check. They're bang on. But they seem to work loose after the first lap or so. Dihedral is another matter. If you have any kind of vortex reducing tip changing the dihedral is just not worth the problems caused. The high pressure under the wing doesn't amount to anything compared to the low pressure above it in terms of lift. If anything, a high dihedral wing would probably have nearly the same lift due to what you loose on the bottom you gain back on the top. Flying them is ok if it is a work airplane that you intend to fly every minute. It's like flying with a set of cuffs mounted 1/4 inch too low. Yea it lifts like crazy but it wants to go every where but straight ahead. Not too cool for a sport / recreation airplane.
Aside from that, I have a question for some of you high time stock and extended wing pilots. Here's the problem. You are five miles from a 5K' runway. Your ailerons and elevators are locked in cruise position. You have only throttle and rudder. Can you land the airplane? I would like to hear your results. Here's what happened to me. If I was (extremely) diligent on the rudder and nothing over a 2 deg bank I could survive. Otherwise I couldn't stop the turn. When I was given 1/2" aileron ( 1/4" either way it was a no brainer. The elevator was no problem until within 5 or 6 feet above the runway. Ground effect caused it to nose down sharply. It could be caught with power but then I was back where I started. After about 5 of these oscillations I let it drop a little more and ended up in a nose low wheel landing. I had opted to use only 20deg flaps. How about posting your results. Know thine airplane. :) Jerry.

cubdrvr
08-01-2005, 12:45 PM
Thanks Jer............that's what I wuz lookin' for........... 8)

T.J.
08-01-2005, 12:47 PM
delete

Jerry Burr
08-01-2005, 04:27 PM
Hi TJ. I agree with you on the fool, that's why I said it. The term (whole wing stalls at the same time) had to begin with a person with a lot of book learning and no practical. I refer now to a -18 wing with at least 20deg of flaps deployed. The first disruption of air or first element of the stall if you prefer is at center chord at the juncture of the flap/aileron. The next is the inboard end of the aileron. (aerodynamically this is a lousy setup) The disruption will go approx 1 foot ahead of the false spar and out to the control horn. Then both of these areas expand. Finally the rear of the wing root will become disturbed. Then all of these areas will move forward (by this time the complete aileron is involved) to the rear of the leading edge. Assuming Micro VG's are installed the entire wing rearward of the leading edge is in reality stalled. Is the whole wing stalled at the same time? I would say so with the exception of the leading edge. The airplane is mushy and buffeting but still flying. Finally the vortex's are overwhelmed and the airplane goes into a mush stall. There is nowhere enough break to enter a spin, a spiral is just about the best you can expect. You have to take a run at the stall to get a good break for a spin. The full stall airspeed isn't the same because with a majorly twisted wing the inboard end does stall first and the inboard leading edge is of no use to you in truly slow flight. If it wasn't for the aileron problems the twisted wing theory would be closer to reality. Also the pre stall warning that you refer to is originating from the tail buffet not the wing. It's going to be there either way, assuming some flaps are deployed. The wing will cause a sharp or mushy stall. As a follow up to my previous post about not being able to rudder the wings level, that was with Demer Tips. Out of curiosity I tried the same thing with X/wind tips and was able to rudder level from a steep turn. Demers will hold the leading wing tip down in a major skid. :) Jerry.

fobjob
08-01-2005, 06:08 PM
Jerry, so I gather from this that a fence under the wing between the flap and aileron would delay involving the aileron in stall turbulence? I don't recall rolling sharply at stall, so the present setup can't have a huge effect on the roll axis stability.....??

Jerry Burr
08-01-2005, 06:56 PM
Hi Fobjob. I tried a dam in that spot. Roughly 12 by 28" and it had no effect on the cyclone action at mid chord on top of the wing caused by this mismatch of pressures. I attatched it to my top fence for lack of a better mount. There was no way to make it stiff enough so as to not adversely rub on the end of the aileron without making it very heavy. The aileron problem is caused by the slot at it's leading edge and has nothing to do with the flap. Other than that the flap is creating extra high pressure under the wing. As the high pressure air under the wing is forced up through the aileron slot it goes straight up, destroying what should be a smooth airflow over the leading edge of the aileron. The pressure is higher closer to the wing root so the problem starts at the butt end of the aileron and gets worse or consumes more of the aileron as the AOA increases. You don't notice it because both of them are doing it at the same time, no matter if they are in the up or down position. A -12 aileron is completely different, I believe that's why Piper changed them. My understanding is that someone has already put a -12 false spar on a -18 wing full length. If you are reading this or know of them please join in. :) Jerry.

RPURCELL
08-01-2005, 07:25 PM
Some time back the AOPA magazine had an article on a large banner towing service. The article mentioned their work on modifying Cubs to fly slow. I can't remeber the name anymore. I called the owner and we had a very interesting discusion about all kinds of wing mods. They have about 40 cubs in their fleet. He joked he had a "million hours of cub time" because the company has had so many cubs in the air for so many years. He said they have modified many PA-18s by installing the 12/14 style false spare and adding a piece of aluminum to the leading edge of the PA-18 aileron to match the 12/14 profile. He maintained that it improved roll control at the airspeeds they tow at, which is in the 1.2 to 1.3 range. These airplanes are in the Restricted Category and they have a DER they use for their approvals. He has used Gurney strips inboard of the ailerons on flapless cubs with success as well. He may be on this site for all I know. He was very interesting to talk to and was truely generous with his time.

Crash
08-01-2005, 11:24 PM
PA-18 flap gap seal (metal strip that is standard only in the flap area) run all the way out to the full outboard aileron bay rib and adjusted tight (1/8") to the aileron. Then covered with a 6" wide tape, gives pretty quick aileron response. No need for VG's here for aileron response.

Most of the PA-18's I've looked at have huge gaps between the flaps and the standard gap seal, and even bigger ones in the aileron area. No wonder they have a slow roll rate and turn like dogs. Crash