rigging Cub wings

[Gordon Misch]

Agreed Pete. Yes, I'm aware of the stall scenario, but I also know that Bob Turner reported his Decathalon has zero washout and "stalls just fine". Certainly other means can be used to help out the ailerons near the stall - maybe VGs, maybe inboard stall strips, etc. That's why I'm soliciting experience (not necessarily just opinions) Thanks - -

[skywagon8a]

Bob's Decathalon is aerobatic so has different requirements. Thus should not be used as an example in your application.

[BC12D-4-85]

Besides having done it that way (the 2.5* washout) since the 1930's, is there some performance requirement via CAR 4a (J-3; see Sec. 04.7 for performance requirements) then later CAR 3 (PA-18; also see Sec. 3.81 on) that determined that value? Or was it just done and left alone? I prefer 1* on Cub and Taylorcraft but my Champs have been flat by factory design.

Gary

Edit: There's also wing heaviness - elevator and trim deflection/drag to adjust for and wash has an effect. Edit: Meant nose or tail heaviness as affected by washout which affects lift from both wings.

[Gordon Misch]

Couldn't really find much in CAR 3. Speaking of wing heaviness, I assume you're referring to differential wing wash, rather than nominal.

[BC12D-4-85]

Couldn't really find much in CAR 3. Speaking of wing heaviness, I assume you're referring to differential wing wash, rather than nominal.

CAR 4 and 3 list performance requirements. How wash affected the results during certification is a question that may never get answered - I don't have an answer - but I assume it's related to meeting those requirements or at least being benign enough to permit design acceptance.

By heaviness I meant the relationship between wing wash and resulting overall wing lift versus the requirement for down force on the tail in all flight regimes for desired flight. I guess nominal applies if that means close to equal wash for both wings rather than one wing heaviness versus the other. Down force required on the tail has consequences. Edit: nose versus tail heaviness is a better term in this case. My winter Solstice fumbling.

Wing devices change the behavior and washout may be less of a concern unless personal testing proves otherwise.

Gary

[AkPA/18]

Gordon I really don't mean to hijack This Thread into another Direction. I just glanced through all the posts on this thread and wanted to comment on the washout portion. The goal is not to have identical twist in each wing. The goal whether using a digital level or a bubble level is to have the same angle at one aileron Bay rib as the opposite side.

[Gordon Misch]

Gordon I really don't mean to hijack This Thread into another Direction. I just glanced through all the posts on this thread and wanted to comment on the washout portion. The goal is not to have identical twist in each wing. The goal whether using a digital level or a bubble level is to have the same angle at one aileron Bay rib as the opposite side.

Well, sorta, I think. Let's assume that the incidence at the fuselage fittings differs between the two sides. Then, if the wing tips are at the same angle in reference to something, say the Horiz Ref Line, the wing roots will differ, and lift will differ because the average incidence across the span will differ. Same result if the wings each have the same twist.

If the fuselage is "right", then either approach will yield the same, and proper, result. Piper's Service Memo is consistent with what you're saying.

Please correct me if you think I'm wrong or missing something here.

This is a new, jig-built fuselage by Steve Furjesi, and I'll bet that the wing incidence is very close to identical on each side. Probably worth double-checking though.

Thanks for your input!

[Gordon Misch]

Good stuff so far; thanks and please keep it up. Back to my original question - I know how to rig the wings to a given spec. What I don't know is what the preferred washout spec is among those who have flown different than the factory spec, and why.

[AkPA/18]

It can be confusing Gordon and I wish I could explain stuff better in text. I will try with an extreme example. Suppose you have a fuselage with an 18 angle of incidence on one side and a 12 angle of incidence on the other side. If you put in the same wash on each wing no way will the aircraft Fly level. The 18 side will have considerably more lift than the 12 side. If you match the wing tips there will be considerably more wash taking away lift on the 18 side. This will give you a chance for the airplane to Fly level. That is all they are doing in the original Piper rigging instruction. They completely disregarded angle of incidence and Wing wash in the instructions and went right to matching the tips. I rarely come across an airplane with an identical angle of incidence on each side. This is probably confusing also but the best I've got at the moment. while the wash you have on your Cub is very important to know, if you match the tips you have a very good chance of a level flying cub.

[BC12D-4-85]

2nd hand personal comment to me from an experienced pilot that flew at altitude and lots on skis...flatter wing = less "mush" and uncertainty on takeoff and landing. He wanted lift that could be expected and depended upon when needed. Cruise speed was not a concern. Stock PA-18 wings and engine with factory flat prop.

Gary

[BC12D-4-85]

"...I'm looking for some guidance on an EAB -12 build I'm working on...I'd like to learn what the consensus might be for the "best" washout setting..."

Gordon it's your turn. What's your design goal(s) for the new plane? That might help with any replies.

Gary

[Gordon Misch]

It can be confusing Gordon and I wish I could explain stuff better in text. I will try with an extreme example. Suppose you have a fuselage with an 18 angle of incidence on one side and a 12 angle of incidence on the other side. If you put in the same wash on each wing no way will the aircraft Fly level. The 18 side will have considerably more lift than the 12 side. If you match the wing tips there will be considerably more wash taking away lift on the 18 side. This will give you a chance for the airplane to Fly level. That is all they are doing in the original Piper rigging instruction. They completely disregarded angle of incidence and Wing wash in the instructions and went right to matching the tips. I rarely come across an airplane with an identical angle of incidence on each side. This is probably confusing also but the best I've got at the moment. while the wash you have on your Cub is very important to know, if you match the tips you have a very good chance of a level flying cub.

That makes perfect sense. Thank you.

[Gordon Misch]

Gordon it's your turn. What's your design goal(s) for the new plane? That might help with any replies.

Good question - This plane will spend time on floats as well as wheels. Likely more on floats. So we're thinking that with reduced washout it might come off the water (and ground) a little quicker and with a little more authority, and maybe even cruise slightly faster and more nose-down. Naturally we wonder if slow flight stability could be adversely affected. It will have Dakota squared off wings, with extended flaps. No slots. There's no intent for the crazy-short gravel bar stuff, however high density altitude strips (Idaho, Utah, etc) would be in the picture. The plane will have increased gross weight, probably 2200.

Thanks for asking, and lemme know if this doesn't answer.

[BC12D-4-85]

That's a good plan Gordon. I guess once built you'll have an opportunity to experiment with washout versus tail control effectiveness and trim over the range of airspeeds and CG.

Edit: Also consider having adjustment for the rear strut length on floats for tuning to the fuselage. Depending on strut type and fitting block size there's potentially room for change (http://www.stoneylake.org/pipcom/frey.htm). Atlee's rear fittings with a solid cross drilled strut to fitting interblock allow for variable length. Straps can change rear wire length.

Edit: Will you have an option for building a partial slot into the Dakota Cub wing? I'm thinking Stinson-like in front of the aileron and then a flatter wing would have less loss of aileron in a stall.

Here's the plot of Cl, L/D, and Cd to play with. Varying washout might be a good tool to fine tune the performance.

[RVBottomly]

It will have Dakota squared off wings, with extended flaps. No slots.

I can't remember where I read it, but I remember a discussion that squared-off wings don't really need washout. Something about diagonal flow across the trailing edge.

[RVBottomly]

Found one place discussing rectangular wings not needing washout:

https://aviation.stackexchange.com/q...st-at-the-root

[BC12D-4-85]

A SUPERCUB Classic: https://www.supercub.org/forum/showt...s-wing-washout

[BC12D-4-85]

Here's a great read about aerodynamics. See pages 61 on for planform effects and 79-80 for pics of tufted rectangular wings during a stall. I keep one in the airplane shelf.

Naval Aviators. https://www.faa.gov/regulations_poli.../00-80t-80.pdf

Same here referenced above: https://ntrs.nasa.gov/archive/nasa/c...9930083818.pdf

The airfoil used is a symmetric NACA 0012 section, or a 23012 like Taylorcraft, Caravan, Beech w/o the drooped leading edge. A Cub wing may differ.

Gary

[mydoghasa170]

One of the Cubs I get to fly on a very regular basis was bought with the wings rigged the way piper wanted them rigged. The previous owners were that kind of crowd.

When we got a hold of it, we thought it was under powered, lacked fuel, or something to that effect. It took at least 2500 rpm (at sea level) to get the tail up in flight. Less than that, and it always felt like it was off step, behind the curve, and dogged. We thought we had a lemon.

Turns out we’d never flown a cub rigged the piper way, only the Alaska way. Took left and right rear struts in two turns and WHAMMO! new cub. Flies like the rest of them now. I surmise that because the entire wing is has a little more AOA in flight, it takes less power (airspeed) to get the required lift. (The ol’ lift equation comes in handy to explain that one).

Now it’s true that nothing is free. When/if a stall occurs, the wing falls off all at once. Properly acknowledged, this is not a major threat in my opinion, though it might be for others.

Short story is I much prefer no washout for the type of operations we do.


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[TurboBeaver]

Gordon,
When the Maine Warden Service first bought PA 12 in 1948 with no flaps and
0235 engines, as a floatplane on Edo 2000s to say they were a dog was an under statement.........
Retired Chief Pilot Andy Stinson told me that their mechanic 'Howard Lambertson'
quickly realized they needed more lift to get off the water loaded on hot days.
He got around it by drooping the ailerons 1"
down and reducing the washout from 2.5 degrees to .5 degrees. Andy told me it made all difference in the world on hot days.
Lambertson' was the man that did the original 'flap conversation' on PA 12s done
with Piper parts for the PA 14. Which puts
the flap handle on the right side of the seat.
He was also responsible for getting the 0290 engine approval first on a PA 12 creating a much better airplane. We all know these conversations today as the
"Marden Airways" mods on PA 12s.
For ever what it's worth that is how the "old timers" rigged em back in the day........
Good luck
E

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[BC12D-4-85]

With a reduced washout and added aileron droop some without rudder training might expect an instant flat spin and DOA. Lift vs factory rigging for numbs.

Gary

[TurboBeaver]

Lol.
Well Gary that is an interesting response.
However if we start down that road far enough, I guess we could all just take the rudder pedals out of our Cubs, compleately,
Rig them up like an Ercoupe and just steer them around???? Or maybe just rig them with 3/4 degrees of wash out to make darn sure the tips stall First ???? I appreciate the fact that lots of pilots do not use their rudders enough for truely coordinate flight.
But suggesting take a couple of turns on the rear struts would make a Cub whip over onto it's back and enter a "flat spin" does sound a bit of a streach in mho.
Best thing to do here is rig em by the "book" and that way you will be safe. I was only posting a tried and true way the Warden Service here; got some extra performance out of the early under powered Cruisers.
Take care
E

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[BC12D-4-85]

Yes it's best to follow factory specs.

Gary

[astjp2]

Old thread, that I'd like to revive tangentially. First, I've been doing a lot of reading of "official" stuff, and can confirm that the washout as specified by Piper is 2-1/2 deg, as Perry correctly explained in #9 and #21. Piper's specified washout angle is independent of the incidence angle, and is the same for PA-12 and PA-18. The approved alternate means of leveling (AC-43-16 beginning page 10 here https://www.faa.gov/aircraft/safety/...7_08_Alert.pdf) in pitch is floorboard between gear fittings. In roll it's the member that supports the front edge of the rear seat. Piper's rigging instructions begin with leveling the airplane, however with digital level that can be bypassed for washout. Just set the twist in the wing to 2-1/2 deg for Piper spec.

The above being settled fact, now my question - -

In other prior threads, there seems to be a preference for setting washout less than the Piper spec. Perhaps on the order of 1 deg. Some folks are advocating zero washout. I'm looking for some guidance on an EAB -12 build I'm working on.

Those of you with experience flying planes with washouts less than Piper's, what is your reaction? Do you experience a stall and/or cruise speed difference? Do you experience a difference in slow-flight stability? Do you experience any adverse stall characteristics? Do you experience any takeoff or landing performance differences? Anything else?

I'd like to learn what the consensus might be for the "best" washout setting.

Thanks!

I know of one of "those guy's" who set the washout and dihedral in a Tri-Pacer to about "0" and it killed 4 people. 4th of july weekend in 98, airplane was heavy, hot day and not climbing, tower asked the pilot if he wanted to come back to the airport. The airplane was able to fly straight and even if it was not climbing the terrain was descending so he could have kept going straight and still gain ground clearance. Pilot decides to return to the airport, airplane stall & spins into a tree and burns. I feel to this day that they may have had a chance if the dihedral and washout was set to book specs. That airplane was known for a nasty stall with a tendency to drop a wing with the non spec rigging. The guy who did the rigging bragged on how much faster it was, if you want to go fast, get an RV or a bonanza, or even a husky...

I have almost stalled and spun into a mountain in Alaska just east of the Richardson Highway, if I would have messed with the washout, the airplane stall characteristics would have not allowed me to recover in time. Gilbert Taylor did a good job engineering these airplanes and their flight envelopes reflect it so I am a believer in book specs. Tim

[BC12D-4-85]

Unexpected upset and resulting spins were a mystery yet common when CG Taylor started in the aviation industry. Rudders on some were often an afterthought both in design and use in initial training. Later flight testing identified various parameters for early aircraft: https://ntrs.nasa.gov/archive/nasa/c...9930082385.pdf Plane #3 is a J-3 and #5 a Taylorcraft. Read the results.

VG's can modify the behavior, especially for a Taylorcraft with the potential for an aft LE flow discontinuity and asymmetric wing stall. Fortunately the rudders on both are effective.

Gary

[astjp2]

Unexpected upset and resulting spins were a mystery yet common when CG Taylor started in the aviation industry. Rudders on some were often an afterthought both in design and use in initial training. Later flight testing identified various parameters for early aircraft: https://ntrs.nasa.gov/archive/nasa/c...9930082385.pdf Plane #3 is a J-3 and #5 a Taylorcraft. Read the results.

VG's can modify the behavior, especially for a Taylorcraft with the potential for an aft LE flow discontinuity and asymmetric wing stall. Fortunately the rudders on both are effective.

Gary

Gary, you read way too much dry crap...Dr. Tim

[BC12D-4-85]

I suggest one test after rigging. In addition to the normal post-build flight involving stalls and other maneuvers, try several extended takeoffs at minimum power. I've found that if one wing is prone to more lift than the other it'll be the first to leave Earth. Quick high power acceleration and prop flow can mask that differential lift effect. It can sometimes be revisited during coordinated stalls with the light wing letting go first with the ailerons neutral. Adjust the wing rigging for uniform lift and stall if possible, and ensure the T&B ball is centered in hands off flight during cruise. Vertical stabilizer offset is our friend.

Gary

[Altmuehltaler]

Hello. I have a question on rigging a PA-18, too. I place it here to not open a new thread so everything is in one place. If I may.
Here is the question: I know SB 910A (Service Memo 19). I would first hang the wings on the leveled fuselage. Then mount the front struts and adjust dihedral. Having done that I would mount the rear struts and adjust wash out. Last step would be mounting the jury struts. Is that correct so far?
I think the main struts might bow slightly without jury struts. So I would mount the jury struts taking care not to alter the bowing of the main struts. Is that correct, too?
Thank you so much! Bjorn

[skywagon8a]

Hello. I have a question on rigging a PA-18, too. I place it here to not open a new thread so everything is in one place. If I may.
Here is the question: I know SB 910A (Service Memo 19). I would first hang the wings on the leveled fuselage. Then mount the front struts and adjust dihedral. Having done that I would mount the rear struts and adjust wash out. Last step would be mounting the jury struts. Is that correct so far? YES
I think the main struts might bow slightly without jury struts. So I would mount the jury struts taking care not to alter the bowing of the main struts. Is that correct, too? NO
Thank you so much! Bjorn

The main struts must be straight. The jury struts are there just to stabilize and prevent the main struts from bowing. They carry no wing loads.

[mike mcs repair]

The main struts must be straight. The jury struts are there just to stabilize and prevent the main struts from bowing. They carry no wing loads.

I wouldn’t say no load. They are very important


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[skywagon8a]

I wouldn’t say no load. They are very important

Yes they are important. Their job is to keep the main struts stiff and straight. They do not carry flight or landing loads.

[mike mcs repair]

Yes they are important. Their job is to keep the main struts stiff and straight. They do not carry flight or landing loads.

they keep the wings from flexing.... using strut in flight as support

go to an uncovered wing hanging on plane with and without rear jury strut and flex at wing tip... huge difference....

[Altmuehltaler]

Thank you for the answers.
Today I removed the jury struts and I have the feeling that the main struts bow slightly without them. I had nothing at the hangar to check it so I might be wrong.
If I my impression doesn't fool me I think I need a gadget to prevent bowing of the main struts while rigging... Or is the bowing without jury struts neglectable?

[AkPA/18]

Thank you for the answers.
Today I removed the jury struts and I have the feeling that the main struts bow slightly without them. I had nothing at the hangar to check it so I might be wrong.
If I my impression doesn't fool me I think I need a gadget to prevent bowing of the main struts while rigging... Or is the bowing without jury struts neglectable?

I don't worry about it. Seems like not a big deal for initial rigging. I have not run into a problem and I rig dihedral first with just the front struts pinned. Good luck.

[mike mcs repair]

T-craft wash out is made by adjusting jury strut length, hence bowing main liftstruts/wing spars...


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[ak49flyer]

T-craft rear strut has adjustable threaded insert at top end- never heard of adjusting jury struts to change washout...

[BC12D-4-85]

My 1941 Taylorcraft has adjustable length jury struts both front and rear. Threaded adjustable fittings at spar bottom/upper jury strut connection. Use them to straighten main struts after rigging. If the mains bend some and are bothered then temporarily tie a piece of tubing, angle, or wood lengthwise to offer support. The potential change in length slightly bowed versus supported and straight is inconsequential for me. Cub jury fittings can be slid up or down the main struts slightly to correct for bowing.

Gary

[Crash, Jr.]

T-craft rear strut has adjustable threaded insert at top end- never heard of adjusting jury struts to change washout...

Yeah, I've never heard of washout being adjusted with jury struts. The rear lift strut has an adjustable barrel for washout.

I can definitely believe they were to adjust for straightening main struts. I though Maule's tolerances on welded parts was bad until I started selling Tcrate struts. Anywhere from 0 to 8 degrees of angle on the rear strut wing attachment. Struts have to be fitted to the individual wing and how it's built. Wouldn't surprise me if the same was true for jury struts.

[skywagon8a]

they keep the wings from flexing.... using strut in flight as support

go to an uncovered wing hanging on plane with and without rear jury strut and flex at wing tip... huge difference....

They are for flutter prevention of both the wing and the long strut. The main struts need to be straight for structural purposes. Granted a small bow may not make much difference, but it is not correct.

[Altmuehltaler]

Successfully rigged. Thank you!