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Move the wing for better CG?

Little_Cub

Little_Cub

MEMBER
Palmer, Alaska
Always thinkin' about that 'next one'.

Couldn't find anything on moving the wing.. sooo

Lotsa folks have issues with the CG of a hi-HP Cub and patches for this have been shortening the mount, shortening the firewall,
moving the battery and even lengthening the tail.

Anyone taken the effort to move the wing? It seems like it would help on both ends and might require far less
movement to afford the same result.

Thoughts? Calculations? Guesses all welcome!
 
great idea,

the original cub, had a certain wing location that matched the weight of engine and extra junk...

so as we add more junk and bigger engine, that ratio get out of wack, and we have to compensate with elevator/stab.. engine mount angle...

much better to get back to a proper wing location...
 
Feeling dumb here - - - how is moving the wing different than moving the other stuff - engine, tail, etc?
 
Gordon Misch said:
Feeling dumb here - - - how is moving the wing different than moving the other stuff - engine, tail, etc?
Click to expand...

not sure if i can express this clearly, it's late.. beer... I've been singing...

kinda a static or dynamic thing?

if the plane flies well, power off, or prop stopped.... its balanced....

but if not balanced, it needs (engine/or stab/elevator) power/input to fly ok, to make up for that imbalance in load/CG...
 
I thought I heard somebody singing :lol:

if the plane flies well, power off, or prop stopped.... its balanced....
Click to expand...
Agreed. But given that, the positions of all the components of an airplane seem entirely relative to me. In other words, for example, moving the wing back would be the same as moving the tail forward and moving the engine forward.
 
Moving the wing would limit the CG envelope. The extended airframe works better for carrying stuff. I guess it depends on what you want your airplane to do.
 
In my design and build I am now pretty well lock down on what the build is, as in power and overall fuselage geometry. The wing has a few more calculations till I am rally happy with it. I have set the incidence which is less than what most Cub guys would build in since my cruse speed is higher and I am letting the monsters double slot flaps take care of the slow speed needs. So my last big design need is setting the fore-aft location of the wing over the fuselage. I expect to have my answer to this in a few months at which time I will then lock it in the metal.
So for me, yes I am considering just how the plane will hang under the wing.
Frank, with your mission I expect this would be very important. Your needs are ultimate importance at a very low speed with minimal weight, you would need to take the pitch moment with flaps and slats extended and get the plane to hang with minimal trim at extremely low speed such as no trim at 30 where my plane is being optimized for no trim at 120 with twice the weight.
FWIW I calculate the wing on most Cub design was optimized for 70 mph @ about 1200#. Obviously Cub designs have varied substantially but I have not seen changes to wing location to optimize for said changes.
 
stewartb said:
Moving the wing would limit the CG envelope. The extended airframe works better for carrying stuff. I guess it depends on what you want your airplane to do.
Click to expand...

Moving the wing will allow for carrying more weight aft in the plane. Our limit of what can be carried is keeping within the CG range of the wing. If you move the wing aft so the light CG is at the forward limit, then you can carry more weight in the aft of the fuselage.
Notice I do not state empty CG since we do not fly an empty airplane.
 
Moving the wing to help with forward/back CG can be done but now you have to deal with the strut attachment/strut length/fuselage cluster/door/window/wind screen. Putting the fuel tank in the tail will do the job, but what happens when you use it. Fly from raised back seat with bubble top for head. This would be pretty simple and kind of how piper did it.
DENNY
 
I assumed Frank was thinking of moving the wing aft to center his CG with minimum loads to benefit STOL performance. For most planes I've flown the light fuel load/single pilot CG is at or near the forward limit. Sometimes I have to put weight in back to achieve that. Since virtually everything I consider useful load moves the CG aft? I want to keep the empty CG forward. If aft CG becomes a threat the practical solution is a belly pod for heavy stuff and lighter stuff goes into the aft baggage.
 
I think he is nose heavy. You could just extend the topdeck forward a few inches, move and gusset wing fittings, maybe move a cross tube or two. Struts would angle forward a bit, might have clearance issue with bottom of rear strut, change to taylorcraft attachment at the bottom? Still dark and wet out I will keep thinking.
DENNY
 
Reduce the wing angle of incidence, and you reduce the pitching moment, resulting in a nose-up condition. At full forward CG, the stab should be slightly lower in it's slot, and the elevator deflected slightly up. When my wing was mounted at zero degrees incidence, (and washout correct) the pitch trim was halfway to the full nose-down position, and the elevator down at a noticeable angle. Other than the vicious spin (seven turns minimum recovery) that resulted from a stall, it still flew pretty good!

*only tried to kill me once.....
 
Seems like I recall reading up on airframe design,
it mentioned establishing the CG at xx% of MAC (mean aerodynamic chord)?
Whether you do that by manipulating location of engine battery seats etc in/on the fuselage,
or by moving the wing fore-or-aft on the fuselage,
should be a matter of which is easier or more convenient.
 
you could actually do this as a bolt on mod, as far as moving wings forward or backwards..

strut at bottom will swivel, would need an adaptor/extender at top of lift strut to fix angles....

cable routing issues? add pulley and extend?
 
ee5cddfc85978ba3c4013fc3681c9f5c.jpg



Sent from my iPhone using SuperCub.Org mobile app
 
hey, you could even make that bolt on thing slide for and aft so you could play with it....(in flight? or ground...??)
 
Frank have you ever thought about a way to change the wing incidence in-flight like the F-8 Crusader? Lift benefits or just a change the deck angle during take-off or landing. A higher aspect ratio wing giving more lift at slower speeds may the only way to go as you've probably maxed everything one can get out of a Cub wing.



Sent from my iPhone using SuperCub.Org
 
wldwzl01 said:
Frank have you ever thought about a way to change the wing incidence in-flight like the F-8 Crusader? Lift benefits or just a change the deck angle during take-off or landing. A higher aspect ratio wing giving more lift at slower speeds may the only way to go as you've probably maxed everything one can get out of a Cub wing.



Sent from my iPhone using SuperCub.Org
Click to expand...

there is an old thread on that on here somewhere... i describe how to do it, how to deal with the strut length issue...
 
mike mcs repair said:
hey, you could even make that bolt on thing slide for and aft so you could play with it....(in flight? or ground...??)
Click to expand...

There are many ways to tweak things and we've tried a few.. tail weights, moving the firewall, fanny tank and even a tail tank. Our plane weighs 800+ pounds empty, with the firewall back 5" we still had nearly 20# at the tail post last year in Valdez. Unless it was adjustable like Mike suggests it will just need to negate the engine moment and rely on a chunk of tail weight for those STOL days.. without adjust-ability (added weight) it just won't fit all occasions perfectly. The effort here is to keep the original Cub balance without feeling trapped in a nose heavy machine or being cramped behind a modified rudder pedal location.
On a fresh build moving the wing attach and even the lower fittings isn't that big a deal, we all like the HP but flying a C-90 frame with a 0-360 doesn't allow all fun to get out!
1- How important is it for the center of lift to be behind the CG window? (stability?)
2- Is it true moving the wing forward does a couple 'relative' things..
a. Moves the center of lift forward
b. Moves the relative CG back.

More yammer please! :)
 
Both a&b are the result.
How much does your trim change with the flaps deployed?
Can the plane settle down hands off with full flaps? I would expect that would be a goal allowing you the most sensitivity for slow approaches.

I expect the wing will only need to move an inch or two but I have not run any numbers I may be well off on that.
 
and the weight would run on a heavier cable, the little cable is just to move it, like on a mining ore tram setup..
 
Has anyone ever flown their empty cub in competion from the back seat? Usually empty cubs with 1 person in front are pretty forward cg. Maybe longer to get tailwheel off, but you could hank harder on the brakes for landing..... just thinking... my Scub is single controls, so I can't try it.
 
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