What does empty cg tell you?

[Cardiff Kook]

I have only really ever flown my super cub. 1033#, 11.4 empty cg

I have heard light cubs are the best flying cubs which makes sense to me.

In discussions on o320 vs o360 many people say the o360 is nose heavy.

Can you tell if a cub will be nose heavy by the empty cg?

I recently saw a 1000 lbs javron cub with a 200hp o360 and a cato prop. That is a light super cub with a monster engine up front. Is it going to be nose heavy? How much extra weight could that engine possibly add if the whole plane only weighs 1000 lbs?

I guess what I am trying to figure out is what you can tell from the empty cg on a Super Cub weight and balance. Dick Williams in “Stolin with a super cub” said “many experienced cub pilots believe the EW CG should be around 12.25”

 

[skywagon8a]

In another thread I showed you some weight and balance on your plane.

With Ballast

Cardiff Kook's Cub​	​	​	​
​	Weight​	Arm​	Moment​
empty​	1033​	11.4​	11776.2​
Fuel​	216​	24​	5184​
Pilot​	170​	11​	1870​
passenger​	180​	37​	6660​
Baggage​	50​	57​	2850​
tail wheel ballast​	17​	200​	3400​
loaded​	1666​	19.1​	31740.2​

Without Ballast

Cardiff Kook's Cub​	​	​	​
​	Weight​	Arm​	Moment​
empty​	1033​	11.4​	11776.2​
Fuel​	216​	24​	5184​
Pilot​	170​	11​	1870​
passenger​	180​	37​	6660​
Baggage​	50​	57​	2850​
tail wheel ballast​	0​	200​	0​
loaded​	1649​	17.2​	28340.2​

​

​

​

​

No passenger...no ballast

Cardiff Kook's Cub​	​	​	​
​	Weight​	Arm​	Moment​
empty​	1033​	11.4​	11776.2​
Fuel​	216​	24​	5184​
Pilot​	170​	11​	1870​
passenger​	0​	37​	0​
Baggage​	50​	57​	2850​
tail wheel ballast​	0​	200​	0​
loaded​	1469​	14.8​	21680.2​

 

[DENNY]

I have only really ever flown my super cub. 1033#, 11.4 empty cg

I have heard light cubs are the best flying cubs which makes sense to me.

In discussions on o320 vs o360 many people say the o360 is nose heavy.

Can you tell if a cub will be nose heavy by the empty cg?

I recently saw a 1000 lbs javron cub with a 200hp o360 and a cato prop. That is a light super cub with a monster engine up front. Is it going to be nose heavy? How much extra weight could that engine possibly add if the whole plane only weighs 1000 lbs?

I guess what I am trying to figure out is what you can tell from the empty cg on a Super Cub weight and balance. Dick Williams in “Stolin with a super cub” said “many experienced cub pilots believe the EW CG should be around 12.25”

"Best flying" is a is a term that means different things to different pilots. Forward CG gives you more stability, great for when are you are in turbulent winds or long cross country. Also allows you carry more weight aft, think big friends, beer, or week long camping trips. Enables you to recover from a spin quickly. That big HP and prop on the front lets you rip the plane off the ground. That starter lets old men with bad shoulders fly. That big Borer prop lets you go through stuff that would splinter a wood one. Just got done flying 1300 miles around Alaska in 5 days with my wife, lots of fuel, camping gear. Once I adjusted trim it was hands off flying. That is some of the "Best flying" flying I can think of. Every cub seems to fly different. CG is a important part, but it is only one of a lot of different factors effecting how a plane flys and handles. The stick controller is the most important factor.

 

[BC12D-4-85]

Cardiff, I don't recall where your battery is located, and what type it is.

Gary

 

[Farmboy]

I may be off base on this, but I enjoy the performance aspects of an aircraft that has its flying CG right at the middle of the envelope. With the CG near the center of the wing lift, one should get the most performance out of the wing with the least amount of power, effort, and drag.
On a Patrol the sweet spot is about 24% MAC, or chord of the wing.
I don’t know where it would be on a PA18.

ForeFlight has a nice weight and balance feature that allows the user to input weights and arms, and switch over to show the data as percentage. Works well.

Peter

 

[BC12D-4-85]

At an empty weight of 1033 a CG of 11.4 is a little forward of the front limit. If true, I'd wonder if it's accurate? As weight is added (full fuel 216 and pilot 170) it weighs 1419 and has a CG of about 13.3. Again, that's at the forward limit for the PA-18-135. See TCDS 1A2

What's odd is the PA-18-150 has a very different loading schedule that allows for a more forward CG at 1419#. Anybody know why the change of allowable CG range between models?

Gary

 

[supercub83a]

Maybe the PA-18-150 mod added bigger balanced tail feathers and that greater authority allows a wider envelope?! Also interesting is that dakota cub and cubcrafters envelopes are different.

 

[Skywalker]

Tail area and fuselage length combine to get tail volume. My friends' Kolb flies fine at 39% due to a noticeably long tail boom. Now that the factory has recommended shortening the boom by a foot, we are going to dial it back with some nose weight. (it's a pusher). On the other hand I once flew an initial test flight at 25% of a Church Midwing, so nose heavy good thing the engine didn't quit.

 

[BC12D-4-85]

Maybe the PA-18-150 mod added bigger balanced tail feathers and that greater authority allows a wider envelope?! Also interesting is that dakota cub and cubcrafters envelopes are different.

I believe Piper used the same general tail configuration/dimensions for the PA-18-105/125/135/150, mainly when flaps were added. Yes, the early -90's were smaller with less authority.

Piper PA-18 Super Cub Interactive Parts Catalog

This interactive catalog of Piper PA-18 Super Cub airplane parts is available free to use courtesy of Univair Aircraft Corporation, the world's largest manufacturer of vintage aircraft parts and supplies. Printed copies can be purchased from our website or by calling our sales office at...

www.univair.com

See pp. 78-79.

Must be a reason for the revision in load limits. May be related to what tests were used for certification?

Gary

 

[skywagon8a]

I may be off base on this, but I enjoy the performance aspects of an aircraft that has its flying CG right at the middle of the envelope. With the CG near the center of the wing lift, one should get the most performance out of the wing with the least amount of power, effort, and drag.
On a Patrol the sweet spot is about 24% MAC, or chord of the wing.
I don’t know where it would be on a PA18.

Peter

The big difference between the Patrol and the Cub is that the Patrol has a fixed stabilizer with elevator trim tabs, while the Cub has a moveable trimming stabilizer. This affects the drag component. The Patrol would only have a streamlined elevator/stabilizer at one speed/CG combination. The Cub's elevator/stabilizer are streamlined at all trim speeds. With an aft CG on a Cub, the stabilizer becomes more streamlined with the wing while lifting the tail, thus reducing drag and aerodynamic download on the tail. A "flying" stabilator, such as on a Cherokee also is always in a streamlined condition. So, whatever CG and speed combination are more efficient with the Patrol will provide a streamlined minimum drag elevator and stabilizer. Minimum drag elevator and stabilizer are when the elevator trails directly in line with the stabilizer. Any angular difference between the two, increases drag.

 

[Farmboy]

Yup for sure Pete. In addition to that I was referencing if the aircraft needed to hold the nose up or tail up due to the center of lift, or balancing point of the wing while using all the wing to work for you.

 

[Steve Pierce]

I have seen quite a few Super Cubs modified with the battery moved under the front seat go on their nose. Moved a few back to the stock location with a light weight SBS J16 battery and they were happy. If you fly loaded all the time then the forward empty weight CG will serve you well.

 

[Cardiff Kook]

Cardiff, I don't recall where your battery is located, and what type it is.

Gary

Under front seat.
Odyssey SBS J16

 

[Cardiff Kook]

At an empty weight of 1033 a CG of 11.4 is a little forward of the front limit. If true, I'd wonder if it's accurate? As weight is added (full fuel 216 and pilot 170) it weighs 1419 and has a CG of about 13.3. Again, that's at the forward limit for the PA-18-135. See TCDS 1A2

What's odd is the PA-18-150 has a very different loading schedule that allows for a more forward CG at 1419#. Anybody know why the change of allowable CG range between models?

Gary

That is interesting, Gary.

Had to do some digging as my w&b did not have the -135 envelope.

The reason is I have the borer gross weight increase to 1750 STC which changes the envelope to that of the -150.

I am not actually sure what that STC entails- or why it would change the limits but the paperwork says it does.

 

[BC12D-4-85]

In case someone wonders what's involved with the SA292AL GW increase, here's some previous links:

STC TO INCREASE GROSS WT FROM 1500 TO 1700#

CAN ANYONE TELL ME IF THERE IS STC TO INCREASE MY PA18-90 FROM 1500 TO 1700# GROSS WEIGHT? APRECIATE YOUR HELP, THANKS

www.supercub.org

Fuselage difference, PA-18 & PA-18-150

Building a pa18 and want to go from stock 90hp to 160hp. I was told that there are some 3/8 tubed that go in somewhere to make it legal. Can anyone show me a picture of these specifically? I have my 18 & 18-150 fuselages right next to each other and they look the same. Thanks

www.supercub.org

Gary

 

[BC12D-4-85]

Under front seat.
Odyssey SBS J16

Move it to the original location to adjust the CG?

Gary

 

[KevinJ]

Or buy a 5lb earthx in the same position saving weight on the shorter cable run.

 

[Dlthig]

902 EW, 15.6 CG on L-18C/PA18-95. 1500 gross. Basically middle of the envelope. No electrical system.

 

[rsrguy3]

Fantastic subject. Im working a project right now in which the original airframe flew extremely sweet according to my friend and his ia... it was "just a cover job" now it's a 3/4 resto with a swapped fuse with ak mods... which is heavier than stock. So my prime objective is to make sure I come in under the original weight with similar or better w&b.
Between oratex, earth x, original style glazing (the frame is set up for a green house) delete on the skylight, fabric interior and a shunt rear panel on the extended baggage.... instead of fully floored and aluminum side walled setup. We should come in under his original wb.... fingers crossed.

 

[Cardiff Kook]

Move it to the original location to adjust the CG?

Gary

Where is the origninal position. Ive owned one cub

 

[Mr. Ed]

What would you high time PA18 folks say is an ideal tail weight when lightly loaded, you and fuel, CG close to the forward limit?

 

[BC12D-4-85]

Where is the origninal position. Ive owned one cub

Piper PA-18 Super Cub Interactive Parts Catalog

This interactive catalog of Piper PA-18 Super Cub airplane parts is available free to use courtesy of Univair Aircraft Corporation, the world's largest manufacturer of vintage aircraft parts and supplies. Printed copies can be purchased from our website or by calling our sales office at...

www.univair.com

See page 125. It's behind and above the rear header tank on a platform.

Gary