The Cessna 120-140 Association Forum

Hello,
I hope you are doing well.

AC Configuration
I just bought a C140 with a o-200 & a 69CK-0-48L.
The A/C come with the STD equipment (generator, vacuum pump) & some added equipments (gps, radio comm/nav, intercom), Cleveland brake with wheel extender, small bush wheel.

Issue
The C140 that I bought weight 975 & a 11.59 CG (see attached excel file).
I was looking at the Type Certificate document & the FAA is saying that the Empty Weight C.G. Range should be in the (+12.3) to (+14.7) Item 402 not installed (my configuration.
link: https://rgl.faa.gov/Regulatory_and_Guid ... Rev_35.pdf

Question for FWD CG
I know that the CG has been shifted a little bit more forward but I'm confortable with the current value.
Is it normal the get a more forward CG with the gear extension?
Anybody got similar values with a o-200 or a C90?
Any idea what can be my problem.

Weight Saving
I was thinking to do the following upgrade ONLY if necessary:

• Lightweight starter
  Lightweight Alternator
  EFIS (instead of Vacuum system)
  Gear Extender Removal

I saw this article for the potential weight saving items: https://cessna120140.com/wp-content/upl ... letter.pdf

Any other ideas for weight reduction?

Many thanks for your help.

The empty CG range is, to paraphrase Captain Jack Sparrow, more like guidelines. If your empty CG falls within the specified range and you load the plane according to the limits for gross weight and baggage, it should be impossible to load it outside of the (operating) CG range (+13.5 to +17.7). Or, as the Aircraft specification states, "(w)hen empty weight C.G. falls within the proper range, computation of critical fore and aft C.G. positions is unnecessary."

Since your empty CG is outside the empty CG range, you have to ensure that, for every phase of every flight, you stay within the operating CG range. This is necessary irrespective of what you may be comfortable with.

If you do the calculations, you will probably find that for your plane there is a no-baggage, low fuel, light weight pilot configuration that would put your CG forward of the +13.5" limit.

Adding gear extenders moves the actual CG slightly forward and changes the ground handling, but does not change the allowable operating CG range.

Fair enough John... I'm just not comfortable to fly with a CG outside of the envelope when I'll be low fuel.

I'll re-do the W&B without the wheel extender just by curiosity

Question? Did you actually weight or have aircraft weighed on certified calibrated scales - not bathroom scales? Or, just accept logbook numbers? If not suggest you do that - experience says many, many aircraft not up to date! Seems like aircraft are like humans, tend to put on weight! with age! I once consulted on an aircraft that had been modified with an O-320 conversion with patroller tanks and was being flown with constant excessive back pressure. IIRC calculations said needed 14# lead at tail end of fuselage - the requestor A&P/IA turned the job down. 2c FWIW

maverick_fa wrote: ↑Wed Oct 13, 2021 9:36 pm I'm just not comfortable to fly with a CG outside of the envelope when I'll be low fuel.

OK, which envelope are you referring to? If you're talking about the empty CG, you are never flying empty (no pilot or fuel), so that's not relevant. There is no reason you cannot safely and comfortably fly your plane as it is; you just need to calculate the situations(s) that will put you outside the envelope, and avoid them. As long as your loaded CG is within the limit (not the empty limits) you're ok. If you're outside those limits and the wheels are off the ground, you should be more than just "not comfortable".

You said "the Empty Weight C.G. Range should be in the (+12.3) to (+14.7)." This is a miss-interpretation. It really means "If it is in the (range) then you don't need to worry about performing CG calculations as long as you adhere to the gross weight and baggage limits." Since your empty CG is outside the range, you need to perform calculations for most forward loading and use those values as your limits.

If you currently have extenders, removing them will move the main gear aft and may be enough to put your empty CG back into the range.

All this aside, as Edd said, if you are not working with valid current weights, all bets are off.

I don't suppose your battery is under the cowl, is it?

There are other reasons why you might want to consider removing the extenders. Also, are you sure you don't have the late style gear legs? If you do, the extenders are not approved, and your wheels are actually twice as far forward as originally designed.

Did you actually weight or have aircraft weighed on certified calibrated scales - not bathroom scales? Or, just accept logbook numbers? If not suggest you do that - experience says many, many aircraft not up to date! Seems like aircraft are like humans, tend to put on weight! with age!

I just bought the AC yesterday. I'm still waiting a response of the insurance to pick it up.
I took the data from the official W&B done by a certified A&P (AME in Canada).
The W&B was done after the engine/prop upgrade in 2010.

The only other ''mods'' that was done is new paint on the H-Stab but it wont affect the W&B that much I believe.
I'll do another W&B with a certified scale.

BTW, the guys with the patrol tanks... do you know if he swapped the wing/struts/flaps or they are bolt-on with a STC. I didn't found any information on the internet.

which envelope are you referring to

The ''Flight Envelope''. Probably not the appropriate term.
The graph that we are using for the W&B based on the FAA TCDS & the Cessna W&B sheet.
link: https://cessna120140.com/wp-content/upl ... alance.pdf

-> 13.5 to 17.7 (max 1450)

I'll fly around the airport & probably return to the airport with 5g of fuel & I'm currently on a diet... so my 185 pounds will probably become a 150.
I'll be outside of the tolerance & I really enjoy aerobatic so I'll probably few spins.

"If it is in the (range) then you don't need to worry about performing CG calculations as long as you adhere to the gross weight and baggage limits."

Even with an Empty Weight CG at 12.3 I'll fall too much forward of the tolerance. I need >=12.7 in the worst configuration to be inside to tolerance

I don't suppose your battery is under the cowl, is it?

No. I don't have this STC.

Also, are you sure you don't have the late style gear legs?

I don't know how the look like. For me they look similar to the 150tw that I flew few weeks ago (see attached pictures)

FYI, I'll remove the extender at some point when I'll be more comfortable with the airplane.



It's funny, I saw 1x C120 & 2x C140 since the beginning of the summer & none of them add a proper W&B sheet.
This one is probably the best one.

maverick_fa wrote: ↑Thu Oct 14, 2021 11:01 am I'll fly around the airport & probably return to the airport with 5g of fuel & I'm currently on a diet... so my 185 pounds will probably become a 150.
I'll be outside of the tolerance & I really enjoy aerobatic so I'll probably few spins.

I don't understand what you're saying, unless you're being facetious...

Even with an Empty Weight CG at 12.3 I'll fall too much forward of the tolerance. I need >=12.7 in the worst configuration to be inside to tolerance

That doesn't make sense. Especially if you're heavier than average.

Also, are you sure you don't have the late style gear legs?

I don't know how the look like. For me they look similar to the 150tw that I flew few weeks ago (see attached pictures)

It's sort of hard to explain. If you see the two side by side it's obvious. If you have the "straight leg" gear the centerline of the leg is perpendicular to the bend where the leg exits the gear box. With the swept gear, the centerline angles forward.

FYI, I'll remove the extender at some point when I'll be more comfortable with the airplane.

You might be more comfortable without them now.

Until you have a chance to weigh the plane, throw a box of tools in the baggage compartment.

That doesn't make sense. Especially if you're heavier than average.

I forgot to mentioned that I'm Canadian & we are using the imperial/metric system.

So let say I weight 150 pounds (68kg).
I'll always be out of the forward tolerance unless I'm full fuel. (REF. IMG_1605, IMG_1606)
*This is with the current empty weight CG at 11.69

I'll be always outside of tolerance with 3.5g of fuel (minimum VFR + unusable fuel) unless the empty weight CG is >=12.7 (REF. IMG_1607)

You might be more comfortable without them now.

Question:
On a 2 points landing, it's impossible to do a nose over without the extender even if I put to much forward pressure on the yoke.
The nose over will only happen if I hit a bump or I ride the brake too hard.
This is correct?

Until you have a chance to weigh the plane, throw a box of tools in the baggage compartment.

lol
Yes Sir!

Here is the excel file if you want to play with the value (see below/attached file)

My two cents:

You may have "new" gear legs, that are swept forward 3" plus extenders adding another 3". If the person doing the W&B didn't level the aircraft then measure the setbacks from the leading edge of the wing then the calculations will be all wrong. The C of G is a calculated value that is derived from how much weight is on the 3 wheels and where in relation to the point of reference. The point of reference is arbitrary, it is just a point that the AC designer picked. In this case its the leading edge of the wing. So, I'd suggest you level it using the horizontal overlap that runs the length of the fuselage, hang a plumbob off the wing leading edge and measure to your mains and tail wheel. From this you can calculate the C of G.