Empty CofG

[BIGK]

Need some help with a C of G Issue please. I have just weighed my BC12-D which resulted in the empty CofG coming out at 19.87 inches aft of rear limit. This is 2 inches behind the aft limit. I would need to shave 15 lbs off the tail or add 60lbs to the firewall. A65 with wood prop. No wheel pants. No headliner.

Using Intercomp digital scales, 3 reading
Datum- Leading edge of wing, Level- Horizontal stabiliser
Weighing figures are. Tail wheel 69lbs at 197.75in, R Mainwheel 355lbs at 2.75in, L Mainwheel 362 at 2.75 in.

I must be missing a really obvious mistake but I cannot see it.

Any ideas?

[N96337]

Re: Empty CofG

Do a loaded check and see how it comes out. The TC will say that if it falls in the empty weight range, you don't have to compute the aft loading or forward loading... see what it looks like when you do the computations. You've got full oil and drained all useable fuel in level flight attitude? Brakes off, and tare weight of the chocks taken out? Measured with a plumb bob hanging off the leading edge?
JH

[lfries]

Re: Empty CofG

You mean datum. Remember your going to have fuel in the header tank which is 72 lbs of fuel and 1 gal of oil which is 7.5 lbs. I believe your number means that you need to do a wt and balance for each passenger/baggage fuel load variation. I cant remember the empty cg numbers that as long as you don't exceed the gross weight you don't need to do a calculation. I have a wood prop and I check the CG each time I fly with a different load.

[3Dreaming]

Re: Empty CofG

First off your measurements are off from what the type certificate calls out. They call the mains at 2" not 2.75". The tailwheel is 193 per the TC instead of your 197.75. That being said I would use the 2" figure, but re-measure the tailwheel distance. Even using the TC distances I came up with 18.77, which is still aft of the EW CG range. Really though the fact that it doesn't fall within the EW CG range just means you need to figure the critical fore and aft CG limits for loading. As long as you are within limits when the airplane is loaded and remains so during flight you will be OK.

With my numbers if you are loaded with 3 gallons of fuel and 396 pounds of people you are still within flight CG limits by .25".

[Hank Jarrett]

Re: Empty CofG

MEASURE all of the distances! Do not trust the TC for the location of the mains or the tail wheel! Minor differences in measurements will change the calculations. There are also two ways to calculate CG WRT the oil. The old system calculated empty weight with NO OIL. The newer method assumes there are 4 quarts. Be sure you know which you are referencing to!

I did mine both ways and also removed a huge mass of unused wires from the tail and a VOR antenna from the fin (interesting since the plane never had a VOR, I guess they used it to dry their T-shirts at hot fly-ins). When I bought the plane the W&B was IDENTICAL to the one in the Taylorcraft literature. Same weight and CG as the factory prototype. Again, with a pile of W&B sheets of different ages, the EW never changed an ounce and the CG never moved a fraction of an inch. Think there was a bit of pencil whipping involved? DON'T TRUST SOMEONE ELSE'S W&B! If there is any doubt, do it again. KNOW THE CONFIGURATION you are calculating from such as if items like headsets, hand held radios, spare batteries, fire extinguishes and first aid kits are on board. Also make absolutely sure how much fuel is aboard! I did one W&B where the owner was CERTAIN the tanks were empty and one wing tank was full. Waste of time and potentially dangerous situation if it hadn't been caught.

When I did mine I leveled the plane using the horizontal stab and the cross tube behind the seat (you are supposed to level BOTH ways). Level the plane ON THE SCALES. Sliding a scale under a tire will change the level.
Drop a plumb line from the leading edge of the wing (use BOTH SIDES about mid span each side and snap a line between them).
Drop a plumb from rudder/hinge line and the CL of the firewall and snap another line. Where they cross is the datum point (is it perpendicular to the CL?).
Drop plumbs from the center of the axle nuts to the ground and connect them with a snap line. This is the location of the mains. Is that line perpendicular to the fuselage center line? I have seen planes where it wasn't! Makes CG calculations a bit more complex, as well as explaining some funky ground handling that should be addressed.
Drop another plumb from the axle nut on the tail wheel and connect the point with a line perpendicular to the CL (the distance is so short here a slight error won't matter but DO BE SURE the tail wheel is straight!)
If the marks are on the floor you don't actually need to snap lines until the plane is moved off the scales....in case you were wondering how to snap lines through the scales and tires. ;-)
Use the weights from the scales and distances from the marks on the floor, NOT THE DISTANCES FROM THE TC to calculate CG!!!!!

Hank

[Guest]

Re: Empty CofG

Need some help with a C of G Issue please. I have just weighed my BC12-D which resulted in the empty CofG coming out at 19.87 inches aft of rear limit. This is 2 inches behind the aft limit. I would need to shave 15 lbs off the tail or add 60lbs to the firewall. A65 with wood prop. No wheel pants. No headliner.

Using Intercomp digital scales, 3 reading
Datum- Leading edge of wing, Level- Horizontal stabiliser
Weighing figures are. Tail wheel 69lbs at 197.75in, R Mainwheel 355lbs at 2.75in, L Mainwheel 362 at 2.75 in.

I must be missing a really obvious mistake but I cannot see it.

Any ideas?

I am an Idiot I hosed up the calc, removing the post, Dave

[PA1195]

Re: Empty CofG

Rather than add useless weight forward install a metal prop...approximately 21# @-46 (+11# over wood). Edit: Run the numbers and see if it helps first.

Is your tail spring correct and not something made for another aircraft?...like heavier and longer? Your tail is heavier than mine (it's 47#) with a Taylorcraft spring and Scott 3200 tail wheel assembly. Datum to tail wheel is similar.

The 4" longer motor mount moves the weight and CG forward.

Gary

[Hank Jarrett]

Re: Empty CofG

Is there ANYONE here who hasn't screwed up a W&B calculation sometime in their life? That is why you do it twice and check the numbers and measurements. It is VERY easy to mess up on!!! Certainly doesn't make someone an idiot!

Hank

I am an Idiot I hosed up the calc, removing the post, Dave

[BIGK]

Re: Empty CofG

Pilot 23" aft
Baggage 40" aft
Is this correcy for loading figures?

[Guest]

Re: Empty CofG

BIGK and all,

The reason that the TCDS says 193" for the tailwheel and we figure something like 198" is because they are two different arms.

The TCDS is telling us that the distance to the center of mass of the tail wheel is 193". That makes sense because the center of mass will be slightly forward of the tail wheel's axle. In other words the center of mass is not located at the axle location.

When we measure to the point of contact on the tail scale we measure to the axle location, a few inches aft of the tail wheel center of mass and get ~198".

In the case of the main wheels (round and center of mass corresponds to the axle location) so if we use the arm for wheels from the TCDS it corresponds (when unmodified or undamaged) to the scale load point.

That's my story and I am sticking to it.

BIGK, I have similar W&B issues as you do. I did an aft loaded CG check and made loading schedules using Microsoft Excel. If you want a copy of that Excel spreadsheet file to modify for yours send me you email address.

Thanks Hank for the kind words.

Dave

[BIGK]

Re: Empty CofG

Thanks Dave. I have set up a spreadsheet myself thanks. I have run several computations with different load patterns. I am starting with a tail heavy figure therefore it will never come back in because all major loading (except fuel) are aft of datum. The cofg figure will only get worse.
Do you ever get a loaded cofg within the specified limits? What are other BC12-D flying with? Are they all in the 19/20 aft region?

I have to submit a cofg figure for a test flight but my authority will never accept a figure outside of the limits. I have already been there with a chipmunk. I just don't understand why it is so far out. There is no wiring or structure to remove from the tail area to lighten by 15lbs as needed.

[Robert Lees]

Re: Empty CofG

Thanks Dave. I have set up a spreadsheet myself thanks. I have run several computations with different load patterns. I am starting with a tail heavy figure therefore it will never come back in because all major loading (except fuel) are aft of datum. The cofg figure will only get worse.
Do you ever get a loaded cofg within the specified limits? What are other BC12-D flying with? Are they all in the 19/20 aft region?

I have to submit a cofg figure for a test flight but my authority will never accept a figure outside of the limits. I have already been there with a chipmunk. I just don't understand why it is so far out. There is no wiring or structure to remove from the tail area to lighten by 15lbs as needed.

It's your EMPTY WEIGHT cg that is out, not your ACTUAL cg. I think that's what Dave et al have been saying. The EMPTY WEIGHT cg is not relevant if you do a computation for every single flight that you do, according to the TCDS (as I understand it).

The advantage of getting the EMPTY WEIGHT cg position between 14.8" and 17.9" aft of datum is that you don't need to do a cg position calculation every time you fly, as long as the weight does not exceed 1200lbs.

For reference, most other UK Taylorcraft BC12D tailweights are between 63 and 85 lbs. My only thought is that your horizontal datum is wrong (is there accident damage in the books, that might cause the tailplane to be in the wrong plane?)

Feel free to come up to Leicester one day; we'll compare notes

Rob

[Guest]

Re: Empty CofG

My first EWCG was at 19.72" with wood prop. I was able to be in the proper range with loading, that was in 1998.

I can use a wood prop or metal and be in range when loaded.

In 1998 my mains were 414, 429 and tail was 70 @ 198" with oil and 12 gal. nose fuel

Have you deducted oil and fuel that was in the plane when weighing in order to calc EWCG?

I swap props now and then and have a loading schedule for each one.

p.s. last page of attachment has been clipped doff

[BIGK]

Re: Empty CofG

Rob thanks. Your right. I have been using the EWCG for loading calculations. I think the term "Muppet" comes to mind. Thank you all for your patience. Check flight next and then new permit hopefully.

[TimHicks]

Re: Empty CofG

When I weighed my '46 BC12-D, I got 759# on the mains and 57# on the tail.
EWCG was at 15.67". In range.
You got 717# mains and 69# tail. So compared to mine, yours looks tail heavy.
I weighed it like you did, horizontal stab level.