Tail weight from your weight and balance

[learaviator]

Weighed my 170A and the tail weighed in at 144 lbs. Can't seem to find another airplane where the tail is this heavy. Kind of suspecting the scales, everything else was right. I was wondering if I could get some tail weights from some people to compare to? Thanks ahead of time.

[canav8]

my B model is 130 just FYI.

[Bruce Fenstermacher]

Hi Steve,

I don't have the records for my first 170B that I actually weighed but seem to remember 110 lbs under a Scott 3200 tail wheel with an arm of 249".

My current 170A has actually NEVER been weighed. Not even by Cessna. Cessna used a COMPUTED weight for the bases of their W&B calculations so I don't have an example of a tail wheel weight.

But reverse calculations of the COMPUTED weight shows the following for an empty aircraft with no excessories, fuel or oil. As you can see the weight at an arm of 246", which is correct for the Scott 3-24B tail wheel is 91.24 lbs

N7A calculated weight

Screen shot 2011-07-19 at 11.45.19 AM.png (9.28 KiB) Viewed 6694 times

Adding fuel and oil to this configuration would bring the tail weight to 118.1 lbs as you can see in the following example.

N7A calculated weight

Screen shot 2011-07-19 at 11.45.36 AM.png (16.25 KiB) Viewed 6694 times

I suspect that 144 lbs might be a bit heavier than you might normally find if all is correct but our 170s at least tend to be nose heavy under normal loading.

As you have, I might suspect the scales. But I think it more likely that when you leveled the top door sill it wasn't perfectly level, leaning towards the tail. As you know a very slight variance here will make a big difference at the rear scale.

You also have to be careful to use the correct tail wheel arm. As I've mentioned the stock Scott 3-24B arm is 246". This is what Cessna used in their basic calculations. Nearly every 170 I see has a Scott 3200 which has an arm of 249". I recall you wanted to run a Gar Aero tailwheel. If that is what you had installed you will need to compare the axle location to that of a stock 3200 and make adjustments or measure the arm of the axle from the datum (fire wall) to be accurate. Of course I know you know this I mention it for others reading.

Another thought. I recall you also have a 0-360 installation. Depending on the prop and your battery location I believe this installation can produce a 170 that is more tail heavy than a stock configuration.

[GAHorn]

I''ve always thought my airplane was tailheavy and for that reason do not believe I can get it into the utility category (and have not contemplated spinning it for that reason, among others.) It's tailwheel weight, (Scott 3200) using FAA-calibrated scales was 135.
The mains were in the 720 lb range, with full fuel and oil.

[wingnut]

I''ve always thought my airplane was tailheavy and for that reason do not believe I can get it into the utility category (and have not contemplated spinning it for that reason, among others.) It's tailwheel weight, (Scott 3200) using FAA-calibrated scales was 135.
The mains were in the 720 lb range, with full fuel and oil.

It's all that perty yeller primer that makes yers so heavy George . Really, it makes a difference.

[Robert Eilers]

My tail wheel weight is 125.

[GAHorn]

I''ve always thought my airplane was tailheavy and for that reason do not believe I can get it into the utility category (and have not contemplated spinning it for that reason, among others.) It's tailwheel weight, (Scott 3200) using FAA-calibrated scales was 135.
The mains were in the 720 lb range, with full fuel and oil.

It's all that perty yeller primer that makes yers so heavy George . Really, it makes a difference.

Well.....when I decide to abandon my motto.... I hope to have YOU convert it to an IO-360 and install those new 175 fuel tanks I've got. That should take care of the CG issue. All you have to do is get the E.W. down.

[learaviator]

Thanks everyone for the replies. Reweighed my plane again, different scales. No fuel on board, left main 646, right main 631, tail 112. Empty weight 1389. I have the 0-360, C.S. prop, battery on the firewall, lightweight starter, one comm and transponder, 180 gear, Scott 3200 tailwheel, 8:00X6 tires, no headliner or carpet, rear seat in. I thought mine would not get in the utility category, but according to Bruces spreadsheet program if I put in up to 25 gallons with just me by myself, it will go in the utility category.

[Bruce Fenstermacher]

Steve did you take into account the 180 gear may move the axels forward so the arm of the weight of the main wheels will not be the stock +22"?

Without taking the 180 gear into account I figured you could put two 200 pounders in the front and about 10 gal usable fuel and be in the utility category. If you had oil and unusable fuel in when you weighed then we would subtract that out further moving you into the utility category. If this is the case when the duplicated weight is removed from the calculations you can have two 200 pounders and more than 20 gal usable and still be in the utility category.

I'll bet we could get George's plane in the utility category as well.

[cmsusllc]

With 0360 % C/S prop and after moving battery behind the baggage, usable fuel, oil, fire ext., gps, normal maps and poh etc.------- left-669, right-668, tail- 100. I'm still nose heavy. Scott 53B

[c170b53]

Mains 645, 643 tail weight much like Roberts, 127 and just like me, she's a porker!

[Bruce Fenstermacher]

Mains 645, 643 tail weight much like Roberts, 127 and just like me, she's a porker!

And more important to the discussion she has a 0-360. So it is possible to get more weight towards the tail.

I'm wondering if some the discrepancy we are seeing is caused by not having the door sill perfectly level. While weighing both my Cub and my first 170 I realized a bubble level isn't that accurate. The other aircraft I've weighed is a UH-1H Huey. I was use to a plumb bob hung from the top back door over a scale several inches long on the floor. It was extremely accurate in comparison to a bubble level.

[GAHorn]

This is another micrometer/grease-pencil/hatchet matter.

If the aircraft is rotated about the datum with a plumb-bob (pendulum) attached near it's CG,.. I don't see how anything but an arc will be scribed by the pendulum.... Unless it's not attached by a string, but instead by a rigid wire or rod, all a pendulum will do is pivot about it's attach-point. (Or, unless the level-point is actually upon the airframe at some point below the pendulum attach-point and the string is used to cross that level-point.) I suspect that Bruce left some aspect out of his description?

Regardless, the minor differences occasioned by a bubble-level at the door sill (about 35 inches aft of the datum of a 170) will not affect the C/G location in any meaningful way.....and therefore will not affect the weight upon the tailwheel (over 200 inches aft) in any worthwhile measure. (A pendulum OR a scale could be placed at it's most sensitive point...AT the tailwheel ...and one could raise/lower that tailwheel until doomsday and little/no difference would be noted until the aircraft was at some extreme attutude other than level. This will be obvious when one considers that in all normal flight attitudes of climb/level/descent....the aircraft C/G must remain within tolerances.)

[jrenwick]

...This will be obvious when one considers that in all normal flight attitudes of climb/level/descent....the aircraft C/G must remain within tolerances.)

I don't understand how aircraft attitude can affect C/G, unless baggage is rolling around on the floor?

[GAHorn]

It doesn't affect the POINT of the C/G (which doesn't move in relation to distance from datum..but does change in relation to LEVEL distance from datum when not level)...but the design-tolerance means that all normal (and most abnormal) attitudes are not adversely affected of that C/G location. For that reason, using a bubble to determine levelling for wt/bal purposes is entirely adequate.

(When UN-level, the CG moves in an arc about the datum point. In any given configuration, so does the Center of Lift. Gravity (weight) does not.)