Weight and Balance - with pax in the back

[AGB]

Hello All,
Last week I flew for the first time with my wife and little daughter. They both sat in the back seat, approximately 70 kg (140 Lb) combined, I weight 85 kg (160lb). I checked the weight and balance and found the CG to be forward of the aft limit. In case anyone would like to do the math: empty 1310 lb @ 39.65 in

Since then I checked and found that I can leave the forward seat empty and sit two 90 kg (180 lb) on the back and still be forward of the aft limit (with myself at the controls of course ). I am doing the math right? Has anyone flown like this? Is there any noticeable degradation in performance or handling? I have always been told that the heaviest people should sit forward, but seems like the 170 is not one of those aircraft.

Some may be ask why leave the front seat empty. Sometimes when you take a couple flying I suppose they would prefer to seat together instead of one in the front and the other in the back. Or there may be a case the pilot prefers to keep the passengers away from the control wheel and brakes.

Good flying,
Donovan

[Bruce Fenstermacher]

To tell the truth I haven't done a W&B on a lot of airplanes but the three that I have, my 170, J3 Cub and a Cherokee 140 were all nose heavy. In my 170 I can not put more than 430 lbs combined in the front seats with full fuel before hitting the forward CG limit still with 217 lbs of useful load left. In a Cherokee with full fuel the limit is less. The solution is to put just about anything in the back.

In my 170 with you (160lb) flying you could put 490lbs in the back seat with full fuel and still be in CG and Weight limits. If you limited your fuel to 20 gal total you could put 530 in the back seat and be within limits.

[pdb]

Hello All,
Last week I flew for the first time with my wife and little daughter. They both sat in the back seat, approximately 70 kg (140 Lb) combined, I weight 85 kg (160lb). I checked the weight and balance and found the CG to be forward of the aft limit. In case anyone would like to do the math: empty 1310 lb @ 39.65 in

Since then I checked and found that I can leave the forward seat empty and sit two 90 kg (180 lb) on the back and still be forward of the aft limit (with myself at the controls of course ). I am doing the math right?

Yes, I think so. .. as I did the math using the data for a 170B at your empty weight and moment, you could have the front pax seat empty, full fuel, and have 500 lbs in the back seat at which point you would be approaching max gross wgt and less than an inch forward of the rear limit of the cg.

At the rear edge of the envelope, an airplane is going to be less stable in pitch and will likely cruise just a bit faster than if it were at the same weight with a more forward cg. With a rearward cg, you theoretically might find that stall recovery isn't quite as prompt but as a practical matter, its going to fly just fine, a wonderful tribute to the Cessna engineers. Those guys really did a great job.

PS: Check my math and keep a copy of the calculation in your plane. The TCDS has the CG limits and arms for the seats, baggage areas, etc so you can readily do the calculation with your aircraft's empty wgt and arm.

[mrpibb]

Just keep in mind of that little placard that states that if both back seats are occupied so must the front. I usually carry 50 lbs of junk in the baggage, it helps keep me aft of the foward limit.

[Bruce Fenstermacher]

Just keep in mind of that little placard that states that if both back seats are occupied so must the front. I usually carry 50 lbs of junk in the baggage, it helps keep me aft of the foward limit.

That placard is only for the '48 and does not apply to the A and B model.

[Robert Eilers]

I find the bigger problem is loading the airplane and staying aft of the forward limit - without someone of some size in the back seat it usually takes about 45 pounds in the baggage compartment .

[GAHorn]

You can enter you own aircraft data in the following wt/bal program:
http://home.new.rr.com/trumpetb/alph/index.html

(Click on the "Active Plot Version" and hit the "Calculate" button to see an instant graphical depiction of the CG.)

[Brad Brady]

You can enter you own aircraft data in the following wt/bal program:
http://home.new.rr.com/trumpetb/alph/index.html

(Click on the "Active Plot Version" and hit the "Calculate" button to see an instant graphical depiction of the CG.)

Cool...and that gives you the AFM for your aircraft?...

[GAHorn]

No. It gives a working wt/bal program. The "AFM" is an entirely different document.

By the way.... when loading the baggage compartment, you'll notice the ARM is 95 inches. That makes an assumption that your baggage will AVERAGE out to be centered at 95 inches.

But clearly if 28 inches of RANGE in the ARM (a guess) is available in the baggage compartment, and if you are carrying two gallon jugs of water for a camping trip, along with tools and heavy steel tie-down stakes, etc etc... and a couple of large goose-down sleeping bags that only weight 9 lbs apiece.... it is better for your CG to load the tools, water, food, stakes, etc. (all the heavy items) FORWARD in that baggage compartment and the lighter stuff like the sleeping bag at the REAR of the baggage compartment in order to avoid a CG too far AFT.

There's no need to make computations regarding that technique, but nonetheless it makes better sense than loading the heavy stuff aft and still presuming that an ARM of 95" still applies!

On a related matter: While it's true that an aft CG (within the limitations of the aircraft) may lessen the workload of the tail and might offer a knot of speed,... and while it may even lower stall speed by a knot or so.... it remains that an AFT CG is more dangerous than a FWD CG in the unfortunate event of an actual stall and an AFT CG will be more difficult to recover from an inadvertent spin. FORWARD CG (within the limits) is a safer alternative in most cases, should the choice exist.

[N2782C]

There's a site on the Internet that works great for the C-170 weight and balance. http://home.new.rr.com/trumpetb/alph/wb170B.html

[aaronhunley]

I have made a W&B spread sheet with a working CG graph for my 48. It seems to be fairly accurate. If anyone is interested in this for the A or B model i can try to redo the graph.

WeightandBalance.xls

(64.5 KiB) Downloaded 557 times

[N2782C]

I think I can work yours for my C-170B. I'll let you know. Thanks.

[Bruce Fenstermacher]

The arm for the fuel is different from a '48 to a A or B model and I seem to remember a few other minor changes. Here is one I did about 5 years ago for the A/B model as well as the A/B model with the Javilen fuel tank and also one for the '48.

170_A_or_B_Model_WB.xls

(30.5 KiB) Downloaded 408 times

170_A_or_B_Model_WB_with_Javelin_Tank.xls

(31.5 KiB) Downloaded 251 times

48-170_WB.xls

(26.5 KiB) Downloaded 413 times

[Dward]

Bruce, that is way cool . Thanks!

[N2782C]

Bruce,

Very nice...am using it as I write. Thanks.