The International Cessna^® 170 Association

There seems to be a problem with the weight and balance data for my airplane. The latest log/337 entry shows an empty weight of 1383, and an index of 43.7. Using this information with the charts in the owner’s manual I’ve done several weight and balance problems and was very surprised by the results. For example, if I am by myself (200lbs) in the airplane with full fuel and no bags, the CG is well forward of the limit! Check my math:
=========Weight========Index
Empty............1383....................43.7
Oil (6qts)...........12.....................-0.2
Pilot.................200......................7.2
Fuel.................222.....................10.7

Total...............1817....................61.4

The approximate forward cg limit at this weight is 67!

Even more surprising, I did a hypothetical problem with me in the front, my wife and daughter in the back, full fuel and 100 lbs of baggage. In this case, I’m still near the forward limit ( ), which doesn’t seem right at all:

=========Weight========Index
Empty..............1383....................43.7
Oil (6qts).............12.....................-0.2
Pilot...................200....................10.7
Rear Pax............200....................14.0
Baggage.............100.....................9.5
Fuel....................222...................10.7

Total..................2117..................84.9

My guess is that somewhere over the years, somebody didn’t do the math right when equipment was added. I’ve combed through all the 337’s and logbook entries, but without the original EW, I’m unable to find the error. It looks like the only way I’ll be able to resolve this is to reweigh the airplane.

In the meantime, I would like to get the EW and Index from a few other 170B’s, hoping to establish some sort of a normal range. (I know there are hundreds of variables, etc.) Also, what practical guidelines would you offer for loading the airplane? My past experience with most single engine airplanes is that it was fairly easy to get out the aft end of the CG envelope when heavy. With the numbers for my airplane – it’s IMPOSSIBLE to get out the aft end!!

Any help or suggestions would be greatly appreciated!!!

Stan Lindholm
N8287A

It seems that your '52 is about 123# heavier than mine. If your added weight is further aft then this data will not be as useful but here it is anyway. (P.S. I had to weigh this bird and establish new logs after a fire in 1980 destroyed my original logs along with all the engine and accessories stored in my shop.)

Empty weight with full oil -----------1255
Center of gravity --------------------- +41.77
Full oil capacity 8 quarts ------------ 15 lbs.

SOLUTION : WEIGHT-# X ARM - " = MOMENT "#

Aircraft as weighed - - - - + 1255# ARM 41.77 = 52421.35"#,

LESS OIL ------------------- -15# ARM -20" = + 300"#,

TOTAL - - - - - - - - - - - - - - 1240#(A) , 52721.35(B)

Empty weight (A) =1240#

Empty Weight C/G B= 52721.35/ (A) 1240 = 42.52

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I don't have any hope that this will come out formatted like I have tried to arrange it but if you will e-mail me I will scan the pages of data I have and e-mail them back to you.

Looks like your CG is towards the forward end too. I did the same problems using your data. In the first case (by myself) in your airplane I would be just outside the forward part of the envelope, which I would buy. The second problem puts your airplane in the forward half of the CG range, which seems odd to me. Oh well...

Sure, scan what you have and send it to me. I'll take anything I can get at this point!

I suspect you may be confusing moment ARM with INDEX UNITS.

The moment ARM is the distance aft (or forward) of the datum (firewall for the C170) thru which the weight acts.

INDEX Units = Weight x ARM / 1000.

If, for your aircraft, 43.7 is the ARM (inches aft of datum) of the Empty Weight of 1383 lbs then the INDEX =

1383 x 43.7 / 1000 = 60.4

In your examples this would give you the following results:

1817 lbs 78.1 INDEX Units
2117 lbs 101.6 INDEX Units

I only have the graphs for the C170A so I am not sure they are the same for the C170B but this looks more like what one would expect - in the second example the CofG is just outside the aft limit.

By the way, I hope you don't try loading as per your second example - the documentation says somewhere that you should fill the front seats before filling the rear seats (not in those words).

I hope this helps

Regards

David.

Yes -- you have the answer!

I've been away from GA for many years before buying 87A, and it's been a LONG time since I've worked my own weight and balance problems. (One of the downsides to being an airline pilot -- you no longer have to think for yourself!)

I think the reason I didn't catch it is the example problem in the manual has an index of 47.9, which seemed rather like my CG of 43.7. My MOMENT from the logs is 60442. I latched onto the 43.7 without really thinking it through...

No, I didn't try to load the airplane as in the second example -- it was just a hypothetical problem. But I do believe the loading instructions in the manual you are referring to are more for practical reasons than W&B -- ie: fold down rear seat to add bags, return to upright, slide the front seats back, then load the pilot and front passenger. Finally, the front seaters can slide up and let their buddies in the back.

Thanks so much for your answer!! I'm slightly embarrassed and feeling like a fool..... but relieved to have the answer!!

Back 3 or 4 years ago when I had probably 25 hours of ticket use, this is the only excuse I have and not a good one, a girlfriend of my daughter's went with us on a weekend trip to Austin. The two girls wanted to both sit in the back so they could talk and play, they were both about 10 years old. I thought well, I am over 200 lbs and they are only little girls, I am sure it will be ok for this big ol 170 to have an empty front seat and two kids in the back. The flying characteristics were not pleasant. It flew like it was out of balance. It was not so bad that I asked one of them to move up front, but it was uncomfortable. I would never do it again.

I also found this a bit confusing as the TCDS WB charts list the moment arm in inches while the POH lists them in index units. Things got confusing when my dad used my garmin 195 to compute the WB (also in inches) and compare that to the POH. As they told us in school...RTFQ!

As an asside, I have flown my 170B at gross and within 1/2 inch of the rear limit. Other than taking longer for the tail to come up on TO roll, I found it to have no unusual or unplesant characteristics.

Bruce

AND BY THE WAY YOU CAN GROSS OUT ( ) YOUR 170B WITH ALL THE STUFF YOU CAN GET INTO THE CABIN AND FULL FUEL TANKS, THEN FLY RIGHT OUT OF C/G IN A COUPLE OF HOURS! I KINDA KNOW WHAT JOE FELT LIKE WHEN HE PUT THE 2 XTRA VIRGINS IN THE BACK SEAT THEN TOOK OFF !

I USED 93D FOR AN AIRBORNE MOVING VAN WHEN I WAS RELOCATING TO LOUISIANA FROM MISSOURI. I WOULD LOAD THE PLANE THROUGH THE WEEK THEN FLY FROM MY HOME STRIP TO TOLEDO BEND ALMOST EVERY WEEKEND. ( FROM JULY 10 TO DECEMBER 4 OF 1991, I MADE 16 OF THOSE ROUND TRIPS AND CARRIED SEVERAL TONS OF STUFF! THAT WAS BECAUSE MY DARLIN HAD ADVISED ME AT THE END OF OUR MONTHS LONG JUNE VACATION AT TOLEDO BEND THAT SHE WAS NOT GOING BACK TO MISSOURI AND WANTED HER STUFF HERE! I WAS STILL EMPLOYED BY TWA IN KANSAS CITY AND HAD SOME MONTHS TO GO BEFORE I COULD ACCRUE ENOUGH POINTS TO RETIRE!)

I SOON LEARNED TO MAKE A COUPLE OF FUEL STOPS AND KEEP THEM TANKS NEAR TOP HALF FULL AND NOT STUFF TOO MUCH JUNK BEHIND THE REAR BAGGAGE COMPARTMENT DIVIDER! DIDN'T TAKE MUCH BACK PRESSURE TO HOLD THE TAIL DOWN ON LANDING EITHER.

Hey Joe,

I had the same experience as you did. On a recent trip down to Memphis, I stopped at Vine Grove KY for some tasty auto gas. My 11 year old wanted to ride up front and my wife then went to the back with our 2 year old girl and her safety seat. On the takeoff run on the grass strip, I thought the tail was glued to the ground I finally got the tail up to accelerate but the lumber yard was coming up rather fast so I tried to rotate....nothing. Too late to stop I just hauled back on the yoke and the tail hit the ground as the mains came off Stall warning chirping as we cleared the lumber yard Now I stick to the rule of having the heaviest folks up front at all times

Does your wife know you're tellin' the whole world she made your airplane tail-heavy?

wa4jr wrote:Hey Joe,

I had the same experience as you did. On a recent trip down to Memphis, I stopped at Vine Grove KY for some tasty auto gas. My 11 year old wanted to ride up front and my wife then went to the back with our 2 year old girl and her safety seat. On the takeoff run on the grass strip, I thought the tail was glued to the ground I finally got the tail up to accelerate but the lumber yard was coming up rather fast so I tried to rotate....nothing. Too late to stop I just hauled back on the yoke and the tail hit the ground as the mains came off Stall warning chirping as we cleared the lumber yard Now I stick to the rule of having the heaviest folks up front at all times

Oh John, so glad you made it. Wouldn't it be fun to have a camara mounted on the panel facing the pilot so that a picture could be snapped when you realize things are not going as planned(ha). When the controls feel weird, I am sure we have some expressions that would be worth capturing on film. I am sure that I did

Ha! Thanks George for bringing yet another error in judgement to my attention Fortunately, my wife is a good sport and is really looking forward to learning to fly. The long trip to SAT really sold her. So glad I do not have to continually justify my midlife purchase
No Joe, don't think I would care to see what I look like as the end of the runway or the tops of the trees draw near I would have loved, however, to have a camera trained on my wife as we did that go-around with 30 degree flaps at T94 in San Antonio Good sport that she is, she put her foot down on that issue....we will NEVER, I SAY NEVER EVER attempt a landing at T94 again. We WILL go to Stinson Field on the south side of town, WON'T WE DEAR Yes dear, by all means we will land at Stinson Field on future visits to San Antonio

San Antonion Int'l (SAT) is not as difficult as it might at first appear. Most FBO's there are very accomodating, even to small aircraft, and at least there's no landing fee. Hawthorne (South) is a short side-walk stroll to the airline terminal, and is close to the main airport entrance. Raytheon, and lot's of others are along the southwest boundary, and most have courtesy cars available if you're willing to pay high prices for fuel. (But I've always considered $2.85 per gallon not a bad trade off for a free car, convenient airport versus expensive taxi's, long distances to downtown, and $1.80 fuel when you're only buying 15 gallons anyway. One short cab ride is usually more than $15 in a large city.) What really sends me to a distant field is an arbitrary landing fee, whether or not fuel is purchased.
Any Signature Flight Support will never get my business until their owners and their name changes. They give Britons a bad reputation.

Unofficially if you're going over the max weight limit, what are the critical things to watch. Seems to me, if you keep the C.G. centered, understand that you're Stall Speed is higher, and you're patient on take off / landing distance, it can be done. I know for sure it can be done!
I keep hearing that you CAN'T take 4 adults in a C170 - 145hp.
Problem: Two 200 lb passengers in front + two 140 lb passengers in back = 680 lbs.

Just for fun,I looked thru all my W&B sheets. The original factory W&B sheet dated 9-13-48 sez 1229 lbs. empty with a 37.6" CG. No weights per wheel listed,so I think that it was estimated,not weighed. An actual weighed figure after a total rebuild in 1960 shows 1297.5# empty with a 39.05" CG. Near as I can figure,the current empty weight is around 1321# empty with a 39.0" CG. All the W&B sheets in the file from all thru the years show an empty CG of 38.4-39.05".
Gary & Stan,your airplanes' CG's seem like they're kinda far aft,at least compared to mine. Of course,you guys own them B models with the funny metal-covered wings. Those were a corruption of the excellent original design,that must account for it.

Eric