Weight & Balance: Front seat, pilot and passenger

[N3548C]

Is there a maximum weight limit for the front seats in the 170B? Does the number "2" on the loading graph indicate that 350 is max front seat weight for two passengers, or for one? Does the fact that the graph tops out at 440 pounds mean that's the limit?
I know that you can lever the CG back into limits by putting some weight in the back seat or baggage compartment. But is it kosher to have 500 pounds up front?

[Robert Eilers]

There are weight limits associated with the seats and the seat tracks they are attached to. I personally don't know what the weight limit is. I suspect the seat limit is 250 lbs. I am sure there is someone on this forum that does.

[Bruce Fenstermacher]

Of course there are structural limits to every component and this includes seat belts. Having said that there are no limits set that I am aware for any of the seats or belts.

The numbers 1 and 2 found on the graph along the line for the front seats (in the 56 owners manual) have no meaning that I can ascertain. The index graph itself does not set a limit simply because the graph ends though in practice you might find it may be hard to load the plane and keep it within CG and weight limits when the graph is exceeded.

A quick check of my 170 shows that I could put 645lb at the front seat location, 120lb in the baggage area and still be within weight and CG limits with 5 gal usable fuel and 7 qts of oil. Is this practical?

The only limit on loading that I know of is 120 lb in the baggage area more specifically +95 as set by the TCDS.

[johneeb]

...............

A quick check of my 170 shows that I could put 645lb at the front seat location, 120lb in the baggage area and still be within weight and CG limits with 5 gal usable fuel and 7 qts of oil. Is this practical?

The only limit on loading that I know of is 120 lb in the baggage area more specifically +95 as set by the TCDS.

It might be if you keep eating the way you do!!!!!1

[n2582d]

I agree with the previous posts -- 350 or even 440 is not a limit. CAR 03.3811(a) lists the ultimate design loads limits for the fuselage "to give reasonable assurance that each occupant, if he makes proper use of belts or harness for whcih provisions are made in the design, will not suffer serious injury during minor crash conditions as a result of contact of any vulnerable part of his body with any penetrating or relatively solid object, ... ." These limits are 3.0 g upward, 9.0 g forward, 1.5 g side. The engineers used a 170 lb. pilot to calculate these loads. So when one shoehorns in a 250 lb. pilot in a seat designed for 170 lbs. he now has 2.04 g upward, 6.12 g forward, and 1.02 g side load protection. Using shoulder harnesses will help with forward loads in an accident. Just make sure and grease your landings--2 g's isn't much, and crash straight ahead--you've not much margin for a side impact!

As has been said the weak link in C-170 seat design is the seat rails. They were not designed for today's pilots. I've thought of adding an inverted hat section or maybe using old seat tracks inverted underneath the floor skin attached to the new seat tracks above the skin. This would help reduce the flexing of the seat tracks and thus reduce cracking.

To determine how much weight you need to add in the baggage compartment (to bring the c.g. back into the envelope) calculate where the c.g. is with the compartment empty, then again with it full--120 lbs. Now draw a line between those two points. Where this line crosses the front of the c.g. envelope will give you your c.g. restricted max. gross weight from which you can determine how much baggage to add in back. One gallon milk jugs filled with water make good ballast weight and can double as emergency drinking water in the event of an accident. Fuel burned brings the c.g. rearward at a steeper angle than the front c.g. limit line so you don't have to worry about being out of the forward c.g. as fuel is burned.

[bigrenna]

delete

[N3548C]

Thanks for the responses. My son weighs close to 300 (6'6" and solid, not fat.) So between us we're around 475 with warm clothes. Someone (N3224A) made a nifty Excel sheet, which I found wandering the web one day, into which you can plug your own airplane's weight and then add pilot, fuel, etc. With the two of us up front the arm is such that with 30 pounds of baggage in the back we can put full fuel in it and fly it with 17 pounds to spare and the CG at 39.95 inches, still within the normal range on the graph, just as long as we don't eat too much before the return flight.

[Bruce Fenstermacher]

Jerry, I created a similar W&B calculator using Excel about 10 years ago. They are available here on the forum. The W&B calculator N3224A created is a web java based calculator and limited to the A&B model which is OK if you have access to the web and you don't have a '48 170.

The Excel sheets can be downloaded to your IPad or IPhone and used interactively anywhere with at least two programs that emulate Excel since there is no Excel for those devices. The first App is Apple Numbers by Apple computer for 9.99. This App will show the graph but is a bit more complicated to use than the second App called Documents To Go by DataViz. Documents To Go has some interfaces to more easily get the file into your device and it will also open Word, Power Point and PDF files. It will not show the graph however but I recently updated the W&B sheets to give the results in digital form as well as graph.

[N3548C]

Jerry, I created a similar W&B calculator using Excel about 10 years ago. They are available here on the forum. The W&B calculator N3224A created is a web java based calculator and limited to the A&B model which is OK if you have access to the web and you don't have a '48 170.

The Excel sheets can be downloaded to your IPad or IPhone and used interactively anywhere with at least two programs that emulate Excel since there is no Excel for those devices. The first App is Apple Numbers by Apple computer for 9.99. This App will show the graph but is a bit more complicated to use than the second App called Documents To Go by DataViz. Documents To Go has some interfaces to more easily get the file into your device and it will also open Word, Power Point and PDF files. It will not show the graph however but I recently updated the W&B sheets to give the results in digital form as well as graph.

Good point on the web access. Eventually, of course, I'd have thought of that!

[MattPilot]

With respect to the loading graph and the number "2" listed, does anyone see a problem with seating 3 on the rear bench seat (kids sharing seat belts and staying within weight and balance of course)? Does anybody do this? Has anyone added a third seatbelt to the rear bench seat?

https://www.federalregister.gov/article ... or-general

[Bruce Fenstermacher]

Matt,

If you look on the 180 lb line you will also see a number 1.

I think what the intent was to indicate you would use the line for 1 or 2 people as that is how many seats sit on that datum.

Would this in itself be limiting. In my opinion no. However it is in line with other things which you might be running foul it you put more than one sole in a seat and belt. First and fore most if you had a total of 5 soles on board you would be running foul of the total number of 4 the aircraft was certified for. Of course this might not be a limit either if you think about it. The FARs allow even an airline to allow children under 2 to be held in the lap of an adult with not restraint. Theoretically it seems a 737 could be full and then with one lap child have more soles on board than seats.

So we have to look at it close. The TCDS says 4 place not 4 persons or soles. So if you can legally place 5 soles in the 4 places your OK IMO. Looking at the FAA interpretation, it would seem you can legally do this if the seat belt and seat where designed to hold more than one. Here is where you might have some trouble. I've never seen any indication that Cessna had in mind to place more than 1 sole per seat. Of course no one cared about such things in the 50's, they just did it. In fact they probably did it well into the 80's according to stories I've heard from past members. Times are different as we all know. What you would have to find is some evidence or proof the seat and belt where designed for more than two or to comply with the FAAs interpretation of the current FAR to be legal IMO.

As for adding seat belts. I'm afraid getting approval to do this would be nearly impossible.

[GAHorn]

There are numerous stories told by caring people who carried 3 kids in the back seat (including our own dears Bickford). There are also several instances of certificated airplanes which provided one seat belt to be worn by more than one occupant ... (tho' I admit at the moment I don't recall which model comes to mind.)

I don't know how an FAA inspector who witnessed such an event might react... nor under what rule he might consider an enforcement action... against a parent who did this in a private part 91 flight. This might be analogous to forgiveness being more easily obtained than permission.

We have several Members present who are employed as inspectors by FAA who do not wish to be identified by user-name (in the good intentions of remaining one of our happy group of conversationalists) and who might offer a private opinion except for the public nature of this forum. May I invite those Members to reply to this thread in a private email to either Bruce or myself, and we can remove identification and post any suggested guidance?

gahorn146ys (at) Hotmail (dot) com
or
gahorn (at) cessna170 (dot) com
or
PM

[MattPilot]

Thanks for the thoughtful reply, Bruce. I know it's definitely not common to add the third seat belt on the bench seat, but it's approved on the Piper Comanche ...

I wonder if something similar could be done on the 170 ... If anyone with experience in this sort of thing could weigh in, I'd appreciate it. I think it would involve some drawings by a DER and then field approval, but I am clueless as to how to start the process. Any mechanical engineers that are familiar with these sort of drawings?

Here are the drawings, specs and approval for the Comanche ...
http://www.hdneubert.com/3rd_Seatbelt_Package.PDF

[GAHorn]

...and there are also examples of a child's seat installed in baggage compartments...

[MattPilot]

I'd love and value to hear directly or second hand what an inspector would say about this ... PLEASE weigh in - thanks!