Weight and Balance

[Lagentium]

Good Evening Ladies and Gentlemen, please help me with my problem

I'm working out a Mass and Balance problem for my aircraft tomorrow and based on my calculations it falls out of the envelope, Am I missing something obvious

Aircraft Weight : 1547 lbs ; Lever Arm : 84.2
Pilot and passenger : 392lbs (15st + 13st) ; Lever Arm : 80.5
Rear Passengers : 0 ; Lever Arm 118.1
Bagage : 0 ; Lever Arm 142.8
Fuel: PA28 Warrior filled up to tabs calculated at 36US gallons at a weight of 217lbs with a Lever Arm of 95.0

Totals:
Weight = 2156lbs
Moments = 182534
Inches aft of Datum = 84.66

This falls out of the envolopes,
Am I missing something obvious? Please feel free to mock me if so, but I'm really struggling to see what it is I am doing wrong?
Thanks!

[GeeWhizz]

A favourite subject of mine

Nope, you're not wrong. But the front end loading is too heavy. Move the passenger (vice either occupant) to the rear or add weight in the back, perhaps only a few lbs in the baggage compartment.

Thanks Gom good spot!

[Gomrath]

Move either occupant to the rear

Perhaps that might have been better worded to 'move the passenger to the rear or add weight..'. (but I know what you mean!)

[Lagentium]

Would an instructor give this as a normal exercise? I even got the wife who has a physics masters involved, she worked it out a few times but I still coulnt understand it! Just one word, why??

[Gomrath]

Would an instructor give this as a normal exercise?

Most certainly.
It is just basic maths and compare the result with the graph or whatever form it is presented in the POH.

[GeeWhizz]

Not sure of your situation etc, but my PPL LST examiner gave me his weight and a baggage weight that deliberately put the mass and balance out. This was merely to see if I'd solve the problem and either make the no-go decision or find a solution i.e. lose the baggage in the C152.

[Lagentium]

Cheers lads, In my head I was trying to fathom what I had done wrong! But couldn't figure what, regardless I understand it's just basic maths and the answers are black and white apart from my brain telling me otherwise, could I just add ballast in the back seats then?

[Gertrude the Wombat]

An instructor got me to do a W&B once which showed the balance too far forward, out of the envelope. He then pointed out that the lever arm for the pilot seats was asctually given as a range, because of course you can move the seats backwards and forwards, and said that heavier pilots are generally(!) taller, so don't have the seats on the forward stops, so you can use a more rearward figure.

[Gomrath]

could I just add ballast in the back seats then?

At this point, I would suggest you go discuss this with your Instructor. W&B is a serious subject and you need to fully understand it.

[thing]

FWIW our 28 is quite sensitive to front seat weight only. Just had a look and it's 440 lb with fuel on tabs. Mind you, it would take a 15 and 13 stone passenger OK.

[GeeWhizz]

could I just add ballast in the back seats then?

Be careful with this. Essentially yes you could add weight to the rear seats, but.
With lots of weight in the front seats, a lot of weight will be needed in the rear seat.

If you have the option of moving the front passenger, this might be the easiest thing to do. However if the front passenger is an examiner or instructor you'd be brave to tell them to move rearward!

To achieve the greatest effect in view of your problem, it would require about 35lbs further aft in the baggage compartment as opposed to roughly 130lbs minimum in the rear seat due to the shorter balance arm.

Hope this helps, and take Gomraths advice and work it over with your instructor.

[Duchess_Driver]

PA28's are known for this. You'll probably find that the battery is forward of the firewall rather than under the back seat.

We fly with 50lbs of sand in a holdall in the baggage compartment when flying without rear seat occupants. I would, however, suggest water in a collapsable container which can easily be drained 'down-route' if the weight/balance needs it.

DD

[p1andy]

When flying with 2 up front i always have two (40lbs) jerry cans of water in the baggage compartment. That should see you ok with the M&B

[Pilot DAR]

In general, over the years, W&B have been the thing I have found most commonly wrong, or otherwise troublesome. Several aircraft I have test flown were found after the flight to have been ballasted wrong, once way aft of the aft limit - now I "reality" check every one, before I fly.

A few times, I have insited that the aircraft be reweighed - getting really foul looks for the maintenance people who have just weighed it. I can't tell you how many times they got a different result on second and subsequent weighings.

Don't under estimate the importance of having the C of G within range. The ability to recover a single engine aircraft from a spin at gross weight is often the basis for establishing the rear C of G limit. Been there, done that! Those circumstances are the very worst time and way to find out the C of G was wrong!

[Maoraigh1]

Our Jodel DR1050 has 2 different C of G positions/ Empty Wts. One for spats on, one for spats off.

[Pilot DAR]

One for spats on, one for spats off

And a third for "spats on, and completely full of mud"?

[B2N2]

Back in the day we would fly our Aztec in "training mode" which is two upfront and full fuel with a 70lbs sandbag secured in the luggage compartment.
You just can't simply drop a weight in the back and call it good.
Pa28 lugage compartments have "walls" that are even less usefull then wet cardboard to contain anything.
Make sure you secure any weight to part of teh structure/frame so it doesn't go flying around in turbulence or during a bad landing or even a go-around.
That's the last thing you want, a 50 lbs weight rolling into the tail.

[LeeP-PA28]

Sure I told you to put your flight bag in the baggage compartment and recalculate

[wsmempson]

There's nothing wrong with your calculations - it's easy to get forward of C of G in a PA28; in my old Cherokee 140, a 14 stone pilot and an A/C filled to the brim with fuel put the aircraft on the ragged edge and made it quite unpleasant to fly. Two large people in the front seats plus full fuel was quite a long way forward of C of G.

Either a large sandbag or a 10 gallon plastic container full of water, strapped down in the baggage compartment will transform matters.

Just make sure you strap it down properly to the attachment points as, in the event of an accident, a sandbag or 10 gallon container of water can make quite a missile.

I found 4 cases of wine bought at a french supermarket restored the c of g nicely.

[Johnm]

Keeping a raft, four life jackets 3 headsets and assorted spare parts in the baggage compartment of my PA28 usually did the trick :-)