Isn't it important anymore?

[turboplanner]

56 minutes ago, old man emu said:

You can say that Piper and Cessna added a fairly big fudge factor in establishing the CofG envelope. Maybe they put Human Factors above aeronautical demands in their design specification.

 

It's probably true that you would bend an aircraft on the ramp by overloading before you felt the effects out on the runway, IF the aircraft was a certified type, or a commonly built experimental. However, it's the one-off homebuilt that could give a nasty bite it loading was not correct.

What sort of crazy numbers did you use, and where did you place the weights?

 

Here's a thought: See how the manufacturer has given the Moments at several station locations for various loading options.  Looking at the cargo carrying options, the Moment aft of the crew seats is given at a single station. In physics calculations,  of which W&B's are a type,  it is assumed that the weight of an object acts through its centre of mass. That's OK for a regularly-shaped object, but what if you were carrying something highly irregular in shape with very scattered localised weights?  I think that the answer to that question lies in having faith in the designer's fudge factors. As long as you remain within the weight limitations for a load area, and the total W&B values put you in the envelope, she's sweet to go!

 

Two things:

1. C172 and PA28 are the "utility" type aircraft I mentioned which are designed for training and work around the flying club, so we would not expect any surprises with them. Cross Country aircraft are the ones where designers might slim down the undercarriage and add more fuel capacity, or extend the caib to take six people and have fore and aft cargo compartments.

 

2. Moments are calculated from the Datum CG to the CG of the Mass.If you have an irrgeular shape object you still have to find its CG and you can do that reasonable accurately by breaking it up into a series of cubes and triangles, arcs etc.  It's when you just guess that it can bite you.

 

 

[Carbon Canary]

1 hour ago, old man emu said:

You can say that Piper and Cessna added a fairly big fudge factor in establishing the CofG envelope. Maybe they put Human Factors above aeronautical demands in their design specification.

 

It's probably true that you would bend an aircraft on the ramp by overloading before you felt the effects out on the runway, IF the aircraft was a certified type, or a commonly built experimental. However, it's the one-off homebuilt that could give a nasty bite it loading was not correct.

What sort of crazy numbers did you use, and where did you place the weights?

 

Here's a thought: See how the manufacturer has given the Moments at several station locations for various loading options.  Looking at the cargo carrying options, the Moment aft of the crew seats is given at a single station. In physics calculations,  of which W&B's are a type,  it is assumed that the weight of an object acts through its centre of mass. That's OK for a regularly-shaped object, but what if you were carrying something highly irregular in shape with very scattered localised weights?  I think that the answer to that question lies in having faith in the designer's fudge factors. As long as you remain within the weight limitations for a load area, and the total W&B values put you in the envelope, she's sweet to go!

 

 

Here's the crazy numbers - a seriously malnourished pilot that carries an extremely large lunch box right at the very back of the aircraft.....and lots of fuel for a very long flight.

 

Type C172   Registration             Start   First Row 40 kgs Second Row 40 kgs Fuel 200 litres Baggage 54.4 kgs Rear baggage 22.7 kgs Fuel consumption 38 Litres/hr Endurance less taxi 309 minutes Flight time 400 minutes Margin excluding reserve -136 minutes       Balance Actual   Takeoff 108.3 (lbs/in) Landing 88.9 (lbs/in)       Weight Actual Max Ramp 2345 2558 Takeoff 2341 2550 Landing 1939 2550

[turboplanner]

3 hours ago, aro said:

We know you were referring to weight.

 

But I haven't encountered small aircraft where the maximum landing weight is less than the maximum takeoff weight. Did you have specific examples in mind?

 

The C210 example is referring to CG. I could not find anything about maximum landing weight.

Whether you have encountered something or not is up to you.

The  C210 example is referring to a permissible landing weight.

To get to that figure moments need to be calculated.

A moment consists of a mass and a distance.

 

Similarly, and Aircraft can have a published MTOW, but you still need to calculate all the moments to ensure your chosen configuration fits into the aircraft envelope. Your critical items might be number of passengers, not fuel or your critica requirement may be range (fuel) and you can drop a couple of passengers. All of this involves moment distances and masses to get to a go/no go result.

 

The Piper Cherokee 6 addresses the landing weight in a simpler way by specifying a gross weight limit of 3112 lbs unless the weight over 3112 lbs is fuel only.

[facthunter]

With wing and tip tanks the fuel load reduces the load the wing structure must carry (bend and shear). A lot of planes operate that way.    Nev

[turboplanner]

4 minutes ago, facthunter said:

With wing and tip tanks the fuel load reduces the load the wing structure must carry (bend and shear). A lot of planes operate that way.    Nev

It also pretty much concentrates fuel load close to the CG.

[facthunter]

Yes it's helpful in that way but more complex with swept back wings.  Nev

[djpacro]

On 23/05/2023 at 8:48 PM, old man emu said:

It must have been produced in Australia as the VH- part of the aircraft identity was already printed on the page before the individual letters were typed on.  Maybe some older person here might know the bloke who did the weighing - B.D. Linard

 

 

He did the same for an airplane that I used to own when it was imported in 1989. I bought it in 2001. Standard format for the old Australian (CAA, before CASA) flight manuals. AN35 is his # as a Weight Control Authority.

[djpacro]

On 24/05/2023 at 7:55 PM, aro said:

What is the smallest aircraft where maximum landing weight is less than maximum takeoff weight?

A few C152's around have the STC for increased MTOW however max landing weight is unchanged.

[djpacro]

On 22/05/2023 at 9:56 PM, Carbon Canary said:

....... Anyhow, to answer the question, I sincerely hope W&B is both taught AND routinely practiced in both GA and RA. ..

Unfortunately not!

I hire my Super Decathlon and insist on reviewing the pilot's completed Endorsement Questionnaire (the CASA template) before they fly it. Almost invariably, pilots who got their tailwheel endorsement from a different instructor or at another local flight school, had not previously done that questionnaire. Nor have they ever done a W&B calculation for the type previously despite undergoing their tailwheel training on it - a CASA requirement for the endorsement ignored by the instructor.

 

A very large percentage of people then get it wrong despite the detailed instructions and sample in the manual.

 

It doesn't help that CASA theory exams still require pilots to learn the old CAA loading systems and "P" charts which are very different from the way they are presented in typical GA POHs.

[aro]

52 minutes ago, djpacro said:

A few C152's around have the STC for increased MTOW however max landing weight is unchanged.

Well there you go... 

38 kg of fuel would take a while to burn off in a 152.

Any examples that were designed that way, i.e. not via STC, Experimental etc?

[aro]

1 hour ago, turboplanner said:

Whether you have encountered something or not is up to you.

The  C210 example is referring to a permissible landing weight.

...

The Piper Cherokee 6 addresses the landing weight in a simpler way by specifying a gross weight limit of 3112 lbs unless the weight over 3112 lbs is fuel only.

djpacro has shown why I phrased it carefully.

The C210 example is still CG, not landing weight (if it is weight, can you tell me the number?)

 

The zero fuel weight in the Cherokee 6 is a different (more common) scenario.

[old man emu]

44 minutes ago, djpacro said:

A very large percentage of people then get it wrong despite the detailed instructions and sample in the manual.

And that brings us back to the very beginning of this thread - ignorance of this area of aircraft performance. 

 

3 hours ago, Carbon Canary said:

a seriously malnourished pilot

Or a mere slip of a lass. Don't forget that there's no sex discrimination in aviation.

 

 That resultant, while within the envelope sure is closer to the rear limit than some would care to fly with.

[aro]

4 hours ago, old man emu said:

Honestly, I think Aro understands the concept of W&B, but not the mathematics of it. 

 

You can't point to a tangible location of an aircraft an say "That point is in the CofG range. What graphical representation the CofG envelope shows is the answer to the summation of the individual Moments. An individual Moment is calculated using the distance of the location of the weight from the aircraft datum point multiplied by the amount of weight.

 

The C172 has a forward limit of 35 inches aft of datum at <1950lb varying to 41 inches aft at 2550lb, and an aft limit of 47.3 inches aft of datum.

 

You can absolutely point to tangible locations between these limits. If you could measure from the datum, draw lines and balance it on your thumbs like a model aircraft between the lines you could say it is within the CG limits.

 

There are 2 graphical representations of the CG limits. One is, as you say, the sum of the moments. This is a looks like a chart skewed sideways.

 

The other is the actual CG. That is a much squarer chart, sometimes e.g. C172, PA28 with corners cut off. You get that by dividing the sum of the moments by the weight. It gives you a number that you can actually measure from the datum and point to on the aircraft.

[turboplanner]

32 minutes ago, aro said:

djpacro has shown why I phrased it carefully.

The C210 example is still CG, not landing weight (if it is weight, can you tell me the number?)

 

The zero fuel weight in the Cherokee 6 is a different (more common) scenario.

Sorry, you're out of questions. I'd suggest to read what some of the people are saying.

[aro]

16 minutes ago, turboplanner said:

Sorry, you're out of questions. I'd suggest to read what some of the people are saying.

Very convenient, when you don't have an answer to a question that must have an answer if you are correct.

 

I have been reading what other people have been saying, and I know who knows what they are talking about and who does not.

[Old Koreelah]

12 hours ago, pmccarthy said:

My simple thinking is that for light aircraft, MTOW assumes that you can make a safe landing immediately after takeoff if required for any reason (eg unlatched door).

One good reason for using the whole strip. Lots of speople start their TO run from the intersection, rather than backtracking; all right if nothing goes wrong.

[kgwilson]

I always use full length of the seal but not the extra 200M of grass. Rolling resistance of the grass means you don't get off much quicker anyway especially when it hasn't been mown for a while. I all depends of the runway length and aircraft performance. At ChCh International with a fully loaded C172 I entered the runway after ATC approval & automatically turned down wind to taxi to the end & got told off straight away by ATC. It was about 1000 metres to the end & 2300 metres in to wind. Enough length to take off & land several times.

Edited May 27, 2023 by kgwilson

[facthunter]

I'm NOT surprised.THEY (ATC) would not be expecting you to do that. IF you have more than adequate runway at an intersection It's a bit hard  to justify  backtracking to get more in those circumstances. The old saying is "use all available runway "but reason has to come into the equation as well. A "rolling start" can help but a power check on brakes is a good idea if you don't want to be rushed. Nev

[old man emu]

Exploring many country town aerodromes, I found that taxiways from terminals to the ends of runways are very rare. When planning The Event, I was lucky to have the room to lay out temporary taxiways the full length of the runway. That eliminated any need to backtrack when going to or from the marshalling area. As a result we were able to dispatch the entrants at roughly 90 second to two minute intervals with very good line-astern separation. It also didn't create the need for returning aircraft to go into holding patterns while preceding aircraft cleared the runway because we included exit lanes from the runway to the taxiway at 200 metre intervals.

 

The wind helped. The end of the active runway that was being used was only 400 metres from the marshaling area, so aircraft were just in the early stages of climb out as they passed the admiring public. During the departure sequence, the place looked like Mascot on a Monday morning with planes following each other along taxiways to the runway threshold.

[facthunter]

Backtracking on runways causes a lot of angst. It's very desirable to have taxiways to BOTH ends.  Nev

[old man emu]

2 hours ago, facthunter said:

It's very desirable to have taxiways to BOTH ends. 

I would say,"essential", but rarely created. That's ridiculous because there's always clear space close enough alongside to lay out a taxiway. 

 

We had 45 metres between a boundary fence and the runway, so we set the runway-side of the taxiway 15 metres from it. Then made the taxiway 10 metres wide, leaving 20 metres to the fence. 

[facthunter]

That's cutting it a bit too fine (in my view) Clowns may see the taxiway as useable runway.  Nev

[Thruster88]

I see there was an unfortunate incident on one of the taxi ways at tooraweena recently. 

 

 

19/5/2023	OCC3272	Tooraweenah	NSW	Jabiru	J160-D	Jabiru	2200B	STATUS: Under review OCCURRENCE DETAILS SUBMITTED TO RAAUS: The pilot was going to go for a short...
STATUS: Under review OCCURRENCE DETAILS SUBMITTED TO RAAUS: The pilot was going to go for a short fly around the Tooraweenah area and was using the marked taxiway to enter the runway, there was an old drainage pipe underneath the taxiway which was broken and had formed a hole around 30cms wide and around 15cms deep. Taxiway had been freshly moved and hole was not visible and encountered a propeller strike with the ground. Because of the broken pipe the front wheel went into the hole and front wheel just stopped causing the prop strike. Front of plane was lifted off the ground when the propeller hit the ground.

[old man emu]

5 hours ago, Thruster88 said:

I see there was an unfortunate incident on one of the taxi ways at tooraweena recently. 

Yes, but not on the taxiway I described above. It was on the original taxiway at the point indicated by the arrow. There was a enclosed drain under the taxiway made up of short lengths of concrete pipe. In several places  the top of the pipe had cracked and the soil on top fell through, making a hole. The whole aerodrome had been slashed not many days before the incident and cut grass was laying over the hole. It was impossible to see any hole, even when walking on the taxiway. What made matters worse was that a con marker had been placed over the end of the pipe, so you didn't even know there was a pipe there. For the pilot it was an unavoidable accident. The taxiway was closed off at that end, and the aerodrome owner had a crew dig out the pipe line a few days later.

 

 

This shows the hole (at the start of the tape measure) and the point where the prop hit the ground (at the case of the tape measure)

You can see for yourself that it would be impossible for the pilot to see that hole.