Isn't it important anymore?

[IanR]

On 23/5/2023 at 9:29 AM, Carbon Canary said:

I was part of a 6 ship safari to White Cliffs a few years ago, with one of the aircraft being a C172B.  The safari was in October and temps were around the high 30's for most of the trip.

We planned a lunch stopover in Louth on our way from Bourke to White Cliffs. The bitumen strip at Louth is long enough, but it was recognised the climb performance of the fully loaded C172B on a hot day would be a critical risk in getting back out.  The command decision was taken by the PIC to forget the stopover, overfly Louth and continue on to White Cliffs.

That flight sounds familiar !

[Area-51]

7 hours ago, aro said:

"Whatever it takes" isn't much help if you don't know what it takes. What it takes is Vy. That's why the number is in the book. Vx, Vy, best glide - they are documented for a reason.

Yep, correct, they sure are...

[facthunter]

I don't know of any light aircraft that can't land at the max TO weight.  With the bigger stuff that applies and there may be a weight above which lesser flap is permitted for landing. You land overweight IF you have to but if it's not a good arrival the plane requires inspection and maybe repair  similar to a HEAVY landing.  Larger planes have the ability to dump fuel and that's the normal process if you return or divert. I've only ever done it ONCE.  Nev

[skippydiesel]

18 hours ago, Area-51 said:

Yep, correct, they sure are...

Out of interest - have you ever verified the  Vx Vy on your Europa -, an aircraft known for having builder induced aerodynamic variations, along with several engine, prop & undercarriage, variants?

[turboplanner]

 weight.

 

 

Edited May 25, 2023 by turboplanner

[turboplanner]

20 hours ago, facthunter said:

I don't know of any light aircraft that can't land at the max TO weight. 

A couple of people have said this and I think one asked me to give an example.

This thread by OME is based on his own current experience with current Pilots in Command at an event; it could equally have been CASA employees doing an unexpected ramp check.

 

In my post on Minimum Landing Weight (MLW) I specifically referred to cross-country aircraft because they are designed light, and therefore can have some extra things to take into account.

 

Just because you haven't heard about it doesn't mean you should encourage others not to lear about it.

 

I was taught about MLW, and the FAA teaches MLW, and  on the the first aircraft I picked, the Manufacturer expects and guides you to do the MLW check.

 

CESSNA 210 POH  

Sample Loading Problem    (Section 4-6)

11. Estimated fuel burn off

12. Subtract [estimated fuel burn off] from total weight and moment.

13. Locate this point (3572 at 187.2) on the COG Moment Envelope. Since this point falls within the overall envelope, the loading may be assumed acceptable for landing.

 

The FAA Pilot's Handbook of Knowledge addresses MLW in the Weight & Balance Section, Chapter 10 (see attached file)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WX00223.pdf

[aro]

The Cessna 210 POH is referring to calculating the CG.

Maintaining CG within limits as fuel is used is important for every aircraft, not just cross country.

It is not a maximum landing weight and doesn't require you to use up fuel before landing.

[old man emu]

1 hour ago, turboplanner said:

it could equally have been CASA employees doing an unexpected ramp check.

I felt neglected that CASA didn't send some inspectors. Not that I wanted anyone "booked", but I figured I jumped through CASA's hoops to get the approval, so I should at least meet the the people who should make sure they are set up correctly.

 

1 hour ago, turboplanner said:

This thread by OME is based on his own current experience with current Pilots in Command at an event

Maybe it was because when I was first engaging in cross-country flying, my friend was working towards his Commercial. So every flight was done with Full Reporting which required ETAs at designated points and reporting at set intervals. And all done with map and whizz-wheel. As I was preparing the conditions for the event, there was a lot of conversation on this site about simply whacking location coordinates and basic performance data into a device  to get the data to complete the plight plan form. While I accept that it is efficient to use the best tools available to us to do a job, we must have the knowledge and ability to do the job with inferior tools, even if that is not as efficient.

 

What worried me from those conversations, and was borne out by the entries I got, was that the basic knowledge was not being insisted upon in the initial introduction to aerial navigation. I don't know what examiners are requiring of applicants when testing navigational skills, but I am of the opinion that software should not be used until a pilot has completed ten or fifteen flights of increasing complexity using the basic tools for planning.

[old man emu]

24 minutes ago, aro said:

The Cessna 210 POH is referring to calculating the CG. ..... It is not a maximum landing weight and doesn't require you to use up fuel before landing.

Aro seems to be talking about two different, but related things, which I'd ask him to clarify.

 

Having the CofG within the approved range ensures that the aerodynamic controls of the aircraft are able to provide full control of the aircraft.  Too far forward and the nose cannot be raised for take off. Too far back and the nose cannot be lowered to keep the Angle of Attack below the stalling angle. Another reason for knowing the total weight of the aircraft is that there is a limit to the lift its wings can produce. Theoretically, you could hang a one tonne weight at the zero Datum point and the Balance would be mathematically correct, but the plane would never get off the ground.

 

The C-210 might be an aircraft that can be loaded in such a way that at the end of a flight, the weight loss due to fuel consumption might result in the CofG being outside the envelope resulting in uncontrollability issues at the  flare. So the manufacturer gives a warning. Such a warning might be unique to this aircraft and not a factor for many others.

 

 

[pmccarthy]

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).

[aro]

Turboplanner wrote:

On 24/05/2023 at 7:09 PM, turboplanner said:

In addition to this your Mass calculations will include your MAXIMUM Landing Mass, which is one of the reasons why doing your fuel burn calculation at regular intervals is important. You may have a sick passenger, but you may have to burn fuel for an hour to come down withing the undercarriage capacity.

Facthunter and I replied:

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?

23 hours ago, facthunter said:

I don't know of any light aircraft that can't land at the max TO weight.

Turboplanner replied:

2 hours ago, turboplanner said:

A couple of people have said this and I think one asked me to give an example.

 

 

 

CESSNA 210 POH  

Sample Loading Problem    (Section 4-6)

11. Estimated fuel burn off

12. Subtract [estimated fuel burn off] from total weight and moment.

13. Locate this point (3572 at 187.2) on the COG Moment Envelope. Since this point falls within the overall envelope, the loading may be assumed acceptable for landing.

 

The FAA Pilot's Handbook of Knowledge addresses MLW in the Weight & Balance Section, Chapter 10 (see attached file)

 

Turboplanner's original post was referring to weight, i.e. you may have to burn fuel before landing. But the C210 POH is referring to CG.

[aro]

38 minutes ago, old man emu said:

Such a warning might be unique to this aircraft and not a factor for many others.

It is fairly common. C210 obviously based on this example. It's well known for Bonanzas. Probably most aircraft where the CG can approach the limits.

 

I'm curious, I will have to work a sample for a C172 and PA28 and see whether you can load it so it goes out of balance as you use fuel.

[facthunter]

Cof G is the issue. Your plane must have it in the range for all inflight conditions including ZERO fuel (All available fuel used) if it varies. Having fuel tanks  away from the C of G makes it more of an issue A plane operating outside of the permitted CofG range is not airworthy. 

  The larger aircraft have  structural design limitations at the higher weights but (as I said) In an emergency you still land overweight and worry about the paperwork later. A heavy landing REQUIRES an Inspection and so does an overweight one. The potential for stressing a plane in the landing is always there and often the last flap  setting is not to be used above certain landing weights.

  You don't want to be complicating things where you don't have to. Just remember that when you're heavier the stall speed is higher  Nev

[Carbon Canary]

1 hour ago, aro said:

It is fairly common. C210 obviously based on this example. It's well known for Bonanzas. Probably most aircraft where the CG can approach the limits.

 

I'm curious, I will have to work a sample for a C172 and PA28 and see whether you can load it so it goes out of balance as you use fuel.

I plugged in some crazy numbers and for a C172 I don’t think you can push it out of balance based solely on fuel burn, if it started in balance. The change in arm with falling fuel load simply slides down the side of the envelope without crossing the boundary. A PA28 may be different but I don’t have a POH with me.

[facthunter]

It perhaps would with some designs where tanks are far from the CofG. Changes to mass where the CofG of it falls within the allowable range cannot take it out of the safe CofG. Nev

[turboplanner]

3 hours ago, aro said:

The Cessna 210 POH is referring to calculating the CG.

Maintaining CG within limits as fuel is used is important for every aircraft, not just cross country.

It is not a maximum landing weight and doesn't require you to use up fuel before landing.

That's correct.

My original post said "What hasn't been mentioned in the WB calculation is maximum landing fuel.

That was due to brain-fade; the last word should have read weight.

 

Factors can be:

Fuel

Passengers

Cargo Compartments

Non Standard Cargo (200 litre drums in rear seat space) etc

Parachutists.

 

These things are included in the add up for MTOW

They are also included in the add up for MLW where it is specified for the aircraft.

 

 

 

 

 

 

 

 

 

 

[aro]

51 minutes ago, turboplanner said:

My original post said "What hasn't been mentioned in the WB calculation is maximum landing fuel.

That was due to brain-fade; the last word should have read weight.

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.

[aro]

1 hour ago, Carbon Canary said:

I plugged in some crazy numbers and for a C172 I don’t think you can push it out of balance based solely on fuel burn, if it started in balance. The change in arm with falling fuel load simply slides down the side of the envelope without crossing the boundary. A PA28 may be different but I don’t have a POH with me.

I agree - the sample for the PA28 looks the same. Partly because of the shape of the envelope. The forward limit reduces with increasing weight, and the CG moves forward as fuel is used. The forward limit moves forward faster than the actual CG as fuel weight decreases.

[old man emu]

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.

1 hour ago, Carbon Canary said:

I plugged in some crazy numbers and for a C172

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!

 

[old man emu]

4 hours ago, old man emu said:

Theoretically, you could hang a one tonne weight at the zero Datum point and the Balance would be mathematically correct,

Will someone let me know if I am correct here in the Physics of levers? 

[rgmwa]

3 minutes ago, old man emu said:

Will someone let me know if I am correct here in the Physics of levers? 

You can put a one tonne weight at the zero datum (pivot point) of a seesaw, and provided both sides are identical the seesaw will remain horizontal. If you hang a weight at the cg position of an aircraft (zero datum for that particular loading configuration), it won't change the balance point either, just increase the total weight. 

[aro]

7 minutes ago, old man emu said:

Will someone let me know if I am correct here in the Physics of levers? 

You could hang a 1 tonne weight in the CG range and balance would be correct (although the permissible range often reduces with weight so there might not be a usable CG range...) 

 

But the zero datum point is just a point chosen as the point to do your measurements from. Usually, it is something easily measurable like the firewall etc. If you put it at the CG you have to work with positive and negative numbers. If you choose a point further forward, all your numbers are positive.

[rgmwa]

Aro is correct. For W&B purposes it depends where you define the zero datum to be for calculating the moment arms.

[old man emu]

3 minutes ago, rgmwa said:

Aro is correct.

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

 

11 minutes ago, aro said:

in the CG range

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. 

 

As Aro says, the datum point is designated arbitrarily by the designer, most often to eliminate negative values for a Moment. In balancing radio controlled models, one usually takes the location equal to 1/4 of the wing chord, because that's pretty close to the Centre of Loft and allows you to add weights to eliminate a tail-down tendency, which of course leads to stalling. In a people-carrying plane, it is easy enough to measure things with a tape. So the reference point can be anywhere. Some designers even put it forward at the tip of the propeller spinner so that the calculated Moment at each station is positive.

[Area-51]

16 hours ago, skippydiesel said:

Out of interest - have you ever verified the  Vx Vy on your Europa -, an aircraft known for having builder induced aerodynamic variations, along with several engine, prop & undercarriage, variants?

Thanks for asking, yes... the aircraft was built by a senior Ansett engineer and performs on spec, however the battery location is at the firewall instead of aft of the luggage well; a common Mod on the europa; even if it was in the factory position would still require 5-10kg at the luggage station to balance out for 1 or 2 up from 2/3 to empty fuel load.

 

To answer the earlier "what ever it takes" rebuttal by someone else there... Every aircraft has a precise performance envelope and anybody flying an aircraft without knowing it intimately is a fool and a tragedy waiting to happen... If "what ever it takes" means a full aileron roll at 150' off the deck to avoid catastrophe i'll do it... if it means purposely turning incipient to avoid a catastrophe i'll do it... if it means full power at 50' flat and low until i see a known required climb out velocity i'll do it; and a 30% reduction in Vx/y on a stinking hot humid 36c day means pulling back trying for 60kt Vx while two up is a great way to end your day with a stick stall scenario (the aircraft was already at 65kt and not responding sufficiently to pitch command). Go fly a 130kt cruise aircraft and time how long it takes to gain 500' from 65kt full power and then do the same from 90kt full power. Pretty sure you will find one way is quicker than the other; somewhere like 30sec V's 10sec.