MTOW calculation

[Gnarly Gnu]

OK, daft question of the day. Wildebeest would like to know how MTOW is calculated against empty weight, particularly for an amateur build.

 

There are two fixed numbers - gross MTOW (we don't want to exceed 600kg) and empty weight, say for example we have an aircraft that has been weighed at 400kg empty. Fine, we can handle 200 kg of pilot / passenger / fuel combined. But the latter can tend to be somewhat variable in reality. What happens if there is another hefty wildebeest right seat, & they bring a hamper of lamb chops....with a nice full tank of Jack Daniels powering the whole show along the MTOW has now crept up to 640kg or whatever. Ignoring any safety aspect for the moment (as it happens the Beestcraft can handle this sort of load OK) does the insurance become null and void in the event of a mishap on takeoff? Or if there was a mishap later in the flight when the JD has gotten somewhat drained and the weight is now below 600kg? Are folk being randomly weighed before they lift off?

 

No, not planning to flout any laws just wondering what ramifications might be if the MTOW was inadvertently exceeded; I suspect it happens. How many of you ask your passenger their exact weight....?

 

And what if the Beestcraft was a 'Carbontax Beest-cub' which already weighed maybe 480kg empty, would this still be accepted for RA registration? In other words is there a standard allowance weight for each person plus the fuel tank size or how does RAAus figure one empty weight is going to be OK while another slightly higher one won't work?

 

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UPDATE: I should have used the phrase "allowable takeoff weight" above rather than MTOW.

 

 

[Guest davidh10]

MTOW is specified for an aircraft by its manufacturer and is a fixed value. Sorry, don't know how it is calculated.

 

MTOW does not creep up through overloading, you simply overload and exceed MTOW.

 

If you exceed MTOW, you become a Test Pilot! The aircraft no longer has the safety margins you expect . The result is, in general terms, unpredictable.

 

Lots of RAA aircraft cannot have two occupants at maximum weight and a full load of fuel. You have to cut back on fuel or occupants to meet MTOW.

 

Yes, Insurance will become null and void, because it is conditional on flying legally.

 

 

[Gnarly Gnu]

the Coroner will work out wat happened

I'm talking about a scenario where the aircraft can handle a little extra gross weight beyond 600kg, as many (but not all) of them can. In other words exceeding the aircraft design weight / balance limits is another different topic. Perhaps I worded it poorly - I'm looking at how the maximum allowable empty weight is determined for registration and potential legal type ramifications of slightly exceeding the MTOW limit.

 

 

[Guest davidh10]

I'm talking about a scenario where the aircraft can handle a little extra gross weight beyond 600kg, as many (but not all) of them can. In other words exceeding the aircraft design weight / balance limits is another different topic. Perhaps I worded it poorly - I'm looking at how the maximum allowable empty weight is determined for registration and potential legal type ramifications of slightly exceeding the MTOW limit.

If you want to look at it from a legal perspective, I think you are misunderstanding MTOW:

The MTOW for the aircraft may be above the allowable takeoff weight. The former is specified by the manufacturer and the latter is specified in the legislation.

 

The CAOs do not refer to MTOW, but rather "take-off weight"

 

in relation to an aeroplane, means the total weight of the

 

aeroplane when it begins to taxi before taking off, including the weight of the

 

pilot and of fuel, oil, recovery and personnel parachutes, flotation equipment,

 

items of optional equipment, tools and baggage.

 

Thus three scenarios are possible if MTOW exceeds the allowable takeoff weight:-

 

1. You exceed MTOW. Cficare's response is appropriate.
    
    
   
2. You exceed the allowable takeoff weight, but not MTOW. You are flying illegally and any / all potential implications or none may befall you. Roll the dice!
    
    
   
3. You do not exceed allowable takeoff weight. You are flying responsibly and within the law from a weight perspective.
    
    
   

 

 

 

 

[Gnarly Gnu]

OK thanks David, call it "allowable takeoff weight" instead of MTOW then - poor choice of wording on my part. And imagine an aircraft like a J230 so that we know lifting off at 625kg isn't a problem for the aircraft itself (limit is 700kg when VH registered).

 

Are you able to advise me how RAAus came to accept the J230 empty weight of 370kg for example? What if another manufacturer came up with say a model J390 which weighed 430kg empty, is this still going to be fine? What criteria determines this?

 

I've heard that in the USA for LSA the FAA have a 900 pound (409kg) empty limit, is there a similar limit in Australia?

 

 

[Guest davidh10]

OK thanks David, call it "allowable takeoff weight" instead of MTOW then. And imagine an aircraft like a J230 so that we know lifting off at 625kg isn't a problem for the aircraft itself.Are you able to advise me how RAAus came to accept the J230 empty weight of 370kg for example? What if another manufacturer came up with say a model J390 which weighed 430kg empty, is this still going to be fine? What criteria determines this?

 

I've heard that in the USA for LSA the FAA have a 900 pound (409kg) empty limit, is there a similar limit in Australia?

Sorry, but cannot answer that one. I think there's some accepted nominal weight for a person and I think there is either in existence or proposed a minimum fuel load of 90 minutes endurance.

Perhaps someone else can expand / confirm or correct?

 

 

[Hildy]

From the new 95.55:

 

For the purposes of sub-subparagraph 1.2 (f) (iv), the minimum useful load for an aeroplane is:

 

(a) if the aeroplane’s engine power is rated in kilowatts — the amount in kilograms worked out in accordance with the formula:

 

(80 x S) + 0.3P; or

 

(b) if the aeroplane’s engine power is rated in brake horse power — the amount in pounds worked out in accordance with the formula:

 

(175 x S) + 0.5P

 

where:

 

S is the number of seats in the aeroplane; and

 

P is the aeroplane’s rated engine power.

 

 

 

[Guest Andys@coffs]

I think you may have your wires crossed. When doing W&B and ensuring you are within the legislated take off weight and under MTOW there are no weights other than "Actual" weights used. You cant fudge by saying 2 POB, ethiopian in nature for W&B purposes, say 40kg each, or some other arbitrary figure.

 

Empty weight for the aircraft you fly is established as part of the Aircraft licensing regeme and is included in the Pilot Operators Handbook (and will be different for each aircraft...believe me Jabirus build process isnt that repeatable yet!) . Further, if anything of significance occurs during the Aircraft life, new avionics, or say change of 6ply to 10ply tires as an example a new Aircraft empty weight should be established. Unfortunately Aircraft are like me, only get heavier as they get older <Sigh!> . Put another way, manufacturers glossy "aint it simply amazing!!" brochure ware minimum weights have a single use purpose of lying to potential customers. They play no part in subsequent licensing or W&B ever!

 

The only way to get to use the full MTOW for a J230 legally is to buy one from Jabiru with it clear that its to be registered VH, or build one yourself and get it on the VH register as experimental, both of course requiring GA PPL and having zero to do with RAA

 

Andy

 

 

[Guest sunfish]

If you read the regs, the "commences taxi for takeoff" definition means that your taxi fuel up to your holding point is not counted.

 

As for exceeding manufacturers MTOW, you are now the test pilot. The worst accidents seem to involve the overloaded aircraft being able to lift off in ground effect, but then be unable to climb out of ground effect, nor accelerate. The obstacles at the end of the strip do the rest.

 

 

[turboplanner]

The Insurance Company also works it out.

 

 

[farri]

I'm looking at how the maximum allowable empty weight is determined for registration and potential legal type ramifications of slightly exceeding the MTOW limit.

I would think that RAA Tech Manager, Steve Bell, is the guy to ask !

 

Regardles of empty weight, MTOW is just that.

 

Legaly, the fact that the aircraft might handle it safely is irrelevant.

 

Frank.

 

 

[Guest turnbase]

MTOW also is can be calculated after all the load testing has been carried out. ie: Spar load limits etc. Therefore MTOW takes into consideration load limits within a given weight range. That is why the 230 which when VH registered can handle 700kg limits as all the testing has been done to the higher limit.

 

 

[Gnarly Gnu]

I would think that RAA Tech Manager, Steve Bell, is the guy to ask !

I was told Steve is off for a few weeks which is why I asked here, thought someone else might know.

 

 

[Guernsey]

Short of weighing the completely loaded aircraft with passenger, fuel,etc,etc, I have always been of the understanding that a passenger was considered to weigh 90 Kilos,

 

am I right? Alan.

 

 

[Guest davidh10]

Short of weighing the completely loaded aircraft with passenger, fuel,etc,etc, I have always been of the understanding that a passenger was considered to weigh 90 Kilos,am I right? Alan.

For the purpose of determining eligibility for registration based on maximum take-off weight (legislative limit), I think you are correct, but for MTOW, it is the actual weight.

That's why you have to know the empty weight of the aircraft, your own weight, that of any tools etc, that may be on-board and how much fuel you can carry if the passenger hits the maximum passenger weight specified for the aircraft. If you have to re-weigh the aircraft without occupants and fuel to re-establish empty weight, then so be it.

 

Don't forget that if you install additional equipment, you need to add its weight to the previous empty weight.

 

 

[fly_tornado]

MTOW on the Tornado is 454kgs. I weigh 88kgs, a full tank of juice weighs 28kgs. plane weighs 240kgs dry, that leaves 98kgs for a passenger/luggage.

 

 

[poteroo]

MTOW is the weight at which clean stall/power off is not >45KCAS. In GA, it doesn't matter that stall is >45, but at some higher weight than the RAAus limit, the aircraft will reach both structural and performance limits.

 

ATOW is the performance limited weight. It may often be lots less, but it will never be more than MTOW.

 

happy days,

 

 

[Guest davidh10]

MTOW is the weight at which clean stall/power off is not >45KCAS. In GA, it doesn't matter that stall is >45, but at some higher weight than the RAAus limit, the aircraft will reach both structural and performance limits.ATOW is the performance limited weight. It may often be lots less, but it will never be more than MTOW.

 

happy days,

It seems we suffer from multiple definitions of the same terms.

I can find no recognition of the term "ATOW" (Google search returns nothing).

 

The XT-912 had its "MTOW" increased from 430Kg to 450Kg (the previous time the weight limits for RAA were increased) simply by replacement of the "plackard" through issue of a Service Bulletin. On this basis:-

 

• at least the 430Kg MTOW figure was not based on Vs, but merely on the legal limitation for the registration being less than the all up design weight.
   
   
  
• the all up design weight was clearly larger than the 430Kg MTOW and at least equal to the 450Kg MTOW.
   
   
  

 

 

The CAOs do not mention MTOW, but to "take-off weight".

 

The RAA Technical Manual says "The MTOW for aircraft in these categories is specified in the CAO" (from CAO-95.32).

 

 

[poteroo]

ATOW = allowable TOW, as referred to in post #5, which is really the TOW referred to in CAO's - post #23. I'd much prefer the term to be Performance Limited TOW.

 

I rather think that Canberra would like another acronym to help fill the huge listing given in every CASA doc.

 

happy days,

 

 

[Guest davidh10]

ATOW = allowable TOW, as referred to in post #5, which is really the TOW referred to in CAO's - post #23. I'd much prefer the term to be Performance Limited TOW.I rather think that Canberra would like another acronym to help fill the huge listing given in every CASA doc.

 

happy days,

Ah, got me... quoting my own term back at me

 

 

[facthunter]

You are required to use actual weights, in an operational situation All the mention of "standard"weights for pax etc are in specific approved environments and would be part of the ops manual, or where you are working to a formula to define a rule.

 

Standard weights for pax, may be approved in airline ops because of the larger numbers involved they would be deemed to average out. If you are doing a charter where the pax are all Sumo wrestlers or such, you wouldn't want to use the normal standard weight as being applicable. The PIC is responsible for operating any aircraft under his/her authority within the specified weight and balance limitations. This really means that you DO have to know all the ACTUAL weights. Do you have to carry around a set of scales? I don't know but that is YOUR problem.

 

AS far as saying if the plane in question was certified VH to a certain weight (Structural) we all really know that it is strong enough in the RAAus environment to go to the same weight. Well, it is strong enough and that should be comforting in turbulence, but nevertheless it is no argument. The Legal weight is just that.

 

The latest definition does not allow for the fuel used in taxiing. That may be for simplicity but the legality would only apply in principle ( in my view only, you fight the court case), if the plane commenced the actual take-off roll over the MTOW.

 

Just an addition reading the two recent posts. Structural and performance limits are different. If we called them what they are we would understand their applicability better. Nev

 

 

[ossie]

ATOW = allowable TOW, as referred to in post #5, which is really the TOW referred to in CAO's - post #23. I'd much prefer the term to be Performance Limited TOW.I rather think that Canberra would like another acronym to help fill the huge listing given in every CASA doc.

 

happy days,

Commonly know in the industry as RTOW - "Regulated" TOW......google it and you'll find a few explanations...

 

RTOW can be limited by a number of things:

 

• MTOW
   
   
  
• Acft Performance
   
   
  
• Climb limits - also know a"'Second Segment" limit
   
   
  
• Max Landing Weight
   
   
  
• Pavement strength (PCN)
   
   
  
• MEL's etc etc..
   
   
  

 

 

 

The manufacture does the MTOW calculation, all we need to do is make sure we're equal to or less than it, taking into account any of the above if relevant.

 

Cheers

 

Os

 

 

[ossie]

Being created..!!!...No, not really...they've all been round for years.!!!

 

 

[ossie]

Yep, that's all we need.!!.......someone making his own ones up.....

 

Oh, I noticed Ian fixed up the TTF's on his WX site, nice of him wasn't it ??

 

Amazing how many were caught out by it, even the more experienced ones.

 

 

[Guest Andys@coffs]

for those discussing the "does it include taxi fuel or not"...Im thinking a degree of desperation must be approaching. Last time I checked at an RAA friendly airport the type of aircraft we have would really strecth a 10 minute taxi, which at an OMG burn rate of 10L/hr (Yep that'll test your brakes!!) means you might actualy get to 1kg of fuel use..... Have a pee before you leave, equally effective.

 

Andy