MTOW that mythical number

[turboplanner]

Just now, lee-wave said:

Maybe a little confusion here...

 

'The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits'..... or have I missed something here....

No, it’s a simple easily understood figure. Sitting under that is calculating Weight and  Balance to ensure the Centre of Gravity at any time is within the envelope of the aircraft. You can avoid a lot of unsafe situations just by doing this.

[spacesailor]

You are thinking  BUREAOCRACY. 

A government law that says,  " your plane won,t fly . if over a stipulated weight ".

Of course if it doe,s fly, you cop a fine + loss of licence,  ' IF '  your  caught.

spacesailor

PS : If your nose heavy put a can of spare fuel in the tail.

    If tail heavy, put a spare battery in the engine bay !.  LoL

PPS  :  IF Hummelbird is nose heavy convert to  ' tail dragger '.

            IF tail heavy,  convert to three wheeler.

 

 

[turboplanner]

16 minutes ago, spacesailor said:

You are thinking  BUREAOCRACY. 

A government law that says,  " your plane won,t fly . if over a stipulated weight ".

Of course if it doe,s fly, you cop a fine + loss of licence,  ' IF '  your  caught.

spacesailor

PS : If your nose heavy put a can of spare fuel in the tail.

    If tail heavy, put a spare battery in the engine bay !.  LoL

PPS  :  IF Hummelbird is nose heavy convert to  ' tail dragger '.

            IF tail heavy,  convert to three wheeler.

 

 

I understand you're not flying, but it's wrong to spout incorrect or misleading information.

MTOW sets the maximum weight of the aircraft and all it contains, whether fuel, people, luggage or extra equipment.

 

All of that has to fit inside the flight envelope of the aircraft which should be shown in the POH.

 

WD calculations show where the COG for that particular flight will be, so you do your checks with simple calculations for each item. There is virtually no aircraft in RA or recreational GA which will be within the WD envelope, or for that matter MTOW with full fuel, full passengers and full luggage, and the calculations make it easy to decide what you have to do to complete a safe flight.

 

WD calculations are taught as part of Performance and Operations in GA, but I've never had a response from anyone in RA to say they had studied a WD or for that matter P&O course, which is odd because it's an easy way to prevent a fatal accident.

[facthunter]

IF your plane operates outside the allowable C of G range it's not safe. Tail heavy is particularly risky and you may lose control. and be unable to lower the nose or raise the tail whichever way you look at it. Your plane is no longer airworthy. If you are overweight for the conditions. eg Density height you won't have the  required performance in climb etc, If you're above the structural limit you risk overloading the structure and reducing it's life and your margins of safety when in gusts etc. Nev

[RossK]

Good post above by TP.

It's not hard to know your MTOW and WB for each flight.

I've got a spread sheet on my phone with a WB envelope. Enter Crew wt, baggage wt and fuel qty and it plots my WB for the endurance of the tanks. example below is from our trip to Mt Gambier, 165kg Crew wt, 17kg baggage, 95lt of fuel. (baggage includes tie down kit, travel cover, headsets, collapsible fuel bags and our travel bag.)

Get a $10 spring balance and everything can be weighed before it goes in the plane. It's not hard.

When we were looking at aircraft to buy, one of the first things we asked for was the planes W&B cert.

I will add, that at YLIL, W&B was taught and tested during RPC training.

 

Edited March 17, 2022 by RossK
spelling

[facthunter]

Useable fuel cannot be used to keep the plane in  balance. At zero fuel Wt it must still be in balance. Nev

[RossK]

13 minutes ago, facthunter said:

Useable fuel cannot be used to keep the plane in  balance. At zero fuel Wt it must still be in balance. Nev

Which is why I plot starting fuel (top right of the red line) all the way to zero fuel (bottom left), at all fuel quanties the CofG is within the envelope.

We saw one W&B cert for a plane that had to have a minimum of 50lt in the tanks to keep within the envelope with 2POB, 90Lt tanks, so usable fuel of 40L!!

[Bruce Tuncks]

I don't want to be a maverick because you guys are sort of right. You certainly have the powers that be on your side.

I just would like if we looked beyond the regulations sometimes to see the real figures.

Here's an interesting thing...  have you ever seen a plane "hovering " tail down and prop up, like a helicopter?

I have watched 3m radio control models do this for real and I have seen a full-size plane do it on video.

Now the models, I know for sure, had a VERY rearmost c of g , way aft of what would be legal in a big plane.

This was a difficult and unstable flight mode. I would never try it in my Jabiru. Not that the Jabiru has thrust greater than the weight.

[turboplanner]

1 hour ago, Bruce Tuncks said:

I don't want to be a maverick because you guys are sort of right. You certainly have the powers that be on your side.

I just would like if we looked beyond the regulations sometimes to see the real figures.

Here's an interesting thing...  have you ever seen a plane "hovering " tail down and prop up, like a helicopter?

I have watched 3m radio control models do this for real and I have seen a full-size plane do it on video.

Now the models, I know for sure, had a VERY rearmost c of g , way aft of what would be legal in a big plane.

This was a difficult and unstable flight mode. I would never try it in my Jabiru. Not that the Jabiru has thrust greater than the weight.

No, the models have a huge power to weight ratio compared to a full size aircraft and can sit on the prop pointing vertivally and shoot straight up to 1000 ft where it starts to get hard to see the results of control inputs other than letting it just leaf its way down closer.

 

The manufacturer's WD envelope gives you safe flights.

[Bruce Tuncks]

I'd just love it if you were to go a little closer to the bone than by saying " the manufacturer's WD envelope gives you safe flights."

[Bruce Tuncks]

Of course it gives you safe flights...  My question is whether or not a 5 knot reduction in the speed would give you flights just as safe, and indeed what that all means.

[spacesailor]

If you took off with  ' over fill ' tanks for that ' safety ' margin, what would the fine be when you arrive. .

spacesailor

[lee-wave]

12 hours ago, facthunter said:

Useable fuel cannot be used to keep the plane in  balance. At zero fuel Wt it must still be in balance. Nev

Useable fuel was used to keep the Concorde in trim for the take off , cruise and landing phase of flight.... in fact the pumping of fuel for and aft to change the C of G was one of the secrets of the design success....

[turboplanner]

2 hours ago, lee-wave said:

Useable fuel was used to keep the Concorde in trim for the take off , cruise and landing phase of flight.... in fact the pumping of fuel for and aft to change the C of G was one of the secrets of the design success....

It was common in the 1940s with RPT aircraft to be pumping fuel around during the trip to keep the aircraft in balance, but it was a complicated process which, as skilled as the airline pilots were, brought some unstuck.

[turboplanner]

8 hours ago, Bruce Tuncks said:

I'd just love it if you were to go a little closer to the bone than by saying " the manufacturer's WD envelope gives you safe flights."

Aircraft manufacturers' test pilots spend a lot of time assessing the aircraft, and from these tests the envelope is produced.

 

It would be ridiculous for someone like myself, or you for that matter to say "Well that's what the test programme showed, but you can go  x kg heavier at this COG", or load outside the manufacturer's envelope tot the rear, esecially when so many pilots don't even do ANY WB checks before each flight and don't even understand how to calculate these things.  

[turboplanner]

I just remembered three good examples for anyone attempting to push the official envelopes.

1. Slartibartfast in a Morgan Cheetah lost control of his aircraft after loading a toolbox in front of the passenger seat. He was lucky enough to regain control and weighed the toolbox at just 15 kg, which was a lesson to us all at the time.

 

2. Another recreational airctraft stalled and crashed on landing at a Natfly after the pilot had loaded it with a BBQ for his stay at Natfly.

 

3. A similar discussion a few years ago on trikes ended when an official, his trike loaded for the holidays presumably in the inventive ways posters were quoting was killed on take off when the aircraft became uncontrollable.

 

These indicate that the margins are slimmer that they are on mass-produced GA aircraft.

[facthunter]

Things like Concord have no relevance to our ops with fuel used for balance. The "doomed" Concorde changed runways and didn't burn off the required fuel to be in balance for the take off. Nev

[spacesailor]

I thought it was the massive leaking fuel ,  that put the balance out, which then, eventually ignited. 

HAa, we live & learn.

Oops fotgot to sign it.

spacesailor

 

Edited March 17, 2022 by spacesailor
Signiture

[Bruce Tuncks]

There was a farmer in South Australia who put his tractor toolbox in his 2.2 jabiru. He put it BEHIND the fuel tank, and crashed on the take-off run...  the plane over-rotated and stalled before leaving the ground. Apparently he climbed out unhurt, a sadder but wiser man.

But, here's some figures which you can easily check out with google... My current J230 has a "max take-off weight =600kg" according to the pilot's manual. This is not much as the airframe weight =360kg and it can carry 90kg of fuel. This only leaves 150kg for 2 people. If the people add up to 200kg then you can only carry 40kg of fuel.

If you google up " Jabiru J230 max take-off weight " the first report is a kitplanes review which states "to meet LSA regulations, J230 and J250 have a normal max gross of 1320 pounds, but if constructed as an amateur-built, can go to the J400 series maximum of 1540 pounds"

So it seemed reasonable for me to see just what these figures meant. Why are these figures what they are?

Well the answer lies in flight envelopes and definitions of just what "rough air" and "smooth air" mean.

 

In the meantime, I sincerely agree with those who say that the official figures be adhered to , lest you go to jail etc.

 

 

[RossK]

Bruce, the figures are also based around stall speeds.

There are some airframes that will happily carry more than 600kg but won't meet the 45kt stall speed.

Our own Sportstar has an official MTOW of 575kg, but there is an Evektor Bulletin that increases this to 600kg with the addition of VG's.

So, pay the $$ to Evektor for the paperwork, fit VGs, submit paperwork to RAA and an extra 25kg presto...🙂

[Bruce Tuncks]

Turbs, I think it is a bit lazy to say that the calculations are too hard for us. Gosh, in high school we would have loved for a WB calculation in the year 12 exams...  it would have been the easiest question by far.

[facthunter]

The calculations are harder to understand when you use basic weight and index figures. You can reduce it to a graphical presentation for any particular plane.   Nev

[turboplanner]

42 minutes ago, Bruce Tuncks said:

Turbs, I think it is a bit lazy to say that the calculations are too hard for us. Gosh, in high school we would have loved for a WB calculation in the year 12 exams...  it would have been the easiest question by far.

If I actually said the calculations are too hard, I need to correct that impression. The base equation is certainly learned in Maths at school, so very simple, which makes me surprised that only RossK has confirmed he does calculations and I'll give Facthunter a free pass because the things he says confirm the knowledge.

 

 

[Bruce Tuncks]

RossK, you are quite right about the stall speeds.

Years ago, we were limited by a requirement for a 40 knot stall speed. This meant that the Jabiru SK was limited to a weight of 430kg kg, which was not really possible to achieve with fuel and 2 people . This was magically fixed by increasing the allowable stall speed to 42 knots. Since the lift equation has a v^2 term, the allowable weight increase was quite a lot.

Right now, the weight increase achieved by the RAAus is not worth much without a ( small ) increase in the stall speed allowed.

 

[Bruce Tuncks]

Oops its 45 knots, which makes the argument even stronger.