structural limits performance limits and regulated limits what are they how many are there and how do we use them day to day in our aircraft let's find out [Music] hi i'm grant and welcome to the third class in the mass and balance series today we're looking at structural performance and regulated limits what are they and how they are important to the safe conduct of every flight we do all at mass that we learned about in the previous class is useful for measuring the mass of an aircraft at one point during the flight when we were actually in the process of flying the mass of the aircraft will change as we burn fuel so we can use multiple masses to refer to different points in the flight primarily we use the takeoff mass and the landing mass takeoff mass or the actual take off mass is defined by taking our all up mass and then taking away whatever fuel we would have used by the time we take off which is our taxi fuel our actual landing mass is defined by taking that actual takeoff mass and then taking off the fuel that we would have burnt by the time we land which would be our trip fuel and we can also see the actual landing mass equals all up mass take away tax fuel and then take away trip fuel structural mass limitations are as the name implies to do with structure and the build of the plane itself these are hard limits that can never ever be exceeded the main ones to be aware of are maximum ramp mass maximum structural takeoff mass maximum structural landing mass and maximum zero fuel mass maximum ramp mass is mainly a limit of the gear wheel assembly has to do with us taxiing around the ramp of an aerodrum the maximum structural takeoff mass is how much the plane can physically carry into the air how much the structure can handle carrying into takeoff the maximum structural landing mass will usually be less than the take-off mass because when we land there's that additional force of us actually hitting the tarmac and the maximum zero fuel mass is to do with the point where the wings attach to the body of the aircraft normally the fuel is stored in the wings so it creates this downward force in the wings if we have zero fuel the lift that goes into the wings could be too much for this point to take and it could break in essence it's important to note that maximum structural landing mass can be the most limiting during takeoff this is because if our actual takeoff mass is greater than the maximum structural landing mass plus trip fuel that means by the time we get to our destination and burn our trip fuel we could still be exceeding our maximum structural landing mass maximum zero fuel mass can also be the most limiting on takeoff that is because if our actual takeoff mass exceeds the maximum zero fuel mass plus takeoff fuel we could get into the position where we burn all of our fuel hopefully not but you could get into that position where you've burned all your fuel and you're still above your maximum zero fuel mass and that would mean that the wing root couldn't take the forces that the lift is adding to the wing this concept is best shown with an example so we've been given a maximum structural learning mass of 40 000 kilograms a maximum structural takeoff mass of 45 000 kilograms and a maximum zero fuel mass of 39 000 kilograms we've also be given our take off fuel which equals 3 000 kgs and our trip fuel which is equal to 2000 kgs so we know from before that our most limiting is either the maximum structural takeoff mass the maximum structural landing mass plus trip or the maximum zero fuel mass plus takeoff so maximum structural takeoff mass we know it's 45 000. our maximum structural landing mass plus our trip fuel we know is 42 000 now we know our max from zero fuel plus takeoff would be also 42 000. so our most limiting and our limit for today's flight would be 42 000 kgs this is because if we took off with our maximum structural takeoff mass of 45 000 kgs by the time we got to landing we've burned our trip fuel we would only be down at 43 000 kgs so we would be above our maximum structural landing mass now this is a lot of acronyms there's ms tom mslm mzfm but it's important to see them out in full otherwise you won't remember what they mean so always say maximum zero fuel mass don't say mzfm because then it just becomes letters and becomes confusing you have to say the amount of fuel so we've got all those structural limitations um so how are they useful for example we've calculated we need 15 000 kilograms of fuel for our flight that's what we need to get from point a to point b and all of our taxi trip cafe the maximum structural takeoff mass of an aircraft golf tango papa lima is 65 000 tons 65 000 kilograms the dry operating mass is 45 000 kilograms and we have a traffic load of 10 000 kilograms so first of all we know we've got dry operating mass traffic and maximum structural takeoff mass so we're mixing things so what we're going to do be very tall for dunking unbelievably awesomely we've got dry operating mass we know that's these two or 45 000 and we have traffic here 10 000 and we've got fuel here so we can calculate a total mass let's do that so we have 45 000 for our dry operating mass we'll add to that the traffic load which is 10 000 and we'll add to that our fuel which is 15. come up with an answer of 70 000 kilograms we can't go above our maximum stretch to take off mass which is 65 000. our all up mass is 70 000 so we can't complete the flight if we keep this exactly the same the solution to this problem is what 45000 is fixed basic empty mass cannot change variable load we could chuck crew off i suppose but we can't really change it our traffic load 10 000 kgs we could change that fuel we can't change that because we know we need 15 000 kilograms for this route for this flight to be legally compliant with all those fuel needs so we have to reduce the traffic load we have to take 5000 kgs worth of traffic load off of our flight it's obviously a very simple example bullet but it illustrates the point so we are not always limited by the maximum structural limits of the aircraft this is something covered a lot more in performance but aviation is a mash-up of all the subjects so i'll cover it briefly but simply we can be performance limited this is due to the engines of the aircraft liking certain conditions more than others and the runways of the world are all in different places at different heights and are all variable in size in general for takeoff cold dense air is preferred to hot non-dense air with a long runway added on this is the ideal condition where is that most dense air it's low down sea level airports are ideal on the contrary if an airport is already at an altitude of 6000 feet in the middle of the desert with a short runway the performance of the aircraft will be terrible so in this fictional desert location it's likely we will be limited by the performance of the engines what they can actually handle these limits are referred to as the performance limited takeoff mass and the performance limited landing mass again as with the structural mass the performance limiting landing mass can be the most limiting if we add our trip fuel by the time we have burnt our trip fuel we might still be above our performance limited landing mass the most restrictive out of our performance limits and our structural limits is the one we use for takeoff calculations and landing calculations this is called our regulated limit this is our regulated takeoff mass for takeoff and regulated laminar mass for landing for example desert high international airport located at 5500 feet above sea level in the middle of the desert and we have calculated our aircraft from before gulf of tango papua to have a performance limited takeoff mass of 63 000 kgs what is our regulated take-off mass well from before in that previous example our aircraft had a maximum structural takeoff mass equal to 65 000 kgs we can never exceed this but we also won't be able to get out of the airport unless we are this weight or lower so our regulated takeoff mass is in this case the performance limiting takeoff mass so our regulate takeoff mass 63 000 kilograms so to summarize let's get some acronyms down on the page we have our actual takeoff mass and actual landing mass what we actually weigh during takeoff and actually way during landing we have our structural limits which are maximum ramp mass maximum structural takeoff mass maximum structural landing mass and maximum zero fuel mass we know that we can be limited not just by our maximum structural takeoff mass but also by our maximum structural landing mass plus the trip fuel and also by the maximum zero fuel mass plus our takeoff fuel so our lowest of maximum structural line of mass plus trip fuel lowest of maximum so our lowest of maximum structural landing mass plus trip fuel maximum structural takeoff mass or maximum zero fuel mass plus takeoff fuel is our limit structurally for takeoff we're not always limited by structure we're also limited by performance so we have our performance limited takeoff mass and also our performance limited landing mass we know that for takeoff we can also be limited by performance limited landing mass plus trip fuel as the same for the structure the regulated takeoff mass is the lower of these two figures and the regulated landing mass again is the lowest of structural versus performance