## 2 Materials and Methods
### Longitudinal Stability  
With reference to the longitudinal stability of the FLT in combination with interchangeable equipment, it is necessary to acquire the following data from the instruction handbook and/or the marking plate on the FLT:  
* The rated capacity (Q\({}_{\mathrm{ij}}\)) with forks according to EN ISO 3691-1 [16]. It can also be defined by means of a load chart depending on the specified height at a specified load centre distance;
* The type of tyres the load chart refers to (if any);
* The fork arm blade thickness(s).
* Similarly, the following data concerning the interchangeable equipment should be acquired in the instruction handbook:
* The total mass of the interchangeable equipment (PCA);
* The distance (L) measured horizontally from the fork carrier to the centre of gravity for the unladen interchangeable equipment;
* The distance (D\({}_{\mathrm{ali}}\)) measured horizontally from the fork carrier to the centre of gravity of the load;
* The maximum load permitted by the manufacturer (Q\({}_{\mathrm{i}}\)).  
Once known, the aforementioned parameters are necessary to calculate the maximum operating longitudinal moment (OLM) according to each value of the actual capacity (Q\({}_{\mathrm{ij}}\)) of the FLT and with respect to the lift height (H\({}_{\mathrm{j}}\)), as follows (see Figure 2):  
\[\mathrm{OLM}=\mathrm{Q_{ij}}\times\mathrm{D_{i}}, \tag{1}\]  
where D\({}_{\mathrm{i}}\) is the sum of the fork arm blade thickness(s) and the specified load centre distance.  
Figure 1: Standard load centre distance.  
On the other hand, for interchangeable equipment, it is necessary to calculate:  
1. The maximum load at the fork carrier (CI) as the sum of the maximum load permitted by the manufacturer (Qi) and the total mass of the interchangeable equipment (PCA);
2. The overall longitudinal moment at the fork carrier (MLA) according to Equation (2) and nomenclature in Figure 3.  
\[\text{MLA}=\text{PCA}\times\text{L}+\text{Q}_{\text{i}}\times\text{D}_{\text{ai}}. \tag{2}\]  
The last step is to verify for each condition the lift height and load distance which is foreseen in the FLT load chart as:  
\[\text{CI}\leq\text{Q}_{\text{ij}}, \tag{3}\]  
and  
\[\text{MLA}\leq\text{OLM}. \tag{4}\]  
Figure 3: Evaluation of MLA: nomenclature. Key: PCA—total mass of the interchangeable equipment; L—distance measured horizontally from the fork carrier to the centre of gravity of the unladen interchangeable equipment; Da—distance measured horizontally from the fork carrier to the centre of gravity of the load; Qi—maximum load permitted by the manufacturer at Da\({}_{\text{i}}\).  
Figure 2: Evaluation of OLM: nomenclature. Key: D\({}_{\text{i}}\)—load centre distance from the fork carrier; Hj—lift height; Qij—rated capacity according to D\({}_{\text{i}}\) and Hj; s—fork arm blade thickness.  
Thus, the actual capacity of the FLT, when combined with interchangeable equipment, is the maximum load that simultaneously satisfies Equations (3) and (4). For this purpose, it could be necessary to limit the value of the maximum load which can be handled with interchangeable equipment. If there are no values of the loads which simultaneously satisfy Equations (3) and (4) for any combination of the lift height and load distance, then the interchangeable equipment is not compatible with the FLT.