MasSD4 is a simple app that can be used for basic Mass, Balance, and Endurance calculations for Viper SD4 RTC Aircraft. It is an unofficial source of such calculations, but it is based on data straight from the Aircraft Flight Manual. The app was made by Ján Richnavský in 2024. It is a result of his Bachelor's thesis on Aeronautical Faculty of Technical University in Košice and is free to use.