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Hereof, how does temperature affect aircraft performance?

Absolutely: thinner air, whether caused by a higher altitude or a higher temperature, decreases aircraft performance in two ways: It decreases the amount of air going into the engine, which means that less fuel can be introduced in order to maintain the correct fuel to air mixture.

Also, what conditions the performance of an aircraft will be the best? A number of factors (altitude/pressure, temperature and humidity) influence air density. A higher altitude, low pressure area, higher temperature and high humidity all have one result: they lower the density of the air. And as a result of that: a reduction in aircraft and engine performance.

Beside this, what factors affect v1?

df1, V1 is affected by temperature, altitude, and takeoff weight. Yes, as weight is increased so is V1. But, this also increases your takeoff distance. By increasing V1 with this weight increase your "balanced field length" is also increased.

What are the effects of less dense air on aircraft performance?

Whether due to high altitude, high temperature, or both, reduced air density (reported in terms of density altitude) adversely affects aerodynamic performance and decreases the engine's horsepower output. Takeoff distance, power available (in normally aspirated engines), and climb rate are all adversely affected.